PROTOPLANETARY DISK STRUCTURE WITH GRAIN EVOLUTION: THE ANDES MODEL

International Nuclear Information System (INIS)

Akimkin, V.; Wiebe, D.; Pavlyuchenkov, Ya.; Zhukovska, S.; Semenov, D.; Henning, Th.; Vasyunin, A.; Birnstiel, T.

2013-01-01

We present a self-consistent model of a protoplanetary disk: 'ANDES' ('AccretioN disk with Dust Evolution and Sedimentation'). ANDES is based on a flexible and extendable modular structure that includes (1) a 1+1D frequency-dependent continuum radiative transfer module, (2) a module to calculate the chemical evolution using an extended gas-grain network with UV/X-ray-driven processes and surface reactions, (3) a module to calculate the gas thermal energy balance, and (4) a 1+1D module that simulates dust grain evolution. For the first time, grain evolution and time-dependent molecular chemistry are included in a protoplanetary disk model. We find that grain growth and sedimentation of large grains onto the disk midplane lead to a dust-depleted atmosphere. Consequently, dust and gas temperatures become higher in the inner disk (R ∼ 50 AU), in comparison with the disk model with pristine dust. The response of disk chemical structure to the dust growth and sedimentation is twofold. First, due to higher transparency a partly UV-shielded molecular layer is shifted closer to the dense midplane. Second, the presence of big grains in the disk midplane delays the freeze-out of volatile gas-phase species such as CO there, while in adjacent upper layers the depletion is still effective. Molecular concentrations and thus column densities of many species are enhanced in the disk model with dust evolution, e.g., CO 2 , NH 2 CN, HNO, H 2 O, HCOOH, HCN, and CO. We also show that time-dependent chemistry is important for a proper description of gas thermal balance.

Gas-Grain Models for Interstellar Anion Chemistry

Science.gov (United States)

Cordiner, M. A.; Charnely, S. B.

2012-01-01

Long-chain hydrocarbon anions C(sub n) H(-) (n = 4, 6, 8) have recently been found to be abundant in a variety of interstellar clouds. In order to explain their large abundances in the denser (prestellar/protostellar) environments, new chemical models are constructed that include gas-grain interactions. Models including accretion of gas-phase species onto dust grains and cosmic-ray-induced desorption of atoms are able to reproduce the observed anion-to-neutral ratios, as well as the absolute abundances of anionic and neutral carbon chains, with a reasonable degree of accuracy. Due to their destructive effects, the depletion of oxygen atoms onto dust results in substantially greater polyyne and anion abundances in high-density gas (with n(sub H2) approx > / cubic cm). The large abundances of carbon-chain-bearing species observed in the envelopes of protostars such as L1527 can thus be explained without the need for warm carbon-chain chemistry. The C6H(-) anion-to-neutral ratio is found to be most sensitive to the atomic O and H abundances and the electron density. Therefore, as a core evolves, falling atomic abundances and rising electron densities are found to result in increasing anion-to-neutral ratios. Inclusion of cosmic-ray desorption of atoms in high-density models delays freeze-out, which results in a more temporally stable anion-to-neutral ratio, in better agreement with observations. Our models include reactions between oxygen atoms and carbon-chain anions to produce carbon-chain-oxide species C6O, C7O, HC6O, and HC7O, the abundances of which depend on the assumed branching ratios for associative electron detachment

Monte Carlo simulation of grain growth

Directory of Open Access Journals (Sweden)

Paulo Blikstein

1999-07-01

Full Text Available Understanding and predicting grain growth in Metallurgy is meaningful. Monte Carlo methods have been used in computer simulations in many different fields of knowledge. Grain growth simulation using this method is especially attractive as the statistical behavior of the atoms is properly reproduced; microstructural evolution depends only on the real topology of the grains and not on any kind of geometric simplification. Computer simulation has the advantage of allowing the user to visualize graphically the procedures, even dynamically and in three dimensions. Single-phase alloy grain growth simulation was carried out by calculating the free energy of each atom in the lattice (with its present crystallographic orientation and comparing this value to another one calculated with a different random orientation. When the resulting free energy is lower or equal to the initial value, the new orientation replaces the former. The measure of time is the Monte Carlo Step (MCS, which involves a series of trials throughout the lattice. A very close relationship between experimental and theoretical values for the grain growth exponent (n was observed.

On the fission gas release from oxide fuels during normal grain growth

International Nuclear Information System (INIS)

Paraschiv, M.C.; Paraschiv, A.; Glodeanu, F.

1997-01-01

A mathematical formalism for calculating the fission gas release from oxide fuels considering an arbitrary distribution of fuel grain size with only zero boundary condition for gas diffusion at the grain boundary is proposed. It has also been proved that it becomes unnecessary to consider the grain volume distribution function for fission products diffusion when the grain boundary gas resolution is considered, if thermodynamic forces on grain boundaries are only time dependent. In order to highlight the effect of the normal grain growth on fission gas release from oxide fuels Hillert's and Lifshitz and Slyozov's theories have been selected. The last one was used to give an adequate treatment of normal grain growth for the diffusion-controlled grain boundary movement in oxide fuels. It has been shown that during the fuel irradiation, the asymptotic form of the grain volume distribution functions given by Hillert and Lifshitz and Slyozov models can be maintained but the grain growth rate constant becomes time dependent itself. Experimental results have been used to correlate the two theoretical models of normal grain growth to the fission gas release from oxide fuels. (orig.)

Vadose Zone Fate and Transport Simulation of Chemicals Associated with Coal Seam Gas Extraction

Science.gov (United States)

Simunek, J.; Mallants, D.; Jacques, D.; Van Genuchten, M.

2017-12-01

The HYDRUS-1D and HYDRUS (2D/3D) computer software packages are widely used finite element models for simulating the one-, and two- or three-dimensional movement of water, heat, and multiple solutes in variably-saturated media, respectively. While the standard HYDRUS models consider only the fate and transport of individual solutes or solutes subject to first-order degradation reactions, several specialized HYDRUS add-on modules can simulate far more complex biogeochemical processes. The objective of this presentation is to provide an overview of the HYDRUS models and their add-on modules, and to demonstrate applications of the software to the subsurface fate and transport of chemicals involved in coal seam gas extraction and water management operations. One application uses the standard HYDRUS model to evaluate the natural soil attenuation potential of hydraulic fracturing chemicals and their transformation products in case of an accidental release. By coupling the processes of retardation, first-order degradation and convective-dispersive transport of the biocide bronopol and its degradation products, we demonstrated how natural attenuation reduces initial concentrations by more than a factor of hundred in the top 5 cm of the vadose zone. A second application uses the UnsatChem module to explore the possible use of coal seam gas produced water for sustainable irrigation. Simulations with different irrigation waters (untreated, amended with surface water, and reverse osmosis treated) provided detailed results regarding chemical indicators of soil and plant health, notably SAR, EC and sodium concentrations. A third application uses the coupled HYDRUS-PHREEQC module to analyze trace metal transport involving cation exchange and surface complexation sorption reactions in the vadose zone leached with coal seam gas produced water following some accidental water release scenario. Results show that the main process responsible for trace metal migration is complexation of

IFPE/GBGI, Grain-Bubble Gas Inter-linkage

International Nuclear Information System (INIS)

2007-01-01

Description: The fuel microstructure examination at the thermocouple tips in the lower and upper part of a steady-state irradiated experimental fuel rod with different as fabricated fuel-to-clad gaps in these two regions revealed on-set of grain boundary gas bubble precipitation in the fuel center of the small-gap/low-temperature region (lower part) and developed inter-linkage in the fuel center of the large-gap/high-temperature region (upper part). By use of a diffusion model and the measured temperatures, corresponding grain boundary gas 'concentrations' were calculated

Retention of radiolytic CO gas in irradiated pepper grains and irradiation detection of spices and dry grains with the level of stocked CO gas

International Nuclear Information System (INIS)

Furuta, M.; Dohmaru, T.; Katayama, T.; Toratani, H.; Takeda, A.

1995-01-01

The release of radiolytic CO gas from 60Co gamma-irradiated pepper seeds was unexpectedly slower than that of radiolytic H2 gas during a storage period after irradiation. These gases were retained in the grains and could be recovered by pulverization under gaslight condition. Using this procedure, 10-kGy-irradiated pepper grains could be distinguished from nonirradiated samples for more than 2 months by the level of CO and H2 gases. The patterns of CO change at 10, 20, and 30 kGy were similar, and the CO amounts were proportional to irradiation doses at any point of the storage period after irradiation. 60Co gamma-irradiated grains of allspice, cinnamon, cumin, polished rice, and wheat could be distinguished from nonirradiated ones by the level of retained CO gas even after 2 months of storage at room temperature. Thus, radiolytic CO gas could be an effective probe for rapid screening of irradiated pepper and dry grains

Evolution of interstellar grains

International Nuclear Information System (INIS)

Greenberg, J.M.

1984-01-01

The principal aim of this chapter is to derive the properties of interstellar grains as a probe of local physical conditions and as a basis for predicting such properties as related to infrared emissivity and radiative transfer which can affect the evolution of dense clouds. The first sections will develop the criteria for grain models based directly on observations of gas and dust. A summary of the chemical evolution of grains and gas in diffuse and dense clouds follows. (author)

Grain boundary motion and grain rotation in aluminum bicrystals: recent experiments and simulations

International Nuclear Information System (INIS)

Molodov, D A; Barrales-Mora, L A; Brandenburg, J-E

2015-01-01

The results of experimental and computational efforts over recent years to study the motion of geometrically different grain boundaries and grain rotation under various driving forces are briefly reviewed. Novel in-situ measuring techniques based on orientation contrast imaging and applied simulation techniques are described. The experimental results obtained on specially grown aluminum bicrystals are presented and discussed. Particularly, the faceting and migration behavior of low angle grain boundaries under the curvature force is addressed. In contrast to the pure tilt boundaries, which remained flat/faceted and immobile during annealing at elevated temperatures, mixed tilt-twist boundaries readily assumed a curved shape and steadily moved under the capillary force. Computational analysis revealed that this behavior is due to the inclinational anisotropy of grain boundary energy, which in turn depends on boundary geometry. The shape evolution and shrinkage kinetics of cylindrical grains with different tilt and mixed boundaries were studied by molecular dynamics simulations. The mobility of low angle <100> boundaries with misorientation angles higher than 10°, obtained by both the experiments and simulations, was found not to differ from that of the high angle boundaries, but decreases essentially with further decrease of misorientation. The shape evolution of the embedded grains in simulations was found to relate directly to results of the energy computations. Further simulation results revealed that the shrinkage of grains with pure tilt boundaries is accompanied by grain rotation. In contrast, grains with the tilt-twist boundaries composed of dislocations with the mixed edge-screw character do not rotate during their shrinkage. Stress driven boundary migration in aluminium bicrystals was observed to be coupled to a tangential translation of the grains. The activation enthalpy of high angle boundary migration was found to vary non-monotonically with

Relativistic Gas Drag on Dust Grains and Implications

Energy Technology Data Exchange (ETDEWEB)

Hoang, Thiem, E-mail: thiemhoang@kasi.re.kr [Korea Astronomy and Space Science Institute, Daejeon 34055 (Korea, Republic of); Korea University of Science and Technology, Daejeon, 34113 (Korea, Republic of)

2017-09-20

We study the drag force on grains moving at relativistic velocities through interstellar gas and explore its application. First, we derive a new analytical formula of the drag force at high energies and find that it is significantly reduced compared to the classical model. Second, we apply the obtained drag force to calculate the terminal velocities of interstellar grains by strong radiation sources such as supernovae and active galactic nuclei (AGNs). We find that grains can be accelerated to relativistic velocities by very luminous AGNs. We then quantify the deceleration of relativistic spacecraft proposed by the Breakthrough Starshot initiative due to gas drag on a relativistic lightsail. We find that the spacecraft’s decrease in speed is negligible because of the suppression of gas drag at relativistic velocities, suggesting that the lightsail may be open for communication during its journey to α Centauri without causing a considerable delay. Finally, we show that the damage to relativistic thin lightsails by interstellar dust is a minor effect.

Mechanical and chemical compaction in fine-grained shallow-water limestones.

Science.gov (United States)

Shinn, E.A.; Robbin, D.M.

1983-01-01

Significant mechanical compaction resulted from pressures simulating less than 305 m of burial. Increasing loads to an equivalent of more than 3400 m did not significantly increase compaction or reduce sediment core length. Chemical compaction (pressure dissolution) was detected only in sediment cores compacted to pressures greater than 3400 m of burial. These short-term experiments suggest that chemical compaction would begin at much shallower depths given geologic time. Compaction experiments that caused chemical compaction lend support to the well-established hypothesis; that cement required to produce a low-porosity/low-permeability fine-grained limestone is derived internally. Dissolution, ion diffusion, and reprecipitation are considered the most likely processes for creating significant thicknesses of dense limestone in the geologic record. Continuation of chemical compaction after significant porosity reduction necessitates expulsion of connate fluids, possibly including hydrocarbons. -from Authors

MULTIGRAIN: a smoothed particle hydrodynamic algorithm for multiple small dust grains and gas

Science.gov (United States)

Hutchison, Mark; Price, Daniel J.; Laibe, Guillaume

2018-05-01

We present a new algorithm, MULTIGRAIN, for modelling the dynamics of an entire population of small dust grains immersed in gas, typical of conditions that are found in molecular clouds and protoplanetary discs. The MULTIGRAIN method is more accurate than single-phase simulations because the gas experiences a backreaction from each dust phase and communicates this change to the other phases, thereby indirectly coupling the dust phases together. The MULTIGRAIN method is fast, explicit and low storage, requiring only an array of dust fractions and their derivatives defined for each resolution element.

Multiscale development of a fission gas thermal conductivity model: Coupling atomic, meso and continuum level simulations

International Nuclear Information System (INIS)

Tonks, Michael R.; Millett, Paul C.; Nerikar, Pankaj; Du, Shiyu; Andersson, David; Stanek, Christopher R.; Gaston, Derek; Andrs, David; Williamson, Richard

2013-01-01

Fission gas production and evolution significantly impact the fuel performance, causing swelling, a reduction in the thermal conductivity and fission gas release. However, typical empirical models of fuel properties treat each of these effects separately and uncoupled. Here, we couple a fission gas release model to a model of the impact of fission gas on the fuel thermal conductivity. To quantify the specific impact of grain boundary (GB) bubbles on the thermal conductivity, we use atomistic and mesoscale simulations. Atomistic molecular dynamic simulations were employed to determine the GB thermal resistance. These values were then used in mesoscale heat conduction simulations to develop a mechanistic expression for the effective GB thermal resistance of a GB containing gas bubbles, as a function of the percentage of the GB covered by fission gas. The coupled fission gas release and thermal conductivity model was implemented in Idaho National Laboratory’s BISON fuel performance code to model the behavior of a 10-pellet LWR fuel rodlet, showing how the fission gas impacts the UO 2 thermal conductivity. Furthermore, additional BISON simulations were conducted to demonstrate the impact of average grain size on both the fuel thermal conductivity and the fission gas release

Enforcing dust mass conservation in 3D simulations of tightly coupled grains with the PHANTOM SPH code

Science.gov (United States)

Ballabio, G.; Dipierro, G.; Veronesi, B.; Lodato, G.; Hutchison, M.; Laibe, G.; Price, D. J.

2018-06-01

We describe a new implementation of the one-fluid method in the SPH code PHANTOM to simulate the dynamics of dust grains in gas protoplanetary discs. We revise and extend previously developed algorithms by computing the evolution of a new fluid quantity that produces a more accurate and numerically controlled evolution of the dust dynamics. Moreover, by limiting the stopping time of uncoupled grains that violate the assumptions of the terminal velocity approximation, we avoid fatal numerical errors in mass conservation. We test and validate our new algorithm by running 3D SPH simulations of a large range of disc models with tightly and marginally coupled grains.

Towards realistic molecular dynamics simulations of grain boundary mobility

International Nuclear Information System (INIS)

Zhou, J.; Mohles, V.

2011-01-01

In order to investigate grain boundary migration by molecular dynamics (MD) simulations a new approach involving a crystal orientation-dependent driving force has been developed by imposing an appropriate driving force on grain boundary atoms and enlarging the effective range of driving force. The new approach has been validated by the work of the driving force associated with the motion of grain boundaries. With the new approach the relation between boundary migration velocity and driving force is found to be nonlinear, as was expected from rate theory for large driving forces applied in MD simulations. By evaluating grain boundary mobility nonlinearly for a set of symmetrical tilt boundaries in aluminum at high temperature, high-angle grain boundaries were shown to move much faster than low-angle grain boundaries. This agrees well with experimental findings for recrystallization and grain growth. In comparison with the available data the simulated mobility of a 38.21 o Σ7 boundary was found to be significantly lower than other MD simulation results and comparable with the experimental values. Furthermore, the average volume involved during atomic jumps for boundary migration is determined in MD simulations for the first time. The large magnitude of the volume indicates that grain boundary migration is accomplished by the correlated motion of atom groups.

Simulating the Fate and Transport of Coal Seam Gas Chemicals in Variably-Saturated Soils Using HYDRUS

Directory of Open Access Journals (Sweden)

Dirk Mallants

2017-05-01

Full Text Available The HYDRUS-1D and HYDRUS (2D/3D computer software packages are widely used finite element models for simulating the one-, and two- or three-dimensional movement of water, heat, and multiple solutes in variably-saturated media, respectively. While the standard HYDRUS models consider only the fate and transport of individual solutes or solutes subject to first-order degradation reactions, several specialized HYDRUS add-on modules can simulate far more complex biogeochemical processes. The objective of this paper is to provide a brief overview of the HYDRUS models and their add-on modules, and to demonstrate possible applications of the software to the subsurface fate and transport of chemicals involved in coal seam gas extraction and water management operations. One application uses the standard HYDRUS model to evaluate the natural soil attenuation potential of hydraulic fracturing chemicals and their transformation products in case of an accidental release. By coupling the processes of retardation, first-order degradation and convective-dispersive transport of the biocide bronopol and its degradation products, we demonstrated how natural attenuation reduces initial concentrations by more than a factor of hundred in the top 5 cm of the soil. A second application uses the UnsatChem module to explore the possible use of coal seam gas produced water for sustainable irrigation. Simulations with different irrigation waters (untreated, amended with surface water, and reverse osmosis treated provided detailed results regarding chemical indicators of soil and plant health, notably SAR, EC and sodium concentrations. A third application uses the HP1 module to analyze trace metal transport involving cation exchange and surface complexation sorption reactions in a soil leached with coal seam gas produced water following some accidental water release scenario. Results show that the main process responsible for trace metal migration in soil is complexation of

Thermodynamics of grain boundary premelting in alloys. II. Atomistic simulation

International Nuclear Information System (INIS)

Williams, P.L.; Mishin, Y.

2009-01-01

We apply the semi-grand-canonical Monte Carlo method with an embedded-atom potential to study grain boundary (GB) premelting in Cu-rich Cu-Ag alloys. The Σ5 GB chosen for this study becomes increasingly disordered near the solidus line while its local chemical composition approaches the liquidus composition at the same temperature. This behavior indicates the formation of a thin layer of the liquid phase in the GB when the grain composition approaches the solidus. The thickness of the liquid layer remains finite and the GB can be overheated/oversaturated to metastable states slightly above the solidus. The premelting behavior found by the simulations is qualitatively consistent with the phase-field model of the same binary system presented in Part I of this work [Mishin Y, Boettinger WJ, Warren JA, McFadden GB. Acta Mater, in press]. Although this agreement is encouraging, we discuss several problems arising when atomistic simulations are compared with phase-field modeling.

Interstellar gas and large grains toward HD 38087

International Nuclear Information System (INIS)

Snow, T.P.; Witt, A.

1989-01-01

High-dispersion IUE spectra have been obtained of HD 38087, a star associated with reflection nebulosity where 2175 A scattering has previously been observed. The presence of 2175 A in emission implies unusually large grains, an attempt was made to see how these unusual grains may have affected the depletions of gas-phase elements onto dust in the line of sight. Even though the observed scattering region constitutes only a fraction of the total column density of dust, it is expected that the present line-of-sight analysis provides useful information on the gas and dust in the scattering nebulosity. Somewhat larger overall depletions than normal are found, and it is found that the depletions of certain elements (manganese and zinc) are enhanced relative to the normal pattern of element-to-element depletions, suggesting that grain growth has occurred with some elements sticking to grains preferentially. The molecular fraction in the line of sight is low, in accord with similar lines of sight having low far-ultraviolet extinction and large depletions. 37 refs

Coarse-grained simulations of polyelectrolyte complexes: MARTINI models for poly(styrene sulfonate) and poly(diallyldimethylammonium)

Energy Technology Data Exchange (ETDEWEB)

Vögele, Martin [Institute for Computational Physics, University of Stuttgart, Stuttgart (Germany); Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Frankfurt a. M. (Germany); Holm, Christian; Smiatek, Jens, E-mail: smiatek@icp.uni-stuttgart.de [Institute for Computational Physics, University of Stuttgart, Stuttgart (Germany)

2015-12-28

We present simulations of aqueous polyelectrolyte complexes with new MARTINI models for the charged polymers poly(styrene sulfonate) and poly(diallyldimethylammonium). Our coarse-grained polyelectrolyte models allow us to study large length and long time scales with regard to chemical details and thermodynamic properties. The results are compared to the outcomes of previous atomistic molecular dynamics simulations and verify that electrostatic properties are reproduced by our MARTINI coarse-grained approach with reasonable accuracy. Structural similarity between the atomistic and the coarse-grained results is indicated by a comparison between the pair radial distribution functions and the cumulative number of surrounding particles. Our coarse-grained models are able to quantitatively reproduce previous findings like the correct charge compensation mechanism and a reduced dielectric constant of water. These results can be interpreted as the underlying reason for the stability of polyelectrolyte multilayers and complexes and validate the robustness of the proposed models.

Coarse-grained simulations of polyelectrolyte complexes: MARTINI models for poly(styrene sulfonate) and poly(diallyldimethylammonium)

International Nuclear Information System (INIS)

Vögele, Martin; Holm, Christian; Smiatek, Jens

2015-01-01

We present simulations of aqueous polyelectrolyte complexes with new MARTINI models for the charged polymers poly(styrene sulfonate) and poly(diallyldimethylammonium). Our coarse-grained polyelectrolyte models allow us to study large length and long time scales with regard to chemical details and thermodynamic properties. The results are compared to the outcomes of previous atomistic molecular dynamics simulations and verify that electrostatic properties are reproduced by our MARTINI coarse-grained approach with reasonable accuracy. Structural similarity between the atomistic and the coarse-grained results is indicated by a comparison between the pair radial distribution functions and the cumulative number of surrounding particles. Our coarse-grained models are able to quantitatively reproduce previous findings like the correct charge compensation mechanism and a reduced dielectric constant of water. These results can be interpreted as the underlying reason for the stability of polyelectrolyte multilayers and complexes and validate the robustness of the proposed models

Atomic-scale simulation of dust grain collisions: Surface chemistry and dissipation beyond existing theory

Science.gov (United States)

Quadery, Abrar H.; Doan, Baochi D.; Tucker, William C.; Dove, Adrienne R.; Schelling, Patrick K.

2017-10-01

The early stages of planet formation involve steps where submicron-sized dust particles collide to form aggregates. However, the mechanism through which millimeter-sized particles aggregate to kilometer-sized planetesimals is still not understood. Dust grain collision experiments carried out in the environment of the Earth lead to the prediction of a 'bouncing barrier' at millimeter-sizes. Theoretical models, e.g., Johnson-Kendall-Roberts and Derjaguin-Muller-Toporov theories, lack two key features, namely the chemistry of dust grain surfaces, and a mechanism for atomic-scale dissipation of energy. Moreover, interaction strengths in these models are parameterized based on experiments done in the Earth's environment. To address these issues, we performed atomic-scale simulations of collisions between nonhydroxylated and hydroxylated amorphous silica nanoparticles. We used the ReaxFF approach which enables modeling chemical reactions using an empirical potential. We found that nonhydroxylated nanograins tend to adhere with much higher probability than suggested by existing theories. By contrast, hydroxylated nanograins exhibit a strong tendency to bounce. Also, the interaction between dust grains has the characteristics of a strong chemical force instead of weak van der Waals forces. This suggests that the formation of strong chemical bonds and dissipation via internal atomic vibration may result in aggregation beyond what is expected based on our current understanding. Our results also indicate that experiments should more carefully consider surface conditions to mimic the space environment. We also report results of simulations with molten silica nanoparticles. It is found that molten particles are more likely to adhere due to viscous dissipation, which supports theories that suggest aggregation to kilometer scales might require grains to be in a molten state.

Mathematical simulation of point defect interaction with grain boundaries

International Nuclear Information System (INIS)

Bojko, V.S.

1987-01-01

Published works, where the interaction of point defects and grain boundaries was studied by mathematical simulation methods, have been analysed. Energetics of the vacancy formation both in nuclei of large-angle special grain boundaries and in lattice regions adjoining them has been considered. The data obtained permit to explain specific features of grain-boundary diffusion processes. Results of mathematical simulation of the interaction of impurity atoms and boundaries have been considered. Specific features of the helium atom interaction with large-angle grain boundaries are analysed as well

A physicochemical mechanism of chemical gas sensors using an AC analysis.

Science.gov (United States)

Moon, Jaehyun; Park, Jin-Ah; Lee, Su-Jae; Lee, Jeong-Ik; Zyung, Taehyong; Shin, Eui-Chol; Lee, Jong-Sook

2013-06-21

Electrical modeling of the chemical gas sensors was successfully applied to TiO2 nanofiber gas sensors by developing an equivalent circuit model where the junction capacitance as well as the resistance can be separated from the comparable stray capacitance. The Schottky junction impedance exhibited a characteristic skewed arc described by a Cole-Davidson function, and the variation of the fit and derived parameters with temperature, bias, and NO2 gas concentration indicated definitely a physicochemical sensing mechanism based on the Pt|TiO2 Schottky junctions against the conventional supposition of the enhanced sensitivity in nanostructured gas sensors with high grain boundary/surface area. Analysis on a model Pt|TiO2|Pt structure also confirmed the characteristic impedance response of TiO2 nanofiber sensors.

Swelling and gas release of grain-boundary pores in uranium dioxide

International Nuclear Information System (INIS)

Schrire, D.I.

1983-12-01

The swelling and gas release of overpressured grain boundary pores is sintered unirradiated uranium dioxide were investigated under isothermal conditions. The pores became overpressured when the ambient pressure was reduced, and the excess pressure driving force caused growth and interconnection of the pores, leading to eventual gas release. Swelling was measured continuously by a linear variable differential transformer, and open and closed porosity fractions were determined after the tests by immersion density and quantitative microscopy measurements. The sinter porosity consisted of pores situated on grain faces, grain edges, and grain corners. Isolated pores maintained their equilibrium shape while growing, without any measurable change in dihedral angle. Interconnection occurred predominantly along grain edges, without any evidence of pore sharpening or crack propagation at low driving forces. Extensive open porosity occurred at a threshold density of about 85% TD. There was an almost linear dependence of the initial swelling rate on the driving force, with an activation energy of 200+- 8 kJ/mole, in good agreement with published values of the activation energy for grain boundary diffusion

CHEMICAL EVOLUTION LIBRARY FOR GALAXY FORMATION SIMULATION

International Nuclear Information System (INIS)

Saitoh, Takayuki R.

2017-01-01

We have developed a software library for chemical evolution simulations of galaxy formation under the simple stellar population (SSP) approximation. In this library, all of the necessary components concerning chemical evolution, such as initial mass functions, stellar lifetimes, yields from Type II and Type Ia supernovae, asymptotic giant branch stars, and neutron star mergers, are compiled from the literature. Various models are pre-implemented in this library so that users can choose their favorite combination of models. Subroutines of this library return released energy and masses of individual elements depending on a given event type. Since the redistribution manner of these quantities depends on the implementation of users’ simulation codes, this library leaves it up to the simulation code. As demonstrations, we carry out both one-zone, closed-box simulations and 3D simulations of a collapsing gas and dark matter system using this library. In these simulations, we can easily compare the impact of individual models on the chemical evolution of galaxies, just by changing the control flags and parameters of the library. Since this library only deals with the part of chemical evolution under the SSP approximation, any simulation codes that use the SSP approximation—namely, particle-base and mesh codes, as well as semianalytical models—can use it. This library is named “CELib” after the term “Chemical Evolution Library” and is made available to the community.

CHEMICAL EVOLUTION LIBRARY FOR GALAXY FORMATION SIMULATION

Energy Technology Data Exchange (ETDEWEB)

Saitoh, Takayuki R., E-mail: saitoh@elsi.jp [Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro, Tokyo, 152-8551 (Japan)

2017-02-01

We have developed a software library for chemical evolution simulations of galaxy formation under the simple stellar population (SSP) approximation. In this library, all of the necessary components concerning chemical evolution, such as initial mass functions, stellar lifetimes, yields from Type II and Type Ia supernovae, asymptotic giant branch stars, and neutron star mergers, are compiled from the literature. Various models are pre-implemented in this library so that users can choose their favorite combination of models. Subroutines of this library return released energy and masses of individual elements depending on a given event type. Since the redistribution manner of these quantities depends on the implementation of users’ simulation codes, this library leaves it up to the simulation code. As demonstrations, we carry out both one-zone, closed-box simulations and 3D simulations of a collapsing gas and dark matter system using this library. In these simulations, we can easily compare the impact of individual models on the chemical evolution of galaxies, just by changing the control flags and parameters of the library. Since this library only deals with the part of chemical evolution under the SSP approximation, any simulation codes that use the SSP approximation—namely, particle-base and mesh codes, as well as semianalytical models—can use it. This library is named “CELib” after the term “Chemical Evolution Library” and is made available to the community.

Mesoscopic simulation of recrystallization and grain growth

International Nuclear Information System (INIS)

Rollett, A.D.

2000-01-01

A brief summary of simulation techniques for recrystallization and grain growth is given. The available methods include surface evolver, front tracking (including finite element methods and vertex methods), networks of curves, phase field, cellular automata, and Monte Carlo. Two of the models that use a regular lattice, the Potts model and the Cellular Automaton (CA) model, have proved to be very useful. Microstructure is represented on a discrete lattice where the value of the field at each point represents the local orientation of the material and boundaries exist between points of unlike orientation. Two issues are discussed: one is a hybrid approach to combining the standard Monte Carlo and cellular automata algorithms for recrystallization modeling. The second is adaptation of the MC method for modeling grain growth (and recrystallization) with physically based boundary properties. Both models have significant limitations in their standard forms. The CA model is very useful and efficient for simulating recrystallization with deterministic motion of the recrystallization fronts. It can be adapted to simulate curvature driven migration provided that multiple sub-lattices are used with a probabilistic switching rule. The Potts model is very successful in modeling curvature driven boundary migration and grain growth. It does not simulate the proportionality between boundary velocity and a stored energy driving force, however, unless rather restricted conditions of stored energy (in relation to the grain boundary energy) and lattice temperature are satisfied. A new approach based on a hybrid of the Potts model (MC) and the Cellular Automaton (CA) model has been developed to obtain the desired limiting behavior for both curvature-driven and stored energy-driven grain boundary migration. The combination of methods is achieved by interleaving the two different types of reorientation event in time. The results show that the hybrid algorithm models the Gibbs

Study of physical properties, gas generation and gas retention in simulated Hanford waste

International Nuclear Information System (INIS)

Bryan, S.A.; Pederson, L.R.; Scheele, R.D.

1993-04-01

The purpose of this study was to establish the chemical and physical processes responsible for the generation and retention of gases within high-level waste from Tank 101-SY on the Hanford Site. This research, conducted using simulated waste on a laboratory scale, supports the development of mitigation/remediation strategies for Tank 101-SY. Simulated waste formulations are based on actual waste compositions. Selected physical properties of the simulated waste are compared to properties of actual Tank 101-SY waste samples. Laboratory studies using aged simulated waste show that significant gas generation occurs thermally at current tank temperatures (∼60 degrees C). Gas compositions include the same gases produced in actual tank waste, primarily N 2 , N 2 O, and H 2 . Gas stoichiometries have been shown to be greatly influenced by several organic and inorganic constituents within the simulated waste. Retention of gases in the simulated waste is in the form of bubble attachment to solid particles. This attachment phenomenon is related to the presence of organic constituents (HEDTA, EDTA, and citrate) of the simulated waste. A mechanism is discussed that relates the gas bubble/particle interactions to the partially hydrophobic surface produced on the solids by the organic constituents

Simulation of pellet-cladding thermomechanical interaction and fission gas release

International Nuclear Information System (INIS)

Denis, Alicia; Soba, Alejandro

2003-01-01

This paper summarizes the present status of a computer code that describes some of the main phenomena occurring in a nuclear fuel rod throughout its life. Temperature distribution, thermal expansion, elastic and plastic strains, creep, mechanical interaction between pellet and cladding, fission gas release, gas mixing, swelling, and densification are modeled. The modular structure of the code allows for the incorporation of models to simulate different phenomena and material properties. Collapsible rods can be also simulated. The code is bidimensional, assumes cylindrical symmetry for the rod and uses the finite element method to integrate the differential equations. The stress-strain and heat conduction problems are nonlinear due to plasticity and to the temperature dependence of the thermal conductivity. The fission gas inventory is calculated with a diffusion model, assuming spherical grains and using a one-dimensional finite element scheme. Pressure increase, swelling and densification are coupled with the stress field. Good results are obtained for the simulation of the irradiation tests of the first argentine prototypes of MOX fuels, where the bamboo effect is clearly observed, and of the FUMEX series for the fuel centerline temperature, the inside rod pressure and the fractional gas release.

Variation in ruminal in situ degradation of crude protein and starch from maize grains compared to in vitro gas production kinetics and physical and chemical characteristics.

Science.gov (United States)

Seifried, Natascha; Steingaß, Herbert; Schipprack, Wolfgang; Rodehutscord, Markus

2016-10-01

The objectives of this study were (1) to evaluate in situ ruminal dry matter (DM), crude protein (CP) and starch degradation characteristics and in vitro gas production (GP) kinetics using a set of 20 different maize grain genotypes and (2) to predict the effective degradation (ED) of CP and starch from chemical and physical characteristics alone or in combination with in vitro GP measurements. Maize grains were characterised by different chemical and physical characteristics. Ruminal in situ degradation was measured in three lactating Jersey cows. Ground grains (sieve size: 2 mm) were incubated in bags for 1, 2, 4, 8, 16, 24, 48 and 72 h. Bag residues were analysed for CP and starch content. Degradation kinetics was determined and the ED of DM, CP and starch calculated using a ruminal passage rate of 5%/h and 8%/h. The GP of the grains (sieve size: 1 mm) was recorded after 2, 4, 6, 8, 12, 24, 48 and 72 h incubation in buffered rumen fluid and fitted to an exponential equation to determine GP kinetics. Correlations and stepwise multiple linear regressions were evaluated for the prediction of ED calculated for a passage rate of 5%/h (ED5) for CP (EDCP5) and starch (EDST5). The in situ parameters and ED5 varied widely between genotypes with average values (±SD) of 64% ± 4.2, 62% ± 4.1 and 65% ± 5.2 for ED5 of DM, EDCP5 and EDST5 and were on average 10 percentage points lower for a passage rate of 8%/h. Degradation rates varied between 4.8%/h and 7.4%/h, 4.1%/h and 6.5%/h and 5.3%/h and 8.9%/h for DM, CP and starch, respectively. These rates were in the same range as GP rates (6.0-8.3%/h). The EDCP5 and EDST5 were related to CP concentration and could be evaluated in detail using CP fractions and specific amino acids. In vitro GP measurements and GP rates correlated well with EDCP5 and EDST5 and predicted EDCP5 and EDST5 in combination with the chemical characteristics of the samples. Equations can be used to obtain quick and cost effective information

Monte carlo simulation of anisotropic grain growth in liquid phase sintering

International Nuclear Information System (INIS)

Han, Yoon Soo; Kim, Do Kyung

2003-01-01

One of the key techniques in modern engineering ceramic system is microstructural control of anisotropic grain growth because grain orientation and shape proved to have an influence on mechanic, dielectric and electric behavior of ceramics. But until now, computer simulation for grain growth has not sufficiently addressed to this subject. The reason is that simulation algorithm was laborious because it has to contain mass transfer through liquid phase and especially anisotropic grain growth has to be considered based on interfacial properties in real system. The goal of present study is simulation of anisotropic grain growth in liquid phase by Q-states model. To give anisotropic inherency to grains, constraint on mobility to specific boundaries was applied. For comparison, we measured grain size distribution and deduced grain growth kinetics from relation ship between average grain size and time. As a result, the grain size distribution functions become broader and the peak height decreases as the anisotropy is increased. The growth exponent 0.67 and 0.47 found by linear fitting have slightly different values in comparison with work of Grest et al. but similar is trend to the decrease of exponent with anisotropy

Simulation study on the growth of grains in dusty plasmas

International Nuclear Information System (INIS)

Sato, Tetsuya; Watanabe, Kunihiko

1997-01-01

A new particle simulation code is developed for studying the dynamics of the grains which are exposed to charging by the background plasma particles. Effects of regular attachment of electrons and ions, effects of secondary electron emission, and coagulation of grains are included in this code. Simulation results show that grains randomly change their charges from negative to positive, or from positive to negative in a 'flip-flop' fashion as a result of competition between the electron attachment and secondary electron emission. It is found that the flip-flop effect becomes remarkable when the radius of grains is of the order of 10 nm, because the attachment of a single electron to a grain is less effective on the surface potential for larger grains, while the average probability of electron attachment is smaller for smaller grains. Grains with opposite charges attract each other to coagulate, so that grains of size of 10 nm are likely to grow in size. The flip-flop effect is found to be essential to the growth of grains. (author)

Chemical composition of the semi-volatile grains of comet 67P/Churyumov-Gerasimenko

Science.gov (United States)

Wurz, Peter; Altwegg, Kathrin; Balsiger, Hans; Berthelier, Jean-Jacques; Bieler, André; Calmonte, Ursina; De Keyser, Johan; Fiethe, Björn; Fuselier, Stefan; Gasc, Sébastien; Gombosi, Tamas; Jäckel, Annette; Korth, Axel; Le Roy, Lena; Mall, Urs; Rème, Henri; Rubin, Martin; Tzou, Chia-Yu

2017-04-01

The European Space Agency's Rosetta spacecraft (Glassmeier et al., 2007) has been in orbit of the comet 67P/Churyumov-Gerasimenko (67P/C-G) since August 2014. On board is the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument suite (Balsiger et al., 2007). ROSINA consists of two mass spectrometers, the Double Focusing Mass Spectrometer (DFMS) and the Reflectron-type Time-Of-Flight (RTOF) (Scherer et al., 2006), as well as the COmet Pressure Sensor (COPS). ROSINA is designed to detect and monitor the neutral gas and thermal plasma environment in the comet's coma by in situ investigation. The two mass spectrometers have high dynamic ranges and complement each other with high mass resolution (DFMS) and high time resolution and large mass range (RTOF). Especially the unprecedented sensitivity and mass resolution of DFMS together with the large mass range of RTOF allow determining precisely light species (e.g. isotopologues) as well as detecting heavy organic species. The pressure sensor COPS measures total gas densities, bulk velocities, and gas temperatures. ROSINA has been collecting data on the composition of the coma and activity of the comet from 3.5 AU to pericentre and out again to 3.5 AU. The Rosetta mission presents a unique opportunity to directly sample the parent species in the thin cometary atmosphere of a Kuiper-belt object at distances in excess of 2.5 AU from the Sun all the way to the pericentre of the cometary orbit at 1.24 AU. The ROSINA experiment continuously measured the chemical composition of the gases in the cometary coma. Occasionally, a dust grain of cometary origin enters the ion source of a ROSINA instrument where the volatile part evaporates since these ion sources are hot. We will report on the first measurements of the volatile inventory of such dust grains. Volatile release from cometary dust grains was observed with all three ROSINA instruments on several occasions. Because the volatile content of such a dust

Metal-assisted chemical etching of CIGS thin films for grain size analysis

Energy Technology Data Exchange (ETDEWEB)

Xue, Chaowei [Research and Development Centre, Hanergy Thin Film Power Group Limited, Chengdu (China); Loi, Huu-Ha; Duong, Anh; Parker, Magdalena [Failure Analysis Department, MiaSole Hi-Tech Corp., Santa Clara, CA (United States)

2016-09-15

Grain size of the CIGS absorber is an important monitoring factor in the CIGS solar cell manufacturing. Electron backscatter diffraction (EBSD) analysis is commonly used to perform CIGS grain size analysis in the scanning electron microscope (SEM). Although direct quantification on SEM image using the average grain intercept (AGI) method is faster and simpler than EBSD, it is hardly applicable on CIGS thin films. The challenge is that, not like polycrystalline silicon, to define grain boundaries by selective chemical etching is not easily realizable for the multi-component CIGS alloy. In this Letter, we present direct quantification of CIGS thin film grain size using the AGI method by developing metal-assisted wet chemical etching process to define CIGS grain boundaries. The calculated value is similar to EBSD result. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Simulation of the thermomechanical interaction between pellet and cladding and fission gas release

International Nuclear Information System (INIS)

Denis, Alicia C.; Soba, Alejandro

2000-01-01

This paper summarizes the present status of a computer code that simulates some of the main phenomena occurring in a fuel element of a nuclear power reactor throughout its life. Temperature distribution, thermal expansion, elastic and plastic strains, creep, mechanical interaction between pellet and cladding, fission gas release, swelling and densification are modeled. Thermal expansion gives origin to elastic or plastic strains, which adequately describe the bamboo effect. The code assumes an axial symmetric rod and hence, cylindrical finite elements are employed for the discretization. The fission gas inventory is calculated by means of a diffusion model, which assumes spherical grains and uses also a finite element scheme. Once the temperature distribution in the pellet and the cladding is obtained and in order to reduce the calculation time, the rod is divided into five cylindrical rings where the temperature is averaged. In each ring the gas diffusion problem is solved in one representative grain and the results are then extended to the whole ring. The pressure, increased by the released gas, interacts with the stress field. Densification and swelling due to solid and gaseous fission products are also considered. Experiments, particularly those of the FUMEX series, are simulated with this code. A good agreement is obtained for the fuel center line temperature, the inside rod pressure and the fractional gas release. (author)

Coarse-grained molecular dynamics simulations of polymerization with forward and backward reactions.

Science.gov (United States)

Krajniak, Jakub; Zhang, Zidan; Pandiyan, Sudharsan; Nies, Eric; Samaey, Giovanni

2018-06-11

We develop novel parallel algorithms that allow molecular dynamics simulations in which byproduct molecules are created and removed because of the chemical reactions during the molecular dynamics simulation. To prevent large increases in the potential energy, we introduce the byproduct molecules smoothly by changing the non-bonded interactions gradually. To simulate complete equilibrium reactions, we allow the byproduct molecules attack and destroy created bonds. Modeling of such reactions are, for instance, important to study the pore formation due to the presence of e.g. water molecules or development of polymer morphology during the process of splitting off byproduct molecules. Another concept that could be studied is the degradation of polymeric materials, a very important topic in a recycling of polymer waste. We illustrate the method by simulating the polymerization of polyethylene terephthalate (PET) at the coarse-grained level as an example of a polycondensation reaction with water as a byproduct. The algorithms are implemented in a publicly available software package and are easily accessible using a domain-specific language that describes chemical reactions in an input configuration file. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc.

Non-periodic molecular dynamics simulations of coarse grained lipid bilayer in water

DEFF Research Database (Denmark)

Kotsalis, E. M.; Hanasaki, I.; Walther, Jens Honore

2010-01-01

We present a multiscale algorithm that couples coarse grained molecular dynamics (CGMD) with continuum solver. The coupling requires the imposition of non-periodic boundary conditions on the coarse grained Molecular Dynamics which, when not properly enforced, may result in spurious fluctuations o...... in simulating more complex systems by performing a non-periodic Molecular Dynamics simulation of a DPPC lipid in liquid coarse grained water.......We present a multiscale algorithm that couples coarse grained molecular dynamics (CGMD) with continuum solver. The coupling requires the imposition of non-periodic boundary conditions on the coarse grained Molecular Dynamics which, when not properly enforced, may result in spurious fluctuations...... of the material properties of the system represented by CGMD. In this paper we extend a control algorithm originally developed for atomistic simulations [3], to conduct simulations involving coarse grained water molecules without periodic boundary conditions. We demonstrate the applicability of our method...

Impact fracture experiments simulating interstellar grain-grain collisions

Science.gov (United States)

Freund, Friedemann; Chang, Sherwood; Dickinson, J. Thomas

1990-01-01

Oxide and silicate grains condensing during the early phases of the formation of the solar system or in the outflow of stars are exposed to high partial pressures of the low-z elements H, C, N and O and their simple gaseous compounds. Though refractory minerals are nominally anhydrous and non-carbonate, if they crystallize in the presence of H2O, N2 and CO or CO2 gases, they dissolve traces of the gaseous components. The question arises: How does the presence of dissolved gases or gas components manifest itself when grain-grain collisions occur. What are the gases emitted when grains are shattered during a collision event. Researchers report on fracture experiments in ultrahigh vacuum (UHV, approximately less than 10 to the -8th power mbar) designed to measure (by means of a quadrupole mass spectrometer, QMS, with microns to ms time resolution) the emission of gases and vapors during and after impact (up to 1.5 sec). Two terrestrial materials were chosen which represent structural and compositional extremes: olivine (San Carlos, AZ), a densely packed Mg-Fe(2+) silicate from the upper mantle, available as 6 to 12 mm single crystals, and obsidian (Oregon), a structurally open, alkaline-SiO2-rich volcanic glass. In the olivine crystals OH- groups have been identified spectroscopically, as well as H2 molecules. Obsidian is a water-rich glass containing OH- besides H2O molecules. Olivine from the mantle often contains CO2, either as CO2-rich fluid in fluid inclusions or structurally dissolved or both. By analogy to synthetic glasses CO2 in the obsidian may be present in form of CO2 molecules in voids of molecular dimensions, or as carbonate anions, CO3(2-). No organic molecules have been detected spectroscopically in either material. Results indicate that refractory oxide/silicates which contain dissolved traces of the H2O and CO/CO2 components but no spectroscopically detectable traces of organics may release complex H-C-O (possibly H-C-N-O) molecules upon fracture

Making coarse grained polymer simulations quantitatively predictive for statics and dynamics

Science.gov (United States)

Kremer, Kurt

2010-03-01

By combining input from short simulation runs of rather small systems with all atomistic details together with properly adapted coarse grained models we are able quantitatively predict static and especially dynamical properties of both pure polymer melts of long fully entangled but also of systems with low molecular weight additives. Comparisons to rather different experiments such as diffusion constant measurements or NMR relaxation experiments show a remarkable quantitative agreement without any adjustable parameter. Reintroduction of chemical details into the coarse grained trajectories allows the study of long time trajectories in all atomistic detail providing the opportunity for rather different means of data analysis. References: V. Harmandaris, K. Kremer, Macromolecules, in press (2009) V. Harmandaris et al, Macromolecules, 40, 7026 (2007) B. Hess, S. Leon, N. van der Vegt, K. Kremer, Soft Matter 2, 409 (2006) D. Fritz et al, Soft Matter 5, 4556 (2009)

Simulation of pellet-cladding thermomechanical interaction and fission gas release

International Nuclear Information System (INIS)

Denis, A.; Soba, A.

2001-01-01

This paper summarizes the present status of a computer code that describes some of the main phenomena occurring in a nuclear fuel element throughout its life. Temperature distribution, thermal expansion, elastic and plastic strains, creep, mechanical interaction between pellet and cladding, fission gas release, swelling and densification are modelized. The code assumes an axi-symmetric rod and hence, cylindrical finite elements are employed for the discretization. Due to the temperature dependence of the thermal conductivity, the heat conduction problem is non-linear. Thermal expansion gives origin to elastic or plastic strains, which adequately describe the bamboo effect. Plasticity renders the stress-strain problem non linear. The fission gas inventory is calculated by means of a diffusion model, which assumes spherical grains and uses a finite element scheme. In order to reduce the calculation time, the rod is divided into five cylindrical rings where the temperature is averaged. In each ring the gas diffusion problem is solved in one grain and the results are then extended to the whole ring. The pressure, increased by the released gas, interacts with the stress field. Densification and swelling due to solid and gaseous fission products are also considered. Experiments, particularly those of the FUMEX series, are simulated with this code. A good agreement is obtained for the fuel center line temperature, the inside rod pressure and the fractional gas release. (author)

Chemical kinetics of gas reactions

CERN Document Server

Kondrat'Ev, V N

2013-01-01

Chemical Kinetics of Gas Reactions explores the advances in gas kinetics and thermal, photochemical, electrical discharge, and radiation chemical reactions. This book is composed of 10 chapters, and begins with the presentation of general kinetic rules for simple and complex chemical reactions. The next chapters deal with the experimental methods for evaluating chemical reaction mechanisms and some theories of elementary chemical processes. These topics are followed by discussions on certain class of chemical reactions, including unimolecular, bimolecular, and termolecular reactions. The rema

Large scale statistics for computational verification of grain growth simulations with experiments

International Nuclear Information System (INIS)

Demirel, Melik C.; Kuprat, Andrew P.; George, Denise C.; Straub, G.K.; Misra, Amit; Alexander, Kathleen B.; Rollett, Anthony D.

2002-01-01

It is known that by controlling microstructural development, desirable properties of materials can be achieved. The main objective of our research is to understand and control interface dominated material properties, and finally, to verify experimental results with computer simulations. We have previously showed a strong similarity between small-scale grain growth experiments and anisotropic three-dimensional simulations obtained from the Electron Backscattered Diffraction (EBSD) measurements. Using the same technique, we obtained 5170-grain data from an Aluminum-film (120 (micro)m thick) with a columnar grain structure. Experimentally obtained starting microstructure and grain boundary properties are input for the three-dimensional grain growth simulation. In the computational model, minimization of the interface energy is the driving force for the grain boundary motion. The computed evolved microstructure is compared with the final experimental microstructure, after annealing at 550 C. Characterization of the structures and properties of grain boundary networks (GBN) to produce desirable microstructures is one of the fundamental problems in interface science. There is an ongoing research for the development of new experimental and analytical techniques in order to obtain and synthesize information related to GBN. The grain boundary energy and mobility data were characterized by Electron Backscattered Diffraction (EBSD) technique and Atomic Force Microscopy (AFM) observations (i.e., for ceramic MgO and for the metal Al). Grain boundary energies are extracted from triple junction (TJ) geometry considering the local equilibrium condition at TJ's. Relative boundary mobilities were also extracted from TJ's through a statistical/multiscale analysis. Additionally, there are recent theoretical developments of grain boundary evolution in microstructures. In this paper, a new technique for three-dimensional grain growth simulations was used to simulate interface migration

Mesoscale simulations of shockwave energy dissipation via chemical reactions.

Science.gov (United States)

Antillon, Edwin; Strachan, Alejandro

2015-02-28

We use a particle-based mesoscale model that incorporates chemical reactions at a coarse-grained level to study the response of materials that undergo volume-reducing chemical reactions under shockwave-loading conditions. We find that such chemical reactions can attenuate the shockwave and characterize how the parameters of the chemical model affect this behavior. The simulations show that the magnitude of the volume collapse and velocity at which the chemistry propagates are critical to weaken the shock, whereas the energetics in the reactions play only a minor role. Shock loading results in transient states where the material is away from local equilibrium and, interestingly, chemical reactions can nucleate under such non-equilibrium states. Thus, the timescales for equilibration between the various degrees of freedom in the material affect the shock-induced chemistry and its ability to attenuate the propagating shock.

Grain-gas interaction in envelopes of red giants

International Nuclear Information System (INIS)

Maciel, W.J.

1976-01-01

A model for the ejection of the dust shell of red giant stars through the action of the stellar radiation pressure is developed. Being momentum-coupled to the gas, the dust shell can drive an effective mass loss. On the other hand, the grain injection rate into the interstellar space can be estimated [pt

Dynamical simulation of structural multiplicity in grain boundaries

International Nuclear Information System (INIS)

Majid, I.; Bristowe, P.D.

1987-06-01

Work on a computer simulation study of a low-energy high-angle boundary structure which is not periodic have been recently reported. This result is of interest since grain boundary structures are usually assumed to have a periodicity corresponding to the appropriate coincidence site lattice (CSL) and many experimental observations of the structure of grain boundaries performed using conventional and high-resolution electron microscopy, electron diffraction and x-ray diffraction appear to support this work. However, this work, using empirical interatomic pair potentials and the relaxation method of molecular statics, have simulated a Σ = 5 36.87 0 (001) twist boundary and found a low energy structure having a larger repeat cell than the CSL and is composed of two different types of structural unit that are randomly distributed in the boundary plane. This result, which has been termed the multiplicity of grain boundary structures, has also been found in the simulation of tilt boundaries. The multiplicity phenomenon is of special interest in twist boundaries since it is used as a structural model to explain the x-ray scattering from a Σ = 5 boundary in gold. These scattering patterns had previously remained unexplained using stable structures that had simple CSL periodicity. Also, the effect of having a multiple number of low energy structural units coexisting in the grain boundary is of more general interest since it implies that the boundary structures may be quasi-periodic and, in some circumstances, may even result in a roughening of the boundary plane. This paper extends this work by showing, using molecular dynamics, that a multiplicity of structural units can actually nucleate spontaneously in a high-angle grain boundary at finite temperatures

An international effort to compare gas hydrate reservoir simulators

Energy Technology Data Exchange (ETDEWEB)

Wilder, J.W. [Akron Univ., Akron, OH (United States). Dept. of Theoretical and Applied Math; Moridis, G.J. [California Univ., Berkely, CA (United States). Earth Sciences Div., Lawrence Berkely National Lab.; Wilson, S.J. [Ryder Scott Co., Denver, CO (United States); Kurihara, M. [Japan Oil Engineering Co. Ltd., Tokyo (Japan); White, M.D. [Pacific Northwest National Laboratory Hydrology Group, Richland, WA (United States); Masuda, Y. [Tokyo Univ., Tokyo (Japan). Dept. of Geosystem Engineering; Anderson, B.J. [National Energy Technology Lab., Morgantown, WV (United States)]|[West Virginia Univ., Morgantown, WV (United States). Dept. of Chemical Engineering; Collett, T.S. [United States Geological Survey, Denver, CO (United States); Hunter, R.B. [ASRC Energy Services, Anchorage, AK (United States); Narita, H. [National Inst. of Advanced Industrial Science and Technology, MEthane hydrate Research Lab., Sapporo (Japan); Pooladi-Darvish, M. [Fekete Associates Inc., Calgary, AB (Canada); Rose, K.; Boswell, R. [National Energy Technology Lab., Morgantown, WV (United States)

2008-07-01

In this study, 5 different gas hydrate production scenarios were modeled by the CMG STARS, HydateResSim, MH-21 HYDRES, STOMP-HYD and the TOUGH+HYDRATE reservoir simulators for comparative purposes. The 5 problems ranged in complexity from 1 to 3 dimensional with radial symmetry, and in horizontal dimensions of 20 meters to 1 kilometer. The scenarios included (1) a base case with non-isothermal multi-fluid transition to equilibrium, (2) a base case with gas hydrate (closed-domain hydrate dissociation), (3) dissociation in a 1-D open domain, (4) gas hydrate dissociation in a one-dimensional radial domain, similarity solutions, (5) gas hydrate dissociation in a two-dimensional radial domain. The purpose of the study was to compare the world's leading gas hydrate reservoir simulators in an effort to improve the simulation capability of experimental and naturally occurring gas hydrate accumulations. The problem description and simulation results were presented for each scenario. The results of the first scenario indicated very close agreement among the simulators, suggesting that all address the basics of mass and heat transfer, as well as overall process of gas hydrate dissociation. The third scenario produced the initial divergence among the simulators. Other differences were noted in both scenario 4 and 5, resulting in significant corrections to algorithms within several of the simulators. The authors noted that it is unlikely that these improvements would have been identified without this comparative study due to a lack of real world data for validation purposes. It was concluded that the solution for gas hydrate production involves a combination of highly coupled fluid, heat and mass transport equations combined with the potential for formation or disappearance of multiple solid phases in the system. The physical and chemical properties of the rocks containing the gas hydrate depend on the amount of gas hydrate present in the system. Each modeling and

Long time scale simulation of a grain boundary in copper

DEFF Research Database (Denmark)

Pedersen, A.; Henkelman, G.; Schiøtz, Jakob

2009-01-01

A general, twisted and tilted, grain boundary in copper has been simulated using the adaptive kinetic Monte Carlo method to study the atomistic structure of the non-crystalline region and the mechanism of annealing events that occur at low temperature. The simulated time interval spanned 67 mu s...... was also observed. In the final low-energy configurations, the thickness of the region separating the crystalline grains corresponds to just one atomic layer, in good agreement with reported experimental observations. The simulated system consists of 1307 atoms and atomic interactions were described using...

Fission gas induced deformation model for FRAP-T6 and NSRR irradiated fuel test simulations

Energy Technology Data Exchange (ETDEWEB)

Nakamura, Takehiko; Sasajima, Hideo; Fuketa, Toyoshi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Hosoyamada, Ryuji; Mori, Yukihide

1996-11-01

Pulse irradiation tests of irradiated fuels under simulated reactivity initiated accidents (RIAs) have been carried out at the Nuclear Safety Research Reactor (NSRR). Larger cladding diameter increase was observed in the irradiated fuel tests than in the previous fresh fuel tests. A fission gas induced cladding deformation model was developed and installed in a fuel behavior analysis code, FRAP-T6. The irradiated fuel tests were analyzed with the model in combination with modified material properties and fuel cracking models. In Test JM-4, where the cladding temperature rose to higher temperatures and grain boundary separation by the pulse irradiation was significant, the fission gas model described the cladding deformation reasonably well. The fuel had relatively flat radial power distribution and the grain boundary gas from the whole radius was calculated to contribute to the deformation. On the other hand, the power density in the irradiated LWR fuel rods in the pulse irradiation tests was remarkably higher at the fuel periphery than the center. A fuel thermal expansion model, GAPCON, which took account of the effect of fuel cracking by the temperature profile, was found to reproduce well the LWR fuel behavior with the fission gas deformation model. This report present details of the models and their NSRR test simulations. (author)

Effects of dormancy-breaking chemicals on ABA levels in barley grain embryos

NARCIS (Netherlands)

Wang, M.; Meulen, R.M. van der; Visser, K.; Schalk, H.P. van; Duijn, B. van; Boer, A.H. de

1998-01-01

The endogenous ABA contents of dormant and nondormant barley grains were determined following application of different compounds to break dormancy. The chemicals used for breaking of dormancy in intact dormant grains were weak and strong acids, alcohols,. hydrogen peroxide, cyanide, nitrate,

TMVOC, simulator for multiple volatile organic chemicals

International Nuclear Information System (INIS)

Pruess, Karsten; Battistelli, Alfredo

2003-01-01

TMVOC is a numerical simulator for three-phase non-isothermal flow of water, soil gas, and a multicomponent mixture of volatile organic chemicals (VOCs) in multidimensional heterogeneous porous media. It is an extension of the TOUGH2 general-purpose simulation program developed at the Lawrence Berkeley National Laboratory. TMVOC is designed for applications to contamination problems that involve hydrocarbon fuel or organic solvent spills in saturated and unsaturated zones. It can model contaminant behavior under ''natural'' environmental conditions, as well as for engineered systems, such as soil vapor extraction, groundwater pumping, or steam-assisted source remediation. TMVOC is upwards compatible with T2VOC (Falta et al., 1995) and can be initialized from T2VOC-style initial conditions. The main enhancements in TMVOC relative to T2VOC are as follows: a multicomponent mixture of volatile organic chemicals can be modeled; any and all combinations of the three phases water-oil-gas are treated; several non-condensible gases may be present; diffusion is treated in all phases in a manner that is fully coupled with phase partitioning. This paper gives a brief summary of the methodology used in TMVOC as well as highlighting some implementation issues. Simulation of a NAPL spill and subsequent remediation is discussed for a 2-D vertical section of a saturated-unsaturated flow problem

Simulation of growing grains under orientation relation - dependent quadruple point dragging

International Nuclear Information System (INIS)

Ito, K

2015-01-01

The growth behaviour of a specified grain embedded in matrix grains, for which the migration mobility of the quadruple points depended on the relation between the orientations of the growing and shrinking grains, was studied using a modified Potts MC-type threedimensional simulation. Large embedded grains continued to grow without being overcome by coarsening matrix grains, whereas small embedded grains disappeared, under the influence of the relative mobilities of the quadruple points, the composition of the matrix grain texture and the width of the grain size distribution of the matrix grains. These results indicate that orientation relation-dependent quadruple point dragging can affect the recrystallization texture during the grain coarsening stage. (paper)

Grain-scale imaging and compositional characterization of cryo-preserved India NGHP 01 gas-hydrate-bearing cores

Science.gov (United States)

Stern, Laura A.; Lorenson, T.D.

2014-01-01

We report on grain-scale characteristics and gas analyses of gas-hydrate-bearing samples retrieved by NGHP Expedition 01 as part of a large-scale effort to study gas hydrate occurrences off the eastern-Indian Peninsula and along the Andaman convergent margin. Using cryogenic scanning electron microscopy, X-ray spectroscopy, and gas chromatography, we investigated gas hydrate grain morphology and distribution within sediments, gas hydrate composition, and methane isotopic composition of samples from Krishna–Godavari (KG) basin and Andaman back-arc basin borehole sites from depths ranging 26 to 525 mbsf. Gas hydrate in KG-basin samples commonly occurs as nodules or coarse veins with typical hydrate grain size of 30–80 μm, as small pods or thin veins 50 to several hundred microns in width, or disseminated in sediment. Nodules contain abundant and commonly isolated macropores, in some places suggesting the original presence of a free gas phase. Gas hydrate also occurs as faceted crystals lining the interiors of cavities. While these vug-like structures constitute a relatively minor mode of gas hydrate occurrence, they were observed in near-seafloor KG-basin samples as well as in those of deeper origin (>100 mbsf) and may be original formation features. Other samples exhibit gas hydrate grains rimmed by NaCl-bearing material, presumably produced by salt exclusion during original hydrate formation. Well-preserved microfossil and other biogenic detritus are also found within several samples, most abundantly in Andaman core material where gas hydrate fills microfossil crevices. The range of gas hydrate modes of occurrence observed in the full suite of samples suggests a range of formation processes were involved, as influenced by local in situconditions. The hydrate-forming gas is predominantly methane with trace quantities of higher molecular weight hydrocarbons of primarily microbial origin. The composition indicates the gas hydrate is Structure I.

Simulations of Propane and Butane Gas Sensor Based on Pristine Armchair Graphene Nanoribbon

Science.gov (United States)

Rashid, Haroon; Koel, Ants; Rang, Toomas

2018-05-01

Over the last decade graphene and its derivatives have gained a remarkable place in research field. As silicon technology is approaching to its geometrical limits so there is a need of alternate that can replace it. Graphene has emerged as a potential candidate for future nano-electronics applications due to its exceptional and extraordinary chemical, optical, electrical and mechanical properties. Graphene based sensors have gained significance for a wide range of sensing applications like detection of biomolecules, chemicals and gas molecules. It can be easily used to make electrical contacts and manipulate them according to the requirements as compared to the other nanomaterials. The intention of the work presented in this article is to contribute in this field by simulating a novel and cheap graphene nanoribbon sensor for the household gas leakage detection. QuantumWise Atomistix (ATK) software is used for the simulations of propane and butane gas sensor. Projected device density of the states (PDDOS) and the transmission spectrum of the device in the proximity of gas molecules are calculated and discussed. The change in the electric current through the device in the presence of the gas molecules is used as a gas detection mechanism for the simulated sensor.

Design and simulation of betavoltaic battery using large-grain polysilicon

International Nuclear Information System (INIS)

Yao, Shulin; Song, Zijun; Wang, Xiang; San, Haisheng; Yu, Yuxi

2012-01-01

In this paper, we present the design and simulation of a p–n junction betavoltaic battery based on large-grain polysilicon. By the Monte Carlo simulation, the average penetration depth were obtained, according to which the optimal depletion region width was designed. The carriers transport model of large-grain polysilicon is used to determine the diffusion length of minority carrier. By optimizing the doping concentration, the maximum power conversion efficiency can be achieved to be 0.90% with a 10 mCi/cm 2 Ni-63 source radiation. - Highlights: ► Ni 63 is employed as the pure beta radioisotope source. ► The planar p–n junction betavoltaic battery is based on large-grain polysilicon. ► The carriers transport model of large-grain polysilicon is used to determine the diffusion length of minority carrier. ► The average penetration depth was obtained by using the Monte Carlo Method.

Simulated experiment for elimination of chemical and biological warfare agents by making use of microwave plasma torch

International Nuclear Information System (INIS)

Hong, Yong C.; Kim, Jeong H.; Uhm, Han S.

2004-01-01

The threat of chemical and biological warfare agents in a domestic terrorist attack and in military conflict is increasing worldwide. Elimination and decontamination of chemical and biological warfare (CBW) agents are immediately required after such an attack. Simulated experiment for elimination of CBW agents by making use of atmospheric-pressure microwave plasma torches is carried out. Elimination of biological warfare agents indicated by the vitrification or burnout of sewage sludge powders and decomposition of toluene gas as a chemical agent stimulant are presented. A detailed characterization for the elimination of the simulant chemicals using Fourier transform infrared and gas chromatography is also presented

Simulated experiment for elimination of chemical and biological warfare agents by making use of microwave plasma torch

Science.gov (United States)

Hong, Yong C.; Kim, Jeong H.; Uhm, Han S.

2004-02-01

The threat of chemical and biological warfare agents in a domestic terrorist attack and in military conflict is increasing worldwide. Elimination and decontamination of chemical and biological warfare (CBW) agents are immediately required after such an attack. Simulated experiment for elimination of CBW agents by making use of atmospheric-pressure microwave plasma torches is carried out. Elimination of biological warfare agents indicated by the vitrification or burnout of sewage sludge powders and decomposition of toluene gas as a chemical agent stimulant are presented. A detailed characterization for the elimination of the simulant chemicals using Fourier transform infrared and gas chromatography is also presented.

Tholins - Organic chemistry of interstellar grains and gas

Science.gov (United States)

Sagan, C.; Khare, B. N.

1979-01-01

The paper discusses tholins, defined as complex organic solids formed by the interaction of energy - for example, UV light or spark discharge - with various mixtures of cosmically abundant gases - CH4, C2H6, NH3, H2O, HCHO, and H2S. It is suggested that tholins occur in the interstellar medium and are responsible for some of the properties of the interstellar grains and gas. Additional occurrences of tholins are considered. Tholins have been produced experimentally; 50 or so pyrolytic fragments of the brown, sometimes sticky substances have been identified by gas chromatography-mass spectrometry, and the incidence of these fragments in tholins produced by different procedures is reported.

In vitro gas production of wheat grain flour coated with different fat ...

African Journals Online (AJOL)

Gas production (GP) is a rapid method for feedstuffs assessment. A study was done to investigate wheat grain coated with hydrogenated tallow (HT) and hydrogenated palm oil (HP) of different fatty acids types and levels to study total gas production. Approximately, 200 mg (DM basis) of sample was weighed and inserted in ...

Modelling isothermal fission gas release

International Nuclear Information System (INIS)

Uffelen, P. van

2002-01-01

The present paper presents a new fission gas release model consisting of two coupled modules. The first module treats the behaviour of the fission gas atoms in spherical grains with a distribution of grain sizes. This module considers single atom diffusion, trapping and fission induced re-solution of gas atoms associated with intragranular bubbles, and re-solution from the grain boundary into a few layers adjacent to the grain face. The second module considers the transport of the fission gas atoms along the grain boundaries. Four mechanisms are incorporated: diffusion controlled precipitation of gas atoms into bubbles, grain boundary bubble sweeping, re-solution of gas atoms into the adjacent grains and gas flow through open porosity when grain boundary bubbles are interconnected. The interconnection of the intergranular bubbles is affected both by the fraction of the grain face occupied by the cavities and by the balance between the bubble internal pressure and the hydrostatic pressure surrounding the bubbles. The model is under validation. In a first step, some numerical routines have been tested by means of analytic solutions. In a second step, the fission gas release model has been coupled with the FTEMP2 code of the Halden Reactor Project for the temperature distribution in the pellets. A parametric study of some steady-state irradiations and one power ramp have been simulated successfully. In particular, the Halden threshold for fission gas release and two simplified FUMEX cases have been computed and are summarised. (author)

Constitutive modelling of the undrained shear strength of fine grained soils containing gas

Energy Technology Data Exchange (ETDEWEB)

Grozic, J.L.H. [Calgary Univ., AB (Canada); Nadim, F.; Kvalstad, T.J. [Norwegian Geotechnical Inst., Oslo (Norway)

2002-07-01

The behaviour of fine grained gassy soils was studied in order to develop a technique to quantitatively evaluate geohazards. Gas can occur in seabeds either in solution in pore water, undissolved in the form of gas filled voids, or as gas hydrates. In offshore soils, the degree of saturation is generally greater than 90 per cent, resulting in a soil structure with a continuous water phase and a discontinuous gas phase. The presence of methane gas will impact the strength of the soil, which alters its resistance to submarine sliding. This paper presents a constitutive model for determining the undrained shear strength of fine-grained gassy soils to assess the stability of deep water marine slopes for offshore developments. Methane gas is shown to have a beneficial effect on the soil strength in compressive loading, but the peak strength is achieved at larger deformations. The increased strength is a result of compression and solution gas which cause partial drainage and reduced pore pressures. The undrained shear strength of gassy soils was shown to increase with increasing initial consolidation stress, increasing volumetric coefficient of solubility, and increasing initial void ratio. 9 refs., 3 tabs., 6 figs.

Compaction wave profiles: Simulations of gas gun experiments

International Nuclear Information System (INIS)

Menikoff, Ralph

2001-01-01

Mesoscale simulations of a compaction wave in a granular bed of HMX have been performed. The grains are fully resolved in order that the compaction, i.e., the porosity behind the wave front, is determined by the elastic-plastic response of the grains rather than by an empirical law for the porosity as a function of pressure. Numerical wave profiles of the pressure and velocity are compared with data from a gas gun experiment. The experiment used an initial porosity of 36%, and the wave had a pressure comparable to the yield strength of the grains. The profiles are measured at the front and back of the granular bed. The transit time for the compaction wave to propagate between the gauges determines the wave speed. The wave speed depends on the porosity behind the wave and is affected by the strength model. The yield strength needed to match the experimental wave speed is discussed. Analysis of the lead wave through the granular bed, based on impedance matches using the Hugoniot loci, indicates that the compaction wave triggers a small amount of burn, less than 1% mass fraction, on the microsecond time scale of the experiment. copyright 2001 American Institute of Physics

Exploration of bulk and interface behavior of gas molecules and 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid using equilibrium and nonequilibrium molecular dynamics simulation and quantum chemical calculation.

Science.gov (United States)

Yang, Quan; Achenie, Luke E K

2018-04-18

Ionic liquids (ILs) show brilliant performance in separating gas impurities, but few researchers have performed an in-depth exploration of the bulk and interface behavior of penetrants and ILs thoroughly. In this research, we have performed a study on both molecular dynamics (MD) simulation and quantum chemical (QC) calculation to explore the transport of acetylene and ethylene in the bulk and interface regions of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]-[BF4]). The diffusivity, solubility and permeability of gas molecules in the bulk were researched with MD simulation first. The subdiffusion behavior of gas molecules is induced by coupling between the motion of gas molecules and the ions, and the relaxation processes of the ions after the disturbance caused by gas molecules. Then, QC calculation was performed to explore the optical geometry of ions, ion pairs and complexes of ions and penetrants, and interaction potential for pairs and complexes. Finally, nonequilibrium MD simulation was performed to explore the interface structure and properties of the IL-gas system and gas molecule behavior in the interface region. The research results may be used in the design of IL separation media.

Competitive grain growth in directional solidification investigated by phase field simulation

International Nuclear Information System (INIS)

Li Junjie; Wang Zhijun; Wang Jincheng; Yang Yujuan

2012-01-01

During directional solidification, the competitive dendritic growth between various oriented grains is a key factor to obtain desirable texture. In order to understand the mechanism of competitive dendritic growth, the phase field method was adopted to simulate the microstructure evolution of bicrystal samples. The simulation has well reproduced the whole competitive growth process for both diverging and converging dendrites. In converging case, besides the block of the unfavorably oriented dendrite by the favorably oriented one, the unfavorably oriented dendrite is also able to overgrow the favorable one under the condition of relatively low pulling velocity. This unusual overgrowth is dictated by the solute interaction of the converging dendrite tips. In diverging case, it was found that the grain boundary can be either inclined or parallel to the favorably oriented grain depending on the disposition of two grains.

MESOSCALE SIMULATIONS OF MICROSTRUCTURE AND TEXTURE EVOLUTION DURING DEFORMATION OF COLUMNAR GRAINS

International Nuclear Information System (INIS)

Sarma, G.

2001-01-01

In recent years, microstructure evolution in metals during deformation processing has been modeled at the mesoscale by combining the finite element method to discretize the individual grains with crystal plasticity to provide the constitutive relations. This approach allows the simulations to capture the heterogeneous nature of grain deformations due to interactions with neighboring grains. The application of this approach to study the deformations of columnar grains present in solidification microstructures is described. The microstructures are deformed in simple compression, assuming the easy growth direction of the columnar grains to be parallel to the compression axis in one case, and perpendicular in the other. These deformations are similar to those experienced by the columnar zones of a large cast billet when processed by upsetting and drawing, respectively. The simulations show that there is a significant influence of the initial microstructure orientation relative to the loading axis on the resulting changes in grain shape and orientation

Chemical composition of distillers grains, a review.

Science.gov (United States)

Liu, KeShun

2011-03-09

In recent years, increasing demand for ethanol as a fuel additive and decreasing dependency on fossil fuels have resulted in a dramatic increase in the amount of grains used for ethanol production. Dry-grind is the major process, resulting in distillers dried grains with solubles (DDGS) as a major coproduct. Like fuel ethanol, DDGS has quickly become a global commodity. However, high compositional variation has been the main problem hindering its use as a feed ingredient. This review provides updated information on the chemical composition of distillers grains in terms of nutrient levels, changes during dry-grind processing, and causes for large variation. The occurrence in grain feedstock and the fate of mycotoxins during processing are also covered. During processing, starch is converted to glucose and then to ethanol and carbon dioxide. Most other components are relatively unchanged but concentrated in DDGS about 3-fold over the original feedstock. Mycotoxins, if present in the original feedstock, are also concentrated. Higher fold of increases in S, Na, and Ca are mostly due to exogenous addition during processing, whereas unusual changes in inorganic phosphorus (P) and phytate P indicate phytate hydrolysis by yeast phytase. Fermentation causes major changes, but other processing steps are also responsible. The causes for varying DDGS composition are multiple, including differences in feedstock species and composition, process methods and parameters, the amount of condensed solubles added to distiller wet grains, the effect of fermentation yeast, and analytical methodology. Most of them can be attributed to the complexity of the dry-grind process itself. It is hoped that information provided in this review will improve the understanding of the dry-grind process and aid in the development of strategies to control the compositional variation in DDGS.

Systematic and simulation-free coarse graining of homopolymer melts: A structure-based study

International Nuclear Information System (INIS)

Yang, Delian; Wang, Qiang

2015-01-01

We propose a systematic and simulation-free strategy for coarse graining of homopolymer melts, where each chain of N m monomers is uniformly divided into N segments, with the spatial position of each segment corresponding to the center-of-mass of its monomers. We use integral-equation theories suitable for the study of equilibrium properties of polymers, instead of many-chain molecular simulations, to obtain the structural and thermodynamic properties of both original and coarse-grained (CG) systems, and quantitatively examine how the effective pair potentials between CG segments and the thermodynamic properties of CG systems vary with N. Our systematic and simulation-free strategy is much faster than those using many-chain simulations, thus effectively solving the transferability problem in coarse graining, and provides the quantitative basis for choosing the appropriate N-values. It also avoids the problems caused by finite-size effects and statistical uncertainties in many-chain simulations. Taking the simple hard-core Gaussian thread model [K. S. Schweizer and J. G. Curro, Chem. Phys. 149, 105 (1990)] as the original system, we demonstrate our strategy applied to structure-based coarse graining, which is quite general and versatile, and compare in detail the various integral-equation theories and closures for coarse graining. Our numerical results show that the effective CG potentials for various N and closures can be collapsed approximately onto the same curve, and that structure-based coarse graining cannot give thermodynamic consistency between original and CG systems at any N < N m

A simple method to evaluate the fission gas release at fuel grain boundary including the grain growth both at constant and at transient power histories

International Nuclear Information System (INIS)

Paraschiv, M.; Paraschiv, A.

1991-01-01

A method to rewrite Fick's second law for a region with a moving boundary when the moving law in time of this boundary is known, has been proposed. This method was applied to Booth's sphere model for radioactive and stable fission product diffusion from the oxide fuel grain in order to take into account the grain growth. The solution of this new equation was presented in the mathematical formulation for power histories from ANS 5.4 model for the stable species. It is very simple to apply and very accurate. The results obtained with this solution for constant and transient temperatures show that the fission gas release (FGR) at grain boundary is strongly dependent on kinetics of grain growth. The utilization of two semiempirical grain growth laws, from published information, shows that the fuel microstructural properties need to be multicitly considered in the fission gas release for every manufacturer of fuel. (orig.)

Adaptive resolution simulation of polarizable supramolecular coarse-grained water models

International Nuclear Information System (INIS)

Zavadlav, Julija; Praprotnik, Matej; Melo, Manuel N.; Marrink, Siewert J.

2015-01-01

Multiscale simulations methods, such as adaptive resolution scheme, are becoming increasingly popular due to their significant computational advantages with respect to conventional atomistic simulations. For these kind of simulations, it is essential to develop accurate multiscale water models that can be used to solvate biophysical systems of interest. Recently, a 4-to-1 mapping was used to couple the bundled-simple point charge water with the MARTINI model. Here, we extend the supramolecular mapping to coarse-grained models with explicit charges. In particular, the two tested models are the polarizable water and big multiple water models associated with the MARTINI force field. As corresponding coarse-grained representations consist of several interaction sites, we couple orientational degrees of freedom of the atomistic and coarse-grained representations via a harmonic energy penalty term. This additional energy term aligns the dipole moments of both representations. We test this coupling by studying the system under applied static external electric field. We show that our approach leads to the correct reproduction of the relevant structural and dynamical properties

Fission gas release during post irradiation annealing of large grain size fuels from Hinkley point B

International Nuclear Information System (INIS)

Killeen, J.C.

1997-01-01

A series of post-irradiation anneals has been carried out on fuel taken from an experimental stringer from Hinkley Point B AGR. The stringer was part of an experimental programme in the reactor to study the effect of large grain size fuel. Three differing fuel types were present in separate pins in the stringer. One variant of large grain size fuel had been prepared by using an MgO dopant during fuel manufactured, a second by high temperature sintering of standard fuel and the third was a reference, 12μm grain size fuel. Both large grain size variants had similar grain sizes around 35μm. The present experiments took fuel samples from highly rated pins from the stringer with local burn-up in excess of 25GWd/tU and annealed these to temperature of up to 1535 deg. C under reducing conditions to allow a comparison of fission gas behaviour at high release levels. The results demonstrate the beneficial effect of large grain size on release rate of 85 Kr following interlinkage. At low temperatures and release rates there was no difference between the fuel types, but at temperatures in excess of 1400 deg. C the release rate was found to be inversely dependent on the fuel grain size. The experiments showed some differences between the doped and undoped large grains size fuel in that the former became interlinked at a lower temperature, releasing fission gas at an increased rate at this temperature. At higher temperatures the grain size effect was dominant. The temperature dependence for fission gas release was determined over a narrow range of temperature and found to be similar for all three types and for both pre-interlinkage and post-interlinkage releases, the difference between the release rates is then seen to be controlled by grain size. (author). 4 refs, 7 figs, 3 tabs

Fission gas release during post irradiation annealing of large grain size fuels from Hinkley point B

Energy Technology Data Exchange (ETDEWEB)

Killeen, J C [Nuclear Electric plc, Barnwood (United Kingdom)

1997-08-01

A series of post-irradiation anneals has been carried out on fuel taken from an experimental stringer from Hinkley Point B AGR. The stringer was part of an experimental programme in the reactor to study the effect of large grain size fuel. Three differing fuel types were present in separate pins in the stringer. One variant of large grain size fuel had been prepared by using an MgO dopant during fuel manufactured, a second by high temperature sintering of standard fuel and the third was a reference, 12{mu}m grain size fuel. Both large grain size variants had similar grain sizes around 35{mu}m. The present experiments took fuel samples from highly rated pins from the stringer with local burn-up in excess of 25GWd/tU and annealed these to temperature of up to 1535 deg. C under reducing conditions to allow a comparison of fission gas behaviour at high release levels. The results demonstrate the beneficial effect of large grain size on release rate of {sup 85}Kr following interlinkage. At low temperatures and release rates there was no difference between the fuel types, but at temperatures in excess of 1400 deg. C the release rate was found to be inversely dependent on the fuel grain size. The experiments showed some differences between the doped and undoped large grains size fuel in that the former became interlinked at a lower temperature, releasing fission gas at an increased rate at this temperature. At higher temperatures the grain size effect was dominant. The temperature dependence for fission gas release was determined over a narrow range of temperature and found to be similar for all three types and for both pre-interlinkage and post-interlinkage releases, the difference between the release rates is then seen to be controlled by grain size. (author). 4 refs, 7 figs, 3 tabs.

Gas Removal in the Ursa Minor Galaxy: Linking Hydrodynamics and Chemical Evolution Models

Energy Technology Data Exchange (ETDEWEB)

Caproni, Anderson; Lanfranchi, Gustavo Amaral; Baio, Gabriel Henrique Campos; Kowal, Grzegorz [Núcleo de Astrofísica Teórica, Universidade Cruzeiro do Sul, R. Galvão Bueno 868, Liberdade, 01506-000, São Paulo, SP (Brazil); Falceta-Gonçalves, Diego, E-mail: anderson.caproni@cruzeirodosul.edu.br [Escola de Artes, Ciências e Humanidades, Universidade de São Paulo, Rua Arlindo Bettio 1000, CEP 03828-000 São Paulo (Brazil)

2017-04-01

We present results from a non-cosmological, three-dimensional hydrodynamical simulation of the gas in the dwarf spheroidal galaxy Ursa Minor. Assuming an initial baryonic-to-dark-matter ratio derived from the cosmic microwave background radiation, we evolved the galactic gas distribution over 3 Gyr, taking into account the effects of the types Ia and II supernovae. For the first time, we used in our simulation the instantaneous supernovae rates derived from a chemical evolution model applied to spectroscopic observational data of Ursa Minor. We show that the amount of gas that is lost in this process is variable with time and radius, being the highest rates observed during the initial 600 Myr in our simulation. Our results indicate that types Ia and II supernovae must be essential drivers of the gas loss in Ursa Minor galaxy (and probably in other similar dwarf galaxies), but it is ultimately the combination of galactic winds powered by these supernovae and environmental effects (e.g., ram-pressure stripping) that results in the complete removal of the gas content.

Experiments on chemical and physical evolution of interstellar grain mantles

International Nuclear Information System (INIS)

Greenberg, J.M.

1984-01-01

The Astrophysical Laboratory at the University of Leiden is the first to succeed in simulating the essential conditions in interstellar space as they affect the evolution of interstellar grains. (author)

Archie's Saturation Exponent for Natural Gas Hydrate in Coarse-Grained Reservoirs

Science.gov (United States)

Cook, Ann E.; Waite, William F.

2018-03-01

Accurately quantifying the amount of naturally occurring gas hydrate in marine and permafrost environments is important for assessing its resource potential and understanding the role of gas hydrate in the global carbon cycle. Electrical resistivity well logs are often used to calculate gas hydrate saturations, Sh, using Archie's equation. Archie's equation, in turn, relies on an empirical saturation parameter, n. Though n = 1.9 has been measured for ice-bearing sands and is widely used within the hydrate community, it is highly questionable if this n value is appropriate for hydrate-bearing sands. In this work, we calibrate n for hydrate-bearing sands from the Canadian permafrost gas hydrate research well, Mallik 5L-38, by establishing an independent downhole Sh profile based on compressional-wave velocity log data. Using the independently determined Sh profile and colocated electrical resistivity and bulk density logs, Archie's saturation equation is solved for n, and uncertainty is tracked throughout the iterative process. In addition to the Mallik 5L-38 well, we also apply this method to two marine, coarse-grained reservoirs from the northern Gulf of Mexico Gas Hydrate Joint Industry Project: Walker Ridge 313-H and Green Canyon 955-H. All locations yield similar results, each suggesting n ≈ 2.5 ± 0.5. Thus, for the coarse-grained hydrate bearing (Sh > 0.4) of greatest interest as potential energy resources, we suggest that n = 2.5 ± 0.5 should be applied in Archie's equation for either marine or permafrost gas hydrate settings if independent estimates of n are not available.

CHEMICAL SIMULATIONS OF PREBIOTIC MOLECULES: INTERSTELLAR ETHANIMINE ISOMERS

Energy Technology Data Exchange (ETDEWEB)

Quan, Donghui; Durr, Allison [Department of Chemistry, Eastern Kentucky University, Richmond, KY 40475 (United States); Herbst, Eric [Departments of Chemistry and Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Corby, Joanna F. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Hassel, George [Physics and Astronomy Department, Siena College, Loudonville, NY 12211 (United States)

2016-06-20

The E- and Z- isomers of ethanimine (CH{sub 3}CHNH) were recently detected toward the star-forming region Sagittarius (Sgr) B2(N) using the Green Bank Telescope PRIMOS cm-wave spectral data, and imaged by the Australia Telescope Compact Array. Ethanimine is not reported in the hot cores of Sgr B2, but only in gas that absorbs at +64 and +82 km s{sup −1} in the foreground of continuum emission generated by H ii regions. The ethanimine isomers can serve as precursors of the amino acid alanine and may play important roles in forming biological molecules in the interstellar medium. Here we present a study of the chemistry of ethanimine using a gas-grain simulation based on rate equations, with both isothermal and warm-up conditions. In addition, the density, kinetic temperature, and cosmic ray ionization rate have been varied. For a variety of physical conditions in the warm-up models for Sgr B2(N) and environs, the simulations show reasonable agreement with observationally obtained abundances. Isothermal models of translucent clouds along the same line of sight yield much lower abundances, so that ethanimine would be much more difficult to detect in these sources despite the fact that other complex molecules have been detected there.

Chemical Simulations of Prebiotic Molecules: Interstellar Ethanimine Isomers

Science.gov (United States)

Quan, Donghui; Herbst, Eric; Corby, Joanna F.; Durr, Allison; Hassel, George

2016-06-01

The E- and Z-isomers of ethanimine (CH3CHNH) were recently detected toward the star-forming region Sagittarius (Sgr) B2(N) using the Green Bank Telescope PRIMOS cm-wave spectral data, and imaged by the Australia Telescope Compact Array. Ethanimine is not reported in the hot cores of Sgr B2, but only in gas that absorbs at +64 and +82 km s-1 in the foreground of continuum emission generated by H II regions. The ethanimine isomers can serve as precursors of the amino acid alanine and may play important roles in forming biological molecules in the interstellar medium. Here we present a study of the chemistry of ethanimine using a gas-grain simulation based on rate equations, with both isothermal and warm-up conditions. In addition, the density, kinetic temperature, and cosmic ray ionization rate have been varied. For a variety of physical conditions in the warm-up models for Sgr B2(N) and environs, the simulations show reasonable agreement with observationally obtained abundances. Isothermal models of translucent clouds along the same line of sight yield much lower abundances, so that ethanimine would be much more difficult to detect in these sources despite the fact that other complex molecules have been detected there.

Predictable topography simulation of SiO2 etching by C5F8 gas combined with a plasma simulation, sheath model and chemical reaction model

International Nuclear Information System (INIS)

Takagi, S; Onoue, S; Iyanagi, K; Nishitani, K; Shinmura, T; Kanoh, M; Itoh, H; Shioyama, Y; Akiyama, T; Kishigami, D

2003-01-01

We have developed a simulation for predicting reactive ion etching (RIE) topography, which is a combination of plasma simulation, the gas reaction model, the sheath model and the surface reaction model. The simulation is applied to the SiO 2 etching process of a high-aspect-ratio contact hole using C 5 F 8 gas. A capacitively coupled plasma (CCP) reactor of an 8-in. wafer was used in the etching experiments. The baseline conditions are RF power of 1500 W and gas pressure of 4.0 Pa in a gas mixture of Ar, O 2 and C 5 F 8 . The plasma simulation reproduces the tendency that CF 2 radical density increases rapidly and the electron density decreases gradually with increasing gas flow rate of C 5 F 8 . In the RIE topography simulation, the etching profiles such as bowing and taper shape at the bottom are reproduced in deep holes with aspect ratios greater than 19. Moreover, the etching profile, the dependence of the etch depth on the etching time, and the bottom diameter can be predicted by this simulation

Comments on "Advantages and challenges in coupling an ideal gas to atomistic models in adaptive resolution simulations" by K. Kreis, A.C. Fogarty, K. Kremer and R. Potestio

Science.gov (United States)

Klein, R.

2015-09-01

Kreis et al. (Eur. Phys. J. Special Topics, this issue, 2015, doi: 10.1140/epjst/e2015-02412-1) discuss the option of minimizing the complexity of the coarse-grained model in adaptive resolution molecular dynamics simulations (AdResS) by adopting a collisionless ideal gas model for this purpose. Here we discuss the technical detail of how an ideal gas model is implemented, the effective role in the simulation that is left to the coarse-grained model when it is drastically simplified as suggested, and relations between the force and potential interpolations adopted in different variants of AdResS.

Physiological Response of Wheat to Chemical Desiccants Used to Simulate Post-Anthesis Drought Stress

Directory of Open Access Journals (Sweden)

Nasrein Mohamed Kamal

2018-04-01

Full Text Available Post-anthesis drought stress is one of the main constraints on the production of wheat (Triticum aestivum L.. Because field screening for post-anthesis drought tolerance is difficult, effective and validated methods to simulate drought in order to identify sources of tolerance can facilitate screening of breeding materials. Chemical desiccants are widely used to simulate post-anthesis drought stress. We aimed to identify physiological traits that respond to desiccants as they do to drought. We examined the responses of ‘Norin 61’ to six treatments in a greenhouse: irrigated control, drought after anthesis, and 2% or 4% potassium chlorate (KClO3 at anthesis (A or grain filling (GF. We measured δ13C in leaves, aboveground fresh biomass, stomatal conductance, chlorophyll content, harvest index, and grain yield. Both 2% and 4% KClO3 at both A and GF simulated the effect of drought stress. Selection of drought-tolerant genotypes can be aided by chlorophyll content and δ13C measurement of leaves when 2% or 4% KClO3 is used to simulate drought.

Chemical composition, secondary metabolites, in vitro gas ...

African Journals Online (AJOL)

Chemical composition, secondary metabolites, in vitro gas production characteristics and acceptability study of some forage for ruminant feeding in South-Western Nigeria. ... Chemical composition and qualitative analysis of saponins, phenol and steroids of the plants were determined. In vitro gas production (IVGP) was ...

Thermodynamic simulation of biomass gas steam reforming for a solid oxide fuel cell (SOFC system

Directory of Open Access Journals (Sweden)

A. Sordi

2009-12-01

Full Text Available This paper presents a methodology to simulate a small-scale fuel cell system for power generation using biomass gas as fuel. The methodology encompasses the thermodynamic and electrochemical aspects of a solid oxide fuel cell (SOFC, as well as solves the problem of chemical equilibrium in complex systems. In this case the complex system is the internal reforming of biomass gas to produce hydrogen. The fuel cell input variables are: operational voltage, cell power output, composition of the biomass gas reforming, thermodynamic efficiency, electrochemical efficiency, practical efficiency, the First and Second law efficiencies for the whole system. The chemical compositions, molar flows and temperatures are presented to each point of the system as well as the exergetic efficiency. For a molar water/carbon ratio of 2, the thermodynamic simulation of the biomass gas reforming indicates the maximum hydrogen production at a temperature of 1070 K, which can vary as a function of the biomass gas composition. The comparison with the efficiency of simple gas turbine cycle and regenerative gas turbine cycle shows the superiority of SOFC for the considered electrical power range.

Three-dimensional cellular automaton-finite element modeling of solidification grain structures for arc-welding processes

International Nuclear Information System (INIS)

Chen, Shijia; Guillemot, Gildas; Gandin, Charles-André

2016-01-01

Solidification grain structure has significant impact on the final properties of welded parts using fusion welding processes. Direct simulation of grain structure at industrial scale is yet rarely reported in the literature and remains a challenge. A three-dimensional (3D) coupled Cellular Automaton (CA) – Finite Element (FE) model is presented that predicts the grain structure formation during multiple passes Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW). The FE model is established in a level set (LS) approach that tracks the evolution of the metal-shielding gas interface due to the addition of metal. The FE method solves the mass, energy and momentum conservation equations for the metal plus shielding gas system based on an adaptive mesh (FE mesh). Fields are projected in a second FE mesh, named CA mesh. A CA grid made of a regular lattice of cubic cells is created to overlay the fixed CA mesh. The CA model based on the CA grid simulates the melting and growth of the grain boundaries in the liquid pool. In order to handle large computational domains while keeping reasonable computational costs, parallel computations and dynamic strategies for the allocation/deallocation of the CA grid are introduced. These strategies correspond to significant optimizations of the computer memories that are demonstrated. The 3D CAFE model is first applied to the simple configuration of single linear passes by GTAW of a duplex stainless steel URANUS 2202. It is then applied to a more persuasive example considering GMAW in spray transfer mode during multiple passes to fill a V-groove chamfer. Simulations reveal the possibility to handle domains with millions of grains in representative domain sizes while following the formation of textures that result from the growth competition among columnar grains. -- Graphical abstract: Simulated 3D grain structure (3D CAFE model) for GTAW multiple linear passes at the surface of a duplex stainless steel (URANUS 22002

New chemical-DSMC method in numerical simulation of axisymmetric rarefied reactive flow

Science.gov (United States)

Zakeri, Ramin; Kamali Moghadam, Ramin; Mani, Mahmoud

2017-04-01

The modified quantum kinetic (MQK) chemical reaction model introduced by Zakeri et al. is developed for applicable cases in axisymmetric reactive rarefied gas flows using the direct simulation Monte Carlo (DSMC) method. Although, the MQK chemical model uses some modifications in the quantum kinetic (QK) method, it also employs the general soft sphere collision model and Stockmayer potential function to properly select the collision pairs in the DSMC algorithm and capture both the attraction and repulsion intermolecular forces in rarefied gas flows. For assessment of the presented model in the simulation of more complex and applicable reacting flows, first, the air dissociation is studied in a single cell for equilibrium and non-equilibrium conditions. The MQK results agree well with the analytical and experimental data and they accurately predict the characteristics of the rarefied flowfield with chemical reaction. To investigate accuracy of the MQK chemical model in the simulation of the axisymmetric flow, air dissociation is also assessed in an axial hypersonic flow around two geometries, the sphere as a benchmark case and the blunt body (STS-2) as an applicable test case. The computed results including the transient, rotational and vibrational temperatures, species concentration in the stagnation line, and also the heat flux and pressure coefficient on the surface are compared with those of the other chemical methods like the QK and total collision energy (TCE) models and available analytical and experimental data. Generally, the MQK chemical model properly simulates the chemical reactions and predicts flowfield characteristics more accurate rather than the typical QK model. Although in some cases, results of the MQK approaches match with those of the TCE method, the main point is that the MQK does not need any experimental data or unrealistic assumption of specular boundary condition as used in the TCE method. Another advantage of the MQK model is the

Direct numerical simulation of stratified gas-liquid flow

International Nuclear Information System (INIS)

Lombardi, P.; De Angelis, V.; Banerjee, S.

1996-01-01

Interactions through an interface between two turbulent flows play an important role in many environmental and industrial problems, e.g. in determining the coupling fluxes of heat mass and momentum, between the ocean and atmosphere, and in the design of gas-liquid contractors for the chemical industry, as well as in determining interactions between phases in nuclear transients that are accompanied by system voiding e.g. LOCAs. Here, the Direct Numerical Simulation (DNS) of the interaction of two turbulent fluids through a flat interface has been simulated. The flow and the temperature fields are computed using a pseudospectral method. This study shows that shear stress at the interface correlates well with the heat flux. Extensive analysis of the near interface turbulence structure has been performed using quadrant analysis. From this it is clear that gas-side sweeps dominate over the high shear stress regions. This suggests that simple parameterizations based on sweep frequency may be adequate for predictions of scalar transport rates

Numerical simulation of flue gas purification from NOx, SO2 by electron beam

International Nuclear Information System (INIS)

Morgunov, V.V.; Shkilko, A.M.; Fainchtein, O.L.

2011-01-01

Complete text of publication follows. The paper is devoted to numerical simulation of radiation-chemical processes in gas phase, which are take place during electron beam (EB) treatments of flue gases. A mathematical model of EB processes in gas phase was created. Also, a computer code which numerically simulates radiation-chemical processes during EB treatment of flue gases was created. The needed data such as chemical species, radiation-chemical yields and rate constants of the chemical reactions were collected and putted into database. The computer code allows do following: 1. The following technological parameters: irradiation dose, temperature, initial composition of the flue gases, time of irradiation (time which flue gases spend in an irradiation zone), one- or two-stage irradiation can be defined by the user in the code shell; 2. In accordance with the initial composition of flue gases selects chemical species from database of the chemical species (total amount of species in database is 522) which took part in simulation taking into account species that are formed due to irradiation; 3. In accordance with the selected chemical species selects chemical and radiation-chemical reactions from the database of reactions (total amount of chemical and radiation-chemical reaction is 2275) which are took part in the simulation; 4. Creates a stiff system of ordinary differential equations (ODEs) which describes chemical and radiation-chemical reactions; 5. Solves the received system of ODEs by backward differentiation formula (Gear's method); 6. Creates plots of dependencies: concentrations of chemical species versus time of irradiation under different parameters of modeled EB-processes. The received results. For the following technological parameters: irradiation dose is 8.0 kGy; two stage irradiation; initial temperature is 353 deg K; time of the irradiation - 4 s; initial composition of the flue gases - typical for power plant, following removal efficiencies were

Austenite grain growth and microstructure control in simulated heat affected zones of microalloyed HSLA steel

Energy Technology Data Exchange (ETDEWEB)

Zhang, Lei [Department of Machine Tools and Factory Management, Technical University of Berlin, Pascalstraße 8 – 9, 10587, Berlin (Germany); Federal Institute for Materials Research and Testing, Unter den Eichen 87, 12205, Berlin (Germany); Kannengiesser, Thomas [Federal Institute for Materials Research and Testing, Unter den Eichen 87, 12205, Berlin (Germany); Institute of Materials and Joining Technology, Otto von Guericke University Magdeburg, Universitetsplatz 2, 39106, Magdeburg (Germany)

2014-09-08

The roles of microalloying niobium, titanium and vanadium for controlling austenite grain growth, microstructure evolution and hardness were investigated at different simulated heat affected zones (HAZ) for high strength low alloy (HSLA) S690QL steel. High resolution FEG-SEM has been used to characterize fine bainitic ferrite, martensite and nanosized second phases at simulated coarse and fine grain HAZs. It was found that for Ti bearing steel (Ti/N ratio is 2) austenite grain had the slowest growth rate due to the presence of most stable TiN. The fine cuboidal particles promoted intragranular acicular ferrite (IGF) formation. Nb bearing steel exhibited relatively weaker grain growth retardation compared with titanium bearing steels and a mixed microstructure of bainite and martensite was present for all simulated HAZs. IGF existed at coarse grain HAZ of Ti+V bearing steel but it was totally replaced by bainite at fine grain HAZs. Hardness result was closely related to the morphology of bainitic ferrite, intragranular ferrite and second phases within ferrite. The microstructure and hardness results of different simulated HAZs were in good agreement with welded experimental results.

Simulating gas-aerosol-cirrus interactions: Process-oriented microphysical model and applications

Directory of Open Access Journals (Sweden)

B. Kärcher

2003-01-01

Full Text Available This work describes a process-oriented, microphysical-chemical model to simulate the formation and evolution of aerosols and ice crystals under the conditions prevailing in the upper troposphere and lower stratosphere. The model can be run as a box model or along atmospheric trajectories, and considers mixing, gas phase chemistry of aerosol precursors, binary homogeneous aerosol nucleation, homogeneous and heterogeneous ice nucleation, coagulation, condensation and dissolution, gas retention during particle freezing, gas trapping in growing ice crystals, and reverse processes. Chemical equations are solved iteratively using a second order implicit integration method. Gas-particle interactions and coagulation are treated over various size structures, with fully mass conserving and non-iterative numerical solution schemes. Particle types include quinternary aqueous solutions composed of H2SO4, HNO3, HCl, and HBr with and without insoluble components, insoluble aerosol particles, and spherical or columnar ice crystals deriving from each aerosol type separately. Three case studies are discussed in detail to demonstrate the potential of the model to simulate real atmospheric processes and to highlight current research topics concerning aerosol and cirrus formation near the tropopause. Emphasis is placed on how the formation of cirrus clouds and the scavenging of nitric acid in cirrus depends on small-scale temperature fluctuations and the presence of efficient ice nuclei in the tropopause region, corroborating and partly extending the findings of previous studies.

Thermodynamic forces in coarse-grained simulations

Science.gov (United States)

Noid, William

Atomically detailed molecular dynamics simulations have profoundly advanced our understanding of the structure and interactions in soft condensed phases. Nevertheless, despite dramatic advances in the methodology and resources for simulating atomically detailed models, low-resolution coarse-grained (CG) models play a central and rapidly growing role in science. CG models not only empower researchers to investigate phenomena beyond the scope of atomically detailed simulations, but also to precisely tailor models for specific phenomena. However, in contrast to atomically detailed simulations, which evolve on a potential energy surface, CG simulations should evolve on a free energy surface. Therefore, the forces in CG models should reflect the thermodynamic information that has been eliminated from the CG configuration space. As a consequence of these thermodynamic forces, CG models often demonstrate limited transferability and, moreover, rarely provide an accurate description of both structural and thermodynamic properties. In this talk, I will present a framework that clarifies the origin and impact of these thermodynamic forces. Additionally, I will present computational methods for quantifying these forces and incorporating their effects into CG MD simulations. As time allows, I will demonstrate applications of this framework for liquids, polymers, and interfaces. We gratefully acknowledge the support of the National Science Foundation via CHE 1565631.

The turbulent life of dust grains in the supernova-driven, multiphase interstellar medium

Science.gov (United States)

Peters, Thomas; Zhukovska, Svitlana; Naab, Thorsten; Girichidis, Philipp; Walch, Stefanie; Glover, Simon C. O.; Klessen, Ralf S.; Clark, Paul C.; Seifried, Daniel

2017-06-01

Dust grains are an important component of the interstellar medium (ISM) of galaxies. We present the first direct measurement of the residence times of interstellar dust in the different ISM phases, and of the transition rates between these phases, in realistic hydrodynamical simulations of the multiphase ISM. Our simulations include a time-dependent chemical network that follows the abundances of H+, H, H2, C+ and CO and take into account self-shielding by gas and dust using a tree-based radiation transfer method. Supernova explosions are injected either at random locations, at density peaks, or as a mixture of the two. For each simulation, we investigate how matter circulates between the ISM phases and find more sizeable transitions than considered in simple mass exchange schemes in the literature. The derived residence times in the ISM phases are characterized by broad distributions, in particular for the molecular, warm and hot medium. The most realistic simulations with random and mixed driving have median residence times in the molecular, cold, warm and hot phase around 17, 7, 44 and 1 Myr, respectively. The transition rates measured in the random driving run are in good agreement with observations of Ti gas-phase depletion in the warm and cold phases in a simple depletion model. ISM phase definitions based on chemical abundance rather than temperature cuts are physically more meaningful, but lead to significantly different transition rates and residence times because there is no direct correspondence between the two definitions.

Energy and greenhouse gas profiles of polyhydroxybutyrates derived from corn grain: a life cycle perspective.

Science.gov (United States)

Kim, Seungdo; Dale, Bruce E

2008-10-15

Polyhydroxybutyrates (PHB) are well-known biopolymers derived from sugars orvegetable oils. Cradle-to-gate environmental performance of PHB derived from corn grain is evaluated through life cycle assessment (LCA), particularly nonrenewable energy consumption and greenhouse gas emissions. Site-specific process information on the corn wet milling and PHB fermentation and recovery processes was obtained from Telles. Most of energy used in the corn wet milling and PHB fermentation and recovery processes is generated in a cogeneration power plant in which corn stover, assumed to be representative of a variety of biomass sources that could be used, is burned to generate electricity and steam. County level agricultural information is used in estimating the environmental burdens associated with both corn grain and corn stover production. Results show that PHB derived from corn grain offers environmental advantages over petroleum-derived polymers in terms of nonrenewable energy consumption and greenhouse gas emissions. Furthermore, PHB provides greenhouse gas credits, and thus PHB use reduces greenhouse gas emissions compared to petroleum-derived polymers. Corn cultivation is one of the environmentally sensitive areas in the PHB production system. More sustainable practices in corn cultivation (e.g., using no-tillage and winter cover crops) could reduce the environmental impacts of PHB by up to 72%.

The computer simulation of 3d gas dynamics in a gas centrifuge

Science.gov (United States)

Borman, V. D.; Bogovalov, S. V.; Borisevich, V. D.; Tronin, I. V.; Tronin, V. N.

2016-09-01

We argue on the basis of the results of 2D analysis of the gas flow in gas centrifuges that a reliable calculation of the circulation of the gas and gas content in the gas centrifuge is possible only in frameworks of 3D numerical simulation of gas dynamics in the gas centrifuge (hereafter GC). The group from National research nuclear university, MEPhI, has created a computer code for 3D simulation of the gas flow in GC. The results of the computer simulations of the gas flows in GC are presented. A model Iguassu centrifuge is explored for the simulations. A nonaxisymmetric gas flow is produced due to interaction of the hypersonic rotating flow with the scoops for extraction of the product and waste flows from the GC. The scoops produce shock waves penetrating into a working camera of the GC and form spiral waves there.

The computer simulation of 3d gas dynamics in a gas centrifuge

International Nuclear Information System (INIS)

Borman, V D; Bogovalov, S V; Borisevich, V D; Tronin, I V; Tronin, V N

2016-01-01

We argue on the basis of the results of 2D analysis of the gas flow in gas centrifuges that a reliable calculation of the circulation of the gas and gas content in the gas centrifuge is possible only in frameworks of 3D numerical simulation of gas dynamics in the gas centrifuge (hereafter GC). The group from National research nuclear university, MEPhI, has created a computer code for 3D simulation of the gas flow in GC. The results of the computer simulations of the gas flows in GC are presented. A model Iguassu centrifuge is explored for the simulations. A nonaxisymmetric gas flow is produced due to interaction of the hypersonic rotating flow with the scoops for extraction of the product and waste flows from the GC. The scoops produce shock waves penetrating into a working camera of the GC and form spiral waves there. (paper)

A plug flow model for chemical reactions and aerosol nucleation and growth in an alkali-containing flue gas

DEFF Research Database (Denmark)

Christensen, K. A.; Livbjerg, Hans

2000-01-01

multicomponent growth models are treated. The local gas phase composition is determined from a gas phase chemical equilibrium calculation combined with finite reaction rate kinetics for slower reactions. The model is useful in the analysis of boiler operation with respect to the formation of particles, HCl, SO2......The paper presents a numerical model for the simulation of gas to particle conversion and the chemical changes during cooling of a flue gas from the combustion of fuels rich in volatile alkali species. For the homogeneous nucleation of alkali species the model uses the classical theory modified...

Systematic Search for Chemical Reactions in Gas Phase Contributing to Methanol Formation in Interstellar Space.

Science.gov (United States)

Gamez-Garcia, Victoria G; Galano, Annia

2017-10-05

A massive search for chemical routes leading to methanol formation in gas phase has been conducted using computational chemistry, at the CBS-QB3 level of theory. The calculations were performed at five different temperatures (100, 80, 50, 20, and 10 K) and at three pressures (0.1, 0.01, and 0.001 atm) for each temperature. The search was focused on identifying reactions with the necessary features to be viable in the interstellar medium (ISM). A searching strategy was applied to that purpose, which allowed to reduce an initial set of 678 possible reactions to a subset of 11 chemical routes that are recommended, for the first time, as potential candidates for contributing to methanol formation in the gas phase of the ISM. They are all barrier-less, and thus they are expected to take place at collision rates. Hopefully, including these reactions in the currently available models, for the gas-phase methanol formation in the ISM, would help improving the predicted fractional abundance of this molecule in dark clouds. Further investigations, especially those dealing with grain chemistry and electronic excited states, would be crucial to get a complete picture of the methanol formation in the ISM.

Preparation, analysis, and release of simulated interplanetary grains into low earth orbit

International Nuclear Information System (INIS)

Stephens, J.R.; Strong, I.B.; Kunkle, T.D.

1985-01-01

Astronomical observations which reflect the optical and dynamical properties of interstellar and interplanetary grains are the primary means of identifying the shape, size, and the chemistry of extraterrestrial grain materials and is a major subject of this workshop. Except for recent samplings of extraterrestrial particles in near-Earth orbit and in the stratosphere, observations have been the only method of deducing the properties of extraterrestrial particles. Terrestrial laboratory experiments typically seek not to reproduce astrophysical conditions but to illuminate fundamental dust processes and properties which must be extrapolated to interesting astrophysical conditions. In this report, we discuss the formation and optical characterization of simulated interstellar and interplanetary dust with particular emphasis on studying the properties on irregularly shaped particles. We also discuss efforts to develop the techniques to allow dust experiments to be carried out in low-Earth orbit, thus extending the conditions under which dust experiments may be performed. The objectives of this study are threefold: (1) Elucidate the optical properties, including scattering and absorption, of simulated interstellar grains including SiC, silicates, and carbon grains produced in the laboratory. (2) Develop the capabilities to release grains and volatile materials into the near-Earth environment and study their dynamics and optical properties. (3) Study the interaction of released materials with the near-Earth environment to elucidate grain behavior in astrophysical environments. Interaction of grains with their environment may, for example, lead to grain alignment or coagulation, which results in observable phenomena such as polarization of lighter or a change of the scattering properties of the grains

GADEN: A 3D Gas Dispersion Simulator for Mobile Robot Olfaction in Realistic Environments.

Science.gov (United States)

Monroy, Javier; Hernandez-Bennets, Victor; Fan, Han; Lilienthal, Achim; Gonzalez-Jimenez, Javier

2017-06-23

This work presents a simulation framework developed under the widely used Robot Operating System (ROS) to enable the validation of robotics systems and gas sensing algorithms under realistic environments. The framework is rooted in the principles of computational fluid dynamics and filament dispersion theory, modeling wind flow and gas dispersion in 3D real-world scenarios (i.e., accounting for walls, furniture, etc.). Moreover, it integrates the simulation of different environmental sensors, such as metal oxide gas sensors, photo ionization detectors, or anemometers. We illustrate the potential and applicability of the proposed tool by presenting a simulation case in a complex and realistic office-like environment where gas leaks of different chemicals occur simultaneously. Furthermore, we accomplish quantitative and qualitative validation by comparing our simulated results against real-world data recorded inside a wind tunnel where methane was released under different wind flow profiles. Based on these results, we conclude that our simulation framework can provide a good approximation to real world measurements when advective airflows are present in the environment.

Morphology of Gas Release in Physical Simulants

Energy Technology Data Exchange (ETDEWEB)

Daniel, Richard C.; Burns, Carolyn A.; Crawford, Amanda D.; Hylden, Laura R.; Bryan, Samuel A.; MacFarlan, Paul J.; Gauglitz, Phillip A.

2014-07-03

This report documents testing activities conducted as part of the Deep Sludge Gas Release Event Project (DSGREP). The testing described in this report focused on evaluating the potential retention and release mechanisms of hydrogen bubbles in underground radioactive waste storage tanks at Hanford. The goal of the testing was to evaluate the rate, extent, and morphology of gas release events in simulant materials. Previous, undocumented scoping tests have evidenced dramatically different gas release behavior from simulants with similar physical properties. Specifically, previous gas release tests have evaluated the extent of release of 30 Pa kaolin and 30 Pa bentonite clay slurries. While both materials are clays and both have equivalent material shear strength using a shear vane, it was found that upon stirring, gas was released immediately and completely from bentonite clay slurry while little if any gas was released from the kaolin slurry. The motivation for the current work is to replicate these tests in a controlled quality test environment and to evaluate the release behavior for another simulant used in DSGREP testing. Three simulant materials were evaluated: 1) a 30 Pa kaolin clay slurry, 2) a 30 Pa bentonite clay slurry, and 3) Rayleigh-Taylor (RT) Simulant (a simulant designed to support DSGREP RT instability testing. Entrained gas was generated in these simulant materials using two methods: 1) application of vacuum over about a 1-minute period to nucleate dissolved gas within the simulant and 2) addition of hydrogen peroxide to generate gas by peroxide decomposition in the simulants over about a 16-hour period. Bubble release was effected by vibrating the test material using an external vibrating table. When testing with hydrogen peroxide, gas release was also accomplished by stirring of the simulant.

Dew point, internal gas pressure, and chemical composition of the gas within the free volume of DWPF canistered waste forms

International Nuclear Information System (INIS)

Harbour, J.R.; Herman, D.T.; Crump, S.; Miller, T.J.; McIntosh, J.

1996-01-01

The Defense Waste Processing Facility (DWPF) produced 55 canistered waste forms containing simulated waste glass during the four Waste Qualification campaigns of the DWPF Startup Test Program. Testing of the gas within the free volume of these canisters for dew point, internal gas pressure, and chemical composition was performed as part of a continuing effort to demonstrate compliance with the Waste Acceptance Product Specifications. Results are presented for six glass-filled canisters. The dew points within the canisters met the acceptance criterion of < 20 degrees C for all six canisters. Factors influencing the magnitude of the dew point are presented. The chemical composition of the free volume gas was indistinguishable from air for all six canisters. Hence, no foreign materials were present in the gas phase of these canisters. The internal gas pressures within the sealed canisters were < 1 atm at 25 degrees C for all six canisters which readily met the acceptance criterion of an internal gas pressure of less than 1.5 atm at 25 degrees C. These results provided the evidence required to demonstrate compliance with the Waste Acceptance Product Specifications

Enhanced Generic Phase-field Model of Irradiation Materials: Fission Gas Bubble Growth Kinetics in Polycrystalline UO2

Energy Technology Data Exchange (ETDEWEB)

Li, Yulan; Hu, Shenyang Y.; Montgomery, Robert O.; Gao, Fei; Sun, Xin

2012-05-30

Experiments show that inter-granular and intra-granular gas bubbles have different growth kinetics which results in heterogeneous gas bubble microstructures in irradiated nuclear fuels. A science-based model predicting the heterogeneous microstructure evolution kinetics is desired, which enables one to study the effect of thermodynamic and kinetic properties of the system on gas bubble microstructure evolution kinetics and morphology, improve the understanding of the formation mechanisms of heterogeneous gas bubble microstructure, and provide the microstructure to macroscale approaches to study their impact on thermo-mechanical properties such as thermo-conductivity, gas release, volume swelling, and cracking. In our previous report 'Mesoscale Benchmark Demonstration, Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing', we developed a phase-field model to simulate the intra-granular gas bubble evolution in a single crystal during post-irradiation thermal annealing. In this work, we enhanced the model by incorporating thermodynamic and kinetic properties at grain boundaries, which can be obtained from atomistic simulations, to simulate fission gas bubble growth kinetics in polycrystalline UO2 fuels. The model takes into account of gas atom and vacancy diffusion, vacancy trapping and emission at defects, gas atom absorption and resolution at gas bubbles, internal pressure in gas bubbles, elastic interaction between defects and gas bubbles, and the difference of thermodynamic and kinetic properties in matrix and grain boundaries. We applied the model to simulate gas atom segregation at grain boundaries and the effect of interfacial energy and gas mobility on gas bubble morphology and growth kinetics in a bi-crystal UO2 during post-irradiation thermal annealing. The preliminary results demonstrate that the model can produce the equilibrium thermodynamic properties and the morphology of gas

The Martini Coarse-Grained Force Field

NARCIS (Netherlands)

Periole, X.; Marrink, S.J.; Monticelli, Luca; Salonen, Emppu

2013-01-01

The Martini force field is a coarse-grained force field suited for molecular dynamics simulations of biomolecular systems. The force field has been parameterized in a systematic way, based on the reproduction of partitioning free energies between polar and apolar phases of a large number of chemical

NUMERICAL SIMULATIONS OF SUPERNOVA DUST DESTRUCTION. I. CLOUD-CRUSHING AND POST-PROCESSED GRAIN SPUTTERING

International Nuclear Information System (INIS)

Silvia, Devin W.; Smith, Britton D.; Michael Shull, J.

2010-01-01

We investigate through hydrodynamic simulations the destruction of newly formed dust grains by sputtering in the reverse shocks of supernova (SN) remnants. Using an idealized setup of a planar shock impacting a dense, spherical clump, we implant a population of Lagrangian particles into the clump to represent a distribution of dust grains in size and composition. We then post-process the simulation output to calculate the grain sputtering for a variety of species and size distributions. We explore the parameter space appropriate for this problem by altering the overdensity of the ejecta clumps and the speed of the reverse shocks. Since radiative cooling could lower the temperature of the medium in which the dust is embedded and potentially protect the dust by slowing or halting grain sputtering, we study the effects of different cooling methods over the timescale of the simulations. In general, our results indicate that grains with radii less than 0.1 μm are sputtered to much smaller radii and often destroyed completely, while larger grains survive their interaction with the reverse shock. We also find that, for high ejecta densities, the percentage of dust that survives is strongly dependent on the relative velocity between the clump and the reverse shock, causing up to 50% more destruction for the highest velocity shocks. The fraction of dust destroyed varies widely across grain species, ranging from total destruction of Al 2 O 3 grains to minimal destruction of Fe grains (only 20% destruction in the most extreme cases). C and SiO 2 grains show moderate to strong sputtering as well, with 38% and 80% mass loss. The survival rate of grains formed by early SNe is crucial in determining whether or not they can act as the 'dust factories' needed to explain high-redshift dust.

Hybrid framework for the simulation of stochastic chemical kinetics

International Nuclear Information System (INIS)

Duncan, Andrew; Erban, Radek; Zygalakis, Konstantinos

2016-01-01

Stochasticity plays a fundamental role in various biochemical processes, such as cell regulatory networks and enzyme cascades. Isothermal, well-mixed systems can be modelled as Markov processes, typically simulated using the Gillespie Stochastic Simulation Algorithm (SSA) [25]. While easy to implement and exact, the computational cost of using the Gillespie SSA to simulate such systems can become prohibitive as the frequency of reaction events increases. This has motivated numerous coarse-grained schemes, where the “fast” reactions are approximated either using Langevin dynamics or deterministically. While such approaches provide a good approximation when all reactants are abundant, the approximation breaks down when one or more species exist only in small concentrations and the fluctuations arising from the discrete nature of the reactions become significant. This is particularly problematic when using such methods to compute statistics of extinction times for chemical species, as well as simulating non-equilibrium systems such as cell-cycle models in which a single species can cycle between abundance and scarcity. In this paper, a hybrid jump-diffusion model for simulating well-mixed stochastic kinetics is derived. It acts as a bridge between the Gillespie SSA and the chemical Langevin equation. For low reactant reactions the underlying behaviour is purely discrete, while purely diffusive when the concentrations of all species are large, with the two different behaviours coexisting in the intermediate region. A bound on the weak error in the classical large volume scaling limit is obtained, and three different numerical discretisations of the jump-diffusion model are described. The benefits of such a formalism are illustrated using computational examples.

Hybrid framework for the simulation of stochastic chemical kinetics

Science.gov (United States)

Duncan, Andrew; Erban, Radek; Zygalakis, Konstantinos

2016-12-01

Stochasticity plays a fundamental role in various biochemical processes, such as cell regulatory networks and enzyme cascades. Isothermal, well-mixed systems can be modelled as Markov processes, typically simulated using the Gillespie Stochastic Simulation Algorithm (SSA) [25]. While easy to implement and exact, the computational cost of using the Gillespie SSA to simulate such systems can become prohibitive as the frequency of reaction events increases. This has motivated numerous coarse-grained schemes, where the "fast" reactions are approximated either using Langevin dynamics or deterministically. While such approaches provide a good approximation when all reactants are abundant, the approximation breaks down when one or more species exist only in small concentrations and the fluctuations arising from the discrete nature of the reactions become significant. This is particularly problematic when using such methods to compute statistics of extinction times for chemical species, as well as simulating non-equilibrium systems such as cell-cycle models in which a single species can cycle between abundance and scarcity. In this paper, a hybrid jump-diffusion model for simulating well-mixed stochastic kinetics is derived. It acts as a bridge between the Gillespie SSA and the chemical Langevin equation. For low reactant reactions the underlying behaviour is purely discrete, while purely diffusive when the concentrations of all species are large, with the two different behaviours coexisting in the intermediate region. A bound on the weak error in the classical large volume scaling limit is obtained, and three different numerical discretisations of the jump-diffusion model are described. The benefits of such a formalism are illustrated using computational examples.

Hybrid framework for the simulation of stochastic chemical kinetics

Energy Technology Data Exchange (ETDEWEB)

Duncan, Andrew, E-mail: a.duncan@imperial.ac.uk [Department of Mathematics, Imperial College, South Kensington Campus, London, SW7 2AZ (United Kingdom); Erban, Radek, E-mail: erban@maths.ox.ac.uk [Mathematical Institute, University of Oxford, Radcliffe Observatory Quarter, Woodstock Road, Oxford, OX2 6GG (United Kingdom); Zygalakis, Konstantinos, E-mail: k.zygalakis@ed.ac.uk [School of Mathematics, University of Edinburgh, Peter Guthrie Tait Road, Edinburgh, EH9 3FD (United Kingdom)

2016-12-01

Stochasticity plays a fundamental role in various biochemical processes, such as cell regulatory networks and enzyme cascades. Isothermal, well-mixed systems can be modelled as Markov processes, typically simulated using the Gillespie Stochastic Simulation Algorithm (SSA) [25]. While easy to implement and exact, the computational cost of using the Gillespie SSA to simulate such systems can become prohibitive as the frequency of reaction events increases. This has motivated numerous coarse-grained schemes, where the “fast” reactions are approximated either using Langevin dynamics or deterministically. While such approaches provide a good approximation when all reactants are abundant, the approximation breaks down when one or more species exist only in small concentrations and the fluctuations arising from the discrete nature of the reactions become significant. This is particularly problematic when using such methods to compute statistics of extinction times for chemical species, as well as simulating non-equilibrium systems such as cell-cycle models in which a single species can cycle between abundance and scarcity. In this paper, a hybrid jump-diffusion model for simulating well-mixed stochastic kinetics is derived. It acts as a bridge between the Gillespie SSA and the chemical Langevin equation. For low reactant reactions the underlying behaviour is purely discrete, while purely diffusive when the concentrations of all species are large, with the two different behaviours coexisting in the intermediate region. A bound on the weak error in the classical large volume scaling limit is obtained, and three different numerical discretisations of the jump-diffusion model are described. The benefits of such a formalism are illustrated using computational examples.

Quantitative Phase-Field Approach for Simulating Grain Growth in Anisotropic Systems with Arbitrary Inclination and Misorientation Dependence

International Nuclear Information System (INIS)

Moelans, N.; Blanpain, B.; Wollants, P.

2008-01-01

A phase-field approach for quantitative simulations of grain growth in anisotropic systems is introduced, together with a new methodology to derive appropriate model parameters that reproduce given misorientation and inclination dependent grain boundary energy and mobility in the simulations. The proposed model formulation and parameter choice guarantee a constant diffuse interface width and consequently give high controllability of the accuracy in grain growth simulations

Grain rotation and lattice deformation during photoinduced chemical reactions revealed by in situ X-ray nanodiffraction.

Science.gov (United States)

Huang, Zhifeng; Bartels, Matthias; Xu, Rui; Osterhoff, Markus; Kalbfleisch, Sebastian; Sprung, Michael; Suzuki, Akihiro; Takahashi, Yukio; Blanton, Thomas N; Salditt, Tim; Miao, Jianwei

2015-07-01

In situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to investigate many physical science phenomena, ranging from phase transitions, chemical reactions and crystal growth to grain boundary dynamics. A major limitation of in situ XRD and TEM is a compromise that has to be made between spatial and temporal resolution. Here, we report the development of in situ X-ray nanodiffraction to measure high-resolution diffraction patterns from single grains with up to 5 ms temporal resolution. We observed, for the first time, grain rotation and lattice deformation in chemical reactions induced by X-ray photons: Br(-) + hv → Br + e(-) and e(-) + Ag(+) → Ag(0). The grain rotation and lattice deformation associated with the chemical reactions were quantified to be as fast as 3.25 rad s(-1) and as large as 0.5 Å, respectively. The ability to measure high-resolution diffraction patterns from individual grains with a temporal resolution of several milliseconds is expected to find broad applications in materials science, physics, chemistry and nanoscience.

Comparative analysis of physico-chemical and gas sensing characteristics of two different forms of SnO_2 films

International Nuclear Information System (INIS)

Kwoka, M.; Ottaviano, L.; Szuber, J.

2017-01-01

Highlights: • Two different forms of SnO_2 deposited on Si substrate. • Crystallinity and surface/subsurface morphology controlled by XRD, SEM and AFM. • Surface/subsurface chemistry including stoichiometry and contaminations derived from XPS. • Comparative analysis of gas sensor characteristics of SnO_2 in NO_2 atmosphere. • Correlations between physico-chemical properties and gas sensor characteristics. - Abstract: In this paper the results of studies of comparative studies on the crystallinity, morphology and chemistry combined with the gas sensor response of two different forms of tin dioxide (SnO_2) films prepared by the Rheotaxial Growth and Thermal Oxidation (RGTO) and by the Laser-enhanced Chemical Vapour Deposition (L-CVD) methods, respectively, are presented. For this purpose the X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and X-ray Photoelectron spectroscopy (XPS) have been used. XRD studies for both samples show the contribution from the crystalline SnO_2 in the cassiterite rutile phase without any evident contribution from the tin oxide (SnO) phase. SEM and AFM studies show that the surface morphology of RGTO and L-CVD SnO_2 samples are characterized by grains/nanograins of different size and surface roughness. In turn XPS studies confirm that for both SnO_2 samples a slight nonstoichiometry with a relative [O]/[Sn] concentration of 1.8, and slightly different amount of C contamination at the surface of internal grains with relative [C]/[Sn] concentration of 3.5 and 3.2, respectively. This undesired C contamination cannot be ignored because it creates an uncontrolled barrier for the potential gas adsorption at the internal surface of sensor material. This is confirmed by the gas sensor response in NO_2 atmosphere of both SnO_2 samples because the sensitivity is evidently smaller for RGTO SnO_2 with respect to the L-CVD SnO_2 samples, whereas the response time showed a completely opposite tendency

Chemical Transformation Simulator

Science.gov (United States)

The Chemical Transformation Simulator (CTS) is a web-based, high-throughput screening tool that automates the calculation and collection of physicochemical properties for an organic chemical of interest and its predicted products resulting from transformations in environmental sy...

Grain-boundary melting: A Monte Carlo study

DEFF Research Database (Denmark)

Besold, Gerhard; Mouritsen, Ole G.

1994-01-01

Grain-boundary melting in a lattice-gas model of a bicrystal is studied by Monte Carlo simulation using the grand canonical ensemble. Well below the bulk melting temperature T(m), a disordered liquidlike layer gradually emerges at the grain boundary. Complete interfacial wetting can be observed...... when the temperature approaches T(m) from below. Monte Carlo data over an extended temperature range indicate a logarithmic divergence w(T) approximately - ln(T(m)-T) of the width of the disordered layer w, in agreement with mean-field theory....

Changes in the metallicity of gas giant planets due to pebble accretion

Science.gov (United States)

Humphries, R. J.; Nayakshin, S.

2018-06-01

We run numerical simulations to study the accretion of gas and dust grains on to gas giant planets embedded into massive protoplanetary discs. The outcome is found to depend on the disc cooling rate, planet mass, grain size, and irradiative feedback from the planet. If radiative cooling is efficient, planets accrete both gas and pebbles rapidly, open a gap, and usually become massive brown dwarfs. In the inefficient cooling case, gas is too hot to accrete on to the planet but pebble accretion continues and the planets migrate inward rapidly. Radiative feedback from the planet tends to suppress gas accretion. Our simulations predict that metal enrichment of planets by dust grain accretion inversely correlates with the final planet mass, in accordance with the observed trend in the inferred bulk composition of Solar system and exosolar giant planets. To account for observations, however, as many as ˜30-50 per cent of the dust mass should be in the form of large grains.

Fission gas release and grain growth in THO2-UO2 fuel irradiated at high temperature

International Nuclear Information System (INIS)

Goldberg, I.; Waldman, L.A.; Giovengo, J.F.; Campbell, W.R.

1979-01-01

Data are presented on fission gas release and grain growth in ThO 2 -UO 2 fuels irradiated as part of the LWBR fuel element development program. These data for rods that experienced peak linear power outputs ranging from 15 to 22 KW/ft supplement fission gas release data previously reported for 51 rods containing ThO 2 and ThO 2 -UO 2 fuel irradiated at peak linear powers predominantly below 14 KW/ft. Fission gas release was relatively high (up to 15.0 percent) for the rods operated at high power in contrast to the relatively low fission gas release (0.1 to 5.2 percent) measured for the rods operated at lower power. Metallographic examination revealed extensive equiaxed grain growth in the fuel at the high power axial locations of the three rods

Laboratory simulation of interstellar grain chemistry and the production of complex organic molecules

Science.gov (United States)

Allamandola, L. J.; Sandford, S. A.; Valero, G. J.

1990-01-01

During the past 15 years considerable progress in observational techniques has been achieved in the middle infrared (5000 to 500 cm(-1), 2 to 20 microns m), the spectral region most diagnostic of molecular vibrations. Spectra of many different astronomical infrared sources, some deeply embedded in dark molecular clouds, are now available. These spectra provide a powerful probe, not only for the identification of interstellar molecules in both the gas solid phases, but also of the physical and chemical conditions which prevail in these two very different domains. By comparing these astronomical spectra with the spectra of laboratory ices one can determine the composition and abundance of the icy materials frozen on the cold (10K) dust grains present in the interior of molecular clouds. These grains and their ice mantles may well be the building blocks from which comets are made. As an illustration of the processes which can take place as an ice is irradiated and subsequently warmed, researchers present the infrared spectra of the mixture H2O:CH3OH:CO:NH3:C6H14 (100:50:10:10:10). Apart from the last species, the ratio of these compounds is representative of the simplest ices found in interstellar clouds. The last component was incorporated into this particular experiment as a tracer of the behavior of a non-aromatic hydrocarbon. The change in the composition that results from ultraviolet photolysis of this ice mixture using a UV lamp to simulate the interstellar radiation field is shown. Photolysis produces CO, CO2, CH4, HCO, H2CO, as well as a family of moderately volatile hydrocarbons. Less volatile carbonaceous materials are also produced. The evolution of the infrared spectrum of the ice as the sample is warmed up to room temperature is illustrated. Researchers believe that the changes are similar to those which occur as ice is ejected from a comet and warmed up by solar radiation. The warm-up sequence shows that the nitrile or iso-nitrile bearing compound

Coarse-grained stochastic processes and kinetic Monte Carlo simulators for the diffusion of interacting particles

Science.gov (United States)

Katsoulakis, Markos A.; Vlachos, Dionisios G.

2003-11-01

We derive a hierarchy of successively coarse-grained stochastic processes and associated coarse-grained Monte Carlo (CGMC) algorithms directly from the microscopic processes as approximations in larger length scales for the case of diffusion of interacting particles on a lattice. This hierarchy of models spans length scales between microscopic and mesoscopic, satisfies a detailed balance, and gives self-consistent fluctuation mechanisms whose noise is asymptotically identical to the microscopic MC. Rigorous, detailed asymptotics justify and clarify these connections. Gradient continuous time microscopic MC and CGMC simulations are compared under far from equilibrium conditions to illustrate the validity of our theory and delineate the errors obtained by rigorous asymptotics. Information theory estimates are employed for the first time to provide rigorous error estimates between the solutions of microscopic MC and CGMC, describing the loss of information during the coarse-graining process. Simulations under periodic boundary conditions are used to verify the information theory error estimates. It is shown that coarse-graining in space leads also to coarse-graining in time by q2, where q is the level of coarse-graining, and overcomes in part the hydrodynamic slowdown. Operation counting and CGMC simulations demonstrate significant CPU savings in continuous time MC simulations that vary from q3 for short potentials to q4 for long potentials. Finally, connections of the new coarse-grained stochastic processes to stochastic mesoscopic and Cahn-Hilliard-Cook models are made.

Heat transfer simulation in a furnace for steam reformer. Gas kaishitsu ronai no dennetsu simulation ni kansuru kenkyu

Energy Technology Data Exchange (ETDEWEB)

Kudo, K; Taniguchi, H; Guo, K [Hokkaido Univ., Sapporo (Japan). Faculty of Engineering; Katayama, T; Nagata, T [Tokyo Gas Co. Ltd., Tokyo (Japan)

1991-01-10

This paper discusses the heat transfer analysis in a furnace for LPG reforming to produce gas enriched hydrogen. The three-dimensional combined radiative and convective heat transfer processes in a furnace for LPG reforming is simulated by introducing the radiosity concept into the radiative heat ray method for an accurate radiative heat transfer analysis. Together with an analysis of the chemical reaction in the reactor tubes of the furnace, the heat transfer simulation gives the three-dimensional profile of the combustion gas temperature in the furnace, the tube-surface heat-flux distribution and the composition of the reformed gas. From the results of the analysis, it was clarified that increasing the jet angle of the heating burner raises the gas temperature and the tube surface heat flux near the burner entrance, and that the flame shape is the most important factor for deciding the heat flux distribution of the tube surface because the heat transfer effect by flame radiation is much more than that by convection of the combustion gas. 18 refs., 9 figs., 2 tabs.

Enhancing of chemical compound and drug name recognition using representative tag scheme and fine-grained tokenization.

Science.gov (United States)

Dai, Hong-Jie; Lai, Po-Ting; Chang, Yung-Chun; Tsai, Richard Tzong-Han

2015-01-01

The functions of chemical compounds and drugs that affect biological processes and their particular effect on the onset and treatment of diseases have attracted increasing interest with the advancement of research in the life sciences. To extract knowledge from the extensive literatures on such compounds and drugs, the organizers of BioCreative IV administered the CHEMical Compound and Drug Named Entity Recognition (CHEMDNER) task to establish a standard dataset for evaluating state-of-the-art chemical entity recognition methods. This study introduces the approach of our CHEMDNER system. Instead of emphasizing the development of novel feature sets for machine learning, this study investigates the effect of various tag schemes on the recognition of the names of chemicals and drugs by using conditional random fields. Experiments were conducted using combinations of different tokenization strategies and tag schemes to investigate the effects of tag set selection and tokenization method on the CHEMDNER task. This study presents the performance of CHEMDNER of three more representative tag schemes-IOBE, IOBES, and IOB12E-when applied to a widely utilized IOB tag set and combined with the coarse-/fine-grained tokenization methods. The experimental results thus reveal that the fine-grained tokenization strategy performance best in terms of precision, recall and F-scores when the IOBES tag set was utilized. The IOBES model with fine-grained tokenization yielded the best-F-scores in the six chemical entity categories other than the "Multiple" entity category. Nonetheless, no significant improvement was observed when a more representative tag schemes was used with the coarse or fine-grained tokenization rules. The best F-scores that were achieved using the developed system on the test dataset of the CHEMDNER task were 0.833 and 0.815 for the chemical documents indexing and the chemical entity mention recognition tasks, respectively. The results herein highlight the importance

Testing thermal gradient driving force for grain boundary migration using molecular dynamics simulations

International Nuclear Information System (INIS)

Bai, Xian-Ming; Zhang, Yongfeng; Tonks, Michael R.

2015-01-01

Strong thermal gradients in low-thermal-conductivity ceramics may drive extended defects, such as grain boundaries and voids, to migrate in preferential directions. In this work, molecular dynamics simulations are conducted to study thermal gradient driven grain boundary migration and to verify a previously proposed thermal gradient driving force equation, using uranium dioxide as a model system. It is found that a thermal gradient drives grain boundaries to migrate up the gradient and the migration velocity increases under a constant gradient owing to the increase in mobility with temperature. Different grain boundaries migrate at very different rates due to their different intrinsic mobilities. The extracted mobilities from the thermal gradient driven simulations are compared with those calculated from two other well-established methods and good agreement between the three different methods is found, demonstrating that the theoretical equation of the thermal gradient driving force is valid, although a correction of one input parameter should be made. The discrepancy in the grain boundary mobilities between modeling and experiments is also discussed.

THE EFFECTS OF GRAIN SIZE AND TEMPERATURE DISTRIBUTIONS ON THE FORMATION OF INTERSTELLAR ICE MANTLES

Energy Technology Data Exchange (ETDEWEB)

Pauly, Tyler; Garrod, Robin T., E-mail: tap74@cornell.edu [Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY 14853-6801 (United States)

2016-02-01

Computational models of interstellar gas-grain chemistry have historically adopted a single dust-grain size of 0.1 micron, assumed to be representative of the size distribution present in the interstellar medium. Here, we investigate the effects of a broad grain-size distribution on the chemistry of dust-grain surfaces and the subsequent build-up of molecular ices on the grains, using a three-phase gas-grain chemical model of a quiescent dark cloud. We include an explicit treatment of the grain temperatures, governed both by the visual extinction of the cloud and the size of each individual grain-size population. We find that the temperature difference plays a significant role in determining the total bulk ice composition across the grain-size distribution, while the effects of geometrical differences between size populations appear marginal. We also consider collapse from a diffuse to a dark cloud, allowing dust temperatures to fall. Under the initial diffuse conditions, small grains are too warm to promote grain-mantle build-up, with most ices forming on the mid-sized grains. As collapse proceeds, the more abundant, smallest grains cool and become the dominant ice carriers; the large population of small grains means that this ice is distributed across many grains, with perhaps no more than 40 monolayers of ice each (versus several hundred assuming a single grain size). This effect may be important for the subsequent processing and desorption of the ice during the hot-core phase of star formation, exposing a significant proportion of the ice to the gas phase, increasing the importance of ice-surface chemistry and surface–gas interactions.

The Effects of Grain Size and Temperature Distributions on the Formation of Interstellar Ice Mantles

Science.gov (United States)

Pauly, Tyler; Garrod, Robin T.

2016-02-01

Computational models of interstellar gas-grain chemistry have historically adopted a single dust-grain size of 0.1 micron, assumed to be representative of the size distribution present in the interstellar medium. Here, we investigate the effects of a broad grain-size distribution on the chemistry of dust-grain surfaces and the subsequent build-up of molecular ices on the grains, using a three-phase gas-grain chemical model of a quiescent dark cloud. We include an explicit treatment of the grain temperatures, governed both by the visual extinction of the cloud and the size of each individual grain-size population. We find that the temperature difference plays a significant role in determining the total bulk ice composition across the grain-size distribution, while the effects of geometrical differences between size populations appear marginal. We also consider collapse from a diffuse to a dark cloud, allowing dust temperatures to fall. Under the initial diffuse conditions, small grains are too warm to promote grain-mantle build-up, with most ices forming on the mid-sized grains. As collapse proceeds, the more abundant, smallest grains cool and become the dominant ice carriers; the large population of small grains means that this ice is distributed across many grains, with perhaps no more than 40 monolayers of ice each (versus several hundred assuming a single grain size). This effect may be important for the subsequent processing and desorption of the ice during the hot-core phase of star formation, exposing a significant proportion of the ice to the gas phase, increasing the importance of ice-surface chemistry and surface-gas interactions.

Study on the Effect of Diamond Grain Size on Wear of Polycrystalline Diamond Compact Cutter

Science.gov (United States)

Abdul-Rani, A. M.; Che Sidid, Adib Akmal Bin; Adzis, Azri Hamim Ab

2018-03-01

Drilling operation is one of the most crucial step in oil and gas industry as it proves the availability of oil and gas under the ground. Polycrystalline Diamond Compact (PDC) bit is a type of bit which is gaining popularity due to its high Rate of Penetration (ROP). However, PDC bit can easily wear off especially when drilling hard rock. The purpose of this study is to identify the relationship between the grain sizes of the diamond and wear rate of the PDC cutter using simulation-based study with FEA software (ABAQUS). The wear rates of a PDC cutter with a different diamond grain sizes were calculated from simulated cuttings of cutters against granite. The result of this study shows that the smaller the diamond grain size, the higher the wear resistivity of PDC cutter.

Archie’s saturation exponent for natural gas hydrate in coarse-grained reservoirs

Science.gov (United States)

Cook, Ann E.; Waite, William F.

2018-01-01

Accurately quantifying the amount of naturally occurring gas hydrate in marine and permafrost environments is important for assessing its resource potential and understanding the role of gas hydrate in the global carbon cycle. Electrical resistivity well logs are often used to calculate gas hydrate saturations, Sh, using Archie's equation. Archie's equation, in turn, relies on an empirical saturation parameter, n. Though n = 1.9 has been measured for ice‐bearing sands and is widely used within the hydrate community, it is highly questionable if this n value is appropriate for hydrate‐bearing sands. In this work, we calibrate n for hydrate‐bearing sands from the Canadian permafrost gas hydrate research well, Mallik 5L‐38, by establishing an independent downhole Sh profile based on compressional‐wave velocity log data. Using the independently determined Sh profile and colocated electrical resistivity and bulk density logs, Archie's saturation equation is solved for n, and uncertainty is tracked throughout the iterative process. In addition to the Mallik 5L‐38 well, we also apply this method to two marine, coarse‐grained reservoirs from the northern Gulf of Mexico Gas Hydrate Joint Industry Project: Walker Ridge 313‐H and Green Canyon 955‐H. All locations yield similar results, each suggesting n ≈ 2.5 ± 0.5. Thus, for the coarse‐grained hydrate bearing (Sh > 0.4) of greatest interest as potential energy resources, we suggest that n = 2.5 ± 0.5 should be applied in Archie's equation for either marine or permafrost gas hydrate settings if independent estimates of n are not available.

The MARTINI force field : Coarse grained model for biomolecular simulations

NARCIS (Netherlands)

Marrink, Siewert J.; Risselada, H. Jelger; Yefimov, Serge; Tieleman, D. Peter; de Vries, Alex H.

2007-01-01

We present an improved and extended version of our coarse grained lipid model. The new version, coined the MARTINI force field, is parametrized in a systematic way, based on the reproduction of partitioning free energies between polar and apolar phases of a large number of chemical compounds. To

Dust grain charging in a wake of other grains

International Nuclear Information System (INIS)

Miloch, W. J.; Block, D.

2012-01-01

The charging of dust grain in the wake of another grains in sonic and supersonic collisionless plasma flows is studied by numerical simulations. We consider two grains aligned with the flow, as well as dust chains and multiple grain arrangements. It is found that the dust charge depends significantly on the flow speed, distance between the grains, and the grain arrangement. For two and three grains aligned, the charges on downstream grains depend linearly on the flow velocity and intergrain distance. The simulations are carried out with DiP3D, a three dimensional particle-in-cell code with both electrons and ions represented as numerical particles [W. J. Miloch et al., Phys. Plasmas 17, 103703 (2010)].

Aerosol simulation including chemical and nuclear reactions

International Nuclear Information System (INIS)

Marwil, E.S.; Lemmon, E.C.

1985-01-01

The numerical simulation of aerosol transport, including the effects of chemical and nuclear reactions presents a challenging dynamic accounting problem. Particles of different sizes agglomerate and settle out due to various mechanisms, such as diffusion, diffusiophoresis, thermophoresis, gravitational settling, turbulent acceleration, and centrifugal acceleration. Particles also change size, due to the condensation and evaporation of materials on the particle. Heterogeneous chemical reactions occur at the interface between a particle and the suspending medium, or a surface and the gas in the aerosol. Homogeneous chemical reactions occur within the aersol suspending medium, within a particle, and on a surface. These reactions may include a phase change. Nuclear reactions occur in all locations. These spontaneous transmutations from one element form to another occur at greatly varying rates and may result in phase or chemical changes which complicate the accounting process. This paper presents an approach for inclusion of these effects on the transport of aerosols. The accounting system is very complex and results in a large set of stiff ordinary differential equations (ODEs). The techniques for numerical solution of these ODEs require special attention to achieve their solution in an efficient and affordable manner. 4 refs

DUST DYNAMICS IN PROTOPLANETARY DISK WINDS DRIVEN BY MAGNETOROTATIONAL TURBULENCE: A MECHANISM FOR FLOATING DUST GRAINS WITH CHARACTERISTIC SIZES

Energy Technology Data Exchange (ETDEWEB)

Miyake, Tomoya; Suzuki, Takeru K.; Inutsuka, Shu-ichiro, E-mail: miyake.tomoya@e.mbox.nagoya-u.ac.jp, E-mail: stakeru@nagoya-u.jp [Department of Physics, Nagoya University, Nagoya, Aichi 464-8602 (Japan)

2016-04-10

We investigate the dynamics of dust grains of various sizes in protoplanetary disk winds driven by magnetorotational turbulence, by simulating the time evolution of the dust grain distribution in the vertical direction. Small dust grains, which are well-coupled to the gas, are dragged upward with the upflowing gas, while large grains remain near the midplane of a disk. Intermediate-size grains float near the sonic point of the disk wind located at several scale heights from the midplane, where the grains are loosely coupled to the background gas. For the minimum mass solar nebula at 1 au, dust grains with size of 25–45 μm float around 4 scale heights from the midplane. Considering the dependence on the distance from the central star, smaller-size grains remain only in an outer region of the disk, while larger-size grains are distributed in a broader region. We also discuss the implications of our result for observations of dusty material around young stellar objects.

Coupled Thermo-Hydro-Mechanical-Chemical Modeling of Water Leak-Off Process during Hydraulic Fracturing in Shale Gas Reservoirs

Directory of Open Access Journals (Sweden)

Fei Wang

2017-11-01

Full Text Available The water leak-off during hydraulic fracturing in shale gas reservoirs is a complicated transport behavior involving thermal (T, hydrodynamic (H, mechanical (M and chemical (C processes. Although many leak-off models have been published, none of the models fully coupled the transient fluid flow modeling with heat transfer, chemical-potential equilibrium and natural-fracture dilation phenomena. In this paper, a coupled thermo-hydro-mechanical-chemical (THMC model based on non-equilibrium thermodynamics, hydrodynamics, thermo-poroelastic rock mechanics, and non-isothermal chemical-potential equations is presented to simulate the water leak-off process in shale gas reservoirs. The THMC model takes into account a triple-porosity medium, which includes hydraulic fractures, natural fractures and shale matrix. The leak-off simulation with the THMC model involves all the important processes in this triple-porosity medium, including: (1 water transport driven by hydraulic, capillary, chemical and thermal osmotic convections; (2 gas transport induced by both hydraulic pressure driven convection and adsorption; (3 heat transport driven by thermal convection and conduction; and (4 natural-fracture dilation considered as a thermo-poroelastic rock deformation. The fluid and heat transport, coupled with rock deformation, are described by a set of partial differential equations resulting from the conservation of mass, momentum, and energy. The semi-implicit finite-difference algorithm is proposed to solve these equations. The evolution of pressure, temperature, saturation and salinity profiles of hydraulic fractures, natural fractures and matrix is calculated, revealing the multi-field coupled water leak-off process in shale gas reservoirs. The influences of hydraulic pressure, natural-fracture dilation, chemical osmosis and thermal osmosis on water leak-off are investigated. Results from this study are expected to provide a better understanding of the

Simulation of granular and gas-solid flows using discrete element method

Science.gov (United States)

Boyalakuntla, Dhanunjay S.

2003-10-01

In recent years there has been increased research activity in the experimental and numerical study of gas-solid flows. Flows of this type have numerous applications in the energy, pharmaceuticals, and chemicals process industries. Typical applications include pulverized coal combustion, flow and heat transfer in bubbling and circulating fluidized beds, hopper and chute flows, pneumatic transport of pharmaceutical powders and pellets, and many more. The present work addresses the study of gas-solid flows using computational fluid dynamics (CFD) techniques and discrete element simulation methods (DES) combined. Many previous studies of coupled gas-solid flows have been performed assuming the solid phase as a continuum with averaged properties and treating the gas-solid flow as constituting of interpenetrating continua. Instead, in the present work, the gas phase flow is simulated using continuum theory and the solid phase flow is simulated using DES. DES treats each solid particle individually, thus accounting for its dynamics due to particle-particle interactions, particle-wall interactions as well as fluid drag and buoyancy. The present work involves developing efficient DES methods for dense granular flow and coupling this simulation to continuum simulations of the gas phase flow. Simulations have been performed to observe pure granular behavior in vibrating beds. Benchmark cases have been simulated and the results obtained match the published literature. The dimensionless acceleration amplitude and the bed height are the parameters governing bed behavior. Various interesting behaviors such as heaping, round and cusp surface standing waves, as well as kinks, have been observed for different values of the acceleration amplitude for a given bed height. Furthermore, binary granular mixtures (granular mixtures with two particle sizes) in a vibrated bed have also been studied. Gas-solid flow simulations have been performed to study fluidized beds. Benchmark 2D

Simulation of an integrated gasification combined cycle with chemical-looping combustion and carbon dioxide sequestration

International Nuclear Information System (INIS)

Jiménez Álvaro, Ángel; López Paniagua, Ignacio; González Fernández, Celina; Rodríguez Martín, Javier; Nieto Carlier, Rafael

2015-01-01

Highlights: • A chemical-looping combustion based integrated gasification combined cycle is simulated. • The energetic performance of the plant is analyzed. • Different hydrogen-content synthesis gases are under study. • Energy savings accounting carbon dioxide sequestration and storage are quantified. • A notable increase on thermal efficiency up to 7% is found. - Abstract: Chemical-looping combustion is an interesting technique that makes it possible to integrate power generation from fuels combustion and sequestration of carbon dioxide without energy penalty. In addition, the combustion chemical reaction occurs with a lower irreversibility compared to a conventional combustion, leading to attain a somewhat higher overall thermal efficiency in gas turbine systems. This paper provides results about the energetic performance of an integrated gasification combined cycle power plant based on chemical-looping combustion of synthesis gas. A real understanding of the behavior of this concept of power plant implies a complete thermodynamic analysis, involving several interrelated aspects as the integration of energy flows between the gasifier and the combined cycle, the restrictions in relation with heat balances and chemical equilibrium in reactors and the performance of the gas turbines and the downstream steam cycle. An accurate thermodynamic modeling is required for the optimization of several design parameters. Simulations to evaluate the energetic efficiency of this chemical-looping-combustion based power plant under diverse working conditions have been carried out, and a comparison with a conventional integrated gasification power plant with precombustion capture of carbon dioxide has been made. Two different synthesis gas compositions have been tried to check its influence on the results. The energy saved in carbon capture and storage is found to be significant and even notable, inducing an improvement of the overall power plant thermal efficiency of

Impact of chemical leaching on permeability and cadmium removal from fine-grained soils.

Science.gov (United States)

Lin, Zhongbing; Zhang, Renduo; Huang, Shuang; Wang, Kang

2017-08-01

The aim of this study was to investigate the influence of chemical leaching on permeability and Cd removal from fine-grained polluted soils. Column leaching experiments were conducted using two types of soils (i.e., artificially Cd-polluted loam and historically polluted silty loam). Chemical agents of CaCl 2 , FeCl 3 , citric acid, EDTA, rhamnolipid, and deionized water were used to leach Cd from the soils. Results showed that organic agents reduced permeability of both soils, and FeCl 3 reduced permeability of loam soil, compared with inorganic agents and deionized water. Entrapment and deposition of colloids generated from the organic agents and FeCl 3 treatments reduced the soil permeability. The peak Cd effluence from the artificially polluted loam columns was retarded. For the artificially polluted soils treated with EDTA and the historically polluted soils with FeCl 3 , Cd precipitates were observed at the bottom after chemical leaching. When Cd was associated with large colloid particles, the reduction of soil permeability caused Cd accumulation in deeper soil. In addition, the slow process of disintegration of soil clay during chemical leaching might result in the retardation of peak Cd effluence. These results suggest the need for caution when using chemical-leaching agents for Cd removal in fine-grained soils.

ANALYSIS AND IDENTIFICATION SPIKING CHEMICAL COMPOUNDS RELATED TO CHEMICAL WEAPON CONVENTION IN UNKNOWN WATER SAMPLES USING GAS CHROMATOGRAPHY AND GAS CHROMATOGRAPHY ELECTRON IONIZATION MASS SPECTROMETRY

Directory of Open Access Journals (Sweden)

Harry Budiman

2010-06-01

Full Text Available The identification and analysis of chemical warfare agents and their degradation products is one of important component for the implementation of the convention. Nowadays, the analytical method for determination chemical warfare agent and their degradation products has been developing and improving. In order to get the sufficient analytical data as recommended by OPCW especially in Proficiency Testing, the spiking chemical compounds related to Chemical Weapon Convention in unknown water sample were determined using two different techniques such as gas chromatography and gas chromatography electron-impact ionization mass spectrometry. Neutral organic extraction, pH 11 organic extraction, cation exchanged-methylation, triethylamine/methanol-silylation were performed to extract the chemical warfare agents from the sample, before analyzing with gas chromatography. The identification of chemical warfare agents was carried out by comparing the mass spectrum of chemicals with mass spectrum reference from the OPCW Central Analytical Database (OCAD library while the retention indices calculation obtained from gas chromatography analysis was used to get the confirmation and supported data of  the chemical warfare agents. Diisopropyl methylphosphonate, 2,2-diphenyl-2-hydroacetic acid and 3-quinuclidinol were found in unknown water sample. Those chemicals were classified in schedule 2 as precursor or reactant of chemical weapons compound in schedule list of Chemical Weapon Convention.   Keywords: gas chromatography, mass spectrometry, retention indices, OCAD library, chemical warfare agents

Laser diagnostics of a diamond depositing chemical vapour deposition gas-phase environment

International Nuclear Information System (INIS)

Smith, James Anthony

2002-01-01

Studies have been carried out to understand the gas-phase chemistry underpinning diamond deposition in hot filament and DC-arcjet chemical vapour deposition (CVD) systems. Resonance enhanced Multiphoton lonisation (REMPI) techniques were used to measure the relative H atom and CH 3 radical number densities and local gas temperatures prevalent in a hot filament reactor, operating on Ch 4 /H 2 and C 2 H 2 /H 2 gas mixtures. These results were compared to a 3D-computer simulation, and hence provided an insight into the nature of the gas-phase chemistry with particular reference to C 2 →C 1 species conversion. Similar experimental and theoretical studies were also carried out to explain the chemistry involved in NH 3 /CH 4 /H 2 and N 2 /CH 4 /H 2 gas mixtures. It was demonstrated that the reactive nature of the filament surface was dependent on the addition of NH 3 , influencing atomic hydrogen production, and thus the H/C/N gas-phase chemistry. Studies of the DC-arcjet diamond CVD reactor consisted of optical emission spectroscopic studies of the plume during deposition from an Ar/H 2 /CH 4 /N 2 gas mixture. Spatially resolved species emission intensity maps were obtained for C 2 (d→a), CN(B→X) and H β from Abel-inverted datasets. The C 2 (d→a) and CN(B→X) emission intensity maps both show local maxima near the substrate surface. SEM and Laser Raman analyses indicate that N 2 additions lead to a reduction in film quality and growth rate. Photoluminescence and SIMS analyses of the grown films provide conclusive evidence of nitrogen incorporation (as chemically bonded CN). Absolute column densities of C 2 (a) in a DC-arcjet reactor operating on an Ar/H 2 /CH 4 gas mixture, were measured using Cavity ring down spectroscopy. Simulations of the measured C 2 (v=0) transition revealed a rotational temperature of ∼3300 K. This gas temperature is similar to that deduced from optical emission spectroscopy studies of the C 2 (d→a) transition. (author)

Effect of Time-Dependent Pinning Pressure on Abnormal Grain Growth: Phase Field Simulation

Science.gov (United States)

Kim, Jeong Min; Min, Guensik; Shim, Jae-Hyeok; Lee, Kyung Jong

2018-05-01

The effect of the time-dependent pinning pressure of precipitates on abnormal grain growth has been investigated by multiphase field simulation with a simple precipitation model. The application of constant pinning pressure is problematic because it always induces abnormal grain growth or no grain growth, which is not reasonable considering the real situation. To produce time-dependent pinning pressure, both precipitation kinetics and precipitate coarsening kinetics have been considered with two rates: slow and fast. The results show that abnormal grain growth is suppressed at the slow precipitation rate. At the slow precipitation rate, the overall grain growth caused by the low pinning pressure in the early stage indeed plays a role in preventing abnormal grain growth by reducing the mobility advantage of abnormal grains. In addition, the fast precipitate coarsening rate tends to more quickly transform abnormal grain growth into normal grain growth by inducing the active growth of grains adjacent to the abnormal grains in the early stage. Therefore, the present study demonstrates that the time dependence of the pinning pressure of precipitates is a critical factor that determines the grain growth mode.

Hormonal changes in the grains of rice subjected to water stress during grain filling.

Science.gov (United States)

Yang, J; Zhang, J; Wang, Z; Zhu, Q; Wang, W

2001-09-01

Lodging-resistant rice (Oryza sativa) cultivars usually show slow grain filling when nitrogen is applied in large amounts. This study investigated the possibility that a hormonal change may mediate the effect of water deficit that enhances whole plant senescence and speeds up grain filling. Two rice cultivars showing high lodging resistance and slow grain filling were field grown and applied with either normal or high amount nitrogen (HN) at heading. Well-watered and water-stressed (WS) treatments were imposed 9 days post anthesis to maturity. Results showed that WS increased partitioning of fixed (14)CO(2) into grains, accelerated the grain filling rate but shortened the grain filling period, whereas the HN did the opposite way. Cytokinin (zeatin + zeatin riboside) and indole-3-acetic acid contents in the grains transiently increased at early filling stage and WS treatments hastened their declines at the late grain filling stage. Gibberellins (GAs; GA(1) + GA(4)) in the grains were also high at early grain filling but HN enhanced, whereas WS substantially reduced, its accumulation. Opposite to GAs, abscisic acid (ABA) in the grains was low at early grain filling but WS remarkably enhanced its accumulation. The peak values of ABA were significantly correlated with the maximum grain filling rates (r = 0.92**, P water stress during grain filling, especially a decrease in GAs and an increase in ABA, enhances the remobilization of prestored carbon to the grains and accelerates the grain filling rate.

The Effect of High Temperature Annealing on the Grain Characteristics of a Thin Chemical Vapor Deposition Silicon Carbide Layer.

Energy Technology Data Exchange (ETDEWEB)

Isabella J van Rooyen; Philippus M van Rooyen; Mary Lou Dunzik-Gougar

2013-08-01

The unique combination of thermo-mechanical and physiochemical properties of silicon carbide (SiC) provides interest and opportunity for its use in nuclear applications. One of the applications of SiC is as a very thin layer in the TRi-ISOtropic (TRISO) coated fuel particles for high temperature gas reactors (HTGRs). This SiC layer, produced by chemical vapor deposition (CVD), is designed to withstand the pressures of fission and transmutation product gases in a high temperature, radiation environment. Various researchers have demonstrated that macroscopic properties can be affected by changes in the distribution of grain boundary plane orientations and misorientations [1 - 3]. Additionally, various researchers have attributed the release behavior of Ag through the SiC layer as a grain boundary diffusion phenomenon [4 - 6]; further highlighting the importance of understanding the actual grain characteristics of the SiC layer. Both historic HTGR fission product release studies and recent experiments at Idaho National Laboratory (INL) [7] have shown that the release of Ag-110m is strongly temperature dependent. Although the maximum normal operating fuel temperature of a HTGR design is in the range of 1000-1250°C, the temperature may reach 1600°C under postulated accident conditions. The aim of this specific study is therefore to determine the magnitude of temperature dependence on SiC grain characteristics, expanding upon initial studies by Van Rooyen et al, [8; 9].

Simulating of Top-Cross system for enhancement of antioxidants in maize grain

Directory of Open Access Journals (Sweden)

Jelena Vancetovic

2014-04-01

Full Text Available Blue maize (Zea mays L. is grown for its high content of antioxidants. Conversion of yellow and white to blue maize is time consuming because several genes affect blue color. After each backcross selfing is needed for color to be expressed. In order to overcome the problem of time and effort needed for conversion to blue kernel color, we have set a pilot experiment simulating a Top-cross system for increasing antioxidants in maize grain. The idea is to alternately sow six rows of sterile standard quality hybrid and two rows of blue maize in commercial production. Five commercial ZP hybrids were crossed with a blue pop-corn population. Xenia effect caused by cross-pollination produced blue grain on all hybrids in the same year. Chemical analyses of the grains of five selfed original hybrids, five cross-pollinated hybrids and selfed blue popcorn pollinator were performed. Cross-fertilization with blue popcorn had different impact on antioxidant capacity and phytonutrients, increasing them significantly in some but not all cross-pollinated hybrids. Popcorn blue pollinator had higher values for all the analyzed traits than either selfed or cross-pollinated hybrids. Selfed vs. pollinated hybrids showed significant difference for total antioxidant capacity (p<0.1, total phenolics and total yellow pigments (p<0.01, with the increase of total phenolics and decrease of total yellow pigments in pollinated ones. Total flavonoids showed a little non-significant decrease in pollinated hybrids, while total anthocyanins were not detected in selfed yellow hybrids. Blue maize obtained this way has shown good potential for growing high quality phytonutrient genotypes.

SIMULATION AND PRELIMINARY ECONOMIC ANALYSIS OF A COMPLEX OF NUTRIENTS USING CAMISEA GAS

OpenAIRE

Porlles L., J.; Cárdenas R., J.

2014-01-01

Peru is in fact a country with important reservoirs of natural gas as Camisea and it opens potential opportunities for gas chemical development. In a mark of a higher enterprise competitiveness, in industry any time is more generalized to account with tools as support for enhanced of process and cost savings. The simulation and optimization of industrial process aided by computer is a powerful alternative. This work has as propose to make the design of a process an economical analysis with pr...

Constraining gas hydrate occurrence in the northern Gulf of Mexico continental slope : fine scale analysis of grain-size in hydrate-bearing sediments

Energy Technology Data Exchange (ETDEWEB)

Hangsterfer, A.; Driscoll, N.; Kastner, M. [Scripps Inst. of Oceanography, La Jolla, CA (United States). Geosciences Research Division

2008-07-01

Methane hydrates can form within the gas hydrate stability zone (GHSZ) in sea beds. The Gulf of Mexico (GOM) contains an underlying petroleum system and deeply buried, yet dynamic salt deposits. Salt tectonics and fluid expulsion upward through the sediment column result in the formation of fractures, through which high salinity brines migrate into the GHSZ, destabilizing gas hydrates. Thermogenic and biogenic hydrocarbons also migrate to the seafloor along the GOMs northern slope, originating from the thermal and biogenic degradation of organic matter. Gas hydrate occurrence can be controlled by either primary permeability, forming in coarse-grained sediment layers, or by secondary permeability, forming in areas where hydrofracture and faulting generate conduits through which hydrocarbon-saturated fluids flow. This paper presented a study that attempted to determine the relationship between grain-size, permeability, and gas hydrate distribution. Grain-size analyses were performed on cores taken from Keathley Canyon and Atwater Valley in the GOM, on sections of cores that both contained and lacked gas hydrate. Using thermal anomalies as proxies for the occurrence of methane hydrate within the cores, samples of sediment were taken and the grain-size distributions were measured to see if there was a correlation between gas hydrate distribution and grain-size. The paper described the methods, including determination of hydrate occurrence and core analysis. It was concluded that gas hydrate occurrence in Keathley Canyon and Atwater Valley was constrained by secondary permeability and was structurally controlled by hydrofractures and faulting that acted as conduits through which methane-rich fluids flowed. 11 refs., 2 tabs., 5 figs.

Grain preservation in SSSR

International Nuclear Information System (INIS)

Trisviatski, L.A.

1973-01-01

First the importance of cereals collected in the S.S.S.R., the reason why the government had to put in practice a storage chain, composed of large capacity store houses (200 000 metric tonnes, or more) is reminded. When climatic conditions result in wet harvested grains, cereals are dried either in state enterprise dryers (32 to 50 tonnes/hour) or in kolkhozes' dryers (2 to 16 tonnes/hour). A new type of drying with recycling, has been developped, economizing 10 to 15 p. 100. Then the possibilities offered by the technique of partial drying of very wet grains are studied and the preservation processes using fresh ventilation, or hot ventilation with drying effect are described. The question of silage of wet grains destined to animal consumption is then examined as well as preservation by sodium pyrosulfide; the use of propionic acid, little developped in SSSR, is studied now, just as storage with inert gas. The struggle technics against insects, either with chemical agents, or with irradiation are described. Finally the modalities of technicians formation, specialized in preservation, are discussed [fr

An Ideal Gas Law Simulator for Atmospheric Gas Molecules ...

African Journals Online (AJOL)

The ideal gas law which is the equation of state of a hypothetical ideal gas that allows us to gain useful insights into the behavior of most real gases at low densities was utilized in this work to conceptualize, design and develop the ideal gas law simulator in a 3 dimensional space using Microsoft Visual Studio, Microsoft ...

Effect of Strain Restored Energy on Abnormal Grain Growth in Mg Alloy Simulated by Phase Field Methods

Science.gov (United States)

Wu, Yan; Huang, Yuan-yuan

2018-03-01

Abnormal grain growth of single phase AZ31 Mg alloy in the spatio-temporal process has been simulated by phase field models, and the influencing factors of abnormal grain growth are studied in order to find the ways to control secondary recrystallization in the microstructure. The study aims to find out the mechanisms for abnormal grain growth in real alloys. It is shown from the simulated results that the abnormal grain growth can be controlled by the strain restored energy. Secondary recrystallization after an annealing treatment can be induced if there are grains of a certain orientation in the microstructure with local high restored energy. However, if the value of the local restored energy at a certain grain orientation is not greater than 1.1E 0, there may be no abnormal grain growth in the microstructure.

Cohesion of Mm- to Cm-Sized Asteroid Simulant Grains: An Experimental Study

Science.gov (United States)

Brisset, Julie; Colwell, Joshua E.; Dove, Adrienne; Jarmak, Stephanie; Anderson, Seamus

2017-10-01

The regolith covering the surfaces of asteroids and planetary satellites is very different from terrestrial soil particles and subject to environmental conditions very different from what is found on Earth. The loose, unconsolidated granular material has angular-shaped grains and a broad size distribution. On small and airless bodies (Earth surface gravity, the cohesion behavior of the regolith grains will dictate the asteroid’s surface morphology and its response to impact or spacecraft contact.Previous laboratory experiments on low-velocity impacts into regolith simulant with grain sizes landing missions to small bodies such as asteroids or Martian moons.

Origin of chemically distinct discs in the Auriga cosmological simulations

Science.gov (United States)

Grand, Robert J. J.; Bustamante, Sebastián; Gómez, Facundo A.; Kawata, Daisuke; Marinacci, Federico; Pakmor, Rüdiger; Rix, Hans-Walter; Simpson, Christine M.; Sparre, Martin; Springel, Volker

2018-03-01

The stellar disc of the Milky Way shows complex spatial and abundance structure that is central to understanding the key physical mechanisms responsible for shaping our Galaxy. In this study, we use six very high resolution cosmological zoom-in simulations of Milky Way-sized haloes to study the prevalence and formation of chemically distinct disc components. We find that our simulations develop a clearly bimodal distribution in the [α/Fe]-[Fe/H] plane. We find two main pathways to creating this dichotomy, which operate in different regions of the galaxies: (a) an early (z > 1) and intense high-[α/Fe] star formation phase in the inner region (R ≲ 5 kpc) induced by gas-rich mergers, followed by more quiescent low-[α/Fe] star formation; and (b) an early phase of high-[α/Fe] star formation in the outer disc followed by a shrinking of the gas disc owing to a temporarily lowered gas accretion rate, after which disc growth resumes. In process (b), a double-peaked star formation history around the time and radius of disc shrinking accentuates the dichotomy. If the early star formation phase is prolonged (rather than short and intense), chemical evolution proceeds as per process (a) in the inner region, but the dichotomy is less clear. In the outer region, the dichotomy is only evident if the first intense phase of star formation covers a large enough radial range before disc shrinking occurs; otherwise, the outer disc consists of only low-[α/Fe] sequence stars. We discuss the implication that both processes occurred in the Milky Way.

The Chemical Product Simulator - ProCAPD

DEFF Research Database (Denmark)

Kalakul, Sawitree; Eden, Mario Richard; Gani, Rafiqul

2017-01-01

In this paper, a chemical product design simulator called ProCAPD is presented. ProCAPD works in the same way as a chemical process simulator, that is, it helps to verify product design decisions and generates information that can be used to make design decisions. Like the contents of the process...... simulator, the product simulator needs a database of chemicals and properties, a library of models, numerical routines to solve mathematical problems as well as various calculation options. Also, like the process simulator, the product simulator comes with a user-interface to describe the problems.......); calculation tools (product attributes, blend compositions, environmental impact, etc.); design templates (single molecules, blends, formulations, emulsions, devices); and, design-simulation-analysis functions. All these capabilities are based on the prototype tool developed by Kalakul et al. (2017...

Carbon-Nanotube-Based Chemical Gas Sensor

Science.gov (United States)

Kaul, Arunpama B.

2010-01-01

Conventional thermal conductivity gauges (e.g. Pirani gauges) lend themselves to applications such as leak detectors, or in gas chromatographs for identifying various gas species. However, these conventional gauges are physically large, operate at high power, and have a slow response time. A single-walled carbon-nanotube (SWNT)-based chemical sensing gauge relies on differences in thermal conductance of the respective gases surrounding the CNT as it is voltage-biased, as a means for chemical identification. Such a sensor provides benefits of significantly reduced size and compactness, fast response time, low-power operation, and inexpensive manufacturing since it can be batch-fabricated using Si integrated-circuit (IC) process technology.

Direct Monte Carlo simulation of nanoscale mixed gas bearings

Directory of Open Access Journals (Sweden)

Kyaw Sett Myo

2015-06-01

Full Text Available The conception of sealed hard drives with helium gas mixture has been recently suggested over the current hard drives for achieving higher reliability and less position error. Therefore, it is important to understand the effects of different helium gas mixtures on the slider bearing characteristics in the head–disk interface. In this article, the helium/air and helium/argon gas mixtures are applied as the working fluids and their effects on the bearing characteristics are studied using the direct simulation Monte Carlo method. Based on direct simulation Monte Carlo simulations, the physical properties of these gas mixtures such as mean free path and dynamic viscosity are achieved and compared with those obtained from theoretical models. It is observed that both results are comparable. Using these gas mixture properties, the bearing pressure distributions are calculated under different fractions of helium with conventional molecular gas lubrication models. The outcomes reveal that the molecular gas lubrication results could have relatively good agreement with those of direct simulation Monte Carlo simulations, especially for pure air, helium, or argon gas cases. For gas mixtures, the bearing pressures predicted by molecular gas lubrication model are slightly larger than those from direct simulation Monte Carlo simulation.

Chemical behaviour of zinc in cover gas environments

International Nuclear Information System (INIS)

Thorley, A.W; Blundell, A.; Lloyd, R.

1987-01-01

The possibility that enhancement of 65-Zn in the cover gas regions of reactor plant may increase levels of radioactivity and provide potential embrittlement situations has lead to a limited metallurgical and chemical investigation into how this element behaves in cover gas environments. This paper reports the chemical findings from those investigations and compare results obtained with those anticipated from thermodynamic predictions

Computer simulation of 2D grain growth using a cellular automata model based on the lowest energy principle

International Nuclear Information System (INIS)

He Yizhu; Ding Hanlin; Liu Liufa; Shin, Keesam

2006-01-01

The morphology, topology and kinetics of normal grain growth in two-dimension were studied by computer simulation using a cellular automata (Canada) model based on the lowest energy principle. The thermodynamic energy that follows Maxwell-Boltzmann statistics has been introduced into this model for the calculation of energy change. The transition that can reduce the system energy to the lowest level is chosen to occur when there is more than one possible transition direction. The simulation results show that the kinetics of normal grain growth follows the Burke equation with the growth exponent m = 2. The analysis of topology further indicates that normal grain growth can be simulated fairly well by the present CA model. The vanishing of grains with different number of sides is discussed in the simulation

Prediction of methylmercury accumulation in rice grains by chemical extraction methods

International Nuclear Information System (INIS)

Zhu, Dai-Wen; Zhong, Huan; Zeng, Qi-Long; Yin, Ying

2015-01-01

To explore the possibility of using chemical extraction methods to predict phytoavailability/bioaccumulation of soil-bound MeHg, MeHg extractions by three widely-used extractants (CaCl 2 , DTPA, and (NH 4 ) 2 S 2 O 3 ) were compared with MeHg accumulation in rice grains. Despite of variations in characteristics of different soils, MeHg extracted by (NH 4 ) 2 S 2 O 3 (highly affinitive to MeHg) correlated well with grain MeHg levels. Thus (NH 4 ) 2 S 2 O 3 extraction, solubilizing not only weakly-bound and but also strongly-bound MeHg, may provide a measure of ‘phytoavailable MeHg pool’ for rice plants. Besides, a better prediction of grain MeHg levels was obtained when growing condition of rice plants was also considered. However, MeHg extracted by CaCl 2 or DTPA, possibly quantifying ‘exchangeable MeHg pool’ or ‘weakly-complexed MeHg pool’ in soils, may not indicate phytoavailable MeHg or predict grain MeHg levels. Our results provided the possibility of predicting MeHg phytoavailability/bioaccumulation by (NH 4 ) 2 S 2 O 3 extraction, which could be useful in screening soils for rice cultivation in contaminated areas. - Highlights: • MeHg extraction by (NH 4 ) 2 S 2 O 3 correlates well with its accumulation in rice grains. • MeHg extraction by (NH 4 ) 2 S 2 O 3 provides a measure of phytoavailable MeHg in soils. • Some strongly-bound MeHg could be desorbed from soils and available to rice plants. • MeHg extraction by CaCl 2 or DTPA could not predict grain MeHg levels. - Methylmercury extraction from soils by (NH 4 ) 2 S 2 O 3 could possibly be used for predicting methylmercury phytoavailability and its bioaccumulation in rice grains

CHARMM-GUI Martini Maker for Coarse-Grained Simulations with the Martini Force Field

NARCIS (Netherlands)

Qi, Yifei; Ingolfsson, Helgi I.; Cheng, Xi; Lee, Jumin; Marrink, Siewert J.; Im, Wonpil

Coarse-grained simulations are widely used to study large biological systems. Nonetheless, building such simulation systems becomes nontrivial, especially when membranes with various lipid types are involved. Taking advantage of the frameworks in all-atom CHARMM-GUI modules, we have developed

Dynamic simulation of a furnace of steam reforming of natural gas

International Nuclear Information System (INIS)

Acuna, A; Fuentes, C; Smith, C A

1999-01-01

Steam reforming of natural gas is a very important industrial process in refineries and ammonia and methanol plants. Hydrogen is produced by reforming methane with steam. This hydrogen is essential in the hydro-treating process in the refineries thus, it is important to supervise and control the performance of the hydrogen plant. Mathematical models of refineries and chemical plants are used to simulate the behavior of the process units. However, the models especially of reactors like reformers are not very reliable. This paper presents a dynamic model of a furnace-reactor. The simulation results are validated with industrial data

Synthesis of few layer single crystal graphene grains on platinum by chemical vapour deposition

Directory of Open Access Journals (Sweden)

S. Karamat

2015-08-01

Full Text Available The present competition of graphene electronics demands an efficient route which produces high quality and large area graphene. Chemical vapour deposition technique, where hydrocarbons dissociate in to active carbon species and form graphene layer on the desired metal catalyst via nucleation is considered as the most suitable method. In this study, single layer graphene with the presence of few layer single crystal graphene grains were grown on Pt foil via chemical vapour deposition. The higher growth temperature changes the surface morphology of the Pt foil so a delicate process of hydrogen bubbling was used to peel off graphene from Pt foil samples with the mechanical support of photoresist and further transferred to SiO2/Si substrates for analysis. Optical microscopy of the graphene transferred samples showed the regions of single layer along with different oriented graphene domains. Two type of interlayer stacking sequences, Bernal and twisted, were observed in the graphene grains. The presence of different stacking sequences in the graphene layers influence the electronic and optical properties; in Bernal stacking the band gap can be tunable and in twisted stacking the overall sheet resistance can be reduced. Grain boundaries of Pt provides low energy sites to the carbon species, therefore the nucleation of grains are more at the boundaries. The stacking order and the number of layers in grains were seen more clearly with scanning electron microscopy. Raman spectroscopy showed high quality graphene samples due to very small D peak. 2D Raman peak for single layer graphene showed full width half maximum (FWHM value of 30 cm−1. At points A, B and C, Bernal stacked grain showed FWHM values of 51.22, 58.45 and 64.72 cm−1, while twisted stacked grain showed the FWHM values of 27.26, 28.83 and 20.99 cm−1, respectively. FWHM values of 2D peak of Bernal stacked grain showed an increase of 20–30 cm−1 as compare to single layer graphene

Investigating the influence of lithologic heterogeneity on gas hydrate formation and methane recycling at the base of the gas hydrate stability zone in channelized systems

Energy Technology Data Exchange (ETDEWEB)

Daigle, Hugh; Nole, Michael; Cook, Ann; Malinverno, Alberto

2017-12-14

In marine environments, gas hydrate preferentially accumulates in coarse-grained sediments. At the meso- to micro-scale, however, hydrate distribution in these coarse-grained units is often heterogeneous. We employ a methane hydrate reservoir simulator coupling heat and mass transfer as well as capillary effects to investigate how capillary controls on methane solubility affect gas and hydrate accumulations in reservoirs characterized by graded bedding and alternating sequences of coarse-grained sands and fine-grained silt and clay. Simulations bury a channelized reservoir unit encased in homogeneous, fine-grained material characterized by small pores (150 nm) and low permeability (~1 md in the absence of hydrate). Pore sizes within each reservoir bed between vary between coarse sand and fine silt. Sands have a median pore size of 35 microns and a lognormal pore size distribution. We also investigate how the amount of labile organic carbon (LOC) affects hydrate growth due to microbial methanogenesis within the sediments. In a diffusion-dominated system, methane movies into reservoir layers along spatial gradients in dissolved methane concentration. Hydrate grows in such a way as to minimize these concentration gradients by accumulating slower in finer-grained reservoir layers and faster in coarser-grained layers. Channelized, fining-upwards sediment bodies accumulate hydrate first along their outer surfaces and thence inward from top to bottom. If LOC is present in thin beds within the channel, higher saturations of hydrate will be distributed more homogeneously throughout the unit. When buried beneath the GHSZ, gas recycling can occur only if enough hydrate is present to form a connected gas phase upon dissociation. Simulations indicate that this is difficult to achieve for diffusion-dominated systems, especially those with thick GHSZs and/or small amounts of LOC. However, capillary-driven fracturing behavior may be more prevalent in settings with thick GHSZs.

An analytical coarse-graining method which preserves the free energy, structural correlations, and thermodynamic state of polymer melts from the atomistic to the mesoscale.

Science.gov (United States)

McCarty, J; Clark, A J; Copperman, J; Guenza, M G

2014-05-28

Structural and thermodynamic consistency of coarse-graining models across multiple length scales is essential for the predictive role of multi-scale modeling and molecular dynamic simulations that use mesoscale descriptions. Our approach is a coarse-grained model based on integral equation theory, which can represent polymer chains at variable levels of chemical details. The model is analytical and depends on molecular and thermodynamic parameters of the system under study, as well as on the direct correlation function in the k → 0 limit, c0. A numerical solution to the PRISM integral equations is used to determine c0, by adjusting the value of the effective hard sphere diameter, dHS, to agree with the predicted equation of state. This single quantity parameterizes the coarse-grained potential, which is used to perform mesoscale simulations that are directly compared with atomistic-level simulations of the same system. We test our coarse-graining formalism by comparing structural correlations, isothermal compressibility, equation of state, Helmholtz and Gibbs free energies, and potential energy and entropy using both united atom and coarse-grained descriptions. We find quantitative agreement between the analytical formalism for the thermodynamic properties, and the results of Molecular Dynamics simulations, independent of the chosen level of representation. In the mesoscale description, the potential energy of the soft-particle interaction becomes a free energy in the coarse-grained coordinates which preserves the excess free energy from an ideal gas across all levels of description. The structural consistency between the united-atom and mesoscale descriptions means the relative entropy between descriptions has been minimized without any variational optimization parameters. The approach is general and applicable to any polymeric system in different thermodynamic conditions.

Comparative analysis of physico-chemical and gas sensing characteristics of two different forms of SnO{sub 2} films

Energy Technology Data Exchange (ETDEWEB)

Kwoka, M., E-mail: Monika.Kwoka@polsl.pl [Institute of Electronics, Silesian University of Technology, 44-100 Gliwice (Poland); Ottaviano, L. [CNR- SPIN & Department of Physics and Chemical Sciences, University of L’Aquila, 67100 (Italy); Szuber, J. [Institute of Electronics, Silesian University of Technology, 44-100 Gliwice (Poland)

2017-04-15

Highlights: • Two different forms of SnO{sub 2} deposited on Si substrate. • Crystallinity and surface/subsurface morphology controlled by XRD, SEM and AFM. • Surface/subsurface chemistry including stoichiometry and contaminations derived from XPS. • Comparative analysis of gas sensor characteristics of SnO{sub 2} in NO{sub 2} atmosphere. • Correlations between physico-chemical properties and gas sensor characteristics. - Abstract: In this paper the results of studies of comparative studies on the crystallinity, morphology and chemistry combined with the gas sensor response of two different forms of tin dioxide (SnO{sub 2}) films prepared by the Rheotaxial Growth and Thermal Oxidation (RGTO) and by the Laser-enhanced Chemical Vapour Deposition (L-CVD) methods, respectively, are presented. For this purpose the X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and X-ray Photoelectron spectroscopy (XPS) have been used. XRD studies for both samples show the contribution from the crystalline SnO{sub 2} in the cassiterite rutile phase without any evident contribution from the tin oxide (SnO) phase. SEM and AFM studies show that the surface morphology of RGTO and L-CVD SnO{sub 2} samples are characterized by grains/nanograins of different size and surface roughness. In turn XPS studies confirm that for both SnO{sub 2} samples a slight nonstoichiometry with a relative [O]/[Sn] concentration of 1.8, and slightly different amount of C contamination at the surface of internal grains with relative [C]/[Sn] concentration of 3.5 and 3.2, respectively. This undesired C contamination cannot be ignored because it creates an uncontrolled barrier for the potential gas adsorption at the internal surface of sensor material. This is confirmed by the gas sensor response in NO{sub 2} atmosphere of both SnO{sub 2} samples because the sensitivity is evidently smaller for RGTO SnO{sub 2} with respect to the L-CVD SnO{sub 2} samples, whereas

Simulation of grain boundary effects on electronic transport in metals, and detailed causes of scattering

Energy Technology Data Exchange (ETDEWEB)

Feldman, Baruch [Process Technology Modeling, Design and Technology Solutions, Technology and Manufacturing Group, Intel Corporation, Santa Clara, CA 95052 (United States); Department of Physics, University of Washington, Seattle, WA 98195 (United States); Park, Seongjun; Haverty, Michael; Shankar, Sadasivan [Process Technology Modeling, Design and Technology Solutions, Technology and Manufacturing Group, Intel Corporation, Santa Clara, CA 95052 (United States); Dunham, Scott T. [Department of Physics, University of Washington, Seattle, WA 98195 (United States); Department of Electrical Engineering, University of Washington, Seattle, WA 98195 (United States)

2010-07-15

We present first-principles simulations of single grain boundary reflectivity of electrons in noble metals, Cu and Ag. We examine twin and non-twin grain boundaries using non-equilibrium Green's function and first principles methods. We also investigate the determinants of reflectivity in grain boundaries by modeling atomic vacancies, disorder, and orientation and find that both the change in grain orientation and disorder in the boundary itself contribute significantly to reflectivity. We find that grain boundary reflectivity may vary widely depending on the grain boundary structure, consistent with published experimental results. Finally, we examine the reflectivity from multiple grain boundaries and find that grain boundary reflectivity may depend on neighboring grain boundaries. This study raises some potential limitations in the independent grain boundary assumptions of the Mayadas-Shatzkes (MS) model. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

Chemical pre-processing of cluster galaxies over the past 10 billion years in the IllustrisTNG simulations

Science.gov (United States)

Gupta, Anshu; Yuan, Tiantian; Torrey, Paul; Vogelsberger, Mark; Martizzi, Davide; Tran, Kim-Vy H.; Kewley, Lisa J.; Marinacci, Federico; Nelson, Dylan; Pillepich, Annalisa; Hernquist, Lars; Genel, Shy; Springel, Volker

2018-06-01

We use the IllustrisTNG simulations to investigate the evolution of the mass-metallicity relation (MZR) for star-forming cluster galaxies as a function of the formation history of their cluster host. The simulations predict an enhancement in the gas-phase metallicities of star-forming cluster galaxies (109 cluster galaxies appears prior to their infall into the central cluster potential, indicating for the first time a systematic `chemical pre-processing' signature for infalling cluster galaxies. Namely, galaxies that will fall into a cluster by z = 0 show a ˜0.05 dex enhancement in the MZR compared to field galaxies at z ≤ 0.5. Based on the inflow rate of gas into cluster galaxies and its metallicity, we identify that the accretion of pre-enriched gas is the key driver of the chemical evolution of such galaxies, particularly in the stellar mass range (109 clusters. Our results motivate future observations looking for pre-enrichment signatures in dense environments.

A coarse-graining approach for molecular simulation that retains the dynamics of the all-atom reference system by implementing hydrodynamic interactions

Energy Technology Data Exchange (ETDEWEB)

Markutsya, Sergiy [Ames Laboratory, Iowa State University, Ames, Iowa 50011 (United States); Lamm, Monica H., E-mail: mhlamm@iastate.edu [Ames Laboratory, Iowa State University, Ames, Iowa 50011 (United States); Department of Chemical and Biological Engineering, Iowa State University, Ames, Iowa 50011 (United States)

2014-11-07

We report on a new approach for deriving coarse-grained intermolecular forces that retains the frictional contribution that is often discarded by conventional coarse-graining methods. The approach is tested for water and an aqueous glucose solution, and the results from the new implementation for coarse-grained molecular dynamics simulation show remarkable agreement with the dynamics obtained from reference all-atom simulations. The agreement between the structural properties observed in the coarse-grained and all-atom simulations is also preserved. We discuss how this approach may be applied broadly to any existing coarse-graining method where the coarse-grained models are rigorously derived from all-atom reference systems.

A coarse-graining approach for molecular simulation that retains the dynamics of the all-atom reference system by implementing hydrodynamic interactions

International Nuclear Information System (INIS)

Markutsya, Sergiy; Lamm, Monica H.

2014-01-01

We report on a new approach for deriving coarse-grained intermolecular forces that retains the frictional contribution that is often discarded by conventional coarse-graining methods. The approach is tested for water and an aqueous glucose solution, and the results from the new implementation for coarse-grained molecular dynamics simulation show remarkable agreement with the dynamics obtained from reference all-atom simulations. The agreement between the structural properties observed in the coarse-grained and all-atom simulations is also preserved. We discuss how this approach may be applied broadly to any existing coarse-graining method where the coarse-grained models are rigorously derived from all-atom reference systems

Laser diagnostics of a diamond depositing chemical vapour deposition gas-phase environment

Energy Technology Data Exchange (ETDEWEB)

Smith, James Anthony

2002-07-01

Studies have been carried out to understand the gas-phase chemistry underpinning diamond deposition in hot filament and DC-arcjet chemical vapour deposition (CVD) systems. Resonance enhanced Multiphoton lonisation (REMPI) techniques were used to measure the relative H atom and CH{sub 3} radical number densities and local gas temperatures prevalent in a hot filament reactor, operating on Ch{sub 4}/H{sub 2} and C{sub 2}H{sub 2}/H{sub 2} gas mixtures. These results were compared to a 3D-computer simulation, and hence provided an insight into the nature of the gas-phase chemistry with particular reference to C{sub 2}{yields}C{sub 1} species conversion. Similar experimental and theoretical studies were also carried out to explain the chemistry involved in NH{sub 3}/CH{sub 4}/H{sub 2} and N{sub 2}/CH{sub 4}/H{sub 2} gas mixtures. It was demonstrated that the reactive nature of the filament surface was dependent on the addition of NH{sub 3}, influencing atomic hydrogen production, and thus the H/C/N gas-phase chemistry. Studies of the DC-arcjet diamond CVD reactor consisted of optical emission spectroscopic studies of the plume during deposition from an Ar/H{sub 2}/CH{sub 4}/N{sub 2} gas mixture. Spatially resolved species emission intensity maps were obtained for C{sub 2}(d{yields}a), CN(B{yields}X) and H{sub {beta}} from Abel-inverted datasets. The C{sub 2}(d{yields}a) and CN(B{yields}X) emission intensity maps both show local maxima near the substrate surface. SEM and Laser Raman analyses indicate that N{sub 2} additions lead to a reduction in film quality and growth rate. Photoluminescence and SIMS analyses of the grown films provide conclusive evidence of nitrogen incorporation (as chemically bonded CN). Absolute column densities of C{sub 2}(a) in a DC-arcjet reactor operating on an Ar/H{sub 2}/CH{sub 4} gas mixture, were measured using Cavity ring down spectroscopy. Simulations of the measured C{sub 2}(v=0) transition revealed a rotational temperature of {approx

The HIFI spectral survey of AFGL 2591 (CHESS). III. Chemical structure of the protostellar envelope

Science.gov (United States)

Kaźmierczak-Barthel, M.; Semenov, D. A.; van der Tak, F. F. S.; Chavarría, L.; van der Wiel, M. H. D.

2015-02-01

Aims: The aim of this work is to understand the richness of chemical species observed in the isolated high-mass envelope of AFGL 2591, a prototypical object for studying massive star formation. Methods: Based on HIFI and JCMT data, the molecular abundances of species found in the protostellar envelope of AFGL 2591 were derived with a Monte Carlo radiative transfer code (Ratran), assuming a mixture of constant and 1D stepwise radial profiles for abundance distributions. The reconstructed 1D abundances were compared with the results of the time-dependent gas-grain chemical modeling, using the best-fit 1D power-law density structure. The chemical simulations were performed considering ages of 1-5 × 104 years, cosmic ray ionization rates of 5-500 × 10-17 s-1, uniformly-sized 0.1-1 μm dust grains, a dust/gas ratio of 1%, and several sets of initial molecular abundances with C/O 1. The most important model parameters varied one by one in the simulations are age, cosmic ray ionization rate, external UV intensity, and grain size. Results: Constant abundance models give good fits to the data for CO, CN, CS, HCO+, H2CO, N2H+, CCH, NO, OCS, OH, H2CS, O, C, C+, and CH. Models with an abundance jump at 100 K give good fits to the data for NH3, SO, SO2, H2S, H2O, HCl, and CH3OH. For HCN and HNC, the best models have an abundance jump at 230 K. The time-dependent chemical model can accurately explain abundance profiles of 15 out of these 24 species. The jump-like radial profiles for key species like HCO+, NH3, and H2O are consistent with the outcome of the time-dependent chemical modeling. The best-fit model has a chemical age of ~10-50 kyr, a solar C/O ratio of 0.44, and a cosmic-ray ionization rate of ~5 × 10-17 s-1. The grain properties and the intensity of the external UV field do not strongly affect the chemical structure of the AFGL 2591 envelope, whereas its chemical age, the cosmic-ray ionization rate, and the initial abundances play an important role. Conclusions: We

Microgravity experiments on a granular gas of elongated grains

Science.gov (United States)

Harth, K.; Trittel, T.; Kornek, U.; Höme, S.; Will, K.; Strachauer, U.; Stannarius, R.

2013-06-01

Granular gases represent well-suited systems to investigate statistical granular dynamics. The literature comprises numerous investigations of ensembles of spherical or irregularly shaped grains. Mainly computer models, analytical theories and experiments restricted to two dimensions were reported. In three-dimensions, the gaseous state can only be maintained by strong external excitation, e. g. vibrations or electro-magnetic fields, or in microgravity. A steady state, where the dynamics of a weakly disturbed granular gas are governed by particle-particle collisions, is hard to realize with spherical grains due to clustering. We present the first study of a granular gas of elongated cylinders in three dimensions. The mean free path is considerably reduced with respect to spheres at comparable filling fractions. The particles can be tracked in 3D over a sequence of frames. In a homogeneous steady state, we find non-Gaussian velocity distributions and a lack of equipartition of kinetic energy. We discuss the relations between energy input and vibrating plate accelerations. At the request of the authors and the Proceedings Editors, the PDF file of this article has been updated to amend some references present in the PDF file submitted to AIP Publishing. The references affected are listed here:[1] (c) K. Nichol and K. E. Daniels, Phys. Rev. Lett. 108, 018001 (2012); [11] (e) P. G. de Gennes and J. Prost, The Physics of Liquid Crystals, Clarendon Press, Oxford (1993); [17] (b) K. Harth, et al., Phys. Rev. Lett. 110, 144102 (2013).A LaTeX processing error resulted in changes to the authors reference formatting, which was not detected prior to publication. Due apologies are given to the authors for this oversight. The updated article PDF was published on 12 August 2013.

Nuclear spin relaxation due to chemical shift anisotropy of gas-phase 129Xe.

Science.gov (United States)

Hanni, Matti; Lantto, Perttu; Vaara, Juha

2011-08-14

Nuclear spin relaxation provides detailed dynamical information on molecular systems and materials. Here, first-principles modeling of the chemical shift anisotropy (CSA) relaxation time for the prototypic monoatomic (129)Xe gas is carried out, both complementing and predicting the results of NMR measurements. Our approach is based on molecular dynamics simulations combined with pre-parametrized ab initio binary nuclear shielding tensors, an "NMR force field". By using the Redfield relaxation formalism, the simulated CSA time correlation functions lead to spectral density functions that, for the first time, quantitatively determine the experimental spin-lattice relaxation times T(1). The quality requirements on both the Xe-Xe interaction potential and binary shielding tensor are investigated in the context of CSA T(1). Persistent dimers Xe(2) are found to be responsible for the CSA relaxation mechanism in the low-density limit of the gas, completely in line with the earlier experimental findings.

Influence of titanium–boron additions on grain refinement of AA6082 gas tungsten arc welds

International Nuclear Information System (INIS)

Kishore Babu, N.; Talari, Mahesh Kumar; Dayou, Pan; Zheng, Sun; Jun, Wei; SivaPrasad, K.

2012-01-01

Highlights: ► Ti in the weld metal resulted in grain refinement due to growth restriction effect. ► Weld metal strength improved due to grain refinement caused by Tibor™ addition. ► Weld metal responded to post-weld ageing treatment due to dilution from base metal. ► Weld metal with AA5356 filler are stronger then AA4043 for all Tibor™ additions. -- Abstract: Grain refinement of weld metal plays a vital role in improving mechanical properties (ductility and toughness) as well as weldability. The present study has investigated the influence of Tibor™ additions on the structure and mechanical properties of AA6082 gas tungsten arc (GTA) weldments. Controlled amounts of Tibor™ grain refiner (containing Ti and B in a ratio of 5:1) were introduced into the molten pool of AA6082 by pre-deposited cast inserts (AA4043 and AA5356) under different welding conditions by GTA welding. Full penetration GTA welds were prepared using alternating current (AC). It was observed that grain size was decreased with increasing amounts of Tibor™. The grain refinement is mainly caused grain nucleation associated with constitutional undercooling during solidification. It has been shown that welds prepared with 5356 cast insert exhibited high strength and ductility when compared with other welds. The observed grain refinement was shown to result in an appreciable increase in fusion zone hardness, strength and ductility.

Inhomogeneous Oxygen Vacancy Distribution in Semiconductor Gas Sensors: Formation, Migration and Determination on Gas Sensing Characteristics.

Science.gov (United States)

Liu, Jianqiao; Gao, Yinglin; Wu, Xu; Jin, Guohua; Zhai, Zhaoxia; Liu, Huan

2017-08-10

The density of oxygen vacancies in semiconductor gas sensors was often assumed to be identical throughout the grain in the numerical discussion of the gas-sensing mechanism of the devices. In contrast, the actual devices had grains with inhomogeneous distribution of oxygen vacancy under non-ideal conditions. This conflict between reality and discussion drove us to study the formation and migration of the oxygen defects in semiconductor grains. A model of the gradient-distributed oxygen vacancy was proposed based on the effects of cooling rate and re-annealing on semiconductive thin films. The model established the diffusion equations of oxygen vacancy according to the defect kinetics of diffusion and exclusion. We described that the steady-state and transient-state oxygen vacancy distributions, which were used to calculate the gas-sensing characteristics of the sensor resistance and response to reducing gases under two different conditions. The gradient-distributed oxygen vacancy model had the applications in simulating the sensor performances, such as the power law, the grain size effect and the effect of depletion layer width.

Inhomogeneous Oxygen Vacancy Distribution in Semiconductor Gas Sensors: Formation, Migration and Determination on Gas Sensing Characteristics

Directory of Open Access Journals (Sweden)

Jianqiao Liu

2017-08-01

Full Text Available The density of oxygen vacancies in semiconductor gas sensors was often assumed to be identical throughout the grain in the numerical discussion of the gas-sensing mechanism of the devices. In contrast, the actual devices had grains with inhomogeneous distribution of oxygen vacancy under non-ideal conditions. This conflict between reality and discussion drove us to study the formation and migration of the oxygen defects in semiconductor grains. A model of the gradient-distributed oxygen vacancy was proposed based on the effects of cooling rate and re-annealing on semiconductive thin films. The model established the diffusion equations of oxygen vacancy according to the defect kinetics of diffusion and exclusion. We described that the steady-state and transient-state oxygen vacancy distributions, which were used to calculate the gas-sensing characteristics of the sensor resistance and response to reducing gases under two different conditions. The gradient-distributed oxygen vacancy model had the applications in simulating the sensor performances, such as the power law, the grain size effect and the effect of depletion layer width.

Grain-resolving simulations of settling cohesive sediment

Science.gov (United States)

Vowinckel, Bernhard; Whithers, Jade; Meiburg, Eckart; Luzzatto-Fegiz, Paolo

2017-11-01

Cohesive sediment is ubiquitous in natural environments such as rivers, lakes and coastal ecosystems. For this type of sediment, we can no longer ignore the short-range attractive forces that result in flocculation of aggregates much larger than the individual grain size. Hence, understanding the complex dynamics of the interplay between flocculated sediment and the ambient fluid is of prime interest for managing aquatic environments, although a comprehensive understanding of these phenomena is still lacking. In the present study, we address this issue by carrying out grain-resolved simulations of cohesive particles settling under gravity using the Immersed Boundary Method. We present a computational model formulation to accurately resolve the process of flocculation. The cohesive model is then applied to a complex test case. A randomly distributed ensemble of 1261 polydisperse particles is released in a tank of quiescent fluid. Subsequently, particles start to settle, thereby replacing fluid at the bottom of the tank, which induces a counter flow opposing the settling direction. This mechanism will be compared to experimental studies from the literature, as well as to the non-cohesive counterpart to assessthe impact of flocculation on sedimentation.

The Effect of Zeolite Composition and Grain Size on Gas Sensing Properties of SnO2/Zeolite Sensor

Directory of Open Access Journals (Sweden)

Yanhui Sun

2018-01-01

Full Text Available In order to improve the sensing properties of tin dioxide gas sensor, four kinds of different SiO2/Al2O3 ratio, different particle size of MFI type zeolites (ZSM-5 were coated on the SnO2 to prepared zeolite modified gas sensors, and the gas sensing properties were tested. The measurement results showed that the response values of ZSM-5 zeolite (SiO2/Al2O3 = 70, grain size 300 nm coated SnO2 gas sensors to formaldehyde vapor were increased, and the response to acetone decreased compared with that of SnO2 gas sensor, indicating an improved selectivity property. The other three ZSM-5 zeolites with SiO2/Al2O3 70, 150 and 470, respectively, and grain sizes all around 1 μm coated SnO2 sensors did not show much difference with SnO2 sensor for the response properties to both formaldehyde and acetone. The sensing mechanism of ZSM-5 modified sensors was briefly analyzed.

Origins of GEMS Grains

Science.gov (United States)

Messenger, S.; Walker, R. M.

2012-01-01

Interplanetary dust particles (IDPs) collected in the Earth s stratosphere contain high abundances of submicrometer amorphous silicates known as GEMS grains. From their birth as condensates in the outflows of oxygen-rich evolved stars, processing in interstellar space, and incorporation into disks around new stars, amorphous silicates predominate in most astrophysical environments. Amorphous silicates were a major building block of our Solar System and are prominent in infrared spectra of comets. Anhydrous interplanetary dust particles (IDPs) thought to derive from comets contain abundant amorphous silicates known as GEMS (glass with embedded metal and sulfides) grains. GEMS grains have been proposed to be isotopically and chemically homogenized interstellar amorphous silicate dust. We evaluated this hypothesis through coordinated chemical and isotopic analyses of GEMS grains in a suite of IDPs to constrain their origins. GEMS grains show order of magnitude variations in Mg, Fe, Ca, and S abundances. GEMS grains do not match the average element abundances inferred for ISM dust containing on average, too little Mg, Fe, and Ca, and too much S. GEMS grains have complementary compositions to the crystalline components in IDPs suggesting that they formed from the same reservoir. We did not observe any unequivocal microstructural or chemical evidence that GEMS grains experienced prolonged exposure to radiation. We identified four GEMS grains having O isotopic compositions that point to origins in red giant branch or asymptotic giant branch stars and supernovae. Based on their O isotopic compositions, we estimate that 1-6% of GEMS grains are surviving circumstellar grains. The remaining 94-99% of GEMS grains have O isotopic compositions that are indistinguishable from terrestrial materials and carbonaceous chondrites. These isotopically solar GEMS grains either formed in the Solar System or were completely homogenized in the interstellar medium (ISM). However, the

Micromagnetic simulation of the orientation dependence of grain boundary properties on the coercivity of Nd-Fe-B sintered magnets

Directory of Open Access Journals (Sweden)

Jun Fujisaki

2016-05-01

Full Text Available This paper is focused on the micromagnetic simulation study about the orientation dependence of grain boundary properties on the coercivity of polycrystalline Nd-Fe-B sintered magnets. A multigrain object with a large number of meshes is introduced to analyze such anisotropic grain boundaries and the simulation is performed by combining the finite element method and the parallel computing. When the grain boundary phase parallel to the c-plane is less ferromagnetic the process of the magnetization reversal changes and the coercivity of the multigrain object increases. The simulations with various magnetic properties of the grain boundary phases are executed to search for the way to enhance the coercivity of polycrystalline Nd-Fe-B sintered magnets.

Tracer concentration contours in grain lattice and grain boundary diffusion

International Nuclear Information System (INIS)

Kim, Y. S.; Olander, D. R.

1997-01-01

Grain boundary diffusion plays a significant role in fission gas release, which is one of the crucial processes dominating nuclear fuel performance. Gaseous fission products such as Xe and Kr generated during nuclear fission have to diffuse in the grain lattice and the boundary inside fuel pellets before they reach the open spaces in a fuel rod. These processes can be studied by 'tracer diffusion' techniques, by which grain boundary diffusivity can be estimated and directly used for low burn-up fission gas release analysis. However, only a few models accounting for the both processes are available and mostly handle them numerically due to mathematical complexity. Also the numerical solution has limitations in a practical use. In this paper, an approximate analytical solution in case of stationary grain boundary in a polycrystalline solid is developed for the tracer diffusion techniques. This closed-form solution is compared to available exact and numerical solutions and it turns out that it makes computation not only greatly easier but also more accurate than previous models. It can be applied to theoretical modelings for low burn-up fission gas release phenomena and experimental analyses as well, especially for PIE (post irradiation examination). (author)

Simulation of the operation of an industrial wet flue gas desulfurization system

International Nuclear Information System (INIS)

Kallinikos, L.E.; Farsari, E.I.; Spartinos, D.N.; Papayannakos, N.G.

2010-01-01

In this work the simulation of a wet flue gas desulfurization (FGD) unit with spray tower of a power plant is presented, aiming at an efficient follow-up and the optimization of the FGD system operation. The dynamic model developed to simulate the performance of the system has been validated with operation data collected over a long period of time. All the partaking physical and chemical processes like the limestone dissolution, the crystallization of calcium sulfite and gypsum and the oxidation of sulfite ions have been taken into account for the development of the simulation model while the gas absorption by the liquid droplets was based on the two-film theory. The effect of the mean diameter of the slurry droplets on the performance of the system was examined, as it was used as an index factor of the normal operation of the system. The operation limits of the system were investigated on the basis of the model developed. It is concluded that the model is capable of simulating the system for significantly different SO 2 loads and that the absorption rate of SO 2 is strongly affected by the liquid dispersion in the tower. (author)

A UNIFIED MODEL OF GRAIN ALIGNMENT: RADIATIVE ALIGNMENT OF INTERSTELLAR GRAINS WITH MAGNETIC INCLUSIONS

Energy Technology Data Exchange (ETDEWEB)

Hoang, Thiem [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Lazarian, A. [Department of Astronomy, University of Wisconsin-Madison (United States)

2016-11-10

The radiative torque (RAT) alignment of interstellar grains with ordinary paramagnetic susceptibilities has been supported by earlier studies. The alignment of such grains depends on the so-called RAT parameter q {sup max}, which is determined by the grain shape. In this paper, we elaborate on our model of RAT alignment for grains with enhanced magnetic susceptibility due to iron inclusions, such that RAT alignment is magnetically enhanced, which we term the MRAT mechanism. Such grains can be aligned with high angular momentum at the so-called high- J attractor points, achieving a high degree of alignment. Using our analytical model of RATs, we derive the critical value of the magnetic relaxation parameter δ {sub m} to produce high- J attractor points as functions of q {sup max} and the anisotropic radiation angle relative to the magnetic field ψ . We find that if about 10% of the total iron abundance present in silicate grains is forming iron clusters, this is sufficient to produce high- J attractor points for all reasonable values of q {sup max}. To calculate the degree of grain alignment, we carry out numerical simulations of MRAT alignment by including stochastic excitations from gas collisions and magnetic fluctuations. We show that large grains can achieve perfect alignment when the high- J attractor point is present, regardless of the values of q {sup max}. Our obtained results pave the way for the physical modeling of polarized thermal dust emission as well as magnetic dipole emission. We also find that millimeter-sized grains in accretion disks may be aligned with the magnetic field if they are incorporated with iron nanoparticles.

Simulations of small solid accretion on to planetesimals in the presence of gas

Science.gov (United States)

Hughes, A. G.; Boley, A. C.

2017-12-01

The growth and migration of planetesimals in a young protoplanetary disc are fundamental to planet formation. In all models of early growth, there are several processes that can inhibit grains from reaching larger sizes. Nevertheless, observations suggest that growth of planetesimals must be rapid. If a small number of 100 km sized planetesimals do manage to form in the disc, then gas drag effects could enable them to efficiently accrete small solids from beyond their gravitationally focused cross-section. This gas-drag-enhanced accretion can allow planetesimals to grow at rapid rates, in principle. We present self-consistent hydrodynamics simulations with direct particle integration and gas-drag coupling to estimate the rate of planetesimal growth due to pebble accretion. Wind tunnel simulations are used to explore a range of particle sizes and disc conditions. We also explore analytic estimates of planetesimal growth and numerically integrate planetesimal drift due to the accretion of small solids. Our results show that, for almost every case that we consider, there is a clearly preferred particle size for accretion that depends on the properties of the accreting planetesimal and the local disc conditions. For solids much smaller than the preferred particle size, accretion rates are significantly reduced as the particles are entrained in the gas and flow around the planetesimal. Solids much larger than the preferred size accrete at rates consistent with gravitational focusing. Our analytic estimates for pebble accretion highlight the time-scales that are needed for the growth of large objects under different disc conditions and initial planetesimal sizes.

Simulation and Experimental Studies on Grain Selection and Structure Design of the Spiral Selector for Casting Single Crystal Ni-Based Superalloy.

Science.gov (United States)

Zhang, Hang; Xu, Qingyan

2017-10-27

Grain selection is an important process in single crystal turbine blades manufacturing. Selector structure is a control factor of grain selection, as well as directional solidification (DS). In this study, the grain selection and structure design of the spiral selector were investigated through experimentation and simulation. A heat transfer model and a 3D microstructure growth model were established based on the Cellular automaton-Finite difference (CA-FD) method for the grain selector. Consequently, the temperature field, the microstructure and the grain orientation distribution were simulated and further verified. The average error of the temperature result was less than 1.5%. The grain selection mechanisms were further analyzed and validated through simulations. The structural design specifications of the selector were suggested based on the two grain selection effects. The structural parameters of the spiral selector, namely, the spiral tunnel diameter ( d w ), the spiral pitch ( h b ) and the spiral diameter ( h s ), were studied and the design criteria of these parameters were proposed. The experimental and simulation results demonstrated that the improved selector could accurately and efficiently produce a single crystal structure.

Effects of snow grain non-sphericity on climate simulations: Sensitivity tests with the NorESM model

Science.gov (United States)

Räisänen, Petri; Makkonen, Risto; Kirkevåg, Alf

2017-04-01

Snow grains are non-spherical and generally irregular in shape. Still, in radiative transfer calculations, they are often treated as spheres. This also applies to the computation of snow albedo in the Snow, Ice, and Aerosol Radiation (SNICAR) model and in the Los Alamos sea ice model, version 4 (CICE4), both of which are employed in the Community Earth System Model and in the Norwegian Earth System Model (NorESM). In this work, we evaluate the effect of snow grain shape on climate simulated by NorESM in a slab ocean configuration of the model. An experiment with spherical snow grains (SPH) is compared with another (NONSPH) in which the snow shortwave single-scattering properties are based on a combination of non-spherical snow grain shapes optimized using measurements of angular scattering by blowing snow. The key difference between these treatments is that the asymmetry parameter is smaller in the non-spherical case (≈ 0.78 in the visible region) than in the spherical case (≈ 0.89). Therefore, for a given snow grain size, the use of non-spherical snow grains yields a higher snow broadband albedo, typically by ≈0.03. Consequently, considering the spherical case as the baseline, the use of non-spherical snow grains results in a negative radiative forcing (RF), with a global-mean top-of-the-model value of ≈ -0.22 W m-2. Although this global-mean RF is modest, it has a rather substantial impact on the climate simulated by NoRESM. In particular, the global annual-mean 2-m air temperature in NONSPH is 1.17 K lower than in SPH, with substantially larger differences at high latitudes. The climatic response is amplified by strong snow and sea ice feedbacks. It is further found that the difference between NONSPH and SPH could be largely "tuned away" by adjusting the snow grain size in the NONSPH experiment by ≈ 70%. The impact of snow grain shape on the radiative effect (RE) of absorbing aerosols in snow (black carbon and mineral dust) is also discussed. For an

Mechanical properties of granular materials: A variational approach to grain-scale simulations

Energy Technology Data Exchange (ETDEWEB)

Holtzman, R.; Silin, D.B.; Patzek, T.W.

2009-01-15

The mechanical properties of cohesionless granular materials are evaluated from grain-scale simulations. A three-dimensional pack of spherical grains is loaded by incremental displacements of its boundaries. The deformation is described as a sequence of equilibrium configurations. Each configuration is characterized by a minimum of the total potential energy. This minimum is computed using a modification of the conjugate gradient algorithm. Our simulations capture the nonlinear, path-dependent behavior of granular materials observed in experiments. Micromechanical analysis provides valuable insight into phenomena such as hysteresis, strain hardening and stress-induced anisotropy. Estimates of the effective bulk modulus, obtained with no adjustment of material parameters, are in agreement with published experimental data. The model is applied to evaluate the effects of hydrate dissociation in marine sediments. Weakening of the sediment is quantified as a reduction in the effective elastic moduli.

Simulation of the Fuel Reactor of a Coal-Fired Chemical Looping Combustor

Science.gov (United States)

Mahalatkar, Kartikeya; O'Brien, Thomas; Huckaby, E. David; Kuhlman, John

2009-06-01

removed from the bed and returned to the air reactor without any accompanying unburned fuel. This paper presents a simulation of the gas-particle granular flow, with heat transfer and chemical reactions, in the FR. Accurate simulation of the segregation processes, depending on particle density and size differences between the carrier and the fuel, allows the design of a reactor with the desired behavior.

The international symposium on 'chemical engineering of gas-liquid-solid catalyst reactions'

Energy Technology Data Exchange (ETDEWEB)

Hammer, H

1978-06-01

A report on the International Symposium on ''Chemical Engineering of Gas-Liquid-Solid Catalyst Reactions'', sponsored by the University of Liege (3/2-3/78), covers papers on the hydrodynamics, modeling and simulation, operating behavior, and chemical kinetics of trickle-bed reactors; scale-up of a trickle-bed reactor for hydrotreating Kuwait vacuum distillate; experimental results obtained in trickle-bed reactors for hydroprocessing atmospheric residua, hydrogenation of methylstyrene, hydrogenation of butanone, and hydrodemetallization of petroleum residua; advantages and disadvantages of various three-phase reactor types (e.g., for the liquid-phase hydrogenation of carbon monoxide to benzene, SNG, or methanol) and hydrodynamics, mass and heat transfer, and modeling of bubble columns with suspended catalysts (slurry reactors), and their applications (e.g., in SNG and fermentation processes).

Grain processes in massive star formation

International Nuclear Information System (INIS)

Wolfire, M.G.; Cassinelli, J.P.

1986-01-01

Observational evidence suggests that stars greater than 100 M(solar) exist in the Galaxy and Large Magellanic Cloud (LMC), however classical star formation theory predicts stellar mass limits of only approx. 60 M(solar). A protostellar accretion flow consists of inflowing gas and dust. Grains are destroyed as they are near the central protostar creating a dust shell or cocoon. Radiation pressure acting on the grain can halt the inflow of material thereby limiting the amount of mass accumulated by the protostar. We first consider rather general constraints on the initial grain to gas ratio and mass accretion rates that permit inflow. We further constrain these results by constructing a numerical model. Radiative deceleration of grains and grain destruction processes are explicitly accounted for in an iterative solution of the radiation-hydrodynamic equations. Findings seem to suggest that star formation by spherical accretion requires rather extreme preconditioning of the grain and gas environment

Laboratory Studies on the Formation of Carbon-Bearing Molecules in Extraterrestrial Environments: From the Gas Phase to the Solid State

Science.gov (United States)

Jamieson, C. S.; Guo, Y.; Gu, X.; Zhang, F.; Bennett, C. J.; Kaiser, R. I.

2006-01-01

A detailed knowledge of the formation of carbon-bearing molecules in interstellar ices and in the gas phase of the interstellar medium is of paramount interest to understand the astrochemical evolution of extraterrestrial environments (1). This research also holds strong implications to comprehend the chemical processing of Solar System environments such as icy planets and their moons together with the atmospheres of planets and their satellites (2). Since the present composition of each interstellar and Solar System environment reflects the matter from which it was formed and the processes which have changed the chemical nature since the origin (solar wind, planetary magnetospheres, cosmic ray exposure, photolysis, chemical reactions), a detailed investigation of the physicochemical mechanisms altering the pristine environment is of paramount importance to grasp the contemporary composition. Once these underlying processes have been unraveled, we can identify those molecules, which belonged to the nascent setting, distinguish molecular species synthesized in a later stage, and predict the imminent chemical evolution of, for instance, molecular clouds. Laboratory experiments under controlled physicochemical conditions (temperature, pressure, chemical composition, high energy components) present ideal tools for simulating the chemical evolution of interstellar and Solar System environments. Here, laboratory experiments can predict where and how (reaction mechanisms; chemicals necessary) in extraterrestrial environments and in the interstellar medium complex, carbon bearing molecules can be formed on interstellar grains and in the gas phase. This paper overviews the experimental setups utilized in our laboratory to mimic the chemical processing of gas phase and solid state (ices) environments. These are a crossed molecular beams machine (3) and a surface scattering setup (4). We also present typical results of each setup (formation of amino acids, aldehydes, epoxides

Dust evolution, a global view: III. Core/mantle grains, organic nano-globules, comets and surface chemistry

Science.gov (United States)

2016-01-01

Within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), this work explores the surface processes and chemistry relating to core/mantle interstellar and cometary grain structures and their influence on the nature of these fascinating particles. It appears that a realistic consideration of the nature and chemical reactivity of interstellar grain surfaces could self-consistently and within a coherent framework explain: the anomalous oxygen depletion, the nature of the CO dark gas, the formation of ‘polar ice’ mantles, the red wing on the 3 μm water ice band, the basis for the O-rich chemistry observed in hot cores, the origin of organic nano-globules and the 3.2 μm ‘carbonyl’ absorption band observed in comet reflectance spectra. It is proposed that the reaction of gas phase species with carbonaceous a-C(:H) grain surfaces in the interstellar medium, in particular the incorporation of atomic oxygen into grain surfaces in epoxide functional groups, is the key to explaining these observations. Thus, the chemistry of cosmic dust is much more intimately related with that of the interstellar gas than has previously been considered. The current models for interstellar gas and dust chemistry will therefore most likely need to be fundamentally modified to include these new grain surface processes. PMID:28083090

Molecular dynamics simulation of coarse-grained poly(L-lysine) dendrimers.

Science.gov (United States)

Rahimi, Ali; Amjad-Iranagh, Sepideh; Modarress, Hamid

2016-03-01

Poly(L-lysine) (PLL) dendrimer are amino acid based macromolecules and can be used as drug delivery agents. Their branched structure allows them to be functionalized by various groups to encapsulate drug agents into their structure. In this work, at first, an attempt was made on all-atom simulation of PLL dendrimer of different generations. Based on all-atom results, a course-grained model of this dendrimer was designed and its parameters were determined, to be used for simulation of three generations of PLL dendrimer, at two pHs. Similar to the all-atom, the coarse-grained results indicated that by increasing the generation, the dendrimer becomes more spherical. At pH 7, the dendrimer had larger size, whereas at pH 12, due to back folding of branching chains, they had the tendency to penetrate into the inner layers. The calculated radial probability and radial distribution functions confirm that at pH 7, the PLL dendrimer has more cavities and as a result it can encapsulate more water molecules into its inner structure. By calculating the moment of inertia and the aspect ratio, the formation of spherical structure for PLL dendrimer was confirmed.

Finite element simulation of fission gas release and swelling in UO2 fuel pellets

International Nuclear Information System (INIS)

Denis, Alicia C.

1999-01-01

A fission gas release model is presented, which solves the atomic diffusion problem with xenon and krypton elements tramps produced by uranium fission during UO 2 nuclear fuel irradiation. The model considers intra and intergranular precipitation bubbles, its re dissolution owing to highly energetic fission products impact, interconnection of intergranular bubbles and gas sweeping by grain border in movement because of grain growth. In the model, the existence of a thermal gradient in the fuel pellet is considered, as well as temporal variations of fission rate owing to changes in the operation lineal power. The diffusion equation is solved by the finite element method and results of gas release and swelling calculation owing to gas fission are compared with experimental data. (author)

Molecular Dynamics Simulations of Grain Boundary and Bulk Diffusion in Metals.

Science.gov (United States)

Plimpton, Steven James

Diffusion is a microscopic mass transport mechanism that underlies many important macroscopic phenomena affecting the structural, electrical, and mechanical properties of metals. This thesis presents results from atomistic simulation studies of diffusion both in bulk and in the fast diffusion paths known as grain boundaries. Using the principles of molecular dynamics single boundaries are studied and their structure and dynamic properties characterized. In particular, tilt boundary bicrystal and bulk models of fcc Al and bcc alpha-Fe are simulated. Diffusion coefficients and activation energies for atomic motion are calculated for both models and compared to experimental data. The influence of the interatomic pair potential on the diffusion is studied in detail. A universal relation between the melting temperature that a pair potential induces in a simulated bulk model and the potential energy barrier height for atomic hopping is derived and used to correlate results for a wide variety of pair potentials. Using these techniques grain boundary and bulk diffusion coefficients for any fcc material can be estimated from simple static calculations without the need to perform more time-consuming dynamic simulations. The influences of two other factors on grain boundary diffusion are also studied because of the interest of the microelectronics industry in the diffusion related reliability problem known as electromigration. The first factor, known to affect the self diffusion rate of Al, is the presence of Cu impurity atoms in Al tilt boundaries. The bicrystal model for Al is seeded randomly with Cu atoms and a simple hybrid Morse potential used to model the Al-Cu interaction. While some effect due to the Cu is noted, it is concluded that pair potentials are likely an inadequate approximation for the alloy system. The second factor studied is the effect of the boundary orientation angle on the diffusion rate. Symmetric bcc Fe boundaries are relaxed to find optimal

Chemical discrimination in turbulent gas mixtures with MOX sensors validated by gas chromatography-mass spectrometry.

Science.gov (United States)

Fonollosa, Jordi; Rodríguez-Luján, Irene; Trincavelli, Marco; Vergara, Alexander; Huerta, Ramón

2014-10-16

Chemical detection systems based on chemo-resistive sensors usually include a gas chamber to control the sample air flow and to minimize turbulence. However, such a kind of experimental setup does not reproduce the gas concentration fluctuations observed in natural environments and destroys the spatio-temporal information contained in gas plumes. Aiming at reproducing more realistic environments, we utilize a wind tunnel with two independent gas sources that get naturally mixed along a turbulent flow. For the first time, chemo-resistive gas sensors are exposed to dynamic gas mixtures generated with several concentration levels at the sources. Moreover, the ground truth of gas concentrations at the sensor location was estimated by means of gas chromatography-mass spectrometry. We used a support vector machine as a tool to show that chemo-resistive transduction can be utilized to reliably identify chemical components in dynamic turbulent mixtures, as long as sufficient gas concentration coverage is used. We show that in open sampling systems, training the classifiers only on high concentrations of gases produces less effective classification and that it is important to calibrate the classification method with data at low gas concentrations to achieve optimal performance.

[Chemical hazards arising from shale gas extraction].

Science.gov (United States)

Pakulska, Daria

2015-01-01

The development of the shale industry is gaining momentum and hence the analysis of chemical hazards to the environment and health of the local population is extreiely timely and important. Chemical hazards are created during the exploitation of all minerals, but in the case of shale gas production, there is much more uncertainty as regards to the effects of new technologies application. American experience suggests the increasing risk of environmental contamination, mainly groundwater. The greatest, concern is the incomplete knowledge of the composition of fluids used for fracturing shale rock and unpredictability of long-term effects of hydraulic fracturing for the environment and health of residents. High population density in the old continent causes the problem of chemical hazards which is much larger than in the USA. Despite the growing public discontent data on this subject are limited. First of all, there is no epidemiological studies to assess the relationship between risk factors, such as air and water pollution, and health effects in populations living in close proximity to gas wells. The aim of this article is to identify and discuss existing concepts on the sources of environmental contamination, an indication of the environment elements under pressure and potential health risks arising from shale gas extraction.

Coarse-grained molecular simulations of allosteric cooperativity

Energy Technology Data Exchange (ETDEWEB)

Nandigrami, Prithviraj; Portman, John J. [Department of Physics, Kent State University, Kent, Ohio 44242 (United States)

2016-03-14

Interactions between a protein and a ligand are often accompanied by a redistribution of the population of thermally accessible conformations. This dynamic response of the protein’s functional energy landscape enables a protein to modulate binding affinities and control binding sensitivity to ligand concentration. In this paper, we investigate the structural origins of binding affinity and allosteric cooperativity of binding two Ca{sup 2+} ions to each domain of Calmodulin (CaM) through simulations of a simple coarse-grained model. In this model, the protein’s conformational transitions between open and closed conformational ensembles are simulated explicitly and ligand binding and unbinding are treated implicitly within the grand canonical ensemble. Ligand binding is cooperative because the binding sites are coupled through a shift in the dominant conformational ensemble upon binding. The classic Monod-Wyman-Changeux model of allostery with appropriate binding free energies to the open and closed ensembles accurately describes the simulated binding thermodynamics. The simulations predict that the two domains of CaM have distinct binding affinity and cooperativity. In particular, the C-terminal domain binds Ca{sup 2+} with higher affinity and greater cooperativity than the N-terminal domain. From a structural point of view, the affinity of an individual binding loop depends sensitively on the loop’s structural compatibility with the ligand in the bound ensemble, as well as the conformational flexibility of the binding site in the unbound ensemble.

Coarse-grained simulation of polymer-filler blends

Science.gov (United States)

Legters, Gregg; Kuppa, Vikram; Beaucage, Gregory; Univ of Dayton Collaboration; Univ of Cincinnati Collaboration

The practical use of polymers often relies on additives that improve the property of the mixture. Examples of such complex blends include tires, pigments, blowing agents and other reactive additives in thermoplastics, and recycled polymers. Such systems usually exhibit a complex partitioning of the components. Most prior work has either focused on fine-grained details such as molecular modeling of chains at interfaces, or on coarse, heuristic, trial-and-error approaches to compounding (eg: tire industry). Thus, there is a significant gap in our understanding of how complex hierarchical structure (across several decades in length) develops in these multicomponent systems. This research employs dissipative particle thermodynamics in conjunction with a pseudo-thermodynamic parameter derived from scattering experiments to represent polymer-filler interactions. DPD simulations will probe how filler dispersion and hierarchical morphology develops in these complex blends, and are validated against experimental (scattering) data. The outcome of our approach is a practical solution to compounding issues, based on a mutually validating experimental and simulation methodology. Support from the NSF (CMMI-1636036/1635865) is gratefully acknowledged.

Chemical durability of borosilicate glasses containing simulated high-level nuclear wastes, 1

International Nuclear Information System (INIS)

Hara, Shigeo; Terai, Ryohei; Yamanaka, Hiroshi

1983-01-01

The Soxhlet-type leaching test apparatus has been developed to evaluate the chemical durability of some borosilicate glasses containing simulated High-Level nuclear Wastes, HLW. After the leaching over the temperature range of 50 0 -95 0 C, the weight loss of specimens with time was determined on both the samples of blocks and grains, and various components dissolved into water were analyzed by atomic absorption and colorimetry technique. It was found that Soxhlet-type test method was more useful than JIS test method, because the specimens in Soxhlet type apparatus were forced always to react with pure water and the mechanism of leaching could be evaluate accurately. The chemical durability of commercial glasses decreases generally with increasing of alkali contents in glasses. In the case of these borosilicate glasses containing HLW, however, the leachability was apparently independent on the alkali contents because of the complexity of these glass compositions. The variation of leaching rate with temperature suggests that dissolution mechanism changes with temperature. (author)

Computational fluid dynamics simulation for chemical looping combustion of coal in a dual circulation fluidized bed

International Nuclear Information System (INIS)

Su, Mingze; Zhao, Haibo; Ma, Jinchen

2015-01-01

Highlights: • CFD simulation of a 5 kW_t_h CLC reactor of coal was conducted. • Gas leakage, flow pattern and combustion efficiency of the reactor was analyzed. • Optimal condition was achieved based on operation characteristics understanding. - Abstract: A dual circulation fluidized bed system is widely accepted for chemical looping combustion (CLC) for enriching CO_2 from the utilization of fossil fuels. Due to the limitations of the measurement, the details of multiphase reactive flows in the interconnected fluidized bed reactors are difficult to obtain. Computational Fluid Dynamics (CFD) simulation provides a promising method to understand the hydrodynamics, chemical reaction, and heat and mass transfers in CLC reactors, which are very important for the rational design, optimal operation, and scaling-up of the CLC system. In this work, a 5 kW_t_h coal-fired CLC dual circulation fluidized bed system, which was developed by our research group, was first simulated for understanding gas leakage, flow pattern and combustion efficiency. The simulation results achieved good agreement with the experimental measurements, which validates the simulation model. Subsequently, to improve the combustion efficiency, a new operation condition was simulated by increasing the reactor temperature and decreasing the coal feeding. An improvement in the combustion efficiency was attained, and the simulation results for the new operation condition were also validated by the experimental measurements in the same CLC combustor. All of the above processes demonstrated the validity and usefulness of the simulation results to improve the CLC reactor operation.

Kinetic simulation of neutral/ionized gas and electrically charged dust in the coma of comet 67P/Churyumov-Gerasimenko

International Nuclear Information System (INIS)

Tenishev, Valeriy; Rubin, Martin; Combi, Michael R.

2011-01-01

The cometary coma is a unique phenomenon in the solar system being a planetary atmosphere influenced by little or no gravity. As a comet approaches the sun, the water vapor with some fraction of other gases sublimate, generating a cloud of gas, ice and other refractory materials (rocky and organic dust) ejected from the surface of the nucleus. Sublimating gas molecules undergo frequent collisions and photochemical processes in the near-nucleus region. Owing to its negligible gravity, comets produce a large and highly variable extensive dusty coma with a size much larger than the characteristic size of the cometary nucleus.The Rosetta spacecraft is en route to comet 67P/Churyumov-Gerasimenko for a rendezvous, landing, and extensive orbital phase beginning in 2014. Both, interpretation of measurements and safety consideration of the spacecraft require modeling of the comet's dusty gas environment.In this work we present results of a numerical study of multispecies gaseous and electrically charged dust environment of comet Chyuryumov-Gerasimenko. Both, gas and dust phases of the coma are simulated kinetically. Photolytic reactions are taken into account. Parameters of the ambient plasma as well as the distribution of electric/magnetic fields are obtained from an MHD simulation of the coma connected to the solar wind. Trajectories of ions and electrically charged dust grains are simulated by accounting for the Lorentz force and the nucleus gravity.

Coarse-grained simulation of a real-time process control network under peak load

International Nuclear Information System (INIS)

George, A.D.; Clapp, N.E. Jr.

1992-01-01

This paper presents a simulation study on the real-time process control network proposed for the new ANS reactor system at ORNL. A background discussion is provided on networks, modeling, and simulation, followed by an overview of the ANS process control network, its three peak-load models, and the results of a series of coarse-grained simulation studies carried out on these models using implementations of 802.3, 802.4, and 802.5 standard local area networks

Rarefield gas dynamics fundamentals, simulations and micro flows

CERN Document Server

Shen, Ching

2006-01-01

This book elucidates the methods of molecular gas dynamics or rarefied gas dynamics which treat the problems of gas flows when the discrete molecular effects of the gas prevail under the circumstances of low density, the emphasis being on the basis of the methods, the direct simulation Monte Carlo method applied to the simulation of non-equilibrium effects and the frontier subjects related to low speed microscale rarefied gas flows. It provides a solid basis for the study of molecular gas dynamics for senior students and graduates in the aerospace and mechanical engineering departments of universities and colleges. It gives a general acquaintance of modern developments of rarefied gas dynamics in various regimes and leads to the frontier topics of non-equilibrium rarefied gas dynamics and low speed microscale gas dynamics. It will be also of benefit to the scientific and technical researchers engaged in aerospace high altitude aerodynamic force and heating design and in the research on gas flow in MEMS.

Performance evaluation of non-thermal plasma injection for elemental mercury oxidation in a simulated flue gas

Energy Technology Data Exchange (ETDEWEB)

An, Jiutao; Shang, Kefeng; Lu, Na [Institute of Electrostatics and Special Power, Dalian University of Technology, Dalian 116024 (China); Key Laboratory of Industrial Ecology and Environmental Engineering, Ministry of Education of the People' s Republic of China, Dalian 116024 (China); Jiang, Yuze [Shandong Electric Power Research Institute, Jinan 250002 (China); Wang, Tiecheng [Institute of Electrostatics and Special Power, Dalian University of Technology, Dalian 116024 (China); Key Laboratory of Industrial Ecology and Environmental Engineering, Ministry of Education of the People' s Republic of China, Dalian 116024 (China); Li, Jie, E-mail: lijie@dlut.edu.cn [Institute of Electrostatics and Special Power, Dalian University of Technology, Dalian 116024 (China); Key Laboratory of Industrial Ecology and Environmental Engineering, Ministry of Education of the People' s Republic of China, Dalian 116024 (China); Wu, Yan [Institute of Electrostatics and Special Power, Dalian University of Technology, Dalian 116024 (China); Key Laboratory of Industrial Ecology and Environmental Engineering, Ministry of Education of the People' s Republic of China, Dalian 116024 (China)

2014-03-01

Graphical abstract: - Highlights: • The use of non-thermal plasma injection approach to oxidize Hg{sup 0} in simulated flue gas at 110 °C was studied. • A high Hg{sup 0} oxidation efficiency was observed in the mixed flue gas that included O{sub 2}, H{sub 2}O, SO{sub 2}, NO and HCl. • Chemical and physical processes (e.g., ozone, N{sub 2} metastable states and UV-light) contributed to Hg{sup 0} oxidation. • Mercury species mainly existed in the form of HgO(s) adhering to the suspended aerosols in the gas-phase. - Abstract: The use of non-thermal plasma (NTP) injection approach to oxidize elemental mercury (Hg{sup 0}) in simulated flue gas at 110 °C was studied, where a surface discharge plasma reactor (SDPR) inserted in the simulated flue duct was used to generate and inject active species into the flue gas. Approximately 81% of the Hg{sup 0} was oxidized and 20.5 μg kJ{sup −1} of energy yield was obtained at a rate of 3.9 J L{sup −1}. A maximal Hg{sup 0} oxidation efficiency was found with a change in the NTP injection air flow rate. A high Hg{sup 0} oxidation efficiency was observed in the mixed flue gas that included O{sub 2}, H{sub 2}O, SO{sub 2}, NO and HCl. Chemical and physical processes (e.g., ozone, N{sub 2} metastable states and UV-light) were found to contribute to Hg{sup 0} oxidation, with ozone playing a dominant role. The deposited mercury species on the internal surface of the flue duct was analyzed using X-ray photoelectron spectroscopy (XPS) and electronic probe microanalysis (EPMA), and the deposit was identified as HgO. The mercury species is thought to primarily exist in the form of HgO(s) by adhering to the suspended aerosols in the gas-phase.

Grain dissection as a grain size reducing mechanism during ice microdynamics

Science.gov (United States)

Steinbach, Florian; Kuiper, Ernst N.; Eichler, Jan; Bons, Paul D.; Drury, Martin R.; Griera, Albert; Pennock, Gill M.; Weikusat, Ilka

2017-04-01

Ice sheets are valuable paleo-climate archives, but can lose their integrity by ice flow. An understanding of the microdynamic mechanisms controlling the flow of ice is essential when assessing climatic and environmental developments related to ice sheets and glaciers. For instance, the development of a consistent mechanistic grain size law would support larger scale ice flow models. Recent research made significant progress in numerically modelling deformation and recrystallisation mechanisms in the polycrystalline ice and ice-air aggregate (Llorens et al., 2016a,b; Steinbach et al., 2016). The numerical setup assumed grain size reduction is achieved by the progressive transformation of subgrain boundaries into new high angle grain boundaries splitting an existing grain. This mechanism is usually termed polygonisation. Analogue experiments suggested, that strain induced grain boundary migration can cause bulges to migrate through the whole of a grain separating one region of the grain from another (Jessell, 1986; Urai, 1987). This mechanism of grain dissection could provide an alternative grain size reducing mechanism, but has not yet been observed during ice microdynamics. In this contribution, we present results using an updated numerical approach allowing for grain dissection. The approach is based on coupling the full field theory crystal visco-plasticity code (VPFFT) of Lebensohn (2001) to the multi-process modelling platform Elle (Bons et al., 2008). VPFFT predicts the mechanical fields resulting from short strain increments, dynamic recrystallisation process are implemented in Elle. The novel approach includes improvements to allow for grain dissection, which was topologically impossible during earlier simulations. The simulations are supported by microstructural observations from NEEM (North Greenland Eemian Ice Drilling) ice core. Mappings of c-axis orientations using the automatic fabric analyser and full crystallographic orientations using electron

Computer simulation of chemical nucleation

International Nuclear Information System (INIS)

Turner, J.S.

1979-01-01

The problem of nucleation at chemical instabilities is investigated by means of microscopic computer simulation. The first-order transition of interest involves a new kind of nucleation arising from chemical transformations rather than physical forces. Here it is the chemical state of matter, and not matter itself, which is spatially localized to form the nucleus for transition between different chemical states. First, the concepts of chemical instability, nonequilibrium phase transition, and dissipative structure are reviewed briefly. Then recently developed methods of reactive molecular dynamics are used to study chemical nucleation in a simple model chemical reactions. Finally, the connection of these studies to nucleation and condensation processes involving physical and chemical interactions is explored. (orig.)

Significance of the molecular diffusion for chemical and isotopic separation during the formation and degradation of natural gas reservoirs

International Nuclear Information System (INIS)

Hermichen, W.D.; Schuetze, H.

1987-01-01

Investigations at natural gas fields as well as modelling experiments have pointed out that changes of the chemical and isotopic composition occur in the course of migration, accumulation and dispersion of natural gas. Dissolution and sorption processes as well as in particular the diffusion process are considered to be the elementary separation processes. The influences on dissolved and freely flowing gases and on stationary gas accumulation are described by differential equations. The simulation of the following phenomena is shown: (1) immigration of gas into the pore space which is hydrodynamically passive, (2) diffusive migration of gas into the environment of the accumulation, and (3) diffusive 'decompression' into the roof and the floor of a gas bed and a gas containing subsoil water stratum, respectively. (author)

A SIMULATION MODEL OF THE GAS COMPLEX

Directory of Open Access Journals (Sweden)

Sokolova G. E.

2016-06-01

Full Text Available The article considers the dynamics of gas production in Russia, the structure of sales in the different market segments, as well as comparative dynamics of selling prices on these segments. Problems of approach to the creation of the gas complex using a simulation model, allowing to estimate efficiency of the project and determine the stability region of the obtained solutions. In the presented model takes into account the unit repayment of the loan, allowing with the first year of simulation to determine the possibility of repayment of the loan. The model object is a group of gas fields, which is determined by the minimum flow rate above which the project is cost-effective. In determining the minimum source flow rate for the norm of discount is taken as a generalized weighted average percentage on debt and equity taking into account risk premiums. He also serves as the lower barrier to internal rate of return below which the project is rejected as ineffective. Analysis of the dynamics and methods of expert evaluation allow to determine the intervals of variation of the simulated parameters, such as the price of gas and the exit gas complex at projected capacity. Calculated using the Monte Carlo method, for each random realization of the model simulated values of parameters allow to obtain a set of optimal for each realization of values minimum yield of wells, and also allows to determine the stability region of the solution.

Performance of process-based models for simulation of grain N in crop rotations across Europe

DEFF Research Database (Denmark)

Yin, Xiaogang; Kersebaum, KC; Kollas, C

2017-01-01

The accurate estimation of crop grain nitrogen (N; N in grain yield) is crucial for optimizing agricultural N management, especially in crop rotations. In the present study, 12 process-based models were applied to simulate the grain N of i) seven crops in rotations, ii) across various pedo...... (Brassica napus L.). These differences are linked to the intensity of parameterization with better parameterized crops showing lower prediction errors. The model performance was influenced by N fertilization and irrigation treatments, and a majority of the predictions were more accurate under low N...

Structural and morphological properties of electroceramics for chemical sensors

International Nuclear Information System (INIS)

Tor Vergata, Via della Ricerca Scientifica, Roma (Italy). Dipartimento di Scienze e Tecnologie Chimiche)" data-affiliation=" (Universita' di Roma Tor Vergata, Via della Ricerca Scientifica, Roma (Italy). Dipartimento di Scienze e Tecnologie Chimiche)" >Enrico Traversa

1996-01-01

Ceramic materials possess a unique structure consisting of grains, grain boundaries, surfaces and pores, which makes them suitable for chemical sensors. The control of the chemical composition and microstructure of electrochemicals is fundamental for controlling their properties. Ceramics with a given composition and microstructure can be produced by controlling the different steps of their processing. The chemical processing of ceramics offer many advantages in terms of control and reproducibility, with respect to the conventional ceramics processing. Results are reported about the chemical processing of perovskite-type oxides for gas sensors and about the novel humidity-sensitive electrical properties of sol-gel processed alkali-doped titania films. The structural and morphological characterization of these materials permits the understanding of the sensitive electrical properties of the ceramics (71 refs.)

Software for natural gas pipeline design and simulation (gaspisim ...

African Journals Online (AJOL)

Software for natural gas pipeline design and simulation (gaspisim) ... This paper focuses on the development of software for optimum design and simulation of natural gas pipeline. General ... EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT

Modification of UO2 grain re-crystallization temperature in function of burn-up as a base for Vitanza experimental curve reconstruction

International Nuclear Information System (INIS)

Szuta, M.; Dąbrowski, L.

2013-01-01

Crossing the experimental critical fuel temperature dependent on burn-up, an onset of fission gas burst release is observed. This observed phenomena can be explained by assumption that the fission gas immobilization in the uranium dioxide irradiated to a fluency of greater than 10 19 fissions/cm 3 is mainly due to radiation induced chemical activity. Application of the “ab initio” method show that the bond energy of Xenon and Krypton is equal to –1.23 eV, and –3.42 eV respectively. Assuming further that the gas chemically bound can be released mainly in the process of re-crystallization and modifying the differential equation of Ainscough of grain growth by including the burn-up dependence and the experimental data of limiting grain size in function of the fuel temperature for the un-irradiated and irradiated fuel we can re-construct the experimental curve of Vitanza. (authors)

Effects of storage temperature on the fungal and chemical spoilage of maize grains and flour

International Nuclear Information System (INIS)

Akhter, T.; Sattar, A.; Khan, I.; Ahmed, A.

1989-01-01

The chemical and fungal spoilage of maize grains and flour of Sarhad White and Sarhad Yellow varieties in relation to time temperature (10 C, 15 C, 20 C and room (30-56 C) storage period at 8-12 months was studied. The results showed that total fungal counts and percent infestation markedly increased with advanced storage and increased temperature. Percentage germination generally decreased during extended storage. Peroxide values of both the grain and flour increased with increasing temperature and storage time. At the end of one year storage the total fungal counts in the grain and flour of Sarhad White and Sarhad Yellow ranged 13.6x10/sup 12/ - 20.0x10/sup 13/ and Yellow ranged 17.1x10/sup 13/ - 22.1x10/sup 14/ respectively. germination and infestation percentage of the grains of Sarhad White and Sarhad Yellow ranged 76-78% and 96-99%. The peroxide value ranged 6.6-7.0 and 6.4-6.8 meg/Kg in the grain and flour of Sarhad White respectively after one year storage. There was more fungal infestation, fungal counts and peroxidation in the grain and flour Sarhad Yellow than that of Sarhad White. (author)

Computer simulation of dust grain evolution

Science.gov (United States)

Liffman, K.

1989-01-01

The latest results are reported from a Monte Carlo code that is being developed at NASA Ames. The goal of this program, is to derive from the observed and presumed properties of the interstellar medium (ISM) the following information: (1) the size spectrum of interstellar dust; (2) the chemical structure of interstellar dust; (3) interstellar abundances; and (4) the lifetime of a dust grain in the ISM. Presently this study is restricted to refractory interstellar material, i.e., the formation and destruction of ices are not included in the program. The program is embedded in an analytic solution for the bulk chemical evolution of a two-phase interstellar medium in which stars are born in molecular clouds, but new nucleosynthesis products and stellar return are entered into a complementary intercloud medium. The well-mixed matter of each interstellar phase is repeatedly cycled stochastically through the complementary phase and back. Refractory dust is created by thermal condensation as stellar matter flows away from sites of nucleosynthesis such as novae and supernovae and/or from the matter returned from evolved intermediate stars. The history of each particle is traced by standard Monte Carlo techniques as it is sputtered and fragmented by supernova shock waves in the intercloud medium. It also accretes an amorphous mantle of gaseous refractory atoms when its local medium joins with the molecular cloud medium. Finally it encounters the possibility of astration (destruction by star formation) within the molecular clouds.

Chemical hazards arising from shale gas extraction

Directory of Open Access Journals (Sweden)

Daria Pakulska

2015-02-01

Full Text Available The development of the shale industry is gaining momentum and hence the analysis of chemical hazards to the environment and health of the local population is extremely timely and important. Chemical hazards are created during the exploitation of all minerals, but in the case of shale gas production, there is much more uncertainty as regards to the effects of new technologies application. American experience suggests the increasing risk of environmental contamination, mainly groundwater. The greatest concern is the incomplete knowledge of the composition of fluids used for fracturing shale rock and unpredictability of long-term effects of hydraulic fracturing for the environment and health of residents. High population density in the old continent causes the problem of chemical hazards which is much larger than in the USA. Despite the growing public discontent data on this subject are limited. First of all, there is no epidemiological studies to assess the relationship between risk factors, such as air and water pollution, and health effects in populations living in close proximity to gas wells. The aim of this article is to identify and discuss existing concepts on the sources of environmental contamination, an indication of the environment elements under pressure and potential health risks arising from shale gas extraction. Med Pr 2015;66(1:99–117

Role of Surface Chemistry in Grain Adhesion and Dissipation during Collisions of Silica Nanograins

Energy Technology Data Exchange (ETDEWEB)

Quadery, Abrar H.; Tucker, William C.; Dove, Adrienne R.; Schelling, Patrick K. [Department of Physics, University of Central Florida, Orlando, FL 32816-2385 (United States); Doan, Baochi D., E-mail: patrick.schelling@ucf.edu [Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32816-2385 (United States)

2017-08-01

The accretion of dust grains to form larger objects, including planetesimals, is a central problem in planetary science. It is generally thought that weak van der Waals interactions play a role in accretion at small scales where gravitational attraction is negligible. However, it is likely that in many instances, chemical reactions also play an important role, and the particular chemical environment on the surface could determine the outcomes of dust grain collisions. Using atomic-scale simulations of collisional aggregation of nanometer-sized silica (SiO{sub 2}) grains, we demonstrate that surface hydroxylation can act to weaken adhesive forces and reduce the ability of mineral grains to dissipate kinetic energy during collisions. The results suggest that surface passivation of dangling bonds, which generally is quite complete in an Earth environment, should tend to render mineral grains less likely to adhere during collisions. It is shown that during collisions, interactions scale with interparticle distance in a manner consistent with the formation of strong chemical bonds. Finally, it is demonstrated that in the case of collisions of nanometer-scale grains with no angular momentum, adhesion can occur even for relative velocities of several kilometers per second. These results have significant implications for early planet formation processes, potentially expanding the range of collision velocities over which larger dust grains can form.

Grain refinement control in TIG arc welding

Science.gov (United States)

Iceland, W. F.; Whiffen, E. L. (Inventor)

1975-01-01

A method for controlling grain size and weld puddle agitation in a tungsten electrode inert gas welding system to produce fine, even grain size and distribution is disclosed. In the method the frequency of dc welding voltage pulses supplied to the welding electrode is varied over a preselected frequency range and the arc gas voltage is monitored. At some frequency in the preselected range the arc gas voltage will pass through a maximum. By maintaining the operating frequency of the system at this value, maximum weld puddle agitation and fine grain structure are produced.

Grain topology in Ti-6Al-4V welds-Monte Carlo simulation and experiments

International Nuclear Information System (INIS)

Mishra, S; DebRoy, T

2004-01-01

The importance of topological features of grains in the evolution of grain structure is well recognized in isothermal systems. However, during fusion welding, strong spatial gradients of temperature exist in the heat-affected zone (HAZ), and this region undergoes rapid heating and cooling. The effects of spatial and temporal variations of temperature on the topological class distribution, relationship between size and topology of grains and the interdependence between grain topology and its neighbours are not known. Topological features of grains in the HAZ of Ti-6Al-4V alloy welds were measured for various heat inputs in the range 0.55-4.33 MJ m -1 . The topological class distributions were also calculated using a three-dimensional Monte Carlo model utilizing thermal cycles computed from a well tested numerical heat transfer and fluid flow model. The computed results showed that the topological class distributions were unaffected by the spatial and temporal variations of temperature. Experimental investigations of a few sections confirmed the simulation results. The average grain size for each edge class varied linearly with the edge class number. The local topological environment, i.e. the average number of sides of neighbours, n n , varied linearly with the inverse of the number of sides of grains, 1/n r , at a given location in the HAZ. Locations with the same topological environment showed the same grain size, indicating the significant influence of grain topology on grain growth in the HAZ

Coupled LBM-DEM Three-phase Simulation on Seepage of CO2 Stored under the Seabed.

Science.gov (United States)

Kano, Y.; Sato, T.

2017-12-01

Concerning the seepage of CO2 stored in a subsea formation, CO2 bubble/droplet rises to the sea-surface dissolving into the seawater, and the acidification of local seawater will be a problem. Previous research indicated that seepage rate and bubble size significantly affect its behaviour (Kano et al., 2009; Dewar et al., 2013). On the other hand, Kawada's experiments (2014) indicated that grain size affects formation of gas channels and bubbles through granular media. CO2 seepage through marine sediments probably shows similar behaviour. Additionally, such mobilisation and displacement of sand grains by gas migration may also cause capillary fracturing of CO2 in the reservoir and seal. To predict these phenomena, it is necessary to reveal three-phase behaviour of gas-water-sediment grains. We built gas-liquid-solid three-phase flow 3D simulator by coupling LBM-DEM program, and simulation results showed that the mobilisation of sand grain forms gas channels and affects bubble formation compared with that through solid porous media (Kano and Sato, 2017). In this presentation, we will report simulation results on effects of porosity, grain size and gas flow rate on the formation of gas channels and bubble and their comparison with laboratory experimental data. The results indicate that porosity and grain size of sand gravels affect the width of formed gas channels and resulting formed bubble size on the order of supposed seepage rate in the CO2 storage and that in most of experiment's conditions. References: Abe, S., Place, D., Mora, P., 2004. Pure. Appl. Geophys., 161, 2265-2277. (accessed Aug 01, 2017). Dewar, M., Wei, W., McNeil, D., Chen, B., 2013. Marine Pollution Bulletin 73(2), 504-515. Kano, Y., Sato, T., Kita, J., Hirabayashi, S., Tabeta, S., 2009. Int. J. Greenhouse Gas Control, Vol. 3(5), 617-625. Kano, Y. and Sato, T., 2017. In Proceeding of GHGT-13, Lausanne, Switzerland, Nov. 14-18, 2016. Kawada, R. 2014. Graduation thesis. Faculty of Engineering, The

3D random Voronoi grain-based models for simulation of brittle rock damage and fabric-guided micro-fracturing

Directory of Open Access Journals (Sweden)

E. Ghazvinian

2014-12-01

Full Text Available A grain-based distinct element model featuring three-dimensional (3D Voronoi tessellations (random poly-crystals is proposed for simulation of crack damage development in brittle rocks. The grain boundaries in poly-crystal structure produced by Voronoi tessellations can represent flaws in intact rock and allow for numerical replication of crack damage progression through initiation and propagation of micro-fractures along grain boundaries. The Voronoi modelling scheme has been used widely in the past for brittle fracture simulation of rock materials. However the difficulty of generating 3D Voronoi models has limited its application to two-dimensional (2D codes. The proposed approach is implemented in Neper, an open-source engine for generation of 3D Voronoi grains, to generate block geometry files that can be read directly into 3DEC. A series of Unconfined Compressive Strength (UCS tests are simulated in 3DEC to verify the proposed methodology for 3D simulation of brittle fractures and to investigate the relationship between each micro-parameter and the model's macro-response. The possibility of numerical replication of the classical U-shape strength curve for anisotropic rocks is also investigated in numerical UCS tests by using complex-shaped (elongated grains that are cemented to one another along their adjoining sides. A micro-parameter calibration procedure is established for 3D Voronoi models for accurate replication of the mechanical behaviour of isotropic and anisotropic (containing a fabric rocks.

A triple-scale crystal plasticity modeling and simulation on size effect due to fine-graining

International Nuclear Information System (INIS)

Kurosawa, Eisuke; Aoyagi, Yoshiteru; Tadano, Yuichi; Shizawa, Kazuyuki

2010-01-01

In this paper, a triple-scale crystal plasticity model bridging three hierarchical material structures, i.e., dislocation structure, grain aggregate and practical macroscopic structure is developed. Geometrically necessary (GN) dislocation density and GN incompatibility are employed so as to describe isolated dislocations and dislocation pairs in a grain, respectively. Then the homogenization method is introduced into the GN dislocation-crystal plasticity model for derivation of the governing equation of macroscopic structure with the mathematical and physical consistencies. Using the present model, a triple-scale FE simulation bridging the above three hierarchical structures is carried out for f.c.c. polycrystals with different mean grain size. It is shown that the present model can qualitatively reproduce size effects of macroscopic specimen with ultrafine-grain, i.e., the increase of initial yield stress, the decrease of hardening ratio after reaching tensile strength and the reduction of tensile ductility with decrease of its grain size. Moreover, the relationship between macroscopic yielding of specimen and microscopic grain yielding is discussed and the mechanism of the poor tensile ductility due to fine-graining is clarified. (author)

Grain boundary embrittlement and cohesion enhancement in copper

Energy Technology Data Exchange (ETDEWEB)

Paxton, Anthony; Lozovoi, Alexander [Atomistic Simulation Centre, Queen' s University Belfast, BT7 1NN (United Kingdom); Schweinfest, Rainer [Science+Computing ag, Hagellocher Weg 71-5, 720270 T ubingen (Germany); Finnis, Michael [Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom)

2008-07-01

There has been a long standing debate surrounding the mechanism of grain boundary embrittlement and cohesion enhancement in metals. Embrittlement can lead to catastrophic failure such as happened in the Hinkley Point disaster, or indeed in the case of the Titanic. This kind of embrittlement is caused by segregation of low solubility impurities to grain boundaries. While the accepted wisdom is that this is a phenomenon driven by electronic or chemical factors, using language such as charge transfer and electronegativity difference; we believe that in copper, at least, both cohesion enhancement and reduction are caused by a simple size effect. We have developed a theory that allows us to separate unambiguously, if not uniquely, chemical and structural factors. We have studied a large number of solutes in copper using first principles atomistic simulation to support this argument, and the results of these calculations are presented here.

Dynamic coarse-graining fills the gap between atomistic simulations and experimental investigations of mechanical unfolding

Science.gov (United States)

Knoch, Fabian; Schäfer, Ken; Diezemann, Gregor; Speck, Thomas

2018-01-01

We present a dynamic coarse-graining technique that allows one to simulate the mechanical unfolding of biomolecules or molecular complexes on experimentally relevant time scales. It is based on Markov state models (MSMs), which we construct from molecular dynamics simulations using the pulling coordinate as an order parameter. We obtain a sequence of MSMs as a function of the discretized pulling coordinate, and the pulling process is modeled by switching among the MSMs according to the protocol applied to unfold the complex. This way we cover seven orders of magnitude in pulling speed. In the region of rapid pulling, we additionally perform steered molecular dynamics simulations and find excellent agreement between the results of the fully atomistic and the dynamically coarse-grained simulations. Our technique allows the determination of the rates of mechanical unfolding in a dynamical range from approximately 10-8/ns to 1/ns thus reaching experimentally accessible time regimes without abandoning atomistic resolution.

The composition of interstellar grain mantles

International Nuclear Information System (INIS)

Tielens, A.G.G.M.

1984-01-01

The molecular composition of interstellar grain mantles employing gas phase as well as grain surface reactions has been calculated. The calculated mixtures consist mainly of the molecules H 2 O H 2 CO, N 2 , CO, O 2 , CO 2 , H 2 O 2 , NH 3 , and their deuterated counterparts in varying ratios. The exact compositions depend strongly on the physical conditions in the gas phase. The calculated mixtures are compared to the observations by using laboratory spectra of grain mantle analogs. (author)

Effects of simulated flue gas on components of Scenedesmus raciborskii WZKMT.

Science.gov (United States)

Li, Xie-kun; Xu, Jing-liang; Guo, Ying; Zhou, Wei-zheng; Yuan, Zhen-hong

2015-08-01

Scenedesmus raciborskii WZKMT cultured with simulated flue gas was investigated. Cellular components, including total sugar, starch, chlorophyll, protein and lipid, were compared between simulated flue gas and 7% (v/v) CO2. Dissolution of SO2 and NO in simulated flue gas led to pH decrease and toxicity to microalgae cells. Furthermore, the death or aging of microalgae cells reduced the buffer capacity and caused decrease of simulated flue gas absorption. With 7% CO2, the highest total sugar and starch content could attain to 66.76% and 53.16%, respectively, which indicated S. raciborskii WZKMT is a desired feedstock candidate for bioethanol production. Microalgae growth and starch accumulation was inhibited, while cells produced more chlorophyll, protein and lipid when simulated flue gas was the carbon source. Fatty acids composition analysis indicated that there was no significant distinction on fatty acids relative content (fatty acid/TFA) between cells aerated using simulated flue gas and 7% CO2. Copyright © 2015 Elsevier Ltd. All rights reserved.

Connecting the Interstellar Gas and Dust Properties in Distant Galaxies Using Quasar Absorption Systems

Science.gov (United States)

Aller, Monique C.; Dwek, Eliahu; Kulkarni, Varsha P.; York, Donald G.; Welty, Daniel E.; Vladilo, Giovanni; Som, Debopam; Lackey, Kyle; Dwek, Eli; Beiranvand, Nassim;

An overview of molecular dynamics simulations of oxidized lipid systems, with a comparison of ELBA and MARTINI force fields for coarse grained lipid simulations

DEFF Research Database (Denmark)

Siani, Pablo; de Souza, R M; Dias, L G

2016-01-01

our new data of all-atom and coarse-grained simulations of hydroperoxidized lipid monolayer and bilayer systems and (iii) provide a comparison of the MARTINI and ELBA coarse grained force fields for lipid bilayer systems. We show that the better electrostatic treatment of interactions in ELBA is able...

Coarse grain model for coupled thermo-mechano-chemical processes and its application to pressure-induced endothermic chemical reactions

International Nuclear Information System (INIS)

Antillon, Edwin; Banlusan, Kiettipong; Strachan, Alejandro

2014-01-01

We extend a thermally accurate model for coarse grain dynamics (Strachan and Holian 2005 Phys. Rev. Lett. 94 014301) to enable the description of stress-induced chemical reactions in the degrees of freedom internal to the mesoparticles. Similar to the breathing sphere model, we introduce an additional variable that describes the internal state of the particles and whose dynamics is governed both by an internal potential energy function and by interparticle forces. The equations of motion of these new variables are derived from a Hamiltonian and the model exhibits two desired features: total energy conservation and Galilean invariance. We use a simple model material with pairwise interactions between particles and study pressure-induced chemical reactions induced by hydrostatic and uniaxial compression. These examples demonstrate the ability of the model to capture non-trivial processes including the interplay between mechanical, thermal and chemical processes of interest in many applications. (paper)

The RealGas and RealGasH2O Options of the TOUGH+ Code for the Simulation of Coupled Fluid and Heat Flow in Tight/Shale Gas Systems

Energy Technology Data Exchange (ETDEWEB)

Moridis, George; Freeman, Craig

2013-09-30

We developed two new EOS additions to the TOUGH+ family of codes, the RealGasH2O and RealGas . The RealGasH2O EOS option describes the non-isothermal two-phase flow of water and a real gas mixture in gas reservoirs, with a particular focus in ultra-tight (such as tight-sand and shale gas) reservoirs. The gas mixture is treated as either a single-pseudo-component having a fixed composition, or as a multicomponent system composed of up to 9 individual real gases. The RealGas option has the same general capabilities, but does not include water, thus describing a single-phase, dry-gas system. In addition to the standard capabilities of all members of the TOUGH+ family of codes (fully-implicit, compositional simulators using both structured and unstructured grids), the capabilities of the two codes include: coupled flow and thermal effects in porous and/or fractured media, real gas behavior, inertial (Klinkenberg) effects, full micro-flow treatment, Darcy and non-Darcy flow through the matrix and fractures of fractured media, single- and multi-component gas sorption onto the grains of the porous media following several isotherm options, discrete and fracture representation, complex matrix-fracture relationships, and porosity-permeability dependence on pressure changes. The two options allow the study of flow and transport of fluids and heat over a wide range of time frames and spatial scales not only in gas reservoirs, but also in problems of geologic storage of greenhouse gas mixtures, and of geothermal reservoirs with multi-component condensable (H2O and CH4) and non-condensable gas mixtures. The codes are verified against available analytical and semi-analytical solutions. Their capabilities are demonstrated in a series of problems of increasing complexity, ranging from isothermal flow in simpler 1D and 2D conventional gas reservoirs, to non-isothermal gas flow in 3D fractured shale gas reservoirs involving 4 types of fractures, micro-flow, non-Darcy flow and gas

DECODING THE MESSAGE FROM METEORITIC STARDUST SILICON CARBIDE GRAINS

International Nuclear Information System (INIS)

Lewis, Karen M.; Lugaro, Maria; Gibson, Brad K.; Pilkington, Kate

2013-01-01

Micron-sized stardust grains that originated in ancient stars are recovered from meteorites and analyzed using high-resolution mass spectrometry. The most widely studied type of stardust is silicon carbide (SiC). Thousands of these grains have been analyzed with high precision for their Si isotopic composition. Here we show that the distribution of the Si isotopic composition of the vast majority of stardust SiC grains carries the imprints of a spread in the age-metallicity distribution of their parent stars and of a power-law increase of the relative formation efficiency of SiC dust with the metallicity. This result offers a solution for the long-standing problem of silicon in stardust SiC grains, confirms the necessity of coupling chemistry and dynamics in simulations of the chemical evolution of our Galaxy, and constrains the modeling of dust condensation in stellar winds as a function of the metallicity.

Stress-assisted grain growth in nanocrystalline metals: Grain boundary mediated mechanisms and stabilization through alloying

International Nuclear Information System (INIS)

Zhang, Yang; Tucker, Garritt J.; Trelewicz, Jason R.

2017-01-01

The mechanisms of stress-assisted grain growth are explored using molecular dynamics simulations of nanoindentation in nanocrystalline Ni and Ni-1 at.% P as a function of grain size and deformation temperature. Grain coalescence is primarily confined to the high stress region beneath the simulated indentation zone in nanocrystalline Ni with a grain size of 3 nm. Grain orientation and atomic displacement vector mapping demonstrates that coalescence transpires through grain rotation and grain boundary migration, which are manifested in the grain interior and grain boundary components of the average microrotation. A doubling of the grain size to 6 nm and addition of 1 at.% P eliminates stress-assisted grain growth in Ni. In the absence of grain coalescence, deformation is accommodated by grain boundary-mediated dislocation plasticity and thermally activated in pure nanocrystalline Ni. By adding solute to the grain boundaries, the temperature-dependent deformation behavior observed in both the lattice and grain boundaries inverts, indicating that the individual processes of dislocation and grain boundary plasticity will exhibit different activity based on boundary chemistry and deformation temperature.

Retained Gas Sampler Calibration and Simulant Tests

Energy Technology Data Exchange (ETDEWEB)

CRAWFORD, B.A.

2000-01-05

This test plan provides a method for calibration of the retained gas sampler (RGS) for ammonia gas analysis. Simulant solutions of ammonium hydroxide at known concentrations will be diluted with isotopically labeled 0.04 M ammonium hydroxide solution. Sea sand solids will also be mixed with ammonium hydroxide solution and diluent to determine the accuracy of the system for ammonia gas analysis.

Retained Gas Sampler Calibration and Simulant Tests

International Nuclear Information System (INIS)

CRAWFORD, B.A.

2000-01-01

This test plan provides a method for calibration of the retained gas sampler (RGS) for ammonia gas analysis. Simulant solutions of ammonium hydroxide at known concentrations will be diluted with isotopically labeled 0.04 M ammonium hydroxide solution. Sea sand solids will also be mixed with ammonium hydroxide solution and diluent to determine the accuracy of the system for ammonia gas analysis

Numerical simulation of air hypersonic flows with equilibrium chemical reactions

Science.gov (United States)

Emelyanov, Vladislav; Karpenko, Anton; Volkov, Konstantin

2018-05-01

The finite volume method is applied to solve unsteady three-dimensional compressible Navier-Stokes equations on unstructured meshes. High-temperature gas effects altering the aerodynamics of vehicles are taken into account. Possibilities of the use of graphics processor units (GPUs) for the simulation of hypersonic flows are demonstrated. Solutions of some test cases on GPUs are reported, and a comparison between computational results of equilibrium chemically reacting and perfect air flowfields is performed. Speedup of solution on GPUs with respect to the solution on central processor units (CPUs) is compared. The results obtained provide promising perspective for designing a GPU-based software framework for practical applications.

Chemisputtering of interstellar graphite grains

International Nuclear Information System (INIS)

Draine, B.T.

1979-01-01

The rate of erosion of interstellar graphite grains as a result of chemical reaction with H, N, and O is estimated using the available experiment evidence. It is argued that ''chemical sputtering'' yields for interstellar graphite grains will be much less than unity, contrary to earlier estimates by Barlow and Silk. Chemical sputtering of graphite grains in evolving H II regions is found to be unimportant, except in extremely compact (n/sub H/> or approx. =10 5 cm -3 ) H II regions. Alternative explanations are considered for the apparent weakness of the lambda=2175 A extinction ''bump'' in the direction of several early type stars

Effects of snow grain shape on climate simulations: sensitivity tests with the Norwegian Earth System Model

Science.gov (United States)

Räisänen, Petri; Makkonen, Risto; Kirkevåg, Alf; Debernard, Jens B.

2017-12-01

Snow consists of non-spherical grains of various shapes and sizes. Still, in radiative transfer calculations, snow grains are often treated as spherical. This also applies to the computation of snow albedo in the Snow, Ice, and Aerosol Radiation (SNICAR) model and in the Los Alamos sea ice model, version 4 (CICE4), both of which are employed in the Community Earth System Model and in the Norwegian Earth System Model (NorESM). In this study, we evaluate the effect of snow grain shape on climate simulated by NorESM in a slab ocean configuration of the model. An experiment with spherical snow grains (SPH) is compared with another (NONSPH) in which the snow shortwave single-scattering properties are based on a combination of three non-spherical snow grain shapes optimized using measurements of angular scattering by blowing snow. The key difference between these treatments is that the asymmetry parameter is smaller in the non-spherical case (0.77-0.78 in the visible region) than in the spherical case ( ≈ 0.89). Therefore, for the same effective snow grain size (or equivalently, the same specific projected area), the snow broadband albedo is higher when assuming non-spherical rather than spherical snow grains, typically by 0.02-0.03. Considering the spherical case as the baseline, this results in an instantaneous negative change in net shortwave radiation with a global-mean top-of-the-model value of ca. -0.22 W m-2. Although this global-mean radiative effect is rather modest, the impacts on the climate simulated by NorESM are substantial. The global annual-mean 2 m air temperature in NONSPH is 1.17 K lower than in SPH, with substantially larger differences at high latitudes. The climatic response is amplified by strong snow and sea ice feedbacks. It is further demonstrated that the effect of snow grain shape could be largely offset by adjusting the snow grain size. When assuming non-spherical snow grains with the parameterized grain size increased by ca. 70 %, the

Meso-microstructural computational simulation of the hydrogen permeation test to calculate intergranular, grain boundary and effective diffusivities

Energy Technology Data Exchange (ETDEWEB)

Jothi, S., E-mail: s.jothi@swansea.ac.uk [College of Engineering, Swansea University, Singleton Park, Swansea SA2 8PP (United Kingdom); Winzer, N. [Fraunhofer Institute for Mechanics of Materials IWM, Wöhlerstraße 11, 79108 Freiburg (Germany); Croft, T.N.; Brown, S.G.R. [College of Engineering, Swansea University, Singleton Park, Swansea SA2 8PP (United Kingdom)

2015-10-05

Highlights: • Characterized polycrystalline nickel microstructure using EBSD analysis. • Development meso-microstructural model based on real microstructure. • Calculated effective diffusivity using experimental electrochemical permeation test. • Calculated intergranular diffusivity of hydrogen using computational FE simulation. • Validated the calculated computation simulation results with experimental results. - Abstract: Hydrogen induced intergranular embrittlement has been identified as a cause of failure of aerospace components such as combustion chambers made from electrodeposited polycrystalline nickel. Accurate computational analysis of this process requires knowledge of the differential in hydrogen transport in the intergranular and intragranular regions. The effective diffusion coefficient of hydrogen may be measured experimentally, though experimental measurement of the intergranular grain boundary diffusion coefficient of hydrogen requires significant effort. Therefore an approach to calculate the intergranular GB hydrogen diffusivity using finite element analysis was developed. The effective diffusivity of hydrogen in polycrystalline nickel was measured using electrochemical permeation tests. Data from electron backscatter diffraction measurements were used to construct microstructural representative volume elements including details of grain size and shape and volume fraction of grains and grain boundaries. A Python optimization code has been developed for the ABAQUS environment to calculate the unknown grain boundary diffusivity.

submitter Thermal stability of interface voids in Cu grain boundaries with molecular dynamic simulations

CERN Document Server

Xydou, A; Aicheler, M; Djurabekova, F

2016-01-01

By means of molecular dynamic simulations, the stability of cylindrical voids is examined with respect to the diffusion bonding procedure. To do this, the effect of grain boundaries between the grains of different crystallographic orientations on the void closing time was studied at high temperatures from 0.7 up to 0.94 of the bulk melting temperature $(T_m)$. The diameter of the voids varied from 3.5 to 6.5 nm. A thermal instability occurring at high temperatures at the surface of the void placed in a grain boundary triggered the eventual closure of the void at all examined temperatures. The closing time has an exponential dependence on the examined temperature values. A model based on the defect diffusion theory is developed to predict the closing time for voids of macroscopic size. The diffusion coefficient within the grain boundaries is found to be overall higher than the diffusion coefficient in the region around the void surface. The activation energy for the diffusion in the grain boundary is calculate...

Parallelization of simulation code for liquid-gas model of lattice-gas fluid

International Nuclear Information System (INIS)

Kawai, Wataru; Ebihara, Kenichi; Kume, Etsuo; Watanabe, Tadashi

2000-03-01

A simulation code for hydrodynamical phenomena which is based on the liquid-gas model of lattice-gas fluid is parallelized by using MPI (Message Passing Interface) library. The parallelized code can be applied to the larger size of the simulations than the non-parallelized code. The calculation times of the parallelized code on VPP500 (Vector-Parallel super computer with dispersed memory units), AP3000 (Scalar-parallel server with dispersed memory units), and a workstation cluster decreased in inverse proportion to the number of processors. (author)

Simulation, integration, and economic analysis of gas-to-liquid processes

International Nuclear Information System (INIS)

Bao, Buping; El-Halwagi, Mahmoud M.; Elbashir, Nimir O.

2010-01-01

Gas-to-liquid (GTL) involves the chemical conversion of natural gas into synthetic crude that can be upgraded and separated into different useful hydrocarbon fractions including liquid transportation fuels. Such technology can also be used to convert other abundant natural resources such as coal and biomass to fuels and value added chemicals (referred to as coal-to-liquid (CTL) and biomass-to-liquid (BTL)). A leading GTL technology is the Fischer-Tropsch (FT) process. The objective of this work is to provide a techno-economic analysis of the GTL process and to identify optimization and integration opportunities for cost saving and reduction of energy usage while accounting for the environmental impact. First, a base-case flowsheet is synthesized to include the key processing steps of the plant. Then, a computer-aided process simulation is carried out to determine the key mass and energy flows, performance criteria, and equipment specifications. Next, energy and mass integration studies are performed to address the following items: (a) heating and cooling utilities, (b) combined heat and power (process cogeneration), (c) management of process water, (c) optimization of tail gas allocation, and (d) recovery of catalyst-supporting hydrocarbon solvents. Finally, these integration studies are conducted and the results are documented in terms of conserving energy and mass resources as well as providing economic impact. Finally, an economic analysis is undertaken to determine the plant capacity needed to achieve the break-even point and to estimate the return on investment for the base-case study. (author)

Zirconia-based solid state chemical gas sensors

CERN Document Server

Zhuiykov, S

2000-01-01

This paper presents an overview of chemical gas sensors, based on solid state technology, that are sensitive to environmental gases, such as O sub 2 , SO sub x , NO sub x , CO sub 2 and hydrocarbons. The paper is focussed on performance of electrochemical gas sensors that are based on zirconia as a solid electrolyte. The paper considers sensor structures and selection of electrode materials. Impact of interfaces on sensor performance is discussed. This paper also provides a brief overview of electrochemical properties of zirconia and their effect on sensor performance. Impact of auxiliary materials on sensors performance characteristics, such as sensitivity, selectivity, response time and recovery time, is also discussed. Dual gas sensors that can be applied for simultaneous monitoring of the concentration of both oxygen and other gas phase components, are briefly considered

Microfabricated Gas Phase Chemical Analysis Systems

International Nuclear Information System (INIS)

FRYE-MASON, GREGORY CHARLES; HELLER, EDWIN J.; HIETALA, VINCENT M.; KOTTENSTETTE, RICHARD; LEWIS, PATRICK R.; MANGINELL, RONALD P.; MATZKE, CAROLYN M.; WONG, CHUNGNIN C.

1999-01-01

A portable, autonomous, hand-held chemical laboratory ((micro)ChemLab(trademark)) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described

Alternative Fuels and Chemicals from Synthesis Gas

Energy Technology Data Exchange (ETDEWEB)

None, None

1998-12-02

The overall objectives of this program are to investigate potential technologies for the conversion of synthesis gas to oxygenated and hydrocarbon fuels and industrial chemicals, and to demonstrate the most promising technologies at DOE's LaPorte, Texas, Slurry Phase Alternative Fuels Development Unit (AFDU). The program will involve a continuation of the work performed under the Alternative Fuels from Coal-Derived Synthesis Gas Program and will draw upon information and technologies generated in parallel current and future DOE-funded contracts.

Alternative fuels and chemicals from synthesis gas

Energy Technology Data Exchange (ETDEWEB)

Unknown

1998-08-01

The overall objectives of this program are to investigate potential technologies for the conversion of synthesis gas to oxygenated and hydrocarbon fuels and industrial chemicals, and to demonstrate the most promising technologies at DOE's LaPorte, Texas, Slurry Phase Alternative Fuels Development Unit (AFDU). The program will involve a continuation of the work performed under the Alternative Fuels from Coal-Derived Synthesis Gas Program and will draw upon information and technologies generated in parallel current and future DOE-funded contracts.

ALTERNATIVE FUELS AND CHEMICALS FROM SYNTHESIS GAS

Energy Technology Data Exchange (ETDEWEB)

Unknown

1999-01-01

The overall objectives of this program are to investigate potential technologies for the conversion of synthesis gas to oxygenated and hydrocarbon fuels and industrial chemicals, and to demonstrate the most promising technologies at DOE's LaPorte, Texas, Slurry Phase Alternative Fuels Development Unit (AFDU). The program will involve a continuation of the work performed under the Alternative Fuels from Coal-Derived Synthesis Gas Program and will draw upon information and technologies generated in parallel current and future DOE-funded contracts.

Alternative Fuels and Chemicals From Synthesis Gas

Energy Technology Data Exchange (ETDEWEB)

none

1998-07-01

The overall objectives of this program are to investigate potential technologies for the conversion of synthesis gas to oxygenated and hydrocarbon fuels and industrial chemicals, and to demonstrate the most promising technologies at DOE's LaPorte, Texas, Slurry Phase Alternative Fuels Development Unit (AFDU). The program will involve a continuation of the work performed under the Alternative Fuels from Coal-Derived Synthesis Gas Program and will draw upon information and technologies generated in parallel current and future DOE-funded contracts.

Molecular dynamics simulation of Xe bubble nucleation in nanocrystalline UO2 nuclear fuel

International Nuclear Information System (INIS)

Moore, Emily; René Corrales, L.; Desai, Tapan; Devanathan, Ram

2011-01-01

Highlights: ► We simulated the interactions of defects and fission gas with grain boundaries in nuclear fuel. ► We observed the formation of Xe bubble nuclei that are difficult to observe experimentally. ► The bubble nuclei form by vacancy-assisted diffusion of Xe atoms. ► We also observed the initial stages of grain boundary motion. ► The study offers insights to the design of nuclear fuel to control fission gas release. - Abstract: We have performed molecular dynamics (MD) simulations to investigate the dynamical interactions between vacancy defects, fission gas atoms (Xe), and grain boundaries in a model of polycrystalline UO 2 nuclear fuel with average grain diameter of about 20 nm. We followed the mobility and aggregation of Xe atoms in the vacancy-saturated model compound for up to 2 ns. During this time we observed the aggregation of Xe atoms into nuclei, which are possible precursors to Xe bubbles. The nucleation was driven by the migration of Xe atoms via vacancy-assisted diffusion. The Xe clusters aggregate faster than grain boundary diffusion rates and are smaller than experimentally observed bubbles. As the system evolves towards equilibrium, the Xe atom cluster growth slows down significantly, and the lattice relaxes around the cluster. These simulations provide insights into fundamental physical processes that are inaccessible to experiment.

Analysis of Chlorine Gas Incident Simulation and Dispersion Within a Complex and Populated Urban Area Via Computation Fluid Dynamics

Directory of Open Access Journals (Sweden)

Eslam Kashi

2015-04-01

Full Text Available In some instances, it is inevitable that large amounts of potentially hazardous chemicals like chlorine gas are stored and used in facilities in densely populated areas. In such cases, all safety issues must be carefully considered. To reach this goal, it is important to have accurate information concerning chlorine gas behaviors and how it is dispersed in dense urban areas. Furthermore, maintaining adequate air movement and the ability to purge ambient from potential toxic and dangerous chemicals like chlorine gas could be helpful. These are among the most important actions to be taken toward the improvement of safety in a big metropolis like Tehran. This paper investigates and analyzes chlorine gas leakage scenarios, including its dispersion and natural air ventilation  effects on how it might be geographically spread in a city, using computational  fluid dynamic (CFD. Simulations of possible hazardous events and solutions for preventing or reducing their probability are presented to gain a better insight into the incidents. These investigations are done by considering hypothetical scenarios which consist of chlorine gas leakages from pipelines or storage tanks under different conditions. These CFD simulation results are used to investigate and analyze chlorine gas behaviors, dispersion, distribution, accumulation, and other possible hazards by means of a simplified CAD model of an urban area near a water-treatment facility. Possible hazards as well as some prevention and post incident solutions are also suggested.

The effects of cytoplasmic male sterility and xenia on the chemical composition of maize grain

Directory of Open Access Journals (Sweden)

Vančetović Jelena

2009-01-01

Full Text Available Sterile hybrids often outyield their fertile counterparts, especially if pollinated by a genetically unrelated pollinator. The combined effect of cms and xenia is referred to as the Plus-hybrid effect. The objective of this study was to determine the individual, as well as, combining effect of cms and xenia on the maize grain chemical composition. The percent of oil, protein and starch in the grain was also observed. Two sterile hybrids, their fertile counterparts and five fertile pollinator-hybrids were selected for the studies. The three-replicate trial set up according to the split-plot experimental design was performed at Zemun Polje in 2008. The obtained results show that the effects of cms on the oil percent was not significant in the studied hybrid ZP 341, while it increased at the significance level of P = 0.1 in the second observed hybrid ZP 360. The effect of this factor on the protein and starch percent was also significant (P = 0.01 in some hybrid combinations. Xenia effects on all three chemical parameters were significant (P = 0.01 in some hybrid combinations. The gained results indicate that the identification of a good combination of two hybrids, in which one would be a sterile female component, and the other a pollinator, would end up not only in the increased yield, but also in the improved maize grain quality.

Discrete-Event Simulation in Chemical Engineering.

Science.gov (United States)

Schultheisz, Daniel; Sommerfeld, Jude T.

1988-01-01

Gives examples, descriptions, and uses for various types of simulation systems, including the Flowtran, Process, Aspen Plus, Design II, GPSS, Simula, and Simscript. Explains similarities in simulators, terminology, and a batch chemical process. Tables and diagrams are included. (RT)

Grain size increase in pentacene thin films prepared in low-pressure gas ambient

International Nuclear Information System (INIS)

Yokoyama, Takamichi; Park, Chang Bum; Nagashio, Kosuke; Kita, Koji; Toriumi, Akira

2009-01-01

We studied a mechanism of grain size increase (that is, island density decrease) in pentacene film prepared in hydrogen (H 2 ) ambient. The island densities of pentacene films prepared in helium and deuterium were lower than those of vacuum-deposited films. This indicates that the decrease in the island density was not due to the chemical interaction between H 2 and pentacene or the substrate surface. Furthermore, the temperature dependence of the island density indicates that there is no difference in the surface diffusion energy in a vacuum and in H 2 . We also improved mobility significantly in the pentacene thin film transistor fabricated on film grown in H 2 ambient on a chemically treated substrate.

Gas analysis during the chemical vapor deposition of carbon

International Nuclear Information System (INIS)

Lieberman, M.L.; Noles, G.T.

1973-01-01

Gas chromatographic analyses were performed during the chemical vapor deposition of carbon in both isothermal and thermal gradient systems. Such data offer insight into the gas phase processes which occur during deposition and the interrelations which exist between gas composition, deposition rate, and resultant structure of the deposit. The results support a carbon CVD model presented previously. The application of chromatographic analysis to research, development, and full-scale facilities is shown. (U.S.)

Analysis of fission gas release in LWR fuel using the BISON code

Energy Technology Data Exchange (ETDEWEB)

G. Pastore; J.D. Hales; S.R. Novascone; D.M. Perez; B.W. Spencer; R.L. Williamson

2013-09-01

Recent advances in the development of the finite-element based, multidimensional fuel performance code BISON of Idaho National Laboratory are presented. Specifically, the development, implementation and testing of a new model for the analysis of fission gas behavior in LWR-UO2 fuel during irradiation are summarized. While retaining a physics-based description of the relevant mechanisms, the model is characterized by a level of complexity suitable for application to engineering-scale nuclear fuel analysis and consistent with the uncertainties pertaining to some parameters. The treatment includes the fundamental features of fission gas behavior, among which are gas diffusion and precipitation in fuel grains, growth and coalescence of gas bubbles at grain faces, grain growth and grain boundary sweeping effects, thermal, athermal, and transient gas release. The BISON code incorporating the new model is applied to the simulation of irradiation experiments from the OECD/NEA International Fuel Performance Experiments database, also included in the IAEA coordinated research projects FUMEX-II and FUMEX-III. The comparison of the results with the available experimental data at moderate burn-up is presented, pointing out an encouraging predictive accuracy, without any fitting applied to the model parameters.

Heat Integration of the Water-Gas Shift Reaction System for Carbon Sequestration Ready IGCC Process with Chemical Looping

Energy Technology Data Exchange (ETDEWEB)

Juan M. Salazara; Stephen E. Zitney; Urmila M. Diwekara

2010-01-01

Integrated gasification combined cycle (IGCC) technology has been considered as an important alternative for efficient power systems that can reduce fuel consumption and CO2 emissions. One of the technological schemes combines water-gas shift reaction and chemical-looping combustion as post gasification techniques in order to produce sequestration-ready CO2 and potentially reduce the size of the gas turbine. However, these schemes have not been energetically integrated and process synthesis techniques can be applied to obtain an optimal flowsheet. This work studies the heat exchange network synthesis (HENS) for the water-gas shift reaction train employing a set of alternative designs provided by Aspen energy analyzer (AEA) and combined in a process superstructure that was simulated in Aspen Plus (AP). This approach allows a rigorous evaluation of the alternative designs and their combinations avoiding all the AEA simplifications (linearized models of heat exchangers). A CAPE-OPEN compliant capability which makes use of a MINLP algorithm for sequential modular simulators was employed to obtain a heat exchange network that provided a cost of energy that was 27% lower than the base case. Highly influential parameters for the pos gasification technologies (i.e. CO/steam ratio, gasifier temperature and pressure) were calculated to obtain the minimum cost of energy while chemical looping parameters (oxidation and reduction temperature) were ensured to be satisfied.

Sticking properties of ice grains

Science.gov (United States)

Jongmanns, M.; Kumm, M.; Wurm, G.; Wolf, D. E.; Teiser, J.

2017-06-01

We study the size dependence of pull-off forces of water ice in laboratory experiments and numerical simulations. To determine the pull-off force in our laboratory experiments, we use a liquid nitrogen cooled centrifuge. Depending on its rotation frequency, spherical ice grains detach due to the centrifugal force which is related to the adhesive properties. Numerical simulations are conducted by means of molecular dynamics simulations of hexagonal ice using a standard coarse-grained water potential. The pull-off force of a single contact between two spherical ice grains is measured due to strain controlled simulations. Both, the experimental study and the simulations reveal a dependence between the pull-off force and the (reduced) particle radii, which differ significantly from the linear dependence of common contact theories.

Numerical Simulation and Experimental Study on Formation of High Concentration of H2 Generated by Gas Explosion

Directory of Open Access Journals (Sweden)

Lei Baiwei

2016-10-01

Full Text Available In coal mine fire rescues, if the abnormal increase of gas concentration occurs, it is the primary thing to analyze the reasons and identify sources of the abnormal forming, which is also the basis of judge the combustion state of fire area and formulate proper fire reliefs. Nowadays, related researches have recognized the methane explosion as the source of high concentration of H2 formation, but there are few studies about the conditions and reaction mechanism of gas explosion generating high concentration of H2.Therefore, this paper uses the chemical kinetic calculation software, ChemKin, and the 20L spherical explosion experimental device to simulate the generating process and formation conditions of H2 in gas explosion. The experimental results show that: the decomposition of water vapor is the main base element reaction (R84 which leads to the generation of H2.The free radical H is the key factor to influence the formation of H2 generated from gas explosion. With the gradual increase of gas explosion concentration, the explosive reaction becomes more incomplete, and then the generating quantity of H2 increases gradually. Experimental results of 20L spherical explosion are consistent with the change trend about simulation results, which verifies the accuracy of simulation analysis. The results of explosion experiments show that when gas concentration is higher than 9%, the incomplete reaction of methane explosion increases which leads to the gradual increase of H2 formation.

Off-gas adsorption model and simulation - OSPREY

Energy Technology Data Exchange (ETDEWEB)

Rutledge, V.J. [Idaho National Laboratory, P. O. Box 1625, Idaho Falls, ID (United States)

2013-07-01

A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes is expected to provide substantial cost savings and many technical benefits. To support this capability, a modeling effort focused on the off-gas treatment system of a used nuclear fuel recycling facility is in progress. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed within Multi-physics Object Oriented Simulation Environment (MOOSE) developed at the Idaho National Laboratory (INL). Off-gas Separation and Recovery (OSPREY) models the adsorption of offgas constituents for dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions. Inputs to the model include gas composition, sorbent and column properties, equilibrium and kinetic data, and inlet conditions. The simulation outputs component concentrations along the column length as a function of time from which breakthrough data can be obtained. The breakthrough data can be used to determine bed capacity, which in turn can be used to size columns. In addition to concentration data, the model predicts temperature along the column length as a function of time and pressure drop along the column length. A description of the OSPREY model, results from krypton adsorption modeling and plans for modeling the behavior of iodine, xenon, and tritium will be discussed. (author)

Dynamic metabolome profiling reveals significant metabolic changes during grain development of bread wheat (Triticum aestivum L.).

Science.gov (United States)

Zhen, Shoumin; Dong, Kun; Deng, Xiong; Zhou, Jiaxing; Xu, Xuexin; Han, Caixia; Zhang, Wenying; Xu, Yanhao; Wang, Zhimin; Yan, Yueming

2016-08-01

Metabolites in wheat grains greatly influence nutritional values. Wheat provides proteins, minerals, B-group vitamins and dietary fiber to humans. These metabolites are important to human health. However, the metabolome of the grain during the development of bread wheat has not been studied so far. In this work the first dynamic metabolome of the developing grain of the elite Chinese bread wheat cultivar Zhongmai 175 was analyzed, using non-targeted gas chromatography/mass spectrometry (GC/MS) for metabolite profiling. In total, 74 metabolites were identified over the grain developmental stages. Metabolite-metabolite correlation analysis revealed that the metabolism of amino acids, carbohydrates, organic acids, amines and lipids was interrelated. An integrated metabolic map revealed a distinct regulatory profile. The results provide information that can be used by metabolic engineers and molecular breeders to improve wheat grain quality. The present metabolome approach identified dynamic changes in metabolite levels, and correlations among such levels, in developing seeds. The comprehensive metabolic map may be useful when breeding programs seek to improve grain quality. The work highlights the utility of GC/MS-based metabolomics, in conjunction with univariate and multivariate data analysis, when it is sought to understand metabolic changes in developing seeds. © 2015 Society of Chemical Industry. © 2015 Society of Chemical Industry.

On the enrichment of low-abundant isotopes of light chemical elements by gas centrifuges

International Nuclear Information System (INIS)

Borisevich, V.D.; Morozov, O.E.; Zaozerskiy, Yu.P.; Shmelev, G.M.; Shipilov, Yu.D.

2000-01-01

A brief review of the main areas for the application of the isotopes 15 N and 13 C is made. Separation of the nitrogen isotopes in a single gas centrifuge in the form of pure nitrogen, ammonia, and trifluoride of nitrogen as well as the carbon isotopes in the form of carbon dioxide has been studied by means of numerical simulation. The parameters of the centrifugal machine investigated were close to the parameters of the Iguassu machine. The dependence of the efficiency criterion versus the basic parameters of the separation process has been explored in the computational experiments. Comparisons of the calculated results with the experimental data have shown good agreement. The results obtained have demonstrated the possibility of using gas centrifuge technology to enrich successfully the low-abundant isotopes of light chemical elements

Effects of snow grain shape on climate simulations: sensitivity tests with the Norwegian Earth System Model

Directory of Open Access Journals (Sweden)

P. Räisänen

2017-12-01

Full Text Available Snow consists of non-spherical grains of various shapes and sizes. Still, in radiative transfer calculations, snow grains are often treated as spherical. This also applies to the computation of snow albedo in the Snow, Ice, and Aerosol Radiation (SNICAR model and in the Los Alamos sea ice model, version 4 (CICE4, both of which are employed in the Community Earth System Model and in the Norwegian Earth System Model (NorESM. In this study, we evaluate the effect of snow grain shape on climate simulated by NorESM in a slab ocean configuration of the model. An experiment with spherical snow grains (SPH is compared with another (NONSPH in which the snow shortwave single-scattering properties are based on a combination of three non-spherical snow grain shapes optimized using measurements of angular scattering by blowing snow. The key difference between these treatments is that the asymmetry parameter is smaller in the non-spherical case (0.77–0.78 in the visible region than in the spherical case ( ≈  0.89. Therefore, for the same effective snow grain size (or equivalently, the same specific projected area, the snow broadband albedo is higher when assuming non-spherical rather than spherical snow grains, typically by 0.02–0.03. Considering the spherical case as the baseline, this results in an instantaneous negative change in net shortwave radiation with a global-mean top-of-the-model value of ca. −0.22 W m−2. Although this global-mean radiative effect is rather modest, the impacts on the climate simulated by NorESM are substantial. The global annual-mean 2 m air temperature in NONSPH is 1.17 K lower than in SPH, with substantially larger differences at high latitudes. The climatic response is amplified by strong snow and sea ice feedbacks. It is further demonstrated that the effect of snow grain shape could be largely offset by adjusting the snow grain size. When assuming non-spherical snow grains with the parameterized grain

A fission gas release model

Energy Technology Data Exchange (ETDEWEB)

Denis, A; Piotrkowski, R [Argentine Atomic Energy Commission, Buenos Aires (Argentina)

1997-08-01

The hypothesis contained in the model developed in this work are as follows. The UO{sub 2} is considered as a collection of spherical grains. Nuclear reactions produce fission gases, mainly Xe and Kr, within the grains. Due to the very low solubility of these gases in UO{sub 2}, intragranular bubbles are formed, of a few nanometers is size. The bubbles are assumed to be immobile and to act as traps which capture gas atoms. Free atoms diffuse towards the grain boundaries, where they give origin to intergranular, lenticular bubbles, of the order of microns. The gas atoms in bubbles, either inter or intragranular, can re-enter the matrix through the mechanism of resolution induced by fission fragment impact. The amount of gas stored in intergranular bubbles grows up to a saturation value. Once saturation is reached, intergranular bubbles inter-connect and the gas in excess is released through different channels to the external surface of the fuel. The resolution of intergranular bubbles particularly affects the region of the grain adjacent to the grain boundary. During grain growth, the grain boundary traps the gas atoms, either free or in intragranular bubbles, contained in the swept volume. The grain boundary is considered as a perfect sink, i.e. the gas concentration is zero at that surface of the grain. Due to the spherical symmetry of the problem, the concentration gradient is null at the centre of the grain. The diffusion equation was solved using the implicit finite difference method. The initial solution was analytically obtained by the Laplace transform. The calculations were performed at different constant temperatures and were compared with experimental results. They show the asymptotic growth of the grain radius as a function of burnup, the gas distribution within the grain at every instant, the growth of the gas content at the grain boundary up to the saturation value and the fraction of gas released by the fuel element referred to the total gas generated

Efficient Monte Carlo Simulations of Gas Molecules Inside Porous Materials.

Science.gov (United States)

Kim, Jihan; Smit, Berend

2012-07-10

Monte Carlo (MC) simulations are commonly used to obtain adsorption properties of gas molecules inside porous materials. In this work, we discuss various optimization strategies that lead to faster MC simulations with CO2 gas molecules inside host zeolite structures used as a test system. The reciprocal space contribution of the gas-gas Ewald summation and both the direct and the reciprocal gas-host potential energy interactions are stored inside energy grids to reduce the wall time in the MC simulations. Additional speedup can be obtained by selectively calling the routine that computes the gas-gas Ewald summation, which does not impact the accuracy of the zeolite's adsorption characteristics. We utilize two-level density-biased sampling technique in the grand canonical Monte Carlo (GCMC) algorithm to restrict CO2 insertion moves into low-energy regions within the zeolite materials to accelerate convergence. Finally, we make use of the graphics processing units (GPUs) hardware to conduct multiple MC simulations in parallel via judiciously mapping the GPU threads to available workload. As a result, we can obtain a CO2 adsorption isotherm curve with 14 pressure values (up to 10 atm) for a zeolite structure within a minute of total compute wall time.

Origins of amorphous interstellar grains

International Nuclear Information System (INIS)

Hasegawa, H.

1984-01-01

The existence of amorphous interstellar grains has been suggested from infrared observations. Some carbon stars show the far infrared emission with a lambda -1 wavelength dependence. Far infrared emission supposed to be due to silicate grains often show the lambda -1 wavelength dependence. Mid infrared spectra around 10 μm have broad structure. These may be due to the amorphous silicate grains. The condition that the condensed grains from the cosmic gas are amorphous is discussed. (author)

Models of gas-grain chemistry in interstellar cloud cores with a stochastic approach to surface chemistry

Science.gov (United States)

Stantcheva, T.; Herbst, E.

2004-08-01

We present a gas-grain model of homogeneous cold cloud cores with time-independent physical conditions. In the model, the gas-phase chemistry is treated via rate equations while the diffusive granular chemistry is treated stochastically. The two phases are coupled through accretion and evaporation. A small network of surface reactions accounts for the surface production of the stable molecules water, formaldehyde, methanol, carbon dioxide, ammonia, and methane. The calculations are run for a time of 107 years at three different temperatures: 10 K, 15 K, and 20 K. The results are compared with those produced in a totally deterministic gas-grain model that utilizes the rate equation method for both the gas-phase and surface chemistry. The results of the different models are in agreement for the abundances of the gaseous species except for later times when the surface chemistry begins to affect the gas. The agreement for the surface species, however, is somewhat mixed. The average abundances of highly reactive surface species can be orders of magnitude larger in the stochastic-deterministic model than in the purely deterministic one. For non-reactive species, the results of the models can disagree strongly at early times, but agree to well within an order of magnitude at later times for most molecules. Strong exceptions occur for CO and H2CO at 10 K, and for CO2 at 20 K. The agreement seems to be best at a temperature of 15 K. As opposed to the use of the normal rate equation method of surface chemistry, the modified rate method is in significantly better agreement with the stochastic-deterministic approach. Comparison with observations of molecular ices in dense clouds shows mixed agreement.

Compression of turbulent magnetized gas in giant molecular clouds

Science.gov (United States)

Birnboim, Yuval; Federrath, Christoph; Krumholz, Mark

2018-01-01

Interstellar gas clouds are often both highly magnetized and supersonically turbulent, with velocity dispersions set by a competition between driving and dissipation. This balance has been studied extensively in the context of gases with constant mean density. However, many astrophysical systems are contracting under the influence of external pressure or gravity, and the balance between driving and dissipation in a contracting, magnetized medium has yet to be studied. In this paper, we present three-dimensional magnetohydrodynamic simulations of compression in a turbulent, magnetized medium that resembles the physical conditions inside molecular clouds. We find that in some circumstances the combination of compression and magnetic fields leads to a rate of turbulent dissipation far less than that observed in non-magnetized gas, or in non-compressing magnetized gas. As a result, a compressing, magnetized gas reaches an equilibrium velocity dispersion much greater than would be expected for either the hydrodynamic or the non-compressing case. We use the simulation results to construct an analytic model that gives an effective equation of state for a coarse-grained parcel of the gas, in the form of an ideal equation of state with a polytropic index that depends on the dissipation and energy transfer rates between the magnetic and turbulent components. We argue that the reduced dissipation rate and larger equilibrium velocity dispersion has important implications for the driving and maintenance of turbulence in molecular clouds and for the rates of chemical and radiative processes that are sensitive to shocks and dissipation.

Branching-induced grain boundary evolution during directional solidification of columnar dendritic grains

International Nuclear Information System (INIS)

Guo, Chunwen; Li, Junjie; Yu, Honglei; Wang, Zhijun; Lin, Xin; Wang, Jincheng

2017-01-01

We present an investigation of secondary and tertiary branching behavior in diverging grain boundaries (GBs) between two columnar dendritic grains with different crystallographic orientations, both by two-dimensional phase-field simulations and thin-sample experiments. The stochasticity of the GB trajectories and the statistically averaged GB orientations were analyzed in detail. The side-branching dynamics and subsequent branch competition behaviors found in the simulations agreed well with the experimental results. When the orientations of two grains are given, the experimental results indicated that the average GB orientation was independent of the pulling velocity in the dendritic growth regime. The simulation and experimental results, as well as the results reported in the literature exhibit a uniform relation between the percentage of the whole gap region occupied by the favorably oriented grain and the difference in the absolute values of the secondary arm growth directions of the two competitive grains. By describing such a uniform relation with a simple fitting equation, we proposed a simple analytical model for the GB orientation at diverging GBs, which gives a more accurate description of GB orientation selection than the existing models.

Identification of vapor-phase chemical warfare agent simulants and rocket fuels using laser-induced breakdown spectroscopy

International Nuclear Information System (INIS)

Stearns, Jaime A.; McElman, Sarah E.; Dodd, James A.

2010-01-01

Application of laser-induced breakdown spectroscopy (LIBS) to the identification of security threats is a growing area of research. This work presents LIBS spectra of vapor-phase chemical warfare agent simulants and typical rocket fuels. A large dataset of spectra was acquired using a variety of gas mixtures and background pressures and processed using partial least squares analysis. The five compounds studied were identified with a 99% success rate by the best method. The temporal behavior of the emission lines as a function of chamber pressure and gas mixture was also investigated, revealing some interesting trends that merit further study.

Identification of vapor-phase chemical warfare agent simulants and rocket fuels using laser-induced breakdown spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Stearns, Jaime A.; McElman, Sarah E.; Dodd, James A.

2010-05-01

Application of laser-induced breakdown spectroscopy (LIBS) to the identification of security threats is a growing area of research. This work presents LIBS spectra of vapor-phase chemical warfare agent simulants and typical rocket fuels. A large dataset of spectra was acquired using a variety of gas mixtures and background pressures and processed using partial least squares analysis. The five compounds studied were identified with a 99% success rate by the best method. The temporal behavior of the emission lines as a function of chamber pressure and gas mixture was also investigated, revealing some interesting trends that merit further study.

Numerical simulation research on gas migration with Y type ventilation

Science.gov (United States)

Gou, Yanan; Han, Xuezheng

2018-01-01

The ventilation way of the working face has a great influence to goaf flow field and gas migration, the existing U-shaped ventilation face wind serious overrun, Y type ventilation mode is put forward, and the mathematic control equation of the gas moving rule is established. Put the Gaozhuang coal mine west five mining area as the model, set up calculation model. And the gas concentration is simulated, the simulation results show that the Y type ventilation ways can intercept goaf gas into the corner on the working plane and return air lane, effectively avoid the work of top corner gas accumulation.

MP CBM-Z V1.0: design for a new CBM-Z gas-phase chemical mechanism architecture for next generation processors

OpenAIRE

Wang, Hui; Lin, Junmin; Wu, Qizhong; Chen, Huansheng; Tang, Xiao; Wang, Zifa; Chen, Xueshun; Cheng, Huaqiong; Wang, Lanning

2018-01-01

Precise and rapid air quality simulation and forecasting are limited by the computation performance of the air quality model, and the gas-phase chemistry module is the most time-consuming function in the air quality model. In this study, we designed a new framework for the widely used Carbon Bond Mechanism Z (CBM-Z) gas-phase chemical kinetics kernel to adapt the Single Instruction Multiple Data (SIMD) technology in the next-generation processors for improving its calculation performance. The...

Grain-boundary engineering applied to grain growth in a high temperature material

International Nuclear Information System (INIS)

Huda, Z.

1993-01-01

Crystallography of grain boundaries are determined for a high temperature material, before and after grain growth processes, so as to study the induction of special properties useful for application in components of a gas-turbine engine. The philosophy of grain-boundary engineering is applied to grain growth in APK-6, a powder formed nickel-base superalloy so as to establish the possible structure/property relationships. The alloy in the as received condition is shown to possess a strong texture and contained coincident site lattices (CSL) boundaries with most boundaries having sigma values in the range of 3 > sigma > 25. A normal grain-growth heat treatment result in a good population of low angle grain boundaries, and drastically reduces the proportion of CSL boundaries. A strong [011] annealing texture is observed after an intermediate grain growth; most grain boundaries, here, tend to be high angle indicating a possibility of possessing special properties. (author)

Atmospheric dispersion simulations of volcanic gas from Miyake Island by SPEEDI

International Nuclear Information System (INIS)

Nagai, Haruyasu; Furuno, Akiko; Terada, Hiroaki; Umeyama, Nobuaki; Yamazawa, Hiromi; Chino, Masamichi

2001-03-01

Japan Atomic Energy Research Institute is advancing the study for prediction of material circulation in the environment to cope with environmental pollution, based on SPEEDI (System for Prediction of Environmental Emergency Dose Information) and WSPEEDI (Worldwide version of SPEEDI), which are originally developed aiming at real-time prediction of atmospheric dispersion of radioactive substances accidentally released from nuclear facility. As a part of this study, dispersion simulation of volcanic gas erupted from Miyake Island is put into practice. After the stench incident at the west Kanto District on 28 August 2000 caused by volcanic gas from Miyake Island, the following simulations dealing with atmospheric dispersion of volcanic gas from Miyake Island have been carried out. (1) Retrospective simulation to analyze examine the mechanism of the transport of high concentration volcanic gas to the west Kanto District on 28 August and to estimate the release amount of volcanic gas. (2) Retrospective simulation to analyze the mechanism of the transport of volcanic gas to Tokai and Kansai districts in a case of stench incident on 13 September. (3) Automated real-time simulation from the acquisition of meteorological data to the output of figures for operational prediction of the transport of volcanic gas to Tokai and Kanto districts. This report describes the details of these studies. (author)

Flexible Graphene-Based Wearable Gas and Chemical Sensors.

Science.gov (United States)

Singh, Eric; Meyyappan, M; Nalwa, Hari Singh

2017-10-11

Wearable electronics is expected to be one of the most active research areas in the next decade; therefore, nanomaterials possessing high carrier mobility, optical transparency, mechanical robustness and flexibility, lightweight, and environmental stability will be in immense demand. Graphene is one of the nanomaterials that fulfill all these requirements, along with other inherently unique properties and convenience to fabricate into different morphological nanostructures, from atomically thin single layers to nanoribbons. Graphene-based materials have also been investigated in sensor technologies, from chemical sensing to detection of cancer biomarkers. The progress of graphene-based flexible gas and chemical sensors in terms of material preparation, sensor fabrication, and their performance are reviewed here. The article provides a brief introduction to graphene-based materials and their potential applications in flexible and stretchable wearable electronic devices. The role of graphene in fabricating flexible gas sensors for the detection of various hazardous gases, including nitrogen dioxide (NO 2 ), ammonia (NH 3 ), hydrogen (H 2 ), hydrogen sulfide (H 2 S), carbon dioxide (CO 2 ), sulfur dioxide (SO 2 ), and humidity in wearable technology, is discussed. In addition, applications of graphene-based materials are also summarized in detecting toxic heavy metal ions (Cd, Hg, Pb, Cr, Fe, Ni, Co, Cu, Ag), and volatile organic compounds (VOCs) including nitrobenzene, toluene, acetone, formaldehyde, amines, phenols, bisphenol A (BPA), explosives, chemical warfare agents, and environmental pollutants. The sensitivity, selectivity and strategies for excluding interferents are also discussed for graphene-based gas and chemical sensors. The challenges for developing future generation of flexible and stretchable sensors for wearable technology that would be usable for the Internet of Things (IoT) are also highlighted.

Sticking properties of ice grains

Directory of Open Access Journals (Sweden)

Jongmanns M.

2017-01-01

Full Text Available We study the size dependence of pull-off forces of water ice in laboratory experiments and numerical simulations. To determine the pull-off force in our laboratory experiments, we use a liquid nitrogen cooled centrifuge. Depending on its rotation frequency, spherical ice grains detach due to the centrifugal force which is related to the adhesive properties. Numerical simulations are conducted by means of molecular dynamics simulations of hexagonal ice using a standard coarse-grained water potential. The pull-off force of a single contact between two spherical ice grains is measured due to strain controlled simulations. Both, the experimental study and the simulations reveal a dependence between the pull-off force and the (reduced particle radii, which differ significantly from the linear dependence of common contact theories.

Simulations of overall flow in gas centrifuge considering feed jet

International Nuclear Information System (INIS)

He Liang; Jiang Dongjun; Ying Chuntong

2010-01-01

A coupled method for the numerical solution of the flow in rapidly rotating gas centrifuge was presented. An iteration process of DSMC and CFD was performed to analyze the overall flow in radial direction, in which DSMC was adopted to simulate the rarefied region, and CFD was adopted to the counter-current of gas centrifuge to discrete the model equations. It was applied to simulate the 2D symmetrical flow model considering the rarefied region with the feed jet flow. A series of illustrative numerical examples were given. The flow structures of the feed jet in the rarefied gas flow region were shown. The results suggest that DSMC CFD coupled method is competent to the simulations of overall flow in a gas centrifuge. (authors)

Simulating the probability of grain sorghum maturity before the first frost in northeastern Colorado

Science.gov (United States)

Expanding grain sorghum [Sorghum bicolor (L.) Moench] production northward from southeastern Colorado is thought to be limited by shorter growing seasons due to lower temperatures and earlier frost dates. This study used a simulation model for predicting crop phenology (PhenologyMMS) to predict the ...

NEAMS FPL M2 Milestone Report: Development of a UO₂ Grain Size Model using Multicale Modeling and Simulation

Energy Technology Data Exchange (ETDEWEB)

Tonks, Michael R [Idaho National Lab. (INL), Idaho Falls, ID (United States); Zhang, Yongfeng [Idaho National Lab. (INL), Idaho Falls, ID (United States); Bai, Xianming [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2014-06-01

This report summarizes development work funded by the Nuclear Energy Advanced Modeling Simulation program's Fuels Product Line (FPL) to develop a mechanistic model for the average grain size in UO₂ fuel. The model is developed using a multiscale modeling and simulation approach involving atomistic simulations, as well as mesoscale simulations using INL's MARMOT code.

Grain fragmentation in ultrasonic-assisted TIG weld of pure aluminum.

Science.gov (United States)

Chen, Qihao; Lin, Sanbao; Yang, Chunli; Fan, Chenglei; Ge, Hongliang

2017-11-01

Under the action of acoustic waves during an ultrasonic-assisted tungsten inert gas (TIG) welding process, a grain of a TIG weld of aluminum alloy is refined by nucleation and grain fragmentation. Herein, effects of ultrasound on grain fragmentation in the TIG weld of aluminum alloy are investigated via systematic welding experiments of pure aluminum. First, experiments involving continuous and fixed-position welding are performed, which demonstrate that ultrasound can break the grain of the TIG weld of pure aluminum. The microstructural characteristics of an ultrasonic-assisted TIG weld fabricated by fixed-position welding are analyzed. The microstructure is found to transform from plane crystal, columnar crystal, and uniform equiaxed crystal into plane crystal, deformed columnar crystal, and nonuniform equiaxed crystal after application of ultrasound. Second, factors influencing ultrasonic grain fragmentation are investigated. The ultrasonic amplitude and welding current are found to have a considerable effect on grain fragmentation. The degree of fragmentation first increases and then decreases with an increase in ultrasonic amplitude, and it increases with an increase in welding current. Measurement results of the vibration of the weld pool show that the degree of grain fragmentation is related to the intensity of acoustic nonlinearity in the weld pool. The greater the intensity of acoustic nonlinearity, the greater is the degree of grain fragmentation. Finally, the mechanism of ultrasonic grain fragmentation in the TIG weld of pure aluminum is discussed. A finite element simulation is used to simulate the acoustic pressure and flow in the weld pool. The acoustic pressure in the weld pool exceeds the cavitation threshold, and cavitation bubbles are generated. The flow velocity in the weld pool does not change noticeably after application of ultrasound. It is concluded that the high-pressure conditions induced during the occurrence of cavitation, lead to grain

UNRES server for physics-based coarse-grained simulations and prediction of protein structure, dynamics and thermodynamics.

Science.gov (United States)

Czaplewski, Cezary; Karczynska, Agnieszka; Sieradzan, Adam K; Liwo, Adam

2018-04-30

A server implementation of the UNRES package (http://www.unres.pl) for coarse-grained simulations of protein structures with the physics-based UNRES model, coined a name UNRES server, is presented. In contrast to most of the protein coarse-grained models, owing to its physics-based origin, the UNRES force field can be used in simulations, including those aimed at protein-structure prediction, without ancillary information from structural databases; however, the implementation includes the possibility of using restraints. Local energy minimization, canonical molecular dynamics simulations, replica exchange and multiplexed replica exchange molecular dynamics simulations can be run with the current UNRES server; the latter are suitable for protein-structure prediction. The user-supplied input includes protein sequence and, optionally, restraints from secondary-structure prediction or small x-ray scattering data, and simulation type and parameters which are selected or typed in. Oligomeric proteins, as well as those containing D-amino-acid residues and disulfide links can be treated. The output is displayed graphically (minimized structures, trajectories, final models, analysis of trajectory/ensembles); however, all output files can be downloaded by the user. The UNRES server can be freely accessed at http://unres-server.chem.ug.edu.pl.

Grain scale simulation of multiphase flow through porous media; Simulacao em escala granular do escoamento multifasico em meio poroso

Energy Technology Data Exchange (ETDEWEB)

Domingos, Ricardo Golghetto; Cheng, Liang-Yee [Universidade de Sao Paulo (USP), SP (Brazil). Escola Politecnica

2012-07-01

Since the grain scale modeling of multi-phase flow in porous media is of great interest for the oil industry, the aim of the present research is to show an implementation of Moving Particle Semi-Implicit (MPS) method for the grain scale simulation of multi-phase flow in porous media. Geometry data obtained by a high-resolution CT scan of a sandstone sample has been used as input for the simulations. The results of the simulations performed considering different resolutions are given, the head loss and permeability obtained numerically, as well as the influence of the wettability of the fluids inside the sample of the reservoir's sandstone. (author)

Simulating the evolution of glyphosate resistance in grains farming in northern Australia.

Science.gov (United States)

Thornby, David F; Walker, Steve R

2009-09-01

The evolution of resistance to herbicides is a substantial problem in contemporary agriculture. Solutions to this problem generally consist of the use of practices to control the resistant population once it evolves, and/or to institute preventative measures before populations become resistant. Herbicide resistance evolves in populations over years or decades, so predicting the effectiveness of preventative strategies in particular relies on computational modelling approaches. While models of herbicide resistance already exist, none deals with the complex regional variability in the northern Australian sub-tropical grains farming region. For this reason, a new computer model was developed. The model consists of an age- and stage-structured population model of weeds, with an existing crop model used to simulate plant growth and competition, and extensions to the crop model added to simulate seed bank ecology and population genetics factors. Using awnless barnyard grass (Echinochloa colona) as a test case, the model was used to investigate the likely rate of evolution under conditions expected to produce high selection pressure. Simulating continuous summer fallows with glyphosate used as the only means of weed control resulted in predicted resistant weed populations after approx. 15 years. Validation of the model against the paddock history for the first real-world glyphosate-resistant awnless barnyard grass population shows that the model predicted resistance evolution to within a few years of the real situation. This validation work shows that empirical validation of herbicide resistance models is problematic. However, the model simulates the complexities of sub-tropical grains farming in Australia well, and can be used to investigate, generate and improve glyphosate resistance prevention strategies.

Ionizing radiation for insect control in grain and grain products

International Nuclear Information System (INIS)

Tilton, E.W.; Brower, J.H.

1987-01-01

A technical review summarizes and discusses information on various aspects of the use of ionizing radiation for the control of insect infestation in grains and grain products. Topics include: the effects of ionizing radiation on insects infesting stored-grain products; the 2 main types of irradiators (electron accelerators; radioisotopes (e.g.: Co-60; Cs-137); dosimetry systems and methodology; variations in radiation resistance by stored-product pests; the proper selection of radiation dose; the effects of combining various treatments (temperature, infrared/microwave radiation, hypoxia, chemicals) with ionizing radiation; sublethal radiation for controlling bulk grain insects; the feeding capacity of irradiated insects; the susceptibility of insecticide-resistant insects to ionizing radiation; and the possible resistance of insects to ionizing radiation. Practical aspects of removing insects from irradiated grain also are discussed

Simulating the Probability of Grain Sorghum Maturity before the First Frost in Northeastern Colorado

Directory of Open Access Journals (Sweden)

Gregory S. McMaster

2016-09-01

Full Text Available Expanding grain sorghum [Sorghum bicolor (L. Moench] production northward from southeastern Colorado is thought to be limited by shorter growing seasons due to lower temperatures and earlier frost dates. This study used a simulation model for predicting crop phenology (PhenologyMMS to estimate the probability of reaching physiological maturity before the first fall frost for a variety of agronomic practices in northeastern Colorado. Physiological maturity for seven planting dates (1 May to 12 June, four seedbed moisture conditions affecting seedling emergence (from Optimum to Planted in Dust, and three maturity classes (Early, Medium, and Late were simulated using historical weather data from nine locations for both irrigated and dryland phenological parameters. The probability of reaching maturity before the first frost was slightly higher under dryland conditions, decreased as latitude, longitude, and elevation increased, planting date was delayed, and for later maturity classes. The results provide producers with estimates of the reliability of growing grain sorghum in northeastern Colorado.

TEMPERATURE SPECTRA OF INTERSTELLAR DUST GRAINS HEATED BY COSMIC RAYS. I. TRANSLUCENT CLOUDS

Energy Technology Data Exchange (ETDEWEB)

Kalvāns, Juris, E-mail: juris.kalvans@venta.lv [Engineering Research Institute “Ventspils International Radio Astronomy Center” of Ventspils University College, Inzenieru 101, Ventspils, LV-3601 (Latvia)

2016-06-01

Heating of whole interstellar dust grains by cosmic-ray (CR) particles affects the gas–grain chemistry in molecular clouds by promoting molecule desorption, diffusion, and chemical reactions on grain surfaces. The frequency of such heating, f{sub T}, s{sup −1}, determines how often a certain temperature T{sub CR}, K, is reached for grains hit by CR particles. This study aims to provide astrochemists with a comprehensive and updated data set on CR-induced whole-grain heating. We present calculations of f{sub T} and T{sub CR} spectra for bare olivine grains with radius a of 0.05, 0.1, and 0.2 μ m and such grains covered with ice mantles of thickness 0.1 a and 0.3 a . Grain shape and structure effects are considered, as well as 30 CR elemental constituents with an updated energy spectrum corresponding to a translucent cloud with A{sub V} = 2 mag. Energy deposition by CRs in grain material was calculated with the srim program. We report full T{sub CR} spectra for all nine grain types and consider initial grain temperatures of 10 K and 20 K. We also provide frequencies for a range of minimum T{sub CR} values. The calculated data set can be simply and flexibly implemented in astrochemical models. The results show that, in the case of translucent clouds, the currently adopted rate for heating of whole grains to temperatures in excess of 70 K is underestimated by approximately two orders of magnitude in astrochemical numerical simulations. Additionally, grains are heated by CRs to modest temperatures (20–30 K) with intervals of a few years, which reduces the possibility of ice chemical explosions.

Dual-Function Metal-Organic Framework as a Versatile Catalyst for Detoxifying Chemical Warfare Agent Simulants.

Science.gov (United States)

Liu, Yangyang; Moon, Su-Young; Hupp, Joseph T; Farha, Omar K

2015-12-22

The nanocrystals of a porphyrin-based zirconium(IV) metal-organic framework (MOF) are used as a dual-function catalyst for the simultaneous detoxification of two chemical warfare agent simulants at room temperature. Simulants of nerve agent (such as GD, VX) and mustard gas, dimethyl 4-nitrophenyl phosphate and 2-chloroethyl ethyl sulfide, have been hydrolyzed and oxidized, respectively, to nontoxic products via a pair of pathways catalyzed by the same MOF. Phosphotriesterase-like activity of the Zr6-containing node combined with photoactivity of the porphyrin linker gives rise to a versatile MOF catalyst. In addition, bringing the MOF crystals down to the nanoregime leads to acceleration of the catalysis.

Equi-axed and columnar grain growth in UO2

International Nuclear Information System (INIS)

White, R.J.

1997-01-01

The grain size of UO 2 is an important parameter in the actual performance and the modelling of the performance of reactor fuel elements. Many processes depend critically on the grain size, for example, the degree of initial densification, the evolution rate of stable fission gases, the release rates of radiologically hazardous fission products, the fission gas bubble swelling rates and the fuel creep. Many of these processes are thermally activated and further impact on the fuel thermal behavior thus creating complex feedback processes. In order to model the fuel performance accurately it is necessary to model the evolution of the fuel grain radius. When UO 2 is irradiated, the fission gases xenon and krypton are created from the fissioning uranium nucleus. At high temperatures these gases diffuse rapidly to the grain boundaries where they nucleate immobile lenticular shaped fission gas bubbles. In this paper the Hillert grain growth model is adapted to account for the inhibiting ''Zener'' effects of grain boundary fission gas porosity on grain boundary mobility and hence grain growth. It is shown that normal grain growth ceases at relatively low levels of irradiation. At high burnups, high temperatures and in regions of high temperature gradients, columnar grain growth is often observed, in some cases extending over more than fifty percent of the fuel radius. The model is further extended to account for the de-pinning of grains in the radial direction by the thermal gradient induced force on a fission gas grain boundary bubble. The observed columnar/equi-axed boundary is in fair agreement with the predictions of an evaporation/condensation model. The grain growth model described in this paper requires information concerning the scale of grain boundary porosity, the local fuel temperature and the local temperature gradient. The model is currently used in the Nuclear Electric version of the ENIGMA fuel modelling code. (author). 14 refs, 3 figs, 1 tab

Grain dynamics and inter-grain coupling in dusty plasma Coulomb crystals

International Nuclear Information System (INIS)

Rahman, H.U.; Mohideen, U.; Smith, M.A.; Rosenberg, M.; Mendis, D.A.

2001-01-01

We review our results on the lattice structure and the lattice dynamics of dusty plasma Coulomb crystals formed in rectangular conductive grooves. The basic structure appears to be made of mutually repulsive columns of grains confined by the walls of the groove. The columns are oriented along the direction of the electrode sheath electric field. Inter-grain coupling as a function of plasma temperature and density were investigated by measurement of these parameters. A simple phenomenological model wherein the inter-grain spacing along the column results from an attractive electric field induced dipole-dipole force balanced by a repulsive monopole Coulomb force is consistent with observed features of the Coulomb crystal. In addition, here we present some preliminary measurements of the vibration and rotation dynamics of the individual grains in the Coulomb crystal. The thermal energy of the dust grain thus calculated is much less than the inter-grain Coulomb potential energy as required for the formation of stable structures. Also the observed rotational frequency is consistent with the assumption of thermal equilibrium between the dust grains and the neutral gas. (orig.)

Compositional simulations of producing oil-gas ratio behaviour in low permeable gas condensate reservoir

OpenAIRE

Gundersen, Pål Lee

2013-01-01

Master's thesis in Petroleum engineering Gas condensate flow behaviour below the dew point in low permeable formations can make accurate fluid sampling a difficult challenge. The objective of this study was to investigate the producing oil-gas ratio behaviour in the infinite-acting period for a low permeable gas condensate reservoir. Compositional isothermal flow simulations were performed using a single-layer, radial and two-dimensional, gas condensate reservoir model with low permeabili...

Experiences on dynamic simulation software in chemical engineering education

DEFF Research Database (Denmark)

Komulainen, Tiina M.; Enemark-rasmussen, Rasmus; Sin, Gürkan

2012-01-01

Commercial process simulators are increasing interest in the chemical engineer education. In this paper, the use of commercial dynamic simulation software, D-SPICE® and K-Spice®, for three different chemical engineering courses is described and discussed. The courses cover the following topics...

Effect of ozone gas processing on physical and chemical properties ...

African Journals Online (AJOL)

Purpose: To investigate the effects of ozone treatment on chemical and physical properties of wheat (Triticum aestivum L.) gluten, glutenin and gliadin. Methods: Wheat proteins isolated from wheat flour were treated with ozone gas. The physical and chemical properties of gluten proteins were investigated after treatment ...

Prediction of the Grain-Microstructure Evolution Within a Friction Stir Welding (FSW) Joint via the Use of the Monte Carlo Simulation Method

Science.gov (United States)

Grujicic, M.; Ramaswami, S.; Snipes, J. S.; Avuthu, V.; Galgalikar, R.; Zhang, Z.

2015-09-01

A thermo-mechanical finite element analysis of the friction stir welding (FSW) process is carried out and the evolution of the material state (e.g., temperature, the extent of plastic deformation, etc.) monitored. Subsequently, the finite-element results are used as input to a Monte-Carlo simulation algorithm in order to predict the evolution of the grain microstructure within different weld zones, during the FSW process and the subsequent cooling of the material within the weld to room temperature. To help delineate different weld zones, (a) temperature and deformation fields during the welding process, and during the subsequent cooling, are monitored; and (b) competition between the grain growth (driven by the reduction in the total grain-boundary surface area) and dynamic-recrystallization grain refinement (driven by the replacement of highly deformed material with an effectively "dislocation-free" material) is simulated. The results obtained clearly revealed that different weld zones form as a result of different outcomes of the competition between the grain growth and grain refinement processes.

THE L1157-B1 ASTROCHEMICAL LABORATORY: MEASURING THE TRUE FORMALDEHYDE DEUTERATION ON GRAIN MANTLES

International Nuclear Information System (INIS)

Fontani, F.; Codella, C.; Ceccarelli, C.; Lefloch, B.; Viti, S.; Benedettini, M.

2014-01-01

L1157 is a prototypical chemically active outflow driven by a low-mass class-0 protostar, and B1 is its brightest bow shock. Toward L1157-B1, several emission lines of deuterated molecules have been detected for the first time by Codella et al. The authors suggested that these were formed on grain mantles, and then released into the gas phase by the passage of the shock. In this Letter we report observations obtained at high angular resolution with the Plateau de Bure Interferometer of HDCO and CH 2 DOH. The emission of HDCO perfectly delineates the region of the interface between the fast jet and the slower ambient material, confirming the predictions of the previous work that deuterated species were formed on grain mantles and then released into the gas phase by the passage of the shock. CH 2 DOH emission is fainter and thus its emitting region is not well determined. The deuterated fraction HDCO/H 2 CO is ∼0.1 in the HDCO emitting region, an order of magnitude larger than the upper limit found in the surrounding material, probably dominated by warm-gas chemistry and less affected by grain evaporation. Our study represents the first clear evidence ever found of a deuterated molecule as shock tracer, and yields an indirect but ''clean'' measurement of the deuteration of the ices covering the dust grains during the cold pre-protostellar phase

Conservative and dissipative force field for simulation of coarse-grained alkane molecules: A bottom-up approach

Energy Technology Data Exchange (ETDEWEB)

Trément, Sébastien; Rousseau, Bernard, E-mail: bernard.rousseau@u-psud.fr [Laboratoire de Chimie-Physique, UMR 8000 CNRS, Université Paris-Sud, Orsay (France); Schnell, Benoît; Petitjean, Laurent; Couty, Marc [Manufacture Française des Pneumatiques MICHELIN, Centre de Ladoux, 23 place des Carmes, 63000 Clermont-Ferrand (France)

2014-04-07

We apply operational procedures available in the literature to the construction of coarse-grained conservative and friction forces for use in dissipative particle dynamics (DPD) simulations. The full procedure rely on a bottom-up approach: large molecular dynamics trajectories of n-pentane and n-decane modeled with an anisotropic united atom model serve as input for the force field generation. As a consequence, the coarse-grained model is expected to reproduce at least semi-quantitatively structural and dynamical properties of the underlying atomistic model. Two different coarse-graining levels are studied, corresponding to five and ten carbon atoms per DPD bead. The influence of the coarse-graining level on the generated force fields contributions, namely, the conservative and the friction part, is discussed. It is shown that the coarse-grained model of n-pentane correctly reproduces self-diffusion and viscosity coefficients of real n-pentane, while the fully coarse-grained model for n-decane at ambient temperature over-predicts diffusion by a factor of 2. However, when the n-pentane coarse-grained model is used as a building block for larger molecule (e.g., n-decane as a two blobs model), a much better agreement with experimental data is obtained, suggesting that the force field constructed is transferable to large macro-molecular systems.

Development of a Persistent Chemical Agent Simulator System (PCASS)

Science.gov (United States)

Mcginness, W. G.

1983-01-01

The development of a persistent chemical agent simulation system (PCASS) is described. This PCASS is to be used for the military training of troops to simulate actual chemical warfare. The purpose of this system is to facilitate in the determination of chemical contamination and effectiveness of decontamination for training purposes. The fluorescent tracer employed has no daylight activation, but yet is easily removed with a decontaminate solution or water and surfactants. Also employed is a time delayed color developing system. When an individual is subjected to the PCASS and does not decontaminate adequately, red blotches or red coloration will develop as a function of time and temperature. The intent of this is to simulate the delayed chemical reaction of mustard contaminates.

Influence of thermal barrier effect of grain boundaries on bulk cascades in alpha-zirconium revealed by molecular dynamics simulation

Energy Technology Data Exchange (ETDEWEB)

Jin, Yanan; Lai, Wensheng, E-mail: wslai@tsinghua.edu.cn

2016-03-15

The effect of grain boundaries (GBs) on bulk cascades in nano-structured alpha-zirconium has been studied by molecular dynamics (MD) simulations. It turns out that the existence of GBs increases the defect productivity in grains, suggesting that the GBs may act as a thermal barrier and postpone the annihilation of defects within grains. Moreover, it is found that the thermal barrier effect of GBs facilitates the shift of symmetric tilt GBs to the grain with higher temperature, and the smaller the tilt angle is, the easier the boundary shift will be. Thus, the influence of GBs on radiation damage in the nano-structured materials comes from the competition between damage increase in grains and defect annihilation at GBs.

Force-field parameters from the SAFT-γ equation of state for use in coarse-grained molecular simulations.

Science.gov (United States)

Müller, Erich A; Jackson, George

2014-01-01

A description of fluid systems with molecular-based algebraic equations of state (EoSs) and by direct molecular simulation is common practice in chemical engineering and the physical sciences, but the two approaches are rarely closely coupled. The key for an integrated representation is through a well-defined force field and Hamiltonian at the molecular level. In developing coarse-grained intermolecular potential functions for the fluid state, one typically starts with a detailed, bottom-up quantum-mechanical or atomic-level description and then integrates out the unwanted degrees of freedom using a variety of techniques; an iterative heuristic simulation procedure is then used to refine the parameters of the model. By contrast, with a top-down technique, one can use an accurate EoS to link the macroscopic properties of the fluid and the force-field parameters. We discuss the latest developments in a top-down representation of fluids, with a particular focus on a group-contribution formulation of the statistical associating fluid theory (SAFT-γ). The accurate SAFT-γ EoS is used to estimate the parameters of the Mie force field, which can then be used with confidence in direct molecular simulations to obtain thermodynamic, structural, interfacial, and dynamical properties that are otherwise inaccessible from the EoS. This is exemplified for several prototypical fluids and mixtures, including carbon dioxide, hydrocarbons, perfluorohydrocarbons, and aqueous surfactants.

Using cheminformatics to find simulants for chemical warfare agents

Energy Technology Data Exchange (ETDEWEB)

Lavoie, J.; Srinivasan, Sree [Molecular Sciences and Engineering Team, U.S. Army Natick Soldier Research, Development and Engineering Center, 15 Kansas Street, Natick, MA 01760 (United States); Nagarajan, R., E-mail: Ramanathan.Nagarajan@us.army.mil [Molecular Sciences and Engineering Team, U.S. Army Natick Soldier Research, Development and Engineering Center, 15 Kansas Street, Natick, MA 01760 (United States)

2011-10-30

Highlights: {yields} Summary of chemical warfare agent (CWA) simulants in current use. {yields} Application of method of molecular similarity to CWA and simulants. {yields} Quantitative metric for CWA-simulant similarity. {yields} Rank ordering of simulants in current use. {yields} Potential of method to identify simulants for emerging agents. - Abstract: Direct experimentation with chemical warfare agents (CWA) to study important problems such as their permeation across protective barrier materials, decontamination of equipment and facilities, or the environmental transport and fate of CWAs is not feasible because of the obvious toxicity of the CWAs and associated restrictions on their laboratory use. The common practice is to use 'simulants,' namely, analogous chemicals that closely resemble the CWAs but are less toxic, with the expectation that the results attained for simulants can be correlated to how the CWAs would perform. Simulants have been traditionally chosen by experts, by means of intuition, using similarity in one or more physical properties (such as vapor pressure or aqueous solubility) or in the molecular structural features (such as functional groups) between the stimulant and the CWA. This work is designed to automate the simulant identification process backed by quantitative metrics, by means of chemical similarity search software routinely used in pharmaceutical drug discovery. The question addressed here is: By the metrics of such software, how similar are traditional simulants to CWAs? That is, what is the numerical 'distance' between each CWA and its customary simulants in the quantitative space of molecular descriptors? The answers show promise for finding close but less toxic simulants for the ever-increasing numbers of CWAs objectively and fast.

Using cheminformatics to find simulants for chemical warfare agents

International Nuclear Information System (INIS)

Lavoie, J.; Srinivasan, Sree; Nagarajan, R.

2011-01-01

Highlights: → Summary of chemical warfare agent (CWA) simulants in current use. → Application of method of molecular similarity to CWA and simulants. → Quantitative metric for CWA-simulant similarity. → Rank ordering of simulants in current use. → Potential of method to identify simulants for emerging agents. - Abstract: Direct experimentation with chemical warfare agents (CWA) to study important problems such as their permeation across protective barrier materials, decontamination of equipment and facilities, or the environmental transport and fate of CWAs is not feasible because of the obvious toxicity of the CWAs and associated restrictions on their laboratory use. The common practice is to use 'simulants,' namely, analogous chemicals that closely resemble the CWAs but are less toxic, with the expectation that the results attained for simulants can be correlated to how the CWAs would perform. Simulants have been traditionally chosen by experts, by means of intuition, using similarity in one or more physical properties (such as vapor pressure or aqueous solubility) or in the molecular structural features (such as functional groups) between the stimulant and the CWA. This work is designed to automate the simulant identification process backed by quantitative metrics, by means of chemical similarity search software routinely used in pharmaceutical drug discovery. The question addressed here is: By the metrics of such software, how similar are traditional simulants to CWAs? That is, what is the numerical 'distance' between each CWA and its customary simulants in the quantitative space of molecular descriptors? The answers show promise for finding close but less toxic simulants for the ever-increasing numbers of CWAs objectively and fast.

DUST PROPERTIES AND DISK STRUCTURE OF EVOLVED PROTOPLANETARY DISKS IN Cep OB2: GRAIN GROWTH, SETTLING, GAS AND DUST MASS, AND INSIDE-OUT EVOLUTION

International Nuclear Information System (INIS)

Sicilia-Aguilar, Aurora; Henning, Thomas; Dullemond, Cornelis P.; Bouwman, Jeroen; Sturm, Bernhard; Patel, Nimesh; Juhász, Attila

2011-01-01

We present Spitzer/Infrared Spectrograph spectra of 31 T Tauri stars (TTS) and IRAM/1.3 mm observations for 34 low- and intermediate-mass stars in the Cep OB2 region. Including our previously published data, we analyze 56 TTS and 3 intermediate-mass stars with silicate features in Tr 37 (∼4 Myr) and NGC 7160 (∼12 Myr). The silicate emission features are well reproduced with a mixture of amorphous (with olivine, forsterite, and silica stoichiometry) and crystalline grains (forsterite, enstatite). We explore grain size and disk structure using radiative transfer disk models, finding that most objects have suffered substantial evolution (grain growth, settling). About half of the disks show inside-out evolution, with either dust-cleared inner holes or a radially dependent dust distribution, typically with larger grains and more settling in the innermost disk. The typical strong silicate features nevertheless require the presence of small dust grains, and could be explained by differential settling according to grain size, anomalous dust distributions, and/or optically thin dust populations within disk gaps. M-type stars tend to have weaker silicate emission and steeper spectral energy distributions than K-type objects. The inferred low dust masses are in a strong contrast with the relatively high gas accretion rates, suggesting global grain growth and/or an anomalous gas-to-dust ratio. Transition disks in the Cep OB2 region display strongly processed grains, suggesting that they are dominated by dust evolution and settling. Finally, the presence of rare but remarkable disks with strong accretion at old ages reveals that some very massive disks may still survive to grain growth, gravitational instabilities, and planet formation.

Coarse-grained Simulations of Substrate Export through Multidrug Efflux Transporter AcrB

Science.gov (United States)

Jewel, Yead; Dutta, Prashanta; Liu, Jin

2017-11-01

The treatment of bacterial infectious diseases hampered by the overexpression of multidrug resistance (MDR) systems. The MDR system actively pumps the antibiotic drugs as well as other toxic compounds out of the cells. During the pumping, AcrB (one of the key MDR components) undergoes a series of large-scale proton/substrate dependent conformational changes. In this work, we implement a hybrid coarse-grained PACE force field that couples the united-atom protein model with the coarse-grained MARTINI water/lipid, to investigate the conformational changes of AcrB. We first develop the substrate force field which is compatible with PACE, then we implement the force field to explore large scale structural changes of AcrB in microsecond simulations. The effects of the substrate and the protonation states of two key residues: Asp407 and Asp408, are investigated. Our results show that the drug export through AcrB is proton as well as substrate dependent. Our simulations explain molecular mechanisms of substrate transport through AcrB complex, as well as provide valuable insights for designing proper antibiotic drugs. Research reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under Award Number R01GM122081.

The shear response of copper bicrystals with Σ11 symmetric and asymmetric tilt grain boundaries by molecular dynamics simulation

Science.gov (United States)

Zhang, Liang; Lu, Cheng; Tieu, Kiet; Zhao, Xing; Pei, Linqing

2015-04-01

Grain boundaries (GBs) are important microstructure features and can significantly affect the properties of nanocrystalline materials. Molecular dynamics simulation was carried out in this study to investigate the shear response and deformation mechanisms of symmetric and asymmetric Σ11 tilt GBs in copper bicrystals. Different deformation mechanisms were reported, depending on GB inclination angles and equilibrium GB structures, including GB migration coupled to shear deformation, GB sliding caused by local atomic shuffling, and dislocation nucleation from GB. The simulation showed that migrating Σ11(1 1 3) GB under shear can be regarded as sliding of GB dislocations and their combination along the boundary plane. A non-planar structure with dissociated intrinsic stacking faults was prevalent in Σ11 asymmetric GBs of Cu. This type of structure can significantly increase the ductility of bicrystal models under shear deformation. A grain boundary can be a source of dislocation and migrate itself at different stress levels. The intrinsic free volume involved in the grain boundary area was correlated with dislocation nucleation and GB sliding, while the dislocation nucleation mechanism can be different for a grain boundary due to its different equilibrium structures.Grain boundaries (GBs) are important microstructure features and can significantly affect the properties of nanocrystalline materials. Molecular dynamics simulation was carried out in this study to investigate the shear response and deformation mechanisms of symmetric and asymmetric Σ11 tilt GBs in copper bicrystals. Different deformation mechanisms were reported, depending on GB inclination angles and equilibrium GB structures, including GB migration coupled to shear deformation, GB sliding caused by local atomic shuffling, and dislocation nucleation from GB. The simulation showed that migrating Σ11(1 1 3) GB under shear can be regarded as sliding of GB dislocations and their combination along the

Modelling and Simulation of Gas Engines Using Aspen HYSYS

Directory of Open Access Journals (Sweden)

M. C. Ekwonu

2013-12-01

Full Text Available In this paper gas engine model was developed in Aspen HYSYS V7.3 and validated with Waukesha 16V275GL+ gas engine. Fuel flexibility, fuel types and part load performance of the gas engine were investigated. The design variability revealed that the gas engine can operate on poor fuel with low lower heating value (LHV such as landfill gas, sewage gas and biogas with biogas offering potential integration with bottoming cycles when compared to natural gas. The result of the gas engine simulation gave an efficiency 40.7% and power output of 3592kW.

Analysis of nanowire transistor based nitrogen dioxide gas sensor – A simulation study

Directory of Open Access Journals (Sweden)

Gaurav Saxena

2015-06-01

Full Text Available Sensors sensitivity, selectivity and stability has always been a prime design concern for gas sensors designers. Modeling and simulation of gas sensors aids the designers in improving their performance. In this paper, different routes for the modeling and simulation of a semiconducting gas sensor is presented. Subsequently, by employing one of the route, the response of Zinc Oxide nanowire transistor towards nitrogen dioxide ambient is simulated. In addition to the sensing mechanism, simulation study of gas species desorption by applying a recovery voltage is also presented.

Transient β-hairpin formation in α-synuclein monomer revealed by coarse-grained molecular dynamics simulation

Energy Technology Data Exchange (ETDEWEB)

Yu, Hang; Ma, Wen [Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Han, Wei [Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Schulten, Klaus, E-mail: kschulte@ks.uiuc.edu [Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

2015-12-28

Parkinson’s disease, originating from the intrinsically disordered peptide α-synuclein, is a common neurodegenerative disorder that affects more than 5% of the population above age 85. It remains unclear how α-synuclein monomers undergo conformational changes leading to aggregation and formation of fibrils characteristic for the disease. In the present study, we perform molecular dynamics simulations (over 180 μs in aggregated time) using a hybrid-resolution model, Proteins with Atomic details in Coarse-grained Environment (PACE), to characterize in atomic detail structural ensembles of wild type and mutant monomeric α-synuclein in aqueous solution. The simulations reproduce structural properties of α-synuclein characterized in experiments, such as secondary structure content, long-range contacts, chemical shifts, and {sup 3}J(H{sub N}H{sub C{sub α}})-coupling constants. Most notably, the simulations reveal that a short fragment encompassing region 38-53, adjacent to the non-amyloid-β component region, exhibits a high probability of forming a β-hairpin; this fragment, when isolated from the remainder of α-synuclein, fluctuates frequently into its β-hairpin conformation. Two disease-prone mutations, namely, A30P and A53T, significantly accelerate the formation of a β-hairpin in the stated fragment. We conclude that the formation of a β-hairpin in region 38-53 is a key event during α-synuclein aggregation. We predict further that the G47V mutation impedes the formation of a turn in the β-hairpin and slows down β-hairpin formation, thereby retarding α-synuclein aggregation.

Effect of hydrogen environment on the separation of Fe grain boundaries

International Nuclear Information System (INIS)

Wang, Shuai; Martin, May L.; Robertson, Ian M.; Sofronis, Petros

2016-01-01

A density-functional theory based empirical potential was used to explore the energies of different types of Fe grain boundaries and free surfaces in thermodynamic equilibrium with a hydrogen environment. The classical model for calculating the ideal work of separation with solute atoms is extended to account for every trapping site. This yields the lowest-energy structures at different hydrogen chemical potentials (or gas pressures). At hydrogen gas pressures lower than 1000 atm, the reduction of the reversible work of separation is less than 33% and it increases to 36% at a gas pressure of 5000 atm. Near the hydride formation limit, 5 × 10 4  atm, the reduction is 44%. Based on the magnitude of these reductions for complete decohesion, and accounting for experimental observations of the microstructure associated with hydrogen-induced intergranular fracture of Fe, it is posited that hydrogen-enhanced plasticity and attendant effects establish the local conditions responsible for the transition in fracture mode from transgranular to intergranular. The conclusion is reached that intergranular failure occurs by a reduction of the cohesive energy but with contributions from structural as well as compositional changes in the grain boundary that are driven by hydrogen-enhanced plasticity processes.

Effect of different methods of soil fertility increasing via application of organic, chemical and biological fertilizers on grain yield and quality of canola (Brassica napus L.

Directory of Open Access Journals (Sweden)

K. Mohammadi

2016-05-01

Full Text Available Different resource of fertilizers had an effect on grain yield, oil and grain quality. Information regarding the effect of simultaneous application of organic, chemical and biological fertilizers on canola (Brassica napus L. traits is not available. In order to study the effect of different systems of soil fertility on grain yield and quality of canola (Talayeh cultivar, an experiment was conducted at experimental farm of Agricultural Research Center of Sanandaj, Iran, during two growing seasons of 2007-2008 and 2008-2009. The experimental units were arranged as split plots based on randomized complete blocks design with three replications. Main plots consisted of five methods for obtaining the basal fertilizers requirement including (N1: farm yard manure; (N2: compost; (N3: chemical fertilizers; (N4: farm yard manure + compost and (N5: farm yard manure + compost + chemical fertilizers; and control (N6. Sub plots consisted four levels of biofertilizers were (B1: Bacillus lentus and Pseudomonas putida; (B2: Trichoderma harzianum; (B3: Bacillus lentus and Pseudomonas putida and Trichoderma harzianum; and (B4: control, (without biofertilizers. Results showed that basal fertilizers and biofertilizers have a significant effect on grain yield. The highest grain yield was obtained from N5 treatment in which organic and chemical fertilizers were applied simultaneously applied. Basal fertilizers, biofertilizers have a significant effect on leaf chlorophyll. The highest nitrogen content (42.85 mg.g-1 and least amount of (N/S were obtained from N5 treatment. The highest oil percent was obtained from N1 and N2 treatments and highest oil yield was obtained from N5 treatment. Finally, application of organic manure and biofertilizers with chemical fertilizer led to an increase in yield and quality of canola grain.

Simulation of ion beam scattering in a gas stripper

Energy Technology Data Exchange (ETDEWEB)

Maxeiner, Sascha, E-mail: maxeiner@phys.ethz.ch; Suter, Martin; Christl, Marcus; Synal, Hans-Arno

2015-10-15

Ion beam scattering in the gas stripper of an accelerator mass spectrometer (AMS) enlarges the beam phase space and broadens its energy distribution. As the size of the injected beam depends on the acceleration voltage through phase space compression, the stripper becomes a limiting factor of the overall system transmission especially for low energy AMS system in the sub MV region. The spatial beam broadening and collisions with the accelerator tube walls are a possible source for machine background and energy loss fluctuations influence the mass resolution and thus isotope separation. To investigate the physical processes responsible for these effects, a computer simulation approach was chosen. Monte Carlo simulation methods are applied to simulate elastic two body scattering processes in screened Coulomb potentials in a (gas) stripper and formulas are derived to correctly determine random collision parameters and free path lengths for arbitrary (and non-homogeneous) gas densities. A simple parametric form for the underlying scattering cross sections is discussed which features important scaling behaviors. An implementation of the simulation was able to correctly model the data gained with the TANDY AMS system at ETH Zurich. The experiment covered transmission measurements of uranium ions in helium and beam profile measurements after the ion beam passed through the He-stripper. Beam profiles measured up to very high stripper densities could be understood in full system simulations including the relevant ion optics. The presented model therefore simulates the fundamental physics of the interaction between an ion beam and a gas stripper reliably. It provides a powerful and flexible tool for optimizing existing AMS stripper geometries and for designing new, state of the art low energy AMS systems.

Influência de cortes similando pastejo na composição química de grãos de cereais de inverno Cut effects simulating grazing on the chemical composition of grains of winter cereals

Directory of Open Access Journals (Sweden)

Leo de Jesus Antunes Del Duca

1999-09-01

Full Text Available A demanda crescente pela integração lavoura-pecuária no planalto sul-rio-grandense direciona ao aproveitamento dos cereais de inverno para duplo propósito (forragem e grão. Assim, é necessário um melhor conhecimento dessas culturas relativamente à utilização como forragem e ao valor econômico dos grãos no uso potencial para alimentação humana ou animal. O objetivo deste estudo foi avaliar a influência de cortes (um e dois, simulando pastejo bovino, na composição química dos grãos de aveia-branca (UPF 14, de aveia-preta (comum, de centeio (BR 1, de triticale (BR 4, de cevada (BR 2 e de trigo (IPF 55204 e PF 87451. Os cortes não afetaram, na média dos cereais, os valores de fibra bruta, de extrato etéreo, de energia bruta e de atividade ureática, tendo o teor de matéria mineral aumentado com dois cortes. Excetuando aveia-preta e cevada, com os cortes verificou-se incremento nos percentuais de proteína bruta. Entretanto, observou-se, na média dos cereais, redução com os cortes nos teores de extrativos não-nitrogenados. Os resultados obtidos conduzem à possibilidade de uso dos cereais de inverno para duplo propósito, com aproveitamento dos grãos sem maiores prejuízos à sua composição química.An increased demand for activities integrating crop-cattle production in the Rio Grande do Sul plateau has contributed to a dual purpose use (forage and grain of winter small grains. Therefore, a better knowledge on how to use these cereals for pasture, as well as on the economic value of grains and their potential use in human and animal foods, is necessary. The objective of this study was to evaluate the influence of cuts (one and two simulating cattle grazing in the chemical composition of the grain of white oats (UPF 14, black oats Avena strigosa (comum, rye (BR 1, triticale (BR 4, barley (BR 2, and wheat (IPF 55204 and PF 87451. In the cereal average, cuts did not affect the values of crude fiber, fat, crude energy, and

Systematic chemical decontamination using IF7 gas - 59036

International Nuclear Information System (INIS)

Hata, Haruhi; Yokoyama, Kaoru; Sugitsue, Noritake

2012-01-01

Since 1979, Uranium enrichment technology has been researched through the gas centrifuge method, at Ningyo-toge Environmental Engineering Center of Japan Atomic Energy Agency (JAEA). In addition, the Demonstration Plant, that is final stage test facilities, was operating continuously from 1988 to 2001. As a result, a lot of residues accumulated in the plant. Most of this accumulation was found be uranium intermediate fluoride. The basic decommission policy of JAEA is that equipments of gas centrifuge will be decontaminated by sulfuric acid immersion method for clearance and reuse. In our plan, approximately 90% of metals will be cleared and reused, and then the remaining 10% will be disposed of radioactive waste. We propose a combination of sulfuric acid immersion method and the systematic chemical decontamination as an efficient method for decontamination of uranium enrichment facilities. This paper focuses on the method and performance of systematic chemical decontamination using IF 7 gas. The following (Figure 1) shows our decommission policy and position of systematic chemical decontamination by IF 7 gas for uranium enrichment plant. The IF 7 treatment technique belongs to the systematic decontamination technology. It has the high performance decontamination technique for the plant that accumulates the uranium intermediate fluoride, such as UF 4 , UF 5 , U 2 F 9 , and U 4 F 17 , which exist in the uranium enrichment plant through the Gas Centrifuge, called GCF. The one of characteristics of the IF 7 treatment, the secondary waste is just an IF 5 and little residues. In addition, this IF 5 can be reused as materials for making new IF 7 gas. The IF 7 treatment can also be performed in the room temperature and very low pressure like a 10-45 hPa. Furthermore, the IF 7 treatment is a simple method using chemical reaction. For this reason, we hardly need to care about secondary reaction with the exception of the reaction with IF 7 gasand the uranium intermediate

Simulations of Micro Gas Flows by the DS-BGK Method

KAUST Repository

Li, Jun

2011-01-01

For gas flows in micro devices, the molecular mean free path is of the same order as the characteristic scale making the Navier-Stokes equation invalid. Recently, some micro gas flows are simulated by the DS-BGK method, which is convergent to the BGK equation and very efficient for low-velocity cases. As the molecular reflection on the boundary is the dominant effect compared to the intermolecular collisions in micro gas flows, the more realistic boundary condition, namely the CLL reflection model, is employed in the DS-BGK simulation and the influence of the accommodation coefficients used in the molecular reflection model on the results are discussed. The simulation results are verified by comparison with those of the DSMC method as criteria. Copyright © 2011 by ASME.

Whole grain gluten-free egg-free pasta

Science.gov (United States)

The USDA food guide recommends that at least ½ of all the grains eaten should be whole grains. The FDA allows food Health Claim labels for food containing 51% whole grains and 11 g of dietary fiber. This is the only report demonstrating innovative whole grain gluten free, egg free (no chemicals adde...

Effect of grain boundary phase on the magnetization reversal process of nanocrystalline magnet using large-scale micromagnetic simulation

Directory of Open Access Journals (Sweden)

Hiroshi Tsukahara

2018-05-01

Full Text Available We investigated the effects of grain boundary phases on magnetization reversal in permanent magnets by performing large-scale micromagnetic simulations based on Landau–Lifshitz–Gilbert equation under a periodic boundary. We considered planar grain boundary phases parallel and perpendicular to an easy axis of the permanent magnet and assumed the saturation magnetization and exchange stiffness constant of the grain boundary phase to be 10% and 1%, respectively, for Nd2Fe14B grains. The grain boundary phase parallel to the easy axis effectively inhibits propagation of magnetization reversal. In contrast, the domain wall moves across the grain boundary perpendicular to the easy axis. These properties of the domain wall motion are explained by dipole interaction, which stabilizes the antiparallel magnetic configuration in the direction perpendicular to the magnetization orientation. On the other hand, the magnetization is aligned in the same direction by the dipole interaction parallel to the magnetization orientation. This anisotropy of the effect of the grain boundary phase shows that improvement of the grain boundary phase perpendicular to the easy axis effectively enhances the coercivity of permanent magnets.

Numerical simulation of temperature distribution using finite difference equations and estimation of the grain size during friction stir processing

International Nuclear Information System (INIS)

Arora, H.S.; Singh, H.; Dhindaw, B.K.

2012-01-01

Highlights: ► Magnesium alloy AE42 was friction stir processed under different cooling conditions. ► Heat flow model was developed using finite difference heat equations. ► Generalized MATLAB code was developed for solving heat flow model. ► Regression equation for estimation of grain size was developed. - Abstract: The present investigation is aimed at developing a heat flow model to simulate temperature history during friction stir processing (FSP). A new approach of developing implicit form of finite difference heat equations solved using MATLAB code was used. A magnesium based alloy AE42 was friction stir processed (FSPed) at different FSP parameters and cooling conditions. Temperature history was continuously recorded in the nugget zone during FSP using data acquisition system and k type thermocouples. The developed code was validated at different FSP parameters and cooling conditions during FSP experimentation. The temperature history at different locations in the nugget zone at different instants of time was further utilized for the estimation of grain growth rate and final average grain size of the FSPed specimen. A regression equation relating the final grain size, maximum temperature during FSP and the cooling rate was developed. The metallurgical characterization was done using optical microscopy, SEM, and FIB-SIM analysis. The simulated temperature profiles and final average grain size were found to be in good agreement with the experimental results. The presence of fine precipitate particles generated in situ in the investigated magnesium alloy also contributed in the evolution of fine grain structure through Zener pining effect at the grain boundaries.

Equi-axed and columnar grain growth in UO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

White, R J [Berkely Technology Centre, Nuclear Electric plc, Berkeley (United Kingdom)

1997-08-01

The grain size of UO{sub 2} is an important parameter in the actual performance and the modelling of the performance of reactor fuel elements. Many processes depend critically on the grain size, for example, the degree of initial densification, the evolution rate of stable fission gases, the release rates of radiologically hazardous fission products, the fission gas bubble swelling rates and the fuel creep. Many of these processes are thermally activated and further impact on the fuel thermal behavior thus creating complex feedback processes. In order to model the fuel performance accurately it is necessary to model the evolution of the fuel grain radius. When UO{sub 2} is irradiated, the fission gases xenon and krypton are created from the fissioning uranium nucleus. At high temperatures these gases diffuse rapidly to the grain boundaries where they nucleate immobile lenticular shaped fission gas bubbles. In this paper the Hillert grain growth model is adapted to account for the inhibiting ``Zener`` effects of grain boundary fission gas porosity on grain boundary mobility and hence grain growth. It is shown that normal grain growth ceases at relatively low levels of irradiation. At high burnups, high temperatures and in regions of high temperature gradients, columnar grain growth is often observed, in some cases extending over more than fifty percent of the fuel radius. The model is further extended to account for the de-pinning of grains in the radial direction by the thermal gradient induced force on a fission gas grain boundary bubble. The observed columnar/equi-axed boundary is in fair agreement with the predictions of an evaporation/condensation model. The grain growth model described in this paper requires information concerning the scale of grain boundary porosity, the local fuel temperature and the local temperature gradient. The model is currently used in the Nuclear Electric version of the ENIGMA fuel modelling code. (author). 14 refs, 3 figs, 1 tab.

Classical density functional theory & simulations on a coarse-grained model of aromatic ionic liquids.

Science.gov (United States)

Turesson, Martin; Szparaga, Ryan; Ma, Ke; Woodward, Clifford E; Forsman, Jan

2014-05-14

A new classical density functional approach is developed to accurately treat a coarse-grained model of room temperature aromatic ionic liquids. Our major innovation is the introduction of charge-charge correlations, which are treated in a simple phenomenological way. We test this theory on a generic coarse-grained model for aromatic RTILs with oligomeric forms for both cations and anions, approximating 1-alkyl-3-methyl imidazoliums and BF₄⁻, respectively. We find that predictions by the new density functional theory for fluid structures at charged surfaces are very accurate, as compared with molecular dynamics simulations, across a range of surface charge densities and lengths of the alkyl chain. Predictions of interactions between charged surfaces are also presented.

Modeling and Simulation of the Sulfur-Iodine Process Coupled to a Very High-Temperature Gas-Cooled Nuclear Reactor

International Nuclear Information System (INIS)

Shin, Youngjoon; Lee, Taehoon; Lee, Kiyoung; Kim, Minhwan

2015-01-01

Hydrogen produced from water using nuclear energy will avoid both the use of fossil fuel and CO 2 emission presumed to be the dominant reason for global warming. A thermo-chemical sulfur-iodine (SI) process coupled to a Very High Temperature Gas-Cooled Reactor(VHTR) is one of the most prospective hydrogen production methods that split water using nuclear energy because the SI process is suitable for large-scale hydrogen production without CO 2 emission. The dynamic simulation code to evaluate the start-up behavior of the chemical reactors placed on the secondary helium loop of the SI process has been developed and partially verified using the steady state values obtained from the Aspen Plus TM Code simulation. As the start-up dynamic simulation results of the SI process coupled to the IHX, which is one of components in the VHTR system, it is expected that the integrated secondary helium loop of the SI process can be successfully and safely approach the steady state condition

Effects of particle size of processed barley grain, enzyme addition and microwave treatment on disappearance and gas production for feedlot cattle

Directory of Open Access Journals (Sweden)

Shin-ichi Tagawa

2017-04-01

Full Text Available Objective The effects of particle size of processed barley grain, enzyme addition and microwave treatment on in vitro dry matter (DM disappearance (DMD, gas production and fermentation pH were investigated for feedlot cattle. Methods Rumen fluid from four fistulated feedlot cattle fed a diet of 860 dry-rolled barley grain, 90 maize silage and 50 supplement g/kg DM was used as inoculum in 3 batch culture in vitro studies. In Experiment 1, dry-rolled barley and barley ground through a 1-, 2-, or 4-mm screen were used to obtain four substrates differing in particle size. In Experiment 2, cellulase enzyme (ENZ from Acremonium cellulolyticus Y-94 was added to dry-rolled and ground barley (2-mm at 0, 0.1, 0.5, 1, and 2 mg/g, while Experiment 3 examined the interactions between microwaving (0, 30, and 60 s microwaving and ENZ addition (0, 1, and 2 mg/g using dry-rolled barley and 2-mm ground barley. Results In Experiment 1, decreasing particle size increased DMD and gas production, and decreased fermentation pH (p<0.01. The DMD (g/kg DM of the dry-rolled barley after 24 h incubation was considerably lower (p<0.05 than that of the ground barley (119.1 dry-rolled barley versus 284.8 for 4-mm, 341.7 for 2-mm; and 358.6 for 1-mm. In Experiment 2, addition of ENZ to dry-rolled barley increased DMD (p<0.01 and tended to increase (p = 0.09 gas production and decreased (p<0.01 fermentation pH, but these variables were not affected by ENZ addition to ground barley. In Experiment 3, there were no interactions between microwaving and ENZ addition after microwaving for any of the variables. Microwaving had minimal effects (except decreased fermentation pH, but consistent with Experiment 2, ENZ addition increased (p<0.01 DMD and gas production, and decreased (p<0.05 fermentation pH of dry-rolled barley, but not ground barley. Conclusion We conclude that cellulase enzymes can be used to increase the rumen disappearance of barley grain when it is coarsely processed

Simulation of gas turbines operating in off-design condition

Energy Technology Data Exchange (ETDEWEB)

Walter, Arnaldo [Universidade Estadual de Campinas, SP (Brazil). Faculdade de Engenharia Mecanica. Dept. de Energia]. E-mail: walter@fem.unicamp.br

2000-07-01

In many countries thermal power plants based on gas turbines have been the main option for new investment into the electric system due to their relatively high efficiency and low capital cost. Cogeneration systems based on gas turbines have also been an important option for the electric industry. Feasibility studies of power plants based on gas turbine should consider the effect of atmospheric conditions and part-load operation on the machine performance. Doing this, an off-design procedure is required. A G T off-design simulation procedure is described in this paper. Ruston R M was used to validate the simulation procedure that, general sense, presents deviations lower than 2.5% in comparison to manufacturer's data. (author)

Some regularity of the grain size distribution in nuclear fuel with controllable structure

International Nuclear Information System (INIS)

Loktev, Igor

2008-01-01

It is known, the fission gas release from ceramic nuclear fuel depends from average size of grains. To increase grain size they use additives which activate sintering of pellets. However, grain size distribution influences on fission gas release also. Fuel with different structures, but with the same average size of grains has different fission gas release. Other structure elements, which influence operational behavior of fuel, are pores and inclusions. Earlier, in Kyoto, questions of distribution of grain size for fuel with 'natural' structure were discussed. Some regularity of grain size distribution of fuel with controllable structure and high average size of grains are considered in the report. Influence of inclusions and pores on an error of the automated definition of parameters of structure is shown. The criterion, which describe of behavior of fuel with specific grain size distribution, is offered

Basic chemically recuperated gas turbines--power plant optimization and thermodynamics second law analysis

International Nuclear Information System (INIS)

Alves, Lourenco Gobira; Nebra, Silvia Azucena

2004-01-01

One of the proposals to increase the performance of the gas turbines is to improve chemical recuperated cycle. In this cycle, the heat in the turbine exhaust gases is used to heat and modify the chemical characteristics of the fuel. One mixture of natural gas and steam receives heat from the exhaust turbine gases; the mixture components react among themselves producing hot synthesis gas. In this work, an analysis and nonlinear optimization of the cycle were made in order to investigate the temperature and pressure influence on the global cycle performance. The chemical composition in the reformer was assumed according to chemical equilibrium equations, which presents good agreement with data from literature. The mixture of hot gases was treated like ideal gases. The maximum net profit was achieved and a thermodynamic second law analysis was made in order to detect the greatest sources of irreversibility

Chemical equilibrium. [maximizing entropy of gas system to derive relations between thermodynamic variables

Science.gov (United States)

1976-01-01

The entropy of a gas system with the number of particles subject to external control is maximized to derive relations between the thermodynamic variables that obtain at equilibrium. These relations are described in terms of the chemical potential, defined as equivalent partial derivatives of entropy, energy, enthalpy, free energy, or free enthalpy. At equilibrium, the change in total chemical potential must vanish. This fact is used to derive the equilibrium constants for chemical reactions in terms of the partition functions of the species involved in the reaction. Thus the equilibrium constants can be determined accurately, just as other thermodynamic properties, from a knowledge of the energy levels and degeneracies for the gas species involved. These equilibrium constants permit one to calculate the equilibrium concentrations or partial pressures of chemically reacting species that occur in gas mixtures at any given condition of pressure and temperature or volume and temperature.

Influence of grain size on the mechanical properties of nano-crystalline copper; insights from molecular dynamics simulation

Science.gov (United States)

Rida, A.; Makke, A.; Rouhaud, E.; Micoulaut, M.

2017-10-01

We use molecular dynamics simulations to study the mechanical properties of a columnar nanocrystalline copper with a mean grain size between 8.91 nm and 24 nm. The used samples were generated by using a melting cooling method. These samples were submitted to uniaxial tensile test. The results reveal the presence of a critical mean grain size between 16 and 20 nm, where there is an inversion in the conventional Hall-Petch tendency. This inversion is illustrated by the increase of flow stress with the increase of the mean grain size. This transition is caused by shifting of the deformation mechanism from dislocations to a combination of grain boundaries sliding and dislocations. Moreover, the effect of temperature on the mechanical properties of nanocrystalline copper has been investigated. The results show a decrease of the flow stress and Young's modulus when the temperature increases.

Simulations of a Circulating Fluidized Bed Chemical Looping Combustion System Utilizing Gaseous Fuel; Simulation de la combustion en boucle chimique d'une charge gazeuse dans un lit fluidise circulant

Energy Technology Data Exchange (ETDEWEB)

Mahalatkar, K.; Kuhlman, J. [West Virginia University, Dept. of Mechanical and Aerospace Engineering, Morgantown, WV, 26506 (United States); Mahalatkar, K. [ANSYS Inc., 3647 Collins Ferry Road Suite A, Morgantown, WV, 26505 (United States); Kuhlman, J.; Huckaby, E.D.; O' Brien, T. [National Energy Technology Laboratory, 3610 Collins Ferry Road, Morgantown, WV, 26507 (United States)

2011-03-15

Numerical studies using Computational Fluid Dynamics (CFD) have been carried out for a complete circulating fluidized bed chemical looping combustor described in the literature (Abad et al., 2006 Fuel 85, 1174-1185). There have been extensive experimental studies in Chemical Looping Combustion (CLC), however CFD simulations of this concept are quite limited. The CLC experiments that were simulated used methane as fuel. A 2-D continuum model was used to describe both the gas and solid phases. Detailed sub-models to account for fluid-particle and particle-particle interaction forces were included. Global models of fuel and carrier chemistry were utilized. The results obtained from CFD were compared with experimental outlet species concentrations, solid circulation rates, solid mass distribution in the reactors, and leakage and dilution rates. The transient CFD simulations provided a reasonable match with the reported experimental data. (authors)

Interstellar silicate analogs for grain-surface reaction experiments: Gas-phase condensation and characterization of the silicate dust grains

Energy Technology Data Exchange (ETDEWEB)

Sabri, T.; Jäger, C. [Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena (Germany); Gavilan, L.; Lemaire, J. L.; Vidali, G. [Observatoire de Paris/Université de Cergy-Pontoise, 5 mail Gay Lussac, F-95000 Cergy-Pontoise (France); Mutschke, H. [Laboratory Astrophysics Group of the Astrophysical Institute and University Observatory, Friedrich Schiller University Jena Schillergässchen 3, D-07743 Jena (Germany); Henning, T., E-mail: tolou.sabri@uni-jena.de [Max Planck Institute for Astronomy Königstuhl 17, D-69117 Heidelberg (Germany)

2014-01-10

Amorphous, astrophysically relevant silicates were prepared by laser ablation of siliceous targets and subsequent quenching of the evaporated atoms and clusters in a helium/oxygen gas atmosphere. The described gas-phase condensation method can be used to synthesize homogeneous and astrophysically relevant silicates with different compositions ranging from nonstoichiometric magnesium iron silicates to pyroxene- and olivine-type stoichiometry. Analytical tools have been used to characterize the morphology, composition, and spectral properties of the condensates. The nanometer-sized silicate condensates represent a new family of cosmic dust analogs that can generally be used for laboratory studies of cosmic processes related to condensation, processing, and destruction of cosmic dust in different astrophysical environments. The well-characterized silicates comprising amorphous Mg{sub 2}SiO{sub 4} and Fe{sub 2}SiO{sub 4}, as well as the corresponding crystalline silicates forsterite and fayalite, produced by thermal annealing of the amorphous condensates, have been used as real grain surfaces for H{sub 2} formation experiments. A specifically developed ultra-high vacuum apparatus has been used for the investigation of molecule formation experiments. The results of these molecular formation experiments on differently structured Mg{sub 2}SiO{sub 4} and Fe{sub 2}SiO{sub 4} described in this paper will be the topic of the next paper of this series.

A comparison of grain boundary evolution during grain growth in fcc metals

International Nuclear Information System (INIS)

Brons, J.G.; Thompson, G.B.

2013-01-01

Grain growth of Cu and Ni thin films, subjected to in situ annealing within a transmission electron microscope, has been quantified using a precession-enhanced electron diffraction technique. The orientation of each grain and its misorientation with respect to its neighboring grains were calculated. The Cu underwent grain growth that maintained a monomodal grain size distribution, with its low-angle grain boundaries being consumed, and the Ni exhibited grain size distributions in stages, from monomodal to bimodal to monomodal. The onset of Ni’s abnormal grain growth was accompanied by a sharp increase in the Σ3 and Σ9 boundary fractions, which is attributed to simulation predictions of their increased mobility. These Σ3 and Σ9 fractions then dropped to their room temperature values during the third stage of grain growth. In addition to the Σ3 and Σ9 boundaries, the Σ5 and Σ7 boundaries also underwent an increase in total boundary fraction with increasing temperature in both metals

Methanol ice co-desorption as a mechanism to explain cold methanol in the gas-phase

Science.gov (United States)

Ligterink, N. F. W.; Walsh, C.; Bhuin, R. G.; Vissapragada, S.; van Scheltinga, J. Terwisscha; Linnartz, H.

2018-05-01

Context. Methanol is formed via surface reactions on icy dust grains. Methanol is also detected in the gas-phase at temperatures below its thermal desorption temperature and at levels higher than can be explained by pure gas-phase chemistry. The process that controls the transition from solid state to gas-phase methanol in cold environments is not understood. Aims: The goal of this work is to investigate whether thermal CO desorption provides an indirect pathway for methanol to co-desorb at low temperatures. Methods: Mixed CH3OH:CO/CH4 ices were heated under ultra-high vacuum conditions and ice contents are traced using RAIRS (reflection absorption IR spectroscopy), while desorbing species were detected mass spectrometrically. An updated gas-grain chemical network was used to test the impact of the results of these experiments. The physical model used is applicable for TW Hya, a protoplanetary disk in which cold gas-phase methanol has recently been detected. Results: Methanol release together with thermal CO desorption is found to be an ineffective process in the experiments, resulting in an upper limit of ≤ 7.3 × 10-7 CH3OH molecules per CO molecule over all ice mixtures considered. Chemical modelling based on the upper limits shows that co-desorption rates as low as 10-6 CH3OH molecules per CO molecule are high enough to release substantial amounts of methanol to the gas-phase at and around the location of the CO thermal desorption front in a protoplanetary disk. The impact of thermal co-desorption of CH3OH with CO as a grain-gas bridge mechanism is compared with that of UV induced photodesorption and chemisorption.

A Grid-Based Cyber Infrastructure for High Performance Chemical Dynamics Simulations

Directory of Open Access Journals (Sweden)

Khadka Prashant

2008-10-01

Full Text Available Chemical dynamics simulation is an effective means to study atomic level motions of molecules, collections of molecules, liquids, surfaces, interfaces of materials, and chemical reactions. To make chemical dynamics simulations globally accessible to a broad range of users, recently a cyber infrastructure was developed that provides an online portal to VENUS, a popular chemical dynamics simulation program package, to allow people to submit simulation jobs that will be executed on the web server machine. In this paper, we report new developments of the cyber infrastructure for the improvement of its quality of service by dispatching the submitted simulations jobs from the web server machine onto a cluster of workstations for execution, and by adding an animation tool, which is optimized for animating the simulation results. The separation of the server machine from the simulation-running machine improves the service quality by increasing the capacity to serve more requests simultaneously with even reduced web response time, and allows the execution of large scale, time-consuming simulation jobs on the powerful workstation cluster. With the addition of an animation tool, the cyber infrastructure automatically converts, upon the selection of the user, some simulation results into an animation file that can be viewed on usual web browsers without requiring installation of any special software on the user computer. Since animation is essential for understanding the results of chemical dynamics simulations, this animation capacity provides a better way for understanding simulation details of the chemical dynamics. By combining computing resources at locations under different administrative controls, this cyber infrastructure constitutes a grid environment providing physically and administratively distributed functionalities through a single easy-to-use online portal

Lattice gas automata simulations of flow through porous media

International Nuclear Information System (INIS)

Matsukuma, Yosuke; Abe, Yutaka; Adachi, Hiromichi; Takahashi, Ryoichi

1998-01-01

In the course of a severe accident, a debris bed may be formed from once- molten and fragmented fuel elements. In order to avoid further degradation of the reactor core, it is necessary to remove the heat from the debris bed since the debris bed still release the decay heat. So as to predict the coolability of the debris bed, it is important to precisely estimate flow patterns through complex geometry of debris bed in microscopic level. Lattice gas automata could be powerful tool to simulate such a complex geometry. As a first step of the study, fundamental numerical simulation were conducted in two dimensional systems by using the lattice gas automata method to clarify single phase flow patterns through porous media in mesoscopic level. Immiscible lattice gas model is one of the lattice gas automata method and utilized for spinodal decomposition simulation of binary fluids. This model was applied to generate the complex flow geometry simulating porous media. It was approved that the complex flow geometries were successfully generated by the present method. Flow concentration was observed in specified flow channels for lower Reynolds number. Two dimensional flow concentration was caused by the irregular flow geometry generated by the present method, since the flow selects the channels of lower friction. Two dimensional pressure distribution was observed relating to the concentrations of flow in specified channels. The simulating results of the flow through the porous media by the present method qualitatively agree with the Ergun's equation. Quantitatively, the present results approach to Ergun's equation in higher Reynolds number than 10, although concentration of the flow in a specified flow channels were observed in lower Reynolds number than 10. It can be concluded that this technique is useful is useful to simulate flow through complex geometry like porous media. (author)

Effect of backbone chemistry on hybridization thermodynamics of oligonucleic acids: a coarse-grained molecular dynamics simulation study.

Science.gov (United States)

Ghobadi, Ahmadreza F; Jayaraman, Arthi

2016-02-28

In this paper we study how varying oligonucleic acid backbone chemistry affects the hybridization/melting thermodynamics of oligonucleic acids. We first describe the coarse-grained (CG) model with tunable parameters that we developed to enable the study of both naturally occurring oligonucleic acids, such as DNA, and their chemically-modified analogues, such as peptide nucleic acids (PNAs) and locked nucleic acids (LNAs). The DNA melting curves obtained using such a CG model and molecular dynamics simulations in an implicit solvent and with explicit ions match with the melting curves obtained using the empirical nearest-neighbor models. We use these CG simulations to then elucidate the effect of backbone flexibility, charge, and nucleobase spacing along the backbone on the melting curves, potential energy and conformational entropy change upon hybridization and base-pair hydrogen bond residence time. We find that increasing backbone flexibility decreases duplex thermal stability and melting temperature mainly due to increased conformational entropy loss upon hybridization. Removing charges from the backbone enhances duplex thermal stability due to the elimination of electrostatic repulsion and as a result a larger energetic gain upon hybridization. Lastly, increasing nucleobase spacing decreases duplex thermal stability due to decreasing stacking interactions that are important for duplex stability.

Modeling the effects of cooling rate, hydrogen content, grain refiner and modifier on microporosity formation in Al A356 alloys

Energy Technology Data Exchange (ETDEWEB)

Conley, J.G.; Huang, J.; Asada, J.; Akiba, K. [Northwestern Univ., Evanston, IL (United States). Dept. of Mechanical Engineering

2000-06-15

Cast Aluminum-Silicon alloys are used in numerous automotive and industrial weight sensitive applications because of their low density and excellent castability. The presence of trapped gas and or shrinkage pores in certain locations within castings has been shown to influence fatigue life. These micromechanical defects can be found most anywhere in a casting depending on processing conditions. A large amount of porosity located in the center of the cast material thickness may have no effect on mechanical properties or fatigue performance. A smaller, isolated pore near a surface may have a significant impact on mechanical properties. Hence, it is important to develop a comprehensive model to predict the size, location and distribution of microporosity in castings. In this work, we model the effect of various casting process parameters on microporosity formation for aluminum A356 alloy castings. The process parameters include cooling rate, hydrogen content, grain refiner and modifier. The proposed two-dimensional model predicts the size, morphology and distribution of microporosity at a given location in the casting. The method couples a mathematical model of porosity evolution with a probabilistic grain structure prediction model. The porosity evolution model is based on the simultaneous solution of the continuity and momentum equations for the metal and the mass conservation equation for the dissolved gas. The nucleation and growth of grains are simulated with a probabilistic method that uses the information from a heat transfer simulation, i.e. temperature and solid fraction, to determine the transition rules for grain evolution. The simulation results correlate well with experimental observation of porosity in cast structures. (orig.)

Effects of grain-producing cover crops on rice grain yield in Cabo Delgado, Mozambique

Directory of Open Access Journals (Sweden)

Adriano Stephan Nascente

Full Text Available ABSTRACT Besides providing benefits to the environment such as soil protection, release of nutrients, soil moisture maintenance, and weed control, cover crops can increase food production for grain production. The aim of this study was to evaluate the production of biomass and grain cover crops (and its respective effects on soil chemical and physical attributes, yield components, and grain yield of rice in Mozambique. The study was conducted in two sites located in the province of Cabo Delgado, in Mozambique. The experimental design was a randomized block in a 2 × 6 factorial, with four repetitions. Treatments were carried out in two locations (Cuaia and Nambaua with six cover crops: Millet (Pennisetum glaucum L.; namarra bean (Lablab purpureus (L. Sweet, velvet beans (Mucuna pruriens L., oloco beans (Vigna radiata (L. R. Wilczek, cowpea (Vigna unguiculata L., and fallow. Cover crops provided similar changes in chemical and physical properties of the soil. Lablab purpureus, Vigna unguiculata, and Mucuna pruriens produced the highest dry matter biomass. Vigna unguiculada produced the highest amount of grains. Rice grain yields were similar under all cover crops and higher in Cuaia than Nambaua.

Effects of Textural Properties on the Response of a SnO2-Based Gas Sensor for the Detection of Chemical Warfare Agents

Directory of Open Access Journals (Sweden)

Duk Dong Lee

2011-07-01

Full Text Available The sensing behavior of SnO2-based thick film gas sensors in a flow system in the presence of a very low concentration (ppb level of chemical agent simulants such as acetonitrile, dipropylene glycol methyl ether (DPGME, dimethyl methylphosphonate (DMMP, and dichloromethane (DCM was investigated. Commercial SnO2 [SnO2(C] and nano-SnO2 prepared by the precipitation method [SnO2(P] were used to prepare the SnO2 sensor in this study. In the case of DCM and acetonitrile, the SnO2(P sensor showed higher sensor response as compared with the SnO2(C sensors. In the case of DMMP and DPGME, however, the SnO2(C sensor showed higher responses than those of the SnO2(P sensors. In particular, the response of the SnO2(P sensor increased as the calcination temperature increased from 400 °C to 800 °C. These results can be explained by the fact that the response of the SnO2-based gas sensor depends on the textural properties of tin oxide and the molecular size of the chemical agent simulant in the detection of the simulant gases (0.1–0.5 ppm.

Lattice gas simulations of replicating domains

International Nuclear Information System (INIS)

Dawson, S.P.; Hasslacher, B.; Pearson, J.E.

1993-01-01

We use the lattice gas cellular automation (LGCA) developed to simulate a process of pattern-formation recently observed in reaction-diffusion systems. We study the reaction mechanism, which is an extension of the Selkov model for glycolytic oscillations. We are able to reproduce the self-replicating domains observed in this work. We use the LGCA simulation to estimate the smallest length-scale on which this process can occur under conditions encountered in the cell. These estimates are similar to those obtained for Turing patterns in the same setting

Lattice gas simulations of replicating domains

Energy Technology Data Exchange (ETDEWEB)

Dawson, S.P.; Hasslacher, B.; Pearson, J.E.

1993-12-31

We use the lattice gas cellular automation (LGCA) developed to simulate a process of pattern-formation recently observed in reaction-diffusion systems. We study the reaction mechanism, which is an extension of the Selkov model for glycolytic oscillations. We are able to reproduce the self-replicating domains observed in this work. We use the LGCA simulation to estimate the smallest length-scale on which this process can occur under conditions encountered in the cell. These estimates are similar to those obtained for Turing patterns in the same setting.

Algorithm for simulation of quantum many-body dynamics using dynamical coarse-graining

International Nuclear Information System (INIS)

Khasin, M.; Kosloff, R.

2010-01-01

An algorithm for simulation of quantum many-body dynamics having su(2) spectrum-generating algebra is developed. The algorithm is based on the idea of dynamical coarse-graining. The original unitary dynamics of the target observables--the elements of the spectrum-generating algebra--is simulated by a surrogate open-system dynamics, which can be interpreted as weak measurement of the target observables, performed on the evolving system. The open-system state can be represented by a mixture of pure states, localized in the phase space. The localization reduces the scaling of the computational resources with the Hilbert-space dimension n by factor n 3/2 (ln n) -1 compared to conventional sparse-matrix methods. The guidelines for the choice of parameters for the simulation are presented and the scaling of the computational resources with the Hilbert-space dimension of the system is estimated. The algorithm is applied to the simulation of the dynamics of systems of 2x10 4 and 2x10 6 cold atoms in a double-well trap, described by the two-site Bose-Hubbard model.

Phase field simulation of grain growth in porous uranium dioxide

International Nuclear Information System (INIS)

Ahmed, Karim; Pakarinen, Janne; Allen, Todd; El-Azab, Anter

2014-01-01

Graphical abstract: Display Omitted -- Abstract: A novel phase field model has been developed to investigate grain growth in porous polycrystalline UO 2 . Based on a system of Cahn–Hilliard and Allen–Cahn equations, the model takes into consideration both the curvature driven grain boundary motion and pore migration by surface diffusion. As such, the model accounts for the interaction between pore and grain boundary kinetics, which tends to retard the growth process. The phase field model parameters are found in terms of measurable material properties. Hence, quantitative results that can be compared with experiments were obtained. The model has been used to investigate the effect of porosity on the kinetics of grain growth in UO 2 . It is found that, as the amount of porosity increases, grain growth in UO 2 gradually changes from boundary controlled growth to pore controlled growth. For high porosity levels, the grain growth completely stops after a short evolution time. It is also found that the inhomogeneous distribution of pores leads to abnormal grain growth even without taking into account the anisotropy in grain boundary energy and mobility. The effects of porosity, temperature and initial microstructure on grain growth were thoroughly investigated. The model predictions are in good agreement with published experimental results of grain growth in UO 2

Concentration contours in lattics and grain boundary diffusion in a polycrystalline solid

International Nuclear Information System (INIS)

Kim, Yong Soo; Jae, Won Mok; El Saied, Usama; Olander, Donald R.

1995-01-01

Grain boundary diffusion plays significant role in the fission gas release, which is one of the crucial processes dominating nuclear fuel performance. Gaseous fission products such as Xe and Kr generated inside fuel pellet have to diffuse in the lattice and in the grain boundary before they reach open space in the fuel rod. In the mean time, the grains in the fuel pellet grow and shrink according to grain growth kinetics, especially at elevated temperature at which nuclear reactors are operating. Thus the boundary movement ascribed to the grain growth greatly influences the fission gas release rate by lengthening or shortening the lattice diffusion distance, which is the rate limiting step. Sweeping fission gases by the moving boundary contributes to the increment of the fission gas release as well. Lattice and grain boundary diffusion processes in the fission gas release can be studied by 'tracer diffusion' technique, by which grain boundary diffusivity can be estimated and used directly for low burn up fission gas release analysis. However, even for tracer diffusion analysis, taking both the intragranular grain growth and the diffusion processes simultaneously into consideration is not easy. Only a few models accounting for the both processes are available and mostly handle them numerically. Numerical solutions are limited in the practical use. Here in this paper, an approximate analytical solution of the lattice and stationary grain boundary diffusion in a polycrystalline solid is developed for the tracer diffusion techniques. This short closed form solution is compared to available exact and numerical solutions and turns out to be acceptably accurate. It can be applied to the theoretical modeling and the experimental analysis, especially PIE (post irradiation examination), of low burn up fission gas release

Effects of product form and boron addition on the creep damage in the modified Hastelloy X alloys in a simulated HTGR helium gas environment

International Nuclear Information System (INIS)

Nakasone, Yuji; Tanabe, Tatsuhiko; Tsuji, Hirokazu; Nakajima, Hajime.

1992-01-01

The present paper investigates early-stage-creep damage of Hastelloy XR and XR-II alloys, modified versions of Hastelloy X alloy, which have been developed in Japan as most promising candidate structural alloys for Japanese high-temperature gas-cooled reactors (HTGRs). Creep tests were made on Hastelloy XR forging, tube and XR-II tube at 1,123 to 1,273 K in a simulated HTGR helium gas environment. The tests were interrupted at different strain levels of up to 5 % in order to evaluate creep damage via intergranular voids. The void sizes along grain boundaries and the A-parameter, the ratio of the number of damaged grain boundaries, on which one or more voids are found, to that of the total grain boundaries observed are used in order to evaluate creep damage. Statistical analysis of the A-parameter as well as the void sizes reveals that the values of the parameter show wide variations and follow the Weibull distribution, reflecting spatial randomness of the voids. The void sizes along grain boundaries, on the other hand, follow the log-normal distribution. The maximum void size d max and the mean value of the A-parameter A m are calculated and plotted against interruption creep strain ε int . The resultant d max vs. ε int and A m vs. ε int diagrams show that Hastelloy XR forging had suffered more damage than Hastelloy XR tube; nevertheless, the forging has longer interruption life, or the time to reach a given interruption creep strain. The result indicates that grains may have been deformed more easily in Hastelloy XR in the form of tube than in the form of forging. The diagrams also imply that the addition of boron has suppressed the nucleation as well as the growth of voids and thus has brought about longer interruption life of Hastelloy XR-II. (author)

Composition, preparation, and gas generation results from simulated wastes of Tank 241-SY-101

International Nuclear Information System (INIS)

Bryan, S.A.; Pederson, L.R.

1994-08-01

This document reviews the preparation and composition of simulants that have been developed to mimic the wastes temporarily stored in Tank 241-SY-101 at Hanford. The kinetics and stoichiometry of gases that are generated using these simulants are also compared, considering the roles of hydroxide, chloride, and transition metal ions; the identities of organic constituents; and the effects of dilution, radiation, and temperature. Work described in this report was conducted for the Flammable Gas Safety Program at Pacific Northwest Laboratory, (a) whose purpose is to develop information that is necessary to mitigate potential safety hazards associated with waste tanks at the Hanford Site. The goal of this research and of related efforts at the Georgia Institute of Technology (GIT), Argonne National Laboratory (ANL), and Westinghouse Hanford Company (WHC) is to determine the thermal and thermal/radiolytic mechanisms by which flammable and other gases are produced in Hanford wastes, emphasizing those stored in Tank 241-SY-101. A variety of Tank 241-SY-101 simulants have been developed to date. The use of simulants in laboratory testing activities provides a number of advantages, including elimination of radiological risks to researchers, lower costs associated with experimentation, and the ability to systematically alter simulant compositions to study the chemical mechanisms of reactions responsible for gas generation. The earliest simulants contained the principal inorganic components of the actual waste and generally a single complexant such as N-(2-hydroxyethyl) ethylenediaminetriacetic acid (HEDTA) or ethylenediaminetriacetic acid (EDTA). Both homogeneous and heterogeneous compositional forms were developed. Aggressive core sampling and analysis activities conducted during Windows C and E provided information that was used to design new simulants that more accurately reflected major and minor inorganic components

Laboratory Studies of the Optical Properties and Condensation Processes of Cosmic Dust Grains

Science.gov (United States)

Abbas, M. M.; Craven, P. D.; Spann, J. F.; Tankosic, D.; LeClair, A.; West, E.; Sheldon, R.; Witherow, W. K.; Gallagher, D. L.; Adrian, M. L.

2002-01-01

A laboratory facility for conducting a variety of experiments on single isolated dust particles of astrophysical interest levitated in an electrodynamics balance has been developed at NASA/Marshall Space Flight Center. The objective of the research is to employ this experimental technique for studies of the physical and optical properties of individual cosmic dust grains of 0.1-100 micron size in controlled pressure/temperatures environments simulating astrophysical conditions. The physical and optical properties of the analogs of interstellar and interplanetary dust grains of known composition and size distribution will be investigated by this facility. In particular, we will carry out three classes of experiments to study the micro-physics of cosmic dust grains. (1) Charge characteristics of micron size single dust grains to determine the photoelectric efficiencies, yields, and equilibrium potentials when exposed to UV radiation. (2) Infrared optical properties of dust particles (extinction coefficients and scattering phase functions) in the 1-30 micron region using infrared diode lasers and measuring the scattered radiation. (3) Condensation experiments to investigate the condensation of volatile gases on colder nucleated particles in dense interstellar clouds and lower planetary atmospheres. The condensation experiments will involve levitated nucleus dust grains of known composition and initial mass (or m/q ratio), cooled to a temperature and pressure (or scaled pressure) simulating the astrophysical conditions, and injection of a volatile gas at a higher temperature from a controlled port. The increase in the mass due to condensation on the particle will be monitored as a function of the dust particle temperature and the partial pressure of the injected volatile gas. The measured data will permit determination of the sticking coefficients of volatile gases and growth rates of dust particles of astrophysical interest. Some preliminary results based on

Optimization of droplets for UV-NIL using coarse-grain simulation of resist flow

Science.gov (United States)

Sirotkin, Vadim; Svintsov, Alexander; Zaitsev, Sergey

2009-03-01

A mathematical model and numerical method are described, which make it possible to simulate ultraviolet ("step and flash") nanoimprint lithography (UV-NIL) process adequately even using standard Personal Computers. The model is derived from 3D Navier-Stokes equations with the understanding that the resist motion is largely directed along the substrate surface and characterized by ultra-low values of the Reynolds number. By the numerical approximation of the model, a special finite difference method is applied (a coarse-grain method). A coarse-grain modeling tool for detailed analysis of resist spreading in UV-NIL at the structure-scale level is tested. The obtained results demonstrate the high ability of the tool to calculate optimal dispensing for given stamp design and process parameters. This dispensing provides uniform filled areas and a homogeneous residual layer thickness in UV-NIL.

Effects of particle size of processed barley grain, enzyme addition and microwave treatment on in vitro disappearance and gas production for feedlot cattle.

Science.gov (United States)

Tagawa, Shin-Ichi; Holtshausen, Lucia; McAllister, Tim A; Yang, Wen Zhu; Beauchemin, Karen Ann

2017-04-01

The effects of particle size of processed barley grain, enzyme addition and microwave treatment on in vitro dry matter (DM) disappearance (DMD), gas production and fermentation pH were investigated for feedlot cattle. Rumen fluid from four fistulated feedlot cattle fed a diet of 860 dry-rolled barley grain, 90 maize silage and 50 supplement g/kg DM was used as inoculum in 3 batch culture in vitro studies. In Experiment 1, dry-rolled barley and barley ground through a 1-, 2-, or 4-mm screen were used to obtain four substrates differing in particle size. In Experiment 2, cellulase enzyme (ENZ) from Acremonium cellulolyticus Y-94 was added to dry-rolled and ground barley (2-mm) at 0, 0.1, 0.5, 1, and 2 mg/g, while Experiment 3 examined the interactions between microwaving (0, 30, and 60 s microwaving) and ENZ addition (0, 1, and 2 mg/g) using dry-rolled barley and 2-mm ground barley. In Experiment 1, decreasing particle size increased DMD and gas production, and decreased fermentation pH (pgas production and decreased (pgas production, and decreased (p<0.05) fermentation pH of dry-rolled barley, but not ground barley. We conclude that cellulase enzymes can be used to increase the rumen disappearance of barley grain when it is coarsely processed as in the case of dry-rolled barley. However, microwaving of barley grain offered no further improvements in ruminal fermentation of barley grain.

Monte-Carlo simulations in a gas centrifuge

International Nuclear Information System (INIS)

Roblin, Ph.; Doneddu, F.

2000-01-01

This paper is associated with the centrifugation process for isotope separation, using the principle of a cylinder rotating at high speed in a vacuum casing. As in the most widely used configuration, the gas containing the isotope mixture is introduced by a fixed axial feed pipe and expands in the cylinder. It is subjected to high centrifugal acceleration, undergoes rigid body rotation and stratifies radially according to a barometric-type pressure law. By pressure diffusion, the heavier isotopes migrate to the cylinder wall and the lighter to the center. A temperature gradient on the wall and the presence of a scoop in the fluid, produce a vertical countercurrent which transforms the radial separation effect into an axial effect. The scoop extracts the gas depleted in light isotopes, called W, and another is used to recover the gas enriched in light isotopes, called P. Practically all the gas is governed by the Navier-Stokes equations in 2D axial symmetry. Due to the strong pressure stratification, continuous fluid equations are not valid in the whole cylinder, with or without linearization of the model. Consequently, an internal boundary separates the continuum domain from a rarefied domain in which the feed gas expands. The radial position of this cut-off then approaches the cylinder wall with increasing rotation speeds. In the rarefied domain, the Boltzmann equation is solved and a well suited numerical method is the Monte-Carlo method. A complete simulation of feed gas expansion and interaction with rotating gas, presented here with the DSMC (Direct Simulation Monte-Carlo) code, provides realistic boundary conditions for fluid flow calculations. The reference centrifuge is a hypothetical machine enabling the scientific community to compare results obtained for the optimization of separation performance. Its radius a is 6 cm, and its peripheral speed a is 600 m/s. The selected gas, containing the isotopes, is UF 6 . The gas pressure p(a) at the cylinder wall is

Three-Dimensional Neutral Transport Simulations of Gas Puff Imaging Experiments

International Nuclear Information System (INIS)

Stotler, D.P.; DIppolito, D.A.; LeBlanc, B.; Maqueda, R.J.; Myra, J.R.; Sabbagh, S.A.; Zweben, S.J.

2003-01-01

Gas Puff Imaging (GPI) experiments are designed to isolate the structure of plasma turbulence in the plane perpendicular to the magnetic field. Three-dimensional aspects of this diagnostic technique as used on the National Spherical Torus eXperiment (NSTX) are examined via Monte Carlo neutral transport simulations. The radial width of the simulated GPI images are in rough agreement with observations. However, the simulated emission clouds are angled approximately 15 degrees with respect to the experimental images. The simulations indicate that the finite extent of the gas puff along the viewing direction does not significantly degrade the radial resolution of the diagnostic. These simulations also yield effective neutral density data that can be used in an approximate attempt to infer two-dimensional electron density and temperature profiles from the experimental images

Process/Equipment Co-Simulation on Syngas Chemical Looping Process

Energy Technology Data Exchange (ETDEWEB)

Zeng, Liang; Zhou, Qiang; Fan, Liang-Shih

2012-09-30

The chemical looping strategy for fossil energy applications promises to achieve an efficient energy conversion system for electricity, liquid fuels, hydrogen and/or chemicals generation, while economically separate CO{sub 2} by looping reaction design in the process. Chemical looping particle performance, looping reactor engineering, and process design and applications are the key drivers to the success of chemical looping process development. In order to better understand and further scale up the chemical looping process, issues such as cost, time, measurement, safety, and other uncertainties need to be examined. To address these uncertainties, advanced reaction/reactor modeling and process simulation are highly desired and the modeling efforts can accelerate the chemical looping technology development, reduce the pilot-scale facility design time and operating campaigns, as well as reduce the cost and technical risks. The purpose of this work is thus to conduct multiscale modeling and simulations on the key aspects of chemical looping technology, including particle reaction kinetics, reactor design and operation, and process synthesis and optimization.

Efficient radiative transfer in dust grain mixtures

OpenAIRE

Wolf, S.

2002-01-01

The influence of a dust grain mixture consisting of spherical dust grains with different radii and/or chemical composition on the resulting temperature structure and spectral energy distribution of a circumstellar shell is investigated. The comparison with the results based on an approximation of dust grain parameters representing the mean optical properties of the corresponding dust grain mixture reveal that (1) the temperature dispersion of a real dust grain mixture decreases substantially ...

Mechanical Behavior of Nanostructured and Ultrafine Grained Materials under Shock Wave Loadings. Experimental Data and Results of Computer Simulation.

Science.gov (United States)

Skripnyak, Vladimir

2011-06-01

Features of mechanical behavior of nanostructured (NS) and ultrafine grained (UFG) metal and ceramic materials under quasistatic and shock wave loadings are discussed in this report. Multilevel models developed within the approach of computational mechanics of materials were used for simulation mechanical behavior of UFG and NS metals and ceramics. Comparisons of simulation results with experimental data are presented. Models of mechanical behavior of nanostructured metal alloys takes into account a several structural factors influencing on the mechanical behavior of materials (type of a crystal lattice, density of dislocations, a size of dislocation substructures, concentration and size of phase precipitation, and distribution of grains sizes). Results show the strain rate sensitivity of the yield stress of UFG and polycrystalline alloys is various in a range from 103 up to 106 1/s. But the difference of the Hugoniot elastic limits of a UFG and coarse-grained alloys may be not considerable. The spall strength, the yield stress of UFG and NS alloys are depend not only on grains size, but a number of factors such as a distribution of grains sizes, a concentration and sizes of voids and cracks, a concentration and sizes of phase precipitation. Some titanium alloys with grain sizes from 300 to 500 nm have the quasi-static yield strength and the tensile strength twice higher than that of coarse grained counterparts. But the spall strength of the UFG titanium alloys is only 10 percents above than that of coarse grained alloys. At the same time it was found the spall strength of the bulk UFG aluminium and magnesium alloys with precipitation strengthening is essentially higher in comparison of coarse-grained counterparts. The considerable decreasing of the strain before failure of UFG alloys was predicted at high strain rates. The Hugoniot elastic limits of oxide nanoceramics depend not only on the porosity, but also on sizes and volume distribution of voids.

Simulation and validation of chemical-looping combustion using ASPEN plus

Energy Technology Data Exchange (ETDEWEB)

Zhou, Ling [Research Center of Fluid Machinery Engineering and Technology, Jiangsu University, Zhenjiang 212013 (China); Department of Mechanical Engineering and Materials Science, Washington University, St. Louis, MO 63130 (United States); Zhang, Zheming; Agarwal, Ramesh K. [Department of Mechanical Engineering and Materials Science, Washington University, St. Louis, MO 63130 (United States)

2013-07-01

Laboratory-scale experimental studies have demonstrated that Chemical-Looping Combustion (CLC) is an advanced technology which holds great potential for high-efficiency low-cost carbon capture. The generated syngas in CLC is subsequently oxidized to CO2 and H2O by reaction with an oxygen carrier. In this paper, process-level models of CLC are established in ASPEN Plus code for detailed simulations. The entire CLC process, from the beginning of coal gasification to reduction and oxidation of the oxygen carrier is modeled. The heat content of each major component such as fuel and air reactors and air/flue gas heat exchangers is carefully examined. Large amount of energy is produced in the fuel reactor, but energy needs to be supplied to the air reactor. The overall performance and efficiency of the modeled CLC systems are also evaluated.

Gas chromatographic simulated distillation-mass spectrometry for the determination of the boiling point distributions of crude oils

Science.gov (United States)

Roussis; Fitzgerald

2000-04-01

The coupling of gas chromatographic simulated distillation with mass spectrometry for the determination of the distillation profiles of crude oils is reported. The method provides the boiling point distributions of both weight and volume percent amounts. The weight percent distribution is obtained from the measured total ion current signal. The total ion current signal is converted to weight percent amount by calibration with a reference crude oil of a known distillation profile. Knowledge of the chemical composition of the crude oil across the boiling range permits the determination of the volume percent distribution. The long-term repeatability is equivalent to or better than the short-term repeatability of the currently available American Society for Testing and Materials (ASTM) gas chromatographic method for simulated distillation. Results obtained by the mass spectrometric method are in very good agreement with results obtained by conventional methods of physical distillation. The compositional information supplied by the method can be used to extensively characterize crude oils.

Abnormal grain growth: a non-equilibrium thermodynamic model for multi-grain binary systems

International Nuclear Information System (INIS)

Svoboda, J; Fischer, F D

2014-01-01

Abnormal grain growth as the abrupt growth of a group of the largest grains in a multi-grain system is treated within the context of unequal retardation of grain growth due to the segregation of solute atoms from the bulk of the grains into the grain boundaries. During grain boundary migration, the segregated solute atoms are dragged under a small driving force or left behind the migrating grain boundary under a large driving force. Thus, the solute atoms in the grain boundaries of large grains, exhibiting a large driving force, can be released from the grain boundary. The mobility of these grain boundaries becomes significantly higher and abnormal grain growth is spontaneously provoked. The mean-field model presented here assumes that each grain is described by its grain radius and by its individual segregation parameter. The thermodynamic extremal principle is engaged to obtain explicit evolution equations for the radius and segregation parameter of each grain. Simulations of grain growth kinetics for various conditions of segregation with the same initial setting (100 000 grains with a given radius distribution) are presented. Depending on the diffusion coefficients of the solute in the grain boundaries, abnormal grain growth may be strongly or marginally pronounced. Solute segregation and drag can also significantly contribute to the stabilization of the grain structure. Qualitative agreement with several experimental results is reported. (paper)

Probing the folded state and mechanical unfolding pathways of T4 lysozyme using all-atom and coarse-grained molecular simulation

Energy Technology Data Exchange (ETDEWEB)

Zheng, Wenjun, E-mail: wjzheng@buffalo.edu; Glenn, Paul [Department of Physics, University at Buffalo, Buffalo, New York 14260 (United States)

2015-01-21

The Bacteriophage T4 Lysozyme (T4L) is a prototype modular protein comprised of an N-terminal and a C-domain domain, which was extensively studied to understand the folding/unfolding mechanism of modular proteins. To offer detailed structural and dynamic insights to the folded-state stability and the mechanical unfolding behaviors of T4L, we have performed extensive equilibrium and steered molecular dynamics simulations of both the wild-type (WT) and a circular permutation (CP) variant of T4L using all-atom and coarse-grained force fields. Our all-atom and coarse-grained simulations of the folded state have consistently found greater stability of the C-domain than the N-domain in isolation, which is in agreement with past thermostatic studies of T4L. While the all-atom simulation cannot fully explain the mechanical unfolding behaviors of the WT and the CP variant observed in an optical tweezers study, the coarse-grained simulations based on the Go model or a modified elastic network model (mENM) are in qualitative agreement with the experimental finding of greater unfolding cooperativity in the WT than the CP variant. Interestingly, the two coarse-grained models predict different structural mechanisms for the observed change in cooperativity between the WT and the CP variant—while the Go model predicts minor modification of the unfolding pathways by circular permutation (i.e., preserving the general order that the N-domain unfolds before the C-domain), the mENM predicts a dramatic change in unfolding pathways (e.g., different order of N/C-domain unfolding in the WT and the CP variant). Based on our simulations, we have analyzed the limitations of and the key differences between these models and offered testable predictions for future experiments to resolve the structural mechanism for cooperative folding/unfolding of T4L.

Gas flows in the circumgalactic medium around simulated high-redshift galaxies

Science.gov (United States)

Mitchell, Peter D.; Blaizot, Jérémy; Devriendt, Julien; Kimm, Taysun; Michel-Dansac, Léo; Rosdahl, Joakim; Slyz, Adrianne

2018-03-01

We analyse the properties of circumgalactic gas around simulated galaxies in the redshift range z ≥ 3, utilizing a new sample of cosmological zoom simulations. These simulations are intended to be representative of the observed samples of Lyman α (Ly α) emitters recently obtained with the multi unit spectroscopic explorer (MUSE) instrument (halo masses ˜1010-1011 M⊙). We show that supernova feedback has a significant impact on both the inflowing and outflowing circumgalactic medium (CGM) by driving outflows, reducing diffuse inflow rates, and by increasing the neutral fraction of inflowing gas. By temporally stacking simulation outputs, we find that significant net mass exchange occurs between inflowing and outflowing phases: none of the phases are mass-conserving. In particular, we find that the mass in neutral outflowing hydrogen declines exponentially with radius as gas flows outwards from the halo centre. This is likely caused by a combination of both fountain-like cycling processes and gradual photoionization/collisional ionization of outflowing gas. Our simulations do not predict the presence of fast-moving neutral outflows in the CGM. Neutral outflows instead move with modest radial velocities (˜50 km s-1), and the majority of the kinetic energy is associated with tangential rather than radial motion.

CHEMICAL AND PHYSICAL CHARACTERIZATION OF COLLAPSING LOW-MASS PRESTELLAR DENSE CORES

Energy Technology Data Exchange (ETDEWEB)

Hincelin, U. [Department of Chemistry, University of Virginia, Charlottesville, VA 22904 (United States); Commerçon, B. [Ecole Normale Supérieure de Lyon, CRAL, UMR 5574 du CNRS, Université Lyon I, 46 Allée d’Italie, F-69364 Lyon cedex 07 (France); Wakelam, V.; Hersant, F.; Guilloteau, S. [Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac (France); Herbst, E., E-mail: ugo.hincelin@gmail.com [Departments of Chemistry and Astronomy, University of Virginia, Charlottesville, VA 22904 (United States)

2016-05-01

The first hydrostatic core, also called the first Larson core, is one of the first steps in low-mass star formation as predicted by theory. With recent and future high-performance telescopes, the details of these first phases are becoming accessible, and observations may confirm theory and even present new challenges for theoreticians. In this context, from a theoretical point of view, we study the chemical and physical evolution of the collapse of prestellar cores until the formation of the first Larson core, in order to better characterize this early phase in the star formation process. We couple a state-of-the-art hydrodynamical model with full gas-grain chemistry, using different assumptions for the magnetic field strength and orientation. We extract the different components of each collapsing core (i.e., the central core, the outflow, the disk, the pseudodisk, and the envelope) to highlight their specific physical and chemical characteristics. Each component often presents a specific physical history, as well as a specific chemical evolution. From some species, the components can clearly be differentiated. The different core models can also be chemically differentiated. Our simulation suggests that some chemical species act as tracers of the different components of a collapsing prestellar dense core, and as tracers of the magnetic field characteristics of the core. From this result, we pinpoint promising key chemical species to be observed.

Deformation mechanisms and grain size evolution in the Bohemian granulites - a computational study

Science.gov (United States)

Maierova, Petra; Lexa, Ondrej; Jeřábek, Petr; Franěk, Jan; Schulmann, Karel

2015-04-01

A dominant deformation mechanism in crustal rocks (e.g., dislocation and diffusion creep, grain boundary sliding, solution-precipitation) depends on many parameters such as temperature, major minerals, differential stress, strain rate and grain size. An exemplary sequence of deformation mechanisms was identified in the largest felsic granulite massifs in the southern Moldanubian domain (Bohemian Massif, central European Variscides). These massifs were interpreted to result from collision-related forced diapiric ascent of lower crust and its subsequent lateral spreading at mid-crustal levels. Three types of microstructures were distinguished. The oldest relict microstructure (S1) with large grains (>1000 μm) of feldspar deformed probably by dislocation creep at peak HT eclogite facies conditions. Subsequently at HP granulite-facies conditions, chemically- and deformation- induced recrystallization of feldspar porphyroclasts led to development of a fine-grained microstructure (S2, ~50 μm grain size) indicating deformation via diffusion creep, probably assisted by melt-enhanced grain-boundary sliding. This microstructure was associated with flow in the lower crust and/or its diapiric ascent. The latest microstructure (S3, ~100 μm grain size) is related to the final lateral spreading of retrograde granulites, and shows deformation by dislocation creep at amphibolite-facies conditions. The S2-S3 switch and coarsening was interpreted to be related with a significant decrease in strain rate. From this microstructural sequence it appears that it is the grain size that is critically linked with specific mechanical behavior of these rocks. Thus in this study, we focused on the interplay between grain size and deformation with the aim to numerically simulate and reinterpret the observed microstructural sequence. We tested several different mathematical descriptions of the grain size evolution, each of which gave qualitatively different results. We selected the two most

Pushing the frontiers of first-principles based computer simulations of chemical and biological systems.

Science.gov (United States)

Brunk, Elizabeth; Ashari, Negar; Athri, Prashanth; Campomanes, Pablo; de Carvalho, F Franco; Curchod, Basile F E; Diamantis, Polydefkis; Doemer, Manuel; Garrec, Julian; Laktionov, Andrey; Micciarelli, Marco; Neri, Marilisa; Palermo, Giulia; Penfold, Thomas J; Vanni, Stefano; Tavernelli, Ivano; Rothlisberger, Ursula

2011-01-01

The Laboratory of Computational Chemistry and Biochemistry is active in the development and application of first-principles based simulations of complex chemical and biochemical phenomena. Here, we review some of our recent efforts in extending these methods to larger systems, longer time scales and increased accuracies. Their versatility is illustrated with a diverse range of applications, ranging from the determination of the gas phase structure of the cyclic decapeptide gramicidin S, to the study of G protein coupled receptors, the interaction of transition metal based anti-cancer agents with protein targets, the mechanism of action of DNA repair enzymes, the role of metal ions in neurodegenerative diseases and the computational design of dye-sensitized solar cells. Many of these projects are done in collaboration with experimental groups from the Institute of Chemical Sciences and Engineering (ISIC) at the EPFL.

A novel grain cluster-based homogenization scheme

International Nuclear Information System (INIS)

Tjahjanto, D D; Eisenlohr, P; Roters, F

2010-01-01

An efficient homogenization scheme, termed the relaxed grain cluster (RGC), for elasto-plastic deformations of polycrystals is presented. The scheme is based on a generalization of the grain cluster concept. A volume element consisting of eight (= 2 × 2 × 2) hexahedral grains is considered. The kinematics of the RGC scheme is formulated within a finite deformation framework, where the relaxation of the local deformation gradient of each individual grain is connected to the overall deformation gradient by the, so-called, interface relaxation vectors. The set of relaxation vectors is determined by the minimization of the constitutive energy (or work) density of the overall cluster. An additional energy density associated with the mismatch at the grain boundaries due to relaxations is incorporated as a penalty term into the energy minimization formulation. Effectively, this penalty term represents the kinematical condition of deformation compatibility at the grain boundaries. Simulations have been performed for a dual-phase grain cluster loaded in uniaxial tension. The results of the simulations are presented and discussed in terms of the effective stress–strain response and the overall deformation anisotropy as functions of the penalty energy parameters. In addition, the prediction of the RGC scheme is compared with predictions using other averaging schemes, as well as to the result of direct finite element (FE) simulation. The comparison indicates that the present RGC scheme is able to approximate FE simulation results of relatively fine discretization at about three orders of magnitude lower computational cost

Health benefits of ancient grains. Comparison among bread made with ancient, heritage and modern grain flours in human cultured cells.

Science.gov (United States)

Valli, Veronica; Taccari, Annalisa; Di Nunzio, Mattia; Danesi, Francesca; Bordoni, Alessandra

2018-05-01

Nowadays the higher nutritional value of whole grains compared to refined grains is recognized. In the last decade, there has been a renewed interest in the ancient wheat varieties for producing high-value food products with enhanced health benefits. This study compared two ancient grains, two heritage grains, and four modern grains grown in the same agronomic conditions considering not only their chemical characteristics, but also their biological effects. Whole grain flours were obtained and used to make bread. Bread was in vitro digested, the digesta were supplemented to HepG2 cells, and the biological effects of supplementation were evaluated. In addition, cells previously supplemented with the different digested bread types were then exposed to inflammatory agents to evidence possible protective effects of the pre-treatments. Despite the impossibility to discriminate bread made with different grains based on their chemical composition, results herein reported evidence that their supplementation to cultured cells exerts different effects, confirming the potential health benefits of ancient grains. This research represents an advancement for the evaluation of the apparent positive effects of ancient grains and the formulation of cereal-based products with added nutritional value. Copyright © 2018 Elsevier Ltd. All rights reserved.

Dust trap formation in a non-self-sustained discharge with external gas ionization

International Nuclear Information System (INIS)

Filippov, A. V.; Babichev, V. N.; Pal’, A. F.; Starostin, A. N.; Cherkovets, V. E.; Rerikh, V. K.; Taran, M. D.

2015-01-01

Results from numerical studies of a non-self-sustained gas discharge containing micrometer dust grains are presented. The non-self-sustained discharge (NSSD) was controlled by a stationary fast electron beam. The numerical model of an NSSD is based on the diffusion drift approximation for electrons and ions and self-consistently takes into account the influence of the dust component on the electron and ion densities. The dust component is described by the balance equation for the number of dust grains and the equation of motion for dust grains with allowance for the Stokes force, gravity force, and electric force in the cathode sheath. The interaction between dust grains is described in the self-consistent field approximation. The height of dust grain levitation over the cathode is determined and compared with experimental results. It is established that, at a given gas ionization rate and given applied voltage, there is a critical dust grain size above which the levitation condition in the cathode sheath cannot be satisfied. Simulations performed for the dust component consisting of dust grains of two different sizes shows that such grains levitate at different heights, i.e., size separation of dust drains levitating in the cathode sheath of an NSSD takes place

Dust trap formation in a non-self-sustained discharge with external gas ionization

Energy Technology Data Exchange (ETDEWEB)

Filippov, A. V., E-mail: fav@triniti.ru; Babichev, V. N.; Pal’, A. F.; Starostin, A. N.; Cherkovets, V. E.; Rerikh, V. K.; Taran, M. D. [Troitsk Institute for Innovation and Fusion Research (Russian Federation)

2015-11-15

Results from numerical studies of a non-self-sustained gas discharge containing micrometer dust grains are presented. The non-self-sustained discharge (NSSD) was controlled by a stationary fast electron beam. The numerical model of an NSSD is based on the diffusion drift approximation for electrons and ions and self-consistently takes into account the influence of the dust component on the electron and ion densities. The dust component is described by the balance equation for the number of dust grains and the equation of motion for dust grains with allowance for the Stokes force, gravity force, and electric force in the cathode sheath. The interaction between dust grains is described in the self-consistent field approximation. The height of dust grain levitation over the cathode is determined and compared with experimental results. It is established that, at a given gas ionization rate and given applied voltage, there is a critical dust grain size above which the levitation condition in the cathode sheath cannot be satisfied. Simulations performed for the dust component consisting of dust grains of two different sizes shows that such grains levitate at different heights, i.e., size separation of dust drains levitating in the cathode sheath of an NSSD takes place.

Emergent dynamic structures and statistical law in spherical lattice gas automata

Science.gov (United States)

Yao, Zhenwei

2017-12-01

Various lattice gas automata have been proposed in the past decades to simulate physics and address a host of problems on collective dynamics arising in diverse fields. In this work, we employ the lattice gas model defined on the sphere to investigate the curvature-driven dynamic structures and analyze the statistical behaviors in equilibrium. Under the simple propagation and collision rules, we show that the uniform collective movement of the particles on the sphere is geometrically frustrated, leading to several nonequilibrium dynamic structures not found in the planar lattice, such as the emergent bubble and vortex structures. With the accumulation of the collision effect, the system ultimately reaches equilibrium in the sense that the distribution of the coarse-grained speed approaches the two-dimensional Maxwell-Boltzmann distribution despite the population fluctuations in the coarse-grained cells. The emergent regularity in the statistical behavior of the system is rationalized by mapping our system to a generalized random walk model. This work demonstrates the capability of the spherical lattice gas automaton in revealing the lattice-guided dynamic structures and simulating the equilibrium physics. It suggests the promising possibility of using lattice gas automata defined on various curved surfaces to explore geometrically driven nonequilibrium physics.

Emergent dynamic structures and statistical law in spherical lattice gas automata.

Science.gov (United States)

Yao, Zhenwei

2017-12-01

Various lattice gas automata have been proposed in the past decades to simulate physics and address a host of problems on collective dynamics arising in diverse fields. In this work, we employ the lattice gas model defined on the sphere to investigate the curvature-driven dynamic structures and analyze the statistical behaviors in equilibrium. Under the simple propagation and collision rules, we show that the uniform collective movement of the particles on the sphere is geometrically frustrated, leading to several nonequilibrium dynamic structures not found in the planar lattice, such as the emergent bubble and vortex structures. With the accumulation of the collision effect, the system ultimately reaches equilibrium in the sense that the distribution of the coarse-grained speed approaches the two-dimensional Maxwell-Boltzmann distribution despite the population fluctuations in the coarse-grained cells. The emergent regularity in the statistical behavior of the system is rationalized by mapping our system to a generalized random walk model. This work demonstrates the capability of the spherical lattice gas automaton in revealing the lattice-guided dynamic structures and simulating the equilibrium physics. It suggests the promising possibility of using lattice gas automata defined on various curved surfaces to explore geometrically driven nonequilibrium physics.

Semiconductor device-based sensors for gas, chemical, and biomedical applications

CERN Document Server

Ren, Fan

2011-01-01

Sales of U.S. chemical sensors represent the largest segment of the multi-billion-dollar global sensor market, which includes instruments for chemical detection in gases and liquids, biosensors, and medical sensors. Although silicon-based devices have dominated the field, they are limited by their general inability to operate in harsh environments faced with factors such as high temperature and pressure. Exploring how and why these instruments have become a major player, Semiconductor Device-Based Sensors for Gas, Chemical, and Biomedical Applications presents the latest research, including or

Simulating the control of molecular reactions via modulated light fields: from gas phase to solution

Science.gov (United States)

Thallmair, Sebastian; Keefer, Daniel; Rott, Florian; de Vivie-Riedle, Regina

2017-04-01

Over the past few years quantum control has proven to be very successful in steering molecular processes. By combining theory with experiment, even highly complex control aims were realized in the gas phase. In this topical review, we illustrate the past achievements on several examples in the molecular context. The next step for the quantum control of chemical processes is to translate the fruitful interplay between theory and experiment to the condensed phase and thus to the regime where chemical synthesis can be supported. On the theory side, increased efforts to include solvent effects in quantum control simulations were made recently. We discuss two major concepts, namely an implicit description of the environment via the density matrix algorithm and an explicit inclusion of solvent molecules. By application to chemical reactions, both concepts conclude that despite environmental perturbations leading to more complex control tasks, efficient quantum control in the condensed phase is still feasible.

Influence of aging on culinary and chemical properties of basmati 385 rice grain

International Nuclear Information System (INIS)

Ali, L.; Ali, A.; Karim, M.A.; Ali, S.S.; Hassan, G.

2004-01-01

The influence of aging of milled rice on physico-chemical characteristics was studied during 1989-90 and 1990-91. Rice from freshly harvested paddy was stored in a cloth bag at room temperature. Analysis of rice was done for 24-months, starting from zero at a uniform interval of one month. However the effect of aging on cooking time was not significant. Water absorption and volume expansion increased throughout the aging period. Similarly, cooked grain length was minimum (13.9 mm) in freshly milled rice, it increased gradually with the storage period and obtained a maximum value (15.5 mm) after 2-year storage. Bursting of grains during cooking decreased from 11.5% to 2.0% on storage. Loss of total solids in washing water and gruel was the highest (14.9%) at the beginning of the experiment which decreased significantly and reached the lowest value (3.2%) at the completion of the studies. The effect of aging on protein content, alkali spreading value and gel length was, however, non-significant. Amylose content decreased slightly during aging but remained in the intermediate amylose group. (author)

Micromagnetic simulation of anisotropic grain boundary diffusion for sintered Nd-Fe-B magnets

Science.gov (United States)

Li, W.; Zhou, Q.; Zhao, L. Z.; Wang, Q. X.; Zhong, X. C.; Liu, Z. W.

2018-04-01

A systematic investigation on the anisotropic grain boundary diffusion in sintered Nd-Fe-B magnets is carried out by micromagnetic simulation. The results indicate that the critical reason for the anisotropic diffusion effect is not the difference in the amount of Dy diffused along different directions but the macroscopic demagnetizing field. The diffusion parallel to the easy axis from both pole surfaces of the magnet can increase the nucleation fields in the two major regions with large macroscopic demagnetizing fields, where the reverse domains can nucleate easily. As a consequence, the grain boundary diffusion along the directions parallel to the easy axis from two pole surfaces is more effective to improve the coercivity of the magnets than that along other directions. It is also found that, to enhance the coercivity, only a limited diffusion depth is required. The present result is in good agreement with the recent experimental findings.

Comparison of chemical, rheological and sensory properties of kefir produced by kefir grains and commercial kefir starter

Directory of Open Access Journals (Sweden)

Irena Barukčić

2017-01-01

Full Text Available The main objective of this study was to compare chemical, rheological and sensory characteristics of kefir produced by using kefir grains and kefir starter. The intent was also to investigate whether it is plausible to use a combined inoculum (kefir grains and starter in order to obtain a kefir with improved characteristics in terms of sensory and rheological characteristics. Kefir samples were produced at 25 °C and 35 °C by using starter culture XPL-1, kefir grains and their combinations. All of the produced kefir samples were analysed for acidity, total dry matter, ethanol content, syneresis, viscosity and were sensory evaluated by a specially trained panel. There were no significant differences considering the total dry matter, syneresis, ethanol content and acidity. Excess viscosity was observed in samples produced by starter culture at 35 °C, which was described as untypical, yoghurt like and unsatisfactory by a sensory panel. The sample produced at 25 °C by equal amounts of kefir grains and starter culture received the highest scores at sensory evaluation and showed the best potential for optimizing the further use. Further investigations need to focus on examining kefir properties during the storage period, especially regarding microbiological and sensory properties, ethanol content and texture profile.

Essentials of water systems design in the oil, gas, and chemical processing industries

CERN Document Server

Bahadori, Alireza; Boyd, Bill

2013-01-01

Essentials of Water Systems Design in the Oil, Gas and Chemical Processing Industries provides valuable insight for decision makers by outlining key technical considerations and requirements of four critical systems in industrial processing plants—water treatment systems, raw water and plant water systems, cooling water distribution and return systems, and fire water distribution and storage facilities. The authors identify the key technical issues and minimum requirements related to the process design and selection of various water supply systems used in the oil, gas, and chemical processing industries. This book is an ideal, multidisciplinary work for mechanical engineers, environmental scientists, and oil and gas process engineers.

CHEMSIMUL: A simulator for chemical kinetics

DEFF Research Database (Denmark)

Kirkegaard, P.; Bjergbakke, E.

1999-01-01

CHEMSIMUL is a computer program system for numerical simulation of chemical reaction systems. It can be used for modeling complex kinetics in many contexts, in particular radiolytic processes. It contains a translator module and a module for solving theresulting coupled nonlinear ordinary...

Chemical sensors and gas sensors for process control in biotechnology

International Nuclear Information System (INIS)

Williams, D.E.

1988-04-01

This paper is concerned with the possibilities for chemical measurement of the progress of biotechnological processes which are offered by devices already developed for other demanding applications. It considers the potential use of ultrasonic instrumentation originally developed for the nuclear industry, gas measurement methods from the fields of environmental monitoring and combustion control, nuclear instruments developed for the oil, mining and chemical industries, robotic systems and advanced control techniques. (author)

Modeling and Simulation of the Sulfur-Iodine Process Coupled to a Very High-Temperature Gas-Cooled Nuclear Reactor