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Sample records for layer evolution model

  1. Modelling of the layer evolution during nitriding processes

    SciTech Connect

    Figueroa, U.; Oseguera, J.; Schabes, P.

    1995-12-31

    The evolution of concomitant layers of nitrides is presented. The layer formation is experimentally achieved through two processes: Nitriding with a weakly ionized plasma and nitrogen post-discharge nitriding. The nitriding processes were performed on samples of pure iron and carbon steel. Nitriding temperatures were close but different from the eutectoid transformation point temperature. The experimental layer growth pattern is compared with a model of mass transfer, in which interface mass balance is considered. In the model the authors have considered the formation of one and two compact nitride layers. For short time of treatment, it is shown that a parabolic profile does not satisfactorily describe the layer growth.

  2. Uranus evolution models with simple thermal boundary layers

    NASA Astrophysics Data System (ADS)

    Nettelmann, Nadine; Redmer, Ronald; Fortney, Jonathan J.; Hamel, Sebastien; Bethkenhagen, Mandy

    2016-04-01

    The strikingly low luminosity of Uranus imposes a long-standing challenge to our understanding of Ice Giant planets. Similar to the Earth, Uranus appears to evolve in equilibrium with the solar incident flux (Teq). Here we present the first Uranus structure and evolution models that are constructed to agree with both the observed low luminosity and the gravity field data. Our models make use of modern ab initio equations of state at high pressures for the icy components water, methane, and ammonia. We argue that the transition between the ice/rock-rich interior and the H/He-rich outer envelope should be stably stratified. Therefore, we introduce a simple thermal boundary layer (TBL) and adjust it to reproduce the luminosity. Due to this TBL, the deep interior of the Uranus models are up to a factor 3 warmer than adiabatic models, necessitating the presence of rocks there with a possible I:R of 1 x solar. Furthermore, we also allow for an equilibrium evolution (Teff ~ Teq) that begun prior to the present day, which would therefore no longer constitute a "special time" in Uranus' evolution. Once Teff ~ Teq happens, a shallow, subadiabatic zone in the atmosphere begins to develop. Its depth is adjusted to meet the luminosity constraint. This work provides a simple foundation for future Ice Giant structure and evolution models, that can be improved by properly treating the heat and particle fluxes in the diffusive zones.

  3. A model for plate tectonic evolution of mantle layers.

    PubMed

    Dickinson, W R; Luth, W C

    1971-10-22

    In plate tectonic theory, lithosphere that descends into the mantle has a largely derivative composition, because it is produced as a refractory residue by partial melting, and cannot be resorbed readily by the parent mantle. We suggest that lithosphere sinks through the asthenosphere, or outer mantle, and accumulates progressively beneath to form an accretionary mesosphere, or inner mantle. According to this model, there is an irreversible physicochemical evolution of the mantle and its layers. We make the key assumption that the rate at which mass has been transferred from the lithosphere to the mesosphere is proportional to the rate of radiogenic heat production. Calculations of mass transfer with time demonstrate that the entire mass of the present mesosphere could have been produced in geologically reasonable times (3 x 10(9) to 4.5 x 10(9) years). The model is consistent with the generation of the continental crust during the last 3 x 1O(9) years and predicts an end to plate tectonic behavior within the next 10(9) years. PMID:17796091

  4. Uranus evolution models with simple thermal boundary layers

    NASA Astrophysics Data System (ADS)

    Nettelmann, N.; Wang, K.; Fortney, J. J.; Hamel, S.; Yellamilli, S.; Bethkenhagen, M.; Redmer, R.

    2016-09-01

    The strikingly low luminosity of Uranus (Teff ≃ Teq) constitutes a long-standing challenge to our understanding of Ice Giant planets. Here we present the first Uranus structure and evolution models that are constructed to agree with both the observed low luminosity and the gravity field data. Our models make use of modern ab initio equations of state at high pressures for the icy components water, methane, and ammonia. Proceeding step by step, we confirm that adiabatic models yield cooling times that are too long, even when uncertainties in the ice:rock ratio (I:R) are taken into account. We then argue that the transition between the ice/rock-rich interior and the H/He-rich outer envelope should be stably stratified. Therefore, we introduce a simple thermal boundary and adjust it to reproduce the low luminosity. Due to this thermal boundary, the deep interior of the Uranus models are up to 2-3 warmer than adiabatic models, necessitating the presence of rocks in the deep interior with a possible I:R of 1 × solar. Finally, we allow for an equilibrium evolution (Teff ≃ Teq) that begun prior to the present day, which would therefore no longer require the current era to be a "special time" in Uranus' evolution. In this scenario, the thermal boundary leads to more rapid cooling of the outer envelope. When Teff ≃ Teq is reached, a shallow, subadiabatic zone in the atmosphere begins to develop. Its depth is adjusted to meet the luminosity constraint. This work provides a simple foundation for future Ice Giant structure and evolution models, that can be improved by properly treating the heat and particle fluxes in the diffusive zones.

  5. Saturn layered structure and homogeneous evolution models with different EOSs

    NASA Astrophysics Data System (ADS)

    Nettelmann, Nadine; Püstow, Robert; Redmer, Ronald

    2013-07-01

    The core mass of Saturn is commonly assumed to be 10-25M⊕ as predicted by interior models with various equations of state (EOSs) and the Voyager gravity data, and hence larger than that of Jupiter (0-10M⊕). We here re-analyze Saturn's internal structure and evolution by using more recent gravity data from the Cassini mission and different physical equations of state: the ab initio LM-REOS which is rather soft in Saturn's outer regions but stiff at high pressures, the standard Sesame-EOS which shows the opposite behavior, and the commonly used SCvH-i EOS. For all three EOS we find similar core mass ranges, i.e. of 0-20M⊕ for SCvH-i and Sesame EOS and of 0-17M⊕ for LM-REOS. Assuming an atmospheric helium mass abundance of 18%, we find maximum atmospheric metallicities, Zatm of 7× solar for SCvH-i and Sesame-based models and a total mass of heavy elements, MZ of 25-30M⊕. Some models are Jupiter-like. With LM-REOS, we find MZ = 16-20M⊕, less than for Jupiter, and Zatm ≲ 3× solar. For Saturn, we compute moment of inertia values λ = 0.2355(5). Furthermore, we confirm that homogeneous evolution leads to cooling times of only ˜2.5 Gyr, independent on the applied EOS. Our results demonstrate the need for accurately measured atmospheric helium and oxygen abundances, and of the moment of inertia for a better understanding of Saturn's structure and evolution.

  6. Numerical modeling studies of wake vortex transport and evolution within the planetary boundary layer

    NASA Technical Reports Server (NTRS)

    Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael L.

    1994-01-01

    The proposed research involves four tasks. The first of these is to simulate accurately the turbulent processes in the atmospheric boundary layer. TASS was originally developed to study meso-gamma scale phenomena, such as tornadic storms, microbursts and windshear effects in terminal areas. Simulation of wake vortex evolution, however, will rely on appropriate representation of the physical processes in the surface layer and mixed layer. This involves two parts. First, a specified heat flux boundary condition must be implemented at the surface. Using this boundary condition, simulation results will be compared to experimental data and to other model results for validation. At this point, any necessary changes to the model will be implemented. Next, a surface energy budget parameterization will be added to the model. This will enable calculation of the surface fluxes by accounting for the radiative heat transfer to and from the ground and heat loss to the soil rather than simple specification of the fluxes. The second task involves running TASS with prescribed wake vortices in the initial condition. The vortex models will be supplied by NASA Langley Research Center. Sensitivity tests will be performed on different meteorological environments in the atmospheric boundary layer, which include stable, neutral, and unstable stratifications, calm and severe wind conditions, and dry and wet conditions. Vortex strength may be varied as well. Relevant non-dimensional parameters will include the following: Richardson number or Froude number, Bowen ratio, and height to length scale ratios. The model output will be analyzed and visualized to better understand the transport, decay, and growth rates of the wake vortices. The third task involves running simulations using observed data. MIT Lincoln Labs is currently planning field experiments at the Memphis airport to measure both meteorological conditions and wake vortex characteristics. Once this data becomes available, it can be

  7. Three-layered supernetwork evolution model and the application for China-world's top 500 enterprises supernetwork

    NASA Astrophysics Data System (ADS)

    Liu, Qiang; Fang, Jin-Qing; Li, Yong

    2014-12-01

    Network of network (NON) or so-called supernetwork extensively exists in the real world. However, so far the definition of NON is not mutually recognized, relevant theory is rather lacking. In order to reveal certain characteristics of NON, we proposed four kinds of three-layered supernetwork evolution models (TLSEM) based on WS small-world and BA scale-free model, and defined two kinds of layer cross-degrees as new measures of cooperative-competition relationship for different layer nodes. The idea and methods of TLSEM are applied to the construction and analysis of China-world's top 500 enterprises supernetworks as a typical empirical example. The analytical results show that the layer cross-degree is better description than other network characteristics, and TLSEM may lay a certain foundation and extend to study more multilevel supernetworks.

  8. Development of a temporal evolution model for aero-optical effects caused by vortices in the supersonic mixing layer.

    PubMed

    Guo, Guangming; Liu, Hong; Zhang, Bin

    2016-04-01

    The vortices inside mixing layers impose remarkable aero-optical distortions on a beam even at moderate subsonic speeds. Knowledge about aero-optical effects caused by vortices in the flow field, especially their spatial and temporal evolution, is limited for supersonic mixing layers because the flows have very high speeds. In this paper, the temporal evolution of aero-optical effects caused by vortices in the supersonic mixing layer was investigated. A large eddy simulation was used to simulate the supersonic flow. A novel approach, coordinate extraction of vortex core, which is based on the relationship between vortices and the profile of the optical path length over the flow field, was proposed to quantitatively calculate the radii and convective speeds of vortices. A model used to quantitatively describe the temporal evolution of aero-optical effects caused by vortices in the supersonic mixing layer was developed and validated with data of numerical calculation. The results indicated that the model is available. Finally, several conclusions drawn from this work were presented. PMID:27139676

  9. Three-layered models of Ganymede and Callisto - Compositions, structures, and aspects of evolution

    NASA Technical Reports Server (NTRS)

    Mueller, Steve; Mckinnon, William B.

    1988-01-01

    The structural models presently defined for Ganymede and Callisto, which encompass a pure-ice upper layer, a mixed ice/rock lower mantle, and a rock core, incorporate three alternative rock component candidates representing various degrees of silicate hydration and oxidation. The three-layered model facilitates close study of the radius increase required for the internal differentiation of an ice-rock satellite; such expansion is determined to be most significant early in the process, and less so as differentiation approaches completion. The probability of postaccretional melting due to radiogenic heating is calculated.

  10. Three-layered models of Ganymede and Callisto - compositions, structures, and aspects of evolution

    SciTech Connect

    Mueller, S.; Mckinnon, W.B.

    1988-12-01

    The structural models presently defined for Ganymede and Callisto, which encompass a pure-ice upper layer, a mixed ice/rock lower mantle, and a rock core, incorporate three alternative rock component candidates representing various degrees of silicate hydration and oxidation. The three-layered model facilitates close study of the radius increase required for the internal differentiation of an ice-rock satellite; such expansion is determined to be most significant early in the process, and less so as differentiation approaches completion. The probability of postaccretional melting due to radiogenic heating is calculated. 78 references.

  11. Modelling Layer parallel stylolites

    NASA Astrophysics Data System (ADS)

    Koehn, Daniel; Pataki Rood, Daisy; Beaudoin, Nicolas

    2016-04-01

    We modeled the geometrical roughening of mainly layer-dominated stylolites in order to understand their structural evolution, to present an advanced classification of stylolite shapes and to relate this classification to chemical compaction and stylolite sealing capabilities. Our simulations show that layer-dominated stylolites can grow in three distinct stages, an initial slow nucleation, a fast layer-pinning phase and a final freezing stage if the layer dissolves completely during growth. Dissolution of the pinning layer and thus destruction of the compaction tracking capabilities is a function of the background noise in the rock and the dissolution rate of the layer itself. Low background noise needs a slower dissolving layer for pinning to be successful but produces flatter teeth than higher background noise. We present an advanced classification based on our simulations and separate stylolites into four classes: rectangular layer type, seismogram pinning type, suture/sharp peak type and simple wave-like type.

  12. Modeling the space-time evolution of pore pressure in layered shallow covers

    NASA Astrophysics Data System (ADS)

    Salciarini, Diana; Cuomo, Sabatino; Castorino, Giuseppe; Fanelli, Giulia; Tamagnini, Claudio

    2015-04-01

    In most of the available models for the prediction of shallow landslide susceptibility, the potentially unstable soil cover is considered uniform and homogeneous, over an impervious underlying bedrock (see, e.g., Baum et al. 2008; Salciarini et al. 2006, 2012). However, in several case studies, this was proven to be unlikely, for example in the case of pyroclastic soil covers, where two clearly separated layers are detectable (Cascini et al., 2008, 2011). The possibility of taking into account the detailed configuration of the soil cover allows having a more accurate estimate of the potentially unstable volumes, which significantly modify the intensity of the considered phenomena. To take into account the possibility of having layers in the soil cover with different permeability, the existing routines of the TRIGRS code (Baum et al. 2008) devoted to the hydrologic process modeling have been modified. The closed-form solution by Srivastava & Yeh (1991) implemented into TRIGRS was substituted with the numerical solution of the mass balance equation governing the infiltration process. A parametric analysis was carried out by varying the permeability ratio between the two layers, with the aim of examining the influence of such parameter on the pore-pressure distribution along the vertical profile. As expected, as the permeability ratio increases, the underlying layer tends to behave as an impervious boundary. This increases the chance that only the most superficial soil layer fails. An analysis of the routine performance and efficiency was also done to investigate the response of the model with different tolerances and different time steps of the integration procedure, and different spatial discretizations along the vertical profile.

  13. Main Sequence Evolution with Layered Semiconvection

    NASA Astrophysics Data System (ADS)

    Moore, Kevin; Garaud, Pascale

    2016-01-01

    Semiconvection is a form of mixing in thermally unstable regions that are partially stabilized by composition gradients. It has the greatest potential impact on the evolution of the cores of main sequence stars in the mass range 1.2 {M}⊙ -1.7 {M}⊙ . We present the first stellar evolution calculations using the new prescription for semiconvective mixing proposed by Wood et al. Semiconvection in stars is predominately layered semiconvection. In our model, the layer height is an adjustable parameter analogous to the mixing length in convection. The rate of mixing inside semiconvective regions is sensitively dependent on the layer height. We find a critical layer height that separates weak semiconvective mixing (where stellar evolution is well-approximated by ignoring semiconvection entirely and using the Ledoux criterion for convection) from strong semiconvective mixing (where all composition gradients are rapidly mixed, so stellar evolution is well-approximated by ignoring them altogether and using the Schwarzschild criterion for convection instead). This critical layer height is much smaller than the minimum layer height derived from simulations so we predict that stellar evolution is nearly the same as in models ran with the Schwarzschild criterion. We also investigate the effects of composition gradient smoothing, finding that it causes convective cores to artificially shrink in the absence of additional mixing beyond the convective boundary. Layered semiconvection with realistic layer heights provides enough such mixing to avoid this problem. Finally, we discuss the potential of detecting layered semiconvection and its implication on convective core sizes in solar-like oscillators.

  14. Numerical Modeling Studies of Wake Vortex Transport and Evolution Within the Planetary Boundary Layer

    NASA Technical Reports Server (NTRS)

    Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael L.; Han, Jongil

    2000-01-01

    The fundamental objective of this research is study behavior of aircraft wake vortices within atmospheric boundary layer (ABL) in support of developing the system, Aircraft VOrtex Spacing System (AVOSS), under NASA's Terminal Area Productivity (TAR) program that will control aircraft spacing within the narrow approach corridors of airports. The purpose of the AVOSS system is to increase airport capacity by providing a safe reduction in separation of aircraft compared to the now-existing flight rules. In our first funding period (7 January 19994 - 6 April 1997), we have accomplished extensive model development and validation of ABL simulations. Using the validated model, in our second funding period (7 April 1997 - 6 April 2000) we have investigated the effects of ambient atmospheric turbulence on vortex decay and descent, Crow instability, and wake vortex interaction with the ground. Recognizing the crucial influence of ABL turbulence on wake vortex behavior, we have also developed a software generating vertical profiles of turbulent kinetic energy (TKE) or energy dissipation rate (EDR), which are, in turn, used as input data in the AVOSS prediction algorithms.

  15. A two-layer diagnostic model of the long-term physical evolution of warm-core ring 82B

    NASA Technical Reports Server (NTRS)

    Olson, D. B.; Schmitt, R. W.; Kennelly, M.; Joyce, T. M.

    1985-01-01

    The present shipboard data in the 1982 time series on a single Gulf Stream warm core ring are composited on a cylindrical coordinate system following ring motion; 10 C-isotherm depth measurements are used in a two-layer model of the ring's structure to compute gradient current, kinetic energy, available potential energy (APE), and potential vorticity. The ring's evolution can be divided into two periods: April-late June, while the ring is isolated from strong Gulf Stream interaction, during which the ring loses APE at a low rate, and from July onward, following ring interactions with the Gulf Stream and topography with much higher energy loss. Within measurement errors, the potential vorticity at the center of the ring is conserved from April through August, implying nearly inviscid dynamics.

  16. Layered Model for Radiation-Induced Chemical Evolution of Icy Surface Composition on Kuiper Belt and Oort Cloud Bodies

    NASA Technical Reports Server (NTRS)

    Cooper, John F.; Hill, Matthew E.; Richardson, John D.; Sturner, Steven J.

    2010-01-01

    The diversity of albedos and surface colors on observed Kuiper Belt and Inner Oort Cloud objects remains to be explained in terms of competition between primordial intrinsic versus exogenic drivers of surface and near-surface evolution. Earlier models have attempted without success to attribute this diversity to the relations between surface radiolysis from cosmic ray irradiation and gardening by meteoritic impacts. A more flexible approach considers the different depth-dependent radiation profiles produced by low-energy plasma, suprathermal, and maximally penetrating charged particles of the heliospheric and local interstellar radiation environments. Generally red objects of the dynamically cold (low inclination, circular orbit) Classical Kuiper Belt might be accounted for from erosive effects of plasma ions and reddening effects of high energy cosmic ray ions, while suprathermal keV-MeV ions could alternatively produce more color neutral surfaces. The deepest layer of more pristine ice can be brought to the surface from meter to kilometer depths by larger impact events and potentially by cryovolcanic activity. The bright surfaces of some larger objects, e.g. Eris, suggest ongoing resurfacing activity. Interactions of surface irradiation, resultant chemical oxidation, and near-surface cryogenic fluid reservoirs have been proposed to account for Enceladus cryovolcanism and may have further applications to other icy irradiated bodies. The diversity of causative processes must be understood to account for observationally apparent diversities of the object surfaces.

  17. Layered Model for Radiation-Induced Chemical Evolution of Icy Surface Composition on Kuiper Belt and Oort Cloud Bodies

    NASA Astrophysics Data System (ADS)

    Cooper, John F.; Hill, M. E.; Richardson, J. D.; Sturner, S. J.

    2010-10-01

    The diversity of albedos and surface colors on observed Kuiper Belt and Inner Oort Cloud objects remains to be explained in terms of competition between primordial intrinsic versus exogenic drivers of surface and near-surface evolution. Earlier models have attempted without success to attribute this diversity to the relations between surface radiolysis from cosmic ray irradiation and gardening by meteoritic impacts. A more flexible approach considers the different depth-dependent radiation profiles produced by low-energy plasma, suprathermal, and maximally penetrating charged particles of the heliospheric and local interstellar radiation environments. Generally red objects of the dynamically cold (low inclination, circular orbit) Classical Kuiper Belt might be accounted for from erosive effects of plasma ions and reddening effects of high energy cosmic ray ions, while suprathermal keV-MeV ions could alternatively produce more color neutral surfaces. The deepest layer of more pristine ice can be brought to the surface from meter to kilometer depths by larger impact events and potentially by cryovolcanic activity. The bright surfaces of some larger objects, e.g. Eris, suggest ongoing resurfacing activity. Interactions of surface irradiation, resultant chemical oxidation, and near-surface cryogenic fluid reservoirs have been proposed to account for Enceladus cryovolcanism (Cooper et al., Plan. Sp. Sci., 2009) and may have further applications to other icy irradiated bodies. The diversity of causative processes must be understood to account for observationally apparent diversities of the object surfaces.

  18. Simulation of Seasonal Snow Microwave TB Using Coupled Multi-Layered Snow Evolution and Microwave Emission Models

    NASA Technical Reports Server (NTRS)

    Brucker, Ludovic; Royer, Alain; Picard, Ghislain; Langlois, Alex; Fily, Michel

    2014-01-01

    The accurate quantification of SWE has important societal benefits, including improving domestic and agricultural water planning, flood forecasting and electric power generation. However, passive-microwave SWE algorithms suffer from variations in TB due to snow metamorphism, difficult to distinguish from those due to SWE variations. Coupled snow evolution-emission models are able to predict snow metamorphism, allowing us to account for emissivity changes. They can also be used to identify weaknesses in the snow evolution model. Moreover, thoroughly evaluating coupled models is a contribution toward the assimilation of TB, which leads to a significant increase in the accuracy of SWE estimates.

  19. Thermal and compositional evolution of a three-layer Titan

    NASA Astrophysics Data System (ADS)

    Bland, Michael T.; McKinnon, William. B.

    2012-04-01

    Cassini gravity data indicate that Titan is only partially differentiated. Two-layer models of Titan’s internal structure have been proposed consisting of an ice layer (ice I and high-pressure phases) and a “core” (mixed rock and ice, or low-density, hydrated rock); however, such two-layer models face fundamental difficulties (see McKinnon and Bland, AGU abs. P33F-04, 2011). An alternative to these models are three-layer models that assume a pure ice layer (including high-pressure phases and a sandwiched ocean), a mixed ice+rock layer, and a silicate core. Here we model the thermal and compositional evolution of hypothetical Titans to examine whether three-layer internal structures are thermally stable over Solar System history (i.e., can a three-layer Titan avoid further differentiation?) Our thermal model assumes an initial three-layer internal structure and calculates the temperature of each layer, following the numerical approach in Bland et al. (2008, Icarus 198, 384-399) and Bland et al. (2009, Icarus 200, 207-221). Both conduction and convection are permitted in each layer. Heating by decay of long-lived radiogenic species is included in both the mixed ice-rock and silicate layer. If the temperature of the ice or mixed ice-rock layer exceeds the minimum melting point of pure ice, melting and ocean formation occurs (if not present post-accretion). Melting of the mixed layer liberates silicate material, which is assumed to sink to the top of the silicate layer over time scale short relative to simulation time scales. We find that melting of Titan’s pure ice shell is common early in Solar System history and that melting can extend into Titan’s nominal mixed ice-rock layer. Such melting leads to irreversible unmixing of some of the mixed ice-rock layer. Long-lived radiogenic species are generally incapable of completely melting and separating Titan’s mixed layer, however. Titan’s current moment of inertia can therefore be achieved using a thermally

  20. Principle Component Analysis of the Evolution of the Saharan Air Layer and Dust Transport: Comparisons between a Model Simulation and MODIS Retrievals

    NASA Technical Reports Server (NTRS)

    Wong, S.; Colarco, P. R.; Dessler, A.

    2006-01-01

    The onset and evolution of Saharan Air Layer (SAL) episodes during June-September 2002 are diagnosed by applying principal component analysis to the NCEP reanalysis temperature anomalies at 850 hPa, where the largest SAL-induced temperature anomalies are located. The first principal component (PC) represents the onset of SAL episodes, which are associated with large warm anomalies located at the west coast of Africa. The second PC represents two opposite phases of the evolution of the SAL. The positive phase of the second PC corresponds to the southwestward extension of the warm anomalies into the tropical-subtropical North Atlantic Ocean, and the negative phase corresponds to the northwestward extension into the subtropical to mid-latitude North Atlantic Ocean and the southwest Europe. A dust transport model (CARMA) and the MODIS retrievals are used to study the associated effects on dust distribution and deposition. The positive (negative) phase of the second PC corresponds to a strengthening (weakening) of the offshore flows in the lower troposphere around 10deg - 20degN, causing more (less) dust being transported along the tropical to subtropical North Atlantic Ocean. The variation of the offshore flow indicates that the subseasonal variation of African Easterly Jet is associated with the evolution of the SAL. Significant correlation is found between the second PC time series and the daily West African monsoon index, implying a dynamical linkage between West African monsoon and the evolution of the SAL and Saharan dust transport.

  1. Evolution of a forced stratified mixing layer

    NASA Astrophysics Data System (ADS)

    Rotter, J.; Fernando, H. J. S.; Kit, E.

    2007-06-01

    Laboratory measurements were carried out in a spatially developing stably stratified shear layer generated downstream of a splitter plate. The instabilities were controlled using a flapper spanning the entire shear layer, with the flapper forced at the fastest growing frequency of the primary [Kelvin-Helmholtz (KH)] instability. The measurements were taken as the KH instabilities roll up, break down, and degenerate into stratified turbulence. Both stratified and homogeneous shear layers were considered, the latter acting as the "baseline" case. The measurements included the streamwise and vertical velocities (made using X-wire hot film probes), which allowed calculation of the mean and rms velocities, turbulent kinetic energy (TKE) dissipation, and TKE production. The density and its gradients were measured using miniature conductivity probes. The measurements and flow visualization elicited interesting features of KH evolution, namely that KH billows may be turbulent from the onset, the TKE dissipation is largest at early stages of evolution, the production of TKE is a maximum at the breakdown of billows, the decay of turbulence to fossilized motions and concomitant formation of fine (layered) structure occur rapidly after the breakdown of billows, and episodic rebirth of (zombie) turbulence develops before a final permanently fossilized state is achieved.

  2. On Multiobjective Evolution Model

    NASA Astrophysics Data System (ADS)

    Ahmed, E.; Elettreby, M. F.

    Self-Organized Criticality (SOC) phenomena could have a significant effect on the dynamics of ecosystems. The Bak-Sneppen (BS) model is a simple and robust model of biological evolution that exhibits punctuated equilibrium behavior. Here, we will introduce random version of BS model. We also generalize the single objective BS model to a multiobjective one.

  3. Evolution of density compensated fronts in simulated ocean mixed layers

    NASA Astrophysics Data System (ADS)

    Helber, R. W.; Hebert, D. A.; Koch, A.

    2015-12-01

    Observations within the ocean surface mixed layer indicate a tendency for temperature gradients to form that are compensated for their effect on density by salinity gradients. These density compensated fronts tend to occur in the absence of strong surface forcing and thus weak vertical mixing. Observations show that density compensated fronts are quickly erased by surface cooling events. The presence of density compensated gradients in the surface mixed layer, however, are not well represented in regional and global ocean circulation model predictions. In these models, subgrid-scale processes are parameterized with minimal ability to represent double diffusion. Recent advances in parameterizations have been developed to model the re-stratification of the mixed layer by sub-mesoscale eddies. These ageostrophic dynamics can lead to long filaments that are governed by process on length scales from 100 m to 10 km and time scales near a day. The impact of these processes in model physics on density compensated fronts is unclear. To improve our understanding of compensated front evolution in the ocean, three different mixing schemes are tested to evaluate the creation of horizontally density compensated gradients in model simulations. One scheme extracts potential energy of ocean fronts for mixing dependent on horizontal and vertical buoyancy gradients, mixed layer depth, and inertial period. The other two schemes mix temperature and salinity horizontally dependent on the buoyancy gradient. All schemes provide a three dimensional approach to mixing that differentiates the horizontal eddy diffusion of temperature and salinity.

  4. Comet 46P/Wirtanen: Evolution of the Subsurface Layer

    NASA Astrophysics Data System (ADS)

    Kossacki, Konrad J.; Szutowicz, S. Ławomira; Leliwa-Kopystyński, Jacek

    1999-11-01

    Cometary nuclei are composed mostly of water ice and mineral grains. When a comet passes near the Sun, volatiles sublimate. This process leads to the formation of a dust layer covering the nucleus. Various other metamorphic processes are also predicted to modify the subsurface layer of the nucleus. Consequently, it should become stratified and more cohesive than initially. At present, because of preparations for the Rosetta mission to Comet 46P/Wirtanen, it is especially important to understand the processes responsible for the evolution of a cometary nucleus. This can be of key importance to a successful landing on the nucleus and further interpretation of the results of the mission. This work is intended primarily to estimate how quickly the process of grain sintering can modify the outer part of the nucleus. Other effects, such as crystallization of water ice, are, however, also taken into account. The simulation is performed for the period 1944 to 2016 taking into account the orbit of the comet perturbed by planets and by nongravitational effects. The numerical procedure used to simulate the evolution of the material texture and temperature distribution below the dust layer is based on the self-consistent model of the thermal and structural evolution of an initially homogeneous ice-dust mixture. The original model is, however, significantly extended. The present analysis includes the possible presence of amorphous water ice and other, nonwater volatiles. They are assumed to be initially trapped in amorphous water ice. It was found that a cohesive layer from about 1 m to about 10 m thick can be formed, depending on the size of the ice grains and the properties of the dust mantle.

  5. Comet 46P/Wirtanen: evolution of the subsurface layer

    NASA Astrophysics Data System (ADS)

    Kossacki, K. J.; Szutowicz, S.; Leliwa-Kopystynski, J.

    1998-09-01

    The cometary nuclei are composed mostly of water ice and mineral grains. Volatiles sublimate however when a comet passes near the Sun, leading to the formation of a dust layer covering the nucleus. Various other metamorphic processes are also predicted to modify the subsurface layer of the nucleus. Consequently, it should become stratified and more cohesive than initially. At present, due to the preparation of the mission Rosetta to the comet 46P/Wirtanen it is especially important to understand the processes responsible for the evolution of a cometary nucleus. This can be of key importance for the successful landing on the nucleus and further interpretation of the results of the mission. This work is mostly intended to estimate how quickly the process of grain sintering could modify the outer part of nucleus. The other effects, like crystallization of water ice are however also taken into account. The simulation is performed for the time period from 1948 to 2016. The orbit of the comet is calculated according to the forced precession model. The evolution of the material texture and temperature distribution below the dust layer is simulated according to the selfconsistent model of the thermal and structural evolution of an initially homogeneous ice--dust mixture. The present analysis includes the presence of amorphous water ice and other, non-water volatiles. They are assumed initially trapped in amorphous water ice. It is found, that the cohesive layer from about one meter up to about ten meters thick can be formed, depending on the size of ice grains and the properties of the dust mantle.

  6. Layered Model for Radiation-Induced Chemical Evolution of Icy Surface Composition and Dynamics on Kuiper Belt and Oort Cloud Bodies

    NASA Technical Reports Server (NTRS)

    Cooper, John F.; Richardson, John D.

    2010-01-01

    The diversity of albedos and surface colors on observed Kuiper Belt and Inner Oort Cloud objects remains to be explained in terms of competition between primordial intrinsic versus exogenic drivers of surface and near-surface evolution. Earlier models have attempted without success to attribute this diversity to the relations between surface radiolysis from cosmic ray irradiation and gardening by meteoritic impacts. A more flexible approach considers the different depth-dependent radiation profiles produced by low-energy plasma, suprathermal, and maximally penetrating charged particles of the heliospheric and local interstellar radiation environment. Generally red objects of the dynamically cold (low inclination, circular orbit) Classical Kuiper Belt might be accounted for from erosive effects of plasma ions and reddening effects of high energy cosmic ray ions, while suprathermal keV-MeV ions could alternatively produce more color neutral surfaces. The deepest layer of more pristine ice can be brought to the surface from meter to kilometer depths by larger impact events and potentially by cryovolcanic activity. The bright surfaces of some larger objects, e.g. Eris, suggest ongoing resurfacing activity. Cycles of atmospheric formation and surface freezeout can further account for temporal variation as observed on Pluto. The diversity of causative processes must therefore be understood to account for observationally apparent diversities of the object surfaces.

  7. Dynamics of hydrofracturing and permeability evolution in layered reservoirs

    NASA Astrophysics Data System (ADS)

    Ghani, Irfan; Koehn, Daniel; Toussaint, Renaud; Passchier, Cees

    2015-09-01

    A coupled hydro-mechanical model is presented to model fluid driven fracturing in layered porous rocks. In the model the solid elastic continuum is described by a discrete element approach coupled with a fluid continuum grid that is used to solve Darcy based pressure diffusion. The model assumes poro-elasto-plastic effects and yields real time dynamic aspects of the fracturing and effective stress evolution under the influence of excess fluid pressure gradients. We show that the formation and propagation of hydrofractures are sensitive to mechanical and tectonic conditions of the system. In cases where elevated fluid pressure is the sole driving agent in a stable tectonic system, sealing layers induce permutations between the principal directions of the local stress tensor, which regulate the growth of vertical fractures and may result in irregular pattern formation or sub-horizontal failure below the seal. Stiffer layers tend to concentrate differential stresses and lead to vertical fracture growth, whereas the layer-contact tends to fracture if the strength of the neighboring rock is comparably high. If the system has remained under extension for a longer time period, the developed hydrofractures propagate by linking up confined tensile fractures in competent layers. This leads to the growth of large-scale normal faults in the layered systems, so that subsequently the effective permeability is highly variable over time and the faults drain the system. The simulation results are shown to be consistent with some of the field observations carried out in the Oman Mountains, where abnormal fluid pressure is reported to be a significant factor in the development of several generations of local and regional fracture and fault sets.

  8. Evolution of models for evolution. [of life

    NASA Technical Reports Server (NTRS)

    Rohlfing, D. L.

    1974-01-01

    The paper discusses models of evolution and their values, and some critiques of these models and the value of these critiques. A model is investigated which involves the formation of prebiotic protein from amino acids. Its formation by four theoretical critiques that suggest alternative environmental conditions is discussed. Experiments are reviewed so as to illustrate the experimental testing of the possible weaknesses of a model for a single molecular evolutionary phase and to suggest some necessary changes in the model.

  9. Columnar modelling of nucleation burst evolution in the convective boundary layer - first results from a feasibility study Part III: Preliminary results on physicochemical model performance using two "clean air mass" reference scenarios

    NASA Astrophysics Data System (ADS)

    Hellmuth, O.

    2006-09-01

    In Paper I of four papers, a revised columnar high-order model to investigate gas-aerosol-turbulence interactions in the convective boundary layer (CBL) was proposed. In Paper II, the model capability to predict first-, second- and third-order moments of meteorological variables in the CBL was demonstrated using available observational data. In the present Paper III, the high-order modelling concept is extended to sulphur and ammonia chemistry as well as to aerosol dynamics. Based on the previous CBL simulation, a feasibility study is performed using two "clean air mass" scenarios with an emission source at the ground but low aerosol background concentration. Such scenarios synoptically correspond to the advection of fresh post-frontal air in an anthropogenically influenced region. The aim is to evaluate the time-height evolution of ultrafine condensation nuclei (UCNs) and to elucidate the interactions between meteorological and physicochemical variables in a CBL column. The scenarios differ in the treatment of new particle formation (NPF), whereas homogeneous nucleation according to the classical nucleation theory (CNT) is considered. The first scenario considers nucleation of a binary system consisting of water vapour and sulphuric acid (H2SO4) vapour, the second one nucleation of a ternary system additionally involving ammonia (NH3). Here, the two synthetic scenarios are discussed in detail, whereas special attention is payed to the role of turbulence in the formation of the typical UCN burst behaviour, that can often be observed in the surface layer. The intercomparison of the two scenarios reveals large differences in the evolution of the UCN number concentration in the surface layer as well as in the time-height cross-sections of first-order moments and double correlation terms. Although in both cases the occurrence of NPF bursts could be simulated, the burst characteristics and genesis of the bursts are completely different. It is demonstrated, that

  10. Vapor layer evolution during drop impact on a heated surface

    NASA Astrophysics Data System (ADS)

    Lee, Sanghyeon; Lee, Sangjun; Lee, Jisan; Fezzaa, Kamel; Je, Jung Ho

    2015-11-01

    When a liquid drop impacts on a sufficiently hot surface above the boiling point, a vapor layer is formed between the drop and the surface, preventing direct contact between them and as a result levitating the drop, known as the Leidenfrost effect. Understanding the evolution of the vapor layer is largely unexplored despite its importance in estimating heat transfer in cooling systems of thermal or nuclear power plants. The side-profile visualization of the vapor layer, as absolutely required for investigating its evolution, has been however unavailable by conventional optical microscopy. In this study, by employing ultrafast X-ray phase contrast imaging, we directly visualize the profiles of the vapor layers during liquid drop impact on a hot surface and elucidate the evolution of the vapor layers during spreading and retraction of the drop as functions of impact height and surface temperature. We reveal that the evolution is governed by the propagation of capillary waves generated in retraction and the wavelength of capillary waves λ is inversely proportional to the impact height h with a relation ~σ/ρh ~We-1 where We is weber number. Capillary waves that converge at the center of the vapor layers are linked to the bouncing behavior of the drop.

  11. Modeling the urban boundary layer

    NASA Technical Reports Server (NTRS)

    Bergstrom, R. W., Jr.

    1976-01-01

    A summary and evaluation is given of the Workshop on Modeling the Urban Boundary Layer; held in Las Vegas on May 5, 1975. Edited summaries from each of the session chairpersons are also given. The sessions were: (1) formulation and solution techniques, (2) K-theory versus higher order closure, (3) surface heat and moisture balance, (4) initialization and boundary problems, (5) nocturnal boundary layer, and (6) verification of models.

  12. Two-layer Tripole Model

    NASA Astrophysics Data System (ADS)

    Sokolovskiy, M. A.; Verron, J.; Yakovenko, O. I.

    Three-vortex filament problem for the case of both zero average circulation and im- pulse in a 2D two-layer incompressible fluid is investigated. In this framework, a model of tripolar structures is constructed with one vortex located in the upper layer and two vortices situated in the lower layer. Two special cases of the intensity dis- tribution were studied: (-2; 1, 1) ­ a strong central vortex is over two week vortices placed in the lower layer; (-1; 2, -1) ­ a strong central vortex is in the lower layer, and the week vortices are located one in the upper, and the second in the lower layers. The results give two types of stationary axially symmetrical configurations in the first case: a) an ordinary roundabout ­ two lower-layer vortices are rotating in the direction in- duced by the central vortex; b) an inversed roundabout ­ the lower-layer vortices are rotating in the direction opposite to the central upper layer vortex because of the in- tralayer interaction prevalence. In the second case, all three vortices form a colinear configuration and always rotate around the common vorticity center in the direction implied by the stronger vortex. Such configuration received the name of eccentric roundabout. Comparison of calcu- lation results for discrete and finite-core vortices is made. Support of RFBR (Grant 01-05-64646) is gratefully acknowledged.

  13. Pressure evolution in the shear layer of forming vortex rings

    NASA Astrophysics Data System (ADS)

    Schlueter-Kuck, Kristy; Dabiri, John O.

    2016-05-01

    This study investigated the relationship between the pinch-off of axisymmetric vortex rings and the evolution of pressure in the shear layer being entrained into the vortex rings. A piston-cylinder apparatus was used to generate the vortex rings, and five cases of constant piston acceleration over distances ranging from zero (impulsive start) to eight piston diameters were investigated. It was determined that increasing the distance over which the piston accelerated increased the dimensionless formation time at which the vortex ring pinches off, consistent with previous observations. A limiting value of vortex ring formation number of approximately seven is approached when the piston is accelerated over more than six piston diameters. For each case, the evolution of pressure in the shear layer was calculated based on PIV measurements of the velocity field and spatial integration of the corresponding pressure gradients using a recently developed algorithm. Plots of the shear layer pressure in X-T diagrams aided in identifying key features of the pressure associated with the evolution of vortex rings, including a high-pressure region that forms behind the leading ring. By extrapolating the motion of this high-pressure region back to the nozzle exit plane in the X-T diagram, its time of first appearance can be estimated. It is found that the appearance of the extrapolated local pressure maximum in the shear layer at the nozzle exit plane coincides with vortex ring pinch-off, as conventionally quantified by the vortex ring formation number.

  14. TMDs: Evolution, modeling, precision

    NASA Astrophysics Data System (ADS)

    D'Alesio, Umberto; Echevarría, Miguel G.; Melis, Stefano; Scimemi, Ignazio

    2015-01-01

    The factorization theorem for qT spectra in Drell-Yan processes, boson production and semi-inclusive deep inelastic scattering allows for the determination of the non-perturbative parts of transverse momentum dependent parton distribution functions. Here we discuss the fit of Drell-Yan and Z-production data using the transverse momentum dependent formalism and the resummation of the evolution kernel. We find a good theoretical stability of the results and a final χ2/points ≲ 1. We show how the fixing of the non-perturbative pieces of the evolution can be used to make predictions at present and future colliders.

  15. The structure and evolution of boundary layers in stratified convection

    NASA Astrophysics Data System (ADS)

    Anders, Evan H.; Brown, Benjamin; Brandenburg, Axel; Rast, Mark

    2016-05-01

    Solar convection is highly stratified, and the density in the Sun increases by many orders of magnitude from the photosphere to the base of the convection zone. The photosphere is an important boundary layer, and interactions between the surface convection and deep convection may lie at the root of the solar convection conundrum, where observed large-scale velocities are much lower than predicted by full numerical simulations. Here, we study the structure and time evolution of boundary layers in numerical stratified convection. We study fully compressible convection within plane-parallel layers using the Dedalus pseudospectral framework. Within the context of polytropic stratification, we study flows from low (1e-3) to moderately high (0.1) Mach number, and at moderate to high Rayleigh number to study both laminar and turbulent convective transport. We aim to characterize the thickness and time variation of velocity and thermal (entropy) boundary layers at the top and bottom boundaries of the domain.

  16. Polar firn layering in radiative transfer models

    NASA Astrophysics Data System (ADS)

    Linow, Stefanie; Hoerhold, Maria

    2016-04-01

    For many applications in the geosciences, remote sensing is the only feasible method of obtaining data from large areas with limited accessibility. This is especially true for the cryosphere, where light conditions and cloud coverage additionally limit the use of optical sensors. Here, instruments operating at microwave frequencies become important, for instance in polar snow parameters / SWE (snow water equivalent) mapping. However, the interaction between snow and microwave radiation is a complex process and still not fully understood. RT (radiative transfer) models to simulate snow-microwave interaction are available, but they require a number of input parameters such as microstructure and density, which are partly ill-constrained. The layering of snow and firn introduces an additional degree of complexity, as all snow parameters show a strong variability with depth. Many studies on RT modeling of polar firn deal with layer variability by using statistical properties derived from previous measurements, such as the standard deviations of density and microstructure, to configure model input. Here, the variability of microstructure parameters, such as density and particle size, are usually assumed to be independent of each other. However, in the case of the firn pack of the polar ice sheets, we observe that microstructure evolution depends on environmental parameters, such as temperature and snow deposition. Accordingly, density and microstructure evolve together within the snow and firn. Based on CT (computer tomography) microstructure measurements of antarctic firn, we can show that: first, the variability of density and effective grain size are linked and can thus be implemented in the RT models as a coupled set of parameters. Second, the magnitude of layering is captured by the measured standard deviation. Based on high-resolution density measurements of an Antarctic firn core, we study the effect of firn layering at different microwave wavelengths. By means of

  17. Growth mode evolution of hafnium oxide by atomic layer deposition

    SciTech Connect

    Nie, Xianglong; Ma, Fei; Ma, Dayan; Xu, Kewei

    2014-01-15

    HfO{sub 2} thin films were deposited using tetrakis-ethylmethylamido hafnium and H{sub 2}O as precursors on silicon by atomic layer deposition (ALD). The morphology and microstructures at different ALD cycles were characterized by atomic force microscopy and high-resolution transmission electron microscopy. Based on the height–height correlation function and power spectral density function, quantitative analysis of surface morphologies was performed. Three characteristic dimensions (ξ{sub 1}, ξ{sub 2}, and ξ{sub 3}) corresponding to three surface structures, islands, local and global fluctuations, were identified. The evolution of ALD growth mode at range of the three critical scales was investigated, respectively. It suggests the transformation of growth mode from quasi two-dimensional layer-by-layer to three-dimensional island for global fluctuations.

  18. Modeling Protein Evolution

    NASA Astrophysics Data System (ADS)

    Goldstein, Richard; Pollock, David

    The study of biology is fundamentally different from many other scientific pursuits, such as geology or astrophysics. This difference stems from the ubiquitous questions that arise about function and purpose. These are questions concerning why biological objects operate the way they do: what is the function of a polymerase? What is the role of the immune system? No one, aside from the most dedicated anthropist or interventionist theist, would attempt to determine the purpose of the earth's mantle or the function of a binary star. Among the sciences, it is only biology in which the details of what an object does can be said to be part of the reason for its existence. This is because the process of evolution is capable of improving an object to better carry out a function; that is, it adapts an object within the constraints of mechanics and history (i.e., what has come before). Thus, the ultimate basis of these biological questions is the process of evolution; generally, the function of an enzyme, cell type, organ, system, or trait is the thing that it does that contributes to the fitness (i.e., reproductive success) of the organism of which it is a part or characteristic. Our investigations cannot escape the simple fact that all things in biology (including ourselves) are, ultimately, the result of an evolutionary process.

  19. A comparative study of the role of the Saharan air layer in the evolution of two disparate Atlantic tropical cyclones using WRF model simulations and energetics calculations

    NASA Astrophysics Data System (ADS)

    Ross, Robert S.; Krishnamurti, T. N.; Chaney, Kirsten M.

    2016-02-01

    The Weather Research and Forecasting (WRF) Model 5-day simulations of Major Hurricane Julia (2010) and Tropical Storm Florence (2012), both of which developed from African easterly waves, are used to conduct a complete energetics study to explain why one storm became a major hurricane while the other weakened to a wave. The disparate intensity outcomes are caused by significant differences in the energetics of the two systems that emerge in their storm stages due to differences in the impact of the Saharan air layer (SAL). In their wave stages both waves exhibit a convectively driven energy production cycle, in which the regions of positive barotropic and baroclinic energy conversion and of diabatic heating and rainfall are all superimposed. Convection induces barotropic instability which then enhances the baroclinic overturning through a resonance of the two instabilities, which together produce the eddy kinetic energy. Diabatic heating in the convection generates eddy available potential energy which, along with the eddy kinetic energy, defines the total eddy energy of the system. Florence loses the convectively driven energy production cycle in the storm stage and begins to weaken, while Julia maintains this cycle and becomes a major hurricane. The disruption of the convection in Florence is due to the drying, stabilizing, and vertical shearing effects of an expansive SAL to the north of the storm, effects not present in the Julia case. Consideration is given to the different effects of the SAL on 6-10 day waves (Florence wave) versus 3-5 day waves (Julia wave).

  20. Multi Layer Contaminant Migration Model

    Energy Science and Technology Software Center (ESTSC)

    1999-07-28

    This computer software augments and enhances certain calculation included in the previously copyrighted Vadose Zone Contaminant Migration Model. The computational method used in this model recognizes the heterogenous nature of the soils and attempts to account for the variability by using four separate layers to simulate the flow of water through the vadose zone. Therefore, the pore-water velocity calculated by the code will be different than the previous model because it accounts for a widermore » variety of soil properties encountered in the vadose zone. This model also performs an additional screening step than in the previous model. In this model the higher value of two different types of Soil Screening Levels are compared to soil concentrations of contaminants. If the contaminant concentration exceeds the highest of two SSLs, then that contaminant is listed. This is consistent with USEPA's Soil Screening Guidance.« less

  1. Nonlinear spatial evolution of inviscid instabilities on hypersonic boundary layers

    NASA Technical Reports Server (NTRS)

    Wundrow, David W.

    1996-01-01

    The spatial development of an initially linear vorticity-mode instability on a compressible flat-plate boundary layer is considered. The analysis is done in the framework of the hypersonic limit where the free-stream Mach number M approaches infinity. Nonlinearity is shown to become important locally, in a thin critical layer, when sigma, the deviation of the phase speed from unity, becomes o(M(exp -8/7)) and the magnitude of the pressure fluctuations becomes 0(sigma(exp 5/2)M(exp 2)). The unsteady flow outside the critical layer takes the form of a linear instability wave but with its amplitude completely determined by the nonlinear flow within the critical layer. The coupled set of equations which govern the critical-layer dynamics reflect a balance between spatial-evolution, (linear and nonlinear) convection and nonlinear vorticity-generation terms. The numerical solution to these equations shows that nonlinear effects produce a dramatic reduction in the instability-wave amplitude.

  2. Microstructure evolution with varied layer thickness in magnetron-sputtered Ni/C multilayer films

    PubMed Central

    Peng, Jichang; Li, Wenbin; Huang, Qiushi; Wang, Zhanshan

    2016-01-01

    The microstructure evolution of magnetron-sputtered Ni/C multilayers was investigated by varying the Ni and C layer thickness in the region of a few nanometers. For the samples having 2.6-nm-thick C layers, the interface width increases from 0.37 to 0.81 nm as the Ni layer thickness decreases from 4.3 to 1.3 nm. Especially for the samples with Ni layers less than 2.0 nm, the interface width changes significantly due to the discontinuously distributed Ni crystallites. For the samples having 2.8-nm-thick Ni layers, the interface width increases from 0.37 to 0.59 nm when the C layer thickness decreases from 4.3 to 0.7 nm. The evolution of interface microstructures with varied Ni and C layers is explained based on a proposed simple growth model of Ni and C layers. PMID:27515586

  3. Open source layered sensing model

    NASA Astrophysics Data System (ADS)

    Rovito, Todd V.; Abayowa, Bernard O.; Talbert, Michael L.

    2011-06-01

    This paper will look at using open source tools (Blender [17], LuxRender [18], and Python [19]) to build an image processing model for exploring combinations of sensors/platforms for any given image resolution. The model produces camera position, camera attitude, and synthetic camera data that can be used for exploitation purposes. We focus on electro-optical (EO) visible sensors to simplify the rendering but this work could be extended to use other rendering tools that support different modalities. Due to the computational complexity of ray tracing we employ the Amazon Elastic Cloud Computer to help speed up the generation of large ray traced scenes. The key idea of the paper is to provide an architecture for layered sensing simulation which is modular in design and constructed on open-source off-the-shelf software. This architecture shows how leveraging existing open-source software allows for practical layered sensing modeling to be rapidly assimilated and utilized in real-world applications. In this paper we demonstrate our model output is automatically exploitable by using generated data with an innovative video frame mosaic algorithm.

  4. Two types of asthenospheric layers and their evolution

    NASA Astrophysics Data System (ADS)

    Czechowski, Leszek; Grad, Marek

    2016-04-01

    range 60-100 km, which could be interpreted as mechanical low Vp velocity zones, in contrast to thermal velocity zone in deeper asthenosphere. Conclusions 1. In general, two kinds of asthenospheres could exist: mainly of mechanical origin (or shear stress origin) and mainly of thermal origin. In our calculations the role of shear stresses and thermal effects is of the same order. 2. The evolution of σ could be very fast, so the asthenosphere of shear stress origin could be a transient, time-dependent feature. 3. The evolution of the system of two asthenospheres leads usually to origin of a thick lithosphere with characteristic two low S-wave velocity layers. We suggest that at least some of the observed thick continental lithospheres are of this origin. Acknowledgments This work was partially supported by the National Science Centre (grant 2011/01/B/ST10/06653). Computer resources of Interdisciplinary Centre for Mathematical and Computational Modeling of University of Warsaw were also used in the research

  5. Evolution of a barotropic shear layer into elliptical vortices.

    PubMed

    Guha, Anirban; Rahmani, Mona; Lawrence, Gregory A

    2013-01-01

    When a barotropic shear layer becomes unstable, it produces the well-known Kelvin-Helmholtz instability (KHI). The nonlinear manifestation of the KHI is usually in the form of spiral billows. However, a piecewise linear shear layer produces a different type of KHI characterized by elliptical vortices of constant vorticity connected via thin braids. Using direct numerical simulation and contour dynamics, we show that the interaction between two counterpropagating vorticity waves is solely responsible for this KHI formation. We investigate the oscillation of the vorticity wave amplitude, the rotation and nutation of the elliptical vortex, and straining of the braids. Our analysis also provides a possible explanation for the formation and evolution of elliptical vortices appearing in geophysical and astrophysical flows, e.g., meddies, stratospheric polar vortices, Jovian vortices, Neptune's Great Dark Spot, and coherent vortices in the wind belts of Uranus. PMID:23410439

  6. Modelling the transitional boundary layer

    NASA Technical Reports Server (NTRS)

    Narasimha, R.

    1990-01-01

    Recent developments in the modelling of the transition zone in the boundary layer are reviewed (the zone being defined as extending from the station where intermittency begins to depart from zero to that where it is nearly unity). The value of using a new non-dimensional spot formation rate parameter, and the importance of allowing for so-called subtransitions within the transition zone, are both stressed. Models do reasonably well in constant pressure 2-dimensional flows, but in the presence of strong pressure gradients further improvements are needed. The linear combination approach works surprisingly well in most cases, but would not be so successful in situations where a purely laminar boundary layer would separate but a transitional one would not. Intermittency-weighted eddy viscosity methods do not predict peak surface parameters well without the introduction of an overshooting transition function whose connection with the spot theory of transition is obscure. Suggestions are made for further work that now appears necessary for developing improved models of the transition zone.

  7. CMS computing model evolution

    NASA Astrophysics Data System (ADS)

    Grandi, C.; Bonacorsi, D.; Colling, D.; Fisk, I.; Girone, M.

    2014-06-01

    The CMS Computing Model was developed and documented in 2004. Since then the model has evolved to be more flexible and to take advantage of new techniques, but many of the original concepts remain and are in active use. In this presentation we will discuss the changes planned for the restart of the LHC program in 2015. We will discuss the changes planning in the use and definition of the computing tiers that were defined with the MONARC project. We will present how we intend to use new services and infrastructure to provide more efficient and transparent access to the data. We will discuss the computing plans to make better use of the computing capacity by scheduling more of the processor nodes, making better use of the disk storage, and more intelligent use of the networking.

  8. Nanostructural Evolution of Hard Turning Layers in Carburized Steel

    NASA Astrophysics Data System (ADS)

    Bedekar, Vikram

    The mechanisms of failure for components subjected to contact fatigue are sensitive to the structure and properties of the material surface. Although, the bulk material properties are determined by the steel making, forming and the heat treatment; the near surface material properties are altered during final material removal processes such as hard turning or grinding. Therefore, the ability to optimize, modulate and predict the near surface properties during final metal removal operations would be extremely useful in the enhancement of service life of a component. Hard machining is known to induce severely deformed layers causing dramatic microstructural transformations. These transformations occur via grain refinement or thermal phenomena depending upon cutting conditions. The aim of this work is to engineer the near surface nanoscale structure and properties during hard turning by altering strain, strain rate, temperature and incoming microstructure. The near surface material transformations due to hard turning were studied on carburized SAE 8620 bearing steel. Variations in parent material microstructures were introduced by altering the retained austenite content. The strain, strain rate and temperature achieved during final metal cutting were altered by varying insert geometry, insert wear and cutting speed. The subsurface evolution was quantified by a series of advanced characterization techniques such as transmission electron microscopy (TEM), glancing angle X-ray diffraction (GAXRD), X-ray stress evaluation and nanoindentation which were coupled with numerical modeling. Results showed that the grain size of the nanocrystalline near surface microstructure can be effectively controlled by altering the insert geometry, insert wear, cutting speed and the incoming microstructure. It was also evident that the near surface retained austenite decreased at lower cutting speed indicating transformation due to plastic deformation, while it increased at higher cutting

  9. Recent and Future Evolution of the Stratospheric Ozone Layer

    NASA Astrophysics Data System (ADS)

    Dameris, Martin; Loyola, Diego

    Since the early 1980s significant depletion of the ozone layer in the stratosphere, in other words the ozone hole, has been observed every year over the South Pole area in Antarctic spring. In the meantime destruction of stratospheric ozone has been detected globally. Emissions of man-made halogenated chemicals play a dominant role in ozone loss. Combined analyses of observations and numerical modeling help to understand the complex interplay of the dynamic and chemical processes involved. Evaluated models provide a base for predicting the future recovery of the ozone layer expected for the middle of this century.

  10. The nonlinear evolution of modes on unstable stratified shear layers

    NASA Technical Reports Server (NTRS)

    Blackaby, Nicholas; Dando, Andrew; Hall, Philip

    1993-01-01

    The nonlinear development of disturbances in stratified shear flows (having a local Richardson number of value less than one quarter) is considered. Such modes are initially fast growing but, like related studies, we assume that the viscous, non-parallel spreading of the shear layer results in them evolving in a linear fashion until they reach a position where their amplitudes are large enough and their growth rates have diminished sufficiently so that amplitude equations can be derived using weakly nonlinear and non-equilibrium critical-layer theories. Four different basic integro-differential amplitude equations are possible, including one due to a novel mechanism; the relevant choice of amplitude equation, at a particular instance, being dependent on the relative sizes of the disturbance amplitude, the growth rate of the disturbance, its wavenumber, and the viscosity of the fluid. This richness of choice of possible nonlinearities arises mathematically from the indicial Frobenius roots of the governing linear inviscid equation (the Taylor-Goldstein equation) not, in general, differing by an integer. The initial nonlinear evolution of a mode will be governed by an integro-differential amplitude equations with a cubic nonlinearity but the resulting significant increase in the size of the disturbance's amplitude leads on to the next stage of the evolution process where the evolution of the mode is governed by an integro-differential amplitude equations with a quintic nonlinearity. Continued growth of the disturbance amplitude is expected during this stage, resulting in the effects of nonlinearity spreading to outside the critical level, by which time the flow has become fully nonlinear.

  11. Evolution of the Raman spectra from single-, few-, and many-layer graphene with increasing disorder

    SciTech Connect

    Martins Ferreira, E. H.; Stavale, F.; Moutinho, Marcus V. O.; Lucchese, M. M.; Capaz, Rodrigo B.; Achete, C. A.; Jorio, A.

    2010-09-15

    We report on the micro-Raman spectroscopy of monolayer, bilayer, trilayer, and many layers of graphene (graphite) bombarded by low-energy argon ions with different doses. The evolution of peak frequencies, intensities, linewidths, and areas of the main Raman bands of graphene is analyzed as function of the distance between defects and number of layers. We describe the disorder-induced frequency shifts and the increase in the linewidth of the Raman bands by means of a spatial-correlation model. Also, the evolution of the relative areas A{sub D}/A{sub G}, A{sub D}{sup '}/A{sub G}, and A{sub G}{sup '}/A{sub G} is described by a phenomenological model. The present results can be used to fully characterize disorder in graphene systems.

  12. Near-inertial kinetic energy budget of the mixed layer and shear evolution in the transition layer in the Arabian Sea during the monsoons

    NASA Astrophysics Data System (ADS)

    Majumder, Sudip; Tandon, Amit; Rudnick, Daniel L.; Thomas Farrar, J.

    2015-09-01

    We present the horizontal kinetic energy (KE) balance of near-inertial currents in the mixed layer and explain shear evolution in the transition layer using observations from a mooring at 15.26° N in the Arabian Sea during the southwest monsoon. The highly sheared and stratified transition layer at the mixed-layer base varies between 5 m and 35 m and correlates negatively with the wind stress. Results from the mixed layer near-inertial KE (NIKE) balance suggest that wind energy at times can energize the transition layer and at other times is fully utilized within the mixed layer. A simple two layer model is utilized to study the shear evolution in the transition layer and shown to match well with observations. The shear production in this model arises from alignment of wind stress and shear. Although the winds are unidirectional during the monsoon, the shear in the transition layer is predominantly near-inertial. The near-inertial shear bursts in the observations show the same phasing and magnitude at near-inertial frequencies as the wind-shear alignment term.

  13. Evolution models with extremal dynamics.

    PubMed

    Kärenlampi, Petri P

    2016-08-01

    The random-neighbor version of the Bak-Sneppen biological evolution model is reproduced, along with an analogous model of random replicators, the latter eventually experiencing topology changes. In the absence of topology changes, both types of models self-organize to a critical state. Species extinctions in the replicator system degenerates the self-organization to a random walk, as does vanishing of species interaction for the BS-model. A replicator model with speciation is introduced, experiencing dramatic topology changes. It produces a variety of features, but self-organizes to a possibly critical state only in a few special cases. Speciation-extinction dynamics interfering with self-organization, biological macroevolution probably is not a self-organized critical system. PMID:27626090

  14. Three-layer model for exchange anisotropy

    NASA Astrophysics Data System (ADS)

    Rezende, S. M.; Azevedo, A.; de Aguiar, F. M.; Fermin, J. R.; Egelhoff, W. F.; Parkin, S. S.

    2002-08-01

    Recent x-ray absorption measurements have indicated that the interface between the antiferromagnetic (AF) and the ferromagnetic (FM) layers in AF/FM bilayers instead of being abrupt, consists of a thin layer with uncompensated spins. Here the effect of an interfacial layer between the AF and FM layers on the ferromagnetic resonance response is investigated using a three-layer model for the exchange anisotropy. The calculated dependence of the resonance field with the azimuthal angle of the in-plane external field agrees quite well with experimental data in several samples, lending support to the existence of the uncompensated interfacial layer.

  15. Modeling turbulent boundary layers in adverse pressure gradients

    NASA Technical Reports Server (NTRS)

    Belcher, Stephen E.

    1991-01-01

    Many of the turbulent layers encountered in practical flows develop in adverse pressure gradients; hence, the dynamics of the thickening and possible separation of the boundary layer has important implications for design practices. What are the key physical processes that govern how a turbulent boundary layer responds to an adverse pressure gradient, and how should these processes be modeled? Despite the ubiquity of such flows in engineering and nature, these equations remain largely unanswered. The turbulence closure models presently used to describe these flows commonly use 'wall functions' that have ad hoc corrections for the effects of pressure gradients. There is, therefore, a practical and theoretical need to examine the effects of adverse pressure gradients on wall bounded turbulent flows in order to develop models based on sound physical principle. The evolution of a turbulent boundary layer on a flat wall with an externally imposed pressure gradient is studied.

  16. Combined effects of surface conditions, boundary layer dynamics and chemistry on diurnal SOA evolution

    NASA Astrophysics Data System (ADS)

    Janssen, R. H. H.; Vilà-Guerau de Arellano, J.; Ganzeveld, L. N.; Kabat, P.; Jimenez, J. L.; Farmer, D. K.; van Heerwaarden, C. C.; Mammarella, I.

    2012-08-01

    We study the combined effects of land surface conditions, atmospheric boundary layer dynamics and chemistry on the diurnal evolution of biogenic secondary organic aerosol in the atmospheric boundary layer, using a model that contains the essentials of all these components. First, we evaluate the model for a case study in Hyytiälä, Finland, and find that it is able to satisfactorily reproduce the observed dynamics and gas-phase chemistry. We show that the exchange of organic aerosol between the free troposphere and the boundary layer (entrainment) must be taken into account in order to explain the observed diurnal cycle in organic aerosol (OA) concentration. An examination of the budgets of organic aerosol and terpene concentrations show that the former is dominated by entrainment, while the latter is mainly driven by emission and chemical transformation. We systematically investigate the role of the land surface, which governs both the surface energy balance partitioning and terpene emissions, and the large-scale atmospheric process of vertical subsidence. Entrainment is especially important for the dilution of organic aerosol concentrations under conditions of dry soils and low terpene emissions. Subsidence suppresses boundary layer growth while enhancing entrainment. Therefore, it influences the relationship between organic aerosol and terpene concentrations. Our findings indicate that the diurnal evolution of secondary organic aerosols (SOA) in the boundary layer is the result of coupled effects of the land surface, dynamics of the atmospheric boundary layer, chemistry, and free troposphere conditions. This has potentially some consequences for the design of both field campaigns and large-scale modeling studies.

  17. The fast debris evolution model

    NASA Astrophysics Data System (ADS)

    Lewis, H. G.; Swinerd, G. G.; Newland, R. J.; Saunders, A.

    2009-09-01

    The 'particles-in-a-box' (PIB) model introduced by Talent [Talent, D.L. Analytic model for orbital debris environmental management. J. Spacecraft Rocket, 29 (4), 508-513, 1992.] removed the need for computer-intensive Monte Carlo simulation to predict the gross characteristics of an evolving debris environment. The PIB model was described using a differential equation that allows the stability of the low Earth orbit (LEO) environment to be tested by a straightforward analysis of the equation's coefficients. As part of an ongoing research effort to investigate more efficient approaches to evolutionary modelling and to develop a suite of educational tools, a new PIB model has been developed. The model, entitled Fast Debris Evolution (FADE), employs a first-order differential equation to describe the rate at which new objects ⩾10 cm are added and removed from the environment. Whilst Talent [Talent, D.L. Analytic model for orbital debris environmental management. J. Spacecraft Rocket, 29 (4), 508-513, 1992.] based the collision theory for the PIB approach on collisions between gas particles and adopted specific values for the parameters of the model from a number of references, the form and coefficients of the FADE model equations can be inferred from the outputs of future projections produced by high-fidelity models, such as the DAMAGE model. The FADE model has been implemented as a client-side, web-based service using JavaScript embedded within a HTML document. Due to the simple nature of the algorithm, FADE can deliver the results of future projections immediately in a graphical format, with complete user-control over key simulation parameters. Historical and future projections for the ⩾10 cm LEO debris environment under a variety of different scenarios are possible, including business as usual, no future launches, post-mission disposal and remediation. A selection of results is presented with comparisons with predictions made using the DAMAGE environment model

  18. XMM tests galaxy evolutions models

    NASA Astrophysics Data System (ADS)

    Miniati, Francesco

    2011-10-01

    Current models of galaxy evolution rely critically on feedback supernova and AGN feedback processes. The energy released by past star formation and AGN activity imprints a fossil record on the thermodynamic properties of the intra-group-medium (IGM). This can be decoded by studying the X-ray emission. for an unbiased sample of groups with known galaxy and AGN properties. Therefore we propose an X-ray survey with XMM-Newton for 255 ksec to observe 17 galaxy groups with Msim10(13) M_odot selected from our Zurich ENvironmental Survey that host >8 members.

  19. Neutral Models of Microbiome Evolution

    PubMed Central

    Zeng, Qinglong; Sukumaran, Jeet; Wu, Steven; Rodrigo, Allen

    2015-01-01

    There has been an explosion of research on host-associated microbial communities (i.e.,microbiomes). Much of this research has focused on surveys of microbial diversities across a variety of host species, including humans, with a view to understanding how these microbiomes are distributed across space and time, and how they correlate with host health, disease, phenotype, physiology and ecology. Fewer studies have focused on how these microbiomes may have evolved. In this paper, we develop an agent-based framework to study the dynamics of microbiome evolution. Our framework incorporates neutral models of how hosts acquire their microbiomes, and how the environmental microbial community that is available to the hosts is assembled. Most importantly, our framework also incorporates a Wright-Fisher genealogical model of hosts, so that the dynamics of microbiome evolution is studied on an evolutionary timescale. Our results indicate that the extent of parental contribution to microbial availability from one generation to the next significantly impacts the diversity of microbiomes: the greater the parental contribution, the less diverse the microbiomes. In contrast, even when there is only a very small contribution from a constant environmental pool, microbial communities can remain highly diverse. Finally, we show that our models may be used to construct hypotheses about the types of processes that operate to assemble microbiomes over evolutionary time. PMID:26200800

  20. Sangamon field experiments: observations of the diurnal evolution of the planetary boundary layer over land

    SciTech Connect

    Hicks, B.B.; Hess, G.D.; Wesely, M.L.; Yamada, T.; Frenzen, P.; Hart, R.L.; Sisterson, D.L.; Hess, P.E.; Kulhanek, F.C.; Lipschutz, R.C.; Zerbe, G.A.

    1981-09-01

    Two complementary experimental studies of the evolving structure of the lower 2 km of the atmosphere, conducted over farmlands in central Illinois during essentially the same mid-summer weeks of two successive years, are described. The first experiment (21 July - 13 August 1975) investigated the early morning break up of the nocturnal stable layer and the rapid growth of the mixed layer before noon; the second (16 to 30 July 1976) examined the decline of the mixed layer through the late afternoon and evening, and the formation and intensification of the ground-based inversion before midnight. Methods of observation and data reduction are summarized in some detail, and the data obtained in the form of hourly wind and temperature profiles, plus sufficient surface flux information to characterize the lower boundary conditions, are tabulated in a series of appendices. These results constitute complete data sets which may be used to test models of the diurnal evolution of the lower atmosphere.

  1. The Fast Debris Evolution Model

    NASA Astrophysics Data System (ADS)

    Lewis, Hugh G.; Swinerd, Graham; Newland, Rebecca; Saunders, Arrun

    The ‘Particles-in-a-box' (PIB) model introduced by Talent (1992) removed the need for computerintensive Monte Carlo simulation to predict the gross characteristics of an evolving debris environment. The PIB model was described using a differential equation that allows the stability of the low Earth orbit (LEO) environment to be tested by a straightforward analysis of the equation's coefficients. As part of an ongoing research effort to investigate more efficient approaches to evolutionary modelling and to develop a suite of educational tools, a new PIB model has been developed. The model, entitled Fast Debris Evolution (FaDE), employs a first-order differential equation to describe the rate at which new objects (˜ 10 cm) are added and removed from the environment. Whilst Talent (1992) based the collision theory for the PIB approach on collisions between gas particles and adopted specific values for the parameters of the model from a number of references, the form and coefficients of the FaDE model equations can be inferred from the outputs of future projections produced by high-fidelity models, such as the DAMAGE model. The FaDE model has been implemented as a client-side, web-based service using Javascript embedded within a HTML document. Due to the simple nature of the algorithm, FaDE can deliver the results of future projections immediately in a graphical format, with complete user-control over key simulation parameters. Historical and future projections for the ˜ 10 cm low Earth orbit (LEO) debris environment under a variety of different scenarios are possible, including business as usual, no future launches, post-mission disposal and remediation. A selection of results is presented with comparisons with predictions made using the DAMAGE environment model. The results demonstrate that the FaDE model is able to capture comparable time-series of collisions and number of objects as predicted by DAMAGE in several scenarios. Further, and perhaps more importantly

  2. Modeling the summertime Arctic cloudy boundary layer

    SciTech Connect

    Curry, J.A.; Pinto, J.O.; McInnes, K.L.

    1996-04-01

    Global climate models have particular difficulty in simulating the low-level clouds during the Arctic summer. Model problems are exacerbated in the polar regions by the complicated vertical structure of the Arctic boundary layer. The presence of multiple cloud layers, a humidity inversion above cloud top, and vertical fluxes in the cloud that are decoupled from the surface fluxes, identified in Curry et al. (1988), suggest that models containing sophisticated physical parameterizations would be required to accurately model this region. Accurate modeling of the vertical structure of multiple cloud layers in climate models is important for determination of the surface radiative fluxes. This study focuses on the problem of modeling the layered structure of the Arctic summertime boundary-layer clouds and in particular, the representation of the more complex boundary layer type consisting of a stable foggy surface layer surmounted by a cloud-topped mixed layer. A hierarchical modeling/diagnosis approach is used. A case study from the summertime Arctic Stratus Experiment is examined. A high-resolution, one-dimensional model of turbulence and radiation is tested against the observations and is then used in sensitivity studies to infer the optimal conditions for maintaining two separate layers in the Arctic summertime boundary layer. A three-dimensional mesoscale atmospheric model is then used to simulate the interaction of this cloud deck with the large-scale atmospheric dynamics. An assessment of the improvements needed to the parameterizations of the boundary layer, cloud microphysics, and radiation in the 3-D model is made.

  3. Microstructural and continuum evolution modeling of sintering.

    SciTech Connect

    Braginsky, Michael V.; Olevsky, Eugene A.; Johnson, D. Lynn; Tikare, Veena; Garino, Terry J.; Arguello, Jose Guadalupe, Jr.

    2003-12-01

    All ceramics and powder metals, including the ceramics components that Sandia uses in critical weapons components such as PZT voltage bars and current stacks, multi-layer ceramic MET's, ahmindmolybdenum & alumina cermets, and ZnO varistors, are manufactured by sintering. Sintering is a critical, possibly the most important, processing step during manufacturing of ceramics. The microstructural evolution, the macroscopic shrinkage, and shape distortions during sintering will control the engineering performance of the resulting ceramic component. Yet, modeling and prediction of sintering behavior is in its infancy, lagging far behind the other manufacturing models, such as powder synthesis and powder compaction models, and behind models that predict engineering properties and reliability. In this project, we developed a model that was capable of simulating microstructural evolution during sintering, providing constitutive equations for macroscale simulation of shrinkage and distortion during sintering. And we developed macroscale sintering simulation capability in JAS3D. The mesoscale model can simulate microstructural evolution in a complex powder compact of hundreds or even thousands of particles of arbitrary shape and size by 1. curvature-driven grain growth, 2. pore migration and coalescence by surface diffusion, 3. vacancy formation, grain boundary diffusion and annihilation. This model was validated by comparing predictions of the simulation to analytical predictions for simple geometries. The model was then used to simulate sintering in complex powder compacts. Sintering stress and materials viscous module were obtained from the simulations. These constitutive equations were then used by macroscopic simulations for simulating shrinkage and shape changes in FEM simulations. The continuum theory of sintering embodied in the constitutive description of Skorohod and Olevsky was combined with results from microstructure evolution simulations to model shrinkage and

  4. Uncertainties in Surface Layer Modeling

    NASA Astrophysics Data System (ADS)

    Pendergrass, W.

    2015-12-01

    A central problem for micrometeorologists has been the relationship of air-surface exchange rates of momentum and heat to quantities that can be predicted with confidence. The flux-gradient profile developed through Monin-Obukhov Similarity Theory (MOST) provides an integration of the dimensionless wind shear expression where is an empirically derived expression for stable and unstable atmospheric conditions. Empirically derived expressions are far from universally accepted (Garratt, 1992, Table A5). Regardless of what form of these relationships might be used, their significance over any short period of time is questionable since all of these relationships between fluxes and gradients apply to averages that might rarely occur. It is well accepted that the assumption of stationarity and homogeneity do not reflect the true chaotic nature of the processes that control the variables considered in these relationships, with the net consequence that the levels of predictability theoretically attainable might never be realized in practice. This matter is of direct relevance to modern prognostic models which construct forecasts by assuming the universal applicability of relationships among averages for the lower atmosphere, which rarely maintains an average state. Under a Cooperative research and Development Agreement between NOAA and Duke Energy Generation, NOAA/ATDD conducted atmospheric boundary layer (ABL) research using Duke renewable energy sites as research testbeds. One aspect of this research has been the evaluation of legacy flux-gradient formulations (the ϕ functions, see Monin and Obukhov, 1954) for the exchange of heat and momentum. At the Duke Energy Ocotillo site, NOAA/ATDD installed sonic anemometers reporting wind and temperature fluctuations at 10Hz at eight elevations. From these observations, ϕM and ϕH were derived from a two-year database of mean and turbulent wind and temperature observations. From this extensive measurement database, using a

  5. Influence of combined primordial layering and recycled MORB on the coupled thermal evolution of Earth's mantle and core

    NASA Astrophysics Data System (ADS)

    Nakagawa, Takashi; Tackley, Paul

    2014-05-01

    A thermo-chemical mantle convection model with both primordial compositional layering and recycling of mid-ocean ridge basalt (MORB) coupled to a parameterized core heat balance model is used to investigate how the thermo-chemical evolution of the mantle affects the thermal history of the core including primordial material proposed by early Earth hypotheses. The viscosity formulation has been improved from our previous works. The amount of MORB that accumulates above the CMB is strongly dependent on effective Rayleigh number, such that more accumulates at higher Ra (lower viscosity), but a continuous layer of MORB is not obtained here. With initial primordial layering, large-scale thermo-chemical anomalies are found in the deep mantle, which are generated mainly by the primordial material with small amount of segregated basaltic material on top of it, localized in the hot upwelling region. A successful core evolution can only be obtained when initial primordial layering is present. In conclusion, primordial material above the CMB originated from early mantle differentiation might be needed to construct a realistic model of a coupled mantle and core evolution. Nakagawa, T. and P. J. Tackley, Influence of combined primordial layering and recycled MORB on the coupled thermal evolution of Earth's mantle and core, Geochem. Geophys. Geosyst., in press

  6. Modelling microstructure evolution during recrystallization

    NASA Astrophysics Data System (ADS)

    Brahme, Abhijit P.

    The main aim of this work was to model microstructural evolution during recrystallization. This was achieved by characterizing it in terms of recrystallization kinetics and texture development and by identifying factors that exert the greatest effect on the recrystallization process. To achieve the above, geometric and crystallographic observations from two orthogonal sections through a polycrystal were used. Using these as input to the computer simulations, a statistically representative three dimensional model was created. Assignment of orientations to the grains was done such that nearest neighbor relationships match the observed distributions. The microstructures thus obtained were allowed to evolve using a Monte-Carlo simulation. A parametric study was done to study the effects of various factors on recrystallization kinetics and texture development during microstructural evolution. A set of software tools (Microstructure builder) were developed to generate the microstructures. The process involved the use of a ellipsoidal packing method combined with a voxel-based tessellation technique to create a 3 dimensional digital microstructure having the desired set of grain aspect ratios. Orientation assignment to the grains in the microstructure was done using a simulated annealing method that minimized the error between the orientation distribution function (ODF) and misorientation distribution function (MDF) of the measured and simulated materials. The effect of grain geometry and placement of nuclei on recrystallization kinetics was studied. A close match in the recrystallization kinetics as measured in the experiments and the simulations was found to be most sensitive to the accuracy with which the geometry of the simulated microstructure matched that observed in experiments. Also the effects of anisotropy, both in energy and in mobility, stored energy and oriented nucleation on overall texture development were studied in the light of various established

  7. Analytical steam injection model for layered systems

    SciTech Connect

    Abdual-Razzaq; Brigham, W.E.; Castanier, L.M.

    1993-08-01

    Screening, evaluation and optimization of the steam flooding process in homogeneous reservoirs can be performed by using simple analytical predictive models. In the absence of any analytical model for layered reservoirs, at present, only numerical simulators can be used. And these are expensive. In this study, an analytical model has been developed considering two isolated layers of differing permeabilities. The principle of equal flow potential is applied across the two layers. Gajdica`s (1990) single layer linear steam drive model is extended for the layered system. The formulation accounts for variation of heat loss area in the higher permeability layer, and the development of a hot liquid zone in the lower permeability layer. These calculations also account for effects of viscosity, density, fractional flow curves and pressure drops in the hot liquid zone. Steam injection rate variations in the layers are represented by time weighted average rates. For steam zone calculations, Yortsos and Gavalas`s (1981) upper bound method is used with a correction factor. The results of the model are compared with a numerical simulator. Comparable oil and water flow rates, and breakthrough times were achieved for 100 cp oil. Results with 10 cp and 1000 cp oils indicate the need to improve the formulation to properly handle differing oil viscosities.

  8. Snow Model for the F-Layer

    NASA Astrophysics Data System (ADS)

    Lasbleis, M.; Hernlund, J. W.; Labrosse, S.

    2015-12-01

    Seismic observations of the Earth's core reveal a complex structure: radial and lateral heterogeneities in seismic anisotropy and attenuation in the solid inner core, but also discrepancies between observed P-wave velocity and homogeneous PREM model in the deep liquid outer core. In this work, we focus on the 200km anomalous layer at the bottom of the outer core that exhibits seismic velocities lower than the PREM model. It has been interpreted as a layer depleted in light elements, whereas the usual model considers that light elements are expelled at the surface of the inner core by freezing of the outer core alloy. Recent models of core formation argued for an early stratified liquid core, and the stratified layers at the top and bottom of the outer core would be a vestige of this primordial stratification. However, freezing of the inner core at the inner core boundary releases light elements that provide buoyancy fluxes that would mix the stratified liquid above with small scale buoyant plumes. To model the F-layer, we consider that the freezing of the iron alloy and the release of light elements have to occur in the bulk of the layer. Iron snow forms and settles in the layer, buffering the thermal and chemical profile to the liquidus. We show that this dynamics can both sustain and stabilize the stratified layer in the liquid outer core while simultaneously matching the seismic observations. However, the expected layer is stable only for a given set of parameters, in particular when a high thermal diffusivity (>100 W/m/K) is employed. If freezing of the iron alloy of the outer core occurs in the bulk of the layer, several assumptions for both the outer and inner core has to be discussed: the F-layer acts as a boundary layer for both composition and temperature, and modifies the quantity of light elements expelled into the outer core as well as the composition that freezes to form the inner core.

  9. A hemodynamic model for layered BOLD signals.

    PubMed

    Heinzle, Jakob; Koopmans, Peter J; den Ouden, Hanneke E M; Raman, Sudhir; Stephan, Klaas Enno

    2016-01-15

    High-resolution blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) at the sub-millimeter scale has become feasible with recent advances in MR technology. In principle, this would enable the study of layered cortical circuits, one of the fundaments of cortical computation. However, the spatial layout of cortical blood supply may become an important confound at such high resolution. In particular, venous blood draining back to the cortical surface perpendicularly to the layered structure is expected to influence the measured responses in different layers. Here, we present an extension of a hemodynamic model commonly used for analyzing fMRI data (in dynamic causal models or biophysical network models) that accounts for such blood draining effects by coupling local hemodynamics across layers. We illustrate the properties of the model and its inversion by a series of simulations and show that it successfully captures layered fMRI data obtained during a simple visual experiment. We conclude that for future studies of the dynamics of layered neuronal circuits with high-resolution fMRI, it will be pivotal to include effects of blood draining, particularly when trying to infer on the layer-specific connections in cortex--a theme of key relevance for brain disorders like schizophrenia and for theories of brain function such as predictive coding. PMID:26484827

  10. Coupled wake boundary layer model of windfarms

    NASA Astrophysics Data System (ADS)

    Stevens, Richard; Gayme, Dennice; Meneveau, Charles

    2014-11-01

    We present a coupled wake boundary layer (CWBL) model that describes the distribution of the power output in a windfarm. The model couples the traditional, industry-standard wake expansion/superposition approach with a top-down model for the overall windfarm boundary layer structure. Wake models capture the effect of turbine positioning, while the top-down approach represents the interaction between the windturbine wakes and the atmospheric boundary layer. Each portion of the CWBL model requires specification of a parameter that is unknown a-priori. The wake model requires the wake expansion rate, whereas the top-down model requires the effective spanwise turbine spacing within which the model's momentum balance is relevant. The wake expansion rate is obtained by matching the mean velocity at the turbine from both approaches, while the effective spanwise turbine spacing is determined from the wake model. Coupling of the constitutive components of the CWBL model is achieved by iterating these parameters until convergence is reached. We show that the CWBL model predictions compare more favorably with large eddy simulation results than those made with either the wake or top-down model in isolation and that the model can be applied successfully to the Horns Rev and Nysted windfarms. The `Fellowships for Young Energy Scientists' (YES!) of the Foundation for Fundamental Research on Matter supported by NWO, and NSF Grant #1243482.

  11. Wetting layer evolution and its temperature dependence during self-assembly of InAs/GaAs quantum dots

    PubMed Central

    2012-01-01

    For InAs/GaAs(001) quantum dot (QD) system, the wetting layer (WL) evolution and its temperature dependence were studied using reflectance difference spectroscopy and were analyzed with a rate equation model. WL thicknesses showed a monotonic increase at relatively low growth temperatures but showed an initial increase and then decrease at higher temperatures, which were unexpected from a thermodynamic understanding. By adopting a rate equation model, the temperature dependence of QD formation rate was assigned as the origin of different WL evolutions. A brief discussion on the indium desorption was given. Those results gave hints of the kinetic aspects of QD self-assembly. PMID:23110846

  12. A layered network model of sensory cortex

    SciTech Connect

    Travis, B.J.

    1986-01-01

    An integrated computational approach to modeling sensory systems which couples realistic layered neural models of sensory cortex and midbrain nuclei to detailed models of the sense organs (e.g., retina or cochlea) is described. The approach is applied to the auditory system. Through an exercise of the model, it is shown that spatial location of sounds may be a natural consequence of the way cochlear response is mapped onto the cortex. 31 refs., 23 figs., 3 tabs.

  13. The evolution of a thin phytoplankton layer in strong turbulence

    NASA Astrophysics Data System (ADS)

    Wang, Zhankun; Goodman, Louis

    2010-01-01

    Simultaneous and collocated spatial measurements of turbulence, fine structure, and chlorophyll a fields were made from the Autonomous Underwater Vehicle T-REMUS as a part of the Layered Organization in the Coastal Ocean (LOCO) experiment. The T-REMUS was operated in a cycling 5° yo-yo mode. Deployments were of 8 h duration and consisted of a series of across isobath legs, each of 2.5 km in extent. From the suite of sensors onboard the T-REMUS vehicle we are able to measure directly the turbulent eddy velocity, we=√{ɛ/N}, and turbulent Reynolds number, Re b=( ɛ/ vN2), in the vicinity of a thin chlorophyll a layer. Using the turbulent eddy velocity, we develop criteria for when phytoplankton will behave as passive Lagrangian tracers. The turbulent Reynolds number is used as an indicator of turbulence strength, with the criterion of Re b=200 the boundary between weak and strong turbulence. We present data for the case of a spatially extensive thin layer being advected into the T-REMUS LOCO site. Using the above criterion, we observe that thin chlorophyll a layers can exist and be embedded as passive Lagrangian tracers in both weak and strong turbulent conditions. During a time period of weak turbulence Re b<200 little diffusion occurs and the thin layer remains compact. Under strong turbulence Re b>200 the thin layer weakens and diffuses as it is advected through the experimental site.

  14. Extreme model reduction of shear layers

    NASA Astrophysics Data System (ADS)

    Qawasmeh, Bashar Rafee

    The aim of this research is to develop nonlinear low-dimensional models (LDMs) to describe vortex dynamics in shear layers. A modified Proper Orthogonal Decomposition (POD)/Galerkin projection method is developed to obtain models at extremely low dimension for shear layers. The idea is to dynamically scale the shear layer along y direction to factor out the shear layer growth and capture the dynamics by only a couple of modes. The models are developed for two flows, incompressible spatially developing and weakly compressible temporally developing shear layers, respectively. To capture basic dynamics, the low-dimensional models require only two POD modes for each wavenumber/frequency. Thus, a two-mode model is capable of representing single-wavenumber/frequency dynamics such as vortex roll-up, and a four-mode model is capable of representing the nonlinear dynamics involving a fundamental wavenumber/frequency and its subharmonic, such as vortex pairing/merging. Most of the energy is captured by the first mode of each wavenumber/frequency, the second POD mode, however, plays a critical role and needs to be included. In the thesis, we first apply the approach on temporally developing weakly compressible shear layers. In compressible flows, the thermodynamic variables are dynamically important, and must be considered. We choose isentropic Navier-Stokes equations for simplicity, and choose a proper inner product to present both kinetic energy and thermal energy. Two cases of convective Mach numbers are studied for low compressibility and moderate compressibility. Moreover, we study the sensitivity of the compressible four-mode model to several flow parameters: Mach number, the strength of initial perturbations of the fundamental and its subharmonic, and Reynolds number. Secondly we apply the approach on spatially developing incompressible shear layers with periodicity in time. We consider a streamwise parabolic form of the Navier-Stokes equations. When we add arbitrary

  15. Ternary NiFeMn layered double hydroxides as highly-efficient oxygen evolution catalysts.

    PubMed

    Lu, Zhiyi; Qian, Li; Tian, Yang; Li, Yaping; Sun, Xiaoming; Duan, Xue

    2016-01-18

    Layered double hydroxides (LDHs) are a family of layer materials that receive heightened attention. Herein a ternary NiFeMn-LDH is investigated with superior oxygen evolution activity, which is attributed to the Mn(4+) doping in the intralayer, which modifies the electronic structure and improves the conductivity of the electrocatalyst. PMID:26579843

  16. A microwave scattering model for layered vegetation

    NASA Technical Reports Server (NTRS)

    Karam, Mostafa A.; Fung, Adrian K.; Lang, Roger H.; Chauhan, Narinder S.

    1992-01-01

    A microwave scattering model was developed for layered vegetation based on an iterative solution of the radiative transfer equation up to the second order to account for multiple scattering within the canopy and between the ground and the canopy. The model is designed to operate over a wide frequency range for both deciduous and coniferous forest and to account for the branch size distribution, leaf orientation distribution, and branch orientation distribution for each size. The canopy is modeled as a two-layered medium above a rough interface. The upper layer is the crown containing leaves, stems, and branches. The lower layer is the trunk region modeled as randomly positioned cylinders with a preferred orientation distribution above an irregular soil surface. Comparisons of this model with measurements from deciduous and coniferous forests show good agreements at several frequencies for both like and cross polarizations. Major features of the model needed to realize the agreement include allowance for: (1) branch size distribution, (2) second-order effects, and (3) tree component models valid over a wide range of frequencies.

  17. Radiative effects of tropospheric aerosols on the evolution of the atmospheric boundary layer and its feedback on the haze formation

    NASA Astrophysics Data System (ADS)

    Wei, Chao; Su, Hang; Cheng, Yafang

    2016-04-01

    Planetary boundary layer (PBL) plays a key role in air pollution dispersion and influences day-to-day air quality. Some studies suggest that high aerosol loadings during severe haze events may modify PBL dynamics by radiative effects and hence enhance the development of haze. This study mainly investigates the radiative effects of tropospheric aerosols on the evolution of the atmospheric boundary layer by conducting simulations with Weather Research and Forecasting single-column model (WRF-SCM). We find that high aerosol loading in PBL depressed boundary layer height (PBLH). But the magnitude of the changes of PBLH after adding aerosol loadings in our simulations are small and can't explain extreme high aerosol concentrations observed. We also investigate the impacts of the initial temperature and moisture profiles on the evolution of PBL. Our studies show that the impact of the vertical profile of moisture is comparable with aerosol effects.

  18. Influence of combined primordial layering and recycled MORB on the coupled thermal evolution of Earth's mantle and core

    NASA Astrophysics Data System (ADS)

    Nakagawa, Takashi; Tackley, Paul J.

    2014-03-01

    thermo-chemical mantle convection model with both primordial compositional layering and recycling of mid-ocean ridge basalt (MORB) coupled to a parameterized core heat balance model is used to investigate how the thermo-chemical evolution of the mantle affects the thermal history of the core including primordial material proposed by early Earth hypotheses. The viscosity formulation has been improved from our previous works. The amount of MORB that accumulates above the CMB is strongly dependent on effective Rayleigh number, such that more accumulates at higher Ra (lower viscosity), but a continuous layer of MORB is not obtained here. With initial primordial layering, large-scale thermo-chemical anomalies are found in the deep mantle, which are generated mainly by the primordial material with small amount of segregated basaltic material on top of it, localized in the hot upwelling region. A successful core evolution can only be obtained when initial primordial layering is present. In conclusion, primordial material above the CMB originated from early mantle differentiation might be needed to construct a realistic model of a coupled mantle and core evolution. However, in the current study, the convective vigor is lower than realistic and we only consider the case that primordial material is denser than MORB.

  19. Modeling Regional Seawater Intrusion Using One Model Layer Per Aquifer

    NASA Astrophysics Data System (ADS)

    Bakker, M.; Schaars, F.

    2012-12-01

    Seawater intrusion is an ongoing and expanding problem in coastal aquifers. A Dupuit formulation was developed to make it possible to simulate seawater intrusion using one model layer per aquifer. The formulation is implemented in the SWI package for MODFLOW. Aquifers don't need to be discretized vertically so that the evolution of the salinity distribution may be simulated in a timely manner on a regular Mac or PC. SWI may be applied to simulate seawater intrusion with an existing MODFLOW model through the addition of just one input file. SWI is envisioned to be complimentary to codes that solve the coupled flow and transport equations, such as SEAWAT and SUTRA: SWI may be used to simulate regional flow including density effects, and other codes may be used to simulate local seawater intrusion, including dispersive mixing. Since its first release in 2004, SWI has been benchmarked against several other codes and was shown to perform well, even when a moderate amount of dispersion was included in the simulations. SWI has recently been implemented in MODFLOW2005. The new implementation includes a number of enhancements such as variable time stepping, separate budgets for fresh and salt water, and the ability to simulate upconing through aquitards. In the presentation, the main features of the SWI package are discussed, the new capabilities are showcased, and several examples are presented.

  20. Modelling language evolution: Examples and predictions.

    PubMed

    Gong, Tao; Shuai, Lan; Zhang, Menghan

    2014-06-01

    We survey recent computer modelling research of language evolution, focusing on a rule-based model simulating the lexicon-syntax coevolution and an equation-based model quantifying the language competition dynamics. We discuss four predictions of these models: (a) correlation between domain-general abilities (e.g. sequential learning) and language-specific mechanisms (e.g. word order processing); (b) coevolution of language and relevant competences (e.g. joint attention); (c) effects of cultural transmission and social structure on linguistic understandability; and (d) commonalities between linguistic, biological, and physical phenomena. All these contribute significantly to our understanding of the evolutions of language structures, individual learning mechanisms, and relevant biological and socio-cultural factors. We conclude the survey by highlighting three future directions of modelling studies of language evolution: (a) adopting experimental approaches for model evaluation; (b) consolidating empirical foundations of models; and (c) multi-disciplinary collaboration among modelling, linguistics, and other relevant disciplines. PMID:24286718

  1. Modelling language evolution: Examples and predictions

    NASA Astrophysics Data System (ADS)

    Gong, Tao; Shuai, Lan; Zhang, Menghan

    2014-06-01

    We survey recent computer modelling research of language evolution, focusing on a rule-based model simulating the lexicon-syntax coevolution and an equation-based model quantifying the language competition dynamics. We discuss four predictions of these models: (a) correlation between domain-general abilities (e.g. sequential learning) and language-specific mechanisms (e.g. word order processing); (b) coevolution of language and relevant competences (e.g. joint attention); (c) effects of cultural transmission and social structure on linguistic understandability; and (d) commonalities between linguistic, biological, and physical phenomena. All these contribute significantly to our understanding of the evolutions of language structures, individual learning mechanisms, and relevant biological and socio-cultural factors. We conclude the survey by highlighting three future directions of modelling studies of language evolution: (a) adopting experimental approaches for model evaluation; (b) consolidating empirical foundations of models; and (c) multi-disciplinary collaboration among modelling, linguistics, and other relevant disciplines.

  2. On a Nonlinear Model in Adiabatic Evolutions

    NASA Astrophysics Data System (ADS)

    Sun, Jie; Lu, Song-Feng

    2016-08-01

    In this paper, we study a kind of nonlinear model of adiabatic evolution in quantum search problem. As will be seen here, for this problem, there always exists a possibility that this nonlinear model can successfully solve the problem, while the linear model can not. Also in the same setting, when the overlap between the initial state and the final stare is sufficiently large, a simple linear adiabatic evolution can achieve O(1) time efficiency, but infinite time complexity for the nonlinear model of adiabatic evolution is needed. This tells us, it is not always a wise choice to use nonlinear interpolations in adiabatic algorithms. Sometimes, simple linear adiabatic evolutions may be sufficient for using. Supported by the National Natural Science Foundation of China under Grant Nos. 61402188 and 61173050. The first author also gratefully acknowledges the support from the China Postdoctoral Science Foundation under Grant No. 2014M552041

  3. The Evolution of Flow Stripes and Internal Layers on Kamb Ice Stream, Antarctica

    NASA Astrophysics Data System (ADS)

    Campbell, I.; Welch, B.; Jacobel, R.; Pettersson, R.

    2006-12-01

    Flowstripes are ubiquitous features indicating fast ice flow on glaciers, ice streams and floating ice shelves. Model studies show that they are an expected consequence where flow is strongly convergent, or whenever velocity at the bed is large compared to shearing through the ice thickness (Gudmundsson et al., 1998). Under these conditions, basal undulations are effectively transmitted to the surface where they are advected for long distances downstream. Folding of internal layers depicted in radar profiles is also a common occurrence in ice streams. In the case of Kamb Ice Stream (KIS), "stacks" of internal layers folds on the scale of 1-3 kilometers in wavelength in the cross-flow direction have been traced for over 100 kilometers (Ng and Conway, 2004). The question is: What relationship, if any, do these folds have with respect to surface flowstripes? We have traced surface flowstripes in Radarsat and MODIS imagery for several hundred kilometers on KIS from the onset of streaming flow into the stagnant trunk. We compare the morphology and evolution of these features at the surface to the internal layer folds in cross-ice stream profiles at five transects along the length of KIS, including those analyzed by Ng and Conway (2004). We find little correspondence between the internal layer folds in the cross-flow radar profiles and the flowstripes seen on the surface directly above. The initial wavelengths of internal layer folds are generally in the range of 1-3 km and tend to converge downstream, ending with wavelengths typically less than a kilometer. Surface flowstripes, though having similar wavelengths (on the order of 1.5 to 3 km at onset), remain roughly subparallel for tens to hundreds of kilometers, eventually becoming less distinct as the ice stagnates but retaining their wavelength and spacing. We are thus able to identify examples where flowstripes cross above internal layers. The amplitude of internal layer folds we have measured decreases towards the

  4. Granular flows on erodible layers: type and evolution of flow and deposit structures

    NASA Astrophysics Data System (ADS)

    Crosta, G.; De Blasio, F.; De Caro, M.; Volpi, G.; Frattini, P.

    2012-04-01

    The interaction of a fast moving landslide mass with the basal layer over which movement takes place has been discussed in previous contributions. Nevertheless, the evolution of the structures within the moving mass and the erodible layer are still to be described in detail (Hungr and Evans, 2004; Crosta et al., 1992, 2006, 2009, 2011; Dufresne et al., 2010; Mangeney et al., 2010) and modeling results (Crosta et al., 2006, 2009, 2011; Mangeney et al., 2010). We present some of the results from a campaign of laboratory experiments aimed at studying the evolution of a granular flow at the impact with and during the successive spreading over a cohesionless erodible layer. We performed these test to study the processes and to collect data and evidences to compare them with the results of numerical simulations and to verify capabilities of numerical codes. The laboratory setup consists of an inclined slope and an horizontal sector where release and transport, and deposition take place, respectively. Materials used for the tests are: a uniform rounded siliceous sand (Hostun sand; 0.125-0.5 mm) commonly adopted in lab tests because free of scale effects, and a gravel made of angular elements (12 mm in ave. size). Both the materials have been tested in dry conditions. Different slope angles have been tested (40, 45, 50, 55, 50, 66°) as well as different thicknesses of the erodible layer (0, 0.5, 1, 2 cm) and volumes of the released material (1.5, 3, 5, 9.6 liters). Tests have been monitored by means of a high speed camera and the pre- and post-failure geometries have been surveyed by means of a laser scanner. Deposit description allowed also the computation of volumes and the characterization of the different structures developed and frozen into the deposit. Experiments allowed us to observe the extreme processes occurring during the movement and the mise en place of the deposits. In particular, we observe the formation of a clear wave-like feature developing during the

  5. Molecular models and simulations of layered materials.

    SciTech Connect

    Kalinichev, Andrey G.; Cygan, Randall Timothy; Heinz, Hendrik; Greathouse, Jeffery A.

    2008-11-01

    The micro- to nano-sized nature of layered materials, particularly characteristic of naturally occurring clay minerals, limits our ability to fully interrogate their atomic dispositions and crystal structures. The low symmetry, multicomponent compositions, defects, and disorder phenomena of clays and related phases necessitate the use of molecular models and modern simulation methods. Computational chemistry tools based on classical force fields and quantum-chemical methods of electronic structure calculations provide a practical approach to evaluate structure and dynamics of the materials on an atomic scale. Combined with classical energy minimization, molecular dynamics, and Monte Carlo techniques, quantum methods provide accurate models of layered materials such as clay minerals, layered double hydroxides, and clay-polymer nanocomposites.

  6. Evolution of seismic layer 2B across the Juan de Fuca Ridge from hydrophone streamer 2-D traveltime tomography

    NASA Astrophysics Data System (ADS)

    Newman, Kori R.; Nedimović, Mladen R.; Canales, J. Pablo; Carbotte, Suzanne M.

    2011-05-01

    How oceanic crust evolves has important implications for understanding both subduction earthquake hazards and energy and mass exchange between the Earth's interior and the oceans. Although considerable work has been done characterizing the evolution of seismic layer 2A, there has been little analysis of the processes that affect layer 2B after formation. Here we present high-resolution 2-D tomographic models of seismic layer 2B along ˜300 km long multichannel seismic transects crossing the Endeavour, Northern Symmetric, and Cleft segments of the Juan de Fuca Ridge. These models show that seismic layer 2B evolves rapidly following a different course than layer 2A. The upper layer 2B velocities increase on average by 0.8 km/s and reach a generally constant velocity of 5.2 ± 0.3 km/s within the first 0.5 Myr after crustal formation. This suggests that the strongest impact on layer 2B evolution may be that of mineral precipitation due to "active" hydrothermal circulation centered about the ridge crest and driven by the heat from the axial magma chamber. Variations in upper layer 2B velocity with age at time scales ≥0.5 Ma show correlation about the ridge axis indicating that in the long term, crustal accretion processes affect both sides of the ridge axis in a similar way. Below the 0.5 Ma threshold, differences in 2B velocity are likely imprinted during crustal formation or early crustal evolution. Layer 2B velocities at propagator wakes (5.0 ± 0.2 km/s), where enhanced faulting and cracking are expected, and at areas that coincide with extensional or transtensional faulting are on average slightly slower than in normal mature upper layer 2B. Analysis of the layer 2B velocities from areas where the hydrothermal patterns are known shows that the locations of current and paleohydrothermal discharge and recharge zones are marked by reduced and increased upper layer 2B velocities, respectively. Additionally, the distance between present up-flow and down-flow zones is

  7. An asymptotic model of the F layer

    NASA Astrophysics Data System (ADS)

    Oliver, W. L.

    2012-01-01

    A model of the F layer of the ionosphere is presented that consists of a bottomside asymptote that ignores transport and a topside asymptote that ignores chemistry. The asymptotes connect at the balance height dividing the chemistry and transport regimes. A combination of these two asymptotes produces a good approximation to the true F layer. Analogously, a model of F layer response to an applied vertical drift is presented that consists of two asymptotic responses, one that ignores transport and one that ignores chemistry. The combination of these asymptotic responses produces a good approximation to the response of the true F layer. This latter response is identical to the “servo” response of Rishbeth et al. (1978), derived from the continuity equation. The asymptotic approach bypasses the continuity equation in favor of “force balance” arguments and so replaces a differential equation with simpler algebraic equations. This new approach provides a convenient and intuitive mean for first-order estimates of the change in F layer peak height and density in terms of changes in neutral density, composition, temperature, winds, and electric fields. It is applicable at midlatitudes and at magnetically quiet times at high latitudes. Forensic inverse relations are possible but are not unique. The validity of the asymptotic relations is shown through numerical simulation.

  8. Surface morphological evolution during annealing of epitaxial Cu(001) layers

    SciTech Connect

    Purswani, J. M.; Gall, D.

    2008-08-15

    Single crystal Cu(001) layers were grown on MgO(001) by ultrahigh vacuum magnetron sputtering at T{sub s}=100 deg. C. Quantitative surface morphological analyses by in situ scanning tunneling microscopy show that the surfaces exhibit self-affine mound structures with a scaling exponent of 0.82{+-}0.03 and a mound radius r{sub c} that increases from 31{+-}8 to 39{+-}6 nm for increasing layer thickness t=24-120 nm. In situ annealing at 200 and 300 deg. C leads to a thermodynamically driven mass transport that minimizes the surface step density, resulting in broader mounds and a smaller root mean square surface roughness {sigma}. This effect is most pronounced for t=24 nm, for which r{sub c} increases from 31{+-}8 to 70{+-}20 nm and {sigma} decreases from 1.3{+-}0.1 to 0.74{+-}0.08 nm, resulting in a decrease in the average surface slope from {chi}=7 deg. to 2 deg. and an increase in the average terrace width w{sub T} by more than a factor of 4. In contrast, w{sub T} increases by only 20% for t=120 nm. This remarkable difference between 'thin' and 'thick' layers is attributed to diverging surface morphological pathways during annealing: The strong smoothening for t=24 nm is due to a competitive coalescence process where some mounds grow laterally at the expense of their smaller neighbors, which die out. In contrast, the initially wider mounds of thicker layers (t=120 nm) combine to form a quasistable surface morphology that exhibits anisotropic mound structures, which limit mass transport and stabilize the surface step density.

  9. Surface morphological evolution of epitaxial CrN(001) layers

    SciTech Connect

    Frederick, J.R.; Gall, D.

    2005-09-01

    CrN layers, 57 and 230 nm thick, were grown on MgO(001) at T{sub s}=600-800 deg. C by ultrahigh-vacuum magnetron sputter deposition in pure N{sub 2} discharges from an oblique deposition angle {alpha}=80 deg. . Layers grown at 600 deg. C nucleate as single crystals with a cube-on-cube epitaxial relationship with the substrate. However, rough surfaces with cauliflower-type morphologies cause the nucleation of misoriented CrN grains that develop into cone-shaped grains that protrude out of the epitaxial matrix to form triangular faceted surface mounds. The surface morphology of epitaxial CrN(001) grown at 700 deg. C is characterized by dendritic ridge patterns extending along the orthogonal <110> directions superposed by square-shaped super mounds with <100> edges. The ridge patterns are attributed to a Bales-Zangwill instability while the supermounds form due to atomic shadowing which leads to the formation of epitaxial inverted pyramids that are separated from the surrounding layer by tilted nanovoids. Growth at 800 deg. C yields complete single crystals with smooth surfaces. The root-mean-square surface roughness for 230-nm-thick layers decreases from 18.8 to 9.3 to 1.1 nm as T{sub s} is raised from 600 to 700 to 800 deg. C. This steep decrease is due to a transition in the roughening mechanism from atomic shadowing to kinetic roughening. Atomic shadowing is dominant at 600 and 700 deg. C, where misoriented grains and supermounds, respectively, capture a larger fraction of the oblique deposition flux in comparison to the surrounding epitaxial matrix, resulting in a high roughening rate that is described by a power law with an exponent {beta}>0.5. In contrast, kinetic roughening controls the surface morphology for T{sub s}=800 deg. C, as well as the epitaxial fraction of the layers grown at 600 and 700 deg. C, yielding relatively smooth surfaces and {beta}{<=}0.27.

  10. Geologic Evolution of Mars' North Polar Layered Deposits and Related Materials from Mars Odyssey THEMIS

    NASA Technical Reports Server (NTRS)

    Vasavada, A. R.; Richardson, M. I.; Byrne, S.; Ivanov, A. B.; Christensen, P. R.

    2003-01-01

    The presence of a thick sequence of horizontal layers of ice-rich material at Mars north pole, dissected by troughs and eroding at its margins, is undoubtedly telling us something about the evolution of Mars climate we just don't know what yet. The North Polar Layered Deposits (NPLD) most likely formed as astronomically driven climate variations led to the deposition of conformable, areally extensive layers of ice and dust over the polar region. More recently, the balance seems to have fundamentally shifted to net erosion, as evidenced by the many troughs within the NPLD and the steep, arcuate scarps present near its margins, both of which expose layering.

  11. Quantitative Models of CAI Rim Layer Growth

    NASA Astrophysics Data System (ADS)

    Ruzicka, A.; Boynton, W. V.

    1995-09-01

    . None of these variations in rim layers are correlated with the modal compositions of the CAIs. In our models, we investigated the reaction of CAI interiors (containing M + S + F) with various proportions of vapor (V), O, and D in the 5-component system MgO-AlO(sub)3/2- CaO-SiO2-TiO2. Representative compositions were assumed for the solids. Most likely, a vapor reacting with CAIs would have small (e.g., solar) or trivial abundances of Al, Ca, and Ti compared to Si and Mg, and such Al-, Ca-, and Ti-poor compositions were assumed for the vapor. The model zone sequence MSF|S|A|D|V can form when Mg/[Mg+Si] 0.28-0.47 in the vapor, and is consistent with rims that contain an A layer but that lack an O layer. The zone sequence MSF|S|D|VO, which can form when Mg/[Mg+Si] 0-0.47 in the vapor, may explain rims that lack an A (and M) layer and that have an porous (or poorly compacted) O layer. Finally, the model zone sequence MSF|S|A|D|O +/- D is consistent with rims that contain both an A layer and an compact O layer, but this sequence can form only if the system experienced open-system loss of Ca at the D-O contact, with Ca-poor vapor being a possible open-system sink for Ca. The occasional presence of M in a mono- or bi-mineralic layer within rims apparently cannot be explained by the models, possibly indicating that the rims did not fully attain a steady-state condition. References: [1] Boynton W. V. and Wark D. A. (1985) Meteoritics, 20, 117-118. [2] Murrell M. T. and Burnett D. S. (1987) GCA, 51, 985-999. [3] Ruzicka A. and Boynton W. V. (1994) Meteoritics, 29, 529. [4] MacPherson G. J. et al. (1981) Proc. LPS 12B, 1079-1091. [5] Wark D. A. et al. (1988) LPS XIX, 1230-1231.

  12. Long-term Evolution of Protostellar and Protoplanetary Disks. II. Layered Accretion with Infall

    NASA Astrophysics Data System (ADS)

    Zhu, Zhaohuan; Hartmann, Lee; Gammie, Charles

    2010-04-01

    We use one-dimensional two-zone time-dependent accretion disk models to study the long-term evolution of protostellar disks subject to mass addition from the collapse of a rotating cloud core. Our model consists of a constant surface density magnetically coupled active layer, with transport and dissipation in inactive regions only via gravitational instability. We start our simulations after a central protostar has formed, containing ~10% of the mass of the protostellar cloud. Subsequent evolution depends on the angular momentum of the accreting envelope. We find that disk accretion matches the infall rate early in the disk evolution because much of the inner disk is hot enough to couple to the magnetic field. Later infall reaches the disk beyond ~10 AU, and the disk undergoes outbursts of accretion in FU Ori-like events as described by Zhu et al. If the initial cloud core is moderately rotating, most of the central star's mass is built up by these outburst events. Our results suggest that the protostellar "luminosity problem" is eased by accretion during these FU Ori-like outbursts. After infall stops, the disk enters the T Tauri phase. An outer, viscously evolving disk has a structure that is in reasonable agreement with recent submillimeter studies and its surface density evolves from Σ vprop R -1 to R -1.5. An inner, massive belt of material—the "dead zone"—would not have been observed yet but should be seen in future high angular resolution observations by EVLA and ALMA. This high surface density belt is a generic consequence of low angular momentum transport efficiency at radii where the disk is magnetically decoupled, and would strongly affect planet formation and migration.

  13. Trends in substitution models of molecular evolution.

    PubMed

    Arenas, Miguel

    2015-01-01

    Substitution models of evolution describe the process of genetic variation through fixed mutations and constitute the basis of the evolutionary analysis at the molecular level. Almost 40 years after the development of first substitution models, highly sophisticated, and data-specific substitution models continue emerging with the aim of better mimicking real evolutionary processes. Here I describe current trends in substitution models of DNA, codon and amino acid sequence evolution, including advantages and pitfalls of the most popular models. The perspective concludes that despite the large number of currently available substitution models, further research is required for more realistic modeling, especially for DNA coding and amino acid data. Additionally, the development of more accurate complex models should be coupled with new implementations and improvements of methods and frameworks for substitution model selection and downstream evolutionary analysis. PMID:26579193

  14. Trends in substitution models of molecular evolution

    PubMed Central

    Arenas, Miguel

    2015-01-01

    Substitution models of evolution describe the process of genetic variation through fixed mutations and constitute the basis of the evolutionary analysis at the molecular level. Almost 40 years after the development of first substitution models, highly sophisticated, and data-specific substitution models continue emerging with the aim of better mimicking real evolutionary processes. Here I describe current trends in substitution models of DNA, codon and amino acid sequence evolution, including advantages and pitfalls of the most popular models. The perspective concludes that despite the large number of currently available substitution models, further research is required for more realistic modeling, especially for DNA coding and amino acid data. Additionally, the development of more accurate complex models should be coupled with new implementations and improvements of methods and frameworks for substitution model selection and downstream evolutionary analysis. PMID:26579193

  15. General models of multilocus evolution.

    PubMed Central

    Kirkpatrick, Mark; Johnson, Toby; Barton, Nick

    2002-01-01

    In 1991, Barton and Turelli developed recursions to describe the evolution of multilocus systems under arbitrary forms of selection. This article generalizes their approach to allow for arbitrary modes of inheritance, including diploidy, polyploidy, sex linkage, cytoplasmic inheritance, and genomic imprinting. The framework is also extended to allow for other deterministic evolutionary forces, including migration and mutation. Exact recursions that fully describe the state of the population are presented; these are implemented in a computer algebra package (available on the Web at http://helios.bto.ed.ac.uk/evolgen). Despite the generality of our framework, it can describe evolutionary dynamics exactly by just two equations. These recursions can be further simplified using a "quasi-linkage equilibrium" (QLE) approximation. We illustrate the methods by finding the effect of natural selection, sexual selection, mutation, and migration on the genetic composition of a population. PMID:12196414

  16. Experimental "evolutional machines": mathematical and experimental modeling of biological evolution

    NASA Astrophysics Data System (ADS)

    Brilkov, A. V.; Loginov, I. A.; Morozova, E. V.; Shuvaev, A. N.; Pechurkin, N. S.

    Experimentalists possess model systems of two major types for study of evolution continuous cultivation in the chemostat and long-term development in closed laboratory microecosystems with several trophic structure If evolutionary changes or transfer from one steady state to another in the result of changing qualitative properties of the system take place in such systems the main characteristics of these evolution steps can be measured By now this has not been realized from the point of view of methodology though a lot of data on the work of both types of evolutionary machines has been collected In our experiments with long-term continuous cultivation we used the bacterial strains containing in plasmids the cloned genes of bioluminescence and green fluorescent protein which expression level can be easily changed and controlled In spite of the apparent kinetic diversity of evolutionary transfers in two types of systems the general mechanisms characterizing the increase of used energy flow by populations of primer producent can be revealed at their study According to the energy approach at spontaneous transfer from one steady state to another e g in the process of microevolution competition or selection heat dissipation characterizing the rate of entropy growth should increase rather then decrease or maintain steady as usually believed The results of our observations of experimental evolution require further development of thermodynamic theory of open and closed biological systems and further study of general mechanisms of biological

  17. Turbulence models for compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Huang, P. G.; Bradshaw, P.; Coakley, T. J.

    1994-01-01

    It is shown that to satisfy the general accepted compressible law of the wall derived from the Van Driest transformation, turbulence modeling coefficients must actually be functions of density gradients. The transformed velocity profiles obtained by using standard turbulence model constants have too small a value of the effective von Karman constant kappa in the log-law region (inner layer). Thus, if the model is otherwise accurate, the wake component is overpredicted and the predicted skin friction is lower than the expected value.

  18. Protoplanetary Disk Structure with Grain Evolution: The ANDES Model

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    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) and lower in the outer 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., CO2, NH2CN, HNO, H2O, HCOOH, HCN, and CO. We also show that time-dependent chemistry is important for a proper description of gas thermal balance.

  19. PROTOPLANETARY DISK STRUCTURE WITH GRAIN EVOLUTION: THE ANDES MODEL

    SciTech Connect

    Akimkin, V.; Wiebe, D.; Pavlyuchenkov, Ya.; Zhukovska, S.; Semenov, D.; Henning, Th.; Vasyunin, A.; Birnstiel, T. E-mail: dwiebe@inasan.ru E-mail: zhukovska@mpia.de E-mail: henning@mpia.de E-mail: tbirnstiel@cfa.harvard.edu

    2013-03-20

    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 {approx}< 50 AU) and lower in the outer disk (R {approx}> 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{sub 2}, NH{sub 2}CN, HNO, H{sub 2}O, HCOOH, HCN, and CO. We also show that time-dependent chemistry is important for a proper description of gas thermal balance.

  20. Application of Quasi-Separatrix Layer Maps to Understanding the Structure and Evolution of Sigmoids

    NASA Astrophysics Data System (ADS)

    Savcheva, Antonia; DeLuca, E.; Van Ballegooijen, A.

    2010-05-01

    We present some preliminary work in attempt to utilize Quasi-Separatrix Layer (QSL) maps for understanding the structure and evolution of sigmoids. We show sample QSL maps calculated at different heights above the photosphere and different times over the evolution of the quiescent sigmoid from February, 2007, observed with Hinode/XRT. The QSL maps use already existing static MHD models of the sigmoid, based on the flux rope insertion method. We give a short overview of the method used to set-up these maps. By comparing current distributions and the squashing factors at different height and cross sections over the sigmoid location we suggest the use of QSLs as tracers of surface and/or volumetric currents. We look at the distribution, structure, and concentration of QSLs in combination with the size and location of bald patches at different stages of the sigmoid development. We attempt to use this analysis to help us discriminate between the main scenarios for the formation and X-ray appearance of the S-like structure - flux emergence (or cancellation) and twisting foot point motions. This method may possibly shed some light on the pre-eruption configuration and eruption mechanism in sigmoids as well.

  1. Modeling the evolution of galactic magnetic fields

    SciTech Connect

    Yar-Mukhamedov, D.

    2015-04-15

    An analytic model for evolution of galactic magnetic fields in hierarchical galaxy formation frameworks is introduced. Its major innovative components include explicit and detailed treatment of the physics of merger events, mass gains and losses, gravitational energy sources and delays associated with formation of large-scale magnetic fields. This paper describes the model, its implementation, and core results obtained by its means.

  2. Influence of depositional setting and sedimentary fabric on mechanical layer evolution in carbonate aquifers

    USGS Publications Warehouse

    Graham, Wall B.R.

    2006-01-01

    Carbonate aquifers in fold-thrust belt settings often have low-matrix porosity and permeability, and thus groundwater flow pathways depend on high porosity and permeability fracture and fault zones. Methods from sedimentology and structural geology are combined to understand the evolution of fracture controlled flow pathways and determine their spatial distribution. Through this process bed-parallel pressure-solution surfaces (PS1) are identified as a fracture type which influences fragmentation in peritidal and basinal carbonate, and upon shearing provides a major flow pathway in fold - thrust belt carbonate aquifers. Through stratigraphic analysis and fracture mapping, depositional setting is determined to play a critical role in PS1 localization and spacing where peritidal strata have closer spaced and less laterally continuous PS1 than basinal strata. In the peritidal platform facies, units with planar lamination have bed-parallel pressure-solution seams along mudstone laminae. In contrast, burrowed units of peritidal strata have solution seams with irregular and anastamosing geometries. Laminated units with closely spaced bed-parallel solution seams are more fragmented than bioturbated units with anastamosing solution seams. In the deeper-water depositional environment, pelagic settling and turbidity currents are the dominant sedimentation processes, resulting in laterally continuous deposits relative to the peritidal platform environment. To quantify the fracture patterns in the basinal environment, mechanical layer thickness values were measured from regions of low to high bed dip. The results define a trend in which mechanical layer thickness decreases as layer dip increases. A conceptual model is presented that emphasizes the link between sedimentary and structural fabric for the peritidal and basinal environments, where solution seams localize in mud-rich intervals, and the resulting pressure-solution surface geometry is influenced by sedimentary geometry

  3. Chemical evolution models of Local Group galaxies

    NASA Astrophysics Data System (ADS)

    Tosi, Monica

    Status quo and perspectives of standard chemical evolution models of Local Group galaxies are summarized, and what we have learned from them is discussed, as well as what we have not learned yet, and what I think will be learned in the near future. Galactic chemical evolution models have shown that: I) stringent constraints on primordial nucleosynthesis can be derived from the observed Galactic abundances of the light elements; II) the Milky Way has been accreting external gas from early epochs to the present time; and III) the vast majority of Galactic halo stars have formed quite rapidly at early epochs. Chemical evolution models for the closest dwarf galaxies, although still uncertain, are expected to become extremely reliable in the immediate future, thanks to the quality of new generation photometric and spectroscopic data which are currently being acquired.

  4. Supersonic boundary-layer flow turbulence modeling

    NASA Technical Reports Server (NTRS)

    Wang, Chi-Rong

    1993-01-01

    Baldwin-Lomax and kappa-epsilon turbulence models were modified for use in Navier-Stokes numerical computations of Mach 2.9 supersonic turbulent boundary layer flows along compression ramps. The computational results of Reynolds shear stress profiles were compared with experimental data. The Baldwin-Lomax model was modified to account for the Reynolds shear stress amplification within the flow field. A hybrid kappa-epsilon model with viscous sublayer turbulence treatment was constructed to predict the Reynolds shear stress profiles within the entire flow field. These modified turbulence models were effective for the computations of the surface pressure and the skin friction factor variations along an 8 deg ramp surface. The hybrid kappa-epsilon model could improve the predictions of the Reynolds shear stress profile and the skin friction factor near the corner of a 16 deg ramp.

  5. A model of layered prismatic shells

    NASA Astrophysics Data System (ADS)

    Jaiani, George

    2016-05-01

    The present paper is devoted to a model for elastic layered prismatic shells which is constructed by means of a suggested in the paper approach which essentially differs from the known approaches for constructing models of laminated structures. Using Vekua's dimension reduction method after appropriate modifications, hierarchical models for elastic layered prismatic shells are constructed. We get coupled governing systems for the whole structure in the projection of the structure. The advantage of this model consists in the fact that we solve boundary value problems separately for each ply. In addition, beginning with the second ply, we use a solution of a boundary value problem of the preceding ply. We indicate ways of investigating boundary value problems for the governing systems. For the sake of simplicity, we consider the case of two plies, in the zeroth approximation. However, we also make remarks concerning the cases when either the number of plies is more than two or higher-order approximations (hierarchical models) should be applied. As an example, we consider a special case of deformation and solve the corresponding boundary value problem in the explicit form.

  6. Modeling Layered Accretion and the Magnetorotational Instability in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Lesniak, Michael V., III

    2012-05-01

    Understanding the temperature structure of protoplanetary disks (PPDs) is paramount to modeling disk evolution and future planet formation. PPDs around T Tauri stars have two primary heating sources, protostellar irradiation, which depends on the flaring of the disk, and accretional heating as viscous coupling between annuli dissipate energy. I have written a "1.5-D" radiative transfer code to calculate disk temperatures assuming hydrostatic and radiative equilibrium. The model solves for the temperature at all locations simultaneously using Rybicki's method, converges rapidly at high optical depth, and retains full frequency dependence. The likely cause of accretional heating in PPDs is the magnetorotational instability (MRI), which acts where gas ionization is sufficiently high for gas to couple to the magnetic field. This will occur in surface layers of the disk, leaving the interior portions of the disk inactive ("dead zone"). I calculate temperatures in PPDs undergoing such "layered accretion." Since the accretional heating is concentrated far from the midplane, temperatures in the disk's interior are lower than in PPDs modeled with vertically uniform accretion. The method is used to study for the first time disks evolving via the magnetorotational instability, which operates primarily in surface layers. I find that temperatures in layered accretion disks do not significantly differ from those of "passive disks," where no accretional heating exists. Emergent spectra are insensitive to active layer thickness, making it difficult to observationally identify disks undergoing layered vs. uniform accretion. I also calculate the ionization chemistry in PPDs, using an ionization network including multiple charge states of dust grains. Combined with a criterion for the onset of the MRI, I calculate where the MRI can be initiated and the extent of dead zones in PPDs. After accounting for feedback between temperature and active layer thickness, I find the surface

  7. One-dimensional mixing layer model for a shear Hele-Shaw flow

    NASA Astrophysics Data System (ADS)

    Kovtunenko, P. V.

    2016-06-01

    A shear flow of a viscosity-stratified fluid in a Hele-Shaw cell is considered. The long-wave approximation is applied to the governing equations. To describe the evolution of the mixing layer, a special flow with a three-layered structure is considered. A one-dimensional model is derived by averaging the motion equations over the cell width, taking into account the flow structure. For a stationary flow, solutions of motion equations are constructed. The influence of viscosity on the mixing layer evolution is investigated by performing a numerical experiment for a flow with different viscosities in the layers and for a flow with always zero viscosity. It is shown that viscosity has a significant influence on the flow evolution.

  8. Early geomorphological evolution of the North Polar Layered Deposits, Mars, from SHARAD radar-facies mapping

    NASA Astrophysics Data System (ADS)

    Nerozzi, Stefano; Holt, John W.

    2014-05-01

    The north polar layered deposits (NPLD) are the largest accumulation of water ice in the northern hemisphere of Mars. Since their discovery, they are thought to hold a valuable record of recent climate change within their stratigraphy (Murray et al., Icarus, 1972; Cutts, JGR, 1973b), yet little is known about their age and accumulation history. Due to exposures in trough walls, detailed stratigraphy of the uppermost layers and their evolution have been studied extensively since the first Mariner 9 images of the NPLD (e.g. Soderblom et al., JGR, 1973). However, large portions of the polar cap are still unmapped and no detailed studies of the lowermost layered deposits have been performed to date, primarily due to a general lack of visible exposures. Correlation of reflectors within radargrams acquired by the Shallow Radar (SHARAD) (Seu et al., Planet. Space Sci., 2004) onboard Mars Reconnaissance Orbiter makes a detailed stratigraphic reconstruction of the NPLD possible. An extensive set of radargrams is available over Planum Boreum and individual reflectors can be traced over hundreds of kilometers (Seu et al., JGR, 2007a; Putzig et al., Icarus, 2009; Holt et al., Nature, 2010) with a theoretical vertical resolution of ~9 m in water ice (Seu et al., JGR, 2007a). In this study, we present a highly-detailed stratigraphic reconstruction of the first ~500 m of the NPLD at a scale down to the single reflector. A set of 8 horizons was tracked across 700+ radargrams, and thicknesses were calculated for each stratigraphic interval assuming a bulk composition of water ice. Along with the quantitative analysis of derived isopach maps, this study is based on the qualitative comparison of "radar facies" in different locations of Planum Boreum with techniques borrowed from traditional sequence stratigraphy. In general, the NPLD is characterized by uniform layering. However, important layer extent and thickness variations are observed within the lowermost sequence. Limited

  9. Magnetic field and angular momentum evolution models

    NASA Astrophysics Data System (ADS)

    Gallet, F.

    2013-11-01

    The magnetic field in young stellar object is clearly the most important component when one dealing with the angular momentum evolution of solar-like stars. It controls this latter one from the pre-main sequence, during the ``disk locking'' phase where the stars magnetically interact with their surrounding disk, to the main-sequence through powerful stellar winds that remove angular momentum from the stellar surface. We present new models for the rotational evolution of solar-like stars between 1 Myr and 10 Gyr with the aim to reproduce the distributions of rotational periods observed for star forming regions and young open clusters within this age range. Our simulations are produced by a recent model dedicated to the study of the angular momentum evolution of solar-type stars. This model include a new wind braking law based on recent numerical simulations of magnetized stellar winds and a specific dynamo and mass-loss prescription are used to link the angular momentum loss-rate to angular velocity evolution. The model additionally allows for a core/envelope decoupling with an angular momentum transfer between these two regions. Since this former model didn't include any physical star/disk interaction description, two star/disk interaction processes are eventually added to it in order to reproduce the apparent small angular velocities to which the stellar surface is subject during the disk accretion phase. We have developed rotational evolution models for slow, median and fast rotators including two star/disk interaction scenarios that are the magnetospheric ejection and the accretion powered stellar winds processes. The models appear to fail at reproducing the rotational behaviour of solar-type stars except when a more intense magnetic field is used during the disk accretion phase.

  10. Quantum and Lattice Models of Biological Evolution

    NASA Astrophysics Data System (ADS)

    Hu, Chin-Kun

    2007-07-01

    Noise in environments can cause mutation in genetic materials of biological systems. In this paper, I first introduce some molecular models of biological evolution, including Eigen model with connected mutation-selection scheme and Crow-Kimura (CK) model with parallel mutation-selection scheme. Baake et al. mapped the CK model into a quantum spin model. Recently, Saakian and I did the similar mapping for the Eigen model. Using Suzuki-Trottere formalism, we studied statics and dynamics of the Eigen model and the CK model with the single-peak fitness function and found that the relaxation in the parallel model is faster than that in the connected model. We studied both models with rather general fitness functions and obtained error thresholds for various cases. We studied the Eigen model with multiple peaks which can represent virus or cancer cells attached by drug or the immune systems. Finally, we studied a lattice model for co-evolution of virus and immune system and found that the model shows self-organized behavior.

  11. Experimental characterization of initial conditions and spatio-temporal evolution of a small Atwood number Rayleigh-Taylor mixing layer

    SciTech Connect

    Mueschke, N J; Andrews, M J; Schilling, O

    2006-03-24

    The initial multi-mode interfacial velocity and density perturbations present at the onset of a small Atwood number, incompressible, miscible, Rayleigh-Taylor instability-driven mixing layer have been quantified using a combination of experimental techniques. The streamwise interfacial and spanwise interfacial perturbations were measured using high-resolution thermocouples and planar laser-induced fluorescence (PLIF), respectively. The initial multi-mode streamwise velocity perturbations at the two-fluid density interface were measured using particle-image velocimetry (PIV). It was found that the measured initial conditions describe an initially anisotropic state, in which the perturbations in the streamwise and spanwise directions are independent of one another. The evolution of various fluctuating velocity and density statistics, together with velocity and density variance spectra, were measured using PIV and high-resolution thermocouple data. The evolution of the velocity and density statistics is used to investigate the early-time evolution and the onset of strongly-nonlinear, transitional dynamics within the mixing layer. The early-time evolution of the density and vertical velocity variance spectra indicate that velocity fluctuations are the dominant mechanism driving the instability development. The implications of the present experimental measurements on the initialization of Reynolds-averaged turbulent transport and mixing models and of direct and large-eddy simulations of Rayleigh-Taylor instability-induced turbulence are discussed.

  12. Experimental characterization of initial conditions and spatio-temporal evolution of a small Atwood number Rayleigh-Taylor mixing layer

    SciTech Connect

    Mueschke, N J; Andrews, M J; Schilling, O

    2005-09-26

    The initial multi-mode interfacial velocity and density perturbations present at the onset of a small Atwood number, incompressible, miscible, Rayleigh-Taylor instability-driven mixing layer have been quantified using a combination of experimental techniques. The streamwise interfacial and spanwise interfacial perturbations were measured using high-resolution thermocouples and planar laser-induced fluorescence (PLIF), respectively. The initial multi-mode streamwise velocity perturbations at the two-fluid density interface were measured using particle-image velocimetry (PIV). It was found that the measured initial conditions describe an initially anisotropic state, in which the perturbations in the streamwise and spanwise directions are independent of one another. The evolution of various fluctuating velocity and density statistics, together with velocity and density variance spectra, were measured using PIV and high-resolution thermocouple data. The evolution of the velocity and density statistics is used to investigate the early-time evolution and the onset of strongly-nonlinear, transitional dynamics within the mixing layer. The early-time evolution of the density and vertical velocity variance spectra indicate that velocity fluctuations are the dominant mechanism driving the instability development. The implications of the present experimental measurements on the initialization of Reynolds-averaged turbulent transport and mixing models and of direct and large-eddy simulations of Rayleigh-Taylor instability-induced turbulence are discussed.

  13. Frequency Domain Modelling of Electromagnetic Wave Propagation in Layered Media

    NASA Astrophysics Data System (ADS)

    Schmidt, Felix; Lünenschloss, Peter; Mai, Juliane; Wagner, Norman; Töpfer, Hannes; Bumberger, Jan

    2016-04-01

    The amount of water in porous media such as soils and rocks is a key parameter when water resources are under investigation. Especially the quantitative spatial distribution and temporal evolution of water contents in soil formations are needed. In high frequency electromagnetic applications soil water content is quantitatively derived from the propagation behavior of electromagnetic waves along waveguides embedded in soil formations. The spatial distribution of the dielectric material properties along the waveguide can be estimated by numerical solving of the inverse problem based on the full wave forward model in time or frequency domain. However, current approaches mostly neglect or approximate the frequency dependence of the electromagnetic material properties of transfer function of the waveguide. As a first prove of concept a full two port broadband frequency domain forward model for propagation of transverse electromagnetic (TEM) waves in coaxial waveguide has been implemented. It is based on the propagation matrix approach for layered transmission line sections. Depending on the complexity of the material different models for the frequency dependent complex permittivity were applied. For the validation of the model a broadband frequency domain measurement with network analyzer technique was used. The measurement is based on a 20 cm long 50 Ohm 20/46 coaxial transmission line cell considering inhomogeneous material distributions. This approach allows (i) an increase of the waveguide calibration accuracy in comparison to conventional TDR based technique and (ii) the consideration of the broadband permittivity spectrum of the porous material. In order to systematic analyze the model, theoretical results were compared with measurements as well as 3D broadband finite element modeling of homogeneous and layered media in the coaxial transmission line cell. Defined standards (Teflon, dry glass beads, de-ionized water) were placed inside the line as the dielectric

  14. Frequency Domain Modelling of Electromagnetic Wave Propagation in Layered Media

    NASA Astrophysics Data System (ADS)

    Schmidt, Felix; Wagner, Norman; Lünenschloß, Peter; Toepfer, Hannes; Dietrich, Peter; Kaliorias, Andreas; Bumberger, Jan

    2015-04-01

    The amount of water in porous media such as soils and rocks is a key parameter when water resources are under investigation. Especially the quantitative spatial distribution and temporal evolution of water contents in soil formations are needed. In high frequency electromagnetic applications soil water content is quantitatively derived from the propagation behavior of electromagnetic waves along waveguides embedded in soil formations. The spatial distribution of the dielectric material properties along the waveguide can be estimated by numerical solving of the inverse problem based on the full wave forward model in time or frequency domain. However, current approaches mostly neglect or approximate the frequency dependence of the electromagnetic material properties of transfer function of the waveguide. As a first prove of concept a full two port broadband frequency domain forward model for propagation of transverse electromagnetic (TEM) waves in coaxial waveguide has been implemented. It is based on the propagation matrix approach for layered transmission line sections Depending on the complexity of the material different models for the frequency dependent complex permittivity were applied. For the validation of the model a broadband frequency domain measurement with network analyzer technique was used. The measurement is based on a 20 cm long 50 Ohm 20/46 coaxial transmission line cell considering inhomogeneous material distributions. This approach allows (i) an increase of the waveguide calibration accuracy in comparison to conventional TDR based technique and (ii) the consideration of the broadband permittivity spectrum of the porous material. In order to systematic analyze the model, theoretical results were compared with measurements as well as 3D broadband finite element modeling of homogeneous and layered media in the coaxial transmission line cell. Defined standards (Teflon, dry glass beads, de-ionized water) were placed inside the line as the dielectric

  15. The role of boundary layer dynamics on the diurnal evolution of isoprene and the hydroxyl radical over tropical forests

    NASA Astrophysics Data System (ADS)

    Vilã-Guerau de Arellano, Jordi; Patton, Edward G.; Karl, Thomas; van den Dries, Kees; Barth, Mary C.; Orlando, John J.

    2011-04-01

    We investigate diurnal variability of isoprene and related chemical species in the Amazonian region. The dynamics and chemistry of an atmospheric boundary layer are studied with a large-eddy simulation code and a mixed-layer model which are guided by observations available for the same area. The main features of isoprene and related species are reproduced well, but their evolution raises questions regarding the physical and chemical processes responsible for the observed diurnal behaviors. To address these questions, we systematically examine the role of (1) the exchange of chemical species between the free troposphere and the atmospheric boundary layer (entrainment), (2) surface isoprene and nitric oxide emissions, and (3) new chemical pathways to recycle the hydroxyl radical. The entrainment flux of isoprene is shown to be equally important as surface isoprene emissions in determining the isoprene temporal evolution. Varying the relationship between the initial isoprene mixing ratio in the boundary layer and that in the overlying free troposphere in the early morning results in an 50% increase/decrease in isoprene mixing ratio or more within the atmospheric boundary layer at noon. Entrainment of free tropospheric nitrogen oxides creates changes of similar magnitude to the boundary layer isoprene mixing ratio. These effects of entrainment and surface emissions on isoprene are found for two different chemical regimes. The introduction of an OH recycling pathway in the chemical mechanism increases midday OH. Our findings show that atmospheric dynamics and chemistry are equally important for interpreting the diurnal observation of reactants and for including in regional-scale modeling efforts where turbulence is parameterized.

  16. Modelling of the Evolving Stable Boundary Layer

    NASA Astrophysics Data System (ADS)

    Sorbjan, Zbigniew

    2014-06-01

    A single-column model of the evolving stable boundary layer (SBL) is tested for self-similar properties of the flow and effects of ambient forcing. The turbulence closure of the model is diagnostic, based on the K-theory approach, with a semi-empirical form of the mixing length, and empirical stability functions of the Richardson number. The model results, expressed in terms of local similarity scales, are universal functions, satisfied in the entire SBL. Based on similarity expression, a realizability condition is derived for the minimum allowable turbulent heat flux in the SBL. Numerical experiments show that the development of "horse-shoe" shaped, fixed-elevation hodographs in the interior of the SBL around sunrise is controlled by effects imposed by surface thermal forcing.

  17. Diurnal ocean surface layer model validation

    NASA Technical Reports Server (NTRS)

    Hawkins, Jeffrey D.; May, Douglas A.; Abell, Fred, Jr.

    1990-01-01

    The diurnal ocean surface layer (DOSL) model at the Fleet Numerical Oceanography Center forecasts the 24-hour change in a global sea surface temperatures (SST). Validating the DOSL model is a difficult task due to the huge areas involved and the lack of in situ measurements. Therefore, this report details the use of satellite infrared multichannel SST imagery to provide day and night SSTs that can be directly compared to DOSL products. This water-vapor-corrected imagery has the advantages of high thermal sensitivity (0.12 C), large synoptic coverage (nearly 3000 km across), and high spatial resolution that enables diurnal heating events to be readily located and mapped. Several case studies in the subtropical North Atlantic readily show that DOSL results during extreme heating periods agree very well with satellite-imagery-derived values in terms of the pattern of diurnal warming. The low wind and cloud-free conditions necessary for these events to occur lend themselves well to observation via infrared imagery. Thus, the normally cloud-limited aspects of satellite imagery do not come into play for these particular environmental conditions. The fact that the DOSL model does well in extreme events is beneficial from the standpoint that these cases can be associated with the destruction of the surface acoustic duct. This so-called afternoon effect happens as the afternoon warming of the mixed layer disrupts the sound channel and the propagation of acoustic energy.

  18. Metamorphic and geochemical evolution of an amphibolite layer in the Chugach Metamorphic Complex (Alaska)

    NASA Astrophysics Data System (ADS)

    Bruand, E.; Gasser, D.; Stuewe, K.

    2010-12-01

    metapelites of the CMC (Bruand et al., 2010) which has pointed out much higher pressure (5 to 13kb) than previously believed (~3kb; Sisson et al., 1989). We integrate our new petrological and geochemical data to the geodynamic history of the CMC and test different geodynamic models to explain the presence of such an amphibolite layer in southern Alaska: seamount subduction, ridge subduction and obduction. Bruand E, Gasser D & Stüwe K, 2010. Metamorphic evolution and new PT estimates for the Chugach Metamorphic Complex (Alaska) - implications for the ridge subduction model. In review. JMG. Lull J & Plafker G 1990. Geochemistry and Paleotectonic Implications of Metabasaltic Rocks in the Valdez Group, Southern Alaska. In: Dover J, Galloway J (eds) Geological Studies in Alaska by the U.S. Geological Survey, 1946, 29-38. Sisson V, Hollister L & Onstott, 1989. Petrologic and age constraints on the origin of a low-pressure/high-temperature metamorphic complex, Southern Alaska. JGR, 94, 4392-4410.

  19. Reversible adapting layer produces robust single-crystal electrocatalyst for oxygen evolution

    PubMed Central

    Tung, Ching-Wei; Hsu, Ying-Ya; Shen, Yen-Ping; Zheng, Yixin; Chan, Ting-Shan; Sheu, Hwo-Shuenn; Cheng, Yuan-Chung; Chen, Hao Ming

    2015-01-01

    Electrochemically converting water into oxygen/hydrogen gas is ideal for high-density renewable energy storage in which robust electrocatalysts for efficient oxygen evolution play crucial roles. To date, however, electrocatalysts with long-term stability have remained elusive. Here we report that single-crystal Co3O4 nanocube underlay with a thin CoO layer results in a high-performance and high-stability electrocatalyst in oxygen evolution reaction. An in situ X-ray diffraction method is developed to observe a strong correlation between the initialization of the oxygen evolution and the formation of active metal oxyhydroxide phase. The lattice of skin layer adapts to the structure of the active phase, which enables a reversible facile structural change that facilitates the chemical reactions without breaking the scaffold of the electrocatalysts. The single-crystal nanocube electrode exhibits stable, continuous oxygen evolution for >1,000 h. This robust stability is attributed to the complementary nature of defect-free single-crystal electrocatalyst and the reversible adapting layer. PMID:26315066

  20. Reversible adapting layer produces robust single-crystal electrocatalyst for oxygen evolution

    NASA Astrophysics Data System (ADS)

    Tung, Ching-Wei; Hsu, Ying-Ya; Shen, Yen-Ping; Zheng, Yixin; Chan, Ting-Shan; Sheu, Hwo-Shuenn; Cheng, Yuan-Chung; Chen, Hao Ming

    2015-08-01

    Electrochemically converting water into oxygen/hydrogen gas is ideal for high-density renewable energy storage in which robust electrocatalysts for efficient oxygen evolution play crucial roles. To date, however, electrocatalysts with long-term stability have remained elusive. Here we report that single-crystal Co3O4 nanocube underlay with a thin CoO layer results in a high-performance and high-stability electrocatalyst in oxygen evolution reaction. An in situ X-ray diffraction method is developed to observe a strong correlation between the initialization of the oxygen evolution and the formation of active metal oxyhydroxide phase. The lattice of skin layer adapts to the structure of the active phase, which enables a reversible facile structural change that facilitates the chemical reactions without breaking the scaffold of the electrocatalysts. The single-crystal nanocube electrode exhibits stable, continuous oxygen evolution for >1,000 h. This robust stability is attributed to the complementary nature of defect-free single-crystal electrocatalyst and the reversible adapting layer.

  1. Convective boundary layer and modeling of dispersion

    NASA Astrophysics Data System (ADS)

    Ahmed, Nizam Uddin

    Looping, bifurcation, and meandering of a plume are generally observed in a convective field. The blobby or puffy concentration patterns associated with these plumes are marked deviations from what is expected from either conventional K-theory or Gaussian distribution formulae. A numerical model was developed for material dispersion in a convective boundary layer from both elevated and ground sources. Mechanistic formulation, rather than parameterization, or statistical behavior of planetary boundary layer (PBL) phenomena, was used as a basis. The dispersion mechanism is considered to be due to mixing between the updraft and the downdraft. This model uses two universal constants, (turbulent entrainment constant, a, and decay constant A) and a mixing scheme directly supported by observations. Researchers examined the dispersion pattern from the elevated and ground sources. For elevated sources, the maximum concentration descends first to the ground level at some distance downwind, and then rises, depending on the inversion height, the mean wind and height at which material is released. The updrafts have a higher velocity than the downdrafts and consequently the downdrafts occupy a larger horizontal area. In some cases the updrafts and downdrafts are comparable and materials are caught equally in the updrafts and downdrafts. The concentration of materials is split into two parts, one moving downward and the other upward. It is shown using the same mechanistic principles, that different convective situations cause different concentration patterns (for example, looping, bifurcating of a plume, and ascending of center line).

  2. The accretion model of Neandertal evolution.

    PubMed

    Hawks, J D; Wolpoff, M H

    2001-07-01

    The Accretion model of Neandertal evolution specifies that this group of Late Pleistocene hominids evolved in partial or complete genetic isolation from the rest of humanity through the gradual accumulation of distinctive morphological traits in European populations. As they became more common, these traits also became less variable, according to those workers who developed the model. Its supporters propose that genetic drift caused this evolution, resulting from an initial small European population size and either complete isolation or drastic reduction in gene flow between this deme and contemporary human populations elsewhere. Here, we test an evolutionary model of gene flow between regions against fossil data from the European population of the Middle and Late Pleistocene. The results of the analysis clearly show that the European population was not significantly divergent from its contemporaries, even in a subset of traits chosen to show the maximum differences between Europeans and other populations. The pattern of changes, over time within Europe of the traits in this subset, does not support the Accretion model, either because the characters did not change in the manner specified by the model or because the characters did not change at all. From these data, we can conclude that special phenomena such as near-complete isolation of the European population during the Pleistocene are not required to explain the pattern of evolution in this region. PMID:11525469

  3. Engineering Glass Passivation Layers -Model Results

    SciTech Connect

    Skorski, Daniel C.; Ryan, Joseph V.; Strachan, Denis M.; Lepry, William C.

    2011-08-08

    The immobilization of radioactive waste into glass waste forms is a baseline process of nuclear waste management not only in the United States, but worldwide. The rate of radionuclide release from these glasses is a critical measure of the quality of the waste form. Over long-term tests and using extrapolations of ancient analogues, it has been shown that well designed glasses exhibit a dissolution rate that quickly decreases to a slow residual rate for the lifetime of the glass. The mechanistic cause of this decreased corrosion rate is a subject of debate, with one of the major theories suggesting that the decrease is caused by the formation of corrosion products in such a manner as to present a diffusion barrier on the surface of the glass. Although there is much evidence of this type of mechanism, there has been no attempt to engineer the effect to maximize the passivating qualities of the corrosion products. This study represents the first attempt to engineer the creation of passivating phases on the surface of glasses. Our approach utilizes interactions between the dissolving glass and elements from the disposal environment to create impermeable capping layers. By drawing from other corrosion studies in areas where passivation layers have been successfully engineered to protect the bulk material, we present here a report on mineral phases that are likely have a morphological tendency to encrust the surface of the glass. Our modeling has focused on using the AFCI glass system in a carbonate, sulfate, and phosphate rich environment. We evaluate the minerals predicted to form to determine the likelihood of the formation of a protective layer on the surface of the glass. We have also modeled individual ions in solutions vs. pH and the addition of aluminum and silicon. These results allow us to understand the pH and ion concentration dependence of mineral formation. We have determined that iron minerals are likely to form a complete incrustation layer and we plan

  4. Overturn of magma ocean ilmenite cumulate layer: Implications for lunar magmatic evolution and formation of a lunar core

    NASA Technical Reports Server (NTRS)

    Hess, P. C.; Parmentier, E. M.

    1993-01-01

    We explore a model for the chemical evolution of the lunar interior that explains the origin and evolution of lunar magmatism and possibly the existence of a lunar core. A magma ocean formed during accretion differentiates into the anorthositic crust and chemically stratified cumulate mantle. The cumulative mantle is gravitationally unstable with dense ilmenite cumulate layers overlying olivine-orthopyroxene cumulates with Fe/Mg that decreases with depth. The dense ilmenite layer sinks to the center of the moon forming the core. The remainder of the gravitationally unstable cumulate pile also overturns. Any remaining primitive lunar mantle rises to its level of neutral buoyancy in the cumulate pile. Perhaps melting of primitive lunar mantle due to this decompression results in early lunar Mg-rich magmatism. Because of its high concentration of incompatible heat producing elements, the ilmenite core heats the overlying orthopyroxene-bearing cumulates. As a conductively thickening thermal boundary layer becomes unstable, the resulting mantle plumes rise, decompress, and partially melt to generate the mare basalts. This model explains both the timing and chemical characteristics of lunar magmatism.

  5. Spanwise domain effects on the evolution of the plane turbulent mixing layer

    NASA Astrophysics Data System (ADS)

    McMullan, W. A.

    2015-07-01

    Large Eddy Simulation is used to simulate a series of plane mixing layers. The influence of the spanwise domain on the development of the mixing layer, and the evolution of the coherent structures, are considered. The mixing layers originate from laminar conditions, and an idealised inflow condition is found to produce accurate flow predictions when the spanwise computational domain extent is sufficient to avoid confinement effects. Spanwise domain confinement of the flow occurs when the ratio of spanwise domain extent to local momentum thickness reaches a value of ten. Flow confinement results in changes to both the growth mechanism of the turbulent coherent structures, and the nature of the interactions that occur between them. The results demonstrate that simulations of the two-dimensional mixing layer flow requires a three-dimensional computational domain in order that the flow will evolve in a manner that is free from restraints imposed by the spanwise domain.

  6. REvolver: modeling sequence evolution under domain constraints.

    PubMed

    Koestler, Tina; von Haeseler, Arndt; Ebersberger, Ingo

    2012-09-01

    Simulating the change of protein sequences over time in a biologically realistic way is fundamental for a broad range of studies with a focus on evolution. It is, thus, problematic that typically simulators evolve individual sites of a sequence identically and independently. More realistic simulations are possible; however, they are often prohibited by limited knowledge concerning site-specific evolutionary constraints or functional dependencies between amino acids. As a consequence, a protein's functional and structural characteristics are rapidly lost in the course of simulated evolution. Here, we present REvolver (www.cibiv.at/software/revolver), a program that simulates protein sequence alteration such that evolutionarily stable sequence characteristics, like functional domains, are maintained. For this purpose, REvolver recruits profile hidden Markov models (pHMMs) for parameterizing site-specific models of sequence evolution in an automated fashion. pHMMs derived from alignments of homologous proteins or protein domains capture information regarding which sequence sites remained conserved over time and where in a sequence insertions or deletions are more likely to occur. Thus, they describe constraints on the evolutionary process acting on these sequences. To demonstrate the performance of REvolver as well as its applicability in large-scale simulation studies, we evolved the entire human proteome up to 1.5 expected substitutions per site. Simultaneously, we analyzed the preservation of Pfam and SMART domains in the simulated sequences over time. REvolver preserved 92% of the Pfam domains originally present in the human sequences. This value drops to 15% when traditional models of amino acid sequence evolution are used. Thus, REvolver represents a significant advance toward a realistic simulation of protein sequence evolution on a proteome-wide scale. Further, REvolver facilitates the simulation of a protein family with a user-defined domain architecture at

  7. Coupling Landform Evolution and Soil Pedogenesis - Initial Results From the SSSPAM5D Model

    NASA Astrophysics Data System (ADS)

    Willgoose, G. R.; Welivitiya, W. D. D. P.; Hancock, G. R.; Cohen, S.

    2015-12-01

    Evolution of soil on a dynamic landform is a crucial next step in landscape evolution modelling. Some attempts have been taken such as MILESD by Vanwalleghem et al. to develop a first model which is capable of simultaneously evolving both the soil profile and the landform. In previous work we have presented physically based models for soil pedogenesis, mARM and SSSPAM. In this study we present the results of coupling a landform evolution model with our SSSPAM5D soil pedogenesis model. In previous work the SSSPAM5D soil evolution model was used to identify trends of the soil profile evolution on a static landform. Two pedogenetic processes, namely (1) armouring due to erosion, and (2) physical and chemical weathering were used in those simulations to evolve the soil profile. By incorporating elevation changes (due to erosion and deposition) we have advanced the SSSPAM5D modelling framework into the realm of landscape evolution. Simulations have been run using elevation and soil grading data of the engineered landform (spoil heap) at the Ranger Uranium Mine, Northern Territory, Australia. The results obtained for the coupled landform-soil evolution simulations predict the erosion of high slope areas, development of rudimentary channel networks in the landform and deposition of sediments in lowland areas, and qualitatively consistent with landform evolution models on their own. Examination of the soil profile characteristics revealed that hill crests are weathering dominated and tend to develop a thick soil layer. The steeper hillslopes at the edge of the landform are erosion dominated with shallow soils while the foot slopes are deposition dominated with thick soil layers. The simulation results of our coupled landform and soil evolution model provide qualitatively correct and timely characterization of the soil evolution on a dynamic landscape. Finally we will compare the characteristics of erosion and deposition predicted by the coupled landform-soil SSSPAM

  8. Global models of planet formation and evolution

    NASA Astrophysics Data System (ADS)

    Mordasini, C.; Mollière, P.; Dittkrist, K.-M.; Jin, S.; Alibert, Y.

    2015-04-01

    Despite the strong increase in observational data on extrasolar planets, the processes that led to the formation of these planets are still not well understood. However, thanks to the high number of extrasolar planets that have been discovered, it is now possible to look at the planets as a population that puts statistical constraints on theoretical formation models. A method that uses these constraints is planetary population synthesis where synthetic planetary populations are generated and compared to the actual population. The key element of the population synthesis method is a global model of planet formation and evolution. These models directly predict observable planetary properties based on properties of the natal protoplanetary disc, linking two important classes of astrophysical objects. To do so, global models build on the simplified results of many specialized models that address one specific physical mechanism. We thoroughly review the physics of the sub-models included in global formation models. The sub-models can be classified as models describing the protoplanetary disc (of gas and solids), those that describe one (proto)planet (its solid core, gaseous envelope and atmosphere), and finally those that describe the interactions (orbital migration and N-body interaction). We compare the approaches taken in different global models, discuss the links between specialized and global models, and identify physical processes that require improved descriptions in future work. We then shortly address important results of planetary population synthesis like the planetary mass function or the mass-radius relationship. With these statistical results, the global effects of physical mechanisms occurring during planet formation and evolution become apparent, and specialized models describing them can be put to the observational test. Owing to their nature as meta models, global models depend on the results of specialized models, and therefore on the development of

  9. Hierarchical Layered WS2 /Graphene-Modified CdS Nanorods for Efficient Photocatalytic Hydrogen Evolution.

    PubMed

    Xiang, Quanjun; Cheng, Feiyue; Lang, Di

    2016-05-10

    Graphene-based ternary composite photocatalysts with genuine heterostructure constituents have attracted extensive attention in photocatalytic hydrogen evolution. Here we report a new graphene-based ternary composite consisting of CdS nanorods grown on hierarchical layered WS2 /graphene hybrid (WG) as a high-performance photocatalyst for hydrogen evolution under visible light irradiation. The optimal content of layered WG as a co-catalyst in the ternary CdS/WS2 /graphene composites was found to be 4.2 wt %, giving a visible light photocatalytic H2 -production rate of 1842 μmol h(-1)  g(-1) with an apparent quantum efficiency of 21.2 % at 420 nm. This high photocatalytic H2 -production activity is due to the deposition of CdS nanorods on layered WS2 /graphene sheets, which can efficiently suppress charge recombination, improve interfacial charge transfer, and provide reduction active sites. The proposed mechanism for the enhanced photocatalytic activity of CdS nanorods modified with hierarchical layered WG was further confirmed by transient photocurrent response. This work shows that a noble-metal-free hierarchical layered WS2 /graphene nanosheets hybrid can be used as an effective co-catalyst for photocatalytic water splitting. PMID:27059296

  10. Spatial Evolution of Resonant Harmonic Mode Triads in a Blasius Boundary Layer

    NASA Technical Reports Server (NTRS)

    Davila, Jose B.; King, Rudolph A.

    2007-01-01

    Blasius boundary layer evolution is studies by means of bicoherence calculations. The layer is acoustically excited at the T-S frequency to provide a controlled transition. Measurements are made using a smooth surface as well as various roughness patterns. The bicoherence calculations are used to determine the extent to which frequency resonant velocity fluctuation waves can participate in energy exchange. The emphasis is on downstream variation of the individual interactions among harmonic modes. A limited picture of the role of quadratic wave interactions is revealed.

  11. Exact evolution of discrete relativistic cosmological models

    SciTech Connect

    Clifton, Timothy; Tavakol, Reza; Gregoris, Daniele; Rosquist, Kjell E-mail: danielegregoris@libero.it E-mail: r.tavakol@qmul.ac.uk

    2013-11-01

    We study the effects of inhomogeneities on the evolution of the Universe, by considering a range of cosmological models with discretized matter content. This is done using exact and fully relativistic methods that exploit the symmetries in and about submanifolds of spacetimes that themselves possess no continuous global symmetries. These methods allow us to follow the evolution of our models throughout their entire history, far beyond what has previously been possible. We find that while some space-like curves collapse to anisotropic singularities in finite time, others remain non-singular forever. The resulting picture is of a cosmological spacetime in which some behaviour remains close to Friedmann-like, while other behaviours deviate radically. In particular, we find that large-scale acceleration is possible without any violation of the energy conditions.

  12. Modeling Olfactory Bulb Evolution through Primate Phylogeny

    PubMed Central

    Heritage, Steven

    2014-01-01

    Adaptive characterizations of primates have usually included a reduction in olfactory sensitivity. However, this inference of derivation and directionality assumes an ancestral state of olfaction, usually by comparison to a group of extant non-primate mammals. Thus, the accuracy of the inference depends on the assumed ancestral state. Here I present a phylogenetic model of continuous trait evolution that reconstructs olfactory bulb volumes for ancestral nodes of primates and mammal outgroups. Parent-daughter comparisons suggest that, relative to the ancestral euarchontan, the crown-primate node is plesiomorphic and that derived reduction in olfactory sensitivity is an attribute of the haplorhine lineage. The model also suggests a derived increase in olfactory sensitivity at the strepsirrhine node. This oppositional diversification of the strepsirrhine and haplorhine lineages from an intermediate and non-derived ancestor is inconsistent with a characterization of graded reduction through primate evolution. PMID:25426851

  13. LAF: Theoretical Model of Large Amplitude Folding of a Single Viscous Layer

    NASA Astrophysics Data System (ADS)

    Adamuszek, M.; Schmid, D. W.; Dabrowski, M.

    2012-04-01

    We present a theoretical model for Large Amplitude Folding (LAF) during buckling of a single, viscous layer. The model accurately predicts the evolution of geometrical fold parameters (amplitude, wavelength, and thickness) and is not restricted to any viscosity ratio or type of perturbation. The model employs two corrections to the formula of the initial growth rate of folds that is calculated using the thick-plate solution of Fletcher (Tectonophysics, 1977). The growth rate is modified by incorporating 1) the evolution of wavelength to thickness ratio, after Fletcher (American Journal of Science, 1974) and 2) the reduction of the growth rate, originally introduced by Schmalholz and Podladchikov (EPSL, 2000). The former correction is a consequence of the layer shortening and thickening. The latter modification is the result of using an effective rate of layer shortening as the driving force for fold growth, rather than the applied background shortening rate. The effective rate of the layer shortening is approximated by the rate of fold arclength shortening. In the model, we use an analytical expression derived based on the evolution of sinusoidal waveforms. These two modifications to the growth rate were already separately employed in previous studies. Through comparison with numerical models, we show that the simultaneous application of both corrections in LAF provides a better prediction of the evolution of the fold geometry parameters up to large amplitudes, compared to the models with only one correction. Our studies of the fold evolution from initial single and multiple (random noise, step and bell-shape function) waveforms show a remarkable fit between LAF and the numerical results. In the multiple waveform models, we predict a coupling between the components. In LAF, folds developed from initial random perturbations exhibit irregular but periodic shapes, characteristic for folds observed in nature. We also show that the evolution of folds from localized

  14. Evolution of flare ribbons, electric currents, and quasi-separatrix layers during an X-class flare

    NASA Astrophysics Data System (ADS)

    Janvier, M.; Savcheva, A.; Pariat, E.; Tassev, S.; Millholland, S.; Bommier, V.; McCauley, P.; McKillop, S.; Dougan, F.

    2016-07-01

    Context. The standard model for eruptive flares has been extended to three dimensions (3D) in the past few years. This model predicts typical J-shaped photospheric footprints of the coronal current layer, forming at similar locations as the quasi-separatrix layers (QSLs). Such a morphology is also found for flare ribbons observed in the extreme ultraviolet (EUV) band, and in nonlinear force-free field (NLFFF) magnetic field extrapolations and models. Aims: We study the evolution of the photospheric traces of the current density and flare ribbons, both obtained with the Solar Dynamics Observatory instruments. We aim to compare their morphology and their time evolution, before and during the flare, with the topological features found in a NLFFF model. Methods: We investigated the photospheric current evolution during the 06 September 2011 X-class flare (SOL2011-09-06T22:20) occurring in NOAA AR 11283 from observational data of the magnetic field obtained with the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory. We compared this evolution with that of the flare ribbons observed in the EUV filters of the Atmospheric Imager Assembly. We also compared the observed electric current density and the flare ribbon morphology with that of the QSLs computed from the flux rope insertion method-NLFFF model. Results: The NLFFF model shows the presence of a fan-spine configuration of overlying field lines, due to the presence of a parasitic polarity, embedding an elongated flux rope that appears in the observations as two parts of a filament. The QSL signatures of the fan configuration appear as a circular flare ribbon that encircles the J-shaped ribbons related to the filament ejection. The QSLs, evolved via a magnetofrictional method, also show similar morphology and evolution as both the current ribbons and the EUV flare ribbons obtained several times during the flare. Conclusions: For the first time, we propose a combined analysis of the photospheric

  15. Modelling sediment clasts transport during landscape evolution

    NASA Astrophysics Data System (ADS)

    Carretier, S.; Martinod, P.; Reich, M.; Godderis, Y.

    2015-10-01

    Over thousands to millions of years, the landscape evolution is predicted by models based on fluxes of eroded, transported and deposited material. The laws describing these fluxes, corresponding to averages over many years, are difficult to prove with the available data. On the other hand, sediment dynamics are often tackled by studying the distribution of certain grain properties in the field (e.g. heavy metals, detrial zircons, 10Be in gravel, magnetic tracers, etc.). There is a gap between landscape evolution models based on fluxes and these field data on individual clasts, which prevent the latter from being used to calibrate the former. Here we propose an algorithm coupling the landscape evolution with mobile clasts. Our landscape evolution model predicts local erosion, deposition and transfer fluxes resulting from hillslope and river processes. Clasts of any size are initially spread in the basement and are detached, moved and deposited according to probabilities using these fluxes. Several river and hillslope laws are studied. Although the resulting mean transport rate of the clasts does not depend on the time step or the model cell size, our approach is limited by the fact that their scattering rate is cell-size dependent. Nevertheless, both their mean transport rate and the shape of the scattering-time curves fit the predictions. Different erosion-transport laws generate different clast movements. These differences show that studying the tracers in the field may provide a way to establish these laws on the hillslopes and in the rivers. Possible applications include the interpretation of cosmogenic nuclides in individual gravel deposits, provenance analyses, placers, sediment coarsening or fining, the relationship between magnetic tracers in rivers and the river planform, and the tracing of weathered sediment.

  16. Modelling sediment clasts transport during landscape evolution

    NASA Astrophysics Data System (ADS)

    Carretier, Sébastien; Martinod, Pierre; Reich, Martin; Godderis, Yves

    2016-03-01

    Over thousands to millions of years, the landscape evolution is predicted by models based on fluxes of eroded, transported and deposited material. The laws describing these fluxes, corresponding to averages over many years, are difficult to prove with the available data. On the other hand, sediment dynamics are often tackled by studying the distribution of certain grain properties in the field (e.g. heavy metals, detrital zircons, 10Be in gravel, magnetic tracers). There is a gap between landscape evolution models based on fluxes and these field data on individual clasts, which prevent the latter from being used to calibrate the former. Here we propose an algorithm coupling the landscape evolution with mobile clasts. Our landscape evolution model predicts local erosion, deposition and transfer fluxes resulting from hillslope and river processes. Clasts of any size are initially spread in the basement and are detached, moved and deposited according to probabilities using these fluxes. Several river and hillslope laws are studied. Although the resulting mean transport rate of the clasts does not depend on the time step or the model cell size, our approach is limited by the fact that their scattering rate is cell-size-dependent. Nevertheless, both their mean transport rate and the shape of the scattering-time curves fit the predictions. Different erosion-transport laws generate different clast movements. These differences show that studying the tracers in the field may provide a way to establish these laws on the hillslopes and in the rivers. Possible applications include the interpretation of cosmogenic nuclides in individual gravel deposits, provenance analyses, placers, sediment coarsening or fining, the relationship between magnetic tracers in rivers and the river planform, and the tracing of weathered sediment.

  17. Evolving hardware as model of enzyme evolution.

    PubMed

    Lahoz-Beltra, R

    2001-06-01

    Organism growth and survival is based on thousands of enzymes organized in networks. The motivation to understand how a large number of enzymes evolved so fast inside cells may be relevant to explaining the origin and maintenance of life on Earth. This paper presents electronic circuits called 'electronic enzymes' that model the catalytic function performed by biological enzymes. Electronic enzymes are the hardware realization of enzymes defined as molecular automata with a finite number of internal conformational states and a set of Boolean operators modelling the active groups of the active site. One of the main features of electronic enzymes is the possibility of evolution finding the proper active site by means of a genetic algorithm yielding a metabolic ring or k-cycle that bears a resemblance to Krebs (k=7) or Calvin (k=4) cycles present in organisms. The simulations are consistent with those results obtained in vitro evolving enzymes based on polymerase chain reaction (PCR) as well as with the general view that suggests the main role of recombination during enzyme evolution. The proposed methodology shows how molecular automata with evolvable features that model enzymes or other processing molecules provide an experimental framework for simulation of the principles governing metabolic pathways evolution and self-organization. PMID:11448522

  18. Folder: a MATLAB-based tool for modelling deformation in layered media subject to layer parallel shortening or extension

    NASA Astrophysics Data System (ADS)

    Adamuszek, Marta; Dabrowski, Marcin; Schmid, Daniel W.

    2016-04-01

    We present Folder, a numerical tool to simulate and analyse the structure development in mechanically layered media during the layer parallel shortening or extension. Folder includes a graphical user interface that allows for easy designing of complex geometrical models, defining material parameters (including linear and non-linear rheology), and specifying type and amount of deformation. It also includes a range of features that facilitate the visualization and examination of various relevant quantities e.g. velocities, stress, rate of deformation, pressure, and finite strain. Folder contains a separate application, which illustrates analytical solutions of growth rate spectra for layer parallel shortening and extension of a single viscous layer. In the study, we also demonstrate a Folder application, where the role of confinement on the growth rate spectrum and the fold shape evolution during the deformation of a single layer subject to the layer parallel shortening is presented. In the case of the linear viscous materials used for the layer and matrix, the close wall proximity leads to a decrease of the growth rate values. The decrease is more pronounced for the larger wavelengths than for the smaller wavelengths. The growth rate reduction is greater when the walls are set closer to the layer. The presence of the close confinement can also affect the wavelength selection process and significantly shift the position of the dominant wavelength. The influence of the wall proximity on the growth rate spectrum for the case of non-linear viscous materials used for the layer and/or matrix is very different as compared to the linear viscous case. We observe a multiple maxima in the growth rate spectrum. The number of the growth rate maxima, their value and the position strongly depend on the closeness of the confinement. The maximum growth rate value for a selected range of layer-wall distances is much larger than in the case when the confinement effect is not taken

  19. A self-excited wire method for control of the evolution of a turbulent mixing layer

    NASA Astrophysics Data System (ADS)

    Vandsburger, U.; Ding, C.

    1993-01-01

    A new technique for the control of the evolution of a turbulent two-stream (planar) mixing layer is presented. A (music) wire strung across the flow and placed in the zone near the trailing edge of the splitter plate is employed to excite the flow. The vibrating wire triggers the shedding of multiple vortical structures in the near field, and eventually locks the large coherent structures to the excitation frequency in the far field.

  20. Interannual active layer thermal and dynamics evolution at the crater Lake CALM site, Deception Island (Antarctica).

    NASA Astrophysics Data System (ADS)

    Ramos, Miguel; Vieira, Gonzalo; Ángel De Pablo, Miguel; Molina, Antonio; Abramov, Andrey

    2015-04-01

    Deception Island, is an active strato-volcano on South Shetland Archipelago of Antarctica (62° 55' 0″ S, 60° 37' 0″ W), is a cold region with harsh remote and hostile environmental conditions. The permafrost and active layer existence, and the cold climate conditions together with volcanic material with height water content inside made this region of the Earth a perfect site to study the active layer and permafrost evolution involved in the Circumpolar Active Layer South (CALM-S) program. The active layer is measured in late January or firs february (during the end of the thaw period) at the "Crater Lake" CALM site (62°58'06.7''; 60°40'44.8'') on Deception Island, Antarctica, at the period 2006 to 2014 we obtained a mean annual value of 29,7±2 cm. In this paper, we describe the spatial active layer thickness distribution and report the reduction on the mean thickness between February 2006 and 2014. Below the active layer, permafrost could be also reported (with a mean thickness of 4.5± 0.5 m.) based on the temperature data acquired by sensors installed at different depth inside the soil; three different shallow boreholes was drilled (1.0 m., 1.6 m., 4.5 m. in depth) and we have been registered its temperature gradient at the 2010 to 2013 period. Here we use all those data 1) to describe the thermal behavior of the permafrost at the CALM site, and 2) to describe its evolution (aggradation/degradation) along fourteen years of continuous measurements. We develop this study, to known the thermal behavior of the permafrost and the active layer related with the air/soil interaction being one of the most important factors the snow layer that was measured by the installation of termo-snowmeters with the complement of an automatic digital camera during the 2008 to 2014 period. On the other hand, the pyroclastics soil materials has a very high values of water content then the latent heat in the freezing/thawing process controls the active layer evolution and the

  1. Multi-Model approach to reconstruct the Mediterranean Freshwater Evolution

    NASA Astrophysics Data System (ADS)

    Simon, Dirk; Marzocchi, Alice; Flecker, Rachel; Lunt, Dan; Hilgen, Frits; Meijer, Paul

    2016-04-01

    Today the Mediterranean Sea is isolated from the global ocean by the Strait of Gibraltar. This restricted nature causes the Mediterranean basin to react more sensitively to climatic and tectonic related phenomena than the global ocean. Not just eustatic sea-level and regional river run-off, but also gateway tectonics and connectivity between sub-basins are leaving an enhanced fingerprint in its geological record. To understand its evolution, it is crucial to understand how these different effects are coupled. The Miocene-Pliocene sedimentary record of the Mediterranean shows alternations in composition and colour and has been astronomically tuned. Around the Miocene-Pliocene Boundary the most extreme changes occur in the Mediterranean Sea. About 6% of the salt in the global ocean deposited in the Mediterranean Region, forming an approximately 2 km thick salt layer, which is still present today. This extreme event is named the Messinian Salinity Crisis (MSC, 5.97-5.33 Ma). The gateway and climate evolution is not well constrained for this time, which makes it difficult to distinguish which of the above mentioned drivers might have triggered the MSC. We, therefore, decided to tackle this problem via a multi-model approach: (1) We calculate the Mediterranean freshwater evolution via 30 atmosphere-ocean-vegetation simulations (using HadCM3L), to which we fitted to a function, using a regression model. This allows us to directly relate the orbital curves to evaporation, precipitation and run off. The resulting freshwater evolution can be directly correlated to other sedimentary and proxy records in the late Miocene. (2) By feeding the new freshwater evolution curve into a box/budget model we can predict the salinity and strontium evolution of the Mediterranean for a certain Atlantic-Mediterranean gateway. (3) By comparing these results to the known salinity thresholds of gypsum and halite saturation of sea water, but also to the late Miocene Mediterranean strontium

  2. The nonlinear evolution of inviscid Goertler vortices in three-dimensional boundary layers

    NASA Technical Reports Server (NTRS)

    Blackaby, Nicholas; Dando, Andrew; Hall, Philip

    1995-01-01

    The nonlinear development of inviscid Gortler vortices in a three-dimensional boundary layer is considered. We do not follow the classical approach of weakly nonlinear stability problems and consider a mode which has just become unstable. Instead we extend the method of Blackaby, Dando, and Hall (1992), which considered the closely related nonlinear development of disturbances in stratified shear flows. The Gortler modes we consider are initially fast growing and we assume, following others, that boundary-layer spreading results in them evolving in a linear fashion until they reach a stage where their amplitudes are large enough and their growth rates have diminished sufficiently so that amplitude equations can be derived using weakly nonlinear and non-equilibrium critical-layer theories. From the work of Blackaby, Dando and Hall (1993) is apparent, given the range of parameters for the Gortler problem, that there are three possible nonlinear integro-differential evolution equations for the disturbance amplitude. These are a cubic due to viscous effects, a cubic which corresponds to the novel mechanism investigated in this previous paper, and a quintic. In this paper we shall concentrate on the two cubic integro-differential equations and in particular, on the one due to the novel mechanism as this will be the first to affect a disturbance. It is found that the consideration of a spatial evolution problem as opposed to temporal (as was considered in Blackaby, Dando, and Hall, 1992) causes a number of significant changes to the evolution equations.

  3. LAPSUS: soil erosion - landscape evolution model

    NASA Astrophysics Data System (ADS)

    van Gorp, Wouter; Temme, Arnaud; Schoorl, Jeroen

    2015-04-01

    LAPSUS is a soil erosion - landscape evolution model which is capable of simulating landscape evolution of a gridded DEM by using multiple water, mass movement and human driven processes on multiple temporal and spatial scales. It is able to deal with a variety of human landscape interventions such as landuse management and tillage and it can model their interactions with natural processes. The complex spatially explicit feedbacks the model simulates demonstrate the importance of spatial interaction of human activity and erosion deposition patterns. In addition LAPSUS can model shallow landsliding, slope collapse, creep, solifluction, biological and frost weathering, fluvial behaviour. Furthermore, an algorithm to deal with natural depressions has been added and event-based modelling with an improved infiltration description and dust deposition has been pursued. LAPSUS has been used for case studies in many parts of the world and is continuously developing and expanding. it is now available for third-party and educational use. It has a comprehensive user interface and it is accompanied by a manual and exercises. The LAPSUS model is highly suitable to quantify and understand catchment-scale erosion processes. More information and a download link is available on www.lapsusmodel.nl.

  4. Modeling spatio-temporal field evolution

    NASA Astrophysics Data System (ADS)

    Borštnik Bračič, A.; Grabec, I.; Govekar, E.

    2009-06-01

    Prediction of spatio-temporal field evolution is based on the extraction of a physical law from joint experimental data. This extraction is usually described by a set of differential equations. If the only source of information is a field record, a method of field generators based on nonparametric modeling by conditional average can successfully replace differential equations. In this article we apply the method of field generators to a two-dimensional chaotic field record that describes the asynchronous motion of high-amplitude striations. We show how to choose the model structure in order to optimize the quality of the prediction process.

  5. Evolution of multidimensional flat anisotropic cosmological models

    SciTech Connect

    Beloborodov, A. ); Demianski, M. Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw International Center for Relativistic Astrophysics , Universita di Roma I, La Sapienza, Rome ); Ivanov, P.; Polnarev, A.G. )

    1993-07-15

    We study the dynamics of a flat multidimensional anisotropic cosmological model filled with an anisotropic fluidlike medium. By an appropriate choice of variables, the dynamical equations reduce to a two-dimensional dynamical system. We present a detailed analysis of the time evolution of this system and the conditions of the existence of spacetime singularities. We investigate the conditions under which violent, exponential, and power-law inflation is possible. We show that dimensional reduction cannot proceed by anti-inflation (rapid contraction of internal space). Our model indicates that it is very difficult to achieve dimensional reduction by classical means.

  6. Fluxon Modeling of Active Region Evolution

    NASA Astrophysics Data System (ADS)

    Deforest, C. E.; Kankelborg, C. C.; Davey, A. R.; Rachmeler, L.

    2006-12-01

    We present current results and status on fluxon modeling of free energy buildup and release in active regions. Our publicly available code, FLUX, has the unique ability to track magnetic energy buildup with a truly constrained topology in evolving, nonlinear force-free conditions. Recent work includes validation of the model against Low &Lou force-free field solutions, initial evolution studies of idealized active regions, and inclusion of locally parameterized reconnection into the model. FLUX is uniquely able to simulate complete active regions in 3-D on a single workstation; we estimate that a parallelized fluxon model, together with computer vision code to ingest solar data, could run faster than real time on a cluster of \\textasciitilde 30 CPUs and hence provide a true predictive space weather model in the style of predictive simulations of terrestrial weather.

  7. Cancer Evolution: Mathematical Models and Computational Inference

    PubMed Central

    Beerenwinkel, Niko; Schwarz, Roland F.; Gerstung, Moritz; Markowetz, Florian

    2015-01-01

    Cancer is a somatic evolutionary process characterized by the accumulation of mutations, which contribute to tumor growth, clinical progression, immune escape, and drug resistance development. Evolutionary theory can be used to analyze the dynamics of tumor cell populations and to make inference about the evolutionary history of a tumor from molecular data. We review recent approaches to modeling the evolution of cancer, including population dynamics models of tumor initiation and progression, phylogenetic methods to model the evolutionary relationship between tumor subclones, and probabilistic graphical models to describe dependencies among mutations. Evolutionary modeling helps to understand how tumors arise and will also play an increasingly important prognostic role in predicting disease progression and the outcome of medical interventions, such as targeted therapy. PMID:25293804

  8. Optimal evolution models for quantum tomography

    NASA Astrophysics Data System (ADS)

    Czerwiński, Artur

    2016-02-01

    The research presented in this article concerns the stroboscopic approach to quantum tomography, which is an area of science where quantum physics and linear algebra overlap. In this article we introduce the algebraic structure of the parametric-dependent quantum channels for 2-level and 3-level systems such that the generator of evolution corresponding with the Kraus operators has no degenerate eigenvalues. In such cases the index of cyclicity of the generator is equal to 1, which physically means that there exists one observable the measurement of which performed a sufficient number of times at distinct instants provides enough data to reconstruct the initial density matrix and, consequently, the trajectory of the state. The necessary conditions for the parameters and relations between them are introduced. The results presented in this paper seem to have considerable potential applications in experiments due to the fact that one can perform quantum tomography by conducting only one kind of measurement. Therefore, the analyzed evolution models can be considered optimal in the context of quantum tomography. Finally, we introduce some remarks concerning optimal evolution models in the case of n-dimensional Hilbert space.

  9. Modeling Evolution of Weighted Clique Networks

    NASA Astrophysics Data System (ADS)

    Yang, Xu-Hua; Jiang, Feng-Ling; Chen, Sheng-Yong; Wang, Wan-Liang

    2011-11-01

    We propose a weighted clique network evolution model, which expands continuously by the addition of a new clique (maximal complete sub-graph) at each time step. And the cliques in the network overlap with each other. The structural expansion of the weighted clique network is combined with the edges' weight and vertices' strengths dynamical evolution. The model is based on a weight-driven dynamics and a weights' enhancement mechanism combining with the network growth. We study the network properties, which include the distribution of vertices' strength and the distribution of edges' weight, and find that both the distributions follow the scale-free distribution. At the same time, we also find that the relationship between strength and degree of a vertex are linear correlation during the growth of the network. On the basis of mean-field theory, we study the weighted network model and prove that both vertices' strength and edges' weight of this model follow the scale-free distribution. And we exploit an algorithm to forecast the network dynamics, which can be used to reckon the distributions and the corresponding scaling exponents. Furthermore, we observe that mean-field based theoretic results are consistent with the statistical data of the model, which denotes the theoretical result in this paper is effective.

  10. Tidal dissipation in stars and fluid planetary layers and its impact on the evolution of star-planet systems

    NASA Astrophysics Data System (ADS)

    Auclair-Desrotour, P.; Mathis, S.; Le Poncin-Lafitte, C.

    2015-09-01

    Tidal dissipation in stars and planets is one of the key physical mechanisms that drive the evolution of planetary systems. It intrinsically depends on the nature of the tidal response of celestial bodies, which is directly linked to their internal structure and friction. Indeed, it is highly resonant in the case of fluids. In this work, we present a local analytical modeling of tidal gravito-inertial waves, which can be excited in stars and fluid planetary layers. This model allows us to understand the properties of their resonant dissipation as a function of the excitation frequencies, the rotation, the stratification, and the viscous and thermal properties of the studied fluid regions. Next, we introduce such a complex tidal dissipation frequency-spectra in a celestial mechanics numerical code to give a qualitative overview of its impact on the evolution of planetary systems. We consider the example of a two-body coplanar system with a punctual perturber orbiting a central fluid body. We demonstrate how the viscous dissipation of tidal waves can lead to a strongly erratic orbital evolution. Finally, we characterize such a non-regular dynamics as a function of the properties of resonances, which have been determined thanks to our local fluid model.

  11. Lagrangian mixed layer modeling of the western equatorial Pacific

    NASA Technical Reports Server (NTRS)

    Shinoda, Toshiaki; Lukas, Roger

    1995-01-01

    Processes that control the upper ocean thermohaline structure in the western equatorial Pacific are examined using a Lagrangian mixed layer model. The one-dimensional bulk mixed layer model of Garwood (1977) is integrated along the trajectories derived from a nonlinear 1 1/2 layer reduced gravity model forced with actual wind fields. The Global Precipitation Climatology Project (GPCP) data are used to estimate surface freshwater fluxes for the mixed layer model. The wind stress data which forced the 1 1/2 layer model are used for the mixed layer model. The model was run for the period 1987-1988. This simple model is able to simulate the isothermal layer below the mixed layer in the western Pacific warm pool and its variation. The subduction mechanism hypothesized by Lukas and Lindstrom (1991) is evident in the model results. During periods of strong South Equatorial Current, the warm and salty mixed layer waters in the central Pacific are subducted below the fresh shallow mixed layer in the western Pacific. However, this subduction mechanism is not evident when upwelling Rossby waves reach the western equatorial Pacific or when a prominent deepening of the mixed layer occurs in the western equatorial Pacific or when a prominent deepening of the mixed layer occurs in the western equatorial Pacific due to episodes of strong wind and light precipitation associated with the El Nino-Southern Oscillation. Comparison of the results between the Lagrangian mixed layer model and a locally forced Eulerian mixed layer model indicated that horizontal advection of salty waters from the central Pacific strongly affects the upper ocean salinity variation in the western Pacific, and that this advection is necessary to maintain the upper ocean thermohaline structure in this region.

  12. Diffuse Interface Model for Microstructure Evolution

    NASA Astrophysics Data System (ADS)

    Nestler, Britta

    A phase-field model for a general class of multi-phase metallic alloys is proposed which describes both, multi-phase solidification phenomena as well as polycrystalline grain structures. The model serves as a computational method to simulate the motion and kinetics of multiple phase boundaries and enables the visualization of the diffusion processes and of the phase transitions in multi-phase systems. Numerical simulations are presented which illustrate the capability of the phase-field model to recover a variety of complex experimental growth structures. In particular, the phase-field model can be used to simulate microstructure evolutions in eutectic, peritectic and monotectic alloys. In addition, polycrystalline grain structures with effects such as wetting, grain growth, symmetry properties of adjacent triple junctions in thin film samples and stability criteria at multiple junctions are described by phase-field simulations.

  13. A mathematical model of biological evolution.

    PubMed

    Ishii, K; Matsuda, H; Ogita, N

    1982-01-01

    In order to understand generally how the biological evolution rate depends on relevant parameters such as mutation rate, intensity of selection pressure and its persistence time, the following mathematical model is proposed: dNn(t)/dt = (mn(t) - mu)Nn(t) + muNn-1(t) (n = 0,1,2,3,...), where Nn(t) and mn(t) are respectively the number and Malthusian parameter of replicons with step number n in a population at time t and mean is the mutation rate, assumed to be a positive constant. The step number of each replicon is defined as either equal to or larger by one than that of its parent, the latter case occurring when and only when mutation has taken place. The average evolution rate defined by v infinity identical to lim t leads to infinity sigma infinity n = o nNn(t)/t sigma infinity n = o Nn(t) is rigorously obtained for the case (i) mn(t) = mn is independent of t (constant fitness model), where mn is essentially periodic with respect to n, and for the case (ii) mn(t) = s(-1) n+[t/tau] (periodic fitness model), together with the long time average -m infinity of the average Malthusian parameter -m identical to sigma infinity n = o mn(t)Nn(t)/sigma infinity n = o Nn(t). The biological meaning of the results is discussed, comparing them with the features of actual molecular evolution and with some results of computer simulation of the model for finite populations. PMID:7119589

  14. Testing spherical evolution for modelling void abundances

    NASA Astrophysics Data System (ADS)

    Achitouv, Ixandra; Neyrinck, Mark; Paranjape, Aseem

    2015-08-01

    We compare analytical predictions of void volume functions to those measured from N-body simulations, detecting voids with the ZOBOV void finder. We push to very small, non-linear voids, below few Mpc radius, by considering the unsampled dark matter density field. We also study the case where voids are identified using haloes. We develop analytical formula for the void abundance of both the excursion set approach and the peaks formalism. These formulas are valid for random walks smoothed with a top-hat filter in real space, with a large class of realistic barrier models. We test the extent to which the spherical evolution approximation, which forms the basis of the analytical predictions, models the highly aspherical voids that occur in the cosmic web, and are found by a watershed-based algorithm such as ZOBOV. We show that the volume function returned by ZOBOV is quite sensitive to the choice of treatment of subvoids, a fact that has not been appreciated previously. For reasonable choices of subvoid exclusion, we find that the Lagrangian density δv of the ZOBOV voids - which is predicted to be a constant δv ≈ -2.7 in the spherical evolution model - is different from the predicted value, showing substantial scatter and scale dependence. This result applies to voids identified at z = 0 with effective radius between 1 and 10 h-1 Mpc. Our analytical approximations are flexible enough to give a good description of the resulting volume function; however, this happens for choices of parameter values that are different from those suggested by the spherical evolution assumption. We conclude that analytical models for voids must move away from the spherical approximation in order to be applied successfully to observations, and we discuss some possible ways forward.

  15. Modeling marine boundary-layer clouds with a two-layer model: A one-dimensional simulation

    NASA Technical Reports Server (NTRS)

    Wang, Shouping

    1993-01-01

    A two-layer model of the marine boundary layer is described. The model is used to simulate both stratocumulus and shallow cumulus clouds in downstream simulations. Over cold sea surfaces, the model predicts a relatively uniform structure in the boundary layer with 90%-100% cloud fraction. Over warm sea surfaces, the model predicts a relatively strong decoupled and conditionally unstable structure with a cloud fraction between 30% and 60%. A strong large-scale divergence considerably limits the height of the boundary layer and decreases relative humidity in the upper part of the cloud layer; thus, a low cloud fraction results. The efffects of drizzle on the boundary-layer structure and cloud fraction are also studied with downstream simulations. It is found that drizzle dries and stabilizes the cloud layer and tends to decouple the cloud from the subcloud layer. Consequently, solid stratocumulus clouds may break up and the cloud fraction may decrease because of drizzle.

  16. A Distributed Snow Evolution Modeling System (SnowModel)

    NASA Astrophysics Data System (ADS)

    Liston, G. E.; Elder, K.

    2004-12-01

    A spatially distributed snow-evolution modeling system (SnowModel) has been specifically designed to be applicable over a wide range of snow landscapes, climates, and conditions. To reach this goal, SnowModel is composed of four sub-models: MicroMet defines the meteorological forcing conditions, EnBal calculates surface energy exchanges, SnowMass simulates snow depth and water-equivalent evolution, and SnowTran-3D accounts for snow redistribution by wind. While other distributed snow models exist, SnowModel is unique in that it includes a well-tested blowing-snow sub-model (SnowTran-3D) for application in windy arctic, alpine, and prairie environments where snowdrifts are common. These environments comprise 68% of the seasonally snow-covered Northern Hemisphere land surface. SnowModel also accounts for snow processes occurring in forested environments (e.g., canopy interception related processes). SnowModel is designed to simulate snow-related physical processes occurring at spatial scales of 5-m and greater, and temporal scales of 1-hour and greater. These include: accumulation from precipitation; wind redistribution and sublimation; loading, unloading, and sublimation within forest canopies; snow-density evolution; and snowpack ripening and melt. To enhance its wide applicability, SnowModel includes the physical calculations required to simulate snow evolution within each of the global snow classes defined by Sturm et al. (1995), e.g., tundra, taiga, alpine, prairie, maritime, and ephemeral snow covers. The three, 25-km by 25-km, Cold Land Processes Experiment (CLPX) mesoscale study areas (MSAs: Fraser, North Park, and Rabbit Ears) are used as SnowModel simulation examples to highlight model strengths, weaknesses, and features in forested, semi-forested, alpine, and shrubland environments.

  17. A boundary layer model for magnetospheric substorms

    NASA Technical Reports Server (NTRS)

    Rostoker, Gordon; Eastman, Tim

    1987-01-01

    An alternative framework for understanding magnetospheric substorm activity is presented. It is argued that observations of magnetic field and plasma flow variations in the magnetotail can be explained in terms of the passage of the plasma sheet boundary layer over the satellite detecting the tail signatures. It is shown that field-aligned currents and particle acceleration processes on magnetic field lines threading the ionospheric Harang discontinuity lead to the distinctive particle and field signatures observed in the magnetotail during substorms. It is demonstrated that edge effects of field-aligned currents associated with the westward traveling surge can lead to the negative B(z) perturbations observed in the tail that are presently attributed to observations made on the anti-earthward side of a near-earth neutral line. Finally, it is shown that the model can provide a physical explanation of both the driven system and the loading-unloading system whose combined effects provide the observed substorm perturbation pattern in the magnetosphere and ionosphere.

  18. The evolution of the boundary layer in turbulent Rayleigh-Bénard convection in air

    NASA Astrophysics Data System (ADS)

    du Puits, R.; Willert, C.

    2016-04-01

    We report measurements of the near-wall flow field in turbulent Rayleigh-Bénard convection in air (Pr = 0.7) using particle image velocimetry. The measurements were performed in a thin, rectangular sample at fixed Rayleigh number Ra = 1.45 × 1010. In particular, we focus on the evolution of the boundary layer that a single convection roll generates along its path at the lower horizontal plate. We identify three specific flow regions along this path: (i) a region of wall-normal impingement of the down flow close to one corner of the sample, (ii) a region where a shear layer with almost constant thickness evolves, and (iii) a region in which this boundary layer grows and eventually detaches from the plate surface at the opposite corner of the sample. Our measurements with a spatial resolution better than 1/500 of the total thickness of the boundary layer show that the typical velocity field as well as its statistics qualitatively varies between the three flow regions. In particular, it could be verified that the shear layer region covering about 75% of the total area of the plate is in transition to turbulence at the Rayleigh number as low as investigated in the present work.

  19. Observations of the magnetopause current layer: Cases with no boundary layer and tests of recent models

    NASA Technical Reports Server (NTRS)

    Eastman, Timothy E.

    1995-01-01

    Evidence for the probable existence of magnetospheric boundary layers was first presented by Hones, et al. (1972), based on VELA satellite plasma observations (no magnetic field measurements were obtained). This magnetotail boundary layer is now known to be the tailward extension of the high-latitude boundary layer or plasma mantle (first uniquely identified using HEOS 2 plasma and field observations by Rosenbauer et al., 1975) and the low-latitude boundary layer (first uniquely identified using IMP 6 plasma and field observations by Eastman et al., 1976). The magnetospheric boundary layer is the region of magnetosheath-like plasma located Earthward of, but generally contiguous with the magnetopause. This boundary layer is typically identified by comparing low-energy (less than 10 keV) ion spectra across the magnetopause. Low-energy electron measurements are also useful for identifying the boundary layer because the shocked solar wind or magnetosheath has a characteristic spectral signature for electrons as well. However, there are magnetopause crossings where low-energy electrons might suggest a depletion layer outside the magnetopause even though the traditional field-rotation signature indicates that this same region is a boundary layer Earthward of the current layer. Our analyses avoided crossings which exhibit such ambiguities. Pristine magnetopause crossings are magnetopause crossings for which the current layer is well defined and for which there is no adjoining magnetospheric boundary layer as defined above. Although most magnetopause models to date apply to such crossings, few comparisons between such theory and observations of pristine magnetopause crossings have been made because most crossings have an associated magnetospheric boundary layer which significantly affects the applicable boundary conditions for the magnetopause current layer. Furthermore, almost no observational studies of magnetopause microstructure have been done even though key

  20. Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries.

    PubMed

    Lin, Feng; Markus, Isaac M; Nordlund, Dennis; Weng, Tsu-Chien; Asta, Mark D; Xin, Huolin L; Doeff, Marca M

    2014-01-01

    The present study sheds light on the long-standing challenges associated with high-voltage operation of LiNi(x)Mn(x)Co(1-2x)O2 cathode materials for lithium-ion batteries. Using correlated ensemble-averaged high-throughput X-ray absorption spectroscopy and spatially resolved electron microscopy and spectroscopy, here we report structural reconstruction (formation of a surface reduced layer, to transition) and chemical evolution (formation of a surface reaction layer) at the surface of LiNi(x)Mn(x)Co(1-2x)O2 particles. These are primarily responsible for the prevailing capacity fading and impedance buildup under high-voltage cycling conditions, as well as the first-cycle coulombic inefficiency. It was found that the surface reconstruction exhibits a strong anisotropic characteristic, which predominantly occurs along lithium diffusion channels. Furthermore, the surface reaction layer is composed of lithium fluoride embedded in a complex organic matrix. This work sets a refined example for the study of surface reconstruction and chemical evolution in battery materials using combined diagnostic tools at complementary length scales. PMID:24670975

  1. Uncertainties in Galactic Chemical Evolution Models

    NASA Astrophysics Data System (ADS)

    Côté, Benoit; Ritter, Christian; O’Shea, Brian W.; Herwig, Falk; Pignatari, Marco; Jones, Samuel; Fryer, Chris L.

    2016-06-01

    We use a simple one-zone galactic chemical evolution model to quantify the uncertainties generated by the input parameters in numerical predictions for a galaxy with properties similar to those of the Milky Way. We compiled several studies from the literature to gather the current constraints for our simulations regarding the typical value and uncertainty of the following seven basic parameters: the lower and upper mass limits of the stellar initial mass function (IMF), the slope of the high-mass end of the stellar IMF, the slope of the delay-time distribution function of Type Ia supernovae (SNe Ia), the number of SNe Ia per M ⊙ formed, the total stellar mass formed, and the final mass of gas. We derived a probability distribution function to express the range of likely values for every parameter, which were then included in a Monte Carlo code to run several hundred simulations with randomly selected input parameters. This approach enables us to analyze the predicted chemical evolution of 16 elements in a statistical manner by identifying the most probable solutions, along with their 68% and 95% confidence levels. Our results show that the overall uncertainties are shaped by several input parameters that individually contribute at different metallicities, and thus at different galactic ages. The level of uncertainty then depends on the metallicity and is different from one element to another. Among the seven input parameters considered in this work, the slope of the IMF and the number of SNe Ia are currently the two main sources of uncertainty. The thicknesses of the uncertainty bands bounded by the 68% and 95% confidence levels are generally within 0.3 and 0.6 dex, respectively. When looking at the evolution of individual elements as a function of galactic age instead of metallicity, those same thicknesses range from 0.1 to 0.6 dex for the 68% confidence levels and from 0.3 to 1.0 dex for the 95% confidence levels. The uncertainty in our chemical evolution model

  2. Incorporation of the planetary boundary layer in atmospheric models

    NASA Technical Reports Server (NTRS)

    Moeng, Chin-Hoh; Wyngaard, John; Pielke, Roger; Krueger, Steve

    1993-01-01

    The topics discussed include the following: perspectives on planetary boundary layer (PBL) measurements; current problems of PBL parameterization in mesoscale models; and convective cloud-PBL interactions.

  3. Green House Gases Flux Model in Boundary Layer

    NASA Astrophysics Data System (ADS)

    Nurgaliev, Ildus

    Analytical dynamic model of the turbulent flux in the three-layer boundary system is presented. Turbulence is described as a presence of the non-zero vorticity. The generalized advection-diffusion-reaction equation is derived for an arbitrary number of components in the flux. The fluxes in the layers are objects for matching requirements on the boundaries between the layers. Different types of transport mechanisms are dominant on the different levels of the layers.

  4. Lidar observations of mixed layer dynamics - Tests of parameterized entrainment models of mixed layer growth rate

    NASA Technical Reports Server (NTRS)

    Boers, R.; Eloranta, E. W.; Coulter, R. L.

    1984-01-01

    Ground based lidar measurements of the atmospheric mixed layer depth, the entrainment zone depth and the wind speed and wind direction were used to test various parameterized entrainment models of mixed layer growth rate. Six case studies under clear air convective conditions over flat terrain in central Illinois are presented. It is shown that surface heating alone accounts for a major portion of the rise of the mixed layer on all days. A new set of entrainment model constants was determined which optimized height predictions for the dataset. Under convective conditions, the shape of the mixed layer height prediction curves closely resembled the observed shapes. Under conditions when significant wind shear was present, the shape of the height prediction curve departed from the data suggesting deficiencies in the parameterization of shear production. Development of small cumulus clouds on top of the layer is shown to affect mixed layer depths in the afternoon growth phase.

  5. Nematode model systems in evolution and development.

    PubMed

    Sommer, Ralf J; Bumbarger, Daniel J

    2012-01-01

    The free-living nematode Caenorhabditis elegans is one of the most important model organisms in all areas of modern biology. Using the knowledge about C. elegans as a baseline, nematodes are now intensively studied in evolution and development. Evolutionary developmental biology or for short, 'evo-devo' has been developed as a new research discipline during the last two decades to investigate how changes in developmental processes and mechanisms result in the modification of morphological structures and phenotypic novelty. In this article, we review the concepts that make nematode evo-devo a successful approach to evolutionary biology. We introduce selected model systems for nematode evo-devo and provide a detailed discussion of four selected case studies. The most striking finding of nematode evo-devo is the magnitude of developmental variation in the context of a conserved body plan. Detailed investigation of early embryogenesis, gonad formation, vulva development, and sex determination revealed that molecular mechanisms evolve rapidly, often in the context of a conserved body plan. These studies highlight the importance of developmental systems drift and neutrality in evolution. PMID:23801489

  6. Modeling the Evolution of Incised Streams: III. Model Application

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Incision and ensuing widening of alluvial stream channels is widespread in the midsouth and midwestern United States and represents an important form of channel adjustment. Two accompanying papers have presented a robust computational model for simulating the long-term evolution of incised and resto...

  7. Modeling of the internal solibore evolution

    NASA Astrophysics Data System (ADS)

    Talipova, Tatiana; Kurkina, Oxana; Naumov, Aleksandr; Kurkin, Andrey

    2016-04-01

    Numerical modeling of dispersive shock waves called solibore in a stratified fluid is conducted. The theoretical model is based on the extended version of the Korteweg-de Vries equation which takes into account the effects of cubic nonlinearity, dissipation in near-bottom turbulent layer and Earth rotation. This model is now very popular in the physical oceanography. Initial conditions for simulations correspond to the real internal waves of shock-like shape in the Pechora Sea (south-eastern part of Barents Sea), the Arctic observed in 1998. The density stratification of this area is not well known and we study the sensitivity of our numerical results to density profile approximation. It is shown that although the wave kinematic parameters are sensitive for these factors nevertheless a sharp drop (like kink in the soliton theory) in the depth of the thermocline is conserved at a distance of one-three kilometers, and then it is transformed into dispersive shock waves (solibore).

  8. Genealogies in simple models of evolution

    NASA Astrophysics Data System (ADS)

    Brunet, Éric; Derrida, Bernard

    2013-01-01

    We review the statistical properties of the genealogies of a few models of evolution. In the asexual case, selection leads to coalescence times which grow logarithmically with the size of the population, in contrast with the linear growth of the neutral case. Moreover for a whole class of models, the statistics of the genealogies are those of the Bolthausen-Sznitman coalescent rather than the Kingman coalescent in the neutral case. For sexual reproduction in the neutral case, the time to reach the first common ancestors for the whole population and the time for all individuals to have all their ancestors in common are also logarithmic in the population size, as predicted by Chang in 1999. We discuss how these times are modified by introducing selection in a simple way.

  9. Mathematical Model of Evolution of Brain Parcellation.

    PubMed

    Ferrante, Daniel D; Wei, Yi; Koulakov, Alexei A

    2016-01-01

    We study the distribution of brain and cortical area sizes [parcellation units (PUs)] obtained for three species: mouse, macaque, and human. We find that the distribution of PU sizes is close to lognormal. We propose the mathematical model of evolution of brain parcellation based on iterative fragmentation and specialization. In this model, each existing PU has a probability to be split that depends on PU size only. This model suggests that the same evolutionary process may have led to brain parcellation in these three species. Within our model, region-to-region (macro) connectivity is given by the outer product form. We show that most experimental data on non-zero macaque cortex macroscopic-level connections can be explained by the outer product power-law form suggested by our model (62% for area V1). We propose a multiplicative Hebbian learning rule for the macroconnectome that could yield the correct scaling of connection strengths between areas. We thus propose an evolutionary model that may have contributed to both brain parcellation and mesoscopic level connectivity in mammals. PMID:27378859

  10. Mathematical Model of Evolution of Brain Parcellation

    PubMed Central

    Ferrante, Daniel D.; Wei, Yi; Koulakov, Alexei A.

    2016-01-01

    We study the distribution of brain and cortical area sizes [parcellation units (PUs)] obtained for three species: mouse, macaque, and human. We find that the distribution of PU sizes is close to lognormal. We propose the mathematical model of evolution of brain parcellation based on iterative fragmentation and specialization. In this model, each existing PU has a probability to be split that depends on PU size only. This model suggests that the same evolutionary process may have led to brain parcellation in these three species. Within our model, region-to-region (macro) connectivity is given by the outer product form. We show that most experimental data on non-zero macaque cortex macroscopic-level connections can be explained by the outer product power-law form suggested by our model (62% for area V1). We propose a multiplicative Hebbian learning rule for the macroconnectome that could yield the correct scaling of connection strengths between areas. We thus propose an evolutionary model that may have contributed to both brain parcellation and mesoscopic level connectivity in mammals. PMID:27378859

  11. Modeling postshock evolution of large electropores

    NASA Astrophysics Data System (ADS)

    Neu, John C.; Krassowska, Wanda

    2003-02-01

    The Smoluchowski equation (SE), which describes the evolution of pores created by electric shocks, cannot be applied to modeling large and long-lived pores for two reasons: (1) it does not predict pores of radius above 20 nm without also predicting membrane rupture; (2) it does not predict postshock growth of pores. This study proposes a model in which pores are coupled by membrane tension, resulting in a nonlinear generalization of SE. The predictions of the model are explored using examples of homogeneous (all pore radii r are equal) and heterogeneous (0⩽r⩽rmax) distributions of pores. Pores in a homogeneous population either shrink to zero or assume a stable radius corresponding to the minimum of the bilayer energy. For a heterogeneous population, such a stable radius does not exist. All pores, except rmax, shrink to zero and rmax grows to infinity. However, the unbounded growth of rmax is not physical because the number of pores per cell decreases in time and the continuum model loses validity. When the continuum formulation is replaced by the discrete one, the model predicts the coarsening process: all pores, except rmax, shrink to zero and rmax assumes a stable radius. Thus, the model with tension-coupled pores does not predict membrane rupture and the predicted postshock growth of pores is consistent with experimental evidence.

  12. Atmospheric Boundary Layer Height Evolution with Lidar in Buenos Aires from 2008 to 2011

    NASA Astrophysics Data System (ADS)

    Pawelko, Ezequiel Eduardo; Salvador, Jacobo Omar; Ristori, Pablo Roberto; Pallotta, Juan Vicente; Otero, Lidia Ana; Quel, Eduardo Jaime

    2016-06-01

    The analysis of the atmospheric boundary layer top height evolution is obtained from 2008 to 2011 in Buenos Aires using the multiwavelength lidar located at CEILAP (CITEDEF-CONICET) (34°33' S; 58°30' W; 17 m asl). Algorithms recognition based on covariance wavelet transform are applied to obtain seasonal statistics. This method is being evaluated for use in the Lidar Network in Argentina and it is being deployed in Patagonia region currently. The technique operates in real time in both low and high aerosol loads and with almost no human supervision.

  13. Evolution of resonant wave triads in three-dimensional boundary layers

    NASA Technical Reports Server (NTRS)

    El-Hady, Nabil M.

    1988-01-01

    An analysis is presented that examines the modulation of different instability modes satisfying the triad resonance condition in time and space in a three-dimensional boundary-layer flow. Detuning parameters are used for the wavenumbers and the frequencies. The nonparallelism of the mean flow is taken into account in the analysis. At the leading-edge region of an infinite swept wing, different resonant triads are investigated that are comprised of traveling crossflow, stationary crossflow, vertical vorticity, and Tollmien-Schlichting modes. The spatial evolution of the resonating triad components are studied.

  14. Evolution of crystal structure during the initial stages of ZnO atomic layer deposition

    DOE PAGESBeta

    Boichot, R.; Tian, L.; Richard, M. -I.; Crisci, A.; Chaker, A.; Cantelli, V.; Coindeau, S.; Lay, S.; Ouled, T.; Guichet, C.; et al

    2016-01-05

    In this study, a complementary suite of in situ synchrotron X-ray techniques is used to investigate both structural and chemical evolution during ZnO growth by atomic layer deposition. Focusing on the first 10 cycles of growth, we observe that the structure formed during the coalescence stage largely determines the overall microstructure of the film. Furthermore, by comparing ZnO growth on silicon with a native oxide with that on Al2O3(001), we find that even with lattice-mismatched substrates and low deposition temperatures, the crystalline texture of the films depend strongly on the nature of the interfacial bonds.

  15. Evolution of species from Darwin theory: A simple model

    NASA Astrophysics Data System (ADS)

    Moret, M. A.; Pereira, H. B. B.; Monteiro, S. L.; Galeão, A. C.

    2012-04-01

    Evolution of species is a complex phenomenon. Some theoretical models take into account evolution of species, like the Bak-Sneppen model that obtain punctuated equilibrium from self-organized criticality and the Penna model for biological aging that consists in a bit-string model subjected to aging, reproduction and death. In this work we propose a simple model to study different scenarios used to simulate the evolution of species. This model is based on Darwin's ideas of evolution. The present findings show that punctuated equilibria and stasis seem to be obtained directly from the mutation, selection of parents and the genetic crossover, and are very close to the fossil data analysis.

  16. On the evolution of centrifugal instabilities within curved incompressible mixing layers

    NASA Technical Reports Server (NTRS)

    Otto, S. R.; Jackson, T. L.; Hu, F. Q.

    1994-01-01

    It is known that certain configurations which possess curvature are prone to a class of instabilities which their 'flat' counterparts will not support. The main thrust of the study of these centrifugal instabilities has concentrated on curved solid boundaries and their effect on the fluid motion. In this article attention is shifted towards a fluid-fluid interface observed within a curved incompressible mixing layer. Experimental evidence is available to support the conjecture that this situation may be subjected to centrifugal instabilities. The evolution of modes with wavelengths comparable with the layer's thickness is considered and the high Taylor/Gortler number regime is also discussed which characterizes the ultimate fate of the modes.

  17. Modeling Co-evolution of Speech and Biology.

    PubMed

    de Boer, Bart

    2016-04-01

    Two computer simulations are investigated that model interaction of cultural evolution of language and biological evolution of adaptations to language. Both are agent-based models in which a population of agents imitates each other using realistic vowels. The agents evolve under selective pressure for good imitation. In one model, the evolution of the vocal tract is modeled; in the other, a cognitive mechanism for perceiving speech accurately is modeled. In both cases, biological adaptations to using and learning speech evolve, even though the system of speech sounds itself changes at a more rapid time scale than biological evolution. However, the fact that the available acoustic space is used maximally (a self-organized result of cultural evolution) is constant, and therefore biological evolution does have a stable target. This work shows that when cultural and biological traits are continuous, their co-evolution may lead to cognitive adaptations that are strong enough to detect empirically. PMID:26936622

  18. Past changes, current state and future evolution of the ozone layer

    NASA Astrophysics Data System (ADS)

    Godin-Beekmann, S.

    2013-05-01

    The ozone layer has been under scrutiny since the discovery of the ozone hole over Antarctica in the mid-eighties (Farman et al., 1985). The rapid disclosure of the main processes involved in polar ozone destruction lead to the signature of the Montreal Protocol that regulates the emission of ozone depleting substances (ODS). The objective of this presentation is to review the current understanding of past changes and current state of the ozone layer, the evolution of ODS concentration in the atmosphere and assess the projections of ozone recovery. Satellite measurements revealed a peak of ODS concentration in the mid and end of the nineties and ODS concentrations have started to decrease, albeit at a slower pace than during the increase period due to the atmospheric lifetimes of these compounds. The total ozone content has stabilized at global scale since the beginning of the 21st century. In 2009, integrated ozone content was about 3.5 % smaller in the 60°S-60°N region compared to values prior to 1980 (WMO, 2011). Climate change will influence the recovery of stratospheric. Both ozone depletion and increase of carbon dioxide induce a cooling of the stratosphere. In the winter polar stratosphere, this cooling enhances the formation of polar stratospheric clouds involved in the formation of the ozone hole. In the high stratosphere, it slows the chemical reactions destroying ozone and accelerates its reformation (WMO, 2011). Besides, most chemistry-climate models predict an acceleration of the stratospheric meridional circulation, which would speed up the ozone recovery (Eyring et al., 2010). This recovery is forecasted in periods ranging between 2015 and 2030 and between 2030 and 2040 in the northern and southern hemispheres, respectively. The Antarctic ozone hole will not disappear before 2050. Because of the acceleration of the meridional circulation, models simulate a super-recovery of ozone in the high latitude regions and an under recovery in the tropics. At

  19. Characteristic modes and evolution processes of shear-layer vortices in an elevated transverse jet

    NASA Astrophysics Data System (ADS)

    Huang, Rong F.; Lan, Jen

    2005-03-01

    Characteristics and evolution processes of the traveling coherent flow structure in the shear layer of an elevated round jet in crossflow are studied experimentally in an open-loop wind tunnel. Streak pictures of the smoke flow patterns illuminated by the laser-light sheet in the median and horizontal planes are recorded with a high speed digital camera. Time histories of the instantaneous velocity of the vortical flows in the shear layer are digitized by a hot-wire anemometer through a high-speed data acquisition system. By analyzing the streak pictures of the smoke flow visualization, five characteristic flow structures, mixing-layer type vortices, backward-rolling vortices, forward-rolling vortices, swing-induced mushroom vortices, and jet-type vortices, are identified in the shear layer evolving from the up-wind edge of the jet exit. The behaviors and mechanisms of the vortical flow structure in the bent shear layer are prominently distinct in different flow regimes. The frequency characteristics, Strouhal number, power-spectrum density functions, autocorrelation coefficient, as well as the time and length scales of the coherent structure and the Lagrangian integral scales are obtained by processing the measured instantaneous velocity data. The Strouhal number is found to decay exponentially with the increase of the jet-to-crossflow momentum flux ratio. The autocorrelation coefficients provide the information for calculating the statistical time scales of the coherent structure and the integral time scales of turbulence fluctuations. The corresponding length scales of the vortical structure and the integral length scales of turbulence in the shear layer are therefore obtained and discussed.

  20. LIDAR OBSERVATIONS OF MIXED LAYER DYNAMICS: TESTS OF PARAMETERIZED ENTRAINMENT MODELS OF MIXED LAYER GROWTH RATE

    EPA Science Inventory

    Lidar measurements of the atmospheric boundary layer height, the entrainment zone, wind speed and direction, ancillary temperature profiles and surface flux data were used to test current parameterized entrainment models of mixed layer growth rate. Six case studies under clear ai...

  1. Gpgpu Accelerated Landscape-Evolution Modelling

    NASA Astrophysics Data System (ADS)

    Maddy, D.; McGough, A. S.; Wainwright, J.; Trueman, A.

    2011-12-01

    Existing Landscape-Evolution Models (LEMs) have tended to be applied at relatively coarse spatial resolution and over comparatively short timescales (years-centuries). Extending these models to encompass landscape evolution at the scale of, for example, an entire river basin and over important landscape-forming timescales (i.e. tens of thousands of years) is computationally challenging. In order to address this challenge we are currently reformulating and extending an existing LEM, CybErosion, in order to create a new, highly optimised model, called CUDAscape. CUDAscape is being coded for parallel processing in order to exploit CUDA (Compute Unified Device Architecture), the parallel programming architecture developed by NVIDIA. CybErosion, a cellular erosion model written in C++, implements erosion, sediment transport and deposition processes at individual cell level, with each cell storing the cumulative changes in cell value (height) over the duration of the model run. Using a 5,000 cell DEM, and a simulated annual time step over 800k years, the original CybErosion code has an execution time of approximately 22 hours on an Intel 980X hexacore processor. Sequential code optimization has reduced this to ~4.5 hours but to achieve the modelling of grids comprising millions of cells requires orders of magnitude improvements in performance, an objective unlikely to be reached via advances in conventional CPU architectures within the foreseeable future. In this paper we will present our initial results for the CUDA implementation of a number of key methods including sink filling, flat routing, flow direction (D8, steepest descent) and flow accumulation (kernels that potentially have widespread application in a whole range of Earth System Models), the key bottlenecks in the current generation of LEMs (taking >75% of the execution time of the sequential execution of CybErosion). Using a single NVIDIA Tesla C2050 GPGPU we have seen speedup in excess of x100 on both flow

  2. Automata network models of galaxy evolution

    NASA Technical Reports Server (NTRS)

    Chappell, David; Scalo, John

    1993-01-01

    Two ideas appear frequently in theories of star formation and galaxy evolution: (1) star formation is nonlocally excitatory, stimulating star formation in neighboring regions by propagation of a dense fragmenting shell or the compression of preexisting clouds; and (2) star formation is nonlocally inhibitory, making H2 regions and explosions which can create low-density and/or high temperature regions and increase the macroscopic velocity dispersion of the cloudy gas. Since it is not possible, given the present state of hydrodynamic modeling, to estimate whether one of these effects greatly dominates the other, it is of interest to investigate the predicted spatial pattern of star formation and its temporal behavior in simple models which incorporate both effects in a controlled manner. The present work presents preliminary results of such a study which is based on lattice galaxy models with various types of nonlocal inhibitory and excitatory couplings of the local SFR to the gas density, temperature, and velocity field meant to model a number of theoretical suggestions.

  3. Modelling the Evolution of Dark Matter Subhaloes

    NASA Astrophysics Data System (ADS)

    Gan, J. L.

    2012-01-01

    In the popular cold dark matter (CDM) model, the structure is formed during the collapse of dark matter due to gravitational instability,and the virial structure is seen as dark matter halo. The baryonic gases condense in the radiative cooling, fall into the halo, and finally form a galaxy. The halo formation is processed in a hierarchical manner that small haloes form first, and they subsequently merge to form bigger haloes. After the merger, the small haloes survive as self-bound entities and become the substructures (subhaloes) of the bigger halo (host halo). The galaxy in the subhalo is the satellite galaxy of the central galaxy formed in the host halo. The satellite galaxies usually have low masses and luminosities, and are observed as dwarf galaxies. When the subhalo falls into the host halo, it will merge with the host halo center due to dynamical friction. The time interval needed for the merger is called the dynamical friction timescale Tdf. The dynamical evolution model for subhalo includes some important physical processes such as the dynamical friction, tidal mass stripping, tidal heating and tidal disruption.We find that the Tdf depends strongly on the efficiency of tidal stripping. The Tdf increases with the increasing tidal strippingefficiency, and this is the main reason for the discrepancies among the previous results. We also find that the dependence of Tdf on orbital circularity is determined by the merging samples, in which the distribution of mass ratio between the subhalo and host halo is crucial. With respect to the late stage of subhalo evolution, we find that the tidal mass stripping is only efficient in the early stage, but this effect can be ignored in the late evolution. The Coulomb logarithm in the dynamical friction has not been well stated. By comparing the predicted Tdf with simulation, we give a fitting formula of Coulomb logarithm. Combining the dynamical model with the halo formation histories (merger trees) predicted by the

  4. Io - Thermal models and chemical evolution

    NASA Technical Reports Server (NTRS)

    Consolmagno, G. J.

    1981-01-01

    A combined thermal and chemical evolution model of Io is presented, outlining limits on the possible starting materials, heating history, chemical history, and present state of Io. Our best scenario starts with Io being accreted from material in a proto-Jovian nebula which condensed between 400-600 K. Radionuclides and tidal heating would lead to large-scale convection within Io and chemical reactions leading to the outgassing of water and methane. Reactions between Fe(0)-FeS and water, at least near the surface, go to completion, resulting in all Fe being oxidized with elemental sulfur producing a low-conductivity crust. In the deep interior, these reactions may not completely exhaust Fe metal, and an FeS-rich core may be formed.

  5. Models of Protocellular Structure, Function and Evolution

    NASA Technical Reports Server (NTRS)

    New, Michael H.; Pohorille, Andrew; Szostak, Jack W.; Keefe, Tony; Lanyi, Janos K.; DeVincenzi, Donald L. (Technical Monitor)

    2001-01-01

    In the absence of any record of protocells, the most direct way to test our understanding, of the origin of cellular life is to construct laboratory models that capture important features of protocellular systems. Such efforts are currently underway in a collaborative project between NASA-Ames, Harvard Medical School and University of California. They are accompanied by computational studies aimed at explaining self-organization of simple molecules into ordered structures. The centerpiece of this project is a method for the in vitro evolution of protein enzymes toward arbitrary catalytic targets. A similar approach has already been developed for nucleic acids in which a small number of functional molecules are selected from a large, random population of candidates. The selected molecules are next vastly multiplied using the polymerase chain reaction.

  6. Cinematic modeling of local morphostructures evolution

    NASA Astrophysics Data System (ADS)

    Bronguleev, Vadim

    2013-04-01

    With the use of a simple 3-dimensional cinematic model of slope development some characteristic features of morphostructure evolution were shown. We assume that the velocity of slope degradation along normal vector to a surface is determined by three morphological parameters: slope angle, its profile curvature and its plan curvature. This leads to the equation of parabolic type: where h=h(x,y,t) is the altitude of slope surface, Kpr(x,y,t)is the profile curvature of the slope, Kpl(x,y,t) is the plan curvature, f(x,y,t) is the velocity of tectonic deformation (or base level movement), A, B, and C are the coefficients which may depend on coordinates and time. The first term in the right part of the equation describes parallel slope retreat, typical to arid environment, the second term describes slope vertical grading due to viscous flow, typical to humid conditions, and the third term is responsible for slope plan grading due to such processes as desquamation, frost weathering, etc. This simple model describes a wide range of local morphostructures evolution: stepped slopes and piedmont benchlands, lithogenic forms - terraces and passages, flattened summits and rounded hills. Using different types of the function f (block rise, swell, tilt), we obtained interesting reformations of initial tectonic landforms during the concurrent action of denudation processes. The result of such action differs from that of the successive action of tectonic movements and denudation. The relation of rates of the endogenous and exogenous processes strongly affects the formation of local morphostructures. Preservation of initial features of slope such as steps or bends as well as their formation due to tectonics or lithology is possible if coefficients B and Care small in comparison toA.

  7. A 'Turing' Test for Landscape Evolution Models

    NASA Astrophysics Data System (ADS)

    Parsons, A. J.; Wise, S. M.; Wainwright, J.; Swift, D. A.

    2008-12-01

    Resolving the interactions among tectonics, climate and surface processes at long timescales has benefited from the development of computer models of landscape evolution. However, testing these Landscape Evolution Models (LEMs) has been piecemeal and partial. We argue that a more systematic approach is required. What is needed is a test that will establish how 'realistic' an LEM is and thus the extent to which its predictions may be trusted. We propose a test based upon the Turing Test of artificial intelligence as a way forward. In 1950 Alan Turing posed the question of whether a machine could think. Rather than attempt to address the question directly he proposed a test in which an interrogator asked questions of a person and a machine, with no means of telling which was which. If the machine's answer could not be distinguished from those of the human, the machine could be said to demonstrate artificial intelligence. By analogy, if an LEM cannot be distinguished from a real landscape it can be deemed to be realistic. The Turing test of intelligence is a test of the way in which a computer behaves. The analogy in the case of an LEM is that it should show realistic behaviour in terms of form and process, both at a given moment in time (punctual) and in the way both form and process evolve over time (dynamic). For some of these behaviours, tests already exist. For example there are numerous morphometric tests of punctual form and measurements of punctual process. The test discussed in this paper provides new ways of assessing dynamic behaviour of an LEM over realistically long timescales. However challenges remain in developing an appropriate suite of challenging tests, in applying these tests to current LEMs and in developing LEMs that pass them.

  8. Friction phenomena in the overdamped three-layer model

    NASA Astrophysics Data System (ADS)

    Jia, Li-Ping; Tekić, Jasmina; Yang, Yang; Wang, Cang-Long; Duan, Wen-Shan; Yang, Lei

    2015-02-01

    An overdamped three-layer model consisting of two harmonic chains of interacting particles, representing the upper and the middle layers, which move over the substrate potential, is studied in the present paper. A dc +ac force is applied only on the upper harmonic chain, and dynamics of both layers are investigated. The results show that the dynamical mode locking and Shapiro steps appear not only in the upper layer but also in the middle one. It is noted that the motion of particles in the upper layer corresponds to the standard Frenkel-Kontorova model. The dependence of the Shapiro steps of the middle layer on the system parameters are determined. It is shown that the height of the first Shapiro step of the upper layer is unrelated to the interaction parameters of the particles of both the upper and the middle layers, while the height of the first Shapiro step of the middle layer depend only on the interaction parameters of the particles of the middle layers. Two critical forces which transfer from locked state to the sliding one of both the upper and the middle layers are also studied. They depend on the amplitude and the frequency of the external ac driving force.

  9. Linear and nonlinear evolution and diffusion layer selection in electrokinetic instability

    NASA Astrophysics Data System (ADS)

    Demekhin, E. A.; Shelistov, V. S.; Polyanskikh, S. V.

    2011-09-01

    In the present work, four nontrivial stages of electrokinetic instability are identified by direct numerical simulation (DNS) of the full Nernst-Planck-Poisson-Stokes system: (i) a stage of the influence of the initial conditions (milliseconds); (ii) one-dimensional (1D) self-similar evolution (milliseconds-seconds); (iii) a primary instability of the self-similar solution (seconds); (iv) a nonlinear stage with secondary instabilities. The self-similar character of evolution at moderately large times is confirmed. Rubinstein and Zaltzman instability and noise-driven nonlinear evolution toward overlimiting regimes in ion-exchange membranes are numerically simulated and compared with theoretical and experimental predictions. The primary instability which happens during this stage is found to arrest a self-similar growth of the diffusion layer. It also specifies its characteristic length as was first experimentally predicted by Yossifon and Chang [G. Yossifon and H.-C. Chang, Phys. Rev. Lett.10.1103/PhysRevLett.101.254501 101, 254501 (2008)]. A novel principle for the characteristic wave-number selection from the broadband initial noise is established.

  10. A new automatic Planetary Boundary Layers height detection and diurnal evolution with compact EZ Lidar

    NASA Astrophysics Data System (ADS)

    Loaec, S.; Boquet, M.,; Sauvage, L.; Lolli, S.; Rouget, V.

    2009-04-01

    Bigger strongly urbanized cities in the world are often exposed to atmospheric pollution events. To understand the chemical and physical processes that are taking place in these areas it is necessary to describe correctly the Planetary Boundary Layer (PBL) dynamics and the PBL height evolution. For these proposals, a compact and rugged eye safe UV Lidar, the EZLIDAR™, was developed together by CEA/LMD and LEOSPHERE (France) to study and investigate structural and optical properties of clouds and aerosols and PBL time evolution. EZLIDAR™ has been validated by different remote and in-situ instruments as MPL Type-4 Lidar manufactured by NASA at ARM/SGP site or the LNA (Lidar Nuage Aerosol) at the Laboratoire de Metereologie Dynamique LMD (France) and during several intercomparison campaigns. EZLIDAR™ algorithm retrieves automatically the PBL height in real-time. The method is based on the detection of the slope of the signal linked to a sharp change in concentration of the aerosols. Once detected, the different layers are filtered on a 15mn sample and classified between nocturnal, convective or residual layer, depending on the time and date. This method has been validated against those retrieved by the algorithm STRAT from data acquired at IPSL, France, showing 95% of correlation. In this paper are presented the results of the intercomparison campaign that took place in Orleans, France in the framework of ICOS (Integrated Carbon Observation System) project, where the EZ Lidar™ worked under all weather conditions, clear sky, fog, low clouds, during the whole month of October 2008. Moreover, thanks to its 3D scanning capability, the EZLIDAR was able to provide the variability of the PBL height around the site, enabling the scientists to estimate the flux intensities that play a key role in the radiative transfer budget and in the atmospheric pollutants dispersion.

  11. Kinematically consistent models of viscoelastic stress evolution

    NASA Astrophysics Data System (ADS)

    DeVries, Phoebe M. R.; Meade, Brendan J.

    2016-05-01

    Following large earthquakes, coseismic stresses at the base of the seismogenic zone may induce rapid viscoelastic deformation in the lower crust and upper mantle. As stresses diffuse away from the primary slip surface in these lower layers, the magnitudes of stress at distant locations (>1 fault length away) may slowly increase. This stress relaxation process has been used to explain delayed earthquake triggering sequences like the 1992 Mw = 7.3 Landers and 1999 Mw = 7.1 Hector Mine earthquakes in California. However, a conceptual difficulty associated with these models is that the magnitudes of stresses asymptote to constant values over long time scales. This effect introduces persistent perturbations to the total stress field over many earthquake cycles. Here we present a kinematically consistent viscoelastic stress transfer model where the total perturbation to the stress field at the end of the earthquake cycle is zero everywhere. With kinematically consistent models, hypotheses about the potential likelihood of viscoelastically triggered earthquakes may be based on the timing of stress maxima, rather than on any arbitrary or empirically constrained stress thresholds. Based on these models, we infer that earthquakes triggered by viscoelastic earthquake cycle effects may be most likely to occur during the first 50% of the earthquake cycle regardless of the assumed long-term and transient viscosities.

  12. Modeling of electrochemical double layers in thermodynamic non-equilibrium.

    PubMed

    Dreyer, Wolfgang; Guhlke, Clemens; Müller, Rüdiger

    2015-10-28

    We consider the contact between an electrolyte and a solid electrode. At first we formulate a thermodynamic consistent model that resolves boundary layers at interfaces. The model includes charge transport, diffusion, chemical reactions, viscosity, elasticity and polarization under isothermal conditions. There is a coupling between these phenomena that particularly involves the local pressure in the electrolyte. Therefore the momentum balance is of major importance for the correct description of the boundary layers. The width of the boundary layers is typically very small compared to the macroscopic dimensions of the system. In the second step we thus apply the method of asymptotic analysis to derive a simpler reduced bulk model that already incorporates the electrochemical properties of the double layers into a set of new boundary conditions. With the reduced model, we analyze the double layer capacitance for a metal-electrolyte interface. PMID:26415592

  13. Construction and Magmatic Evolution of a Vertically Layered Mid-Crustal Gabbroic Complex (Punta Falcone, Sardinia)

    NASA Astrophysics Data System (ADS)

    Hauser, A. C.; Bussy, F.

    2014-12-01

    The granite-hosted mid-crustal complex of Punta Falcone consists of transitional tholeiitic to calc-alkaline high-Al gabbros. Its pervasive vertical structure is the result of injection of at least 6 distinct pulses forming 10 to 60m wide individual cooling units. The complex was built symmetrically by injection of each new pulse in the centre of the system. Contacts between the units are well-defined and present slight chilled margins speaking against a continuous magma flux which would have had a marked thermal impact on the adjacent units. All units have a common magma source (radiogenic isotopes), but show differences as the system evolves. An80-90 plg is the liquidus phase in all units and crystallized in the source region. In the early units it is followed by sub-/euhedral amph of mm-size with a wide range of compositions dominated by the edenite-type substitution, evidencing relatively fast, isobaric cooling at emplacement level. The later units accumulated high-An plg and fractionated Fe-Ti oxides before ascent as indicated by whole-rock chemistry. After emplacement and due to the thermal maturation of the system, they isobarically crystallized big, cm-sized oikocrysts of px enclosing high-An plg, closely followed by amph with the same texture. This led to an An-content jump in the subsequently crystallizing plg rims, whose absence in the mafic phases indicates a strong crystallinity increase over a small T interval. The geometry, size, number of pulses and emplacement chronology of the complex yield constraints on the thermal evolution of the system. Numerical modelling shows that the periodic injection of magma and the latent heat of crystallization of px and amph maintained the latest pulse at high T for several hundreds of years. This induced a slow and regular inward migration of the crystallization front on both sides of the central unit, which allowed the development of a spectacular vertical, cm-scale, rhythmic magmatic layering.

  14. Biological models for Mesozoic reef evolution

    SciTech Connect

    Kauffman, E.G. )

    1990-11-01

    Throughout the Mesozoic, shallow-water carbonate ramps and platforms of the circumequatorial Tethyan Ocean were characterized by extensive development of reef ecosystems, especially during times of eustatic highstand, expansion of the Tropics, and warm equable global climates. The greatest reef development was north of the paleoequator in the Caribbean and Indo-Mediterranean provinces. These reefs and associated debris facies comprise major petroleum reservoirs, in some cases with remarkable porosity and permeability normally attributed to a combination of sedimentologic, tectonic, and diagenetic factors. The biological evolution of Mesozoic reefs also has had an important, and in some cases dominant, role in determining reservoir quality. Three major biological factors are critical to mesozoic reef-associated reservoir development: (1) the replacement/competitive displacement of coral-algal dominated, highly integrated reef ecosystems by loosely packed rudistid bivalve-dominated reef ecosystems in the Barremian-Albian; (2) the evolution of dominantly aragonitic, highly porous shells among framework-building rudistids in the middle and Late Cretaceous; and (3) competitive strategies among rudistids that effectively prevented widespread biological binding of Cretaceous reefs, leading to the production of large marginal fans that comprise major carbonate reservoirs. Detailed studies of these evolutionary trends in reef/framework development and of the distribution of different groups of bioconstructors on reefs lead to predictive modeling for primary and secondary porosity development in mesozoic carbonate reservoirs. The competitive displacement of coral-algal communities by rudistids on Cretaceous reefs was so effective that, even after Maastrichtian mass extinction of rudistids and other important groups comprising Mesozoic reef/carbonate platform ecosystems, coral-algal reef-building communities did not evolve again until the late Eocene.

  15. Hierarchical construction of an ultrathin layered double hydroxide nanoarray for highly-efficient oxygen evolution reaction

    NASA Astrophysics Data System (ADS)

    Yang, Qiu; Li, Tian; Lu, Zhiyi; Sun, Xiaoming; Liu, Junfeng

    2014-09-01

    Efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) are essential components of renewable energy technologies, such as solar fuel synthesis and water splitting processes for powering fuel cells. Here, ultrathin NiCoFe layered double hydroxide (LDH) nanoplates, which directly grow on a cobalt-based nanowire array, forming a hierarchical nanoarray structure, are constructed as efficient oxygen evolution electrodes. In alkaline media, the ordered ultrathin hierarchical LDH nanoarray electrode shows dramatically increased catalytic activity compared to that of LDH nanoparticles and pure nanowire arrays due to the small size, large surface area, and high porosity of the NiCoFe LDH nanoarray. Only a small water oxidation overpotential (η) of 257 mV is needed for a current density of 80 mA cm-2 with a Tafel slope of 53 mV per decade. The hierarchical LDH nanoarray also shows excellent structural stability in alkaline media. After continuous testing under a high OER current density (~300 mA cm-2) for 10 h, the sample maintains the ordered hierarchical structure with no significant deactivation of the catalytic properties.Efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) are essential components of renewable energy technologies, such as solar fuel synthesis and water splitting processes for powering fuel cells. Here, ultrathin NiCoFe layered double hydroxide (LDH) nanoplates, which directly grow on a cobalt-based nanowire array, forming a hierarchical nanoarray structure, are constructed as efficient oxygen evolution electrodes. In alkaline media, the ordered ultrathin hierarchical LDH nanoarray electrode shows dramatically increased catalytic activity compared to that of LDH nanoparticles and pure nanowire arrays due to the small size, large surface area, and high porosity of the NiCoFe LDH nanoarray. Only a small water oxidation overpotential (η) of 257 mV is needed for a current density of 80 mA cm-2 with a

  16. ON AERODYNAMIC AND BOUNDARY LAYER RESISTANCES WITHIN DRY DEPOSITION MODELS

    EPA Science Inventory

    There have been many empirical parameterizations for the aerodynamic and boundary layer resistances proposed in the literature, e.g. those of the Meyers Multi-Layer Deposition Model (MLM) used with the nation-wide dry deposition network. Many include arbitrary constants or par...

  17. The three-dimensional evolution of a plane mixing layer - Pairing and transition to turbulence

    NASA Technical Reports Server (NTRS)

    Moser, Robert D.; Rogers, Michael M.

    1993-01-01

    The evolution of three-dimensional temporally evolving plane mixing layers through as many as three pairings has been simulated numerically. All simulations were begun from a few low-wavenumber disturbances, usually derived from linear stability theory, in addition to the mean velocity. Three-dimensional perturbations were used with amplitudes ranging from infinitesimal to large enough to trigger a rapid transition to turbulence. Pairing is found to inhibit the growth of infinitesimal three-dimensional disturbances, and to trigger the transition to turbulence in highly three-dimensional flows. The mechanisms responsible for the growth of three-dimensionality and onset of transition to turbulence are described. The transition to turbulence is accompanied by the formation of thin sheets of spanwise vorticity, which undergo secondary rollups. The post-transitional simulated flow fields exhibit many properties characteristic of turbulent flows.

  18. Discrete layers of interacting growing protein seeds: convective and morphological stages of evolution.

    PubMed

    Lappa, Marcello

    2005-03-01

    The growth of several macromolecular seeds uniformly distributed on the bottom of a protein reactor (i.e., a discrete layer of N crystals embedded within a horizontal layer of liquid with no-slip boundaries) under microgravity conditions is investigated for different values of N and for two values of the geometrical aspect ratio of the container. The fluid dynamics of the growth reactor and the morphological (shape-change) evolution of the crystals are analyzed by means of a recently developed moving boundary method based on differential equations coming from the protein "surface incorporation kinetics." The face growth rates are found to depend on the complex multicellular structure of the convective field and on associated "pluming phenomena." This correspondence is indirect evidence of the fact that mass transport in the bulk and surface attachment kinetics are competitive as rate-limiting steps for growth. Significant adjustments in the roll pattern take place as time passes. The convective field undergoes an interesting sequence of transitions to different values of the mode and to different numbers of rising solutal jets. The structure of the velocity field and the solutal effects, in turn, exhibit sensitivity to the number of interacting crystals if this number is small. In the opposite case, a certain degree of periodicity can be highlighted for a core zone not affected by edge effects. The results with no-slip lateral walls are compared with those for periodic boundary conditions to assess the role played by geometrical constraints in determining edge effects and the wavelength selection process. The numerical method provides "microscopic" and "morphological" details as well as general rules and trends about the macroscopic evolution (i.e., "ensemble behaviors") of the system. PMID:15903456

  19. Digital morphology: modelling anatomy and evolution.

    PubMed

    Bruner, Emiliano; Bastir, Markus

    2008-01-01

    The morphology and anatomy of a biological structure can be seen as a structural and functional system, the final results of evolutionary pressures and stochastic processes related to the actual physical and physiological environment of its components. The current imaging techniques (digital anthropology) and the multivariate approaches to the study of geometric covariation (geometric morphometrics) provide a quantitative exploration of the extant and extinct human variability. Such tools allow the recognition of morphological relationships within anatomical systems, and their variation within phylogenetic processes. We apply these techniques and principles to the study of the cranial variability and integration, mostly within the framework of the evolution of the human genus. The craniofacial system is investigated in terms of modules and spatial relationships, along ontogenetic and phylogenetic trajectories. The reciprocal influences between the splanchnocranial, basicranial, and neurocranial components, as well as those between the hard (bones) and soft (brain, connectives, muscles) tissues are modelled using geometrical analyses and multivariate ordination methods, trying to localise adaptations and constraints. The main target is a dynamic and visualisation-based interpretation of the evolutionary changes, not grounded on the variation of single traits but on the covariation of the whole system. PMID:19934466

  20. Models of protocellular structures, functions and evolution

    NASA Technical Reports Server (NTRS)

    Pohorille, Andrew; New, Michael H.; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    The central step in the origin of life was the emergence of organized structures from organic molecules available on the early earth. These predecessors to modern cells, called 'proto-cells,' were simple, membrane bounded structures able to maintain themselves, grow, divide, and evolve. Since there is no fossil record of these earliest of life forms, it is a scientific challenge to discover plausible mechanisms for how these entities formed and functioned. To meet this challenge, it is essential to create laboratory models of protocells that capture the main attributes associated with living systems, while remaining consistent with known, or inferred, protobiological conditions. This report provides an overview of a project which has focused on protocellular metabolism and the coupling of metabolism to energy transduction. We have assumed that the emergence of systems endowed with genomes and capable of Darwinian evolution was preceded by a pre-genomic phase, in which protocells functioned and evolved using mostly proteins, without self-replicating nucleic acids such as RNA.

  1. Models of Protocellular Structure, Function and Evolution

    NASA Technical Reports Server (NTRS)

    New, Michael H.; Pohorille, Andrew; Szostak, Jack W.; Keefe, Tony; Lanyi, Janos K.

    2001-01-01

    In the absence of any record of protocells, the most direct way to test our understanding of the origin of cellular life is to construct laboratory models that capture important features of protocellular systems. Such efforts are currently underway in a collaborative project between NASA-Ames, Harvard Medical School and University of California. They are accompanied by computational studies aimed at explaining self-organization of simple molecules into ordered structures. The centerpiece of this project is a method for the in vitro evolution of protein enzymes toward arbitrary catalytic targets. A similar approach has already been developed for nucleic acids in which a small number of functional molecules are selected from a large, random population of candidates. The selected molecules are next vastly multiplied using the polymerase chain reaction. A mutagenic approach, in which the sequences of selected molecules are randomly altered, can yield further improvements in performance or alterations of specificities. Unfortunately, the catalytic potential of nucleic acids is rather limited. Proteins are more catalytically capable but cannot be directly amplified. In the new technique, this problem is circumvented by covalently linking each protein of the initial, diverse, pool to the RNA sequence that codes for it. Then, selection is performed on the proteins, but the nucleic acids are replicated. Additional information is contained in the original extended abstract.

  2. Weakly nonlinear models for turbulent mixing in a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Liou, William W.; Morris, Philip J.

    1992-01-01

    New closure models for turbulent free shear flows are presented in this paper. They are based on a weakly nonlinear theory with a description of the dominant large-scale structures as instability waves. Two models are presented that describe the evolution of the free shear flows in terms of the time-averaged mean flow and the dominant large-scale turbulent structure. The local characteristics of the large-scale motions are described using linear theory. Their amplitude is determined from an energy integral analysis. The models have been applied to the study of an incompressible mixing layer. For both models, predictions of the mean flow developed are made. In the second model, predictions of the time-dependent motion of the large-scale structures in the mixing layer are made. The predictions show good agreement with experimental observations.

  3. Modeling rocky coastline evolution and equilibrium

    NASA Astrophysics Data System (ADS)

    Limber, P. W.; Murray, A. B.

    2010-12-01

    Many of the world’s rocky coastlines exhibit planform roughness in the form of alternating headlands and embayments. Along cliffed coasts, it is often assumed that headlands consist of rock that is more resistant to wave attack than in neighboring bays, because of either structural or lithologic variations. Bays would then retreat landward faster than headlands, creating the undulating planform profiles characteristic of a rocky coastal landscape. While the interplay between alongshore rock strength and nearshore wave energy is, in some circumstances, a fundamental control on coastline shape, beach sediment is also important. Laboratory experiments and field observations have shown that beach sediment, in small volumes, can act as an abrasive tool to encourage sea cliff retreat. In large volumes, though, sediment discourages wave attack on the cliff face, acting as a protective barrier. This nonlinearity suggests a means for headland persistence, even without alongshore variations in rock strength: bare-rock headlands could retreat more slowly than, or at the same rate as, neighboring sediment-filled embayments because of alongshore variations in the availability of beach sediment. Accordingly, nearshore sediment dynamics (i.e. sediment production from sea cliff retreat and alongshore sediment transport) could promote the development of autogenic planform geometry. To explore these ideas, we present numerical and analytical modeling of large-scale (> one kilometer) and long-term (millennial-scale) planform rocky coastline evolution, in which sediment is supplied by both sea cliff erosion and coastal rivers and is distributed by alongshore sediment transport. We also compare model predictions with real landscapes. Previously, our modeling exercises focused on a basic rocky coastline configuration where lithologically-homogeneous sea cliffs supplied all beach sediment and maintained a constant alongshore height. Results showed that 1) an equilibrium alongshore

  4. Modelling the low-latitude boundary layer with reconnection entry

    NASA Technical Reports Server (NTRS)

    Song, P.; Holzer, T. E.; Russell, C. T.; Wang, Z.

    1994-01-01

    We develop a one-dimensional Low Latitude Boundary Layer (LLBL) model for northward interplanetary magnetic field (IMF). The boundary layer in this model is uniform in the direction normal to the magnetopause, a 'plateau-type' boundary layer. The boundary layer motion is decoupled from the magnetosheath motion and driven by the plasma pressure associated with the incoming solar wind plasma near local noon, which has become entrained on closed field lines as a result of reconnection in the cusp region. Dissipation in the ionosphere at the feet of the boundary layer field lines opposes this motion. There are two physical solutions for the model. In one, the boundary layer reaches a terminal velocity in the tail as the boundary layer plasma effectively joins the solar wind flow. In the other solution, the flow is nearly stopped in the far tail. In combination with other mechanisms, this latter solution may correspond to the case in which the boundary layer plasma participates in magnetospheric convection and returns sunward. The density, velocity, and thickness as functions of distance from local noon are studied, assuming that the magnetopause hasa elliptical shape and the magnetospheric field is dipolar.

  5. The evolution of the boundary layer and its effect on air chemistry in the Phoenix area.

    SciTech Connect

    Fast, J. D.; Doran, J. C.; Shaw, W. J.; Coulter, R. L.; Martin, T. J.; Environmental Research; PNNL

    2000-09-27

    During a 4-week period in May and June of 1998, meteorological and chemical measurements were made as part of a field campaign carried out in the Phoenix area. Data from the field campaign provide the first detailed measurements of the properties of the convective boundary layer in this area and of the effects of these properties on ozone levels. The meteorological and chemical measurements have been combined with results from a set of meteorological, particle, and chemistry models to study ozone production, transport, and mixing in the vicinity of Phoenix. Good agreement between the simulations and observations was obtained, and the results have been used to illustrate several important factors affecting ozone patterns in the region. Heating of the higher terrain north and east of Phoenix regularly produced thermally driven circulations from the south and southwest through most of the boundary layer during the afternoon, carrying the urban ozone plume to the northeast. The combination of deep mixed layers and moderate winds aloft provided good ventilation of the Phoenix area on most days so that multiday buildups of locally produced ozone did not appear to contribute significantly to ozone levels during the study period. Sensitivity simulations determined that 20 to 40% of the afternoon surface ozone mixing ratios (corresponding to 15 to 35 ppb) were due to vertical mixing processes that entrained reservoirs of ozone into the growing convective boundary layer. The model results also indicated that ozone production in the region is volatile organic compound limited.

  6. Modelling 3D Chemical Weathering Evolution Using Dissolving and Moving Clasts in a Landscape Evolution Model

    NASA Astrophysics Data System (ADS)

    Carretier, S.; Martinez, J.; Martinod, P.; Reich, M.; Godderis, Y.

    2014-12-01

    During mountain uplift, fresh silicate rocks are exhumed and broken into small pieces, potentially increasing their chemical weathering rate and thus the consumption of atmospheric CO2. This process remains debated because although erosion provides fresh rocks, it may also decrease their residence time near Earth's surface where clasts weather. Several recent publications also emphasized the key role of forelands in the weathering of clasts exported from the mountains by erosion. Predicting the chemical outflux of mountains requires to account for the chemical evolution of these rocks from their source to outlet. Powerful chemical models based on diffusion-advection of species between rocks and water have been developed at pedon scale, and recently at hillslope scale. In order to track the weathered material, we have developed a different approach based on the introduction into a 3D landscape evolution model (CIDRE) of dissolving discrete spherical clasts that move downslope. In CIDRE, local erosion and deposition depend on slope and water discharge which adapt dynamically during the topographical evolution. On a cell, bedrock is converted to soil at a rate depending on soil thickness. Clasts are initially spread at specified depths. They have a specified initial size and mineralogical composition. Once they enter the soil, they begins to dissolve at a rate depending on their minerals, temperature and exposed area, which decreases the clast size. Clasts move downstream according to probabilities depending on the ratio between the calculated local deposition and erosion fluxes. Chemical outflux is calculated for each clast during its life. At pedon scale, the model predicts chemical depleted fractions close to that obtained with advection-diffusion models and in agreement with measurements. An integrated chemical flux is estimated for the whole landscape from the clast dissolution rates. This flux reaches a stable solution using a suitable number of initial clasts

  7. Nonlinear evolution of subsonic and supersonic disturbances on a compressible free shear layer

    NASA Technical Reports Server (NTRS)

    Leib, S. J.

    1991-01-01

    The effects of a nonlinear-nonequilibrium-viscous critical layer on the spatial evolution of subsonic and supersonic instability modes on a compressible free shear layer is considered. It is shown that the instability wave amplitude is governed by an integrodifferential equation with cubic-type nonlinearity. Numerical and asymptotic solutions to this equation show that the amplitude either ends in a singularity at a finite downstream distance or reaches an equilibrium value, depending on the Prandtl number, viscosity law, viscous parameter and a real parameter which is determined by the linear inviscid stability theory. A necessary condition for the existence of the equilibrium solution is derived, and whether or not this condition is met is determined numerically for a wide range of physical parameters including both subsonic and supersonic disturbances. it is found that no equilibrium solution exists for the subsonic modes unless the temperature ratio of the low-to-high-speed streams exceeds a critical value, while equilibrium solutions for the most rapidly growing supersonic mode exist over most of the parameter range examined.

  8. Re-Evaluating the Role of the Saharan Air Layer in Atlantic Tropical Cyclogenesis and Evolution

    NASA Technical Reports Server (NTRS)

    Braun, Scott A.

    2010-01-01

    The existence of the Saharan air layer (SAL), a layer of warm, dry, dusty air frequently present over the tropical Atlantic Ocean, has long been appreciated. The nature of its impact on hurricanes remains unclear, however, with some researchers arguing that the SAL amplifies hurricane development and with others arguing that it inhibits it. Most research in recent years has emphasized the potential negative impacts of the SAL, but is this emphasis justified? The potential negative impacts of the SAL include 1) vertical wind shear associated with the African easterly jet; 2) warm air aloft, which increases thermodynamic stability at the base of the SAL; and 3) dry air, which produces cold downdrafts. Multiple NASA satellite data sets and NCEP global analyses are used to characterize the SAL's properties and evolution in relation to tropical cyclones and to evaluate these potential negative influences. The results suggest that the negative influences of the SAL have been significantly over-emphasized, in part because of several false assumptions about the structure and role of the SAL.

  9. Lidar Applications in Atmospheric Dynamics: Measurements of Wind, Moisture and Boundary Layer Evolution

    NASA Technical Reports Server (NTRS)

    Demoz, Belay; Whiteman, David; Gentry, Bruce; Schwemmer, Geary; Evans, Keith; DiGirolamo, Paolo; Comer, Joseph

    2005-01-01

    A large array of state-of-the-art ground-based and airborne remote and in-situ sensors were deployed during the International H2O Project (THOP), a field experiment that took place over the Southern Great Plains (SGP) of the United States from 13 May to 30 June 2002. These instruments provided extensive measurements of water vapor mixing ratio in order to better understand the influence of its variability on convection and on the skill of quantitative precipitation prediction (Weckwerth et all, 2004). Among the instrument deployed were ground based lidars from NASA/GSFC that included the Scanning Raman Lidar (SRL), the Goddard Laboratory for Observing Winds (GLOW), and the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE). A brief description of the three lidars is given below. This study presents ground-based measurements of wind, boundary layer structure and water vapor mixing ratio measurements observed by three co-located lidars during MOP at the MOP ground profiling site in the Oklahoma Panhandle (hereafter referred as Homestead). This presentation will focus on the evolution and variability of moisture and wind in the boundary layer when frontal and/or convergence boundaries (e.g. bores, dry lines, thunderstorm outflows etc) were observed.

  10. Nickel-cobalt layered double hydroxide nanosheets as high-performance electrocatalyst for oxygen evolution reaction

    NASA Astrophysics Data System (ADS)

    Jiang, Jing; Zhang, Ailing; Li, Lili; Ai, Lunhong

    2015-03-01

    Developing the first-row transition-metal-based oxygen evolution reaction (OER) catalysts with highly efficient electrocatalytic activity to replace precious catalysts, such as RuO2 and IrO2 have recently attracted considerable attention because of their earth abundant nature, low cost, environmentally friendly, multiple valence state and high theoretical activity. In this work, an advanced integrated electrode for high-performance electrochemical water oxidation has been designed and fabricated by directly growing binary nickel-cobalt layered double hydroxide (NiCo-LDH) nanosheet arrays on nickel foam. Such economical, earth abundant NiCo-LDH nanosheets show excellent OER activity in alkaline medium with an onset overpotential as low as 290 mV, large anodic current density and excellent durability, which makes them comparable to the most active RuO2 catalyst and better than the Pt/C catalyst. The outstanding OER activity of the NiCo-LDH nanosheets can be attributed to their intrinsic layered structure, interconnected nanoarray configuration and unique redox characteristics.

  11. Large-scale structure evolution in axisymmetric, compressible free-shear layers

    SciTech Connect

    Aeschliman, D.P.; Baty, R.S.

    1997-05-01

    This paper is a description of work-in-progress. It describes Sandia`s program to study the basic fluid mechanics of large-scale mixing in unbounded, compressible, turbulent flows, specifically, the turbulent mixing of an axisymmetric compressible helium jet in a parallel, coflowing compressible air freestream. Both jet and freestream velocities are variable over a broad range, providing a wide range mixing layer Reynolds number. Although the convective Mach number, M{sub c}, range is currently limited by the present nozzle design to values of 0.6 and below, straightforward nozzle design changes would permit a wide range of convective Mach number, to well in excess of 1.0. The use of helium allows simulation of a hot jet due to the large density difference, and also aids in obtaining optical flow visualization via schlieren due to the large density gradient in the mixing layer. The work comprises a blend of analysis, experiment, and direct numerical simulation (DNS). There the authors discuss only the analytical and experimental efforts to observe and describe the evolution of the large-scale structures. The DNS work, used to compute local two-point velocity correlation data, will be discussed elsewhere.

  12. A simplified Reynolds stress model for unsteady turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Fan, Sixin; Lakshminarayana, Budugur

    1993-01-01

    A simplified Reynolds stress model has been developed for the prediction of unsteady turbulent boundary layers. By assuming that the net transport of Reynolds stresses is locally proportional to the net transport of the turbulent kinetic energy, the time dependent full Reynolds stress model is reduced to a set of ordinary differential equations. These equations contain only time derivatives and can be readily integrated in a time dependent boundary layer or Navier-Stokes code. The turbulent kinetic energy and dissipation rate needed for the model are obtained by solving the k-epsilon equations. This simplified Reynolds stress turbulence model (SRSM) does not use the eddy viscosity assumption, which may not be valid for unsteady turbulent flows. The anisotropy of both the steady and the unsteady turbulent normal stresses can be captured by the SRSM model. Through proper damping of the shear stresses, the present model can be used in the near wall region of turbulent boundary layers. This model has been validated against data for steady and unsteady turbulent boundary layers, including periodic turbulent boundary layers subjected to a mean adverse pressure gradient. For the cases tested, the predicted unsteady velocity and turbulent stress components agree well with the experimental data. Comparison between the predictions from the SRSM model and a k-epsilon model is also presented.

  13. A thermal plume model for the Martian convective boundary layer

    NASA Astrophysics Data System (ADS)

    Colaïtis, A.; Spiga, A.; Hourdin, F.; Rio, C.; Forget, F.; Millour, E.

    2013-07-01

    The Martian planetary boundary layer (PBL) is a crucial component of the Martian climate system. Global climate models (GCMs) and mesoscale models (MMs) lack the resolution to predict PBL mixing which is therefore parameterized. Here we propose to adapt the "thermal plume" model, recently developed for Earth climate modeling, to Martian GCMs, MMs, and single-column models. The aim of this physically based parameterization is to represent the effect of organized turbulent structures (updrafts and downdrafts) on the daytime PBL transport, as it is resolved in large-eddy simulations (LESs). We find that the terrestrial thermal plume model needs to be modified to satisfyingly account for deep turbulent plumes found in the Martian convective PBL. Our Martian thermal plume model qualitatively and quantitatively reproduces the thermal structure of the daytime PBL on Mars: superadiabatic near-surface layer, mixing layer, and overshoot region at PBL top. This model is coupled to surface layer parameterizations taking into account stability and turbulent gustiness to calculate surface-atmosphere fluxes. Those new parameterizations for the surface and mixed layers are validated against near-surface lander measurements. Using a thermal plume model moreover enables a first-order estimation of key turbulent quantities (e.g., PBL height and convective plume velocity) in Martian GCMs and MMs without having to run costly LESs.

  14. Application of a Reynolds stress model to separating boundary layers

    NASA Technical Reports Server (NTRS)

    Ko, Sung HO

    1993-01-01

    Separating turbulent boundary layers occur in many practical engineering applications. Nonetheless, the physics of separation/reattachment of flows is poorly understood. During the past decade, various turbulence models were proposed and their ability to successfully predict some types of flows was shown. However. prediction of separating/reattaching flows is still a formidable task for model developers. The present study is concerned with the process of separation from a smooth surface. Features of turbulent separating boundary layers that are relevant to modeling include the following: the occurrence of zero wall shear stress, which causes breakdown of the boundary layer approximation; the law of the wall not being satisfied in the mean back flow region; high turbulence levels in the separated region; a significant low-frequency motion in the separation bubble; and the turbulence structure of the separated shear layer being quite different from that of either the mixing layers or the boundary layers. These special characteristics of separating boundary layers make it difficult for simple turbulence models to correctly predict their behavior.

  15. The Zodiacal Cloud Model applied to the Martian atmosphere. Diurnal variations in Meteoric ion layers

    NASA Astrophysics Data System (ADS)

    Diego Carrillo-Sánchez, Juan; Plane, John M. C.; Withers, Paul; Fallows, Kathryn; Nesvorný, David; Pokorný, Petr; Feng, Wuhu

    2016-04-01

    Sporadic metal layers have been detected in the Martian atmosphere by radio occultation measurements using the Mars Express Orbiter and Mars Global Surveyor spacecraft. More recently, metallic ion layers produced by the meteor storm event following the close encounter between Comet Siding Spring (C/2013 A1) and Mars were identified by the Imaging UltraViolet Spectrograph (IUVS) aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. However, the background metal layers produced by the influx of sporadic meteors have not yet been detected at Mars (contrary to the permanent metal layers identified in the Earth's atmosphere). The Zodiacal Dust Cloud (ZDC) model for particle populations released by asteroids (AST), and dust grains from Jupiter Family Comets (JFC) and Halley-Type Comets (HTC) has been combined with a Monte Carlo sampling method and the Chemical ABlation MODel (CABMOD) to predict the ablation rates of Na, K, Fe, Si, Mg, Ca and Al above 40 km altitude in the Martian atmosphere. CABMOD considers the standard treatment of meteor physics, including the balance of frictional heating by radiative losses and the absorption of heat energy through temperature increases, melting phase transitions and vaporization, as well as sputtering by inelastic collisions with the air molecules. These vertical profiles are input into the Leeds 1-D Mars atmospheric model which includes photo-ionization, and gas-phase ion-molecule and neutral chemistry, in order to explore the evolution of the resulting metallic ions and atoms. We conclude that the formation of the sporadic ion layers observed below 100 km with a plasma density exceeding 104 cm-3 requires the combination of the three different influx sources considered by the ZDC model, with a significant asteroidal contribution. Finally, we explore the changes of the neutral and ionized Mg and Fe layers over a diurnal cycle.

  16. Evolution of desert pavements and the vesicular layer in soils of the Transantarctic Mountains

    NASA Astrophysics Data System (ADS)

    Bockheim, James G.

    2010-06-01

    Compared to mid-latitude deserts, the properties, formation and evolution of desert pavements and the underlying vesicular layer in Antarctica are poorly understood. This study examines the desert pavements and the vesicular layer from seven soil chronosequences in the Transantarctic Mountains that have developed on two contrasting parent materials: sandstone-dolerite and granite-gneiss. The pavement density commonly ranges from 63 to 92% with a median value of 80% and does not vary significantly with time of exposure or parent material composition. The dominant size range of clasts decreases with time of exposure, ranging from 16-64 mm on Holocene and late Quaternary surfaces to 8-16 mm on surfaces of middle Quaternary and older age. The proportion of clasts with ventifaction increases progressively through time from 20% on drifts of Holocene and late Quaternary age to 35% on Miocene-aged drifts. Desert varnish forms rapidly, especially on dolerite clasts, with nearly 100% cover on surfaces of early Quaternary and older age. Macropitting occurs only on clasts that have been exposed since the Miocene. A pavement development index, based on predominant clast-size class, pavement density, and the proportion of clasts with ventifaction, varnish, and pits, readily differentiated pavements according to relative age. From these findings we judge that desert pavements initially form from a surficial concentration of boulders during till deposition followed by a short period of deflation and a longer period of progressive chemical and physical weathering of surface clasts. The vesicular layer that underlies the desert pavement averages 4 cm in thickness and is enriched in silt, which is contributed primarily by weathering rather than eolian deposition. A comparison is made between desert pavement properties in mid-latitude deserts and Antarctic deserts.

  17. Layered Chalcogenides beyond Graphene: from Electronic Structure Evolution to the Spin Transport

    NASA Astrophysics Data System (ADS)

    Yuan, Hongtao

    2014-03-01

    Recent efforts on graphene-like atomic layer materials, aiming at novel electronic properties and quantum phenomena beyond graphene, have attracted much attention for potential electronics/spintronics applications. Compared to the weak spin-orbit-interaction (SOI) in graphene, metal chalcogenides MX2 have heavy 4d/5d elements with strong atomic SOI, providing a unique way for generating spin polarization based on valleytronics physics. Indeed, such a spin-polarized band structure has been demonstrated theoretically and supported by optical investigations. However, despite these exciting progresses, following two important issues in MX2 community remain elusive: 1. the quantitative band structure of MX2 compounds (where are the valleys -band maxima/minima- locating in the BZ) have not been experimentally confirmed. Especially for those cleaved ultrathin mono- and bi-layer flakes hosting most of recently-reported exotic phenomena at the 2D limit, the direct detection for band dispersion becomes of great importance for valleytronics. 2. Spin transports have seldom been reported even though such a strong SOI system can serve as an ideal platform for the spin polarization and spin transport. In this work, we started from the basic electronic structures of representative MX2, obtained by ARPES, and investigated both the band variation between these compounds and their band evolution from bulk to the monolayer limit. After having a systematic understanding on band structures, we reported a giant Zeeman-type spin-polarization generated and modulated by an external electric field in WSe2 electric-double-layer transistors. The non-magnetic approach for realizing such an intriguing spin splitting not only keeps the system time-reversally invariant but also suggests a new paradigm for manipulating the spin-degrees of freedom of electrons. Acknowledge the support from DoE, BES, Division of MSE under contract DE-AC02-76SF00515.

  18. Considering bioactivity in modelling continental growth and the Earth's evolution

    NASA Astrophysics Data System (ADS)

    Höning, D.; Spohn, T.

    2013-09-01

    The complexity of planetary evolution increases with the number of interacting reservoirs. On Earth, even the biosphere is speculated to interact with the interior. It has been argued (e.g., Rosing et al. 2006; Sleep et al, 2012) that the formation of continents could be a consequence of bioactivity harvesting solar energy through photosynthesis to help build the continents and that the mantle should carry a chemical biosignature. Through plate tectonics, the surface biosphere can impact deep subduction zone processes and the interior of the Earth. Subducted sediments are particularly important, because they influence the Earth's interior in several ways, and in turn are strongly influenced by the Earth's biosphere. In our model, we use the assumption that a thick sedimentary layer of low permeability on top of the subducting oceanic crust, caused by a biologically enhanced weathering rate, can suppress shallow dewatering. This in turn leads to greater vailability of water in the source region of andesitic partial melt, resulting in an enhanced rate of continental production and regassing rate into the mantle. Our model includes (i) mantle convection, (ii) continental erosion and production, and (iii) mantle water degassing at mid-ocean ridges and regassing at subduction zones. The mantle viscosity of our model depends on (i) the mantle water concentration and (ii) the mantle temperature, whose time dependency is given by radioactive decay of isotopes in the Earth's mantle. Boundary layer theory yields the speed of convection and the water outgassing rate of the Earth's mantle. Our results indicate that present day values of continental surface area and water content of the Earth's mantle represent an attractor in a phase plane spanned by both parameters. We show that the biologic enhancement of the continental erosion rate is important for the system to reach this fixed point. An abiotic Earth tends to reach an alternative stable fixed point with a smaller

  19. Lidar Observations and Numerical Modeling Studies of Thermospheric Metal Layers and Solar Effects on Mesospheric Fe Layers

    NASA Astrophysics Data System (ADS)

    Yu, Zhibin

    By blocking extreme hazards from space and regulating radio wave propagation, the space-atmosphere interaction region (SAIR) -- our window to open space -- is essential for life on Earth and modern society. However, the physical and chemical processes governing the SAIR are not sufficiently understood due to the woefully incomplete measurements of neutral properties in this region, especially between 100 and 200 km altitude. Thermospheric Fe layers extending from ~70 to 170 km discovered by the Fe Boltzmann lidar at McMurdo, Antarctica have opened a new door to observing the neutral thermosphere and mesosphere. This thesis is aimed at revealing such new discoveries, and advancing our understanding of the thermospheric Fe layer formation, through analyzing the lidar data collected by the author in Antarctic winter and developing the first thermospheric Fe/Fe+ model. A one-dimensional high-latitude Fe/Fe+ model based on physical and chemical first principles has been developed to quantitatively explore the source, formation and evolution of thermospheric Fe layers. We demonstrate that the observed Fe layers are produced by neutralization of converged Fe+, mainly through the direct electron-Fe+ recombination. We find that the polar electric field is capable of uplifting Fe+ ions from the main deposition region into the thermosphere, supplying the source of neutral Fe. Both gravity-wave-induced wind shears and the polar electric field can converge Fe+ layers. Vertical wind plays a key role in transporting Fe to form the observed wave structures, but horizontal divergence can largely offset the vertical convergence effects. These theoretical studies lay the foundation for exploring the thermosphere by resonance lidars. The diurnal variations of Fe layers in the mesopause region are characterized with our lidar observations at McMurdo. A new finding is the solar effect on the Fe layer bottomside --- daytime downward extension and nighttime upward contraction. We explain

  20. Modeling the Urban Boundary and Canopy Layers

    EPA Science Inventory

    Today, we are confronted with increasingly more sophisticated application requirements for urban modeling. These include those that address emergency response to acute exposures from toxic releases, health exposure assessments from adverse air quality, energy usage, and character...

  1. Mineralogy and geochemical evolution of the Little Three pegmatite-aplite layered intrusive, Ramona, California.

    USGS Publications Warehouse

    Stern, L.A.; Brown, Gordon E., Jr.; Bird, D.K.; Jahns, R.H.; Foord, E.E.; Shigley, J.E.; Spaulding, L.B., Jr.

    1986-01-01

    Several layered pegmatite-aplite intrusives exposed at the Little Three mine, Ramona, display closely associated fine-grained to giant-textured mineral assemblages which are believed to have co-evolved from a hydrous aluminosilicate residual melt with an exsolved supercritical vapour phase. Calculations of phase relations between the major pegmatite-aplite mineral assemblages and supercritical aqueous fluid were made, assuming equilibrium and closed-system behaviour as a first-order model.-J.A.Z.

  2. A depletable micro-layer model for nucleate pool boiling

    NASA Astrophysics Data System (ADS)

    Sato, Yohei; Niceno, Bojan

    2015-11-01

    A depletable micro-layer model has been developed for the simulation of nucleate pool boiling within the framework of Computational Fluid Dynamics (CFD) modeling using an interface-tracking method. A micro-layer model is required for the CFD simulation to take into account vaporization from the thin liquid film - called the micro-layer - existing beneath a growing vapor bubble on a hot surface. In our model, the thickness of the micro-layer is a variable defined at each discretized fluid cell adjacent to the heat-transfer surface; the layer decreases due to vaporization, and can finally disappear. Compared to existing micro-region models, most of them based on the concept of contact-line evaporation, as originally proposed by Stephan and Busse, and by Lay and Dhir, our model incorporates simplified modeling ideas, but can nonetheless predict the temperature field beneath the growing bubble accurately. The model proposed in this paper has been validated against measurements of pool boiling in water at atmospheric pressure. Specifically, the bubble principal dimensions and the temperature distribution over the heat-transfer surface are in good agreement with experimental data.

  3. Two-Layer Models for Landslide-Generated Tsunamis

    NASA Astrophysics Data System (ADS)

    Kirby, J. T., Jr.; Nicolsky, D.; Ma, G.; Shi, F.; Hsu, T. J.; Schnyder, J. S. D.

    2014-12-01

    We describe the development of a model for landslide tsunami generation based on a depth-integrated, fully deformable lower layer, and apply the resulting model to several laboratory and field cases. The approach follows on earlier studies where models for the slide layer and overlying water layer are formulated in the depth integrated, shallow water approximation, with kinematic and pressure coupling between the layers. In the present study, we use the 3D nonhydrostatic model of Ma et al (2012) to retain fully dispersive behavior in the upper fluid layer. In perfect fluid applications for shallow or intermediate depth waves, the model has been shown to predict tsunami response to solid slides (Enet and Grilli, 2007) with good accuracy using only three vertical sigma levels, making it computationally competitive with weakly dispersive Boussinesq formulations using a single depth-integrated layer. The effect of non-hydrostatic acceleration effects in the lower, depth integrated layer (resulting from steep substrate slopes) is implemented using the approach of Yamazaki et al (2009), who used a layer-averaged approximation for vertical acceleration to correct the hydrostatic pressure distribution. The two coupled models are formulated using a finite volume, TVD approach. Lateral boundaries of the slide volume may be arbitrarily approached relative to the initial still water shoreline, and thus the triggering event may be either submarine, subaerial, or a combination of the two. In our first implementation, we assume the lower layer to be a simple, viscous Newtonian fluid, following the approach of Jiang and LeBlond (1994) as corrected by Fine et al (1998). An alternate model is also constructed based on a rheology model representing a granular or debris flow supported by intergranular stresses, following Savage and Hutter (1989) and Iverson (1997). Both models amount to the addition of a single mass and horizontal momentum equation to the three-layer perfect fluid

  4. The stratospheric sulfate aerosol layer - Processes, models, observations, and simulations

    NASA Technical Reports Server (NTRS)

    Whitten, R. C.; Toon, O. B.; Turco, R. P.

    1980-01-01

    After briefly reviewing the observational data on the stratospheric sulfate aerosol layer, the chemical and physical processes that are likely to fix the properties of the layer are discussed. We present appropriate continuity equations for aerosol particles, and show how to solve the equations on a digital computer. Simulations of the unperturbed aerosol layer by various published models are discussed and the sensitivity of layer characteristics to variations in several aerosol model parameters is studied. We discuss model applications to anthropogenic pollution problems and demonstrate that moderate levels of aerospace activity (supersonic transport and Space Shuttle operations) will probably have only a negligible effect on global climate. Finally, we evaluate the possible climatic effect of a ten-fold increase in the atmospheric abundance of carbonyl sulfide.

  5. Galactic evolution. I - Single-zone models. [encompassing stellar evolution and gas-star dynamic theories

    NASA Technical Reports Server (NTRS)

    Thuan, T. X.; Hart, M. H.; Ostriker, J. P.

    1975-01-01

    The two basic approaches of physical theory required to calculate the evolution of a galactic system are considered, taking into account stellar evolution theory and the dynamics of a gas-star system. Attention is given to intrinsic (stellar) physics, extrinsic (dynamical) physics, and computations concerning the fractionation of an initial mass of gas into stars. The characteristics of a 'standard' model and its variants are discussed along with the results obtained with the aid of these models.

  6. Bacterial Evolution and the Bak-Sneppen Model

    NASA Astrophysics Data System (ADS)

    Bose, Indrani; Chaudhuri, Indranath

    Recently, Lenski et al.1-3 have carried out several experiments on bacterial evolution. Their findings support the theory of punctuated equilibrium in biological evolution. They have further quantified the relative contributions of adaptation, chance and history to bacterial evolution. In this paper, we show that a modified M-trait Bak-Sneppen model can explain many of the experimental results in a qualitative manner.

  7. 21 Layer troposphere-stratosphere climate model

    NASA Technical Reports Server (NTRS)

    Rind, D.; Suozzo, R.; Lacis, A.; Russell, G.; Hansen, J.

    1984-01-01

    The global climate model is extended through the stratosphere by increasing the vertical resolution and raising the rigid model top to the 0.01 mb (75 km) level. The inclusion of a realistic stratosphere is necessary for the investigation of the climate effects of stratospheric perturbations, such as changes of ozone, aerosols or solar ultraviolet irradiance, as well as for studying the effect on the stratosphere of tropospheric climate changes. The observed temperature and wind patterns throughout the troposphere and stratosphere are simulated. In addition to the excess planetary wave amplitude in the upper stratosphere, other model deficiences include the Northern Hemisphere lower stratospheric temperatures being 5 to 10 C too cold in winter at high latitudes and the temperature at 50 to 60 km altitude near the equator are too cold. Methods of correcting these deficiencies are discussed.

  8. How can a dusty cold pool change the diurnal evolution of the Saharan Atmospheric Boundary Layer ?

    NASA Astrophysics Data System (ADS)

    Kocha, Cécile; Flamant, Cyrille; Berckmans, Julie; Fink, Andreas; Garcia-Carreras, Luis; Knippertz, Peter; Lafore, Jean-Philippe; Marnas, Fabien; Marsham, John; Parker, Doug; Rosenberg, Philip; Ryder, Claire; Tulet, Pierre; Washington, Richard

    2013-04-01

    In the framework of the Fennec 2011 Special Observing period, a large and dusty density current (known as a haboob) was observed on the 21 June to cover half of the western part of the Sahara. Thanks to the AROME high resolution model used to forecast this event in real time, two research aircraft (the SAFIRE Falcon and the FAAM BAe 146) operated over Mauritania and Mali on that day, and we are able to document its characteristics in detail. Particularly large dust particles were observed in this haboob. These particles are known to absorb and scatter solar and thermal radiation. The comparison of AROME simulations with and without coupling with dust shows that the radiative impact of the dust induced a decrease of sensible heat fluxes by 200W/m²/AOD and an increase of the temperature in the atmospheric boundary layer by 1°C. Surface fluxes are one of the principal parameters controlling the growth of the boundary layer. However, during the day, the simulation coupled with dust shows a deeper boundary layer (reaching ~5km high) than the simulation without dust. Here, we explore the competition between surface heating and elevated heating in the boundary-layer development.

  9. Multilabel Image Annotation Based on Double-Layer PLSA Model

    PubMed Central

    Zhang, Jing; Li, Da; Hu, Weiwei; Chen, Zhihua; Yuan, Yubo

    2014-01-01

    Due to the semantic gap between visual features and semantic concepts, automatic image annotation has become a difficult issue in computer vision recently. We propose a new image multilabel annotation method based on double-layer probabilistic latent semantic analysis (PLSA) in this paper. The new double-layer PLSA model is constructed to bridge the low-level visual features and high-level semantic concepts of images for effective image understanding. The low-level features of images are represented as visual words by Bag-of-Words model; latent semantic topics are obtained by the first layer PLSA from two aspects of visual and texture, respectively. Furthermore, we adopt the second layer PLSA to fuse the visual and texture latent semantic topics and achieve a top-layer latent semantic topic. By the double-layer PLSA, the relationships between visual features and semantic concepts of images are established, and we can predict the labels of new images by their low-level features. Experimental results demonstrate that our automatic image annotation model based on double-layer PLSA can achieve promising performance for labeling and outperform previous methods on standard Corel dataset. PMID:24999490

  10. Subgrid-scale Modeling in the Atmospheric Surface Layer^1

    NASA Astrophysics Data System (ADS)

    Khanna, S.; Wyngaard, J. C.; Brasseur, J. G.

    1996-11-01

    Subgrid-scale (SGS) modeling is crucial in the surface layer of wall-bounded flows where the vertical velocity fluctuations cannot be well resolved. We focus on the distinct characteristics of the surface layer of the atmospheric boundary layer (ABL), and analyze, from a highly resolved surface-layer field of a moderately convective ABL, the extent to which Smagorinsky-based SGS models predict these characteristics. The fields were generated using a nested-mesh large-eddy simulation (LES) with the finest mesh having an effective grid resolution of 512^3 covering 1/16^th of the boundary-layer depth. At a height where the fine mesh resolves 90 % of the total fluxes and variances, the resolved fields were treated as surrogate fully resolved fields that were filtered onto a coarser mesh to get ``resolvable'' and ``subgrid'' fields. Preliminary results show that Smagorinsky-based models fail to capture many of the distinctive characteristics of the ABL surface layer. For example, they do not capture the anisotropic distribution of subgrid-scale energy among the horizontal and the vertical components, and they grossly underestimate the SGS horizontal temperature flux. Currently we are focusing on more suitable closures for the atmospheric surface layer. A DNS-based study is also underway and will be used to supplement this analysis. ^1 supported by ARO (# DAAL03-92-G-0117) and ONR (# N00014-92-J-1688)

  11. Modeling the evolution of infrared galaxies: a parametric backward evolution model

    NASA Astrophysics Data System (ADS)

    Béthermin, M.; Dole, H.; Lagache, G.; Le Borgne, D.; Penin, A.

    2011-05-01

    Aims: We attempt to model the infrared galaxy evolution in as simple a way as possible and reproduce statistical properties such as the number counts between 15 μm and 1.1 mm, the luminosity functions, and the redshift distributions. We then use the fitted model to interpret observations from Spitzer, AKARI, BLAST, LABOCA, AzTEC, SPT, and Herschel, and make predictions for Planck and future experiments such as CCAT or SPICA. Methods: This model uses an evolution in density and luminosity of the luminosity function parametrized by broken power-laws with two breaks at redshift ~0.9 and 2, and contains the two populations of the Lagache model: normal and starburst galaxies. We also take into account the effect of the strong lensing of high-redshift sub-millimeter galaxies. This effect is significant in the sub-mm and mm range near 50 mJy. It has 13 free parameters and eight additional calibration parameters. We fit the parameters to the IRAS, Spitzer, Herschel, and AzTEC measurements with a Monte Carlo Markov chain. Results: The model adjusted to deep counts at key wavelengths reproduces the counts from mid-infrared to millimeter wavelengths, as well as the mid-infrared luminosity functions. We discuss the contribution to both the cosmic infrared background (CIB) and the infrared luminosity density of the different populations. We also estimate the effect of the lensing on the number counts, and discuss the discovery by the South Pole Telescope (SPT) of a very bright population lying at high redshift. We predict the contribution of the lensed sources to the Planck number counts, the confusion level for future missions using a P(D) formalism, and the Universe opacity to TeV photons caused by the CIB. Material of the model (software, tables and predictions) is available online.

  12. Cold-air outbreak during GALE - Lidar observations and modeling of boundary layer dynamics

    NASA Technical Reports Server (NTRS)

    Boers, Reinout; Melfi, S. H.; Palm, Stephen P.

    1991-01-01

    Two cold-air outbreaks were studied during the Genesis of Atlantic Lows Experiment. A lidar system was operated to observe the boundary layer evolution and the development of clouds. On the first day (January 30, 1986) boundary layer rise was less than 50 percent of the value for the second day (March 2, 1986). On the first day only a thin broken cloud cover formed, while on the second day a thick solid cloud deck formed - although the average moisture content was 60 percent of that on the first day. A trajectory slab model was employed to simulate the evolution of the layer over the ocean near the east Atlantic shore. The model allows for vertical gradients in conservative variables under neutrally buoyant conditions. The primary effect of these assumptions, which are based on observed thermodynamic profiles, is to reduce cloudiness to be more in line with observations. Boundary-layer depth was reasonably well predicted as was sensible and latent heat flux.

  13. Orbiter Boundary Layer Transition Stability Modeling at Flight Entry Conditions

    NASA Technical Reports Server (NTRS)

    Bartkowicz, Matt; Johnson, Heath; Candler, Graham; Campbell, Charles H.

    2009-01-01

    State of the art boundary layer stability modeling capabilities are increasingly seeing application to entry flight vehicles. With the advent of user friendly and robust implementations of two-dimensional chemical nonequilibrium stability modeling with the STABL/PSE-CHEM software, the need for flight data to calibrate such analyses capabilities becomes more critical. Recent efforts to perform entry flight testing with the Orbiter geometry related to entry aerothermodynamics and boundary layer transition is allowing for a heightened focus on the Orbiter configuration. A significant advancement in the state of the art can likely be achieved by establishing a basis of understanding for the occurrence of boundary layer transition on the Orbiter due to discrete protruding gap fillers and the nominal distributed roughness of the actual thermal protection system. Recent success in demonstrating centerline two-dimensional stability modeling on the centerline of the Orbiter at flight entry conditions provides a starting point for additional investigations. The more detailed paper will include smooth Orbiter configuration boundary layer stability results for several typical orbiter entry conditions. In addition, the numerical modeling approach for establishing the mean laminar flow will be reviewed and the method for determining boundary layer disturbance growth will be overviewed. In addition, if actual Orbiter TPS surface data obtained via digital surface scans become available, it may be possible to investigate the effects of an as-flown flight configuration on boundary layer transition compared to a smooth CAD reference.

  14. Material parameter computation for multi-layered vocal fold models

    PubMed Central

    Schmidt, Bastian; Stingl, Michael; Leugering, Günter; Berry, David A.; Döllinger, Michael

    2011-01-01

    Today, the prevention and treatment of voice disorders is an ever-increasing health concern. Since many occupations rely on verbal communication, vocal health is necessary just to maintain one’s livelihood. Commonly applied models to study vocal fold vibrations and air flow distributions are self sustained physical models of the larynx composed of artificial silicone vocal folds. Choosing appropriate mechanical parameters for these vocal fold models while considering simplifications due to manufacturing restrictions is difficult but crucial for achieving realistic behavior. In the present work, a combination of experimental and numerical approaches to compute material parameters for synthetic vocal fold models is presented. The material parameters are derived from deformation behaviors of excised human larynges. The resulting deformations are used as reference displacements for a tracking functional to be optimized. Material optimization was applied to three-dimensional vocal fold models based on isotropic and transverse-isotropic material laws, considering both a layered model with homogeneous material properties on each layer and an inhomogeneous model. The best results exhibited a transversal-isotropic inhomogeneous (i.e., not producible) model. For the homogeneous model (three layers), the transversal-isotropic material parameters were also computed for each layer yielding deformations similar to the measured human vocal fold deformations. PMID:21476672

  15. The near‐global mesospheric potassium layer: Observations and modeling

    PubMed Central

    Dawkins, E. C. M.; Chipperfield, M. P.; Feng, W.

    2015-01-01

    Abstract The meteoric metal layers act as unique tracers of chemistry and dynamics in the upper atmosphere. Existing lidar studies from a few locations show that K exhibits a semiannual seasonality (winter and summer maxima), quite unlike the annual seasonality (winter maximum and summer minimum) seen with Na and Fe. This work uses spaceborne observations made with the Optical Spectrograph and InfraRed Imager System instrument on the Odin satellite to retrieve the near‐global K layer for the first time. The satellite data (2004 to mid‐2013) are used to validate the implementation of a recently proposed potassium chemistry scheme in a whole atmosphere chemistry climate model, which provides a chemical basis for this semiannual seasonal behavior. The satellite and model data show that this semiannual seasonality is near global in extent, with the strongest variation at middle and high latitudes. The column abundance, centroid layer height, and root‐mean‐square width of the K layer are consistent with the limited available lidar record. The K data set is then used to investigate the impact of polar mesospheric clouds on the metal layers at high latitudes during summer. Finally, the occurrence frequency of sporadic K layers and their possible link to sporadic E layers are examined. PMID:27478716

  16. Residual layer effects on the modeling of convective boundary layer growth rates with a slab model using FIFE data

    NASA Astrophysics Data System (ADS)

    Freire, Livia S.; Dias, Nelson L.

    2013-12-01

    The ability of slab models for the growth of the convective boundary layer (CBL) to work in the presence of residual layers above is analyzed in detail with a large data set from the First International Satellite Land Surface Climatology Project Field Experiment (FIFE)-87 and FIFE-89 experiments. We confirm that the critical element that allows the models to predict the growth as the CBL coalesces with the residual layer is the adoption of a variable lapse rate above the growing CBL. This is not a new finding per se, as several previous studies in the literature have adopted this strategy. Different parameterizations of a slab model, based on the turbulence kinetic energy budget at the top of the CBL, were tested, and the inclusion of the storage and dissipation terms did not improve the model. Among the alternatives for choosing the lapse rate as the CBL grows, fair results are obtained with a simple choice of two values, with absolute mean errors of the order of 270 m for cases with and without a residual layer. Both lapse rates, representative of the residual layer and the free atmosphere, are obtained from the first morning sounding. Finally, an alternative model for the CBL growth into a residual layer that assumes a zero-lapse rate above the CBL did not perform well with the FIFE data.

  17. Evolution of the planetary boundary layer in the presence of fog and plume

    NASA Astrophysics Data System (ADS)

    Wang, Longlong; Stanič, Samo; Gregorič, Asta; Bergant, Klemen; Mole, Maruška; Vučković, Marko

    2016-04-01

    Vipava valley (100 m a.s.l.), enclosed between the Trnovski gozd ridge (1500 m a.s.l.) and Karst plateau (500 m a.s.l.), is in autumn and winter months in stable weather conditions exposed to relatively large aerosol loading, often exceeding daily PM10 limit of 50 μg/m3. Using an infra-red Mie scattering lidar in the center of the valley (Ajdovščina, 45.93° N, 13.91° E) as the main detection tool, planetary boundary layer (PBL) and backscatter coefficient profiles were investigated in November and December 2015. Wind speeds in the observed period remained below 1 m/s. Backscatter coefficients were obtained using the Klett method. In this period, foggy weather, prevailing in the morning, on certain days cleared during the day. The fog was frequently mixed with aerosols, emitted from local biomass burning sources and traffic within the valley. Fog is an indicator of constant PBL height during the day, as it generally evolves only in periods with stable weather and temperature inversion in orographically enclosed areas. We investigated the evolution of the PBL in the case of fog and plume. In the first case, PBL height remained constant at about 200 to 300 m while in the second case it followed the typical daily evolution pattern and increased during the morning. In both cases lidar backscatter coefficients within the PBL were found to be increased for a factor of 0.5 to 2 with respect to clear weather conditions. In the periods of elevated aerosol loading in Ajdovščina observed by lidar, elevated PM10 concentrations in Nova Gorica, 20 km away along the valley, were also detected as expected, due to similar local aerosol sources throughout the valley.

  18. Modeling of turbulent transport in the surface layer

    NASA Technical Reports Server (NTRS)

    Smith, G. L.

    1973-01-01

    The turbulence equations as written by Donaldson using the method of invariant modeling have been applied to the following limiting cases of the surface or constant flux layer of the planetary boundary layer: (1) Neutrally stable; (2) stable (above influence of surface roughness); (3) nearly neutrally stable; and (4) very unstable (free convection). For the neutrally stable case, the equations are shown to admit as a solution the familiar logarithmic profile. By use of this result, boundary conditions suitable for the surface layer are defined and are simple to apply to rough surfaces.

  19. MICROSTRUCTURE EVOLUTION MODELING FOR SOLUTION TREATMENT OF ALUMINUM ALLOYS

    SciTech Connect

    Yin, Hebi; Sabau, Adrian S; Skszek, Timothy; Niu, X

    2013-01-01

    The microstructure evolution during solution treatment plays an important role in mechanical properties of heat-treated aluminum alloys. In this paper, models were reviewed that can predict the microstructure evolution during the solutionizing process of the aging heat treatment of aluminum alloys. The dissolution of Mg2Si particles has been modeled as a diffusion process of Mg in the -Al matrix. The evolution of volumetric fraction of fragmented silicon as a function of time and temperature was also considered. The growth and coarsening of silicon particles during the heat treatment was considered. It was found that constitutive equations and required property data for most of the phenomena that need to be considered are available. Several model parameters that need to be obtained from material characterization were identified. Pending the availability of these model parameters, this comprehensive model can be used to describe the microstructure evolution of aluminum alloys in order to optimize the solutionizing heat treatment for energy savings.

  20. A comprehensive study on atomic layer deposition of molybdenum sulfide for electrochemical hydrogen evolution

    NASA Astrophysics Data System (ADS)

    Kwon, Do Hyun; Jin, Zhenyu; Shin, Seokhee; Lee, Wook-Seong; Min, Yo-Sep

    2016-03-01

    Atomic layer deposition (ALD) has emerged as an efficient method to design and prepare catalysts with atomic precision. Here, we report a comprehensive study on ALD of molybdenum sulfide (MoSx) for an electrocatalytic hydrogen evolution reaction. By using molybdenum hexacarbonyl and dimethyldisulfide as the precursors of Mo and S, respectively, the MoSx catalysts are grown at 100 °C on porous carbon fiber papers (CFPs). The ALD process results in the growth of particle-like MoSx on the CFP due to the lack of adsorption sites, and its crystallographic structure is a mixture of amorphous and nano-crystalline phases. In order to unveil the intrinsic activity of the ALD-MoSx, the exchange current densities, Tafel slopes, and turnover frequencies of the catalysts grown under various ALD conditions have been investigated by considering the fractional surface coverage of MoSx on the CFP and catalytically-active surface area. In addition, the ALD-MoSx/CFP catalysts exhibit excellent catalytic stability due to the strong adhesion of MoSx on the CFP and the mixed phase.Atomic layer deposition (ALD) has emerged as an efficient method to design and prepare catalysts with atomic precision. Here, we report a comprehensive study on ALD of molybdenum sulfide (MoSx) for an electrocatalytic hydrogen evolution reaction. By using molybdenum hexacarbonyl and dimethyldisulfide as the precursors of Mo and S, respectively, the MoSx catalysts are grown at 100 °C on porous carbon fiber papers (CFPs). The ALD process results in the growth of particle-like MoSx on the CFP due to the lack of adsorption sites, and its crystallographic structure is a mixture of amorphous and nano-crystalline phases. In order to unveil the intrinsic activity of the ALD-MoSx, the exchange current densities, Tafel slopes, and turnover frequencies of the catalysts grown under various ALD conditions have been investigated by considering the fractional surface coverage of MoSx on the CFP and catalytically

  1. The Essential Role of Tethered Balloons in Characterizing Boundary Layer Structure and Evolution during Discover-AQ

    NASA Astrophysics Data System (ADS)

    Clark, R. D.

    2014-12-01

    The NASA DISCOVER-AQ (Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality) provided the opportunity to observe the influence of local and regional circulations on the structure and evolution of the boundary layer (BL) and in turn study the associated effects on air quality and aerosol trends within four different airsheds. An extended network of ground-based instruments, balloon-borne profilers, and remote sensing instruments supported the in-situ airborne measurements made by the NASA aircraft in capturing the structure and evolution of the daytime BL. The Millersville University Atmospheric Research and Aerostat Facility (MARAF) is one of many assets deployed for DISCOVER-AQ. Central to MARAF is a heavy-lift-capacity tethered balloon (aerostat) used to obtain high resolution profiles of meteorological variables, trace gases, and particulates in the BL. The benefit of including a tethered balloon is that it can fill a data void between the surface and the lowest altitudes flown by the aircraft and provide critical time-height series for ground-based remote sensing instruments in the layer below their first range gate. MARAF also includes an acoustic sodar with RASS, MPL4 micropulse Lidar, 4-meter flux tower, rawinsonde system, and a suite of trace gas analyzers (O3, NOx/NO2/NO, CO, and SO2), 3-wavelength nephelometer, and particle sizers/counters spanning the range from 10 nm to 10 microns. MARAF is capable of providing a detailed and nearly continuous Eulerian characterization of the surface layer and lower BL, and with proper FAA airspace authorization, can be deployed both day and night. Three case studies will be presented that incorporate the MARAF into the combined assets of DISCOVER-AQ to better characterize: 1) bay breeze convergence, recirculation, and ramp-up events in Edgewood, MD in July 2011; 2) aerosol transport over Central Valley, CA in January 2013; and 3) multiple sea-bay breeze

  2. Boundary layer integral matrix procedure: Verification of models

    NASA Technical Reports Server (NTRS)

    Bonnett, W. S.; Evans, R. M.

    1977-01-01

    The three turbulent models currently available in the JANNAF version of the Aerotherm Boundary Layer Integral Matrix Procedure (BLIMP-J) code were studied. The BLIMP-J program is the standard prediction method for boundary layer effects in liquid rocket engine thrust chambers. Experimental data from flow fields with large edge-to-wall temperature ratios are compared to the predictions of the three turbulence models contained in BLIMP-J. In addition, test conditions necessary to generate additional data on a flat plate or in a nozzle are given. It is concluded that the Cebeci-Smith turbulence model be the recommended model for the prediction of boundary layer effects in liquid rocket engines. In addition, the effects of homogeneous chemical reaction kinetics were examined for a hydrogen/oxygen system. Results show that for most flows, kinetics are probably only significant for stoichiometric mixture ratios.

  3. Temporal and spatial evolution characteristics of disturbance wave in a hypersonic boundary layer due to single-frequency entropy disturbance.

    PubMed

    Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing; Shi, Jianqiang

    2014-01-01

    By using a high-order accurate finite difference scheme, direct numerical simulation of hypersonic flow over an 8° half-wedge-angle blunt wedge under freestream single-frequency entropy disturbance is conducted; the generation and the temporal and spatial nonlinear evolution of boundary layer disturbance waves are investigated. Results show that, under the freestream single-frequency entropy disturbance, the entropy state of boundary layer is changed sharply and the disturbance waves within a certain frequency range are induced in the boundary layer. Furthermore, the amplitudes of disturbance waves in the period phase are larger than that in the response phase and ablation phase and the frequency range in the boundary layer in the period phase is narrower than that in these two phases. In addition, the mode competition, dominant mode transformation, and disturbance energy transfer exist among different modes both in temporal and in spatial evolution. The mode competition changes the characteristics of nonlinear evolution of the unstable waves in the boundary layer. The development of the most unstable mode along streamwise relies more on the motivation of disturbance waves in the upstream than that of other modes on this motivation. PMID:25143983

  4. Temporal and Spatial Evolution Characteristics of Disturbance Wave in a Hypersonic Boundary Layer due to Single-Frequency Entropy Disturbance

    PubMed Central

    Lv, Hongqing; Shi, Jianqiang

    2014-01-01

    By using a high-order accurate finite difference scheme, direct numerical simulation of hypersonic flow over an 8° half-wedge-angle blunt wedge under freestream single-frequency entropy disturbance is conducted; the generation and the temporal and spatial nonlinear evolution of boundary layer disturbance waves are investigated. Results show that, under the freestream single-frequency entropy disturbance, the entropy state of boundary layer is changed sharply and the disturbance waves within a certain frequency range are induced in the boundary layer. Furthermore, the amplitudes of disturbance waves in the period phase are larger than that in the response phase and ablation phase and the frequency range in the boundary layer in the period phase is narrower than that in these two phases. In addition, the mode competition, dominant mode transformation, and disturbance energy transfer exist among different modes both in temporal and in spatial evolution. The mode competition changes the characteristics of nonlinear evolution of the unstable waves in the boundary layer. The development of the most unstable mode along streamwise relies more on the motivation of disturbance waves in the upstream than that of other modes on this motivation. PMID:25143983

  5. A layered neural network model applied to the auditory system

    NASA Astrophysics Data System (ADS)

    Travis, Bryan J.

    1986-08-01

    The structure of the auditory system is described with emphasis on the cerebral cortex. A layered neural network model incorporating much of the known structure of the cortex is applied to word discrimination. The concepts of iterated maps and atrractive fixed points are used to enable the model to recognize words despite variations in pitch, intensity and duration.

  6. Computational and mathematical models of microstructural evolution

    SciTech Connect

    Bullard, J.W.; Chen, L.Q.; Kalia, R.K.; Stoneham, A.M.

    1998-12-31

    This symposium was designed to bring together the foremost materials theorists and applied mathematicians from around the world to share and discuss some of the newest and most promising mathematical and computational tools for simulating, understanding, and predicting the various complex processes that occur during the evolution of microstructures. Separate abstracts were prepared for 25 papers.

  7. Modeling the iron cycling in the mixed layer

    NASA Astrophysics Data System (ADS)

    Weber, L.; Voelker, C.; Schartau, M.; Wolf-Gladrow, D.

    2003-04-01

    We present a comprehensive model of the iron cycling within the mixed layer of the ocean, which predicts the time course of iron concentration and speciation. The speciation of iron within the mixed layer is heavily influenced by photochemistry, organic complexation, colloid formation and aggregation, as well as uptake and release by marine biota. The model is driven by mixed layer dynamics, dust deposition and insolation, as well as coupled to a simple ecosystem model (based on Schartau at al.2001: Deep-Sea Res.II.48,1769-1800) and applied to the site of the Bermuda Atlantic Time-series Study (BATS). Parameters in the model were chosen to reproduce the small number of available speciation measurements resolving a daily cycle. The model clearly reproduces the available Fe concentration at the BATS station but the annual balance of Fe fluxes at BATS is less constrained, due to uncertainties in the model parameters. Hence we discuss the model's sensitivity to parameter uncertainties and which observations might help to better constrain the relevant model parameters. Futher we discuss how the most important model parameters are constrained by the data. The mixed layer cycle in the model strongly influences seasonality of primary production as well as light dependency of photoreductive processes and therefore controlls iron speciation. Futhermore short events within a day (e.g. heavy rain, change of irradiance, intense dust deposition and temporary deepening of the mixed layer) may push processes like colloidal aggregation. For this reason we compare two versions of the model: The first one is forced by monthly averaged climatological variables, the second one by daily climatological variabilities.

  8. A MODEL OF THE SPECTRAL EVOLUTION OF PULSAR WIND NEBULAE

    SciTech Connect

    Tanaka, Shuta J.; Takahara, Fumio

    2010-06-01

    We study the spectral evolution of pulsar wind nebulae (PWNe) taking into account the energy injected when they are young. We model the evolution of the magnetic field inside a uniformly expanding PWN. Considering time-dependent injection from the pulsar and coolings by radiative and adiabatic losses, we solve the evolution of the particle distribution function. The model is calibrated by fitting the calculated spectrum to the observations of the Crab Nebula at an age of a thousand years. The spectral evolution of the Crab Nebula in our model shows that the flux ratio of TeV {gamma}-rays to X-rays increases with time, which implies that old PWNe are faint in X-rays, but not in TeV {gamma}-rays. The increase of this ratio is because the magnetic field decreases with time and is not because the X-ray emitting particles are cooled more rapidly than the TeV {gamma}-ray emitting particles. Our spectral evolution model matches the observed rate of the radio flux decrease of the Crab Nebula. This result implies that our magnetic field evolution model is close to the reality. Finally, from the viewpoint of the spectral evolution, only a small fraction of the injected energy from the Crab Pulsar needs to go to the magnetic field, which is consistent with previous studies.

  9. Modelling Scalar Skewness in Cloudy Boundary Layers

    NASA Astrophysics Data System (ADS)

    Mironov, Dmitrii; Machulskaya, Ekaterina; Naumann, Ann Kristin; Seifert, Axel; Mellado, Juan Pedro

    2015-04-01

    Following the pioneering work of Sommeria and Deardorff (1977), statistical cloud schemes are widely used in numerical weather prediction (NWP) and climate models to parameterize the effect of shallow clouds on turbulent mixing and radiation fluxes. Statistical cloud schemes compute the cloud fraction, the amount of cloud condensate and the effect clouds on the buoyancy flux in a given atmospheric-model grid box. This is done with due regard for the sub-grid scale (SGS) fluctuations of temperature and humidity (and possibly the vertical velocity), thus providing an important coupling between cloudiness and the SGS mixing processes. The shape of the PDF of fluctuating fields is assumed, whereas the PDF moments should be provided to the cloud scheme as an input. For non-precipitation clouds, the mixing schemes are usually formulated in terms of quasi-conservative variable, e.g. the liquid (total) water potential temperature and the total water specific humidity. Then, the cloud schemes are conveniently cast in terms of the linearized saturation deficit, referred to as the "s" variable (Mellor 1977), that accounts for the combined effect of the two scalars. If a simple two-parameter single-Gaussian PDF is used, the only "turbulence" parameter to be provided to the cloud scheme is the variance of s. The single-Gaussian PDF ignores the skewed nature of SGS motions and fails to describe many important regimes, e.g. shallow cumuli. A number of more flexible skewed PDFs have been proposed to date. A three-parameter PDF, based on a double-Gaussian distribution and diagnostic relations between some PDF parameters derived from LES and observational data (Naumann et al. 2013), appears to be a good compromise between physical realism and computational economy. A crucial point is that the cloud schemes using non-Gaussian PDFs require the scalar skewness as an input. Using rather mild non-restrictive assumptions, we develop a transport equation for the s-variable triple

  10. Modeling the growth of an altered layer in mineral weathering

    NASA Astrophysics Data System (ADS)

    Reis, Fábio D. A. Aarão

    2015-10-01

    A stochastic reaction-diffusion model on a lattice is introduced to describe the growth kinetics of an altered layer in the weathering of a mineral. Particles R represent H2O that permanently fills the outer surface and diffuse on M (mineral) and A (altered) sites with coefficients DM and DA , respectively. The transformation M + R → A occurs with rate r, representing the irreversible formation of the altered material in a region of molecular size, viz. the lattice site of size a. These assumptions agree with predictions of the interfacial dissolution-reprecipitation mechanism, although the model does not describe the chemistry of dissolution reactions or precipitation processes. Scaling concepts are used to distinguish kinetic regimes and their crossovers, and are supported by simulation results. In the short time reactive regime, the thickness of the altered layer increases linearly in time and filling of that layer by particles R is high. In the long time diffusive regime, the altered layer thickness grows as (DA t) 1 / 2 . Modeling of single crystals require very small values of DM , which produces atomically narrow interfaces between the altered material and the mineral and absence of R in the latter, in agreement with recent experimental results. If r layer by a factor lAM / a , but no fluid in the bulk mineral. Estimates of the order of magnitude of transformation rates and of diffusion coefficients are obtained by application of the model to some recently studied systems: calcite dissolution, labradorite weathering, and silicate glass weathering. Effects of dissolution of the altered layer are analyzed. Significant differences between the model and leached layer theories are discussed.