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Last update: November 12, 2013.

1

NASA Astrophysics Data System (ADS)

Hypocenter determination of micro-earthquakes of Mount "X-1" geothermal field has been conducted using simulated annealing and guided error search method using a 1D seismic velocity model. In order to speed up the hypocenter determination process a three-circle intersection method has been used to guide the simulated annealing and guided error search process. We used P and S arrival time's microseismic data. In the simulated annealing and guided error search processes, the minimum travel time from a source to a receiver has been calculated by employing ray tracing with shooting method. The resulting hypocenters from the above process occurred at depths of 3-4 km below mean sea level. These hypocenter distributions are correlated with previous study which was concluded that the most active microseismic area in which the site of many fractures and also vertical circulation place. Later on, resulting hypocenters location was used as input to determine 1-D seismic velocity using joint hypocenter determination method. The results of VELEST indicate show low Vp/Vs ratio value at depths of 3-4 km. Our interpretation is this anomaly may be related to a rock layer which is saturated by vapor (gas or steam). Another feature is high Vp/Vs ratio value at depths of 1-3 km that may related to a rock layer which is saturated by fluid or partial melting. We also analyze the focal mechanism of microseismic using ISOLA method to determine the source characteristic of this event.

Akbar, Akhmad Fanani; Nugraha, Andri Dian; Sule, Rachmat; Juanda, Aditya Abdurrahman

2013-09-01

2

NASA Astrophysics Data System (ADS)

We present a 1-D velocity model of the Earth's crust in Campania-Lucania region obtained by solving the coupled hypocentre-velocity inverse problem for 1312 local earthquakes recorded at a dense regional network. The model is constructed using the VELEST program, which calculates 1-D `minimum' velocity model from body wave traveltimes, together with station corrections, which account for deviations from the simple 1-D structure. The spatial distribution of station corrections correlates with the P-wave velocity variations of a preliminary 3-D crustal velocity model that has been obtained from the tomographic inversion of the same data set of P traveltimes. We found that station corrections reflect not only inhomogeneous near-surface structures, but also larger-scale geological features associated to the transition between carbonate platform outcrops at Southwest and Miocene sedimentary basins at Northeast. We observe a significant trade-off between epicentral locations and station corrections, related to the existence of a thick low-velocity layer to the NE. This effect is taken into account and minimized by re-computing station corrections, fixing the position of a subset of well-determined hypocentres, located in the 3-D tomographic model.

Matrullo, Emanuela; De Matteis, Raffaella; Satriano, Claudio; Amoroso, Ortensia; Zollo, Aldo

2013-10-01

3

A method is presented for deriving 1-D velocity depth models from earthquake bulletin data. The models can be used as initial\\u000a models for more advanced modelling techniques such as tomographic inversion. The method is useful when there is little or\\u000a no refraction and long-range reflection survey data. The bulletin travel times are subjected to an analysis of variance, where\\u000a they

David C. Booth

2010-01-01

4

A 1-D model of sinking particles

NASA Astrophysics Data System (ADS)

Acidification of the surface ocean due to increased atmospheric CO2 levels is altering its saturation state with respect to calcium carbonate (Orr et al., 2005) and the ability of calcifying phytoplankton to calcify (Riebesell et al., 2000). Sequestration of atmospheric carbon dioxide into the deep ocean is affected by this, because calcite is the key component in ballasting sinking particles (Klaas and Archer, 2001). The settling velocity of particles is not explicitly modeled but often represented as a constant in climate models. That is clearly inaccurate as the composition of particles changes with depth as bacteria and dissolution processes act on its different components, changing their ratio with depth. An idealized, mechanistic model of particles has been developed where settling velocity is calculated from first principles. The model is forced 100m below the surface with export ratios (organic carbon/calcium carbonate) corresponding to different CO2 levels according to Riebesell et al. The resulting flux is compared to the flux generated by the same model where the settling velocity is held constant. The model produces a relatively constant rain ratio regardless of the amount of calcite available to ballast the particle, which is what data suggests (Conte et al., 2001), whereas a constant velocity model does not. Comparing the flux of particulate organic carbon to the seafloor with increasing CO2 levels, the outcome of the constant velocity model is an increase whereas when the velocity is calculated a decrease results. If so, the change in export ratio with an increase in CO2 concentrations acts as a positive feedback: as increased atmospheric CO2 levels lead to the ocean pH being lowered, reduced calcification of marine organisms results and a decrease in particulate organic carbon flux to the deep ocean, which again raises CO2 concentrations. Conte, M.,, N. Ralph, E. Ross, Seasonal and interannual variability in deep ocean particle fluxes at the Oceanic Flux Program (OFP)/Bermuda Atlantic Time Series (BATS) site in the western Sargasso Sea near Bermuda, Deep-Sea Research II 48 1471-1505, 2001 Klaas, C., and D.E. Archer, Association of sinking organic matter with various types of mineral ballast in the deep sea: Implications for the rain ratio, Global Biogeochemical Cycles, 16, 2002. Orr, J. C. and et. al. Anthropogenic ocean acidification over calcifying organisms. Nature, 437(29):681 686, 2005. U. Riebesell, I. Zondervan, B. Rost, P.D. Tortell, R.E. Zeebe, and F.M.M.Morel. Reduced calcification of marine plankton in response to increased atmospheric CO2. Nature, 407:364 368, 2000.

Jokulsdottir, T.; Archer, D.

2006-12-01

5

1D toy model for magnetic trapping

NASA Astrophysics Data System (ADS)

We study, both classically and quantum mechanically, the problem of a neutral particle with a spin angular momentum S, mass m, and magnetic moment ?, moving in one dimension in an inhomogeneous magnetic field given by B=B0?+B?'x?. This problem serves for us as a toy model to study the trapping of neutral particles. We identify K?[S2(B?')2/?mB03], which is the ratio between the precessional frequency of the particle and its vibrational frequency, as the relevant parameter of the problem. Classically, we find that when ? is antiparallel to B, the particle is trapped provided that K<0.5. We also find that viscous friction, be it translational or precessional, destabilizes the system. Quantum mechanically, we study the problem of a spin S=?/2 particle in the same field. Treating K as a small parameter for the perturbation from the adiabatic Hamiltonian, we find that the lifetime Tesc of the particle in its trapped ground state is Tesc=(Tvib/2?)(1/8?K)exp(2/K), where Tvib=2?mB0/?(B?')2 is the classical period of the particle when placed in the adiabatic potential V=?|B|.

Gov, S.; Shtrikman, S.; Thomas, H.

2000-04-01

6

ERIC Educational Resources Information Center

|Using a simultaneously falling softball as a stopwatch, the terminal velocity of a whiffle ball can be obtained to surprisingly high accuracy with only common household equipment. This classroom activity engages students in an apparently daunting task that nevertheless is tractable, using a simple model and mathematical techniques at their…

Brand, Neal; Quintanilla, John A.

2013-01-01

7

GIS-BASED 1-D DIFFUSIVE WAVE OVERLAND FLOW MODEL

This paper presents a GIS-based 1-d distributed overland flow model and summarizes an application to simulate a flood event. The model estimates infiltration using the Green-Ampt approach and routes excess rainfall using the 1-d diffusive wave approximation. The model was designed to use readily available topographic, soils, and land use/land cover data and rainfall predictions from a meteorological model. An assessment of model performance was performed for a small catchment and a large watershed, both in urban environments. Simulated runoff hydrographs were compared to observations for a selected set of validation events. Results confirmed the model provides reasonable predictions in a short period of time.

KALYANAPU, ALFRED [Los Alamos National Laboratory; MCPHERSON, TIMOTHY N. [Los Alamos National Laboratory; BURIAN, STEVEN J. [NON LANL

2007-01-17

8

A 1-D morphodynamic model for rill erosion

The key objective of this paper is to develop a 1-D hydrodynamic and sediment transport model, namely, RILL1D, that handles transcritical flows over abrupt changes (e.g., formation of pool crests and width change) in a single rill and also predicts changes in rill bed elevation. Replication of rill conditions in terms of flow and bed evolution changes necessitated the use

Athanasios N. Papanicolaou; John T. Sanford; Dimitrios C. Dermisis; Gabriel A. Mancilla

2010-01-01

9

Updated Western Montana Velocity Model With Regional Model Comparison

NASA Astrophysics Data System (ADS)

We determined a new crust and upper mantle velocity model for western Montana using a 1-D layered earth approach. P-wave arrival times recorded on 358 stations from 1,432 well recorded earthquakes provided input for a sparse damped least squares sensitivity matrix. We solved for 1-D velocity structure, depth boundary (refractor) positions, station corrections, and hypocentral positions from calculations of travel-time residuals. The final model showed the first layer having a velocity of 5.7 km/s and a depth of 7.0 km, the second layer having a velocity of 6.1 km/s and a depth of 19.8 km, the third layer having a velocity of 6.5 km/s and a depth of 39.7 km, and an upper mantel velocity of 8.0 km/s. We split the study area into subregions and separately determined 1-D velocity models for each subregion to observe lateral velocity variations. Velocity models determined for subregions showed a maximum difference of 0.25 km/s velocity and 3.5 km layer-thickness variations from the model obtained for the entire study area. Station corrections computed for the subregions and the entire study area were correlated to local travel-time anomalies rather than anomalies of wider extents associated with multiple stations. The new model and station corrections improve resolution and accuracy of hypocenter locations for western Montana earthquakes. A comparison of published velocity models for the Intermountain Seismic Belt of western Montana shows significant trends of the crustal thickness changes. 1-D velocity models from eastern Washington, the Yellowstone Caldera, the Snake River Plain, and eastern Montana suggest that the crust gradually thickens from NW to SE across the region. The subregions velocity model analysis showed a thicker high velocity layer for the central part of the study area. A 3-D velocity model in development for our study area should refine this interpretation.

Zeiler, C. P.; Stickney, M. C.; Speece, M. A.

2003-12-01

10

Quantum Phase Transition in 1-D Extended Hubbard Model

NASA Astrophysics Data System (ADS)

Recently Nakamura has re-examined the 1-D Extended Hubbard Model (EHM) at half-filling and has argued for the existence of a Bond Order Wave (BOW) phase in a narrow strip around U ? 2V between the well-known phases with dominant Spin Density Wave (SDW) correlations (for lower V/U) and the long-range Charge Density Wave (CDW) (for higher V/U). To investigate further this surprising result, we study the ground state phase diagram of the 1-D EHM in this region using a Quantum Monte Carlo method. Our results confirm the existence of the long-range BOW phase. We examine in detail the CDW to BOW transition and determine the location of the tricritical point where the transition changes from a continuous CDW-BOW to a discontinuous, direct CDW-SDW with no intervening BOW phase.

Sengupta, Pinaki; Sandvik, Anders; Campbell, David K.

2000-03-01

11

Aging in 1D Discrete Spin Models and Equivalent Systems

We derive exact expressions for a number of aging functions that are scaling limits of nonequilibrium correlations, R(t{sub w},t{sub w}+t) as t{sub w}ââ , t\\/t{sub w}âÎ¸ , in the 1D homogenous q -state Potts model for all q with T=0 dynamics following a quench from T=â . One such quantity is <{rvec Ï}â( t{sub w})Â·{rvec Ï}{sub n}(t{sub w}+t)> when n\\/t{sub

L. R. G. Fontes; M. Isopi; C. M. Newman; D. L. Stein

2001-01-01

12

Examination of 1D Solar Cell Model Limitations Using 3D SPICE Modeling: Preprint

To examine the limitations of one-dimensional (1D) solar cell modeling, 3D SPICE-based modeling is used to examine in detail the validity of the 1D assumptions as a function of sheet resistance for a model cell. The internal voltages and current densities produced by this modeling give additional insight into the differences between the 1D and 3D models.

McMahon, W. E.; Olson, J. M.; Geisz, J. F.; Friedman, D. J.

2012-06-01

13

A 1-D model for highly sensitive tubular reactors

We consider the steady state operation of wall-cooled, fixed-bed tubular reactors. In these reactors the temperature rise ..delta..T must normally be limited to small fractions of the adiabatic temperature rise ..delta..T/sub ad/, both to avoid runaway and maintain product selectivity. Yet ..delta..T/..delta..T/sub ad/ << 1 can only occur if eta = t/sub dif//t/sub reac/ << 1, where t/sub dif/ is the timescale on which heat escapes the reactor by ''diffusing'' to the cooled walls, and t/sub reac/ is the timescale over which the reaction occurs. So here we use asymptotic methods based on eta << 1 to analyze the 2-d reactor equations, and find the radial concentration and temperature profiles to leading order in eta. We then obtain a 1-d model of the reactor by substituting these asymptotically correct profiles into the reactor equations and averaging over r. This model, the ..cap alpha..-model, is identical to the standard (Beek and Singer) 1-d model, except that the reactor's overall heat transfer coefficient U is a decreasing function of the temperature rise ..delta..T. This occurs because as ..delta..T increases, the reaction becomes increasingly concentrated near r = 0, causing a decreased heat transfer efficiency through the reactor's walls. By comparing it with numerical solutions of the original 2-d reactor equations, we find that the ..cap alpha..-model simulates the 2-d equations very accurately, even for highly sensitive reactors operated near runaway. We also find that a runaway criterion derived from the ..cap alpha..-model predicts the runaway transition of the original 2-d equations accurately, especially for highly sensitive reactors. 19 refs.

Hagan, P.S.; Herskowitz, M.; Pirkle, J.C.

1987-01-01

14

A 1-D model for highly sensitive tubular reactors

The authors consider the steady state operation of wall-cooled, fixed-bed tubular reactors. In these reactors the temperature rise ..delta..T must normally be limited to small fractions of the adiabatic temperature rise ..delta..T/sub ad/, both to avoid runaway and maintain product selectivity. Yet ..delta..T/..delta..T/sub ad/<< 1 can only occur if eta = t/sub dif//t/sub reac/ << 1, where t/sub dif/ is the timescale on which heat escapes the reactor by ''diffusing'' to the cooled walls, and t/sub reac/ is the timescale over which the reaction occurs. So here the authors use asymptotic methods based on eta << 1 to analyze the 2-d reactor equations, and find the radial concentration and temperature profiles to leading order in eta. The authors then obtain a 1-d model of the reactor by substituting these asymptotically correct profiles into the reactor equations and averaging over r. This model, the ..cap alpha..-model, is identical to the standard (Beek and Singer) 1-d model, except that the reactor's overall heat transfer coefficient U is a decreasing function at the temperature rise ..delta..T. This occurs because as ..delta..T increases, the reaction becomes increasingly concentrated near r=O, causing a decreased heat transfer efficiency through the reactor's wall. By comparing it with numerical solutions of the original 2-d reactor equations, the authors find that the ..cap alpha..-model simulates the 2-d equations very accurately, even for highly sensitive reactors operated near runaway. They also find that a runaway criterion derived from the ..cap alpha..-model predicts the runaway transition of the original 2-d equations accurately, especially for highly sensitive reactors.

Hagan, P.S.; Herskowitz, M.; Pirkle, J.C.

1987-01-01

15

DETERMINATION OF 1-D SHEAR WAVE VELOCITIES USING THE REFRACTION MICROTREMOR METHOD

Current commonly used techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use in most urban areas. They require large sources to be effective in noisy urban settings, or specialized independent recorders laid out in an extensive array. The refraction microtremor (ReMi) method (Louie, 2001) overcomes these problems by using standard P-wave recording

Satish Pullammanappallil; William Honjas; John N. Louie

2003-01-01

16

1D Hydrodynamical Models of Wind Driven Shocks in RS Ophiuchi (2006)

NASA Astrophysics Data System (ADS)

Following the early Swift X-ray observations of the latest outburst of RS Oph tep{bode06_vay}, we present new 1D hydrodynamical models of the system which take into account all three phases of the remnant evolution. The differences between this wind model and previous Primakoff-type simulations are described. A more complex structure, even in 1D, is revealed and key outburst parameters are varied. The shock velocities as a function of time are compared to the ones derived in Bode et al. (2006). We show how the manner in which the matter is ejected controls the evolution of the shock and for a well-cooled remnant, how the shock deceleration rate depends on the amount of energy that is radiated away.

Vaytet, N. M. H.; O'Brien, T. J.; Bode, M. F.

2008-12-01

17

a 1-D Toy Model of Globular Cluster Formation

NASA Astrophysics Data System (ADS)

We introduce a one-dimensional toy model of globular clusters which is a version of the gravitational sheets system, where mass and energy loss due to the evaporation of stars at the boundaries are taken into account. The system relaxes to a quasi-equilibrium state whose velocity distribution is well fitted by a truncated Gaussian, in agreement with King's suggestion. Moreover, we guess a form of the density profile inspired by Rybicki's isothermal solution, which is in good agreement with numerical data.

Fanelli, D.; Merafina, M.; Ruffo, S.

2002-12-01

18

3-D velocity model beneath Taal Volcano, Luzon Island Philippines

NASA Astrophysics Data System (ADS)

We derive a three dimensional velocity model of seismic waves beneath Taal Volcano, Philippines, from about 2300 local earthquakes recorded by the Taal Volcano seismic network during the time period from March 2008 to March 2010. In the early data processing stage, with the cross-correlation functions of continuous record of station pairs, unexpected linear drifting of clock time was clearly identified. The drifting rates of each problematic station were determined and the errors were corrected before further processing. With the corrected data, we first determined initial locations by using the program HYPO71 and the reference 1-D global model ak135. 749 well-located events with 3381 P-wave and 2896 S-wave arrivals were used to derive the 'minimum 1-D velocity model' with the program VELEST developed by Kissling to further improve the 1-D velocity model and event locations. With the robust 1-D velocity model and improved event locations, we inverted a high-resolution 3-D velocity model by using the program LOTOS-10 developed by Koulakov. We present the derived 3-D model and discuss its tectonic implications.

You, S.; Konstantinou, K. I.; Gung, Y.; Lin, C.

2011-12-01

19

NASA Astrophysics Data System (ADS)

There are several 3-D velocity structural models for the Kanto Basin in Japan. However, the velocity models are different because they have been constructed with separate data sets such as, geophysical, geological, and earthquake data. It is, therefore, important for the reliable prediction of long-period ground motions to validate those models based on the observed earthquake recordings. Tsuno et al. (2011) revised the depths of the seismic basement and sedimentary layer interfaces in the Yamanaka and Yamada (2006) model of the Kanto Basin by the inversion of H/V-spectra of coda waves. In this paper, we perform 1-D simulation of long-period S-waves (2-10 s) to verify the velocity structures in the Kanto Basin inverted from H/V-spectra of earthquake ground motions. Considering the simplicity in the estimation of source parameters, we simulate the long-period S-waves for the nearby intermediate depth moderate earthquakes. We compare only the first cycle of the observed and synthetic S-waveforms. Consequently, the comparison of the time window for velocity waveforms will be sufficiently ahead of the 3-D basin effects. References Tsuno, S., H. Yamanaka, S. Sakai, N. Hirata, K. Kasahara, H. Kimura, T. Aketagawa [2011], "Deep S-wave Velocity Structures in the Tokyo Metropolitan Area estimated by the H/V Spectral Ratio Using coda waves, 4th IASPEI/IAEE International Symposium on Effects of Surface Geology on Seismic Motion, UCSB, Aug 23-26. Yamanaka, H. and N. Yamada [2006], "Modeling 3D S-wave Velocity Structure of Kanto Basin for Estimation of Earthquake Ground Motion", Butsuri-Tansa, Vol. 59, No. 6, pp. 549-560 (in Japanese with English abstract).

Dhakal, Y. P.; Tsuno, S.; Yamanaka, H.

2011-12-01

20

Geostatistical Modeling of Pore Velocity

A significant part of evaluating a geologic formation as a nuclear waste repository involves the modeling of contaminant transport in the surrounding media in the event the repository is breached. The commonly used contaminant transport models are deterministic. However, the spatial variability of hydrologic field parameters introduces uncertainties into contaminant transport predictions. This paper discusses the application of geostatistical techniques to the modeling of spatially varying hydrologic field parameters required as input to contaminant transport analyses. Kriging estimation techniques were applied to Hanford Reservation field data to calculate hydraulic conductivity and the ground-water potential gradients. These quantities were statistically combined to estimate the groundwater pore velocity and to characterize the pore velocity estimation error. Combining geostatistical modeling techniques with product error propagation techniques results in an effective stochastic characterization of groundwater pore velocity, a hydrologic parameter required for contaminant transport analyses.

Devary, J.L.; Doctor, P.G.

1981-06-01

21

In this paper we derive one space dimensional, reduced systems of equations (1-D closure models) for viscoelastic free jets. We begin with the three-dimensional system of conservation laws and a Maxwell-Jeffreys constitutive law for an incompressible viscoelastic fluid. First, we exhibit exact truncations to a finite, closed system of 1-D equations based on classical velocity assumptions of von Karman. Next, we demonstrate that the 3-D free surface boundary conditions overconstrain these truncated systems, so that only a very limited class of solutions exist. We then proceed to derive approximate 1-D closure theories through a slender jet asymptotic scaling, combined with appropriate definitions of velocity, pressure and stress unknowns. Our nonaxisymmetric 1-D slender jet models incorporate the physical effects of inertia, viscoelasticity (viscosity, relaxation and retardation), gravity, surface tension, and properties of the ambient fluid, and include shear stresses and time dependence. Previous special 1-D slender jet models correspond to the lowest order equations in the present asymptotic theory by an a posteriori suppression to leading order of some of these effects, and a reduction to axisymmetry. Solutions of the lowest order system of equations in this asymptotic analysis are presented: For the special cases of elliptical inviscid and Newtonian free jets, subject to the effects of surface tension and gravity, our model predicts oscillation of the major axis of the free surface elliptical cross section between perpendicular directions with distance down the jet, and drawdown of the cross section, in agreement with observed behavior. 15 refs.

Bechtel, S.E.; Forest, M.G.; Holm, D.D.; Lin, K.J.

1988-01-01

22

Validation of 1-D transport and sawtooth models for ITER

In this paper the authors describe progress on validating a number of local transport models by comparing their predictions with relevant experimental data from a range of tokamaks in the ITER profile database. This database, the testing procedure and results are discussed. In addition a model for sawtooth oscillations is used to investigate their effect in an ITER plasma with alpha-particles.

Connor, J.W.; Turner, M.F. [UKAEA, Culham (United Kingdom); Attenberger, S.E.; Houlberg, W.A. [ORNL, Oak Ridge, TN (United States)] [and others

1996-12-31

23

Control oriented 1D electrochemical model of lithium ion battery

Lithium ion (Li-ion) batteries provide high energy and power density energy storage for diverse applications ranging from cell phones to hybrid electric vehicles (HEVs). For efficient and reliable systems integration, low order dynamic battery models are needed. This paper introduces a general method to generate numerically a fully observable\\/controllable state variable model from electrochemical kinetic, species and charge partial differential

Kandler A. Smith; Christopher D. Rahn; Chao-Yang Wang

2007-01-01

24

Despite a high degree of conservation, subtle but important differences exist between the CD1d antigen presentation pathways of humans and mice. These differences may account for the minimal success of natural killer T (NKT) cell-based antitumor therapies in human clinical trials, which contrast strongly with the powerful antitumor effects in conventional mouse models. To develop an accurate model for in vivo human CD1d (hCD1d) antigen presentation, we have generated a hCD1d knock-in (hCD1d-KI) mouse. In these mice, hCD1d is expressed in a native tissue distribution pattern and supports NKT cell development. Reduced numbers of invariant NKT (iNKT) cells were observed, but at an abundance comparable to that in most normal humans. These iNKT cells predominantly expressed mouse V?8, the homolog of human V?11, and phenotypically resembled human iNKT cells in their reduced expression of CD4. Importantly, iNKT cells in hCD1d knock-in mice exert a potent antitumor function in a melanoma challenge model. Our results show that replacement of mCD1d by hCD1d can select a population of functional iNKT cells closely resembling human iNKT cells. These hCD1d knock-in mice will allow more accurate in vivo modeling of human iNKT cell responses and will facilitate the preclinical assessment of iNKT cell-targeted antitumor therapies. PMID:23382238

Wen, Xiangshu; Rao, Ping; Carreño, Leandro J; Kim, Seil; Lawrenczyk, Agnieszka; Porcelli, Steven A; Cresswell, Peter; Yuan, Weiming

2013-02-04

25

Kinetic and Stochastic Models of 1D yeast ``prions"

NASA Astrophysics Data System (ADS)

Mammalian prion proteins (PrP) are of public health interest because of mad cow and chronic wasting diseases. Yeasts have proteins, which can undergo similar reconformation and aggregation processes to PrP; yeast ``prions" are simpler to experimentally study and model. Recent in vitro studies of the SUP35 protein (1), showed long aggregates and pure exponential growth of the misfolded form. To explain this data, we have extended a previous model of aggregation kinetics along with our own stochastic approach (2). Both models assume reconformation only upon aggregation, and include aggregate fissioning and an initial nucleation barrier. We find for sufficiently small nucleation rates or seeding by small dimer concentrations that we can achieve the requisite exponential growth and long aggregates.

Kunes, Kay

2005-03-01

26

Kinetic Model for 1D aggregation of yeast ``prions''

NASA Astrophysics Data System (ADS)

Mammalian prion proteins (PrP) are of public health interest because of mad cow and chronic wasting diseases. Yeast have proteins which can undergo similar reconformation and aggregation processes to PrP; yeast forms are simpler to experimentally study and model. Recent in vitro studies of the SUP35 protein(1), showed long aggregates and pure exponential growth of the misfolded form. To explain this data, we have extended a previous model of aggregation kinetics(2). The model assumes reconformation only upon aggregation, and includes aggregate fissioning and an initial nucleation barrier. We find for sufficiently small nucleation rates or seeding by small dimer concentrations that we can achieve the requisite exponential growth and long aggregates. We will compare to a more realistic stochastic kinetics model and present prelimary attempts to describe recent experiments on SUP35 strains. *-Supported by U.S. Army Congressionally Mandated Research Fund. 1) P. Chien and J.S. Weissman, Nature 410, 223 (2001); http://online.kitp.ucsb.edu/online/bionet03/collins/. 2) J. Masel, V.A.> Jansen, M.A. Nowak, Biophys. Chem. 77, 139 (1999).

Kunes, Kay; Cox, Daniel; Singh, Rajiv

2004-03-01

27

Phase separation in the 1-D extended Hubbard model

We study phase boundary between phase separation region and region where superconducting pairing correlation functions show power law divergence for the one dimensional extended Hubbard model, for a wide range of parameters. Phase diagram are obtained from the second order perturbation theory, the mean-field approximation, quantum Monte Carlo simulations, and exact diagonalization studies. Analytical arguments for the general features of

H. Q. Lin; E. Gagliano; D. K. Campbell

1997-01-01

28

1D thermonuclear model for x-ray transients

The thermonuclear evolution of a 1.41 M solar mass neutron star, with a radius of 14.3 km, accreting various mixtures of hydrogen, helium, and heavy elements at rates of 10/sup -11/ to 10/sup -10/ M solar mass/yr is examined, in conjunction with S.E. Woosley and T.A. Weaver, using a one-dimensional numerical model. We have ignored any effects due to general relativity or magnetic fields. Two cases shall be discussed. In both models, the accretion rate is such that the hydrogen shell burns to helium in steady state, with the hydrogen burning stabilized by the ..beta..-limited CNO cycle. A thick helium shell is produced, which is eventually ignited under extremely degenerate conditions, producing a thermonuclear runaway.

Wallace, R.K.

1982-01-01

29

The exact solution of the 1-d Hubbard model

This paper presents a detailed discussion of the Bethe-Ansatz solution of the Hubbard model. The same spin formalism, previously employed for solving the Heisenberg, Kondo, and Backscattering (Gross-Neveu) models, can be applied, leading to a unified picture of the solutions and of the resulting physical consequences such as charge-spin decoupling and the occurrence of spin-1/2 excitations in the spin sector. These consequences are believed to hold in 2-dimensions and have shaped the understanding of high T{sub c} superconductivity within the strong correlation approach. This paper is outlined as follows: The model is transformed to a first quantized language where it describes particles hopping on the lattice interacting via spin exchanges. The author proceeds to construct eigenstates which have Bethe-Ansatz form and demonstrate the consistency of the approach. The imposition of periodic boundary conditions leads to an eigenstate problem in spin space which is solved via the Inverse Scattering method. As a result one obtains a set of coupled algebraic equations whose solutions are labeled by integers playing the roles of quantum numbers. Each label consists of a set of spin quantum number and a set of charge quantum numbers.

Andrei, N. (Rutgers State Univ. of New Jersey, Dept. of Physics and Astronomy, Piscataway, NJ (US))

1992-03-01

30

Model 1D (LHD) and 3D (CO5BOLD) spectra (Allende Prieto+, 2013)

NASA Astrophysics Data System (ADS)

Model spectral fluxes for late-type stars computed from 3D hydrodynamical simulations of surface convection performed with the CO5BOLD code. Their 1D hydrostatic counterparts are included, based on the LHD code, sharing the same microphysics as the CO5BOLD models. The fluxes for both the 3D and 1D models are calculated with the same opacities and radiative transfer code (ASSET). (6 data files).

Allende Prieto, C.; Koesterke, L. Ludwig H.-G.; Freytag, B.; Caffau, E.

2012-11-01

31

Metal-insulator transition in 1D Hubbard model

For the one-dimensional Hubbard model we extended the bosonization technique, away from half-filling, in such a way that a general formula is obtained for the zero temperature single-particle Green function with validity over the whole doping range. Our method allows us to calculate, for the first time, the one-body Green function in both Tomonaga-Luttinger and Luther-Emery universality classes, to characterize the crossover between these two behaviors and thus, to describe the metal-insulator transition. We have found that the transition can be characterized as a Brinkman-Rice transition with a diverging effective mass.

Gulacsi, M.; Bedell, K.S. (Theoretical Division, Los Alamos National Laboratory, MS-B262, Los Alamos, New Mexico 87545 (United States))

1994-04-25

32

Rattling and freezing in a 1D transport model

NASA Astrophysics Data System (ADS)

We consider a heat conduction model introduced by Collet and Eckmann (2009 Commun. Math. Phys. 287 1015-38). This is an open system in which particles exchange momentum with a row of (fixed) scatterers. We assume simplified bath conditions throughout, and give a qualitative description of the dynamics extrapolating from the case of a single particle for which we have a fairly clear understanding. The main phenomenon discussed is freezing, or the slowing down of particles with time. As particle number is conserved, this means fewer collisions per unit time, and less contact with the baths; in other words, the conductor becomes less effective. Careful numerical documentation of freezing is provided, and a theoretical explanation is proposed. Freezing being an extremely slow process; however, the system behaves as though it is in a steady state for long durations. Quantities such as energy and fluxes are studied, and are found to have curious relationships with particle density.

Eckmann, Jean-Pierre; Young, Lai-Sang

2011-01-01

33

Impurity of arbitrary spin embed in the 1-D Hubbard model with open boundary conditions

In this letter we study the exact solution of the 1-D Hubbard model with arbitrary spin impurity under the open boundary conditions by the coordinate Bethe ansatz method, then derive the eigenvalue and the corresponding Bethe ansatz equations

Bo-Yu Hou; Xiao-Qiang Xi; Rui-Hong Yue

1999-01-01

34

Coupled 1D-3D hydrodynamic modelling, with application to the Pearl River Delta

Within the hydrodynamic modelling community, it is common practice to apply different modelling systems for coastal waters and river systems. Whereas for coastal waters 3D finite difference or finite element grids are commonly used, river systems are generally modelled using 1D networks. Each of these systems is tailored towards specific applications. Three-dimensional coastal water models are designed to model the

Daniel J. Twigt; Erik D. de Goede; Firmijn Zijl; Dirk Schwanenberg; Alex Y. W. Chiu

2009-01-01

35

Surface impedance model for extraordinary transmission in 1D metallic and dielectric screens.

Extraordinary Optical Transmission of TM waves impinging at oblique incidence on metallic or high permittivity dielectric screens with a periodic distribution of 1D slits or any other kind of 1D defects is analyzed. Generalized waveguide theory altogether with the surface impedance concept are used for modeling such phenomena. A numerical analysis based on the mode matching technique proves to be an efficient tool for the characterization of these structures for any angle of incidence and slit or defect apertures. PMID:22273919

Delgado, V; Marqués, R

2011-12-01

36

NASA Astrophysics Data System (ADS)

Constructing seismic models of the Earth crust serves two major purposes: (i) helping to understand a geologic structure, and (ii) enabling investigations of earthquakes in terms of their location, centroid-moment-tensors, and/or slip-history on faults. We follow line (ii) where even good 1D models are still important. Should the 1D models be usable in seismic waveform modeling, the natural way is to derive them from full waveforms. We developed and tested a method in which full waveforms of an earthquake recorded in a network of local-to-regional stations are inverted into a 1D crustal model, optimally representing the seismic wave propagation. A single-point source approximation is used. The hypocenter position, origin time and a double-couple focal mechanism are fixed at previously determined values. The forward problem is solved by the Discrete Wavenumber method (Bouchon, 1981; Coutant 1989). The inverse problem is solved by the Neighborhood Algorithm (Sambridge, 1999), providing a suite of the well-fitting velocity models. The misfit function is the L2 norm of the difference between the observed and synthetic seismograms. The performance of the method is illustrated on the largest event (Mw 5.3) of the 2010 Efpalio earthquake sequence, Greece (Sokos et al., 2012). Broad-band data at 8 stations are used, spanning epicentral distances from 13 to 100 km. Several different parametrizations are tested. The most interesting results are obtained in the frequency range of 0.05-0.20 Hz for varying 7 layer thicknesses, their Vp and Vs. The corresponding waveform match (variance reduction VR~0.6) is significantly better than with the previously existing models of the region. It strengthens a chance to study some details of the space-time rupture process of future significant events in the Corinth Gulf. As revealed by the correlation and covariance matrices, the mutual trade-off between the thicknesses and velocities, as well as between Vp and Vs is negligible. The resolution decreases with depth. The best resolved is a significant Vs increase in the topmost 4 km; the Vp/Vs ratio in this layer is as large as ~2 - 2.5. Several path-dependent (single-station) 1D models were also constructed whose main importance was the stability check. Investigation of lateral crustal variations would require more earthquakes.

Plicka, Vladimir; Zahradnik, Jiri

2013-04-01

37

NASA Astrophysics Data System (ADS)

We propose a new quantitative determination of shear wave velocities for distinct geological units in the Bohemian Massif, Czech Republic (Central Europe). The phase velocities of fundamental Love wave modes are measured along two long profiles (~200 km) crossing three major geological units and one rift-like structure of the studied region. We have developed a modified version of the classical multiple filtering technique for the frequency-time analysis and we apply it to two-station phase velocity estimation. Tests of both the analysis and inversion are provided. Seismograms of three Aegean Sea earthquakes are analyzed. One of the two profiles is further divided into four shorter sub-profiles. The long profiles yield smooth dispersion curves; while the curves of the sub-profiles have complicated shapes. Dispersion curve undulations are interpreted as period-dependent apparent velocity anomalies caused both by different backazimuths of surface wave propagation and by surface wave mode coupling. An appropriate backazimuth of propagation is found for each period, and the dispersion curves are corrected for this true propagation direction. Both the curves for the long and short profiles are inverted for a 1D shear wave velocity model of the crust. Subsurface shear wave velocities are found to be around 2.9 km/s for all four studied sub-profiles. Two of the profiles crossing the older Moldanubian and Teplá-Barrandian units are characterized by higher velocities of 3.8 km/s in the upper crust while for the Saxothuringian unit we find the velocity slightly lower, around 3.6 km/s at the same depths. We obtain an indication of a shear wave low velocity zone above Moho in the Moldanubian and Teplá-Barrandian units. The area of the Eger Rift (Teplá-Barrandian-Saxothuringian unit contact) is significantly different from all other three units. Low upper crust velocities suggest sedimentary and volcanic filling of the rift as well as fluid activity causing the earthquake swarms. Higher velocities in the lower crust together with weak or even missing Moho implies the upper mantle updoming.

Kolínský, Petr; Málek, Ji?í; Brokešová, Johana

2011-01-01

38

The application of the Refraction Microtremor (ReMi) method on slopes affected by or prone to landsliding is complicated by the presence of lateral lithological heterogeneities and irregular topography, which may hinder the extension of the geophone array to the minimum lengths (100–200m) usually adopted in standard applications of this technique. We focus on deriving one-dimensional shear-wave velocity (Vs) vertical profiles

S. Coccia; V. Del Gaudio; N. Venisti; J. Wasowski

2010-01-01

39

SCEC UCVM - Unified California Velocity Model

NASA Astrophysics Data System (ADS)

The SCEC Unified California Velocity Model (UCVM) is a software framework for a state-wide California velocity model. UCVM provides researchers with two new capabilities: (1) the ability to query Vp, Vs, and density from any standard regional California velocity model through a uniform interface, and (2) the ability to combine multiple velocity models into a single state-wide model. These features are crucial in order to support large-scale ground motion simulations and to facilitate improvements in the underlying velocity models. UCVM provides integrated support for the following standard velocity models: SCEC CVM-H, SCEC CVM-S and the CVM-SI variant, USGS Bay Area (cencalvm), Lin-Thurber Statewide, and other smaller regional models. New models may be easily incorporated as they become available. Two query interfaces are provided: a Linux command line program, and a C application programming interface (API). The C API query interface is simple, fully independent of any specific model, and MPI-friendly. Input coordinates are geographic longitude/latitude and the vertical coordinate may be either depth or elevation. Output parameters include Vp, Vs, and density along with the identity of the model from which these material properties were obtained. In addition to access to the standard models, UCVM also includes a high resolution statewide digital elevation model, Vs30 map, and an optional near-surface geo-technical layer (GTL) based on Ely's Vs30-derived GTL. The elevation and Vs30 information is bundled along with the returned Vp,Vs velocities and density, so that all relevant information is retrieved with a single query. When the GTL is enabled, it is blended with the underlying crustal velocity models along a configurable transition depth range with an interpolation function. Multiple, possibly overlapping, regional velocity models may be combined together into a single state-wide model. This is accomplished by tiling the regional models on top of one another in three dimensions in a researcher-specified order. No reconciliation is performed within overlapping model regions, although a post-processing tool is provided to perform a simple numerical smoothing. Lastly, a 3D region from a combined model may be extracted and exported into a CVM-Etree. This etree may then be queried by UCVM much like a standard velocity model but with less overhead and generally better performance due to the efficiency of the etree data structure.

Small, P.; Maechling, P. J.; Jordan, T. H.; Ely, G. P.; Taborda, R.

2011-12-01

40

Validation of a Person Specific 1-D Model of the Systemic Arterial Tree

\\u000a The aim of this study is to validate a personspecific distributed model of the main systemic arterial tree, coupled to a model\\u000a of the left ventricle of the heart. This model is built and validated with non-invasive measurements on the same person, leading\\u000a therefore to a coherent set of physiological data. Although previous studies have been done on 1-D model

P. Reymond; Y. Bohraus; F. Perren; F. Lazeyras; N. Stergiopulos

41

An upper-mantle S-wave velocity model for Northern Europe from Love and Rayleigh group velocities

NASA Astrophysics Data System (ADS)

A model of upper-mantle S-wave velocity and transverse anisotropy beneath northwestern Europe is presented, based on regional surface wave observations. Group velocities for both Love and Rayleigh surface waves are measured on waveform data from international and regional data archives (including temporary deployments) and then inverted for group velocity maps, using a method accounting for Fresnel zone sensitivity. The group velocity variations are larger than in global reference maps, and we are able to resolve unprecedented details. We then apply a linear inversion scheme to invert for local 1-D shear wave velocity profiles which are consequently assembled to a 3-D model. By choosing conservative regularization parameters in the 2-D inversion, we ensure the smoothness of the group velocity maps and hence of the resulting 3-D shear wave speed model. To account for the different tectonic regimes in the study region and investigate the sensitivity of the 1-D inversions to inaccuracies in crustal parameters, we analyse inversions with different reference models of increasing complexity (pure 1-D, 3-D crust/1-D mantle and pure 3-D). We find that all inverted models are very consistent at depths below 70 km. At shallower depths, the constraints put by the reference models, primarily Moho depth which we do not invert for, remain the main cause for uncertainty in our inversion. The final 3-D model shows large variations in S-wave velocity of up to +/-12 per cent. We image an intriguing low-velocity anomaly in the depth range 70-150 km that extends from the Iceland plume beneath the North Atlantic and in a more than 400 km wide channel under Southern Scandinavia. Beneath Southern Norway, the negative perturbations are around 10 per cent with respect to ak135, and a shallowing of the anomaly is indicated which could be related to the sustained uplift of Southern Scandinavia in Neogene times. Furthermore, our upper-mantle model reveals good alignment to ancient plate boundaries and first-order crustal fronts around the triple junction of the Baltica-Avalonia-Laurentia collision in the North Sea.

Weidle, Christian; Maupin, Valérie

2008-12-01

42

Heat-transfer and solidification model of continuous slab casting: CON1D

A simple, but comprehensive model of heat transfer and solidification of the continuous casting of steel slabs is described,\\u000a including phenomena in the mold and spray regions. The model includes a one-dimensional (1-D) transient finite-difference\\u000a calculation of heat conduction within the solidifying steel shell coupled with two-dimensional (2-D) steady-state heat conduction\\u000a within the mold wall. The model features a detailed

Ya Meng; Brian G. Thomas

2003-01-01

43

Superposition of local zoom models and simultaneous calibration for 1D-2D shallow water flows

We address the problem of coupling 1D St-Venant equations (Shallow Water) with 2D ones, as applied to floodplain flows (river hydraulics). Continuous coupling condi- tions are derived, while numerical coupling is done using optimal control processes. In a variationnal data assimilation context, this approach allows to couple both models and assimilate data simultaneously. Two different versions of Joint Assimi- lation

J. Marin; Jérôme Monnier

2009-01-01

44

A simple 1D model with thermomechanical coupling for superelastic SMAs

NASA Astrophysics Data System (ADS)

This paper presents an outline for a new uniaxial model for shape memory alloys that accounts for thermomechanical coupling. The coupling provides an explanation of the dependence of SMA behavior on the loading rate. 1D simulations are carried in Matlab using simple finite-difference discretization of the mechanical and thermal equations.

Zaki, W.; Morin, C.; Moumni, Z.

2010-06-01

45

Thermodynamics of 1D N-Component Bariev Model Under Open Boundary Conditions

NASA Astrophysics Data System (ADS)

The thermodynamic Bethe ansatz equations and free energy for 1D N-component Bariev model under open boundary conditions are derived based on the string hypothesis for both, a repulsive and an attractive interaction. These equations are discussed in some limiting cases, such as the ground state, weak and strong couplings.

Wang, Chun; Ke, San-Min; Yue, Rui-Hong

2006-08-01

46

Quasi1D and 3D TPOX porous media diffuser reformer model

This paper focuses on the numerical simulations of methane thermal partial oxidation reforming process within inert porous media and their comparison with experiments. In order to produce hydrogen rich mixtures and for the sake of reaction stability, the reformer consists on a diffuser filled with porous media. The validity of using a quasi-1D approach to model this system is explored

J. M. C. Pereira; M. A. A. Mendes; D. Trimis; J. C. F. Pereira

2010-01-01

47

Minimal representations of supersymmetry and 1D N-Extended {sigma} models

We discuss the minimal representations of the 1D N-Extended Supersymmetry algebra (the Z{sub 2}-graded symmetry algebra of the Supersymmetric Quantum Mechanics) linearly realized on a finite number of fields depending on a real parameter t, the time. Their knowledge allows to construct onedimensional sigma-models with extended off-shell supersymmetries without using superfields.

Toppan, F., E-mail: toppan@cbpf.b [Centro Brasileiro de Pesquisa Fisicas (Brazil)

2010-03-15

48

NASA Astrophysics Data System (ADS)

It is well-known that meander bends impose local losses of energy to the flow in rivers. These local losses should be added together with friction loss to get the total loss of energy. In this work, we strive to develop a framework that considers the effect of bends in meandering rivers for one-dimensional (1-D) homogenous equations of flow. Our objective is to develop a simple, yet physically sound, and efficient model for carrying out engineering computations of flow through meander bends. We consider several approaches for calculating 1-D hydraulic properties of meandering rivers such as friction factor and Manning coefficient. The method of Kasper et al. (2005), which is based on channel top width, aspect ratio and radius of curvature, is adopted for further calculations. In this method, a correction is implemented in terms of local energy loss, due to helical motion and secondary currents of fluid particles driven by centrifugal force, in meanders. To validate the model, several test cases are simulated and the computed results are compared with the reported data in the literature in terms of water surface elevation, shear velocity, etc. For all cases the computed results are in reasonable agreement with the experimental data. 3-D RANS turbulent flow simulations are also carried out, using the method of Kang et al. (Adv. In Water Res., vol. 34, 2011), for different geometrical parameters of Kinoshita Rivers to determine the spatial distribution of shear stress on river bed and banks, which is the key factor in scour/deposition patterns. The 3-D solutions are then cross-sectionally averaged and compared with the respective solutions from the 1-D model. The comparisons show that the improved 1D model, which incorporates the effect of local bend loss, captures key flow parameters with reasonable accuracy. Our results also underscore the range of validity and limitations of 1D models for meander bend simulations. This work was supported by NSF Grants (as part of the National Center for Earth-Surface Dynamics). Computational resources were provided by the University of Minnesota Supercomputing Institute.

Haji Mohammadi, M.; Kang, S.; Sotiropoulos, F.

2011-12-01

49

Velocity-jump models with crowding effects

NASA Astrophysics Data System (ADS)

Velocity-jump processes are discrete random-walk models that have many applications including the study of biological and ecological collective motion. In particular, velocity-jump models are often used to represent a type of persistent motion, known as a run and tumble, that is exhibited by some isolated bacteria cells. All previous velocity-jump processes are noninteracting, which means that crowding effects and agent-to-agent interactions are neglected. By neglecting these agent-to-agent interactions, traditional velocity-jump models are only applicable to very dilute systems. Our work is motivated by the fact that many applications in cell biology, such as wound healing, cancer invasion, and development, often involve tissues that are densely packed with cells where cell-to-cell contact and crowding effects can be important. To describe these kinds of high-cell-density problems using a velocity-jump process we introduce three different classes of crowding interactions into a one-dimensional model. Simulation data and averaging arguments lead to a suite of continuum descriptions of the interacting velocity-jump processes. We show that the resulting systems of hyperbolic partial differential equations predict the mean behavior of the stochastic simulations very well.

Treloar, Katrina K.; Simpson, Matthew J.; McCue, Scott W.

2011-12-01

50

Implementation and Validation of a 1D Fluid Model for Collapsible Channels.

A 1D fluid model is implemented for the purpose of fluid-structure interaction (FSI) simulations in complex and completely collapsible geometries, particularly targeting the case of obstructive sleep apnea (OSA). The fluid mechanics are solved separately from any solid mechanics, making possible the use of a highly complex and/or black-box solver for the solid mechanics. The fluid model is temporally discretized with a second-order scheme and spatially discretized with an asymmetrical fourth-order scheme that is robust in highly uneven geometries. A completely collapsing and reopening geometry is handled smoothly using a modified area function. The numerical implementation is tested with two driven-geometry cases: (1) an inviscid analytical solution and (2) a completely closing geometry with viscous flow. Three-dimensional fluid simulations in static geometries are performed to examine the assumptions of the 1D model, and with a well-defined pressure-recovery constant the 1D model agrees well with 3D models. The model is very fast computationally, is robust, and is recommended for OSA simulations where the bulk flow pressure is primarily of interest. PMID:24008973

Anderson, Peter; Fels, Sidney; Green, Sheldon

2013-11-01

51

Coupled 1D-3D hydrodynamic modelling, with application to the Pearl River Delta

NASA Astrophysics Data System (ADS)

Within the hydrodynamic modelling community, it is common practice to apply different modelling systems for coastal waters and river systems. Whereas for coastal waters 3D finite difference or finite element grids are commonly used, river systems are generally modelled using 1D networks. Each of these systems is tailored towards specific applications. Three-dimensional coastal water models are designed to model the horizontal and vertical variability in coastal waters and are less well suited for representing the complex geometry and cross-sectional areas of river networks. On the other hand, 1D river network models are designed to accurately represent complex river network geometries and complex structures like weirs, barrages and dams. A disadvantage, however, is that they are unable to resolve complex spatial flow variability. In real life, however, coastal oceans and rivers interact. In deltaic estuaries, both tidal intrusion of seawater into the upstream river network and river discharge into open waters play a role. This is frequently approached by modelling the systems independently, with off-line coupling of the lateral boundary forcing. This implies that the river and the coastal model run sequentially, providing lateral discharge (1D) and water level (3D) forcing to each other without the possibility of direct feedback or interaction between these processes. An additional disadvantage is that due to the time aggregation usually applied to exchanged quantities, mass conservation is difficult to ensure. In this paper, we propose an approach that couples a 3D hydrodynamic modelling system for coastal waters (Delft3D) with a 1D modelling system for river hydraulics (SOBEK) online. This implies that contrary to off-line coupling, the hydrodynamic quantities are exchanged between the 1D and 3D domains during runtime to resolve the real-time exchange and interaction between the coastal waters and river network. This allows for accurate and mass conserving modelling of complex coastal waters and river network systems, whilst the advantages of both systems are maintained and used in an optimal and computationally efficient way. The coupled 1D-3D system is used to model the flows in the Pearl River Delta (Guangdong, China), which are determined by the interaction of the upstream network of the Pearl River and the open waters of the South China Sea. The highly complex upstream river network is modelled in 1D, simulating river discharges for the dry and wet monsoon periods. The 3D coastal model simulates the flow due to the external (ocean) periodic tidal forcing, the salinity distribution for both dry and wet seasons, as well as residual water levels (sea level anomalies) originating from the South China Sea. The model is calibrated and its performance extensively assessed against field measurements, resulting in a mean root mean square (RMS) error of below 6% for water levels over the entire Pearl River Delta. The model also represents both the discharge distribution over the river network and salinity transport processes with good accuracy, resolving the discharge distribution over the main branches of the river network within 5% of reported annual mean values and RMS errors for salinity in the range of 2 ppt (dry season) to 5 ppt (wet season).

Twigt, Daniel J.; de Goede, Erik D.; Zijl, Firmijn; Schwanenberg, Dirk; Chiu, Alex Y. W.

2009-12-01

52

On Parallel Computation of Blood Flow in Human Arterial Network Based on 1-D Modelling

In this study, parallel computation of blood flow in a 1-D model of human arterial network has been carried out employing a Taylor Galerkin Finite Element Method. Message passing interface libraries have been used on Origin 2000 SGI machine. A Greedy strategy for load-distribution has been devised and data-flow graphs necessary for parallelization have been generated. The performance of parallel

B. V. Rathish Kumar; Alfio Quarteroni; Luca Formaggia; Daniele Lamponi

2003-01-01

53

HELIOS-CR – A 1-D radiation-magnetohydrodynamics code with inline atomic kinetics modeling

HELIOS-CR is a user-oriented 1D radiation-magnetohydrodynamics code to simulate the dynamic evolution of laser-produced plasmas and z-pinch plasmas. It includes an in-line collisional-radiative (CR) model for computing non-LTE atomic level populations at each time step of the hydrodynamics simulation. HELIOS-CR has been designed for ease of use, and is well-suited for experimentalists, as well as graduate and undergraduate student researchers.

J. J. MacFarlane; I. E. Golovkin; P. R. Woodruff

2006-01-01

54

HELIOS-CR - A 1-D Radiation-Magnetohydrodynamics Code with Inline Atomic Kinetics Modeling

HELIOS-CR is a user-oriented 1D radiation-magnetohydrodynamics code to simulate the dynamic evolution of laser-produced plasmas and z-pinch plasmas. It includes an in-line collisional-radiative (CR) model for computing non-LTE atomic level populations at each time step of the hydrodynamics simulation. HELIOS-CR has been designed for ease of use, and is well-suited for experimentalists, as well as graduate and undergraduate student researchers.

J. J. MacFarlane; I. E. Golovkin; P. R. Woodruff

2005-01-01

55

Assessment of global phase velocity models

NASA Astrophysics Data System (ADS)

We construct new Love and Rayleigh wave phase velocity models based on measurements made from an aspherical starting model and strict data quality control derived from cluster analyses. These new models are in good agreement with previous ones and the question arises whether the slight changes show an improved capacity to explain the data. To this effect, we propose an objective method to compare different phase velocity models published in recent literature. The method is based on comparing calculated synthetics to raw seismograms. We find a reassuring convergence, between all the models we tested, at the longest periods and more scatter at the shorter periods. At 40s, the different models show gains of up to 3.5 cycles over PREM. Generally, the higher the gain over PREM, the smaller the period considered, which confirms that the Earth's heterogeneity is strongest in the uppermost parts of the Earth. Apart from assessing different models against each other, our method gives an estimate, comparable to cluster analyses, of the underlying data errors that went into the construction of the models themselves. Moreover, ray coverage is still far from perfect for constructing phase velocity models. As a result, we find that without precaution, degree zero is biased through spectral leakage by 0.1 to 0.2 per cent with respect to PREM.

Trampert, Jeannot; Woodhouse, and John H.

2001-01-01

56

The Hubbard model and optics: reflectivity of 1D and 2D systems

NASA Astrophysics Data System (ADS)

The Hubbard model (HM) was proposed around the middle of the last century as a model of the behavior of correlated electrons. It has so far been solved only in the 1D case. The HM is used in condensed matter physics in work on high Tc superconductors, organic conductors, graphene,... It is known that reflectivity is related to the electrical conductivity, and both quantities can be measured. This paper is divided into several sections. It begins with a brief introduction to the HM, and the links between the reflectivity and conductivity of a material with its parameters. In the second and third parts, the explicit calculations of the reflectivity of a 1D and 2D square rectangular lattices will be presented. Expressions for the reflectivity thus obtained are tied to the material parameters via previous results of the author on the conductivity of a 1D lattice. We attempt to find a set of material parameters in both cases of lattices, for which the reflectivity becomes close to zero, or equal to an arbitrary constant. If such a set of material parameters could be found, it could have interesting applications in material science such as invisibility.

Celebonovic, Vladan

2012-12-01

57

Emergent 1d Ising Behavior in AN Elementary Cellular Automaton Model

NASA Astrophysics Data System (ADS)

The fundamental nature of an evolving one-dimensional (1D) Ising model is investigated with an elementary cellular automaton (CA) simulation. The emergent CA simulation employs an ensemble of cells in one spatial dimension, each cell capable of two microstates interacting with simple nearest-neighbor rules and incorporating an external field. The behavior of the CA model provides insight into the dynamics of coupled two-state systems not expressible by exact analytical solutions. For instance, state progression graphs show the causal dynamics of a system through time in relation to the system's entropy. Unique graphical analysis techniques are introduced through difference patterns, diffusion patterns, and state progression graphs of the 1D ensemble visualizing the evolution. All analyses are consistent with the known behavior of the 1D Ising system. The CA simulation and new pattern recognition techniques are scalable (in both dimension, complexity, and size) and have many potential applications such as complex design of materials, control of agent systems, and evolutionary mechanism design.

Kassebaum, Paul G.; Iannacchione, Germano S.

58

Modeling of the diffraction pattern of 1D-disordered silicon carbide

A method for calculating the diffraction pattern of a 1D-disordered crystal structure is considered by the example of silicon carbide. One-dimensional disordering is described using a cell setting the mutual position of all close-packed crystal layers. Two models of structure disordering during the polytypic transformation of the silicon carbide cubic modification into hexagonal are discussed. The results of the calculation of the diffraction spectrum in different stages of polytypic transformation are reported. It is shown that 1D disordering leads to the formation of a set of weak diffraction reflections. The experimentally observed changes in the diffraction pattern can be interpreted within the hypothesis on crystal structure disordering through displacement of adjacent close-packed layers.

Popenko, V. A., E-mail: pvapds@mail.ru [Research Industrial Association Luch (Russian Federation)

2008-09-15

59

Model Sensitivity to Parameters in the Simple 1-D Land-Atmosphere Model

NASA Astrophysics Data System (ADS)

Large scale effects are generally more important to the regional climate than local effects, such as land cover. However there is rarely any comparison of the two types of effects due to the complexity of the land-atmosphere system and the difficulties in controlling different climate drivers. Here we look into this matter from a model perspective. The modified simple 1-D land-atmosphere model based on D'Andrea (2006) and Baudena (2008) is used to investigate the relative sensitivity of climate variables (air temperature and precipitation) to the external forcing and local forcing. The model has two properties: firstly, it is an equilibrium model and secondly, it requires a small set of parameters. Therefore, this model is suitable for sensitivity analysis in which the effect of change in one factor can be isolated. In this study, we perform sensitivity analysis on the effects of four parameters. External forcing is represented by solar radiation (100 - 800 W m2) and moisture influx (0 - 1 mm hr-1) to the region. Local forcing is represented by the initial leaf area index (LAI, 0 - 10) and the initial soil wetness (0.13 - 0.63). A normalized index is used to access the sensitivity of the model outputs to the parameters. The index is defined as SI = dmax -dmin, Dmean ·r where dmax and dmin represent the local extremes; Dmean is the mean value for the whole domain and r is the proportion of the whole domain from which the local extremes are taken. Precipitation and air temperature output both responded nonlinearly to the tested parameters. Precipitation is resistant to changes when parameters are near to the lower end of value ranges until a threshold is hit. On the other hand, temperature is more sensitive to the low parameter values than the high parameter values. Hence, precipitation is suppressed and temperature remains high due to lack of vegetation cover, or low soil moisture, or negligible moisture influx from outside the region. Both precipitation and temperature are low when radiation is insufficient (in this case, < 456 W m2). For the tested range, the system reveals that both the initial soil moisture as shown by D'Andrea (2006) and other conditions can lead to multiple equilibriums. The sensitivity indexes show that precipitation is generally more sensitive to the changes in radiation and moisture influx, both with SI > 2 in the middle ranges. The sensitivity of precipitation to the changes in soil wetness and LAI are below 0.5. This could be an indication that external forcing is more important than local forcing in determining the local climate. However, the results also suggest the local effects can contribute to the local climate variation.

Liang, C.; Van Ogtrop, F.; Willem, V.

2012-04-01

60

Optimal velocity model for traffic flow

We present the Optimal Velocity (OV) model for traffic flow, which shows spontaneous formation of a jam cluster. We investigate the phase diagram and the general bound of induced time delay which plays an essential role in the jam flow solution.

Yuki Sugiyama

1999-01-01

61

NASA Astrophysics Data System (ADS)

We use an estimator of quantum criticality based on the entanglement entropy to discuss the ground state properties of the 1D anisotropic Kondo necklace model. We found that the T=0 phase diagram of the model is described by a critical line separating an antiferromagnetic phase from a Kondo singlet state. Moreover we calculate the conformal anomaly on the critical line and obtain that c tends to 0.5 as the thermodynamic limit is reached. Hence we conclude that these transitions belong to Ising universality class being, therefore, second order transitions instead of infinite order as claimed before.

Saguia, A.

2013-11-01

62

Resistivity structure of Sumatran Fault (Aceh segment) derived from 1-D magnetotelluric modeling

NASA Astrophysics Data System (ADS)

Sumatran Fault Zone is the most active fault in Indonesia as a result of strike-slip component of Indo-Australian oblique convergence. With the length of 1900 km, Sumatran fault was divided into 20 segments starting from the southernmost Sumatra Island having small slip rate and increasing to the north end of Sumatra Island. There are several geophysical methods to analyze fault structure depending on physical parameter used in these methods, such as seismology, geodesy and electromagnetic. Magnetotelluric method which is one of geophysical methods has been widely used in mapping and sounding resistivity distribution because it does not only has the ability for detecting contras resistivity but also has a penetration range up to hundreds of kilometers. Magnetotelluric survey was carried out in Aceh region with the 12 total sites crossing Sumatran Fault on Aceh and Seulimeum segments. Two components of electric and magnetic fields were recorded during 10 hours in average with the frequency range from 320 Hz to 0,01 Hz. Analysis of the pseudosection of phase and apparent resistivity exhibit vertical low phase flanked on the west and east by high phase describing the existence of resistivity contras in this region. Having rotated the data to N45°E direction, interpretation of the result has been performed using three different methods of 1D MT modeling i.e. Bostick inversion, 1D MT inversion of TM data, and 1D MT inversion of the impedance determinant. By comparison, we concluded that the use of TM data only and the impedance determinant in 1D inversion yield the more reliable resistivity structure of the fault compare to other methods. Based on this result, it has been shown clearly that Sumatra Fault is characterized by vertical contras resistivity indicating the existence of Aceh and Seulimeum faults which has a good agreement with the geological data.

Nurhasan; Sutarno, D.; Bachtiar, H.; Sugiyanto, D.; Ogawa, Y.; Kimata, F.; Fitriani, D.

2012-06-01

63

Models of high velocity impact phenomena

Models of craters formed by impacts at velocities of up to 27 km/sec have been computed using the Smooth Particle Hydrodynamics, MESA, EPIC and CALE codes. These modeling efforts will be compared to data obtained from the Hypervelocity Microparticle Impact project at Los Alamos using the van de Graaff accelerator. This work aids in understanding the fine features and scaling laws found in the experimental results.

Wingate, C.A.; Stellingwerf, R.F.; Davidson, R.F.; Burkett, M.W.

1992-09-01

64

Models of high velocity impact phenomena

Models of craters formed by impacts at velocities of up to 27 km/sec have been computed using the Smooth Particle Hydrodynamics, MESA, EPIC and CALE codes. These modeling efforts will be compared to data obtained from the Hypervelocity Microparticle Impact project at Los Alamos using the van de Graaff accelerator. This work aids in understanding the fine features and scaling laws found in the experimental results.

Wingate, C.A.; Stellingwerf, R.F.; Davidson, R.F.; Burkett, M.W.

1992-01-01

65

This technical report describes the new one-dimensional (1D) hydrodynamic and sediment transport model EFDC1D. This model that can be applied to stream networks. The model code and two sample data sets are included on the distribution CD. EFDC1D can simulate bi-directional unstea...

66

1D modelling of very viscous dripping flows with surface tension

NASA Astrophysics Data System (ADS)

Honey dripping from an upturned spoon is an everyday example of a flow that extends and breaks up into drops. Such flows have been of interest for over 300 years, attracting the attention of Plateau and Rayleigh among others. Ink-jet printing has motivated considerable interest in recent times. Nevertheless aspects of these flows are still not fully understood. One that has been relatively unexplored is the influence of initial conditions on the evolution of a drop and filament and the final breakup. We consider a drop of very viscous fluid hanging beneath a solid boundary, similar to honey dripping from a spoon. Potentially, gravity, surface tension and inertia all play a role. We here focus on 1D modelling including gravity and surface tension but neglecting inertia which has little effect for some time. The inclusion of surface tension in a 1D model presents a challenge, since the model breaks down at the very bottom of the drop. We present a method for solving the outer problem.

Stokes, Yvonne; Tuck, Ernie; Voyce, Christopher; Bradshaw-Hajek, Bronwyn

2007-11-01

67

Cosmological velocity correlations - Observations and model predictions

NASA Astrophysics Data System (ADS)

By applying the present simple statistics for two-point cosmological peculiar velocity-correlation measurements to the actual data sets of the Local Supercluster spiral galaxy of Aaronson et al. (1982) and the elliptical galaxy sample of Burstein et al. (1987), as well as to the velocity field predicted by the distribution of IRAS galaxies, a coherence length of 1100-1600 km/sec is obtained. Coherence length is defined as that separation at which the correlations drop to half their zero-lag value. These results are compared with predictions from two models of large-scale structure formation: that of cold dark matter and that of baryon isocurvature proposed by Peebles (1980). N-body simulations of these models are performed to check the linear theory predictions and measure sampling fluctuations.

Gorski, Krzysztof M.; Davis, Marc; Strauss, Michael A.; White, Simon D. M.; Yahil, Amos

1989-09-01

68

Modeling 1-D elastic P-waves in a fractured rock with hyperbolic jump conditions

NASA Astrophysics Data System (ADS)

The propagation of elastic waves in a fractured rock is investigated, both theoretically and numerically. Outside the fractures, the propagation of compressional waves is described in the simple framework of 1-D linear elastodynamics. The focus here is on the interactions between the waves and fractures: for this purpose, the mechanical behavior of the fractures is modeled using nonlinear jump conditions deduced from the Bandis-Barton model classically used in geomechanics. Well-posedness of the initial-boundary value problem thus obtained is proved. Numerical modeling is performed by coupling a time-domain finite-difference scheme with an interface method accounting for the jump conditions. The numerical experiments show the effects of contact nonlinearities. The harmonics generated may provide a nondestructive means of evaluating the mechanical properties of fractures.

Lombard, Bruno; Piraux, Joel

2007-07-01

69

NASA Astrophysics Data System (ADS)

We examine a novel simulation scheme called ``equation free projective integration'' which has the potential to allow global simulations which still include microscale physics, a necessary ingredient in order to model multiscale problems. Such codes could be used to examine the global effects of reconnection and turbulence in tokamaks, the Earth's magnetosphere, and the solar corona. Using this method to simulate the propagation and steepening of a 1D ion acoustic wave, we have already achieved excellent agreement between full particle codes and equation free with a factor of 20 speed-up. In this method of simulation, the global plasma variables stepped forward in time are not time-integrated directly using dynamical differential equations, hence the name ``equation free.'' Instead, these variables are represented on a microgrid using a kinetic simulation. This microsimulation is integrated forward long enough to determine the time derivatives of the global plasma variables, which are then used to integrate forward the global variables with much larger timesteps. Results will be presented of the successful application of equation free to 1-D ion acoustic wave steepening with a PIC code serving as the underlying kinetic model. Initial results of this technique applied to magnetic reconnection will also be discussed.

Shay, Michael; Drake, J.

2005-10-01

70

NASA Astrophysics Data System (ADS)

We study at particle and kinetic level a collective behavior model based on three phenomena: self-propulsion, friction (Rayleigh effect) and an attractive/repulsive (Morse) potential rescaled so that the total mass of the system remains constant independently of the number of particles N. In the first part of the paper, we introduce the particle model: the agents are numbered and described by their position and velocity. We identify five parameters that govern the possible asymptotic states for this system (clumps, spheres, dispersion, mills, rigid-body rotation, flocks) and perform a numerical analysis on the 3D setting. Then, in the second part of the paper, we describe the kinetic system derived as the limit from the particle model as N tends to infinity; we propose, in 1D, a numerical scheme for the simulations, and perform a numerical analysis devoted to trying to recover asymptotically patterns similar to those emerging for the equivalent particle systems, when particles originally evolved on a circle.

Vecil, Francesco; Lafitte, Pauline; Rosado Linares, Jesús

2013-10-01

71

1-D COMPUTATIONAL MODEL OF A MOTIVE NOZZLE FOR THE R744

The paper presents the results of a theoretical analysis performed for a motive nozzle of a two-phase R744 ejector at steady-state conditions. The model takes into consideration one-dimensional flow of real fluid through the converging-diverging nozzle. The proposed approach allows the determination of one- dimensional distributions of pressure, velocity and density. The simulated profiles take account of local values of

TWO-PHASE EJECTOR

2010-01-01

72

A one-dimensional (1D) coupled physical–microbiological model has been applied to a site in the central North Sea. The impact of the choice of the turbulence closure scheme on the modelling the primary production has been investigated.The model was run with four different parameterisations of vertical mixing of heat, momentum and dissolved and suspended matters, using M2 tidal forcing and the

F. Chen; J. D Annan

2000-01-01

73

The validation of a coupled 1D-0D model of the lower-limb arterial hemodynamics is presented. This study focuses on pathological subjects (6 patients, 72.7±11.1years) suffering from atherosclerosis who underwent a femoro-popliteal bypass surgery. The 1D model comprises four vessels from the upper-leg, peripheral networks are modeled with three-element windkessels and in vivo velocity is prescribed at the inlet. The model is patient-specific: its parameters reflect the physiological condition of the subjects. In vivo data are acquired invasively during bypass surgery using B-mode ultrasonography and catheter. Simulations from the model compare well with measured velocity (u) and pressure (p) waveforms: average relative root-mean-square error between numerical and experimental waveforms are limited to ?p=9.6%, ?u=16.0%. The model is able to reproduce the intensity and shape of waveforms observed in different clinical cases. This work also details the introduction of blood leakages along the pathological arterial network, and the sensitivity of the model to its parameters. This study constitutes a first validation of a patient-specific numerical model of a pathological arterial network. It presents an efficient tool for engineers and clinicians to help them improve their understanding of the hemodynamics in diseased arteries. PMID:23701843

Willemet, Marie; Lacroix, Valérie; Marchandise, Emilie

2013-05-21

74

- Seismic event locations based on regional 1-D velocity-depth sections can have bias errors caused by travel-time variations within different tectonic provinces and due to ray-paths crossing boundaries between tectonic provinces with different crustal and upper mantle velocity structures. Seismic event locations based on 3-D velocity models have the potential to overcome these limitations. This paper summarizes preliminary results for

V. Ryaboy; D. R. Baumgardt; P. Firbas; A. M. Dainty

2001-01-01

75

Full Waveform 3D Synthetic Seismic Algorithm for 1D Layered Anelastic Models

NASA Astrophysics Data System (ADS)

Numerical calculation of synthetic seismograms for 1D layered earth models remains a significant aspect of amplitude-offset investigations, surface wave studies, microseismic event location approaches, and reflection interpretation or inversion processes. Compared to 3D finite-difference algorithms, memory demand and execution time are greatly reduced, enabling rapid generation of seismic data within workstation or laptop computational environments. We have developed a frequency-wavenumber forward modeling algorithm adapted to realistic 1D geologic media, for the purpose of calculating seismograms accurately and efficiently. The earth model consists of N layers bounded by two halfspaces. Each layer/halfspace is a homogeneous and isotropic anelastic (attenuative and dispersive) solid, characterized by a rectangular relaxation spectrum of absorption mechanisms. Compressional and shear phase speeds and quality factors are specified at a particular reference frequency. Solution methodology involves 3D Fourier transforming the three coupled, second- order, integro-differential equations for particle displacements to the frequency-horizontal wavenumber domain. An analytic solution of the resulting ordinary differential system is obtained. Imposition of welded interface conditions (continuity of displacement and stress) at all interfaces, as well as radiation conditions in the two halfspaces, yields a system of 6(N+1) linear algebraic equations for the coefficients in the ODE solution. An optimized inverse 2D Fourier transform to the space domain gives the seismic wavefield on a horizontal plane. Finally, three-component seismograms are obtained by accumulating frequency spectra at designated receiver positions on this plane, followed by a 1D inverse FFT from angular frequency ? to time. Stress-free conditions may be applied at the top or bottom interfaces, and seismic waves are initiated by force or moment density sources. Examples reveal that including attenuation stabilizes the numerical calculations, and reduces wraparound artifacts associated with the spatially-periodic 2D Fourier transform. Sandia National Laboratories is a multiprogram science and engineering facility operated by Sandia Corporation, a Lockheed-Martin company, for the US DOE under contract DE-AC04-94AL85000.

Schwaiger, H. F.; Aldridge, D. F.; Haney, M. M.

2007-12-01

76

Present nitrogen and carbon dynamics in the Scheldt estuary using a novel 1-D model

NASA Astrophysics Data System (ADS)

A 1-D, pelagic, reactive-transport model of a completely mixed, turbid, heterotrophic estuary the Scheldt estuary is presented. The model resolves major carbon and nitrogen species and oxygen, as well as pH. The model features two organic matter degradation pathways, oxic mineralisation and denitrification, and includes primary production as well as nitrification. Apart from advective-dispersive transport along the length axis, the model also describes O2, CO2, and N2 air-water exchange. The aim of this study is to present a model which is as simple as possible but still fits the data well enough to determine the fate and turnover of nutrients entering the estuary and their spatial patterns in the years 2000 to 2004. Nitrification is identified as one of the most important processes in the estuary, consuming a comparable amount of oxygen as oxic mineralisation (1.7 Gmol O2 y-1 vs. 2.7 Gmol O2 y-1). About 10% of the 2.5 Gmol of nitrogen entering the estuary per year is lost within the estuary due to denitrification. Nitrogen and carbon budgets are compared to budgets from the seventies and eighties, showing that nitrification activity has peaked in the eighties, while denitrification steadily declined. Our model estimates an average CO2 emission of 3.3 Gmol y-1 in the years 2001 to 2004, which is a comparatively low estimate in the context of previous estimates of CO2 export from the Scheldt estuary.

Hofmann, A. F.; Soetaert, K.; Middelburg, J. J.

2008-07-01

77

Exploring triggers for polar tropospheric ODEs, using a 1-D snow photochemistry model (MISTRA-SNOW).

NASA Astrophysics Data System (ADS)

Tropospheric Ozone Depletion Events (ODEs) have been known to occur in polar regions for over 20 years. During such events, ozone concentrations can fall from background amounts to below instrumental detection limits within a few minutes and remain suppressed for on the order of hours to days. The chemical destruction of ozone is driven by halogens (especially bromine radicals) that have a source associated with the sea ice zone. Although our knowledge of ODEs has increased greatly since their discovery, some of the key processes involved are not yet fully understood. We now know that heterogeneous reactions lead to the activation of Br2 and BrCI, via uptake of HOBr onto aqueous salt solutions /aerosol/ surface snowpack (Fickert et al., 1999), and it is widely accepted that bromine catalytic reaction cycles (the 'bromine explosion') in the gas phase are responsible for surface ozone destruction (Simpson et al., 2007). There is still much debate over the source of bromine in the atmosphere that drives ODEs, but there is strong evidence to suggest a source associated with the sea ice zone. A 1D Marine Boundary Layer (MBL) chemistry model (MISTRA; von Glasow et al., 2002) has been modified to be representative of Antarctic conditions. The chemistry module includes chemical reactions in the gas phase, in and on aerosol particles and takes into account transfer between the gas and aqueous phase. A new snow-photochemistry module has been developed which includes chemistry which takes place in the quasi-liquid layer on aerosol (Thomas et al., 2011), which is of great importance to our understanding of the chemistry which initiates a bromine explosion. Here we use this newly developed 1-D snow photochemistry model (MISTRA-SNOW) to look at some of the suggested triggers for, and the different meteorological conditions required to produce, tropospheric ODEs in polar regions.

Buys, Z.; Jones, A. E.; von Glasow, R.

2012-04-01

78

NASA Astrophysics Data System (ADS)

We examine a novel simulation scheme called "equation free projective integration"[1] which has the potential to allow global simulations which still include microscale physics, a necessary ingredient in order to model multiscale problems. Such codes could be used to examine the global effects of reconnection and turbulence in the Earth's magnetosphere, and the solar corona, as well as in laboratory Tokamaks. Using this method to simulate the propagation and steepening of a 1D ion acoustic wave, we have already achieved excellent agreement between full particle codes and equation free with a factor of 20 speed-up. This speedup appears to scale linearly with system size, so large scale 2D and 3D simulations using this method will show a speedup of 100 or more. In this method of simulation, the global plasma variables stepped forward in time are not time-integrated directly using dynamical differential equations, hence the name "equation free." Instead, these variables are represented on a microgrid using a kinetic simulation. This microsimulation is integrated forward long enough to determine the time derivatives of the global plasma variables, which are then used to integrate forward the global variables with much larger timesteps. Results will be presented of the successful application of equation free to 1-D ion acoustic wave steepening with a PIC code serving as the underlying kinetic model. Initial results of this technique applied to magnetic reconnection will also be discussed. 1 I. G. Kevrekidis et. al., Equation-free multiscale computation: Enabling microscopic simulators to perform system-level tasks, arXiv:physics/0209043.

Shay, M. A.; Dorland, B.; Drake, J. F.; Stantchev, G.

2005-12-01

79

1D Chemical Modeling of coupled snow-atmosphere chemistry at Dome C Antarctica

NASA Astrophysics Data System (ADS)

High levels of nitrogen oxides NOx (NOx=NO+NO2) generated by the photolysis of nitrate present in surface snow profoundly impact atmospheric composition and oxidizing capacity in the Antarctic boundary layer. In particular, NOx emissions from sunlit snow increase OH values by effectively recycling HO2 to OH. In order to better characterize this chemistry the OPALE campaign was conducted in December 2011/January 2012 at Dome C, Antarctica (altitude of 3,233 meters, 75 ° S, 123 ° E). The campaign included boundary layer profiling, measurements of the physical properties of snow, as well as a comprehensive suite of atmospheric chemistry measurements (including NOx, HONO, OH and RO2, H2O2, CH2O, O3). We present results using the 1-D coupled snow-boundary layer model MISTRA-SNOW in combination with observations made during the measurement campaign to understand this chemistry. The model includes both chemistry at the surface of snow grains (aqueous chemistry), in firn air (gas phase chemistry), and gas/aerosol chemistry in the boundary layer. Model predictions of NOx mixing ratios using a model sensitivity analysis approach are presented. The model was initialized using measured snow properties, including temperature, density, and snow grain size. In addition, the model dynamics are driven using the measured surface temperature at Dome C. To calculate the rate of snowpack ventilation, measured wind speeds during the campaign were used. The model was run varying the amount of nitrate and bromide available for reaction at the surface of snow grains and results are compared to measurements made in the atmospheric boundary from 2-4 January 2012. We test the hypothesis that very low concentrations of bromine may alter the ratio of NO/NO2. We also investigate the influence of NOx emissions from snow, and bromine (if present), on OH concentrations in the boundary layer on the Antarctic plateau.

Gil, Jaime E.; Thomas, Jennie; von Glasgow, Roland; Bekki, Slimane; Kukui, Alexandre; Frey, Markus; Jourdain, Bruno; Kerbrat, Michel; Genthon, Christophe; Preuknert, Susanne; Legrand, Michel

2013-04-01

80

NASA Astrophysics Data System (ADS)

In the context of an ongoing study on seismic response of landslide-prone hill-slopes in Central Italy (area of Caramanico Terme), we tested the applicability of the Refraction Microtremor (ReMi) analysis technique (Louie, 2001) to obtain geometrical and physical parameters needed for numerical modelling. In particular, we used this technique to determine one-dimensional shear-wave velocity profiles (Vs) at sites located on and close to a recent landslide that mobilized 30-40 m thick Quaternary colluvium overlying Pliocene mudstones. The use of this technique in unstable slope areas presents difficulties related to rough topography and lateral lithological heterogeneities, which prevent the extension of geophone array up to the minimum lengths (100 - 200 m) commonly adopted in standard applications. Moreover, sites distant from anthropic sources of microtremors can have unfavourable noise conditions in comparison with other well established cases of application. To check the stability of the ReMi data in these operative conditions and the confidence level of the results, three ReMi campaigns were conducted at different times using different acquisition parameters (seismograph channel number, geophone frequency and spacing). We also tested simultaneous noise recording along orthogonal arrays to investigate a possible presence of directional variations of soil properties. The Rayleigh wave velocity dispersion data derived from picking carried out on p (slowness)-f (frequency) matrix showed the presence in noise recordings of different Rayleigh wave vibration modes (fundamental and first two higher modes), which prevail at different frequency intervals. This indicates that it is essential to correctly identify the different vibration modes to avoid erroneous data interpretation (e.g. fictitious identification of velocity decrease with depth). An analysis of the influence of changing environmental conditions and of different acquisition parameters was conducted through the comparison of data obtained from different campaigns with equal acquisition parameters and from simultaneous acquisition with different parameters. We show that different data acquisition can give quite stable results if spatial aliasing does not contaminate the signal in the p-f matrix near the picking area. Regarding the presence of directional variations, the differences found between velocities measured in two orthogonal directions were not very large (up to 10-20 %). These differences were more probably due to an anisotropic distribution of the noise sources rather than to lateral variations in material properties. The Rayleigh wave velocity dispersion curves, obtained from microseismic noise recording, were then inverted with the software Dinver (Wathelet, 2005) to derive shear-wave vertical distribution. This resulted in a large number of models compatible with data uncertainties estimated from measurement repetitions. The major variability characterizing the models at depth implies that this part of profiles is poorly constrained. However, if different vibration modes are recognised, the number of solutions can be considerably reduced by simultaneously inverting the relative dispersion curves and also by introducing into the models additional constraints (e.g. subsurface information from boreholes and seismic refraction data). References Louie J.N.; 2001: Shear wave velocity to 100 meters depth from refraction microtremor arrays. Bull. Seism. Soc. Am., 91, (2), 347-364. Wathelet M.; 2005: Array recordings of ambient vibrations: surface-wave inversion. PhD thesis, Université de Liège, Belgium.

Coccia, S.; Del Gaudio, V.; Venisti, N.; Wasowski, J.

2009-04-01

81

1D Modeling of Catalyzed Monopropellant H2O2 Decomposition in Microchannels

NASA Astrophysics Data System (ADS)

The modeling of the chemical decomposition of hydrogen-peroxide monopropellant flow in a catalytic microchannel is described. This process can be used to provide a micro-propulsion mechanism required for miniaturized satellites (“nanosats”). Based on the largely gaseous nature of the flow and microchannel geometries, a 1D reacting flow model is assumed. The decomposition is modeled by first-order kinetics and a temperature-dependent Arrhenius law; the latter is justified for typical catalysts. Simulations are performed for realistic operating parameters designed to provide thrust levels of 100-500 micro-N. The outcome is a prediction of a critical catalyst chamber length required for complete decomposition; this is shown to depend upon the Damkohler number, Zeldovich number and the non-dimensional heat release rate of the monopropellant. A “thermal detonation” behavior is observed whereby the decomposition process goes to completion instantaneously. Inclusion of heat loss through microchannel walls can significantly increase critical decomposition length and reduce the available energy for the micropropulsion.

Zhou, Xu; Hitt, Darren

2003-11-01

82

NASA Astrophysics Data System (ADS)

The understanding of electrokinetics for unsaturated conditions is crucial for numerous of geophysical data interpretation. Nevertheless, the behaviour of the streaming potential coefficient C as a function of the water saturation Sw is still discussed. We propose here to model both the Richards' equation for hydrodynamics and the Poisson's equation for electrical potential for unsaturated conditions using 1-D finite element method. The equations are first presented and the numerical scheme is then detailed for the Poisson's equation. Then, computed streaming potentials (SPs) are compared to recently published SP measurements carried out during drainage experiment in a sand column. We show that the apparent measurement of ?V/?P for the dipoles can provide the SP coefficient in these conditions. Two tests have been performed using existing models for the SP coefficient and a third one using a new relation. The results show that existing models of unsaturated SP coefficients C(Sw) provide poor results in terms of SP magnitude and behaviour. We demonstrate that the unsaturated SP coefficient can be until one order of magnitude larger than Csat, its value at saturation. We finally prove that the SP coefficient follows a non-monotonous behaviour with respect to water saturation.

Allègre, V.; Lehmann, F.; Ackerer, P.; Jouniaux, L.; Sailhac, P.

2012-04-01

83

Testing the Two Water Worlds Hypothesis: column experiments and 1D transport modeling

NASA Astrophysics Data System (ADS)

Many studies have demonstrated links between vegetation water-use and streamflow at the headwater catchment scale which has led to the conceptual model of piston-like flow of water through a watershed and the assumption of complete mixing of water in the soil. Recent field experiments at the H.J. Andrews Experimental Forest, Oregon, USA, however, have seriously challenged this paradigm (Brooks, J.R., Barnard, H., Coulombe, R. and McDonnell, J.J.: Two water worlds paradox: Trees and streams return different water pools to the hydrosphere. In review, Nature Geoscience.). Using a dual isotope approach, the study showed that tightly-bound water retained in the soil and used by plants does not mix with mobile water in the soil or enter the stream. Soil water exhibits a distinct isotopic pattern in the soil profile that cannot be explained by piston flow concepts. It was hypothesized that this pattern reflects how the soil profile wets up during the first precipitation events in fall after a dry summer whereby increasingly isotopically-depleted precipitation through the event recharges deeper and deeper soils. This soil water is then locked into the micropore spaces and does not mix with precipitation falling subsequently in winter. The work described in this presentation was designed to test if these field observations can be replicated under controlled conditions using a soil core in the laboratory and simulated with a 1D flow and transport model. Irrigation experiments were performed on soil cores taken at the H.J. Andrews Forest, and the isotopic signatures of irrigation water, soil water and leachate were determined. Results showed distinct differences in isotopic signatures between leachate and water extracted from the core after the experiment, indicating the existence of more than one pool of water. Using the flow and transport model HYDRUS-1D we then tested if common single- and dual-porosity approaches were able to describe the partitioning of the irrigation water within the soil core and if initial soil moisture state affected this partitioning.

Hopp, L.; Sayama, T.; Brooks, J. R.; McDonnell, J. J.

2009-12-01

84

NASA Astrophysics Data System (ADS)

The slope of the continental margin of the northern Gulf of Mexico is riddled with small basins resulting from salt tectonics. Each such minibasin is the result of local subsidence due to salt withdrawal, and is isolated from neighboring basins by ridges formed due to compensational uplift. The minibasins are gradually filled by turbidity currents, which are active at low sea stand. Experiments in a 1-D minibasin reveal that a turbidity current flowing into a deep minibasin must undergo a hydraulic jump and form a muddy pond. This pond may not spill out of the basin even with continuous inflow. The reason for this is the detrainment of water across the settling interface that forms at the top of the muddy pond. Results of both experiments and numerical modeling of the flow and the evolution of the deposit are presented. The numerical model is the first of its kind to capture both the hydraulic jump and the effect of detrainment in ponded turbidity currents.

Lamb, M.; Toniolo, H.; Parker, G.

2001-12-01

85

Velocity Profiles and Unsteady Pipe Friction in Transient Flow

Transient conditions in closed conduits have traditionally been modeled as 1D flows with the implicit assumption that velocity profile and friction losses can be accurately predicted using equivalent 1D velocities. Although more complex fluid models have been suggested, there has been little direct experimental basis for selecting one model over another. This paper briefly reviews the significance of the 1D

Bruno Brunone; Bryan W. Karney; Michele Mecarelli; Marco Ferrante

2000-01-01

86

Volcano inflation prior to eruption: Calculation based on a 1-D conduit magma flow model

NASA Astrophysics Data System (ADS)

Recent geodetic observations at active volcanoes that erupt with Vulcanian or Strombolian type have succeeded in detecting volcano inflation prior to each explosion. Theoretical considerations of such eruptions based on the basic processes of magma behavior suggest that temporal changes of the volcano inflation are affected by gas bubble growth in magma (Nishimura, 2008). However in realistic volcanic eruptions, these basic processes interact each other, so numerical investigations using the basic equations on magmatic flow is necessary. In this study, we examine the temporal change of volcano deformation due to magma ascent using a 1-D conduit magma flow model. We consider 1-D conduit magma flow in an open conduit, because when volcanoes repeatedly erupt in a short time, the volcanic conduit is considered not to close after each eruption. We assume that the conduit has a constant diameter and the magma contains tiny gas bubbles in viscous melt. We express the magma flow in the conduit using the equation of mass conservation, the equation of momentum conservation and the equation of state of magma. The gas bubble growth process in magma is formulated by the equation of motion for the interface between the gas bubble and melt, and the diffusion equation of volatiles in melt. These equations are characterized by the Poiseuille flow time scale (Tp), the viscous deformation time scale (Tv) and diffusion time scale (Td). For boundary condition, the pressure at the top of the magma in the conduit is set to be equal to the atmospheric pressure, and the pressure at the bottom of conduit is fixed at the reservoir pressure. For initial condition, the pressure in gas bubble is higher than the melt pressure, since sudden pressure decrease by eruption may cause a supersaturated condition in magma. We apply a finite difference method for the calculation of above mentioned equations. We consider that magma pressure in the conduit deforms the volcano edifice. We assume a uniform elastic half-space and the conduit diameter sufficiently small compared with the distance from the vent to a station. We use the analytical solutions of the displacement field by pressurized open conduit, and calculate temporal change of volcano deformation applying the temporal and spacial change of magma pressure in the conduit obtained from the 1-D conduit magma flow model. The main results obtained from the calculations are as follows. When the observing point is near to the vent, volcano inflation continues until the magma reaches the ground surface. When the initial pressure difference between gas bubbles and melt is large, the volcano inflation is accelerated because of rapid expansion of gas bubbles. When the observing point is far from the vent, the volcano deformation ceases before the magma reaches the ground surface. Temporal change of volcano deformation is also affected by the three time scales. When Tp / Tv is about 1, the magma ascent rate is almost constant, because the gas bubble growth in magma act as a driving force during the magma ascent. On the other hand, when Tp / Tv is large enough, the magma ascent rate gradually decreases with time, because the effect of gas bubble growth is small. As a result, in the latter case, the volcano inflation rate gradually decreases with time.

Kawaguchi, R.; Nishimura, T.; Sato, H.

2009-12-01

87

A model for the azimuthal plasma velocity in Saturn's magnetosphere

We present a model for Saturn's magnetospheric azimuthal plasma velocities measured by Voyager 1 and 2. The observed velocity profiles deviate from full corotation and show two dips slightly outside the orbits of Dione and Rhea, for both spacecraft respectively. Our velocity model includes as sources for the deviation: radial mass transport,friction between magnetospheric ions and neutrals, and ion pickup.

Joachim Saur; Barry H. Mauk; F. M. Neubauer

2004-01-01

88

Parameter sensitivities in a 1-D model for DMS and sulphur cycling in the upper ocean

NASA Astrophysics Data System (ADS)

We have developed a marine DMS (dimethylsulfide) module and implemented it in a 1-D coupled atmosphere-ocean-biogeochemical model. In developing the marine sulphur model we have found that several parameters used in the model are not known to even an order of magnitude. Our approach is used to test the model's sensitivity to these parameters. A parameter change of ±25% is applied to test the respective range of changes in the DMS fluxes. The model is run for a 3-year time period as well as for the time period of the Subarctic Ecosystem Response to Iron Enrichment Study (SERIES) in July 2002. The simulated seasonal cycle is in agreement with available observations: Near surface DMS concentrations vary from 1.5nmolL-1 in winter to 13.5nmolL-1 in summer. Simulated DMS production is found to be most sensitive to variations of the S:N ratio and the bacterial consumption rate of DMS. Implementing light or UV limited bacterial activity shows a negligible effect in winter and increases DMS concentrations by 0.2- 0.6nmolL-1 in summer. Similarly a yield increase under UV stress increases summer values by 1- 2nmolL-1. The simulated diel cycle in surface DMS concentration is no more than 2.5nmolL-1, even when light-dependent changes in bacterial activity are considered. Simulating the DMS response to iron fertilization with the standard run leads to overestimation during an initial bloom of small phytoplankton. While implementing light-dependent bacterial activity has a minor effect, the implementation of yields that depend on nutrient availability significantly improves the results. The model confirms earlier results showing the importance of including atmospheric DMS concentrations in gas flux calculations when there are high surface concentrations and small atmospheric boundary layer heights. Simulated summer concentrations in the upper layer can be underestimated by 2nmolL-1 or more if the atmospheric concentration is set to zero. Our study shows that inclusion of mechanistic DMS modules in comprehensive climate models requires better knowledge of the variation of key parameters in the marine sulphur cycle. Even though there are still open questions, the model reasonably reproduces the mean annual cycle; and including variable DMS yield improves the simulation of the DMS response to iron fertilization during SERIES.

Steiner, N.; Denman, K.

2008-07-01

89

Cardiomyocyte Contractile Dysfunction in the APPswe/PS1dE9 Mouse Model of Alzheimer's Disease

Objectives Ample clinical and experimental evidence indicated that patients with Alzheimer's disease display a high incidence of cardiovascular events. This study was designed to examine myocardial histology, cardiomyocyte shortening, intracellular Ca2+ homeostasis and regulatory proteins, electrocardiogram, adrenergic response, endoplasmic reticulum (ER) stress and protein carbonyl formation in C57 wild-type (WT) mice and an APPswe/PS1dE9 transgenic (APP/PS1) model for Alzheimer's disease. Methods Cardiomyocyte mechanical properties were evaluated including peak shortening (PS), time-to-PS (TPS), time-to-relengthening (TR), maximal velocity of shortening and relengthening (±dL/dt), intracellular Ca2+ transient rise and decay. Results Little histological changes were observed in APP/PS1 myocardium. Cardiomyocytes from APP/PS1 but not APP or PS1 single mutation mice exhibited depressed PS, reduced±dL/dt, normal TPS and TR compared with WT mice. Rise in intracellular Ca2+ was lower accompanied by unchanged resting/peak intracellular Ca2+ levels and intracellular Ca2+ decay in APP/PS1 mice. Cardiomyocytes from APP/PS1 mice exhibited a steeper decline in PS at high frequencies. The responsiveness to adrenergic agonists was dampened although ?1-adrenergic receptor expression was unchanged in APP/PS1 hearts. Expression of the Ca2+ regulatory protein phospholamban and protein carbonyl formation were downregulated and elevated, respectively, associated with unchanged SERCA2a, Na+-Ca2+ exchanger and ER stress markers in APP/PS1 hearts. Our further study revealed that antioxidant N-acetylcysteine attenuated the contractile dysfunction in APP/PS1 mice. Conclusions Our results depicted overt cardiomyocyte mechanical dysfunction in the APP/PS1 Alzheimer's disease model, possibly due to oxidative stress.

Turdi, Subat; Guo, Rui; Huff, Anna F.; Wolf, Eliza M.; Culver, Bruce; Ren, Jun

2009-01-01

90

NASA Astrophysics Data System (ADS)

- Seismic event locations based on regional 1-D velocity-depth sections can have bias errors caused by travel-time variations within different tectonic provinces and due to ray-paths crossing boundaries between tectonic provinces with different crustal and upper mantle velocity structures. Seismic event locations based on 3-D velocity models have the potential to overcome these limitations. This paper summarizes preliminary results for calibration of IMS for North America using 3-D velocity model. A 3-D modeling software was used to compute Source-Station Specific Corrections (SSSCs(3-D)) for Pn travel times utilizing 3-D crustal and upper mantle velocity model for the region. This research was performed within the framework of the United States/Russian Federation Joint Program of Seismic Calibration of the International Monitoring System (IMS) in Northern Eurasia and North America.An initial 3-D velocity model for North America was derived by combining and interpolating 1-D velocity-depth sections for different tectonic units. In areas where no information on 1-D velocity-depth sections was available, tectonic regionalization was used to extrapolate or interpolate. A Moho depth map was integrated. This approach combines the information obtained from refraction profiles with information derived from local and regional network data. The initial 3-D velocity model was tested against maps of Pn travel-time residuals for eight calibration explosions; corrections to the 3-D model were made to fit the observed residuals. Our goal was to find a 3-D crustal and upper mantle velocity model capable predicting Pn travel times with an accuracy of 1.0-1.5 seconds (r.m.s.).The 3-D velocity model for North America that gave the best fit to the observed travel times, was used to produce maps of SSSCs(3-D) for seismic stations. The computed SSSCs(3-D) vary approximately from +5 seconds to -5 seconds for the western USA and the Pre-Cambrian platform, respectively. These SSSCs(3-D) along with estimated modeling and measurement errors were used to relocate, using regional data, an independent set of large chemical explosions (with known locations and origin times) detonated within various tectonic provinces of North America. Utilization of the 3-D velocity model through application of the computed SSSCs(3-D) resulted in a substantial improvement in seismic event location accuracy and in a significant decrease of error ellipse area for all events analyzed in comparison both with locations based on the IASPEI91 travel times and locations based on 1-D regional velocity models.

Ryaboy, V.; Baumgardt, D. R.; Firbas, P.; Dainty, A. M.

91

Embedding a 1D calving ice model into a large-scale 3D ice dynamical model for Greenland.

NASA Astrophysics Data System (ADS)

With a large-scale 3D ice dynamical model a reconstruction of the Greenland ice sheet is carried out over the period 1960-2100 with boundary conditions from the latest Ice2Sea topographic data set and the RACMO regional climate forcing fields. The Ice2Sea and RACMO fields have been remapped with an optimal centered oblique stereographic projection. The spatial resolution of most of the large scale ice sheet models is not enough to resolve the dynamics of narrow deep outlet glaciers. Processes acting at the marine boundary such as calving and submarine melt can not be represented in enough detail. To improve the large-scale ice model, a detailed 1D calving ice model is embedded at the location of an important outlet system. Here we present results for Jakobshavn Isbræ. Both models exchange information with the mapping tool OBLIMAP at as many time steps as required by the user. The coupling can be done at various levels of detail. A first order coupling considers the geometrical adaptation of the ice sheet. A more sophisticated coupling takes in addition the ice fluxes precisely into account. Results are compared with stand-alone 1D flow line results indicating the importance of the coupling process.

Reerink, Thomas; Nick, Faezeh; van de Wal, Roderik

2013-04-01

92

The Bethe ansatz equations of the 1-D Hubbard model under open boundary conditions are systematically derived by diagonalizing the inhomogeneous transfer matrix of the XXX model with open boundaries. Through the finite-size correction, we obtain the energy spectrum of the open chain and discuss the effects of boundary magnetic fields applied only at the edges of the chain. Several physical

Tetsuo Deguchi; Ruihong Yue

1997-01-01

93

Comparison of 1D and 2D CSR Models with Application to the FERMI@ELETTRA Bunch Compressors

We compare our 2D mean field (Vlasov-Maxwell) treatment of coherent synchrotron radiation (CSR) effects with 1D approximations of the CSR force which are commonly implemented in CSR codes. In our model we track particles in 4D phase space and calculate 2D forces [1]. The major cost in our calculation is the computation of the 2D force. To speed up the computation and improve 1D models we also investigate approximations to our exact 2D force. As an application, we present numerical results for the Fermi{at}Elettra first bunch compressor with the configuration described in [1].

Bassi, G.; Ellison, J.A.; Heinemann, K.

2011-03-28

94

Evaluation of a 1-D snowpack model SMAP applied in the Greenland ice sheet

NASA Astrophysics Data System (ADS)

Snow and ice on the Greenland ice sheet (GrIS) are melting rapidly in recent years. In order to understand the mechanism and to perform reliable future projection on the mass balance of GrIS, we employ the 1-D physical snowpack model named Snow Metamorphism and Albedo Process (SMAP), which was originally developed and validated against seasonal snowpack, and adapt it for the simulation of polar snowpack. In the present study we tested SMAP using the data obtained during the 2012 intensive field observations (30 June to 13 July, 2012) conducted in the site SIGMA-A, which locates on northwest part of GrIS (78° 03'N, 67° 38'W, 1,490 m a.s.l.). During the latter half of the expedition period we encountered the record melt event where surface snow and ice over 97% of GrIS melted abruptly. In the model test the initial physical states of snowpack were given from those obtained by snow-pit observations carried out on 30 June. From the initial state we calculated temporal evolution of physical parameters of snowpack by forcing measured meteorological data, mass concentrations of snow impurities, and snow temperature at the depth of bottom ice formation in the latest annual layer (initial depth was 88 cm). The model performance was evaluated in terms of snow surface temperature, shortwave albedo, relative snow depth (to the ice formation in the latest annual layer), profiles of snow temperature, and snow density. Regarding snow surface temperature and shortwave albedo SMAP overestimated both, nevertheless biases were small (+0.143 ° C and +0.014, respectively), suggesting that the snow-atmosphere energy exchange (snow surface energy balance) is modeled adequately. To calculate accurate relative snow depth it is necessary to simulate mass balance precisely. The acquired small bias (-0.026 m) shows that SMAP estimates mass balance successfully. Finally, as for profiles of snow temperature and snow density we found that SMAP tended to underestimate the former, while overestimate the latter. However, obtained small biases (less than 1 ° C and ranged between 30 and 90 kg m-3, respectively) indicate that SMAP calculates internal physical properties of snowpack in an appropriate manner if relevant upper and lower boundary conditions are imposed.

Niwano, Masashi; Aoki, Teruo; Matoba, Sumito; Yamaguchi, Satoru; Tanikawa, Tomonori; Motoyama, Hideaki; Kuchiki, Katsuyuki

2013-04-01

95

Optimal velocity difference model for a car-following theory

In this Letter, we present a new optimal velocity difference model for a car-following theory based on the full velocity difference model. The linear stability condition of the new model is obtained by using the linear stability theory. The unrealistically high deceleration does not appear in OVDM. Numerical simulation of traffic dynamics shows that the new model can avoid the

G. H. Peng; X. H. Cai; C. Q. Liu; B. F. Cao; M. X. Tuo

2011-01-01

96

Modeling of general 1-D periodic leaky-wave antennas in layered media with EIGER.

This paper presents a mixed-potential integral-equation formulation for analyzing 1-D periodic leaky-wave antennas in layered media. The structures are periodic in one dimension and finite in the other two dimensions. The unit cell consists of an arbitrary-shaped metallic/dielectric structure. The formulation has been implemented in the EIGER{trademark} code in order to obtain the real and complex propagation wavenumbers of the bound and leaky modes of such structures. Validation results presented here include a 1-D periodic planar leaky-wave antenna and a fully 3-D waveguide test case.

Wilton, Donald R.; Basilio, Lorena I.; Celepcikay, F. T. (University of Houston, Houston TX); Johnson, William Arthur; Baccarelli, Paolo (University of Rome); Valerio, G. (University of Rome); Paulotto, Simone (University of Houston, Houston TX); Langston, William L.; Jackson, David R. (University of Houston, Houston TX)

2010-06-01

97

NASA Astrophysics Data System (ADS)

Three dimensional velocity models constructed through seismic tomography are seldom digitally processed further for imaging structural features. A study conducted to evaluate the potential for imaging subsurface discontinuities in horizontal and vertical direction from three dimensional velocity models using image processing/computer vision techniques has provided significant results. Three-dimensional velocity models constructed through tomographic inversion of active source and/or earthquake traveltime data are generally built from an initial 1-D velocity model that varies only with depth. Regularized tomographic inversion algorithms impose constraints on the roughness of the model that help to stabilize the inversion process. Final velocity models obtained from regularized tomographic inversions have smooth three-dimensional structures that are required by the data. Final velocity models are usually analyzed and interpreted either as a perturbation velocity model or as an absolute velocity model. Compared to perturbation velocity model, absolute velocity model has an advantage of providing constraints on lithology. Both velocity models lack the ability to provide sharp constraints on subsurface faults. However, results from the analysis of the 3-D velocity model from northern Cascadia using Roberts, Prewitt, Sobel, and Canny operators show that subsurface faults that are not clearly interpretable from velocity model plots can be identified through this approach. This analysis resulted in inferring the locations of Tacoma Fault, Seattle Fault, Southern Whidbey Island Fault, and Darrington Devils Mountain fault much clearly. The Coast Range Boundary Fault, previously hypothesized on the basis of sedimentological and tectonic observations is inferred clearly from processed images. Many of the fault locations so imaged correlate with earthquake hypocenters indicating their seismogenic nature.

Ramachandran, K.

2011-12-01

98

MODELLING TRANSIENT VARIABLY SATURATED FLOW IN SILT LOAM SOILS USING HYDRUS-1D

Technology Transfer Automated Retrieval System (TEKTRAN)

The Hydrus-1D software package (Simunek et al., 1998), based on the Richards equation, was used to study variably saturated flow and deep drainage in an old abandoned terraced area under grass. The field site was located in the Vallcebre research catchment of the Eastern Pyrenees in North-Eastern Sp...

99

MODELLING TRANSIENT VARIABLY SATURATED FLOW UNDER NATURAL CONDITIONS USING HYDRUS-1D

Technology Transfer Automated Retrieval System (TEKTRAN)

The Hydrus-1D software package (Simunek et al., 1998), based on the Richards equation, was used to study variably saturated flow and deep drainage in an old abandoned terraced area under grass. The field site was located in the Vallcebre research catchment of the Eastern Pyrenees in North-Eastern Sp...

100

A 1-D Computer Simulation Model of Collective Ion Acceleration by Linear Electron Beams.

National Technical Information Service (NTIS)

A 1-d electrostatic and relativistic particle code has been built in order to simulate a self-consistent way the time-dependent behavior of collective ion acceleration produced by linear electron beams injected into evacuated drift tubes. The simulation r...

A. Sternlieb H. S. Ulm

1979-01-01

101

Traveling waves in an optimal velocity model of freeway traffic

Car-following models provide both a tool to describe traffic flow and algorithms for autonomous cruise control systems. Recently developed optimal velocity models contain a relaxation term that assigns a desirable speed to each headway and a response time over which drivers adjust to optimal velocity conditions. These models predict traffic breakdown phenomena analogous to real traffic instabilities. In order to

Peter Berg; Andrew Woods

2001-01-01

102

Oxidation mechanisms and kinetics of 1D-SiC/C/SiC composite materials; 2: Modeling

A model, based on a simple axisymmetrical fiber/interphase/matrix assembly, is derived to depict the oxidation behavior of 1D-SiC/C/SiC composites within the temperature range 900--1300 C and for 10

Filipuzzi, L.; Naslain, R. (Domaine Univ., Pessac (France). Lab. des Composites Thermostructuraux)

1994-02-01

103

Multi-objective optimisation of cost-benefit of urban flood management using a 1D2D coupled model.

This paper presents a multi-objective optimisation (MOO) tool for urban drainage management that is based on a 1D2D coupled model of SWMM5 (1D sub-surface flow model) and BreZo (2D surface flow model). This coupled model is linked with NSGA-II, which is an Evolutionary Algorithm-based optimiser. Previously the combination of a surface/sub-surface flow model and evolutionary optimisation has been considered to be infeasible due to the computational demands. The 1D2D coupled model used here shows a computational efficiency that is acceptable for optimisation. This technological advance is the result of the application of a triangular irregular discretisation process and an explicit finite volume solver in the 2D surface flow model. Besides that, OpenMP based parallelisation was employed at optimiser level to further improve the computational speed of the MOO tool. The MOO tool has been applied to an existing sewer network in West Garforth, UK. This application demonstrates the advantages of using multi-objective optimisation by providing an easy-to-comprehend Pareto-optimal front (relating investment cost to expected flood damage) that could be used for decision making processes, without repeatedly going through the modelling-optimisation stage. PMID:21411958

Delelegn, S W; Pathirana, A; Gersonius, B; Adeogun, A G; Vairavamoorthy, K

2011-01-01

104

Brain glucose supplies most of the carbon required for acetyl-coenzyme A (acetyl-CoA) generation (an important step for myelin synthesis) and for neurotransmitter production via further metabolism of acetyl-CoA in the tricarboxylic acid (TCA) cycle. However, it is not known whether reduced brain glucose transporter type I (GLUT-1) activity, the hallmark of the GLUT-1 deficiency (G1D) syndrome, leads to acetyl-CoA, TCA or neurotransmitter depletion. This question is relevant because, in its most common form in man, G1D is associated with cerebral hypomyelination (manifested as microcephaly) and epilepsy, suggestive of acetyl-CoA depletion and neurotransmitter dysfunction, respectively. Yet, brain metabolism in G1D remains underexplored both theoretically and experimentally, partly because computational models of limited brain glucose transport are subordinate to metabolic assumptions and partly because current hemizygous G1D mouse models manifest a mild phenotype not easily amenable to investigation. In contrast, adult antisense G1D mice replicate the human phenotype of spontaneous epilepsy associated with robust thalamocortical electrical oscillations. Additionally, and in consonance with human metabolic imaging observations, thalamus and cerebral cortex display the lowest GLUT-1 expression and glucose uptake in the mutant mouse. This depletion of brain glucose is associated with diminished plasma fatty acids and elevated ketone body levels, and with decreased brain acetyl-CoA and fatty acid contents, consistent with brain ketone body consumption and with stimulation of brain beta-oxidation and/or diminished cerebral lipid synthesis. In contrast with other epilepsies, astrocyte glutamine synthetase expression, cerebral TCA cycle intermediates, amino acid and amine neurotransmitter contents are also intact in G1D. The data suggest that the TCA cycle is preserved in G1D because reduced glycolysis and acetyl-CoA formation can be balanced by enhanced ketone body utilization. These results are incompatible with global cerebral energy failure or with neurotransmitter depletion as responsible for epilepsy in G1D and point to an unknown mechanism by which glycolysis critically regulates cortical excitability.

Marin-Valencia, Isaac; Good, Levi B.; Ma, Qian; Duarte, Joao; Bottiglieri, Teodoro; Sinton, Christopher M.; Heilig, Charles W.; Pascual, Juan M.

2012-01-01

105

NASA Astrophysics Data System (ADS)

The Bindo-Cortenova landslide is a large, active slope failure located in the Italian Prealps close to the Lake of Cuomo. The unstable area covers 1.2 km2 and extends between 450 and 1200 m a.s.l. The landslide site is formed by the paleo-landslide material that consists of large to extremely large blocks of reddish sandstone and conglomerate (Verrucano Lombardo) immersed in a matrix of gravely sand, from coarse to fine. A first major landslide of about 80.000 m3 took place on 29 Novembre 2002, two days after a second landslide involved about 1 to 1.2 million m3 of debris covering a slope sector of about 85.000 m2 and causing important damages on properties. These failures coincide with a period of extraordinary heavy rainfall, 493 up to 875 mm of cumulative rainfall were measured in Novembre 2002 and the most intensive rainfall season is generally in May with the average monthly precipitation between 160 and 190 mm. Until today field observations show a close relation between ground movement and rainfall intensity. Monitoring and modeling are two important tools to predict the landslide behavior and prediction is necessary to guarantee the safety of this area. This work presents a simple 1D infinite slope model to reproduce slow landslides mobility directly from the known daily rainfall intensity. The model reproduces in a simple coupling way: rainfall infiltration, ground water changes and kinematic deformation. Concerning rainfall infiltration, changes in groundwater level have been taken directly proportional to the rainfall intensity and governed by a dissipation model of the excess pore-fluid through a simple consolidation equation. Concerning the kinematic deformation, the 1D infinite slope model assumes a pre-existing slip surface where the shear strength is at residual conditions and includes a viscoplastic behavior, the predicted movements are concentrated within a relatively narrow shear zone above which the sliding mass moves essentially as a rigid body. The time evolution of the computed ground water level has been compared to the recorded data given by a borehole. In turn, computed deformation evolution has been compared to the ground displacement data given by novel inSAR monitoring system. The main advantage of such a model lies in its relatively simple applicability, very few parameters are needed to reproduce qualitatively and "quantitatively" the recorded motion. The main drawback is that the computed solution depends strongly on the given input data, that means that very slight changes in an input parameter induce important changes in the computed solution.

Fernandez Merodo, Jose Antonio; Battista Crosta, Giovanni; Secondi, Marco

2010-05-01

106

NASA Astrophysics Data System (ADS)

With the advent of airborne electromagnetic (AEM), large areas can be investigated with a high density of geophysical soundings: flight lines are typically tens of kilometers long with a sounding for each 3-30m and line spacing of 200-1000m. AEM soundings are usually inverted to 1D layered-earth resistivity models, possibly with spatially constrained inversion algorithms which take into account neighboring soundings for the inversion and provide a more consistent set of resistivity models. But as 3D inversion of AEM data remains unsolved, the visualization of these rich datasets representing 3D geological structures is often limited to 2D cross-sections and thematic maps. We present a new methodology to tackle the need for 3D visualization of resistivity structures. Our method is based on the regional 2D interpolation of the geophysical model parameters: layer thicknesses and resistivities obtained from geophysical inversion are mapped in the 2D horizontal space. From these maps, a 3D irregular mesh is generated according to the geometry of the 1D geophysical models. The cells constituting the 3D grid are irregular hexahedra which accurately follow the geometry of geophysical interfaces. This produces very fine, but memory-light 3D grids of resistivity at low computational cost. The 3D grid is then written to VTK standards and can be read with a powerful 3D visualization software which is freely available. The error from inversion, expressed as the standard deviation of model parameters, is used to weight each sounding during interpolation, which gives more importance to 1D models with a low residual between the sounding data and the 1D geophysical model. The propagation of uncertainty during interpolation is quantified and expressed as a standard deviation factor in each cell of the model. This is made possible by the use of kriging for interpolation, and allows the extraction of regions of the 3D grid which match given quality criteria. The reliability of the 3D grid, and its ability to represent heterogeneities present in the 1D models depend on the resolution of the 3D grid and the quality of the interpolation. The 3D grid is provided with a quantification of the loss of detail due to gridding process. The method is largely illustrated with a case study based on a SkyTEM airborne transient electromagnetic geophysical survey conducted on two islands in Galápagos Archipelago in 2006. The 3D resistivity grid of this extensive survey provides unprecedented images. Resistivity thresholds applied to the 3D grid allows the delineation of 3D geological bodies, providing unprecedented insights into the hydrogeology and geological structures of these volcanic islands.

Pryet, A.; Ramm, J.; Auken, E.; Chilès, J.; Violette, S.; D'Ozouville, N.; Deffontaines, B.

2010-12-01

107

1D radiative transfer models of 21 and 30 ?m emission features in proto-planetary nebulae

NASA Astrophysics Data System (ADS)

Spectral energy distributions of six proto-planetary nebulae showing 21 and 30? features were fit with models obtained from 1D radiative transfer code, taking FeO and MgS respectively are the carriers of the features. Atomic abundances of these carrier materials were derived and they are lower or comparable to their stellar photospheric values. This stregthens the possibility of these materials to become the carriers of their respective features.

Muthumariappan, Chinnathambi; Reddy, Bacham E.

2012-08-01

108

NASA Astrophysics Data System (ADS)

The development of velocity models for the continental crust and lithosphere is critical in supporting ongoing efforts to monitor for clandestine nuclear explosions within the Comprehensive Nuclear-Test Ban Treaty (CTBT). Detailed velocity models are required to accurately predict travel-times for local and regional phases, such as Pg, Pn, Sn, and Lg, as well as body waves at upper-mantle triplication distances, and thus improve our ability to accurately locate small-yield events with sparse seismic networks. Taking advantage of the vast amounts of open data accumulated over the past decades at the Incorporated Research Institute for Seismology (IRIS), we are developing regionalized models of lithospheric velocity structure for a wide variety of tectonic regions throughout Eurasia and the Middle East. Velocity models have traditionally been obtained from separate analysis of different seismic observations, each having its own sensitivities, resolving power, and trade-offs. Our approach consists of combining complementary seismic observations through a joint inversion scheme to produce integrated velocity models that bridge resolution gaps and minimize trade-offs. Seismic observations in our study include P- and S-wave receiver functions for all the open broadband stations within the study area archived at the IRIS Data Management Center, and fundamental-mode, Rayleigh-wave group velocities from an independent, continental-scale surface-wave tomography study. We first obtain joint inversion models consisting of 1D velocity-depth profiles local to the recording stations, where crustal thickness is constrained by P-wave receiver functions, lithospheric thickness is constrained by S-wave receiver functions, and background S-velocity is constrained by surface-wave dispersion, and then combine the velocity-depth profiles within geologic/tectonic provinces to produce average velocity models for each region. Validation of the resulting velocity models through full waveform modeling of well-located local and regional events reveals that, in general, minor tuning of the regionalized models is required to satisfactorily explain the waveforms.

Julia, J.; Matzel, E.; Nyblade, A.; Rodgers, A. J.

2010-12-01

109

A Distributed Highway Velocity Model for Traffic State Reconstruction

This article is motivated by the practical problem of highway traffic estimation using velocity measurements from GPS enabled mobile devices such as cell phones. In order to simplify the estimation procedure, a velocity model for highway traffic is constructed, which results in a dynamical system in which the observation operator is linear. This article presents a new scalar hyperbolic partial

Daniel B. Work; Sébastien Blandin; Olli-Pekka Tossavainen; Benedetto Piccoli; Alexandre M. Bayen

2009-01-01

110

The Velocity Model of Chinese Continent Established by GNSS Observations

With the high precision repeated GNSS observations, the Multi-quadric equations interpolation method is used to establish the velocity model of Chinese continent's crustal movement. The valuable present-day horizontal and vertical crustal movement velocity images are obtained. The eastwardly movement trend of Chinese continent is quite evident, and there is a trend of clockwise rolling, from northeast to east, then to

Y. Yao

2009-01-01

111

Modeling maximum astrophysical gravitational recoil velocities

We measure the recoil velocity as a function of spin for equal-mass, highly spinning black-hole binaries, with spins in the orbital plane, equal in magnitude, and opposite in direction. We confirm that the leading-order effect is linear in the spin and the cosine of angle between the spin direction and the infall direction at the merger. We find higher-order corrections that are proportional to the odd powers in both the spin and cosine of this angle. Taking these corrections into account, we predict that the maximum recoil will be 3680{+-}130 km s{sup -1}.

Lousto, Carlos O.; Zlochower, Yosef [Center for Computational Relativity and Gravitation, School of Mathematical Sciences, Rochester Institute of Technology, 78 Lomb Memorial Drive, Rochester, New York 14623 (United States)

2011-01-15

112

Continuous model of the regional velocity field for Poland

NASA Astrophysics Data System (ADS)

The poster presents modern determinations of the regional velocity field for Poland. The research is based on the ASG-EUPOS, Polish multifunctional GNNS network and performed within the developmental project of the Polish Ministry of Science and Higher Education. The network of the satellite-based sites consisted of above 130 Polish sites together with the selected number of European sites operating within EPN (EUREF Permanent Network). Data came from three-year period, which is the minimum number for the horizontal velocity determinations. The velocities were calculated within the discrete network related to the GNSS sites' distribution and then interpolated to the regular grid. The discussion on the interpolation methods is also included. To the interpolation of the velocity field kriging, spline and other functions were used. Assessment of the accuracy of the velocity on the interpolated points and tests of significance were also described. Developed models of the velocities field could indicate geodynamical activity on the area of Poland.

Bogusz, J.; Figurski, M.; Kontny, B.; Grzempowski, P.; Klos, A.

2012-04-01

113

A Vs30-derived Near-surface Seismic Velocity Model

NASA Astrophysics Data System (ADS)

Shallow material properties, S-wave velocity in particular, strongly influence ground motions, so must be accurately characterized for ground-motion simulations. Available near-surface velocity information generally exceeds that which is accommodated by crustal velocity models, such as current versions of the SCEC Community Velocity Model (CVM-S4) or the Harvard model (CVM-H6). The elevation-referenced CVM-H voxel model introduces rasterization artifacts in the near-surface due to course sample spacing, and sample depth dependence on local topographic elevation. To address these issues, we propose a method to supplement crustal velocity models, in the upper few hundred meters, with a model derived from available maps of Vs30 (the average S-wave velocity down to 30 meters). The method is universally applicable to regions without direct measures of Vs30 by using Vs30 estimates from topographic slope (Wald, et al. 2007). In our current implementation for Southern California, the geology-based Vs30 map of Wills and Clahan (2006) is used within California, and topography-estimated Vs30 is used outside of California. Various formulations for S-wave velocity depth dependence, such as linear spline and polynomial interpolation, are evaluated against the following priorities: (a) capability to represent a wide range of soil and rock velocity profile types; (b) smooth transition to the crustal velocity model; (c) ability to reasonably handle poor spatial correlation of Vs30 and crustal velocity data; (d) simplicity and minimal parameterization; and (e) computational efficiency. The favored model includes cubic and square-root depth dependence, with the model extending to a depth of 350 meters. Model parameters are fit to Boore and Joyner's (1997) generic rock profile as well as CVM-4 soil profiles for the NEHRP soil classification types. P-wave velocity and density are derived from S-wave velocity by the scaling laws of Brocher (2005). Preliminary assessment of the new model is preformed with ground motion simulations for a selection of likely M > 7 scenario events for Southern California (as define by the SCEC Big Ten project).

Ely, G. P.; Jordan, T. H.; Small, P.; Maechling, P. J.

2010-12-01

114

A 1D model for tides waves and fine sediment in short tidal basins—Application to the Wadden Sea

NASA Astrophysics Data System (ADS)

In order to simulate the dynamics of fine sediments in short tidal basins, like the Wadden Sea basins, a 1D cross-sectional averaged model is constructed to simulate tidal flow, depth-limited waves, and fine sediment transport. The key for this 1D model lies in the definition of the geometry (width and depth as function of the streamwise coordinate). The geometry is computed by implementing the water level and flow data, from a 2D flow simulation, and the hypsometric curve in the continuity equation. By means of a finite volume method, the shallow-water equations and sediment transport equations are solved. The bed shear stress consists of the sum of shear stresses by waves and flow, in which the waves are computed with a depth-limited growth equation for wave height and wave frequency. A new formulation for erosion of fines from a sandy bed is proposed in the transport equation for fine sediment. It is shown by comparison with 2D simulations and field measurements that a 1D schematization gives a proper representation of the dynamics in short tidal basins.

van Prooijen, Bram Christiaan; Wang, Zheng Bing

2013-09-01

115

In this project, we are developing models of lithospheric structure for a wide variety of tectonic regions throughout Eurasia and the Middle East by regionalizing 1D velocity models obtained by jointly inverting P-wave and S-wave receiver functions with Rayleigh wave group and phase velocities. We expect the regionalized velocity models will improve our ability to predict travel-times for local and regional phases, such as Pg, Pn, Sn and Lg, as well as travel-times for body-waves at upper mantle triplication distances in both seismic and aseismic regions of Eurasia and the Middle East. We anticipate the models will help inform and strengthen ongoing and future efforts within the NNSA labs to develop 3D velocity models for Eurasia and the Middle East, and will assist in obtaining model-based predictions where no empirical data are available and for improving locations from sparse networks using kriging. The codes needed to conduct the joint inversion of P-wave receiver functions (PRFs), S-wave receiver functions (SRFs), and dispersion velocities have already been assembled as part of ongoing research on lithospheric structure in Africa. The methodology has been tested with synthetic 'data' and case studies have been investigated with data collected at an open broadband stations in South Africa. PRFs constrain the size and S-P travel-time of seismic discontinuities in the crust and uppermost mantle, SRFs constrain the size and P-S travel-time of the lithosphere-asthenosphere boundary, and dispersion velocities constrain average S-wave velocity within frequency-dependent depth-ranges. Preliminary results show that the combination yields integrated 1D velocity models local to the recording station, where the discontinuities constrained by the receiver functions are superimposed to a background velocity model constrained by the dispersion velocities. In our first year of this project we will (i) generate 1D velocity models for open broadband seismic stations in the western half of the study area (Eurasia and the Middle East) and (ii) identify well located seismic events with event-station paths isolated to individual tectonic provinces within the study area and collect broadband waveforms and source parameters for the selected events. The 1D models obtained from the joint inversion will then be combined with published geologic terrain maps to produce regionalized models for distinctive tectonic areas within the study area, and the models will be validated through full waveform modeling of well-located seismic events recorded at local and regional distances.

Julia, J; Nyblade, A; Hansen, S; Rodgers, A; Matzel, E

2009-07-06

116

An improved velocity increment model based on Kolmogorov equation of filtered velocity

NASA Astrophysics Data System (ADS)

The velocity increment (VI) model, which was introduced by Brun et al., is improved by employing the Kolmogorov equation of filtered velocity in this paper. This model has two different formulations: a dynamic formulation and a simplified constant form in high Reynolds number turbulence. A priori tests in isotropic turbulence and wall-bounded turbulence are performed. A posteriori tests of decaying turbulence and channel Poiseuille flow are made to testify the model performance, especially on the energy backscatter. The simple constant coefficient formulation has good performance, and avoids the ensemble average operation, which exists in other subgrid models. This constant improved VI model is particularly proposed in complicated large-eddy simulation projects.

Fang, L.; Shao, L.; Bertoglio, J. P.; Cui, G. X.; Xu, C. X.; Zhang, Z. S.

2009-06-01

117

Evaluating 3-D and 1-D mathematical models for mass transport in heterogeneous biofilms

Results from a three dimensional model for heterogeneous biofilms including the numerical solution of hydrodynamics were compared to simplified one dimensional models. A one dimensional model with a variable diffusion coefficient over the thickness of the biofilm was well suited to approximate average concentration profiles of three dimensional simulations of rough biofilms. A new compartmentalized one dimensional model is presented

E. Morgenroth; H. Eberl; M. C. M van Loosdrecht

2000-01-01

118

Friction model for the velocity dependence of nanoscale friction

NASA Astrophysics Data System (ADS)

The velocity dependence of nanoscale friction is studied for the first time over a wide range of velocities between 1 µm s-1 and 10 mm s-1 on large scan lengths of 2 and 25 µm. High sliding velocities are achieved by modifying an existing commercial atomic force microscope (AFM) setup with a custom calibrated nanopositioning piezo stage. The friction and adhesive force dependences on velocity are studied on four different sample surfaces, namely dry (unlubricated), hydrophilic Si(100); dry, partially hydrophobic diamond-like carbon (DLC); a partially hydrophobic self-assembled monolayer (SAM) of hexadecanethiol (HDT); and liquid perfluoropolyether lubricant, Z-15. The friction force values are seen to reverse beyond a certain critical velocity for all the sample surfaces studied. A comprehensive friction model is developed to explain the velocity dependence of nanoscale friction, taking into consideration the contributions of adhesion at the tip-sample interface, high impact velocity-related deformation at the contacting asperities and atomic scale stick-slip. A molecular spring model is used for explaining the velocity dependence of friction force for HDT.

Tambe, Nikhil S.; Bhushan, Bharat

2005-10-01

119

The bimolecular reaction O({sup 1}D)+N{sub 2}O{yields}NO+NO was photoinitiated in the (N{sub 2}O){sub 2} dimer at a wavelength of 193 nm and was investigated by three-dimensional (3D) velocity map imaging. State selective 3D momentum vector distributions were monitored and analyzed. For the first time, kinetic energy resolution and stereodynamic information about the reaction under constrained geometry conditions is available. Directly observable NO products exhibit moderate vibrational excitation and are rotationally and translationally cold. Speed and spatial distributions suggest a pronounced backward scattering of the observed products with respect to the direction of motion of the O({sup 1}D) atom. Forward scattered partner products, which are not directly detectable are also translationally cold, but carry very large internal energy as vibration or rotation. The results confirm and extend previous studies on the complex initiated reaction system. The restricted geometry of the van der Waals complex seems to favor an abstraction reaction of the terminal nitrogen atom by the O({sup 1}D) atom, which is in striking contrast to the behavior observed for the unrestricted gas phase reaction under bulk conditions.

Goedecke, Niels; Maul, Christof; Kauczok, Sebastian; Gericke, Karl-Heinz [Institut fuer Physikalische und Theoretische Chemie, Technische Universitaet Braunschweig, Braunschweig (Germany); Chichinin, Alexey I. [Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk (Russian Federation)

2009-08-07

120

NASA Astrophysics Data System (ADS)

Vegetation fires emit hot gases and particles which are rapidly transported upward by the positive buoyancy generated by the combustion process. In general, the final vertical height that the smoke plumes reach is controlled by the thermodynamic stability of the atmospheric environment and the surface heat flux released by the fire. However, the presence of a strong horizontal wind can enhance the lateral entrainment and induce additional drag, particularly for small fires, impacting the smoke injection height. In this paper, we revisit the parameterization of the vertical transport of hot gases and particles emitted from vegetation fires, described in Freitas et al. (2007), to include the effects of environmental wind on transport and dilution of the smoke plume at its scale. This process is quantitatively represented by introducing an additional entrainment term to account for organized inflow of a mass of cooler and drier ambient air into the plume and its drag by momentum transfer. An extended set of equations including the horizontal motion of the plume and the additional increase of the plume radius is solved to simulate the time evolution of the plume rise and the smoke injection height. One-dimensional (1-D) model results are presented for two deforestation fires in the Amazon basin with sizes of 10 and 50 ha under calm and windy atmospheric environments. The results are compared to corresponding simulations generated by the complex non-hydrostatic three-dimensional (3-D) Active Tracer High resolution Atmospheric Model (ATHAM). We show that the 1-D model results compare well with the full 3-D simulations. The 1-D model may thus be used in field situations where extensive computing facilities are not available, especially under conditions for which several optional cases must be studied.

Freitas, S. R.; Longo, K. M.; Trentmann, J.; Latham, D.

2010-01-01

121

NASA Astrophysics Data System (ADS)

We revisit the parameterization of the vertical transport of hot gases and particles emitted from biomass burning, described in Freitas et al. (2007), to include the effects of environmental wind on transport and dilution of the smoke plume at the cloud scale. Typically, the final vertical height that the smoke plumes reach is controlled by the thermodynamic stability of the atmospheric environment and the surface heat flux released by the fire. However, the presence of a strong horizontal wind can enhance the lateral entrainment and induce additional drag, particularly for small fires, impacting the smoke injection height. This process is quantitatively represented by introducing an additional entrainment term to account for organized inflow of a mass of cooler and drier ambient air into the plume and its drag by momentum transfer. An extended set of equations including the horizontal motion of the plume and the additional increase of the plume radius is solved to explicitly simulate the time evolution of the plume rise with the additional mass and momentum. One-dimensional (1-D) model results are presented for two deforestation fires in the Amazon basin with sizes of 10 and 50 ha under calm and windy atmospheric environments. The results are compared to corresponding simulations generated by the complex non-hydrostatic three dimensional (3-D) Active Tracer High resolution Atmospheric Model (ATHAM). We show that the 1-D model results compare well with the full 3-D simulations. The 1-D model may thus be used in field situations where extensive computing facilities are not available, especially under conditions for which several optional cases must be studied.

Freitas, S. R.; Longo, K. M.; Trentmann, J.; Latham, D.

2009-07-01

122

A case study comparing 1-D and 3-D analytical modeling methods for vehicle intake system design

NASA Astrophysics Data System (ADS)

There is intense competition among automakers to create ever-quieter vehicles and powertrains. Exterior and interior noise of many vehicles is significantly influenced by noise coming from the engine intake system. In order to address this source, significant effort needs to be expended on the noise design of an engine's intake system. Cost and time constraints tend to make intake designers ignore many complexities in their modeling efforts, specifically in assuming rigid walls, and using 1D model methods. This paper, presents a case study comparing results for a particular intake system between a 1D model, the 3-D boundary element analysis (BEA) method, both coupled and uncoupled to the structure and the new ACTRAN code by fft/MSC of analyzing coupled structure/fluid systems. The structure accuracy of the result is compared to measurements of a physical prototype. Costs and time required are compared, as well as some of the modeling issues encountered and the relative accuracy of each method.

Aubert, Allan C.; Green, Ed; Bastiaan, Jennifer; Leclercq, Thomas

2005-09-01

123

Quantum analysis of Jackiw and Teitelboim's model for (1 + 1)D gravity and topological gauge theory

NASA Astrophysics Data System (ADS)

We study the BRST quantization of the (1 + 1)-dimensional gravity model proposed by Jackiw and Teitelboim and also the topological gauge model which is equivalent to the gravity model at least classically. The gravity model quantized in the light-cone gauge is found to be a free theory with a nilpotent BRST charge. We show also that there exist twisted N = 2 superconformal algebras in the Jackiw-Teitelboim model as well as in the topological gauge model. We discuss the quantum equivalence between the gravity theory and the topological gauge theory. It is shown that these theories are indeed equivalent to each other in the light-cone gauge. Research supported in part by Sasakawa Scientific Research Grants of the Japan Science Society.

Terao, Haruhiko

1993-05-01

124

NASA Astrophysics Data System (ADS)

Recently, efforts have been done forward the development of methodologies to obtain flow estimates from time series of water height at virtual stations (VS - intersections between satellite tracks and water surfaces) from Topex/Poseidon (TP) and ENVISAT radar mission measurements. Relatively simple 1D propagation models such as Muskingum-Cunge (M-C) Routing Model have presented good results in the water flow propagation in Amazonian rivers. These regions suffer, in most cases, of lack of information witch constrains more accurate hydrologic and hydraulic studies. Nevertheless, these M-C models make a lot of simplification witch may cause the lost of important information that these quasi-ungaged basins can offer. This paper presents a comparison between two propagation models to the estimation of water flow series constrained by T/P and ENVISAT data. The models are: ProGUM, a Muskingum-Cunge flow routing model with diffusion-cum-dynamic wave propagation, and HEC-RAS, a well-known 1D hydrodynamic model. The verification was made in four reaches in the Negro River Basin. Each of these reaches are limited by two gauge stations, one upstream and the other one downstream. A total of five VS distributed over the reaches were analyzed. Previous studies have shown that ProGUM may yield errors less then 10% in validation phases. Here, it is demonstrated that, no much improvements can be achieved by using a more complete model capable to absorb the available data and simplifications of a M-C Model do not make significant modifications in the results of rating curve generation from satellite altimetry.

Getirana, A. C.; Bonnet, M.; Roux, E.; Rotunno, O. C.

2007-12-01

125

Asymptotic form of level density distributions for a class of inhomogeneous 1D vertex models

NASA Astrophysics Data System (ADS)

Level density distributions for some Haldane-Shastry like spin chains associated with AN-1 root system have been computed recently by Enciso et al., using the connection of these spin chains with inhomogeneous one-dimensional vertex models. The energy functions of such vertex models are given by specific polynomials of first or second degree. Here we consider a much broader class of one-dimensional vertex models whose energy functions are given by arbitrary polynomials of any possible degree and show that the level densities for this class of vertex models asymptotically follow the Gaussian distribution for large number of vertices.

Banerjee, P.; Basu-Mallick, B.

2013-01-01

126

NASA Astrophysics Data System (ADS)

Ambient noise records, processed through spectral ratio techniques were used to assess the dynamic properties of a sample survey of both reinforced concrete and masonry buildings. Soil-structure interactions were also investigated using simple 1D modeling to evaluate site amplifications, comparing the results with target spectra postulated by Eurocode8 requirements. The experimental periods obtained are always lower than those proposed by the building regulations. Therefore one has to pay attention in estimating seismic actions, particularly in those sites of the urban area where there are outcrops of either volcanic products or soft coarse materials.

Panzera, F.; Lombardo, G.; Muzzetta, I.

127

A thermomechanical model for a 1-D shape memory alloy wire with propagating instabilities

A thermomechanical boundary value problem and constitutive model are presented for a shape memory alloy (SMA) wire under uniaxial loading. The intent is to develop a one-dimensional continuum model of an SMA element that includes all the relevant thermomechanical couplings and is suitable for inclusion in finite element analyses. Thermodynamic relations are derived from phenomenological considerations consistent with recent experimental

John A. Shaw

2002-01-01

128

Structure preserving model order reduction of heterogeneous 1-D distributed systems

We consider the problem of model order reduction for spatially-varying interconnected systems distributed in one spatial dimension. The sequentially semi-separable matrix structure of such systems can be exploited to allow efficient structure preserving model order reduction using the matrix sign function. Iterative algorithms are provided for fast computation, which is demonstrated on an example.

Justin K. Rice; Michel Verhaegen

2009-01-01

129

This paper presents the results of a study to determine the capability of a computational simulation model, CCHE1D, for simulating unsteady flow, sediment transport and morphodynamic processes in natural rivers during flood propagation. The results convincingly confirmed that the CCHE1D is capable of predicting the water elevations, the flow discharges and the morphodynamic changes of the main streams of two

Sam S. Y. Wang; Weiming Wu; Han-Min Hsia; Chang-Chi Cheng

130

Low-velocity shocks models (Lesaffre+, 2013)

NASA Astrophysics Data System (ADS)

Outputs from the grids of shock runs used in the paper. * The first level of the directory tree decides the value for the magnetic field (b=(B/Bo)/sqrt(nH), with Bo=1?Gauss=10-10T): b0.1/ for b=0.1 b1/ for b=1 * The second level decides the value for the density and the type of shock: b0.1/J2g0/ has J-type shocks for nH=102cm-3 b0.1/J3g0/ has J-type shocks for nH=103cm-3 b0.1/J4g0/ has J-type shocks for nH=104cm-3 b1/J2g0/ has J-type shocks for nH=102cm-3 b1/J3g0/ has J-type shocks for nH=103cm-3 b1/J4g0/ has J-type shocks for nH=104cm-3 b1/C2g0/ has C-type shocks for nH=102cm-3 b1/C3g0/ has C-type shocks for nH=103cm-3 b1/C4g0/ has C-type shocks for nH=104cm-3 * The third level contains : - static/ the run to get the pre-shock thermal and chemical equilibrium - steady/ the 'PDR' run from these pre-shock conditions. - u

Lesaffre, P.; Pineau Des Forets, G.; Godard, B.; Guillard, P.; Boulanger, F.; Falgarone, E.

2012-11-01

131

SCEC CVM-Toolkit (CVM-T) -- High Performance Meshing Tools for SCEC Community Velocity Models

NASA Astrophysics Data System (ADS)

The SCEC Community Velocity Model Toolkit (CVM-T) enables earthquake modelers to quickly build, visualize, and validate large-scale 3D velocity meshes using SCEC CVM-H or CVM-4. CVM-T is comprised of three main components: (1) a current SCEC community velocity model for Southern California, (2) tools for extracting meshes from this model and visualizing them, and (3) an automated test framework for evaluating new releases of CVMs using SCEC’s AWP-ODC forward wave propagation software and one, or more, ground motion goodness of fit (GoF) algorithms. CVM-T is designed to help SCEC modelers build large-scale velocity meshes by extracting material properties from the most current version of Community Velocity Model H (CVM-H) and to provide a consistent interface as new CVM-H versions are developed. The CVM-T software provides a highly-scalable interface to CVM-H 6.2 (and later) voxets. Along with an improved interface to CVM-H material properties, the CVM-T software adds a geotechnical layer (GTL) to CVM-H 6.2+ based on Ely’s Vs30-derived GTL. The initial release of CVM-T also extends the coverage region for CVM-H 6.2 with a Hadley-Kanamori 1D background. Smoothing is performed within the transition boundary between the core model and the 1D background. The user interface now includes a C API that allows applications to query the model either by elevation or depth. The Extraction and Visualization Tools (EVT) include a parallelized 3D mesh generator which can quickly generate meshes (consisting of Vp, Vs, and density) from either CVM-H or CVM-4 with over 100 billion points. Python plotting scripts can be employed to plot horizontal or profile slices from existing meshes or directly from either CVM. The Automated Test Framework (ATF) is a system for quantitatively evaluating new versions of CVM-H and ensuring that the model improves against prior versions. The ATF employs the CruiseControl build and test framework to run an AWP-ODC simulation for the 2008 Chino Hills event (Mw = 5.39) and perform a goodness of fit statistics calculation on the generated synthetic and recorded observed seismograms using the GoF algorithm, based on comparison of synthetic peak amplitudes to observed peak amplitudes, used in the SCEC Broadband platform. CVM-T produced plots include comparisons of synthetic and observed seismograms, plots of bias versus period, and spatial plots of the pseudo-AA bias over the entire region.

Small, P.; Maechling, P. J.; Ely, G. P.; Olsen, K. B.; Withers, K.; Graves, R. W.; Jordan, T. H.; Plesch, A.; Shaw, J. H.

2010-12-01

132

A P wave velocity model of Earth's core

NASA Astrophysics Data System (ADS)

Present Earth core models derived from the retrieval of global Earth structure are based on absolute travel times, mostly from the International Seismological Centre (ISC), and/or free-oscillation eigenfrequencies. Many core phase data are left out of these constructions, e.g., PKP differential travel times, amplitude ratios, and waveforms. This study is an attempt to utilize this additional information to construct a model of core P wave velocity which is consistent with the different types of core phase data available. In conjunction with our waveform modeling we used 150 differential time measurements and 87 amplitude ratio measurements, which were the highest-quality observations chosen from a large population of Global Digital Seismograph Network (GDSN) records. As a result of fitting these various data sets, a one-dimensional P wave velocity model of the core, PREM2, is proposed. This model, modified from the Preliminary Reference Earth Model (PREM) (Dziewonski and Anderson, 1981), shows a better fit to the combined data set than any of the existing core models. Major features of the model include a sharp velocity discontinuity at the inner core boundary (ICB), with a large jump (0.78 km/s), and a low velocity gradient at the base of the fluid core. The velocity is nearly constant over the lower 100 km of the outer core. The model features a depth-dependent Q? structure in the inner core such that a constant t* for the inner core fits the amplitude ratios and waveforms of short-period waves moderately well. This means the top of the inner core is more attenuating than the deeper part of the inner core. In addition, the P velocity in the lowermost mantle is reduced from that of PREM as a baseline adjustment for the observed separations of the DF and AB branches of PKP at large distances.

Song, Xiaodong; Helmberger, Don V.

1995-06-01

133

Kovacs effect and fluctuation dissipation relations in 1D kinetically constrained models

NASA Astrophysics Data System (ADS)

Strong and fragile glass relaxation behaviours are obtained simply changing the constraints of the kinetically constrained Ising chain from symmetric to purely asymmetric. We study the out-of-equilibrium dynamics of these two models focusing on the Kovacs effect and the fluctuation-dissipation (FD) relations. The Kovacs or memory effect, commonly observed in structural glasses, is present for both constraints but enhanced with the asymmetric ones. Most surprisingly, the related FD relations satisfy the FD theorem in both cases. This result strongly differs from the simple quenching procedure where the asymmetric model presents strong deviations from the FD theorem.

Buhot, Arnaud

2003-12-01

134

3-D crustal velocity model for Lithuania and its application to local event studies

NASA Astrophysics Data System (ADS)

PASSEQ 2006-2008 project (PASsive Seismic Experiment in TESZ) aimed at studying the lithosphere-asthenosphere system around the TransEuropean Suture Zone (TESZ)- the transition between old Proterozoic platform of north and east Europe and younger Phanerozoic platform in central and western Europe. The experiment was a seismic array research aiming to retrieve the structure of the crust and Earth's mantle down to the mantle transition zone, including mapping of upper mantle seismic velocity variations and discontinuities (Moho, lithosphere-asthenosphere boundary, mantle transition zone) using all available techniques. During the experiment 26 seismic stations (including four broadband stations) were installed in Lithuania and operated since June, 2006 till January, 2008. One of the main reasons of PASSEQ deployment in Lithuania is identification and characterisation of the local seismic activity. During the data acquisition period a number of local seismic events was identified and preliminary event location was made using LocSat and VELEST algorithms and 1-D velocity models. These standard procedures is not enough precise for Lithuania, however, because the thickness of the crust varies significantly in the region (from 45 to 55 km). Another problem was low quality of S-wave arrivals due to thick (up to 2 km) sediments in most part of Lithuania. In order to improve event location, we compiled a 3-D seismic velocity model of the crust down to a depth of 60 km. The model, consisting of four major layers (sediments, upper crust, middle crust, lower crust and uppermost mantle) was interpolated from 2-D velocity models along previous wide-angle reflection and refraction profiles into a regular grid. The quality of the approximation was analysed using comparison of travel times of P-waves recorded by controlled source experiments and calculated travel times through the 3-D velocity model. The model was converted into a density model using a special procedure, in which the density model is approximated by relationship between seismic velocity and density and the latter is found using inversion of the Bouguer anomaly. Comparison of the inversion result to the observed Bouguer anomaly showed that the upper part of the model needs to be corrected, in particular, in the areas not covered by the profiles. The corrected velocity model was then used to improve location of local events. The epicenters of events relocated with the use of a 3-D model are much less scattered and some of the clusters are confined to known areas of human activity.

Budraitis, M.; Kozlovskaya, E.; Janutyte, I.; Motuza, G.

2009-12-01

135

Exact solution of the 1D Hubbard model with NN and NNN interactions in the narrow-band limit

NASA Astrophysics Data System (ADS)

We present the exact solution, obtained by means of the Transfer Matrix (TM) method, of the 1D Hubbard model with nearest-neighbor (NN) and next-nearest-neighbor (NNN) Coulomb interactions in the atomic limit (t = 0). The competition among the interactions (U, V1, and V2) generates a plethora of T = 0 phases in the whole range of fillings. U, V1, and V2 are the intensities of the local, NN and NNN interactions, respectively. We report the T = 0 phase diagram, in which the phases are classified according to the behavior of the principal correlation functions, and reconstruct a representative electronic configuration for each phase. In order to do that, we make an analytic limit T ? 0 in the transfer matrix, which allows us to obtain analytic expressions for the ground state energies even for extended transfer matrices. Such an extension of the standard TM technique can be easily applied to a wide class of 1D models with the interaction range beyond NN distance, allowing for a complete determination of the T = 0 phase diagrams.

Mancini, Ferdinando; Plekhanov, Evgeny; Sica, Gerardo

2013-10-01

136

1D Computational model of a two-phase R744 ejector for expansion work recovery

A one-dimensional mathematical model of the R744 two-phase ejector for expansion work recovery is presented in this paper. Governing equations were formulated for all passages of the ejector based on the differential equations for mass, momentum, and energy balance as well as a differential representation for the equation of state. For two-flow sections (mixer and diffuser) closing equations for mass,

Krzysztof Banasiak; Armin Hafner

2011-01-01

137

Canonical phase diagrams of the 1D Falicov-Kimball model at T = 0

The Falicov-Kimball model of spinless quantum electrons hopping on a 1-dimensional lattice and of immobile classical ions occupying some lattice sites, with only intrasite coupling between those particles, have been studied at zero temperature by means of well-controlled numerical procedures. For selected values of the unique coupling parameter U the restricted phase diagrams (based on all the periodic configurations of

Z. Gajek; J. Jedrzejewski; R. Lemanski

1996-01-01

138

Cellular Dynamical Mean Field Theory for the 1D Extended Hubbard Model

We explore the use of exact diagonalization methods for solving the self\\u000aconsistent equations of the cellular dynamical mean field theory (CDMFT) for\\u000athe one dimensional regular and extended Hubbard models. We investigate the\\u000anature of the Mott transition and convergence of the method as a function of\\u000acluster size as well as the optimal allocation of computational resources\\u000abetween

C. J. Bolech; S. S. Kancharla; G. Kotliar

2002-01-01

139

A 1D coupled Schrödinger drift-diffusion model including collisions

We consider a one-dimensional coupled stationary Schrödinger drift-diffusion model for quantum semiconductor device simulations. The device domain is decomposed into a part with large quantum effects (quantum zone) and a part where quantum effects are negligible (classical zone). We give boundary conditions at the classic–quantum interface which are current preserving. Collisions within the quantum zone are introduced via a Pauli

M.. Baro; N. Ben. Abdallah; P.. Degond; A.. El Ayyadi

2005-01-01

140

Hydrodynamic 1D model of the Amazon river applied to the sediment transport.

NASA Astrophysics Data System (ADS)

We are building a one-dimensional hydrodynamic model of Amazon river and its main tributaries, which takes also into account the solid transport capacities. The model is now performed on a large part of the Brasilian network. At first, the fit of the hydrodynamic model on the observed flood hydrographs in Manaus and Obidos permits us to estimate the part of the floodable areas on the flows (major bed and varzeas) Complementarily, the use of the laws of solid transport capacities depending on the hydraulic conditions is a good tool to analyse, understand and quantify the processes of erosion or deposit. Campaign of measurements are done at different periods of the hydrologic cycle on Amazon, Madeira, Solimoes and Rio Negro rivers: cross sections, bed levels, hydraulic discharges and current profiles with ADCP. The solid discharges are also estimated by measuring a lot of vertical concentration profiles (by sampling, in three verticals for each cross section) in different reaches of the rivers. Grain size distributions are then obtained in laboratory. These data permit us to define the balances and fluxes of suspended matter. A loading law (Dauber-Lebreton or Han formulations) is used in the sediment transport model under non equilibrium conditions. That permits us to propose some assumptions on the reaches in which occur phenomena of deposition or erosion according the flow regime (high or low water). At least, the contribution of the flooded areas is considered. Measurements are done to estimate the input and output flows of suspended matter in the varzea of Curuai, which is choosen as a specimen of a flooded area. The obtained data give some interesting informations on the behaviour of such areas in the balance of sediments.

Baume, J. P.; Kosuth, P.; Le Guennec, B.; Netto, A.; Nicod, J.

2003-04-01

141

Shock formation and traffic jam induced by a crossing in the 1D asymmetric exclusion model

The asymmetric simple-exclusion model on two-crossing one-dimensional lattices is considered for studying shock formation and traffic jams induced by a crossing. The condition for shock formation is derived for car densities p1 and p2 of the first and second street. The phase diagram and the dependence of the traffic current on the car densities are shown. We compare the present

T. Nagatani

1993-01-01

142

A 1-D model of physical chemistry in Saturn's inner magnetosphere

NASA Astrophysics Data System (ADS)

Water vapor spewed out of Enceladus' geysers spreads across the Saturn system through dissociation, charge exchange, and neutral-neutral collisions. The combined effects of impact ionization by suprathermal electrons, charge-exchange between ions and neutrals, and radial transport of the plasma produce the observed distribution of ions and their temperature in the magnetosphere of Saturn. In this paper we combine our physical chemistry model with the neutral cloud model of Cassidy and Johnson (2010) to explore how the spatial distributions of hot electrons and of neutrals, as well as radial transport rates, produce the observed ion properties between 4 and 10 RS (where RS is the radius of Saturn). We investigate the sensitivity of the model output to radial transport rates and the radial profile of hot electron density. Selected results are as follows: (1) Hot electrons (e.g., tens to hundreds eV) at 4 RS (Enceladus' orbit) make up between ?0.25% and 0.5% of the total electron density, consistent with our previous findings, increasing to ˜10% at 10 RS. (2) The region over which chemistry plays a dominant role extends to 7 RS. Beyond 7 RS radial transport takes over, establishing the rate of plasma outflow from Saturn's plasma torus. (3) The plasma radial transport rate at 10 RS is found to be between 20 and 80 kg/s for reasonable choices of hot electron density, radial transport rate, and neutral hydrogen and H2O densities.

Fleshman, B. L.; Delamere, P. A.; Bagenal, F.; Cassidy, T.

2013-08-01

143

Biot-JKD model: Simulation of 1D transient poroelastic waves with fractional derivatives

NASA Astrophysics Data System (ADS)

A time-domain numerical modeling of Biot poroelastic waves is presented. The viscous dissipation occurring in the pores is described using the dynamic permeability model developed by Johnson-Koplik-Dashen (JKD). Some of the coefficients in the Biot-JKD model are proportional to the square root of the frequency: in the time-domain, these coefficients introduce order 1/2 shifted fractional derivatives involving a convolution product. Based on a diffusive representation, the convolution kernel is replaced by a finite number of memory variables that satisfy local-in-time ordinary differential equations. Thanks to the dispersion relation, the coefficients in the diffusive representation are obtained by performing an optimization procedure in the frequency range of interest. A splitting strategy is then applied numerically: the propagative part of Biot-JKD equations is discretized using a fourth-order ADER scheme on a Cartesian grid, whereas the diffusive part is solved exactly. Comparisons with analytical solutions show the efficiency and the accuracy of this approach.

Blanc, Emilie; Chiavassa, Guillaume; Lombard, Bruno

2013-03-01

144

Cosmological model with variable light velocity

The model with variable c,G,h is extended to electromagnetism. The entropy is found to vary like log t and, in a space-entropy representation, the metric is conformally flat. A new gauge relations is suggested, based on geometrical considerations, which corresponds to a Rydberg constant varying like R. The Hubble's law still applies. The age of the universe is unchanged while its span is found to be half of the Mattig's value. The complete decoding of the red shift can be done. The distances of the sources are very similar. The large volumic power densities of distant quasars could have been greatly overestimated, while the increase of their absolute magnitude, as derived from the classical theory, could be due to the secular variation of absolute magnitude, as derived from the classical theory, could be due to the secular variation of c. Assuming the electron-proton mass ratio to vary like R, the authors get a fine structure constant ..cap alpha.., a Bohr radius and a ratio of electromagnetic force to gravitational force which behave like absolute constants.

Petit, J.P.

1988-12-01

145

On nonminimal N=4 supermultiplets in 1D and their associated {sigma}-models

We construct the nonminimal linear representations of the N=4 extended supersymmetry in one-dimension. They act on eight bosonic and eight fermionic fields. Inequivalent representations are specified by the mass-dimension of the fields and the connectivity of the associated graphs. The oxidation to minimal N=5 linear representations is given. Two types of N=4{sigma}-models based on nonminimal representations are obtained: the resulting off-shell actions are either manifestly invariant or depend on a constrained prepotential. The connectivity properties of the graphs play a decisive role in discriminating inequivalent actions. These results find application in partial breaking of supersymmetric theories.

Gonzales, Marcelo; Khodaee, Sadi; Toppan, Francesco [CBPF, Rua Dr. Xavier Sigaud 150, cep 22290-180, Rio de Janeiro (RJ) (Brazil)

2011-01-15

146

Comprehensive 1D Modelling of Reactive Chemical Transport in Unsaturated Soil

NASA Astrophysics Data System (ADS)

Computer models for simulating environmental processes of water flow, solute transport and geochemical reactions have greatly advanced during recent years. However, there is still demand for the development of programs that a capable of simulating the numerous interactions between physical transport processes and biogeochemical reactions in natural soils. We present a new tool for simulating transient vadose zone flow and solute transport according to the moisture- based form of Richards' equation within the widely used geochemical software PHREEQC. The direct implementation into the geochemical framework provides access to comprehensive geochemical models, giving capabilities beyond existing software for coupled unsaturated flow and reaction. Possible reactions include complex aqueous speciation, cation exchange, equilibrium phase dissolution and precipitation, formation of solid solutions, redox reactions, gas phase exchange, surface adsorption considering electrostatics and kinetic reactions with user-defined rate equations, among others. As a result of the close coupling procedure, the influence of geochemical reactions on water content, e.g., through dissolution or precipitation of water-containing phases, can be investigated. For the solution of the partial differential equations of flow and transport, an explicit finite-difference formulation with a second-order space discretization and first-order time discretization was employed. The use of integrated diffusivities transforms Richards' equation into a simple advection-diffusion equation. Changes in water content and solute concentration were conceptualized as local kinetic reactions of individual elements where changes in moisture content result from fluxes of oxygen and hydrogen across cell boundaries. Reactions and chemical element transport are coupled via sequential two-step operator splitting. The scheme was implemented into PHREEQC without any source code modification such that it can be applied by an experienced user within the existing freely available software. In this presentation, we show results from extensive code verification and demonstrate the unique capabilities of the model for simulating surface sorption to variable charge surface sites including the development of a diffuse double layer as well as dissolution reactions with effects on soil moisture.

Wissmeier, L.; Barry, D. A.

2007-12-01

147

1D kinetic modelling of the JET SOL with tungsten divertor plates

NASA Astrophysics Data System (ADS)

In this work a fully kinetic model of the JET SOL with tungsten divertor plates has been developed. It includes the dynamics of main-ions (D+) and electrons, the neutrals (D, C, W) and the impurity particles (C+m, W+n). Our simulations show extremely low concentration of W impurity. We identify two reasons which are responsible for this effect: (1) for low temperature divertor plasma the energy of most of the main-ions and the impurities in a low-ionization state impinging the divertor plates is below the W-sputtering threshold energy; (2) with increasing temperature the W-sputtering increases, but the potential drop across the divertor plasma increases too, so that most of the W ions are reabsorbed at the divertors.

JET EFDA contributors Tskhakaya, D.; Groth, M.

2013-07-01

148

Fully Coupled 1D Model for the Response of a Membrane in a Thin Air-Filled Cavity.

NASA Astrophysics Data System (ADS)

A fully coupled 1D model based on a spring-mass system is derived for the response of a membrane subject to a time varying electrostatic charge in a thin air filled cavity. The elasticity of the membrane, the time dependent electric field, and the fluid flow are included in the model. The fluid film of air in the gap between the fixed electrode and deformable membrane is modeled using the linearized compressible Reynolds gas film equation, modified to account for the membrane deformation. From this, a fluid damping and spring coefficient are computed, which are used to calculate the fluid force on the membrane. A stiffness coefficient accounts for both linear and nonlinear membrane deformation. A capacitance-based generalized equation is used for the electrostatic field. Frequency and voltage are the only required inputs. It is found that there are distinct overdamped regimes consistent with spring-mass systems. The response computed from the model is compared to that obtained with a fully coupled 3D finite element solver. Excellent agreement is seen between the model and FEM results, with the model having a great advantage in the time necessary to obtain a solution for the response. The model is deemed a powerful tool in the design of microsystems with moving structures in which fluid damping plays a critical role in the structure's response.

Roman, Max; Goullet, Arnaud; Aubry, Nadine

2006-11-01

149

Numerical Models of Multi-Velocity Rift Evolution

NASA Astrophysics Data System (ADS)

Numerical models are a useful tool to combine present-day knowledge on plate kinematics and lithosphere rheology in order to reveal the complex relations between deformation modes, margin asymmetry and crustal hyperextension. We investigate how long rift duration and distinct successive extensional velocities influence lithospheric localization and final margin geometry. Our scenarios are computed using a thermo-mechanical, finite element model that includes elasto-visco-plastic rheology and a free surface. The model allows for high resolution of 1 km in a 2d setup with 500 km width and 200 km depth range. We highlight the importance of strain hardening for slow rifting (~ 5 mm/yr full extension velocity) where cooling of uplifted mantle material promotes continuous lateral migration of the rift center. Despite initially symmetric extension, strain hardening can lead both to significant late rift asymmetry and to crustal hyperextension. We use our model to understand the South Atlantic conjugate margin geometries. We thereby build upon a new plate kinematic model for the South Atlantic rift which integrates time-dependent information on crustal deformation within a global self-consistent plate rotation framework. Here, the intial continental separation between South America and Africa starts in the Early Cretaceous at low velocities, controlled by African intracontinental rifting. After 20-25 Ma of rifting, loss of lithospheric strength in the Equatorial Atlantic domain results in a significant increase in extensional velocities and a change in extensional direction from 120 Ma onwards. We investigate the impact of this multi-velocity extension history on the spatio-temporal margin evolution and compare our results with conjugate margin cross-sections at representative locations in the South Atlantic. We couple observations on continental extension from global scale plate tectonic models with high resolution, thermo-mechanical models of lithosphere deformation. This approach offers a powerful way of converging to robust regional tectonic models and link plate-scale kinematics to lithospheric deformation modeling and smaller scale tectonics analysis.

Brune, S.; Heine, C.

2012-04-01

150

Sea-air fluxes and 1-D ocean modelling of volatile photolabile iodocarbons

NASA Astrophysics Data System (ADS)

Recent research carried out at the Cape Verde Observatory has demonstrated that reactive iodine chemistry can contribute significantly to photochemical ozone depletion within the marine boundary layer of the atmosphere. Organoiodine compounds emitted from the oceans have been proposed as a major source of atmospheric iodine, however there is currently considerable ambiguity associated with estimates of iodocarbon sea-air fluxes, and hence the global importance of these gases as an I atom source to the atmosphere remains unclear. During the MAP (Marine Aerosol Production) and RHaMBLe (Reactive Halogens in the Marine Boundary Layer experiment) cruises in the Atlantic Ocean during summer 2006 and 2007 respectively, we made simultaneous measurements of a range of iodocarbons in surface seawater (2 - 6 m depth) and in marine air, using two GC-MS systems. Our measurements suggest that the dihalomethanes CH2I2, CH2IBr and CH2ICl may provide a combined global I atom source which is comparable to that of CH3I, and are the dominant organic source of iodine in the marine boundary layer. However, since the dihalomethanes are rapidly photolysed within the top few metres of the water column, deriving sea-air fluxes for these short-lived gases based on their sub-surface seawater concentrations is more complex than for the longer-lived iodocarbons such as CH3I. Consequently, we have developed an oceanic mixed layer model to predict the difference between the true surface and sub-surface dihalomethane concentrations, based on a combination of meteorological, biological and physical ocean parameters, in order to obtain more accurate sea-air fluxes for these gases.

Jones, C. E.; Hornsby, K. E.; Dunk, R.; McFiggans, G.; Carpenter, L. J.

2009-04-01

151

NASA Astrophysics Data System (ADS)

Earthen flood defence embankments are linear structures, raised above the flood plain, that are commonly used as flood defences in rural settings; these are often relatively old structures constructed using locally garnered material and of which little is known in terms of design and construction. Alarmingly, it is generally reported that a number of urban developments have expanded to previously rural areas; hence, acquiring knowledge about the flood defences protecting these areas has risen significantly in the agendas of basin and asset managers. This paper focusses, by reporting two case studies, on electromagnetic induction (EMI) methods that would efficiently complement routine visual inspections and would represent a first step to more detailed investigations. Evaluation of the results is presented by comparison with ERT profiles and intrusive investigation data. The EM data, acquired using a GEM-2 apparatus for frequency sounding and an EM-31 apparatus for geometrical sounding, has been handled using the prototype eGMS software tool, being developed by the eGMS international research consortium; the depth sounding data interpretation was assisted by 1D inversions obtained with the EM1DFM software developed by the University of British Columbia. Although both sounding methods showed some limitations, the models obtained were consistent with ERT models and the techniques were useful screening methods for the identification of areas of interest, such as material interfaces or potential seepage areas, within the embankment structure: 1D modelling improved the rapid assessment of earthen flood defence embankments in an estuarine environment; evidence that EMI sounding could play an important role as a monitoring tool or as a first step towards more detailed investigations.

Viganotti, Matteo; Jackson, Ruth; Krahn, Hartmut; Dyer, Mark

2013-05-01

152

NASA Astrophysics Data System (ADS)

Spontaneous formation of a vorticity staircase and multiple jets is simulated using a one dimensional barotropic model on a beta-plane with parameterized eddy mixing. The model represents nearly inviscid geostrophic turbulence characterized by a uniform forcing of pseudomomentum, nonuniform dissipation due to mixing, and no frictional damping of the mean flow. The dissipation of pseudomomentum (diffusive flux of vorticity) is modeled with the effective diffusivity parameterization proposed recently by Ferrari and Nikurashin(2009). Rossby wave dynamics and upscale energy cascade are not modeled explicitly but implicit in the parameterization. The parameterized effective diffusivity is a decreasing function of squared vorticity gradient, revealing the active role of (potential) vorticity gradient as a barrier to mixing, consistent with the Rossby elasticity idea. Not only does the parameterized diffusivity agree well with the effective diffusivity of a direct numerical simulation, but it allows the 1D model to reproduce other salient features of the direct simulation, most notably the formation of a welldefined vorticity staircase from a uniform vorticity gradient, through inhomogeneous mixing of vorticity. The staircase formation starts as a small-scale, antidiffusive instability in vorticity gradient that develops when the eddy scale is comparable to the Rhines scale. This spawns numerous gaps (barriers) in diffusivity and corresponding small steps in vorticity, but many of them become unstable and disappear later, until a few stable ones remain. The final number of barriers (vorticity steps) is predictable to a good approximation with a few model parameters.

Zhu, D.; Nakamura, N.

2009-12-01

153

Three-dimensional seismic velocity model of the West Bohemia/Vogtland seismoactive region

NASA Astrophysics Data System (ADS)

In this paper, we present a smooth 3-D seismic model WB2012 for the West Bohemia/Vogtland earthquake swarm region derived by means of seismic tomography. Inverted data were represented by a set of 2920 P-wave traveltimes from controlled shots fired in a framework of different experiments and a set of 11339 P- and S-wave arrival times from 661 local earthquakes between 1991 December and 2010 March. We used a standard tomographic approach for independent calculation of P- and S-wave velocity fields in a rectangular grid whose size was 1 km in all coordinates. The traveltimes and rays were calculated by a numerical solution of the eiconal equation. While locating seismic events, our new WB2012 model yielded arrival time residuals on average by 13 per cent lower and hypocentre depths by 0.95 km shallower compared to the locations of the foci in the standard 1-D vertically inhomogeneous isotropic velocity model of the West Bohemia swarm region WB2005. Further, we converted the P- and S-wave velocities to the bulk modulus K and Poisson's ratio ?. The bulk modulus (˜40-70 GPa) correlates acceptably with the tectonic and geological structure of the area. The anomalously low values of the Poisson's ratio (˜0.15) are typical for the most active focal zones of Nový Kostel and Lazy in West Bohemia.

R?žek, Bohuslav; Horálek, Josef

2013-11-01

154

Three-dimensional seismic velocity model of the West Bohemia/Vogtland seismoactive region

NASA Astrophysics Data System (ADS)

In this paper, we present a smooth 3-D seismic model WB2012 for the West Bohemia/Vogtland earthquake swarm region derived by means of seismic tomography. Inverted data were represented by a set of 2920 P-wave traveltimes from controlled shots fired in a framework of different experiments and a set of 11339 P- and S-wave arrival times from 661 local earthquakes between 1991 December and 2010 March. We used a standard tomographic approach for independent calculation of P- and S-wave velocity fields in a rectangular grid whose size was 1 km in all coordinates. The traveltimes and rays were calculated by a numerical solution of the eiconal equation. While locating seismic events, our new WB2012 model yielded arrival time residuals on average by 13 per cent lower and hypocentre depths by 0.95 km shallower compared to the locations of the foci in the standard 1-D vertically inhomogeneous isotropic velocity model of the West Bohemia swarm region WB2005. Further, we converted the P- and S-wave velocities to the bulk modulus K and Poisson's ratio ?. The bulk modulus (˜40-70 GPa) correlates acceptably with the tectonic and geological structure of the area. The anomalously low values of the Poisson's ratio (˜0.15) are typical for the most active focal zones of Nový Kostel and Lazy in West Bohemia.

R?žek, Bohuslav; Horálek, Josef

2013-08-01

155

Tuning a Physically-Based Model of the air-sea gas Transfer Velocity

NASA Astrophysics Data System (ADS)

Gas transfer velocities are estimated for one year using a 1-d upper-ocean model and a modified NOAA- COARE transfer velocity parameterization. Tuning parameters are evaluated with the aim of bringing the parameterization in line with current estimates based on simple wind-speed dependent models, derived from bomb-radiocarbon inventories and deliberate tracer release experiments. This is an important step toward more reliable estimates of air-sea gas transfer. We suggest that A=1.3 and B=1.0, for the sub-layer scaling parameter and bubble mediated exchange respectively, are suitable for calculating the global average CO2 transfer velocity k. Using these parameters and a simple polynomial approximation we estimate a global annual average k of 16.4±4.7 cm hr-1 when using global mean winds of 6.89 m s-1 from the NCEP/NCAR Reanalysis 1 1954--2000. Given the non-specific nature of the parameterization, global k for DMS and CH4 (11.9 and 18.0 cm hr-1 respectively) is also estimated, highlighting the importance of continued development of physically-based models.

Jeffery, C. D.; Robinson, I. S.; Woolf, D. K.

2008-12-01

156

Velocity prediction errors related to flow model calibration uncertainty

At the Savannah River Site (SRS), a United States Department of Energy facility in South Carolina, a three-dimensional, steady-state numerical model has been developed for a four aquifer, three aquitard groundwater flow system. This model has been used for numerous predictive simulation applications at SRS, and since the initial calibration, the model has been refined several times. Originally, calibration of the model was accomplished using a nonlinear least-squares inverse technique for a set of 50 water-level calibration targets non-uniformly distributed in the four aquifers. The estimated hydraulic properties from this calibration generally showed reasonable agreement with values estimated from field tests. Subsequent model refinements and application of this model to field problems have shown that uncertainties in the model parameterization become much more apparent in the prediction of the velocity field than in the simulation of the distribution of hydraulic heads. The combined use of three types of information (hydraulic head distributions, geologic framework models, and velocity field monitoring) provide valuable calibration data for flow modeling investigations; however, calibration of a flow model typically relies upon measured water levels. For a given set of water-level calibration targets, the uncertainties associated with imperfect knowledge of physical system parameters or groundwater velocities may not be discernable in the calibrated hydraulic head distribution. In this paper, modeling results from studies at SRS illustrate examples of model inadequacy resulting from calibrating only on observed water levels, and the effects of these inadequacies on velocity field prediction are discussed. 14 refs., 6 figs.

Stephenson, D.E. (Westinghouse Savannah River Co., Aiken, SC (USA)); Duffield, G.M.; Buss, D.R. (Geraghty and Miller, Inc., Reston, VA (USA))

1990-01-01

157

Solutions for the velocity-dependent Krook (VDK) model using Helmoltz equations

NASA Astrophysics Data System (ADS)

Our previous treatment for the solutions of the VDK model involved the use of a Green's function [1]. We now solve directly the Helmoltz equation describing the model in 1D (and 2D as previously described in ref.2). This involves the numerical solution of a diffusion-like equation for each energy group in steady-state. We present comparisons between the two methods of solution on test problems and on one typical implosion calculation [2]. Sensitivity of the solution to the number of energy (velocity) groups is also presented since this is an important component affecting the total computing time for this model. Further work will also be discussed. [4pt] [1] W. Manheimer, D. Colombant and V. Goncharov, Phys. Plasmas 15, 083103 (2008).[0pt] [2] W. Manheimer, D. Colombant and A.J. Schmitt, Phys. Plasmas 19, 056317 (2012).

Colombant, Denis; Manheimer, Wallace; Schmitt, Andrew

2012-10-01

158

Shallow and deep crustal velocity models of Northeast Tibet

NASA Astrophysics Data System (ADS)

The INDEPTH IV seismic profile in Northeast Tibet is the highest resolution wide-angle refraction experiment imaging the Qaidam Basin, North Kunlun Thrusts (NKT), Kunlun Mountains, North and South Kunlun Faults (NKT, SKT), and Songpan-Ganzi terrane (SG). First arrival refraction modeling using ray tracing and least squares inversion has yielded a crustal p-wave velocity model, best resolved for the top 20 km. Ray tracing of deeper reflections shows considerable differences between the Qaidam Basin and the SG, in agreement with previous studies of those areas. The Moho ranges from about 52 km beneath the Qaidam Basin to 63 km with a slight northward dip beneath the SG. The 11-km change must occur between the SKF and the southern edge of the Qaidam Basin, just north of the NKT, allowing the possibility of a Moho step across the NKT. The Qaidam Basin velocity-versus-depth profile is more similar to the global average than the SG profile, which bears resemblance to previously determined “Tibet-type” velocity profiles with mid to lower crustal velocities of 6.5 to 7.0 km/s appearing at greater depths. The highest resolution portion of the profile (100-m instrument spacing) features two distinct, apparently south-dipping low-velocity zones reaching about 2-3 km depth that we infer to be the locations of the NKF and SKF. A strong reflector at 35 km, located entirely south of the SKF and truncated just south of it, may be cut by a steeply south-dipping SKF. Elevated velocities at depth beneath the surface location of the NKF may indicate the south-dipping NKF meets the SKF between depths of 5 and 10 km. Undulating regions of high and low velocity extending about 1-2 km in depth near the southern border of the Qaidam Basin likely represent north-verging thrust sheets of the NKT.

Karplus, M.; Klemperer, S. L.; Mechie, J.; Shi, D.; Zhao, W.; Brown, L. D.; Wu, Z.

2009-12-01

159

3-D crustal velocity model for Lithuania and its application to local event studies

NASA Astrophysics Data System (ADS)

PASSEQ 2006-2008 project (PASsive Seismic Experiment in TESZ) aimed at studying the lithosphere-asthenosphere system around the TransEuropean Suture Zone (TESZ)- the transition between old Proterozoic platform of north and east Europe and younger Phanerozoic platform in central and western Europe. The experiment was a seismic array research aiming to retrieve the structure of the crust and Earth's mantle down to the mantle transition zone, including mapping of upper mantle seismic velocity variations and discontinuities (Moho, lithosphere-asthenosphere boundary, mantle transition zone) using all available techniques. During the experiment 26 seismic stations (including four broadband stations) were installed in Lithuania. One of the main targets of PASSEQ deployment in Lithuania was identification and characterization of the local seismic activity. The PASSEQ stations in Lithuania were in operation since June, 2006 till January, 2008. During this period a number of local seismic events was recorded and preliminary event location was made using the LocSat algorithm and 1-D velocity model. This standard procedure is not enough precise for Lithuania, however, because the thickness of the crust varies significantly in the region (from 45 to 55 km). In order to improve event location, we separated the events into several groups and located each group separately using a VELEST algorithms and own 1-D velocity model for each group. We also compiled a 3-D seismic velocity of the crust down to a depth of 60 km. The model, consisting of four major layers (sediments, upper crust, middle crust, lower crust and uppermost mantle) was interpolated from 2-D velocity models along previous wide-angle reflection and refraction profiles into a regular grid. The quality of the approximation was analysed using comparison of travel times of P-waves recorded along previous controlled source profiles and synthetic travel times calculated using the 3-D velocity model. The model was converted into a density model using a special procedure, in which the density model is approximated by relationship between seismic velocity and density and the latter is found by inverting of the Bouguer anomaly. Comparison of the inversion results to the observed Bouguer anomaly showed that the upper part of the model needs to be corrected, in particular, in the regions not covered by the profiles. The epicentres of events relocated with the use of both VELEST algorithm and a 3-D velocity model are much less scattered and can be grouped into several clusters, some of which are confined to known areas of human activity. However, one group of events is spatially coincident with the region of two large earthquakes in Kaliningrad region in September, 2004, while another cluster shows good coincidence with known region of historical seismicity in Latvia.

Kozlovskaya, Elena; Budraitis, Mantas; Janutyte, Ilma; Motuza, Gediminas; Lazauskiene, Jurga; Passeq-Working Group

2010-05-01

160

Calculation of Rayleigh-wave phase velocities due to models with a high-velocity surface layer

NASA Astrophysics Data System (ADS)

Rayleigh-wave phase velocities have been utilized to determine shear (S)-wave velocities in near-surface geophysics since early 1980s. One of the key steps is to calculate theoretical dispersion curves of an earth model. When the S-wave velocity of the surface layer is higher than some of the layers below, however, the Rayleigh-wave phase velocity in a high-frequency range calculated by existing algorithms approaches the lowest S-wave velocity among the layers above the half-space, rather than a value related to the S-wave velocity of the surface layer. According to our numerical modeling results based on wave equation, trends of the Rayleigh-wave dispersive energy approach about a 91% of the S-wave velocity of the surface layer at a high-frequency range when its wavelength is much shorter than the thickness of the surface layer, which cannot be fitted by a dispersion curve calculated by existing algorithms. We propose a method to calculate Rayleigh-wave phase velocities of models with a high-velocity surface layer by considering its penetration depth. We build a substituted model that only contains the layer with the lowest S-wave velocity among the layers above the half-space and the layers above it. We use the substituted model to replace the original model to calculate phase velocities when the Rayleigh-wave wavelength is not long enough to penetrate the lowest S-wave velocity layer. Several synthetic models are used to verify fitness between the dispersion curve calculated by our proposed method and the trend of the highest dispersive energy. Examples of inversion also demonstrate high accuracy of using our method as the forward calculation method during the inversions.

Pan, Yudi; Xia, Jianghai; Gao, Lingli; Shen, Chao; Zeng, Chong

2013-09-01

161

On dynamic geodynamo models with imposed velocity as energy source

NASA Astrophysics Data System (ADS)

The first step of a project to study three-dimensional numerical dynamo models in a rapidly rotating sphere is reported. We aim at finding solutions in the magnetostrophic regime, where the Taylor's condition is obeyed. Viscous terms, including the Ekman suction at the boundary, are discarded. At this stage, our project consists of investigating the coupling of the momentum and induction equations. The energy equation is ignored and an imposed velocity provides the energy source. We present our code and we show that the algorithm to calculate the geostrophic velocity is stable.

Jault, D.; Cardin, P.

1999-02-01

162

A simple model for flyer velocity from laser-induced forward transfer with a dynamic release layer

NASA Astrophysics Data System (ADS)

A simple 1-D model has been developed for the velocity of flyers in vacuum generated by laser-induced forward transfer (LIFT) with a dynamic release layer (DRL). It is an extension of a laser ablation model for metal flyer plates based on the Gurney model of explosive output for driving metal fragments. The model has been extended to the bilayer system of a DRL overlain with a transfer layer. The suitability of the model has been checked with experimental velocity data obtained from shadowgraphy. The experiments used bilayer samples of triazene polymer/aluminium, ablated from the backside through the substrate at reduced pressure (5 × 10-2 mbar). The results suggest that the Gurney energy approach provides the basis of a viable, physically relevant, algebraic model for LIFT, but other loss mechanisms still need be incorporated, particularly thermal loss into the fused silica substrate.

Shaw-Stewart, James; Lippert, Thomas; Nagel, Matthias; Nüesch, Frank; Wokaun, Alexander

2012-09-01

163

Analytic solutions for seismic travel time and ray path geometry through simple velocity models.

The geometry of ray paths through realistic Earth models can be extremely complex due to the vertical and lateral heterogeneity of the velocity distribution within the models. Calculation of high fidelity ray paths and travel times through these models generally involves sophisticated algorithms that require significant assumptions and approximations. To test such algorithms it is desirable to have available analytic solutions for the geometry and travel time of rays through simpler velocity distributions against which the more complex algorithms can be compared. Also, in situations where computational performance requirements prohibit implementation of full 3D algorithms, it may be necessary to accept the accuracy limitations of analytic solutions in order to compute solutions that satisfy those requirements. Analytic solutions are described for the geometry and travel time of infinite frequency rays through radially symmetric 1D Earth models characterized by an inner sphere where the velocity distribution is given by the function V (r) = A-Br{sup 2}, optionally surrounded by some number of spherical shells of constant velocity. The mathematical basis of the calculations is described, sample calculations are presented, and results are compared to the Taup Toolkit of Crotwell et al. (1999). These solutions are useful for evaluating the fidelity of sophisticated 3D travel time calculators and in situations where performance requirements preclude the use of more computationally intensive calculators. It should be noted that most of the solutions presented are only quasi-analytic. Exact, closed form equations are derived but computation of solutions to specific problems generally require application of numerical integration or root finding techniques, which, while approximations, can be calculated to very high accuracy. Tolerances are set in the numerical algorithms such that computed travel time accuracies are better than 1 microsecond.

Ballard, Sanford

2007-12-01

164

NASA Astrophysics Data System (ADS)

The effects of mix at the unstable inner surface of imploding shells of direct-drive cryogenic DT ignition capsules are simulated in 1-D. We evaluate the resulting changes in the central hot spot, changes in the implosion-energy ignition margin, and the tolerance of ignition to variations in the sources of implosion nonuniformity, such as drive nonuniformity and shell surface roughness. Mix is modeled as a diffusive transport process within the hydrodynamic simulation, affecting the transport of momentum, thermal energy, and turbulent mix-motion energy within the mix region. Initial conditions of the mix model include the acceleration nonuniformity due to beam-energy imbalance, the hydrodynamic imprint of short-scale laser nonuniformity, and roughness of the inner and outer surfaces of the target shell. The linear growth rates and the feedthrough coupling between perturbations of different unstable interfaces are obtained analytically in terms of the one-dimensional fluid profiles. Hydrodynamic perturbations are calculated through all phases of acceleration and deceleration, and the effects of geometrically converging, compressible flow are taken into account. The applicability of modeling of this kind will be confirmed using comparisons with full 2-D hydrodynamic simulations. This work was supported by the U.S. DOE Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.

Epstein, R.; Collins, T. J. B.; Delettrez, J. A.; Goncharov, V. N.; McKenty, P. W.; Radha, P. B.; Skupsky, S.

2002-11-01

165

An Elicitation of the Dynamic Nature of Water Vapor Feedback in Climate Change Using a 1D Model.

NASA Astrophysics Data System (ADS)

The concept of feedback has been used by several authors in the field of climate science to describe the behavior of models and to assess the importance of the different mechanisms at stake. Here, a simple 1D model of climate has been built to analyze the water vapor feedback. Beyond a static quantification of the water feedback, a more general formal definition of feedback gain based on the tangent linear system is introduced. This definition reintroduces the dynamical aspect of the system response to perturbation from Bode's original concept.In the model here, it is found that, even though the water vapor static gain proves consistent with results from GCMs, it turns out to be negative for time scales below 4 yr and positive only for longer time scales. These results suggest two conclusions: (i) that the water vapor feedback may be fully active only in response to long-lived perturbations; and (ii) that the water vapor feedback could reduce the natural variability due to tropospheric temperature perturbations over short time scales, while enhancing it over longer time scales. This second conclusion would be consistent with studies investigating the influence of air sea coupling on variability on different time scales.

Hallegatte, Stéphane; Lahellec, Alain; Grandpeix, Jean-Yves

2006-07-01

166

A New Mixed Model Based on the Velocity Structure Function

NASA Astrophysics Data System (ADS)

We propose a new mixed model for Large Eddy-Simulation based on the 3D spatial velocity increment. This approach blends the non-linear properties of the Increment model (Brun & Friedrich (2001)) with the eddy viscosity characteristics of the Structure Function model (Métais & Lesieur (1992)). The behaviour of this subgrid scale model is studied both via a priori tests of a plane jet at ReH=3000 and Large Eddy-Simulation of a round jet at ReD=25000. This approach allows to describe both forward and backward energy transfer encountered in transitional shear flows.

Brun, Christophe; Friedrich, Rainer; Da Silva, Carlos B.; Métais, Olivier

167

Transport of a 1D viscoelastic actin-myosin strip of gel as a model of a crawling cell

Cell crawling is an important biological phenomenon because it underlies coordinated cell movement in morphogenesis, cancer and wound healing. This phenomenon is based on protrusion at the cell's leading edge, retraction at the rear, contraction and graded adhesion powered by the dynamics of actin and myosin protein networks. A few one-dimensional models successfully explain an anteroposterior organization of the motile cell, but don't sufficiently explore the viscoelastic nature of the actin-myosin gel. We develop and numerically solve a model of a treadmilling strip of viscoelastic actin-myosin gel. The results show that the strip translocates steadily as a traveling pulse, without changing length, and that protein densities, velocities and stresses become stationary. The simulations closely match the observed forces, movements and protein distributions in the living cell.

Larripa, Kamila; Mogilner, Alex

2008-01-01

168

Building velocity model for anisotropic PSDM: A TTI modeling example

Steeply dipping shale and interbedded sandstone and shale formations in fold and thrust belt areas, such as Alberta Rocky Mountain Foothills, exhibits seismic velocity anisotropy. Transverse isotropy with a tilted symmetry axis (TTI medium) has been recognized as a major anisotropic feature of shale formation in the Western Canada sedimentary basin. Since TTI medium in the overburden of subsurface targets

Lanlan Yan; Larry R. Lines; Don C. Lawton

169

Exact solution of the 1D Hubbard model in the atomic limit with inter-site magnetic coupling

NASA Astrophysics Data System (ADS)

In this paper, we present for the first time the exact solution in the narrow-band limit of the 1D extended Hubbard model with nearest-neighbour spin-spin interactions described by an exchange constant J. An external magnetic field h is also taken into account. This result has been obtained in the framework of the Green's functions formalism, using the composite operator method. By means of this theoretical background, we have studied some relevant features such as double occupancy, magnetization, spin-spin and charge-charge correlation functions and derived a phase diagram for both ferro (J > 0) and anti-ferro (J < 0) coupling in the limit of zero temperature. We also report a study on density of states, specific heat, charge and spin susceptibilities. In the limit of zero temperature, we show that the model exhibits a very rich phase diagram characterized by different magnetic orders and by the coexistence of charge and spin orderings at commensurate filling. Moreover, our analysis at finite temperature of density of states and response functions shows the presence of low-temperature charge and spin excitations near the phase boundaries.

Mancini, Ferdinando; Plekhanov, Evgeny; Sica, Gerardo

2013-05-01

170

Insights into brine dynamics and sea ice desalination from a 1-D model study of gravity drainage

NASA Astrophysics Data System (ADS)

We study gravity drainage using a new 1-D, multiphase sea ice model. A parametrization of gravity drainage based on the convective nature of gravity drainage is introduced, whose free parameters are determined by optimizing model output against laboratory measurements of sea ice salinity evolution. Optimal estimates of the free parameters as well as the parametrization performance remain stable for vertical grid resolutions from 1 to 30 mm. We find a strong link between sea ice growth rate and bulk salinity for constant boundary conditions but only a weak link for more realistic boundary conditions. We also demonstrate that surface warming can trigger brine convection over the whole ice layer. Over a growth season, replacing the convective parametrization with constant initial salinities leads to an overall 3% discrepancy of stored energy, thermal resistance, and salt release. We also derive from our convective parametrization a simplified, numerically cheap and stable gravity-drainage parametrization. This parametrization results in an approximately 1% discrepancy of stored energy, thermal resistance, and salt release compared to the convective parametrization. A similarly low discrepancy to our complex parametrization can be reached by simply prescribing a depth-dependent salinity profile.

Griewank, Philipp J.; Notz, Dirk

2013-07-01

171

Some T cells react with lipid antigens bound to antigen-presenting molecule CD1d. Numbers and functions of a subset of such lipid-reactive T cells are reduced in patients with systemic lupus erythematosus (SLE) and their relatives, as well as in genetically susceptible and chemically induced animal models of lupus-like disease. We have reported that the germline deletion of CD1d exacerbates lupus, suggesting a protective role of these cells in the development of lupus. The use of a knockout mouse model in this study, however, did not allow examination of the role of these cells at different stages of disease. Here, we describe an approach to deplete CD1d-dependent T cells, which allowed us to investigate the role of these cells at different stages of disease in genetically lupus-prone NZB/NZW F1 (BWF1) mice. Repeated intravenous injections of large numbers of CD1d-transfected cells resulted in ~50–75% reduction in these cells, as defined by the expression of CD4, NK1.1 and CD122, and lack of expression of CD62 ligand. TCR ?? +NK1.1+ cells were also reduced in the recipients of CD1d-transfected cells as compared with control recipients. Such depletion of CD1d-reactive T cells in preclinical BWF1 mice resulted in disease acceleration with a significant increase in proteinuria and mortality. In older BWF1 mice having advanced nephritis, however, such depletion of CD1d-reactive T cells resulted in some disease improvement. Taken together, these data as well as our published studies suggest that CD1d-reactive T cells protect against the development of lupus in animal models. However, these cells appear to be unable to suppress established lupus nephritis in these animals, and might even play a disease aggravating role in late stages of disease.

Jacinto, J; Kim, PJ; Singh, RR

2012-01-01

172

NASA Astrophysics Data System (ADS)

Ground-based observations of Mars atmospheric temperatures, water, and aerosols have suggested that water ice clouds may regulate vertical distribution of dust and, hence, the global radiation balance, with strong seasonal forcing (Clancy et al., 1996). Under specific Martian conditions, condensation of atmospheric water occurs on the dust as Aitken cores, without external sources, dust is efficiently confined below the saturation level of water vapor. This in turn forces the thermal regime and the saturation conditions, particularly around the aphelion northern summer (Clancy et al., 1996). This effect is studied with two 1-D models, a time marching simulation (time step is 4 min), and reduced local steady-state model. Both models treat aerosol particle microphysics, turbulent transport and thermal enforcement interactively, including radiation transfer consistent with derived aerosol vertical and size distributions. Simulations show that in the aphelion season, when clouds are formed below or near 10 km, strong nonlinearity of cloud thermal feedback results in nonuniqueness of a steady-state solution with water vapor saturation level varying by as high as 5-7 km. Such model behavior appears related to observations of rapid variations of a global-average, lower atmosphere temperature over the planet in northern summer (Clancy, 1997). The stability of thermal equilibrium state is controlled by water vapor abundance and the strength of the dust source at the surface. Time marching simulations provide access to the dynamics of seasonal global dust storm relaxation that may play an important role in interannual climate variations on Mars. References: Clancy, R.T., A.W. Grossman, M.J. Wolff, P.B. James, Y.N. Billawala, B.J. Sandor, S.W. Lee, and D.J. Rudy. Water vapor saturation at low altitudes around Mars aphelion: A key to Mars climate? Icarus, 122, 36-62, 1996.

Rodin, A. V.; Clancy, R. T.; Wilson, R. J.; Richardson, M.; Wolff, M.; Woods, S.

1997-07-01

173

Velocity profiles in idealized model of human respiratory tract

NASA Astrophysics Data System (ADS)

This article deals with numerical simulation focused on velocity profiles in idealized model of human upper airways during steady inspiration. Three r gimes of breathing were investigated: Resting condition, Deep breathing and Light activity which correspond to most common regimes used for experiments and simulations. Calculation was validated with experimental data given by Phase Doppler Anemometry performed on the model with same geometry. This comparison was made in multiple points which form one cross-section in trachea near first bifurcation of bronchial tree. Development of velocity profile in trachea during steady inspiration was discussed with respect for common phenomenon formed in trachea and for future research of transport of aerosol particles in human respiratory tract.

Elcner, J.; Jedelsky, J.; Lizal, F.; Jicha, M.

2013-04-01

174

Modelling of the pressure-velocity correlation in turbulence diffusion

NASA Astrophysics Data System (ADS)

In the context of second-moment closure, the mechanism of turbulence diffusion consists of mainly two parts: a triple velocity correlation and a pressure-velocity correlation. The first correlation is measurable and can be analyzed theoretically through its transport equation. The second correlation cannot, however, be obtained directly from experiments and knowledge about it is comparatively limited. Most current computations of turbulent flows adopt diffusion models which neglect the effect of the pressure-velocity correlation in the diffusion process. The importance of this correlation effect is elucidated; the neglect of this effect constitutes some of the major defects in the application of the second-moment closures. Through the relation between the two correlations, established by Lumley (1978), we propose a new type of turbulence diffusion model which takes into account the pressure effect. Application of this new model in the computation of the turbulence shearless mixing layer and plane- and round-jet flows shows that the spreading rates of these flows can be captured satisfactorily.

Fu, Song

1993-05-01

175

NASA Astrophysics Data System (ADS)

This paper presents a one-dimensional Ecosystem Model. Mathematically, the pelagic variables in the model are described by a second-order partial differential equation of the diffusion type with biogeochemical sources and sinks. The temporal changes in the phytoplankton biomass are caused by primary production, respiration, mortality, grazing by zooplankton and sinking. The zooplankton biomass is affected by ingestion, excretion, respiration, fecal production, mortality, and carnivorous grazing. The changes in the pelagic detritus concentration are determined by input of: dead phytoplankton and zooplankton, natural mortality of predators, fecal pellets, and sinks: sedimentation, zooplankton grazing and decomposition. The nutrient concentration is caused by nutrient release, zooplankton excretion, predator excretion, detritus decomposition and benthic regeneration as sources and by nutrient uptake by phytoplankton as sinks. However, the benthic detritus is described by phytoplankton sedimentation, detritus sedimentation and remineralisation. The particulate organic carbon concentration is determined as the sum of phytoplankton, zooplankton and dead organic matter (detritus) concentrations. The 1D ecosystem model was used to simulate the seasonal dynamics of pelagic variables (phytoplankton, zooplankton, pelagic detritus and POC) in the southern Baltic Sea (Gda?sk Deep, Bornholm Deep and Gotland Deep). The calculations were made assuming: 1) increase in the water temperature in the upper layer - 0.008oC per year, 2) increase in the available light - 0.2% per year. Based on this trend, daily, monthly and seasonal and annual variability of phytoplankton, zooplankton, pelagic detritus and particulate organic carbon in different areas of the southern Baltic Sea (Gda?sk Deep, Borrnholm Deep and Gotland Deep) in the euphotic layer was calculated for the years: 2000, 2010, 2020, 2030, 2040 and 2050.

Dzierzbicka-Glowacka, L.; Maciejewska, A.; Osi?ski, R.; Jakacki, J.; J?drasik, J.

2009-04-01

176

Modeling a 1-D bremsstrahlung and neutron imaging array for use on Sandia`s Z machine

Inertial confinement fusion is being studied on the Z facility at Sandia National Laboratories. Z is a large z-pinch machine which can provide 20 MA of current to z-pinch loads producing {approximately}1.8 MJ of soft x-rays in less than 10 ns. Within the pinch region, decelerated electrons produce a strong source of bremsstrahlung radiation which varies from shot to shot. Additionally, a variety of ICF targets produce fusion neutrons whose intensity and distribution depend on the temperature and density of the target compression in the pinch. This paper describes the computer modeling behind the shielding design of a simple time-resolved, 1-D imaging array which can provide a time history of both the bremsstrahlung and neutron production as a function of height within the target region. It is demonstrated that by building an array of scintillator fibers separated by long, thin tungsten collimator plates, a spatial resolution of 0.254 mm at the target can be achieved. The corresponding channel-to-channel discrimination for such a design is shown to be better than 1000::1 for <4 MeV photons and 100::1 for 2.45 MeV neutrons. By coupling scintillator fibers to a fiber-optic streak camera system, the signal can also be given as a function of time with a temporal resolution of about 1.2 ns.

Rochau, G.A.; Derzon, M.S.; Fehl, D.; Rochau, G.E. [Sandia National Labs., Albuquerque, NM (United States); Lazier, S. [Ktech Corp., Albuquerque, NM (United States); Droemer, D. [Bechtel Nevada (United States)

1998-06-01

177

Models and numerical simulation of velocity distribution of pickup ions

NASA Astrophysics Data System (ADS)

Large manned spacecraft release and carry up a huge amounts of water in its orbital motion. Some of the neutral water molecules undergo charge exchange with the ambient ionospheric plasma and become what are called pick-up ions at Low Earth Orbit (LEO) altitudes. The purpose of this dissertation is to model those ions and predicts their effect on a space vehicle mounted ion probe so that a comparison between the model and measured data can be made. The velocity distribution of the pickup ions ( H2O+ ), which are created by charge exchange between released neutral water molecules from a space shuttle orbiter and the ambient ionospheric plasma at LEO altitudes, is systematically studied. The factors which affect the velocity distribution of the pickup ions are discussed. A partial differential equation of the pickup ion's distribution function in the frame fixed on the earth is derived based on the analysis of the pickup ion's source, loss, and collisions with other particles. The trajectories of the pickup ions in the frame moving with the space orbiter are analyzed. The influence of collisions between the pickup ions and other particles on the number of the ions collected by a payload ion probe is discussed and the probability of the collision in the path of the pickup ions from their creation place to an instrument mounted on the orbiter is studied. Three integral models are developed to calculated the velocity distribution of the pickup ions in the frame moving with the orbiter. The first one is for the pickup ions created in very cold neutral water gas, the second one is for the pickup ions created in warm neutral water gas and the third one is for the pickup ions created in very hot neutral water gas. The algorithms are discussed to numerically calculate the velocity distribution of the pickup ions in the frame fixed on the orbiter with the three models. To compare the models with the data from the Spherical Retarding Potential Analyzer (SRPA) mounted on the orbital space shuttle, a model and an algorithm are developed to calculate the velocity magnitude distribution of the pickup ions in the frame moving with the orbiter. The method to numerically simulate a payload SRPA output is studied and a method to estimate the ratio of the pickup ions in the total ions collected by the payload SRPA is obtained. The comparison between the simulation result and actual measurement data from the SRPA on mission TSS-1R and earlier missions on which the SRPA was flown shows that the models and algorithms obtained in the dissertation are correct for the situation of a large space platform at LEO altitudes and useful in analyzing the data of the ion probes mounted on similar spacecraft. With the models obtained in the dissertation, the influence of some factors to the velocity magnitude distribution of the ions collected by the payload SRPA and the to the telemetered output signal of the payload SRPA are analyzed. These factors include the angle between the magnetic induction vector of the geomagnetic field and the orbital velocity vector of the orbiter, the density of the released water source of the orbiter, some selected attitude angles of the orbiter and the payload position of the payload SRPA.

Zhang, Yinghui

1998-10-01

178

Sleipner CCS site: velocity and attenuation model from seismic tomography

NASA Astrophysics Data System (ADS)

The results of the travel-time and frequency shift tomographic inversion of the seismic data from one of the high-resolution lines acquired in 2006 on the Sleipner CO2 geological storage site are here presented. The work has been performed within the European project CO2ReMoVe, to produce an accurate model in-depth, of both seismic velocities and attenuation, to constrain better the quantification studies of the project's partners. Tomographic techniques have the advantage of not assuming horizontal layering or uniform lateral velocities, and of enabling an easy comparison of models, even if resulting from seismic data acquired with different geometries, unavoidable in a time-lapse data set. Through an iterative process, the differences in travel-times between observed direct, reflected or refracted arrivals and the same, calculated on a discrete model, with a ray-tracing based on the Fermat's principle, are minimized. Other minimization procedures provide the reflector/refractor geometries in -depth. Analogously, in attenuation tomography, the minimization process takes into account the observed and calculated spectral-centroid frequency-shift, due to the loss of the highest frequency of the seismic wave, while crossing an attenuating medium. The result is a seismic quality factor (Q) model in-depth, and hence of the attenuation that is known to be more sensitive to subtle changes in physical properties than seismic velocity. The model is across the center of the CO2 plume, on the in-line 1838, and is constituted by nine layers, four resulting by a preliminary analysis of the pre-injection 1994 data set, i.e. seabed, a strong reflection in the overburden and the top and bottom of the Utsira Sand, plus additional five horizons, four of which within Utsira Sands, and one just above the top of it. The layers within the reservoir are very close to each other and in some cases they merge together laterally. The accumulation of CO2 in the uppermost layer of the reservoir, observed by other analyses, is confirmed by our analysis, whereas within the plume, lateral variations of both seismic velocity and Q values are observed. The presence of fine shale lenses, and their impact on the CO2 distribution within the plume may be the reason for these lateral variations. The seismic velocity and Q tomographic values have been compared with the theoretical curves from petrophysics studies, so to give to the results an interpretation in terms of effective variations in CO2 saturation and heterogeneity within the plume.

Rossi, G.; Chadwick, R. A.; Williams, G. A.

2012-04-01

179

This paper presents cell-layer-scale multidomain dynamic 1-D proton-exchange-membrane fuel-cell (PEMFC) stack model using VHDL-AMS modeling language. The model covers three main fuel-cell energy domains: electrical, fluidic, and thermal. The performance and advantages of the VHDL-AMS language are shown in the first part. Then, by means of the ??top-down?? modeling approach, the electrical-, fluidic-, and thermal-domain models of the PEMFC stack

Fei Gao; Benjamin Blunier; Abdellatif Miraoui; Abdellah El Moudni

2010-01-01

180

Measured and modeled dry deposition velocities over the ESCOMPTE area

NASA Astrophysics Data System (ADS)

Measurements of the dry deposition velocity of ozone have been made by the eddy correlation method during ESCOMPTE (Etude sur Site pour COntraindre les Modèles de Pollution atmosphérique et de Transport d'Emissions). The strong local variability of natural ecosystems was sampled over several weeks in May, June and July 2001 for four sites with varying surface characteristics. The sites included a maize field, a Mediterranean forest, a Mediterranean shrub-land, and an almost bare soil. Measurements of nitrogen oxide deposition fluxes by the relaxed eddy correlation method have also been carried out at the same bare soil site. An evaluation of the deposition velocities computed by the surface module of the multi-scale Chemistry and Transport Model MOCAGE is presented. This module relies on a resistance approach, with a detailed treatment of the stomatal contribution to the surface resistance. Simulations at the finest model horizontal resolution (around 10 km) are compared to observations. If the seasonal variations are in agreement with the literature, comparisons between raw model outputs and observations, at the different measurement sites and for the specific observing periods, are contrasted. As the simulated meteorology at the scale of 10 km nicely captures the observed situations, the default set of surface characteristics (averaged at the resolution of a grid cell) appears to be one of the main reasons for the discrepancies found with observations. For each case, sensitivity studies have been performed in order to see the impact of adjusting the surface characteristics to the observed ones, when available. Generally, a correct agreement with the observations of deposition velocities is obtained. This advocates for a sub-grid scale representation of surface characteristics for the simulation of dry deposition velocities over such a complex area. Two other aspects appear in the discussion. Firstly, the strong influence of the soil water content to the plant response, specifically in conditions of stress, is confirmed. Second, we point out the difficulty in interpreting measurements of nitrogen oxide deposition velocities: a synergetic approach combining measurements and modeling is practical.

Michou, M.; Laville, P.; Serça, D.; Fotiadi, A.; Bouchou, P.; Peuch, V.-H.

2005-03-01

181

ABSTRACTION OF INFORMATION FROM 2- AND 3DIMENSIONAL PORFLOW MODELS INTO A 1-D GOLDSIM MODEL - 11404

The Savannah River National Laboratory has developed a 'hybrid' approach to Performance Assessment modeling which has been used for a number of Performance Assessments. This hybrid approach uses a multi-dimensional modeling platform (PorFlow) to develop deterministic flow fields and perform contaminant transport. The GoldSim modeling platform is used to develop the Sensitivity and Uncertainty analyses. Because these codes are performing

G. Taylor; R. Hiergesell

2010-01-01

182

Differential cell proliferation in the cortex of the APPswePS1dE9 Alzheimer's disease mouse model.

Plaque deposition in Alzheimer's disease (AD) is known to decrease proliferation in neurogenic niches in AD mouse models, but the effects on cell proliferation and differentiation in other brain areas have not been studied in detail. We analyzed cell proliferation in the cortex of wild type (WT) and APPswePS1dE9 transgenic (AD) mice at different ages. Mice were studied shortly after the last BrdU injection (BrdU[ST]). In AD mice, the number of proliferating cells increased fourfold, coinciding with plaque appearance and its associated reactive gliosis and activation of microglia. An increase in the number of BrdU[ST]-cells expressing markers for activated microglia is underlying the enhanced proliferation. Cortical reactive astrocytes did not become proliferative since BrdU[ST]-cells were negative for different astrocyte-specific markers. The number of Olig2-positive oligodendrocyte precursor cells was unchanged. Four weeks after the last BrdU application, the number of BrdU[LT]-cells with an activated microglia signature was still enhanced in AD mice. None of the newborn cells had differentiated into oligodendrocytes, astrocytes, or neurons. On the basis of these observations, we conclude that amyloid plaque deposition increases proliferation of microglia around plaques but does not affect the proliferation of cortical oligodendrocyte precursor cells. No evidence was found for damage-induced proliferation of reactive astrocytes or for a redirected neurogenesis from the subventricular zone. The proliferation of microglia contributes to the rapid accumulation of microglia around plaques and may play a role in limitating plaque expansion. PMID:22262260

Kamphuis, Willem; Orre, Marie; Kooijman, Lieneke; Dahmen, Maurice; Hol, Elly M

2012-01-19

183

Floodplain mapping via 1D and quasi-2D numerical models in the valley of Thessaly, Greece

NASA Astrophysics Data System (ADS)

The European Union Floods Directive defines a flood as 'a covering by water of land not normally covered by water'. Human activities, such as agriculture, urban development, industry and tourism, contribute to an increase in the likelihood and adverse impacts of flood events. The study of the hydraulic behaviour of a river is important in flood risk management. Here, we investigate the behaviour of three hydraulic models, with different theoretical frameworks, in a real case scenario. The area is located in the Penios river basin, in the plain of Thessaly (Greece). The three models used are the one-dimensional HEC-RAS and the quasi two-dimensional LISFLOOD-FP and FLO-2D which are compared to each other, in terms of simulated maximum water depth as well as maximum flow velocity, and to a real flood event. Moreover, a sensitivity analysis is performed to determine how each simulation is affected by the river and floodplain roughness coefficient, in terms of flood inundation.

Oikonomou, Athanasios; Dimitriadis, Panayiotis; Koukouvinos, Antonis; Tegos, Aristoteles; Pagana, Vasiliki; Panagopoulos, Panayiotis-Dionisios; Mamassis, Nikolaos; Koutsoyiannis, Demetris

2013-04-01

184

Central United States Velocity Model Version 1: Description and Validation

NASA Astrophysics Data System (ADS)

We describe and test via numerical simulations a velocity model of the Central United States (CUSVM Version 1). Our model covers an area of 650,000 km2 and includes parts of Arkansas, Mississippi, Alabama, Illinois, Missouri, Kentucky and Tennessee. The model represents the compilation of research carried out for decades consisting of seismic refraction and reflection lines, geophysical logs, and inversions of the regional seismic properties. The CUSVM has a higher resolution description around Memphis and St. Louis, two of the largest urban areas in the Central United States. The density, p- and s-wave velocities are synthesized in a stand-alone spatial data base that can be queried to generate the required input for numerical simulations. We calibrate the CUSVM using three earthquakes located N, SW and SE of the zone encompassed by the model to sample different paths of propagation. The selected stations in the comparisons reflect different geological site conditions and cover distances ranging from 50 to 450 km away from the epicenters. The results indicate that both within and outside the Mississippi embayment, the CUSVM satisfactorily reproduces: a) the body wave arrival times and b) the observed regional variations in ground motion amplitude and duration in the frequency range 0-0.75Hz.

Ramirez Guzman, L.; Williams, R. A.; Boyd, O. S.; Hartzell, S.

2009-12-01

185

Preliminary Velocity Measurements in the Wake of a Submarine Model

NASA Astrophysics Data System (ADS)

Preliminary Particle Image Velocimetry (PIV) over a submarine shape has been conducted in a low speed wind tunnel at Princeton University. The model is a 1/67 replica of the USS Albacore, an experimental submarine designed to achieve maximum underwater performance, and based on "bodies of revolution." The model is tested with a sail, and different tail appendages. Velocity vector fields and flow visualizations in the wake region are presented for Reynolds numbers based on model length up to 10^5. The experiments establish the groundwork for future investigations of submarine models in the new High Reynolds Number Test Facility (http://www.princeton.edu/ gasdyn/HRTF.html). Supported by ONR Grants N00014-97-1-0325, N00014-97-1-0340 and N00014-97-1-0618.

Jimenez, J. M.; Reynolds, R.; Smits, A. J.

2000-11-01

186

A modified Green–Ampt model was developed in this study to describe water infiltration through a 300-cm long and five-layered soil column. In the modified Green–Ampt model, a saturation coefficient was introduced to determine the water content and hydraulic conductivity of the wetted zone. The saturation coefficient was determined by the ratio between measured moisture volume and total saturated moisture volume

Ying Ma; Shaoyuan Feng; Dongyuan Su; Guangyao Gao; Zailin Huo

2010-01-01

187

Modeling the exit velocity of a compressed air cannon

NASA Astrophysics Data System (ADS)

The use of compressed air cannons in an undergraduate laboratory provides a way to illustrate the connection between diverse physics concepts, such as conservation of momentum, the work-kinetic energy theorem, gas expansion, air drag, and elementary Newtonian mechanics. However, it is not clear whether the expansion of the gas in the cannon is an adiabatic or an isothermal process. We built an air cannon that utilizes a diaphragm valve to release the pressurized gas and found that neither process accurately predicts the exit velocity of our projectile. We discuss a model based on the flow of air through the valve, which is in much better agreement with our data.

Rohrbach, Z. J.; Buresh, T. R.; Madsen, M. J.

2012-01-01

188

NASA Astrophysics Data System (ADS)

Thermal-wave methods are magnificent tool for visualisation and analysis of thermal non-uniformity in solids. Special case of thermal non-uniformity is lack of adhesion in multilayer structures. This very important parameter effects on efficiency of draining of the heat and the reliability of many of semiconductor devices. This paper presents possibility of detection of exfoliation in high-power thyristor structure with the help of photoacoustic microscope. Values of temperature contrasts were evaluated from thermal-wave images, which were registered in harmonic modulation and pulse modulation modes. Both methods are characterised by similar sensitiveness for lack of adhesion, however pulse modulation mode makes the time of investigation significantly shorter. Comparison of experimental data with 1-D modelling results shows differences between theoretical and experimental values of temperature contrast in range of low frequencies (harmonic modulation mode) and long times of registration (pulse modulation mode). These differences appear because the 1-D model does not take limited lateral dimensions of excitation and thermal non-uniformity into consideration. Therefore 2-D modelling process was performed in order to explain the influence of geometrical factors on temperature contrasts. On the other hand, analysis of results of 2-D modelling makes the estimation of real delamination more accurate.

Suszy?ski, Z.; Duer, R.; Arsoba, R.

2004-10-01

189

Nondissipative Velocity and Pressure Regularizations for the ICON Model

NASA Astrophysics Data System (ADS)

A challenging aspect in the numerical simulation of atmospheric and oceanic flows is the multiscale character of the problem both in space and time. The small spacial scales are generated by the turbulent energy and enstrophy cascades, and are usually dealt with by means of turbulence parametrizations, while the small temporal scales are governed by the propagation of acoustic and gravity waves, which are of little importance for the large scale dynamics and are often eliminated by means of a semi-implicit time discretization. We propose to treat both phenomena of subgrid turbulence and temporal scale separation in a unified way by means of nondissipative regularizations of the underlying model equations. More precisely, we discuss the use of two regularized equation sets: the velocity regularization, also know as Lagrangian averaged Navier-Stokes system, and the pressure regularization. Both regularizations are nondissipative since they do not enhance the dissipation of energy and enstrophy of the flow. The velocity regularization models the effects of the subgrid velocity fluctuations on the mean flow, it has thus been proposed as a turbulence parametrization and it has been found to yield promising results in ocean modeling [HHPW08]. In particular, the velocity regularization results in a higher variability of the numerical solution. The pressure regularization, discussed in [RWS07], modifies the propagation of acoustic and gravity waves so that the resulting system can be discretized explicitly in time with time steps analogous to those allowed by a semi-implicit method. Compared to semi-implicit time integrators, however, the pressure regularization takes fully into account the geostrophic balance of the flow. We discuss here the implementation of the velocity and pressure regularizations within the numerical framework of the ICON general circulation model (GCM) [BR05] for the case of the rotating shallow water system, showing how the original numerical formulation can be extended to the regularized systems retaining discrete conservation of mass and potential enstrophy. We also present some numerical results both in planar, doubly periodic geometry and in spherical geometry. These results show that our numerical formulation correctly approximates the behavior of the regularized models, and are a first step toward the use of the regularization idea within a complete, three-dimensional GCM. References [BR05] L. Bonaventura and T. Ringler. Analysis of discrete shallow-water models on geodesic Delaunay grids with C-type staggering. Mon. Wea. Rev., 133(8):2351-2373, August 2005. [HHPW08] M.W. Hecht, D.D. Holm, M.R. Petersen, and B.A. Wingate. Implementation of the LANS-? turbulence model in a primitive equation ocean model. J. Comp. Phys., 227(11):5691-5716, May 2008. [RWS07] S. Reich, N. Wood, and A. Staniforth. Semi-implicit methods, nonlinear balance, and regularized equations. Atmos. Sci. Lett., 8(1):1-6, 2007.

Restelli, M.; Giorgetta, M.; Hundertmark, T.; Korn, P.; Reich, S.

2009-04-01

190

Modelling of the pressure-velocity correlation in turbulence diffusion

NASA Astrophysics Data System (ADS)

Most current computations of trubulent flows with second-moment closure adopt the diffusion models which neglect the effect of pressure-velocity correlation. In the present paper the importance of this correlation effect is elucidated the neglect of this effect accounts for some major defects in the wide application of the second-moment closures. Through the relation betweenoverline {pu_i } andoverline {u_i u_p u_p } , established by Lumley, we propose here a new turbulence diffusion model which takes into consideration the pressure effect. Applications of this new model in the computation of shearless turbulence mixing layer and plane and round-jet flows show that the spreading rate of these flows can be satisfactorily captured.

Song, Fu

1992-08-01

191

A wave propagation model for the high velocity impact response of a composite sandwich panel

A solution methodology to predict the residual velocity of a hemispherical-nose cylindrical projectile impacting a composite sandwich panel at high velocity is presented. The term high velocity impact is used to describe impact scenarios where the projectile perforates the panel and exits with a residual velocity. The solution is derived from a wave propagation model involving deformation and failure of

Michelle S. Hoo Fatt; Dushyanth Sirivolu

2010-01-01

192

Mean velocity and moments of turbulent velocity fluctuations in the wake of a model ship propulsor

NASA Astrophysics Data System (ADS)

Pod drives are modern outboard ship propulsion systems with a motor encapsulated in a watertight pod, whose shaft is connected directly to one or two propellers. The whole unit hangs from the stern of the ship and rotates azimuthally, thus providing thrust and steering without the need of a rudder. Force/momentum and phase-resolved laser Doppler anemometry (LDA) measurements were performed for in line co-rotating and contra-rotating propellers pod drive models. The measurements permitted to characterize these ship propulsion systems in terms of their hydrodynamic characteristics. The torque delivered to the propellers and the thrust of the system were measured for different operation conditions of the propellers. These measurements lead to the hydrodynamic optimization of the ship propulsion system. The parameters under focus revealed the influence of distance between propeller planes, propeller frequency of rotation ratio and type of propellers (co- or contra-rotating) on the overall efficiency of the system. Two of the ship propulsion systems under consideration were chosen, based on their hydrodynamic characteristics, for a detailed study of the swirling wake flow by means of laser Doppler anemometry. A two-component laser Doppler system was employed for the velocity measurements. A light barrier mounted on the axle of the rear propeller motor supplied a TTL signal to mark the beginning of each period, thus providing angle information for the LDA measurements. Measurements were conducted for four axial positions in the slipstream of the pod drive models. The results show that the wake of contra-rotating propeller is more homogeneous than when they co-rotate. In agreement with the results of the force/momentum measurements and with hypotheses put forward in the literature (see e.g. Poehls in Entwurfsgrundlagen für Schraubenpropeller, 1984; Schneekluth in Hydromechanik zum Schiffsentwurf, 1988; Breslin and Andersen in Hydrodynamics of ship propellers, 1996; Schneekluth and Bertram in Ship design for efficiency and economy, 1998), the co-rotating propellers model showed a much stronger swirl in the wake of the propulsor. The anisotropy of turbulence was analyzed using the anisotropy tensor introduced by Lumley and Newman (J Fluid Mech 82(1):161-178, 1977). The invariants of the anisotropy tensor of the wake flow were computed and were plotted in the Lumley-Newman-diagram. These measurements revealed that the anisotropy tensor in the wake of ship propellers is located near to the borders of the invariant map, showing a large degree of anisotropy. They will be presented and will be discussed with respect to applications of turbulence models to predict swirling flows.

Pêgo, J. P.; Lienhart, H.; Durst, F.

2007-08-01

193

Traveling waves in an optimal velocity model of freeway traffic

NASA Astrophysics Data System (ADS)

Car-following models provide both a tool to describe traffic flow and algorithms for autonomous cruise control systems. Recently developed optimal velocity models contain a relaxation term that assigns a desirable speed to each headway and a response time over which drivers adjust to optimal velocity conditions. These models predict traffic breakdown phenomena analogous to real traffic instabilities. In order to deepen our understanding of these models, in this paper, we examine the transition from a linear stable stream of cars of one headway into a linear stable stream of a second headway. Numerical results of the governing equations identify a range of transition phenomena, including monotonic and oscillating travelling waves and a time- dependent dispersive adjustment wave. However, for certain conditions, we find that the adjustment takes the form of a nonlinear traveling wave from the upstream headway to a third, intermediate headway, followed by either another traveling wave or a dispersive wave further downstream matching the downstream headway. This intermediate value of the headway is selected such that the nonlinear traveling wave is the fastest stable traveling wave which is observed to develop in the numerical calculations. The development of these nonlinear waves, connecting linear stable flows of two different headways, is somewhat reminiscent of stop-start waves in congested flow on freeways. The different types of adjustments are classified in a phase diagram depending on the upstream and downstream headway and the response time of the model. The results have profound consequences for autonomous cruise control systems. For an autocade of both identical and different vehicles, the control system itself may trigger formations of nonlinear, steep wave transitions. Further information is available [Y. Sugiyama, Traffic and Granular Flow (World Scientific, Singapore, 1995), p. 137].

Berg, Peter; Woods, Andrew

2001-03-01

194

Traveling waves in an optimal velocity model of freeway traffic.

Car-following models provide both a tool to describe traffic flow and algorithms for autonomous cruise control systems. Recently developed optimal velocity models contain a relaxation term that assigns a desirable speed to each headway and a response time over which drivers adjust to optimal velocity conditions. These models predict traffic breakdown phenomena analogous to real traffic instabilities. In order to deepen our understanding of these models, in this paper, we examine the transition from a linear stable stream of cars of one headway into a linear stable stream of a second headway. Numerical results of the governing equations identify a range of transition phenomena, including monotonic and oscillating travelling waves and a time- dependent dispersive adjustment wave. However, for certain conditions, we find that the adjustment takes the form of a nonlinear traveling wave from the upstream headway to a third, intermediate headway, followed by either another traveling wave or a dispersive wave further downstream matching the downstream headway. This intermediate value of the headway is selected such that the nonlinear traveling wave is the fastest stable traveling wave which is observed to develop in the numerical calculations. The development of these nonlinear waves, connecting linear stable flows of two different headways, is somewhat reminiscent of stop-start waves in congested flow on freeways. The different types of adjustments are classified in a phase diagram depending on the upstream and downstream headway and the response time of the model. The results have profound consequences for autonomous cruise control systems. For an autocade of both identical and different vehicles, the control system itself may trigger formations of nonlinear, steep wave transitions. Further information is available [Y. Sugiyama, Traffic and Granular Flow (World Scientific, Singapore, 1995), p. 137]. PMID:11308709

Berg, P; Woods, A

2001-02-21

195

Purpose We compared cadherin 23 (Cdh23) mRNA and protein variants in the inner ear and retina of wild-type and mutant mice and primates to better understand the pleiotropic effects of Cdh23 mutations, and specifically to understand the absence of retinal degeneration in Cdh23 mutant mice. Methods Semiquantitative real-time PCR was used to compare the level of expression of Cdh23 alternative transcripts in the inner ear and retina of wild-type and homozygous Cdh23v-6J (waltzer) mice. Antibodies generated against CDH23 isoforms were used in immunohistochemistry, immunohistology, electron microscopy, and western blot analyses of mouse and primate inner ear and retina to study the distribution of these isoforms in various cellular compartments. Results Cdh23 mRNA alternative splice variants were temporally and spatially regulated in the inner ear and retina. In the mature mouse retina, CDH23 isoforms were broadly expressed in various cellular compartments of the photoreceptor layer. The wild-type CDH23_V3 protein isoform, which has PDZ binding motifs but neither extracellular domains nor a transmembrane domain, localized exclusively to the outer plexiform layer of the retina containing photoreceptor cell synapses and to the synaptic region of auditory and vestibular hair cells. The longest CDH23 protein isoform, CDH23_V1, appeared by western blotting to be the only one affected by the Cdh23v-6J mutation; it was expressed in the wild-type mouse inner ear, but not in the mouse retina. However, CDH23_V1 was detected in western blot analyses of monkey and human retinas. Conclusions The time- and tissue-dependent expression patterns that we have shown for Cdh23 alternative transcripts suggest developmental roles and tissue-specific functions for the various transcripts. Many of these isoforms continue to be expressed in waltzer mice. The longest CDH23 isoform (CDH23_V1), however, is not expressed in mutant mice and is necessary for normal inner ear function. The longest isoform is expressed in the retinas of primates, but not detected in the mouse retina. This species difference suggests that the mouse may not be a suitable model for studying the retinitis pigmentosa phenotype of human Usher syndrome type 1D.

Lagziel, Ayala; Overlack, Nora; Bernstein, Steven L.; Morell, Robert J.; Wolfrum, Uwe

2009-01-01

196

Interest in patient-specific blood-flow circulation modeling has increased substantially in recent years. The availability of clinical data for geometric and elastic properties together with efficient numerical methods has now made model rendering feasible. This work uses 3-D fluid-structure interaction (FSI) to provide physiological simulation resulting in modeling with a high level of detail. Comparisons are made between results using FSI and rigid wall models. The relevance of wall compliance in determining parameters of clinical importance, such as wall shear stress, is discussed together with the significance of differences found in the pressure and flow waveforms when using the 1-D model. Patient-specific geometry of the aorta and its branches was based on MRI angiography data. The arterial wall was created with a variable thickness. The boundary conditions for the fluid domain were pressure waveform at the ascending aorta and flow for each outlet. The waveforms were obtained using a 1-D model validated by in vivo measurements performed on the same person. In order to mimic the mechanical effect of surrounding tissues in the simulation, a stress-displacement relation was applied to the arterial wall. The temporal variation and spatial patterns of wall shear stress are presented in the aortic arch and thoracic aorta together with differences using rigid wall and FSI models. A comparison of the 3-D simulations to the 1-D model shows good reproduction of the pressure and flow waveforms. PMID:22981220

Reymond, Philippe; Crosetto, Paolo; Deparis, Simone; Quarteroni, Alfio; Stergiopulos, Nikos

2012-09-12

197

NASA Astrophysics Data System (ADS)

Earthquake hazard in the Salt Lake City, Utah region is strongly dominated by the potential for a M7 event on the Salt Lake segment of the Wasatch fault. The lack of instrumental records due to the long recurrence intervals on the fault and the inability of ground motion prediction equations to capture the effects of the basin structure make the estimation of earthquake ground motions from 3-D deterministic simulations an attractive approach to characterizing hazard in the region. Our simulations investigate the effect of velocity perturbations in the seismic material model on earthquake ground motions for a M7 event on the Wasatch fault. The reference seismic velocity model is the Wasatch Front community velocity model (WCVM). Earthquake simulations are carried out with the reference seismic material model and for models in which we make perturbations to the regional seismic velocity model and to the seismic velocities of the deep sedimentary basins. We construct a kinematic fault model that defines the slip amplitudes, rupture velocities and rise times and model seismic wave propagation using the Hercules finite element tool-chain (Tu et al., 2006). We obtain displacement time histories and compare ground motion parameters from the reference and perturbed velocity models. Ground motion parameters that are of greatest importance in engineering seismology (e.g., peak ground motions, spectral accelerations, etc.) are selected for the comparisons. Differential wave propagation through the reference and perturbed seismic velocity models explains the variations in earthquake ground motions. We also present recent results from a comprehensive validation of the WCVM and the perturbed velocity models to characterize the fit between observed and synthetic seismograms from small magnitude (M3-4.5) earthquakes in the region. Overall, we find that the WCVM can reproduce the waveform parameters that are of greatest interest in seismic hazard studies to a fair degree, up to a high-frequency corner of 0.5 Hz for two of the simulated earthquakes and to 0.1 Hz for one of the events. Spatial variation in the GOF is high but strong-motion records generally show poorer fits at the seismographs located atop thick sediments and near basin-edges. In addition, we find a correlation between the discrepancies in peak ground motions (velocity and acceleration) for the observed and synthetic seismograms and distance for two of the modeled earthquakes for the higher frequency band measurements. The effect of velocity perturbations in the sedimentary basins on ground motions increases with the frequency band of the measurement and suggests that knowledge about the velocity structure of the sedimentary basins has important consequences for accurately predicting earthquake ground motions. Our results suggest that future modifications to the WCVM focus on improving the seismic velocity structure of the deeper parts of the sedimentary basins.

Moschetti, M. P.; Ramirez Guzman, L.

2011-12-01

198

Gradient sensing, polarization, and chemotaxis of motile cells involves the actin cytoskeleton, and regulatory modules, including the phosphoinositides (PIs), their ki- nases\\/phosphatases, and small GTPases (Rho proteins). Here we model their indi- vidual components (PIP, PIP2, PIP3; PTEN, PI3K, PI5K; Cdc42, Rac, Rho; Arp2\\/3, and actin), their interconversions, interactions, and modular functions in the context of a 1D dynamic model

Adriana T. Dawes; Leah Edelstein-Keshet

199

NASA Astrophysics Data System (ADS)

A simple method intended to quickly assess the net acceleration of particle populations due to wave heating is proposed. It adopts the philosophy proposed by Stix (1975 Nucl. Fusion 15 737; 1992 Waves in Plasmas (New York: AIP) pp 510-3) to compute the 1D distribution function of ion cyclotron resonance frequency heated species, but extends it on various fronts to allow describing tail formation of both minority and majority populations at any cyclotron harmonic. All plasma constituents are evolved by solving a set of coupled Fokker-Planck equations iteratively. As electrons easily reach high velocities, the relativistic collision operator for electron self-collisions has been implemented. Including a constant finite energy confinement time allows us to incorporate local losses qualitatively.

Van Eester, Dirk; Lerche, Ernesto

2011-09-01

200

Molecular Ion and Non-Zero Birth Velocity Effects in IEC Modeling

NASA Astrophysics Data System (ADS)

An inertial-electrostatic confinement (IEC) chamber contains nearly transparent, concentric wire grids with a high voltage difference between them. At typical ˜0.3 Pa (˜2 mtorr) pressures, atomic and molecular processes can be important. Source region ions pass through the anode grid as a mixture of D^+, D2^+, and D3^+ ions, accelerate radially, and interact with the background gas to produce a cold ions (D^+ and D2^+) through interactions with the background D2 gas. These cold ions accelerate and produce additional cold ions through interactions with the background gas. A 1-D model for the effect of various molecular and atomic processes between deuterium ions (D^+, D2^+, and D3^+) and the background gas on the performance of spherical, gridded IEC devices has been developed. This formalism includes the bouncing motion of ions in the potential well and sums over all generations of cold ions. This leads to a set of coupled Volterra integral equations, which are solved numerically to yield the energy spectrum of the ion and fast neutral flux plus the neutron production. Recent improvements in the model, including non-zero ion birth velocities, will be discussed. Parametric surveys and comparison with experimental data for the Wisconsin IEC devices will be presented.

Emmert, Gilbert; Santarius, John

2008-11-01

201

Noise Induced Congested Traffic Flow in Coupled Map Optimal Velocity Model

The optimal velocity traffic flow model is one of the car-followingmodels which describe the behavior of cars by differential equations.In that model, each car controls its speed toward an optimal (safety)velocity, which depends only on the headway. We constructed a newcar-following type simulation model for traffic flow in a coupled mapform based on the optimal velocity model. We can easily

Shin-ichi Tadaki; Macoto Kikuchi; Yuki Sugiyama; Satoshi Yukawa

1999-01-01

202

SCEC CVM-Toolkit (CVM-T) -- High Performance Meshing Tools for SCEC Community Velocity Models

The SCEC Community Velocity Model Toolkit (CVM-T) enables earthquake modelers to quickly build, visualize, and validate large-scale 3D velocity meshes using SCEC CVM-H or CVM-4. CVM-T is comprised of three main components: (1) a current SCEC community velocity model for Southern California, (2) tools for extracting meshes from this model and visualizing them, and (3) an automated test framework for

P. Small; P. J. Maechling; G. P. Ely; K. B. Olsen; K. Withers; R. W. Graves; T. H. Jordan; A. Plesch; J. H. Shaw

2010-01-01

203

Impact of the vertical velocity scheme on modeling transport in the tropical tropopause layer

To assess the impact of the vertical velocity scheme on modeling transport in the tropical tropopause layer (TTL), 3 month backward trajectories are initialized in the TTL for boreal winter and summer 2002. The calculations are done in either a kinematic scenario with pressure tendency as the vertical velocity or in a diabatic scenario with cross-isentropic velocity deduced from various

F. Ploeger; P. Konopka; G. Günther; J.-U. Grooß; R. Müller

2010-01-01

204

Modelling the outcomes of high-velocity impacts between small solarsystem bodies

We present a self-consistent numerical algorithm aimed at predicting the outcomes of high-velocity impacts between asteroids (or other small bodies of the solar system), based on a set of model input parameters which can be estimated from the available experimental evidence, and including the possible gravitational reaccumulation of ejected fragments whose velocity is less than a suitably defined escape velocity.

Jean-Marc Petit; Paolo Farinella

1993-01-01

205

Combining flow routing modelling and direct velocity measurement for optimal discharge estimation

NASA Astrophysics Data System (ADS)

A new procedure is proposed for estimating river discharge hydrographs during flood events, using only water level data measured at a gauged site, as well as 1-D shallow water modelling and sporadic maximum surface flow velocity measurements. During flood, the piezometric level is surmised constant in the vertical plane of the river section, where the top of the banks is always above the river level, and is well represented by the recorded stage hydrograph. The river is modelled along the reach directly located downstream the upstream gauged section, where discharge hydrograph is sought after. For the stability with respect to the topographic error, as well as for the simplicity of the data required to satisfy the boundary conditions, a diffusive hydraulic model is adopted for flow routing. Assigned boundary conditions are: (1) the recorded stage hydrograph at the upstream river site and (2) the zero diffusion condition at the downstream end of the reach. The MAST algorithm is used for the numerical solution of the flow routing problem, which is embedded in the Brent algorithm used for the computation of the optimum Manning coefficient. Based on synthetic tests concerning a broad prismatic channel, the optimal reach length is chosen so that the approximated downstream boundary condition effects on discharge hydrograph assessment at upstream end are negligible. The roughness Manning coefficient is calibrated by using sporadic instantaneous surface velocity measurements during the rising limb of flood that are turned into instantaneous discharges through the solid of velocity estimated by a two-dimensional entropic model. Several historical events, occurring in three gauged sites along the upper Tiber River wherein a reliable rating curve is available, have been used for the validation. The analysis outcomes can be so summarized: (1) criteria adopted for selecting the optimal channel length and based on synthetic tests have been proved reliable by using field data of three gauged river sites. Indeed, for each of them a downstream reach, long not more than 500 m, is turned out fair for achieving good performances of the diffusive hydraulic model, thus allowing to drastically reducing the topographical data of river cross-sections; (2) the procedure for Manning's coefficient calibration allowed to get high performance of the hydraulic model just considering the observed water levels and sporadic measurements of maximum surface flow velocity during the rising limb of flood. Indeed, in terms of errors in magnitude on peak discharge, for the optimal calibration, they were found, in average, not exceeding 5% for all events observed in the three investigated gauged sections, while the Nash-Sutcliff efficiency was, in average, greater than 0.95. Therefore, the proposed procedure, apart from to have turned out reliable for the rating curve assessment at ungauged sites, can be applied in realtime for whatever flood conditions and this is of great interest for the practice hydrology seeing that, looking at new monitoring technologies, it will be possible to carry out velocity measurements by hand-held radar sensors in different river sites and for the same flood.

Corato, G.; Moramarco, T.; Tucciarelli, T.

2011-03-01

206

NASA Astrophysics Data System (ADS)

Helicopter borne time domain EM systems historically measure only the Z-component of the secondary field, whereas fixed wing systems often measure all field components. For the latter systems the X-component is often used to map discrete conductors, whereas it finds little use in the mapping of layered settings. Measuring the horizontal X-component with an offset loop helicopter system probes the earth with a complementary sensitivity function that is very different from that of the Z-component, and could potentially be used for improving resolution of layered structures in one dimensional modeling. This area is largely unexplored in terms of quantitative results in the literature, since measuring and inverting X-component data from a helicopter system is not straightforward: The signal strength is low, the noise level is high, the signal is very sensitive to the instrument pitch and the sensitivity function also has a complex lateral behavior.The basis of our study is a state of the art inversion scheme, using a local 1D forward model description, in combination with experiences gathered from extending the SkyTEM system to measure the X component. By means of a 1D sensitivity analysis we motivate that in principle resolution of layered structures can be improved by including an X-component signal in a 1D inversion, given the prerequisite that a low-pass filter of suitably low cut-off frequency can be employed. In presenting our practical experiences with modifying the SkyTEM system we discuss why this prerequisite unfortunately can be very difficult to fulfill in practice. Having discussed instrumental limitations we show what can be obtained in practice using actual field data. Here, we demonstrate how the issue of high sensitivity towards instrument pitch can be overcome by including the pitch angle as an inversion parameter and how joint inversion of the Z- and X-components produces virtually the same model result as for the Z-component alone. We conclude that adding helicopter system X-component to a 1D inversion can be used to facilitate higher confidence in the layered result, as the requirements for fitting the data into a 1D model envelope becomes more stringent and the model result thus less prone to misinterpretation.

Kirkegaard, Casper; Foged, Nikolaj; Auken, Esben; Christiansen, Anders Vest; Sørensen, Kurt

2012-09-01

207

NASA Astrophysics Data System (ADS)

A coupled biological-physical model was developed and tested in one-dimensional (1-D, vertical) and two-dimensional (2-D, cross-sectional) domains to examine the spring phytoplankton bloom and associated lower trophic level food web dynamics on Georges Bank (GB). The biological model consists of nine compartments: dissolved inorganic nutrients (nitrate, ammonium and silicate), phytoplankton (large and small size classes), zooplankton (large and small size classes), and detrital organic nitrogen and biogenic silica. The 1-D model results showed that in the shallow central bank, the timing and duration of spring blooms are closely linked to the light intensity and its downward penetration, while the intensity of blooms is regulated by initial nutrient concentrations and zooplankton grazing pressure. In the deeper flank area, the bloom dynamics is directly controlled by the seasonal development of stratification. The interactions between the shallow and deep regions of the bank were examined by a 2-D model, which showed that the cross-sectional gradients of biological quantities were caused mainly by the shallow-deep topographic transition and tidal mixing. Between the shallow and deep regions, a possible phytoplankton maximum concentration area was seen in the model at the time before the formation of the tidal-mixing front. Once the tidal-mixing front was established during late spring, the model showed a relatively high concentration of phytoplankton near the front as the result of the tidally driven up-front nutrient flux. Both the 1-D and 2-D models captured the basic seasonal cycles of the nutrients and phytoplankton in the central bank, but failed to reproduce those patterns in the deep flank regions, where horizontal advection might play a significant role.

Ji, Rubao; Chen, Changsheng; Franks, Peter J. S.; Townsend, David W.; Durbin, Edward G.; Beardsley, Robert C.; Gregory Lough, R.; Houghton, Robert W.

2006-11-01

208

The velocity-density relation in the spherical model

NASA Astrophysics Data System (ADS)

We study the cosmic velocity-density relation using the spherical collapse model (SCM) as a proxy to non-linear dynamics. Although the dependence of this relation on cosmological parameters is known to be weak, we retain the density parameter ?m in SCM equations, in order to study the limit ?m -> 0. We show that in this regime the considered relation is strictly linear, for arbitrary values of the density contrast, on the contrary to some claims in the literature. On the other hand, we confirm that for realistic values of ?m the exact relation in the SCM is well approximated by the classic formula of Bernardeau, both for voids (? < 0) and overdensities up to ? ~ 2-3. Inspired by this fact, we find further analytic approximations to the relation for the whole range ? ? [- 1, ?). Our formula for voids accounts for the weak ?m-dependence of their maximal rate of expansion, which for ?m < 1 is slightly smaller that 3/2. For positive density contrasts, we find a simple relation that works very well up to the turnaround (i.e. up to ? <~ 13.5 for ?m = 0.25 and neglected ??). Having the same second-order expansion as the formula of Bernardeau, it can be regarded as an extension of the latter for higher density contrasts. Moreover, it gives a better fit to the results of cosmological numerical simulations.

Bilicki, M.; Chodorowski, M. J.

2008-12-01

209

NASA Astrophysics Data System (ADS)

The dome-building eruption at Mount St. Helens has occurred through glacial ice and snow that would be expected to substantially affect the character of the eruption. Nevertheless, the role of water in the eruption to date has not always been clear. For example, on March 8, 2005, a half-hour-long tephra blast sent a plume to a maximum of ~9 km above the vent (based on pilot reports); seismicity and plume heights were greatest during the first ~10 minutes, then persisted for another ~15 minutes at a lower level before the eruption stopped. Tephra volume within 5 km2 downwind of the vent was ~5x104 m3 DRE, but trace amounts were reported at least to Ellensburg, WA (150 km NE), suggesting a total areal coverage >5,000 km2 and total volume >1x105 m3. Assuming that most of this material was expelled in the first ten minutes and had a density of 2500 kg/m3, the mass flow rate (M) during the vigorous phase was >~4x105 kg/s. The tephra, composed primarily of non-pumiceous broken and decrepitated dome rock, could have been expelled either by groundwater and steam at relatively modest (boiling-point) temperatures, or by magmatic gas at much higher temperatures. The high plume, however, suggested significant buoyancy, perhaps driven by temperatures closer to magmatic. To assess the effect of magmatic heat on plume height, we employ a 1-D steady volcanic plume model that uses specified vent diameter, exit velocity, eruption temperature, mass fractions of gas and added external water, and profiles of atmospheric temperature and humidity, to calculate plume height and plume properties as a function of elevation. The model considers the enthalpy of equilibrium water condensation and of ice formation. Model results show that, under atmospheric temperature and humidity profiles measured near Mount St. Helens on the afternoon of March 8, 2005, a plume height (h) of 7-9 km could have developed with eruption temperatures (T) as low as 100° C, provided the mass fraction of water vapor in the plume (n) exceeded ~0.25 (mixtures containing less gas at this temperature would collapse before reaching 7-9 km height). At T=100° C and n=0.25, however, a mass flux of 0.6-1x105 kg/s will generate the observed 7-9km plume height, whereas a mass flow rate >~4x105 kg/s, in line with observations, results in h>~11 km. Under more typical magmatic temperatures (900° C) and gas mass fractions (0.02-0.03), plume heights of 7-9 km require M=4-6x105 kg/s -- nearly an order of magnitude greater than the vapor-rich, boiling point mixture, but more in line with the estimated mass flow rate of this eruption. These results, though not definitive, suggest that magmatic heat may have been important in driving the March 8 eruption. Relationships between mass flow rate and plume height may be useful in assessing the roles of magmatic and phreatic sources during other small eruptions.

Mastin, L. G.; Sherrod, D. R.; Vallance, J. W.; Thornber, C. T.; Ewert, J. W.

2005-12-01

210

Crowd instability analysis using velocity-field based social force model

This paper proposes a novel method to locate crowd behavior instability spatio-temporally using a velocity-field based social force model. Considering the impacts of velocity field on interaction force between individuals, we establish an improved social force model by introducing collision probability in view of velocity distribution. As compared with commonly-used social force model, which defines interaction force as a dependent

Jing Zhao; Yi Xu; Xiaokang Yang; Qing Yan

2011-01-01

211

NASA Astrophysics Data System (ADS)

Fluvial sediment transport creates great challenges for river scientists and engineers. The interaction between the fluid (water) and the solid (dispersed sediment particles) phases is crucial in morphodynamics. The process of sediment transport and the resulting morphological evolution of rivers get more complex with the exposure of the fluvial systems to the natural and variable environment (climatic, geological, ecological and social, etc.). The earlier efforts in mathematical river modelling were almost exclusively built on traditional fluvial hydraulics. The last half century has seen more and more developments and applications of mathematical models for fluvial flow, sediment transport and morphological evolution. The first attempts for a quantitative description and simulation of basin filling in geological time scales started in the late 60´s of the last century (eg. Schwarzacher, 1966; Briggs & Pollack, 1967). However, the quality of this modelling practice has emerged as a crucial issue for concern, which is widely viewed as the key that could unlock the full potential of computational fluvial hydraulics. Most of the models presently used to study fluvial basin filling are of the "diffusion type" (Flemmings and Jordan, 1989). It must be noted that this type of models do not assume that the sediment transport is performed by a physical diffusive process. Rather they are synthetic models based on mass conservation. In the "synthesist" viewpoint (Tipper, 1992; Goldenfeld & Kadanoff, 1999; Werner, 1999 in Paola, 2000) the dynamics of complex systems may occur on many levels (time or space scales) and the dynamics of higher levels may be more or less independent of that at lower levels. In this type of models the low frequency dynamics is controlled by only a few important processes and the high frequency processes are not included. In opposition to this is the "reductionist" viewpoint that states that there is no objective reason to discard high frequency processes. In this viewpoint the system is broken down into its fundamental components and processes and the model is build up by selecting the important processes regardless of its time and space scale. This viewpoint was only possible to pursue in the recent years due to improvement in system knowledge and computer power (Paola, 2000). The primary aim of this paper is to demonstrate that it is possible to simulate the evolution of the sediment river bed, traditionally studied with synthetic models, with a process-based hydrodynamic, sediment transport and morphodynamic model, solving explicitly the mass and momentum conservation equations. With this objective, a comparison between two mathematical models for alluvial rivers is made to simulate the evolution of the sediment river bed of a conceptual 1D embayment for periods in the order of a thousand years: the traditional synthetic basin infilling aggregate diffusive type model based on the diffusion equation (Paola, 2000), used in the "synthesist" viewpoint and the process-based model MOHID (Miranda et al., 2000). The simulation of the sediment river bed evolution achieved by the process-based model MOHID is very similar to those obtained by the diffusive type model, but more complete due to the complexity of the process-based model. In the MOHID results it is possible to observe a more comprehensive and realistic results because this type of model include processes that is impossible to a synthetic model to describe. At last the combined effect of tide, sea level rise and river discharges was investigated in the process based model. These effects cannot be simulated using the diffusive type model. The results demonstrate the feasibility of using process based models to perform studies in scales of 10000 years. This is an advance relative to the use of synthetic models, enabling the use of variable forcing. REFERENCES • Briggs, L.I. and Pollack, H.N., 1967. Digital model of evaporate sedimentation. Science, 155, 453-456. • Flemmings, P.B. and Jordan, T.E., 19

Laginha Silva, Patricia; Martins, Flávio A.; Boski, Tomász; Sampath, Dissanayake M. R.

2010-05-01

212

T-complex testis expressed protein 1 domain containing 4 (TCTEX1D4) contains the canonical phosphoprotein phosphatase 1 (PPP1) binding motif, composed by the amino acid sequence RVSF. We identified and validated the binding of TCTEX1D4 to PPP1 and demonstrated that indeed this protein is a novel PPP1 interacting protein. Analyses of twenty-one mammalian species available in public databases and seven Lagomorpha sequences obtained in this work showed that the PPP1 binding motif 90RVSF93 is present in all of them and is flanked by a palindromic sequence, PLGS, except in three species of pikas (Ochotona princeps, O. dauurica and O. pusilla). Furthermore, for the Ochotona species an extra glycosylation site, motif 96NLS98, and the loss of the palindromic sequence were observed. Comparison with other lagomorphs suggests that this event happened before the Ochotona radiation. The dN/dS for the sequence region comprising the PPP1 binding motif and the flanking palindrome highly supports the hypothesis that for Ochotona species this region has been evolving under positive selection. In addition, mutational screening shows that the ability of pikas TCTEX1D4 to bind to PPP1 is maintained, although the PPP1 binding motif is disrupted, and the N- and C-terminal surrounding residues are also abrogated. These observations suggest pika as an ideal model to study novel PPP1 complexes regulatory mechanisms.

Korrodi-Gregorio, Luis; Margarida Lopes, Ana; Esteves, Sara L. C.; Afonso, Sandra; Lemos de Matos, Ana; Lissovsky, Andrey A.; da Cruz e Silva, Odete A. B.; Esteves, Pedro Jose; Fardilha, Margarida

2013-01-01

213

The aim of this study was to use a combined structure and pharmacophore modeling approach to extract information regarding dopamine D1 receptor agonism and D1/D2 agonist selectivity. A 3D structure model of the D1 receptor in its agonist-bound state was constructed with a full D1 agonist present in the binding site. Two different binding modes were identified using (+)-doxanthrine or SKF89626 in the modeling procedure. The 3D model was further compared with a selective D1 agonist pharmacophore model. The pharmacophore feature arrangement was found to be in good agreement with the binding site composition of the receptor model, but the excluded volumes did not fully reflect the shape of the agonist binding pocket. A new receptor-based pharmacophore model was developed with forbidden volumes centered on atom positions of amino acids in the binding site. The new pharmacophore model showed a similar ability to discriminate as the previous model. A comparison of the 3D structures and pharmacophore models of D1 and D2 receptors revealed differences in shape and ligand-interacting features that determine selectivity of D1 and D2 receptor agonists. A hydrogen bond pharmacophoric feature (Ser-TM5) was shown to contribute most to the selectivity. Non-conserved residues in the binding pocket that strongly contribute to D1/D2 receptor agonist selectivity were also identified; those were Ser/Cys3.36, Tyr/Phe5.38, Ser/Tyr5.41, and Asn/His6.55 in the transmembrane (TM) helix region, together with Ser/Ile and Leu/Asn in the second extracellular loop (EC2). This work provides useful information for the design of new selective D1 and D2 agonists. The combined receptor structure and pharmacophore modeling approach is considered to be general, and could therefore be applied to other ligand–protein interactions for which experimental information is limited.

Malo, Marcus; Brive, Lars; Luthman, Kristina; Svensson, Peder

2012-01-01

214

The objective of this study was to fit a simple ecosystem model to climatological nitrogen cycle data in the Gulf of Maine, in order to calibrate the biological model for use in future 3-D modelling studies. First depth-dependent monthly climatologies of nitrate, ammonium, chlorophyll, zooplankton, detritus and primary production data from Wilkinson Basin, Gulf of Maine, were created. A 6-box

Laurence A. Anderson

2009-01-01

215

Photocurrent generated by ionizing radiation represents a threat to microelectronics in radiation environments. Circuit simulation tools such as SPICE [1] can be used to analyze these threats, and typically rely on compact models for individual electrical components such as transistors and diodes. Compact models consist of a handful of differential and/or algebraic equations, and are derived by making simplifying assumptions to any of the many semiconductor transport equations. Historically, many photocurrent compact models have suffered from accuracy issues due to the use of qualitative approximation, rather than mathematically correct solutions to the ambipolar diffusion equation. A practical consequence of this inaccuracy is that a given model calibration is trustworthy over only a narrow range of operating conditions. This report describes work to produce improved compact models for photocurrent. Specifically, an analytic model is developed for epitaxial diode structures that have a highly doped subcollector. The analytic model is compared with both numerical TCAD calculations, as well as the compact model described in reference [2]. The new analytic model compares well against TCAD over a wide range of operating conditions, and is shown to be superior to the compact model from reference [2].

Verley, Jason C.; Axness, Carl L.; Hembree, Charles Edward; Keiter, Eric Richard; Kerr, Bert (New Mexico Institute of Mining and Technology, Socorro, NM)

2012-04-01

216

Alzheimer's disease (AD) is hallmarked by amyloid-? (A?) peptides accumulation and aggregation in extracellular plaques, preceded by intracellular accumulation. We examined whether intracellular A? can be cleared by cytosolic peptidases and whether this capacity is affected during progression of sporadic AD (sAD) in humans and in the commonly used APPswePS1dE9 and 3xTg-AD mouse models. A quenched A? peptide that becomes fluorescent upon degradation was used to screen for A?-degrading cytoplasmic peptidases cleaving the aggregation-prone KLVFF region of the peptide. In addition, this quenched peptide was used to analyze A?-degrading capacity in the hippocampus of sAD patients with different Braak stages as well as APPswePS1dE9 and 3xTg-AD mice. Insulin-degrading enzyme (IDE) was found to be the main peptidase that degrades cytoplasmic, monomeric A?. Oligomerization of A? prevents its clearance by IDE. Intriguingly, the A?-degrading capacity decreases already during the earliest Braak stages of sAD, and this decline correlates with IDE protein levels, but not with mRNA levels. This suggests that decreased IDE levels could contribute to early sAD. In contrast to the human data, the commonly used APPswePS1dE9 and 3xTg-AD mouse models do not show altered A? degradation and IDE levels with AD progression, raising doubts whether mouse models that overproduce A? peptides are representative for human sAD. PMID:23534431

Stargardt, Anita; Gillis, Judith; Kamphuis, Willem; Wiemhoefer, Anne; Kooijman, Lieneke; Raspe, Marcel; Benckhuijsen, Willemien; Drijfhout, Jan W; Hol, Elly M; Reits, Eric

2013-04-23

217

Modeling studentsâ conceptual understanding of force, velocity, and acceleration

NSDL National Science Digital Library

We have developed a multiple choice test designed to probe studentsâ conceptual understanding of the relationships among the directions of force, velocity, and acceleration. The test was administered to more than 800 students enrolled in standard or honors introductory physics courses or a second-year physics majors course. The test was found to be reasonably statistically reliable, and correlations of test score with grade, course level, and the Force Concept Inventory were moderate to strong. Further analysis revealed that in addition to the common incorrect response that velocity must be in the direction of the acceleration or net force, up to 30% of students gave âpartially correctâ responses, for example that velocity can be either opposite to or in the direction of the acceleration or net force but not zero. The data also suggests that for some students their evolution of understanding may progress through this kind of partially incorrect understanding.

Rosenblatt, Rebecca; Sayre, Eleanor C.; Heckler, Andrew F.

2010-01-19

218

Network velocity gradients in the photosphere. I. Modeling

NASA Astrophysics Data System (ADS)

We present an extension of the Unno-Rachkovsky solution that provides the theoretical profiles coming out of a Milne-Eddington atmosphere imbedded in a magnetic field, and that then takes a vertical velocity gradient into account. Thus, the theoretical profiles may display asymmetries as do the observed profiles, which facilitates the inversion based on the Unno-Rachkovsky theory, and leads to the additional determination of the vertical velocity gradient. We present UNNOFIT inversion on synthetic data and spectropolarimetric observations performed on an active region of the Sun with the French-Italian telescope THEMIS operated by CNRS and CNR on the island of Tenerife.

Molodij, G.; Bommier, V.; Rayrole, J.

2011-07-01

219

Independent active microplate tectonics of northeast Asia from GPS velocities and block modeling

Independent Okhotsk and Amurian microplate motions are tested using velocities from 123 GPS sites (80 from within the proposed OKH and AMU plate boundaries) used to constrain the plate kinematics of northeast Asia. A block modeling approach is used to incorporate both rigid block rotation and near-boundary elastic strain accumulation effects in a formal inversion of the GPS velocities. Models

E. V. Apel; R. Bürgmann; G. Steblov; N. Vasilenko; R. King; A. Prytkov

2006-01-01

220

Analytical representation of the fault slip velocity from spontaneous dynamic earthquake models

NASA Astrophysics Data System (ADS)

We have analyzed the most relevant features of three different analytical representations of the time evolution of the cosesimic slip velocity derived from theoretical basis; the so-called modified Yoffe function (MY), which pertains to a singular crack solution, the solution for a nonspontaneous crack obeying a position-weakening governing equation (PR) and the solution for a 1-D fault model subject to a linear slip-weakening friction law (B). By considering the same input parameters, we quantitatively compare these slip velocity functions (SVF) and we found that the time evolutions of the velocity and the correspondent slip predicted by the MY and B functions are very similar, while the PR predicts a very sharp peak. Correspondingly, the PR SVF is richer in high frequency and the fall off of its spectrum at high frequencies goes roughly as ?-1.5, while those of MY and B more closely follow ?-2. Then we select two spontaneous, 3-D, dynamic, subshear models, representing a crack-like or a pulse-like rupture and we account for both homogeneous and heterogeneous configurations. We then compare the three SVF in order to see how they are able to reproduce the 3-D solutions; we also show how the input parameters of the SVF can be constrained from the results of the dynamic models. In the homogeneous cases our results indicate that the MY and the PR SVF reproduce adequately well the main features of a dynamic solution in the case of a crack-like rupture. The PR function overestimates vpeak and the MY SVF predicts a too rapid deceleration. In the case of a pulse-like rupture both the MY and the B SVF tend to underestimate vpeak , but all of them capture very well the final cumulated fault slip. Moreover, the B function fits better that the MY the overall behavior of the fault slip. The considered SVF are able to reproduce the spectral fall off of a 3-D solution at intermediate frequencies (for ? < 20 Hz), the MY and the PR for a crack-like rupture and the MY and the B SVF for a pulse-like rupture. In particular, for ? < 10 Hz the spectral content of the B function is practically indistinguishable from that of the spontaneous pulse-like solution. In the heterogeneous configurations the analytical functions cannot reproduce all the spectral details of the numerical solutions, but we see how it is possible to fit the overall behavior of a single pulse in fault the slip velocity time history. The thorough analysis performed in this work can contribute to the discussion about the debated choice of the source time function to be used in the kinematic models, which in turn is extremely important in the contest of hazard assessment and ground motions generation, although stress heterogeneities, geometrical irregularities, attenuation and free surface effects can definitively smear the details of the analytical functions.

Bizzarri, Andrea

2012-06-01

221

1D Physical Non-Quasi Static BJT Circuit Model Based on the Equivalent Transmission Line Analysis

We describe a novel physically based non-quasi-static (NQS) bipolar junction transistor (BJT) model derived from theoretical analysis of the equivalent transmission line representing the one-dimensional minority carrier transport trough silicon quasi-neutral regions (QNRs). The NQS BJT model holds for arbitrarily doped BJTs operating at all injection levels. It also incorporates most important high-injection effects (Webster effect, Kirk effect, Early effect)

Nebojsa D. Jankovic; Tatjana V. Pesic; Jugoslav P. Karamarkovic

2004-01-01

222

Strong solutions for a 1D fluid-particle interaction non-newtonian model: The bubbling regime

NASA Astrophysics Data System (ADS)

This paper is concerned with the one dimensional fluid-particle interaction model in the so-called bubbling regime which describes the evolution of particles dispersed in a viscous compressible non-Newtonian fluid. We obtained the existence of unique local strong solution to this model. The main difficulty is due to the strong nonlinearity of the system and the initial fluid density admitting vacuum.

Song, Yukun; Yuan, Hongjun; Chen, Yang; Guo, Zhidong

2013-09-01

223

Recently, phase separation has been found in the ferromagnetic Kondo model(S. Yunoki, J. Hu, A. L. Malvezzi, A. Moreo, N. Furukawa, and E. Dagotto, cond-mat\\/9706014, to appear in Phys. Rev. Lett.). This result may be relevant for the understanding of the phase diagram of manganese oxide compounds. The effect of an extended Coulomb interaction on the phase diagram of the

A. L. Malvezzi; S. Yunoki; E. Dagotto

1998-01-01

224

Estimation of maize canopy properties from remote sensing by inversion of 1-D and 4-D models

The inversion of canopy reflectance models is widely used for the retrieval of vegetation properties from remote sensing.\\u000a However the accuracy of the estimates depends on a range of factors, most notably the realism with which the canopy is represented\\u000a by the models and the possibility of introducing a priori knowledge on canopy characteristics to constrain the inversion procedure.\\u000a The

R. Casa; F. Baret; S. Buis; R. Lopez-Lozano; S. Pascucci; A. Palombo; H. G. Jones

2010-01-01

225

The authors have implemented a series of state of the art radiation transport submodels in previously developed one dimensional and two dimensional chemical transport models of the troposphere and stratosphere. These submodels provide the capability of calculating accurate solar and infrared heating rates. They are a firm basis for further radiation submodel development as well as for studying interactions between radiation and model dynamics under varying conditions of clear sky, clouds, and aerosols. 37 refs., 3 figs.

Grant, K.E.; Taylor, K.E.; Ellis, J.S.; Wuebbles, D.J.

1987-07-01

226

A transient one-dimensional finite-difference model was developed to determine the hydrogen concentration variation with position in a closed containment compartment due to radiolysis following a LOCA. The model includes mixing due to molecular and eddy diffusion and natural convection. For representative compartments, the maximum hydrogen concentration difference between the bottom and top of the compartment never exceeds 0.25 volume percent when all three mixing mechanisms are considered for a range of parameters.

Willcutt, G.J.E. Jr.; Gido, R.G.; Koestel, A.

1980-01-01

227

Analysis of peripheral artery velocity tracing in a porcine model

Background The aim of the study was to trace the peripheral artery velocity with ultrasound in pigs and provide inference on diagnosis of the type, location and severity of vascular diseases. Materials and methods Limb tightening, adrenaline administration and arterial wall pinching were performed independently in six pigs, and then the evolution of the external iliac artery or femoral artery velocity tracing were monitored. Results With the increase of the extents of hindlimb tightening, peak systolic velocity (PSV) of ipsilateral external iliac artery turned from 36.33±1.77 cm/s to 59.72±2.67 cm/s, minimum post-principal wave velocity (MPV from 13.68±1.11 cm/s to ?7.48±0.82 cm/s, peak diastolic velocity (PDV) from 19.31±0.86 cm/s to 8.98±0.45 cm/s, and, end diastolic velocity (EDV) from 13.2±0.45 cm/s to 0. With the increase of the dose of the epinephrine injection, PSV increased from 36.33±1.77 cm/s to 43.97±2.15 cm/s but then decreased to 35.43±3.01 cm/s, and MPV negatively increased to ?23.53±0.82 cm/s after decreasing from 13.68±1.11 cm/s to 0. PDV and EDV gradually decreased to zero. With the increase of the stenosis severity in the abdominal aortic wall pinching, PSV was reduced and had a linearly negative correlation with the stenosis severity (R=0.983, R2=0.967). MPV gradually increased, and its direction reversed when the stenosis severity increased, then diminished when the blood flow was occluded by more than 2/3. Conclusions The formation of peripheral artery velocity is the result of concurrent effects of cardiac ejection, vascular resistance, effective circulating blood volume and elastic recoil. Vascular resistance exerts pronounced effects on the diastolic waveform, and the occurrence of backward wave indicates that the downstream circulation resistance significantly increases.

Meng, Qingxin; Ding, Weiwei; Yang, Bin; Fu, Ninghua; Lu, Guangming

2011-01-01

228

NASA Astrophysics Data System (ADS)

Combined state-parameter estimation in ocean biogeochemical models with ensemble-based Kalman filters is a challenging task due to the non-linearity of the models, the constraints of positiveness that apply to the variables and parameters, and the non-Gaussian distribution of the variables in which they result. Furthermore, these models are sensitive to numerous parameters that are poorly known. Previous works [1] demonstrated that the Gaussian anamorphosis extensions of ensemble-based Kalman filters were relevant tools to perform combined state-parameter estimation in such non-Gaussian framework. In this study, we focus on the estimation of the grazing preferences parameters of zooplankton species. These parameters are introduced to model the diet of zooplankton species among phytoplankton species and detritus. They are positive values and their sum is equal to one. Because the sum-to-one constraint cannot be handled by ensemble-based Kalman filters, a reformulation of the parameterization is proposed. We investigate two types of changes of variables for the estimation of sum-to-one constrained parameters. The first one is based on Gelman [2] and leads to the estimation of normal distributed parameters. The second one is based on the representation of the unit sphere in spherical coordinates and leads to the estimation of parameters with bounded distributions (triangular or uniform). These formulations are illustrated and discussed in the framework of twin experiments realized in the 1D coupled model GOTM-NORWECOM with Gaussian anamorphosis extensions of the deterministic ensemble Kalman filter (DEnKF). [1] Simon E., Bertino L. : Gaussian anamorphosis extension of the DEnKF for combined state and parameter estimation : application to a 1D ocean ecosystem model. Journal of Marine Systems, 2011. doi :10.1016/j.jmarsys.2011.07.007 [2] Gelman A. : Method of Moments Using Monte Carlo Simulation. Journal of Computational and Graphical Statistics, 4, 1, 36-54, 1995.

Simon, E.; Bertino, L.; Samuelsen, A.

2011-12-01

229

Mouse models of Alzheimer's disease (AD) are often tested for learning and memory deficits using visuo-spatial tasks such as the Morris water maze. Performance on these tasks is dependent on vision and the APPswe/PS1dE9 mouse model has amyloid beta plaques in their retinas which might influence their performance in these tasks. In a visual learning task, old (20-26 months) transgenic mice and their wildtype littermates of both sexes had poorer visual ability than young (5-8 months) mice and old transgenic mice had poorer visual acuity than old wildtype mice. Old transgenic mice also had deficits in visuo-spatial learning and memory on the Morris water maze. The transgenic mice had no deficits in the conditioned odour preference or conditioned taste aversion memory tests at any age. These results indicate that the old APPswe/PS1dE9 mice and their wildtype littermates both have a deficit in their visual ability and that visually dependent measures alone should not be used to assess learning and memory in this strain. PMID:22409975

Stover, Kurt R; Brown, Richard E

2012-03-03

230

Solar velocity references from 3D HD photospheric models

NASA Astrophysics Data System (ADS)

Context. The measurement of Doppler velocities in spectroscopic solar observations requires a reference for the local frame of rest. The rotational and radial velocities of the Earth and the rotation of the Sun introduce velocity offsets in the observations. Normally, good references for velocities are missing (e.g. telluric lines), especially in filter-based spectropolarimetric observations. Aims: We determine an absolute reference for line-of-sight velocities measured from solar observations for any heliocentric angle, calibrating the convective line shift of spatially-averaged profiles on quiet sun from a 3D hydrodynamical simulation. This method works whenever there is quiet sun in the field-of-view, and it has the advantage of being relatively insensitive to uncertainties in the atomic data. Methods: We carry out radiative transfer computations in LTE for selected C i and Fe i lines, whereas the Ca ii infrared lines are synthesized in non-LTE. Radiative transfer calculations are done with a modified version of Multi, using the snapshots of a non-magnetic 3D hydrodynamical simulation of the photosphere. Results: The resulting synthetic profiles show the expected C-shaped bisector at disk center. The degree of asymmetry and the line shifts, however, show a clear dependence on the heliocentric angle and the properties of the lines. The profiles at ? = 1 are compared with observed profiles to prove their reliability, and they are tested against errors induced by the LTE calculations, inaccuracies in the atomic data and the 3D simulation. Conclusions: Theoretical quiet-sun profiles of lines commonly used by solar observers are provided to the community. Those can be used as absolute references for line-of-sight velocities. The limb effect is produced by the projection of the 3D atmosphere along the line of sight. Non-LTE effects on Fe i lines are found to have a small impact on the convective shifts of the lines, reinforcing the usability of the LTE approximation in this case. We estimate the precision of the disk-center line shifts to be approximately 50 m s-1, but the off-center profiles remain to be tested against observations. The spectral profiles are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/528/A113

de la Cruz Rodríguez, J.; Kiselman, D.; Carlsson, M.

2011-04-01

231

New phases and structural phase transitions in the 1-D Falicov-Kimball model at T=0

The Falicov-Kimball model of spinless itinerant fermions and localized classical ions, on a one-dimensional lattice and at zero temperature, has been studied by means of restricted phase diagrams in the grand-canonical ensemble. Compared with earlier investigations a more efficient numerical procedure has been applied and consequently more precise phase diagrams have been obtained. For small and large values of the

Z. Gajek; J. Jezejewski; R. Lema?ski

1996-01-01

232

The magnetic susceptibility and the low-temperature specific heat of the\\u000a1-dimensional Hubbard model under the integrable open-boundary conditions are\\u000adiscussed through the Bethe ansatz with the string hypothesis. The\\u000acontributions of the boundary fields to both the susceptibility and the\\u000aspecific heat are obtained, and their exact expressions are analytically\\u000aderived.

Ruihong Yue; Tetsuo Deguchi

1997-01-01

233

NUVEL-1 is a new global model of current relative plate velocities which differ significantly from those of prior models. Here the authors incorporate NUVEL-1 into HS2-NUVEL1, a new global model of plate velocities relative to the hotspots. HS2-NUVEL1 was determined from the hotspot data and errors used by Minster and Jordan (1978) to determine AM1-2, which is their model of

Alice E. Gripp; Richard G. Gordon

1990-01-01

234

Pulmonary blood velocity patterns in lamb models of pulmonary vascular impairment

Summary To provide a comprehensive picture of the interaction between abnormal pulmonary hemodynamics and pulmonary blood velocity patterns in the young, we have developed infant animal models of pulmonary hypertension and\\/or elevated pulmonary blood flow. This report focuses on relationships between selected velocity waveform shape-dependent variables — i.e., the time between the onset of systole and peak velocity (rise time),

Carol L. Lucas; G. William Henry; Belinda Ha; Jose I. Ferreiro; Hiroshi Katayama; Elman G. Frantz; Benson R. Wilcox

1994-01-01

235

NASA Astrophysics Data System (ADS)

Since the discovery of anthropogenic ozone depletion more than 30 year ago, the scientific community has shown an increasing interest in UV-B radiation. Nowadays, ground-based high quality measurements of spectrally resolved UV-radiation are available. On the other hand, 1-D- and 3-D models have been developed, that describe the radiative transfer through the atmosphere physically very accurately. Another approach for determining the UV-irradiance at the surface of the earth is the use of satellite-based reflectance measurements as input for retrieval algorithms. At the moment, the research focuses on the impact of clouds on UV-radiation, but the impact of mountains on UV-radiation, especially in combination with high surface albedo due to snowcover, is also very strong and detailed comparisons between measurements and modelling are lacking. Therefore, three measurement campaigns had been conducted in alpine areas of Austria (Innsbruck and Hoher Sonnblick). The goal was to investigate the impact of alpine terrain in combination with snowcover on spectral UV-irradiance and actinic flux. This contribution uses the ground-based UV-irradiance measurements to evaluate three different UV-irradiance calculation methods. Results from three different calculation methods (satellite retrieval, 1-D- and 3-D radiative transfer model) for UV radiation in terms of UV-Index, erythemally weighted daily doses and spectrally resolved UV-Irradiance at 305, 310, 324 and 380nm are presented and compared with ground-based high quality measurements. The real case study is performed in very inhomogenous terrain under clear sky conditions. The values of the different methods are not only compared for the measurements sites, but additionally the impact of altitude is investigated. So far it seems, that 1-D simulations show the best agreement (±10%) with the measurements whereas the 3-D model simulations and satellite retrieved values differ much more. Satellite retrieved values significantly underestimate radiation at most stations. All three approaches show an increase of UV radiation with altitude. There are big uncertainties, since high surface albedo and obstraction of the horizon has a big impact and is difficult to take into account. The 3-D-model enables a more detailed study of the altitude effect. The separation of sun facing and sun averted slopes shows increasing UV radiation for sun facing and decreasing UV radiation for sun averted slopes with altitude.

Wagner, J. E.; Arola, A.; Blumthaler, M.; Fitzka, M.; Kift, R.; Kreuter, A.; Rieder, H. E.; Simic, S.; Webb, A.; Weihs, P.

2009-04-01

236

Correlation length of the 1D Hubbard model at half-filling: Equal-time one-particle Green's function

NASA Astrophysics Data System (ADS)

The asymptotics of the equal-time one-particle Green's function of the half-filled one-dimensional Hubbard model is studied at finite temperature. We calculate its correlation length by evaluating the largest and the second largest eigenvalues of the Quantum Transfer Matrix (QTM). In order to allow for the genuinely fermionic nature of the one-particle Green's function, we employ the fermionic formulation of the QTM based on the fermionic R-operator of the Hubbard model. The purely imaginary value of the second largest eigenvalue reflects the kF( = ?/2) oscillations of the one-particle Green's function at half-filling. By solving numerically the Bethe ansatz equations with Trotter numbers up to N = 10240, we obtain accurate data for the correlation length at finite temperatures down into the very low-temperature region. The correlation length remains finite even at T = 0 due to the existence of the charge gap. Our numerical data confirm Stafford and Millis' conjecture regarding an analytic expression for the correlation length at T = 0.

Umeno, Y.; Shiroishi, M.; Klümper, A.

2003-05-01

237

A global 3D P-velocity model of the Earth's crust and mantle for improved event location.

To test the hypothesis that high quality 3D Earth models will produce seismic event locations which are more accurate and more precise, we are developing a global 3D P wave velocity model of the Earth's crust and mantle using seismic tomography. In this paper, we present the most recent version of our model, SALSA3D (SAndia LoS Alamos) version 1.4, and demonstrate its ability to reduce mislocations for a large set of realizations derived from a carefully chosen set of globally-distributed ground truth events. Our model is derived from the latest version of the Ground Truth (GT) catalog of P and Pn travel time picks assembled by Los Alamos National Laboratory. To prevent over-weighting due to ray path redundancy and to reduce the computational burden, we cluster rays to produce representative rays. Reduction in the total number of ray paths is > 55%. The model is represented using the triangular tessellation system described by Ballard et al. (2009), which incorporates variable resolution in both the geographic and radial dimensions. For our starting model, we use a simplified two layer crustal model derived from the Crust 2.0 model over a uniform AK135 mantle. Sufficient damping is used to reduce velocity adjustments so that ray path changes between iterations are small. We obtain proper model smoothness by using progressive grid refinement, refining the grid only around areas with significant velocity changes from the starting model. At each grid refinement level except the last one we limit the number of iterations to prevent convergence thereby preserving aspects of broad features resolved at coarser resolutions. Our approach produces a smooth, multi-resolution model with node density appropriate to both ray coverage and the velocity gradients required by the data. This scheme is computationally expensive, so we use a distributed computing framework based on the Java Parallel Processing Framework, providing us with {approx}400 processors. Resolution of our model is assessed using a variation of the standard checkerboard method, as well as by directly estimating the diagonal of the model resolution matrix based on the technique developed by Bekas, et al. We compare the travel-time prediction and location capabilities of this model over standard 1D models. We perform location tests on a global, geographically-distributed event set with ground truth levels of 5 km or better. These events generally possess hundreds of Pn and P phases from which we can generate different realizations of station distributions, yielding a range of azimuthal coverage and proportions of teleseismic to regional arrivals, with which we test the robustness and quality of relocation. The SALSA3D model reduces mislocation over standard 1D ak135, especially with increasing azimuthal gap. The 3D model appears to perform better for locations based solely or dominantly on regional arrivals, which is not unexpected given that ak135 represents a global average and cannot therefore capture local and regional variations.

Ballard, Sanford; Encarnacao, Andre Villanova; Begnaud, Michael A. (Los Alamos National Laboratories); Rowe, Charlotte A. (Los Alamos National Laboratories); Lewis, Jennifer E.; Young, Christopher John; Chang, Marcus C.; Hipp, James Richard

2010-04-01

238

We analyze dilepton emission from hot and dense matter using a hybrid approach based on the ultrarelativistic quantum molecular dynamics (UrQMD) transport model with an intermediate hydrodynamic stage for the description of heavy-ion collisions at relativistic energies. During the hydrodynamic stage, the production of lepton pairs is described by radiation rates for a strongly interacting medium in thermal equilibrium. In the low-mass region, hadronic thermal emission is evaluated by assuming vector meson dominance including in-medium modifications of the {rho} meson spectral function through scattering from nucleons and pions in the heat bath. In the intermediate-mass region, the hadronic rate is essentially determined by multipion annihilation processes. Emission from quark-antiquark annihilation in the quark gluon plasma (QGP) is taken into account as well. When the system is sufficiently dilute, the hydrodynamic description breaks down and a transition to a final cascade stage is performed. In this stage dimuon emission is evaluated as commonly done in transport models. By focusing on the enhancement with respect to the contribution from long-lived hadron decays after freezeout observed at the SPS in the low-mass region of the dilepton spectra, the relative importance of the different thermal contributions and of the two dynamical stages is investigated. We find that three separated regions can be identified in the invariant mass spectra. Whereas the very low and the intermediate-mass regions mostly receive contribution from the thermal dilepton emission, the region around the vector meson peak is dominated by the cascade emission. Above the {rho}-peak region the spectrum is driven by QGP radiation. Analysis of the dimuon transverse mass spectra reveals that the thermal hadronic emission shows an evident mass ordering not present in the emission from the QGP. A comparison of our calculation to recent acceptance-corrected NA60 data on invariant as well as transverse mass spectra is performed.

Santini, E.; Steinheimer, J.; Bleicher, M. [Institut fuer Theoretische Physik, Goethe-Universitaet, Max-von-Laue-Str. 1, D-60438 Frankfurt am Main (Germany); Frankfurt Institute for Advanced Studies (FIAS), Ruth-Moufang-Str. 1, D-60438 Frankfurt am Main (Germany); Schramm, S. [Frankfurt Institute for Advanced Studies (FIAS), Ruth-Moufang-Str. 1, D-60438 Frankfurt am Main (Germany)

2011-07-15

239

NASA Astrophysics Data System (ADS)

To investigate the impact of ocean stratifications on the ice cover, a one-dimensional numerical model (Björk, 1989) is used to compute oceanic heat flux and ice thickness development, during the ice growth season. The Arctic Ocean is divided into six regions according to their stratification of the upper layer. Observed salinity and temperature profiles, from several stations within each region, are used as initial conditions in the model. Observed data come from the NODC data base. Resent observations, from ice tethered profilers (IT?s) deployed during the IPY period, is also used to increase the spatial coverage. The computations show that the central regions have a largest ice growth, more than 0.7 m, over one growth season, using an initial ice thickness of 2 m. The large ice growth is due to the present cold halocline layer preventing upward mixing of heat from below. The weak stratification in the Nansen Basin enables deeper mixing into the warm Atlantic layer, which reduces the ice growth to a minimum of 0.25 m at some locations. In the Canada Basin the inflow of warm Pacific summer water generates a temperature maximum at 50 m. This heat reservoir is large enough to reduce the ice growth to about 0.55 m, in spite of the strong salinity stratification in the region. The regions with the largest ice growth have correspondingly the lowest annual mean oceanic heat fluxes, around 0.5 W m-2. However some locations in the Nansen and Canada Basins have heat fluxes larger than 1 W m-2. In our investigation we found a net melting over a full year only for one station, located close to the Bering Strait.

Linders, J.; Björk, G.

2009-04-01

240

The (1)H and (13)C NMR spectra of 10-deoxymethynolide (1), 8.9-dihydro-10-deoxymethynolide (2) and its glycosylated derivatives (3-9) were analyzed using gradient-selected NMR techniques, including 1D TOCSY, gCOSY, 1D NOESY (DPFGSENOE), NOESY, gHMBC, gHSQC and gHSQC-TOCSY. The NMR spectral parameters (chemical shifts and coupling constants) of 1-9 were determined by iterative analysis. For the first time, complete and unambiguous assignment of the (1)H NMR spectrum of 10-deoxymethynolide (1) has been achieved in CDCl(3), CD(3)OD and C(6)D(6) solvents. The (1)H NMR spectrum of 8,9-dihydro-10-deoxymethynolide (2) was recorded in CDCl(3), (CD(3))(2)CO and CD(3)OD solutions to determine the conformation. NMR-based conformational analysis of 1 and 2 in conjugation with molecular modeling concluded that the 12-membered ring of the macrolactones may predominantly exist in a single stable conformation in all solvents examined. In all cases, a change in solvent caused only small changes in chemical shifts and coupling constants, suggesting that all glycosylated methymycin analogs exist with similar conformations of the aglycone ring in solution. PMID:23364799

Akhmedov, Novruz G; Gannett, Peter M; Wu, Bulan; Cummings, Matthew M; Train, Brian C

2013-01-31

241

Peak ground velocity ShakeMaps derived from geodetic slip models

NASA Astrophysics Data System (ADS)

We develop a methodology to derive fast and reliable peak ground velocity (PGV) ShakeMaps from kinematic finite-source models of earthquake rupture inferred from geodetic static displacements. The temporal variations in slip on the fault are based on the simple assumption that larger slip takes longer time to accumulate. Assuming constant rupture and slip velocities, slip is distributed in time to produce a variable rise-time model. Sensitivity tests on finite-source models of the 1994 Mw 6.7 Northridge, California earthquake show that distribution of peak ground velocities derived using 3.0 km s-1 rupture velocity and 76.8 cm s-1 slip velocity matches, to a large extent, observed PGV, suggesting that rapid assessment of strong ground motions derived from geodetic data can aid emergency response, particularly in areas with sparse seismic station coverage.

Rhie, Junkee; Dreger, Douglas S.; Murray, Mark; Houlié, Nicolas

2009-11-01

242

Noise Induced Congested Traffic Flow in Coupled Map Optimal Velocity Model

NASA Astrophysics Data System (ADS)

The optimal velocity traffic flow model is one of the car-followingmodels which describe the behavior of cars by differential equations.In that model, each car controls its speed toward an optimal (safety)velocity, which depends only on the headway. We constructed a newcar-following type simulation model for traffic flow in a coupled mapform based on the optimal velocity model. We can easily simulate openroad systems with the model. The emergence of weakly congested flowinduced by noise is investigated. We observe the enhancement of thecar density induced by noise. The strong traffic jam hardly occurs inopen road systems. We discuss the problems of unrealisticacceleration in the optimal velocity model and the possibility ofspontaneous formation of strong traffic jams.

Tadaki, Shin-ichi; Kikuchi, Macoto; Sugiyama, Y?ki; Yukawa, Satoshi

1999-09-01

243

Many-flavor phase diagram of the (2 + 1)d Gross–Neveu model at finite temperature

NASA Astrophysics Data System (ADS)

We study the phase diagram of the Gross–Neveu model in d = 2 + 1 space-time dimensions in the plane spanned by temperature and the number of massless fermion flavors. We use a functional renormalization group approach based on a nonperturbative derivative expansion that accounts for fermionic as well as composite bosonic fluctuations. We map out the phase boundary separating the ordered massive low-temperature phase from the disordered high-temperature phase. The phases are separated by a second-order phase transition in the 2d Ising universality class. We determine the size of the Ginzburg region and show that it scales to zero for large Nf following a powerlaw, in agreement with large-Nf and lattice studies. We also study the regimes of local order above as well as the classical regime below the critical temperature. Our results could be of interest for the finite-temperature behavior of condensed-matter realizations of Dirac fermions, as e.g. electrons on the graphene honeycomb with a short-range interaction.

Scherer, Daniel D.; Braun, Jens; Gies, Holger

2013-07-01

244

NASA Astrophysics Data System (ADS)

Nitrous acid, HONO, is an important precursor for OH radicals in the polluted atmosphere. HONO accumulates in the nocturnal boundary layer (NBL) and its photolysis at sunrise is often the dominant OH source at the ground. Although it is well known that HONO is formed by the heterogeneous conversion of NO2, the surfaces involved in this process have not been clearly identified. The concentrations of HONO also depend strongly on the stability of the NBL. Many of the uncertainties about HONO formation in the atmosphere originate in the poorly understood role of the various urban surfaces and the influence of vertical mixing, which can lead to strong vertical concentration gradients of both HONO and NO2. In recent years we have performed several field experiments to study the NO2 - HONO system in the polluted boundary layer (e.g. TEXAQS, 2000, NEAQS/NAOPEX, 2002). In all studies we measured vertical concentration profiles of NO2, HONO, and various other trace gases in the boundary layer by Differential Optical Absorption Spectroscopy continuously throughout the night and the following morning. Here we present a comprehensive analysis of the vertical distribution of NO2 and HONO in these urban environments. The observations will be compared with results from a one-dimensional chemical transport model in order to investigate the influence of the ground, building surfaces, and aerosol on the formation of HONO. The altitude dependence of the early morning OH formation will also be discussed.

Stutz, J.; Geyer, A.; Wang, S.

2003-12-01

245

Relations Among Fault Behavior, Subsurface Geology, and Three-Dimensional Velocity Models

The development of three-dimensional P-wave velocity models for the regions surrounding five large earthquakes in California has lead to the recognition of relations among fault behavior and the material properties of the rocks that contact the fault at seismogenic depths; regions of high moment release appear to correlate with high seismic velocities whereas rupture initiation or termination may be associated

Andrew J. Michael; Donna Eberhart-Phillips

1991-01-01

246

Upper mantle SH and P-velocity structures and compositional models beneath southern Africa

We constrain SH and P wave velocity structures in the upper mantle beneath southern Africa, using triplicated phases recorded in the epicentral distance range of 11°–28° for one shallow event. We then explore thermal and compositional models appropriate for explaining the inferred seismic structures in the region. Both SH and P wave data suggest presence of a low velocity zone

Yi Wang; Lianxing Wen; Donald Weidner

2008-01-01

247

Wind tunnel studies of a ship model using vortex generators to improve wake velocities

Severe vibration during trials of a 13,000 ton displacement cargo ship was attributed to the propeller working in a strongly non-uniform velocity field. This report gives the results of a series of wind tunnel experiments performed on a reflex model fitted with vortex generators which substantially improved the wake velocity distribution. It was recommended that these generators be geometrically scaled

N. Matheson

1974-01-01

248

NASA Astrophysics Data System (ADS)

Determination of earthquake hypocenter in Indonesia conducted by the Meteorological, Climatological, and Geophysical Agency (MCGA) has still used a 1-D seismic velocity model. In this research, we have applied a Fast Grid Search (FGM) method and a 3-D velocity model resulting from tomographic imaging to relocate earthquakes in the Sumatran region. The data were taken from the MCGA data catalog from 2009 to 2011 comprising of subduction zone and on land fault earthquakes with magnitude greater than 4 Mw. Our preliminary results show some significant changes in the depths of the relocated earthquakes which are in general deeper than the depths of hypocenters from the MCGA data catalog. The residual times resulting from the relocation process are smaller than those prior to the relocation. Encouraged by these results, we will continue to conduct hypocenter relocation for all events from the MCGA data catalog periodically in order to produce a new data catalog with good quality. We hope that the new data catalog will be useful for further studies.

Nugroho, Hendro; Widiyantoro, Sri; Nugraha, Andri Dian

2013-09-01

249

Rare events and their impact on velocity diffusion in a stochastic Fermi-Ulam model.

A simplified version of the stochastic Fermi-Ulam model is investigated in order to elucidate the effect of a class of rare low-velocity events on the velocity diffusion process and consequently Fermi acceleration. The relative fraction of these events, for sufficiently large times, decreases monotonically with increasing variance of the magnitude of the particle velocity. However, a treatment of the diffusion problem which totally neglects these events, gives rise to a glaring inconsistency associated with the mean value of the magnitude of the velocity in the ensemble. We propose a general scheme for treating the diffusion process in velocity space, which succeeds in capturing the effect of the low-velocity events on the diffusion, providing a consistent description of the acceleration process. The present study exemplifies the influence of low-probability events on the transport properties of time-dependent billiards. PMID:18999514

Karlis, A K; Diakonos, F K; Constantoudis, V; Schmelcher, P

2008-10-21

250

Peak velocity estimation in arterial stenosis models using colour vector Doppler.

Maximum velocity as measured from spectral Doppler is dependent on the angle theta between the bean and the direction of motion of blood. The Doppler shift is dependent on the velocity component in the direction of the ultrasound beam, hence theta cannot be determined accurately. These factors produce errors in the estimation of arterial stenosis from velocity. In this study, a 2D colour vector Doppler technique was tested using a flow model with simulated arterial stenoses. Colour-flow images obtained from different bean directions were compounded, giving estimates of velocity magnitude and angle. The maximum velocity magnitude increased with the degree of stenosis, and there was no dependence on the beam-vessel angle. This technique does not require manual entry of beam-vessel angle, nor does it have the angle dependence associated with spectral estimation of maximum velocity. This may help reduce the errors in assessment of arterial stenosis. PMID:9300993

Hoskins, P R

1997-01-01

251

Velocity-field characteristics in the multivalley model of gallium arsenide

NASA Astrophysics Data System (ADS)

The drift-velocity response to an applied electric field is investigated in a model based on an anisotropic distribution function of electrons. The randomly oriented velocity vectors in equilibrium transform to streamlined velocity vectors in a very high electric field, thereby yielding a saturation drift velocity that is comparable to the thermal velocity in the nondegenerate approximation. A clear distinction is made between the density-of-states effective mass and the conductivity effective mass for ellipsoidal valleys in gallium arsenide (GaAs). The effective mean free path, and hence the effective mobility, degrades as the electric field is increased. It is shown that as the applied electric field increases, electrons tend to follow the velocity-field profiles of those valleys with a higher Ohmic mean free path. The results are shown to be in excellent agreement with experimental data and with empirical relations obtained from the Monte Carlo simulations.

Sharma, Ankur; Arora, Vijay K.

2005-05-01

252

Particle Velocity Interpolation in Block-Centered Finite Difference Groundwater Flow Models

NASA Astrophysics Data System (ADS)

A block-centered, finite difference model of two-dimensional groundwater flow yields velocity values at the midpoints of interfaces between adjacent blocks. Method of characteristics, random walk and particle-tracking models of solute transport require velocities at arbitrary particle locations within the finite difference grid. Particle path lines and travel times are sensitive to the spatial interpolation scheme employed, particularly in heterogeneous aquifers. This paper briefly reviews linear and bilinear interpolation of velocity and introduces a new interpolation scheme. Linear interpolation of velocity is consistent with the numerical solution of the flow equation and preserves discontinuities in velocity caused by abrupt (blocky) changes in transmissivity or hydraulic conductivity. However, linear interpolation yields discontinuous and somewhat unrealistic velocities in homogeneous aquifers. Bilinear interpolation of velocity yields continuous and realistic velocities in homogeneous and smoothly heterogeneous aquifers but does not preserve discontinuities in velocity at abrupt transmissivity boundaries. The new scheme uses potentiometric head gradients and offers improved accuracy for nonuniform flow in heterogeneous aquifers with abrupt changes in transmissivity. The new scheme is equivalent to bilinear interpolation in homogeneous media and is equivalent to linear interpolation where gradients are uniform. Selecting the best interpolation scheme depends, in part, on the conceptualization of aquifer heterogeneity, that is, whether changes in transmissivity occur abruptly or smoothly.

Goode, Daniel J.

1990-05-01

253

Study on Estimation of Subsurface Velocity Structure Model using Waveform Inversion

NASA Astrophysics Data System (ADS)

The estimation of layered velocity model by waveform inversion using observed ground motion records is one of ways for modeling deep subsurface structure for the numerical simulation of long-period ground motion. The effectiveness and problem of the estimation by waveform inversion are examined. The numerical test of the waveform inversion using simulated waveform gives good estimation of velocity model assumed beforehand, without constraints of number of layers and velocity of each layers. The case study of application to strong ground motion records at OJIYA, K-NET is conducted. The estimated velocity model by waveform inversion corresponds to the estimated velocity models based on geophysical exploration, geomorphology and geology in previous research. The effect of spatial irregularity of subsurface structure is examined using FDM simulation and waveform inversion. In waveform inversion, the waveform affected by spatial irregularity of subsurface structure gives distorted estimations of the velocity structure. In the region around epicenter, the waveform is not affected by spatial irregularity of subsurface structure so much. In the estimation of velocity model, therefore, the effect of spatial irregularity is small in the region.

Hikita, Tomoki; Kasamatsu, Kentaro

254

Modeled velocity of airflow in the airways during various respiratory patterns.

Our modeling and simulation of the respiratory system with Weibel's morphometry shows that the average velocity of expiratory airflow is always greater than the average velocity of inspiratory airflow during tidal breathing when the intervals of inspiration and expiration are same. A nonlinear circuit model was developed comprised with the upper airway, the conducting airways (trachea approximately terminal bronchioles), and the lumped alveolar space. These compartments are established with known physiologic pulmonary characteristics that are represented by nonlinear resistors and capacitors. In this paper we set up the circuit model reflecting the geometric variation of airways during tidal breathing, and demonstrated computation results for the velocity of airflow along the airways based on 16 different respiratory patterns. The circuit model offers a convenient method that can be used to investigate the velocity of airflow and its interaction with mucus, as well as suggests a basic model for our future research on analyzing airway clearance techniques. PMID:17271155

Sohn, Kiwon; Holte, James; Phillips, James; Warwick, Warren

2004-01-01

255

Geologically constrained migration velocity analysis

NASA Astrophysics Data System (ADS)

In areas of complex geology, prestack depth migration is the only way to produce an accurate image of the subsurface. Prestack depth migration requires an accurate interval velocity model. With few exceptions, the subsurface velocities are not known beforehand and must be estimated. When the velocity structure is complex, with significant lateral variations, reflection tomography methods must be applied. Unfortunately, reflection tomography often converges slowly, to a model that geologically unreasonable, or not at all. One reason for this slow or non-convergence is that reflection tomography attempts to simultaneously estimate reflector position (mapping velocity) and image the data (focusing velocity). In this dissertation, I present a new approach to finding an acceptable interval velocity model for prestack migration. By performing tomography in vertical travel-time space, I avoid estimating mapping velocity, instead concentrating on focusing velocity. The large null space of reflection tomography problems forces a sparse parameterization of the model and/or regularization criteria to be added to the estimation. Standard tomography schemes tend to create isotropic features in velocity that are inconsistent with geology. These isotropic features are due in large part to using symmetric regularization operators or by choosing a poor model parameterization. By replacing these symmetric operators with operators that tend to spread information along structural dips, I can generate velocity models that are more geologically reasonable. In addition, by forming these operators in helical 1-D space and performing polynomial division, I can find the inverse of these space-varying anisotropic operators. These inverse operators can be used as a preconditioner to a standard tomography problem, significantly improving convergence speed compared to the typical, regularized inversion problem. Results from synthetic, 2-D field, and 3-D field data are shown. In each case the velocity obtained improves the focusing of the migrated image.

Clapp, Robert G.

256

Velocity weakening in a dynamical model of friction

We introduce a discrete model for friction between rough elastic surfaces which is based on the microscopic description of contacts between asperities. Rough surfaces are modeled as spring-mass arrays with superposed asperities. The linear elastodynamics of the underlying surfaces is treated in the model separately from the nonlinear contact behavior of asperities. Unlike usual spring-block models, noa priori friction law

Dmitri Pisarenko; Peter Mora

1994-01-01

257

Local Mass Conservation and Velocity Splitting In Pv-conserving Balanced Models

The most accurate potential-vorticity-conserving balanced models (PVBMs) do not conserve mass locally. A PVBM, in the sense understood here, has two defining prop- erties. First, a PVBM is a balanced model formulated in terms of a unique velocity field v , which advects the model's potential vorticity (PV) and which is obtainable by PV inversion. Second, the model's PV is

A. R. Mohebalhojeh; M. E. McIntyre

2002-01-01

258

NASA Astrophysics Data System (ADS)

The impact of the dust sea-surface forcing (DSSF) on the oceanic Primary Production (PP) is investigated here by using 1D modelling approach coupling an atmospheric radiative transfer model and a simple PP model. Simulations reveal that dust are able to induce a significant decrease of PP due to the attenuation of light by about 15-25% for dust optical depth (DOD) larger than 0.6-0.7 (at 550 nm). For DOD lower than ˜0.2-0.3, the influence of dust on PP is weak (˜5%). In addition to DOD, the important role played by dust single scattering albedo (DSSA) is also shown. Realistic applications over the Senegal coast are studied using SeaWiFS and AERONET observations. The analysis showed that PP could be reduced by about 15-20% during the spring period. This study highlights that dust/light interactions need to be parameterized in coupled ocean-atmosphere models used to estimate PP at regional scales.

Marc, Mallet; Chami, Malik; Gentili, Bernard; Sempéré, Richard; Dubuisson, P.

2009-08-01

259

Modeling of meteoroid streams: The velocity of ejection of meteoroids from comets (a review)

NASA Astrophysics Data System (ADS)

An analytical review of the models of ejection of meteoroids from cometary nuclei is presented. Different formulas for the ejection velocity of meteoroids and the corresponding parameters are discussed and compared with the use of comet Halley and the Geminids meteoroid stream as examples. The ejection velocities obtained from observations of the dust trails of comets are discussed, and the values for comets 2P/Encke, 4P/Faye, 17P/Holmes, 22P/Kopff, and 67P/Churyumov-Gerasimenko are compared to the velocities yielded by Whipple's model. The uncertainty intervals of the results are estimated.

Ryabova, G. O.

2013-05-01

260

Particle Velocity Interpolation in Block-Centered Finite Difference Groundwater Flow Models

A block-centered, finite difference model of two-dimensional groundwater flow yields velocity values at the midpoints of interfaces between adjacent blocks. Method of characteristics, random walk and particle-tracking models of solute transport require velocities at arbitrary particle locations within the finite difference grid. Particle path lines and travel times are sensitive to the spatial interpolation scheme employed, particularly in heterogeneous aquifers.

Daniel J. Goode

1990-01-01

261

Particle velocity interpolation in block-centered finite difference groundwater flow models

A block-centered, finite difference model of two-dimensional groundwater flow yields velocity values at the midpoints of interfaces between adjacent blocks. Method of characteristics, random walk and particle-tracking models of solute transport require velocities at arbitrary particle locations within the finite difference grid. Particle path lines and travel times are sensitive to the spatial interpolation scheme employed, particularly in heterogeneous aquifers.

Daniel J. Goode

1990-01-01

262

NUVEL-1 is a new global model of current relative plate velocities which differ significantly from those of prior models. Here the authors incorporate NUVEL-1 into HS2-NUVEL1, a new global model of plate velocities relative to the hotspots. HS2-NUVEL1 was determined from the hotspot data and errors used by Minster and Jordan (1978) to determine AM1-2, which is their model of plate velocities relative to the hotspots. AM1-2 is consistent with Minster and Jordan's relative plate velocity model RM2. Here the authors compare HS2-NUVEL1 with AM1-2 and examine how their differences relate to differences between NUVEL-1 and RM2. HS2-NUVEL1 plate velocities relative to the hotspots are mainly similar to those of AM1-2. Minor differences between the two models include the following: (1) in HS2-NUVEL1 the speed of the partly continental, apparently non-subducting Indian plate is greater than that of the purely oceanic, subducting Nazca plate; (2) in places the direction of motion of the African, Antarctic, Arabian, Australian, Caribbean, Cocos, Eurasian, North American, and South American plates differs between models by more than 10{degree}; (3) in places the speed of the Australian, Caribbean, Cocos, Indian, and Nazca plates differs between models by more than 8 mm/yr. Although 27 of the 30 RM2 Euler vectors differ with 95% confidence from those of NUVEL-1, only the AM1-2 Arabia-hotspot and India-hotspot Euler vectors differ with 95% confidence from those of HS2-NUVEL1. Thus, substituting NUVEL-1 for RM2 in the inversion for plate velocities relative to the hotspots changes few Euler vectors significantly, presumably because the uncertainty in the velocity of a plate relative to the hotspots is much greater than the uncertainty in its velocity relative to other plates.

Gripp, A.E.; Gordon, R.G. (Northwestern Univ., Evanston, IL (USA))

1990-07-01

263

Modeling of satellite borne TDI CCD pitching imaging image motion velocity vector

In order to obtain three-dimensional observation effect with single satellite borne time delay and integrate charge coupled device (TDI-CCD), pitching imaging is required. More accurate real-time image motion velocity vector computational model of space camera is also necessary to make the imaging perfect. Imaging motion velocity vector computation model must be set up on image plane at pitching imaging. According

Liu Zhang; Shujun Li; Guang Jin; Xiubin Yang

2009-01-01

264

Finite-Source Inversion for the 2004 Parkfield Earthquake using 3D Velocity Model Green's Functions

We determine finite fault models of the 2004 Parkfield earthquake using 3D Green's functions. Because of the dense station coverage and detailed 3D velocity structure model in this region, this earthquake provides an excellent opportunity to examine how the 3D velocity structure affects the finite fault inverse solutions. Various studies (e.g. Michaels and Eberhart-Phillips, 1991; Thurber et al., 2006) indicate

A. Kim; D. Dreger; S. Larsen

2008-01-01

265

Vascular disorders can either be cause or consequence in the pathophysiology of Alzheimer's disease (AD). To comprehensively characterize the occurrence of vascular impairment in a double transgenic mouse model for AD (APPswe/PS1dE9) during aging, we developed a new method to obtain microvascular relative cerebral blood volume (rCBV(micro)) maps from gradient echo MR imaging by histogram evaluation and we applied a voxel-wise approach to detect rCBV(micro) changes. With this methodology the development of cerebral microvascular impairments can be described in vivo with 0.16 mm isotropic resolution for the whole mouse brain. At 8 months, impaired rCBV(micro) appeared in some cortical regions and in the thalamus, which spreads over several sub-cortical areas and the hippocampus at 13 months. With a ROI-based approach, we further showed that hippocampal rCBV(micro) in 13-month-old wild-type and APP(swe)/PS1(dE9) mice correlates well with capillary density measured with immunohistochemical staining. However, no differences in capillary density were detected between genotypes. The rCBV(micro) values showed no significant correlation with amyloid-? (A?) plaque deposition, A? at blood vessel walls and biochemically measured levels of A?????, A????? oligomers and fibrillar forms. These results suggest that rCBV(micro) reduction is caused by an impaired vasoactivity of capillaries and arterioles, which is not directly correlated with the amount of A? deposition in parenchyma nor blood vessel walls. PMID:22892904

Zerbi, Valerio; Jansen, Diane; Dederen, Pieter J; Veltien, Andor; Hamans, Bob; Liu, Yang; Heerschap, Arend; Kiliaan, Amanda J

2012-08-15

266

Comparison of predicted and measured velocities in a compressor disk drum model

NASA Astrophysics Data System (ADS)

LDV measurements of tangential velocity distributions in the bleed and the trapped cavities of an 11-cavity compressor drum model were obtained at disk tangential Reynolds numbers of about 2 x 10 to the 6th and compared with predicted values. Experimental results show the tangential velocity profiles in the bleed cavity to vary from near-solid-body at low flow rates to near-free-vortex at the highest flow rates. A decrease in tangential velocity strength in the trapped flow cavities with distance from the bleed cavity was also noted. The flow in the bleed and trapped cavities were modeled using an analysis coupling the flow in a core region with the flow in the disk boundary layers. The analytical model is shown to accurately predict the tangential velocity distribution, and hence the pressure drop, for a range of flow conditions and cavity locations.

Alberga, D. G.; Stephens, G. E.; Johnson, B. V.

1987-05-01

267

Quantifying Uncertainty in Velocity Models using Bayesian Methods

NASA Astrophysics Data System (ADS)

Quanitifying uncertainty in models derived from observed data is a major issue. Public and political understanding of uncertainty is poor and for industry inadequate assessment of risk costs money. In this talk we will examine the geological structure of the subsurface, however our principal exploration tool, controlled source seismology, gives its data in time. Inversion tools exist to map these data into a depth model but a full exploration of the uncertainty of the model is rarely done because robust strategies do not exist for large non-linear complex systems. There are two principal sources of uncertainty: the first comes from the input data which is noisy and bandlimited; the second, and more sinister, is from the model parameterisation and forward algorithms themselves, which approximate to the physics to make the problem tractable. To address these issues we propose a Bayesian approach. One philosophy is to estimate the uncertainty in a possible model derived using standard inversion tools. During the inversion stage we can use our geological prejudice to derive an acceptable model. Then we use a local random walk using the Metropolis- Hastings algorithm to explore the model space immediately around a possible solution. For models with a limited number of parameters we can use the forward modeling step from the inversion code. However as the number of parameters increase and/or the cost of the forward modeling step becomes significant, we need to use fast emulators to act as proxies so a sufficient number of iterations can be performed on which to base our statistical measures of uncertainty. In this presentation we show examples of uncertainty estimation using both pre- and post-critical seismic data. In particular, we will demonstrate uncertainty introduced by the approximation of the physics by using a tomographic inversion of bandlimited data and show that uncertainty increases as the central frequency of the data decreases. This is consistent with the infinite frequency approximation in the tomographic modeling step becoming increasing compromised.

Hobbs, R.; Caiado, C.; Majda?ski, M.

2008-12-01

268

NASA Astrophysics Data System (ADS)

Deep convection plays a key role in determining global atmospheric composition of the upper troposphere by the fast uplift of HOx radical and ozone precursors to the upper troposphere. Formaldehyde (HCHO) is one important gas precursor. It is the most abundant carbonyl compound originating from both primary processes and photooxidation of volatile organic compounds. Thus, determining its source strength to the upper troposphere is important for estimating ozone production. However processes governing its fate are multiple and complex including dynamics (entrainment and detrainment), multiphase chemistry and cloud microphysics. As a result, the flux of formaldehyde to the upper troposphere is still uncertain. The goal of this study is to examine the redistribution of formaldehyde in tropical mesoscale convective systems (MSC) and to estimate its sources and sinks during convective transport to the upper troposphere. The novelty here is to combine 1D modelling (Meso NH model) and formaldehyde aircraft observations. Observations were collected over West Africa during the monsoon period (July-August 2006) of the AMMA experiment. Four aircrafts (English BAe-146, French ATR-42 and Falcon-20 and German Falcon-20) were deployed over a large domain (long.: -8°E-5°W, lat. 4°N-20°N, alt.: 0 12 km) with formaldehyde measuring instruments on board. First, this presentation will point out the construction of a comprehensive and consistent data set of formaldehyde by ensuring data comparability thanks to aircraft intercomparison flights, multiple chemical tracer approach (CO, O3 and relative humidity) and a spatial gridding of the domain. Then formaldehyde spatial variability will be examined under background and convective conditions. Finally, the relative importance of transport (entrainment) and wet scavenging will be discussed from selected AMMA flights. For that purpose, the following equation system has been resolved [HCHO]transported to UT=[HCHO]measured - [HCHO]bckgd [HCHO]transported to UT = x[HCHO]BL + y[HCHO]FT - z[HCHO]bckgd - [HCHO]wet scavenging where : BL: boundary layer; FT: free troposphere; bckgd: background and x, y and z fraction of formaldehyde concentration transported from intermediate layers (BL and FT). Two hypotheses have been tested and compared. The first hypothesis only considers entrainment from the boundary layer (0-2 km) (Bertram et al. 2007). This fraction is derived from non reactive hydrocarbons observations on board the French aircrafts (Bechara et al., 2010). The second hypothesis considers additional entrainment and detrainment from intermediate layers (2-6 km). These terms are determined by 1D-modelling for a non reactive tracer (non soluble).

Borbon, A.; Ruiz, M.; Bechara, J.; Afif, C.; Huntrieser, H.; Mills, G.; Mari, C.; Reeves, C.; Schlager, H.

2010-12-01

269

Detailed p- and s-wave velocity models along the LARSE II transect, Southern California

Structural details of the crust determined from P-wave velocity models can be improved with S-wave velocity models, and S-wave velocities are needed for model-based predictions of strong ground motion in southern California. We picked P- and S-wave travel times for refracted phases from explosive-source shots of the Los Angeles Region Seismic Experiment, Phase II (LARSE II); we developed refraction velocity models from these picks using two different inversion algorithms. For each inversion technique, we calculated ratios of P- to S-wave velocities (VP/VS) where there is coincident P- and S-wave ray coverage.We compare the two VP inverse velocity models to each other and to results from forward modeling, and we compare the VS inverse models. The VS and VP/VS models differ in structural details from the VP models. In particular, dipping, tabular zones of low VS, or high VP/VS, appear to define two fault zones in the central Transverse Ranges that could be parts of a positive flower structure to the San Andreas fault. These two zones are marginally resolved, but their presence in two independent models lends them some credibility. A plot of VS versus VP differs from recently published plots that are based on direct laboratory or down-hole sonic measurements. The difference in plots is most prominent in the range of VP = 3 to 5 km=s (or VS ~ 1:25 to 2:9 km/s), where our refraction VS is lower by a few tenths of a kilometer per second from VS based on direct measurements. Our new VS - VP curve may be useful for modeling the lower limit of VS from a VP model in calculating strong motions from scenario earthquakes.

Murphy, J. M.; Fuis, G. S.; Ryberg, T.; Lutter, W. J.; Catchings, R. D.; Goldman, M. R.

2010-01-01

270

Generalized Semiclassical Optical Model and Velocity-Dependent Potentials.

National Technical Information Service (NTIS)

A procedure is developed for the construction of a complex potential in a generalized semiclassical optical model for molecular collisions involving internal nuclear degrees of freedom. The procedure involves a local approximation on the exact quantum opt...

T. F. George I. H. Zimmerman H. D. Franchino

1974-01-01

271

A Theoretical Model for Testing New Product Sales Velocity at Small Format Retail Stores

The present study proposes a theoretical model to test sales velocity for new products introduced in small format retail stores. The model is designed to distinguish fast moving products within a relatively short period. Under the proposed model, the sales of a newly introduced product are monitored for a prespecied period T , e.g. ,o ne week, and if the

Hiroaki Sandoh; Roy Larke

2002-01-01

272

A Simple Model for Evaluating Conditioned Velocities in Premixed Turbulent Flames

A simple model is proposed to evaluate (a) the divergence of velocity vector conditioned on unburned mixture, and (b) the vector component normal to the mean flame brush in the flamelet regime of premixed turbulent combustion. The model involves a single constant and does not invoke an extra balance equation. To perform the first test of the model, six flames

V. A. Sabelnikov; A. N. Lipatnikov

2011-01-01

273

Migraine is a complex neurovascular syndrome, causing a unilateral pulsating headache with accompanying symptoms. The past four decades have contributed immensely to our present understanding of migraine pathophysiology and have led to the introduction of specific antimigraine therapies, much to the relief of migraineurs. Pathophysiological factors culminating into migraine headaches have not yet been completely deciphered and, thus, pose an additional challenge for preclinical research in the absence of any direct experimental marker. Migraine provocation experiments in humans use a head-score to evaluate migraine, as articulated by the volunteer, which cannot be applied to laboratory animals. Therefore, basic research focuses on different symptoms and putative mechanisms, one at a time or in combination, to validate the hypotheses. Studies in several species, utilizing different preclinical approaches, have significantly contributed to the two antimigraine principles in therapeutics, namely: 5-HT(1B/1D) receptor agonists (known as triptans) and CGRP receptor antagonists (known as gepants). This review will analyze the preclinical experimental models currently known for the development of these therapeutic principles, which are mainly based on the vascular and/or neurogenic theories of migraine pathogenesis. These include models based on the involvement of cranial vasodilatation and/or the trigeminovascular system in migraine. Clearly, the preclinical strategies should involve both approaches, while incorporating the newer ideas/techniques in order to get better insights into migraine pathophysiology. PMID:20655327

Gupta, Saurabh; Villalón, Carlos M

2010-07-22

274

Predicting Ground Motions In Seattle Using A New Shear Wave Velocity Model

NASA Astrophysics Data System (ADS)

Much of Seattle lies atop a deep sedimentary basin. The Seattle Basin amplifies and distorts seismic waves in ways that modulate the hazard from earthquakes. Seismic hazard assessments heavily depend upon upper crustal and near-surface S-wave velocity models. Improving the accuracy and resolution of basin S-wave models is key to improving predictions of ground shaking. Tomography, with short-period Rayleigh waves extracted using noise interferometry, can refine S-wave velocity models in urban areas with dense arrays of short period and broadband instruments. We applied this technique to develop a new S-wave velocity model encompassing the upper 3-4 km and covering Seattle and several neighboring cities. We then embed this updated model into the regional velocity model that was used in the development of the USGS seismic hazard maps for Seattle. We collected data from two local earthquakes, one crustal and one Benioff Zone event, which were recorded on many strong motion stations operated by the Pacific Northwest Seismic Network and the USGS Earthquake Hazards program. For the two local earthquakes, we compared amplitudes and waveforms predicted by our new velocity model to predictions made using the older velocity model at stiff soil sites. For the crustal event, the amplitudes predicted by simulations with our new model are closer to the data than those predicted by the previous model. At periods between 1.25-5 seconds our new model makes considerably better predictions, while at periods between 1-1.25 seconds our new model makes better predictions, but the difference is smaller. For the Benioff zone event, the two models’ predictions are both good, but also favor our model. At periods between 1.6-3.3, the previous model makes better predictions while our model makes better predictions at periods between 1-1.6 and 3.3-5 seconds. Our simulations confirm that amplitudes are determined by a complex set of variables including basin velocity structure, wave-guides, and soil type. We are working to improve predicted amplifications to improve seismic hazard assessments. Many new strong motion instruments have been installed within the last year, including Netquakes seismographs operated by the USGS, providing us with a valuable data set for improving our predictions. Shear wave velocities in the Seattle Basin

Delorey, A. A.; Vidale, J. E.

2010-12-01

275

Modeling the effect of varying swim speeds on fish passage through velocity barriers

The distance fish can swim through zones of high-velocity flow is an important factor limiting the distribution and conservation of riverine and diadromous fishes. Often, these barriers are characterized by nonuniform flow conditions, and it is likely that fish will swim at varying speeds to traverse them. Existing models used to predict passage success, however, typically include the unrealistic assumption that fish swim at a constant speed regardless of the speed of flow. This paper demonstrates how the maximum distance of ascent through velocity barriers can be estimated from the swim speed-fatigue time relationship, allowing for variation in both swim speed and water velocity.

Castro-Santos, T.

2006-01-01

276

Measurement of velocity deficit at the downstream of a 1:10 axial hydrokinetic turbine model

Wake recovery constrains the downstream spacing and density of turbines that can be deployed in turbine farms and limits the amount of energy that can be produced at a hydrokinetic energy site. This study investigates the wake recovery at the downstream of a 1:10 axial flow turbine model using a pulse-to-pulse coherent Acoustic Doppler Profiler (ADP). In addition, turbine inflow and outflow velocities were measured for calculating the thrust on the turbine. The result shows that the depth-averaged longitudinal velocity recovers to 97% of the inflow velocity at 35 turbine diameter (D) downstream of the turbine.

Gunawan, Budi [ORNL; Neary, Vincent S [ORNL; Hill, Craig [St. Anthony Falls Laboratory, 2 Third Avenue SE, Minneapolis, MN 55414; Chamorro, Leonardo [St. Anthony Falls Laboratory, 2 Third Avenue SE, Minneapolis, MN 55414

2012-01-01

277

Site-Specific Velocity and Density Model for the Waste Treatment Plant, Hanford, Washington.

This report documents the work conducted under the SBP to develop a shear wave and compressional wave velocity and density model specific to the WTP site. Section 2 provides detailed background information on the WTP site and its underlying geology as well as on the Seismic Boreholes Project activities leading up to the Vs and Vp measurements. In Section 3, methods employed and results obtained are documented for measurements of Vs and Vp velocities in basalts and interbeds. Section 4 provides details on velocity measurements in the sediments underlying the WTP. Borehole gravity measurements of density of the subsurface basalt and sediments are described in Section 5. Section 6 describes the analysis of data presented in section 3-5, and presents the overall velocity and density model for the WTP site.

Rohay, Alan C.; Brouns, Thomas M.

2007-06-27

278

On dynamic geodynamo models with imposed velocity as energy source

The first step of a project to study three-dimensional numerical dynamo models in a rapidly rotating sphere is reported. We aim at finding solutions in the magnetostrophic regime, where the Taylor's condition is obeyed. Viscous terms, including the Ekman suction at the boundary, are discarded. At this stage, our project consists of investigating the coupling of the momentum and induction

D. Jault; P. Cardin

1999-01-01

279

Models and numerical simulation of velocity distribution of pickup ions

Large manned spacecraft release and carry up a huge amounts of water in its orbital motion. Some of the neutral water molecules undergo charge exchange with the ambient ionospheric plasma and become what are called pick-up ions at Low Earth Orbit (LEO) altitudes. The purpose of this dissertation is to model those ions and predicts their effect on a space

Yinghui Zhang

1998-01-01

280

The purpose of this research was to further investigate the hydrodynamics of the United States Pharmacopeia (USP) paddle dissolution\\u000a apparatus using a previously generated computational fluid dynamics (CFD) model. The influence of paddle rotational speed\\u000a on the hydrodynamics in the dissolution vessel was simulated. The maximum velocity magnitude for axial and tangential velocities\\u000a at different locations in the vessel was

Leonard G. McCarthy; Geoff Bradley; James C. Sexton; Owen I. Corrigan; Anne Marie Healy

2004-01-01

281

SALSA3D : a global 3D p-velocity model of the Earth's crust and mantle for improved event location.

To test the hypothesis that high quality 3D Earth models will produce seismic event locations which are more accurate and more precise, we are developing a global 3D P wave velocity model of the Earth's crust and mantle using seismic tomography. In this paper, we present the most recent version of our model, SALSA3D version 1.5, and demonstrate its ability to reduce mislocations for a large set of realizations derived from a carefully chosen set of globally-distributed ground truth events. Our model is derived from the latest version of the Ground Truth (GT) catalog of P and Pn travel time picks assembled by Los Alamos National Laboratory. To prevent over-weighting due to ray path redundancy and to reduce the computational burden, we cluster rays to produce representative rays. Reduction in the total number of ray paths is {approx}50%. The model is represented using the triangular tessellation system described by Ballard et al. (2009), which incorporates variable resolution in both the geographic and radial dimensions. For our starting model, we use a simplified two layer crustal model derived from the Crust 2.0 model over a uniform AK135 mantle. Sufficient damping is used to reduce velocity adjustments so that ray path changes between iterations are small. We obtain proper model smoothness by using progressive grid refinement, refining the grid only around areas with significant velocity changes from the starting model. At each grid refinement level except the last one we limit the number of iterations to prevent convergence thereby preserving aspects of broad features resolved at coarser resolutions. Our approach produces a smooth, multi-resolution model with node density appropriate to both ray coverage and the velocity gradients required by the data. This scheme is computationally expensive, so we use a distributed computing framework based on the Java Parallel Processing Framework, providing us with {approx}400 processors. Resolution of our model is assessed using a variation of the standard checkerboard method. We compare the travel-time prediction and location capabilities of SALSA3D to standard 1D models via location tests on a global event set with GT of 5 km or better. These events generally possess hundreds of Pn and P picks from which we generate different realizations of station distributions, yielding a range of azimuthal coverage and ratios of teleseismic to regional arrivals, with which we test the robustness and quality of relocation. The SALSA3D model reduces mislocation over standard 1D ak135 regardless of Pn to P ratio, with the improvement being most pronounced at higher azimuthal gaps.

Encarnacao, Andre Villanova; Begnaud, Michael A. (Los Alamos National Laboratories); Rowe, Charlotte A. (Los Alamos National Laboratories); Young, Christopher John; Chang, Marcus C.; Ballard, Sally C.; Hipp, James Richard

2010-06-01

282

A global 3D P-velocity model of the Earth's crust and mantle for improved event location : SALSA3D.

To test the hypothesis that high quality 3D Earth models will produce seismic event locations which are more accurate and more precise, we are developing a global 3D P wave velocity model of the Earth's crust and mantle using seismic tomography. In this paper, we present the most recent version of our model, SALSA3D version 1.5, and demonstrate its ability to reduce mislocations for a large set of realizations derived from a carefully chosen set of globally-distributed ground truth events. Our model is derived from the latest version of the Ground Truth (GT) catalog of P and Pn travel time picks assembled by Los Alamos National Laboratory. To prevent over-weighting due to ray path redundancy and to reduce the computational burden, we cluster rays to produce representative rays. Reduction in the total number of ray paths is {approx}50%. The model is represented using the triangular tessellation system described by Ballard et al. (2009), which incorporates variable resolution in both the geographic and radial dimensions. For our starting model, we use a simplified two layer crustal model derived from the Crust 2.0 model over a uniform AK135 mantle. Sufficient damping is used to reduce velocity adjustments so that ray path changes between iterations are small. We obtain proper model smoothness by using progressive grid refinement, refining the grid only around areas with significant velocity changes from the starting model. At each grid refinement level except the last one we limit the number of iterations to prevent convergence thereby preserving aspects of broad features resolved at coarser resolutions. Our approach produces a smooth, multi-resolution model with node density appropriate to both ray coverage and the velocity gradients required by the data. This scheme is computationally expensive, so we use a distributed computing framework based on the Java Parallel Processing Framework, providing us with {approx}400 processors. Resolution of our model is assessed using a variation of the standard checkerboard method. We compare the travel-time prediction and location capabilities of SALSA3D to standard 1D models via location tests on a global event set with GT of 5 km or better. These events generally possess hundreds of Pn and P picks from which we generate different realizations of station distributions, yielding a range of azimuthal coverage and ratios of teleseismic to regional arrivals, with which we test the robustness and quality of relocation. The SALSA3D model reduces mislocation over standard 1D ak135 regardless of Pn to P ratio, with the improvement being most pronounced at higher azimuthal gaps.

Young, Christopher John; Steck, Lee K. (Los Alamos National Laboratory); Phillips, William Scott (Los Alamos National Laboratory); Ballard, Sanford; Chang, Marcus C.; Rowe, Charlotte A. (Los Alamos National Laboratory); Encarnacao, Andre Villanova; Begnaud, Michael A. (Los Alamos National Laboratory); Hipp, James Richard

2010-07-01

283

A distributed, dynamic, parallel computational model: the role of noise in velocity storage.

Networks of neurons perform complex calculations using distributed, parallel computation, including dynamic "real-time" calculations required for motion control. The brain must combine sensory signals to estimate the motion of body parts using imperfect information from noisy neurons. Models and experiments suggest that the brain sometimes optimally minimizes the influence of noise, although it remains unclear when and precisely how neurons perform such optimal computations. To investigate, we created a model of velocity storage based on a relatively new technique--"particle filtering"--that is both distributed and parallel. It extends existing observer and Kalman filter models of vestibular processing by simulating the observer model many times in parallel with noise added. During simulation, the variance of the particles defining the estimator state is used to compute the particle filter gain. We applied our model to estimate one-dimensional angular velocity during yaw rotation, which yielded estimates for the velocity storage time constant, afferent noise, and perceptual noise that matched experimental data. We also found that the velocity storage time constant was Bayesian optimal by comparing the estimate of our particle filter with the estimate of the Kalman filter, which is optimal. The particle filter demonstrated a reduced velocity storage time constant when afferent noise increased, which mimics what is known about aminoglycoside ablation of semicircular canal hair cells. This model helps bridge the gap between parallel distributed neural computation and systems-level behavioral responses like the vestibuloocular response and perception. PMID:22514288

Karmali, Faisal; Merfeld, Daniel M

2012-04-18

284

Variable aspect ratio method in the Xu–White model for shear-wave velocity estimation

NASA Astrophysics Data System (ADS)

Shear-wave velocity logs are useful for various seismic interpretation applications, including bright spot analyses, amplitude-versus-offset analyses and multicomponent seismic interpretations. This paper presents a method for predicting the shear-wave velocity of argillaceous sandstone from conventional log data and experimental data, based on Gassmann's equations and the Xu–White model. This variable aspect ratio method takes into account all the influences of the matrix nature, shale content, porosity size and pore geometry, and the properties of pore fluid of argillaceous sandstone, replacing the fixed aspect ratio assumption in the conventional Xu–White model. To achieve this, we first use the Xu–White model to derive the bulk and shear modulus of dry rock in a sand–clay mixture. Secondly, we use Gassmann's equations to calculate the fluid-saturated elastic properties, including compressional and shear-wave velocities. Finally, we use the variable aspect ratio method to estimate the shear-wave velocity. The numerical results indicate that the variable aspect ratio method provides an important improvement in the application of the Xu–White model for sand–clay mixtures and allows for a variable aspect ratio log to be introduced into the Xu–White model instead of the constant aspect ratio assumption. This method shows a significant improvement in predicting velocities over the conventional Xu–White model.

Bai, Jun-Yu; Yue, Cheng-Qi; Liang, Yi-Qiang; Song, Zhi-Xiang; Ling, Su; Zhang, Yang; Wu, Wei

2013-06-01

285

NASA Astrophysics Data System (ADS)

We derived a nonlocal kinetic traffic model from a generalized car-following model with multiple look-ahead through the BBGKY hierarchy. A nonlocal hydrodynamical model was obtained consistently by the method of kinetic theory. The novel feature of nonlocality in equilibrium velocity and variance as well as in relaxation time was discovered. Simulation results showed that traffic hysteresis was induced by anticipation-dependent equilibrium velocity, relaxation time and equilibrium variance, indicating a 2D-region of synchronized flow. When drivers looked farther ahead, the amplitude of stop-and-go traffic reduced, and the resulting equilibrium velocity and flow increased, thus traffic stabilized as expected. Numerical results also indicated the existence of optimum anticipation vision. Finally, the model could also capture the physical nonlinear dynamic characteristics of metastability and the stop-and-go phenomenon in traffic flow.

Qiu, Yuzhuo; Chen, Senfa

2010-12-01

286

HYDRUS-1D was used to simulate water flow and leaching of fecal coliforms and bromide (Br) through six undisturbed soil lysimeters (70 cm depth by 50 cm diameter) under field conditions. Dairy shed effluent (DSE) spiked with Br was applied to the lysimeters, which contained fine sandy loam layers. This application was followed by fortnightly spray or flood water irrigation. Soil water contents were measured at four soil depths over 171 days, and leachate was collected from the bottom. The post-DSE period simulations yielded a generally decreased saturated water content compared to the pre-DSE period, and an increased saturated hydraulic conductivity and air-entry index, suggesting that changes in soil hydraulic properties (e.g. via changes in structure) can be induced by irrigation and seasonal effects. The single-porosity flow model was successful in simulating water flow under natural climatic conditions and spray irrigation. However, for lysimeters under flood irrigation, when the effect of preferential flow paths becomes more significant, the good agreement between predicted and observed water contents could only be achieved by using a dual-porosity flow model. Results derived from a mobile-immobile transport model suggest that compared to Br, bacteria were transported through a narrower pore-network with less mass exchange between mobile and immobile water zones. Our study suggests that soils with higher topsoil clay content and soils under flood irrigation are at a high risk of bacteria leaching through preferential flow paths. Irrigation management strategies must minimize the effect of preferential flow to reduce bacterial leaching from land applications of effluent. PMID:19775719

Jiang, Shuang; Pang, Liping; Buchan, Graeme D; Sim?nek, Jirí; Noonan, Mike J; Close, Murray E

2009-09-02

287

Amyloid precursor protein transgenic mice modeling Alzheimer's disease display frequent occurrence of seizures peaking at an age when amyloid plaques start to form in the cortex and hippocampus. We tested the hypothesis that numerous reported interactions of amyloid-? with cell surface molecules result in altered excitation-inhibition balance in brain-wide neural networks, eventually leading to epileptogenesis. We examined electroencephalograms (EEGs) and auditory-evoked potentials (AEPs) in freely moving 4-month-old APPswe/PS1dE9 (APdE9) and wild-type (WT) control mice in the hippocampus, cerebral cortex, and thalamus during movement, quiet waking, non-rapid eye movement sleep, and rapid eye movement (REM) sleep. Cortical EEG power was higher in APdE9 mice than in WT mice over a broad frequency range (5-100 Hz) and during all 4 behavioral states. Thalamic EEG power was also increased but in a narrower range (10-80 Hz). Furthermore, APdE9 mice displayed augmented cortical and thalamic AEPs. While power and theta-gamma modulation were preserved in the APdE9 hippocampus, REM sleep-related phase shift of theta-gamma modulation was altered. Our data suggest that at the early stage of amyloid pathology, cortical principal cells become hyperexcitable and via extensive cortico-thalamic connection drive thalamic cells. Minor hippocampal changes are most likely secondary to abnormal entorhinal input. PMID:22581851

Gurevicius, Kestutis; Lipponen, Arto; Tanila, Heikki

2012-05-10

288

New model improves gas migration velocity estimates in shut-in wells

A new model includes the affects of mud compressibility, well bore elasticity, and fluid loss for accurate calculation of the pressure increases in a shut-in well bore following a kick. In the new mode, typical values for elasticity and fluid loss are derived from formation integrity tests for a real well. With these values, the new model calculates rates of pressure rise that are consistent with those observed in the field, even though the gas migration velocity is as large as that measured in the experiments. The model shows that conventional field practices that neglect these effects can underestimate the gas migration velocity by a factor of ten or more.

Johnson, A. (Schlumberger Cambridge Research Ltd., Cambridge (United Kingdom)); Tarvin, J. (Schlumberger-Doll Research, Ridgefield, CT (United States))

1993-11-15

289

NASA Astrophysics Data System (ADS)

Seismic explorations results suggest evidence of free gas beneath a bottom simulating reflector (BSR) because of abrupt changes in seismic velocities. Although it is possible to prospect existence of free gas by using Vp slowness - Vp/Vs crossplot (Brie.1997), an abnormal tendency of Vp and Vp/Vs relationship is also recognized in the free gas zone beneath BSR (Mikada et al .2008). In order to explain the cause of this abnormal trend, and to discuss the existence of the free gas in the formations, we propose a model in which bubbles could increase the sonic velocity. From the log data used in Mikada et al. (2008), we recognized the gas hydrate zone. In this area, BSR was found from seismic exploration, so that we guess the existence of free gas zone beneath gas hydrate zone. We also infer that methane gas bubble rise up in the methane gas saturated pore water (Waseda and Tanahashi. 1998). In addition we generate Vp slowness - Vp/Vs crossplot to identify the gas bearing zone. In this crossplot, compressional sonic velocities are largely reduced in general due to low bulk modulus of gas, while shear velocities are not because of no volumetric changes. Using this interpretation methodology, we classify gas effects in formation water where Vp/Vs ratios deviate towards lower values and 1/Vp to high values. In hydrocarbon explorations, this method has been used to identify gas bearing zones. On the other hand, we find sometimes abnormal distributions of crossplots in free gas zone below BSR in which both Vp/Vs and Vp deviate towards higher values. If formation fluid in these zones bear really free gas, this abnormal distribution indicates that there is another mechanism of velocity change for fluids include gas. To discuss this fact, we firstly verified whether this velocity zone is gas bearing zone or non gas formation, such as shaly sand zone. As a result, we assured that some parts of high velocity zone are surely gas bearing zone from plural crossplot analyses, i.e., neutron porosity - density porosity crossplot, etc. Based on these analyses, we propose a hypothesis that gas bubble in formation water may increase the phase velocity and a new formation velocity model which considers frequency dependency of sonic phase velocities of bubbly fluid. Commander and Prosperetti (1988) derived the frequency dependent compressional velocity of the water that contains gas bubbles. They used the Keller’s equation which describes the radial oscillation of bubbles in liquid. On the basis of their theory, we simulated numerically the sonic compressional velocity of pore water with bubbles. Combining the estimated velocity of pore water and that of formation matrix, we derived the sonic compressional velocity of formation with gas bubbles. As a result, we got formation velocities which depend on frequencies in the range of sonic logging frequencies. We obtained the following conclusions: 1) Gas bubbles may increase the formation velocity depending on the combination of the size of gas bubbles and frequency, 2) Methane hydrate, gas, shale can be clearly identified by combined crossplots analyses for unconsolidated sediments. 3) The model we suggest can explain this velocity increase in free gas zones.

Banno, T.; Mikada, H.; Goto, T.; Takekawa, J.

2009-12-01

290

Car-following model with relative-velocity effect and its experimental verification

In driving a vehicle, drivers respond to the changes of both the headway and the relative velocity to the vehicle in front. In this paper a new car-following model including these maneuvers is proposed. The acceleration of the model becomes infinite (has a singularity) when the distance between two vehicles is zero, and the asymmetry between the acceleration and the

Daisuke Shamoto; Akiyasu Tomoeda; Ryosuke Nishi; Katsuhiro Nishinari

2011-01-01

291

For the evolution of density fluctuation in nonlinear cosmological dynamics, adhesion approximation (AA) is proposed as a phenomenological model, which is especially useful for describing nonlinear evolution. However, the origin of the artificial viscosity in AA is not clarified. Recently, Buchert and Dominguez report if the velocity dispersion of the dust fluid is regarded as isotropic, it works on a principle similar to viscosity or effective pressure, and they consider isotropic velocity dispersion as the origin of the artificial viscosity in AA. They name their model the Euler-Jeans-Newton (EJN) model. In this paper, we focus on the velocity distribution in AA and the EJN model and examine the time evolution in both models. We find the behavior of AA differs from that of the EJN model, i.e., although the peculiar velocity in the EJN model oscillates, that in AA is monotonically decelerated due to viscosity without oscillation. Therefore it is hard to regard viscosity in AA as effective pressure in the EJN model.

Sotani, Hajime [Advanced Research Institute for Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan); Tatekawa, Takayuki [Advanced Research Institute for Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan); Department of Physics, Ochanomizu University, 2-1-1 Otsuka, Bunkyo, Tokyo 112-8610 (Japan); Department of Physics, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan)

2006-01-15

292

HIGH-RESOLUTION SEISMIC VELOCITY AND ATTENUATION MODELS OF THE CAUCASUS-CASPIAN REGION

The southwest edge of Eurasia is a tectonically and structurally complex region that includes the Caspian and Black Sea basins, the Caucasus Mountains, and the high plateaus south of the Caucasus. Crustal and upper mantle velocities show great heterogeneity in this region and regional phases display variations in both amplitudes and travel time. Furthermore, due to a lack of quality data, the region has largely been unexplored in terms of the detailed lithospheric seismic structure. A unified high-resolution 3D velocity and attenuation model of the crust and upper mantle will be developed and calibrated. This model will use new data from 23 new broadband stations in the region analyzed with a comprehensive set of techniques. Velocity models of the crust and upper mantle will be developed using a joint inversion of receiver functions and surface waves. The surface wave modeling will use both event-based methods and ambient noise tomography. Regional phase (Pg, Pn, Sn, and Lg) Q model(s) will be constructed using the new data in combination with existing data sets. The results of the analysis (both attenuation and velocity modeling) will be validated using modeling of regional phases, calibration with selected events, and comparison with previous work. Preliminary analyses of receiver functions show considerable variability across the region. All results will be integrated into the KnowledgeBase.

Mellors, R; Gok, R; Sandvol, E

2007-07-10

293

We consider Discrete Boltzmann Models (DBMs) with two constraints: First, models with an arbitrary number of velocities and speeds and second, for the solutions with two asymptotic states, they will satisfy the mass ratio relation deduced from the continuous theory with two Maxwellian states. Consequently we restrict our study to travelling waves along an x-axis, with two asymptotic states (shock

H. Cornille

1997-01-01

294

A nonlinear least squares modeling procedure has been developed to estimate simultaneously hypocenter parameters, station corrections, and velocity model parameters by using P wave (or S wave) arrivals from local earthquakes at a regional array. This procedure is applied to P wave data obtained from the 14station telemetered seismograph network in the Puget Sound region of western Washington. Forty selected

Robert S. Crosson

1976-01-01

295

Low velocity impact experiments on the explosive LX-10 with modeling of reaction violence

NASA Astrophysics Data System (ADS)

A new gas gun capability designed for the velocity range of ~20-400 m/s was used to study the mechanisms of low-velocity impact ignition and reaction violence of explosive targets in safety studies. Hemispherical charges of the HMX-based explosive LX-10 (95% HMX, 5% Viton binder) assembled in a polycarbonate target ring were impacted by a 6.35 mm diameter hardened steel rod protruding from a projectile at velocities ranging from 36 to 374 m/s. Digital high-speed (Phantom v12) cameras were utilized to capture the times of first ignition and a Photonic Doppler Velocimetry (PDV) probe placed at the rear of the target was used to measure the free surface velocity histories of an aluminum foil on the LX-10 surface to quantify the resulting reaction violence. The Ignition and Growth reactive flow model for LX-10 was used to compare the relative violence of these reactions to the intentional detonation of an equivalent LX-10 charge. It was found that comparing the model results to that of the experiment using this impactor geometry within the tested velocity range, the reaction violence increased with velocity from 45-374 m/s and only a small fraction of material appears to react during the impact.

Chidester, Steven; Garcia, Frank; Vandersall, Kevin S.; Tarver, Craig M.; Ferranti, Louis

2012-03-01

296

NASA Astrophysics Data System (ADS)

Although elastic velocities (Vp, Vs) can be used to assess the distribution and concentration of marine gas hydrates in situ and several existing models relate hydrate saturation to acoustic velocity, the accuracy of these models is uncertain because of the difficulty in determining hydrate saturations and velocities of intact hydrate-bearing sediments. In this paper, the acoustic properties of gas hydrate-bearing consolidated sediments were investigated experimentally. Hydrate saturation (Sh) and acoustic velocities were measured in one system by time domain reflectometry and ultrasonic methods, respectively, during gas hydrate formation and subsequent dissociation in a water-saturated artificial core. Acoustic velocities change little at low hydrate saturations (0% to ˜10%), whereas they increase rapidly when hydrate saturation is between 10% and 30%. We verified two commonly used models, i.e., the weighted equation (WE) and the Biot-Gassmann theory modified by Lee (BGTL). In the 0% to 40% hydrate saturation range, the WE model is consistent with the measured Vp data, while a combination of the WE and the Vp/Vs ratio in the BGTL predicts Vs corresponding to the observed data. As hydrate saturation is more than 30%, however, the BGTL is more suitable for predicting both Vp and Vs. This suggests that gas hydrate may be treated as a component within a matrix of consolidated sediments when hydrate saturation exceeds 30%. However, when Sh is less than 30%, the hydrate locates in the pore fluid or partly adheres to the sediment frame.

Hu, Gao W.; Ye, Yu G.; Zhang, Jian; Liu, Chang L.; Diao, Shao B.; Wang, Jia S.

2010-02-01

297

Shear Wave Velocity Models for Southeasthern Europe from Inversion of Surface Wave Data

NASA Astrophysics Data System (ADS)

Digital seismograms from more than 100 earthquakes located in the southeastern part of Europe, recorded by 3-component very broadband seismometers at 9 stations, were processed to obtain the dispersion properties of Rayleigh and Love surface waves. Regionalized group-velocity patterns for periods in range 8 40 seconds were determined using 2D-tomography method. Local group-velocity curves were constructed in a grid of 1x1 degree. Some phase velocity data were collected from the literature. Both phase and group dispersion data were processed by linear inversion method based on Backus-Gilbert inversion theory. S-wave velocity models were constructed for each local dispersion curve. Comparison between the models obtained by Rayleigh wave inversion and Love wave inversion was done. Models obtained show good correlation with well known geological zones in the studied region. Maps of S-wave velocities at different depths were constructed. The discrepancies between Love and Rayleigh Vs models are considered as an evidence for existence of anisotropic layers in the lithosphere.

Raykova, R.; Nikolova, S. B.

2003-04-01

298

Calculations of Burning Velocity of Turbulent Premixed Flames Using a Flame Surface Density Model

NASA Astrophysics Data System (ADS)

The objective of the present paper is to develop and validate a newly formulated Flame Surface Density (FSD) model able to predict realistic turbulent burning velocities of premixed turbulent propagating flames over a wide range of flow conditions. Non-iterative transient numerical calculations of turbulent flame propagation in one-dimensional space are carried out over a range of turbulence Reynolds number using stoichiometric methane-air mixture. It is found that the new model closely predicts experimental data of turbulent burning velocity by Abdel-Gayed et al. (1987) as well as results from KPP (Kolmogorov, Petrovski, Piskonov) analytical method. The model formulation, and subsequent results of turbulent burning velocity and combustion regimes are presented and discussed in terms of the various physical processes that control flame/flow interactions in premixed combustion.

Patel, Samir N. D. H.; Ibrahim, Salah S.

299

Effects of subfilter velocity modelling on dispersed phase in LES of heated channel flow

NASA Astrophysics Data System (ADS)

A non-isothermal turbulent flow with the dispersed phase is modelled using the Large Eddy Simulation (LES) approach for fluid, one-way coupled with the equations of point-particle evolution. The channel is heated at both walls and isoflux boundary conditions are applied for fluid. Particle velocity and thermal statistics are computed. Of particular interest are the r.m.s. profiles and the probability density function of particle temperature in the near-wall region. We compare our findings with available reference data for particle-laden, heated channel flow. Moreover, an open issue in LES is the influence of non-resolved (residual) scales of fluid velocity and temperature fields on particles. In the present contribution, we apply a stochastic model for subfilter fluid velocity at the particle positions that aims at reconstructing the effects of the smallest scales of turbulence on particle dynamics. We analyse the impact of this model on particle thermal statistics.

Pozorski, Jacek; Knorps, Maria; ?uniewski, Miros?aw

2011-12-01

300

Quasilinear model for energetic particle diffusion in radial and velocity space

NASA Astrophysics Data System (ADS)

A quasilinear model for passive energetic particle (EP) turbulent diffusion in radial and velocity space is fitted and tested against nonlinear gyrokinetic tokamak simulations with the GYRO code [J. Candy and R. E. Waltz, Phys. Rev. Lett. 91, 045001 (2003)]. Off diagonal elements of a symmetric positive definite 2×2 EP diffusion matrix account for fluxes up radial (energy) gradients driven by energy (radial) gradients of the EP velocity space distribution function. The quasilinear ratio kernel of the model is provided by a simple analytic formula for the EP radial and velocity space EP diffusivity relative to radial thermal ion energy diffusivity at each linear mode of the turbulence driven by the thermal plasma. The TGLF [G. M. Staebler, J. E. Kinsey, and R. E. Waltz, Phys. Plasmas 14, 0055909 (2007); ibid. 15, 0055908 (2008)] tokamak transport model provides the linear mode frequency and growth rates to the kernel as well as the nonlinear spectral weight for each mode.

Waltz, R. E.; Bass, E. M.; Staebler, G. M.

2013-04-01

301

Modeling the effect of humidity on the threshold friction velocity of coal particles

NASA Astrophysics Data System (ADS)

Coal particles emission could cause serious air pollution in coal production region and transport region. In coal mining industry, large amounts of water are regularly spayed to coal piles to prevent dust emission from the coal particles. The mechanism behind this measure is to manage the threshold friction velocity, which is an important parameter in controlling wind erosion and dust emission. Bagnold has developed a threshold friction velocity model for soil particles. However, the Bagnold model cannot be applied directly to coal particles as coal particles are quite different from soils in physical and chemical properties. We studied and modeled threshold friction velocity of coal particles under different humidities by using a wind tunnel. Results showed that the effects of humidity on coal particles’ threshold friction velocity are related to the hydrophilic effect and adhesive effect. Bagnold model can be corrected by two new parameter items which explained the two effects. The new model, agreed well with wind tunnel measurements for coal particles with different size categories. Despite the fact the new model was developed for coal particles, its physical basis may allow the model application to other wind susceptible particles.

Zhang, Xiaochun; Chen, Weiping; Ma, Chun; Zhan, Shuifen

2012-09-01

302

NASA Astrophysics Data System (ADS)

As a preliminary feasibility study of a proposed 3D tomographic inversion of new onshore-offshore seismic data, we have carried out a forward modeling exercise of traveltimes using realistic 3D velocity models for Kilauea Volcano. Approximately 2000 km of airgun shots set off during a 1998 marine seismic survey on board the R/V Maurice Ewing over the southern and eastern offshore regions of the island of Hawaii were recorded by the permanent array of on-land seismic stations maintained by Hawaii Volcano Observatory - US Geological Survey. This data set provides the unique opportunity to study regions of Kilauea Volcano that have been poorly imaged by previous passive tomographic inversions. Several 3D velocity models were created to portray the major subsurface features of Kilauea Volcano. In this study, a 1D double-gradient velocity-depth model proposed by Klein (1981) serves as the reference model. Even this simplified model yields good correspondence between predicted and recorded traveltimes for actual shot-receiver geometries. Velocity perturbations based on recent passive seismic tomographic studies of Kilauea's summit and rift zones (e.g., Okubo et al., 1997; Haslinger et al., 2001) were then introduced into the reference model in key regions within the Kilauea subsurface. For example, high VP regions were constructed beneath the active rift zones and summit with velocities of up to 7.6 km/sec and 8.0 km/sec respectively, representing intrusive dikes and cumulate deposits, and a low VP zone with a maximum of only 5.4 km/sec was placed in the coastal and offshore region, denoting either deep seated slump faults or clastic deposits generated by shoreline crossing lava flows. Differences in traveltimes between the reference and alternate models were calculated using actual shot-receiver geometries for several seismic stations, sampling key regions of Kilauea Volcano and the island of Hawaii. As expected, coastal stations were unaffected by the addition of high VP zones in the cores of Kilauea and Mauna Loa Volcanoes, while summit and inland stations showed traveltime drops up to 300 ms for nearshore shots. The opposite occurred with the addition of the coastal and offshore low VP zone, which resulted in significant traveltime increases up to 1200 ms for nearshore shots and up to 500ms at greater shot-station offsets. The observed traveltime differences for the various shot profile-station combinations reflect unique raypath trajectories through the volcanic edifice and underlying ocean crust and mantle. Calculated traveltime perturbations from this study indicate that a full 3D tomographic analysis of the complete onshore-offshore data set will be able to resolve details of many key geologic structures of the dynamic Kilauea Volcano.

Peters, L. E.; Morgan, J. K.; Zelt, C. A.

2001-12-01

303

Joint hypocenter-velocity inversion for the eastern Tennessee seismic zone

A joint hypocenter-velocity inversion for the eastern Tennessee seismic zone (ETSZ) has resolved velocity features in basement rock below detached Appalachian thrust sheets. P and S wave arrival times from 492 earthquakes have been inverted for one- (1-D) and three-dimensional (3-D) velocity models to midcrustal depths. The 3-D P and S wave velocity solutions are computed independently and are very

Gordana Vlahovic; Christine A. Powell; Martin C. Chapman; Matthew S. Sibol

1998-01-01

304

An empirical model of the drift velocity of equatorial plasma depletions

NASA Astrophysics Data System (ADS)

The Far-Ultraviolet Imager on the IMAGE spacecraft (IMAGE-FUV) has been used to observe O+plasma depletions in the post-sunset equatorial ionosphere. Small-scale density irregularities associated with such depletions are believed to adversely affect trans-ionospheric radio signals such as GPS. Prediction of the motion of these plasma depletions is a necessary component of the ability to forecast the occurrence of such radio signal interference. An automated method has recently been developed to identify and track the position and zonal drift velocity of these depletions. Here we use this method to create a large database of the zonal drift velocities of these depletions. We present an empirical model based on these observations that describes the observed drift velocities as a function of both local time and magnetic latitude, which is essential to represent their behavior. A comparison of the observed drift velocities with zonal winds from both an empirical model (Horizontal Wind Model; HWM07) and a first-principles model (the TIEGCM) reveals that the plasma depletions' drift velocities have a latitudinal gradient that cannot be explained solely by the F-region dynamo in the post-sunset period, at least by these climatological models. This suggests that these plasma depletions may not simply drift with the background F-region plasma. It has previously been suggested that vertical polarization electric fields associated with the plasma depletions are responsible for their zonal drifts exceeding the background flow, which may explain the previously-observed discrepancy in the drift velocities and the discrepancy in their gradients reported here.

England, S. L.; Immel, T. J.

2012-12-01

305

Polar versus Cartesian velocity models for maneuvering target tracking with IMM

NASA Astrophysics Data System (ADS)

This paper compares various model sets in different IMM filters for the maneuvering target tracking problem. The aim is to see whether we can improve the tracking performance of what is certainly the most widely used model set in the literature for the maneuvering target tracking problem: a Nearly Constant Velocity model and a Nearly Coordinated Turn model. Our new challenger set consists of a mixed Cartesian position and polar velocity state vector to describe the uniform motion segments and is augmented with the turn rate to obtain the second model for the maneuvering segments. This paper also gives a general procedure to discretize up to second order any non-linear continuous time model with linear diffusion. Comparative simulations on an air defence scenario with a 2D radar, show that this new approach improves significantly the tracking performance in this case.

Laneuville, Dann

306

A Reference Crustal and Plate-Boundary Velocity Model of Japan

NASA Astrophysics Data System (ADS)

The study of velocity structure using earthquake data has been remarkably progressed by development of seismic observation networks, improvement of the methodology, and increase in processing power. Recent studies on 3D velocity structures have produced tomographic images with resolution of a few kilometers (e.g., Matsubara et al., 2005; Nakamichi et al., 2007). In addition to these traveltime analyses, waveform studies such as receiver function analyses have been developed to image the configuration of continental Moho and oceanic plate boundaries (e.g., Yamauchi et al., 2003; Shiomi et al., 2004). Reflection and refraction surveys with controled sources have also been providing information on 2D and 3D velocity structures (e.g., Sato et al., 2005; Special Project for Earthquake Disaster Mitigation in Urban Areas). Thus, plenty of structural property models exist over the Japan islands, but the validity of an individual model is confined to its study area. Therefore, it is essential to build a reference crustal and plate-boundary velocity model for the whole Japan by combining them all together. If this sort of reference velocity model over the Japan islands is available under a unified criterion, it will be valuable for many fields of seismology and Earth sciences. We here construct a reference crustal and plate-boundary velocity model of Japan by integrating 2D models from seismic profiling and receiver functions, 3D models of seismic tomography, and other geophysical data such as gravity anomalies. The goal of this study is to construct a 3D laterally heterogeneous seismic velocity structure model, which clarifies the topography of the Conrad and Moho discontinuities and shapes of the oceanic plates, like the SCEC Unified Velocity Model (e.g., Magistrale et al., 1996). We first make a preliminary Japan model by compiling information on the topography of the Conrad and Moho discontinuities and subducting plates. To this end, we collect 2D seismic velocity models obtained by seismic profiling of reflection/refraction surveys and receiver function analyses, and then integrate them to a 3D velocity model, using complementary information on 3D structures, such as 3D boundary shapes obtained by travel time and gravity anomaly analyses. At this stage, maintaining local structural continuity is a key challenge in the process. We also have to clarify major tectonic features such as the Median Tectonic Line and the Itoigawa-Shizuoka Tectonic Line, and consider the continuity between land-based and offshore models. The integrated 3D reference model will improve the reliability of strong ground motion prediction. Improvements will be the most critical for large-scale ground motion simulations for plate-boundary earthquakes in the Nankai and Tokai regions, which can cause strong shaking in major metropolitan areas of Japan. So, this modeling should be one of the most essential parts of earthquake damage mitigation in Japan.

Ishise, M.; Koketsu, K.; Miyake, H.

2007-12-01

307

We study two-dimensional models of step flow in which the local velocity of a step is expressed as a function of its neighboring terrace widths and the local curvature of the step. Repulsive step interactions modify the velocity functions at short distances and prevent step crossing. When the velocity of a step depends mainly on the width of the terrace

Da-Jiang Liu; Daniel Kandel

1997-01-01

308

NASA Astrophysics Data System (ADS)

In melt-blowing very thin liquid fiber jets are spun due to high-velocity air streams. In literature there is a clear, unsolved discrepancy between the measured and computed jet attenuation (thinning). In this paper we will verify numerically that the turbulent velocity fluctuations causing a random aerodynamic drag on the fiber jets—that has been neglected so far—are the crucial effect to close this gap. For this purpose, we model the velocity fluctuations as vector Gaussian random fields on top of a k- ? turbulence description and develop an efficient sampling procedure. Taking advantage of the special covariance structure the effort of the sampling is linear in the discretization and makes the realization possible. Numerical results are discussed for a simplified melt-blowing model consisting of a system of random ordinary differential equations.

Hübsch, Florian; Marheineke, Nicole; Ritter, Klaus; Wegener, Raimund

2013-03-01

309

Models of Seismic Velocity and Anisotropy For the Great Basin, Nevada

NASA Astrophysics Data System (ADS)

The Great Basin, which lies in the northern Basin and Range Province in the western United States, has a complex deformation history and is currently characterized by significant crustal extension. The region is marked by a semi-circular shear-wave splitting pattern around a weak azimuthal anisotropy zone in central Nevada. This observation led to various interpretations, including the presence of an upwelling, toroidal mantle flow around a slab, and lithospheric drip. Recent research, however, showed that a similar signal of anisotropy can be found in Rayleigh wave phase velocity maps at periods of 16 s and 18 s around a region of locally reduced phase velocities (Beghein, et al., EPSL, 2010). Since surface waves at these periods mostly sample the crust, this suggests that at least part of the observed shear-wave splitting pattern has a crustal origin. In the present study, we employ a forward modeling approach to model the three-dimensional (3-D) variations in shear-wave velocities and azimuthal anisotropy in this area. We first use a fully non-linear forward modeling approach based on the Neighbourhood Algorithm (Sambridge, 1999) to model the isotropic velocity variations. This method enables us to quantitatively assess parameter trade-offs and uncertainties. We use prior constraints for the Moho depth based on receiver function results (Miller and Levander, 2009), but we allow it vary by up to 3%. Our results display uniform S-wave velocities of 3.6 km/s in the crust with a standard deviation of ~0.3 km/s. We also find the presence of a mantle lid of ~45 km thickness, with S-wave velocities up to 4.9 km/s (+/- 0.2 km/s). The posterior Moho depth roughly follows the prior model, and we find that the locally thicker crust located in the southwestern part of the region is sufficient to explain the reduction in phase velocities seen at short periods at the center of the circular anisotropy pattern. Velocities are lower down to at least 100 km depth with Vs=3.9 km/s (+/- 0.3 km/s). We see significant lateral variations in velocity below that depth, accompanied by large uncertainties, which makes the interpretation of the results at those depths difficult. Unlike results from P-wave tomography, we do not observe a faster velocity region in the central Great Basin. This implies that it may be located at larger depths than previously estimated. We also employ the Neighbourhood Algorithm to constrain 3-D variations in azimuthal anisotropy. Our preliminary models display up to 6% Vsv anisotropy in the crust. The uncertainties are relatively small and there are little trade-offs with anisotropy at larger depths. In the upper mantle, our models have a stronger dependence on the regularization and thus have larger uncertainties. Despite the small uncertainties in our crustal anisotropy models, however, the shortest period phase velocities are the most difficult to fit. This suggests that our 16 s and 8 s data are not compatible with the longer period phase velocities, possibly because due to scattering effects that may have affected the measurements. Nevertheless, our most reliable result, which fits the short periods data well, is the amount of crustal anisotropy in central Nevada, where we find ~3% azimuthal anisotropy. This contributes to 3-4 s of shear-wave splitting delay times.

Beghein, C.

2010-12-01

310

NASA Astrophysics Data System (ADS)

In the years 2006 to 2008 we performed Airgun profiles to excite Scholte-waves at different locations in the North and Baltic sea. Scholte-wave energy was recorded using a specially developed Ocean-Bottom-Seismometer. The system is able to sample signals up to 11kHz and can thus be localised at seafloor with an accuracy of a few meters using traveltimes of high frequent seismic signals that are excited in the watercolumn. Scholte-wave recordings are added to common-receiver-gathers which are then inverted for shear-wave velocity structure by fitting modelled phase-slowness frequency dispersion spectra to spectra of the wavefield. By extracting local wavefields from the profile-gathers, multiple 1D Inversions of these fields at different offset-points lead to a 2D shear-wave velocity model of the profile. A new spectral misfit calculation was developed, working without the requirement of identification of the Scholte-wave dispersed modes in the spectra. For minimization of the misfit we implemented a new hybrid method using a combination of particle swarm optimization and a local downhill-simplex resulting in a resolution of global misfit minimum of about 7%. The method was used for shear-wave velocity inversion at four different locations in North and Baltic sea. Resulting models show very good coherence along each Profile and especially a very good correlation to high resolution reflection seismic sections of the same profiles.

Wilken, Dennis; Rabbel, Wolfgang

2010-05-01

311

The SCEC Southern California Reference Three-Dimensional Seismic Velocity Model Version 2

We describe Version 2 of the three-dimensional (3D) seismic velocity model of southern California developed by the Southern California Earthquake Cen- ter and designed to serve as a reference model for multidisciplinary research activities in the area. The model consists of detailed, rule-based representations of the major southern California basins (Los Angeles basin, Ventura basin, San Gabriel Valley, San Fernando

Harold Magistrale; Steven Day; Robert W. Clayton; Robert Graves

2000-01-01

312

Iterative velocity model building for 3-D depth migration by integrating GOCAD and AVS

We have developed a procedure for building a 3-D velocity model starting from a 2-D geological model in order to image 3-D poststack data. The 3-D model was built using GOCAD, and it was iteratively refined by interpreting the result of 3-D poststack depth migrations using AVS. At the beginning of the iterative process, when only few reflectors are detectable

Robert G. Clapp; Biondo Biondi

313

EXPERIMENTAL COMPARISON OF DIFFERENT FRICTION MODELS FOR ACCURATE LOW-VELOCITY TRACKING

http:\\/\\/www.mech.kuleuven.ac.be\\/pma\\/ Abstract Low velocity friction causes positioning and con- touring errors such as the quadrant glitch in machine tool table systems. Numerous comprehensive fric- tion models are described in literature. A compari- son of these models with respect to feedforward fric- tion compensation is not yet available: only com- parisons with the Coulomb friction model are avail- able. This paper

V. Lampaert; J. Swevers; F. Al-bender

314

This paper presents a three-dimensional compressional wave velocity model of the forearc crust and upper mantle and the subducting Juan de Fuca plate beneath southwestern British Columbia and the adjoining straits of Georgia and Juan de Fuca. The velocity model was constructed through joint tomographic inversion of 50,000 first-arrival times from earthquakes and active seismic sources. Wrangellia rocks of the accreted Paleozoic and Mesozoic island arc assemblage underlying southern Vancouver Island in the Cascadia forearc are imaged at some locations with higher than average lower crustal velocities of 6.5-7.2 km/s, similar to observations at other island arc terranes. The mafic Eocene Crescent terrane, thrust landward beneath southern Vancouver Island, exhibits crustal velocities in the range of 6.0-6.7 km/s and is inferred to extend to a depth of more than 20 km. The Cenozoic Olympic Subduction Complex, an accretionary prism thrust beneath the Crescent terrane in the Olympic Peninsula, is imaged as a low-velocity wedge to depths of at least 20 km. Three zones with velocities of 7.0-7.5 km/s, inferred to be mafic and/or ultramafic units, lie above the subducting Juan de Fuca plate at depths of 25-35 km. The forearc upper mantle wedge beneath southeastern Vancouver Island and the Strait of Georgia exhibits low velocities of 7.2-7.5 km/s, inferred to correspond to ???20% serpentinization of mantle peridotites, and consistent with similar observations in other warm subduction zones. Estimated dip of the Juan de Fuca plate beneath southern Vancouver Island is ???11??, 16??, and 27?? at depths of 30, 40, and 50 km, respectively. Copyright 2005 by the American Geophysical Union.

Ramachandran, K.; Dosso, S. E.; Spence, G. D.; Hyndman, R. D.; Brocher, T. M.

2005-01-01

315

NASA Astrophysics Data System (ADS)

This paper presents a three-dimensional compressional wave velocity model of the forearc crust and upper mantle and the subducting Juan de Fuca plate beneath southwestern British Columbia and the adjoining straits of Georgia and Juan de Fuca. The velocity model was constructed through joint tomographic inversion of 50,000 first-arrival times from earthquakes and active seismic sources. Wrangellia rocks of the accreted Paleozoic and Mesozoic island arc assemblage underlying southern Vancouver Island in the Cascadia forearc are imaged at some locations with higher than average lower crustal velocities of 6.5-7.2 km/s, similar to observations at other island arc terranes. The mafic Eocene Crescent terrane, thrust landward beneath southern Vancouver Island, exhibits crustal velocities in the range of 6.0-6.7 km/s and is inferred to extend to a depth of more than 20 km. The Cenozoic Olympic Subduction Complex, an accretionary prism thrust beneath the Crescent terrane in the Olympic Peninsula, is imaged as a low-velocity wedge to depths of at least 20 km. Three zones with velocities of 7.0-7.5 km/s, inferred to be mafic and/or ultramafic units, lie above the subducting Juan de Fuca plate at depths of 25-35 km. The forearc upper mantle wedge beneath southeastern Vancouver Island and the Strait of Georgia exhibits low velocities of 7.2-7.5 km/s, inferred to correspond to ˜20% serpentinization of mantle peridotites, and consistent with similar observations in other warm subduction zones. Estimated dip of the Juan de Fuca plate beneath southern Vancouver Island is ˜11°, 16°, and 27° at depths of 30, 40, and 50 km, respectively.

Ramachandran, K.; Dosso, S. E.; Spence, G. D.; Hyndman, R. D.; Brocher, T. M.

2005-02-01

316

Velocity profile method for time varying resistance in minimal cardiovascular system models

NASA Astrophysics Data System (ADS)

This paper investigates the fluid dynamics governing arterial flow used in lumped parameter cardiovascular system (CVS) models, particularly near the heart where arteries are large. Assumptions made in applying equations conventionally used in lumped parameter models are investigated, specifically that of constant resistance to flow. The Womersley number is used to show that the effects of time varying resistance must be modelled in the pulsatile flow through the large arteries near the heart. It is shown that the equation commonly used to include inertial effects in fluid flow calculations is inappropriate for including time varying resistance. A method of incorporating time varying resistance into a lumped parameter model is developed that uses the Navier-Stokes equations to track the velocity profile. Tests on a single-chamber model show a 17.5% difference in cardiac output for a single-chamber ventricle model when comparing constant resistance models with the velocity profile tracking method modelling time varying resistance. This increase in precision can be achieved using 20 nodes with only twice the computational time required. The method offers a fluid dynamically and physiologically accurate method of calculating large Womersley number pulsatile fluid flows in large arteries around the heart and valves. The proposed velocity profile tracking method can be easily incorporated into existing lumped parameter CVS models, improving their clinical application by increasing their accuracy.

Smith, Bram W.; Chase, J. Geoffrey; Nokes, Roger I.; Shaw, Geoffrey M.; David, Tim

2003-10-01

317

NASA Astrophysics Data System (ADS)

A key consequence of the presence of microcracks within rock is their significant influence upon elastic anisotropy and transport properties. Here two rock types (a basalt and a granite) with contrasting microstructures, dominated by microcracks, have been investigated using an advanced experimental arrangement capable of measuring porosity, P wave velocity, S wave velocity, and permeability contemporaneously at effective pressures up to 100 MPa. Using the Kachanov (1994) noninteractive effective medium theory, the measured elastic wave velocities are inverted using a least squares fit, permitting the recovery of the evolution of crack density and aspect ratio with increasing isostatic pressure. Overall, the agreement between measured and predicted velocities is good, with average error less than 0.05 km/s. At larger scales and above the percolation threshold, macroscopic fluid flow also depends on the crack density and aspect ratio. Using the permeability model of Guéguen and Dienes (1989) and the crack density and aspect ratio recovered from the elastic wave velocity inversion, we successfully predict the evolution of permeability with pressure for direct comparison with the laboratory measurements. We also calculate the evolution of the crack porosity with increasing isostatic pressure, on the basis of the calculated crack density, and compare this directly with the experimentally measured porosity. These combined experimental and modeling results illustrate the importance of understanding the details of how rock microstructures change in response to an external stimulus when predicting the simultaneous evolution of rock physical properties.

Benson, Philip; Schubnel, Alexandre; Vinciguerra, Sergio; Trovato, Concetta; Meredith, Philip; Young, R. Paul

2006-04-01

318

Car-following model with relative-velocity effect and its experimental verification.

In driving a vehicle, drivers respond to the changes of both the headway and the relative velocity to the vehicle in front. In this paper a new car-following model including these maneuvers is proposed. The acceleration of the model becomes infinite (has a singularity) when the distance between two vehicles is zero, and the asymmetry between the acceleration and the deceleration is incorporated in a nonlinear way. The model is simple but contains enough features of driving for reproducing real vehicle traffic. From the linear stability analysis, we confirm that the model shows the metastable homogeneous flow around the critical density, beyond which a traffic jam emerges. Moreover, we perform experiments to verify this model. From the data it is shown that the acceleration of a vehicle has a positive correlation with the relative velocity. PMID:21599238

Shamoto, Daisuke; Tomoeda, Akiyasu; Nishi, Ryosuke; Nishinari, Katsuhiro

2011-04-11

319

Car-following model with relative-velocity effect and its experimental verification

NASA Astrophysics Data System (ADS)

In driving a vehicle, drivers respond to the changes of both the headway and the relative velocity to the vehicle in front. In this paper a new car-following model including these maneuvers is proposed. The acceleration of the model becomes infinite (has a singularity) when the distance between two vehicles is zero, and the asymmetry between the acceleration and the deceleration is incorporated in a nonlinear way. The model is simple but contains enough features of driving for reproducing real vehicle traffic. From the linear stability analysis, we confirm that the model shows the metastable homogeneous flow around the critical density, beyond which a traffic jam emerges. Moreover, we perform experiments to verify this model. From the data it is shown that the acceleration of a vehicle has a positive correlation with the relative velocity.

Shamoto, Daisuke; Tomoeda, Akiyasu; Nishi, Ryosuke; Nishinari, Katsuhiro

2011-04-01

320

A velocity-dependent anomalous radial transport model for (2-D, 2-V) kinetic transport codes

NASA Astrophysics Data System (ADS)

Plasma turbulence constitutes a significant part of radial plasma transport in magnetically confined plasmas. This turbulent transport is modeled in the form of anomalous convection and diffusion coefficients in fluid transport codes. There is a need to model the same in continuum kinetic edge codes [such as the (2-D, 2-V) transport version of TEMPEST, NEO, and the code being developed by the Edge Simulation Laboratory] with non-Maxwellian distributions. We present an anomalous transport model with velocity-dependent convection and diffusion coefficients leading to a diagonal transport matrix similar to that used in contemporary fluid transport models (e.g., UEDGE). Also presented are results of simulations corresponding to radial transport due to long-wavelength ExB turbulence using a velocity-independent diffusion coefficient. A BGK collision model is used to enable comparison with fluid transport codes.

Bodi, Kowsik; Krasheninnikov, Sergei; Cohen, Ron; Rognlien, Tom

2008-11-01

321

NASA Astrophysics Data System (ADS)

To test the hypothesis that high quality 3D Earth models will produce seismic event locations that are more accurate and more precise than currently used 1D and 2/2.5D models, we are developing a global 3D P wave velocity model of the Earth's crust and mantle using seismic tomography. In this paper, we present the most recent version of our model, SALSA3D (SAndia LoS Alamos 3D) version 1.7, and demonstrate its ability to reduce mislocations for a large set of realizations derived from a carefully chosen set of globally-distributed ground truth (GT) events, compared to existing models and/or systems. Our model is derived from the latest version of the GT catalog of P and Pn travel time picks assembled by Los Alamos National Laboratory. To prevent over-weighting due to ray path redundancy and to reduce the computational burden, we cluster rays to produce representative rays. Reduction in the total number of ray paths is ~50%. The model is represented using the triangular tessellation system described by Ballard et al. (2009), which incorporates variable resolution in both the geographic and radial dimensions. For our starting model, we use a simplified layer crustal model derived from the NNSA Unified model in Eurasia and Crust 2.0 model elsewhere, over a uniform ak135 mantle. Sufficient damping is used to reduce velocity adjustments so that ray path changes between iterations are small. We obtain proper model smoothness by using progressive grid refinement, refining the grid only in areas where the data warrant it. In previous versions of SALSA3D, we based this refinement on velocity changes from previous model iterations. For version 1.7, we utilize the diagonal of the model resolution matrix to control where grid refinement occurs, resulting in more consistent and continuous areas of refinement than before. Our approach produces a smooth, multi-resolution model with node density appropriate to both ray coverage and the velocity gradients required by the data. We compare the travel-time prediction and location capabilities of SALSA3D to standard 1D and 2/2.5D models via location tests on a global event set with GT of 5 km or better. These events generally possess hundreds of Pn and P picks from which we generate different realizations of station distributions, yielding a range of azimuthal coverage and ratios of teleseismic to regional arrivals, with which we test the robustness and quality of relocation. The SALSA3D model reduces mislocation over the standard 1D ak135 model regardless of Pn to P ratio, with improvement most pronounced at higher azimuthal gaps. We currently are testing the use of the full model covariance matrix to produce realistic path-dependent travel time uncertainty during location tests, replacing the standard, distance-dependent, path-independent uncertainty typically used in location algorithms.

Begnaud, M. L.; Ballard, S.; Young, C. J.; Hipp, J. R.; Chang, M.; Encarnacao, A.; Rowe, C. A.; Phillips, W. S.; Steck, L.

2011-12-01

322

The APPswe/PS1dE9 mouse is a double transgenic model of Alzheimer's disease, which harbors mutant mouse/human amyloid precursor protein (Swedish K594N/M595L) and presenilin-1 genes (PS1-dE9). These mice develop beta-amyloid plaques and exhibit visuo-spatial learning and memory impairment in the Morris water maze (MWM) at 8-12 and 16-18 months of age. To extend these findings, we tested visuo-spatial learning and memory of male and female APPswe/PS1dE9 mice at 16 months of age on the Barnes maze. APPswe/PS1dE9 mice showed impaired acquisition learning using measures of latency, distance traveled, errors and hole deviation scores, and were less likely to use the spatial search strategy to locate the escape hole than wild-type mice. APPswe/PS1dE9 mice also showed a deficit in memory in probe tests on the Barnes maze relative to wild-type mice. Learning and memory deficits, however, were not found during reversal training and reversal probe tests. Sex differences were observed, as male APPswe/PS1dE9 mice had smaller reversal effects than male wild-type mice, but females of each genotype did not differ. Overall, these results replicate previous findings using the MWM, and indicate that APPswe/PS1dE9 mice have impaired visuo-spatial learning and memory at 16 months of age. PMID:19428625

O'Leary, Timothy P; Brown, Richard E

2009-02-06

323

Isothermal velocity and turbulence measurements downstream of a model multilobed turbofan mixer

An isothermal experimental investigation of the three dimensional flow field downstream of a model multilobed turbofan forced mixer is presented. LDA measurements of the three mean velocities and corresponding turbulence intensities were obtained in the downstream duct where the turbine (primary) and fan (secondary) streams emerging from the lobes mix together. The flow development in the near field was quantified

P. Koutmos; J. J. McGuirk

1989-01-01

324

Modeling the Effect of Varying Swim Speeds on Fish Passage through Velocity Barriers

The distance fish can swim through zones of high-velocity flow is an important factor limiting the distribution and conservation of riverine and diadromous fishes. Often, these barriers are characterized by nonuniform flow conditions, and it is likely that fish will swim at varying speeds to traverse them. Existing models used to predict passage success, however, typically include the unrealistic assumption

Theodore Castro-Santos

2006-01-01

325

Velocity Characteristics of Isothermal and Combusting Flows in a Model Combustor

Mean and rms values of the axial and swirl velocity components obtained by a laser Doppler anemometer in a model can-type gas turbine combustor under isothermal and combusting flow conditions are reported. The results show that the combustor swirl is characterised by a solid body rotation near the axis and a free vortex flow in regions close to the combustor

A. F. BICEN; W. P. JONES

1986-01-01

326

In this paper, an analytical model for perforation of composite sandwich panels with honeycomb core subjected to high-velocity impact has been developed. The sandwich panel consists of a aluminum honeycomb core sandwiched between two thin composite skins. The solution involves a three-stage, perforation process including perforation of the front composite skin, honeycomb core, and bottom composite skin. The strain and

S. Feli; M. H. Namdari Pour

327

Velocity and Pressure Characteristics of a Model SSME High Pressure Fuel Turbopump (Final Report).

National Technical Information Service (NTIS)

Under the present effort an experiment rig has been constructed, an instrumentation package developed and a series of mean and rms velocity and pressure measurements made in a turbopump which modelled the first stage of the Space Shuttle Main Engine (SSME...

D. G. Tse J. S. Sabnis H. Mcdonald

1991-01-01

328

A new method for the size-distribution analysis of polymers by sedimentation velocity analytical ultracentrifugation is described. It exploits the ability of Lamm equation modeling to discriminate between the spreading of the sedimentation boundary arising from sample heterogeneity and from diffusion. Finite element solutions of the Lamm equation for a large number of discrete noninteracting species are combined with maximum entropy

Peter Schuck

2000-01-01

329

The maximum velocity of shortening of a muscle is an important parameter in musculoskeletal models. The most commonly used values are derived from animal studies; however, these values are well above the values that have been reported for human muscle. The purpose of this study was to examine the sensitivity of simulations of maximum vertical jumping performance to the parameters

Zachary J. Domire; John H. Challis

2010-01-01

330

New experimental data for validation of nanoparticle dry deposition velocity models

NASA Astrophysics Data System (ADS)

In Order to evaluate the impact of the aerosol pollution on ecosystems, we have to study the transfer functions of particles on vegetated canopies. One of them is the dry deposition, which is defined by the deposition velocity (Vd): the ratio between particles surface flux and the atmospheric aerosol concentration nearby the surface. This deposition velocity depends on many parameters. For example, the topography ground, the substrate, the micrometeorological conditions (turbulence), the aerosol characteristics (size, electric charge) and external fields (gravity, electric). Nowadays, there are several models of aerosol dry deposition which consider the effects of the turbulence, the particles size for a large range of diameter (some nm to 100 µm). In the case of nanoparticles, there is not enough reliable experimental data to allow a comparison with the dry deposition models. For operative models, the scattering of Vd experimental data of nanoparticles in a rural environment creates uncertainties larger than one order of magnitude. The study of the aerosols dry deposition velocity has remained an international challenge since the sixties and involves an in situ experimental approach, in order to consider the local particularities (substrate, turbulence, vegetated canopies, etc…) The main aim of this study is to obtain experimental data on aerosol dry deposition velocities onto rural areas. Therefore we have developed a direct eddy covariance method. The use of an Electrical Low Pressure Impactor (Outdoor ELPI, Dekati Inc.) for this method enables to calculate dry deposition velocities for atmospheric aerosols sizing from 7 nm to 2 µm. We present our results: discuss the impact of micrometeorological parameters and particle size on the dry deposition velocity and the possibility to apply this method on other environments.

Damay, P. E.; Maro, D.; Coppalle, A.; Lamaud, E.; Connan, O.; Herbert, D.; Talbaut, M.; Irvine, M.

2009-04-01

331

The present paper encompasses an effort on the prediction of flow and heat transfer characteristics in the turbulent axisymmetric impinging jet. This is achieved by applying the realizability constraint in the normal-velocity relaxation (v ? f) model and algebraic turbulent heat flux models to flow and thermal fields, respectively. The realizable v ? f model is capable of improving the predicted velocity

Farzad BAZDIDI-TEHRANI; Alireza IMANIFAR; Siavash KHAJEHHASANI; Mehran RAJABI-ZARGARABADI

2011-01-01

332

The present article encompasses an effort on the prediction of flow and heat transfer characteristics in the turbulent axisymmetric impinging jet. This is achieved by applying the realizability constraint in the normal-velocity relaxation (v ? f) model and algebraic turbulent heat flux models to flow and thermal fields, respectively. The realizable v ? f model is capable of improving the predicted velocity

Farzad Bazdidi-Tehrani; Alireza Imanifar; Siavash Khajehhasani; Mehran Rajabi-Zargarabadi

2012-01-01

333

Relationship between Elastic wave Velocity and Permeability of Rock Model with penny-shaped cracks

NASA Astrophysics Data System (ADS)

Estimating underground fluid-flow is of great importance in petroleum engineering and carbon capture and storage (CCS). Permeability is one of the most important parameters which show how easily fluid passes through rock mass. It could be acquired just by measuring rock samples near borehole in lab-experiments. It means that permeability except near borehole should be estimated, considering other information. In this research, elastic wave velocity is focused as a tool of estimating permeability, because it is one of the most popular parameter which has underground information. The relationship between permeability and elastic wave velocities should be revealed, in order to establish a methodology to estimate rock permeability from elastic wave velocity. These two parameters are controlled by pore geometry of rock. Therefore, we focused on pore geometry as connecting bridge between the two parameters: permeability, elastic wave velocity. We modeled the considering rock as a solid mass containing a lot of same-sized penny-shaped cracks randomly. LBM (Lattice Boltzmann Method), which is one of the computational fluid dynamics methods, is adopted for calculating permeability in our study. This method has a storing point especially under complicated fluid-solid boundary condition. Elastic wave velocities are derived from effective elastic moduli (i.e., bulk modulus, stiffness). They are estimated by self-consistent approximation, which needs porosity of rock model, aspect ratio of penny-shaped cracks and volume fraction of each phase. In this research, we assume that solid phase is composed only by quartz and rock's pore space is filled with water. The simulated results demonstrate that aspect ratio of crack can be estimated by P- and S-wave velocity, and aspect ratio and P-wave velocity can determine porosity. Whereas, the relationship between porosity and permeability is dependent on aspect ratio, which means permeability can be estimated by aspect ratio and porosity. Therefore, this research reveals that permeability can be estimated by P-wave velocity and S-wave velocity if the rock is composed by same-sized penny cracks.

Yamabe, H.; Tsuji, T.; Matsuoka, T.

2011-12-01

334

The large-scale peculiar velocity field in flat models of the universe

The inflationary Universe scenario predicts a flat Universe and both adiabatic and isocurvature primordial density perturbations with the Zel'dovich spectrum. The two simplest realizations, models dominated by hot or cold dark matter, seem to be in conflict with observations. Flat models are examined with two components of mass density, where one of the components of mass density is smoothly distributed and the large-scale (greater than or equal to10h/sup -1/ MpC) peculiar velocity field for these models is considered. For the smooth component relativistic particles, a relic cosmological term, and light strings are considered. At present the observational situation is unsettled; but, in principle, the large-scale peculiar velocity field is very powerful discriminator between these different models. 61 refs.

Vittorio, N.; Turner, M.S.

1986-10-01

335

The maximum velocity of shortening of a muscle is an important parameter in musculoskeletal models. The most commonly used values are derived from animal studies; however, these values are well above the values that have been reported for human muscle. The purpose of this study was to examine the sensitivity of simulations of maximum vertical jumping performance to the parameters describing the force-velocity properties of muscle. Simulations performed with parameters derived from animal studies were similar to measured jump heights from previous experimental studies. While simulations performed with parameters derived from human muscle were much lower than previously measured jump heights. If current measurements of maximum shortening velocity in human muscle are correct, a compensating error must exist. Of the possible compensating errors that could produce this discrepancy, it was concluded that reduced muscle fibre excursion is the most likely candidate. PMID:20162474

Domire, Zachary J; Challis, John H

2010-12-01

336

Low Velocity Impact Experiments plus Modeling of the Resulting Reaction Violence in LX-10 Charges

NASA Astrophysics Data System (ADS)

A new gas gun facility and improved instrumentation were used to study the mechanisms of low velocity impact ignition and growth of violent reaction. Cylindrical charges of the HMX based explosive LX-10 (95% HMX, 5% Viton binder) encased by lexan were impacted by 6.35 mm diameter hardened steel projectiles at velocities ranging from 47 to 500 m/s. Fast Phantom v12 cameras were employed to capture the times of first ignition. The degrees of resulting reaction violence were determined using Photonic Doppler Velocimetry (PDV) probes to measure the free surface velocity histories of attached aluminum foils. Analytical and hydrodynamic reactive flow models were used to estimate the relative violence of these LX-10 reactions compared to the intentional detonation of an equivalent LX-10 charge. This work was performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.

Chidester, Steven; Garcia, Frank; Vandersall, Kevin; Tarver, Craig

2011-06-01

337

Developing a comprehensive seismic velocity model of the Cascadia subduction zone

NASA Astrophysics Data System (ADS)

A comprehensive and high-resolution velocity model is essential to understand the subduction dynamics and continental accretion in the Cascadia subduction zone. In this study, we image the seismic structure of the crust and upper mantle with the application of a full-wave tomographic method. The tomographic result provides important insights on addressing such scientific questions as the along-strike segmentation of Cascadia and the role of (de-)hydration of the slab/crust, which is thought to be critical for the occurrence of the episodic tremor and slip. We use continuous seismic data recorded between 1995 and 2011 by about 600 stations in an area covering from northernmost California to northern Vancouver Island, Canada. The empirical Green's functions are recovered from inter-station cross correlation at periods of 7-200 seconds. At the periods of our interest, the empirical Green's functions from cross correlation of vertical-vertical channels are primarily Rayleigh waves. We simulate full-wave propagation within a 3D reference velocity model. The travel time anomalies are measured from the observed and synthetic Green's functions at stations. The shear and compressional velocities are inverted jointly as Rayleigh waves are sensitive to both Vp and Vs. The solution from inversion is used to iteratively update the 3D reference model. The integration of various waves in a physically consistent way refines absolute P and S velocities and Vp/Vs ratio, which allows for more robust and reliable geodynamic interpretations.

Gao, H.; Shen, Y.

2011-12-01

338

NASA Astrophysics Data System (ADS)

Accurate travel-time and amplitude predictions for regional seismic phases are essential for locating and characterizing small seismic events with the accuracy needed for explosion monitoring decisions. Parameter estimates calculated through 3D Earth models have the best chance of achieving acceptable prediction errors, if the models are constrained by sufficient data. With this motivation, we have developed and applied a joint body- wave/surface-wave inversion method to produce a new 3D P and S velocity model (SAsia3D) for the crust and upper mantle to a depth of 400 km in the region of central and southern Asia between 10-50° N and 40- 110° E. The method uses Pn and Pg arrival times to determine the P velocity structure and Rayleigh-wave group velocities in the period range 10-150 s to constrain the S velocity structure and depth to Moho. The body- wave and surface-wave inverse problems are coupled through an assumed correlation coefficient between P and S velocity perturbations and the imposition of bounds on the velocities and Poisson's ratio as a function of depth. Both body-wave and surface-wave forward modeling are performed in 3D models with the aid of finite-difference numerical raytracing to calculate body-wave raypaths and 2D raytracing to calculate non-great circle surface-wave paths. Nonlinearity is addressed by iterating the inversion method with updated raypaths. The regional P-wave arrival-time observations used to obtain SAsia3D were collected from the Engdahl, van der Hilst and Buland (1998; EHB) bulletin, restricted to well-located earthquakes in the years 1988-2004. The group- velocity measurements were provided by groups at the University of Colorado and Lawrence Livermore National Laboratory. Our initial model for the inversion procedure was taken as a hybrid of the CRUST2.0 3D model (Bassin et al., 2000) and the upper mantle portion of the global 1D AK135 model (Kennett et al., 1995). SAsia3D was obtained with four iterations of our technique, achieving a fifty percent variance reduction for both the body- wave and surface-wave data. Relative velocity (in particular the P velocity) variations with respect to the AK135 mantle model are in good agreement with previous studies and reflect the major tectonic features across southern and central Asia. For example, at 250 km depth, P variations across new model range from -2.0 to +2.3%, while S variations vary from -2.1% to +1.5%. We have also noted intriguing differences between the P and S velocity models in regions of significant tectonic activity, such as the Tibetan Plateau and South Caspian Basin. Some of these variations may prove useful in explaining the tectonic evolution of the Indo-Asian collision zone. We have also completed a number of validation exercises to demonstrate the accuracy of SAsia3D in regional seismic event location. Most notably, SAsia3D performs well when both regional P and S phase arrivals are included in the location. The regional P/S location obtained with SAsia3D are frequently superior to the locations obtained with a large set of teleseismic and regional P arrivals and the AK135 reference model.

Reiter, D.; Rodi, W.

2007-12-01

339

Numerical modelling of foam-cored sandwich plates under high-velocity impact

This paper studies the high-velocity impact response of sandwich plates, with E-glass fibre\\/polyester face-sheets and foam core, using finite-element models developed in ABAQUS\\/explicit code. The failure of the face-sheets was predicted by implementing Hou failure criteria and a procedure to degrade material properties in a user subroutine (VUMAT). The foam core was modelled as a crushable foam material. The numerical

I. Ivañez; C. Santiuste; E. Barbero; S. Sanchez-Saez

2011-01-01

340

A Global Model for the Origin of Pulsar and Runaway OB Star Velocities

We have developed a model to explore the theory that supernovas in massive binary systems can produce the high velocity populations of runaway OB stars, High Mass X-ray Binaries (HMXB's), Be stars and radio pulsars seen in the Galaxy. Our model takes a Galactic population of OB stars (8-40 Modot ) and evolves them off the main-sequence. In short period

James Lewis Terman

1993-01-01

341

Modelling fracture in laminated architectural glass subject to low velocity impact

Standard finite element wave propagation codes are useful for determining stresses caused by colliding bodies; however, their\\u000a applicability to brittle materials is limited because an accurate treatment of the fracture process is difficult to model.\\u000a This paper presents a method that allows traditional wave propagation codes to model low velocity, small missile impact in\\u000a laminated architectural glass such as that

F. W. FLOCKER; L. R DHARANI

1997-01-01

342

The humic colloid borne Am(III) transport was investigated in column experiments for Gorleben groundwater\\/sand systems. It was found that the interaction of Am with humic colloids is kinetically controlled, which strongly influences the migration behavior of Am(III). These kinetic effects have to be taken into account for transport\\/speciation modeling.The kinetically controlled availability model (KICAM) was developed to describe actinide sorption

W. Schüßler; R Artinger; J. I Kim; N. D Bryan; D Griffin

2001-01-01

343

NASA Astrophysics Data System (ADS)

We investigate the behavior of simulated slow slip events using a rate and state friction model that is steady state velocity weakening at low slip speeds but velocity strengthening at high slip speeds. Our simulations are on a one-dimensional (line) fault, but we modify the elastic interactions to mimic the elongate geometry frequently observed in slow slip events. Simulations exhibit a number of small events as well as periodic large events. The large events propagate approximately steadily "along strike," and stress and slip rate decay gradually behind the propagating front. Their recurrence intervals can be determined by considering what is essentially an energy balance requirement for long-distance propagation. It is possible to choose the model parameters such that the simulated events have the stress drops, slip velocities, and propagation rates observed in Cascadia.

Hawthorne, J. C.; Rubin, A. M.

2013-07-01

344

Development of a State-Wide 3-D Seismic Tomography Velocity Model for California

NASA Astrophysics Data System (ADS)

We report on progress towards the development of a state-wide tomographic model of the P-wave velocity for the crust and uppermost mantle of California. The dataset combines first arrival times from earthquakes and quarry blasts recorded on regional network stations and travel times of first arrivals from explosions and airguns recorded on profile receivers and network stations. The principal active-source datasets are Geysers-San Pablo Bay, Imperial Valley, Livermore, W. Mojave, Gilroy-Coyote Lake, Shasta region, Great Valley, Morro Bay, Mono Craters-Long Valley, PACE, S. Sierras, LARSE 1 and 2, Loma Prieta, BASIX, San Francisco Peninsula and Parkfield. Our beta-version model is coarse (uniform 30 km horizontal and variable vertical gridding) but is able to image the principal features in previous separate regional models for northern and southern California, such as the high-velocity subducting Gorda Plate, upper to middle crustal velocity highs beneath the Sierra Nevada and much of the Coast Ranges, the deep low-velocity basins of the Great Valley, Ventura, and Los Angeles, and a high- velocity body in the lower crust underlying the Great Valley. The new state-wide model has improved areal coverage compared to the previous models, and extends to greater depth due to the data at large epicentral distances. We plan a series of steps to improve the model. We are enlarging and calibrating the active-source dataset as we obtain additional picks from investigators and perform quality control analyses on the existing and new picks. We will also be adding data from more quarry blasts, mainly in northern California, following an identification and calibration procedure similar to Lin et al. (2006). Composite event construction (Lin et al., in press) will be carried out for northern California for use in conventional tomography. A major contribution of the state-wide model is the identification of earthquakes yielding arrival times at both the Northern California Seismic Network and the Southern California Seismic Network. These events are critical to the determination of the seismic velocity model in central California, in the former `no-mans-land' between the Northern and Southern California networks. Ultimately, a combination of active-source datasets, composite events, original catalog picks, and differential times from both waveform cross-correlation and catalog picks will be used in a double-difference tomography inversion.

Thurber, C. H.; Lin, G.; Zhang, H.; Hauksson, E.; Shearer, P.; Waldhauser, F.; Hardebeck, J.; Brocher, T.

2007-12-01

345

Three-dimensional P wave velocity model for the San Francisco Bay region, California

NASA Astrophysics Data System (ADS)

A new three-dimensional P wave velocity model for the greater San Francisco Bay region has been derived using the double-difference seismic tomography method, using data from about 5,500 chemical explosions or air gun blasts and approximately 6,000 earthquakes. The model region covers 140 km NE-SW by 240 km NW-SE, extending from 20 km south of Monterey to Santa Rosa and reaching from the Pacific coast to the edge of the Great Valley. Our model provides the first regional view of a number of basement highs that are imaged in the uppermost few kilometers of the model, and images a number of velocity anomaly lows associated with known Mesozoic and Cenozoic basins in the study area. High velocity (Vp > 6.5 km/s) features at ˜15-km depth beneath part of the edge of the Great Valley and along the San Francisco peninsula are interpreted as ophiolite bodies. The relocated earthquakes provide a clear picture of the geometry of the major faults in the region, illuminating fault dips that are generally consistent with previous studies. Ninety-five percent of the earthquakes have depths between 2.3 and 15.2 km, and the corresponding seismic velocities at the hypocenters range from 4.8 km/s (presumably corresponding to Franciscan basement or Mesozoic sedimentary rocks of the Great Valley Sequence) to 6.8 km/s. The top of the seismogenic zone is thus largely controlled by basement depth, but the base of the seismogenic zone is not restricted to seismic velocities of ?6.3 km/s in this region, as had been previously proposed.

Thurber, Clifford H.; Brocher, Thomas M.; Zhang, Haijiang; Langenheim, Victoria E.

2007-07-01

346

NASA Astrophysics Data System (ADS)

Identification of conduits that control groundwater flow is extremely important in understanding karstic systems. This study tests the hypothesis that seismic refraction tomography may be used to identify and map karst features that control groundwater flow, recharge and discharge. Tomography provides velocity images of the subsurface, from traveltimes of seismic waves generated at the surface. Rock properties, other geologic structures and water levels near recharge and discharge points were also investigated using refraction tomography. This study was conducted at two locations: Bear Creek Valley of the Oak Ridge Reservation, TN, and Perry Farm Park, Bourbonnais Township, Kankakee, IL. P-wave velocity refraction-tomography models at Bear Creek Valley mapped lateral variations in the velocity of subsurface rock units and thickness variations of the overburden (0 to 30 ft). Inverted velocities are consistent with the two distinct bedrock groups at this field site---the Nolichucky Shale and Maynardville Limestone. Distinct low-velocity zones have the appearance of "fracture-like" structures. They represent either sediments filling bedrock depressions, or thick zones of highly weathered bedrock along faults and joints. These zones may be water-saturated or partially water-saturated, and probably play an important role in the hydrogeology of the area. Some of these zones also lie directly beneath surface streams, suggesting fault control of these streams, including Bear Creek. In many such locations well logs report the presence of actual fractures, cavities, and water-level fluctuations that cannot be explained by seasonal variations alone. Seismic refraction tomography over thinly mantled (7 to 30 ft) karst at Perry Farm Park may be used to delineate bedrock highs and lows, probably associated with different facies in the dolomite bedrock and/or fracture zones. Conventional refraction surveys, especially with S-waves, appear to delineate fractures. Results suggest that near-vertical fractures may also act as ground water recharge, discharge, and transmission features at the Perry Farm Park site. Borings and piezometers are needed to confirm this hypothesis, however. This study demonstrates that tomographic models are able to estimate subsurface velocity changes associated with geologic structures with better spatial resolution than conventional seismic refraction methods. Tomographic models also provide standard errors and model covariance. The tomographic models, however, are strongly dependent on the choice of initial 1-D model and the nature of shot-point and geophone geometry. They also may include computational artifacts. Thus, independent borehole, geological, and geophysical data must be used to verify tomographic models.

Atre, Shashank Ramchandra

347

NASA Astrophysics Data System (ADS)

We performed numerical experiments to show that Extended Information Criterion (EIC) can be utilized for determining an optimum model in velocity reconstruction problems, in which a wavefront tracing method was employed for finding the minimum travel time raypath. First, travel times were calculated from a specified velocity model, and simulated data were produced by adding random error to the travel times. Velocity models were then reconstructed from the simulated data by employing a Simultaneous Iterative Reconstruction Technique (SIRT) starting from different initial models. Finally, EIC values were calculated for each reconstructed velocity model at every iteration, and were used for selecting an optimum velocity model. Resutls indicated that EIC provides an objective method for selecting an optimum solution from a suite reconstructions obtained from different initial models.

Nishizawa, O.; Lei, Xing-Lin

1995-05-01

348

The spatially resolved phase space distribution was measured for a dusty plasma system. Analysis of the velocity space component of the distributions revealed that the standard assumption of a spherically symmetric velocity space is not applicable to the observed system. The more general, ellipsoidally symmetric, multi-normal distribution function was applied to model the velocity space and is compared to the canonical spherically symmetric model.

Fisher, Ross; Thomas, Edward [Physics Department, Auburn University, Alabama 36849-5311 (United States)

2011-11-15

349

NASA Astrophysics Data System (ADS)

In an effort to better understand the dynamics of westward velocities of the nocturnal F-region plasma, the climatology of the westward traveling plasma bubbles - WTB - occurring during quiettime is studied here. The climatology of the WTB is analyzed here based on airglow images obtained during 14 quiet days between 2001 and 2006 at the Brazilian station São João do Cariri (Geographic 7.45°S, 36.5°W, dip ˜20°S). The frequency of occurrence of the WTB maximizes in the descending phase of the solar cycle. The WTB velocities ranged between ˜20 and 40 ms-1. The frequency of occurrence had a peak value of only 3.65% at 2345 LT. The maximum occurrence of the WTB was in July-September. No WTB have been observed from November until April in all years 2001-2006. We show for the first time theoretically that the WTB dominant forcing mechanisms during geomagnetically quiet days are westward thermospheric winds.

Sobral, José H. A.; de Castilho, Vivian M.; Abdu, M. A.; Takahashi, Hisao; Paulino, I.; Gasparelo, Ulisses A. C.; Arruda, Daniela C. S.; Mascarenhas, Matheus; Zamlutti, C. J.; Denardini, C. M.; Koga, Daiki; de Medeiros, A. F.; Buriti, R. A.

2011-07-01

350

An unequal velocity model for transient two-phase flow by the method of characteristics

A six-equation model for a one-dimensional, transient, two-phase flow is briefly discussed, and the characteristic and compatibility equations are obtained by the method of characteristics. The equations consist of five conservation equations and a constitutive relative-velocity equation. The model equations constitute a well-posed initial value problem and have real characteristics in all flow regimes. The ordinary differential equations obtained are suitable for numerical applications, such as for blowdown analyses. The special case of an isothermal unequal velocity model is applied to the case of inflow of a liquid sodium-argon mixture into a horizontal pipe and to the case of pressure pulse propagation rate in an air-water system. The expected S-shaped curves are obtained for the volume fraction of liquid sodium. The numerical results for the pressure pulse propagation agree with experimental data at low-volume fractions.

Gidaspow, D.; Rasouli, F.; Shin, Y.W.

1983-07-01

351

Mapping high Pn velocity beneath the Colorado Plateau constrains uplift models

NASA Astrophysics Data System (ADS)

The massive International Seismological Centre data set of the past 20 years and the two-station method are used to determine Pn velocities in the mantle lid beneath the Colorado plateau. In this method the event is located at distances where Pn is the first arrival (2°-16°) and the path is in or very near the azimuth of the two-station pair and crosses the plateau. This technique to a large extent minimizes the hypocenter mislocation effect and possible errors due to variations in the crustal structure near the source, since only the difference in travel times at the two stations is used. However, this technique has a few underlying assumptions and possible sources of errors (such as the quality of the Pn data base and station delays caused by varying crustal structure) that require an extremely careful application of the method. A detailed study of the source of errors and a methodology of selection of the data are presented. Application of this method to the Colorado plateau using all possible two-station pairs from 53 stations located within or along the margin of the plateau yields an average high Pn velocity of 8.12±0.09 km/s. This value is considerably larger than the average value of 7.83 km/s based on available but very limited seismic refraction profiles but is remarkably similar to the average value of 8.1 km/s for the relatively stable midcontinent region. Our new Pn velocity for the Colorado plateau eliminates the paradox in the literature that emphasizes the rather close similarity between average Pn velocities beneath the Colorado plateau and the Basin and Range Province while their tectonic and magmatic Cenozoic history is dramatically different. Previous models for the structure and evolution of the plateau have used the low Pn velocity as an important constraint on density and thermal state of the lithosphere. Hence such models should be reexamined on the basis of this new uppermost mantle Pn velocity determination. There are two main models that have been proposed to explain the 2-km uplift of the Colorado plateau. One is based on a combination of thermal thinning of the lithosphere and crustal thickening, and the other involves a combination of the delamination of the subducted, subhorizontal Farallon oceanic plate from the overriding North American plate and crustal thickening. We show that the delamination model is more readily consistent not only with our velocity determination and the elevation of the plateau but also with varied geological observations reported in the literature that concern the Cenozoic evolution of western North America.

Beghoul, Noureddine; Barazangi, Muawia

1989-06-01

352

Time-dependent three dimensional P-wave velocity models derived for the Geysers geothermal field

NASA Astrophysics Data System (ADS)

The Geysers geothermal field is a source of significant small earthquake (M< 2.0) seismicity in northern California. The region has been actively monitored for seismicity, both natural and induced, since the geothermal field has been put into production. A modern digital seismic monitoring network in the area consists of 34 LBNL/Calpine (BG) borehole short-period and 12 Northern California Seismic Network (NCSN) network surface short-period seismic stations. The USGS has auto-located approximately 25,033 earthquakes (NCEDC catalog) for the years 2009 and 2010 combined from the composite seismic network. Using the auto-located solutions and a Geysers specific one-dimensional velocity model (Eberhart-Philips and Oppenheimer, 1984) as a starting point, we have simultaneously inverted for three dimensional P-wave velocities for each year's data set. Before beginning the inversion we established that the automatic S-phase picks were too unstable and thus focused only on the P-wave velocities. After culling events with initial RMS uncertainty greater than 0.06 seconds, we start with 7,403 earthquakes in 2009 and 11,199 earthquakes in 2010. The technique we use is a finite-difference travel time technique that Roecker et al. (Tectonophysics, 2006) used for the Parkfield SAFOD site. We will present the results of the simultaneous inversion for each of the 2009 and 2010 years along with plots of the seismicity relocated using these new velocity models.

Friberg, P. A.; Roecker, S. W.; Dricker, I. G.; Lisowski, S.; Hellman, S. B.

2011-12-01

353

Mass transfer systems based on electrokinetic phenomena (i.e., capillary electrochromatography (CEC)) have shown practical potential in becoming powerful separation methods for the biotechnology and pharmaceutical industries. A mathematical model has been constructed and solved to describe quantitatively the profiles of the electrostatic potential, pressure, and velocity of the electroosmotic flow (EOF) in charged cylindrical capillaries and in capillary columns packed

A. I. Liapis; B. A. Grimes

2000-01-01

354

NASA Astrophysics Data System (ADS)

Spatial gradients of tomographic velocities are seldom used in interpretation of subsurface fault structures. This study shows that spatial velocity gradients can be used effectively in identifying subsurface discontinuities in the horizontal and vertical directions. Three-dimensional velocity models constructed through tomographic inversion of active source and/or earthquake traveltime data are generally built from an initial 1-D velocity model that varies only with depth. Regularized tomographic inversion algorithms impose constraints on the roughness of the model that help to stabilize the inversion process. Final velocity models obtained from regularized tomographic inversions have smooth three-dimensional structures that are required by the data. Final velocity models are usually analyzed and interpreted either as a perturbation velocity model or as an absolute velocity model. Compared to perturbation velocity model, absolute velocity models have an advantage of providing constraints on lithology. Both velocity models lack the ability to provide sharp constraints on subsurface faults. An interpretational approach utilizing spatial velocity gradients applied to northern Cascadia shows that subsurface faults that are not clearly interpretable from velocity model plots can be identified by sharp contrasts in velocity gradient plots. This interpretation resulted in inferring the locations of the Tacoma, Seattle, Southern Whidbey Island, and Darrington Devil's Mountain faults much more clearly. The Coast Range Boundary fault, previously hypothesized on the basis of sedimentological and tectonic observations, is inferred clearly from the gradient plots. Many of the fault locations imaged from gradient data correlate with earthquake hypocenters, indicating their seismogenic nature.

Ramachandran, K.

2012-02-01

355

NASA Astrophysics Data System (ADS)

Spatial gradients of tomographic velocities are seldom used in interpretation of subsurface fault structures. This study shows that spatial velocity gradients can be used effectively in identifying subsurface discontinuities in the horizontal and vertical directions. Three-dimensional velocity models constructed through tomographic inversion of active source and/or earthquake traveltime data are generally built from an initial 1-D velocity model that varies only with depth. Regularized tomographic inversion algorithms impose constraints on the roughness of the model that help to stabilize the inversion process. Final velocity models obtained from regularized tomographic inversions have smooth three-dimensional structures that are required by the data. Final velocity models are usually analyzed and interpreted either as a perturbation velocity model or as an absolute velocity model. Compared to perturbation velocity model, absolute velocity model has an advantage of providing constraints on lithology. Both velocity models lack the ability to provide sharp constraints on subsurface faults. An interpretational approach utilizing spatial velocity gradients applied to northern Cascadia shows that subsurface faults that are not clearly interpretable from velocity model plots can be identified by sharp contrasts in velocity gradient plots. This interpretation resulted in inferring the locations of Tacoma Fault, Seattle Fault, Southern Whidbey Island Fault, and Darrington Devils Mountain fault much clearly. The Coast Range Boundary Fault, previously hypothesized on the basis of sedimentological and tectonic observations, is inferred clearly from the gradient plots. Many of the fault locations imaged from gradient data correlate with earthquake hypocenters indicating their seismogenic nature.

Ramachandran, K.

2011-09-01

356

NASA Astrophysics Data System (ADS)

The aim of this study is to quantify the relationship between the kinematics of subduction, deformation in the overriding plate and the evolution of slab geometry. A 2-D finite element numerical code is used, and a first objective consists in benchmarking previously published analogue models. Far-field plate velocities are applied, and once the subducting plate reaches the 660 km discontinuity, modelled as a rigid base, we obtain two different forms or styles of subduction that depend on the overriding plate velocity vop: if vop > 0, the slab lies forwards on the 660 km discontinuity (style 1), and if vop? 0, the slab lies backwards on the discontinuity (style 2). We also obtain a cyclic pattern with the slab folding on itself repeatedly when vsp > 0 and 2vop+vsp > 0 (where vsp is the subducting plate velocity). These conditions result from the analysis of several simulations in which the subduction velocities and plate viscosities are varied. When the slab periodically folds on the 660 km discontinuity, periods of shallow slab dip and compression in the overriding plate are followed by periods of slab steepening and relative extension in the overriding plate. Folding periodicity is controlled by the slab viscosity and subduction velocity. When a low-viscosity zone is included in the overriding plate, the trench motion is effectively decoupled from the overriding plate velocity, therefore allowing it to be directly controlled by the deep dynamics of the slab. For the cyclic style 2 corresponding to forward folding of the slab, the low-viscosity region in the overriding plate increases the stress amplitudes oscillations, the trench motion and the folding periodicity with time. Therefore the strength of the entire overriding plate is shown to directly control the dynamics of subduction. Using the Nazca and South American plate velocities we produce models of cyclic folding with a period of ca. 22 Ma and a minimal dip angle of ca. 10°. Episodic folding of the slab on the 660 km discontinuity would produce the necessary changes in slab dip and overriding plate deformation that explain episodes of volcanic quiescence alternating with greater rates of shortening along the Andes.

Gibert, G.; Gerbault, M.; Hassani, R.; Tric, E.

2012-05-01

357

Acoustic reconstruction of the velocity field in a furnace using a characteristic flow model.

An acoustic method can provide a noninvasive, efficient and full-field reconstruction of aerodynamic fields in a furnace. A simple yet reasonable model is devised for reconstruction of a velocity field in a cross section of a tangential furnace from acoustic measurements based on typical physical characteristics of the field. The solenoidal component of the velocity field is modeled by a curved surface, derived by rotating a curve of Gaussian distribution, determined by six characteristic parameters, while the nonrotational component is governed by a priori knowledge. Thus the inverse problem is translated into determination of the characteristic parameters using a set of acoustic projection data. First numerical experiments were undertaken to simulate the acoustic measurement, so as to preliminarily validate the effectiveness of the model. Based on this, physical experiments under different operating conditions were performed in a pilot-scale setup to provide a further test. Hot-wire anemometry and strip floating were applied to compare with acoustic measurements. The acoustic measurements provided satisfactory consistency with both of these approaches. Nevertheless, for a field with a relatively large magnitude of air velocities, the acoustic measurement can give more reliable reconstructions. Extension of the model to measurements of hot tangential furnaces is also discussed. PMID:22712914

Li, Yanqin; Zhou, Huaichun; Chen, Shiying; Zhang, Yindi; Wei, Xinli; Zhao, Jinhui

2012-06-01

358

Bayesian Assessment of Mean Velocity Profile Models in Wall-Bounded Turbulence

NASA Astrophysics Data System (ADS)

The form of the mean velocity profile in high-Reynolds-number wall-bounded turbulent shear flows has been the subject of renewed interest in recent years. A number of questions have been raised regarding the universality of the von Karman constant, the dependence of the over-lap layer on Reynolds number and even the appropriateness of a logarithmic description of the overlap layer. The questions have been difficult to resolve because the models predict subtle differences in the mean velocity profiles at finite Reynolds number. However, these subtle differences are important for scaling to very high Reynolds number and for inferring wall shear stress when direct measurements are not available. In this work, Bayesian inference is used to infer parameters (e.g. the Karman constant) and their uncertainty in a variety of turbulent mean velocity representations using experimental data over a wide range of Reynolds number. Moreover, an information theory-based multi-model formalism is used to rank competing models (e.g., the standard log and power laws and finite Reynolds number refinements of these profiles) by a metric that naturally balances data fit versus model complexity. This work is supported by the Department of Energy [National Nuclear Security Administration] under Award Number [DE-FC52-08NA28615].

Moser, Robert; Oliver, Todd

2010-11-01

359

The H_2O(+) Velocity Field in Comet Hale-Bopp, Observations and MHD Models

NASA Astrophysics Data System (ADS)

The 3.5-meter WIYN Telescope and its Multi-Object Spectrograph (MOS)obtained simultaneous spectra at many points in the coma of Comet Hale-Bopp between 1996 October and 1997 April. The "Hydra" fiber positioner was used to sample a ring pattern of points about the nucleus with a minimum spacing of 40 arc seconds and a maximum radius of 22.5 arc minutes. A integral field device called "Densepak" was also used to sample a 7 x 13 rectangular pattern of 91, 3 arc second fibers on 4 arc second centers. The bench spectrograph was used in the echelle mode with an interference filter to isolate a single order and covered the wavelength range from 6100 Angstroms to 6400 Angstroms with resolution of approximately 15,000. This spectral region contains the emission features of H_2O(+) . From these data we have extracted the radial velocity of the H_2O(+) . We find the acceleration in the anit-sun direction to be of the order of 20 cm sec(-) (2) . The measured velocity fields have been compared to full 3D MAUS-MHD models. The models suggest that the degree ofconfinement of the coma and the velocities attained in the anti-sun direction depend sensitively upon the velocity of the ambient solar wind. The observed velocity fields are consistent with the confinement of the near coma by a relatively slow solar wind while the speeds attained at distances of the order of a million kilometers in the anti-sun direction are more like those produced by a fast solar wind. The observations were obtained at a time when Hale-Bopp was at intermediate heliocentric latitudes where the solar wind speed is known to change rapidly from slow to fast modes. This situation is under further investigation.

Anderson, C. M.; Combi, M. R.; Gombosi, T.; Hansen, K. C.

1998-09-01

360

Model-based Estimation for Pose, Velocity of Projectile from Stereo Linear Array Image

NASA Astrophysics Data System (ADS)

The pose (position and attitude) and velocity of in-flight projectiles have major influence on the performance and accuracy. A cost-effective method for measuring the gun-boosted projectiles is proposed. The method adopts only one linear array image collected by the stereo vision system combining a digital line-scan camera and a mirror near the muzzle. From the projectile's stereo image, the motion parameters (pose and velocity) are acquired by using a model-based optimization algorithm. The algorithm achieves optimal estimation of the parameters by matching the stereo projection of the projectile and that of the same size 3D model. The speed and the AOA (angle of attack) could also be determined subsequently. Experiments are made to test the proposed method.

Zhao, Zhuxin; Wen, Gongjian; Zhang, Xing; Li, Deren

2012-01-01

361

We propose a way to introduce in microscopic pedestrian models a “social norm” in collision avoiding and overtaking, i.e. the tendency, shared by pedestrians belonging to the same culture, to avoid collisions and perform overtaking in a preferred direction. The “social norm” is implemented, regardless of the specific collision avoiding model, as a rotation in the perceived velocity vector of the opponent at the moment of computation of the collision avoiding strategy, and justified as an expectation that the opponent will follow the same “social norm” (for example a tendency to avoid on the left and overtake on the right, as proposed in this work for Japanese pedestrians). By comparing with real world data, we show that the introduction of this norm allows for a better reproduction of macroscopic pedestrian density and velocity patterns.

Zanlungo, Francesco; Ikeda, Tetsushi; Kanda, Takayuki

2012-01-01

362

Numerical Modelling of Glass Fibre Reinforced Laminates Subjected to a Low Velocity Impact

This paper presents a series of numerical predictions of the perforation behaviour of glass fibre laminates subjected to quasi-static and low-velocity impact loading. Both shear and tensile failure criteria were used in the finite element models to simulate the post-failure processes via an automatic element removal procedure. The appropriate material properties, obtained through a series of uniaxial tension and bending tests on the composites, were used in the numerical models. Four, eight and sixteen ply glass fibre laminates panels were perforated at quasi-static rates and under low-velocity impact loading. Reasonably good correlation was obtained between the numerical simulations and the experimental results, both in terms of the failure modes and the load-deflection relationships before and during the penetration phase. The predicted impact energies of the GFRP panels were compared with the experimental data and reasonable agreement was observed.

Fan, J. Y.; Guana, Z. W.; Cantwell, W. J. [University of Liverpool, Department of Engineering, Liverpool L69 3GQ (United Kingdom)

2010-05-21

363

A dynamic model for the turbulent burning velocity for large eddy simulation of premixed combustion

Turbulent premixed combustion is particularly difficult to describe using large eddy simulation (LES). In LES, premixed flame structures typically exist on subfilter length scales. Consequently, premixed LES models must be capable of describing how completely unresolved flame structures propagate under the influence of completely unresolved eddies. This description is usually accomplished through the implementation of a model for the turbulent burning velocity. Here, a dynamic model for describing the turbulent burning velocity in the context of LES is presented. This model uses a new surface filtering procedure that is consistent with standard LES filtering. Additionally, it only uses information that comes directly from the flame front. This latter attribute is important for two reasons. First, it guarantees that the model can be consistently applied when level set methods, where arbitrary constraints can be imposed on field variables away from fronts, are used to track the flame. Second, it forces the model to recognize that the physics governing flame front propagation are only valid locally at the front. Results showing model validation in the context of direct numerical simulation (DNS), and model application in the context of LES, are presented. (author)

Knudsen, E.; Pitsch, H. [Department of Mechanical Engineering, Stanford University, Stanford, CA 94305 (United States)

2008-09-15

364

Regional Crustal Velocity Models for Northern Arabian Platform and Turkish-Iranian Plateau

NASA Astrophysics Data System (ADS)

The geological structure of the Northern Arabian platform and surrounding mountains is dominated by the collision and suturing of the Arabian plate with the Eurasian plate and the formation of the Turkish-Iranian plateau. The structure of the Northern Arabian platform and surrounding region is poorly constrained. A recent deployment of 10 broadband seismometers in northern and central Iraq provides an opportunity to refine velocity models of the region. We have applied the Niching Genetic Algorithm waveform inversion technique to Rayleigh and Love waves traversing the Northern Arabian platform, the Zagros fold belt, the southern Turkish Plateau, the Iranian Plateau. Results show variations in crustal thickness and shear wave velocity between the Northern Arabian platform and the Turkish-Iranian plateau. In general the shear wave velocities are higher in the Northern Arabian platform than in the Plateaus. Variation of shear velocities within each of the provinces reflects the diversity in tectonic environment across the Zagros fold belt and the complex tectonic history of the region. Crustal thickness results show little crustal thickening has occurred due to collision.

Aleqabi, G.; Wysession, M.; Ghalib, H.

2008-12-01

365

NASA Astrophysics Data System (ADS)

Proper models of cell geometry are needed for biophysical analysis of cellular electrical phenomena. This work compares various mathematical volume-models for normal human erythrocytes (discocyte) possessing biconcave-discoid form to simulate translational dielectrophoretic velocity spectra of erythrocyte suspensions induced in a traveling electric field over a frequency range from 1 kHz to 15 MHz. The non-spherical volumes of the oblate-spheroid, the prolate-spheroid, and the oval of Cassini and the ``Bun-model'' were numerically evaluated according to the normal range of cellular dimension values for mammalian erythrocytes. The latter model is the novel approach derived to provide a more realistic model for the shape of discocytes in the thin biconcave-disc form with a toroidal rim. The bun model is also more rugged than the Cassini equation. Using the actual cell dimensions for calculations, the numerical results among these calculated cell volumes revealed large and significant differences with respect to the Bun-model of +32.09%, +8.95%, and -8.45% for prolate-spheroid, Cassini's equation, and oblate-spheroid, respectively. These large volume deviations shift the magnitude of the sharp peak in dielectrophoretic velocity spectra to lower values with differences of +189.28%, +7.66%, and -9.49%, respectively. For traveling wave dielectrophoresis, similar results were found for the sharp peak of +145.76%, +7.71%, and -9.50%, respectively. The suitability of the Bun-model was verified by curve-fitting of the cell velocity spectra between experimental and theoretical curves, which gave the maximum discrepancies of less than +/-10%.

Bunthawin, Sakshin; Ritchie, Raymond J.

2013-01-01

366

Density, Velocity, and Magnetic Field Structure in Turbulent Molecular Cloud Models

We use three-dimensional (3D) numerical magnetohydrodynamic simulations to follow the evolution of cold, turbulent, gaseous systems with parameters chosen to represent conditions in giant molecular clouds (GMCs). We present results of three model cloud simulations in which the mean magnetic field strength is varied (B0=1.4-14 muG for GMC parameters), but an identical initial turbulent velocity field is introduced. We describe

Eve C. Ostriker; James M. Stone; Charles F. Gammie

2001-01-01

367

Density, Velocity, and Magnetic Field Structure in Turbulent Molecular Cloud Models

We use 3D numerical MHD simulations to follow the evolution of cold,\\u000aturbulent, gaseous systems with parameters representing GMC conditions. We\\u000astudy three cloud simulations with varying mean magnetic fields, but identical\\u000ainitial velocity fields. We show that turbulent energy is reduced by a factor\\u000atwo after 0.4-0.8 flow crossing times (2-4 Myr), and that the magnetically\\u000asupercritical cloud models

Eve C. Ostriker; James M. Stone; Charles F. Gammie

2000-01-01

368

The viscous froth model: steady states and the high-velocity limit

The steady-state solutions of the Viscous Froth Model for foam dynamics are analyzed, and shown to be of finite extent or to asymptote to straight lines. In the high-velocity limi t the solutions consist of straight lines with isolated poin ts of infinite curvature. This analysis is helpful in the interp retation of observations of anomalous features of mobile two-dimensional

S. J. Cox; D. Weaire; G. Mishuris

2009-01-01

369

Space weather modelling with intelligent hybrid systems: Predicting the solar wind velocity

We are developing a space weather model to predict disturbances of the Earth's magnetosphere\\/ionosphere on four different time-scales: minutes, hours, 1–3 days, and 27 days. The minutes to hours predictions are made from solar-wind measurements, while predictions days in advance are made from solar observations.In this work we concentrate on predictions of solar wind velocities 3 days ahead. Using daily

P. Wintoft; H. Lundstedt

1998-01-01

370

The Bangong-Nujiang suture (BNS) belt separates the Lhasa and Qiangtang plates and, as indicated from previous teleseismic tomography, receiver functions, and active source seismic experiments, record the convergence and collision between the Indian and Eurasian plates. In this study, we construct a crustal composition model along the 400 km long NNW-SSE-oriented INDEPTH III profile by comparing the P-wave velocity (VP),

Xi Zhang; Dennis Brown; Yangfan Deng

2011-01-01

371

HIGH-RESOLUTION SEISMIC VELOCITY AND ATTENUATION MODELS OF THE CAUCASUS-CASPIAN REGION

The southwest edge of Eurasia is a tectonically and structurally complex region that includes the Caspian and Black Sea basins, the Caucasus Mountains, and the high plateaus south of the Caucasus. Using data from 25 broadband stations located in the region, new estimates of crustal and upper mantle thickness, velocity structure, and attenuation are being developed. Receiver functions have been determined for all stations. Depth to Moho is estimated using slant stacking of the receiver functions, forward modeling, and inversion. Moho depths along the Caspian and in the Kura Depression are in general poorly constrained using only receiver functions due to thick sedimentary basin sediments. The best fitting models suggest a low velocity upper crust with Moho depths ranging from 30 to 40 km. Crustal thicknesses increase in the Greater Caucasus with Moho depths of 40 to 50 km. Pronounced variations with azimuth of source are observed indicating 3D structural complexity and upper crustal velocities are higher than in the Kura Depression to the south. In the Lesser Caucasus, south and west of the Kura Depression, the crust is thicker (40 to 50 km) and upper crustal velocities are higher. Work is underway to refine these models with the event based surface wave dispersion and ambient noise correlation measurements from continuous data. Regional phase (Lg and Pg) attenuation models as well as blockage maps for Pn and Sn are being developed. Two methods are used to estimate Q: the two-station method to estimate inter-station Q and the reversed, two-station, two event method. The results are then inverted to create Lg and Pg Q maps. Initial results suggest substantial variations in both Pg and Lg Q in the region. A zone of higher Pg Q extends west from the Caspian between the Lesser and Greater Caucasus and a narrow area of higher Lg Q is observed.

Mellors, R; Gok, R; Pasyanos, M; Skobeltsyn, G; Teoman, U; Godoladze, T; Sandvol, E

2008-07-01

372

Alzheimer's disease (AD) is characterized by progressive cognitive deficits and synaptic dysfunction. Over the last decade phosphodiesterase inhibitors (PDEIs) have received increasing attention as putative cognition enhancers and have been suggested as a novel treatment strategy for AD. Given their ability to prevent hydrolysis of cAMP and/or cGMP, they can stimulate the cAMP/protein kinase A (PKA)/cAMP element-binding protein (CREB) and cGMP/PKG/CREB pathway to enhance synaptic transmission by increasing CREB phosphorylation (pCREB) and brain-derived neurotrophic factor (BDNF) transcription. Based on previous research, we hypothesized that chronic PDE2I treatment would improve AD-related cognitive deficits, by decreasing amyloid-? (A?) plaque load, enhancing pCREB and BDNF levels and increasing synaptic density in the hippocampus of 8-month-old APPswe/PS1dE9 mice. Results indicated that chronic PDE2I treatment could indeed improve memory performance in APPswe/PS1dE9 mice, without affecting anxiety, depressive-like behavior or hypothalamus-pituitary-adrenal axis regulation. However, no treatment effects were observed on A? plaque load, pCREB or BDNF concentrations, or presynaptic density in the hippocampus, suggesting that other signaling pathways and/or effector molecules might be responsible for its cognition-enhancing effects. Presynaptic density in the stratum lucidum of the CA3 subregion was significantly higher in APPswe/PS1dE9 mice compared to WT controls, possibly reflecting a compensatory mechanism. In conclusion, PDEs in general, and PDE2 specifically, could be considered as pro