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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. 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.

  4. 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.

  5. Modeling spatial evolution of aero-optical wave front aberration caused by a supersonic mixing layer

    NASA Astrophysics Data System (ADS)

    Guo, Guangming; Liu, Hong

    2017-03-01

    A method used to build a prediction model for spatial evolution of the aero-optical wave front aberration caused by a supersonic mixing layer is presented. The large eddy simulation is used to visualize the instantaneous dynamical characteristics of vortices inside the flow field. The time-averaged boundary of the supersonic mixing layer is described by a piecewise function in which the two turning points are defined and expressed by a universal formula. The growth rate for supersonic mixing layers is first proposed as a function of the velocity ratio, density ratio, and compressibility of the flow field. A model for spatial evolution of aero-optical wave front aberration caused by a supersonic mixing layer is developed based on experimental data presented in the open literature and validated with numerically simulated data from two typical examples. Finally, the universality and potential application of the model built is also discussed.

  6. Radiative hydrodynamics in the highly super adiabatic layer of stellar evolution models

    NASA Astrophysics Data System (ADS)

    Robinson, F. J.; Demarque, P.; Sofia, S.; Chan, K. L.; Kim, Y.-C.; Guenther, D. B.

    2001-01-01

    We present results of three dimensional simulations of the uppermost part of the sun, at 3 stages of its evolution. Each model includes physically realistic radiative-hydrodynamics (the Eddington approximation is used in the optically thin region), varying opacities and a realistic equation of state (full treatment of the ionization of H and He). In each evolution model, we investigate a domain, which starts at the top of the photosphere and ends just inside the convection zone (about 2400 km in the sun model). This includes all of the super-adiabatic layer (SAL). Due to the different positions of the three models in the log(g) vs logTeff plane, the more evolved models haved lower density atmospheres. The reduction in density causes the extent of overshoot into the radiation layer, to be greater in the more evolved models.

  7. Modelling of active layer thickness evolution on James Ross Island in 2006-2015

    NASA Astrophysics Data System (ADS)

    Hrbáček, Filip; Uxa, Tomáš

    2017-04-01

    Antarctic Peninsula region has been considered as one of the most rapidly warming areas on the Earth. However, the recent studies (Turner et al., 2016; Oliva et al., 2017) showed that significant air temperature cooling began around 2000 and has continued until present days. The climate cooling led to reduction of active layer thickness in several parts of Antarctic Peninsula region during decade 2006-2015, but the information about spatiotemporal variability of active layer thickness across the region remains largely incoherent due to lack of active layer temperature data from deeper profiles. Valuable insights into active layer thickness evolution in Antarctic Peninsula region can be, however, provided by thermal modelling techniques. These have been widely used to study the active layer dynamics in different regions of Arctic since 1990s. By contrast, they have been employed much less in Antarctica. In this study, we present our first results from two equilibrium models, the Stefan and Kudryavtsev equations, that were applied to calculate the annual active layer thickness based on ground temperature data from depth of 5 cm on one site on James Ross Island, Eastern Antarctic Peninsula, in period 2006/07 to 2014/15. Study site (Abernethy Flats) is located in the central part of the major ice-free area of James Ross Island called Ulu Peninsula. Monitoring of air temperature 2 m above ground surface and ground temperature in 50 cm profile began on January 2006. The profile was extended under the permafrost table down to 75 cm in February 2012, which allowed precise determination of active layer thickness, defined as a depth of 0°C isotherm, in period 2012 to 2015. The active layer thickness in the entire observation period was reconstructed using the Stefan and Kudryavtsev models, which were driven by ground temperature data from depth of 5 cm and physical parameters of the ground obtained by laboratory analyses (moisture content and bulk density) and calculations

  8. Model Simulations of the Boundary-Layer Evolution over an Arid Andes Valley

    NASA Astrophysics Data System (ADS)

    Bischoff-Gauß, Inge; Kalthoff, Norbert; Khodayar, Samiro; Fiebig-Wittmaack, Melitta; Montecinos, Sonia

    2008-09-01

    The boundary layer of the Elqui valley in the arid north of Chile exhibits several interesting phenomena, such as a very shallow convective boundary layer (CBL) during the day. In the morning, warming is observed in and above the CBL, while the humidity decreases in the CBL. At midday, in and above the CBL of the valley, the temperature stagnates. In the afternoon in the CBL the temperature decreases and humidity increases, although the latent heat flux is very low. Because the characteristic features of the valley atmosphere are hard to interpret from observations alone, model simulations were applied. The simulations indicate that all components of the budget equations, i.e. the turbulent flux divergences, advection via the sea breeze, the upvalley and upslope wind systems, as well as subsidence, contribute to the evolution of the valley atmosphere.

  9. Observational and modeling studies of urban atmospheric boundary-layer height and its evolution mechanisms

    NASA Astrophysics Data System (ADS)

    He, Q. S.; Mao, J. T.; Chen, J. Y.; Hu, Y. Y.

    With a new retrieval method, the mixed layer height (MLH) over the urban area of Beijing is studied using data observed by an eye-safe, compact micro pulse lidar (MPL). The retrieval results show that the retrieved MLH agrees well with that from radiosonde data. The MLH and its growth rate are estimated from the MPL measurements. Entrainment zone thickness (EZT) is extracted from MPL datasets. Entrainment ratio calculated from MLH and EZT is about 0.24. Regional surface sensible heat fluxes are retrieved with a common thermodynamic model. The contribution of mechanical production on MLH evolution is also studied. These results determined from lidar remote sense are useful for modeling air pollution diffusion and transportation.

  10. Boundary layer evolution over the central Himalayas from radio wind profiler and model simulations

    NASA Astrophysics Data System (ADS)

    Singh, Narendra; Solanki, Raman; Ojha, Narendra; Janssen, Ruud H. H.; Pozzer, Andrea; Dhaka, Surendra K.

    2016-08-01

    We investigate the time evolution of the Local Boundary Layer (LBL) for the first time over a mountain ridge at Nainital (79.5° E, 29.4° N, 1958 m a.m.s.l.) in the central Himalayan region, using a radar wind profiler (RWP) during November 2011 to March 2012, as a part of the Ganges Valley Aerosol Experiment (GVAX). We restrict our analysis to clear-sunny days, resulting in a total of 78 days of observations. The standard criterion of the peak in the signal-to-noise ratio (S / N) profile was found to be inadequate in the characterization of mixed layer (ML) top at this site. Therefore, we implemented a criterion of S / N > 6 dB for the characterization of the ML and the resulting estimations are shown to be in agreement with radiosonde measurements over this site. The daytime average (05:00-10:00 UTC) observed boundary layer height ranges from 440 ± 197 m in November (late autumn) to 766 ± 317 m above ground level (a.g.l.) in March (early spring). The observations revealed a pronounced impact of mountain topography on the LBL dynamics during March, when strong winds (> 5.6 m s-1) lead to LBL heights of 650 m during nighttime. The measurements are further utilized to evaluate simulations from the Weather Research and Forecasting (WRF) model. WRF simulations captured the day-to-day variations up to an extent (r2 = 0.5), as well as the mean diurnal variations (within 1σ variability). The mean biases in the daytime average LBL height vary from -7 % (January) to +30 % (February) between model and observations, except during March (+76 %). Sensitivity simulations using a mixed layer model (MXL/MESSy) indicated that the springtime overestimation of LBL would lead to a minor uncertainty in simulated surface ozone concentrations. However, it would lead to a significant overestimation of the dilution of black carbon aerosols at this site. Our work fills a gap in observations of local boundary layer over this complex terrain in the Himalayas, and highlights the need for

  11. 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

  12. 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.

  13. 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.

  14. Evolution of fault zones in carbonates with mechanical stratigraphy - Insights from scale models using layered cohesive powder

    NASA Astrophysics Data System (ADS)

    van Gent, Heijn W.; Holland, Marc; Urai, Janos L.; Loosveld, Ramon

    2010-09-01

    We present analogue models of the formation of dilatant normal faults and fractures in carbonate fault zones, using cohesive hemihydrate powder (CaSO 4·½H 2O). The evolution of these dilatant fault zones involves a range of processes such as fragmentation, gravity-driven breccia transport and the formation of dilatant jogs. To allow scaling to natural prototypes, extensive material characterisation was done. This showed that tensile strength and cohesion depend on the state of compaction, whereas the friction angle remains approximately constant. In our models, tensile strength of the hemihydrate increases with depth from 9 to 50 Pa, while cohesion increases from 40 to 250 Pa. We studied homogeneous and layered material sequences, using sand as a relatively weak layer and hemihydrate/graphite mixtures as a slightly stronger layer. Deformation was analyzed by time-lapse photography and Particle Image Velocimetry (PIV) to calculate the evolution of the displacement field. With PIV the initial, predominantly elastic deformation and progressive localization of deformation are observed in detail. We observed near-vertical opening-mode fractures near the surface. With increasing depth, dilational shear faults were dominant, with releasing jogs forming at fault-dip variations. A transition to non-dilatant shear faults was observed near the bottom of the model. In models with mechanical stratigraphy, fault zones are more complex. The inferred stress states and strengths in different parts of the model agree with the observed transitions in the mode of deformation.

  15. 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.

  16. 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.; Shen, Shaohua

    1998-01-01

    In support of the wake vortex effect of the Terminal Area Productivity program, we have put forward four tasks to be accomplished in our proposal. The first task is validation of two-dimensional wake vortex-turbulence interaction. The second task is investigation of three-dimensional interaction between wake vortices and atmospheric boundary layer (ABL) turbulence. The third task is ABL studies. The, fourth task is addition of a Klemp-Durran condition at the top boundary for TASS model. The accomplishment of these tasks will increase our understanding of the dynamics of wake vortex and improve forecasting systems responsible for air safety and efficiency. The first two tasks include following three parts: (a) Determine significant length scale for vortex decay and transport, especially the length scales associated with the onset of Crow instability (Crow, 1970); (b) Study the effects of atmospheric turbulence on the decay of the wake vortices; and (c) Determine the relationships between decay rate, transport properties and atmospheric parameters based on large eddy simulation (LES) results and the observational data. These parameters may include turbulence kinetic energy, dissipation rate, wind shear and atmospheric stratification. The ABL studies cover LES modeling of turbulence structure within planetary boundary layer under transition and stable stratification conditions. Evidences have shown that the turbulence in the stable boundary layer can be highly intermittent and the length scales of eddies are very small compared to those in convective case. We proposed to develop a nesting grid mesh scheme and a modified Klemp-Durran conditions (Klemp and Wilhelmson, 1978) at the top boundary for TASS model to simulate planetary boundary layer under stable stratification conditions. During the past year, our group has made great efforts to carry out the above mentioned four tasks simultaneously. The work accomplished in the last year will be described in the next

  17. Evolution of the cross-equatorial atmospheric boundary layer in the east Pacific: Observations and models

    NASA Astrophysics Data System (ADS)

    de Szoeke, Simon P.

    The NCAR C-130 research aircraft flew eight missions observing the atmospheric boundary layer (ABL) along 95°W, 1°S--12°N. The positive air-sea temperature difference over the equatorial cold tongue results in a shallow stable layer with reduced surface winds. Stratocumulus clouds at the ABL top tend to clear over the cold water, especially at times of enhanced humidity above the ABL. In the 0°--4°N ABL heat budget, cold advection and radiative cooling were balanced by surface and entrainment heating, where each of the four terms was about 30 W m-2. The humidity budget was a near balance between dry advection and surface evaporation (each about 150 W m-2). The entrainment rate estimated from the downstream-deepening of the inversion was 12 +/- 3 mm s -1. Principal component analysis of the sea-level pressure along 95°W, 1°S--12°N from daily TAO buoy observations and the eight flights shows that the principal mode of variability in the perturbation pressure explains 77% of the pressure variability. The pressure anomalies are the same at 1.6 km as at the surface. The timeseries of the first mode of the TAO observations shows that most of the variance is in the 2--7 day window. Low pressure at 12°N is associated with southerly and westerly surface wind anomalies, and enhanced convection in the ITCZ. A "quasi-Lagrangian" large-eddy simulation (LES) is used to model the ABL along 95°W from 8°S to 4°N. Large-scale tendencies are prescribed as a function of latitude. Surface stability accounts for the minimum in surface wind over the equatorial cold tongue and the maximum over the warm water to the north, in accordance with Wallace, Mitchell, and Deser (1989). Additional simulations show the robustness of the model ABL to changes in pressure gradients, zonal advection, free-tropospheric humidity, and initial conditions. Once formed at the southern edge of the cold tongue, modeled stratus clouds demonstrate a remarkable ability to maintain themselves over the

  18. 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.

  19. Three-dimensional coupling of landscape evolution and rheologically layered thermomechanical models - towards a tectonic perspective on drainage patterns

    NASA Astrophysics Data System (ADS)

    Ueda, K.; Willett, S.; Gerya, T.

    2012-12-01

    Surface topography and drainage topology contain, amongst others, diverse information about tectonic deformation. Differentiation of the tectonic contribution from climate factors is however controversial, and poses limitations on the potential reconstruction of deformation histories from a first-grade data set. In studying the interplay between tectonics and surface processes, various types of numerical models provide valuable yet partial insights. Landscape evolution models (LEM) capture the operation of an excerpt, according to scale and climate, of fluvial, glacial and hillslope processes. They can be applied to specific problems with simple, feedback-free kinematics to study the response of landscape to tectonics. In contrast, large-scale thermomechanical models incorporate simplified continuous surface functions that do not respect the scale-dependency of surface processes, and that do not reproduce landscape characteristics other than gross elevation. Aiming at combining each side's capabilities, the coupled models that have been brought forward so far have been subjected to limitations like two-dimensionality, lack of rheological layering, and computationally limited resolution, exacerbating the inaccuracy of discretized divide location. They have explored the sensitivity of topography and strain partitioning, on the efficiency of surface processes, but have not advanced to addressing the evolution of drainage patterns. Such research objectives are becoming more feasible as recent developments move towards coupling LEMs to three-dimensional, rheologically layered thermomechanical models at increasing resolution. In this contribution, we present results from coupling a scale-robust LEM with a full thermomechanical model. The new LEM code DAC combines numerical-analytical modelling of fluvial and hillslope processes, and is capable of treating large model domains at feasible numerical resolution without loss of accuracy. First, location and migration of

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Modeling the Evolution of the Atmospheric Boundary Layer Coupled to the Land Surface for Three Contrasting Nights in CASES-99.

    NASA Astrophysics Data System (ADS)

    Steeneveld, G. J.; van de Wiel, B. J. H.; Holtslag, A. A. M.

    2006-03-01

    The modeling and prediction of the stable boundary layer over land is a persistent, problematic feature in weather, climate, and air quality topics. Here, the performance of a state-of-the-art single-column boundary layer model is evaluated with observations from the 1999 Cooperative Atmosphere Surface Exchange Study (CASES-99) field experiment. Very high model resolution in the atmosphere and the soil is utilized to represent three different stable boundary layer archetypes, namely, a fully turbulent night, an intermittently turbulent night, and a radiative night with hardly any turbulence (all at clear skies). Each archetype represents a different class of atmospheric stability. In the current model, the atmosphere is fully coupled to a vegetation layer and the underlying soil. In addition, stability functions (local scaling) are utilized based on in situ observations.Overall it is found that the vertical structure, the surface fluxes (apart from the intermittent character) and the surface temperature in the stable boundary layer can be satisfactorily modeled for a broad stability range (at a local scale) with the current understanding of the physics of the stable boundary layer. This can also be achieved by the use of a rather detailed coupling between the atmosphere and the underlying soil and vegetation, together with high resolution in both the atmosphere and the soil. This is especially true for the very stable nights, when longwave radiative cooling is dominant. Both model outcome and observations show that in the latter case the soil heat flux is a dominant term of the surface energy budget.


  5. Modeling Transport Layer Protocols

    NASA Astrophysics Data System (ADS)

    Sasnauskas, Raimondas; Weingaertner, Elias

    In a layered communication architecture, transport layer protocols handle the data exchange between processes on different hosts over potentially lossy communication channels. Typically, transport layer protocols are either connection-oriented or are based on the transmission of individual datagrams. Well known transport protocols are the connection-oriented Transmission Control Protocol (TCP) [372] and the User Datagram Protocol (UDP) [370] as well as the Stream Control Transmission Protocol (SCTP) [340] and DCCP, the Datagram Congestion Control Protocol [259]. In this chapter, we focus on the modeling process of the transport layer. While we mostly use TCP and UDP as a base of comparison from this point, we emphasize that the methodologies discussed further on are conferrable to virtually any transport layer in any layered communication architecture.

  6. Columnar modelling of nucleation burst evolution in the convective boundary layer - first results from a feasibility study Part II: Meteorological characterisation

    NASA Astrophysics Data System (ADS)

    Hellmuth, O.

    2006-09-01

    While in Paper I of four papers a revised columnar high-order modelling approach to investigate gas-aerosol-turbulence interactions in the convective boundary layer (CBL) was deduced, in the present Paper II the model capability to predict the evolution of meteorological CBL parameters is demonstrated. Based on a model setup to simulate typical CBL conditions, predicted first-, second- and third-order moments were shown to agree very well with those obtained from in situ and remote sensing turbulence measurements such as aircraft, SODAR and LIDAR measurements as well as with those derived from ensemble-averaged large eddy simulations and wind tunnel experiments. The results show, that the model is able to predict the meteorological CBL parameters, required to verify or falsify, respectively, previous hypothesis on the interaction between CBL turbulence and new particle formation.

  7. 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.

  8. 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.

  9. Evolution and formation of shear layers in a developing turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Lee, Junghoon; Monty, Jason; Hutchins, Nicholas

    2016-11-01

    The evolution and formation mechanism of shear layers in the outer region of a turbulent boundary layer are investigated using time-resolved PIV datasets of a developing turbulent boundary layer from inception at the trip up to Reτ = 3000 . An analysis of a sequence of instantaneous streamwise velocity fluctuation fields reveals that strong streamwise velocity gradients are prevalent along interfaces where low- and high-speed regions interact. To provide an insight on how such regions are associated with the formation of shear layers in the outer regions, we compute conditional averages of streamwise velocity fluctuations based on a strong shear layer. Our results reveal that one possible mechanism for the generation of shear layers in the outer region is due to the mismatch in the convection velocities between low- and high-speed regions. The results also indicate that the angle of the inclined shear layer is developing in time. In addition, the conditionally averaged velocity fluctuations exhibit a local instability along these shear layers, leading to a shear layer roll-up event as the layers evolve in time. Based on these findings, we propose a conceptual model which describes dynamic interactions of shear layers and their associated large-scale coherent motions. The authors wish to acknowledge the financial support of the Australian Research Council.

  10. Origin and evolution of asthenospheric layers

    NASA Astrophysics Data System (ADS)

    Czechowski, Leszek; Grad, Marek

    2013-04-01

    is probably in the range from 3 to 5. We investigate the processes of formation and evolution of low viscosity layers ("asthenospheric layers") in the upper mantle. The time scale of the temperature changes is of the order of 10 Myr. The characteristic time of stress changes could be much shorter depending on tectonic processes. Eventually processes of formation and vanishing of low viscosity layers is very dynamical. In a relatively short time (below 1 Myr) the pattern the viscosity distribution and velocity gradient could change substantially. Using results from deep seismic sounding and surface wave tomography we have found that below some regions there are structures in the mantle that could be a forming/vanishing low viscosity layers. Reflectors in the lower lithosphere are observed beneath Trans-European suture zone between Precambrian and Palaeozoic platforms. In a thick Baltic shield lithosphere (200 km or more) low velocity zones and seismic reflectors are observed in the depth range 60-100 km, which could be interpreted as mechanical low Vp velocity zones, in contrast to thermal velocity zone in deeper asthenosphere.

  11. Link Layer Modeling

    NASA Astrophysics Data System (ADS)

    Mühleisen, M.; Bültmann, D.; Klagges, K.; Schinnenburg, M.

    The Data Link Layer (DLL) is located above the PHY layer described in the previous chapter and below the network layer described in Chapter 16. All data received from these layers is digital. Today most parts of the DLL are implemented in software, either as device drivers running on general purpose Central Processing Units (CPUs) or as firmware running on dedicated network interface hardware.

  12. Exfoliation of layered double hydroxides for enhanced oxygen evolution catalysis.

    PubMed

    Song, Fang; Hu, Xile

    2014-07-17

    The oxygen evolution reaction is a key reaction in water splitting. The common approach in the development of oxygen evolution catalysts is to search for catalytic materials with new and optimized chemical compositions and structures. Here we report an orthogonal approach to improve the activity of catalysts without alternating their compositions or structures. Specifically, liquid phase exfoliation is applied to enhance the oxygen evolution activity of layered double hydroxides. The exfoliated single-layer nanosheets exhibit significantly higher oxygen evolution activity than the corresponding bulk layered double hydroxides in alkaline conditions. The nanosheets from nickel iron and nickel cobalt layered double hydroxides outperform a commercial iridium dioxide catalyst in both activity and stability. The exfoliation creates more active sites and improves the electronic conductivity. This work demonstrates the promising catalytic activity of single-layered double hydroxides for the oxygen evolution reaction.

  13. 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.

  14. 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.

  15. Evolution of the Ocean Surface Boundary Layer during 2012-2013 as observed by the OSMOSIS Glider Array; a Challenge for Model Simulations

    NASA Astrophysics Data System (ADS)

    Heywood, K. J.; Damerell, G. M.; Thompson, A. F.; Kaiser, J.; Binetti, U.; Belcher, S. E.; Grant, A. L.; Calvert, D.

    2016-02-01

    As part of the OSMOSIS project, a time series of profiling gliders was maintained at the Porcupine Abyssal Plain site in the northeast Atlantic from September 2012 to September 2013. Vertical resolution of 1 m and profiles every 2 hours allow us to characterize temporal variability throughout the upper 1000 m in temperature, salinity and dissolved oxygen concentration. Mixed/mixing layer depth is determined using a variety of thresholds and techniques; dissolved oxygen concentration identifies the active mixing layer well and tends to be a few meters shallower than the mixed layer depth determined from thresholds in physical parameters. During fall 2012, the mixed layer deepens gradually, but its depth does not vary much on time scales of hours to days. January-April 2013 is characterized by a deep but highly variable mixed layer depth, reaching 390 m in early February. In spring the mixed layer shoals rapidly, followed by periods of intermittent deepening and restratification in May and June. In summer the mixed layer is at its shallowest and least variable. The seasonality in the mixed layer temperature is consistent with the net surface heat flux, whereas the variability in mixed layer salinity is not consistent with the surface freshwater fluxes from the ERA-Interim data set. The glider data set provides a challenge for verification of mixing and stratification processes in numerical models. We compare the observed variability and depth of the mixed layer with that simulated by various one-dimensional mixed layer models, including the new prognostic OSBL model developed during OSMOSIS that includes Langmuir turbulence. This demonstrates remarkable agreement in mixed layer depths between the simulations forced by the ERA-Interim fluxes and the glider observations.

  16. Profile evolution for conformal atomic layer deposition over nanotopography.

    PubMed

    Cleveland, Erin R; Banerjee, Parag; Perez, Israel; Lee, Sang Bok; Rubloff, Gary W

    2010-08-24

    The self-limiting reactions which distinguish atomic layer deposition (ALD) provide ultrathin film deposition with superb conformality over the most challenging topography. This work addresses how the shapes (i.e., surface profiles) of nanostructures are modified by the conformality of ALD. As a nanostructure template, we employ a highly scalloped surface formed during the first anodization of the porous anodic alumina (PAA) process, followed by removal of the alumina to expose a scalloped Al surface. SEM and AFM reveal evolution of surface profiles that change with ALD layer thickness, influenced by the way ALD conformality decorates the underlying topography. The evolution of surface profiles is modeled using a simple geometric 3D extrusion model, which replicates the measured complex surface topography. Excellent agreement is obtained between experimental data and the results from this model, suggesting that for this ALD system conformality is very high even on highly structured, sharp features of the initial template surface. Through modeling and experimentation, the benefits of ALD to manipulate complex surface topographies are recognized and will play an important role in the design and nanofabrication of next generation devices with increasingly high aspect ratios as well as nanoscale features.

  17. Hillslope evolution in landscapes dominated by layered rocks

    NASA Astrophysics Data System (ADS)

    Glade, R.; Anderson, R. S.

    2016-12-01

    Geologic structure and lithology can exert fundamental control over hillslope evolution. Landforms common across the western US, such as mesas, hogbacks, flatirons, and symmetric ridges bounding dikes, develop in the face of differential weathering of layered rocks in a horizontal, tilted, or vertical structural orientation. These features exhibit a characteristic form distinct from that of homogeneous, soil-mantled hillslopes; linear-to-concave up slopes developed on soft underlying rock typically display a thin, non-uniform layer of mobile regolith and are armored by debris derived from the resistant layers. Feedbacks between weathering and transport of both easily eroded rock and embedded resistant material can explain this general form where debris is dominated by large resistant blocks. In the more general case, however, relationships between the size distribution of the resistant material, relative weathering rates, and boundary condition history are not well-understood. Here we use a 1-D numerical model to explore the evolution of two end-member landforms: a hogback associated with a tilted sandstone bed, and a symmetrical ridge associated with a vertical basalt dike, both bounded by shale bedrock. The first, modeled after the Dakota Hogback near Boulder, Colorado, produces large sandstone blocks that both armor the underlying slope from weathering and stall regolith motion. The vertical dike, modeled after Shiprock, New Mexico, produces both large blocks and small basalt chips that armor the bounding slopes. We show that in both settings, feedbacks between armor and soft rock lead to autogenic processes that modulate base level signals, alter hillslope form, and increase relief over time when compared to a control case with no armor. We explore a variety of boundary conditions in which the presence of these feedbacks leads to a quasi-steady state hillslope form that differs both quantitatively and qualitatively from that expected of a traditional parabolic

  18. Evolution of Titan's High-Pressure Ice layer

    NASA Astrophysics Data System (ADS)

    Sotin, C.; Kalousova, K.

    2016-12-01

    Constraints on the present interior structure of Titan come from the gravity science experiment onboard the Cassini spacecraft and from the interpretation of the Extremely Low Frequency (ELF) wave observed by the Huygens probe [1, 2]. From the surface to the center, Titan would be composed of 4 layers: an icy crust, a global salty ocean, a layer of high-pressure ice (HP ice) and a core made of hydrated silicates [2, 3, 4]. The presence of a large amount of 40Ar in Titan's atmosphere argues for a geologically recent exchange process between the silicate core, where 40Ar is produced by the decay of 40K, and the atmosphere. Argon must then be able to be transported from the silicate core to the surface. This study investigates how volatiles can be transported through the HP ice layer.Recent numerical simulations [5] have demonstrated that the dynamics of the HP ice layer is controlled by convection processes in a two-phase material (water and high-pressure ice). The silicate / HP ice interface is maintained at the melting temperature, which might allow for the incorporation of volatiles such as 40Ar into the convecting HP ice. Above the hot thermal boundary layer, the temperature of the convecting HP ice is below the melting temperature, except for the upwelling plumes when they approach the cold thermal boundary layer. The upper part of the HP ice layer is at the melting point and permeable for water transport, providing a path for the transfer of volatiles trapped in the ice towards the ocean.Scaling laws are inferred from the numerical simulations [5]. They are then used to model the evolution of the HP ice layer. Specifically, we look at the effect of (i) ice viscosity, (ii) heat flux at the silicate/HP ice interface, and (iii) presence of anti-freeze compounds in the ocean, on the thickness of the HP ice layer. In addition, our results provide insights on possible resurfacing processes that could explain the geologically young age of Titan's surface. This work

  19. 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.

  20. 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.

  1. Thermal Evolution of The Moon With a Thicker Kreep Layer

    NASA Astrophysics Data System (ADS)

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

    1998-01-01

    The canonical view of the magma ocean is of a monotonically cooling large magma body perhaps enveloping the entire Moon, which solidified within about 100 my of the formation of the Moon. This model is consistent with W-Hf Sm-Nd isotope data, the very old ages of FAN and some magnesian-suite norites and troctolites and the model ages for KREEP. Recently, Korotev and Wieczorek and Phillips have argued that the crystallization of the last dregs of the magma ocean was not only prolonged but large amounts of radiogenic heating resulted in the remelting and dissolution of mafic cumulates by the UrKREEP liquid. These melts are believed to be parent liquids to the magnesian-suite troctolites because they account for the combination of high contents of incompatible trace elements and the very refractory major element composition. This model requires that the heat budget changes from one that cools the magma ocean to one that initiates reheating. About the only way to reverse this cooling trend is to segregate the magma ocean under some portions of the crust. For example, if the residual liquids are locally doubled in thickness the surface cooling is reduced thus reversing the cooling tend. By mass balance some portions of the magma ocean would be thinned and thereby would experience an accelerated cooling.accelerated cooling. We have examined the thermal history of the upper Moon. We formulate models of radioactive heating and conductive cooling to examine the possible role of a thick KREEP-rich layer on lunar regional thermal evolution. The models treat heat transfer by conduction in a spherical geometry with a KREEP layer containing a prescribed rate of radiogenic heating. The region of thick KREEP presumably exists only within the Imbrium-Procellarum region of the Moon. The spherical model is a reasonable representation of this case since the lateral dimensions of the region are large compared to its depth. The edges of the thick KREEP region which are not treated

  2. Evolution of bumpy boundary layers in planetary mantles

    NASA Astrophysics Data System (ADS)

    Hansen, Ulrich; Stein, Claudia

    2017-04-01

    There is much evidence that the core mantle boundary does not resemble the picture of a simple thermal boundary layer, as known from thermal convection at high Rayleigh number. Rather it seems to be of complex structure, possibly induced by compositionally dense material. Present models of mantle convection, aiming at simulating the complex structure and dynamics of the lower boundary layer require several ad hoc assumptions. Most of them postulate the presence of a sufficiently dense layer at the transition from the magma ocean state to solid state mantle convection. Especially the density excess distinct material needs to be assumed. Both conditions are critical for the dynamics in a sense, that too much, too dense material results in a 'pancake-shaped ' flat layer without any topography while for having too little, not sufficiently dense material, thermal convection would simply sponge off the distinct material. Unfortunately the values of excess density and mass can hardly be constrained .Further it seems unlikely that conditions at the end of the magma ocean epoch resembled a chemically homogeneous mantle From a series of model calculations, starting out from an initial mantle as possibly evolve by fractional crystallization, all with realistic rheology, we find that chemical transport across the CMB plays a key role for the formation of a bumpy boundary..Parameterising the chemical transport by diffusion with an extreme low diffusivity, leads selfconsistently (without assuming any pre-exisiting dense material) to the formation of compositional piles with different degrees of complexity. Dense material, slowly entering the mantle is accumulated by thermal advection and thus piles are formed. At the same time the presence of the piles reduces further compositional influx. We find the presence of such piles to significantly influence the thermal - and compositional evolution of the mantle system .

  3. 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.

  4. SNRPy: Supernova remnant evolution modeling

    NASA Astrophysics Data System (ADS)

    Leahy, Denis A.; Williams, Jacqueline

    2017-03-01

    SNRPy (Super Nova Remnant Python) models supernova remnant (SNR) evolution and is useful for understanding SNR evolution and to model observations of SNR for obtaining good estimates of SNR properties. It includes all phases for the standard path of evolution for spherically symmetric SNRs and includes alternate evolutionary models, including evolution in a cloudy ISM, the fractional energy loss model, and evolution in a hot low-density ISM. The graphical interface takes in various parameters and produces outputs such as shock radius and velocity vs. time, SNR surface brightness profile and spectrum.

  5. 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.

  6. A Modeling Pattern for Layered System Interfaces

    NASA Technical Reports Server (NTRS)

    Shames, Peter M.; Sarrel, Marc A.

    2015-01-01

    Communications between systems is often initially represented at a single, high level of abstraction, a link between components. During design evolution it is usually necessary to elaborate the interface model, defining it from several different, related viewpoints and levels of abstraction. This paper presents a pattern to model such multi-layered interface architectures simply and efficiently, in a way that supports expression of technical complexity, interfaces and behavior, and analysis of complexity. Each viewpoint and layer of abstraction has its own properties and behaviors. System elements are logically connected both horizontally along the communication path, and vertically across the different layers of protocols. The performance of upper layers depends on the performance of lower layers, yet the implementation of lower layers is intentionally opaque to upper layers. Upper layers are hidden from lower layers except as sources and sinks of data. The system elements may not be linked directly at each horizontal layer but only via a communication path, and end-to-end communications may depend on intermediate components that are hidden from them, but may need to be shown in certain views and analyzed for certain purposes. This architectural model pattern uses methods described in ISO 42010, Recommended Practice for Architectural Description of Software-intensive Systems and CCSDS 311.0-M-1, Reference Architecture for Space Data Systems (RASDS). A set of useful viewpoints and views are presented, along with the associated modeling representations, stakeholders and concerns. These viewpoints, views, and concerns then inform the modeling pattern. This pattern permits viewing the system from several different perspectives and at different layers of abstraction. An external viewpoint treats the systems of interest as black boxes and focuses on the applications view, another view exposes the details of the connections and other components between the black boxes

  7. 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.

  8. Evolution of planar defects during homoepitaxial growth of β-Ga2O3 layers on (100) substrates—A quantitative model

    NASA Astrophysics Data System (ADS)

    Schewski, R.; Baldini, M.; Irmscher, K.; Fiedler, A.; Markurt, T.; Neuschulz, B.; Remmele, T.; Schulz, T.; Wagner, G.; Galazka, Z.; Albrecht, M.

    2016-12-01

    We study the homoepitaxial growth of β-Ga2O3 (100) grown by metal-organic vapour phase as dependent on miscut-angle vs. the c direction. Atomic force microscopy of layers grown on substrates with miscut-angles smaller than 2° reveals the growth proceeding through nucleation and growth of two-dimensional islands. With increasing miscut-angle, step meandering and finally step flow growth take place. While step-flow growth results in layers with high crystalline perfection, independent nucleation of two-dimensional islands causes double positioning on the (100) plane, resulting in twin lamellae and stacking mismatch boundaries. Applying nucleation theory in the mean field approach for vicinal surfaces, we can fit experimentally found values for the density of twin lamellae in epitaxial layers as dependent on the miscut-angle. The model yields a diffusion coefficient for Ga adatoms of D = 7 × 10-9 cm2 s-1 at a growth temperature of 850 °C, two orders of magnitude lower than the values published for GaAs.

  9. Evolution of a Western Arctic Ice Ocean Boundary Layer and Mixed Layer Across a Developing Thermodynamically Forced Marginal Ice Zone

    DTIC Science & Technology

    2016-09-01

    NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA DISSERTATION Approved for public release. Distribution is unlimited. EVOLUTION ...blank) 2. REPORT DATE September 2016 3. REPORT TYPE AND DATES COVERED Dissertation 4. TITLE AND SUBTITLE EVOLUTION OF A WESTERN ARCTIC ICE...measurements were collected across the Canada Basin to study the summer evolution of the ice-ocean boundary layer (IOBL) and ocean mixed layer (OML

  10. 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

  11. Deep layer malt drying modelling

    SciTech Connect

    Lopez, A.; Virseda, P.; Martinez, G.; Llorca, M.

    1997-05-01

    In malt production drying operation plays an important role in the total processing cost, however there are not many studies on malt drying modeling and optimization. In this paper a deep layer malt drying mathematical model in the form of four partial differential equations is presented. To determine drying constants, malt thin layer drying experiments at several air temperatures and relative humidities were made. The model were validated at industrial scale. The greatest energy savings, approximately 5.5% in fuel and 7.5% in electric energy, were obtained by an additional (and increased) air recirculation, which is carried out during the last 6 hours of the drying process and a significant decrease of air flow-rate during the last 6 hours of the drying process.

  12. Modeling Electrothermal Plasma with Boundary Layer Effects

    NASA Astrophysics Data System (ADS)

    AlMousa, Nouf Mousa A.

    Electrothermal plasma sources produce high-density (1023-10 28 /m3) and high temperature (1-5 eV) plasmas that are of interest for a variety of applications such as hypervelocity launch devices, fusion reactor pellet injectors, and pulsed thrusters for small satellites. Also, the high heat flux (up to 100 GW/m2) and high pressure (100s MPa) of electrothermal (ET) plasmas allow for the use of such facilities as a source of high heat flux to simulate off-normal events in Tokamak fusion reactors. Off-normal events like disruptions, thermal and current quenches, are the perfect recipes for damage of plasma facing components (PFC). Successful operation of a fusion reactor requires comprehensive understanding of material erosion behavior. The extremely high heat fluxes deposited in PFCs melt and evaporate or directly sublime the exposed surfaces, which results in a thick vapor/melt boundary layer adjacent to the solid wall structure. The accumulating boundary layers provide a self-protecting nature by attenuating the radiant energy transport to the PFCs. The ultimate goal of this study is to develop a reliable tool to adequately simulate the effect of the boundary layers on the formation and flow of the energetic ET plasma and its impact on exposed surfaces erosion under disruption like conditions. This dissertation is a series of published journals/conferences papers. The first paper verified the existence of the vapor shield that evolved at the boundary layer under the typical operational conditions of the NC State University ET plasma facilities PIPE and SIRENS. Upon the verification of the vapor shield, the second paper proposed novel model to simulate the evolution of the boundary layer and its effectiveness in providing a self-protecting nature for the exposed plasma facing surfaces. The developed models simulate the radiant heat flux attenuation through an optically thick boundary layer. The models were validated by comparing the simulation results to experimental

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

    PubMed

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

    2016-08-12

    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.

  14. 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

  15. 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.

  16. Nonlinear evolution of Mack modes in a hypersonic boundary layer

    NASA Astrophysics Data System (ADS)

    Chokani, Ndaona

    2005-01-01

    In hypersonic boundary layer flows the nonlinear disturbance evolution occurs relatively slowly over a very long length scale and has a profound effect on boundary layer transition. In the case of low-level freestream disturbances and negligible surface roughness, the transition is due to the modal growth of exponentially growing Mack modes that are destabilized by wall cooling. Cross-bicoherence measurements, derived from hot-wire data acquired in a quiet hypersonic tunnel, are used to identify and quantify phase-locked, quadratic sum and difference interactions involving the Mack modes. In the early stages of the nonlinear disturbance evolution, cross-bicoherence measurements indicate that the energy exchange between the Mack mode and the mean flow first occurs to broaden the sidebands; this is immediately followed by a sum interaction of the Mack mode to generate the first harmonic. In the next stages of the nonlinear disturbance evolution, there is a difference interaction of the first harmonic, which is also thought to contribute to the mean flow distortion. This difference interaction, in the latter stages, is also accompanied by a difference interaction between Mack mode and first harmonic, and a sum interaction, which forces the second harmonic. Analysis using the digital complex demodulation technique, shows that the low-frequency, phase-locked interaction that is identified in the cross bicoherence when the Mack mode and first harmonic have large amplitudes, arises due to the amplitude modulation of Mack mode and first harmonic.

  17. 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.

  18. Two types of asthenospheric layers and their evolution

    NASA Astrophysics Data System (ADS)

    Czechowski, Leszek; Grad, Marek

    2016-04-01

    -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

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. Evolution of structural properties of Si(001) subsurface layer containing He bubbles by low temperature annealing

    NASA Astrophysics Data System (ADS)

    Lomov, Andrey A.; Shcherbachev, Kirill D.; Chesnokov, Yury M.; Kiselev, Dmitrii A.; Miakonkikh, Andrew V.

    2016-12-01

    Transformation of microstructure of the buried He bubbles of silicon surface layer after He+ low energy plasma immersion ion implantation and subsequent low-thermal annealing were studied by high resolution X-ray diffraction and reflectivity, Rutherford backscattering spectroscopy, transmission electron and atomic force microscopy methods. The ion energies varied in the range 2 - 5 keV at constant exposure ion doses 5×·1017 cm-2. Formation of a three-layer structure (amorphous a-SiOx layer at the surface, amorphous a-Si layer with helium bubbles and buried helium bubbles heavy damaged tensile strained crystalline c-Si layer) that is retained after annealing was observed. Helium-filled bubbles are observed in an as-implanted sample. Evolution of the multilayer structure and the bubbles due to annealing are revealed and comparing with the structural parameters of an as-implanted sample was done. The bubbles are shown to trend into two-model distribution after annealing. The characteristic bubble size is determined to be in a range of 2-20 nm. Large size helium-filled bubbles are located in the amorphous a-Si layer. Small size bubbles are revealed inside the damaged crystalline Si layer. These bubbles are a major source of tensile strain in c-Si layer.

  5. The Microcircuit Concept Applied to Cortical Evolution: from Three-Layer to Six-Layer Cortex

    PubMed Central

    Shepherd, Gordon M.

    2011-01-01

    Understanding the principles of organization of the cerebral cortex requires insight into its evolutionary history. This has traditionally been the province of anatomists, but evidence regarding the microcircuit organization of different cortical areas is providing new approaches to this problem. Here we use the microcircuit concept to focus first on the principles of microcircuit organization of three-layer cortex in the olfactory cortex, hippocampus, and turtle general cortex, and compare it with six-layer neocortex. From this perspective it is possible to identify basic circuit elements for recurrent excitation and lateral inhibition that are common across all the cortical regions. Special properties of the apical dendrites of pyramidal cells are reviewed that reflect the specific adaptations that characterize the functional operations in the different regions. These principles of microcircuit function provide a new approach to understanding the expanded functional capabilities elaborated by the evolution of the neocortex. PMID:21647397

  6. Structure evolution in layers of polymer blend nanoparticles.

    PubMed

    Raczkowska, Joanna; Montenegro, Rivelino; Budkowski, Andrzej; Landfester, Katharina; Bernasik, Andrzej; Rysz, Jakub; Czuba, Paweł

    2007-06-19

    The early stages of phase evolution, not available for nanometer polymer blend films spin-cast from solutions of incompatible mixtures, have been examined for films prepared from nanoparticles of deuterated polystyrene/ poly(methyl methacrylate) blends (1:1 mass fraction of dPS/PMMA) with PS-PMMA diblock copolymer additives. The initial phase arrangement, confined to the size of nanoparticles, has provided the homogeneity of the initial film composition. The early stages of structure formation, promoted by annealing and traced with atomic and lateral force microscopy (AFM, LFM) as well as secondary ion mass spectroscopy (SIMS), resulted in bilayers, observed commonly for as-prepared solvent-cast blends. The initiated capillary instability of the upper dPS-rich layer depended on copolymer additives, which enhanced the lateral structures pinning the dewetting process.

  7. Modeling glycocalyx of the tear film as poroelastic layer

    NASA Astrophysics Data System (ADS)

    Siddique, Javed; Mastroberardino, Antonio; Braun, Richard; Anderson, Daniel

    2016-11-01

    In this study we investigate a one-dimensional model for the evolution of the tear film subject to locally elevated evaporation at its anterior surface. We formulate a thin film model based on a combination of lubrication theory and mixture theory in order to understand the dynamics between the aqueous layer and the glycocalyx, which we treat as a poroelastic region. The model includes the physical effects of evaporation, surface tension, and viscosity. Simon Foundation, NSF, NIH.

  8. Evolution of the compositionally dense layer at the bottom of the mantle

    NASA Astrophysics Data System (ADS)

    Pál Farkas, Márton; Galsa, Attila; Herein, Mátyás; Lenkey, László

    2013-04-01

    Two-dimensional numerical models have been carried out in order to investigate how the evolution of the compositionally dense D" layer influences the time series of the heat flux, velocity, temperature and concentration of dense material. The initial density difference between D" and the overlaying mantle, β was the single studied parameter which was varied between 0.1-2%. Based on the time series six stages of the D" evolution were separated from the surface deformation of the dense layer to the totally homogenized mantle. In all studied cases the final state got over the homogenization, even for β=2% when the traditional buoyancy ratio was larger than 1. In order to investigate the evolution of the compositionally dense layer a time-dependent buoyancy ratio, B was defined by the ratio of the chemical and thermal density difference between D" and the overlaying mantle. The decrease in B was deduced from three reasons: (1) the increase in temperature difference between the layers due to the inhibited heat advection as well as the decrease in concentration difference owing to (2) the pollution of the upper layer by surface erosion of the D" and (3) the dilution of the dense layer with light material intermixed from the upper layer facilitated by convection within D". As the value of B approaches to 1, the mixing of the dense material becomes more effective, it is the most vigorous phase of the thermo-chemical convection. For B=0 the mantle is mixed, the homogenization continues protractedly. It was established that larger initial density difference, β has longer/stronger effect on the monitored parameters. An exponential relation was found between the occurrences of different stages characterizing the evolution of D" layer and β. The reduction in B during the erosion/dilution phase ((2) and (3)) and the effective mixing of the dense layer (0˜ B ˜1) can be approximated by a linear function, thus the occurrences of single stages are anticipated. The slope of the

  9. 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.

  10. New model systems for experimental evolution.

    PubMed

    Collins, Sinéad

    2013-07-01

    Microbial experimental evolution uses a few well-characterized model systems to answer fundamental questions about how evolution works. This special section highlights novel model systems for experimental evolution, with a focus on marine model systems that can be used to understand evolutionary responses to global change in the oceans.

  11. 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.

  12. Continuum Modeling of Facet Evolution

    NASA Astrophysics Data System (ADS)

    Kandel, Daniel

    2000-03-01

    Standard continuum models of surface dynamics are very useful for studying thin film evolution on the micron length scale. Unfortunately, they are inadequate below the roughening transition, since they do not appropriately describe faceting. Our goal is to propose a continuum approach which deals with facet dynamics in a physically accurate way. We studied in detail the dynamics of faceting in simple submicron surface structures [1], and proposed two approaches for the development of continuum models. First, we rigorously derived continuum kinetic models of the systems of interest, starting from step flow models. These models break down at singular points, which we identify as facet edges. The models are not applicable on facets, and the surface profile is obtained as a solution of the continuum model with boundary conditions at the singular points. Secondly, we showed [2] that if the existence of both steps and anti-steps in regions of small surface slope is taken into account, it is possible to construct continuum models that are valid even on facets. The solutions of both types of continuum models are in excellent agreement with step flow models. The resulting surface profiles are of relevance to experiments on decay of one dimensional periodic gratings. Our work points to a possible general continuum model for an accurate description of kinetics of crystalline surfaces below the roughening transition. [1] N. Israeli and D. Kandel, Phys. Rev. Lett. 80, 3300 (1998); N. Israeli and D. Kandel, Phys. Rev. B 60, 5946 (1999). [2] N. Israeli and D. Kandel, preprint.

  13. 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

  14. Structural and morphological evolution of thrust wedges above a ductile layer with different viscous behavior

    NASA Astrophysics Data System (ADS)

    Cerca, M.; Barrientos, B.; Garcia-Marquez, J.; Portillo-Pineda, R.; Hernandez-Bernal, C.

    2007-05-01

    A series of scaled physical experiments illustrate the importance of differences in density and viscous behavior of décollement in the structural evolution of thrust wedges during shortening. In particular, we have analyzed the effect of changes in viscosity in the morphological evolution and strain of the brittle overburden surface. Ten models properly scaled in geometry and mechanical behavior of natural geological materials were deformed at the Modeling Laboratory (LAMMG) of UNAM. Mechanical stratification of the models included basal and upper brittle layers of 1 and 2 cm, respectively; separated by an intermediate viscous layer of 0.5 cm. Brittle layers were constructed with grains of quartz sand following a Mohr-Coulomb criterion of faulting and bulk density of ca. 1300 kg m-3. The viscous layer was composed of silicon-sand mixtures having differences in dynamic viscosity (Pa s) and density (kg m-3) as the following cases: (A) 2.0 e 4 and 978, (B) 3.3 e 4 and 1195, (C) 4.7 e 4 and 1270. The experiments were carried out in a Plexiglas box of 40x15x10 cm and deformed by moving a vertical wall at a constant velocity of 1.5 cm hr-1. Cross sections of the experiments were obtained for values of bulk shortening of ca. 20 and 40 percent. The modeling results suggest a close relation of structural style of the thrust wedge with the initial conditions of décollement viscosity. Low viscosity models have a structural development characterized by low angle napes and detachment folds with limb rotation indicating a predominant vergence towards foreland. High viscosity models have a greater mechanical coupling between décollement and overburden and develop preferentially detachment folds with higher elevation and undefined vergence. The evolution of the surface in two models with different initial dynamic viscosity, cases A and B, was analyzed at the optical interferometry laboratory of CIO with two full-field optical techniques: fringe projection and laser speckle

  15. Modeling of Intellite 3 Layer Deformable Mirror

    SciTech Connect

    Papavasiliou, A

    2002-04-15

    This is a report on modeling of the Intellite three layer membrane mirror design. The goal of this project was to provide Intellite with a model that will allow them to design a mirror with confidence.

  16. Mass transfer model for two-layer TBP oxidation reactions

    SciTech Connect

    Laurinat, J.E.

    1994-09-28

    To prove that two-layer, TBP-nitric acid mixtures can be safely stored in the canyon evaporators, it must be demonstrated that a runaway reaction between TBP and nitric acid will not occur. Previous bench-scale experiments showed that, at typical evaporator temperatures, this reaction is endothermic and therefore cannot run away, due to the loss of heat from evaporation of water in the organic layer. However, the reaction would be exothermic and could run away if the small amount of water in the organic layer evaporates before the nitric acid in this layer is consumed by the reaction. Provided that there is enough water in the aqueous layer, this would occur if the organic layer is sufficiently thick so that the rate of loss of water by evaporation exceeds the rate of replenishment due to mixing with the aqueous layer. This report presents measurements of mass transfer rates for the mixing of water and butanol in two-layer, TBP-aqueous mixtures, where the top layer is primarily TBP and the bottom layer is comprised of water or aqueous salt solution. Mass transfer coefficients are derived for use in the modeling of two-layer TBP-nitric acid oxidation experiments. Three cases were investigated: (1) transfer of water into the TBP layer with sparging of both the aqueous and TBP layers, (2) transfer of water into the TBP layer with sparging of just the TBP layer, and (3) transfer of butanol into the aqueous layer with sparging of both layers. The TBP layer was comprised of 99% pure TBP (spiked with butanol for the butanol transfer experiments), and the aqueous layer was comprised of either water or an aluminum nitrate solution. The liquid layers were air sparged to simulate the mixing due to the evolution of gases generated by oxidation reactions. A plastic tube and a glass frit sparger were used to provide different size bubbles. Rates of mass transfer were measured using infrared spectrophotometers provided by SRTC/Analytical Development.

  17. Model of attenuation of long waves under continuous ice layer

    NASA Astrophysics Data System (ADS)

    Kochanov, M. B.; Petrov, B. A.

    2017-01-01

    In this work new mathematical model of long wave propagation on water surface with ice cover is proposed. The model of thin elastic plate is used to describe ice layer movement. Equation for ice cover contain additional term to takes into account dissipation effects in the ice cover to explain wave attenuation. Proposed model was reduced to one nonlinear evolution equation for water level perturbation. The expression for wave energy was obtained under assumption of long waves. Proposed model is numerically studied, energy of system is computed. Obtained results are compared with results of suggested before model that takes into account the flow law of Glen.

  18. 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

  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. 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

  1. 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.

  2. Evolution of disturbances in the shock layer on a flat plate in a flow of vibrationally excited gases

    NASA Astrophysics Data System (ADS)

    Reshetova, A. I.; Poplavskaya, T. V.

    2016-10-01

    The problem of disturbances evolution in a hypersonic viscous shock layer on a flat plate is considered. Numerical simulation was performed by solving 2D Navier-Stokes equations using the ANSYS Fluent software package within the model of thermally perfect gas. The change of vibrational energy was simulated by the Landau-Teller equation, in which the finite time of vibrational relaxation of CO2 molecules was taken into account. The quantitative data on the effect of vibrational relaxation of CO2 molecules on the evolution of acoustic disturbances in the shock layer on a plate is obtained.

  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. Charge Modeling for Metal Layer on Insulating Substrate

    NASA Astrophysics Data System (ADS)

    Okai, Nobuhiro; Yano, Tasuku; Sohda, Yasunari

    2011-06-01

    A charging model for magnification variation in the observation of a metal pattern on an insulating substrate using a scanning electron microscope is proposed. To calculate the time evolution of charging, we replace electron trajectory with current. Negative charging of the metal layer is observed and is caused by the current from the anode, which is set above the sample, to the metal layer. The origin of the current is tertiary electrons produced by backscattered electrons colliding with the anode. By controlling tertiary-electron trajectories through the application of bias voltage to the anode, the magnification variation can be reduced to almost zero.

  5. 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.

  6. The evolution of a wave packet to turbulent spot in the boundary layer at high speeds

    NASA Astrophysics Data System (ADS)

    Sidorenko, A. A.; Polivanov, P. A.; Gromyko, Y. V.; Bountin, D. A.; Maslov, A. A.

    2016-10-01

    Hypersonic boundary layer stability and transition were studied experimentally for the test cases of 7 deg half-angle sharp and blunted cones. The experiments were performed for M=6. Wall pressure pulsations were recorded synchronously with high speed Schlieren visualization. The combined data processing algorithm for coupling of unsteady pressure sensors with high-speed Schlieren images is proposed. Analysis of the wall pressure pulsations evolution reveals that the turbulent spot may arise in different ways. It was found that for the blunted model the role of the second mode in origination of the turbulent spot is more evident.

  7. Evolution of a wave packet to turbulent spot in a boundary layer at high speeds

    NASA Astrophysics Data System (ADS)

    Polivanov, P. A.; Gromiko, Yu. V.; Bountin, D. A.; Sidorenko, A. A.; Maslov, A. A.

    2017-06-01

    Hypersonic boundary layer stability and transition were studied experimentally for the test case of 7 degree half-angle cone with various nose bluntness. The experiments were performed for M = 6. Wall pressure pulsations were recorded synchronously with the high-speed schlieren. The combined data processing algorithm for coupling of unsteady pressure sensors with high-speed schlieren images was proposed. Analysis of the wall pressure pulsations evolution reveals that the turbulent spot may arise in different ways. It was found that for the blunted model, the role of the second mode in origination of the turbulent spot is more evident.

  8. Performance Evaluation Model for Application Layer Firewalls

    PubMed Central

    Yang, Wu; Dong, Hui; Zhang, Jiangchuan

    2016-01-01

    Application layer firewalls protect the trusted area network against information security risks. However, firewall performance may affect user experience. Therefore, performance analysis plays a significant role in the evaluation of application layer firewalls. This paper presents an analytic model of the application layer firewall, based on a system analysis to evaluate the capability of the firewall. In order to enable users to improve the performance of the application layer firewall with limited resources, resource allocation was evaluated to obtain the optimal resource allocation scheme in terms of throughput, delay, and packet loss rate. The proposed model employs the Erlangian queuing model to analyze the performance parameters of the system with regard to the three layers (network, transport, and application layers). Then, the analysis results of all the layers are combined to obtain the overall system performance indicators. A discrete event simulation method was used to evaluate the proposed model. Finally, limited service desk resources were allocated to obtain the values of the performance indicators under different resource allocation scenarios in order to determine the optimal allocation scheme. Under limited resource allocation, this scheme enables users to maximize the performance of the application layer firewall. PMID:27893803

  9. Performance Evaluation Model for Application Layer Firewalls.

    PubMed

    Xuan, Shichang; Yang, Wu; Dong, Hui; Zhang, Jiangchuan

    2016-01-01

    Application layer firewalls protect the trusted area network against information security risks. However, firewall performance may affect user experience. Therefore, performance analysis plays a significant role in the evaluation of application layer firewalls. This paper presents an analytic model of the application layer firewall, based on a system analysis to evaluate the capability of the firewall. In order to enable users to improve the performance of the application layer firewall with limited resources, resource allocation was evaluated to obtain the optimal resource allocation scheme in terms of throughput, delay, and packet loss rate. The proposed model employs the Erlangian queuing model to analyze the performance parameters of the system with regard to the three layers (network, transport, and application layers). Then, the analysis results of all the layers are combined to obtain the overall system performance indicators. A discrete event simulation method was used to evaluate the proposed model. Finally, limited service desk resources were allocated to obtain the values of the performance indicators under different resource allocation scenarios in order to determine the optimal allocation scheme. Under limited resource allocation, this scheme enables users to maximize the performance of the application layer firewall.

  10. Modelling of layered resonators for ultrasonic separation.

    PubMed

    Hill, Martyn; Shen, Yijun; Hawkes, Jeremy J

    2002-05-01

    The potential of ultrasonic techniques for the separation and concentration of particles within a fluid has been investigated in some detail in recent years. Devices for effecting such separation typically consist of a piezoceramic transducer driving into a matching layer, fluid layer and reflector layer. This paper uses an equivalent-circuit transducer model, coupled with acoustic impedance transfer relationships to model such cells with regards to both their electrical characteristics and the strength of the resonance produced under different conditions. The model is compared with experimental results from two different cells and is shown to match experimental values well in terms of electrical characteristics and separator performance. The effects of matching layer thickness are also examined using the model. The importance of the adhesive bonding layer is demonstrated, and it is shown that the model can predict the effects of such a layer. The model is also used to demonstrate the effects of coincident resonances in cell layers and to examine the pressure distribution across cells at key frequencies.

  11. The Impact of Pollution on Stellar Evolution Models

    NASA Astrophysics Data System (ADS)

    Dotter, Aaron; Chaboyer, Brian

    2003-10-01

    An approach is introduced for incorporating the concept of stellar pollution into stellar evolution models. The approach involves enhancing the metal content of the surface layers of stellar models. In addition, the surface layers of stars in the mass range of 0.5-2.0 Msolar are mixed to an artificial depth motivated by observations of lithium abundance. The behavior of polluted stellar evolution models is explored assuming the pollution occurs after the star has left the fully convective pre-main-sequence phase. Stellar models polluted with a few Earth masses (M⊕) of iron are significantly hotter than stars of the same mass with an equivalent bulk metallicity. Polluted stellar evolution models can successfully reproduce the metal-rich, parent star τ Bootis and suggest a slightly lower mass than standard evolution models. Finally, the possibility that stars in the Hyades open cluster have accreted an average of 0.5 M⊕ of iron is explored. The results indicate that it is not possible to rule out stellar pollution on this scale from the scatter of Hyades stars on a color-magnitude diagram. The small amount of scatter in the observational data set does rule out pollution on the order of ~1.5 M⊕ of iron. Pollution effects at the low level of 0.5 M⊕ of iron do not produce substantial changes in a star's evolution.

  12. Modeling the cultural evolution of language

    NASA Astrophysics Data System (ADS)

    Steels, Luc

    2011-12-01

    The paper surveys recent research on language evolution, focusing in particular on models of cultural evolution and how they are being developed and tested using agent-based computational simulations and robotic experiments. The key challenges for evolutionary theories of language are outlined and some example results are discussed, highlighting models explaining how linguistic conventions get shared, how conceptual frameworks get coordinated through language, and how hierarchical structure could emerge. The main conclusion of the paper is that cultural evolution is a much more powerful process that usually assumed, implying that less innate structures or biases are required and consequently that human language evolution has to rely less on genetic evolution.

  13. Temporal evolution of crack propagation propensity in snow in relation to slab and weak layer properties

    NASA Astrophysics Data System (ADS)

    Schweizer, Jürg; Reuter, Benjamin; van Herwijnen, Alec; Richter, Bettina; Gaume, Johan

    2016-11-01

    If a weak snow layer below a cohesive slab is present in the snow cover, unstable snow conditions can prevail for days or even weeks. We monitored the temporal evolution of a weak layer of faceted crystals as well as the overlaying slab layers at the location of an automatic weather station in the Steintälli field site above Davos (Eastern Swiss Alps). We focussed on the crack propagation propensity and performed propagation saw tests (PSTs) on 7 sampling days during a 2-month period from early January to early March 2015. Based on video images taken during the tests we determined the mechanical properties of the slab and the weak layer and compared them to the results derived from concurrently performed measurements of penetration resistance using the snow micro-penetrometer (SMP). The critical cut length, observed in PSTs, increased overall during the measurement period. The increase was not steady and the lowest values of critical cut length were observed around the middle of the measurement period. The relevant mechanical properties, the slab effective elastic modulus and the weak layer specific fracture, overall increased as well. However, the changes with time differed, suggesting that the critical cut length cannot be assessed by simply monitoring a single mechanical property such as slab load, slab modulus or weak layer specific fracture energy. Instead, crack propagation propensity is the result of a complex interplay between the mechanical properties of the slab and the weak layer. We then compared our field observations to newly developed metrics of snow instability related to either failure initiation or crack propagation propensity. The metrics were either derived from the SMP signal or calculated from simulated snow stratigraphy (SNOWPACK). They partially reproduced the observed temporal evolution of critical cut length and instability test scores. Whereas our unique dataset of quantitative measures of snow instability provides new insights into the

  14. The thermodynamic evolution of the hurricane boundary layer during eyewall replacement cycles

    NASA Astrophysics Data System (ADS)

    Williams, Gabriel J.

    2016-12-01

    Eyewall replacement cycles (ERCs) are frequently observed during the lifecycle of mature tropical cyclones. Although the kinematic structure and intensity changes during an ERC have been well-documented, comparatively little research has been done to examine the evolution of the tropical cyclone boundary layer (TCBL) during an ERC. This study will examine how the inner core thermal structure of the TCBL is affected by the presence of multiple concentric eyewalls using a high-resolution moist, hydrostatic, multilayer diagnostic boundary layer model. Within the concentric eyewalls above the cloud base, latent heat release and vertical advection (due to the eyewall updrafts) dominate the heat and moisture budgets, whereas vertical advection (due to subsidence) and vertical diffusion dominate the heat and moisture budgets for the moat region. Furthermore, it is shown that the development of a moat region within the TCBL depends sensitively on the moat width in the overlying atmosphere and the relative strength of the gradient wind field in the overlying atmosphere. These results further indicate that the TCBL contributes to outer eyewall formation through a positive feedback process between the vorticity in the nascent outer eyewall, boundary layer convergence, and boundary layer moist convection.

  15. Evolution of vortex-surface fields in transitional boundary layers

    NASA Astrophysics Data System (ADS)

    Yang, Yue; Zhao, Yaomin; Xiong, Shiying

    2016-11-01

    We apply the vortex-surface field (VSF), a Lagrangian-based structure-identification method, to the DNS database of transitional boundary layers. The VSFs are constructed from the vorticity fields within a sliding window at different times and locations using a recently developed boundary-constraint method. The isosurfaces of VSF, representing vortex surfaces consisting of vortex lines with different wall distances in the laminar stage, show different evolutionary geometries in transition. We observe that the vortex surfaces with significant deformation evolve from wall-parallel planar sheets through hairpin-like structures and packets into a turbulent spot with regeneration of small-scale hairpins. From quantitative analysis, we show that a small number of representative or influential vortex surfaces can contribute significantly to the increase of the drag coefficient in transition, which implies a reduced-order model based on VSF. This work has been supported in part by the National Natural Science Foundation of China (Grant Nos. 11472015, 11522215 and 11521091), and the Thousand Young Talents Program of China.

  16. Simple model for river network evolution

    NASA Astrophysics Data System (ADS)

    Leheny, Robert L.

    1995-11-01

    We simulate the evolution of a drainage basin by erosion from precipitation and avalanching on hillslopes. The avalanches create a competition in growth between neighboring basins and play the central role in driving the evolution. The simulated landscapes form drainage systems that share many qualitative features with Glock's model for natural network evolution and maintain statistical properties that characterize real river networks. We also present results from a second model with a modified, mass conserving avalanche scheme. Although the terrains from these two models are qualitatively dissimilar, their drainage networks share the same general evolution and statistical features.

  17. Simple model for river network evolution

    SciTech Connect

    Leheny, R.L.

    1995-11-01

    We simulate the evolution of a drainage basin by erosion from precipitation and avalanching on hillslopes. The avalanches create a competition in growth between neighboring basins and play the central role in driving the evolution. The simulated landscapes form drainage systems that share many qualitative features with Glock`s model for natural network evolution and maintain statistical properties that characterize real river networks. We also present results from a second model with a modified, mass conserving avalanche scheme. Although the terrains from these two models are qualitatively dissimilar, their drainage networks share the same general evolution and statistical features.

  18. A Model of Active Layer Dynamics

    NASA Astrophysics Data System (ADS)

    Ossola, I.; Travis, B. J.

    2009-12-01

    The role that permafrost plays in the global carbon cycle and its effect on climate change is receiving increasing attention. Permafrost worldwide has been calculated to hold approximately 1600 Gt of carbon, second only to the oceans in capacity. Despite its thinness relative to the permafrost layer below it, the active layer is pivotal since the dynamics of the active layer controls the flow of gases, water and energy between the atmosphere and the permafrost. Further, lateral movement of water through the active layer can impact arctic lakes and rivers. Using the computer code ARCHY we can simulate flow of water and gases (methane, carbon dioxide and oxygen) through multiple layers of varying soil properties, the activity of several microbial species (aerobic and anaerobic), and freezing and thawing in the active layer in response to daily and seasonal temperature oscillations. Our goal is to improve understanding of the active layer by computational modeling of its coupled hydrologic, thermal and microbial processes and relating model response to observations.

  19. Model for the evolution of river networks

    NASA Astrophysics Data System (ADS)

    Leheny, Robert L.; Nagel, Sidney R.

    1993-08-01

    We have developed a model, which includes the effects of erosion both from precipitation and from avalanching of soil on steep slopes, to simulate the formation and evolution of river networks. The avalanches provide a mechanism for competition in growth between neighboring river basins. The changing morphology follows many of the characteristics of evolution set forth by Glock. We find that during evolution the model maintains the statistical characteristics measured in natural river systems.

  20. Model for the evolution of river networks

    SciTech Connect

    Leheny, R.L.; Nagel, S.R. )

    1993-08-30

    We have developed a model, which includes the effects of erosion both from precipitation and from avalanching of soil on steep slopes, to simulate the formation and evolution of river networks. The avalanches provide a mechanism for competition in growth between neighboring river basins. The changing morphology follows many of the characteristics of evolution set forth by Glock. We find that during evolution the model maintains the statistical characteristics measured in natural river systems.

  1. Wave analysis of the evolution of a single wave packet in supersonic boundary layer

    NASA Astrophysics Data System (ADS)

    Yermolaev, Yury G.; Yatskikh, Aleksey A.; Kosinov, Alexander D.; Semionov, Nickolay V.

    2016-10-01

    The evolution of the artificial wave packet in laminar flat-plate boundary layer was experimentally studied by hot-wire measurements at M=2. The localized disturbances were generated by pulse glow discharge. The wave analysis of evolution of wave packet was provided. It was found, that the most unstable waves are oblique, that consistent with results of linear theory.

  2. Cylindrical Mixing Layer Model in Stellar Jet

    NASA Astrophysics Data System (ADS)

    Choe, Seung-Urn; Yu, Kyoung Hee

    1994-12-01

    We have developed a cylindrical mixing layer model of a stellar jet including cooling effect in order to understand an optical emission mechanism along collimated high velocity stellar jets associated with young stellar objects. The cylindrical results have been calculated to be the same as the 2D ones presented by Canto & Raga(1991) because the entrainment efficiency in our cylindrical model has been obtained to be the same value as the 2D model has given. We have discussed the morphological and physical characteristics of the mixing layers by the cooling effect. As the jet Mach number increases, the initial temperature of the mixing layer goes high because the kinetic energy of the jet partly converts to the thermal energy of the mixing layer. The initial cooling of the mixing layer is very severe, changing its outer boundary radius. A subsequent change becomes adiabatic. The number of the Mach disks in the stellar jet and the total radiative luminosity of the mixing layer, based on our cylindrical calculation, have quite agreed with the observation.

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

    NASA Astrophysics Data System (ADS)

    Zhang, Hongyi; Chen, Yonghai; Zhou, Guanyu; Tang, Chenguang; Wang, Zhanguo

    2012-10-01

    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.

  4. A simplified model for understanding the evolution of cirrus clouds

    NASA Astrophysics Data System (ADS)

    Schmidt, Clinton Todd

    Developing an understanding of cloud evolution is central to understanding the climate system as a whole. Stratiform cirrus layers play a significant role in the radiative interaction with the climate system. Radiational effects are a driving force in the dynamic evolution of these layers, particularly in determining the areal coverage, vertical distribution, and microphysical properties of the stratiform clouds. The deposition of energy by radiative flux divergence in a cloud layer provides potential energy to drive cloud evolution. This work uses a large eddy simulation model (LESM) to investigate a number of parameters that can be used to easily predict how a cirrus cloud will evolve. This work also includes a study of the sensitivity of formation of mammatus-like features in clouds to the below cloud layer relative humidity. Three distinct modes of cloud evolution were found to occur due to the radiative processes simulated in this study. These modes include isentropic adjustment, mixing, and evaporation/condensation. These modes of evolution were found to be independent of each other in the sense that one mode did not always occur with either of the other two modes. Similarly, the modes of evolution did not always occur in isolation and were found to simultaneously occur in many cases. Two dimensionless numbers are derived in this work that provide a basic framework for understanding the modes of evolution that can be expected of an initial cloud. These dimensionless numbers are found to have strong predictive power for cloud evolution. The simulations of several clouds produced mammatus-like structures forming at the base of the simulated clouds at the end of the model runs. These formations prompted further investigation of the processes that influence mammatus formation. The theory proposed by this work is that the mammatus cloud formation is a radiative process, mediated by the below cloud layer relative humidity. Several simulations were performed to test

  5. 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.

  6. 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.

  7. 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.

  8. Modeling anisotropic magnetoresistance in layered antiferromagnets

    NASA Astrophysics Data System (ADS)

    Santos, D. L. R.; Pinheiro, F. A.; Velev, J.; Chshiev, M.; Castro, J. d.'Albuquerque e.; Lacroix, C.

    2017-06-01

    We have investigated the electronic transport and the anisotropic magnetoresistance in systems consisting of pairs of antiferromagnetically aligned layers separated by a non-magnetic layer, across which an antiferromagnetic coupling between the double layers is established. Calculations have been performed within the framework of the tight-binding model, taking into account the exchange coupling within the ferromagnetic layers and the Rashba spin-orbit interaction. Conductivities have been evaluated in the ballistic regime, based on Kubo formula. We have systematically studied the dependence of the conductivity and of the anisotropic magnetoresistance on several material and structural parameters, such as the orientation of the magnetic moments relative to the crystalline axis, band filling, out-of-plane hopping and spin-orbit parameter.

  9. Peripapillary Retinal Nerve Fiber Layer Thickness and the Evolution of Cognitive Performance in an Elderly Population

    PubMed Central

    Méndez-Gómez, Juan Luis; Rougier, Marie-Bénédicte; Tellouck, Laury; Korobelnik, Jean-François; Schweitzer, Cédric; Delyfer, Marie-Noëlle; Amieva, Hélène; Dartigues, Jean-François; Delcourt, Cécile; Helmer, Catherine

    2017-01-01

    Retinal nerve fiber layer (RNFL) thickness is reduced in Alzheimer’s patients. However, whether it is associated with early evolution of cognitive function is unknown. Within 427 participants from the Three-City-Alienor longitudinal population-based cohort, we explored the relationship between peripapillary RNFL thicknesses and the evolution of cognitive performance. RNFL was assessed at baseline by spectral domain optical coherence tomography; cognitive performances were assessed at baseline and at 2 years, with the Mini–Mental State Examination, the Isaacs’ set test, and the Free and Cued Selective Reminding Test (FCSRT). Multivariate linear mixed models were performed. The RNFL was not associated with initial cognitive performance. Nevertheless, a thicker RNFL was significantly associated with a better cognitive evolution over time in the free delayed recall (p = 0.0037) and free + cued delayed recall (p = 0.0043) scores of the FCSRT, particularly in the temporal, superotemporal, and inferotemporal segments. No associations were found with other cognitive tests. The RNFL was associated with changes in scores that assess episodic memory. RNFL thickness could reflect a higher risk of developing cognitive impairment over time. PMID:28373855

  10. Nonlinear evolution of oblique waves on compressible shear layers

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Leib, S. J.

    1989-01-01

    The effects of critical-layer nonlinearity on spatially growing oblique instability waves on compressible shear layers between two parallel streams are considered. The analysis shows that mean temperature nonuniformities cause nonlinearity to occur at much smaller amplitudes than it does when the flow is isothermal. The nonlinear instability wave growth rate effects are described by an integrodifferential equation which bears some resemblance to the Landau equation, in that it involves a cubic-type nonlinearity. The numerical solutions to this equation are worked out and discussed in some detail. Inviscid solutions always end in a singularity at a finite downstream distance, but viscosity can eliminate this singularity for certain parameter ranges.

  11. Multi-layer model vs. single-layer model for N and P doped poly layers in etch bias modeling

    NASA Astrophysics Data System (ADS)

    Li, Jianliang; Vidal-Russell, Ezequiel; Beale, Daniel; Wang, Chunqing; Melvin, Lawrence S., III

    2010-09-01

    In modern photolithography, ever smaller critical dimension (CD) budgets require tighter control over the entire process, demanding more accurate practice of optical proximity correction (OPC). In last decade, the model based OPC (MBOPC) has outpaced the rule based OPC (RBOPC) and become widely adopted in semiconductor industry. During the MBOPC process, the physical models are called to compute the signal values at the evaluation points and the design patterns are perturbed such that the final model contours are as close to the targets as possible. It has been demonstrated that in addition to simulating the optics and resist effects, the physical models must accommodate the pattern distortion due to etch process as well. While the etch process may be lumped with optics and resist processes into one model for the 65nm and above nodes, it can no longer be treated as small perturbations on photolithographic effects for more advanced nodes and it is highly desired to build a physics-based etch model formulations that differ from the conventional convolution-based process models used to simulate the optical and resist effect. Our previous studies proposed a novel non-linear etch modeling object in combination with conventional convolution kernels, which simulates the non-optics and non-resist proximity effect successfully. This study examines further the non-linear etch modeling method by checking the different behaviors of N and p doped layers which physically have different etching rates and should be represented differently in etch modeling. The experimental results indicate that the fitting accuracy is significantly improved when the data points are split into N and P groups and calibrated separately. The N and P layer etch models are used in staged MBOPCs and the results are compared with single-layer model as well.

  12. Modelling of backscatter from vegetation layers

    NASA Technical Reports Server (NTRS)

    Van Zyl, J. J.; Engheta, N.; Papas, C. H.; Elachi, C.; Zebker, H.

    1985-01-01

    A simple way to build up a library of models which may be used to distinguish between the different types of vegetation and ground surfaces by means of their backscatter properties is presented. The curve of constant power received by the antenna (Gamma sphere) is calculated for the given Stokes Scattering Operator, and model parameters are adopted of the most similar library model Gamma sphere. Results calculated for a single scattering model resembling coniferous trees are compared with the Gamma spheres of a model resembling tropical region trees. The polarization which would minimize the effect of either the ground surface or the vegetation layer can be calculated and used to analyze the backscatter from the ground surface/vegetation layer combination, and enhance the power received from the desired part of the combination.

  13. Isotopic Modeling of Dynamic Geochemical Layering in the Mantle

    NASA Astrophysics Data System (ADS)

    Lee, V. E.; Depaolo, D. J.

    2005-12-01

    In order to understand the dynamics of the Earth's mantle, it is vitally important to reconcile geophysical and geochemical lines of evidence that suggest discrepant models for mantle convection. For example, seismic tomography provides evidence that subducted slabs of oceanic lithosphere can penetrate through the transition zone into the lower mantle, implying whole-mantle convection, whereas the distinct ranges of isotopic values for mid-ocean ridge basalts (MORB) and ocean island basalts (OIB) has been invoked as evidence for layered mantle convection. We present here a model that results in dynamic geochemical layering in the mantle (allowing for whole-mantle convection while creating distinct isotopic reservoirs in the shallow and deep mantle). A key aspect of this model is that the process of wet partial melting beneath mid-ocean ridges generates three chemically distinct regions: enriched basaltic crust (BC), a depleted harzburgite/lherzolite layer (DHL), and an incipiently melted lherzholite layer (IML) that is only slightly depleted. These three layers can also have different, distinct physical properties as well (e.g., Braun et al. 2000). During subduction and penetration of the subducted slab lithologic column through the transition zone, any preferential separation of the slab material based on physical properties (e.g., retention of low-viscosity DHL material in the upper mantle or penetration of the cold, high-viscosity BC layer to the lower mantle) will result in distinct ɛNd and ɛHf values for the upper and lower mantle. Box models are used to investigate the evolution of ɛNd and ɛHf during Earth's history, and the resulting values are compared to measured values for MORBs and OIBs. These results may have implications for constraining the slab flux from the upper to lower mantle.

  14. 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

  15. 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.

  16. Model of evolution of molecular sequences

    NASA Astrophysics Data System (ADS)

    Luo, Liaofu; Tsai, Lu; Lee, Weijiang

    1990-05-01

    A simplified model of the evolution of molecular sequences is proposed. An ensemble of strings is considered that consists of two letters and undergoes random point mutations and natural selections. A set of evolution equations is deduced. From the solution it is found that the first-order (second-order) informational parameters (redundancies) D1 decrease (D2 increase) in the course of evolution. Furthermore, the statistical correlations of the letters (bases) in the sequences are investigated in detail and the short-distance correlation is demonstrated. These results give a preliminary explanation of some physical aspects in the evolution of nucleic acid sequences.

  17. A statistical model of magnetic islands in a current layer

    SciTech Connect

    Fermo, R. L.; Drake, J. F.; Swisdak, M.

    2010-01-15

    This letter describes a statistical model of the dynamics of magnetic islands in very large current layers that develop in space plasma. Two parameters characterize the island distribution: the flux psi contained in the island and the area A it encloses. The integrodifferential evolution equation for this distribution function is based on rules that govern the small-scale generation of secondary islands, the rates of island growth, and island merging. The numerical solutions of this equation produce island distributions relevant to the magnetosphere and solar corona. The solution of a differential equation for large islands explicitly shows the role merging plays in island growth.

  18. 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.

  19. 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.

  20. 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.

  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. Alpha models and boundary-layer turbulence

    NASA Astrophysics Data System (ADS)

    Cheskidov, Alexey

    We study boundary-layer turbulence using the Navier-Stokes-alpha model obtaining an extension of the Prandtl equations for the averaged flow in a turbulent boundary layer. In the case of a zero pressure gradient flow along a flat plate, we derive a nonlinear fifth-order ordinary differential equation, an extension of the Blasius equation. We study it analytically and prove the existence of a two-parameter family of solutions satisfying physical boundary conditions. From this equation we obtain a theoretical prediction of the skin-friction coefficient in a wide range of Reynolds numbers based on momentum thickness, and deduce the maximal value of the skin-friction coefficient in the turbulent boundary layer. The two-parameter family of solutions to the equation matches experimental data in the transitional boundary layers with different free stream turbulence intensity. A one-parameter sub-family of solutions, obtained using our skin-friction coefficient law, matches experimental data in the turbulent boundary layer for moderately large Reynolds numbers.

  3. A constitutive model for layer development in shear zones near the brittle-ductile transition

    NASA Astrophysics Data System (ADS)

    Montési, Laurent G. J.

    2007-04-01

    The microstructure of ductile shear zones differs from that of surrounding wall rocks. In particular, compositional layering is a hallmark of shear zones. As layered rocks are weaker than their isotropic protolith when loaded in simple shear, layering may hold the key to explain localization of ductile deformation onto ductile shear zones. I propose here a constitutive model for layer development. A two-level mixing theory allows the strength of the aggregate to be estimated at intermediate degrees of layering. A probabilistic failure model is introduced to control how layers develop in a deforming aggregate. This model captures one of the initial mechanism of phase interconnection identified experimentally by Holyoke and Tullis (2006a, 2006b), fracturing of load bearing grains. This model reproduces the strength evolution of these experiments and can now be applied to tectonic modeling.

  4. Novel Continuum Modeling of Crystal Surface Evolution

    NASA Astrophysics Data System (ADS)

    Kandel, Daniel

    2003-03-01

    Below the roughening temperature the evolution of crystal surfaces proceeds by the nucleation, flow and annihilation of discrete atomic steps. The appropriate mathematical model of the evolution of such surfaces is discrete in nature, and consists of coupled equations for the motion, nucelation and annihilation of steps. It is useful, however, to describe surface evolution in terms of continuum models. Such models are more amenable to analytical treatments and have enormous computational advantages over their discrete counterparts. Standard continuum models successfully describe the evolution of surfaces with smooth morphology, but completely fail when the surface has singularities such as facets. It is an interesting and important challenge to develop continuum descriptions of surfaces with singularities, since in many cases the singularities drive the evolution of the whole system. In the talk I will present a conceptually new approach to continuum modeling of surface evolution, termed Configurational Continuum [1], which is valid even in singular regions. The approach consists of a new definition of the continuum limit. It is equivalent to standard continuum for very smooth morphology, but is radically different from it in singular regions, where it becomes equivalent to the discrete models. The validity of configurational continuum will be demonstrated on several simple systems. [1] N. Israeli and D. Kandel, Phys. Rev. Lett. 88, 116103 (2002).

  5. Transient evolution and high stratification scaling in horizontal mixing layers

    NASA Astrophysics Data System (ADS)

    Arratia, C.; Ortiz, S.; Chomaz, J. M.

    Mixing layers (sheared flows in homogeneous or stratified fluid) are present in many geophysical contexts and may lead to turbulence and mixing. In several cases, mixing layers are known to exhibit the Kelvin-Helmholtz instability leading to the roll-up of spanwise vortices, the Kelvin-Helmholtz (KH) billows. This is an essentially two-dimensional (2D) process. In fact, in the homogeneous cases the Squire's theorem implies that the most unstable mode is 2D. However, Squire's theorem applies only for the exponentially growing perturbations that control the large time dynamics and is not valid for the transient dynamics at short time. Indeed, Iams et al.[1] have shown that, in the non-stratified case, the most amplified optimal perturbations for short times are three-dimensional (3D) and result from a cooperation between the lift-up and Orr mechanisms[2]. This provides a finite time mechanism for spanwise scale selection, scale that may persist at later times if nonlinearities are strong enough.

  6. 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

  7. Evolution and dynamics of shear-layer structures in near-wall turbulence

    NASA Technical Reports Server (NTRS)

    Johansson, Arne V.; Alfredsson, P. H.; Kim, John

    1991-01-01

    Near-wall flow structures in turbulent shear flows are analyzed, with particular emphasis on the study of their space-time evolution and connection to turbulence production. The results are obtained from investigation of a database generated from direct numerical simulation of turbulent channel flow at a Reynolds number of 180 based on half-channel width and friction velocity. New light is shed on problems associated with conditional sampling techniques, together with methods to improve these techniques, for use both in physical and numerical experiments. The results clearly indicate that earlier conceptual models of the processes associated with near-wall turbulence production, based on flow visualization and probe measurements need to be modified. For instance, the development of asymmetry in the spanwise direction seems to be an important element in the evolution of near-wall structures in general, and for shear layers in particular. The inhibition of spanwise motion of the near-wall streaky pattern may be the primary reason for the ability of small longitudinal riblets to reduce turbulent skin friction below the value for a flat surface.

  8. 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.

  9. The formation and evolution of layered structures in porous media: effects of porosity and mechanical dispersion

    NASA Astrophysics Data System (ADS)

    Schoofs, Stan; Trompert, Ron A.; Hansen, Ulrich

    2000-03-01

    Horizontally layered structures can develop in porous or partially molten environments, such as hydrothermal systems, magmatic intrusions and the early Earth's mantle. The porosity φ of these natural environments is typically small. Since dissolved chemical elements unlike heat cannot diffuse through the solid rocks, heat and solute influence the interstitial fluid density in a different manner: heat advects slower than solute through the liquid by the factor φ, while diffusion of heat through the bulk porous medium is larger by the factor φ-1 times the ratio between the thermal and chemical diffusivities. By performing numerical experiments in which a rigid low-porosity medium is heated from below, we have studied the formation and evolution of layers in an initially stably stratified liquid. Growth of a convective layer through convective entrainment, the formation of a stable density interface on top of the layer and destabilization of the next layer are intimately linked. By monitoring the heat (solute) fluxes, it is observed that the transport of heat (solute) across the interface changes from convective entrainment towards a regime in which transfer is purely diffusive (dispersive). Because this transition occurs before the stage at which the lower layer arrives at the thermal equilibrium, we conclude that the layer growth stops when the density interface on top has grown sufficiently strong to keep the ascending plumes in the lower layer from convectively entraining more fluid from above. A simple balance between the most important forces, exerted on a fluid parcel in the lower layer, is proposed to determine this transition. This force balance also indicates whether a density interface keeps intact, migrates upwards or breaks down during the further evolution of the layered sequence. Finally, mechanical dispersion tends to increase transport of chemically dissolved elements across the density interface. Since this reduces the density difference between

  10. 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.

  11. 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.

  12. 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

  13. A resonance based model of biological evolution

    NASA Astrophysics Data System (ADS)

    Damasco, Achille; Giuliani, Alessandro

    2017-04-01

    We propose a coarse grained physical model of evolution. The proposed model 'at least in principle' is amenable of an experimental verification even if this looks as a conundrum: evolution is a unique historical process and the tape cannot be reversed and played again. Nevertheless, we can imagine a phenomenological scenario tailored upon state transitions in physical chemistry in which different agents of evolution play the role of the elements of a state transition like thermal noise or resonance effects. The abstract model we propose can be of help for sketching hypotheses and getting rid of some well-known features of natural history like the so-called Cambrian explosion. The possibility of an experimental proof of the model is discussed as well.

  14. 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

  15. A distributed snow-evolution modeling system (SnowModel)

    Treesearch

    Glen E. Liston; Kelly. Elder

    2006-01-01

    SnowModel is a spatially distributed snow-evolution modeling system designed for application in landscapes, climates, and conditions where snow occurs. It is an aggregation of four submodels: MicroMet defines meteorological forcing conditions, EnBal calculates surface energy exchanges, SnowPack simulates snow depth and water-equivalent evolution, and SnowTran-3D...

  16. Modeling of Threading Dislocation Density Reduction in Porous III-Nitride Layers

    NASA Astrophysics Data System (ADS)

    Artemiev, Dmitry M.; Orlova, Tatiana S.; Bougrov, Vladislav E.; Odnoblyudov, Maxim A.; Romanov, Alexei E.

    2015-05-01

    In this work, we report on the results of the theoretical analysis of threading dislocation (TD) density reduction in porous III-nitride layers grown in polar orientation. The reaction-kinetics model originally developed for describing TD evolution in growing bulk layers has been expanded to the case of the porous layer. The developed model takes into account TD inclinations under the influence of the pores as well as trapping TDs into the pores. It is demonstrated that both these factors increase the probability of dislocation reactions thus reducing the total density of TDs. The mean pore diameter acts as an effective interaction radius for the reactions among TDs. The model includes the main experimentally observed features of TD evolution in porous III-nitride layers.

  17. Biological evolution model with conditional mutation rates

    NASA Astrophysics Data System (ADS)

    Saakian, David B.; Ghazaryan, Makar; Bratus, Alexander; Hu, Chin-Kun

    2017-05-01

    We consider an evolution model, in which the mutation rates depend on the structure of population: the mutation rates from lower populated sequences to higher populated sequences are reduced. We have applied the Hamilton-Jacobi equation method to solve the model and calculate the mean fitness. We have found that the modulated mutation rates, directed to increase the mean fitness.

  18. 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.

  19. Spatial evolution of nonlinear acoustic mode instabilities on hypersonic boundary layers

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Wundrow, D. W.

    1990-01-01

    The effects are considered of strong critical layer nonlinearity on the spatial evolution of an initially linear acoustic mode instability wave on a hypersonic flat plate boundary layer. The analysis shows that nonlinearity, which is initially confined to a thin critical layer, first becomes important when the amplitude of the pressure fluctuations become O(1/M exp 4 in M exp 2), where M is the free stream Mach number. The flow outside the critical layer is still determined by linear dynamics and therefore takes the form of a linear instability wave, but with its amplitude completely determined by the flow within the critical layer. The latter flow is determined by a coupled set of nonlinear equations, which were solved numerically.

  20. Spatial evolution of nonlinear acoustic mode instabilities on hypersonic boundary layers

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Wundrow, D. W.

    1989-01-01

    The effects are considered of strong critical layer nonlinearity on the spatial evolution of an initially linear acoustic mode instability wave on a hypersonic flat plate boundary layer. The analysis shows that nonlinearity, which is initially confined to a thin critical layer, first becomes important when the amplitude of the pressure fluctuations become 0(1/M exp 4 In M exp 2), where M is the free stream Mach number. The flow outside the critical layer is still determined by linear dynamics and therefore takes the form of a linear instability wave, but with its amplitude completely determined by the flow within the critical layer. The latter flow is determined by a coupled set of nonlinear equations, which were solved numerically.

  1. Density functional theory calculations for the hydrogen evolution reaction in an electrochemical double layer on the Pt(111) electrode.

    PubMed

    Skúlason, Egill; Karlberg, Gustav S; Rossmeisl, Jan; Bligaard, Thomas; Greeley, Jeff; Jónsson, Hannes; Nørskov, Jens K

    2007-07-07

    We present results of density functional theory calculations on a Pt(111) slab with a bilayer of water, solvated protons in the water layer, and excess electrons in the metal surface. In this way we model the electrochemical double layer at a platinum electrode. By varying the number of protons/electrons in the double layer we investigate the system as a function of the electrode potential. We study the elementary processes involved in the hydrogen evolution reaction, 2(H(+) + e(-)) --> H(2), and determine the activation energy and predominant reaction mechanism as a function of electrode potential. We confirm by explicit calculations the notion that the variation of the activation barrier with potential can be viewed as a manifestation of the Brønsted-Evans-Polanyi-type relationship between activation energy and reaction energy found throughout surface chemistry.

  2. 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

  3. 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

  4. Ultrathin platinum nanowires grown on single-layered nickel hydroxide with high hydrogen evolution activity

    NASA Astrophysics Data System (ADS)

    Yin, Huajie; Zhao, Shenlong; Zhao, Kun; Muqsit, Abdul; Tang, Hongjie; Chang, Lin; Zhao, Huijun; Gao, Yan; Tang, Zhiyong

    2015-03-01

    Design and synthesis of effective electrocatalysts for hydrogen evolution reaction in alkaline environments is critical to reduce energy losses in alkaline water electrolysis. Here we report a hybrid nanomaterial comprising of one-dimensional ultrathin platinum nanowires grown on two-dimensional single-layered nickel hydroxide. Judicious surface chemistry to generate the fully exfoliated nickel hydroxide single layers is explored to be the key for controllable growth of ultrathin platinum nanowires with diameters of about 1.8 nm. Impressively, this hybrid nanomaterial exhibits superior electrocatalytic activity for hydrogen evolution reaction in alkaline solution, which outperforms currently reported catalysts, and the obviously improved catalytic stability. We believe that this work may lead towards the development of single-layered metal hydroxide-based hybrid materials for applications in catalysis and energy conversion.

  5. 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.

  6. 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.

  7. A random distribution reacting mixing layer model

    NASA Technical Reports Server (NTRS)

    Jones, Richard A.

    1994-01-01

    A methodology for simulation of molecular mixing and the resulting velocity and temperature fields has been developed. The ideas are applied to the flow conditions present in the NASA Lewis Planar Reacting Shear Layer (PRSL) facility, and results compared to experimental data. A gaussian transverse turbulent velocity distribution is used in conjunction with a linearly increasing time scale to describe the mixing of different regions of the flow. Equilibrium reaction calculations are then performed on the mix to arrive at a new species composition and temperature. Velocities are determined through summation of momentum contributions. The analysis indicates a combustion efficiency of the order of 80 percent for the reacting mixing layer, and a turbulent Schmidt number of 2/3. The success of the model is attributed to the simulation of large-scale transport of fluid. The favorable comparison shows that a relatively quick and simple PC calculation is capable of simulating the basic flow structure in the reacting and non-reacting shear layer present in the facility given basic assumptions about turbulence properties.

  8. A random distribution reacting mixing layer model

    NASA Technical Reports Server (NTRS)

    Jones, Richard A.; Marek, C. John; Myrabo, Leik N.; Nagamatsu, Henry T.

    1994-01-01

    A methodology for simulation of molecular mixing, and the resulting velocity and temperature fields has been developed. The ideas are applied to the flow conditions present in the NASA Lewis Research Center Planar Reacting Shear Layer (PRSL) facility, and results compared to experimental data. A gaussian transverse turbulent velocity distribution is used in conjunction with a linearly increasing time scale to describe the mixing of different regions of the flow. Equilibrium reaction calculations are then performed on the mix to arrive at a new species composition and temperature. Velocities are determined through summation of momentum contributions. The analysis indicates a combustion efficiency of the order of 80 percent for the reacting mixing layer, and a turbulent Schmidt number of 2/3. The success of the model is attributed to the simulation of large-scale transport of fluid. The favorable comparison shows that a relatively quick and simple PC calculation is capable of simulating the basic flow structure in the reacting and nonreacting shear layer present in the facility given basic assumptions about turbulence properties.

  9. A model of evolution and learning.

    PubMed

    Red'ko, Vladimir G; Mosalov, Oleg P; Prokhorov, Danil V

    2005-01-01

    We study a model of evolving populations of self-learning agents and analyze the interaction between learning and evolution. We consider an agent-broker that predicts stock price changes and uses its predictions for selecting actions. Each agent is equipped with a neural network adaptive critic design for behavioral adaptation. We discuss three cases in which either evolution or learning, or both, are active in our model. We show that the Baldwin effect can be observed in our model, viz. originally acquired adaptive policy of best agent-brokers becomes inherited over the course of the evolution. We also compare the behavioral tactics of our agents to the searching behavior of simple animals.

  10. 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.

  11. 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.

  12. Layer-by-Layer Evolution of a Two-Dimensional Electron Gas Near an Oxide Interface

    NASA Astrophysics Data System (ADS)

    Chang, Young Jun; Moreschini, Luca; Bostwick, Aaron; Gaines, Geoffrey A.; Kim, Yong Su; Walter, Andrew L.; Freelon, Byron; Tebano, Antonello; Horn, Karsten; Rotenberg, Eli

    2013-09-01

    We report the momentum-resolved measurement of a two-dimensional electron gas at the LaTiO3/SrTiO3 interface by angle-resolved photoemission spectroscopy (ARPES). Thanks to an advanced sample preparation technique, the orbital character of the conduction electrons and the electronic correlations can be accessed quantitatively as each unit cell layer is added. We find that all of these quantities change dramatically with distance from the interface. These findings open the way to analogous studies on other heterostructures, which are traditionally a forbidden field for ARPES.

  13. Modeling the evolution of insect phenology.

    PubMed

    Yurk, Brian P; Powell, James A

    2009-05-01

    Climate change is likely to disrupt the timing of developmental events (phenology) in insect populations in which development time is largely determined by temperature. Shifting phenology puts insects at risk of being exposed to seasonal weather extremes during sensitive life stages and losing synchrony with biotic resources. Additionally, warming may result in loss of developmental synchronization within a population making it difficult to find mates or mount mass attacks against well-defended resources at low population densities. It is unknown whether genetic evolution of development time can occur rapidly enough to moderate these effects. We present a novel approach to modeling the evolution of phenology by allowing the parameters of a phenology model to evolve in response to selection on emergence time and density. We use the Laplace method to find asymptotic approximations for the temporal variation in mean phenotype and phenotypic variance arising in the evolution model that are used to characterize invariant distributions of the model under periodic temperatures at leading order. At these steady distributions the mean phenotype allows for parents and offspring to be oviposited at the same time of year in consecutive years. Numerical simulations show that populations evolve to these steady distributions under periodic temperatures. We consider an example of how the evolution model predicts populations will evolve in response to warming temperatures and shifting resource phenology.

  14. Chemical element transport in stellar evolution models

    PubMed Central

    Cassisi, Santi

    2017-01-01

    Stellar evolution computations provide the foundation of several methods applied to study the evolutionary properties of stars and stellar populations, both Galactic and extragalactic. The accuracy of the results obtained with these techniques is linked to the accuracy of the stellar models, and in this context the correct treatment of the transport of chemical elements is crucial. Unfortunately, in many respects calculations of the evolution of the chemical abundance profiles in stars are still affected by sometimes sizable uncertainties. Here, we review the various mechanisms of element transport included in the current generation of stellar evolution calculations, how they are implemented, the free parameters and uncertainties involved, the impact on the models and the observational constraints. PMID:28878972

  15. 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

  16. Feedbacks between roughness and boundary-layer aerodynamics control desert dune field evolution

    NASA Astrophysics Data System (ADS)

    Jerolmack, D. J.; Ewing, R. C.; Falcini, F.; Martin, R. L.; Masteller, C.; Phillips, C. B.; Reitz, M. D.

    2012-12-01

    Spatial variations in sand flux across a desert dune field control dune migrations rates, the viability and density of vegetation, and deposition rates. Many dune fields begin abruptly with a line source of sediment, with either a deflation basin or body of water upstream of them. We hypothesize that this sharp increase in roughness trips the development of an internal boundary layer (IBL), which thickens downwind and causes a spatial decrease in the surface wind stress and hence sediment flux. Although such boundary layers are well-studied at sea-land transitions, there is almost no research conducted in deserts, and the implications for sediment transport have not been explored. We employ classic flat-plate boundary layer theory to compute the expected boundary stress profile downwind of a roughness transition at the desert dunes of White Sands, New Mexico. The required assumptions are severe: a neutrally-buoyant atmospheric boundary layer (ABL), quasi-steady and two-dimensional flow, uniform downstream roughness, etc. Lacking direct observations of the wind stress profile, we used repeat aerial topography surveys to directly measure the sand flux profile over several years. The agreement between the theoretical sand flux profile from IBL theory and that determined from topography data is remarkable, but raises deeper questions about near-bed atmospheric flows and sediment transport. We demonstrate for White Sands that sand-transporting winds are always associated with neutrally-buoyant ABL profiles; is it always the case that winds strong enough to move sand also produce a well-mixed ABL? The separation of scales between intermittency in winds and the migration rate of dunes appears to justify the quasi-steady assumption, but is this the rule for dune fields? Finally, the IBL model predicts that the upwind margins of dune fields should be zones of scour - which is broadly supported at White Sands - however some local accumulation of sand is necessary to spawn

  17. 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.

  18. 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

  19. 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. Copyright © 2013 Elsevier B.V. All rights reserved.

  20. PARALLEL EVOLUTION OF QUASI-SEPARATRIX LAYERS AND ACTIVE REGION UPFLOWS

    SciTech Connect

    Mandrini, C. H.; Cristiani, G. D.; Nuevo, F. A.; Vásquez, A. M.; Baker, D.; Driel-Gesztelyi, L. van; Démoulin, P.; Pick, M.; Vargas Domínguez, S.

    2015-08-10

    Persistent plasma upflows were observed with Hinode’s EUV Imaging Spectrometer (EIS) at the edges of active region (AR) 10978 as it crossed the solar disk. We analyze the evolution of the photospheric magnetic and velocity fields of the AR, model its coronal magnetic field, and compute the location of magnetic null-points and quasi-sepratrix layers (QSLs) searching for the origin of EIS upflows. Magnetic reconnection at the computed null points cannot explain all of the observed EIS upflow regions. However, EIS upflows and QSLs are found to evolve in parallel, both temporarily and spatially. Sections of two sets of QSLs, called outer and inner, are found associated to EIS upflow streams having different characteristics. The reconnection process in the outer QSLs is forced by a large-scale photospheric flow pattern, which is present in the AR for several days. We propose a scenario in which upflows are observed, provided that a large enough asymmetry in plasma pressure exists between the pre-reconnection loops and lasts as long as a photospheric forcing is at work. A similar mechanism operates in the inner QSLs; in this case, it is forced by the emergence and evolution of the bipoles between the two main AR polarities. Our findings provide strong support for the results from previous individual case studies investigating the role of magnetic reconnection at QSLs as the origin of the upflowing plasma. Furthermore, we propose that persistent reconnection along QSLs does not only drive the EIS upflows, but is also responsible for the continuous metric radio noise-storm observed in AR 10978 along its disk transit by the Nançay Radio Heliograph.

  1. Chemical Evolution Model of M33

    NASA Astrophysics Data System (ADS)

    Robles-Valdez, F.; Carigi, L.

    2011-10-01

    We present a chemical evolution model (CEM) of M33 and we find that M33, which is smaller than both M31 and MW, shows a lower gas infall rate, SFR efficiency, and IMF M_{up}. Therefore the CEMs for large spiral galaxies (Carigi et al. 2005; Meneses-Goytia et al. 2011) can be scaled to a smaller galaxy.

  2. A volumetric ablation model of EPDM considering complex physicochemical process in porous structure of char layer

    NASA Astrophysics Data System (ADS)

    Yang, Liu; Xiao-Jing, Yu; Jian-Ming, Ma; Yi-Wen, Guan; Jiang, Li; Qiang, Li; Sa, Yang

    2017-06-01

    A volumetric ablation model for EPDM (ethylene- propylene-diene monomer) is established in this paper. This model considers the complex physicochemical process in the porous structure of a char layer. An ablation physics model based on a porous structure of a char layer and another model of heterogeneous volumetric ablation char layer physics are then built. In the model, porosity is used to describe the porous structure of a char layer. Gas diffusion and chemical reactions are introduced to the entire porous structure. Through detailed formation analysis, the causes of the compact or loose structure in the char layer and chemical vapor deposition (CVD) reaction between pyrolysis gas and char layer skeleton are introduced. The Arrhenius formula is adopted to determine the methods for calculating carbon deposition rate C which is the consumption rate caused by thermochemical reactions in the char layer, and porosity evolution. The critical porosity value is used as a criterion for char layer porous structure failure under gas flow and particle erosion. This critical porosity value is obtained by fitting experimental parameters and surface porosity of the char layer. Linear ablation and mass ablation rates are confirmed with the critical porosity value. Results of linear ablation and mass ablation rate calculations generally coincide with experimental results, suggesting that the ablation analysis proposed in this paper can accurately reflect practical situations and that the physics and mathematics models built are accurate and reasonable.

  3. Observations of the Evolution of Turbulent Dissipation within the Ocean Surface Boundary Layer: an OSMOSIS study

    NASA Astrophysics Data System (ADS)

    Lucas, N. S.; Allen, J.; Belcher, S. E.; Boyd, T.; Brannigan, L.; Inall, M.; Palmer, M.; Polton, J.; Rippeth, T. P.

    2016-02-01

    This study presents a new 9.5 day dataset showing the evolution of the Ocean Surface Boundary Layer (OSBL) and dissipation of turbulence kinetic energy (TKE), carried out as part of OSMOSIS[i], at a location in the North East Atlantic Ocean in September 2012. The TKE dissipation measurements were made using three methods; (i) repeated profiling between 100m and the surface by an Ocean Microstructure glider, (ii) three series of profiles made using a loosely tethered velocity microstructure glider and (iii) a moored pulse-pulse coherent high frequency ADCP. Supporting measurements show the evolution of the water column structure, including surface wave measurements from a TRIAXYS wave buoy. This data shows two distinct regimes; the first, spanning 4 days with relatively low winds, displays a distinct diurnal cycle with the deepening of the active mixing layer during the night which shoaled during the day. The second spanned a significant storm, (with maximum winds speeds reaching 20 m s-1 and significant wave heights reaching 6 m), during which, rather than a deepening of the mixed layer as predicted by classical theory, the primary effect was a broadening of the transition layer, similar to that found by Dohan and Davies (2011). During the storm, significant dissipation was observed throughout the surface mixed layer and into the transition layer, driving fluxes of heat downwards through the base of the surface mixed layer. [i] Ocean Surface Mixing and Submesoscale Interaction Study Dohan, K. & Davis, R.E., 2011. Mixing in the Transition Layer during Two Storm Events. Journal of Physical Oceanography. 41 (1). pp. 42-66.

  4. The Mesoscale Organization, Dynamics, and Evolution of the Marine Planetary Boundary Layer during Cold Air Outbreaks

    NASA Astrophysics Data System (ADS)

    Walter, Bernard A., Jr.

    Satellite imagery along with aircraft data collected off the east coast of the U.S. and over the Bering Sea are used to study the evolution of organized mesoscale convection with fetch during cold air outbreaks. Comparisons between satellite photos of cloud formations during cold air outbreaks and results from Rayleigh -Benard laboratory experiments show a number of similarities. Satellite photos in general show three distinct regions offshore where particular mesoscale convective regimes dominate, while Rayleigh-Benard studies show a transition to different convective forms as the Rayleigh number is increased. Features associated with the increase of cloud stress spacing with fetch are suggestive of mechanisms which cause roll wavelengths to increase as the Rayleigh number is increased in Rayleigh -Benard studies. Off the east coast, rolls present upstream of the coastline were weakened just offshore but still provided a linearizing tendency to the dominant convective forms which were thermal plume-like structures with horizontal scales of 1.5 z(,i). Further offshore, two dimensional linear rolls with wavelengths of 4 z(,i) were dominant. The strengths of individual rolls were found to vary in the crosswind direction, such that the circulations of some rolls did not reach the top of the boundary layer. Aircraft data from over the Bering Sea show a different situation in that cloud streets present at the ice edge, although broadening with distance downstream, still maintain their two dimensional nature. The aircraft data both near the ice edge and further downstream, show organized roll circulations on scales in addition to those seen in the satellite photos. Calculation of an atmospheric Rayleigh number using a value of the eddy viscosity obtained from the aircraft data resulted in the placement of broad bounds on values of the atmospheric Rayleigh number for different convective regimes. Comparison of aircraft observations of boundary layer growth with fetch

  5. 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

  6. 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. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. 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.

  8. Influence of orientation on the evolution of small perturbations in compressible shear layers with inflection points

    NASA Astrophysics Data System (ADS)

    Karimi, Mona; Girimaji, Sharath S.

    2017-03-01

    We investigate the influence of orientation on the evolution of small perturbations in compressible shear layers with inflection points. By using linear analysis, we demonstrate that perturbations along the shear plane are most affected by compressibility. The influence of compressibility gradually diminishes with increasing obliqueness of the perturbations with respect to the shear plane. It is demonstrated that the effective gradient Mach number is an appropriate compressibility parameter. We establish that spanwise perturbations, orthogonal to the shear plane, are impervious to compressibility effects. Direct numerical simulations of compressible mixing layers subject to the perturbations at various obliqueness angles verify the analytical findings.

  9. Evolution of the atmospheric boundary-layer structure of an arid Andes Valley

    NASA Astrophysics Data System (ADS)

    Khodayar, S.; Kalthoff, N.; Fiebig-Wittmaack, M.; Kohler, M.

    2008-04-01

    The boundary-layer structure of the Elqui Valley is investigated, which is situated in the arid north of Chile and extends from the Pacific Ocean in the west to the Andes in the east. The climate is dominated by the south-eastern Pacific subtropical anticyclone and the cold Humboldt Current. This combination leads to considerable temperature and moisture gradients between the coast and the valley and results in the evolution of sea and valley wind systems. The contribution of these mesoscale wind systems to the heat and moisture budget of the valley atmosphere is estimated, based on radiosoundings performed near the coast and in the valley. Near the coast, a well-mixed cloud-topped boundary layer exists. Both, the temperature and the specific humidity do not change considerably during the day. In the stratus layer the potential temperature increases, while the specific humidity decreases slightly with height. The top of the thin stratus layer, about 300 m in depth, is marked by an inversion. Moderate sea breeze winds of 3-4 m s-1 prevail in the sub-cloud and cloud layer during daytime, but no land breeze develops during the night. The nocturnal valley atmosphere is characterized by a strong and 900 m deep stably stratified boundary layer. During the day, no pronounced well-mixed layer with a capping inversion develops in the valley. Above a super-adiabatic surface layer of about 150 m depth, a stably stratified layer prevails throughout the day. However, heating can be observed within a layer above the surface 800 m deep. Heat and moisture budget estimations show that sensible heat flux convergence exceeds cold air advection in the morning, while both processes compensate each other around noon, such that the temperature evolution stagnates. In the afternoon, cold air advection predominates and leads to net cooling of the boundary layer. Furthermore, the advection of moist air results in the accumulation of moisture during the noon and afternoon period, while

  10. 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

  11. Gradation of mechanical properties in gas-diffusion electrode. Part 2: Heterogeneous carbon fiber and damage evolution in cell layers

    NASA Astrophysics Data System (ADS)

    Poornesh, K. K.; Cho, C. D.; Lee, G. B.; Tak, Y. S.

    In PEM fuel cell, gas-diffusion electrode (GDE) plays very significant role in force transmission from bipolar plate to the membrane. This paper investigates the effects of geometrical heterogeneities of gas-diffusion electrode layer (gas-diffusion layer (GDL) and catalyst layer (CL)) on mechanical damage evolution and propagation. We present a structural integrity principle of membrane electrode assembly (MEA) based on the interlayer stress transfer capacity and corresponding cell layer material response. Commonly observable damages such as rupture of hydrophobic coating and breakage of carbon fiber in gas-diffusion layer are attributed to the ductile to brittle phase transition within a single carbon fiber. Effect of material inhomogeneity on change in modulus, hardness, contact stiffness, and electrical contact resistance is also discussed. Fracture statistics of carbon fiber and variations in flexural strength of GDL are studied. The damage propagation in CL is perceived to be influenced by the type of gradation and the vicinity from which crack originates. Cohesive zone model has been proposed based on the traction-separation law to investigate the damage propagation throughout the two interfaces (carbon fiber/CL and CL/membrane).

  12. 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

  13. 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

  14. Modeling of Microstructure Evolution During Alloy Solidification

    NASA Astrophysics Data System (ADS)

    Zhu, Mingfang; Pan, Shiyan; Sun, Dongke

    In recent years, considerable advances have been achieved in the numerical modeling of microstructure evolution during solidification. This paper presents the models based on the cellular automaton (CA) technique and lattice Boltzmann method (LBM), which can reproduce a wide variety of solidification microstructure features observed experimentally with an acceptable computational efficiency. The capabilities of the models are addressed by presenting representative examples encompassing a broad variety of issues, such as the evolution of dendritic structure and microsegregation in two and three dimensions, dendritic growth in the presence of convection, divorced eutectic solidification of spheroidal graphite irons, and gas porosity formation. The simulations offer insights into the underlying physics of microstructure formation during alloy solidification.

  15. Punctuated evolution for the quasispecies model

    NASA Astrophysics Data System (ADS)

    Krug, Joachim; Karl, Christian

    2003-02-01

    Biological evolution in a sequence space with random fitnesses is studied within Eigen's quasispecies model. A strong selection limit is employed, in which the population resides at a single sequence at all times. Evolutionary trajectories start at a randomly chosen sequence and proceed to the global fitness maximum through a small number of intermittent jumps. The distribution of the total evolution time displays a universal power law tail with exponent -2. Simulations show that the evolutionary dynamics is very well represented by a simplified shell model, in which the sub-populations at local fitness maxima grow independently. The shell model allows for highly efficient simulations, and provides a simple geometric picture of the evolutionary trajectories.

  16. 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.

  17. Simulation of a sea ice ecosystem using a hybrid model for slush layer desalination

    NASA Astrophysics Data System (ADS)

    Saenz, Benjamin T.; Arrigo, Kevin R.

    2012-05-01

    Porous, slushy layers are a common feature of Antarctic sea ice and are often colonized by high concentrations of algae. Despite its potential importance to the physics and biogeochemistry of the sea ice ecosystem, current knowledge of the evolution of sea ice slush layers is limited. Here we present a model of sea ice that is capable of reproducing the vertical biophysical evolution of sea ice that contains slush layers. The model uses a novel hybrid desalination scheme to calculate salt fluxes and brine motion during freezing using one of two different methods depending on the brine fraction of the ice. Model runs using atmospheric and snow depth forcing from the Ice Station Weddell experiment show that model is able to simulate the magnitude and timing of sea ice temperature, salinity, and associated algal growth of observed slush layers, as well as the surrounding sea ice. The model was designed with regional-scale simulations in mind and we show that the model performs well at lower vertical resolutions, as long as the slush layer is resolved. Incorporation of our model of slush ice desalination into regional and global simulations has potential to improve model estimates of salt, heat, and biochemical fluxes in polar marine environments.

  18. New applications of a simple mixed-layer model

    NASA Astrophysics Data System (ADS)

    Fitzjarrald, David R.

    1982-04-01

    Model formulation of the balance between surface heat and moisture fluxes and subsidence that determines the state of the mixed layer is used to estimate cooling and drying rates in the mixed layer above the tropical ocean based on GATE observations. Estimated cooling rates are comparable to observed radiative cooling rates for thick mixed layers characteristic of undisturbed conditions but are up to five times larger for shallow mixed layers observed during disturbed periods. The additional cooling and drying in the mixed layer needed to maintain shallow, cool mixed layers is hypothesized to be the net result of an assemblage of downdrafts. A new scaling scheme for non-dimensionalizing the mixed-layer thermodynamic budget equations is introduced. The ratio of subsidence at the top of the mixed layer to the product of the entrainment coefficient, a bulk aerodynamic transfer coefficient, and the surface-layer wind speed is shown theoretically to be a fundamental descriptor of the mixed-layer environment.

  19. Evolution of vortices in 2D boundary layer and in the Couette flow

    NASA Astrophysics Data System (ADS)

    Zametaev, Vladimir B.; Gorbushin, Anton R.

    2016-10-01

    A 2D incompressible laminar boundary layer and the Couette flow having the low velocity fluctuations are considered using asymptotic methods at high Reynolds number. Two classes of solutions for the first order inviscid perturbations have been derived. The integral-differential equation with initial data describing evolution of vortices in time have been solved numerically. It was found that the discontinuities are formed in a smooth solution for a vertical velocity component with the time increase. This first type solution explains instability mechanism in the Couette flow. The second class of solutions contains a singularity at the boundary layer bottom which reminds a source-sink with a variable intensity. The singularity can absorb the fluid from the main part of the boundary layer and eject it back with a possibly "new" vorticity.

  20. 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.

  1. 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

  2. Modeling Marine Boundary-Layer Clouds with a Two-Layer Model: A One-Dimensional Simulation.

    NASA Astrophysics Data System (ADS)

    Wang, Shouping

    1993-12-01

    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 effects 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.

  3. 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.

  4. 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.

  5. 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

  6. A concatenational graph evolution aging model.

    PubMed

    Suo, Jinli; Chen, Xilin; Shan, Shiguang; Gao, Wen; Dai, Qionghai

    2012-11-01

    Modeling the long-term face aging process is of great importance for face recognition and animation, but there is a lack of sufficient long-term face aging sequences for model learning. To address this problem, we propose a CONcatenational GRaph Evolution (CONGRE) aging model, which adopts decomposition strategy in both spatial and temporal aspects to learn long-term aging patterns from partially dense aging databases. In spatial aspect, we build a graphical face representation, in which a human face is decomposed into mutually interrelated subregions under anatomical guidance. In temporal aspect, the long-term evolution of the above graphical representation is then modeled by connecting sequential short-term patterns following the Markov property of aging process under smoothness constraints between neighboring short-term patterns and consistency constraints among subregions. The proposed model also considers the diversity of face aging by proposing probabilistic concatenation strategy between short-term patterns and applying scholastic sampling in aging prediction. In experiments, the aging prediction results generated by the learned aging models are evaluated both subjectively and objectively to validate the proposed model.

  7. Modeling galactic chemical evolution in cosmological simulations

    NASA Astrophysics Data System (ADS)

    Peruta, Carolyn Cynthia

    The most fundamental challenges to models of galactic chemical evolution (GCE) are uncertainties in the basic inputs, including the properties of the stellar initial mass function (IMF), stellar nucleosynthetic yields, and the rate of return of mass and energy to the interstellar and intergalactic medium by Type Ia and II supernovae and stellar winds. In this dissertation, we provide a critical examination of widely available stellar nucleosynthetic yield data, with an eye toward modeling GCE in the broad scope of cosmological hydrodynamical simulations. We examine the implications of uncertain inputs for the Galactic stellar IMF, and nucleosynthetic yields from stellar-evolution calculations, on our ability to ask detailed questions regarding the observed Galactic chemical-abundance patterns. We find a marked need for stellar feedback data from stars of initial mass 8 to 12 Msun and above 40 M sun, and for initial stellar metallicities above and below solar, Z sun=0.02. We find the largest discrepancies amongst nucleosynthetic yield calculations are due to various groups' treatment of hot bottom burning, formation of the 13C pocket in asymptotic giant-branch (AGB) stars, and details of mass loss, rotation, and convection in all stars. Our model of GCE is used to post-process simulations to explore in greater detail the nucleosynthetic evolution of the stellar populations and interstellar/intergalactic medium, and to compare directly to the chemical abundances of the Milky Way stellar halo and dwarf spheroidal galaxy stellar populations.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. From isotropic to layered gabbro: evolution record in the Oman ophiolite

    NASA Astrophysics Data System (ADS)

    Jousselin, D.; Morales, L. G.; Stephant, A.; Nicolle, M.

    2010-12-01

    The origin of gabbro layering in ophiolites is widely debated because it is linked to the processes of melt circulation beneath spreading ridges. The Moho Transition Zone (MTZ) of the Oman ophiolite contains layered gabbro lenses that are tens of meters wide. At meter scale, these rocks are not distinguishable from crustal layered gabbros. We describe the first known occurrence of an outcrop of isotropic gabbro in the Oman ophiolite MTZ; the outcrop extends over three hundreds meters and grades into poorly to nicely layered gabbros towards the periphery of the outcrop. When they are present, layering, and magmatic lineation are parallel to the host peridotite plastic foliation and lineation respectively, with microstructures indicative of simple shear deformation. Dunite heterogeneities within the isotropic gabbro, and diffuse limits, suggest that the isotropic gabbro results from melt impregnation of the host dunite, and that olivine within the gabbro is of mantelic origin. Crystallographic preferred orientations (CPO) measurements of olivine and plagioclase show a progressive evolution from a random fabric in the isotropic gabbro, to a well defined fabric in the roughly to nicely layered gabbros. Olivine show [001] (010) B-TYPE fabrics that we interpret as a magmatic flow fabric. In the most deformed samples, the plagioclase texture remains magmatic but olivine CPO is indicative of plastic deformation with a classic A-TYPE pattern. We argue that as a critical threshold of olivine connectivity is reached in the well defined olivine-rich layers, olivine deformation rapidly switches from magmatic to plastic. This last stage of deformation probably contributes to the layering sharpening, as deformation in olivine and in plagioclase rich layers must tend to be decoupled at this stage. We conclude that our observations illustrate rarely preserved transitional stages for the layered gabbros formation, showing that layering can result from the progressive tectonic

  16. 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.

  17. Modelling the evolution of mutualistic symbioses.

    PubMed

    Friesen, Maren L; Jones, Emily I

    2012-01-01

    Mutualistic microbial symbioses are one of the key innovations in the evolution of biological diversity, enabling the expansion of species' niches and the production of sophisticated structures such as the eukaryotic cell. For some of the best-studied cases, we are beginning to have network models of symbiotic metabolism, but this work is in its infancy and has not been developed with an evolutionary perspective. However, theoreticians have long been interested in how these symbioses arise and persist and have applied modelling approaches from economics, evolution, ecology, and sociobology to a number of fundamental questions. We provide an overview of these questions, followed by specific modelling examples. We cover economic game theory, including the Prisoner's Dilemma, the Snowdrift game, and biological markets. We also describe the eco-evolutionary framework of adaptive dynamics, inclusive fitness, and population genetic models. We aim to provide insight into the strengths and weaknesses of each approach and into how current evolutionary methods can benefit an understanding of the mechanistic basis of host-symbiont interactions elucidated by molecular network models.

  18. 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.

  19. A mesobeta-scale model in boundary-layer coordinates

    SciTech Connect

    Seitter, K.L.; Colby, F.P. Jr. )

    1992-12-01

    A mesobeta-scale numerical model is described that is designed specifically for operational use on relatively small computers (supermicro-class computers of the MicroVAX 3000/4000 type). A major aspect of the model leading to improved computational efficiency is that rather than using many model layers near the surface to resolve the growth and decay of the boundary layer explicitly, the model treats the boundary layer as a single model layer of known structure whose depth can evolve during the integration. The model equations are recast in a coordinate system, referred to as boundary layer coordinates, based on the depth of the evolving boundary layer. The model described here does not include condensation processes, but it does include a radiation parameterization, schemes governing the structure of the stable and unstable boundary layers and the transitions between these regimes, and parameterizations for the fluxes of heat and moisture between the boundary layer and the earth's surface. Simulations have been carried out with a prototype model that has five layers and 20-km grid spacing in the fine grid mesh of its nested domain, Results of these simulations show that the model is capable of reproducing such mesoscale phenomena as mountain lee waves and the Florida sea-breeze circulation fairly well.

  20. 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.

  1. 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

    2014-03-27

    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.

  2. The use of a wave boundary layer model in SWAN

    NASA Astrophysics Data System (ADS)

    Du, Jianting; Bolaños, Rodolfo.; Guo Larsén, Xiaoli

    2017-01-01

    A wave boundary layer model (WBLM) is implemented in the third-generation ocean wave model SWAN to improve the wind-input source function under idealized, fetch-limited condition. Accordingly, the white capping dissipation parameters are recalibrated to fit the new wind-input source function to parametric growth curves. The performance of the new pair of wind-input and dissipation source functions is validated by numerical simulations of fetch-limited evolution of wind-driven waves. As a result, fetch-limited growth curves of significant wave height and peak frequency show close agreement with benchmark studies at all wind speeds (5-60 m s-1) and fetches (1-3000 km). The WBLM wind-input source function explicitly calculates the drag coefficient based on the momentum and kinetic energy conservation. The modeled drag coefficient using WBLM wind-input source function is in rather good agreement with field measurements. Thus, the new pair of wind-input and dissipation source functions not only improve the wave simulation but also have the potential of improving air-sea coupling systems by providing reliable momentum flux estimation at the air-sea interface.

  3. Iron isotopic evolution during fractional crystallization of the uppermost Bushveld Complex layered mafic intrusion

    NASA Astrophysics Data System (ADS)

    Bilenker, Laura D.; VanTongeren, Jill A.; Lundstrom, Craig C.; Simon, Adam C.

    2017-03-01

    We present δ56Fe (56Fe/54Fe relative to standard IRMM-014) data from whole rock and magnetite of the Upper and Upper Main Zones (UUMZ) of the Bushveld Complex. With it, we assess the role of fractional crystallization in controlling the Fe isotopic evolution of a mafic magma. The UUMZ evolved by fractional crystallization of a dry tholeiitic magma to produce gabbros and diorites with cumulus magnetite and fayalitic olivine. Despite previous experimental work indicating a potential for magnetite crystallization to drastically change magma δ56Fe, we observe no change in whole rock δ56Fe above and below magnetite saturation. We also observe no systematic change in whole rock δ56Fe with increasing stratigraphic height, and only a small variation in δ56Fe in magnetite separates above magnetite saturation. Whole rock δ56Fe (errors twice standard deviation, ±2σ) throughout the UUMZ ranges from -0.01 ±0.03‰ to 0.21 ±0.09‰ (δ56FeaverageWR = 0.10 ±0.09‰; n = 21, isotopically light outlier: δ56FeWR = -0.15‰), and magnetites range from 0.28 ±0.04‰ to 0.86 ±0.07‰ (δ56FeaverageMgt = 0.50 ±0.15‰; n = 20), similar to values previously reported for other layered intrusions. We compare our measured δ56FeWR to a model that incorporates the changing normative mineralogy, calculated temperatures, and published fractionation factors of Fe-bearing phases throughout the UUMZ and produces δ56FeWR values that evolve only in response to fractional crystallization. Our results show that the Fe isotopic composition of a multiply saturated (multiple phases on the liquidus) magma is unlikely to change significantly during fractional crystallization of magnetite due to the competing fractionation of other Fe-bearing cumulus phases.

  4. Quantum-like model of partially directed evolution.

    PubMed

    Melkikh, Alexey V; Khrennikov, Andrei

    2016-12-15

    The background of this study is that models of the evolution of living systems are based mainly on the evolution of replicators and cannot explain many of the properties of biological systems such as the existence of the sexes, molecular exaptation and others. The purpose of this study is to build a complete model of the evolution of organisms based on a combination of quantum-like models and models based on partial directivity of evolution. We also used optimal control theory for evolution modeling. We found that partial directivity of evolution is necessary for the explanation of the properties of an evolving system such as the stability of evolutionary strategies, aging and death, the presence of the sexes. The proposed model represents a systems approach to the evolution of species and will facilitate the understanding of the evolution and biology as a whole.

  5. Modeling the Temporal Evolution of Postoperative Complications

    PubMed Central

    Feld, Shara I.; Cobian, Alexander G.; Tevis, Sarah E.; Kennedy, Gregory D.; Craven, Mark W.

    2016-01-01

    Post-operative complications have a significant impact on patient morbidity and mortality; these impacts are exacerbated when patients experience multiple complications. However, the task of modeling the temporal sequencing of complications has not been previously addressed. We present an approach based on Markov chain models for characterizing the temporal evolution of post-operative complications represented in the American College of Surgeons National Surgery Quality Improvement Program database. Our work demonstrates that the models have significant predictive value. In particular, an inhomogenous Markov chain model effectively predicts the development of serious complications (coma longer than a day, cardiac arrest, myocardial infarction, septic shock, renal failure, pneumonia) and interventional complications (unplanned re-intubation, longer than 2 days on a ventilator and bleeding transfusion). PMID:28269851

  6. Validation Test Report for the 1/16 Degree Global NRL Layered Ocean Model Nowcast/Forecast System

    DTIC Science & Technology

    2003-04-14

    2002a), and Zamudio et al. (2002). Robert C. Rhodes et al.2 2. SYSTEM COMPONENTS NRL Layered Ocean Model The NRL Layered Ocean Model is a descendent of...tion, diffusion, entrainment, or relaxation to a density climatology such as MODAS. The latter helps NLOM maintain accurate SSH. Unlike models with fixed ... Zamudio , L., H.E. Hurlburt, E.J. Metzger, and O.M. Smedstad, 2002: On the evolution of coastally trapped waves generated by Hurricane Juliette along the

  7. Cross layers decision making and fusion model in layered sensing systems

    NASA Astrophysics Data System (ADS)

    Khoshnaw, Abdulqadir; Zein-Sabatto, Saleh; Malkani, Mohan

    2012-06-01

    Layered sensing systems involve operation of several layers of sensing with different capabilities integrated into one whole system. The integrated layers of sensing must share information and local decisions across layers for better situation awareness. This research focused on the development of a model for decision making and fusion at the information level in layered sensing systems using the cloud model for uncertainty processing. In this research, the addition of a new processing level to the Joint Directors of Laboratories (JDL) processing model is proposed. The new processing level is called "Information Assessment, Fusion, and Control (IAFC)". Through this level, the different layers of a layered sensing system evaluate information about a given situation in terms of threat level and make a decision. The information assessment and control processing module were able to assess the threat level of a situation accurately and exchange assessments in order to determine the overall situation's threat level among all layers. The uncertain decisions were fused together to a unified decision using the cloud model of uncertainty processing methodology. Using this methodology, a cognitive element was added to the process of information assessment module leading to more accurate situation awareness.

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

    DOE PAGES

    Boichot, R.; Tian, L.; Richard, M. -I.; ...

    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.

  9. 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.

  10. Efficient electrocatalytic oxygen evolution on amorphous nickel-cobalt binary oxide nanoporous layers.

    PubMed

    Yang, Yang; Fei, Huilong; Ruan, Gedeng; Xiang, Changsheng; Tour, James M

    2014-09-23

    Nanoporous Ni-Co binary oxide layers were electrochemically fabricated by deposition followed by anodization, which produced an amorphous layered structure that could act as an efficient electrocatalyst for water oxidation. The highly porous morphologies produced higher electrochemically active surface areas, while the amorphous structure supplied abundant defect sites for oxygen evolution. These Ni-rich (10-40 atom % Co) binary oxides have an increased active surface area (roughness factor up to 17), reduced charge transfer resistance, lowered overpotential (∼325 mV) that produced a 10 mA cm(-2) current density, and a decreased Tafel slope (∼39 mV decade(-1)). The present technique has a wide range of applications for the preparation of other binary or multiple-metals or metal oxides nanoporous films. Fabrication of nanoporous materials using this method could provide products useful for renewable energy production and storage applications.

  11. The three-dimensional evolution of a plane mixing layer - The Kelvin-Helmholtz rollup

    NASA Technical Reports Server (NTRS)

    Rogers, Michael M.; Moser, Robert D.

    1992-01-01

    The hydrodynamic evolution of an incompressible plane mixing layer is addressed to elucidate scalar mixing in free shear flows. A detailed description of the onset of three-dimensionality in a mixing layer before or in the absence of pairing is presented. Various simulations were performed to investigate the sensitivity of these results to variations in initial conditions. These variations included changes in amplitude, wavelength, functional form, and relative phasing of the initial low-wavenumber disturbances. Pierrehumber and Widnall's (1982) translative instability eigenfunctions are found to include rib vortices in the braid region and oppositely signed streamwise vorticity in the roller core. The translative instability is an instability of the late-time oversaturated flow. Three-dimensional perturbation growth similar to that of the translative instability can occur whenever spanwise vorticity is present in the braid region. The nonlinear effects that occur when the initial rib circulation is sufficiently high are discussed.

  12. Electronic quasiparticles and evolution of Fermi level spin states in thin magnetic layers

    NASA Astrophysics Data System (ADS)

    Schäfer, J.; Hoinkis, M.; Schrupp, D.; Rotenberg, Eli; Blaha, P.; Claessen, R.

    2006-09-01

    Here we report on high-resolution photoemission of iron layers grown on a W(1 1 0) substrate. The evolution of the substrate states upon sub-monolayer adsorption of Fe atoms leads to a shift in surface state binding energy. For thicker (1 1 0) films, sharp metallic surface states are obtained. Their dispersion displays the signature of quasiparticle renormalization due to dressing with excitations. The energy scale is characteristic for the spin wave spectrum in iron, thereby giving evidence of electron-magnon coupling. Furthermore, it is found that quantum well states occur as a function of layer thickness. These modify the spin density of states at the Fermi level in the ferromagnetic film.

  13. 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.

  14. Boundary Critical Behaviour of Two-Dimensional Layered Ising Models

    NASA Astrophysics Data System (ADS)

    Pelizzola, Alessandro

    Layered models are models in which the coupling constants depend in an arbitrary way on one spatial coordinate, usually the distance from a free surface or boundary. Here the theory of the boundary critical behaviour of two-dimensional layered Ising models, including the Hilhorst-van Leeuwen model and models for aperiodic systems, is reviewed, with a particular attention to exact results for the critical behaviour and the boundary order parameter.

  15. 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.

  16. A Two-layer Model for the Simulation of the VARTM Process with Resin Distribution Layer

    NASA Astrophysics Data System (ADS)

    Young, Wen-Bin

    2013-12-01

    Vacuum assisted resin transfer molding (VARTM) is one of the important processes to fabricate high performance composites. In this process, resin is drawn into the mold to impregnate the fiber reinforcement to a form composite. A resin distribution layer with high permeability was often introduced on top of the fiber reinforcement to accelerate the filling speed. Due to the difference of the flow resistance in the resin distribution layer and the reinforcement as well as the resulting through thickness transverse flow, the filling flow field is intrinsically three-dimensional. This study developed a two-layer model with two-dimensional formulation to simulate the filling flow of the VARTM process with a resin distribution layer. Two-dimensional flow was considered in each layer and a transverse flow in the thickness direction was estimated between the two layers. Thermal analysis including the transverse convection was also performed to better simulate the temperature distribution.

  17. The Evolution of Microstructure and Magnetic Properties of the Bismuth Layer Compounds with Cobalt Ions Substitution.

    PubMed

    Wang, Weipeng; Shen, Xi; Wang, Wei; Guan, Xiangxiang; Yao, Yuan; Wang, Yanguo; Yu, Richeng

    2017-03-20

    One of the core issues for the A/B site doping in the bismuth layer magnetoelectric materials is to find out the evolution of the magnetic structure, crystal structure and elemental distribution, and the coupling effects between spin and lattice with the increase of ion substitution. Here, we have conducted systematic structural and physical property studies on the series samples of Bi5Ti3Fe1-xCoxO15. This work presents that Bi5Ti3Fe1-xCoxO15 forms a single four layer perovskite-like structure for 0 ≤ x < 0.67, while a three layer perovskite-like structure block begins to arise for x ≥ 0.67. With different cobalt content, the sample demonstrates antiferromagnetism, spin state determined magnetism, or magnetic anisotropy determined magnetism. The weak ferromagnetism is considered to be induced by the larger displacement of Co(3+) ions from the center of octahedra and the change of the spin state of Co(3+) ions. It is also observed that Fe and Co elements are homogeneously substituted in the three layer structure block, accompanied by the rotation (and/or distortion) of BO6 octahedra.

  18. Surface Layer Evolution on Graphite During Electrochemical Sodium-tetraglyme Co-intercalation.

    PubMed

    Maibach, Julia; Jeschull, Fabian; Brandell, Daniel; Edström, Kristina; Valvo, Mario

    2017-04-12

    One obstacle in sodium ion batteries is the lack of suitable anode materials. As recently shown, the most common anode material of the state of the art lithium ion batteries, graphite, can be used for sodium ion storage as well, if ether-based electrolyte solvents are used. These solvents cointercalate with the sodium ions leading to the highly reversible formation of ternary graphite intercalation compounds (t-GIC). In order for the solvent cointercalation to work efficiently, it is expected that only a very thin surface layer forms during electrochemical cycling. In this article, we therefore present the first dedicated study of the surface layer evolution on t-GICs using soft X-ray photoelectron spectroscopy. This technique with its inherent high surface sensitivity and low probing depth is an ideal tool to study the underlying interfacial reactions during the sodiation and desodiation of graphite. In this report, we apply this approach to graphite composite electrodes cycled in Na half cells with a 1 M sodium bis(fluorosulfonyl)imide/tetraethylene glycol dimethyl ether (NaFSI/TEG-DME) electrolyte. We have found a surface layer on the cycled electrodes, mainly composed of salt decomposition products and hydrocarbons, in line with irreversible capacity losses observed in the electrochemical cycling. Although this surface layer does not seem to block cointercalation completely, it seems to affect its efficiency resulting in a low Coulombic efficiency of the studied battery system.

  19. 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

  20. The spatial evolution of the mixing layer in the Kelvin-Helmholtz instability at the Martian ionopause

    NASA Astrophysics Data System (ADS)

    Aizawa, S.; Terada, N.; Kasaba, Y.; Yagi, M.; Matsumoto, Y.

    2016-12-01

    We investigate the growth of the mixing layer thickness in the Kelvin-Helmholtz (KH) instability using an extended-local MHD model to estimate the ion loss rate from the Martian ionopause. This instability is expected to play a major role in transporting mass, momentum and energy across the ionopause between the sheath flow and ionospheric plasmas. Since the mixing layer has a finite thickness between them, this layer has a potential for the removal of a huge amount of ions from Mars through its history. The recent MAVEN observation reported that the density ratio across the ionopause reaches as high as 100 5000. With such a large density ratio, compressible effects are expected to modify the structure of the KH vortices and the evolution of the mixing layer by generating high-amplitude nonlinear fast-mode plane waves from ridges of the KH waves. In order to reproduce a realistic Martian ionopause, we developed an extended-local MHD model with aperiodic boundary condition for the evaluation of traveling waves along the dayside Martian ionopause ( 6,000km). Spatial resolution is set with 3km to resolve the thin mixing layer. We find two factors that accelerate the growth of the mixing layer. Firstly, the KH wave with the fastest growing mode behaves like a wall to the leading vortex in the aperiodic condition. The sheath flow is stagnated by this wall-like structure and induces an enhanced vortex return flow, resulting in a deeper excavation of the ionospheric plasma. Secondly, fast-mode rarefaction waves generated by compressible effects make wall-like structures more effective by lowering pressure around antinodes of the KH waves. Such a pressure profile further accelerates the stagnation and the excavation. Thus, the mixing layer becomes about 1.5 times wider than that obtained from a periodic local model when the density ratio is 100. It indicates that more ionospheric plasmas will escape than expected. The ion loss rate drastically increases after reaching the

  1. Self-Assembly of Single-Layer CoAl-Layered Double Hydroxide Nanosheets on 3D Graphene Network Used as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction.

    PubMed

    Ping, Jianfeng; Wang, Yixian; Lu, Qipeng; Chen, Bo; Chen, Junze; Huang, Ying; Ma, Qinglang; Tan, Chaoliang; Yang, Jian; Cao, Xiehong; Wang, Zhijuan; Wu, Jian; Ying, Yibin; Zhang, Hua

    2016-09-01

    A non-noble metal based 3D porous electrocatalyst is prepared by self-assembly of the liquid-exfoliated single-layer CoAl-layered double hydroxide nanosheets (CoAl-NSs) onto 3D graphene network, which exhibits higher catalytic activity and better stability for electrochemical oxygen evolution reaction compared to the commercial IrO2 nanoparticle-based 3D porous electrocatalyst.

  2. Uncertainties in Galactic Chemical Evolution Models

    SciTech Connect

    Cote, Benoit; Ritter, Christian; Oshea, Brian W.; Herwig, Falk; Pignatari, Marco; Jones, Samuel; Fryer, Christopher Lee

    2016-06-15

    Here 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

  3. Uncertainties in Galactic Chemical Evolution Models

    SciTech Connect

    Cote, Benoit; Ritter, Christian; Oshea, Brian W.; Herwig, Falk; Pignatari, Marco; Jones, Samuel; Fryer, Christopher Lee

    2016-06-15

    Here 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

  4. Uncertainties in Galactic Chemical Evolution Models

    DOE PAGES

    Cote, Benoit; Ritter, Christian; Oshea, Brian W.; ...

    2016-06-15

    Here 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 ofmore » 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

  5. Estimates of the potential temperature profile from lidar measurements of boundary layer evolution

    NASA Astrophysics Data System (ADS)

    Holder, H. E.; Eichinger, W. E.

    2006-10-01

    The Soil Moisture-Atmosphere Coupling Experiment (SMACEX) was conducted in the Walnut Creek Watershed near Ames, Iowa, over the period from 15 June to 11 July 2002. A main focus of SMACEX is the investigation of the interactions between the atmospheric boundary layer, surface moisture, and canopy. A vertically staring elastic lidar was used to provide a high time resolution, continuous record of the mixed layer height at the edge between a soybean and a corn field. The height and thickness of the entrainment zone are used to estimate the vertical potential temperature profile in the boundary layer using surface energy measurements in the Batchvarova-Gryning mixed layer model. Calculated values of potential temperature compared well to radiosonde measurements taken simultaneously with the lidar measurements. The root-mean-square difference between the lidar-derived values and the balloon-based values is 1.20°C.

  6. Friction phenomena in the overdamped three-layer model.

    PubMed

    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.

  7. Two-layer model of coronary artery vasoactivity

    PubMed Central

    Huo, Yunlong; Zhao, Xuefeng; Cheng, Yana; Lu, Xiao

    2013-01-01

    Since vascular tone is regulated by smooth muscle cells in the media layer, a multilayer mechanical model is required for blood vessels. Here, we performed biaxial mechanical tests in the intima-media layer of right coronary artery to determine the passive and active properties in conjunction with the passive properties of adventitia for a full vessel wall model. A two-layer (intima-media and adventitia) model was developed to determine the transmural stress and stretch across the vessel wall. The mean ± SE values of the outer diameters of intima-media layers at transmural pressure of 60 mmHg in active state were 3.17 ± 0.16 and 3.07 ± 0.18 mm at axial stretch ratio of 1.2 and 1.3, respectively, which were significantly smaller than those in passive state (i.e., 3.62 ± 0.19 and 3.49 ± 0.22 mm, respectively, P < 0.05). The inner and outer diameters in no-load state of intima-media layers were 1.17 ± 0.09 and 2.08 ± 0.09 mm, respectively. The opening angles in zero-stress state had values of 159 ± 21° for intima-media layers and 98 ± 15° for adventitia layers, which suggests a residual strain between the two layers. There were slightly decreased active circumferential stresses (<10%), but significantly decreased active axial stresses (>25%) in the intima-media layer compared with those in the intact vessel. This suggests that the adventitia layer affects vascular contraction. The two-layer analysis showed that the intima-media layer bears the majority of circumferential tensions, in contrast to the adventitia layer, while contraction results in decreased stress and stretch in both layers. PMID:23471951

  8. A Profile Evolution Model With Redeposition

    NASA Astrophysics Data System (ADS)

    Jackson, Scott C.; Dalton, Timothy J.

    1990-01-01

    Pattern dependencies in plasma etching processes have been widely noted, but only a limited understanding of the fundamental cause exists. Typical pattern dependencies are variations of the etching rate and sidewall profile with line spacing or other changes of the local topography. The dispersion of the ion impingement angle (caused by scattering within the plasma sheath), scattering of ions (by glancing collisions with the profile features), and redeposition of material emitted in the etching process (which blocks the sidewall etching) are thought to be the primary factors in pattern dependencies. In this work, a string-and-point model has been extended to describe both the wafer surface and the interface between the redeposited layer and the underlying material. The etching rate is modeled as an ion-enhanced etching accompanied by isotropic etching which proceeds at a rate which is inversely related to the redeposited film thickness. The model successfully describes phenomena such as "mouse bites" in which the redeposition layer, which blocks the etching, becomes too thin and cavernous etching proceeds from a point midway along the sidewall.

  9. The spatial evolution of the mixing layer in the Kelvin-Helmholtz instability at the Martian ionopause

    NASA Astrophysics Data System (ADS)

    Aizawa, Sae; Terada, Naoki; Kasaba, Yasumasa; Yagi, Manabu; Matsumoto, Yosuke; Delcourt, Dominique

    2017-04-01

    We investigate the growth of the mixing layer thickness in the Kelvin-Helmholtz instability (KHI) using an extended-local MHD model to estimate the ion loss rate from the Martian ionopause. The KHI is expected to play a major role in transporting mass, momentum and energy across the ionopause between the sheath flow and ionospheric plasmas. Since the mixing layer has a finite thickness between them, this layer has a potential for the removal of a huge amount of ions from Mars through its history. The recent MAVEN observation reported that the density ratio across the ionopause reaches as high as 100 5000. With such a large density ratio, compressible effects are expected to modify the structure of the KH vortices and the evolution of the mixing layer by generating high-amplitude nonlinear fast-mode plane waves from ridges of the KH waves. In order to reproduce Martian ionopause, we developed an extended-local MHD model with aperiodic boundary condition for the evaluation of traveling waves along the dayside Martian ionopause ( 6,000km). Spatial resolution is set with 3km to resolve the thin mixing layer. We find two factors that accelerate the growth of the mixing layer. Firstly, the KH wave with the fastest growing mode behaves like a wall to the leading vortex in the aperiodic condition. The sheath flow is stagnated by this wall-like structure and induces an enhanced vortex return flow, resulting in a deeper excavation of the ionospheric plasma. Secondly, fast-mode rarefaction waves generated by compressible effects make wall-like structures more effective by lowering pressure around antinodes of the KH waves. Such a pressure profile further accelerates the stagnation and the excavation. In addition, KH vortices are merging not one by one but also some vortices are merged together at time. Thus, the large wave like structure can be seen when the effect of compressibility is not so large. The mixing layer spread with the lapse of time and it depends on the density

  10. Evolution model with a cumulative feedback coupling

    NASA Astrophysics Data System (ADS)

    Trimper, Steffen; Zabrocki, Knud; Schulz, Michael

    2002-05-01

    The paper is concerned with a toy model that generalizes the standard Lotka-Volterra equation for a certain population by introducing a competition between instantaneous and accumulative, history-dependent nonlinear feedback the origin of which could be a contribution from any kind of mismanagement in the past. The results depend on the sign of that additional cumulative loss or gain term of strength λ. In case of a positive coupling the system offers a maximum gain achieved after a finite time but the population will die out in the long time limit. In this case the instantaneous loss term of strength u is irrelevant and the model exhibits an exact solution. In the opposite case λ<0 the time evolution of the system is terminated in a crash after ts provided u=0. This singularity after a finite time can be avoided if u≠0. The approach may well be of relevance for the qualitative understanding of more realistic descriptions.

  11. 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.

  12. 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.

  13. Wafer sub-layer impact in OPC/ORC models for advanced node implant layers

    NASA Astrophysics Data System (ADS)

    Le-Denmat, Jean-Christophe; Michel, Jean-Christophe; Sungauer, Elodie; Yesilada, Emek; Robert, Frederic; Lan, Song; Feng, Mu; Wang, Lei; Depre, Laurent; Kapasi, Sanjay

    2014-03-01

    From 28 nm technology node and below optical proximity correction (OPC) needs to take into account light scattering effects from prior layers when bottom anti-reflective coating (BARC) is not used, which is typical for ionic implantation layers. These effects are complex, especially when multiple sub layers have to be considered: for instance active and poly structures need to be accounted for. A new model form has been developed to address this wafer topography during model calibration called the wafer 3D+ or W3D+ model. This model can then be used in verification (using Tachyon LMC) and during model based OPC to increase the accuracy of mask correction and verification. This paper discusses an exploration of this new model results using extended wafer measurements (including SEM). Current results show good accuracy on various representative structures.

  14. 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. Copyright © 2016 Cognitive Science Society, Inc.

  15. Geophysiological modeling: new ideas on modeling the evolution of ecosystems.

    PubMed

    Cerrai, Paola; Cordelli, Alessandro; Galleni, Lodovico; Santini, Francesco

    2002-01-01

    Living organisms evolve within ecological associations (from ecosystems to the biosphere) that are constituted by a biological component and a physico-chemical component. It is generally supposed that interactions such as competition and predation between the biological components of ecosystems are the main cause for the observed organization of ecosystems. We believe that in the search for a more comprehensive theory of evolution a much greater attention should be paid to the ways in which living organisms interact with the physico-chemical environment. To test our ideas, we develop a mathematical model to study the evolution of ecosystems, and we apply it to the study of hydrothermal vents. The model proposed is still a qualitative model. It tries to study, in a first approximation, the behaviours of the biological and chemical components. In the following we hope to develop and to improve it so to give a more realistic model.

  16. A model for brain life history evolution.

    PubMed

    González-Forero, Mauricio; Faulwasser, Timm; Lehmann, Laurent

    2017-03-01

    Complex cognition and relatively large brains are distributed across various taxa, and many primarily verbal hypotheses exist to explain such diversity. Yet, mathematical approaches formalizing verbal hypotheses would help deepen the understanding of brain and cognition evolution. With this aim, we combine elements of life history and metabolic theories to formulate a metabolically explicit mathematical model for brain life history evolution. We assume that some of the brain's energetic expense is due to production (learning) and maintenance (memory) of energy-extraction skills (or cognitive abilities, knowledge, information, etc.). We also assume that individuals use such skills to extract energy from the environment, and can allocate this energy to grow and maintain the body, including brain and reproductive tissues. The model can be used to ask what fraction of growth energy should be allocated at each age, given natural selection, to growing brain and other tissues under various biological settings. We apply the model to find uninvadable allocation strategies under a baseline setting ("me vs nature"), namely when energy-extraction challenges are environmentally determined and are overcome individually but possibly with maternal help, and use modern-human data to estimate model's parameter values. The resulting uninvadable strategies yield predictions for brain and body mass throughout ontogeny and for the ages at maturity, adulthood, and brain growth arrest. We find that: (1) a me-vs-nature setting is enough to generate adult brain and body mass of ancient human scale and a sequence of childhood, adolescence, and adulthood stages; (2) large brains are favored by intermediately challenging environments, moderately effective skills, and metabolically expensive memory; and (3) adult skill is proportional to brain mass when metabolic costs of memory saturate the brain metabolic rate allocated to skills.

  17. 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.

  18. Geostrophic tripolar vortices in a two-layer fluid: Linear stability and nonlinear evolution of equilibria

    NASA Astrophysics Data System (ADS)

    Reinaud, J. N.; Sokolovskiy, M. A.; Carton, X.

    2017-03-01

    We investigate equilibrium solutions for tripolar vortices in a two-layer quasi-geostrophic flow. Two of the vortices are like-signed and lie in one layer. An opposite-signed vortex lies in the other layer. The families of equilibria can be spanned by the distance (called separation) between the two like-signed vortices. Two equilibrium configurations are possible when the opposite-signed vortex lies between the two other vortices. In the first configuration (called ordinary roundabout), the opposite signed vortex is equidistant to the two other vortices. In the second configuration (eccentric roundabouts), the distances are unequal. We determine the equilibria numerically and describe their characteristics for various internal deformation radii. The two branches of equilibria can co-exist and intersect for small deformation radii. Then, the eccentric roundabouts are stable while unstable ordinary roundabouts can be found. Indeed, ordinary roundabouts exist at smaller separations than eccentric roundabouts do, thus inducing stronger vortex interactions. However, for larger deformation radii, eccentric roundabouts can also be unstable. Then, the two branches of equilibria do not cross. The branch of eccentric roundabouts only exists for large separations. Near the end of the branch of eccentric roundabouts (at the smallest separation), one of the like-signed vortices exhibits a sharp inner corner where instabilities can be triggered. Finally, we investigate the nonlinear evolution of a few selected cases of tripoles.

  19. Time-evolution of uniform momentum zones in a turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Laskari, Angeliki; Hearst, R. Jason; de Kat, Roeland; Ganapathisubramani, Bharathram

    2016-11-01

    Time-resolved planar particle image velocimetry (PIV) is used to analyse the organisation and evolution of uniform momentum zones (UMZs) in a turbulent boundary layer. Experiments were performed in a recirculating water tunnel on a streamwise-wall-normal plane extending approximately 0 . 5 δ × 1 . 8 δ , in x and y, respectively. In total 400,000 images were captured and for each of the resulting velocity fields, local peaks in the probability density distribution of the streamwise velocity were detected, indicating the instantaneous presence of UMZs throughout the boundary layer. The main characteristics of these zones are outlined and more specifically their velocity range and wall-normal extent. The variation of these characteristics with wall normal distance and total number of zones are also discussed. Exploiting the time information available, time-scales of zones that have a substantial coherence in time are analysed and results show that the zones' lifetime is dependent on both their momentum deficit level and the total number of zones present. Conditional averaging of the flow statistics seems to further indicate that a large number of zones is the result of a wall-dominant mechanism, while the opposite implies an outer-layer dominance.

  20. Ruthenium/Graphene-like Layered Carbon Composite as an Efficient Hydrogen Evolution Reaction Electrocatalyst.

    PubMed

    Chen, Zhe; Lu, Jinfeng; Ai, Yuejie; Ji, Yongfei; Adschiri, Tadafumi; Wan, Lijun

    2016-12-28

    Efficient water splitting through electrocatalysis has been studied extensively in modern energy devices, while the development of catalysts with activity and stability comparable to those of Pt is still a great challenge. In this work, we successfully developed a facile route to synthesize graphene-like layered carbon (GLC) from a layered silicate template. The obtained GLC has layered structure similar to that of the template and can be used as support to load ultrasmall Ru nanoparticles on it in supercritical water. The specific structure and surface properties of GLC enable Ru nanoparticles to disperse highly uniformly on it even at a large loading amount (62 wt %). When the novel Ru/GLC was used as catalyst on a glass carbon electrode for hydrogen evolution reaction (HER) in a 0.5 M H2SO4 solution, it exhibits an extremely low onset potential of only 3 mV and a small Tafel slope of 46 mV/decade. The outstanding performance proved that Ru/GLC is highly active catalyst for HER, comparable with transition-metal dichalcogenides or selenides. As the price of ruthenium is much lower than platinum, our study shows that Ru/GLC might be a promising candidate as an HER catalyst in future energy applications.

  1. Electrocatalytic Hydrogen Evolution Reaction on Edges of a Few Layer Molybdenum Disulfide Nanodots.

    PubMed

    Benson, John; Li, Meixian; Wang, Shuangbao; Wang, Peng; Papakonstantinou, Pagona

    2015-07-01

    The design and development of inexpensive highly efficient electrocatalysts for hydrogen production underpins several emerging clean-energy technologies. In this work, for the first time, molybdenum disulfide (MoS2) nanodots have been synthesized by ionic liquid assisted grinding exfoliation of bulk platelets and isolated by sequential centrifugation. The nanodots have a thickness of up to 7 layers (∼4 nm) and an average lateral size smaller than 20 nm. Detailed structural characterization established that the nanodots retained the crystalline quality and low oxidation states of the bulk material. The small lateral size and reduced number of layers provided these nanodots with an easier path for the electron transport and plentiful active sites for the catalysis of hydrogen evolution reaction (HER) in acidic electrolyte. The MoS2 nanodots exhibited good durability and a Tafel slope of 61 mV dec(-1) with an estimated onset potential of -0.09 V vs RHE, which are considered among the best values achieved for 2H phase. It is envisaged that this work may provide a simplistic route to synthesize a wide range of 2D layered nanodots that have applications in water splitting and other energy related technologies.

  2. A model for brain life history evolution

    PubMed Central

    Lehmann, Laurent

    2017-01-01

    Complex cognition and relatively large brains are distributed across various taxa, and many primarily verbal hypotheses exist to explain such diversity. Yet, mathematical approaches formalizing verbal hypotheses would help deepen the understanding of brain and cognition evolution. With this aim, we combine elements of life history and metabolic theories to formulate a metabolically explicit mathematical model for brain life history evolution. We assume that some of the brain’s energetic expense is due to production (learning) and maintenance (memory) of energy-extraction skills (or cognitive abilities, knowledge, information, etc.). We also assume that individuals use such skills to extract energy from the environment, and can allocate this energy to grow and maintain the body, including brain and reproductive tissues. The model can be used to ask what fraction of growth energy should be allocated at each age, given natural selection, to growing brain and other tissues under various biological settings. We apply the model to find uninvadable allocation strategies under a baseline setting (“me vs nature”), namely when energy-extraction challenges are environmentally determined and are overcome individually but possibly with maternal help, and use modern-human data to estimate model’s parameter values. The resulting uninvadable strategies yield predictions for brain and body mass throughout ontogeny and for the ages at maturity, adulthood, and brain growth arrest. We find that: (1) a me-vs-nature setting is enough to generate adult brain and body mass of ancient human scale and a sequence of childhood, adolescence, and adulthood stages; (2) large brains are favored by intermediately challenging environments, moderately effective skills, and metabolically expensive memory; and (3) adult skill is proportional to brain mass when metabolic costs of memory saturate the brain metabolic rate allocated to skills. PMID:28278153

  3. 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.

  4. The Impact of Modeling Assumptions in Galactic Chemical Evolution Models

    NASA Astrophysics Data System (ADS)

    Côté, Benoit; O’Shea, Brian W.; Ritter, Christian; Herwig, Falk; Venn, Kim A.

    2017-02-01

    We use the OMEGA galactic chemical evolution code to investigate how the assumptions used for the treatment of galactic inflows and outflows impact numerical predictions. The goal is to determine how our capacity to reproduce the chemical evolution trends of a galaxy is affected by the choice of implementation used to include those physical processes. In pursuit of this goal, we experiment with three different prescriptions for galactic inflows and outflows and use OMEGA within a Markov Chain Monte Carlo code to recover the set of input parameters that best reproduces the chemical evolution of nine elements in the dwarf spheroidal galaxy Sculptor. This provides a consistent framework for comparing the best-fit solutions generated by our different models. Despite their different degrees of intended physical realism, we found that all three prescriptions can reproduce in an almost identical way the stellar abundance trends observed in Sculptor. This result supports the similar conclusions originally claimed by Romano & Starkenburg for Sculptor. While the three models have the same capacity to fit the data, the best values recovered for the parameters controlling the number of SNe Ia and the strength of galactic outflows, are substantially different and in fact mutually exclusive from one model to another. For the purpose of understanding how a galaxy evolves, we conclude that only reproducing the evolution of a limited number of elements is insufficient and can lead to misleading conclusions. More elements or additional constraints such as the Galaxy’s star-formation efficiency and the gas fraction are needed in order to break the degeneracy between the different modeling assumptions. Our results show that the successes and failures of chemical evolution models are predominantly driven by the input stellar yields, rather than by the complexity of the Galaxy model itself. Simple models such as OMEGA are therefore sufficient to test and validate stellar yields. OMEGA

  5. 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.

  6. Afm Study of the Evolution of Double Layer on SiO2 Surface and Self-Assembly Monolayer Induced by the Polarization with DC Voltages

    NASA Astrophysics Data System (ADS)

    Tian, Tian; Zhang, Yong; Wang, Haitao; Huang, Ningping; Xiao, Zhongdang

    AFM was used to study the evolution of double layer on SiO2 surface and self-assembly monolayer induced by the polarization with DC voltages. Approach force curves were recorded when external DC voltages were applied between solution and SiO2 or aminopropyltriethoxysilane (APTES) modified SiO2 surfaces in electrolyte solution. The results showed that the reversing of tip-surface interaction forces between attraction and repulsion could take place only by adjusting DC voltages. It is very useful for biotechnology because the adsorption of biomolecules could be controllable by DC voltages. A model was proposed to explain the behavior of double layer under DC voltages.

  7. Lidar Investigations of Atmospheric Boundary Layer Clouds over Coastal Environment and its Diurnal Evolution

    NASA Astrophysics Data System (ADS)

    Mishra, Manoj; Rajeev, Kunjukrishnapillai; Nair, Anish Kumar M.

    Over the high pressure region, diurnal evolution of atmospheric boundary layer (ABL) leads to the development of fair weather clouds, which in turn play an important role in modulating the thermodynamic structure of ABL, radiation balance at surface, and further development of ABL. As they usually cap the ABL, aerosol-cloud interaction in these clouds are expected to be quite large. Notwithstanding their importance, characteristics of the ABL clouds, their diurnal evolution and the resulting feedback are least explored. Major objectives of this study are to: (i) quantify the diurnal evolution of fair-weather ABL clouds and their characteristics (in terms of their altitude of occurrence, physical thickness and optical depth) based on multi-year (2008-2011) Micropulse Lidar observations at the coastal station, Thumba (8.5(°) N, 77(°) E), and (ii) explore the potential impact of these clouds in modulating the downwelling shortwave radiative flux at surface and further development of ABL. Altitude of occurrence of ABL clouds is found to undergo significant diurnal variation during the development of convective ABL (CABL). Typically, the ABL cloud base increases from <500 m at ˜09 LT to >1500 m at ˜12 LT. Base altitude of the ABL clouds is rather steady during the afternoon, associated with the stabilization of CABL development. Clouds in the nocturnal ABL (NABL) generally occur at the altitude of the preceding afternoon CABL height. Simultaneous occurrence of clouds in the thermal internal boundary layer (TIBL) and developed CABL/residual layer (RL) are also observed, through they are less frequent. The TIBL clouds are distinctly separated from those formed at the top of CABL/RL. Base heights of clouds are distinctly lower in TIBL and evolving CABL compared to those in developed CABL and RL, though their mean physical thickness are comparable (typically ˜250m). Optically thin clouds dominate the TIBL, compared to the other three regimes. Reduction in the

  8. 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.

  9. 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.

  10. 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...

  11. 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...

  12. 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

  13. 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.

  14. 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.

  15. Model for bubble pulsation in liquid between parallel viscoelastic layers

    PubMed Central

    Hay, Todd A.; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F.

    2012-01-01

    A model is presented for a pulsating spherical bubble positioned at a fixed location in a viscous, compressible liquid between parallel viscoelastic layers of finite thickness. The Green’s function for particle displacement is found and utilized to derive an expression for the radiation load imposed on the bubble by the layers. Although the radiation load is derived for linear harmonic motion it may be incorporated into an equation for the nonlinear radial dynamics of the bubble. This expression is valid if the strain magnitudes in the viscoelastic layer remain small. Dependence of bubble pulsation on the viscoelastic and geometric parameters of the layers is demonstrated through numerical simulations. PMID:22779461

  16. 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.

  17. The spatial-temporal evolution of coherent structures in log law region of turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Zheng, Xiao-Bo; Jiang, Nan

    2015-02-01

    The spatial-temporal evolution of coherent structures (CS) is significant for turbulence control and drag reduction. Among the CS, low and high speed streak structures show typical burst phenomena. The analysis was based on a time series of three-dimensional and three-component (3D-3C) velocity fields of the flat plate turbulent boundary layer (TBL) measured by a Tomographic and Time-resolved PIV (Tomo TRPIV) system. Using multi-resolution wavelet transform and conditional sampling method, we extracted the intrinsic topologies and found that the streak structures appear in bar-like patterns. Furthermore, we seized locations and velocity information of transient CS, and then calculated the propagation velocity of CS based on spatial-temporal cross-correlation scanning. This laid a foundation for further studies on relevant dynamics properties.

  18. 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.

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

    SciTech Connect

    Boichot, R.; Tian, L.; Richard, M. -I.; Crisci, A.; Chaker, A.; Cantelli, V.; Coindeau, S.; Lay, S.; Ouled, T.; Blanquet, E.; Deschanvres, J. -L.; Renevier, H.; Chu, M. H.; Aubert, N.; Ciatto, G.; Thomas, O.

    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.

  20. Influence of wet chemical treatments on the evolution of epoxy polymer layer surface roughness for use as a build-up layer

    NASA Astrophysics Data System (ADS)

    Siau, Sam; Vervaet, Alfons; Calster, Andre Van; Swennen, Ives; Schacht, Etienne

    2004-10-01

    The adhesion of plated metal layers to polymer surfaces is of prime importance for the reliability of interconnections in electronics. An increase in the roughness of the polymer surface, caused by chemical treatment, plays an important part in the adhesion strength of plated metal layers by increasing the total area of interface between both layers. Hence, the evolution of polymer surface roughness, with time, due to the chemical treatment is of prime importance for determining the reliability of interconnections. The surface roughness changes due to chemical treatment. In this paper, we consider wet solution swellers and oxidizers. These changes are examined by means of AFM roughness measurements. Each chemical treatment, or combination thereof in a certain sequence, has its influence on the evolution of the roughness. Swellers increase roughness over treatment time without etching the surface. Oxidizers, on the other hand, etch part of the surface away and have a more profound influence on roughness. The evolution of surface roughness with treatment time indicates the mechanisms that cause the formation of roughness on the surface. This work is an original contribution to the understanding of the evolution of roughness on photo-imageable dielectrics.

  1. 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.

  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. 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.

  4. 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.

  5. Pseudohomogeneous catalyst layer model for polymer electrolyte fuel cell

    NASA Astrophysics Data System (ADS)

    Springer, T. E.; Gottesfeld, S.

    We have developed a relatively simple one-dimensional model for the cathode catalyst layer. This model explains certain observed polarization curve features at higher current densities. These features include a change in linear slope, instead of a sharp limiting current feature, and a lower than expected ratio of current density measured using O2 relative to air. Diffusional paths, ionic resistance, and catalyst sites are intimately coupled in a pseudohomogeneous layer using 'effective' parameters.

  6. 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.

  7. 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.

  8. 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.

  9. Coastal Foredune Evolution, Part 2: Modeling Approaches for Meso-Scale Morphologic Evolution

    DTIC Science & Technology

    2017-03-01

    ERDC/CHL CHETN-II-57 March 2017 Approved for public release; distribution is unlimited. Coastal Foredune Evolution , Part 2: Modeling Approaches...for Meso-Scale Morphologic Evolution by Margaret L. Palmsten1, Katherine L. Brodie2, and Nicholas J. Spore2 PURPOSE: This Coastal and Hydraulics...Engineering Technical Note (CHETN) is the second of two CHETNs focused on improving technologies to forecast coastal foredune evolution . Part 1

  10. 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.

  11. Self-optimizing, highly surface-active layered metal dichalcogenide catalysts for hydrogen evolution

    NASA Astrophysics Data System (ADS)

    Liu, Yuanyue; Wu, Jingjie; Hackenberg, Ken P.; Zhang, Jing; Wang, Y. Morris; Yang, Yingchao; Keyshar, Kunttal; Gu, Jing; Ogitsu, Tadashi; Vajtai, Robert; Lou, Jun; Ajayan, Pulickel M.; Wood, Brandon C.; Yakobson, Boris I.

    2017-09-01

    Low-cost, layered transition-metal dichalcogenides (MX2) based on molybdenum and tungsten have attracted substantial interest as alternative catalysts for the hydrogen evolution reaction (HER). These materials have high intrinsic per-site HER activity; however, a significant challenge is the limited density of active sites, which are concentrated at the layer edges. Here we unravel electronic factors underlying catalytic activity on MX2 surfaces, and leverage the understanding to report group-5 MX2 (H-TaS2 and H-NbS2) electrocatalysts whose performance instead mainly derives from highly active basal-plane sites, as suggested by our first-principles calculations and performance comparisons with edge-active counterparts. Beyond high catalytic activity, they are found to exhibit an unusual ability to optimize their morphology for enhanced charge transfer and accessibility of active sites as the HER proceeds, offering a practical advantage for scalable processing. The catalysts reach 10 mA cm‑2 current density at an overpotential of ∼50-60 mV with a loading of 10-55 μg cm‑2, surpassing other reported MX2 candidates without any performance-enhancing additives.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Modelling the deformation and collapse of a weak snow layer

    NASA Astrophysics Data System (ADS)

    Mede, Tijan; Chambon, Guillaume; Hagenmuller, Pascal; Nicot, François

    2017-04-01

    Weak snow layers are thin layers of low cohesion and density, naturally occurring in the snowpack. The understanding of their mechanical behaviour is considered to be of great importance as they are believed to have a decisive effect on dry slab avalanche releases. These layers can be viewed as porous structures of sintered ice grains that collapse under loading, withdrawing support to the overlaying slab layer of snow. Field observations show that weak layers are usually formed by very distinct snow types and microstructures. The extremely fragile nature of these layers makes systematic laboratory experiments notoriously difficult. Here, to investigate the mechanical response of a weak layer under loading, we perform numerical experiments based on the actual microstructure of snow. The simulations are based on a discrete element model (DEM) of the weak layer that utilizes X-ray tomographical images of snow structure as input information. Individual grains are identified in the binary image of the snow matrix and then represented in the DEM model by a computation-efficient approximation based on sets of spheres. A medial axis-based algorithm has been developed in order to obtain a chosen level of grain shape approximation with the minimum number of spherical discrete elements. The optimal level of grain approximation is determined through a sensitivity analysis of different geometrical measures of grain shape to the approximating parameters. Thereby, an optimal balance can be found between computational efficiency and accuracy of the developed DEM model. Finally, by accounting for the fragile cohesion between individual grains of the snow matrix, the model gains ability to follow the material through different stages of deformation - from a porous network of sintered grains to the final stage of a decomposed granular material. The model is applied to multiple snow samples to reveal the effect of microstructure on the macroscopic mechanical response of snow. The

  17. A regularized orthotropic continuum damage model for layered composites: intralaminar damage progression and delamination

    NASA Astrophysics Data System (ADS)

    Simon, Jaan-Willem; Höwer, Daniel; Stier, Bertram; Reese, Stefanie; Fish, Jacob

    2017-05-01

    Predicting progressive damage in composite materials is essential for the design of most lightweight constructions. When laminated composite structures are considered, both intralaminar and interlaminar (delamination) damage evolution need to be addressed. Typically, these different damage modes are treated separately. On the contrary, in this paper, a continuum damage model is presented which is capable of modeling orthotropic damage progression within layers as well as delamination. The model is formulated in a thermodynamically consistent manner. Moreover, the results are mesh independent due to a fracture energy based regularization scheme.

  18. Three models of dust layers on cometary nuclei

    NASA Astrophysics Data System (ADS)

    Brin, G. D.

    1980-04-01

    A previously developed 'loose lattice' model, describing the balance between gravity and the outward thrust of escaping gases on the particles of a surface mantle, is extended to show that short-period comets which exhibit secular decline in activity may do so owing to a buildup of an insulating layer. Further, a second model - the heavy mantle model - is developed in which gas velocity and its attendant effects are seen to depend on level within a dust layer; a technique for predicting the number and size distribution of grains entrained is proposed. Finally, a third model, the 'fluidized bed' model is proposed; according to this model a third type of dust layer, an agitated maelstrom of incompletely entrained particles, is probably present at some stages of a comet's life, particularly near perihelion for dusty comets.

  19. 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...

  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. Diurnal Ocean Surface Layer Model Validation

    DTIC Science & Technology

    1990-05-01

    measurements. matchups betiween day, night MCSST measurements Earlier efforts b. Cornillon and Stramma (1985) and and DOSI . model output but is...experienced diurnal warming in excess the contoured charts; interpolating coarse DOSL values of I ’C up to 30 percent of the time. DOSI . charts were to NICSST...real time, the project data (I km) from either Wallops Island, VA, or the relied on the DOSI . model to indicate which regions NORDA tracking antenna

  2. 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

  3. 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.

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

    USGS Publications Warehouse

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

    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.

  5. 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

  6. Novel Approach for Modeling of Nonuniform Slag Layers and Air Gap in Continuous Casting Mold

    NASA Astrophysics Data System (ADS)

    Wang, Xudong; Kong, Lingwei; Yao, Man; Zhang, Xiaobing

    2017-02-01

    Various kinds of surface defects on the continuous casting slab usually originate from nonuniform heat transfer and mechanical behavior, especially during the initial solidification inside the mold. In this article, a model-coupled inverse heat transfer problem incorporating the effect of slag layers and air gap is developed to study the nonuniform distribution of liquid slag, solid slag, and air gap layers. The model considers not only the formation and evolution of slag layers and air gap but also the temperatures in the mold copper as measured by thermocouples. The simulation results from the model and the measured temperatures from experiments are shown to be in good agreement with each other. At the casting speed of 0.65 m/min, the liquid slag film disappears and transforms into solid slag entirely at about 400 mm away from meniscus, and an air gap begins to form. Until the mold exit, the maximum thickness of the solid slag layer and air gap gradually increases to 1.34 and 0.056 mm, respectively. The results illustrate that the magnitude and nonuniform distribution of the slag layers and air gap along the cross direction, correlating with heat flux between the shell and mold, eventually determine the temperature profiles of the mold hot face and slab surface. The proposed model may provide a convenient approach for analyzing nonuniform heat transfer and mechanical behaviors between the mold and slab in the real casting process.

  7. Geomorphologic model for Mississippi delta evolution

    SciTech Connect

    Boyd, R.; Penland, S.

    1988-09-01

    The Holocene Mississippi delta is over 9000 years old. During this time, the Mississippi River has established six delta complexes. Sediments are currently supplied only to two of these complexes, neither of which is more than 500 years old. Deltaic sedimentation during most of the Holocene has occurred in shoal-water deltas, unlike the modern Balize lobe, which is located at the shelf break. Mississippi delta sedimentation is cyclic and consists of a regressive and a transgressive phase. Each delta complex first experiences progradation until overextension leads to abandonment and reworking. Mississippi deltas undergoing transgression are dominated by subsidence and marine basin processes leading to the formation of sandy barriers and lagoons. Each of the six delta complexes followed a common pattern of development. Current delta geomorphology reflects the variation in age of each delta complex and can be summarizes in a three-stage model beginning with stage 1: erosional headland and flanking barriers. Here, distributary sands are reworked by the retreating shoreface and dispersed laterally by longshore transport into flanking barriers which enclose interdistributary bays. In stage 2, transgressive barrier island arc, submergence of the erosional headland generates an intradeltaic lagoon that separates the barrier island arc from the retreating mainland. The model ends with stage 3, inner shelf shoals, where the retreating barrier-island arc is unable to keep pace with relative sea level rise or the more rapidly retreating mainland. This stage results in submergence of the barrier-island arc, which continues to be reworked as a sandy shoal on the inner continental shelf. This model of delta evolution illustrates mechanisms for generation of both barrier islands (in stages 1 and 2) and continental shelf sand bodies (in stage 3).

  8. Nonseparable data models for a single-layer perceptron

    NASA Astrophysics Data System (ADS)

    Shynk, John J.; Bershad, Neil J.

    1992-07-01

    This paper describes two nonseparable data models that can be used to study the convergence properties of perceptron learning algorithms. A system identification formulation generates the training signal, with an input that is a zero-mean Gaussian random vector. One model is based on a two-layer perceptron configuration, while the second model has only one layer but with a multiplicative output node. The analysis in this paper focuses on Rosenblatt's training procedure, although the approach can be applied to other learning algorithms. Some examples of the performance surfaces are presented to illustrate possible convergence points of the algorithm for both nonseparable data models.

  9. 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.

  10. Modeling evolution using the probability of fixation: history and implications.

    PubMed

    McCandlish, David M; Stoltzfus, Arlin

    2014-09-01

    Many models of evolution calculate the rate of evolution by multiplying the rate at which new mutations originate within a population by a probability of fixation. Here we review the historical origins, contemporary applications, and evolutionary implications of these "origin-fixation" models, which are widely used in evolutionary genetics, molecular evolution, and phylogenetics. Origin-fixation models were first introduced in 1969, in association with an emerging view of "molecular" evolution. Early origin-fixation models were used to calculate an instantaneous rate of evolution across a large number of independently evolving loci; in the 1980s and 1990s, a second wave of origin-fixation models emerged to address a sequence of fixation events at a single locus. Although origin fixation models have been applied to a broad array of problems in contemporary evolutionary research, their rise in popularity has not been accompanied by an increased appreciation of their restrictive assumptions or their distinctive implications. We argue that origin-fixation models constitute a coherent theory of mutation-limited evolution that contrasts sharply with theories of evolution that rely on the presence of standing genetic variation. A major unsolved question in evolutionary biology is the degree to which these models provide an accurate approximation of evolution in natural populations.

  11. Micromagnetic modeling of the shielding properties of nanoscale ferromagnetic layers

    NASA Astrophysics Data System (ADS)

    Iskandarova, I. M.; Knizhnik, A. A.; Popkov, A. F.; Potapkin, B. V.; Stainer, Q.; Lombard, L.; Mackay, K.

    2016-09-01

    Ferromagnetic shields are widely used to concentrate magnetic fields in a target region of space. Such shields are also used in spintronic nanodevices such as magnetic random access memory and magnetic logic devices. However, the shielding properties of nanostructured shields can differ considerably from those of macroscopic samples. In this work, we investigate the shielding properties of nanostructured NiFe layers around a current line using a finite element micromagnetic model. We find that thin ferromagnetic layers demonstrate saturation of magnetization under an external magnetic field, which reduces the shielding efficiency. Moreover, we show that the shielding properties of nanoscale ferromagnetic layers strongly depend on the uniformity of the layer thickness. Magnetic anisotropy in ultrathin ferromagnetic layers can also influence their shielding efficiency. In addition, we show that domain walls in nanoscale ferromagnetic shields can induce large increases and decreases in the generated magnetic field. Therefore, ferromagnetic shields for spintronic nanodevices require careful design and precise fabrication.

  12. The salinity effect in a mixed layer ocean model

    NASA Technical Reports Server (NTRS)

    Miller, J. R.

    1976-01-01

    A model of the thermally mixed layer in the upper ocean as developed by Kraus and Turner and extended by Denman is further extended to investigate the effects of salinity. In the tropical and subtropical Atlantic Ocean rapid increases in salinity occur at the bottom of a uniformly mixed surface layer. The most significant effects produced by the inclusion of salinity are the reduction of the deepening rate and the corresponding change in the heating characteristics of the mixed layer. If the net surface heating is positive, but small, salinity effects must be included to determine whether the mixed layer temperature will increase or decrease. Precipitation over tropical oceans leads to the development of a shallow stable layer accompanied by a decrease in the temperature and salinity at the sea surface.

  13. Thermoacoustic image reconstruction based on layered tissue model

    NASA Astrophysics Data System (ADS)

    Bayıntır, Hazel; Elmas, Demet; Idemen, Mithat; Uzun, Banu; Karaman, Mustafa

    2017-03-01

    We derived analytical forward and inverse solution of thermoacoustic wave equation for inhomogeneous multi- layered planar and cylindrical mediums with the source distribution existing in all layers. These solutions are applicable for imaging of organs such as breast and brain, whose structures are suitable for multi-layer modelling. For qualitative testing and comparison of the point-spread-functions associated with the homogeneous and layered solutions, we performed numerical simulations. Our simulation results show that the conventional inverse solution based on homogeneous medium assumption, as expected, produces incorrect locations of point sources and significantly increased side lobes, whereas our inverse solution involving the multi-layered medium produces point sources at the correct locations with lower side lobes.

  14. The evolution of electronic structure in few-layer graphene revealed by optical spectroscopy

    PubMed Central

    Mak, Kin Fai; Sfeir, Matthew Y.; Misewich, James A.; Heinz, Tony F.

    2010-01-01

    The massless Dirac spectrum of electrons in single-layer graphene has been thoroughly studied both theoretically and experimentally. Although a subject of considerable theoretical interest, experimental investigations of the richer electronic structure of few-layer graphene (FLG) have been limited. Here we examine FLG graphene crystals with Bernal stacking of layer thicknesses N = 1,2,3,…8 prepared using the mechanical exfoliation technique. For each layer thickness N, infrared conductivity measurements over the spectral range of 0.2–1.0 eV have been performed and reveal a distinctive band structure, with different conductivity peaks present below 0.5 eV and a relatively flat spectrum at higher photon energies. The principal transitions exhibit a systematic energy-scaling behavior with N. These observations are explained within a unified zone-folding scheme that generates the electronic states for all FLG materials from that of the bulk 3D graphite crystal through imposition of appropriate boundary conditions. Using the Kubo formula, we find that the complete infrared conductivity spectra for the different FLG crystals can be reproduced reasonably well within the framework a tight-binding model. PMID:20696939

  15. 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.

  16. 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.

  17. 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.

  18. Lidar Measurements of Wind, Moisture and Boundary Layer Evolution in a Dryline During IHOP2002

    NASA Technical Reports Server (NTRS)

    Demoz, Belay; Evans, Keith; DiGirolamo, Paolo; Wang, Zhien; Whiteman, David; Schwemmer, Geary; Gentry, Bruce; Miller, David

    2003-01-01

    Variability in the convective boundary layer moisture, wind and temperature fields and their importance in the forecasting and understanding of storms have been discussed in the literature. These variations have been reported in relation to frontal zones, stationary boundaries and during horizontal convective rolls. While all three vary substantially in the convective boundary layer, moisture poses a particular challenge. Moisture or water vapor concentration (expressed as a mass mixing ratio, g/kg), is conserved in all meteorological processes except condensation and evaporation. The water vapor mixing ratio often remains distinct across an air -mass boundary even when the temperature difference is indistinct. These properties make it an ideal choice in visualizing and understanding many of the atmosphere's dynamic features. However, it also presents a unique measurement challenge because water vapor content can vary by more than three orders of magnitude in the troposphere. Characterization of the 3D-distribution of water vapor is also difficult as water vapor observations can suffer from large sampling errors and substantial variability both in the vertical and horizontal. This study presents groundbased measurements of wind, boundary layer structure and water vapor mixing ratio measurements observed by three co-located lidars. This presentation will focus on the evolution and variability of moisture and wind in the boundary layer during a dry line event that occurred on 22 May 2002. These data sets and analyses are unique in that they combine simultaneous measurements of wind, moisture and CBL structure to study the detailed thermal variability in and around clear air updrafts during a dryline event. It will quantify the variation caused by, in and around buoyant plumes and across a dryline. The data presented here were collected in the panhandle of Oklahoma as part of the International BO Project (IHOP-2002), a field experiment that took place over the

  19. 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

  20. 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

  1. The near-global mesospheric potassium layer: Observations and modeling

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    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.

  2. Modeling the formation of intermediate layers at Arecibo latitudes

    NASA Astrophysics Data System (ADS)

    Osterman, G. B.; Heelis, R. A.; Bailey, G. J.

    1994-06-01

    By using a modified version of the ionospheric model described by Bailey and Sellek (1990), we model the formation of intermediate ionization layers due to meridional neutral winds in the valley region between the E and F regions. The calculations are performed on a single field line with L = 1.4, in order to compare the results with observations of intermediate layers from the incoherent scatter radar at Arecibo. The winds are given a sinusoidal variation in altitude, and the effects of the wind amplitude and wavelength on layer formation are examined. Nighttime ionization rates are artificially specified to correspond with observed rates in the region. Our results show that tidal like meridional wind profiles act to deplete the apparent background ionospheric number density as well as enhance the number density in the intermediate layer. Thus the layer appears as an enhancement above a background that is much smaller than the background that would be present in the absence of a wind. In this way, layers with relatively high molecular ion concentrations can exist. Intermediate layers are seen to form at nulls in the neutral wind altitude profile, but in the altitude region above roughly 160 km this null need not coincide with a zero in the field-aligned ion velocity.

  3. 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

  4. Evolution of the shear layer during unsteady separation over an experimental wind turbine blade

    NASA Astrophysics Data System (ADS)

    Melius, Matthew; Cal, Raul; Mulleners, Karen

    2016-11-01

    Unsteady flow separation in rotationally augmented flow fields plays a significant role in the aerodynamic performance of industrial wind turbines. Current computational models underestimate the aerodynamic loads due to the inaccurate prediction of the emergence and severity of unsteady flow separation in the presence of rotational augmentation. Through the use of time-resolved particle image velocimetry (PIV), the unsteady separation over an experimental wind turbine blade is examined. By applying Empirical Mode Decomposition (EMD), perturbation amplitudes and frequencies within the shear-layer are identified. The time dependent EMD results during the dynamic pitching cycle give insight into the spatio-temporal scales that influence the transition from attached to separated flow. The EMD modes are represented as two-dimensional fields and are analyzed together with the spatial distribution of vortices, the location of the separation point, and velocity contours focusing on the role of vortex shedding and shear layer perturbation in unsteady separation and reattachment.

  5. Models for UT inspection of bolthole cracks in layered structures

    NASA Astrophysics Data System (ADS)

    Grandin, Robert; Gray, Tim; Roberts, Ron

    2017-02-01

    Due to the geometrical complexities of bolted, layered airframe structures, the application of Model Assisted Probability of Detection, or MAPOD, is an important tool for helping to assess the ultrasonic inspectability of those components. Of particular importance is the need to inspect for cracks on or near boltholes in those structures. This presentation describes the development and testing of analytical computer models of and their application to bolthole crack inspection. The modeling approach includes approximate, paraxial, bulk-wave models as well as more rigorous, analytical models that include both bulk and surface/plate modes. The simpler models have the flexibility and computational efficiency to handle complex geometries and structures. The more exact, rigorous models apply to simpler, canonical geometries for use in benchmarking and assessing the accuracy of the paraxial models. Previous model results for single layers will be reviewed and application of the models to multiple layers will be highlighted. Extensions of the models to more complex geometries and materials, computational challenges to future model development, and applications of the models to MAPOD, and will also be addressed.

  6. Mathematical model of layered metallurgical furnaces and units

    NASA Astrophysics Data System (ADS)

    Shvydkiy, V. S.; Spirin, N. A.; Lavrov, V. V.

    2016-09-01

    The basic approaches to mathematical modeling of the layered steel furnaces and units are considered. It is noted that the particular importance have the knowledge about the mechanisms and physical nature of processes of the charge column movement and the gas flow in the moving layer, as well as regularities of development of heat- and mass-transfer in them. The statement and mathematical description of the problem solution targeting the potential gas flow in the layered unit of an arbitrary profile are presented. On the basis of the proposed mathematical model the software implementation of information-modeling system of BF gas dynamics is carried out. The results of the computer modeling of BF non-isothermal gas dynamics with regard to the cohesion zone, gas dynamics of the combustion zone and calculation of hot-blast stoves are provided

  7. Lag model for turbulent boundary layers over rough bleed surfaces

    NASA Astrophysics Data System (ADS)

    Lee, J.; Sloan, M. L.; Paynter, G. C.

    1994-07-01

    Boundary-layer mass removal (bleed) through spanwise bands of holes on a surface is used to prevent or control separation and to stabilize the normal shock in supersonic inlets. The addition of a transport equation lag relationship for eddy viscosity to the rough wall algebraic turbulence model of Cebeci and Chang was found to improve agreement between predicted and measured mean velocity distributions downstream of a bleed band. The model was demonstrated for a range of bleed configurations, bleed rates, and local freestream Mach numbers. In addition, the model was applied to the boundary-layer development over acoustic lining materials for the inlets and nozzles of commercial aircraft. The model was found to yield accurate results for integral boundary-layer properties unless there was a strong adverse pressure gradient.

  8. Modelling of particle distribution in the melting layer

    NASA Astrophysics Data System (ADS)

    de Wolf, D. A.; Russchenberg, H. W. J.; Ligthart, L. P.

    1990-12-01

    The analysis of radiowave propagation through, and radar scattering from, the melting layer requires a model of the melting ice particles with appropriate statistics of shape, size, and orientation distributions. Previous studies have indicated that the melting layer can be modeled by a collection of wet snow spheroids in air, of which the effective permittivity and the volume fraction are the most important parameters. It is proposed that the distribution of spheroid shapes can be modeled by a flat probability density of depolarization parameter lambda (3) between a minimum and a maximum value. The location of the average lambda (3) is crucial; the width is less important.

  9. 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

  10. 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.

  11. 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

  12. 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.

  13. Model Checking the FlexRay Physical Layer Protocol

    NASA Astrophysics Data System (ADS)

    Gerke, Michael; Ehlers, Rüdiger; Finkbeiner, Bernd; Peter, Hans-Jörg

    The FlexRay standard, developed by a cooperation of leading companies in the automotive industry, is a robust communication protocol for distributed components in modern vehicles. In this paper, we present the first timed automata model of its physical layer protocol, and we use automatic verification to prove fault tolerance under several error models and hardware assumptions.

  14. Evolution of asthenospheric layers as a result of changing stress field

    NASA Astrophysics Data System (ADS)

    Czechowski, Leszek; Grad, Marek

    2014-05-01

    is probably in the range from 3 to 5. We investigate the processes of formation and evolution of low viscosity layers ("asthenospheric layers") in the upper mantle. The time scale of the temperature changes is of the order of 10 Myr. The characteristic time of stress changes could be much shorter depending on tectonic processes. Eventually processes of formation and vanishing of low viscosity layers is very dynamical. In a relatively short time (below 1 Myr) the pattern the viscosity distribution and velocity gradient could change substantially. Using results from deep seismic sounding and surface wave tomography we have found that below some regions there are structures in the mantle that could be a forming/vanishing low viscosity layers. Reflectors in the lower lithosphere are observed beneath Trans-European suture zone between Precambrian and Palaeozoic platforms. In a thick Baltic shield lithosphere (200 km or more) low velocity zones and seismic reflectors are observed in the depth range 60-100 km, which could be interpreted as mechanical low Vp velocity zones, in contrast to thermal velocity zone in deeper asthenosphere. Acknowledgments: This work was partially supported by the National Science Centre (grant 2011/01/B/ST10/06653).

  15. Evolution of asthenospheric layers as a result of changing temperature and stress fields

    NASA Astrophysics Data System (ADS)

    Czechowski, Leszek; Grad, Marek

    2015-04-01

    n is probably in the range from 3 to 5. We investigate the processes of formation and evolution of low viscosity layers ('asthenospheric layers') in the upper mantle. The time scale of the temperature changes is of the order of 10 Myr. The characteristic time of stress changes could be much shorter depending on tectonic processes. Eventually processes of formation and vanishing of low viscosity layers is very dynamical. In a relatively short time (below 1 Myr) the pattern the viscosity distribution and velocity gradient could change substantially. Using results from deep seismic sounding and surface wave tomography we have found that below some regions there are structures in the mantle that could be a forming/vanishing low viscosity layers. Reflectors in the lower lithosphere are observed beneath Trans-European suture zone between Precambrian and Palaeozoic platforms. In a thick Baltic shield lithosphere (200 km or more) low velocity zones and seismic reflectors are observed in the depth range 60-100 km, which could be interpreted as mechanical low Vp velocity zones, in contrast to thermal velocity zone in deeper asthenosphere. Acknowledgments: This work was partially supported by the National Science Centre (grant 2011/01/B/ST10/06653).

  16. Dynamic landscapes: a model of context and contingency in evolution.

    PubMed

    Foster, David V; Rorick, Mary M; Gesell, Tanja; Feeney, Laura M; Foster, Jacob G

    2013-10-07

    Although the basic mechanics of evolution have been understood since Darwin, debate continues over whether macroevolutionary phenomena are driven by the fitness structure of genotype space or by ecological interaction. In this paper we propose a simple model capturing key features of fitness-landscape and ecological models of evolution. Our model describes evolutionary dynamics in a high-dimensional, structured genotype space with interspecies interaction. We find promising qualitative similarity with the empirical facts about macroevolution, including broadly distributed extinction sizes and realistic exploration of the genotype space. The abstraction of our model permits numerous applications beyond macroevolution, including protein and RNA evolution.

  17. Decision, Sensation, and Habituation: A Multi-Layer Dynamic Field Model for Inhibition of Return

    PubMed Central

    Ibáñez-Gijón, Jorge; Jacobs, David M.

    2012-01-01

    Inhibition of Return (IOR) is one of the most consistent and widely studied effects in experimental psychology. The effect refers to a delayed response to visual stimuli in a cued location after initial priming at that location. This article presents a dynamic field model for IOR. The model describes the evolution of three coupled activation fields. The decision field, inspired by the intermediate layer of the superior colliculus, receives endogenous input and input from a sensory field. The sensory field, inspired by earlier sensory processing, receives exogenous input. Habituation of the sensory field is implemented by a reciprocal coupling with a third field, the habituation field. The model generates IOR because, due to the habituation of the sensory field, the decision field receives a reduced target-induced input in cue-target-compatible situations. The model is consistent with single-unit recordings of neurons of monkeys that perform IOR tasks. Such recordings have revealed that IOR phenomena parallel the activity of neurons in the intermediate layer of the superior colliculus and that neurons in this layer receive reduced input in cue-target-compatible situations. The model is also consistent with behavioral data concerning temporal expectancy effects. In a discussion, the multi-layer dynamic field account of IOR is used to illustrate the broader view that behavior consists of a tuning of the organism to the environment that continuously and concurrently takes place at different spatiotemporal scales. PMID:22427980

  18. Evolution of deformation heterogeneity at multiple length scales in a strongly textured zinc layer on galvanized steel

    NASA Astrophysics Data System (ADS)

    Ghosh, A.; Gurao, N. P.

    2015-04-01

    The evolution of heterogeneity of plastic deformation in a zinc layer has been probed at multiple length scales using a battery of characterization tools like X-ray diffraction, electron back scatter diffraction (EBSD) and digital image correlation. The experimental results indicate that plastic deformation is heterogeneous at different length scales and the value of micro, meso and macro strain by different characterization techniques shows a different value. The value of strain determined at the meso and micro length scale from EBSD and X-ray diffraction was negligible, however, the macro-strain as determined from X-ray peak shift was significant. EBSD results showed evidence of profuse {101¯2} <101¯1> contraction twinning in the zinc layer with higher intragranular misorientation in the twin compared to the matrix. It is therefore, inferred that the evolution of higher intergranular (between matrix and twin) strain due to prolific contraction twinning contributes to the failure of zinc layer on galvanized steel.

  19. The evolution of co-rotating vortices in a canonical boundary layer with inclined jets

    NASA Astrophysics Data System (ADS)

    Zhang, Xin

    2003-12-01

    The evolution of co-rotating streamwise vortices in a canonical flat plate turbulent boundary layer (thickness of the boundary layer δ0.99=25 mm) is studied. The vortices are produced by an array of inclined jets (diameter D=14 mm) with the same orientation (skew angle β and pitch angle α of 45°). The focus of the investigation is on the immediate vicinity of the jet exit and downstream locations up to 40 D. The Reynolds number based on the diameter of the jet nozzle ranges from 9700 to 29 000, at various jet speed ratios. The main method of investigation is laser Doppler anemometry. Both mean and statistic data are collected and analyzed. The streamwise vortices are a product of complex fluid flow process, featuring horseshoe vortices in front of the nozzle exit, recirculating flow to the lee side of the nozzle, contra-rotating vortices from the rolling up of vortex sheet around the jet, strong and induced spanwise flow. Two types of streamwise vortices are produced: (a) weak vortices at a jet speed ratio λ of 0.5 located close to the wall and featuring diametrically opposed, secondary, near-wall flows in between the vortices, (b) strong vortices at higher jet speed ratio featuring significant spanwise movement. The vortices are accompanied by high levels of turbulence, with distinct normal and shear stress distributions. Both turbulence production and convection play important roles in defining the normal stress but only the turbulence production is important in determining the shear stress.

  20. 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.

  1. 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.

  2. 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.

  3. The layered evolution of fabric and microstructure of snow at Point Barnola, Central East Antarctica

    NASA Astrophysics Data System (ADS)

    Calonne, Neige; Montagnat, Maurine; Matzl, Margret; Schneebeli, Martin

    2017-02-01

    Snow fabric, defined as the distribution of the c-axis orientations of the ice crystals in snow, is poorly known. So far, only one study exits that measured snow fabric based on a statistically representative technique. This recent study has revealed the impact of temperature gradient metamorphism on the evolution of fabric in natural snow, based on cold laboratory experiments. On polar ice sheets, snow properties are currently investigated regarding their strong variability in time and space, notably because of their potential influence on firn processes and consequently on ice core analysis. Here, we present measurements of fabric and microstructure of snow from Point Barnola, East Antarctica (close to Dome C). We analyzed a snow profile from 0 to 3 m depth, where temperature gradients occur. The main contributions of the paper are (1) a detailed characterization of snow in the upper meters of the ice sheet, especially by providing data on snow fabric, and (2) the study of a fundamental snow process, never observed up to now in a natural snowpack, namely the role of temperature gradient metamorphism on the evolution of the snow fabric. Snow samples were scanned by micro-tomography to measure continuous profiles of microstructural properties (density, specific surface area and pore thickness). Fabric analysis was performed using an automatic ice texture analyzer on 77 representative thin sections cut out from the samples. Different types of snow fabric could be identified and persist at depth. Snow fabric is significantly correlated with snow microstructure, pointing to the simultaneous influence of temperature gradient metamorphism on both properties. We propose a mechanism based on preferential grain growth to explain the fabric evolution under temperature gradients. Our work opens the question of how such a layered profile of fabric and microstructure evolves at depth and further influences the physical and mechanical properties of snow and firn. More generally

  4. Thermal Rayleigh-Marangoni convection in a three-layer liquid-metal-battery model.

    PubMed

    Köllner, Thomas; Boeck, Thomas; Schumacher, Jörg

    2017-05-01

    The combined effects of buoyancy-driven Rayleigh-Bénard convection (RC) and surface tension-driven Marangoni convection (MC) are studied in a triple-layer configuration which serves as a simplified model for a liquid metal battery (LMB). The three-layer model consists of a liquid metal alloy cathode, a molten salt separation layer, and a liquid metal anode at the top. Convection is triggered by the temperature gradient between the hot electrolyte and the colder electrodes, which is a consequence of the release of resistive heat during operation. We present a linear stability analysis of the state of pure thermal conduction in combination with three-dimensional direct numerical simulations of the nonlinear turbulent evolution on the basis of a pseudospectral method. Five different modes of convection are identified in the configuration, which are partly coupled to each other: RC in the upper electrode, RC with internal heating in the molten salt layer, and MC at both interfaces between molten salt and electrode as well as anticonvection in the middle layer and lower electrode. The linear stability analysis confirms that the additional Marangoni effect in the present setup increases the growth rates of the linearly unstable modes, i.e., Marangoni and Rayleigh-Bénard instability act together in the molten salt layer. The critical Grashof and Marangoni numbers decrease with increasing middle layer thickness. The calculated thresholds for the onset of convection are found for realistic current densities of laboratory-sized LMBs. The global turbulent heat transfer follows scaling predictions for internally heated RC. The global turbulent momentum transfer is comparable with turbulent convection in the classical Rayleigh-Bénard case. In summary, our studies show that incorporating Marangoni effects generates smaller flow structures, alters the velocity magnitudes, and enhances the turbulent heat transfer across the triple-layer configuration.

  5. Thermal Rayleigh-Marangoni convection in a three-layer liquid-metal-battery model

    NASA Astrophysics Data System (ADS)

    Köllner, Thomas; Boeck, Thomas; Schumacher, Jörg

    2017-05-01

    The combined effects of buoyancy-driven Rayleigh-Bénard convection (RC) and surface tension-driven Marangoni convection (MC) are studied in a triple-layer configuration which serves as a simplified model for a liquid metal battery (LMB). The three-layer model consists of a liquid metal alloy cathode, a molten salt separation layer, and a liquid metal anode at the top. Convection is triggered by the temperature gradient between the hot electrolyte and the colder electrodes, which is a consequence of the release of resistive heat during operation. We present a linear stability analysis of the state of pure thermal conduction in combination with three-dimensional direct numerical simulations of the nonlinear turbulent evolution on the basis of a pseudospectral method. Five different modes of convection are identified in the configuration, which are partly coupled to each other: RC in the upper electrode, RC with internal heating in the molten salt layer, and MC at both interfaces between molten salt and electrode as well as anticonvection in the middle layer and lower electrode. The linear stability analysis confirms that the additional Marangoni effect in the present setup increases the growth rates of the linearly unstable modes, i.e., Marangoni and Rayleigh-Bénard instability act together in the molten salt layer. The critical Grashof and Marangoni numbers decrease with increasing middle layer thickness. The calculated thresholds for the onset of convection are found for realistic current densities of laboratory-sized LMBs. The global turbulent heat transfer follows scaling predictions for internally heated RC. The global turbulent momentum transfer is comparable with turbulent convection in the classical Rayleigh-Bénard case. In summary, our studies show that incorporating Marangoni effects generates smaller flow structures, alters the velocity magnitudes, and enhances the turbulent heat transfer across the triple-layer configuration.

  6. Using Remotely Piloted Aircraft System to Study the Evolution of the Boundary Layer Related to Fog Events

    NASA Astrophysics Data System (ADS)

    Roberts, G. C.; Cayez, G.; Ronflé-Nadaud, C.; Albrand, M.; Dralet, J. P.; Momboisse, G.; Nicoll, K.; Seity, Y.; Bronz, M.; Hattenberger, G.; Gorraz, M.; Bustico, A.

    2014-12-01

    Over the past decade, the scientific community has embraced the use of RPAS (remotely piloted aircraft system) as a tool to improve observations of the Earth's surface and atmospheric phenomena. The use of small RPAS (Remotely Piloted Aircraft System) in atmospheric research has increased because of their relative low-cost, compact size and ease of operation. Small RPAS are especially adapted for observing the atmospheric boundary layer processes at high vertical and temporal resolution. To this end, CNRM, ENAC, and ENM have developed the VOLTIGE (Vecteurs d'Observation de La Troposphere pour l'Investigation et la Gestion de l'Environnement) program to study the life cycle of fog with multiple, small RPAS. The instrumented RPAS flights have successfully observed the evolution of the boundary layer and dissipation of fog events. In addition, vertical profiles from the RPAS have been compared with Météo France forecast models, and the results suggest that forecast models may be improved using high resolution and frequent in-situ measurements. Within the VOLTIGE project, a flying-wing RPAS with four control surfaces was developed to separate elevator and aileron controls in order to reduce the pitch angle envelope and improve turbulence and albedo measurements. The result leads to a small RPAS with the capability of flying up to two hours with 150 grams of payload, while keeping the hand-launch capability as a constraint for regular atmospheric research missions. High frequency data logging has been integrated into the main autopilot in order to synchronize navigation and payload measurements, as well as allowing an efficient sensor-based navigation. The VOLTIGE program also encourages direct participation of students on the advancement of novel observing systems for atmospheric sciences, and provides a step towards deploying small RPAS in an operational network. VOLTIGE is funded by the Agence Nationale de Recherche (ANR-Blanc 2012) and supported by Aerospace

  7. The Zodiacal Cloud Model applied to the Martian atmosphere. Diurnal variations in meteoric ion layers

    NASA Astrophysics Data System (ADS)

    Carrillo-Sánchez, J. D.; Plane, J. M. C.; Withers, P.; Fallows, K.; Nesvorny, D.; Pokorný, P.

    2016-12-01

    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) and the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Work is now in progress to detect the background metal layers produced by the influx of sporadic meteors. In this study we predict the likely appearance of these layers. The Zodiacal Dust Cloud (ZDC) model for particle populations released by asteroids (AST), and dust grains from Jupiter Family Comets (JFCs) and Halley-Type Comets (HTCs) 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. The vertical injection 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 dominant contributor in the Martian's atmosphere is the JFCs over other sources. Finally, we explore the changes of the neutral and ionized Na, Mg and Fe layers over a diurnal cycle.

  8. Evolutions of hairpin vortexes over a superhydrophobic surface in turbulent boundary layer flow

    NASA Astrophysics Data System (ADS)

    Zhang, Jingxian; Tian, Haiping; Yao, Zhaohui; Hao, Pengfei; Jiang, Nan

    2016-09-01

    Turbulent flows over a superhydrophobic surface and a smooth surface have been measured and studied by particle image velocimetry technology at Reθ = 990. The Reynolds shear stress distributions over the two surfaces are significantly different. Specifically, for the superhydrophobic surface, the Reynolds shear stress is suppressed in the near-wall region (y/δ < 0.3, δ is the boundary layer thickness) and increases in the outer region (0.3 < y/δ < 0.5), which forms a second peak of the Reynolds shear stress curve. Evolutions of hairpin vortexes are analyzed to interpret differences in the Reynolds shear stress, based on some comparisons in the low-speed streaks and Q2/Q4 (ejection/sweep) events. The results show that, in the near wall region, the turbulent coherent structures (low-speed streaks and hairpin vortex) over the superhydrophobic surface are more stable and flat, due to the suppression in the strength and the lifting effect of the hairpin vortex. In the outer region, the superhydrophobic surface lifts the hairpin vortex away from the wall with a value of 0.14δ in our experiment, which makes the Q4 events occur further from the wall and contribute less to skin friction.

  9. Evolution of streamwise vortices and generation of small-scale motion in a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Nygaard, K. J.; Glezer, A.

    1991-01-01

    The present study investigates the evolution of streamwise vortices in a plane mixing layer and their role in the generation of small-scale 3D motion in a closed-return water facility. Spanwise-periodic streamwise vortices are excited by a time-harmonic wavetrain with spanwise-periodic amplitude variations synthesized by a mosaic of 32 surface film heaters flush-mounted on the low partition. The onset of streamwise vortices is accompanied by significant distortion in the transverse distribution of the streamwise velocity component. The presence of inflexion points, absent in corresponding velocity distributions of the unforced flow, suggests the formation of locally unstable regions of large shear in which broadband perturbations already present in the base flow undergo rapid amplification, followed by breakdown to small-scale motion. The cores of the primary vortices are significantly altered as a result of spanwise nonuniform excitation. The 3D features of the streamwise vortices and their interaction with the base flow are inferred from surfaces or rms velocity fluctuations and an approximation to cross-stream vorticity using 3D single component velocity data.

  10. Delocalized Spin States in 2D Atomic Layers Realizing Enhanced Electrocatalytic Oxygen Evolution.

    PubMed

    Chen, Shichuan; Kang, Zhixiong; Hu, Xin; Zhang, Xiaodong; Wang, Hui; Xie, Junfeng; Zheng, XuSheng; Yan, Wensheng; Pan, Bicai; Xie, Yi

    2017-08-01

    The electrocatalytic activity of transition-metal-based compounds is strongly related to the spin states of metal atoms. However, the ways for regulation of spin states of catalysts are still limited, and the underlying relationship between the spin states and catalytic activities remains unclear. Herein, for the first time, by taking Ni(II) -based compounds without high or low spin states for example, it is shown that their spin states can be delocalized after introducing structural distortion to the atomic layers. The delocalized spin states for Ni atoms can provide not only high electrical conductivity but also low adsorption energy between the active sites and reaction intermediates for the system. As expected, the ultrathin nanosheets of nickel-chalcogenides with structural distortions show dramatically enhanced activity in electrocatalytic oxygen evolution compared to their corresponding bulk samples. This work establishes new way for the design of advanced electrocatalysts in transition-metal-based compounds via regulation of spin states. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Evolution of Multiple Double Layer in Glow discharge and its inherent Properties

    NASA Astrophysics Data System (ADS)

    Alex, Prince; A, Saravanan; Sinha, Suraj

    2016-10-01

    Formation and evolution of multiple anodic double layers (MADLs) were experimentally studied in glow discharge plasma. The boundary condition for the existence of MADL was identified in terms of threshold bias and ambient working pressure. The MADL formation is accompanied by an explosive growth in anode current and consequent current-voltage characteristics follows a hysteresis loop. The analysis yield that stable MADLs is only observed when the control voltage V2 is between a certain critical values (Vq > νte MADL completely transforms to an intense high current carrying unstable anode glow. The floating potential analysis carried out using three axially positioned electrostatic probes shows a bipolar signature of DL with as the control parameter is varied. The floating potential analysis also shows that hysteresis arises due to the difference in magnitude of electric field required to align the space charges in the DL sheet at the control voltage changes forward and backward. The effect of pressure on MADL indicates that the MADL structure advances towards anode surface as the pressure is increases. The power dumped (W) in the MADL is estimated to decrease with increase in pressure while the same increase in the anode glow.

  12. Characteristics and Evolution of Passive Tracers in the Oceanic Mixed Layer

    NASA Astrophysics Data System (ADS)

    Smith, Katherine; Hamlington, Peter; Fox-Kemper, Baylor

    2015-11-01

    Ocean tracers such as CO2 and plankton reside primarily in the mixed layer where air-sea gas exchange occurs and light is plentiful for photosynthesis. There can be substantial heterogeneity in the distributions of these tracers due to turbulent mixing, particularly in the submesoscale range where partly geostrophic eddies and small-scale 3D turbulence are both active. In this talk, LES spanning scales from 20km down to 5m are used to examine the role of turbulent mixing on nonreactive passive ocean tracers. The simulations include the effects of both wave-driven Langmuir turbulence and submesoscale eddies, and tracers with different initial and boundary conditions are examined. Tracer properties are characterized using spatial fields, statistics, multiscale fluxes, and spectra, and results show that passive tracer mixing depends on air-sea flux rate, release depth, and flow regime. The results indicate that while submesoscale eddies transport buoyancy upward to extract potential energy, the same is not true of passive tracers, whose entrainment is instead suppressed. Early in the evolution of some tracers, counter-gradient transport occurs co-located with regions of negative potential vorticity, suggesting that symmetric instabilities may act to oppose turbulent mixing.

  13. Evolution of streamwise vortices and generation of small-scale motion in a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Nygaard, K. J.; Glezer, A.

    1991-01-01

    The present study investigates the evolution of streamwise vortices in a plane mixing layer and their role in the generation of small-scale 3D motion in a closed-return water facility. Spanwise-periodic streamwise vortices are excited by a time-harmonic wavetrain with spanwise-periodic amplitude variations synthesized by a mosaic of 32 surface film heaters flush-mounted on the low partition. The onset of streamwise vortices is accompanied by significant distortion in the transverse distribution of the streamwise velocity component. The presence of inflexion points, absent in corresponding velocity distributions of the unforced flow, suggests the formation of locally unstable regions of large shear in which broadband perturbations already present in the base flow undergo rapid amplification, followed by breakdown to small-scale motion. The cores of the primary vortices are significantly altered as a result of spanwise nonuniform excitation. The 3D features of the streamwise vortices and their interaction with the base flow are inferred from surfaces or rms velocity fluctuations and an approximation to cross-stream vorticity using 3D single component velocity data.

  14. Synergistic Effect of Cobalt and Iron in Layered Double Hydroxide Catalysts for the Oxygen Evolution Reaction.

    PubMed

    Yang, Fengkai; Sliozberg, Kirill; Sinev, Ilya; Antoni, Hendrik; Bähr, Alexander; Ollegott, Kevin; Xia, Wei; Masa, Justus; Grünert, Wolfgang; Cuenya, Beatriz Roldan; Schuhmann, Wolfgang; Muhler, Martin

    2017-01-10

    Co-based layered double hydroxide (LDH) catalysts with Fe and Al contents in the range of 15 to 45 at % were synthesized by an efficient coprecipitation method. In these catalysts, Fe(3+) or Al(3+) ions play an essential role as trivalent species to stabilize the LDH structure. The obtained catalysts were characterized by a comprehensive combination of surface- and bulk-sensitive techniques and were evaluated for the oxygen evolution reaction (OER) on rotating disk electrodes. The OER activity decreased upon increasing the Al content for the Co- and Al-based LDH catalysts, whereas a synergistic effect in Co- and Fe-based LDHs was observed, which resulted in an optimal Fe content of 35 at %. This catalyst was spray-coated on Ni foam electrodes and showed very good stability in a flow-through cell with a potential of approximately 1.53 V at 10 mA cm(-2) in 1 m KOH for at least 48 h.

  15. Vertical structure and seasonal evolution of the cold intermediate layer in the Baltic Proper

    NASA Astrophysics Data System (ADS)

    Stepanova, N. B.

    2017-08-01

    Vertical T,S structure of waters of the cold intermediate layer (CIL) is examined on the base of high-resolution CTD profiles obtained in the Baltic Sea Proper in spring and early-summer periods. Basic elements of the structure of the CIL are identified and possible mechanisms responsible for their formation are suggested. Seasonal evolution of the CIL structure is considered. Its four stages are discussed: formation in early spring; late-spring adjustment; slow summer-time modification; and fall/winter-time washing-out/preconditioning to the next cycle. The mechanisms of mixing and stirring which could be responsible for the observed features of the CIL structure are discussed. It is proposed to consider the Baltic CIL not as a phenomenon which appears during the warm season only, but as a manifestation of a permanently current process of basin-scale water exchange. Further targeted investigations are urged disclosing the role of this exchange in general thermo-haline circulation of the Baltic Sea.

  16. Evolution of a Canada Basin ice-ocean boundary layer and mixed layer across a developing thermodynamically forced marginal ice zone

    NASA Astrophysics Data System (ADS)

    Gallaher, Shawn G.; Stanton, Timothy P.; Shaw, William J.; Cole, Sylvia T.; Toole, John M.; Wilkinson, Jeremy P.; Maksym, Ted; Hwang, Byongjun

    2016-08-01

    A comprehensive set of autonomous, ice-ocean measurements were collected across the Canada Basin to study the summer evolution of the ice-ocean boundary layer (IOBL) and ocean mixed layer (OML). Evaluation of local heat and freshwater balances and associated turbulent forcing reveals that melt ponds (MPs) strongly influence the summer IOBL-OML evolution. Areal expansion of MPs in mid-June start the upper ocean evolution resulting in significant increases to ocean absorbed radiative flux (19 W m-2 in this study). Buoyancy provided by MP drainage shoals and freshens the IOBL resulting in a 39 MJ m-2 increase in heat storage in just 19 days (52% of the summer total). Following MP drainage, a near-surface fresh layer deepens through shear-forced mixing to form the summer mixed layer (sML). In late summer, basal melt increases due to stronger turbulent mixing in the thin sML and the expansion of open water areas due in part to wind-forced divergence of the sea ice. Thermal heterogeneities in the marginal ice zone (MIZ) upper ocean led to large ocean-to-ice heat fluxes (100-200 W m-2) and enhanced basal ice melt (3-6 cm d-1), well away from the ice edge. Calculation of the upper ocean heat budget shows that local radiative heat input accounted for at least 89% of the observed latent heat losses and heat storage (partitioned 0.77/0.23). These results suggest that the extensive area of deteriorating sea ice observed away from the ice edge during the 2014 season, termed the "thermodynamically forced MIZ," was driven primarily by local shortwave radiative forcing.

  17. Models for the formation of a critical layer in water wave propagation.

    PubMed

    Johnson, R S

    2012-04-13

    A theory is presented which provides a model for the appearance of critical layers within the flow below a water wave. The wave propagates over constant depth, with constant (non-zero) vorticity. The mechanism described here involves adjusting the surface-pressure boundary condition; two models are discussed. In the first, the pressure at the surface is controlled (mimicking the movement of a low-pressure region associated with a storm) so that the speed and development of the pressure region ensure the appearance of a critical layer. In the second, the pressure boundary condition is allowed to accommodate the reduction of pressure with altitude, although the effects have to be greatly enhanced for this mechanism to produce a critical layer. These two problems are analysed using formal parameter asymptotics. In the second problem, this leads to a Korteweg-de Vries equation for the surface wave, and then the evolution of appropriate solutions of this equation gives rise to the appearance of a critical layer near the bottom; the corresponding problem at the surface can be formulated but not completely resolved. The appearance of a stagnation point and then a critical layer, either at the surface or the bottom, are discussed; the nature of the flow, and the corresponding streamlines are obtained and some typical flow fields are depicted.

  18. Knowledge Growth: Applied Models of General and Individual Knowledge Evolution

    ERIC Educational Resources Information Center

    Silkina, Galina Iu.; Bakanova, Svetlana A.

    2016-01-01

    The article considers the mathematical models of the growth and accumulation of scientific and applied knowledge since it is seen as the main potential and key competence of modern companies. The problem is examined on two levels--the growth and evolution of objective knowledge and knowledge evolution of a particular individual. Both processes are…

  19. A terrain-following model of wave boundary layers

    NASA Astrophysics Data System (ADS)

    Yu, Jie

    2016-12-01

    Over a variable seabed, conventional boundary layer approximations are rendered to be inadequate because of the large variations in bed elevation in the direction of wave propagation. Applying the method of conformal transformation to map the flow domain with a corrugated boundary onto a uniform strip, we put forward a terrain-following modeling approach for Stokes boundary layer flows, accompanying the recent development of the exact Floquet theory of water waves over a generally periodic seabed. For a non-steep seabed profile, but not necessarily small undulation height compared with the water depth, we solve the vorticity equation to obtain the analytical solutions for the boundary layer velocities, bed shear stress and rate of viscous dissipation, explicitly showing the variations both across the boundary layer and along the bed. For a relatively steep bed profile, a remedy is proposed that allows the velocity profiles to be locally determined across the boundary layer avoiding solving the 2-D differential equation for the vorticity. The modeling methodology is presented here for a constant viscosity, including the case of constant eddy viscosity, but can be extended to the case of variable eddy viscosity to improve turbulence modeling.

  20. Chempy: A flexible chemical evolution model for abundance fitting

    NASA Astrophysics Data System (ADS)

    Rybizki, J.; Just, A.; Rix, H.-W.; Fouesneau, M.

    2017-02-01

    Chempy models Galactic chemical evolution (GCE); it is a parametrized open one-zone model within a Bayesian framework. A Chempy model is specified by a set of 5-10 parameters that describe the effective galaxy evolution along with the stellar and star-formation physics: e.g. the star-formation history (SFH), the feedback efficiency, the stellar initial mass function (IMF) and the incidence of supernova of type Ia (SN Ia). Chempy can sample the posterior probability distribution in the full model parameter space and test data-model matches for different nucleosynthetic yield sets, performing essentially as a chemical evolution fitting tool. Chempy can be used to confront predictions from stellar nucleosynthesis with complex abundance data sets and to refine the physical processes governing the chemical evolution of stellar systems.

  1. Layer Number Dependence of Li(+) Intercalation on Few-Layer Graphene and Electrochemical Imaging of Its Solid-Electrolyte Interphase Evolution.

    PubMed

    Hui, Jingshu; Burgess, Mark; Zhang, Jiarui; Rodríguez-López, Joaquín

    2016-04-26

    A fundamental question facing electrodes made out of few layers of graphene (FLG) is if they display chemical properties that are different to their bulk graphite counterpart. Here, we show evidence that suggests that lithium ion intercalation on FLG, as measured via stationary voltammetry, shows a strong dependence on the number of layers of graphene that compose the electrode. Despite its extreme thinness and turbostratic structure, Li ion intercalation into FLG still proceeds through a staging process, albeit with different signatures than bulk graphite or multilayer graphene. Single-layer graphene does not show any evidence of ion intercalation, while FLG with four graphene layers displays limited staging peaks, which broaden and increase in number as the layer number increases to six. Despite these mechanistic differences on ion intercalation, the formation of a solid-electrolyte interphase (SEI) was observed on all electrodes. Scanning electrochemical microscopy (SECM) in the feedback mode was used to demonstrate changes in the surface conductivity of FLG during SEI evolution. Observation of ion intercalation on large area FLG was conditioned to the fabrication of "ionic channels" on the electrode. SECM measurements using a recently developed Li-ion sensitive imaging technique evidenced the role of these channels in enabling Li-ion intercalation through localized flux measurements. This work highlights the impact of nanostructure and microstructure on macroscopic electrochemical behavior and provides guidance to the mechanistic control of ion intercalation using graphene, an atomically thin interface where surface and bulk reactivity converge.

  2. Nature, theory and modelling of geophysical convective planetary boundary layers

    NASA Astrophysics Data System (ADS)

    Zilitinkevich, Sergej

    2015-04-01

    Geophysical convective planetary boundary layers (CPBLs) are still poorly reproduced in oceanographic, hydrological and meteorological models. Besides the mean flow and usual shear-generated turbulence, CPBLs involve two types of motion disregarded in conventional theories: 'anarchy turbulence' comprised of the buoyancy-driven plumes, merging to form larger plumes instead of breaking down, as postulated in conventional theory (Zilitinkevich, 1973), large-scale organised structures fed by the potential energy of unstable stratification through inverse energy transfer in convective turbulence (and performing non-local transports irrespective of mean gradients of transporting properties). C-PBLs are strongly mixed and go on growing as long as the boundary layer remains unstable. Penetration of the mixed layer into the weakly turbulent, stably stratified free flow causes turbulent transports through the CPBL outer boundary. The proposed theory, taking into account the above listed features of CPBL, is based on the following recent developments: prognostic CPBL-depth equation in combination with diagnostic algorithm for turbulence fluxes at the CPBL inner and outer boundaries (Zilitinkevich, 1991, 2012, 2013; Zilitinkevich et al., 2006, 2012), deterministic model of self-organised convective structures combined with statistical turbulence-closure model of turbulence in the CPBL core (Zilitinkevich, 2013). It is demonstrated that the overall vertical transports are performed mostly by turbulence in the surface layer and entrainment layer (at the CPBL inner and outer boundaries) and mostly by organised structures in the CPBL core (Hellsten and Zilitinkevich, 2013). Principal difference between structural and turbulent mixing plays an important role in a number of practical problems: transport and dispersion of admixtures, microphysics of fogs and clouds, etc. The surface-layer turbulence in atmospheric and marine CPBLs is strongly enhanced by the velocity shears in

  3. Layering

    NASA Image and Video Library

    2011-04-01

    At the bottom of this image from NASA Mars Odyssey is the cliff-face that is the sidewall of Ophir Chasma. Layering is easily visible in the upper cliff wall, with the thickness of the surface clearly visible.

  4. Promoted photoelectrocatalytic hydrogen evolution of a type II structure via an Al2O3 recombination barrier layer deposited using atomic layer deposition.

    PubMed

    Wang, Yajun; Bai, Weikun; Wang, Haiquan; Jiang, Yao; Han, Shanlei; Sun, Huaqian; Li, Yuming; Jiang, Guiyuan; Zhao, Zhen; Huan, Qing

    2017-08-15

    Constructing a semiconductor type II structure is an effective way to enhance the photogenerated charge separation efficiency. The separation and migration of interfacial photogenerated carriers is a key factor, which influences the photocatalytic activity. In this study, a conformal Al2O3 recombination barrier layer was introduced at the interface between TiO2 nanowires and CdSe nanoparticles, and the application of this composite in photoelectrocatalytic (PEC) hydrogen production was explored. Under visible-light irradiation, the photocurrent response and PEC hydrogen evolution performance increased step-by-step from TiO2 to the Al2O3/TiO2 and CdSe/Al2O3/TiO2 nanowire arrays. Moreover, the H2 evolution rate of CdSe/Al2O3/TiO2 was much higher than that of a different configuration, Al2O3/CdSe/TiO2. The enhanced PEC hydrogen evolution performance was attributed to the prevention of the interfacial charge recombination caused by the Al2O3 recombination barrier layer. Our results may shed new light on developing novel and highly efficient photocatalysts using rational interface design.

  5. Modelling the evolution of complex conductivity during calcite precipitation on glass beads

    NASA Astrophysics Data System (ADS)

    Leroy, Philippe; Li, Shuai; Jougnot, Damien; Revil, André; Wu, Yuxin

    2017-04-01

    When pH and alkalinity increase, calcite frequently precipitates and hence modifies the petrophysical properties of porous media. The complex conductivity method can be used to directly monitor calcite precipitation in porous media because it is sensitive to the evolution of the mineralogy, pore structure and its connectivity. We have developed a mechanistic grain polarization model considering the electrochemical polarization of the Stern and diffuse layers surrounding calcite particles. Our complex conductivity model depends on the surface charge density of the Stern layer and on the electrical potential at the onset of the diffuse layer, which are computed using a basic Stern model of the calcite/water interface. The complex conductivity measurements of Wu et al. on a column packed with glass beads where calcite precipitation occurs are reproduced by our surface complexation and complex conductivity models. The evolution of the size and shape of calcite particles during the calcite precipitation experiment is estimated by our complex conductivity model. At the early stage of the calcite precipitation experiment, modelled particles sizes increase and calcite particles flatten with time because calcite crystals nucleate at the surface of glass beads and grow into larger calcite grains. At the later stage of the calcite precipitation experiment, modelled sizes and cementation exponents of calcite particles decrease with time because large calcite grains aggregate over multiple glass beads and only small calcite crystals polarize.

  6. Modeling the evolution of complex conductivity during calcite precipitation on glass beads

    NASA Astrophysics Data System (ADS)

    Leroy, Philippe; Li, Shuai; Jougnot, Damien; Revil, André; Wu, Yuxin

    2017-01-01

    SUMMARYWhen pH and alkalinity increase, calcite frequently precipitates and hence modifies the petrophysical properties of porous media. The complex conductivity method can be used to directly monitor calcite precipitation in porous media because it is sensitive to the <span class="hlt">evolution</span> of the mineralogy, pore structure and its connectivity. We have developed a mechanistic grain polarization <span class="hlt">model</span> considering the electrochemical polarization of the Stern and diffuse <span class="hlt">layer</span> surrounding calcite particles. Our complex conductivity <span class="hlt">model</span> depends on the surface charge density of the Stern <span class="hlt">layer</span> and on the electrical potential at the onset of the diffuse <span class="hlt">layer</span>, which are computed using a basic Stern <span class="hlt">model</span> of the calcite/water interface. The complex conductivity measurements of Wu et al. (2010) on a column packed with glass beads where calcite precipitation occurs are reproduced by our surface complexation and complex conductivity <span class="hlt">models</span>. The <span class="hlt">evolution</span> of the size and shape of calcite particles during the calcite precipitation experiment is estimated by our complex conductivity <span class="hlt">model</span>. At the early stage of the calcite precipitation experiment, <span class="hlt">modeled</span> particles sizes increase and calcite particles flatten with time because calcite crystals nucleate at the surface of glass beads and grow into larger calcite grains around glass beads. At the later stage of the calcite precipitation experiment, <span class="hlt">modeled</span> sizes and cementation exponents of calcite particles decrease with time because large calcite grains aggregate over multiple glass beads, a percolation threshold is achieved, and small and discrete calcite crystals polarize.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998dssc.conf..167D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998dssc.conf..167D"><span>Gaseous <span class="hlt">models</span> of globular clusters with stellar <span class="hlt">evolution</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Deiters, S.; Spurzem, R.</p> <p></p> <p>Comparing different approaches for <span class="hlt">modelling</span> the <span class="hlt">evolution</span> of star clusters, gaseous <span class="hlt">models</span> have the advantage of high "particle numbers" but --- until now --- the disadvantage of a lack of realism (Giersz & Spurzem 1994, MNRAS 269, 24 1). To improve gaseous <span class="hlt">models</span> towards a more realistic description of globular clusters one has to take the effects of stellar <span class="hlt">evolution</span> and many (primordial) binaries into account and add a consistent treatment of the tidal field of the galaxy (Chernoff & Weinberg 1990, ApJ 351, 121; Portegies Zwart 1998, AA in press). We want to present the first steps on our way towards more realistic gaseous <span class="hlt">models</span>: We show results of the first implementation of stellar <span class="hlt">evolution</span> in a spherically symmetric anisotropic gaseous <span class="hlt">model</span>. We subdivide our <span class="hlt">model</span> in several dynamical components, each with different stellar mass, whose stellar <span class="hlt">evolution</span> is followed in a parameterized way. Thus we can simulate the effects of the <span class="hlt">evolution</span> of stars of different masses in the cluster: During their <span class="hlt">evolution</span> the stars lose a significant amount of their initial mass, which can easily escape from the cluster. Hence the binding energy of the cluster is reduced. We show several <span class="hlt">models</span> with different initial conditions with and without the effects of stellar <span class="hlt">evolution</span>. Their <span class="hlt">evolution</span> is followed into core bounce and during the post-collapse phase. Dynamical properties of the clusters for the different initial conditions are compared. If time allows we will focus briefly on the treatment of a (time-independent) tidal boundary, <span class="hlt">modelling</span> the gravitational field of the mother galaxy in our <span class="hlt">models</span> and give an outlook on the next steps towards more realism in our <span class="hlt">models</span> of globular clusters, e.g. the inclusion of stochastic binaries (Spurzem & Giersz 1996, MNRAS 283, 805) and stellar finite-size effects.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19820059450&hterms=sea+breeze&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dsea%2Bbreeze','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19820059450&hterms=sea+breeze&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dsea%2Bbreeze"><span>Further considerations on <span class="hlt">modeling</span> the sea breeze with a mixed-<span class="hlt">layer</span> <span class="hlt">model</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Anthes, R. A.; Keyser, D.; Deardorff, J. W.</p> <p>1982-01-01</p> <p>Mixed-<span class="hlt">layer</span> <span class="hlt">models</span> have been used to simulate low-level flows under a variety of situations, including flow over complex terrain and in the vicinity of coastal zones. The advantage of mixed-<span class="hlt">layer</span> <span class="hlt">models</span> compared to multilevel <span class="hlt">models</span> is their simplicity and minimal computational requirements. A disadvantage is that the atmosphere above the mixed <span class="hlt">layer</span> is not <span class="hlt">modeled</span> explicitly and approximations pertaining to this <span class="hlt">layer</span> become necessary. This paper examines five approximations for treating this upper <span class="hlt">layer</span> for a simple sea-breeze circulation. Approximating the flow immediately above the mixed-<span class="hlt">layer</span> height h by the mixed-<span class="hlt">layer</span> velocity and using this velocity to advect potential temperature above h gives a better simulation of the sea breeze than the approximation used by Anthes et al. (1980), which neglected horizontal advection at this level.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015CEER...15..127S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015CEER...15..127S"><span>Numerical <span class="hlt">Modelling</span> of Soil Arching in a Shallow Backfill <span class="hlt">Layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Szajna, Waldemar St.</p> <p>2015-03-01</p> <p>The paper presents the application of the finite element method into the <span class="hlt">modelling</span> of soil arching. The phenomenon plays fundamental role in soil-shell flexible structures behaviour. To evaluate the influence of arching on a pressure reduction, a plain strain trapdoor under a shallow <span class="hlt">layer</span> of backfill was simulated. The Coulomb-Mohr plasticity condition and the nonassociated flow rule were used for the soil <span class="hlt">model</span>. The research examines the impact of the internal friction angle and the influence of the backfill <span class="hlt">layer</span> thickness on the value of soil arching. The carried out analyses indicate that the reduction of pressures acting on a structure depends on the value of the internal friction angle, which confirms the earlier research. For a shallow backfill <span class="hlt">layer</span> however, the reduction is only a local phenomenon and can influence only a part of the structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SeScT..31k5014K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SeScT..31k5014K"><span>Electric circuit <span class="hlt">model</span> for strained-<span class="hlt">layer</span> epitaxy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kujofsa, Tedi; Ayers, John E.</p> <p>2016-11-01</p> <p>For the design and analysis of a strained-<span class="hlt">layer</span> semiconductor device structure, the equilibrium strain profile may be determined numerically by energy minimization but this method is computationally intense and non-intuitive. Here we present an electric circuit <span class="hlt">model</span> approach for the equilibrium analysis of an epitaxial stack, in which each sublayer may be represented by an analogous configuration involving a current source, a resistor, a voltage source, and an ideal diode. The resulting node voltages in the analogous electric circuit correspond to the equilibrium strains in the original epitaxial structure. This new approach enables analysis using widely accessible circuit simulators, and an intuitive understanding of electric circuits may be translated to the relaxation of strained-<span class="hlt">layer</span> structures. In this paper, we describe the mathematical foundation of the electrical circuit <span class="hlt">model</span> and demonstrate its application to epitaxial <span class="hlt">layers</span> of Si1-x Ge x grown on a Si (001) substrate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21450911','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21450911"><span>A <span class="hlt">MODEL</span> OF THE SPECTRAL <span class="hlt">EVOLUTION</span> OF PULSAR WIND NEBULAE</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tanaka, Shuta J.; Takahara, Fumio</p> <p>2010-06-01</p> <p>We study the spectral <span class="hlt">evolution</span> of pulsar wind nebulae (PWNe) taking into account the energy injected when they are young. We <span class="hlt">model</span> the <span class="hlt">evolution</span> 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 <span class="hlt">evolution</span> of the particle distribution function. The <span class="hlt">model</span> is calibrated by fitting the calculated spectrum to the observations of the Crab Nebula at an age of a thousand years. The spectral <span class="hlt">evolution</span> of the Crab Nebula in our <span class="hlt">model</span> 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 <span class="hlt">evolution</span> <span class="hlt">model</span> matches the observed rate of the radio flux decrease of the Crab Nebula. This result implies that our magnetic field <span class="hlt">evolution</span> <span class="hlt">model</span> is close to the reality. Finally, from the viewpoint of the spectral <span class="hlt">evolution</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20010062307&hterms=solid+state+synthesis&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dsolid%2Bstate%2Bsynthesis','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20010062307&hterms=solid+state+synthesis&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dsolid%2Bstate%2Bsynthesis"><span>Dynamics in <span class="hlt">Layer</span> <span class="hlt">Models</span> of Solid Flame Propagation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Aldushin, A. P.; Bayliss, A.; Matkowsky, B. J.; Gokoglu, S. (Technical Monitor)</p> <p>2000-01-01</p> <p>Self-propagating high-temperature synthesis (SHS) is a process in which combustion waves, e.g., "solid flames", which are considered here, are employed to synthesize desired materials. Like many other systems, SHS is a pattern forming system. The problem of describing experimentally observed patterns and of predicting new, as yet unobserved, patterns continues to attract the attention of scientists and mathematicians due to the fundamental significance of the phenomena in combustion in particular, and in nonlinear science in general. Here, we analyze the dynamics of solid flame propagation in a 2D region by considering the region to be composed of parallel, identical <span class="hlt">layers</span> aligned along the direction of propagation and having thermal contact. Each <span class="hlt">layer</span> is then described by wave propagation in 1D, with the transverse Laplacian replaced by a term describing heat exchange between neighboring <span class="hlt">layers</span>. This configuration is the simplest <span class="hlt">model</span> of a 2D system because it accounts, in a simple way, for the principal feature of the problem, i.e., heat exchange between neighbors in the transverse direction. For simplicity, we describe the situation for two <span class="hlt">layers</span>. Because the <span class="hlt">layers</span> are identical, uniformly propagating waves in each <span class="hlt">layer</span> must be identical, independent of the heat exchange rate alpha. When the Zeldovich number Z exceeds a critical value Z(sub c), which depends on alpha, uniformly propagating waves become unstable. The stability diagram for the two coupled <span class="hlt">layers</span> reproduces that for the full 2D problem after appropriate identification of parameters in the two problems. Depending on parameter values, we determine three different steady-state dynamical behaviors (though additional behaviors are also expected to occur). The three behaviors are: (i) waves in each <span class="hlt">layer</span> which pulsate in phase as they propagate, so that together they form a single pulsating propagating wave; (ii) the waves in each <span class="hlt">layer</span> are no longer identical, and antiphase pulsations occur, with</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20010062307&hterms=diagram+travel&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Ddiagram%2Btravel','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20010062307&hterms=diagram+travel&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Ddiagram%2Btravel"><span>Dynamics in <span class="hlt">Layer</span> <span class="hlt">Models</span> of Solid Flame Propagation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Aldushin, A. P.; Bayliss, A.; Matkowsky, B. J.; Gokoglu, S. (Technical Monitor)</p> <p>2000-01-01</p> <p>Self-propagating high-temperature synthesis (SHS) is a process in which combustion waves, e.g., "solid flames", which are considered here, are employed to synthesize desired materials. Like many other systems, SHS is a pattern forming system. The problem of describing experimentally observed patterns and of predicting new, as yet unobserved, patterns continues to attract the attention of scientists and mathematicians due to the fundamental significance of the phenomena in combustion in particular, and in nonlinear science in general. Here, we analyze the dynamics of solid flame propagation in a 2D region by considering the region to be composed of parallel, identical <span class="hlt">layers</span> aligned along the direction of propagation and having thermal contact. Each <span class="hlt">layer</span> is then described by wave propagation in 1D, with the transverse Laplacian replaced by a term describing heat exchange between neighboring <span class="hlt">layers</span>. This configuration is the simplest <span class="hlt">model</span> of a 2D system because it accounts, in a simple way, for the principal feature of the problem, i.e., heat exchange between neighbors in the transverse direction. For simplicity, we describe the situation for two <span class="hlt">layers</span>. Because the <span class="hlt">layers</span> are identical, uniformly propagating waves in each <span class="hlt">layer</span> must be identical, independent of the heat exchange rate alpha. When the Zeldovich number Z exceeds a critical value Z(sub c), which depends on alpha, uniformly propagating waves become unstable. The stability diagram for the two coupled <span class="hlt">layers</span> reproduces that for the full 2D problem after appropriate identification of parameters in the two problems. Depending on parameter values, we determine three different steady-state dynamical behaviors (though additional behaviors are also expected to occur). The three behaviors are: (i) waves in each <span class="hlt">layer</span> which pulsate in phase as they propagate, so that together they form a single pulsating propagating wave; (ii) the waves in each <span class="hlt">layer</span> are no longer identical, and antiphase pulsations occur, with</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFDG33009C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFDG33009C"><span>A simple <span class="hlt">model</span> of inertial <span class="hlt">layer</span> dynamics in turbulent boundary <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cuevas, Juan; Ebadi, Alireza; White, Christopher; Chini, Gregory; Klewicki, Joseph</p> <p>2016-11-01</p> <p>Observations (e.g.) indicate that the inertial region of turbulent wall-flows consists of uniform momentum zones segregated by narrow vortical fissures. Multiscale analysis similarly reveals that the mean momentum equation admits a scaling <span class="hlt">layer</span> hierarchy across the inertial region. Here, each <span class="hlt">layer</span> increases in width with wall-normal distance, but the inner-normalized velocity increment remains fixed. The talk reports on a simple <span class="hlt">model</span> that captures the essential elements of these observations and the theoretical scalings. In this <span class="hlt">model</span>, the number of fissures is specified to satisfy the average total velocity increment across the inertial <span class="hlt">layer</span>, while the average wall-normal locations of the fissures and their widths are informed by the theory. Ensembles of statistically independent instantaneous velocity profiles are then created by simply allowing the fissures to randomly displace in the wall normal direction. Results indicate that the <span class="hlt">model</span> identically recovers a logarithmic mean profile, produces a logarithmic decay in the streamwise velocity variance, and generates sub-Gaussian behaviours in its skewness and kurtosis profiles on the inertial domain. These findings along with possible refinements are also discussed. This research was partially supported by the National Science Foundation and partially supported by the Australian Research Council.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24589998','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24589998"><span>A review of molecular <span class="hlt">modelling</span> of electric double <span class="hlt">layer</span> capacitors.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Burt, Ryan; Birkett, Greg; Zhao, X S</p> <p>2014-04-14</p> <p>Electric double-<span class="hlt">layer</span> capacitors are a family of electrochemical energy storage devices that offer a number of advantages, such as high power density and long cyclability. In recent years, research and development of electric double-<span class="hlt">layer</span> capacitor technology has been growing rapidly, in response to the increasing demand for energy storage devices from emerging industries, such as hybrid and electric vehicles, renewable energy, and smart grid management. The past few years have witnessed a number of significant research breakthroughs in terms of novel electrodes, new electrolytes, and fabrication of devices, thanks to the discovery of innovative materials (e.g. graphene, carbide-derived carbon, and templated carbon) and the availability of advanced experimental and computational tools. However, some experimental observations could not be clearly understood and interpreted due to limitations of traditional theories, some of which were developed more than one hundred years ago. This has led to significant research efforts in computational simulation and <span class="hlt">modelling</span>, aimed at developing new theories, or improving the existing ones to help interpret experimental results. This review article provides a summary of research progress in molecular <span class="hlt">modelling</span> of the physical phenomena taking place in electric double-<span class="hlt">layer</span> capacitors. An introduction to electric double-<span class="hlt">layer</span> capacitors and their applications, alongside a brief description of electric double <span class="hlt">layer</span> theories, is presented first. Second, molecular <span class="hlt">modelling</span> of ion behaviours of various electrolytes interacting with electrodes under different conditions is reviewed. Finally, key conclusions and outlooks are given. Simulations on comparing electric double-<span class="hlt">layer</span> structure at planar and porous electrode surfaces under equilibrium conditions have revealed significant structural differences between the two electrode types, and porous electrodes have been shown to store charge more efficiently. Accurate electrolyte and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhRvF...2a4001L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhRvF...2a4001L"><span>Ultraefficient reduced <span class="hlt">model</span> for countercurrent two-<span class="hlt">layer</span> flows</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lavalle, Gianluca; Vila, Jean-Paul; Lucquiaud, Mathieu; Valluri, Prashant</p> <p>2017-01-01</p> <p>We investigate the dynamics of two superposed <span class="hlt">layers</span> with density contrast flowing countercurrent inside a channel, when the lower <span class="hlt">layer</span> is much thinner than the wavelength of interfacial waves. We apply a low-dimensional film <span class="hlt">model</span> to the bottom (heavier) <span class="hlt">layer</span> and introduce a fast and efficient method to predict the onset of flow reversal in this phase. We study three vertical scenarios with different applied pressure gradients and compare the temporal growth rates of linear and weakly nonlinear waves to the Orr-Sommerfeld problem and to the weakly nonlinear theory, respectively. At the loading point, i.e., when a large wave hump stands at the interface, our spatiotemporal analysis shows that the system is absolutely unstable. We then present profiles of nonlinear saturated waves, pressure field, and streamline distribution in agreement with direct numerical simulation. The reduced <span class="hlt">model</span> presented here allows us to explore the effect of the upper-<span class="hlt">layer</span> speed on the wave pattern, showing that the wave profile is very sensitive when the mean film thickness, rather than the liquid flow rate, is maintained constant in the simulation. In addition, we show the strong effect of surface tension on both the maximum wave hump and the crest steepness before the loading point. Finally, we reveal how the nonlinear wave speed affects the vortex distribution within the lower <span class="hlt">layer</span> by analyzing the stream function under different scenarios.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014DSRII.101..193Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014DSRII.101..193Y"><span>A Lagrangian <span class="hlt">model</span> for phototaxis-induced thin <span class="hlt">layer</span> formation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yamazaki, Hidekatsu; Locke, Chris; Umlauf, Lars; Burchard, Hans; Ishimaru, Takashi; Kamykowski, Daniel</p> <p>2014-03-01</p> <p>We have developed a Lagrangian <span class="hlt">model</span> to investigate a potential mechanism based on phototaxis behavior of phytoplankton cells for the formation of thin <span class="hlt">layers</span>. We assume that all cells follow a time-regulated diurnal vertical migration during which they experience photo-acclimation based on the Denman and Marra (1986) <span class="hlt">model</span>. When a cell experiences stress due to strong light that exceeds a threshold level, the cell swims downward, away from the light. We applied the Lagrangian <span class="hlt">model</span> to a one dimensional second order turbulence closure <span class="hlt">model</span> that generates a realistic surface mixing condition for a given set of physical parameters, such as wind and optical water type. For the chosen swimming velocities and prescribed behavior, we found that, in coastal water type and Jerlov III type, thin <span class="hlt">layer</span> formation takes place up to 5 m s-1 winds, while 10 m s-1 winds cause sufficiently strong mixing to prevent the formation of thin <span class="hlt">layer</span>. We have also investigated the effects of changing the irradiance threshold for the onset of the photoinhibition, the initial density profile and random walk swimming. In conclusion, thin <span class="hlt">layer</span> formation due to photoinhibition may be possible for a low value of photoinhibition threshold that may occur either due to upwelling or strong light exposure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.fs.usda.gov/treesearch/pubs/12141','TREESEARCH'); return false;" href="https://www.fs.usda.gov/treesearch/pubs/12141"><span><span class="hlt">Modeling</span> the Atmospheric Dynamics within and Above Vegetation <span class="hlt">Layers</span></span></a></p> <p><a target="_blank" href="http://www.fs.usda.gov/treesearch/">Treesearch</a></p> <p>Warren E. Heilman; John Zasada</p> <p>2000-01-01</p> <p>A critical component of any silvicultural treatment is the creation of suitable microclimatic conditions for desired plant and animal species. One of the most useful tools for examining the microclimatic implications of different vegetation treatments is the use of atmospheric boundary-<span class="hlt">layer</span> <span class="hlt">models</span> that can simulate resulting micrometeorological conditions within and...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.A52A..08S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.A52A..08S"><span>Numerical <span class="hlt">Modeling</span> of the Evolving Stable Boundary <span class="hlt">Layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sorbjan, Z.</p> <p>2013-12-01</p> <p>A single-column <span class="hlt">model</span> of the evolving stable boundary <span class="hlt">layer</span> is tested for the consistency of turbulence parameterization, self-similar properties of the flow, and effects of ambient forcing. The turbulence closure of the <span class="hlt">model</span> is based on the K-theory approach, with stability functions based on empirical data, and a semi-empirical form of the mixing length. The <span class="hlt">model</span> has one internal, governing stability parameter, the Richardson number Ri, which dynamically adjusts to the boundary conditions and to external forcing. <span class="hlt">Model</span> results, expressed in terms of local similarity scales, are universal functions of the Richardson number, i.e. they are satisfied in the entire stable boundary <span class="hlt">layer</span>, for all instants of time, and all kinds of external forcing. Based on similarity expression, a realizability condition is derived for the minimum turbulent heat flux in the stable boundary <span class="hlt">layer</span>. Numerical experiments show that the development of 'horse-shoe' shaped, 'fixed-elevation' wind hodographs in the interior of the stable boundary <span class="hlt">layer</span> are solely caused by effects imposed by surface thermal forcing, and are not related to the inertial oscillation mechanism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AIPC.1332..190S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AIPC.1332..190S"><span><span class="hlt">Layering</span> and wetting transitions for an interface <span class="hlt">model</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Solé, Salvador Miracle</p> <p>2011-03-01</p> <p>We study the solid-on-solid interface <span class="hlt">model</span> above a horizontal wall in three dimensional space, with an attractive interaction when the interface is in contact with the wall, at low temperatures. The system presents a sequence of <span class="hlt">layering</span> transitions, whose levels increase with the temperature, before the complete wetting above a certain value of this quantity.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFMOS31A1241L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFMOS31A1241L"><span>The 2008 North Atlantic Spring Bloom Experiment II: Autonomous Platforms and Mixed <span class="hlt">Layer</span> <span class="hlt">Evolution</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, C. M.; D'Asaro, E. A.; Perry, M.; Fennel, K.; Gray, A.; Rehm, E.; Briggs, N.; Sackmann, B. S.; Gudmundsson, K.</p> <p>2008-12-01</p> <p>The 2008 North Atlantic Spring Bloom Experiment (NAB08) employed a system of drifting floats, mobile gliders and ship-based measurements to resolve patch-scale physical and biological variability over the 3- month course of an entire bloom. Although both autonomous and ship-based elements were essential to achieving NAB08 goals, the autonomous system provided a novel perspective by employing long-range gliders to repeatedly survey the volume surrounding a drifting Lagrangian float, thus characterizing patch- scale bloom <span class="hlt">evolution</span>. Integration of physical and biogeochemical sensors (temperature, conductivity, dissolved oxygen, chlorophyll and CDOM fluorescence, light transmission, optical backscatter, spectral light, and nitrate) and development of in situ calibration techniques were required to support this new autonomous approach. Energetic, small-scale eddy activity at the experiment site (southeast of Iceland, near the Joint Global Ocean Flux Study and Marine Light Mixed <span class="hlt">Layer</span> sites) produced a swift, heterogeneous velocity field that challenged the gliders" operational abilities and drove refinements to the piloting techniques used to maintain float-following surveys. Although intentionally deployed outside of energetic eddies, floats and gliders were rapidly entrained into these features. Floats circulated within eddies near the start and end of the experiment, drifting generally northwest, across the basin, in-between. An eddy sampled late in the deployment provided particularly interesting signatures, with elevated biological signals manifest consistently in one quadrant. As measurements were collected in a parcel-following Lagrangian frame, this suggests energetic small-scale exchange process (such as vertical or lateral mixing) paired with fast-acting biological processes capable of modifying the newly entrained water as it navigates its path around the eddy. Despite this energetic kilometer-scale heterogeneity, broadly distributed platforms appeared to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020025992','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020025992"><span>Cloud-Scale Numerical <span class="hlt">Modeling</span> of the Arctic Boundary <span class="hlt">Layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kruegen, Steven K.; Delnore, Victor E. (Technical Monitor)</p> <p>2002-01-01</p> <p>The research objective of this NASA grant-funded project was to determine in detail how large-scale processes. in combination with cloud-scale radiative, microphysical, and dynamical processes, govern the formation and multi-<span class="hlt">layered</span> structure of Arctic stratus clouds. This information will be useful for developing and improving 1D (one dimensional) boundary <span class="hlt">layer</span> <span class="hlt">models</span> for the Arctic. Also, to quantitatively determine the effects of leads on the large-scale budgets of sensible heat, water vapor, and condensate in a variety of Arctic winter conditions. This information will be used to identify the most important lead-flux processes that require parameterization in climate <span class="hlt">models</span>. Our approach was to use a high-resolution numerical <span class="hlt">model</span>, the 2D (two dimensional) University of Utah Cloud Resolving <span class="hlt">Model</span> (UU CRM), and its 1D version, the University of Utah Turbulence Closure <span class="hlt">Model</span> (UU TCM), a boundary <span class="hlt">layer</span> <span class="hlt">model</span> based on third-moment turbulence closure, as well as a large-eddy simulation (LES) <span class="hlt">model</span> originally developed by C.H. Moeng.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017ApSS..416...24F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017ApSS..416...24F"><span><span class="hlt">Layer-by-layer</span> assemblies of highly connected polyelectrolyte capped-Pt nanoparticles for electrocatalysis of hydrogen <span class="hlt">evolution</span> reaction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fenoy, Gonzalo E.; Maza, Eliana; Zelaya, Eugenia; Marmisollé, Waldemar A.; Azzaroni, Omar</p> <p>2017-09-01</p> <p>Herein we present a simple one-step method to produce polyelectrolyte-capped Pt nanoparticles able to be assembled into <span class="hlt">layer-by-layer</span> arrays with a linear dependence of the amount of deposited material on the number of dipping cycles. The resulting supramolecular films where fully characterized by AFM, XPS and ATR-FTIR. The electrochemical evaluation by cyclic voltammetry showed good electrochemical connection between the nanoparticles in both acidic and neutral solutions. The films assembled on graphite electrodes showed catalysis of the H2 production and the interconnection between nanoparticles proved to be effective up to 20 bilayers. Results presented here reveal an easy procedure to obtain stable arrays of well-dispersed electroactive 2 nm-diameter Pt nanoparticles on a variety of substrates with direct potential applications in energy conversion devices.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999PhDT.......110D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999PhDT.......110D"><span><span class="hlt">Modeling</span> and analysis of ultrasound propagation in <span class="hlt">layered</span>-medium</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dey, Joyoni</p> <p></p> <p>For many medical applications of ultrasonic devices, it is often of interest to determine the distortion of ultrasound waves due to tissue <span class="hlt">layers</span> of fat and muscle. Bending of the acoustic rays due to refraction at intermediate <span class="hlt">layers</span> degrades image resolution, causes distortion and other artifacts in ultrasound images. In this work, ultrasound propagation in <span class="hlt">layered</span> media is <span class="hlt">modeled</span> analytically. Closed-form expressions are presented for the field amplitude of spherical waves for the following cases: (1)transmission through a three-<span class="hlt">layered</span> media, (2)extension to transmission through multi-<span class="hlt">layered</span> medium, (3)a special case of <span class="hlt">modeling</span> received echoes from an interface through two <span class="hlt">layers</span>. In our derivations, ray-acoustic approximations have been assumed. We show that ray-acoustic approximations are valid for wavelengths (relative to medium <span class="hlt">layer</span> dimensions) of interest. The field amplitude is calculated by taking differentials of the rays to form flux tubes and algebraically calculating the ratios of flux-tube areas. We also take into account the frequency dependent attenuation due to absorption and backscattering loss in the media. The interfaces between media are assumed to be arbitrary shaped, but can be broken up into small planar segments. The resulting response can be extended to different aperture geometries and different beam formations by delaying and summing the result for the Huygen waves emanating from the points forming the aperture. We have considered the inversion problem for the case of two <span class="hlt">layers</span> on a reflective interface, where the <span class="hlt">layers</span> are planar and parallel to the aperture. We showed that it is better to use demodulated versions of signal outputs than use the raw signals themselves to avoid local minima at regular intervals around the global minimum. Validation experiments were performed using custom made tissue mimicking phantoms of fat and muscle and a steel- block. We fit the forward-<span class="hlt">model</span> to the experimental data using Levenberg</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AAS...22915426R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AAS...22915426R"><span>A Novel Approach to Constraining Uncertain Stellar <span class="hlt">Evolution</span> <span class="hlt">Models</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rosenfield, Philip; Girardi, Leo; Dalcanton, Julianne; Johnson, L. C.; Williams, Benjamin F.; Weisz, Daniel R.; Bressan, Alessandro; Fouesneau, Morgan</p> <p>2017-01-01</p> <p>Stellar <span class="hlt">evolution</span> <span class="hlt">models</span> are fundamental to nearly all studies in astrophysics. They are used to interpret spectral energy distributions of distant galaxies, to derive the star formation histories of nearby galaxies, and to understand fundamental parameters of exoplanets. Despite the success in using stellar <span class="hlt">evolution</span> <span class="hlt">models</span>, some important aspects of stellar <span class="hlt">evolution</span> remain poorly constrained and their uncertainties rarely addressed. We present results using archival Hubble Space Telescope observations of 10 stellar clusters in the Magellanic Clouds to simultaneously constrain the values and uncertainties of the strength of core convective overshooting, metallicity, interstellar extinction, cluster distance, binary fraction, and age.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AAS...22125214N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AAS...22125214N"><span>Stellar <span class="hlt">Evolution</span> <span class="hlt">Models</span> of Classical Cepheids Require Enhanced Mass Loss</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Neilson, Hilding; Langer, N.; Engle, S. G.; Guinan, E. F.; Izzard, R. G.</p> <p>2013-01-01</p> <p>Measurements of rates of period change of Classical Cepheids probe stellar physics and <span class="hlt">evolution</span>. Additionally, better understanding of Cepheid structure and <span class="hlt">evolution</span> provides greater insight into their use as standard candles and tools for measuring the Hubble constant. In this work, we compare rates of period change measured for about 200 Galactic Cepheids to population synthesis <span class="hlt">models</span> of Cepheids including convective core overshooting and enhanced mass loss. Rates of period change predicted from stellar <span class="hlt">evolution</span> <span class="hlt">models</span> without mass loss do not agree with observed rates whereas including enhanced mass loss yield predicted rates in better agreement with observations. The results suggest that enhanced mass loss must be a ubiquitous property of Classical Cepheids.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000081724','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000081724"><span>An Inherited Efficiencies <span class="hlt">Model</span> of Non-Genomic <span class="hlt">Evolution</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>New, Michael H.; Pohorille, Andrew</p> <p>1999-01-01</p> <p>A <span class="hlt">model</span> for the <span class="hlt">evolution</span> of biological systems in the absence of a nucleic acid-like genome is proposed and applied to <span class="hlt">model</span> the earliest living organisms -- protocells composed of membrane encapsulated peptides. Assuming that the peptides can make and break bonds between amino acids, and bonds in non-functional peptides are more likely to be destroyed than in functional peptides, it is demonstrated that the catalytic capabilities of the system as a whole can increase. This increase is defined to be non-genomic <span class="hlt">evolution</span>. The relationship between the proposed mechanism for <span class="hlt">evolution</span> and recent experiments on self-replicating peptides is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010APS..DFD.GB001G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010APS..DFD.GB001G"><span><span class="hlt">Modeling</span> roughness effects in turbulent boundary <span class="hlt">layers</span> using elliptic relaxation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>George, Jacob; de Simone, Alejandro; Iaccarino, Gianluca; Jimenez, Javier</p> <p>2010-11-01</p> <p>We present results from the efforts towards <span class="hlt">modeling</span> roughness in turbulent boundary <span class="hlt">layers</span> using elliptic relaxation. This scheme, included in the v^2-f <span class="hlt">model</span> and first formulated by Durbin (1993, JFM, vol. 249, p.465) for smooth-walls, uses an elliptic partial differential equation to incorporate near-wall turbulence anisotropy and non-local pressure-strain effects. The use of the elliptic PDE is extended to <span class="hlt">model</span> roughness effects in various transitionally-rough and fully-rough boundary <span class="hlt">layers</span> consisting of a uniform and sparse distribution of cylinders for which experimental data is available. The roughness effects are incorporated through the elliptic PDE by including the length and time scales that the roughness imposes upon the flow, which the experiment has shown to be constant within the rough-walls. Further <span class="hlt">modeling</span> of roughness effects is considered by altering the source terms in the elliptic PDE.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.A31D3055R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.A31D3055R"><span>Transport and <span class="hlt">Evolution</span> of Aerosol Above/Below the Boundary <span class="hlt">Layer</span> in the Western Mediterranean Basin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roberts, G. C.; Corrigan, C.; Ritchie, J.; Pont, V.; Claeys, M.; Sciare, J.; Mallet, M.; Dulac, F.</p> <p>2014-12-01</p> <p>The Mediterranean Region has been identified as sensitive to changes in the hydrological cycle, which could affect the water resources for millions of people by the turn of the century. However, prior to recent observations, most climate <span class="hlt">models</span> have not accounted for the impacts of aerosol in this region. Past airborne studies have shown that aerosol sources from Europe and Africa are often transported throughout the lower troposphere; yet, because of their complex vertical distribution, it is a challenge to capture the variability and quantify the contribution of these sources to the radiative budget and precipitation processes. The PAEROS ChArMEx Mountain Experiment (PACMEx) complemented the regional activities of the ChArMEx/ADRIMED summer 2013 campaign by collecting aerosol data from atop a mountain on the island of Corsica, France in order to assess boundary <span class="hlt">layer</span> / free troposphere atmospheric processes. In June/July 2013, PACMEx instruments were deployed at 2000 m.asl near the center of Corsica to complement ground-based aerosol observations at 550 m.asl on the northern peninsula, as well as airborne measurements. Comparisons between the peninsula site and the mountain site show similar general trends in aerosol properties; yet, differences in aerosol properties reveal the myriad transport mechanisms over the Mediterranean Basin. Using aerosol physicochemical data coupled with back trajectory analysis, different sources have been identified including Saharan dust transport, residual dust mixed with sea salt, anthropogenic emissions from Western Europe, and a period of biomass burning from Eastern Europe. Each period exhibits distinct signatures in the aerosol related to transport processes above and below the boundary <span class="hlt">layer</span>. In addition, the total aerosol concentrations at the mountain site revealed a strong diurnal cycling between the atmospheric boundary <span class="hlt">layer</span> and the free troposphere, which is typical of mountain-top observations. PACMEx was funded by the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MMI....22..915A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MMI....22..915A"><span>Interfacial <span class="hlt">layers</span> <span class="hlt">evolution</span> during annealing in Ti-Al multi-laminated composite processed using hot press and roll bonding</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Assari, A. H.; Eghbali, B.</p> <p>2016-09-01</p> <p>Ti-Al multi-laminated composites have great potential in high strength and low weight structures. In the present study, tri-<span class="hlt">layer</span> Ti-Al composite was synthesized by hot press bonding under 40 MPa at 570 °C for 1 h and subsequent hot roll bonding at about 450 °C. This process was conducted in two accumulative passes to 30% and to 67% thickness reduction in initial and final passes, respectively. Then, the final annealing treatments were done at 550, 600, 650, 700 and 750 °C for 2, 4 and 6 h. Investigations on microstructural <span class="hlt">evolution</span> and thickening of interfacial <span class="hlt">layers</span> were performed by scanning electron microscopes, energy dispersive spectrometer, X-ray diffraction and micro-hardness tests. The results showed that the thickening of diffusion <span class="hlt">layers</span> corresponds to amount of deformation. In addition to thickening of the diffusion <span class="hlt">layers</span>, the thickness of aluminum <span class="hlt">layers</span> decreased and after annealing treatment at 750 °C for 6 h the aluminum <span class="hlt">layers</span> were consumed entirely, which occurred because of the enhanced interdiffusion of Ti and Al elements. Scanning electron microscope equipped with energy dispersive spectrometer showed that the sequence of interfacial <span class="hlt">layers</span> as Ti3Al-TiAl-TiAl2-TiAl3 which are believed to be the result of thermodynamic and kinetic of phase formation. Micro-hardness results presented the variation profile in accordance with the sequence of intermetallic phases and their different structures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150000261','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150000261"><span>The <span class="hlt">Evolution</span> and Role of the Saharan Air <span class="hlt">Layer</span> During Hurricane Helene (2006)</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Braun, Scott A.; Sippel, Jason A.; Shie, Chung-Lin; Boller, Ryan A.</p> <p>2013-01-01</p> <p>The Saharan air <span class="hlt">layer</span> (SAL) has received considerable attention in recent years as a potential negative influence on the formation and development of Atlantic tropical cyclones. Observations of substantial Saharan dust in the near environment of Hurricane Helene (2006) during the National Aeronautics and Space Administration (NASA) African Monsoon Multidisciplinary Activities (AMMA) Experiment (NAMMA) field campaign led to suggestions about the suppressing influence of the SAL in this case. In this study, a suite of satellite remote sensing data, global meteorological analyses, and airborne data are used to characterize the <span class="hlt">evolution</span> of the SAL in the environment of Helene and assess its possible impact on the intensity of the storm. The influence of the SAL on Helene appears to be limited to the earliest stages of development, although the magnitude of that impact is difficult to determine observationally. Saharan dust was observed on the periphery of the storm during the first two days of development after genesis when intensification was slow. Much of the dust was observed to move well westward of the storm thereafter, with little SAL air present during the remainder of the storm's lifetime and with the storm gradually becoming a category-3 strength storm four days later. Dry air observed to wrap around the periphery of Helene was diagnosed to be primarily non-Saharan in origin (the result of subsidence) and appeared to have little impact on storm intensity. The eventual weakening of the storm is suggested to result from an eyewall replacement cycle and substantial reduction of the sea surface temperatures beneath the hurricane as its forward motion decreased.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1618483','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1618483"><span>Hyperelastic <span class="hlt">modelling</span> of arterial <span class="hlt">layers</span> with distributed collagen fibre orientations</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Gasser, T. Christian; Ogden, Ray W; Holzapfel, Gerhard A</p> <p>2005-01-01</p> <p>Constitutive relations are fundamental to the solution of problems in continuum mechanics, and are required in the study of, for example, mechanically dominated clinical interventions involving soft biological tissues. Structural continuum constitutive <span class="hlt">models</span> of arterial <span class="hlt">layers</span> integrate information about the tissue morphology and therefore allow investigation of the interrelation between structure and function in response to mechanical loading. Collagen fibres are key ingredients in the structure of arteries. In the media (the middle <span class="hlt">layer</span> of the artery wall) they are arranged in two helically distributed families with a small pitch and very little dispersion in their orientation (i.e. they are aligned quite close to the circumferential direction). By contrast, in the adventitial and intimal <span class="hlt">layers</span>, the orientation of the collagen fibres is dispersed, as shown by polarized light microscopy of stained arterial tissue. As a result, continuum <span class="hlt">models</span> that do not account for the dispersion are not able to capture accurately the stress–strain response of these <span class="hlt">layers</span>. The purpose of this paper, therefore, is to develop a structural continuum framework that is able to represent the dispersion of the collagen fibre orientation. This then allows the development of a new hyperelastic free-energy function that is particularly suited for representing the anisotropic elastic properties of adventitial and intimal <span class="hlt">layers</span> of arterial walls, and is a generalization of the fibre-reinforced structural <span class="hlt">model</span> introduced by Holzapfel & Gasser (Holzapfel & Gasser 2001 Comput. Meth. Appl. Mech. Eng. 190, 4379–4403) and Holzapfel et al. (Holzapfel et al. 2000 J. Elast. 61, 1–48). The <span class="hlt">model</span> incorporates an additional scalar structure parameter that characterizes the dispersed collagen orientation. An efficient finite element implementation of the <span class="hlt">model</span> is then presented and numerical examples show that the dispersion of the orientation of collagen fibres in the adventitia of human</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16849214','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16849214"><span>Hyperelastic <span class="hlt">modelling</span> of arterial <span class="hlt">layers</span> with distributed collagen fibre orientations.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gasser, T Christian; Ogden, Ray W; Holzapfel, Gerhard A</p> <p>2006-02-22</p> <p>Constitutive relations are fundamental to the solution of problems in continuum mechanics, and are required in the study of, for example, mechanically dominated clinical interventions involving soft biological tissues. Structural continuum constitutive <span class="hlt">models</span> of arterial <span class="hlt">layers</span> integrate information about the tissue morphology and therefore allow investigation of the interrelation between structure and function in response to mechanical loading. Collagen fibres are key ingredients in the structure of arteries. In the media (the middle <span class="hlt">layer</span> of the artery wall) they are arranged in two helically distributed families with a small pitch and very little dispersion in their orientation (i.e. they are aligned quite close to the circumferential direction). By contrast, in the adventitial and intimal <span class="hlt">layers</span>, the orientation of the collagen fibres is dispersed, as shown by polarized light microscopy of stained arterial tissue. As a result, continuum <span class="hlt">models</span> that do not account for the dispersion are not able to capture accurately the stress-strain response of these <span class="hlt">layers</span>. The purpose of this paper, therefore, is to develop a structural continuum framework that is able to represent the dispersion of the collagen fibre orientation. This then allows the development of a new hyperelastic free-energy function that is particularly suited for representing the anisotropic elastic properties of adventitial and intimal <span class="hlt">layers</span> of arterial walls, and is a generalization of the fibre-reinforced structural <span class="hlt">model</span> introduced by Holzapfel & Gasser (Holzapfel & Gasser 2001 Comput. Meth. Appl. Mech. Eng. 190, 4379-4403) and Holzapfel et al. (Holzapfel et al. 2000 J. Elast. 61, 1-48). The <span class="hlt">model</span> incorporates an additional scalar structure parameter that characterizes the dispersed collagen orientation. An efficient finite element implementation of the <span class="hlt">model</span> is then presented and numerical examples show that the dispersion of the orientation of collagen fibres in the adventitia of human iliac</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900004012','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900004012"><span>Application of large eddy interaction <span class="hlt">model</span> to a mixing <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Murthy, S. N. B.</p> <p>1989-01-01</p> <p>The large eddy interaction <span class="hlt">model</span> (LEIM) is a statistical <span class="hlt">model</span> of turbulence based on the interaction of selected eddies with the mean flow and all of the eddies in a turbulent shear flow. It can be utilized as the starting point for obtaining physical structures in the flow. The possible application of the LEIM to a mixing <span class="hlt">layer</span> formed between two parallel, incompressible flows with a small temperature difference is developed by invoking a detailed similarity between the spectra of velocity and temperature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19780004986','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19780004986"><span><span class="hlt">Evolution</span> of the moon: The 1974 <span class="hlt">model</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schmitt, H. H.</p> <p>1977-01-01</p> <p>The interpretive <span class="hlt">evolution</span> of the moon can be divided now into seven major stages beginning sometime near the end of the formation of the solar system. These stages and their approximate durations in time are as follows: (1) The Beginning: 4.6 billion years ago, (2) The Melted Shell: 4.6 to 4.4 billion years ago, (3) The Cratered Highlands: 4.4 to 4.1 billion years ago, (4) The Large Basins: 4.1 to 3.9 billion years ago, (5) The Light-colored Plains: 3.9 to 3.8 billion years ago, (6) The Basaltic Maria: 3.8 to 3.0(?) billion years ago, and (7) The Quiet Crust: 3.0(?) billion years ago to the present. The contributions of the Apollo and Luna exploration toward the study of those stages of <span class="hlt">evolution</span> are reviewed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1184842-misfit-layer-compounds-ferecrystals-model-systems-thermoelectric-nanocomposites','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1184842-misfit-layer-compounds-ferecrystals-model-systems-thermoelectric-nanocomposites"><span>Misfit <span class="hlt">layer</span> compounds and ferecrystals: <span class="hlt">Model</span> systems for thermoelectric nanocomposites</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Merrill, Devin R.; Moore, Daniel B.; Bauers, Sage R.; ...</p> <p>2015-04-22</p> <p>A basic summary of thermoelectric principles is presented in a historical context, following the <span class="hlt">evolution</span> of the field from initial discovery to modern day high-zT materials. A specific focus is placed on nanocomposite materials as a means to solve the challenges presented by the contradictory material requirements necessary for efficient thermal energy harvest. Misfit <span class="hlt">layer</span> compounds are highlighted as an example of a highly ordered anisotropic nanocomposite system. Their <span class="hlt">layered</span> structure provides the opportunity to use multiple constituents for improved thermoelectric performance, through both enhanced phonon scattering at interfaces and through electronic interactions between the constituents. Recently, a class ofmore » metastable, turbostratically-disordered misfit <span class="hlt">layer</span> compounds has been synthesized using a kinetically controlled approach with low reaction temperatures. The kinetically stabilized structures can be prepared with a variety of constituent ratios and <span class="hlt">layering</span> schemes, providing an avenue to systematically understand structure-function relationships not possible in the thermodynamic compounds. We summarize the work that has been done to date on these materials. The observed turbostratic disorder has been shown to result in extremely low cross plane thermal conductivity and in plane thermal conductivities that are also very small, suggesting the structural motif could be attractive as thermoelectric materials if the power factor could be improved. The first 10 compounds in the [(PbSe)1+δ]m(TiSe₂)n family (m, n ≤ 3) are reported as a case study. As n increases, the magnitude of the Seebeck coefficient is significantly increased without a simultaneous decrease in the in-plane electrical conductivity, resulting in an improved thermoelectric power factor.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1184842','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1184842"><span>Misfit <span class="hlt">layer</span> compounds and ferecrystals: <span class="hlt">Model</span> systems for thermoelectric nanocomposites</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Merrill, Devin R.; Moore, Daniel B.; Bauers, Sage R.; Falmbigl, Matthias; Johnson, David C.</p> <p>2015-04-22</p> <p>A basic summary of thermoelectric principles is presented in a historical context, following the <span class="hlt">evolution</span> of the field from initial discovery to modern day high-zT materials. A specific focus is placed on nanocomposite materials as a means to solve the challenges presented by the contradictory material requirements necessary for efficient thermal energy harvest. Misfit <span class="hlt">layer</span> compounds are highlighted as an example of a highly ordered anisotropic nanocomposite system. Their <span class="hlt">layered</span> structure provides the opportunity to use multiple constituents for improved thermoelectric performance, through both enhanced phonon scattering at interfaces and through electronic interactions between the constituents. Recently, a class of metastable, turbostratically-disordered misfit <span class="hlt">layer</span> compounds has been synthesized using a kinetically controlled approach with low reaction temperatures. The kinetically stabilized structures can be prepared with a variety of constituent ratios and <span class="hlt">layering</span> schemes, providing an avenue to systematically understand structure-function relationships not possible in the thermodynamic compounds. We summarize the work that has been done to date on these materials. The observed turbostratic disorder has been shown to result in extremely low cross plane thermal conductivity and in plane thermal conductivities that are also very small, suggesting the structural motif could be attractive as thermoelectric materials if the power factor could be improved. The first 10 compounds in the [(PbSe)<sub>1+δ</sub>]<sub>m</sub>(TiSe₂)<sub>n</sub> family (m, n ≤ 3) are reported as a case study. As n increases, the magnitude of the Seebeck coefficient is significantly increased without a simultaneous decrease in the in-plane electrical conductivity, resulting in an improved thermoelectric power factor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5507028','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5507028"><span>Misfit <span class="hlt">Layer</span> Compounds and Ferecrystals: <span class="hlt">Model</span> Systems for Thermoelectric Nanocomposites</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Merrill, Devin R.; Moore, Daniel B.; Bauers, Sage R.; Falmbigl, Matthias; Johnson, David C.</p> <p>2015-01-01</p> <p>A basic summary of thermoelectric principles is presented in a historical context, following the <span class="hlt">evolution</span> of the field from initial discovery to modern day high-zT materials. A specific focus is placed on nanocomposite materials as a means to solve the challenges presented by the contradictory material requirements necessary for efficient thermal energy harvest. Misfit <span class="hlt">layer</span> compounds are highlighted as an example of a highly ordered anisotropic nanocomposite system. Their <span class="hlt">layered</span> structure provides the opportunity to use multiple constituents for improved thermoelectric performance, through both enhanced phonon scattering at interfaces and through electronic interactions between the constituents. Recently, a class of metastable, turbostratically-disordered misfit <span class="hlt">layer</span> compounds has been synthesized using a kinetically controlled approach with low reaction temperatures. The kinetically stabilized structures can be prepared with a variety of constituent ratios and <span class="hlt">layering</span> schemes, providing an avenue to systematically understand structure-function relationships not possible in the thermodynamic compounds. We summarize the work that has been done to date on these materials. The observed turbostratic disorder has been shown to result in extremely low cross plane thermal conductivity and in plane thermal conductivities that are also very small, suggesting the structural motif could be attractive as thermoelectric materials if the power factor could be improved. The first 10 compounds in the [(PbSe)1+δ]m(TiSe2)n family (m, n ≤ 3) are reported as a case study. As n increases, the magnitude of the Seebeck coefficient is significantly increased without a simultaneous decrease in the in-plane electrical conductivity, resulting in an improved thermoelectric power factor. PMID:28788045</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT........80R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT........80R"><span><span class="hlt">Modeling</span> diffuse reflectance measurements of light scattered by <span class="hlt">layered</span> tissues</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rohde, Shelley B.</p> <p></p> <p>In this dissertation, we first present a <span class="hlt">model</span> for the diffuse reflectance due to a continuous beam incident normally on a half space composed of a uniform scattering and absorbing medium. This <span class="hlt">model</span> is the result of an asymptotic analysis of the radiative transport equation for strong scattering, weak absorption and a defined beam width. Through comparison with the diffuse reflectance computed using the numerical solution of the radiative transport equation, we show that this diffuse reflectance <span class="hlt">model</span> gives results that are accurate for small source-detector separation distances. We then present an explicit <span class="hlt">model</span> for the diffuse reflectance due to a collimated beam of light incident normally on <span class="hlt">layered</span> tissues. This <span class="hlt">model</span> is derived using the corrected diffusion approximation applied to a <span class="hlt">layered</span> medium, and it takes the form of a convolution with an explicit kernel and the incident beam profile. This <span class="hlt">model</span> corrects the standard diffusion approximation over all source-detector separation distances provided the beam is sufficiently wide compared to the scattering mean-free path. We validate this <span class="hlt">model</span> through comparison with Monte Carlo simulations. Then we use this <span class="hlt">model</span> to estimate the optical properties of an epithelial <span class="hlt">layer</span> from Monte Carlo simulation data. Using measurements at small source-detector separations and this <span class="hlt">model</span>, we are able to estimate the absorption coefficient, scattering coefficient and anisotropy factor of epithelial tissues efficiently with reasonable accuracy. Finally, we present an extension of the corrected diffusion approximation for an obliquely incident beam. This <span class="hlt">model</span> is formed through a Fourier Series representation in the azimuthal angle which allows us to exhibit the break in axisymmetry when combined with the previous analysis. We validate this <span class="hlt">model</span> with Monte Carlo simulations. This <span class="hlt">model</span> can also be written in the form of a convolution of an explicit kernel with the incident beam profile. Additionally, it can be used to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22139521','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22139521"><span>A mathematical <span class="hlt">model</span> for <span class="hlt">evolution</span> and SETI.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Maccone, Claudio</p> <p>2011-12-01</p> <p>Darwinian <span class="hlt">evolution</span> theory may be regarded as a part of SETI theory in that the factor f(l) in the Drake equation represents the fraction of planets suitable for life on which life actually arose. In this paper we firstly provide a statistical generalization of the Drake equation where the factor f(l) is shown to follow the lognormal probability distribution. This lognormal distribution is a consequence of the Central Limit Theorem (CLT) of Statistics, stating that the product of a number of independent random variables whose probability densities are unknown and independent of each other approached the lognormal distribution when the number of factors increased to infinity. In addition we show that the exponential growth of the number of species typical of Darwinian <span class="hlt">Evolution</span> may be regarded as the geometric locus of the peaks of a one-parameter family of lognormal distributions (b-lognormals) constrained between the time axis and the exponential growth curve. Finally, since each b-lognormal distribution in the family may in turn be regarded as the product of a large number (actually "an infinity") of independent lognormal probability distributions, the mathematical way is paved to further cast Darwinian <span class="hlt">Evolution</span> into a mathematical theory in agreement with both its typical exponential growth in the number of living species and the Statistical Drake Equation.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.C41B0398G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.C41B0398G"><span>Controls on the Spatiotemporal <span class="hlt">Evolution</span> of the Thawed <span class="hlt">Layer</span> in and around Thermokarst Features</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Godsey, S.; Gooseff, M. N.; Lewkowicz, A. G.</p> <p>2011-12-01</p> <p>Thermokarst formation leads to changes in ground temperature as well as increases in active <span class="hlt">layer</span> thickness. These changes reflect a combination of shifts in the surface energy balance, conductive heat transport, and non-conductive heat transport. Changes in the surface energy balance occur when the vegetation and organic soil horizons are removed during ground collapse, changing the albedo inside the thermokarst feature. Conductive heat transport is also affected by the removal of these surface <span class="hlt">layers</span> because they typically have different thermal properties than the underlying mineral soil. Additionally, thermokarst formation can increase surface topographic gradients, potentially altering soil moisture status, and thus, thermal conductivity inside thermokarst features. Finally, increased topographic gradients may increase water fluxes through these features, leading to additional non-conductive heat transport. We present field evidence from six sites in arctic Alaska describing shifts in ground thermal regimes associated with thermokarst formation, and the relative importance of changes in surface energy balance, conductive heat transport, and non-conductive heat transport. We also show <span class="hlt">model</span> results that suggest that conductive heat transport may be sufficient to explain observed changes in ground thermal regimes and thaw depths. Large changes in the surface energy balance and non-conductive heat transport are not required, but cannot be excluded. Finally, we discuss potential feedbacks and the role of interannual legacies on controlling ground temperatures in regions of permafrost degradation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10145605','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10145605"><span><span class="hlt">Evolution</span> of the lower planetary boundary <span class="hlt">layer</span> over strongly contrasting surfaces</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Coulter, R.L.; Gao, W.; Martin, T.J.; Shannon, J.D.; Doran, J.C.; Hubbe, J.M.; Shaw, W.M.</p> <p>1992-12-31</p> <p>In a multilaboratory field study held near Boardman in northeastern Oregon in June 1991, various properties of the surface and lower atmospheric boundary <span class="hlt">layer</span> over heavily irrigated cropland and adjacent desert steppe were investigated in the initial campaign of the Atmospheric Radiation Measurement (ARM) program. The locale was selected because its disparate characteristics over various spatial scales stress the ability of general circulation <span class="hlt">models</span> (GCMS) to describe lower boundary conditions, particularly across the discontinuity between desert (in which turbulent flux of heat must be primarily as sensible heat) and large irrigated tracts (in which turbulent flux of latent heat should be the larger term). This campaign of ARM seeks to increase knowledge in three critical areas: (1) determination of the relationships between surface heat fluxes measured over multiple scales and the controlling surface parameters within each scale, (2) integration of local and nearly local heat flux estimates to produce estimates appropriate for GCM grid cells of 100-200 km horizontal dimension, and (3) characterization of the growth and development of the atmospheric boundary <span class="hlt">layer</span> near transitions between surfaces with strongly contrasting moisture availabilities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002JAP....91.1933A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002JAP....91.1933A"><span><span class="hlt">Modeling</span> cross-hatch surface morphology in growing mismatched <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andrews, A. M.; Speck, J. S.; Romanov, A. E.; Bobeth, M.; Pompe, W.</p> <p>2002-02-01</p> <p>We propose and investigate a <span class="hlt">model</span> for the development of cross-hatch surface morphology in growing mismatched <span class="hlt">layers</span>. The <span class="hlt">model</span> incorporates two important elements: (i) strain relaxation due to dislocation glide in the <span class="hlt">layer</span> (film) interior that is also associated with misfit dislocation formation at the film/substrate interface and (ii) lateral surface transport that eliminates surface steps that originated from dislocation glide. A combination of dislocation-assisted strain relaxation and surface step flow leads to the appearance of surface height undulations during <span class="hlt">layer</span> growth. A Monte Carlo simulation technique was applied to <span class="hlt">model</span> dislocation nucleation events in the course of strain relaxation. The simulation was used to <span class="hlt">model</span> the influence of dislocations on film surface height profiles. The surface height displacement was calculated from the analytic elasticity solutions for edge dislocations near a free surface. The results of the <span class="hlt">modeling</span> predict that the average amplitude of the surface undulations and their apparent wavelength both increase with increasing film relaxation and film thickness. The developed cross-hatch pattern is characterized by an atomically smooth but mesoscopically (lateral dimensions ˜0.1-10 μm) rough surface morphology. The conclusions of the <span class="hlt">model</span> are in agreement with atomic force microscopy observations of cross-hatch surface relief in In0.25Ga0.75As/GaAs samples grown well beyond the critical thickness for misfit dislocation formation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28089874','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28089874"><span>Mathematical <span class="hlt">modelling</span> of cell <span class="hlt">layer</span> growth in a hollow fibre bioreactor.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chapman, Lloyd A C; Whiteley, Jonathan P; Byrne, Helen M; Waters, Sarah L; Shipley, Rebecca J</p> <p>2017-04-07</p> <p>Generating autologous tissue grafts of a clinically useful volume requires efficient and controlled expansion of cell populations harvested from patients. Hollow fibre bioreactors show promise as cell expansion devices, owing to their potential for scale-up. However, further research is required to establish how to specify appropriate hollow fibre bioreactor operating conditions for expanding different cell types. In this study we develop a simple <span class="hlt">model</span> for the growth of a cell <span class="hlt">layer</span> seeded on the outer surface of a single fibre in a perfused hollow fibre bioreactor. Nutrient-rich culture medium is pumped through the fibre lumen and leaves the bioreactor via the lumen outlet or passes through the porous fibre walls and cell <span class="hlt">layer</span>, and out via ports on the outer wall of the extra-capillary space. Stokes and Darcy equations for fluid flow in the fibre lumen, fibre wall, cell <span class="hlt">layer</span> and extra-capillary space are coupled to reaction-advection-diffusion equations for oxygen and lactate transport through the bioreactor, and to a simple growth law for the <span class="hlt">evolution</span> of the free boundary of the cell <span class="hlt">layer</span>. Cells at the free boundary are assumed to proliferate at a rate that increases with the local oxygen concentration, and to die and detach from the <span class="hlt">layer</span> if the local fluid shear stress or lactate concentration exceed critical thresholds. We use the <span class="hlt">model</span> to predict operating conditions that maximise the cell <span class="hlt">layer</span> growth for different cell types. In particular, we predict the optimal flow rate of culture medium into the fibre lumen and fluid pressure imposed at the lumen outlet for cell types with different oxygen demands and fluid shear stress tolerances, and compare the growth of the cell <span class="hlt">layer</span> when the exit ports on the outside of the bioreactor are open with that when they are closed. <span class="hlt">Model</span> simulations reveal that increasing the inlet flow rate and outlet fluid pressure increases oxygen delivery to the cell <span class="hlt">layer</span> and, therefore, the growth rate of cells that are</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20080036081&hterms=sami&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dsami','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20080036081&hterms=sami&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dsami"><span>A Chapman-<span class="hlt">Layers</span> Ionspheric <span class="hlt">Model</span> for Mars</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pi, Xiaoqing; Edwards, Charles D.; Hajj, George A.; Ao, Chi; Romans, Larry J.; Callas, John L.; Mannucci, Anthony J.; Asmar, Sami W.; Kahan, Daniel S.</p> <p>2008-01-01</p> <p>A numerical <span class="hlt">model</span> (CLIMM) is developed that adopts functions of two Chapman <span class="hlt">layers</span> to compute Mars ionospheric electron densities at given local solar zenith angle and height. Electron density profiles derived from Mars Global Survey (MGS)-to-Earth radio occultation measurements collected during 1998 through 2005 are used to fit the <span class="hlt">model</span>. The present <span class="hlt">model</span> does not include variations with solar extreme ultraviolet (EUV) radiation cycles and seasons, and may have increased errors at lower latitudes. A more sophisticated <span class="hlt">model</span> taking into account these variations is being developed and will be available in the future.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPhCS.753c2061S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPhCS.753c2061S"><span>Wind-tunnel <span class="hlt">modelling</span> of the tip-speed ratio influence on the wake <span class="hlt">evolution</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stein, Victor P.; Kaltenbach, Hans-Jakob</p> <p>2016-09-01</p> <p>Wind-tunnel measurements on the near-wake <span class="hlt">evolution</span> of a three bladed horizontal axis wind turbine <span class="hlt">model</span> (HAWT) in the scale 1:O(350) operating in uniform flow conditions and within a turbulent boundary <span class="hlt">layer</span> at different tip speed ratios are presented. Operational conditions are chosen to exclude Reynolds number effects regarding the turbulent boundary <span class="hlt">layer</span> as well as the rotor performance. Triple-wire anemometry is used to measure all three velocity components in the mid-vertical and mid-horizontal plane, covering the range from the near- to the far-wake region. In order to analyse wake properties systematically, power and thrust coefficients of the turbine were measured additionally. It is confirmed that realistic <span class="hlt">modelling</span> of the wake <span class="hlt">evolution</span> is not possible in a low-turbulence uniform approach flow. Profiles of mean velocity and turbulence intensity exhibit large deviations between the low-turbulence uniform flow and the turbulent boundary <span class="hlt">layer</span>, especially in the far-wake region. For nearly constant thrust coefficients differences in the <span class="hlt">evolution</span> of the near-wake can be identified for tip speed ratios in the range from 6.5 to 10.5. It is shown that with increasing downstream distances mean velocity profiles become indistinguishable whereas for turbulence statistics a subtle dependency on the tip speed ratio is still noticeable in the far-wake region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013IJMPC..2450081X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013IJMPC..2450081X"><span>Dynamic <span class="hlt">Evolution</span> <span class="hlt">Model</span> Based on Social Network Services</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xiong, Xi; Gou, Zhi-Jian; Zhang, Shi-Bin; Zhao, Wen</p> <p>2013-11-01</p> <p>Based on the analysis of evolutionary characteristics of public opinion in social networking services (SNS), in the paper we propose a dynamic <span class="hlt">evolution</span> <span class="hlt">model</span>, in which opinions are coupled with topology. This <span class="hlt">model</span> shows the clustering phenomenon of opinions in dynamic network <span class="hlt">evolution</span>. The simulation results show that the <span class="hlt">model</span> can fit the data from a social network site. The dynamic <span class="hlt">evolution</span> of networks accelerates the opinion, separation and aggregation. The scale and the number of clusters are influenced by confidence limit and rewiring probability. Dynamic changes of the topology reduce the number of isolated nodes, while the increased confidence limit allows nodes to communicate more sufficiently. The two effects make the distribution of opinion more neutral. The dynamic <span class="hlt">evolution</span> of networks generates central clusters with high connectivity and high betweenness, which make it difficult to control public opinions in SNS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AIPC..940...87S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AIPC..940...87S"><span><span class="hlt">Modeling</span> <span class="hlt">Evolution</span> of Regulatory Networks in Artificial Organisms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sánchez-Dehesa, Yolanda; Beslon, Guillaume; Peña, José-María</p> <p>2007-09-01</p> <p>Regulatory networks are not randomly connected. They are modular, scale-free networks and some motifs distribution is clearly different from random distribution. However, the evolutionary causes and consequences of this specific connectivity are mainly unknown. In this paper we propose Raevol, an integrative <span class="hlt">model</span> to study the <span class="hlt">evolution</span> of regulatory networks. While most existing <span class="hlt">models</span> consider direct <span class="hlt">evolution</span> of the regulatory network, Raevol integrates a realistic genotype-phenotype mapping where the genome undergo mutations that indirectly modify the genetic network. Moreover, the organisms are selected at the phenotype level (which is produced by the genome via the regulation network). Thus, in Raevol, the network only indirectly evolve and it can only be selected if its activity influences the phenotype. We plan to use this <span class="hlt">model</span> to better understand the network <span class="hlt">evolution</span> and to study the influence of networks topology on <span class="hlt">evolution</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=426442','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=426442"><span>Nonmathematical <span class="hlt">Models</span> for <span class="hlt">Evolution</span> of Altruism, and for Group Selection</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Darlington, P. J.</p> <p>1972-01-01</p> <p>Mathematical biologists have failed to produce a satisfactory general <span class="hlt">model</span> for <span class="hlt">evolution</span> of altruism, i.e., of behaviors by which “altruists” benefit other individuals but not themselves; kin selection does not seem to be a sufficient explanation of nonreciprocal altruism. Nonmathematical (but mathematically acceptable) <span class="hlt">models</span> are now proposed for <span class="hlt">evolution</span> of negative altruism in dual-determinant and of positive altruism in tri-determinant systems. Peck orders, territorial systems, and an ant society are analyzed as examples. In all <span class="hlt">models</span>, <span class="hlt">evolution</span> is primarily by individual selection, probably supplemented by group selection. Group selection is differential extinction of populations. It can act only on populations preformed by selection at the individual level, but can either cancel individual selective trends (effecting evolutionary homeostasis) or supplement them; its supplementary effect is probably increasingly important in the <span class="hlt">evolution</span> of increasingly organized populations. PMID:4501113</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993mppf.proc...52T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993mppf.proc...52T"><span>Obliquity variation in a Mars climate <span class="hlt">evolution</span> <span class="hlt">model</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tyler, D.; Haberle, Robert M.</p> <p></p> <p>The existence of <span class="hlt">layered</span> terrain in both polar regions of Mars is strong evidence supporting a cyclic variation in climate. It has been suggested that periods of net deposition have alternated with periods of net erosion in creating the <span class="hlt">layered</span> structure that is seen today. The cause for this cyclic climatic behavior is variation in the annually averaged latitudinal distribution of solar insolation in response to obliquity cycles. For Mars, obliquity variation leads to major climatological excursion due to the condensation and sublimation of the major atmospheric constituent, CO2. The atmosphere will collapse into the polar caps, or existing caps will rapidly sublimate into the atmosphere, dependent upon the polar surface heat balance and the direction of the change in obliquity. It has been argued that variations in the obliquity of Mars cause substantial departures from the current climatological values of the surface pressure and the amount of CO2 stored in both the planetary regolith and polar caps. In this new work we have modified the Haberle et al. <span class="hlt">model</span> to incorporate variable obliquity by allowing the polar and equatorial insolation to become functions of obliquity, which we assume to vary sinusoidally in time. As obliquity varies in the <span class="hlt">model</span>, there can be discontinuities in the time <span class="hlt">evolution</span> of the <span class="hlt">model</span> equilibrium values for surface pressure, regolith, and polar cap storage. The time constant, tau r, for the regolith to find equilibrium with the climate is estimated--depending on the depth, thermal conductivity, and porosity of the regolith--between 104 and 106 yr. Thus, using 2000-yr timesteps to move smoothly through the 0.1250 m.y. obliquity cycles, we have an atmosphere/regolith system that cannot be assumed in equilibrium. We have dealt with this problem by limiting the rate at which CO2, can move between the atmosphere and regolith, mimicking the diffusive nature and effects of the temperature and pressure waves, by setting the time rate of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940028730','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940028730"><span>Obliquity variation in a Mars climate <span class="hlt">evolution</span> <span class="hlt">model</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tyler, D.; Haberle, Robert M.</p> <p>1993-01-01</p> <p>The existence of <span class="hlt">layered</span> terrain in both polar regions of Mars is strong evidence supporting a cyclic variation in climate. It has been suggested that periods of net deposition have alternated with periods of net erosion in creating the <span class="hlt">layered</span> structure that is seen today. The cause for this cyclic climatic behavior is variation in the annually averaged latitudinal distribution of solar insolation in response to obliquity cycles. For Mars, obliquity variation leads to major climatological excursion due to the condensation and sublimation of the major atmospheric constituent, CO2. The atmosphere will collapse into the polar caps, or existing caps will rapidly sublimate into the atmosphere, dependent upon the polar surface heat balance and the direction of the change in obliquity. It has been argued that variations in the obliquity of Mars cause substantial departures from the current climatological values of the surface pressure and the amount of CO2 stored in both the planetary regolith and polar caps. In this new work we have modified the Haberle et al. <span class="hlt">model</span> to incorporate variable obliquity by allowing the polar and equatorial insolation to become functions of obliquity, which we assume to vary sinusoidally in time. As obliquity varies in the <span class="hlt">model</span>, there can be discontinuities in the time <span class="hlt">evolution</span> of the <span class="hlt">model</span> equilibrium values for surface pressure, regolith, and polar cap storage. The time constant, tau r, for the regolith to find equilibrium with the climate is estimated--depending on the depth, thermal conductivity, and porosity of the regolith--between 10(exp 4) and 10(exp 6) yr. Thus, using 2000-yr timesteps to move smoothly through the 0.1250 m.y. obliquity cycles, we have an atmosphere/regolith system that cannot be assumed in equilibrium. We have dealt with this problem by limiting the rate at which CO2, can move between the atmosphere and regolith, mimicking the diffusive nature and effects of the temperature and pressure waves, by setting the time</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800015777','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800015777"><span>Simple turbulence <span class="hlt">models</span> and their application to boundary <span class="hlt">layer</span> separation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wadcock, A. J.</p> <p>1980-01-01</p> <p>Measurements in the boundary <span class="hlt">layer</span> and wake of a stalled airfoil are presented in two coordinate systems, one aligned with the airfoil chord, the other being conventional boundary <span class="hlt">layer</span> coordinates. The NACA 4412 airfoil is studied at a single angle of attack corresponding to maximum lift, the Reynolds number based on chord being 1.5 x 10 to the 6th power. Turbulent boundary <span class="hlt">layer</span> separation occurred at the 85 percent chord position. The two-dimensionality of the flow was documented and the momentum integral equation studied to illustrate the importance of turbulence contributions as separation is approached. The assumptions of simple eddy-viscosity and mixing-length turbulence <span class="hlt">models</span> are checked directly against experiment. Curvature effects are found to be important as separation is approached.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27113405','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27113405"><span>Experimental <span class="hlt">evolution</span> in silico: a custom-designed mathematical <span class="hlt">model</span> for virulence <span class="hlt">evolution</span> of Bacillus thuringiensis.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Strauß, Jakob Friedrich; Crain, Philip; Schulenburg, Hinrich; Telschow, Arndt</p> <p>2016-08-01</p> <p>Most mathematical <span class="hlt">models</span> on the <span class="hlt">evolution</span> of virulence are based on epidemiological <span class="hlt">models</span> that assume parasite transmission follows the mass action principle. In experimental <span class="hlt">evolution</span>, however, mass action is often violated due to controlled infection protocols. This "theory-experiment mismatch" raises the question whether there is a need for new mathematical <span class="hlt">models</span> to accommodate the particular characteristics of experimental <span class="hlt">evolution</span>. Here, we explore the experimental <span class="hlt">evolution</span> <span class="hlt">model</span> system of Bacillus thuringiensis as a parasite and Caenorhabditis elegans as a host. Recent experimental studies with strict control of parasite transmission revealed that one-sided adaptation of B. thuringiensis with non-evolving hosts selects for intermediate or no virulence, sometimes coupled with parasite extinction. In contrast, host-parasite coevolution selects for high virulence and for hosts with strong resistance against B. thuringiensis. In order to explain the empirical results, we propose a new mathematical <span class="hlt">model</span> that mimics the basic experimental set-up. The key assumptions are: (i) controlled parasite transmission (no mass action), (ii) discrete host generations, and (iii) context-dependent cost of toxin production. Our <span class="hlt">model</span> analysis revealed the same basic trends as found in the experiments. Especially, we could show that resistant hosts select for highly virulent bacterial strains. Moreover, we found (i) that the evolved level of virulence is independent of the initial level of virulence, and (ii) that the average amount of bacteria ingested significantly affects the <span class="hlt">evolution</span> of virulence with fewer bacteria ingested selecting for highly virulent strains. These predictions can be tested in future experiments. This study highlights the usefulness of custom-designed mathematical <span class="hlt">models</span> in the analysis and interpretation of empirical results from experimental <span class="hlt">evolution</span>. Copyright © 2016 The Authors. Published by Elsevier GmbH.. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26280183','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26280183"><span>Order reduction for an RNA virus <span class="hlt">evolution</span> <span class="hlt">model</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Korobeinikov, Andrei; Archibasov, Aleksei; Sobolev, Vladimir</p> <p>2015-10-01</p> <p>A mathematical or computational <span class="hlt">model</span> in evolutionary biology should necessary combine several comparatively fast processes, which actually drive natural selection and <span class="hlt">evolution</span>, with a very slow process of <span class="hlt">evolution</span>. As a result, several very different time scales are simultaneously present in the <span class="hlt">model</span>; this makes its analytical study an extremely difficult task. However, the significant difference of the time scales implies the existence of a possibility of the <span class="hlt">model</span> order reduction through a process of time separation. In this paper we conduct the procedure of <span class="hlt">model</span> order reduction for a reasonably simple <span class="hlt">model</span> of RNA virus <span class="hlt">evolution</span> reducing the original system of three integro-partial derivative equations to a single equation. Computations confirm that there is a good fit between the results for the original and reduced <span class="hlt">models</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22382152','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22382152"><span>A robust absorbing <span class="hlt">layer</span> method for anisotropic seismic wave <span class="hlt">modeling</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Métivier, L.; Brossier, R.; Labbé, S.; Operto, S.; Virieux, J.</p> <p>2014-12-15</p> <p>When applied to wave propagation <span class="hlt">modeling</span> in anisotropic media, Perfectly Matched <span class="hlt">Layers</span> (PML) exhibit instabilities. Incoming waves are amplified instead of being absorbed. Overcoming this difficulty is crucial as in many seismic imaging applications, accounting accurately for the subsurface anisotropy is mandatory. In this study, we present the SMART <span class="hlt">layer</span> method as an alternative to PML approach. This method is based on the decomposition of the wavefield into components propagating inward and outward the domain of interest. Only outgoing components are damped. We show that for elastic and acoustic wave propagation in Transverse Isotropic media, the SMART <span class="hlt">layer</span> is unconditionally dissipative: no amplification of the wavefield is possible. The SMART <span class="hlt">layers</span> are not perfectly matched, therefore less accurate than conventional PML. However, a reasonable increase of the <span class="hlt">layer</span> size yields an accuracy similar to PML. Finally, we illustrate that the selective damping strategy on which is based the SMART method can prevent the generation of spurious S-waves by embedding the source in a small zone where only S-waves are damped.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040112026&hterms=attachment&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dattachment','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040112026&hterms=attachment&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dattachment"><span>Direct Simulation of <span class="hlt">Evolution</span> and Control of Three-Dimensional Instabilities in Attachment-Line Boundary <span class="hlt">Layers</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Joslin, Ronald D.</p> <p>1995-01-01</p> <p>The spatial <span class="hlt">evolution</span> of three-dimensional disturbances in an attachment-line boundary <span class="hlt">layer</span> is computed by direct numerical simulation of the unsteady, incompressible Navier-Stokes equations. Disturbances are introduced into the boundary <span class="hlt">layer</span> by harmonic sources that involve unsteady suction and blowing through the wall. Various harmonic- source generators are implemented on or near the attachment line, and the disturbance <span class="hlt">evolutions</span> are compared. Previous two-dimensional simulation results and nonparallel theory are compared with the present results. The three-dimensional simulation results for disturbances with quasi-two-dimensional features indicate growth rates of only a few percent larger than pure two-dimensional results; however, the results are close enough to enable the use of the more computationally efficient, two-dimensional approach. However, true three-dimensional disturbances are more likely in practice and are more stable than two-dimensional disturbances. Disturbances generated off (but near) the attachment line spread both away from and toward the attachment line as they evolve. The <span class="hlt">evolution</span> pattern is comparable to wave packets in at-plate boundary-<span class="hlt">layer</span> flows. Suction stabilizes the quasi-two-dimensional attachment-line instabilities, and blowing destabilizes these instabilities; these results qualitatively agree with the theory. Furthermore, suction stabilizes the disturbances that develop off the attachment line. Clearly, disturbances that are generated near the attachment line can supply energy to attachment-line instabilities, but suction can be used to stabilize these instabilities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040112026&hterms=evolution+theory&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Devolution%2Btheory','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040112026&hterms=evolution+theory&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Devolution%2Btheory"><span>Direct Simulation of <span class="hlt">Evolution</span> and Control of Three-Dimensional Instabilities in Attachment-Line Boundary <span class="hlt">Layers</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Joslin, Ronald D.</p> <p>1995-01-01</p> <p>The spatial <span class="hlt">evolution</span> of three-dimensional disturbances in an attachment-line boundary <span class="hlt">layer</span> is computed by direct numerical simulation of the unsteady, incompressible Navier-Stokes equations. Disturbances are introduced into the boundary <span class="hlt">layer</span> by harmonic sources that involve unsteady suction and blowing through the wall. Various harmonic- source generators are implemented on or near the attachment line, and the disturbance <span class="hlt">evolutions</span> are compared. Previous two-dimensional simulation results and nonparallel theory are compared with the present results. The three-dimensional simulation results for disturbances with quasi-two-dimensional features indicate growth rates of only a few percent larger than pure two-dimensional results; however, the results are close enough to enable the use of the more computationally efficient, two-dimensional approach. However, true three-dimensional disturbances are more likely in practice and are more stable than two-dimensional disturbances. Disturbances generated off (but near) the attachment line spread both away from and toward the attachment line as they evolve. The <span class="hlt">evolution</span> pattern is comparable to wave packets in at-plate boundary-<span class="hlt">layer</span> flows. Suction stabilizes the quasi-two-dimensional attachment-line instabilities, and blowing destabilizes these instabilities; these results qualitatively agree with the theory. Furthermore, suction stabilizes the disturbances that develop off the attachment line. Clearly, disturbances that are generated near the attachment line can supply energy to attachment-line instabilities, but suction can be used to stabilize these instabilities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19392048','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19392048"><span>Drop impact onto a liquid <span class="hlt">layer</span> of finite thickness: dynamics of the cavity <span class="hlt">evolution</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Berberović, Edin; van Hinsberg, Nils P; Jakirlić, Suad; Roisman, Ilia V; Tropea, Cameron</p> <p>2009-03-01</p> <p>In the present work experimental, numerical, and theoretical investigations of a normal drop impact onto a liquid film of finite thickness are presented. The dynamics of drop impact on liquid surfaces, the shape of the cavity, the formation and propagation of a capillary wave in the crater, and the residual film thickness on the rigid wall are determined and analyzed. The shape of the crater within the film and the uprising liquid sheet formed upon the impact are observed using a high-speed video system. The effects of various influencing parameters such as drop impact velocity, liquid film thickness and physical properties of the liquids, including viscosity and surface tension, on the time <span class="hlt">evolution</span> of the crater formation are investigated. Complementary to experiments the direct numerical simulations of the phenomena are performed using an advanced free-surface capturing <span class="hlt">model</span> based on a two-fluid formulation of the classical volume-of-fluid (VOF) <span class="hlt">model</span> in the framework of the finite volume numerical method. In this <span class="hlt">model</span> an additional convective term is introduced into the transport equation for phase fraction, contributing decisively to a sharper interface resolution. Furthermore, an analytical <span class="hlt">model</span> for the penetration depth of the crater is developed accounting for the liquid inertia, viscosity, gravity, and surface tension. The <span class="hlt">model</span> agrees well with the experiments at the early times of penetration far from the wall if the impact velocity is high. Finally, a scaling analysis of the residual film thickness on the wall is conducted demonstrating a good agreement with the numerical predictions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22370193','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22370193"><span><span class="hlt">Evolution</span> of magnetohydrodynamic waves in low <span class="hlt">layers</span> of a coronal hole</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Pucci, Francesco; Malara, Francesco; Onofri, Marco</p> <p>2014-11-20</p> <p>Although a coronal hole is permeated by a magnetic field with a dominant polarity, magnetograms reveal a more complex magnetic structure in the lowest <span class="hlt">layers</span>, where several regions of opposite polarity of typical size of the order of 10{sup 4} km are present. This can give rise to magnetic separatrices and neutral lines. MHD fluctuations generated at the base of the coronal hole by motions of the inner <span class="hlt">layer</span> of the solar atmosphere may interact with such inhomogeneities, leading to the formation of small scales. This phenomenon is studied on a 2D <span class="hlt">model</span> of a magnetic structure with an X-point, using 2D MHD numerical simulations. This <span class="hlt">model</span> implements a method of characteristics for boundary conditions in the direction outer-pointing to Sun surface to simulate both wave injection and exit without reflection. Both Alfvénic and magnetosonic perturbations are considered, and they show very different phenomenology. In the former case, an anisotropic power-law spectrum forms with a dominance of perpendicular wavevectors at altitudes ∼10{sup 4} km. Density fluctuations are generated near the X-point by Alfvén wave magnetic pressure and propagate along open fieldlines at a speed comparable to the local Alfvén velocity. An analysis of energy dissipation and heating caused by the formation of small scales for the Alfvénic case is presented. In the magnetosonic case, small scales form only around the X-point, where a phenomenon of oscillating magnetic reconnection is observed to be induced by the periodic deformation of the magnetic structure due to incoming waves.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013NPGeo..20..945C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013NPGeo..20..945C"><span>Numerical investigation of algebraic oceanic turbulent mixing-<span class="hlt">layer</span> <span class="hlt">models</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chacón-Rebollo, T.; Gómez-Mármol, M.; Rubino, S.</p> <p>2013-11-01</p> <p>In this paper we investigate the finite-time and asymptotic behaviour of algebraic turbulent mixing-<span class="hlt">layer</span> <span class="hlt">models</span> by numerical simulation. We compare the performances given by three different settings of the eddy viscosity. We consider Richardson number-based vertical eddy viscosity <span class="hlt">models</span>. Two of these are classical algebraic turbulence <span class="hlt">models</span> usually used in numerical simulations of global oceanic circulation, i.e. the Pacanowski-Philander and the Gent <span class="hlt">models</span>, while the other one is a more recent <span class="hlt">model</span> (Bennis et al., 2010) proposed to prevent numerical instabilities generated by physically unstable configurations. The numerical schemes are based on the standard finite element method. We perform some numerical tests for relatively large deviations of realistic initial conditions provided by the Tropical Atmosphere Ocean (TAO) array. These initial conditions correspond to states close to mixing-<span class="hlt">layer</span> profiles, measured on the Equatorial Pacific region called the West-Pacific Warm Pool. We conclude that mixing-<span class="hlt">layer</span> profiles could be considered as kinds of "absorbing configurations" in finite time that asymptotically evolve to steady states under the application of negative surface energy fluxes.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.B31D0587T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.B31D0587T"><span>Spatio-temporal <span class="hlt">modeling</span> of Active <span class="hlt">Layer</span> Thickness</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Touyz, J.; Apanasovich, T. V.; Streletskiy, D. A.; Shiklomanov, N. I.</p> <p>2015-12-01</p> <p>Arctic Regions are experiencing an unprecedented rate of environmental and climate change. The active <span class="hlt">layer</span> (the uppermost <span class="hlt">layer</span> of soil between the atmosphere and permafrost that freezes in winter and thaws in summer) is sensitive to both climate and environmental changes and plays an important role in the functioning of Arctic ecosystems, planning, and economic activities. Knowledge about spatio-temporal variability of ALT is crucial for environmental and engineering applications. The objective of this study is to provide the methodology to <span class="hlt">model</span> and estimate spatio-temporal variation in the active <span class="hlt">layer</span> thickness (ALT) at several sites located in the Circumpolar region spanning the Alaska North Slope, and to demonstrate its use in spatio-temporal interpolation as well as time-forward prediction. In our data analysis we estimate a parametric trend and examine residuals for the presence of spatial and temporal dependence. We propose <span class="hlt">models</span> that provide a description of residual space-time variability in ALT. Formulations that take into account interaction among spatial and temporal components are also developed. Moreover, we compare our <span class="hlt">models</span> to naive <span class="hlt">models</span> in which residual spatio-temporal and temporal correlations are not considered. The predicted root mean squared and absolute errors are significantly reduced when our approach is employed. While the methodology is developed in the context of ALT, it can also be applied to <span class="hlt">model</span> and predict other environmental variables which use similar spatio-temporal sampling designs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010cosp...38.1511P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010cosp...38.1511P"><span>Towards a global <span class="hlt">model</span> of the meteoric metal <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Plane, John; Feng, Wuhu; Marsh, Daniel; Janches, Diego; Chipperfield, Martyn; Burrows, John P.; Sinnhuber, Miriam</p> <p></p> <p>This paper will describe a major new initiative to develop a global <span class="hlt">model</span> of the Na, Fe, Ca and Mg <span class="hlt">layers</span> which are produced in the upper mesosphere and lower thermosphere by mete-oric ablation. The 4M (Multi-scale <span class="hlt">Modelling</span> of Mesospheric Metals) project brings together three components: the injection of meteoric constituents into the atmosphere; the neutral and ion-molecule chemistries of these four metals; and a general circulation <span class="hlt">model</span> of the whole atmosphere. The injection rates are calculated by combining the meteoric input function (MIF), an astro-nomical <span class="hlt">model</span> which determines the meteoric size distribution and infall velocity distribution as a function of location and time, and a chemical ablation <span class="hlt">model</span> (CABMOD), which calcu-lates the ablation rates of the different meteoric elements for a meteoroid of specified mass and velocity. The atmospheric chemistries of Na, Fe, Ca and Mg are now quite well understood: the kinetics of most of their important atmospheric reactions have been studied in the laboratory under appropriate conditions. This has enabled 1-dimensional <span class="hlt">models</span> of these metallic <span class="hlt">layers</span> to be produced, which compare satisfactorily with observations by ground-based lidar and space-borne spectrometers. The global <span class="hlt">model</span> which has been chosen for the 4M project is the Whole Atmosphere Chemistry Climate <span class="hlt">Model</span> (WACCM), developed at NCAR (Boulder). The <span class="hlt">model</span> extends from 0 -140 km and includes a full treatment of neutral chemistry and lower E region ion chemistry. We will present the initial results on <span class="hlt">modelling</span> the global Na and Fe <span class="hlt">layers</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014IJEaS.103..329A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014IJEaS.103..329A"><span>Kinematic <span class="hlt">evolution</span> of thrusts wedge and erratic line length balancing: insights from deformed sandbox <span class="hlt">models</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ahmad, Mohammad Irfan; Dubey, A. K.; Toscani, Giovanni; Bonini, Lorenzo; Seno, Silvio</p> <p>2014-01-01</p> <p>Kinematic <span class="hlt">evolution</span> of fold-thrust structures has been investigated by analogue <span class="hlt">models</span> that include syntectonic sedimentation. Different decollement dips and basement thicknesses produced different wedge geometries and propagating characteristics. A <span class="hlt">model</span> with one decollement level was characterized by a closely spaced thrust system during early stages of shortening as compared to the late stages. The frequency of fault nucleation was rapid during the early stages of deformation. Conversely, the frequency of fault nucleation was low and thrust spacing was significantly wider in a <span class="hlt">model</span> with two decollement levels. Individual faults became locked at steep dips and deformation stepped forward as a new fault nucleated in-sequence in front of the older locked structure. Once the thrust system was established up to 27 % overall shortening, an overlying bed was introduced to simulate syntectonic deformation. <span class="hlt">Model</span> sand wedge did not grow self similarly but rather its length and height increased episodically with deformation. Restoration of deformed <span class="hlt">models</span> show that <span class="hlt">layer</span> parallel shortening accommodated for approximately half of the total <span class="hlt">model</span> shortening across the multilayers. Calculated error in apparent <span class="hlt">layer</span> shortening from the restored <span class="hlt">layers</span> revealed a direct relation with depth of the <span class="hlt">layers</span> in the <span class="hlt">models</span>. The experimental results are comparable to a natural example from the Northern Apennines fold-and-thrust belts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870026476&hterms=electric+circuit&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Delectric%2Bcircuit','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870026476&hterms=electric+circuit&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Delectric%2Bcircuit"><span>Simulation of double <span class="hlt">layers</span> in a <span class="hlt">model</span> auroral circuit with nonlinear impedance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, R. A.</p> <p>1986-01-01</p> <p>A reduced circuit description of the U-shaped potential structure of a discrete auroral arc, consisting of the flank transmission line plus parallel-electric-field region, is used to provide the boundary condition for one-dimensional simulations of the double-<span class="hlt">layer</span> <span class="hlt">evolution</span>. The <span class="hlt">model</span> yields asymptotic scalings of the double-<span class="hlt">layer</span> potential, as a function of an anomalous transport coefficient alpha and of the perpendicular length scale l(a) of the arc. The arc potential phi(DL) scales approximately linearly with alpha, and for alpha fixed phi (DL) about l(a) to the z power. Using parameters appropriate to the auroral zone acceleration region, potentials of phi (DPL) 10 kV scale to projected ionospheric dimensions of about 1 km, with power flows of the order of magnitude of substorm dissipation rates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870026476&hterms=parallel+circuit&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dparallel%2Bcircuit','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870026476&hterms=parallel+circuit&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dparallel%2Bcircuit"><span>Simulation of double <span class="hlt">layers</span> in a <span class="hlt">model</span> auroral circuit with nonlinear impedance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, R. A.</p> <p>1986-01-01</p> <p>A reduced circuit description of the U-shaped potential structure of a discrete auroral arc, consisting of the flank transmission line plus parallel-electric-field region, is used to provide the boundary condition for one-dimensional simulations of the double-<span class="hlt">layer</span> <span class="hlt">evolution</span>. The <span class="hlt">model</span> yields asymptotic scalings of the double-<span class="hlt">layer</span> potential, as a function of an anomalous transport coefficient alpha and of the perpendicular length scale l(a) of the arc. The arc potential phi(DL) scales approximately linearly with alpha, and for alpha fixed phi (DL) about l(a) to the z power. Using parameters appropriate to the auroral zone acceleration region, potentials of phi (DPL) 10 kV scale to projected ionospheric dimensions of about 1 km, with power flows of the order of magnitude of substorm dissipation rates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.C33A0515F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.C33A0515F"><span>Impact of the seasonal <span class="hlt">evolution</span> of snow properties on microwave emission <span class="hlt">model</span> performance</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fuller, M.; Derksen, C.; Lemmetyinen, J.; Yackel, J.</p> <p>2010-12-01</p> <p>Snow cover exhibits great spatio-temporal variability, and is dynamically coupled with global hydrological and climatological processes. Accounting for snowpack <span class="hlt">evolution</span> related to snow accumulation, metamorphosis, and melt are essential for both <span class="hlt">modeling</span> and remote sensing applications. Microwave emission has frequency dependant relationships with snow water equivalent (SWE), but snow grain-size, snowpack <span class="hlt">layering</span>, and snow liquid-water content can confuse the estimation of snow parameters with empirical stand-alone algorithms. This work presents an overview of seasonal snow and multi-frequency dual-polarization microwave emission measurements collected during the 2009-2010 winter season at a network of sites near Churchill, Manitoba, Canada. These observations were used to parameterize and evaluate <span class="hlt">model</span> simulations of microwave snow emission using the multiple-<span class="hlt">layer</span> version of the Helsinki University of Technology (HUT) microwave emission <span class="hlt">model</span>. The HUT <span class="hlt">model</span> is utilized in the European Space Agency’s (ESA) GlobSnow global snow monitoring service, applied to SWE and snow depth (SD) retrievals for the Northern Hemisphere. The HUT <span class="hlt">model</span> used for forward brightness temperature simulations in the GlobSnow retrieval scheme is currently limited to one <span class="hlt">layer</span> which necessitates idealizing physical properties of the entire snow pack. In this study, we explore the performance of simulations with the addition of a depth hoar <span class="hlt">layer</span> and, when appropriate, an ice lens. Simulations for forest, lake, and open environments were synthesized through a scene simulation formulation of the HUT <span class="hlt">model</span> to produce output suitable for comparison with measured brightness temperatures from the Advanced Microwave Scanning Radiometer (AMSR-E). While the multi-<span class="hlt">layer</span> <span class="hlt">model</span> better represents the vertical complexities of grain size and <span class="hlt">layering</span>, implementation of a multi-<span class="hlt">layer</span> approach remains a challenge due to <span class="hlt">model</span> sensitivity with regard to the method of generalization of a complex snow</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.9389W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.9389W"><span><span class="hlt">Modelling</span> ice <span class="hlt">layer</span> formation using a preferential flow formulation in the physics based multi-<span class="hlt">layer</span> SNOWPACK <span class="hlt">model</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wever, Nander; Würzer, Sebastian; Fierz, Charles; Lehning, Michael</p> <p>2016-04-01</p> <p>For physics based snow cover <span class="hlt">models</span>, simulating the formation of dense ice <span class="hlt">layers</span> inside the snowpack has been a long time challenge. In spite of their small vertical extend, the presence of ice lenses inside the snowpack can have a profound impact on vapor, heat and liquid water flow. These effects may ultimately influence processes on larger scales when, for example, looking at hydrological processes or wet snow avalanche formation. Also microwave emission signals from the snowpack are strongly influenced by the presence of ice <span class="hlt">layers</span>. Recent laboratory experiments and <span class="hlt">modelling</span> techniques of liquid water flow in snow have advanced the understanding of liquid water flow in snow, in particular the formation of preferential flow paths. We present a <span class="hlt">modelling</span> approach in the one-dimensional, multi-<span class="hlt">layer</span> snow cover <span class="hlt">model</span> SNOWPACK for preferential flow that is based on a dual-domain approach (i.e., separation into a matrix flow and a preferential flow domain) and solving Richards equation for both. In recently published laboratory experiments, water ponding inside the snowpack has been identified to initiate preferential flow. Those studies also quantified the part of the snowpack involved in preferential flow as a function of grain size. By combining these concepts with an empirical function to determine refreezing of preferential flow water inside the snowpack, we are able to simulate preferential water flow in the <span class="hlt">model</span>. We found that preferential flow paths arriving at a <span class="hlt">layer</span> transition in the snowpack may lead to ponding conditions. Subsequent refreezing then may form dense ice <span class="hlt">layers</span> (>700 kg/m3). We compare the simulations to 14 years of biweekly snow profiles made at the Weissfluhjoch study plot at 2540m altitude in the Eastern Swiss Alps. We show that we are able to reproduce several ice lenses that were observed in the field, whereas some profiles remain challenging to simulate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012IAUS..283..386H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012IAUS..283..386H"><span>Chemical <span class="hlt">evolution</span> <span class="hlt">models</span> for NGC 6822 using planetary nebulae abundances</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hernández-Martínez, Liliana; Carigi, Leticia; Peña, Miriam; Peimbert, Manuel</p> <p>2012-08-01</p> <p>We present chemical <span class="hlt">evolution</span> <span class="hlt">models</span> for the dwarf irregular NGC 6822, using chemical abundances of Planetary Nebulae (PNe) and HII regions and also the mass of gas (M gas ) as observational constraints. Chemical <span class="hlt">evolution</span> <span class="hlt">models</span> have been calculated to reproduce the abundances as derived from both, collisionally excited lines (CELs) and recombination lines (RLs). In our <span class="hlt">models</span>, the chemical contribution of low and intermediate mass stars (LIMS) is time delayed, while for the massive stars the chemical contribution is instantaneous, as in Franco & Carigi (2008). The chemical contribution of SNIa is included in our <span class="hlt">model</span>, thus we are also able to reproduce the observational Fe/H abundance obtained from A stars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014cosp...40E3743Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014cosp...40E3743Y"><span>The low-mode approximation for <span class="hlt">modeling</span> of stellar activity in single-<span class="hlt">layer</span> and two-<span class="hlt">layer</span> media</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yukhina, Nadezhda; Popova, Helen; Potemina, Ksenia</p> <p></p> <p>The cycles of solar magnetic activity are connected with a solar dynamo that operates in the convective zone. Solar dynamo mechanism is based on the combined action of the differential rotation and the alpha-effect. Application of these concepts allows us to get an oscillating solution as a wave of the toroidal field propagating from middle latitudes to the equator. We investigated the dynamo <span class="hlt">model</span> with the meridional circulation by the low-mode approach. This approach is based on an assumption that the solar magnetic field can be described by non-linear dynamical systems with a relatively small number of parameters. Such non-linear dynamical systems are based on the equations of dynamo <span class="hlt">models</span>. With this method dynamical systems have been built for single and double <span class="hlt">layer</span> media and contain the meridional flow and thickness of the convection zone of the star. It was shown the possibility of coexistence of quiasi-biennial and 22-year cycle and existence of the triple cycle (quasi-biennial, 22- and hundred-year cycles). We obtained the different regimes (oscillations, vacillations, dynamo-bursts) depending on the value of the dynamo-number, the meridional circulation, and thickness of the convection zone. We discuss the features of these regimes and compare them with the observed features of <span class="hlt">evolution</span> of the solar and geo magnetic fields. We built batterfly-diagrams for the helicity, the toroidal and poloidal magnetic field for different regimes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25818366','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25818366"><span>An analytical <span class="hlt">model</span> accounting for tip shape <span class="hlt">evolution</span> during atom probe analysis of heterogeneous materials.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rolland, N; Larson, D J; Geiser, B P; Duguay, S; Vurpillot, F; Blavette, D</p> <p>2015-12-01</p> <p>An analytical <span class="hlt">model</span> describing the field evaporation dynamics of a tip made of a thin <span class="hlt">layer</span> deposited on a substrate is presented in this paper. The difference in evaporation field between the materials is taken into account in this approach in which the tip shape is <span class="hlt">modeled</span> at a mesoscopic scale. It was found that the non-existence of sharp edge on the surface is a sufficient condition to derive the morphological <span class="hlt">evolution</span> during successive evaporation of the <span class="hlt">layers</span>. This <span class="hlt">modeling</span> gives an instantaneous and smooth analytical representation of the surface that shows good agreement with finite difference simulations results, and a specific regime of evaporation was highlighted when the substrate is a low evaporation field phase. In addition, the <span class="hlt">model</span> makes it possible to calculate theoretically the tip analyzed volume, potentially opening up new horizons for atom probe tomographic reconstruction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21124991','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21124991"><span><span class="hlt">Modelling</span> the <span class="hlt">evolution</span> and spread of HIV immune escape mutants.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fryer, Helen R; Frater, John; Duda, Anna; Roberts, Mick G; Phillips, Rodney E; McLean, Angela R</p> <p>2010-11-18</p> <p>During infection with human immunodeficiency virus (HIV), immune pressure from cytotoxic T-lymphocytes (CTLs) selects for viral mutants that confer escape from CTL recognition. These escape variants can be transmitted between individuals where, depending upon their cost to viral fitness and the CTL responses made by the recipient, they may revert. The rates of within-host <span class="hlt">evolution</span> and their concordant impact upon the rate of spread of escape mutants at the population level are uncertain. Here we present a mathematical <span class="hlt">model</span> of within-host <span class="hlt">evolution</span> of escape mutants, transmission of these variants between hosts and subsequent reversion in new hosts. The <span class="hlt">model</span> is an extension of the well-known SI <span class="hlt">model</span> of disease transmission and includes three further parameters that describe host immunogenetic heterogeneity and rates of within host viral <span class="hlt">evolution</span>. We use the <span class="hlt">model</span> to explain why some escape mutants appear to have stable prevalence whilst others are spreading through the population. Further, we use it to compare diverse datasets on CTL escape, highlighting where different sources agree or disagree on within-host evolutionary rates. The several dozen CTL epitopes we survey from HIV-1 gag, RT and nef reveal a relatively sedate rate of <span class="hlt">evolution</span> with average rates of escape measured in years and reversion in decades. For many epitopes in HIV, occasional rapid within-host <span class="hlt">evolution</span> is not reflected in fast <span class="hlt">evolution</span> at the population level.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2987822','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2987822"><span><span class="hlt">Modelling</span> the <span class="hlt">Evolution</span> and Spread of HIV Immune Escape Mutants</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Fryer, Helen R.; Frater, John; Duda, Anna; Roberts, Mick G.; Phillips, Rodney E.; McLean, Angela R.</p> <p>2010-01-01</p> <p>During infection with human immunodeficiency virus (HIV), immune pressure from cytotoxic T-lymphocytes (CTLs) selects for viral mutants that confer escape from CTL recognition. These escape variants can be transmitted between individuals where, depending upon their cost to viral fitness and the CTL responses made by the recipient, they may revert. The rates of within-host <span class="hlt">evolution</span> and their concordant impact upon the rate of spread of escape mutants at the population level are uncertain. Here we present a mathematical <span class="hlt">model</span> of within-host <span class="hlt">evolution</span> of escape mutants, transmission of these variants between hosts and subsequent reversion in new hosts. The <span class="hlt">model</span> is an extension of the well-known SI <span class="hlt">model</span> of disease transmission and includes three further parameters that describe host immunogenetic heterogeneity and rates of within host viral <span class="hlt">evolution</span>. We use the <span class="hlt">model</span> to explain why some escape mutants appear to have stable prevalence whilst others are spreading through the population. Further, we use it to compare diverse datasets on CTL escape, highlighting where different sources agree or disagree on within-host evolutionary rates. The several dozen CTL epitopes we survey from HIV-1 gag, RT and nef reveal a relatively sedate rate of <span class="hlt">evolution</span> with average rates of escape measured in years and reversion in decades. For many epitopes in HIV, occasional rapid within-host <span class="hlt">evolution</span> is not reflected in fast <span class="hlt">evolution</span> at the population level. PMID:21124991</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JPCM...22h4019T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JPCM...22h4019T"><span>Thin film <span class="hlt">evolution</span> equations from (evaporating) dewetting liquid <span class="hlt">layers</span> to epitaxial growth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thiele, U.</p> <p>2010-03-01</p> <p>In the present contribution we review basic mathematical results for three physical systems involving self-organizing solid or liquid films at solid surfaces. The films may undergo a structuring process by dewetting, evaporation/condensation or epitaxial growth, respectively. We highlight similarities and differences of the three systems based on the observation that in certain limits all of them may be described using <span class="hlt">models</span> of similar form, i.e. time <span class="hlt">evolution</span> equations for the film thickness profile. Those equations represent gradient dynamics characterized by mobility functions and an underlying energy functional. Two basic steps of mathematical analysis are used to compare the different systems. First, we discuss the linear stability of homogeneous steady states, i.e. flat films, and second the systematics of non-trivial steady states, i.e. drop/hole states for dewetting films and quantum-dot states in epitaxial growth, respectively. Our aim is to illustrate that the underlying solution structure might be very complex as in the case of epitaxial growth but can be better understood when comparing the much simpler results for the dewetting liquid film. We furthermore show that the numerical continuation techniques employed can shed some light on this structure in a more convenient way than time-stepping methods. Finally we discuss that the usage of the employed general formulation does not only relate seemingly unrelated physical systems mathematically, but does allow as well for discussing <span class="hlt">model</span> extensions in a more unified way.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013SPIE.8683E..14L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013SPIE.8683E..14L"><span>Wafer sub-<span class="hlt">layer</span> impact in OPC/ORC <span class="hlt">models</span> for 2x nm node implant <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Le-Denmat, Jean-Christophe; Martinelli, Catherine; Sungauer, Elodie; Michel, Jean-Christophe; Yesilada, Emek; Robert, Frederic</p> <p>2013-04-01</p> <p>From 28nm technology node and below, Optical Proximity Correction (OPC) needs to take into account light scattering effects from prior <span class="hlt">layers</span> when bottom anti-reflective coating (BARC) is not used, which is typical for implant <span class="hlt">layers</span>. In this paper, we implement a sub-<span class="hlt">layer</span> aware simulation method into a verification tool for Optical Rule Check (ORC) that is used on full 28nm test chip. The sub-<span class="hlt">layer</span> aware verification can predict defects that are missed by standard ORC. SEM-CD review and defectivity analysis were used to confirm the validity of the sub-<span class="hlt">layer</span> aware <span class="hlt">model</span> on wafer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9879E..0VR','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9879E..0VR"><span>Dual polarization micropulse lidar observations of the diurnal <span class="hlt">evolution</span> of atmospheric boundary <span class="hlt">layer</span> over a tropical coastal station</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rajeev, K.; Mishra, Manoj K.; Sunilkumar, S. V.; Sijikumar, S.</p> <p>2016-05-01</p> <p>High-resolution dual polarized micropulse lidar (MPL) observations have been used to investigate the diurnal <span class="hlt">evolution</span> of atmospheric boundary <span class="hlt">layer</span> (ABL) during winter (2008-2011) over Thiruvananthapuram (8.5°N, 77°E), a tropical coastal station located at southwest Peninsular India, adjoining the Arabian Sea. The lidar observations are compared with the boundary <span class="hlt">layer</span> characteristics derived from concurrent balloon-borne radiosonde observations. This study shows that the mixed <span class="hlt">layer</span> height over this coastal station generally increases from <300 m in the morning to 1500 m by the afternoon. Growth rate of the mixed <span class="hlt">layer</span> height is rapid ( 350 m/hr) during 09-11 IST and slows down with time to <150 m/hr during 11-14 IST and <90 m/hr during 14-16 IST. Thermal internal boundary <span class="hlt">layer</span> during the afternoon, caused by sea breeze circulation, extends up to 500 m altitude and is characterized by highly spherical aerosols, while a distinctly non-spherical aerosol <span class="hlt">layer</span> appear above this altitude, in the return flow arising from the landmass.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017OcDyn..67.1163B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017OcDyn..67.1163B"><span>Turbulent behaviour within a coastal boundary <span class="hlt">layer</span>, observations and <span class="hlt">modelling</span> at the Isola del Giglio</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brandini, Carlo; Taddei, Stefano; Doronzo, Bartolomeo; Fattorini, Maria; Costanza, Letizia; Perna, Massimo; Serafino, Francesco; Ludeno, Giovanni</p> <p>2017-09-01</p> <p>The hydrodynamics of coastal areas is characterized by the interaction among phenomena occurring at different spatial and temporal scales, such as the interaction of a large-scale ocean current with the local bathymetry and coastline, and local forcing conditions. In order to take into account all relevant phenomena, the study of the hydrodynamics of coastal zones requires a high-spatial and temporal resolution for both observations and simulation of local currents. This resolution can be obtained by using X-band radar, which allows simultaneous measurement of waves and currents in a range of 1-3 miles from the coastline, as well as high-resolution numerical <span class="hlt">models</span> implemented in the area and configured through multiple nesting techniques in order to reach resolutions comparable to such coastal observations. Such an integrated monitoring system was implemented at the Isola del Giglio in 2012, after the accident of the Costa Concordia ship. Results can be used as a cross-validation of data produced independently by radar observations and numerical <span class="hlt">models</span>. In addition, results give some important insights on the dynamics of the coastal boundary <span class="hlt">layer</span>, both for what concerns the attenuation in the profile of the depth-averaged velocities which typically occur in turbulent boundary <span class="hlt">layers</span>, as well as for the production, detachment and <span class="hlt">evolution</span> of vorticity produced by the interaction of large-scale ocean currents with the coastline and the subsequent time <span class="hlt">evolution</span> of such boundary <span class="hlt">layer</span>. This transition between large-scale regional currents and the coastal boundary <span class="hlt">layer</span> is often neglected in regional forecasting systems, but it has an important role in the ocean turbulence processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017OcDyn.tmp...68B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017OcDyn.tmp...68B"><span>Turbulent behaviour within a coastal boundary <span class="hlt">layer</span>, observations and <span class="hlt">modelling</span> at the Isola del Giglio</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brandini, Carlo; Taddei, Stefano; Doronzo, Bartolomeo; Fattorini, Maria; Costanza, Letizia; Perna, Massimo; Serafino, Francesco; Ludeno, Giovanni</p> <p>2017-07-01</p> <p>The hydrodynamics of coastal areas is characterized by the interaction among phenomena occurring at different spatial and temporal scales, such as the interaction of a large-scale ocean current with the local bathymetry and coastline, and local forcing conditions. In order to take into account all relevant phenomena, the study of the hydrodynamics of coastal zones requires a high-spatial and temporal resolution for both observations and simulation of local currents. This resolution can be obtained by using X-band radar, which allows simultaneous measurement of waves and currents in a range of 1-3 miles from the coastline, as well as high-resolution numerical <span class="hlt">models</span> implemented in the area and configured through multiple nesting techniques in order to reach resolutions comparable to such coastal observations. Such an integrated monitoring system was implemented at the Isola del Giglio in 2012, after the accident of the Costa Concordia ship. Results can be used as a cross-validation of data produced independently by radar observations and numerical <span class="hlt">models</span>. In addition, results give some important insights on the dynamics of the coastal boundary <span class="hlt">layer</span>, both for what concerns the attenuation in the profile of the depth-averaged velocities which typically occur in turbulent boundary <span class="hlt">layers</span>, as well as for the production, detachment and <span class="hlt">evolution</span> of vorticity produced by the interaction of large-scale ocean currents with the coastline and the subsequent time <span class="hlt">evolution</span> of such boundary <span class="hlt">layer</span>. This transition between large-scale regional currents and the coastal boundary <span class="hlt">layer</span> is often neglected in regional forecasting systems, but it has an important role in the ocean turbulence processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://eric.ed.gov/?q=Mayr%2c+AND+Ernst&id=EJ194812','ERIC'); return false;" href="https://eric.ed.gov/?q=Mayr%2c+AND+Ernst&id=EJ194812"><span><span class="hlt">Evolution</span>.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Mayr, Ernst</p> <p>1978-01-01</p> <p>Traces the history of <span class="hlt">evolution</span> theory from Lamarck and Darwin to the present. Discusses natural selection in detail. Suggests that, besides biological <span class="hlt">evolution</span>, there is also a cultural <span class="hlt">evolution</span> which is more rapid than the former. (MA)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/EJ194812.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/EJ194812.pdf"><span><span class="hlt">Evolution</span>.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Mayr, Ernst</p> <p>1978-01-01</p> <p>Traces the history of <span class="hlt">evolution</span> theory from Lamarck and Darwin to the present. Discusses natural selection in detail. Suggests that, besides biological <span class="hlt">evolution</span>, there is also a cultural <span class="hlt">evolution</span> which is more rapid than the former. (MA)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19840048423&hterms=nonlocal+model&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dnonlocal%2Bmodel','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19840048423&hterms=nonlocal+model&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dnonlocal%2Bmodel"><span>Boundary-<span class="hlt">layer</span> <span class="hlt">model</span> of pattern formation in solidification</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ben-Jacob, E.; Goldenfeld, N.; Langer, J. S.; Schon, G.</p> <p>1984-01-01</p> <p>A <span class="hlt">model</span> of pattern formation in crystal growth is proposed, and its analytic properties are investigated. The principal dynamical variables in this <span class="hlt">model</span> are the curvature of the solidification front and the thickness (or heat content) of a thermal boundary <span class="hlt">layer</span>, both taken to be functions of position along the interface. This <span class="hlt">model</span> is mathematically much more tractable than the realistic, fully nonlocal version of the free-boundary problem, and still recaptures many of the features that seem essential for studying dendritic behavior, for example. Preliminary numerical solutions produce snowflakelike patterns similar to those seen in nature.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910008131','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910008131"><span>Computer <span class="hlt">modeling</span> of inversion <span class="hlt">layer</span> MOS solar cells and arrays</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ho, Fat Duen</p> <p>1991-01-01</p> <p>A two dimensional numerical <span class="hlt">model</span> of the inversion <span class="hlt">layer</span> metal insulator semiconductor (IL/MIS) solar cell is proposed by using the finite element method. The two-dimensional current flow in the device is taken into account in this <span class="hlt">model</span>. The electrostatic potential distribution, the electron concentration distribution, and the hole concentration distribution for different terminal voltages are simulated. The results of simple calculation are presented. The existing problems for this <span class="hlt">model</span> are addressed. Future work is proposed. The MIS structures are studied and some of the results are reported.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19840048423&hterms=Jacobs&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DJ.S%2BJacobs','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19840048423&hterms=Jacobs&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DJ.S%2BJacobs"><span>Boundary-<span class="hlt">layer</span> <span class="hlt">model</span> of pattern formation in solidification</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ben-Jacob, E.; Goldenfeld, N.; Langer, J. S.; Schon, G.</p> <p>1984-01-01</p> <p>A <span class="hlt">model</span> of pattern formation in crystal growth is proposed, and its analytic properties are investigated. The principal dynamical variables in this <span class="hlt">model</span> are the curvature of the solidification front and the thickness (or heat content) of a thermal boundary <span class="hlt">layer</span>, both taken to be functions of position along the interface. This <span class="hlt">model</span> is mathematically much more tractable than the realistic, fully nonlocal version of the free-boundary problem, and still recaptures many of the features that seem essential for studying dendritic behavior, for example. Preliminary numerical solutions produce snowflakelike patterns similar to those seen in nature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010MSMSE..18a5001F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010MSMSE..18a5001F"><span>Computational <span class="hlt">modelling</span> of large deformations in <span class="hlt">layered</span>-silicate/PET nanocomposites near the glass transition</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Figiel, Łukasz; Dunne, Fionn P. E.; Buckley, C. Paul</p> <p>2010-01-01</p> <p><span class="hlt">Layered</span>-silicate nanoparticles offer a cost-effective reinforcement for thermoplastics. Computational <span class="hlt">modelling</span> has been employed to study large deformations in <span class="hlt">layered</span>-silicate/poly(ethylene terephthalate) (PET) nanocomposites near the glass transition, as would be experienced during industrial forming processes such as thermoforming or injection stretch blow moulding. Non-linear numerical <span class="hlt">modelling</span> was applied, to predict the macroscopic large deformation behaviour, with morphology <span class="hlt">evolution</span> and deformation occurring at the microscopic level, using the representative volume element (RVE) approach. A physically based elasto-viscoplastic constitutive <span class="hlt">model</span>, describing the behaviour of the PET matrix within the RVE, was numerically implemented into a finite element solver (ABAQUS) using an UMAT subroutine. The implementation was designed to be robust, for accommodating large rotations and stretches of the matrix local to, and between, the nanoparticles. The nanocomposite morphology was reconstructed at the RVE level using a Monte-Carlo-based algorithm that placed straight, high-aspect ratio particles according to the specified orientation and volume fraction, with the assumption of periodicity. Computational experiments using this methodology enabled prediction of the strain-stiffening behaviour of the nanocomposite, observed experimentally, as functions of strain, strain rate, temperature and particle volume fraction. These results revealed the probable origins of the enhanced strain stiffening observed: (a) <span class="hlt">evolution</span> of the morphology (through particle re-orientation) and (b) early onset of stress-induced pre-crystallization (and hence lock-up of viscous flow), triggered by the presence of particles. The computational <span class="hlt">model</span> enabled prediction of the effects of process parameters (strain rate, temperature) on <span class="hlt">evolution</span> of the morphology, and hence on the end-use properties.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150009965','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150009965"><span>RANS <span class="hlt">Modeling</span> of Benchmark Shockwave / Boundary <span class="hlt">Layer</span> Interaction Experiments</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Georgiadis, Nick; Vyas, Manan; Yoder, Dennis</p> <p>2010-01-01</p> <p>This presentation summarizes the computations of a set of shock wave / turbulent boundary <span class="hlt">layer</span> interaction (SWTBLI) test cases using the Wind-US code, as part of the 2010 American Institute of Aeronautics and Astronautics (AIAA) shock / boundary <span class="hlt">layer</span> interaction workshop. The experiments involve supersonic flows in wind tunnels with a shock generator that directs an oblique shock wave toward the boundary <span class="hlt">layer</span> along one of the walls of the wind tunnel. The Wind-US calculations utilized structured grid computations performed in Reynolds-averaged Navier-Stokes mode. Three turbulence <span class="hlt">models</span> were investigated: the Spalart-Allmaras one-equation <span class="hlt">model</span>, the Menter Shear Stress Transport wavenumber-angular frequency two-equation <span class="hlt">model</span>, and an explicit algebraic stress wavenumber-angular frequency formulation. Effects of grid resolution and upwinding scheme were also considered. The results from the CFD calculations are compared to particle image velocimetry (PIV) data from the experiments. As expected, turbulence <span class="hlt">model</span> effects dominated the accuracy of the solutions with upwinding scheme selection indicating minimal effects.!</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JGRC..115.3011S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JGRC..115.3011S"><span>An analytical <span class="hlt">model</span> of capped turbulent oscillatory bottom boundary <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shimizu, Kenji</p> <p>2010-03-01</p> <p>An analytical <span class="hlt">model</span> of capped turbulent oscillatory bottom boundary <span class="hlt">layers</span> (BBLs) is proposed using eddy viscosity of a quadratic form. The common definition of friction velocity based on maximum bottom shear stress is found unsatisfactory for BBLs under rotating flows, and a possible extension based on turbulent kinetic energy balance is proposed. The <span class="hlt">model</span> solutions show that the flow may slip at the top of the boundary <span class="hlt">layer</span> due to capping by the water surface or stratification, reducing the bottom shear stress, and that the Earth's rotation induces current and bottom shear stress components perpendicular to the interior flow with a phase lag (or lead). Comparisons with field and numerical experiments indicate that the <span class="hlt">model</span> predicts the essential characteristics of the velocity profiles, although the agreement is rather qualitative due to assumptions of quadratic eddy viscosity with time-independent friction velocity and a well-mixed boundary <span class="hlt">layer</span>. On the other hand, the predicted linear friction coefficients, phase lead, and veering angle at the bottom agreed with available data with an error of 3%-10%, 5°-10°, and 5°-10°, respectively. As an application of the <span class="hlt">model</span>, the friction coefficients are used to calculate e-folding decay distances of progressive internal waves with a semidiurnal frequency.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21199845','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21199845"><span><span class="hlt">Modelling</span> the <span class="hlt">evolution</span> and diversity of cumulative culture.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Enquist, Magnus; Ghirlanda, Stefano; Eriksson, Kimmo</p> <p>2011-02-12</p> <p>Previous work on mathematical <span class="hlt">models</span> of cultural <span class="hlt">evolution</span> has mainly focused on the diffusion of simple cultural elements. However, a characteristic feature of human cultural <span class="hlt">evolution</span> is the seemingly limitless appearance of new and increasingly complex cultural elements. Here, we develop a general <span class="hlt">modelling</span> framework to study such cumulative processes, in which we assume that the appearance and disappearance of cultural elements are stochastic events that depend on the current state of culture. Five scenarios are explored: <span class="hlt">evolution</span> of independent cultural elements, stepwise modification of elements, differentiation or combination of elements and systems of cultural elements. As one application of our framework, we study the <span class="hlt">evolution</span> of cultural diversity (in time as well as between groups).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3013467','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3013467"><span><span class="hlt">Modelling</span> the <span class="hlt">evolution</span> and diversity of cumulative culture</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Enquist, Magnus; Ghirlanda, Stefano; Eriksson, Kimmo</p> <p>2011-01-01</p> <p>Previous work on mathematical <span class="hlt">models</span> of cultural <span class="hlt">evolution</span> has mainly focused on the diffusion of simple cultural elements. However, a characteristic feature of human cultural <span class="hlt">evolution</span> is the seemingly limitless appearance of new and increasingly complex cultural elements. Here, we develop a general <span class="hlt">modelling</span> framework to study such cumulative processes, in which we assume that the appearance and disappearance of cultural elements are stochastic events that depend on the current state of culture. Five scenarios are explored: <span class="hlt">evolution</span> of independent cultural elements, stepwise modification of elements, differentiation or combination of elements and systems of cultural elements. As one application of our framework, we study the <span class="hlt">evolution</span> of cultural diversity (in time as well as between groups). PMID:21199845</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008PhRvE..78f1920S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008PhRvE..78f1920S"><span><span class="hlt">Evolution</span> <span class="hlt">models</span> with base substitutions, insertions, deletions, and selection</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Saakian, D. B.</p> <p>2008-12-01</p> <p>The <span class="hlt">evolution</span> <span class="hlt">model</span> with parallel mutation-selection scheme is solved for the case when selection is accompanied by base substitutions, insertions, and deletions. The fitness is assumed to be either a single-peak function (i.e., having one finite discontinuity) or a smooth function of the Hamming distance from the reference sequence. The mean fitness is calculated exactly in large-genome limit. In the case of insertions and deletions the <span class="hlt">evolution</span> characteristics depend on the choice of reference sequence.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017ascl.soft08015B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017ascl.soft08015B"><span>TWO-POP-PY: Two-population dust <span class="hlt">evolution</span> <span class="hlt">model</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Birnstiel, T.; Klahr, H.; Ercolano, B.</p> <p>2017-08-01</p> <p>TWO-POP-PY runs a two-population dust <span class="hlt">evolution</span> <span class="hlt">model</span> that follows the upper end of the dust size distribution and the <span class="hlt">evolution</span> of the dust surface density profile and treats dust surface density, maximum particle size, small and large grain velocity, and fragmentation. It derives profiles that describe the dust-to-gas ratios and the dust surface density profiles well in protoplanetary disks, in addition to the radial flux by solid material rain out.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/990150','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/990150"><span>Rationality Validation of a <span class="hlt">Layered</span> Decision <span class="hlt">Model</span> for Network Defense</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wei, Huaqiang; Alves-Foss, James; Zhang, Du; Frincke, Deb</p> <p>2007-08-31</p> <p>We propose a cost-effective network defense strategy built on three key: three decision <span class="hlt">layers</span>: security policies, defense strategies, and real-time defense tactics for countering immediate threats. A <span class="hlt">layered</span> decision <span class="hlt">model</span> (LDM) can be used to capture this decision process. The LDM helps decision-makers gain insight into the hierarchical relationships among inter-connected entities and decision types, and supports the selection of cost-effective defense mechanisms to safeguard computer networks. To be effective as a business tool, it is first necessary to validate the rationality of <span class="hlt">model</span> before applying it to real-world business cases. This paper describes our efforts in validating the LDM rationality through simulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19800028699&hterms=atmospheric+boundary+layer&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Datmospheric%2Bboundary%2Blayer','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19800028699&hterms=atmospheric+boundary+layer&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Datmospheric%2Bboundary%2Blayer"><span>Finite-element numerical <span class="hlt">modeling</span> of atmospheric turbulent boundary <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lee, H. N.; Kao, S. K.</p> <p>1979-01-01</p> <p>A dynamic turbulent boundary-<span class="hlt">layer</span> <span class="hlt">model</span> in the neutral atmosphere is constructed, using a dynamic turbulent equation of the eddy viscosity coefficient for momentum derived from the relationship among the turbulent dissipation rate, the turbulent kinetic energy and the eddy viscosity coefficient, with aid of the turbulent second-order closure scheme. A finite-element technique was used for the numerical integration. In preliminary results, the behavior of the neutral planetary boundary <span class="hlt">layer</span> agrees well with the available data and with the existing elaborate turbulent <span class="hlt">models</span>, using a finite-difference scheme. The proposed dynamic formulation of the eddy viscosity coefficient for momentum is particularly attractive and can provide a viable alternative approach to study atmospheric turbulence, diffusion and air pollution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPhCS.715a2006F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPhCS.715a2006F"><span>Effect of Hydrogen Plasma on <span class="hlt">Model</span> Corrosion <span class="hlt">Layers</span> of Bronze</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fojtíková, P.; Sázavská, V.; Mika, F.; Krčma, F.</p> <p>2016-05-01</p> <p>Our work is about plasmachemical reduction of <span class="hlt">model</span> corrosion <span class="hlt">layers</span>. The <span class="hlt">model</span> corrosion <span class="hlt">layers</span> were produced on bronze samples with size of 10 × 10 × 5 mm3, containing Cu and Sn. Concentrated hydrochloric acid was used as a corrosive environment. The application of reduction process in low-pressure low-temperature hydrogen plasma followed. A quartz cylindrical reactor with two outer copper electrodes was used. Plasma discharge was generated in pure hydrogen by a RF generator. Each corroded sample was treated in different conditions (supplied power and a continual or pulsed regime with a variable duty cycle mode). Process monitoring was ensured by optical emission spectroscopy. After treatment, samples were analyzed by SEM and EDX.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002PhDT........90T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002PhDT........90T"><span>Synthesis, microstructural <span class="hlt">evolution</span>, and properties of polycrystalline and epitaxial metastable titanium tungsten nitride alloy <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tian, Fang</p> <p></p> <p>Phase composition, microstructural <span class="hlt">evolution</span>, and physical properties of Ti1-xWxN alloys with 0:5 ≤ x ≤ 1.0 and superlattice <span class="hlt">layers</span> grown by ultra-high vacuum (UHV) reactive magnetron sputtering were investigated using a combination of x-ray diffraction (XRD), high-resolution reciprocal lattice map (HR-RLM), transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), wavelength-dispersive electron probe microanalysis (EMPA), x-ray photoelectron spectroscopy (XPS), and Hall measurements. Polycrystalline Ti1-xWxN alloys were grown on SiO2 at 500°C. Alloys with 0 ≤ x ≤ 0.70 were single-phase B1-NaCl crystal structure with a nitrogen-to-metal ratio N/(Ti+W) ranging from slightly overstoichiometric to understoichiometric. The relaxed lattice constant ao initially increased slightly with increasing W and then decreased below the stoichiometric TiN value for understoichiometric alloys (x > 0.50). TiN-rich alloys have a columnar microstructure exhibiting strong 111 preferred orientation with underdense column boundaries. The irradiation by energetic N backscattered from the W target resulted in WN-rich alloys having 002 preferred orientations with denser microstructures. The normalized room-temperature resistivity increased linearly at a rate drho/rho TiNdx = 3.5. Epitaxial B1-NaCl structure Ti1-xWxN alloys with 0 ≤ x ≤ 0.6 were grown on MgO(001) substrates at 500°C. Alloys with x ≥ 0.05 are slightly overstoichiometric. The alloy lattice parameter a⊥ along the film growth direction is 4.251 A for x ≤ 0.41 and decreases slightly at higher concentrations. Ti0.5W 0.5N alloy exhibits long-range CuPt-type atomic ordering on the cation sublattice. The room-temperature resistivity increases linearly due primarily to alloy scattering, while the temperature coefficient of resistivity (TCR), switches from positive for x ≤ 0.21 to negative because of weak charge carrier localization. The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100033464','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100033464"><span>Reevaluating the Role of Saharan Air <span class="hlt">Layer</span> in Atlantic Tropical Cyclogenesis and <span class="hlt">Evolution</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Braun, Scott A.</p> <p>2010-01-01</p> <p>The existence of the Saharan air <span class="hlt">layer</span> (SAL), a <span class="hlt">layer</span> of warm, dry, dusty air that frequently moves westward off of the Saharan desert of Africa and over the tropical Atlantic Ocean, has long been appreciated. As air moves over the desert, it is strongly heated from below, producing a very hot air mass at low levels. Because there is no moisture source over the Sahara, the rise in temperature causes a sharp drop in relative humidity, thus drying the air. In addition, the warm air produces a very strong jet of easterly flow in the middle troposphere called the African easterly jet that is thought to play a critical role in hurricane formation. In recent years, there has been an increased focus on the impact that the SAL has on the formation and <span class="hlt">evolution</span> of hurricanes in the Atlantic. However, the nature of its impact remains unclear, with some researchers arguing that the SAL amplifies hurricane development and with others arguing that it inhibits it. The argument for positively influencing hurricane development is based upon the fact that the African easterly jet provides an energy source for the waves that eventually form hurricanes and that it leads to rising motion south of the jet that favors the development of deep thunderstorm clouds. The potential negative impacts of the SAL include 1) low-level vertical wind shear associated with the African easterly jet; 2) warm SAL air aloft, which increases thermodynamic stability and suppresses cloud development; and 3) dry air, which produces cold downdrafts in precipitating regions, thereby removing energy needed for storm development. As part of this recent focus on the SAL and hurricanes (which motivated a 2006 NASA field experiment), there has been little emphasis on the SAL s potential positive influences and almost complete emphasis on its possible negative influences, almost to the point of claims that the SAL is the major suppressing influence on hurricanes in the Atlantic. In this study, multiple NASA</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22251703','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22251703"><span>A stochastic <span class="hlt">model</span> for tumor geometry <span class="hlt">evolution</span> during radiation therapy in cervical cancer</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Liu, Yifang; Lee, Chi-Guhn; Chan, Timothy C. Y.; Cho, Young-Bin; Islam, Mohammad K.</p> <p>2014-02-15</p> <p>Purpose: To develop mathematical <span class="hlt">models</span> to predict the <span class="hlt">evolution</span> of tumor geometry in cervical cancer undergoing radiation therapy. Methods: The authors develop two mathematical <span class="hlt">models</span> to estimate tumor geometry change: a Markov <span class="hlt">model</span> and an isomorphic shrinkage <span class="hlt">model</span>. The Markov <span class="hlt">model</span> describes tumor <span class="hlt">evolution</span> by investigating the change in state (either tumor or nontumor) of voxels on the tumor surface. It assumes that the <span class="hlt">evolution</span> follows a Markov process. Transition probabilities are obtained using maximum likelihood estimation and depend on the states of neighboring voxels. The isomorphic shrinkage <span class="hlt">model</span> describes tumor shrinkage or growth in terms of <span class="hlt">layers</span> of voxels on the tumor surface, instead of <span class="hlt">modeling</span> individual voxels. The two proposed <span class="hlt">models</span> were applied to data from 29 cervical cancer patients treated at Princess Margaret Cancer Centre and then compared to a constant volume approach. <span class="hlt">Model</span> performance was measured using sensitivity and specificity. Results: The Markov <span class="hlt">model</span> outperformed both the isomorphic shrinkage and constant volume <span class="hlt">models</span> in terms of the trade-off between sensitivity (target coverage) and specificity (normal tissue sparing). Generally, the Markov <span class="hlt">model</span> achieved a few percentage points in improvement in either sensitivity or specificity compared to the other <span class="hlt">models</span>. The isomorphic shrinkage <span class="hlt">model</span> was comparable to the Markov approach under certain parameter settings. Convex tumor shapes were easier to predict. Conclusions: By <span class="hlt">modeling</span> tumor geometry change at the voxel level using a probabilistic <span class="hlt">model</span>, improvements in target coverage and normal tissue sparing are possible. Our Markov <span class="hlt">model</span> is flexible and has tunable parameters to adjust <span class="hlt">model</span> performance to meet a range of criteria. Such a <span class="hlt">model</span> may support the development of an adaptive paradigm for radiation therapy of cervical cancer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhyA..392.2240B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhyA..392.2240B"><span>A last updating <span class="hlt">evolution</span> <span class="hlt">model</span> for online social networks</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bu, Zhan; Xia, Zhengyou; Wang, Jiandong; Zhang, Chengcui</p> <p>2013-05-01</p> <p>As information technology has advanced, people are turning to electronic media more frequently for communication, and social relationships are increasingly found on online channels. However, there is very limited knowledge about the actual <span class="hlt">evolution</span> of the online social networks. In this paper, we propose and study a novel <span class="hlt">evolution</span> network <span class="hlt">model</span> with the new concept of “last updating time”, which exists in many real-life online social networks. The last updating <span class="hlt">evolution</span> network <span class="hlt">model</span> can maintain the robustness of scale-free networks and can improve the network reliance against intentional attacks. What is more, we also found that it has the “small-world effect”, which is the inherent property of most social networks. Simulation experiment based on this <span class="hlt">model</span> show that the results and the real-life data are consistent, which means that our <span class="hlt">model</span> is valid.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://eric.ed.gov/?q=PLA&pg=6&id=EJ656051','ERIC'); return false;" href="https://eric.ed.gov/?q=PLA&pg=6&id=EJ656051"><span>The <span class="hlt">Evolution</span> of PLA's Planning <span class="hlt">Model</span>.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Elsner, Edward J.</p> <p>2002-01-01</p> <p>Explores the movement toward community-centered standards in public libraries. Tracks the changes of the Public Library Association's (PLA's) planning <span class="hlt">model</span> through four incarnations, summarizes each <span class="hlt">model</span>, and examines trends and suggests a way to use the various <span class="hlt">models</span> together for an easier planning process. (Author/LRW)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PhLA..375.3055F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PhLA..375.3055F"><span>Jump diffusion <span class="hlt">models</span> and the <span class="hlt">evolution</span> of financial prices</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Figueiredo, Annibal; de Castro, Marcio T.; da Silva, Sergio; Gleria, Iram</p> <p>2011-08-01</p> <p>We analyze a stochastic <span class="hlt">model</span> to describe the <span class="hlt">evolution</span> of financial prices. We consider the stochastic term as a sum of the Wiener noise and a jump process. We point to the effects of the jumps on the return time <span class="hlt">evolution</span>, a central concern of the econophysics literature. The presence of jumps suggests that the process can be described by an infinitely divisible characteristic function belonging to the De Finetti class. We then extend the De Finetti functions to a generalized nonlinear <span class="hlt">model</span> and show the <span class="hlt">model</span> to be capable of explaining return behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JPhCS.811a2005M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JPhCS.811a2005M"><span>A continuous phenotype space <span class="hlt">model</span> of cancer <span class="hlt">evolution</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Masip, David; Korobeinikiov, Andrei</p> <p>2017-02-01</p> <p>It was suggested that the ability of cancer to avoid immune response pressure (that should be expected to be capable to annihilate cancer at its early stage) can be attributed to the ability of the cancer cells to evolve. The goal of this notice is to illustrate this possibility by the means of mathematical <span class="hlt">modelling</span>. In this notice, we construct a simple mechanistic <span class="hlt">model</span> of cancer <span class="hlt">evolution</span>, which is based upon a classical <span class="hlt">model</span> of cancer-immune response interaction. Numerical simulations confirm the hypothesis that if cancer mutates fast enough and if immune response is not sufficiently strong, then cancer is able to avoid immune response pressure by <span class="hlt">evolution</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AnMP..tmp....7K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AnMP..tmp....7K"><span><span class="hlt">Evolution</span> of states in a continuum migration <span class="hlt">model</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kondratiev, Yuri; Kozitsky, Yuri</p> <p>2017-03-01</p> <p>The Markov <span class="hlt">evolution</span> of states of a continuum migration <span class="hlt">model</span> is studied. The <span class="hlt">model</span> describes an infinite system of entities placed in R^d in which the constituents appear (immigrate) with rate b(x) and disappear, also due to competition. For this <span class="hlt">model</span>, we prove the existence of the <span class="hlt">evolution</span> of states μ _0 mapsto μ _t such that the moments μ _t(N_Λ ^n) , nin N, of the number of entities in compact Λ subset R^d remain bounded for all t>0 . Under an additional condition, we prove that the density of entities and the second correlation function remain point-wise bounded globally in time.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980237907','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980237907"><span>Cloud-Scale Numerical <span class="hlt">Modeling</span> of the Arctic Boundary <span class="hlt">Layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Krueger, Steven K.</p> <p>1998-01-01</p> <p>The interactions between sea ice, open ocean, atmospheric radiation, and clouds over the Arctic Ocean exert a strong influence on global climate. Uncertainties in the formulation of interactive air-sea-ice processes in global climate <span class="hlt">models</span> (GCMs) result in large differences between the Arctic, and global, climates simulated by different <span class="hlt">models</span>. Arctic stratus clouds are not well-simulated by GCMs, yet exert a strong influence on the surface energy budget of the Arctic. Leads (channels of open water in sea ice) have significant impacts on the large-scale budgets during the Arctic winter, when they contribute about 50 percent of the surface fluxes over the Arctic Ocean, but cover only 1 to 2 percent of its area. Convective plumes generated by wide leads may penetrate the surface inversion and produce condensate that spreads up to 250 km downwind of the lead, and may significantly affect the longwave radiative fluxes at the surface and thereby the sea ice thickness. The effects of leads and boundary <span class="hlt">layer</span> clouds must be accurately represented in climate <span class="hlt">models</span> to allow possible feedbacks between them and the sea ice thickness. The FIRE III Arctic boundary <span class="hlt">layer</span> clouds field program, in conjunction with the SHEBA ice camp and the ARM North Slope of Alaska and Adjacent Arctic Ocean site, will offer an unprecedented opportunity to greatly improve our ability to parameterize the important effects of leads and boundary <span class="hlt">layer</span> clouds in GCMs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/894329','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/894329"><span><span class="hlt">Evolution</span> of a storm-driven cloudy boundary <span class="hlt">layer</span> in the Arctic</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Inoue, J; Kosovic, B; Curry, J A</p> <p>2003-10-24</p> <p>The cloudy boundary <span class="hlt">layer</span> under stormy conditions during the summertime Arctic has been studied using observation from the SHEBA experiment and large-eddy simulations (LES). On 29 July 1998, a stable Arctic cloudy boundary <span class="hlt">layer</span> event was observed after passage of a synoptic low. The local dynamic and thermodynamic structure of the boundary <span class="hlt">layer</span> was determined from aircraft measurement including analysis of turbulence, cloud microphysics and radiative properties. After the upper cloud <span class="hlt">layer</span> advected over the existing cloud <span class="hlt">layer</span>, the turbulent kinetic energy budget indicated that the cloud <span class="hlt">layer</span> below 200 m was maintained predominantly by shear production. Observations of longwave radiation showed that cloud top cooling at the lower cloud top has been suppressed by radiative effects of the upper cloud <span class="hlt">layer</span>. Our LES results demonstrate the importance of the combination of shear mixing near the surface and radiative cooling at the cloud top in the storm-driven cloudy boundary <span class="hlt">layer</span>. Once the low-level cloud reaches a certain height, depending on the amount of cloud-top cooling, the two sources of TKE production begin to separate in space under continuous stormy conditions, suggesting one possible mechanism for the cloud <span class="hlt">layering</span>. The sensitivity tests suggest that the storm-driven cloudy boundary <span class="hlt">layer</span> is flexibly switched to the shear-driven system due to the advection of upper clouds or the buoyantly driven system due to the lack of the wind shear. A comparison is made of this storm-driven boundary <span class="hlt">layer</span> with the buoyantly driven boundary <span class="hlt">layer</span> previously described in the literature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1913720Q','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1913720Q"><span>Forecasting and <span class="hlt">modelling</span> ice <span class="hlt">layer</span> formation on the snowpack due to freezing precipitations in the Pyrenees</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Quéno, Louis; Vionnet, Vincent; Cabot, Frédéric; Vrécourt, Dominique; Dombrowski-Etchevers, Ingrid</p> <p>2017-04-01</p> <p>In the Pyrenees, freezing precipitations in altitude occur at least once per winter, leading to the formation of a pure ice <span class="hlt">layer</span> on the surface of the snowpack. It may lead to accidents and fatalities among mountaineers and skiers, with sometimes a higher human toll than avalanches. Such events are not predicted by the current operational systems for snow and avalanche hazard forecasting. A crowd-sourced database of surface ice <span class="hlt">layer</span> occurrences is first built up, using reports from Internet mountaineering and ski-touring communities, to mitigate the lack of observations from conventional observation networks. A simple diagnostic of freezing precipitation is then developed, based on the cloud water content and screen temperature forecast by the Numerical Weather Prediction <span class="hlt">model</span> AROME, operating at 2.5-km resolution. The performance of this diagnostic is assessed for the event of 5-6 January 2012, with a good representation of altitudinal and spatial distributions of the ice <span class="hlt">layer</span>. An evaluation of the diagnostic for major events over five winters gives good skills of detection compared to the occurrences reported in the observation database. A new <span class="hlt">modelling</span> of ice formation on the surface of the snowpack due to impinging supercooled water is added to the detailed snowpack <span class="hlt">model</span> Crocus. It is combined to the atmospheric diagnostic of freezing precipitations and resulting snowpack simulations over a winter season capture well the formation of the main ice <span class="hlt">layers</span>. Their influence on the snowpack stratigraphy is also realistically simulated. These simple methods enable to forecast the occurrence of surface ice <span class="hlt">layer</span> formations with good confidence and to simulate their <span class="hlt">evolution</span> within the snowpack, even if an accurate estimation of freezing precipitation amounts remains the main challenge.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983JApMe..22..341B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983JApMe..22..341B"><span>Dynamical <span class="hlt">Model</span> Simulation of the Morning Boundary <span class="hlt">Layer</span> Development in Deep Mountain Valleys.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bader, David C.; McKee, Thomas B.</p> <p>1983-03-01</p> <p>A dry, two-dimensional version of the Colorado State University Multi-dimensional Cloud/Mesoscale <span class="hlt">Model</span> was used to study the cross-valley <span class="hlt">evolution</span> of the wind and temperature structures in an idealized east-west oriented mountain valley. Two simulations were performed, one in which the valley was heated symmetrically and a second in which a mid-latitude heating distribution was imposed. Both runs were initiated identically with a stable <span class="hlt">layer</span> filling the valley to ridgetop and a neutral <span class="hlt">layer</span> above the ridge. A specified sinusoidal surface potential temperature flux function approximating the diurnal cycle forced the <span class="hlt">model</span> at the lower boundary.The results of the two simulations were remarkably similar. The <span class="hlt">model</span> realistically reproduced the gross features found in actual valleys in both structure and timing. The simulated inversions were destroyed three and one-half hours after sunrise as a result of a neutral <span class="hlt">layer</span> growing up from the surface meeting a descending inversion top. Slope winds with speeds of 3-5 m s1 developed over both sidewalls two and one-half hours after sunrise. Both cases revealed the development of strongly stable pockets of air over the sidewalls which form when cold air advected upslope loses its buoyancy at higher elevations. These stable pockets temporarily block the slope flow and force transient cross-valley circulations to form which act to destabilize the valley boundary <span class="hlt">layer</span>. Cross-valley mixing and gravity waves rapidly redistribute heat across the valley to prevent large potential temperature gradients from forming. As a result, oven large differences in heating rates between opposing sidewalls do not result in significant cross-valley potential temperature differences. Organized cross-valley circulations and eddy motions enhance lateral mixing in the stable <span class="hlt">layer</span> as well.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22092071','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22092071"><span>A DATA-DRIVEN <span class="hlt">MODEL</span> FOR THE GLOBAL CORONAL <span class="hlt">EVOLUTION</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Feng Xueshang; Jiang Chaowei; Xiang Changqing; Zhao Xuepu; Wu, S. T. E-mail: cwjiang@spaceweather.ac.cn E-mail: xpzhao@sun.stanford.edu</p> <p>2012-10-10</p> <p>This work is devoted to the construction of a data-driven <span class="hlt">model</span> for the study of the dynamic <span class="hlt">evolution</span> of the global corona that can respond continuously to the changing of the photospheric magnetic field. The data-driven <span class="hlt">model</span> consists of a surface flux transport (SFT) <span class="hlt">model</span> and a global three-dimensional (3D) magnetohydrodynamic (MHD) coronal <span class="hlt">model</span>. The SFT <span class="hlt">model</span> is employed to produce the global time-varying and self-consistent synchronic snapshots of the photospheric magnetic field as the input to drive our 3D numerical global coronal AMR-CESE-MHD <span class="hlt">model</span> on an overset grid of Yin-Yang overlapping structure. The SFT <span class="hlt">model</span> and the 3D global coronal <span class="hlt">model</span> are coupled through the boundary condition of the projected characteristic method. Numerical results of the coronal <span class="hlt">evolution</span> from 1996 September 4 to October 29 provide a good comparison with multiply observed coronal images.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870057876&hterms=simple+circuit&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dsimple%2Bcircuit','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870057876&hterms=simple+circuit&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dsimple%2Bcircuit"><span>Anomalous transport in discrete arcs and simulation of double <span class="hlt">layers</span> in a <span class="hlt">model</span> auroral circuit</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, Robert A.</p> <p>1987-01-01</p> <p>The <span class="hlt">evolution</span> and long-time stability of a double <span class="hlt">layer</span> in a discrete auroral arc requires that the parallel current in the arc, which may be considered uniform at the source, be diverted within the arc to charge the flanks of the U-shaped double-<span class="hlt">layer</span> potential structure. A simple <span class="hlt">model</span> is presented in which this current re-distribution is effected by anomalous transport based on electrostatic lower hybrid waves driven by the flank structure itself. This process provides the limiting constraint on the double-<span class="hlt">layer</span> potential. The flank charging may be represented as that of a nonlinear transmission. A simplified <span class="hlt">model</span> circuit, in which the transmission line is represented by a nonlinear impedance in parallel with a variable resistor, is incorporated in a 1-d simulation <span class="hlt">model</span> to give the current density at the DL boundaries. Results are presented for the scaling of the DL potential as a function of the width of the arc and the saturation efficiency of the lower hybrid instability mechanism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870013892','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870013892"><span>Anomalous transport in discrete arcs and simulation of double <span class="hlt">layers</span> in a <span class="hlt">model</span> auroral circuit</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, Robert A.</p> <p>1987-01-01</p> <p>The <span class="hlt">evolution</span> and long-time stability of a double <span class="hlt">layer</span> (DL) in a discrete auroral arc requires that the parallel current in the arc, which may be considered uniform at the source, be diverted within the arc to charge the flanks of the U-shaped double <span class="hlt">layer</span> potential structure. A simple <span class="hlt">model</span> is presented in which this current redistribution is effected by anomalous transport based on electrostatic lower hybrid waves driven by the flank structure itself. This process provides the limiting constraint on the double <span class="hlt">layer</span> potential. The flank charging may be represented as that of a nonlinear transmission line. A simplified <span class="hlt">model</span> circuit, in which the transmission line is represented by a nonlinear impedance in parallel with a variable resistor, is incorporated in a one-dimensional simulation <span class="hlt">model</span> to give the current density at the DL boundaries. Results are presented for the scaling of the DL potential as a function of the width of the arc and the saturation efficiency of the lower hybrid instability mechanism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870057876&hterms=parallel+circuit&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dparallel%2Bcircuit','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870057876&hterms=parallel+circuit&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dparallel%2Bcircuit"><span>Anomalous transport in discrete arcs and simulation of double <span class="hlt">layers</span> in a <span class="hlt">model</span> auroral circuit</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, Robert A.</p> <p>1987-01-01</p> <p>The <span class="hlt">evolution</span> and long-time stability of a double <span class="hlt">layer</span> in a discrete auroral arc requires that the parallel current in the arc, which may be considered uniform at the source, be diverted within the arc to charge the flanks of the U-shaped double-<span class="hlt">layer</span> potential structure. A simple <span class="hlt">model</span> is presented in which this current re-distribution is effected by anomalous transport based on electrostatic lower hybrid waves driven by the flank structure itself. This process provides the limiting constraint on the double-<span class="hlt">layer</span> potential. The flank charging may be represented as that of a nonlinear transmission. A simplified <span class="hlt">model</span> circuit, in which the transmission line is represented by a nonlinear impedance in parallel with a variable resistor, is incorporated in a 1-d simulation <span class="hlt">model</span> to give the current density at the DL boundaries. Results are presented for the scaling of the DL potential as a function of the width of the arc and the saturation efficiency of the lower hybrid instability mechanism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16..472N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16..472N"><span>Quasi-Stationary Global Auroral Ionospheric <span class="hlt">Model</span>: E-<span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nikolaeva, Vera; Gordeev, Evgeny; Kotikov, Andrey; Makarova, Ludmila; Shirochkov, Aleksander</p> <p>2014-05-01</p> <p>E-<span class="hlt">layer</span> Auroral Ionospheric <span class="hlt">Model</span> (E-AIM) is developed to provide temporal and spatial density distribution of the main ionosphere neutral species (NO, N(4S),N(2D)), and ions (N2+, NO+,O2+,O+) in the altitude range from 90 to 150 km. NRLMSISE-00 <span class="hlt">model</span> [Picone et al., JGR 2003] is used for neutral atmosphere content and temperature determination, that is the input for the E-AIM <span class="hlt">model</span>. The E-AIM <span class="hlt">model</span> based on chemical equilibrium state in E-<span class="hlt">layer</span> that reaches in chemical reactions between ionospheric species considering solar radiation ionization source, superposed with sporadic precipitation of magnetospheric electrons. The chemical equilibrium state in each location under specific solar and geomagnetic activity conditions reaches during numerical solution of the continuity equations for the neutrals and ions using the high-performance Gear method [Gear, 1971] for ordinary differential equation (ODE) systems. Applying the Gear method for solving stiff ODE system strongly reduce the computation time and machine resources comparing to widely used methods and provide an opportunity to calculate the global spatial E-<span class="hlt">layer</span> ion content distribution. In contrast to the mid-latitude ionosphere, structure and dynamics of the auroral zone ionosphere (φ ≡ 60-75° MLat) associated not only with shortwave solar radiation. Precipitating magnetospheric particle flux is the most important ionization source and is the main cause of E-<span class="hlt">layer</span> disturbances. Precipitated electrons with initial energies of 1 - 30 keV influence the auroral ionosphere E-<span class="hlt">layer</span>. E-AIM <span class="hlt">model</span> can estimate ionization rate corresponds to auroral electron precipitation in two different ways: 1. with direct electron flux satellite data; 2. with differential energy spectrum reconstructed from OVATION-Prime empirical <span class="hlt">model</span> [Newell, JGR 2009] average values, that allows to estimate ionosphere ion content for any time and location in the auroral zone. Comparison of E-AIM results with direct ionospheric observations</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950036200&hterms=kuhn&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dkuhn','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950036200&hterms=kuhn&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dkuhn"><span>Incorporation of multiple cloud <span class="hlt">layers</span> for ultraviolet radiation <span class="hlt">modeling</span> studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Charache, Darryl H.; Abreu, Vincent J.; Kuhn, William R.; Skinner, Wilbert R.</p> <p>1994-01-01</p> <p>Cloud data sets compiled from surface observations were used to develop an algorithm for incorporating multiple cloud <span class="hlt">layers</span> into a multiple-scattering radiative transfer <span class="hlt">model</span>. Aerosol extinction and ozone data sets were also incorporated to estimate the seasonally averaged ultraviolet (UV) flux reaching the surface of the Earth in the Detroit, Michigan, region for the years 1979-1991, corresponding to Total Ozone Mapping Spectrometer (TOMS) version 6 ozone observations. The calculated UV spectrum was convolved with an erythema action spectrum to estimate the effective biological exposure for erythema. Calculations show that decreasing the total column density of ozone by 1% leads to an increase in erythemal exposure by approximately 1.1-1.3%, in good agreement with previous studies. A comparison of the UV radiation budget at the surface between a single cloud <span class="hlt">layer</span> method and a multiple cloud <span class="hlt">layer</span> method presented here is discussed, along with limitations of each technique. With improved parameterization of cloud properties, and as knowledge of biological effects of UV exposure increase, inclusion of multiple cloud <span class="hlt">layers</span> may be important in accurately determining the biologically effective UV budget at the surface of the Earth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950036200&hterms=ultraviolet+radiation&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dultraviolet%2Bradiation','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950036200&hterms=ultraviolet+radiation&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dultraviolet%2Bradiation"><span>Incorporation of multiple cloud <span class="hlt">layers</span> for ultraviolet radiation <span class="hlt">modeling</span> studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Charache, Darryl H.; Abreu, Vincent J.; Kuhn, William R.; Skinner, Wilbert R.</p> <p>1994-01-01</p> <p>Cloud data sets compiled from surface observations were used to develop an algorithm for incorporating multiple cloud <span class="hlt">layers</span> into a multiple-scattering radiative transfer <span class="hlt">model</span>. Aerosol extinction and ozone data sets were also incorporated to estimate the seasonally averaged ultraviolet (UV) flux reaching the surface of the Earth in the Detroit, Michigan, region for the years 1979-1991, corresponding to Total Ozone Mapping Spectrometer (TOMS) version 6 ozone observations. The calculated UV spectrum was convolved with an erythema action spectrum to estimate the effective biological exposure for erythema. Calculations show that decreasing the total column density of ozone by 1% leads to an increase in erythemal exposure by approximately 1.1-1.3%, in good agreement with previous studies. A comparison of the UV radiation budget at the surface between a single cloud <span class="hlt">layer</span> method and a multiple cloud <span class="hlt">layer</span> method presented here is discussed, along with limitations of each technique. With improved parameterization of cloud properties, and as knowledge of biological effects of UV exposure increase, inclusion of multiple cloud <span class="hlt">layers</span> may be important in accurately determining the biologically effective UV budget at the surface of the Earth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28478110','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28478110"><span>Empirical genome <span class="hlt">evolution</span> <span class="hlt">models</span> root the tree of life.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Harish, Ajith; Kurland, Charles G</p> <p>2017-07-01</p> <p>A reliable phylogenetic reconstruction of the evolutionary history of contemporary species depends on a robust identification of the universal common ancestor (UCA) at the root of the Tree of Life (ToL). That root polarizes the tree so that the evolutionary succession of ancestors to descendants is discernable. In effect, the root determines the branching order and the direction of character <span class="hlt">evolution</span>. Typically, conventional phylogenetic analyses implement time-reversible <span class="hlt">models</span> of <span class="hlt">evolution</span> for which character <span class="hlt">evolution</span> is un-polarized. Such practices leave the root and the direction of character <span class="hlt">evolution</span> undefined by the data used to construct such trees. In such cases, rooting relies on theoretic assumptions and/or the use of external data to interpret unrooted trees. The most common rooting method, the outgroup method is clearly inapplicable to the ToL, which has no outgroup. Both here and in the accompanying paper (Harish and Kurland, 2017) we have explored the theoretical and technical issues related to several rooting methods. We demonstrate (1) that Genome-level characters and <span class="hlt">evolution</span> <span class="hlt">models</span> are necessary for species phylogeny reconstructions. By the same token, standard practices exploiting sequence-based methods that implement gene-scale substitution <span class="hlt">models</span> do not root species trees; (2) <span class="hlt">Modeling</span> <span class="hlt">evolution</span> of complex genomic characters and processes that are non-reversible and non-stationary is required to reconstruct the polarized <span class="hlt">evolution</span> of the ToL; (3) Rooting experiments and Bayesian <span class="hlt">model</span> selection tests overwhelmingly support the earlier finding that akaryotes and eukaryotes are sister clades that descend independently from UCA (Harish and Kurland, 2013); (4) Consistent ancestral state reconstructions from independent genome samplings confirm the previous finding that UCA features three fourths of the unique protein domain-superfamilies encoded by extant genomes. Copyright © 2017 Elsevier B.V. and Société Française de Biochimie et Biologie</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994PhRvL..73..906D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994PhRvL..73..906D"><span>Simple <span class="hlt">model</span> of self-organized biological <span class="hlt">evolution</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>de Boer, Jan; Derrida, Bernard; Flyvbjerg, Henrik; Jackson, Andrew D.; Wettig, Tilo</p> <p>1994-08-01</p> <p>We give an exact solution of a recently proposed self-organized critical <span class="hlt">model</span> of biological <span class="hlt">evolution</span>. We show that the <span class="hlt">model</span> has a power law distribution of durations of coevolutionary ``avalanches'' with a mean field exponent 3/2. We also calculate analytically the finite size effects which cut off this power law at times of the order of the system size.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://eric.ed.gov/?q=evolutionary+AND+algorithms&pg=2&id=EJ691535','ERIC'); return false;" href="https://eric.ed.gov/?q=evolutionary+AND+algorithms&pg=2&id=EJ691535"><span>Acquisition of Complex Systemic Thinking: Mental <span class="hlt">Models</span> of <span class="hlt">Evolution</span></span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>d'Apollonia, Sylvia T.; Charles, Elizabeth S.; Boyd, Gary M.</p> <p>2004-01-01</p> <p>We investigated the impact of introducing college students to complex adaptive systems on their subsequent mental <span class="hlt">models</span> of <span class="hlt">evolution</span> compared to those of students taught in the same manner but with no reference to complex systems. The students' mental <span class="hlt">models</span> (derived from similarity ratings of 12 evolutionary terms using the pathfinder algorithm)…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=Complex+AND+adaptive+AND+system&pg=5&id=EJ691535','ERIC'); return false;" href="http://eric.ed.gov/?q=Complex+AND+adaptive+AND+system&pg=5&id=EJ691535"><span>Acquisition of Complex Systemic Thinking: Mental <span class="hlt">Models</span> of <span class="hlt">Evolution</span></span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>d'Apollonia, Sylvia T.; Charles, Elizabeth S.; Boyd, Gary M.</p> <p>2004-01-01</p> <p>We investigated the impact of introducing college students to complex adaptive systems on their subsequent mental <span class="hlt">models</span> of <span class="hlt">evolution</span> compared to those of students taught in the same manner but with no reference to complex systems. The students' mental <span class="hlt">models</span> (derived from similarity ratings of 12 evolutionary terms using the pathfinder algorithm)…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3004014','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3004014"><span>Optimality <span class="hlt">models</span> in the age of experimental <span class="hlt">evolution</span> and genomics</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Bull, J. J.; Wang, I.-N.</p> <p>2010-01-01</p> <p>Optimality <span class="hlt">models</span> have been used to predict <span class="hlt">evolution</span> of many properties of organisms. They typically neglect genetic details, whether by necessity or design. This omission is a common source of criticism, and although this limitation of optimality is widely acknowledged, it has mostly been defended rather than evaluated for its impact. Experimental adaptation of <span class="hlt">model</span> organisms provides a new arena for testing optimality <span class="hlt">models</span> and for simultaneously integrating genetics. First, an experimental context with a well-researched organism allows dissection of the evolutionary process to identify causes of <span class="hlt">model</span> failure – whether the <span class="hlt">model</span> is wrong about genetics or selection. Second, optimality <span class="hlt">models</span> provide a meaningful context for the process and mechanics of <span class="hlt">evolution</span>, and thus may be used to elicit realistic genetic bases of adaptation – an especially useful augmentation to well-researched genetic systems. A few studies of microbes have begun to pioneer this new direction. Incompatibility between the assumed and actual genetics has been demonstrated to be the cause of <span class="hlt">model</span> failure in some cases. More interestingly, <span class="hlt">evolution</span> at the phenotypic level has sometimes matched prediction even though the adaptive mutations defy mechanisms established by decades of classic genetic studies. Integration of experimental evolutionary tests with genetics heralds a new wave for optimality <span class="hlt">models</span> and their extensions that does not merely emphasize the forces driving <span class="hlt">evolution</span>. PMID:20646132</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/7152761','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/7152761"><span>Simple <span class="hlt">model</span> of self-organized biological <span class="hlt">evolution</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>de Boer, J.; Derrida, B.; Flyvbjerg, H.; Jackson, A.D.; Wettig, T. The Isaac Newton Institute for Mathematical Sciences, 20 Clarkson Road, Cambridge, CB4 0EH Laboratoire de Physique Statistique, Ecole Normale Superieure, 24 rue Lhomond, F-75005 Paris Service de Physique Theorique, Centre de Etudes Nucleaires de Saclay, F-91191, Gif-Sur-Yvette CONNECT, The Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen )</p> <p>1994-08-08</p> <p>We give an exact solution of a recently proposed self-organized critical <span class="hlt">model</span> of biological <span class="hlt">evolution</span>. We show that the <span class="hlt">model</span> has a power law distribution of durations of coevolutionary avalanches'' with a mean field exponent 3/2. We also calculate analytically the finite size effects which cut off this power law at times of the order of the system size.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ThApC.tmp..256A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ThApC.tmp..256A"><span>Two years observations on the diurnal <span class="hlt">evolution</span> of coastal atmospheric boundary <span class="hlt">layer</span> features over Thiruvananthapuram (8.5∘ N, 76.9∘ E), India</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Anurose, T. J.; Subrahamanyam, D. Bala; Sunilkumar, S. V.</p> <p>2016-10-01</p> <p>The atmospheric boundary <span class="hlt">layer</span> (ABL) over a given coastal station is influenced by the presence of mesoscale sea breeze circulation, together with the local and synoptic weather, which directly or indirectly modulate the vertical thickness of ABL (z ABL). Despite its importance in the characterization of lower tropospheric processes and atmospheric <span class="hlt">modeling</span> studies, a reliable climatology on the temporal <span class="hlt">evolution</span> of z ABL is not available over the tropics. Here, we investigate the challenges involved in determination of the ABL heights, and discuss an objective method to define the vertical structure of coastal ABL. The study presents a two year morphology on the diurnal <span class="hlt">evolution</span> of the vertical thickness of sea breeze flow (z SBF) and z ABL in association with the altitudes of lifting condensation level (z LCL) over Thiruvananthapuram (8.5∘ N, 76.9∘ E), a representative coastal station on the western coastline of the Indian sub-continent. We make use of about 516 balloon-borne GPS sonde measurements in the present study, which were carried out as part of the tropical tropopause dynamics field experiment under the climate and weather of the sun-earth system (CAWSES)-India program. Results obtained from the present study reveal major differences in the temporal <span class="hlt">evolution</span> of the ABL features in relation to the strength of sea breeze circulation and monsoonal wind flow during the winter and summer monsoon respectively. The diurnal <span class="hlt">evolution</span> in z ABL is very prominent in the winter monsoon as against the summer monsoon, which is attributed to the impact of large-scale monsoonal flow over the surface <span class="hlt">layer</span> meteorology. For a majority of the database, the z LCL altitudes are found to be higher than that of the z ABL, indicating a possible decoupling of the ABL with the low-level clouds.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JASTP.134...69M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JASTP.134...69M"><span>On the possible role of zonal dynamics in the formation and <span class="hlt">evolution</span> of F3 <span class="hlt">layers</span> over equator</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mridula, N.; Pant, Tarun Kumar</p> <p>2015-11-01</p> <p>In the present study, occurrences of F3 <span class="hlt">layer</span> over Thiruvananthapuram (8.5°N; 77°E; dip latitude ~0.5°N), a dip equatorial station in India have been investigated using ionosonde data for the years 2004-2007. The F3 <span class="hlt">layers</span> appearing in the ionograms during the pre noon hours only have been included in the analysis. The result indicates that a weak EIA resulting in low ionospheric height and high ionization density prevails before the occurrence of F3 <span class="hlt">layer</span> and serves as an essential condition for its occurrence. The relative Slant Total Electron Content (rSTEC) measured using collocated ground based coherent low earth orbiting (LEO) radio beacon receiver has also been used along with electron densities measured by CHAMP satellite for the year 2006 and 2007 to illustrate this difference in the <span class="hlt">evolution</span> of Equatorial Ionization Anomaly (EIA) on F3 and non F3 days. A new mechanism for F3 generation has been proposed. It has been shown that the coupling of the thermospheric zonal wind jet over equator and enhanced ionospheric density at lower heights over Indian longitude can account for the generation of F3 <span class="hlt">layer</span> through ion-drag. The vertical wind associated with the thermospheric heating resulting from ion-drag causes the generation of an additional eastward field which, along with the prevailing F-region electric field, leads to the upward excursion of the F3 <span class="hlt">layer</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25994213','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25994213"><span><span class="hlt">Layer</span>-controllable WS2-reduced graphene oxide hybrid nanosheets with high electrocatalytic activity for hydrogen <span class="hlt">evolution</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Jian; Wang, Qi; Wang, Lianhui; Li, Xing'ao; Huang, Wei</p> <p>2015-06-21</p> <p>In this study, an efficient poly(vinylpyrrolidone) (PVP)-assisted hydrothermal method for the in situ growth of WS2 nanosheets with <span class="hlt">layer</span>-controllability on reduced graphene oxide (rGO) is reported. The number of <span class="hlt">layers</span> (from a monolayer to ∼25 <span class="hlt">layers</span>) of the exfoliated WS2 can be accurately controlled by adjusting the amount of PVP. The <span class="hlt">layer</span> structure and the morphology of the as-prepared hybrids are confirmed by field emission scanning electron microscopy and high-resolution transmission microscopy. The X-ray diffraction, Raman, and X-ray photoemission spectroscopy of the obtained WS2-rGO hybrid nanosheets indicate highly crystallized structures, a clear Raman shift and a stoichiometry, which is dependent on the number of <span class="hlt">layers</span>. Furthermore, these highly active and durable catalysts exhibit an electrocatalytic current density of 10 mA cm(-2) at a small hydrogen <span class="hlt">evolution</span> reaction (HER) overpotential (-170 mV) and a Tafel slope of 52 mV dec(-1) with an excellent electrocatalytic stability (after 6 months storage).</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Nanos...710391Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Nanos...710391Z"><span><span class="hlt">Layer</span>-controllable WS2-reduced graphene oxide hybrid nanosheets with high electrocatalytic activity for hydrogen <span class="hlt">evolution</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Jian; Wang, Qi; Wang, Lianhui; Li, Xing'ao; Huang, Wei</p> <p>2015-06-01</p> <p>In this study, an efficient poly(vinylpyrrolidone) (PVP)-assisted hydrothermal method for the in situ growth of WS2 nanosheets with <span class="hlt">layer</span>-controllability on reduced graphene oxide (rGO) is reported. The number of <span class="hlt">layers</span> (from a monolayer to ~25 <span class="hlt">layers</span>) of the exfoliated WS2 can be accurately controlled by adjusting the amount of PVP. The <span class="hlt">layer</span> structure and the morphology of the as-prepared hybrids are confirmed by field emission scanning electron microscopy and high-resolution transmission microscopy. The X-ray diffraction, Raman, and X-ray photoemission spectroscopy of the obtained WS2-rGO hybrid nanosheets indicate highly crystallized structures, a clear Raman shift and a stoichiometry, which is dependent on the number of <span class="hlt">layers</span>. Furthermore, these highly active and durable catalysts exhibit an electrocatalytic current density of 10 mA cm-2 at a small hydrogen <span class="hlt">evolution</span> reaction (HER) overpotential (-170 mV) and a Tafel slope of 52 mV dec-1 with an excellent electrocatalytic stability (after 6 months storage).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016OSID...2350016S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016OSID...2350016S"><span>On the General Class of <span class="hlt">Models</span> of Adiabatic <span class="hlt">Evolution</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sun, Jie; Lu, Songfeng; Liu, Fang</p> <p>2016-10-01</p> <p>The general class of <span class="hlt">models</span> of adiabatic <span class="hlt">evolution</span> was proposed to speed up the usual adiabatic computation in the case of quantum search problem. It was shown [8] that, by temporarily increasing the ground state energy of a time-dependent Hamiltonian to a suitable quantity, the quantum computation can perform the calculation in time complexity O(1). But it is also known that if the overlap between the initial and final states of the system is zero, then the computation based on the generalized <span class="hlt">models</span> of adiabatic <span class="hlt">evolution</span> can break down completely. In this paper, we find another severe limitation for this class of adiabatic <span class="hlt">evolution</span>-based algorithms, which should be taken into account in applications. That is, it is still possible that this kind of <span class="hlt">evolution</span> designed to deal with the quantum search problem fails completely if the interpolating paths in the system Hamiltonian are chosen inappropriately, while the usual adiabatic <span class="hlt">evolutions</span> can do the same job relatively effectively. This implies that it is not always recommendable to use nonlinear paths in adiabatic computation. On the contrary, the usual simple adiabatic <span class="hlt">evolution</span> may be sufficient for effective use.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JPhCS.811a2010P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JPhCS.811a2010P"><span>Order reduction for a <span class="hlt">model</span> of marine bacteriophage <span class="hlt">evolution</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pagliarini, Silvia; Korobeinikov, Andrei</p> <p>2017-02-01</p> <p>A typical mechanistic <span class="hlt">model</span> of viral <span class="hlt">evolution</span> necessary includes several time scales which can differ by orders of magnitude. Such a diversity of time scales makes analysis of these <span class="hlt">models</span> difficult. Reducing the order of a <span class="hlt">model</span> is highly desirable when handling such a <span class="hlt">model</span>. A typical approach applied to such slow-fast (or singularly perturbed) systems is the time scales separation technique. Constructing the so-called quasi-steady-state approximation is the usual first step in applying the technique. While this technique is commonly applied, in some cases its straightforward application can lead to unsatisfactory results. In this paper we construct the quasi-steady-state approximation for a <span class="hlt">model</span> of <span class="hlt">evolution</span> of marine bacteriophages based on the Beretta-Kuang <span class="hlt">model</span>. We show that for this particular <span class="hlt">model</span> the quasi-steady-state approximation is able to produce only qualitative but not quantitative fit.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10185545','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10185545"><span><span class="hlt">Modeling</span> the connection between development and <span class="hlt">evolution</span>: Preliminary report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mjolsness, E.; Reinitz, J.; Garrett, C.D.; Sharp, D.H.</p> <p>1993-07-29</p> <p>In this paper we outline a <span class="hlt">model</span> which incorporates development processes into an evolutionary frame work. The <span class="hlt">model</span> consists of three sectors describing development, genetics, and the selective environment. The formulation of <span class="hlt">models</span> governing each sector uses dynamical grammars to describe processes in which state variables evolve in a quantitative fashion, and the number and type of participating biological entities can change. This program has previously been elaborated for development. Its extension to the other sectors of the <span class="hlt">model</span> is discussed here and forms the basis for further approximations. A specific implementation of these ideas is described for an idealized <span class="hlt">model</span> of the <span class="hlt">evolution</span> of a multicellular organism. While this <span class="hlt">model</span> doe not describe an actual biological system, it illustrates the interplay of development and <span class="hlt">evolution</span>. Preliminary results of numerical simulations of this idealized <span class="hlt">model</span> are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PhDT.......219L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PhDT.......219L"><span>Turbulence <span class="hlt">modeling</span> for shock wave/turbulent boundary <span class="hlt">layer</span> interactions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lillard, Randolph Pascal</p> <p></p> <p>Accurate aerodynamic computational predictions are essential for the safety of space vehicles, but these computations are of limited accuracy when large pressure gradients are present in the flow. The goal of the current project is to improve the state of compressible turbulence <span class="hlt">modeling</span> for high speed flows with shock wave / turbulent boundary <span class="hlt">layer</span> interactions (SWTBLI). Emphasis is placed on <span class="hlt">models</span> that can accurately predict the separated region caused by SWTBLI. These flows are classified as nonequilibrium boundary <span class="hlt">layers</span> because of the very large and variable adverse pressure gradients caused by the shock waves. The Lag <span class="hlt">model</span> was designed to <span class="hlt">model</span> these nonequilibrium flows by incorporating history effects. Standard one- and two-equation <span class="hlt">models</span> (Spalart Allmaras and SST) and the Lag <span class="hlt">model</span> are run and compared to the new <span class="hlt">model</span>. The focus of this work is thus to introduce a new <span class="hlt">model</span> that builds on the success of the Lag <span class="hlt">model</span>, but uses the Reynolds Stress Tensor (RST) as the lagged variable. This new <span class="hlt">model</span>, the Reynolds stress tensor lag <span class="hlt">model</span> (lagRST), is assessed against multiple wind tunnel tests and correlations as well as other <span class="hlt">models</span>. The basis of the Lag and lagRST <span class="hlt">models</span> is to preserve the accuracy of the standard turbulence <span class="hlt">models</span> in equilibrium turbulence, when the Reynolds stresses are linearly related to the mean strain rates, but create a lag between mean strain rate effects and turbulence when nonequilibrium effects become important, such as in large pressure gradients. The effect this lag has on the results for SWTBLI and massively separated flows is determined. These computations are done with a modified version of the OVERFLOW code. This code solves the Reynolds Averaged Navier Stokes (RANS) equations on overset grids. It was used for this study for its ability to input very complex geometries into the flow solver, such as the Space Shuttle in the full stack configuration. The <span class="hlt">model</span> was successfully implemented within two versions of the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2935103','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2935103"><span>Experimental <span class="hlt">evolution</span> of viruses: Microviridae as a <span class="hlt">model</span> system</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Wichman, Holly A.; Brown, Celeste J.</p> <p>2010-01-01</p> <p>φX174 was developed as a <span class="hlt">model</span> system for experimental studies of <span class="hlt">evolution</span> because of its small genome size and ease of cultivation. It has been used extensively to address statistical questions about the dynamics of adaptive <span class="hlt">evolution</span>. Molecular changes seen during experimental <span class="hlt">evolution</span> of φX174 under a variety of conditions were compiled from 10 experiments comprising 58 lineages, where whole genomes were sequenced. A total of 667 substitutions was seen. Parallel <span class="hlt">evolution</span> was rampant, with over 50 per cent of substitutions occurring at sites with three or more events. Comparisons of experimentally evolved sites to variation seen among wild phage suggest that at least some of the adaptive mechanisms seen in the laboratory are relevant to adaptation in nature. Elucidation of these mechanisms is aided by the availability of capsid and pro-capsid structures for φX174 and builds on years of genetic studies of the phage life history. PMID:20643739</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001PhFl...13...20G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001PhFl...13...20G"><span>An extended Rayleigh <span class="hlt">model</span> of bubble <span class="hlt">evolution</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Glinsky, Michael E.; Bailey, David S.; London, Richard A.; Amendt, Peter A.; Rubenchik, Alexander M.; Strauss, Moshe</p> <p>2001-01-01</p> <p>An extended Rayleigh <span class="hlt">model</span> for laser generated bubbles in water and soft tissue is presented. This <span class="hlt">model</span> includes surface tension, viscosity, a realistic equation of state, material strength and failure, stress wave emission, and linear growth of interface instabilities. The <span class="hlt">model</span> is validated by comparison to detailed compressible hydrodynamic simulations using the LATIS computer program. The purpose of this study is to investigate the use of the extended Rayleigh <span class="hlt">model</span> as a much faster and simpler substitute for the detailed hydrodynamic simulations when only limited information is needed. It is also meant to benchmark the hydrosimulations and highlight the relevant physics. The extended Rayleigh <span class="hlt">model</span> and the hydrosimulations are compared using both a 1D spherical geometry with a bubble in the center and a 2D cylindrical geometry of a laser fiber immersed in water with a bubble formed at the end of the fiber. Studies are done to test the validity of the material strength and failure, stress wave emission, and the interface instability terms in the extended Rayleigh <span class="hlt">model</span>. The resulting bubble radii, material damage radii, the emitted stress wave energies, and the size of the interface distortions are compared. Many of the trends found in the hydrosimulations are illuminated by the extended Rayleigh <span class="hlt">model</span> owing to its relative simplicity. The extended Rayleigh <span class="hlt">model</span> is very useful since it is accurate over a large range of parameters and it is computationally much faster than the hydrosimulations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22420795','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22420795"><span>Photocatalytic O{sub 2} <span class="hlt">evolution</span> from water over Zn–Cr <span class="hlt">layered</span> double hydroxides intercalated with inorganic anions</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hirata, Naoya; Tadanaga, Kiyoharu; Tatsumisago, Masahiro</p> <p>2015-02-15</p> <p>Graphical abstract: The photocatalytic activity of Zn–Cr LDHs intercalated with various inorganic anions was studied by O{sub 2} <span class="hlt">evolution</span> from aqueous solution of AgNO{sub 3} as a sacrificial agent. All the prepared LDHs showed photocatalytic activity under either UV and/or visible light irradiation. The interlayer anions affected the photocatalytic activity of the LDHs. - Highlights: • Zn–Cr <span class="hlt">layered</span> double hydroxides intercalated with inorganic anions were synthesized. • Photocatalytic activity of the LDHs was studied by O{sub 2} <span class="hlt">evolution</span>. • All the prepared LDHs showed photocatalytic activity under either UV and/or visible light irradiation. • The interlayer anions affected the photocatalytic activity of the LDHs. - Abstract: Zn–Cr <span class="hlt">layered</span> double hydroxides (LDHs) intercalated with inorganic anions (CO{sub 3}{sup 2−}, Cl{sup −}, SO{sub 4}{sup 2−} and NO{sub 3}{sup −}) were synthesized by the co-precipitation method and the anion exchange process. The photocatalytic activity of the LDHs was studied by O{sub 2} <span class="hlt">evolution</span> from aqueous solution of AgNO{sub 3} as a sacrificial agent. All the prepared LDHs showed photocatalytic activity under either UV and/or visible light irradiation. Besides, the interlayer anions affected the photocatalytic activity of the LDHs. After irradiation, Ag particles were formed on the LDHs by accepting the electrons generated during the photocatalytic reaction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JGRE..11512003K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JGRE..11512003K"><span>Shapes of two-<span class="hlt">layer</span> <span class="hlt">models</span> of rotating planets</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kong, D.; Zhang, K.; Schubert, G.</p> <p>2010-12-01</p> <p>To first approximation the interiors of many planetary bodies consist of a core and mantle with significantly different densities. The shapes of the surface and interface between the core and the mantle are basic properties reflecting planetary structure and rotation. In addition, interface shape is an important parameter controlling the dynamics of a fluid core. We present a theory for the rotational distortion of a two-<span class="hlt">layer</span> <span class="hlt">model</span> of a planet (two-<span class="hlt">layer</span> Maclaurin spheroid) that determines the shapes of both the interface and the outer free surface without treating departure from sphericity as a small perturbation. Since the interface and the outer free surface, in general, have different shapes, two different spheroidal coordinates are required in the mathematical analysis, and the transformation between them is at the heart of the complexity of the theory. Furthermore, two different cases have to be considered. In the first case, the core is sufficiently large, or the rate of rotation is sufficiently small, that the foci of the outer free surface are located within the core. In the second case, the core is sufficiently small, or the rate of rotation is sufficiently fast, that the foci of the free surface are located within the outer <span class="hlt">layer</span>. In comparison to the classical Maclaurin solution which is explicitly analytical, the relevant multiple integrals for the equilibrium solution of a two-<span class="hlt">layer</span> Mac