Note: This page contains sample records for the topic 1-d velocity model from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

Minimum 1-D velocity model in Southeastern Sicily (Italy) from local earthquake data: an improvement in location accuracy  

Microsoft Academic Search

The monitoring of seismic activity inSoutheastern Sicily (Italy) has beenrecently improved by a digital seismicnetwork. This effort has produced ahomogeneous and complete dataset which weused to define a reference 1-D velocitymodel. We have inverted P- and S-wavearrival times from 51 selected localearthquakes by using several initialvelocity and layer thickness models. Then,the range of possible velocity modelsobtained was tested with earthquakelocations

Carla Musumeci; Giuseppe Di Grazia; Stefano Gresta

2003-01-01

2

1-D P- and S-wave velocity models for the collision zone between the northern Tianshan mountain and the Junggar basin based on local earthquake data  

NASA Astrophysics Data System (ADS)

We have developed crustal minimum 1-D P- and S-wave velocity models of the collision zone between the northern Tianshan mountain and the Junggar basin (86°E-89°E, 43°N-44.5°N). These two models were created through inversion of 1 370 P- and 1 396 S-wave travel times from 173 well-constrained local earthquakes recorded by the Ürümqi sparse local seismic network and temporary seismic arrays. In contrast to previous models, our results indicate relatively low velocity at both shallow (<10 km) and deep (30-45 km) depths. The shallow zone is interpreted to be the result of thick surficial sedimentary deposits, whereas the deeper anomaly is interpreted to result from ductile shearing and lower crustal flow. Additionally, we detected several transition layers under the lower crust, which may imply structural complexity of the uppermost mantle in this region. The improved models reduce the RMS residual of earthquake locations by 41.7% from 1.2 to 0.5 seconds. The more accurately located hypocenters appear to correlate with prominent local over-thrusts, which underlie an anticlinal fold belt and several blind faults. Positive station corrections are observed near the Junggar basin, which likely reflects low wave velocity; negative corrections near the Tianshan mountain and Bogda mountain suggest high wave velocity.

Sun, Anhui; Sun, Youshun; Zhang, Haijiang; Yu, Diming

2012-12-01

3

1D Seismic Velocity Model with GT5 Events in Brazil and Tests of Crustal Thickness Corrections to Improve the RSTT Model for South America  

NASA Astrophysics Data System (ADS)

A set of 17 reference events, in the magnitude range 4.0 to 5.1 mb, with well determined epicenters in Brazil, were compiled and used to test different velocity models. Only four were truly GT5 events determined by local networks. Most of the reference events had the epicenter assigned to the middle of the aftershock zone determined by aftershock studies, or by detailed macroseismic surveys. The origin times of these "pseudo GT5" events were calculated with the IASP91 table using teleseismic stations (more than 30 degrees distance), which are less affected by large lithospheric heterogeneities. The travel times of the reference events were corrected for event depths, to normalize to surface focus, and compared with the three 1D models: IASP91, Herrin1968, and the Brazilian model NewBR, as well as with the current 3D RSTT model, which is basically CRUST2.0 in South America. The average residual, up to 1640km, was found to be -2.6s ± 1.9s (IASP91), -1.9s ± 1.7s (Herrin1968), and 0.4 ± 1.5s (NewBR). Correction for crustal thicknesses were applied, using the model of Assumpcao et al.(2012), to normalize all travel times to a 40 km standard continental crust. The average residuals changed very little and were -2.2s ± 1.9s (IASP91), -1.4s ± 1.6s (Herrin1968), and 0.8 ± 1.3s (NewBR). The raw travel times (uncorrected for event depth and crustal thickness) were compared with the current RSTT model givine average residuals of +0.2s ± 1.3s, the smallest of all models. We conclude that crustal thickness corrections, while necessary, have limited impact in reducing the scatter in travel time residuals, and that upper mantle heterogeneities (as imbedded in the RSTT 3D model) is the most important factor to improve regional travel times in Brazil.

Assumpcao, M.; Marco, E.; Barbosa, J.

2013-05-01

4

Effects of 1-D versus 3-D velocity models on moment tensor inversion in the Dobrá Voda area in the Little Carpathians region, Slovakia  

NASA Astrophysics Data System (ADS)

Retrieving the parameters of a seismic source from seismograms involves deconvolving the response of the medium from seismic records. Thus, in general, source parameters are determined from both seismograms and the Green functions describing the properties of the medium in which the earthquake focus is buried. The quality of each of these two datasets is equally significant for the successful determination of source characteristics. As a rule, both sets are subject to contamination by effects that decrease the resolution of the source parameters. Seismic records are generally contaminated by noise that appears as a spurious signal unrelated to the source. Since an improper model of the medium is quite often employed, due to poor knowledge of the seismic velocity of the area under study, and since the hypocentre may be mislocated, the Green functions are not without fault. Thus, structures not modelled by Green functions are assigned to the source, distorting the source mechanism. To demonstrate these effects, we performed a synthetic case study by simulating seismic observations in the Dobrá Voda area of the Little Carpathians region of Slovakia. Simplified 1-D and 3-D laterally inhomogeneous structural models were constructed, and synthetic data were calculated using the 3-D model. Both models were employed during a moment tensor inversion. The synthetic data were contaminated by random noise up to 10 and 20 % of the maximum signal amplitude. We compared the influence of these two effects on retrieving moment tensors, and determined that a poor structural model can be compensated for by high-quality data; and that, in a similar manner, a lack of data can be compensated for by a detailed model of the medium. For examples, five local events from the Dobrá Voda area were processed.

Jechumtálová, Zuzana; Bulant, Petr

2014-07-01

5

Variable Selection for 1D Regression Models  

Microsoft Academic Search

Variable selection, the search for j relevant predictor variables from a group of p candidates, is a standard problem in regression analysis. The class of 1D regression models is a broad class that includes generalized linear models. We show that existing variable selection algorithms, originally meant for multiple linear regression and based on ordinary least squares and Mallows' Cp, can

David J. Olive; Douglas M Hawkins

2005-01-01

6

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

7

A 1-D morphodynamic model for rill erosion  

NASA Astrophysics Data System (ADS)

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 of an enhanced TVD-MacCormack scheme with implementation of Tseng's surface gradient method, to provide an oscillation free solution over formed pool crests. The model at the end of each time step calculates the flow depth, velocity, and bed shear stress and provides changes in bed elevation and grain size distribution within a cell. The hydrodynamic performance of RILL1D is evaluated by comparing its results with either analytical solutions or experimental observations from various benchmark tests with rigid bed conditions that include (1) formation of a hydraulic jump in a rectangular channel, (2) steady subcritical and transcritical flow (without a shock) over a hump, (3) formation of a hydraulic jump in a converging-diverging frictionless channel, and (4) flows over step-pools. It is shown that the enhanced TVD-MacCormack scheme adequately simulates transcritical flows by preserving the mass conservation and reducing the artificial numerical error. The scheme also approximates satisfactorily depth and velocity for a single rill, with a fixed bed consisting of steps and pools, except near the pool headwalls where a backroller forms with negative velocities. The sediment component of RILL1D is evaluated by two field investigations of single rills with mobile beds. With the field data the code is tested for its ability to reproduce measured values of sediment transport rates. A sensitivity analysis is performed to assess the effects of cell size and critical erosional strength in the predictive ability of the model. RILL1D performs reasonably well in these simulations in terms of sediment prediction rates and fared adequately in terms of replicating rill bed morphology.

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

2010-09-01

8

Evaluating 1d Seismic Models of the Lunar Interior  

NASA Astrophysics Data System (ADS)

A four station seismic network was established on the Moon from 1969 to 1977 as part of the Apollo Lunar Surface Experiment Package (ALSEP). A total of nine 1D seismic velocity models were generated using a variety of different techniques. In spite of the fact that these models were generated from the same data set, significant differences exist between them. We evaluate these models by comparing predicted travel-times to published catalogs of lunar events. We generate synthetic waveform predictions for 1D lunar models using a modified version of the Green's Function of the Earth by Minor Integration (GEMINI) technique. Our results demonstrate that the mean square errors between predicted and measured P-wave travel times are smaller than those for S-wave travel times in all cases. Moreover, models fit travel times for artificial and meteoroid impacts better than for shallow and deep moonquakes. Overall, models presented by Nakamura [Nakamura, 1983] and Garcia et al. [Garcia et al., 2011] predicted the observed travel times better than all other models and were comparable in their explanation of travel-times. Nevertheless, significant waveform differences exist between these models. In particular, the seismic velocity structure of the lunar crust and regolith strongly affect the waveform characteristics predicted by these models. Further complexity is added by possible mantle discontinuity structure that exists in a subset of these models. We show synthetic waveform predictions for these models demonstrating the role that crustal structure has in generating long duration seismic coda inherent in the lunar waveforms.

Yao, Y.; Thorne, M. S.; Weber, R. C.; Schmerr, N. C.

2012-12-01

9

1D + 1D model of a DMFC: localized solutions and mixedpotential  

Microsoft Academic Search

Our 1D+1D model of DMFC reveals a new effect. At infinitely small total current in the cell, near the channel inlet forms a “bridge”, a narrow region with finite local current density. The bridge short-circuits the electrodes, thus reducing cell open-circuit voltage. In our previous work the effect is described for the case of equal methanol ?a and oxygen ?c

A. A. Kulikovsky

2004-01-01

10

Spectral problems for the discrete velocity models  

NASA Astrophysics Data System (ADS)

We use the discrete velocity models to study the spectral problems related to the 1D plane wave propagation in monatomic gases which are fundamental in the rarefied gases dynamics and nonequilibrium statistical thermodynamics. The results show that 6- and 8-velocity models can only capture the propagation of diffusion mode (entropy wave) in the intermediate Knudsen number regime. 4-velocity model instead captures the propagation of sound mode quite well after the comparison with the continuum-mechanic results.

Kwang-Hua Chu, Aq

1999-07-01

11

Velocity Relaxation of S(1D) by Rare Gases Measured by Doppler Spectroscopy. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

Velocity relaxation of S(1D) by He, Ar, and Xe has been monitored by measuring the Doppler profile of the S(1D) for variable collision partner pressures at a fixed time delay following creation of S(1D) by pulsed laser photolysis of OCS at 222 nm. The nas...

G. Nan P. L. Houston

1992-01-01

12

Ion Cyclotron Waves at Io: 1D Hybrid Modeling  

NASA Astrophysics Data System (ADS)

On Galileo close flybys of Io (1995-2001), the magnetometers detected ElectroMagnetic Ion Cyclotron (EMIC) waves close to the S, O, SO2 and SO ion gyrofrequencies. These waves are produced when the phase-space distribution function of a minor ion species of the torus is non-Maxwellian, as for instance, the result of a pickup of new ions from Io's neutral corona. They were detected far from Io (~ 10-20 Rio), mainly downstream of the moon, and are powerful diagnostic tools for probing Io's extended atmosphere. We investigate the production of EMIC waves with a 1D hybrid model (fluid electrons and kinetic ions). These 1D simulations represent the lifetime of a field line that is entrained around Io by the plasma flow and experiences a variable mass loading of new ions of different composition when the field line interacts with Io's neutral atmosphere. The time-variable mass loading of this field line is based on former simulations of the multi-species chemistry modeling of Io's interaction (Dols et al., 2008), coupled with a MHD modeling of the local electromagnetic interaction (Dols et al., 2011; 2012): a multi-component neutral atmosphere of Io is prescribed in S, O, SO2 and SO; the flow of the plasma is calculated with a MHD model; the mass loading rate of these ions is calculated for different flow lines around Io that follow the MHD flow. These time dependent multi-ion massloading rates and flow velocities are used as inputs to the 1D hybrid simulation. We then make a Fourier analysis of the hybrid-calculated magnetic field variations close to Galileo trajectories, evaluate the power and the resonant frequencies of the EMIC waves and compare to the Galileo magnetometer data. The ultimate goal of the EMIC analysis is to constrain Io's neutral corona, its longitudinal asymmetries and its time variability.

Dols, V. J.; Delamere, P. A.; Bagenal, F.

2012-12-01

13

High velocity lines due to interaction between Type Ia supernova ejecta and a circumstellar shell: 1-D simulations  

NASA Astrophysics Data System (ADS)

Observations of Type Ia supernovae (SN Ia) have shown the presence of Ca, Si, and Fe features with velocities of 8,000-14,000 km/s higher than that associated with the photosphere of the supernova ejecta. Some studies have suggested the high velocity lines could be explained by interaction of the ejecta with a circumstellar medium (CSM). Using FLASH, we perform 1-D hydrodynamic simulation of interaction between the ejecta and a 2×10^{-2} M_? circumstellar shell of solar abundance. We use the Sobolev approximation to estimate the line optical depths as a function of time and position. The results of our simulation show two line generating regions: within the ejecta, and within the fast moving shell. The velocity separation between the line generating regions are consistent with the values observed in actual SN Ia, lending credence to the CSM shell model.

Mulligan, Brian W.; Wheeler, J. C.

2014-01-01

14

Modeling an electric motor in 1-D  

NASA Technical Reports Server (NTRS)

Quite often the dynamicist will be faced with having an electric drive motor as a link in the elastic path of a structure such that the motor's characteristics must be taken into account to properly represent the dynamics of the primary structure. He does not want to model it so accurately that he could get detailed stress and displacements in the motor proper, but just sufficiently to represent its inertia loading and elastic behavior from its mounting bolts to its drive coupling. Described here is how the rotor and stator of such a motor can be adequately modeled as a colinear pair of beams.

Butler, Thomas G.

1991-01-01

15

Modeling Undertow Velocities  

NASA Astrophysics Data System (ADS)

The paper will present a theoretical model for the prediction of undertow velocity profiles in the surf zone due to near-normally incident waves. The waves may be periodic or narrow-banded random waves, and the beach may be plane or barred. The theoretical model consists of three components: (i) breaking wave model; (ii) surface roller model; and (iii) undertow velocity profile model. \\textit{The breaking wave model} (Tajima and Madsen, 2002) is based on the concept of an equivalent linear wave and predicts linear wave characteristics for shoaling, breaking and broken waves. Non-linear wave characteristics, e.g., near-bottom orbital velocity, are obtained from equivalent linear wave characteristics and local bottom slope through use of simple transform formulae. \\textit{The surface roller model} is based on the same principle as Dally et al. (1985), but differs from this by transferring only the potential energy lost from the wave motion into the surface roller and calculating the decay of surface roller energy using a decay coefficient equal to that obtained for the breaking wave dissipation model. \\textit{The undertow velocity profile model} assumes a linearly varying shear stress over the water depth combined with an assumed form of the turbulent eddy viscosity. The shear stress at the surface is obtained from the breaking wave and surface roller models, whereas the bottom shear stress is obtained from considerations of mass conservation, i.e., depth-integrated undertow velocity must equal the volume transport of waves and surface roller above trough level. The near-bottom undertow velocity is calculated at the edge of the wave-bottom boundary layer, from knowledge of near-bottom orbital velocity, bottom shear stress and bottom roughness, using the combined wave-current bottom boundary layer theory by Madsen (1994). Comparison of predicted and measured undertow velocity profiles are performed for periodic and random waves normally incident on plane and barred concrete beaches as well as random waves near-normally incident on barred movable bed beach profiles. In general the agreement between predicted and observed undertow velocities is excellent. It is shown that model predictions are fairly insensitive to the choice of turbulent eddy viscosity, which is the only adjustable quantity in the model.

Tajima, Y.; Madsen, O. S.

2002-12-01

16

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

17

Lifting the Seismic Lid Beneath Cameroon Volcanic Line Using 1D Shear Wave Velocities  

NASA Astrophysics Data System (ADS)

The composition of the lithosphere beneath Cameroon and the origin of the Cameroon Volcanic Line (CVL) is a matter of debate. Although many studies based on regional or global observations provide models for the setting of the CVL, none of them are strong enough to be considered as definitive. We used the joint inversion of Rayleigh wave group velocities and Rayleigh wave group velocities to derive shear wave velocity profiles of the lithosphere beneath Cameroon andshow that lithosphere is, on average, faster beneath the Congo Craton than beneath the Pan-African age crust. Using recently published dispersion curves, we extend the depth of investigation from 60 to 200 km. The calculated velocity-depth profiles do not show any sharp discontinuity that could be interpreted as the lithosphere-asthenosphere transition. Furthermore, there is no clear evidence of the existence of a low velocity zone beneath any geologic province within Cameroon. The smooth velocity variations observed on the velocity models are believed to be influenced by lateral mantle heterogeneities rather than vertical ones. The shear wave velocities for the uppermost mantle are in general greater than 4.3 km/s at all stations. This is higher than the values obtained in the Main Ethiopian Rift, and suggest that the perturbation of the by thermal anomalies does not extend as far as the CVL. This suggests that the source of volcanism along the CVL is from small scale convection in the asthenosphere and controlled by lithospheric fractures that are probably driven by the cold (and fast) edge of the Congo Craton.

Tokam Kamga, Alain; Durrheim, Ray; Tabod, Charles; Nyblade, Andrew; Nguiya, Severin

2014-05-01

18

GIS-BASED 1-D DIFFUSIVE WAVE OVERLAND FLOW MODEL  

SciTech Connect

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

19

Ion velocity distribution at the termination shock: 1-D PIC simulation  

NASA Astrophysics Data System (ADS)

The Voyager 2 (V2) plasma observations of the proton temperature downstream of the quasi-perpendicular heliospheric termination shock (TS) showed that upstream thermal solar wind ions played little role in the shock dissipation mechanism and their downstream temperature is an order of magnitude smaller than predicted by MHD Rankine-Hugoniot conditions. While pickup ions (PUI) are generally expected to play an important role in energy dissipation at the shock, the details remain unclear. Here, one-dimensional (1-D) Particle-in-cell (PIC) code is used to examine kinetic properties and downstream velocity distribution functions of pickup ions (the hot supra-thermal component) and solar wind protons (SWs, the cold component) at the perpendicular heliospheric termination shock. The code treats the pickup ions self-consistently as a third component. Present results show that: (1) both of the incident SWs and PUIs can be separated into two parts: reflected (R) ions and directly transmitted (DT) ions, the energy gain of the R ions at the shock front is much larger than that of the DT ions; (2) the fraction of reflected SWs and their downstream temperature decrease with the relative percentage PUI% (3) no matter how large the PUI% is, the downstream ion velocity distribution function always can be separated into three parts: 1. a high energy tail (i.e. the wings) dominated by the reflected PUIs, 2. a low energy core mainly contributed by the directly transmitted SWs, and 3. a middle energy part which is a complicated superposition of reflected SWs and directly transmitted PUIs. The significance of the presence of pickup ions on shock front micro-structure and nonstationarity is also discussed.

Lu, Quanming; Yang, Zhongwei; Lembège, Bertrand

2012-11-01

20

Ion velocity distribution at the termination shock: 1-D PIC simulation  

SciTech Connect

The Voyager 2 (V2) plasma observations of the proton temperature downstream of the quasi-perpendicular heliospheric termination shock (TS) showed that upstream thermal solar wind ions played little role in the shock dissipation mechanism and their downstream temperature is an order of magnitude smaller than predicted by MHD Rankine-Hugoniot conditions. While pickup ions (PUI) are generally expected to play an important role in energy dissipation at the shock, the details remain unclear. Here, one-dimensional (1-D) Particle-in-cell (PIC) code is used to examine kinetic properties and downstream velocity distribution functions of pickup ions (the hot supra-thermal component) and solar wind protons (SWs, the cold component) at the perpendicular heliospheric termination shock. The code treats the pickup ions self-consistently as a third component. Present results show that: (1) both of the incident SWs and PUIs can be separated into two parts: reflected (R) ions and directly transmitted (DT) ions, the energy gain of the R ions at the shock front is much larger than that of the DT ions; (2) the fraction of reflected SWs and their downstream temperature decrease with the relative percentage PUI%; (3) no matter how large the PUI% is, the downstream ion velocity distribution function always can be separated into three parts: 1. a high energy tail (i.e. the wings) dominated by the reflected PUIs, 2. a low energy core mainly contributed by the directly transmitted SWs, and 3. a middle energy part which is a complicated superposition of reflected SWs and directly transmitted PUIs. The significance of the presence of pickup ions on shock front micro-structure and nonstationarity is also discussed.

Lu Quanming; Yang Zhongwei; Lembege, Bertrand [CAS Key Laboratory of Basic Plasma Physics, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026 (China); SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai 200136 (China); LATMOS-UVSQ-IPSL-CNRS, Guyancourt 78280 (France)

2012-11-20

21

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

22

Electronic properties of the 1D Frenkel-Kontorova model.  

PubMed

The energy spectra and quantum diffusion of an electron in a 1D incommensurate Frenkel-Kontorova model are studied numerically. We found that the spectral and dynamical properties of an electron display quite different behaviors in the invariance circle regime and in the Cantorus regime. In the former case, it is similar to that of the Harper model, whereas in the latter case, it is similar to that of the Fibonacci model. The relationship between spectral and transport properties is discussed. PMID:11801152

Tong, Peiqing; Li, Baowen; Hu, Bambi

2002-01-28

23

Velocity distributions in glottal models.  

PubMed

Velocity distributions within three models of the human larynx, namely, a rigid plexiglas model, an excised canine larynx, and a computational model are investigated with experimental and theoretical analyses. A plexiglas wind tunnel with interchangeable glottal constrictions was used as a two-dimensional steady-flow model to measure velocity and pressure for various glottal shapes. A canine excised larynx was used as a prototype pulsatile flow model to study pressure and velocity variations during phonation. Results of the plexiglas modelling indicated a parabolic laminar velocity profiles upstream of the glottal constriction and turbulent and asymmetric velocity profile downstream of the glottal constriction. The time-averaged velocities of the excised larynx had similarities with the plexiglas model results, and instabilities and asymmetries were also demonstrated by the computational method. PMID:8653178

Alipour, F; Scherer, R; Knowles, J

1996-03-01

24

Data Analysis of cGPS stations in central Greece: station velocities and 1-D strain estimates  

NASA Astrophysics Data System (ADS)

We processed 30-s GPS data from permanent GNSS stations in central Greece, available at NOA since 2006. We obtained position time series along with horizontal and vertical velocities using the Kalman filtering approach and accounting for time-correlated noise content. The station distribution allowed us to draw velocity profiles and to calculate rates of baseline length change (1-D strain). In central Greece, the coherent picture of the velocity pattern for Attica and north-eastern Peloponnese (Corinth) stations (effectively a velocity "plateau" at 30 mm/yr) indicates that these areas belong to the same crustal block, although some internal strain is present within Attica's crust as well as across the Saronic Gulf. Our 1-D strain estimates are in general agreement with geological data (fault slip rates) in central Greece, implying accommodation of this crustal extension along E-W striking active normal faults. Some NE-SW directed shortening is mapped in the wider area to the west of the termination of the North Anatolian Fault (Sporades islands).

Ganas, Athanassios; Chousianitis, Konstantinos; Gianniou, Michalis

2013-04-01

25

Frictional response to velocity steps and 1-D fault nucleation under a state evolution law with stressing-rate dependence  

NASA Astrophysics Data System (ADS)

A new state evolution law has recently been proposed by Nagata et al. (2012) that includes a dependence upon stressing rate through a laboratory derived proportionality constant c. It has been claimed that this law, while retaining the time-dependent healing of the Dieterich (or Aging) law, can also match the symmetric response of the Ruina (or Slip) law to velocity step tests. We show through analytical approximations and numerical results that the new law transitions between the responses of the traditional Aging and Slip laws in velocity step-up/step-down experiments when the value of c is tuned properly. Particularly, for c=0, the response is pure Aging, while for finite, nonzero c one observes Slip law type behavior for small velocity jumps but Aging law type response for larger jumps. The magnitude of the velocity jump required to see this transition between aging and slip behaviors increases as c increases. In the limit of c?1 the response becomes purely Slip law type for all geologically plausible velocity jumps. We also present results from detailed analytical and numerical studies of the mechanism of rupture nucleation on 1-D faults under this new state evolution law to demonstrate that the style of nucleation can also be made to switch from Aging-type (expanding cracks) to Slip-type (slip pulses) by adjusting the value of c as indicated by the velocity step results.

Bhattacharya, P.; Rubin, A. M.

2014-03-01

26

1D Multiphase Modeling of Chemistry Over Remote Ice Sheets  

NASA Astrophysics Data System (ADS)

Motivated by observations of reactive nitrogen and halogen chemistry over the Greenland ice sheet we have developed a 1D model for snow physics and chemistry. This model has been coupled to the boundary layer model MISTRA, which includes detailed multiphase chemistry in the atmosphere. The goal of our project was to provide a framework to quantify the chemistry in the interstitial air and to study the interplay between the chemistry in and above the snow. The methodology for modeling the multiphase in-snow chemistry will be presented along with results from the model, including vertical profiles of ozone, NOx, and halogens in the snow pack and in the atmosphere. Gas-phase and aqueous phase chemical processes controlling these species in snow covered regions are analyzed and the implications for modeling NOx and ozone fluxes over remote ice sheets will be discussed. Model data will be presented in the context of past and ongoing field campaigns at Summit Research Station. The needs for future research on interstitial air gas transport and ice chemistry will be highlighted.

Thomas, J. L.; Stutz, J.; von Glasow, R.

2009-12-01

27

Lanczos diagonalizations of the 1-D Peierls-Hubbard model  

SciTech Connect

In studies of interacting electrons in reduced dimensions'' one is trapped between the Scylla of exponential growth of the number of states in any exact many-body basis and the Charybdis of the failure of mean-field theories to capture adequately the effects of interactions. In the present article we focus on one technique -- the Lanczos method -- which, at least in the case of the 1-D Peierls-Hubbard model, appears to allow us to sail the narrow channel between these two hazards. In contrast to Quantum Monte Carlo methods, which circumvent the exponential growth of states by statistical techniques and importance sampling, the Lanczos approach attacks this problem head-on by diagonalizing the full Hamiltonian. Given the restrictions of present computers, this approach is thus limited to studying finite clusters of roughly 12--14 sites. Fortunately, in one dimension, such clusters are usually sufficient for extracting many of the properties of the infinite system provided that one makes full use of the ability to vary the boundary conditions. In this article we shall apply the Lanczos methodology and novel phase randomization'' techniques to study the 1-D Peierls-Hubbard model, with particular emphasis on the optical absorption properties, including the spectrum of absorptions as a function of photon energy. Despite the discreteness of the eigenstates in our finite clusters, we are able to obtain optical spectra that, in cases where independent tests can be made, agree well with the known exact results for the infinite system. Thus we feel that this combination of techniques represents an important and viable means of studying many interesting novel materials involving strongly correlated electrons. 26 refs., 6 figs.

Loh, E.Y.; Campbell, D.K.; Gammel, J.T.

1989-01-01

28

Flooding flows in city crossroads: experiments and 1-D modelling.  

PubMed

This study focuses on the discharge distribution in an intersection of four channels, similar to a city crossroad. The channels and the intersection are all horizontal. Flow enters through two of the channels, and leaves through the other two. The flow is subcritical everywhere, and flow depths are controlled by vertical weirs at the exits of the outlet channels. The main variables that are measured are the flow rates in the four channels. When the weir heights in the outlet channels are the same, the ratio of flow rates in the outlet channels depends only on the ratio of flow rates in the inlet channels; if the outlet conditions are different, other parameters, such as the total flow rate also become important. The flow has also been simulated numerically using a solution of the 1-D Saint Venant equations, with a simple model to predict flow distribution in the intersection. A comparison with the experimental data shows that this model works well for the limited range of experimental conditions studied here. However, further work is needed on a wider range of conditions, closer to real conditions, before the model can be considered valid for practical applications. PMID:17120636

Rivière, N; Perkins, R J; Chocat, B; Lecus, A

2006-01-01

29

Spin-charge separation in the 1D Hubbard model  

NASA Astrophysics Data System (ADS)

We demonstrate that the Configuration Interaction (CI) Approximation recaptures essential features of the exact solution of the 1D Hubbard model. The CI method systematically describes fluctuation and quantum tunneling corrections to the Hartree-Fock Approximation (HFA). HFA predicts that doping a half-filled Hubbard chain leads to the appearance of charged spin-polarons or charged domain-wall solitons in the antiferromagnetic (AFM) background. The CI method describes the quantum dynamics of these charged magnetic solitons. We test the accuracy of the CI method against the exact solution of the one-dimensional Hubbard model. We find remarkable agreement between the energy of the mobile charged bosonic domain-wall (as given by the CI method) and the exact energy of the doping hole (as given by the Bethe Ansatz) for the entire U/t range. The CI method also leads to a clear demonstration of the spin-charge separation. Addition of one doping hole to the half-filled antiferromagnetic chain results in the appearance of two different carriers: a charged bosonic domain-wall (which carries the charge but no spin) and a neutral spin-1/2 domain wall (which carries the spin but no charge).

Berciu, Mona; John, Sajeev

2000-03-01

30

Normal Modes on 1D Diatomic Lattice Model  

NSDL National Science Digital Library

The Normal Modes on 1D Diatomic Lattice Model shows the motion and the dispersion relation of N diatomic unit cells. Ionic vibrations in a crystal lattice form the basis for understanding many thermal properties found in materials. These vibrations are described as displacement waves traveling through the lattice. These vibrational modes can also be described as bosonic particles called phonons which have quantized energy in much the same way photons do for light. Using a spring model for the inter-ionic interactions, the dispersion relations between the vibrational frequencies and the allowed wave vectors can be analytically solved for the simple one dimensional case with a two atom basis. It is sometimes difficult for students to visualize these modes of vibration and how they relate to the resulting ionic motions in the underlying crystal lattice. This simulation facilitates the understanding of the analytical solutions by graphically representing these modes. The analytical forms of the two dispersion relations (the optical and acoustic branches) are shown along with the allowed normal mode points. Based on the chosen normal mode, the motion of the ions as a function of time is displayed to help visualize the mode. It is easy to see how the chosen mode affects the ion motions inside a unit cell as well as the motions from unit cell to unit cell. Also, the optical and acoustic motions can be readily compared. This model was developed by Richard Charles Andrew using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the jar file will run the program if Java is installed.

Andrew, Richard C.

2013-10-14

31

On Verification of the Deep Velocity Structure of the Kanto Basin inverted from H/V-spectra using 1-D Simulation of Long-period S-waves  

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

32

1-D closure models for slender 3-D viscoelastic free jets: von Karman flow geometry and elliptical cross section  

SciTech Connect

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

33

A One-Dimensional (1-D) Three-Region Model for a Bubbling Fluidized-Bed Adsorber  

SciTech Connect

A general one-dimensional (1-D), three-region model for a bubbling fluidized-bed adsorber with internal heat exchangers has been developed. The model can predict the hydrodynamics of the bed and provides axial profiles for all temperatures, concentrations, and velocities. The model is computationally fast and flexible and allows for any system of adsorption and desorption reactions to be modeled, making the model applicable to any adsorption process. The model has been implemented in both gPROMS and Aspen Custom Modeler, and the behavior of the model has been verified.

Lee, Andrew; Miller, David C.

2012-01-01

34

Generation of a pseudo-2D shear-wave velocity section by inversion of a series of 1D dispersion curves  

USGS Publications Warehouse

Multichannel Analysis of Surface Waves utilizes a multichannel recording system to estimate near-surface shear (S)-wave velocities from high-frequency Rayleigh waves. A pseudo-2D S-wave velocity (vS) section is constructed by aligning 1D models at the midpoint of each receiver spread and using a spatial interpolation scheme. The horizontal resolution of the section is therefore most influenced by the receiver spread length and the source interval. The receiver spread length sets the theoretical lower limit and any vS structure with its lateral dimension smaller than this length will not be properly resolved in the final vS section. A source interval smaller than the spread length will not improve the horizontal resolution because spatial smearing has already been introduced by the receiver spread. In this paper, we first analyze the horizontal resolution of a pair of synthetic traces. Resolution analysis shows that (1) a pair of traces with a smaller receiver spacing achieves higher horizontal resolution of inverted S-wave velocities but results in a larger relative error; (2) the relative error of the phase velocity at a high frequency is smaller than at a low frequency; and (3) a relative error of the inverted S-wave velocity is affected by the signal-to-noise ratio of data. These results provide us with a guideline to balance the trade-off between receiver spacing (horizontal resolution) and accuracy of the inverted S-wave velocity. We then present a scheme to generate a pseudo-2D S-wave velocity section with high horizontal resolution using multichannel records by inverting high-frequency surface-wave dispersion curves calculated through cross-correlation combined with a phase-shift scanning method. This method chooses only a pair of consecutive traces within a shot gather to calculate a dispersion curve. We finally invert surface-wave dispersion curves of synthetic and real-world data. Inversion results of both synthetic and real-world data demonstrate that inverting high-frequency surface-wave dispersion curves - by a pair of traces through cross-correlation with phase-shift scanning method and with the damped least-square method and the singular-value decomposition technique - can feasibly achieve a reliable pseudo-2D S-wave velocity section with relatively high horizontal resolution. ?? 2008 Elsevier B.V. All rights reserved.

Luo, Y.; Xia, J.; Liu, J.; Xu, Y.; Liu, Q.

2008-01-01

35

1D internal structure models of the Moon: the best way to the core?  

NASA Astrophysics Data System (ADS)

Despite recent attempts, the size, state and internal structure of the lunar core remains poorly constrained. The most successful approach to constraint the deep interior structure of the planets is to fit both geodetic and seismic data with consistent 1D internal structure models including seismic velocities and density. We demonstrate that for such models, global geodetic parameters, such as mass, moment of inertia and love numbers, constrain poorly the core size and state. Moreover, the mass and moment of inertia budgets create correlations betwen crust and core density structures. Another source of information comes from the deviations from cassini spin state and the magnetic induction of the lunar core that provides independent constraints on the lunar core size and state. However, seismology remains the best tool to constrain the deep internal structure of the planets. In a previous study, Birch law and adiabaticity physical constraints were used to construct internal structure models of the lunar mantle linking seismic velocities to density. The detection of core reflected seismic phases allowed to obtain a reference model (VPREMOON) including the core. An updated version of this model is presented, in which the P and S propagation times have been more precisely measured, and latest versions of the average crust/mantle density models has been included. Synthetic waveforms of Apollo records are compared to real ones, suggesting that additional core reflected phases may be detected for some deep moonquake events. An analysis of these additional core reflected phases allows to reduce the error bars on the deep internal structure of the Moon. However, the data set is limited by its size, space sampling and frequency bandwidth. Such that, only additional deployments of broad band seismic sensors, through space missions similar to SELENE2 (JAXA) or GEMS (NASA), will precise the deep internal structure at a level allowing unambiguous geochemical interpretations.

Garcia, R. F.; Urvoy, M.; Gagnepain-Beyneix, J.; Chevrot, S.; Lognonne, P.; Mimoun, D.

2011-12-01

36

Quasi 1D Modeling of Mixed Compression Supersonic Inlets  

NASA Technical Reports Server (NTRS)

The AeroServoElasticity task under the NASA Supersonics Project is developing dynamic models of the propulsion system and the vehicle in order to conduct research for integrated vehicle dynamic performance. As part of this effort, a nonlinear quasi 1-dimensional model of the 2-dimensional bifurcated mixed compression supersonic inlet is being developed. The model utilizes computational fluid dynamics for both the supersonic and subsonic diffusers. The oblique shocks are modeled utilizing compressible flow equations. This model also implements variable geometry required to control the normal shock position. The model is flexible and can also be utilized to simulate other mixed compression supersonic inlet designs. The model was validated both in time and in the frequency domain against the legacy LArge Perturbation INlet code, which has been previously verified using test data. This legacy code written in FORTRAN is quite extensive and complex in terms of the amount of software and number of subroutines. Further, the legacy code is not suitable for closed loop feedback controls design, and the simulation environment is not amenable to systems integration. Therefore, a solution is to develop an innovative, more simplified, mixed compression inlet model with the same steady state and dynamic performance as the legacy code that also can be used for controls design. The new nonlinear dynamic model is implemented in MATLAB Simulink. This environment allows easier development of linear models for controls design for shock positioning. The new model is also well suited for integration with a propulsion system model to study inlet/propulsion system performance, and integration with an aero-servo-elastic system model to study integrated vehicle ride quality, vehicle stability, and efficiency.

Kopasakis, George; Connolly, Joseph W.; Paxson, Daniel E.; Woolwine, Kyle J.

2012-01-01

37

Isotropic photon drag: Analytic expressions for velocity (3D) and position (1D) with applications to blackbody friction  

NASA Astrophysics Data System (ADS)

The motion of objects traveling at relativistic speeds and subject only to isotropic photon drag (blackbody friction as a special case) is modeled. The objects are assumed to be perfectly absorbing. Analytic expressions for velocity and position as a function of time for objects subject to photon drag are obtained for the case in which the photons are constrained to one-dimensional motion. If the object is also assumed to be a perfect emitter of energy, analytic expressions are found for time as a function of velocity of the body for photons constrained to one-dimensional motion, and for a full three-dimensional isotropic photon background. The derivations are carried out entirely from the point of view of a reference frame at rest relative to the isotropic photon field, so that no changes of reference frame are involved. The results for the three-dimensional model do not agree with work by previous authors, and this discrepancy is discussed. The derivations are suitable for use in the undergraduate classroom. Example cases for a light sail and a micron-sized sand grain are examined for interactions with the cosmic background radiation, assuming a temperature of 3000 K, the temperature at the time the universe became transparent, and it is found that relativistic speeds would decay on a time scale of years.

West, Joseph

2014-03-01

38

Control oriented 1D electrochemical model of lithium ion battery  

Microsoft Academic Search

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

39

Validation of 1-D transport and sawtooth models for ITER  

SciTech Connect

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

40

1D numerical model of muddy subaqueous and subaerial debris flows  

USGS Publications Warehouse

A 1D numerical model of the downslope flow and deposition of muddy subaerial and subaqueous debris flows is presented. The model incorporates the Herschel-Bulkley and bilinear rheologies of viscoplastic fluid. The more familiar Bingham model is integrated into the Herschel-Bulkley rheological model. The conservation equations of mass and momentum of single-phase laminar debris flow are layer-integrated using the slender flow approximation. They are then expressed in a Lagrangian framework and solved numerically using an explicit finite difference scheme. Starting from a given initial shape, a debris flow is allowed to collapse and propagate over a specified topography. Comparison between the model predictions and laboratory experiments shows reasonable agreement. The model is used to study the effect of the ambient fluid density, initial shape of the failed mass, and rheological model on the simulated propagation of the front and runout characteristics of muddy debris flows. It is found that initial failure shape influence the front velocity but has little bearing on the final deposit shape. In the Bingham model, the excess of shear stress above the yield strength is proportional to the strain rate to the first power. This exponent is free to vary in the Herschel-Bulkley model. When it is set at a value lower than unity, the resulting final deposits are thicker and shorter than in the case of the Bingham rheology. The final deposit resulting from the bilinear model is longer and thinner than that from the Bingham model due to the fact that the debris flow is allowed to act as a Newtonian fluid at low shear rate in the bilinear model.

Imran, J.; Parker, G.; Locat, J.; Lee, H.

2001-01-01

41

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

42

1D thermonuclear model for x-ray transients  

SciTech Connect

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

43

Numerical modeling of textured silicon solar cells using PC1D  

Microsoft Academic Search

PC-1D is a quasi-one-dimensional finite-element program for modeling semiconductor devices on personal computers. The program offers solar cell researchers a convenient user interface with the ability to address complex issues associated with heavy doping, high-level injection, nonplanar structures, and transients. The physical and numerical models used in PC-1D Version 2 that make it possible to approximate the multidimensional effects found

P. A. Basore

1990-01-01

44

Modeling Titan's Upper Atmosphere with 1-D and 3-D Models:  

NASA Astrophysics Data System (ADS)

Titan, the 2nd largest moon in the solar system, contains a substantial atmosphere like present-day Earth. However, its unique nitrile and hydrocarbon composition appears analogous to that of a pre-biotic Earth (Yung, Allen and Pinto 1984). Finally, Titan's position within Saturn's magnetosphere provides a unique plasma environment for further investigation. Given all of these qualities, studying this satellite through numerical models represents an intriguing endeavor in comparative planetary atmospheres. The arrival of Cassini-Huygens at Titan in late October will provide data crucial to better understanding the vertical chemical and thermal structures. In anticipation of this data, a 1-D model of Titan's upper atmosphere has been developed. Currently, this model includes solar heating, coupled photochemical and thermal conduction routines, and a full radiative transfer code of HCN rotational cooling. Also, magnetospheric forcing has been incorporated making use of offline calculations from the Cravens ionospheric model. Results from the 1-D model will be presented, including temperature and density profiles for various solar and Saturn magnetospheric conditions. In addition, preliminary simulations from a new 3-D Titan TGCM will be presented, although the model remains in an early stage of development.

Bell, J. M.; Delahaye, V.; Bougher, S. W.; Waite, J. H.; Cravens, T.

2004-12-01

45

Verification of 1D numerical model for heat conduction in human tissue by means of thermography  

Microsoft Academic Search

The paper presents the results of simulation of the heat transport in the human tissue by means of 1D numerical model and experimentally obtained data. The model is based on the control volume numerical method with the skin temperature and heat losses to the surrounding as the boundary conditions. The thermodynamical properties of the tissue were taken from the relevant

I. Boras; S. Švai?

46

Characteristics of FTU scrape-off layer (SOL) determined by a simple 1-D model.  

National Technical Information Service (NTIS)

A simple 1-D model analytical model has been developed to determine the SOL characteristics from the parameters of the main plasma. The solutions are compared with FTU experimental data. The solutions fit quite well the experimental data and their trend. ...

C. Ferro

1994-01-01

47

Application of Refraction Microtremor (ReMi) technique for determination of 1-D shear wave velocity in a landslide area  

Microsoft Academic Search

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

48

Parameter optimisation modeling using stationary 1D-electrothermal model to improve temperature homogeneity.  

PubMed

A parameter optimisation model is developed to find the parameters that have significant effects on homogeneous temperature distribution during microwave processing of materials. Electromagnetic, thermal and processing parameters are collected for a wide variety of materials and the heating profiles are calculated using a stationary 1D-electrothermal model. A measure of temperature homogeneity is obtained from the heating profiles by statistical calculations of normalised variance (the response variable). The processing parameters (power, temperature, size of the material sample) are optimisedfor all of these materials for a minimum normalised variance which allows maximum change of +/-3% Taverage on the T-distribution to meet most of the industrial process requirements. This mathematical model suggests a group of materials, which requires modifications in processing conditions to achieve uniform heating. PMID:16480157

Paulson, Manju; Feher, Lambert; Thumm, Manfred

2004-01-01

49

Reconstruction of Çokal Dam (Çanakkale-Turkey) Breach Flooding Using 1D Hydraulic Modeling  

Microsoft Academic Search

The aim of the study is modeling of Çokal Dam-Breaching using 1D hydraulic modeling and calibrating of the model result with the real flood event. For these purposes, TIN model which is created 10 m contour interval digitized from 1:25000 topographic maps, land use maps of Evre?e plain, geometric properties of Koca Stream and technical properties of the dam were

Hasan Ozdemir; Cengiz Akbulak; Hasan Özcan

50

Predicting Hail Size Using Model Vertical Velocities.  

National Technical Information Service (NTIS)

A simple test hail growth model is created in order to compare hailstone sizes from model vertical velocities and calculated updrafts from a simple cloud model using forecasted soundings. The models used MM5 model data coinciding with severe hail events c...

G. J. Barnhart

2008-01-01

51

1D plane numerical model for boiling liquid expanding vapor explosion (BLEVE)  

Microsoft Academic Search

The depressurization of a vessel containing saturated or subcooled liquid may occur in a variety of industrial processes and often poses a potentially hazardous situation. A 1D plane numerical model was developed for estimating the thermodynamic and the dynamic state of the boiling liquid during a boiling liquid expanding vapor explosion (BLEVE) event. Based on the choice of the initial

G. A. Pinhasi; A. Ullmann; A. Dayan

2007-01-01

52

Polynomial decay and control of a 1? d model for fluid–structure interaction  

Microsoft Academic Search

We consider a linearized and simplified 1?d model for fluid–structure interaction. The domain where the system evolves consists in two bounded intervals in which the wave and heat equations evolve respectively, with transmission conditions at the point of interface. First, we develop a careful spectral asymptotic analysis on high frequencies. Next, according to this spectral analysis we obtain sharp polynomial

Xu Zhang; Enrique Zuazua

2003-01-01

53

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

SciTech Connect

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

54

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

Microsoft Academic Search

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

55

Theory of the photodissociation of ozone in the Hartley continuum; effect of vibrational excitation and O(1D) atom velocity distribution.  

PubMed

The effect of vibrational excitation on the photodissociation cross section of ozone in the Hartley continuum is examined. The calculations make use of newly computed potential energy and transition dipole moment surfaces. The initial vibrational states of the ozone are computed using grid based techniques and the first few ab initio computed vibrational energy level spacings agree to within 10 cm(-1) with experimental values. The computed total absorption cross sections arising from different initial vibrational states of ozone are discussed in the light of the nature of the transition dipole moment surface. The computed cross section for excitation from the ground vibrational-rotational state is in good agreement with the experimentally measured cross section. Excitation of the asymmetric stretching vibration of ozone has a marked effect on both the form and magnitude of the photodissociation cross section. The velocity distributions of highly reactive O(1D) atoms arising from the photodissociation process in different wavelength ranges is also presented. The results show that the O(1D) atoms travel with a most probable translational velocity of 2.030 km s(-1) corresponding to a translational energy of 0.342 eV or 33.0 kJ mol(-1). PMID:16358032

Baloïtcha, Ezinvi; Balint-Kurti, Gabriel G

2005-11-21

56

A 1D model for the description of mixing-controlled reacting diesel sprays  

SciTech Connect

The paper reports an investigation on the transient evolution of diesel flames in terms of fuel-air mixing, spray penetration and combustion rate. A one-dimensional (1D) spray model, which was previously validated for inert diesel sprays, is extended to reacting conditions. The main assumptions of the model are the mixing-controlled hypothesis and the validity of self-similarity for conservative properties. Validation is achieved by comparing model predictions with both CFD gas jet simulations and experimental diesel spray measurements. The 1D model provides valuable insight into the evolution of the flow within the spray (momentum and mass fluxes, tip penetration, etc.) when shifting from inert to reacting conditions. Results show that the transient diesel flame evolution is mainly governed by two combustion-induced effects, namely the reduction in local density and the increase in flame radial width. (author)

Desantesa, J.M.; Pastor, J.V.; Garcia-Oliver, J.M.; Pastor, J.M. [CMT - Motores Termicos, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022, Valencia (Spain)

2009-01-15

57

Evaluation of 1D and 2D numerical models for predicting river flood inundation  

Microsoft Academic Search

1D and 2D models of flood hydraulics (HEC-RAS, LISFLOOD-FP and TELEMAC-2D) are tested on a 60km reach of the river Severn, UK. Synoptic views of flood extent from radar remote sensing satellites have been acquired for flood events in 1998 and 2000. The three models are calibrated, using floodplain and channel friction as free parameters, against both the observed inundated

M. S. Horritt; P. D. Bates

2002-01-01

58

Implementation and validation of a 1D fluid model for collapsible channels.  

PubMed

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

59

Zero finite-temperature charge stiffness within the half-filled 1D Hubbard model  

SciTech Connect

Even though the one-dimensional (1D) Hubbard model is solvable by the Bethe ansatz, at half-filling its finite-temperature T>0 transport properties remain poorly understood. In this paper we combine that solution with symmetry to show that within that prominent T=0 1D insulator the charge stiffness D(T) vanishes for T>0 and finite values of the on-site repulsion U in the thermodynamic limit. This result is exact and clarifies a long-standing open problem. It rules out that at half-filling the model is an ideal conductor in the thermodynamic limit. Whether at finite T and U>0 it is an ideal insulator or a normal resistor remains an open question. That at half-filling the charge stiffness is finite at U=0 and vanishes for U>0 is found to result from a general transition from a conductor to an insulator or resistor occurring at U=U{sub c}=0 for all finite temperatures T>0. (At T=0 such a transition is the quantum metal to Mott–Hubbard-insulator transition.) The interplay of the ?-spin SU(2) symmetry with the hidden U(1) symmetry beyond SO(4) is found to play a central role in the unusual finite-temperature charge transport properties of the 1D half-filled Hubbard model. -- Highlights: •The charge stiffness of the half-filled 1D Hubbard model is evaluated. •Its value is controlled by the model symmetry operator algebras. •We find that there is no charge ballistic transport at finite temperatures T>0. •The hidden U(1) symmetry controls the U=0 phase transition for T>0.

Carmelo, J.M.P., E-mail: carmelo@fisica.uminho.pt [Center and Department of Physics, University of Minho, Campus Gualtar, P-4710-057 Braga (Portugal) [Center and Department of Physics, University of Minho, Campus Gualtar, P-4710-057 Braga (Portugal); Beijing Computational Science Research Center, Beijing 100084 (China); Institut für Theoretische Physik III, Universität Stuttgart, D-70550 Stuttgart (Germany); Gu, Shi-Jian [Beijing Computational Science Research Center, Beijing 100084 (China) [Beijing Computational Science Research Center, Beijing 100084 (China); Department of Physics and ITP, Chinese University of Hong Kong, Hong Kong (China); Sacramento, P.D. [CFIF, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal) [CFIF, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Beijing Computational Science Research Center, Beijing 100084 (China)

2013-12-15

60

Assessing the impact of uncertainty on flood risk estimates with reliability analysis using 1-D and 2-D hydraulic models  

NASA Astrophysics Data System (ADS)

This paper addresses the use of reliability techniques such as Rosenblueth's Point-Estimate Method (PEM) as a practical alternative to more precise Monte Carlo approaches to get estimates of the mean and variance of uncertain flood parameters water depth and velocity. These parameters define the flood severity, which is a concept used for decision-making in the context of flood risk assessment. The method proposed is particularly useful when the degree of complexity of the hydraulic models makes Monte Carlo inapplicable in terms of computing time, but when a measure of the variability of these parameters is still needed. The capacity of PEM, which is a special case of numerical quadrature based on orthogonal polynomials, to evaluate the first two moments of performance functions such as the water depth and velocity is demonstrated in the case of a single river reach using a 1-D HEC-RAS model. It is shown that in some cases, using a simple variable transformation, statistical distributions of both water depth and velocity approximate the lognormal. As this distribution is fully defined by its mean and variance, PEM can be used to define the full probability distribution function of these flood parameters and so allowing for probability estimations of flood severity. Then, an application of the method to the same river reach using a 2-D Shallow Water Equations (SWE) model is performed. Flood maps of mean and standard deviation of water depth and velocity are obtained, and uncertainty in the extension of flooded areas with different severity levels is assessed. It is recognized, though, that whenever application of Monte Carlo method is practically feasible, it is a preferred approach.

Altarejos-García, L.; Martínez-Chenoll, M. L.; Escuder-Bueno, I.; Serrano-Lombillo, A.

2012-07-01

61

Assessing the impact of uncertainty on flood risk estimates with reliability analysis using 1-D and 2-D hydraulic models  

NASA Astrophysics Data System (ADS)

This paper addresses the use of reliability techniques such as Rosenblueth's Point-Estimate Method (PEM) as a practical alternative to more precise Monte Carlo approaches to get estimates of the mean and variance of uncertain flood parameters water depth and velocity. These parameters define the flood severity, which is a concept used for decision-making in the context of flood risk assessment. The method proposed is particularly useful when the degree of complexity of the hydraulic models makes Monte Carlo inapplicable in terms of computing time, but when a measure of the variability of these parameters is still needed. The capacity of PEM, which is a special case of numerical quadrature based on orthogonal polynomials, to evaluate the first two moments of performance functions such as the water depth and velocity is demonstrated in the case of a single river reach using a 1-D HEC-RAS model. It is shown that in some cases, using a simple variable transformation, statistical distributions of both water depth and velocity approximate the lognormal. As this distribution is fully defined by its mean and variance, PEM can be used to define the full probability distribution function of these flood parameters and so allowing for probability estimations of flood severity. Then, an application of the method to the same river reach using a 2-D Shallow Water Equations (SWE) model is performed. Flood maps of mean and standard deviation of water depth and velocity are obtained, and uncertainty in the extension of flooded areas with different severity levels is assessed. It is recognized, though, that whenever application of Monte Carlo method is practically feasible, it is a preferred approach.

Altarejos-García, L.; Martínez-Chenoll, M. L.; Escuder-Bueno, I.; Serrano-Lombillo, A.

2012-01-01

62

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

Microsoft Academic Search

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

63

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

Microsoft Academic Search

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

64

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

Microsoft Academic Search

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

65

1-D models of induced density enhancements in hot-star winds  

NASA Technical Reports Server (NTRS)

We present a 1-D dynamical model of large-scale flow structures induced in a hot-star wind by an initial density perturbation in the inner wind. The resulting wind response is very complex, but includes strong density enhancements that propagate slowly outward through the wind. These density structures exhibit a very slow outward acceleration reminiscent of the discrete absorption components frequently observed in unsaturated UV lines formed in hot-star winds.

Owocki, S. P.; Fullerton, A. W.; Puls, J.

1994-01-01

66

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

SciTech Connect

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

67

Optimisation of A 1d-ecosystem Model To Observations In The North Atlantic Ocean  

NASA Astrophysics Data System (ADS)

An optimisation experiment is performed with a vertically resolved, nitrogen based ecosystem model, comprising four state variables (1D-NPZD model): dissolved inor- ganic nitrogen (N), phytoplankton (P), herbivorous zooplankton (Z) and detritus (D). Parameter values of the NPZD-model are optimised while regarding observational data from three locations in the North Atlantic simultaneously: Bermuda Atlantic Time-series Study (BATS), data of the North Atlantic Bloom Experiment (NABE) and observations from Ocean Weather Ship-India (OWS-INDIA). The simultaneous opti- misation yields a best parameter set which can be utilized for basin wide simulations in coupled physical-biological (general circulation) models of the North Atlantic. After optimisation of the 1D-NPZD model, systematic discrepancies between 14C-fixation rates and modelled primary production are emphasized. Using the optimal parame- ter estimates for coupled 3D-simulations, the biogeochemical fluxes show substantial differences in contrast to previous model results. For instance, rapid recycling of or- ganic matter enhances primary production rates. This becomes most evident within the oligotrophic regions of the subtropical gyre.

Schartau, M.; Oschlies, A.

68

Non uniqueness in the 1-D linear inverse problem for initial sea level disturbance and current velocities in the tsunami source  

NASA Astrophysics Data System (ADS)

1-D linear inverse problem for initial sea level disturbance in the tsunami source ?0(x) using sea level record f(t) near the shore was investigated. Sea bottom can be considered as the slopping plane and water depthh(x) = k x. Let the function ?(x,t) describing sea level oscillations depending from time t and space coordinate xis satisfying the linear shallow water equation (gkx??x)x = ?tt If initial velocities in the source zone are equal to zero (?t(x,0)=0) than initial sea level disturbance in the tsunami source ?0(x) = ?(x,0) and sea level record (marigram) on the shore f(t) = ?(0,t) are tied by the integral equation of Abel type which has an unique analytical solution. Situation looks different if initial wave field in the tsunami source is related to sea level disturbance and current velocities not equal to zero. In this case specially constructed initial wave field with ?0(x) = ?(x,0) and ?1(x) = ?t(x,0) tied by the integral equation ?0(Z) = -2 ? zZK(° ---- (Z-)2 - 1) z) ? ?1(z)zdz where K is the full elliptic integral and z = 2° -- xkg- = ?2gxh-, gives the tsunami non observed near the shore: ?(0,t)=0. The work was supported by grant 11-05-01054 of the Russian foundation for basic research.

Kaystrenko, Victor; Pelinovsky, Efim

2013-04-01

69

Servo Motor Position and Velocity Control Model  

NSDL National Science Digital Library

The Servo Motor Position and Velocity Control Model simulates the use of a proportional-integral-derivative (PID) controller to run a DC motor. The motor is modeled as a first order system and the simulation allows the user to control either the position of the motor or its velocity. This EJS simulation is based on a real system running at the Spanish Open University for Distance Education (UNED).  The real DC motor is used as a remote laboratory for learning purposes and a different application created with EJS (visually identical to this simulation) serves as graphical user interface to operate the remote laboratory.

De La Torre, Luis; Oyarzun, Hector V.

2014-03-18

70

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

71

A 1-D model study of Arctic sea-ice salinity  

NASA Astrophysics Data System (ADS)

We use a 1-D model to study how salinity evolves in Arctic sea ice. To do so, we first explore how sea-ice surface melt and flooding can be incorporated into the 1-D thermodynamic SAMSIM sea-ice model presented by Griewank and Notz (2013). We introduce flooding and a flushing parametrization which treats sea ice as a hydraulic network of horizontal and vertical fluxes. Forcing SAMSIM with 36 years of ERA-interim atmospheric reanalysis data, we obtain a modeled Arctic sea-ice salinity that agrees well with ice-core measurements. The simulations hence allow us to identify the main drivers of the observed mean salinity profile in Arctic sea ice. Our results show a 1.5-4 g kg-1 decrease of bulk salinity via gravity drainage after ice growth has ceased and before flushing sets in, which hinders approximating bulk salinity from ice thickness beyond the first growth season. In our simulations, salinity variability of first-year ice is mostly restricted to the top 20 cm. We find that ice thickness, thermal resistivity, freshwater column, and stored energy change by less than 5% on average when the full salinity parametrization is replaced with a prescribed salinity profile. We conclude that for earth system models the impact of fully parametrizing the Arctic temporal salinity evolution is too small to justify the increase in computational cost and model complexity.

Griewank, P. J.; Notz, D.

2014-03-01

72

Evaluation of a Revised Interplanetary Shock Prediction Model: 1D CESE-HD-2 Solar-Wind Model  

NASA Astrophysics Data System (ADS)

We modified the one-dimensional conservation element and solution element (CESE) hydrodynamic (HD) model into a new version [ 1D CESE-HD-2], by considering the direction of the shock propagation. The real-time performance of the 1D CESE-HD-2 model during Solar Cycle 23 (February 1997 - December 2006) is investigated and compared with those of the Shock Time of Arrival Model ( STOA), the Interplanetary-Shock-Propagation Model ( ISPM), and the Hakamada-Akasofu-Fry version 2 ( HAFv.2). Of the total of 584 flare events, 173 occurred during the rising phase, 166 events during the maximum phase, and 245 events during the declining phase. The statistical results show that the success rates of the predictions by the 1D CESE-HD-2 model for the rising, maximum, declining, and composite periods are 64 %, 62 %, 57 %, and 61 %, respectively, with a hit window of ± 24 hours. The results demonstrate that the 1D CESE-HD-2 model shows the highest success rates when the background solar-wind speed is relatively fast. Thus, when the background solar-wind speed at the time of shock initiation is enhanced, the forecasts will provide potential values to the customers. A high value (27.08) of ? 2 and low p-value (< 0.0001) for the 1D CESE-HD-2 model give considerable confidence for real-time forecasts by using this new model. Furthermore, the effects of various shock characteristics (initial speed, shock duration, background solar wind, longitude, etc.) and background solar wind on the forecast are also investigated statistically.

Zhang, Y.; Du, A. M.; Du, D.; Sun, W.

2014-08-01

73

1D finite volume model of unsteady flow over mobile bed  

NASA Astrophysics Data System (ADS)

SummaryA one dimensional (1D) finite volume method (FVM) model was developed for simulating unsteady flow, such as dam break flow, and flood routing over mobile alluvium. The governing equation is the modified 1D shallow water equation and the Exner equation that take both bed load and suspended load transport into account. The non-equilibrium sediment transport algorithm was adopted in the model, and the van Rijn method was employed to calculate the bed-load transport rate and the concentration of suspended sediment at the reference level. Flux terms in the governing equations were discretised using the upwind flux scheme, Harten et al. (1983) (HLL) and HLLC schemes, Roe's scheme and the Weighted Average Flux (WAF) schemes with the Double Minmod and Minmod flux limiters. The model was tested under a fixed bed condition to evaluate the performance of several different numerical schemes and then applied to an experimental case of dam break flow over a mobile bed and a flood event in the Rillito River, Tucson, Arizona. For dam break flow over movable bed, all tested schemes were proved to be capable of reasonably simulating water surface profiles, but failed to accurately capture the hydraulic jump. The WAF schemes produced slight spurious oscillations at the water surface and bed profiles and over-estimated the scour depth. When applying the model to the Rillito River, the simulated results generally agreed well with the field measurements of flow discharges and bed elevation changes. Modeling results of bed elevation changes were sensitive to the suspended load recovery coefficient and the bed load adaptation length, which require further theoretical and experimental investigations.

Zhang, Shiyan; Duan, Jennifer G.

2011-07-01

74

Cosmological velocity correlations - Observations and model predictions  

NASA Technical Reports Server (NTRS)

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

1989-01-01

75

Prediction of changes in landslide movements induced by rainfalls: from the use of a black box model to a 1D mechanical model  

NASA Astrophysics Data System (ADS)

Predicting landslide surface displacements is a challenge for scientists, as it may help save human lives and protect individual housing or transport, energetic facilities. One of the main challenges in active landslide monitoring concerns the prediction of slope's movements in the near future. This study focuses on an innovative methodology to predict landslide surface accelerations, based on a black box tool coupled to a 1D mechanical model. These models are able to predict the evolution of the daily displacements according to the variations of precipitation. More specifically, the impulse response model allows predicting the changes in the landslide movements by computing the transfer function between the input signal (precipitation in this case) and the output signal (the displacements). The second model is based on a simple 1D mechanical assumption, with considering a viscoplastic behavior of the landslide's material, and with taking into account the evolution of the pore water pressure in time. These methods have been applied to the Super-Sauze landslide, located in the Southern French Alps, mountainous region. This site is controlled by complex hydrologic processes leading to active movements within black marls, with velocities ranging between 0.002 and 0.4 m per day. After preliminary tests, results show that the snowmelt has to be taken into account in the models, since the phenomena of freezing /thawing has an influence on the water refills, leading to movement changes. Different approaches to integrate rainfall and/or snow-melting inputs are compared and their complementarity is demonstrated. Finally, a validated methodology for predicting movement changes within landslide based on criteria of comparison between the observed and calculated velocities can be proposed. The results suggest that the impulse response model reproduces the observed data with very good accuracy, whereas the mechanical model seems to be more adapted to predict the movements within 10 days. Moreover, the RMSE criterion permits to highlight the occurrence of the flow, with considering all models, 11 days before the flow itself.

Bernardie, S.; Desramaut, N.; Russo, G.; Grandjean, G.

2012-04-01

76

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

Microsoft Academic Search

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

77

Coupled Drives Tension and Velocity Control Model  

NSDL National Science Digital Library

The Coupled Drives Tension and Velocity Control Model simulates the use of a proportional-integral-derivative (PID) controller to he tension and the angular velocity of the pulley in a coupled drive system. This system consist in two drive motors and a pulley which are connected through elastic belts. The jockey pulley is mounted on an arm, that is supported by a spring whose elongation is an indirect measure of the tension in the drive belt. The motors torque can be controlled either manually or with PID, while the motor movement affect the tension and velocity in the pulley. The velocity can be obtained immediately and using the jockey pulley measurements (angle or position) we obtain the tension. This EJS simulation is based on a real system running at the Spanish Open University for Distance Education (UNED).  The real system is used as a remote laboratory for learning purposes and a different application created with EJS (visually identical to this simulation) serves as graphical user interface to operate the remote laboratory.

Saenz, Jacobo; De La Torre, Luis

2014-04-15

78

Patient-specific mean pressure drop in the systemic arterial tree, a comparison between 1-D and 3-D models.  

PubMed

One-dimensional models of the systemic arterial tree are useful tools for studying wave propagation phenomena, however, their formulation for frictional losses is approximate and often based on solutions for developed flow in straight non-tapered arterial segments. Thus, losses due to bifurcations, tortuosity, non-planarity and complex geometry effects cannot be accounted for in 1-D models. This may lead to errors in the estimation of mean pressure. To evaluate these errors, we simulated steady flow in a patient specific model of the entire systemic circulation using a standard CFD code with Newtonian and non-Newtonian blood properties and compared the pressure evolution along three principal and representative arterial pathlines with the prediction of mean pressure, as given by the 1-D model. Pressure drop computed from aortic root up to iliac bifurcation and to distal brachial is less than 1 mmHg and 1-D model predictions agree well with the 3-D model. In smaller vessels like the precerebral and cerebral arteries, the losses are higher (mean pressure drop over 10 mmHg from mean aortic pressure) and are consistently underestimated by the 1-D model. Complex flow patterns resulting from tortuosity, non-planarity and branching yield shear stresses, which are higher than the ones predicted by the 1-D model. In consequence, the 1-D model overestimates mean pressure in peripheral arteries and especially in the cerebral circulation. PMID:22884968

Reymond, Philippe; Perren, Fabienne; Lazeyras, François; Stergiopulos, Nikos

2012-10-11

79

Neural Dynamics of 1-D and 2-D Brightness Perception: A Unified Model of Classical and Recent Phenomena,  

National Technical Information Service (NTIS)

Computer simulations of a neural network model of 1-D and 2-D brightness phenomena are presented. The simulations indicate how configural image properties trigger interactions among spatially organized contrastive, boundary segmentation, and filling-in pr...

S. Grossberg D. Todorovic

1988-01-01

80

Phenomenological 3D and 1D consistent models for shape-memory alloy materials  

NASA Astrophysics Data System (ADS)

The paper deals with the modeling and the development of a numerical procedure for the analysis of shape-memory alloy (SMA) elements in order to predict the main features of SMA devices. A 3D SMA model in the framework of small strain theory is developed starting from the thermo-mechanical model proposed by Souza et al. (Eur J Mech A/Solids 17:789-806, 1998) and modified by Auricchio and Petrini (Int J Numer Methods Eng 55:1255-1284, 2002). The aim of this paper is to propose some more modifications to the original model, to derive its consistent 1D formulation, to clarify the mechanical meaning of the material parameters governing the constitutive model. A robust time integration algorithm is developed in the framework of the finite element method and a new beam finite element is proposed. Some numerical applications and a comparison with experimental data available in literature are carried out in order to assess the ability of the proposed model to describe the SMA behavior.

Evangelista, Veronica; Marfia, Sonia; Sacco, Elio

2009-08-01

81

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

NASA Astrophysics Data System (ADS)

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. The energy equations employed include models for laser energy deposition, radiation from external sources, and high-current discharges. Radiative transport can be calculated using either a multi-frequency flux-limited diffusion model, or a multi-frequency, multi-angle short characteristics model. HELIOS-CR supports the use of SESAME equation of state (EOS) tables, PROPACEOS EOS/multi-group opacity data tables, and non-LTE plasma properties computed using the inline CR modeling. Time-, space-, and frequency-dependent results from HELIOS-CR calculations are readily displayed with the HydroPLOT graphics tool. In addition, the results of HELIOS simulations can be post-processed using the SPECT3D Imaging and Spectral Analysis Suite to generate images and spectra that can be directly compared with experimental measurements. The HELIOS-CR package runs on Windows, Linux, and Mac OSX platforms, and includes online documentation. We will discuss the major features of HELIOS-CR, and present example results from simulations.

Macfarlane, J. J.; Golovkin, I. E.; Woodruff, P. R.

2006-05-01

82

Testing the accuracy of a 1-D volcanic plume model in estimating mass eruption rate  

NASA Astrophysics Data System (ADS)

volcanic eruptions, empirical relationships are used to estimate mass eruption rate from plume height. Although simple, such relationships can be inaccurate and can underestimate rates in windy conditions. One-dimensional plume models can incorporate atmospheric conditions and give potentially more accurate estimates. Here I present a 1-D model for plumes in crosswind and simulate 25 historical eruptions where plume height Hobs was well observed and mass eruption rate Mobs could be calculated from mapped deposit mass and observed duration. The simulations considered wind, temperature, and phase changes of water. Atmospheric conditions were obtained from the National Center for Atmospheric Research Reanalysis 2.5° model. Simulations calculate the minimum, maximum, and average values (Mmin, Mmax, and Mavg) that fit the plume height. Eruption rates were also estimated from the empirical formula Mempir = 140Hobs4.14 (Mempir is in kilogram per second, Hobs is in kilometer). For these eruptions, the standard error of the residual in log space is about 0.53 for Mavg and 0.50 for Mempir. Thus, for this data set, the model is slightly less accurate at predicting Mobs than the empirical curve. The inability of this model to improve eruption rate estimates may lie in the limited accuracy of even well-observed plume heights, inaccurate model formulation, or the fact that most eruptions examined were not highly influenced by wind. For the low, wind-blown plume of 14-18 April 2010 at Eyjafjallajökull, where an accurate plume height time series is available, modeled rates do agree better with Mobs than Mempir.

Mastin, Larry G.

2014-03-01

83

Testing the accuracy of a 1-D volcanic plume model in estimating mass eruption rate  

USGS Publications Warehouse

During volcanic eruptions, empirical relationships are used to estimate mass eruption rate from plume height. Although simple, such relationships can be inaccurate and can underestimate rates in windy conditions. One-dimensional plume models can incorporate atmospheric conditions and give potentially more accurate estimates. Here I present a 1-D model for plumes in crosswind and simulate 25 historical eruptions where plume height Hobs was well observed and mass eruption rate Mobs could be calculated from mapped deposit mass and observed duration. The simulations considered wind, temperature, and phase changes of water. Atmospheric conditions were obtained from the National Center for Atmospheric Research Reanalysis 2.5° model. Simulations calculate the minimum, maximum, and average values (Mmin, Mmax, and Mavg) that fit the plume height. Eruption rates were also estimated from the empirical formula Mempir?=?140Hobs4.14 (Mempir is in kilogram per second, Hobs is in kilometer). For these eruptions, the standard error of the residual in log space is about 0.53 for Mavg and 0.50 for Mempir. Thus, for this data set, the model is slightly less accurate at predicting Mobs than the empirical curve. The inability of this model to improve eruption rate estimates may lie in the limited accuracy of even well-observed plume heights, inaccurate model formulation, or the fact that most eruptions examined were not highly influenced by wind. For the low, wind-blown plume of 14–18 April 2010 at Eyjafjallajökull, where an accurate plume height time series is available, modeled rates do agree better with Mobs than Mempir.

Mastin, Larry G.

2014-01-01

84

Mathematical modeling of 1D binary photonic tuner and realization of temperature sensor  

NASA Astrophysics Data System (ADS)

In recent years photonic crystals have become a favored area of research due to their diversified applications. In this paper we propose a mathematical model for analyzing the photonic band gap of a 1D binary photonic crystal (GaAs and air) which allows us to use it effectively as a photonic tuner which is an integral part of any optical amplifier. As optical parameters like reflection and refraction follows similar pattern from each plane within a photonic crystal, we can take help of characteristic matrix for a single plane and multiply (m) times where the crystal consists of (m) periods. Using the fact that the characteristic matrix comes out to be unimodular and taking help of Cayley-Hamilton theorem and Chebyshev polynomials, we expand the matrix of the entire system to derive the location and width of photonic band gaps. Higher stop bands occur at lower frequency of incoming radiation and central bandgap wavelength decreases with increasing angle of incidence. The power transmitted by the tuning crystal decreases for radiations away from normal. Using a polarizer model, the attenuation is computed to be proportional to log|Cos2?|, where ? is the angle of incidence. The mathematical modeling developed can also be extended for realization of n-array photonic crystal. We have also considered the refractive index modulation with respect to temperature for using it as a temperature sensor.

Lahiri, A.; Chakraborty, M.

2011-09-01

85

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

86

Using 1-D Models to Interpret the Reflectance Anisotropy of 3-D Canopy Targets: Issues and Caveats  

Microsoft Academic Search

This paper evaluates 1) to what extent one-dimensional (1-D) models can be used to represent the magnitude and directionality of the surface reflectance field of heterogeneous canopy targets at different spatial resolutions, and 2) whether this usage results in significant biases in the estimation of the corresponding state variables. It will be seen that when both the 1-D and three-dimensional

Jean-Luc Widlowski; Bernard Pinty; Thomas Lavergne; Michel Max Verstraete; Nadine Gobron

2005-01-01

87

Global 3D P-Velocity Model of the Earth's Crust and Mantle for Improved Event Location.  

National Technical Information Service (NTIS)

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 ma...

C. J. Young J. R. Hipp M. C. Chang M. L. Begnaud S. Ballard

2011-01-01

88

Hybrid 0-D,1-D, and 2-D model of helical explosive-driven magnetic flux compression generator  

Microsoft Academic Search

A hybrid code model of the Sandia National Laboratories' model 632 is described is introduced. A very large explosive driven magnetic flux compression generator. This involves the use of two codes. The first is a coupled 0-D equivalent circuit model and 1-D magnetohydrodynamic computation. The second is the 2-D materials response code, CSQ. This is used to obtain an equivalent

T. J. Burgess

1985-01-01

89

A 1-D atmospheric energy balance model developed for ocean modelling  

Microsoft Academic Search

We present a simple, deterministic energy balance model. The model is designed to represent the atmospheric component of the coupled atmosphere-ocean system. It is a one dimensional, global model with time and space resolutions of one year and 10° of latitude respectively. The model predicts the surface air temperature and estimates the surface freshwater flux diagnostically. The coupling between the

Deliang Chen; Rüdiger Gerdes; Gerrit Lohmann

1995-01-01

90

Intricate heterogeneous structures of the top 300 km of the Earth's inner core inferred from global array data: I. Regional 1D attenuation and velocity profiles  

NASA Astrophysics Data System (ADS)

We apply a waveform inversion method based on simulated annealing to complex core phase data observed by globally deployed seismic arrays, and present regional variation of depth profiles of attenuation and velocity for the top half of the inner core. Whereas measured attenuation parameters exhibit consistent trends for data sampling the eastern hemisphere of the inner core, for the western hemisphere, there is a remarkable difference between data sampling the inner core beneath Africa (W1) and beneath north America (W2). Obtained attenuation profiles suggest that intricate heterogeneities appear to be confined in the top 300 km. The profile for the eastern hemisphere has a high attenuation zone in the top 150 km that gradually diminishes with depth. Conversely, for the western hemisphere, the profile for W1 shows constant low attenuation and that for W2 represents a gradual increase from the inner core boundary to a peak at around 200 km depth. Velocity profiles, obtained from differential traveltimes between PKP(DF) and PKP(CD, BC) phases, for the eastern and western hemispheres are respectively about 0.8% faster and 0.6% slower than the reference model at the top of the inner core, and the difference nearly disappears at about 200 km depth. Our result suggests the presence of intricate quasi-hemispherical structures in the top ˜200-300 km of the inner core.

Iritani, R.; Takeuchi, N.; Kawakatsu, H.

2014-05-01

91

1D and 2D urban dam-break flood modelling in Istanbul, Turkey  

NASA Astrophysics Data System (ADS)

Urban flood events are increasing in frequency and severity as a consequence of several factors such as reduced infiltration capacities due to continued watershed development, increased construction in flood prone areas due to population growth, the possible amplification of rainfall intensity due to climate change, sea level rise which threatens coastal development, and poorly engineered flood control infrastructure (Gallegos et al., 2009). These factors will contribute to increased urban flood risk in the future, and as a result improved modelling of urban flooding according to different causative factor has been identified as a research priority (Gallegos et al., 2009; Ozdemir et al. 2013). The flooding disaster caused by dam failures is always a threat against lives and properties especially in urban environments. Therefore, the prediction of dynamics of dam-break flows plays a vital role in the forecast and evaluation of flooding disasters, and is of long-standing interest for researchers. Flooding occurred on the Ayamama River (Istanbul-Turkey) due to high intensity rainfall and dam-breaching of Ata Pond in 9th September 2009. The settlements, industrial areas and transportation system on the floodplain of the Ayamama River were inundated. Therefore, 32 people were dead and millions of Euros economic loses were occurred. The aim of this study is 1 and 2-Dimensional flood modelling of the Ata Pond breaching using HEC-RAS and LISFLOOD-Roe models and comparison of the model results using the real flood extent. The HEC-RAS model solves the full 1-D Saint Venant equations for unsteady open channel flow whereas LISFLOOD-Roe is the 2-D shallow water model which calculates the flow according to the complete Saint Venant formulation (Villanueva and Wright, 2006; Neal et al., 2011). The model consists a shock capturing Godunov-type scheme based on the Roe Riemann solver (Roe, 1981). 3 m high resolution Digital Surface Model (DSM), natural characteristics of the pond and its breaching such as depth, wide, length, volume and breaching shape and daily total rainfall data were used in the models. The simulated flooding in the both models were compared with the real flood extent which gathered from photos taken after the flood event, high satellite images acquired after 20 days from the flood event, and field works. The results show that LISFLOOD-Roe hydraulic model gives more than 80% fit to the extent of real flood event. Also both modelling results show that the embankment breaching of the Ata Pond directly affected the flood magnitude and intensity on the area. This study reveals that modelling of the probable flooding in urban areas is necessary and very important in urban planning. References Gallegos, H. A., Schubert, J. E., and Sanders, B. F.: Two dimensional, high-resolution modeling of urban dam-break flooding: A case study of Baldwin Hills California, Adv. Water Resour., 32, 1323-1335, 2009. Neal, J., Villanueva, I., Wright, N., Willis, T., Fewtrell, T. and Bates, P.: How mush physical complexity is needed to model flood inundation? Hydrological Processes, DOI: 10.1002/hyp.8339. Ozdemir H., Sampson C., De Almeida G., Bates P.D.: Evaluating scale and roughness effects in urban flood modelling using terrestrial LiDAR data, Hydrology and Earth System Sciences, vol.17, pp.4015-4030, 2013. Roe P.: Approximate Riemann solvers, parameter vectors, and difference-schemes. Journal of Computational Physics 43(2): 357-372, 1981. Villanueva I, Wright NG.: Linking Riemann and storage cell models for flood prediction. Proceedings of the Institution of Civil Engineers, Journal of Water Management 159: 27-33, 2006.

Ozdemir, Hasan; Neal, Jeffrey; Bates, Paul; Döker, Fatih

2014-05-01

92

1-D/3-D geologic model of the Western Canada Sedimentary Basin  

USGS Publications Warehouse

The 3-D geologic model of the Western Canada Sedimentary Basin comprises 18 stacked intervals from the base of the Devonian Woodbend Group and age equivalent formations to ground surface; it includes an estimated thickness of eroded sediments based on 1-D burial history reconstructions for 33 wells across the study area. Each interval for the construction of the 3-D model was chosen on the basis of whether it is primarily composed of petroleum system elements of reservoir, hydrocarbon source, seal, overburden, or underburden strata, as well as the quality and areal distribution of well and other data. Preliminary results of the modeling support the following interpretations. Long-distance migration of hydrocarbons east of the Rocky Mountains is indicated by oil and gas accumulations in areas within which source rocks are thermally immature for oil and (or) gas. Petroleum systems in the basin are segmented by the northeast-trending Sweetgrass Arch; hydrocarbons west of the arch were from source rocks lying near or beneath the Rocky Mountains, whereas oil and gas east of the arch were sourced from the Williston Basin. Hydrocarbon generation and migration are primarily due to increased burial associated with the Laramide Orogeny. Hydrocarbon sources and migration were also influenced by the Lower Cretaceous sub-Mannville unconformity. In the Peace River Arch area of northern Alberta, Jurassic and older formations exhibit high-angle truncations against the unconformity. Potential Paleozoic though Mesozoic hydrocarbon source rocks are in contact with overlying Mannville Group reservoir facies. In contrast, in Saskatchewan and southern Alberta the contacts are parallel to sub-parallel, with the result that hydrocarbon source rocks are separated from the Mannville Group by seal-forming strata within the Jurassic. Vertical and lateral movement of hydrocarbons along the faults in the Rocky Mountains deformed belt probably also resulted in mixing of oil and gas from numerous source rocks in Alberta.

Higley, D. K.; Henry, M.; Roberts, L. N. R.; Steinshouer, D. W.

2005-01-01

93

Iterative calibration of a shape memory alloy constitutive model from 1D and 2D data using optimization methods  

NASA Astrophysics Data System (ADS)

Shape memory alloy constitutive models have been shown to accurately predict 1-D and 3-D material response under general thermomechanical loading. As with any constitutive model, however, the degree to which simulation results match experimental data is dependent on the accurate calibration of model parameters. This work presents a general framework for the identi cation of SMA material parameters using numerical optimization methods and experimental results that include both 1-D data (i.e., stress-strain and strain-temperature line plots) as well as 2-D digital image correlation (DIC) strain eld data. The optimization framework is verified using 1-D and 3-D nite-element-based simulated results as pseudo-experimental data. The study shows that the proposed optimization methods can identify SMA parameters in an automated fashion using data taken from multiple types of experiment, identifying parameters that t very closely to the pseudo-experimental data.

Whitten, Daniel; Hartl, Darren

2014-03-01

94

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

95

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

SciTech Connect

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

96

Improvements to Absolute Locations from an Updated Velocity Model at Mount St. Helens, Washington  

Microsoft Academic Search

Over 700,000 earthquakes have been detected at Mount St. Helens, Washington since it reawakened last fall. Over 99% of these earthquakes have occurred within 1.5 km of the surface, under or near the active dome. Currently, picks of well recorded P-waves on 10 to 15 permanent seismic stations are used with a simple 1-D velocity model with station corrections to

W. A. Thelen; S. D. Malone; T. Qamar; S. Pullammanappallil

2005-01-01

97

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

SciTech Connect

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. (University of Houston); Basilio, Lorena I.; Celepcikay, Ferhat T. (University of Houston); Johnson, William Arthur; Baccarelli, Paolo (Sapienza Universita de Roma); Valerio, Guido (Sapienza Universita de Roma); Paulotto, Simone (University of Houston); Langston, William L.; Jackson, David R. (University of Houston)

2010-09-01

98

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

SciTech Connect

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

99

Seismic Wave Velocities in Rocks I : Modeling Heterogeneous Media and their Elastic Wave Velocities  

Microsoft Academic Search

On the basis of the viewpoint that rocks are typical random heterogeneous media consisting of different minerals and micro-cracks, modeling techniques for predicting seismic wave veloci- ties in crystalline rocks are reviewed. The term seismic velocity is sometimes unclear in its phys- ical meaning in real media that contain heterogeneity and anisotropy. The physical meaning of seismic velocity is first

Osamu NISHIZAWA

100

The USGS 3D Seismic Velocity Model for Northern California  

Microsoft Academic Search

We present a new regional 3D seismic velocity model for Northern California for use in strong motion simulations of the 1906 San Francisco and other earthquakes. The model includes compressional-wave velocity (Vp), shear-wave velocity (Vs), density, and intrinsic attenuation (Qp, Qs). These properties were assigned for each rock type in a 3D geologic model derived from surface outcrops, boreholes, gravity

T. M. Brocher; B. Aagaard; R. W. Simpson; R. C. Jachens

2006-01-01

101

P, S wave velocity model of the crust and upper most mantle of Albania region  

NASA Astrophysics Data System (ADS)

This paper describes the one-dimensional (1D) velocity model computed by VELEST in the SEISAN seismic analysis system, inverting re-picked P-wave and S-wave arrival times recorded during 2002-2006 by the Albanian, Montenegro, Thessalonica and Macedonia seismic networks. The re-picked data yield P-wave and S-wave velocities proved to be more suitable compared to bulletin data for this detailed inversion study. Seismic phases recorded by the Albania seismic network and integrated with data from the Montenegro, Thessalonica and Macedonia networks are used to prepare the Albanian seismic bulletin. Earthquake hypocenters from the Albanian bulletins have also location errors that are negligible for civil protection purposes, large scale seismotectonic analyses and more accurate hypocentral determinations which are necessary for detailed seismotectonic and geodynamic studies. It was noted that the smoothness of the velocity variation increased with depth. A velocity of 5.5 km/s was calculated for the upper crust, 6.1 km/s was calculated for the middle crust and 6.9 km/s was computed for the lower crust. P wave velocity was 7.85 km/s at depth of 50 km and for the upper mantle it is 8.28 km/s. Using the improved velocity model, the earthquakes which occurred in Albania in the past 5 years were able to be relocated, achieving constrained hypocentral determinations for events in Albania. The interpretation of the 1 D velocity models infers interesting features of the deep structure of Albania. These results represent an important step towards more detailed seismotectonic analyses.

Ormeni, Rrapo

2011-01-01

102

The anisotropy1 D604N mutation in the Arabidopsis cellulose synthase1 catalytic domain reduces cell wall crystallinity and the velocity of cellulose synthase complexes.  

PubMed

Multiple cellulose synthase (CesA) subunits assemble into plasma membrane complexes responsible for cellulose production. In the Arabidopsis (Arabidopsis thaliana) model system, we identified a novel D604N missense mutation, designated anisotropy1 (any1), in the essential primary cell wall CesA1. Most previously identified CesA1 mutants show severe constitutive or conditional phenotypes such as embryo lethality or arrest of cellulose production but any1 plants are viable and produce seeds, thus permitting the study of CesA1 function. The dwarf mutants have reduced anisotropic growth of roots, aerial organs, and trichomes. Interestingly, cellulose microfibrils were disordered only in the epidermal cells of the any1 inflorescence stem, whereas they were transverse to the growth axis in other tissues of the stem and in all elongated cell types of roots and dark-grown hypocotyls. Overall cellulose content was not altered but both cell wall crystallinity and the velocity of cellulose synthase complexes were reduced in any1. We crossed any1 with the temperature-sensitive radial swelling1-1 (rsw1-1) CesA1 mutant and observed partial complementation of the any1 phenotype in the transheterozygotes at rsw1-1's permissive temperature (21°C) and full complementation by any1 of the conditional rsw1-1 root swelling phenotype at the restrictive temperature (29°C). In rsw1-1 homozygotes at restrictive temperature, a striking dissociation of cellulose synthase complexes from the plasma membrane was accompanied by greatly diminished motility of intracellular cellulose synthase-containing compartments. Neither phenomenon was observed in the any1 rsw1-1 transheterozygotes, suggesting that the proteins encoded by the any1 allele replace those encoded by rsw1-1 at restrictive temperature. PMID:23532584

Fujita, Miki; Himmelspach, Regina; Ward, Juliet; Whittington, Angela; Hasenbein, Nortrud; Liu, Christine; Truong, Thy T; Galway, Moira E; Mansfield, Shawn D; Hocart, Charles H; Wasteneys, Geoffrey O

2013-05-01

103

AC transfer function of electrostatic capacitive sensors based on the 1-D equivalent model: application to silicon microphones  

Microsoft Academic Search

Parallel plate electrostatic transducers can be described with the one-dimensional (1-D) lumped model. The one-dimensional approximation based on the elastic, the damping and the inertial force is extended with the electrostatic force (due to the electrical biasing) to model the behavior of electrostatic actuators. In case of sensors, the effect of the external excitation has to be also included. The

Rafael Nadal-Guardia; Anna Maria Brosa; Alfons Dehé

2003-01-01

104

Modeling of temporal variation of surface creep on the Chihshang fault in eastern Taiwan with velocity-strengthening friction  

Microsoft Academic Search

We adopted the velocity-strengthening friction law and 1-D groundwater diffusion model to simulate the surface creep along the Chihshang fault in eastern Taiwan at the plate suture between the Philippine Sea plate and Eurasia. In our previous study, a strong seasonal fluctuation of creeps and significant afterslips of the Chengkung earthquake have been successfully simulated. In this study, we used

S. Chang; J. Lee; W. Wang

2009-01-01

105

An evaluation of 1D loss model collections for the off-design performance prediction of automotive turbocharger compressors  

NASA Astrophysics Data System (ADS)

Single-zone modelling is used to assess different collections of impeller 1D loss models. Three collections of loss models have been identified in literature, and the background to each of these collections is discussed. Each collection is evaluated using three modern automotive turbocharger style centrifugal compressors; comparisons of performance for each of the collections are made. An empirical data set taken from standard hot gas stand tests for each turbocharger is used as a baseline for comparison. Compressor range is predicted in this study; impeller diffusion ratio is shown to be a useful method of predicting compressor surge in 1D, and choke is predicted using basic compressible flow theory. The compressor designer can use this as a guide to identify the most compatible collection of losses for turbocharger compressor design applications. The analysis indicates the most appropriate collection for the design of automotive turbocharger centrifugal compressors.

Harley, P.; Spence, S.; Early, J.; Filsinger, D.; Dietrich, M.

2013-12-01

106

Evaluating a 1D and 2D water quality modeling framework: A case study of the lower Bode River, Germany  

NASA Astrophysics Data System (ADS)

The Bode River catchment in the Harz Mountain area of central Germany is heavily influenced by anthropogenic factors. 70% of the catchment is dominated by agriculture, 23 % by forest and the rest 7% is urban in nature. The area of the catchment is approximately 3300 km2 and is characterized by sharp gradients in temperature, precipitation and land use. In order to acquire better understanding of the hydrological nature of the catchment and biogeochemical characteristics of the Bode River various monitoring stations have been deployed as a part of the larger earth observation network initiative named Terrestrial Environmental Observatories. One of the major issues with the catchment is the problem of eutrophication due to solute inputs from agriculture. The research presented here evaluated the application and development of 1D and 2D hydrodynamic and water quality models in the downstream area of the Bode River. A stretch of 30 kms between Hadmersleeben and Stassfurt in the downstream area of the Bode River was modeled using 1D model HEC-RAS, the focus of the water quality modeling was transport and uptake of nitrate in the aforementioned modeled stretch. Flood events of varying peak magnitude at different times of the year were modeled. As regards to 2D modeling, TELEMAC-2D model was applied for the same reach. The hydrodynamic simulation results were validated with the help of free surface elevation at Athensleben, 8 kms upstream from the downstream end at Stassfurt. Water quality modeling, focusing on the Nitrate removal for the aforementioned stretch, is applied and developed for both 1D and 2D modeling framework. Results from hydrodynamic and water quality modeling were validated with RMSE (Root Mean Square Error) value of 0.074 and 0.36 for the modeled state variables across various events simulated. For the nutrient-rich reach modeled in this research it was found that the nutrient removal capacity of the stream is directly proportional to the incoming nitrate concentration.

Sinha, Sumit; Rode, Michael; Borchardt, Dietrich

2014-05-01

107

Quasi-3D resistivity gridding from large AEM datasets of 1D geophysical models: a step toward enhanced geological interpretation  

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

108

Photolysis frequency of O3 to O(1D): Measurements and modeling during the International Photolysis Frequency Measurement and Modeling Intercomparison (IPMMI)  

Microsoft Academic Search

The International Photolysis Frequency Measurement and Modeling Intercomparison (IPMMI) took place at Boulder, Colorado, from 15 to 19 June 1998 and offered the opportunity to test how well experimental techniques and theoretical models can determine the photolysis frequency of O3 -> O(1D) in the troposphere. Different techniques measured the downwelling 2pi sr component of j(O1D) at the ground and were

A. Hofzumahaus; B. L. Lefer; P. S. Monks; S. R. Hall; A. Kylling; B. Mayer; R. E. Shetter; W. Junkermann; A. Bais; J. G. Calvert; C. A. Cantrell; S. Madronich; G. D. Edwards; A. Kraus; M. Müller; B. Bohn; R. Schmitt; P. Johnston; R. McKenzie; G. J. Frost; E. Griffioen; M. Krol; T. Martin; G. Pfister; E. P. Röth; A. Ruggaber; W. H. Swartz; S. A. Lloyd; M. Van Weele

2004-01-01

109

Photolysis frequency of O3 to O(1D): Measurements and modeling during the International Photolysis Frequency Measurement and Modeling Intercomparison (IPMMI)  

Microsoft Academic Search

The International Photolysis Frequency Measurement and Modeling Intercomparison (IPMMI) took place at Boulder, Colorado, from 15 to 19 June 1998 and offered the opportunity to test how well experimental techniques and theoretical models can determine the photolysis frequency of O3 ? O(1D) in the troposphere. Different techniques measured the downwelling 2? sr component of j(O1D) at the ground and were

A. Hofzumahaus; B. L. Lefer; P. S. Monks; S. R. Hall; A. Kylling; B. Mayer; R. E. Shetter; W. Junkermann; A. Bais; J. G. Calvert; C. A. Cantrell; S. Madronich; G. D. Edwards; A. Kraus; M. Müller; B. Bohn; R. Schmitt; P. Johnston; R. McKenzie; G. J. Frost; E. Griffioen; M. Krol; T. Martin; G. Pfister; E. P. Röth; A. Ruggaber; W. H. Swartz; S. A. Lloyd; M. Van Weele

2004-01-01

110

Quasi3D resistivity gridding from large AEM datasets of 1D geophysical models: a step toward enhanced geological interpretation  

Microsoft Academic Search

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

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

2010-01-01

111

Neural dynamics of 1-D and 2-D brightness perception: A unified model of classical and recent phenomena  

Microsoft Academic Search

Computer simulations of a neural network model of 1-D and 2-D brightness phenomena are presented. The simulations indicate\\u000a how configural image properties trigger interactions among spatially organized contrastive, boundary segmentation, and filling-in\\u000a processes to generate emergent percepts. They provide the first unified mechanistic explanation of this set of phenomena,\\u000a a number of which have received no previous mechanistic explanation. Network

Stephen Grossberg; Dejan Todorovic

1988-01-01

112

The 1d Heisenberg Antiferromagnet Model by the Variation after Projection Method  

NASA Astrophysics Data System (ADS)

The four site and eight site 1D anti-ferromagnetic Heisenberg chains in the Jordan-Wigner representation are investigated within the standard Hartree-Fock and random phase approximation (RPA) approaches, both in the symmetry unbroken and in the symmetry broken phases. A translation invariant groundstate, obtained by the projection method as a linear combination of a symmetry-broken HF state and its image under reflection, is also considered, for each chain type. It is found that the projection method considerably improves the HF treatment for instance as far as the groundstate energy is concerned, but also with respect to the RPA energies. The results are furthermore confronted with the ones obtained within so-called SCRPA scheme.

Rabhi, Aziz; Brajczewska, Marta; Schuck, Peter; da Providência, João; Bennaceur, Raouf

2013-06-01

113

Using overlapping sonobuoy data from the Ross Sea to construct a 2D deep crustal velocity model  

NASA Astrophysics Data System (ADS)

Sonobuoys provide an alternative to using long streamers while conducting multi-channel seismic (MCS) studies, in order to provide deeper velocity control. We present analysis and modeling techniques for interpreting the sonobuoy data and illustrate the method with ten overlapping sonobuoys collected in the Ross Sea, offshore from Antarctica. We demonstrate the importance of using the MCS data to correct for ocean currents and changes in ship navigation, which is required before using standard methods for obtaining a 1D velocity profile from each sonobuoy. We verify our 1D velocity models using acoustic finite-difference (FD) modeling and by performing depth migration on the data, and demonstrate the usefulness of FD modeling for tying interval velocities to the shallow crust imaged using MCS data. Finally, we show how overlapping sonobuoys along an MCS line can be used to construct a 2D velocity model of the crust. The velocity model reveals a thin crust (5.5 ± 0.4 km) at the boundary between the Adare and Northern Basins, and implies that the crustal structure of the Northern Basin may be more similar to that of the oceanic crust in the Adare Basin than to the stretched continental crust further south in the Ross Sea.

Selvans, M. M.; Clayton, R. W.; Stock, J. M.; Granot, R.

2012-03-01

114

The self-trapping attractor neural network. I. Analysis of a simple 1-D model  

Microsoft Academic Search

Attractor neural networks (ANNs) based on the Ising model are naturally fully connected and are homogeneous in structure. These features permit a deep understanding of the underlying mechanism, but limit the applicability of these models to the brain. A more biologically realistic model can be derived from an equally simple physical model by utilizing recurrent self-trapping inputs to supplement very

Raymond Pavloski; Majid Karimi

2003-01-01

115

Lithospheric Velocity Models of Eurasia and the Middle East From the Joint Inversion of P- and S-Wave Receiver Functions and Dispersion Velocicities  

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

116

Rift Structure and Distribution of Magmatic Activity of the Southern Chinese Continental Margin Offshore Southern Taiwan from Reflection Imaging, Travel-time Tomography and 1D Thermal Modeling  

NASA Astrophysics Data System (ADS)

We present new multi-channel seismic reflection images and a wide-angle OBS velocity model from offshore southern Taiwan that delineates the rift architecture and spatial distribution of magmatic bodies across the southern Chinese continental margin in the eastern South China Sea. The timing and distribution of magmatic activity is an important component of rift systems that may control the development of rift structures and sediment deposition. The main structural features in these data include ~3-4 km of passive margin strata deposited on moderately extended continental crust along the continental shelf, and a broad zone of hyper-extended and intruded continental crust across the continental slope and deeper basin. Crust rapidly thins from over 20 km along the continental shelf to less than 4 km at the base of the continental slope in a zone characterized by a shoaling Moho, normal-faulted crust and potentially upper mantle, and up to ~6 km of sedimentary strata. Outboard of this zone, we image tilted fault blocks and crust ~12 km thick. The seismic velocity structure here is consistent with the velocity structure of thinned continental crust observed in previous studies throughout the southwest and central South China Sea, but is incompatible with the distinct layer2/layer3 velocity structure of ocean crust. We observe a zone of large volcanic bodies local to the zone of minimal crustal thickness. The thinned continental crust contains a high-velocity lower crustal layer ~3-5 km thick with seismic velocities of ~6.9 - 7.5 km/s. Such a layer may indicate gabbroic underplating, presumably emplaced by decompression melting during or shortly after rifting. Despite the lower crustal layer and zone of volcanic bodies, there is little evidence for significant extrusive syn-rift magmatism, such as seaward-dipping reflectors. Numerous sills occur throughout the post-rift sedimentary section and post-rift strata are frequently deformed over volcanic bodies, indicating post-rift magmatic activity. We compare our new observations of rift structure and magmatic material with estimates of melt production calculated from a 1D thermal model of pure shear rifting to provide further insights into the interplay between structure and magmatism during rifting.

Lester, R.; McIntosh, K. D.; Lavier, L. L.; Van Avendonk, H. J.

2012-12-01

117

Technical Note: Sensitivity of 1-D smoke plume rise models to the inclusion of environmental wind drag  

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

118

Technical Note: Sensitivity of 1-D smoke plume rise models to the inclusion of environmental wind drag  

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

119

Developing regionalized models of lithospheric thickness and velocity structure across Eurasia and the Middle East from jointly inverting P-wave and S-wave receiver functions with Rayleigh wave group and phase velocities  

SciTech Connect

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

120

The stability analysis of the full velocity and acceleration velocity model  

Microsoft Academic Search

The stability analysis is one of the important problems in the traffic flow theory, since the congestion phenomena can be regarded as the instability and the phase transition of a dynamical system. Theoretically, we analyze the stable conditions of the full velocity and acceleration difference model (FVADM), which is proposed by introducing the acceleration difference term based on the previous

Zhao Xiaomei; Gao Ziyou

2007-01-01

121

Recovery of partial volume losses in cardiac mouse PET imaging using a combined 1D\\/2D and a combined 1D\\/3D model  

Microsoft Academic Search

Micro-PET image resolution is on the order of the left ventricle (LV) wall thickness in a mouse heart. Mouse LV images are thus subject to partial volume (PV) losses, impeding the ability to quantify tracer activity in cardiac muscle. In this study, 2D and 3D PV correction (PVC) models are proposed for mouse imaging. ECG gated PET images are acquired

Tyler Dumouchel; Robert A. de Kemp

2010-01-01

122

Friction of the short model ski at low velocity  

NASA Astrophysics Data System (ADS)

Frictional coefficients of a model ski (10 cm length) were measured at low velocity (0.005 ~ 1 m/s) by means of the tribometer method. The coefficient values depend on sliding velocity, snow temperature and snow grain size. No load effect was observed for any temperature. The static frictional coefficient was depended on the logarithm of the contact time. Further, the coefficient increased with the temperature going up for the smaller grain snow. These experimental results show that the origin of the friction force of the model ski at low velocity is the shearing force of the adhesion between snow and polyethylene.

Takeda, Maiko; Nikki, Kunio; Nishizuka, Takaaki; Abe, Osamu

2010-11-01

123

Differential and integrated form consistency in 1-D phenomenological models for shape memory alloy constitutive behavior  

Microsoft Academic Search

Shape memory alloys are being explored increasingly for developing smart structures and devices in aerospace, automotive and other application areas. The material behavior is highly nonlinear with coupled thermomechanical response involving temperature and\\/or stress induced phase transformations. Modeling the constitutive behavior of these materials poses several challenges and a few phenomenological models exist that provide a quick and reasonable approach

Vidyashankar R. Buravalla; Ashish Khandelwal

2007-01-01

124

Radon exhalation from uranium mill tailings: experimental validation of a 1-D model  

Microsoft Academic Search

TRACI, a model based on the physical mechanisms governing the migration of radon in unsaturated soils, has been developed to evaluate the radon flux density at the surface of uranium mill tailings. To check the validity of the TRACI model and the effectiveness of cover layers, an in situ study was launched in 1997 with the French uranium mining company,

Cécile Ferry; Patrick Richon; Alain Beneito; Marie-Christine Robé

2001-01-01

125

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

126

1-D DC Resistivity Modeling and Interpretation in Anisotropic Media Using Particle Swarm Optimization  

NASA Astrophysics Data System (ADS)

We examine the one-dimensional direct current method in anisotropic earth formation. We derive an analytic expression of a simple, two-layered anisotropic earth model. Further, we also consider a horizontally layered anisotropic earth response with respect to the digital filter method, which yields a quasi-analytic solution over anisotropic media. These analytic and quasi-analytic solutions are useful tests for numerical codes. A two-dimensional finite difference earth model in anisotropic media is presented in order to generate a synthetic data set for a simple one-dimensional earth. Further, we propose a particle swarm optimization method for estimating the model parameters of a layered anisotropic earth model such as horizontal and vertical resistivities, and thickness. The particle swarm optimization is a naturally inspired meta-heuristic algorithm. The proposed method finds model parameters quite successfully based on synthetic and field data. However, adding 5 % Gaussian noise to the synthetic data increases the ambiguity of the value of the model parameters. For this reason, the results should be controlled by a number of statistical tests. In this study, we use probability density function within 95 % confidence interval, parameter variation of each iteration and frequency distribution of the model parameters to reduce the ambiguity. The result is promising and the proposed method can be used for evaluating one-dimensional direct current data in anisotropic media.

Pek?en, Ertan; Yas, Türker; K?yak, Alper

2014-03-01

127

Theoretical Models of High-Velocity Clouds  

NASA Astrophysics Data System (ADS)

Three theories for the origin of the HVC and IVC are considered: galactic fountains, infall of gas removed from dwarf galaxies, and remnants of galaxy formation in the Local Group. Distance is a key discriminator for these theories, so we examine whether the intensity of the H alpha emission can be used to estimate distances. Based upon the H alpha brightness of the Magellanic Stream and HVC Complexes A and M, 1% of the ionizing radiation from the galaxy reaches these clouds, about an order of magnitude lower than that required to ionize the Reynolds layer, but consistent with the clouds having z > 1 kpc. If other HVC have distances of 3-10 kpc, their H alpha brightness should be similar to Complexes A and M, and observations of other HVC should be available soon. We review the state of galactic fountains, of which a key requirement is that breakout of hot gas into the halo occurs. Observational support for breakout is strong both for the Milky Way and other galaxies, and with temperatures that will keep the gas gravitationally bound to the systems. The mass flux rate is difficult to determine directly from the X-ray observations because most of the radiation occurs in the inaccessible EUV band. Evidence from several wavelength bands is consistent with a mass flux rate of 1-10 Modot yr^{-1}. Whereas galactic fountains can produce the intermediate velocity gas and some of the HVC, it is unlikely to be able to account for certain features, including some extremely long complexes. We suggest that a second mechanism is essential and that the most likely candidate is the gas that is removed from dwarfs either through tidal effects or ram pressure stripping.

Bregman, Joel N.

128

Space-based observational constraints for 1-D fire smoke plume-rise models  

NASA Astrophysics Data System (ADS)

We use a plume height climatology derived from space-based Multiangle Imaging Spectroradiometer (MISR) observations to evaluate the performance of a widely used plume-rise model. We initialize the model with assimilated meteorological fields from the NASA Goddard Earth Observing System and estimated fuel moisture content at the location and time of the MISR measurements. Fire properties that drive the plume-rise model are difficult to constrain, and we test the model with four estimates each of active fire area and total heat flux, obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) fire radiative power (FRP) thermal anomalies available for each MISR plume and other empirical data. We demonstrate the degree to which the fire dynamical heat flux (related to active fire area and sensible heat flux) and atmospheric stability structure influence plume rise, although entrainment and possibly other less well constrained factors are also likely to be significant. Using atmospheric stability conditions, MODIS FRP, and MISR plume heights, we find that smoke plumes reaching high altitudes are characterized by higher FRP and weaker atmospheric stability conditions than those at low altitude, which tend to remain confined below the boundary layer, consistent with earlier results. However, over the diversity of conditions studied, the model simulations generally underestimate the plume height dynamic range observed by MISR and do not reliably identify plumes injected into the free troposphere, key information needed for atmospheric models to simulate smoke dispersion. We conclude that embedding in large-scale atmospheric studies an advanced plume-rise model using currently available fire constraints remains a difficult proposition, and we propose a simplified model that crudely constrains plume injection height based on two main physical factors for which some observational constraints often exist. Field experiments aimed at directly measuring fire and smoke plume properties in detail are likely to produce the next major advances in plume-rise modeling.

Val Martin, Maria; Kahn, Ralph A.; Logan, Jennifer A.; Paugam, Ronan; Wooster, Martin; Ichoku, Charles

2012-11-01

129

An Extended Global Sensitivity Analysis Implemented on a 1D Land Biosphere Model  

NASA Astrophysics Data System (ADS)

The implementation of sophisticated mathematical models is undoubtedly becoming increasingly widely used in a variety of fields in geosciences. SimSphere belongs to a special category of land biosphere models called Soil Vegetation Atmosphere Transfer (SVAT) models. Those provide representations, in a vertical profile, of the physical mechanisms controlling the physical interactions occurring in the soil/vegetation/atmosphere continuum at a temporal resolution that is in good agreement with the dynamic timescale of the atmospheric and surface processes. This study builds on previous works conducted by the authors and aims at extending our understanding of this model structure and further establishing its coherence. Herein we present the results from a thorough sensitivity analysis (SA) performed on SimSphere using a cutting edge and robust Global Sensitivity Analysis (GSA) approach, based on the use of the Gaussian Emulation Machine for Sensitivity Analysis (GEM-SA) tool. In particular, the sensitivity of selected key variables characterising land surface interactions simulated by SimSphere were evaluated at different times of model output. All model inputs were assumed to be normally distributed with their probability distribution functions (PDFs) defined using mean and variance taken from the entire theoretical range that these inputs can take in SimSphere. The sensitivity of the following SimSphere outputs was evaluated: Daily Average Net Radiation, Daily Average Latent Heat flux, Daily Average Sensible Heat flux, Daily Average Air Temperature , Daily Average Radiometric Temperature, Daily Average Surface Moisture Availability, Daily Average Evaporative Fraction and Daily Average Non-Evaporative Fraction. Our results showed largely comparable trends in terms of identifying the most sensitive model inputs in respect to the model outputs examined. In addition, a high percentage of first order interactions between the model inputs were reported, suggesting strong model coherence between inputs and outputs. Among the most sensitive model inputs for the outputs examined were the Fractional Vegetation Cover, Soil Moisture and topographically-related parameters (i.e. slope, aspect). Our study represents a significant step forward in the global efforts towards SimSphere verification given that its use is progressively expanding including present efforts to explore its synergy with Earth Observation for operationally deriving key land surface parameters at a global scale from space. KEYWORDS: Global Sensitivity Analysis, BACCO method, GEM-SA

Ioannou-Katidis, Pavlos; Petropoulos, George; Griffiths, Hywel; Bevan, Rhodri

2014-05-01

130

A 1-D Size Specific Numerical Model for Gravel Transport That Includes Sediment Exchange with a Floodplain  

NASA Astrophysics Data System (ADS)

Sedimentary deposits adjacent to rivers can represent important sources and sinks for bed material sediment, particularly on decadal and longer timescales. The Morphodynamics and Sediment Tracers in 1-D model (MAST-1D) is a size-specific sediment transport model that allows for active exchange between channel and floodplain sediment on river reaches of tens to hundreds of kilometers in length. The model is intended to provide a mechanism for performing a first-order assessment of the likely importance of off-channel sediment exchange in controlling decadal-scale geomorphic trends, thereby helping plan and/or prioritize field data collection and higher resolution modeling work. The model develops a sediment budget for short segments of an alluvial valley. Each segment encompasses several active river bends. In each segment, a sediment transport capacity computation is performed to determine the downstream flux of bed material sediment, following the approach of most other 1-D sediment transport models. However, the model differs from most other bed evolution models in that sediment can be exchanged with the floodplain in each segment, and mass conservation is applied to both the active layer and floodplain sediment storage reservoirs. The potential for net imbalances in overall exchange as well as the size specific nature of the computations allows the model to simulate reach-scale aggradation/degradation and/or changes in bed texture. The inclusion of fine sediment in the model allows it to track geochemical tracer material and also provides a mechanism to simulate, to first order, the effects of changes in the supply of silt and clay on overall channel hydraulic capacity. The model is applied to a ~40 km reach of the Ain River, a tributary of the Rhône River in eastern France that has experienced a significant sediment deficit as a result of the construction of several dams between 1920 and 1970. MAST-1D simulations result in both incision and the formation of a bed armor near the upstream end of the study reach, where sediment load has been disrupted. The inclusion of active exchange with the floodplain allows the floodplain evolve into a net source of bed material sediment as the channel incises. This effect prevents the sediment deficit from reaching the confluence with the Rhone for several simulated decades. When spatially variable migration rates similar to those measured from aerial photography are used to drive sediment exchange, the model shows complex interaction between bed and bank sediment, with the relatively fine-grained bank sediment supply mobilizing the coarser fraction of the active layer within rapidly shifting portions of the channel. This increases overall transport rates and leads to additional channel incision relative to what is simulated without bank sediment supply in these rapidly shifting reaches. The model is also helpful for evaluating the potential reach-scale effects of gravel augmentation downstream of the dams.

Lauer, Wesley; Viparelli, Enrica; Piegay, Herve

2014-05-01

131

Regional Travel-Time Uncertainty and Seismic Location Improvement Using 3-Dimensional a priori Velocity Models  

NASA Astrophysics Data System (ADS)

We assess the ability of 3-D velocity models to better predict regional seismic travel times, relative to 1-D models, as well as quantify the travel time uncertainties. Accurate travel time prediction and uncertainty characterization is essential for properly identifying regional seismic phases and computing seismic event locations with representative error ellipses. To accomplish this we use an a priori, 3-D velocity model of Western Eurasia developed at LLNL [Pasyanos et al., 2003] and a dataset of P and Pn phase picks from a catalog of calibration events which meet strict network criteria as investigated by Bondar et al., [2003]. We evaluate the predictive power of the model by computing the median residuals between the observed arrivals and those predicted by 3-D finite difference computations. Statistical assessment of prediction accuracy is made in a non-stationary framework. We conclude that 1-D velocity models are not able to accurately characterize travel time uncertainties; not even radially symmetric models will work. Also, statistical estimates of uncertainty must be made in a region-specific framework (i.e., 3-D). These results demonstrate quantitatively that 3-D velocity models accomplish two goals: improving travel-time prediction (by reducing overall variance of residuals), and reducing the dimensionality of the uncertainties by accounting for the non-stationary component. We also investigate improvement in seismic location using an adaptive station correction approach which combines both model predictions and empirical data. We find that no individual Earth model provides optimal travel-time prediction everywhere. We have, therefore, geographically merged travel-time predictions from a variety of different models and empirical observations to form a travel-time model (correction surface) for each station. Our approach combines the extrapolative advantages of model-based corrections and the interpolative/geostatistical advantages of kriging [Schultz et al., 1998] to produce hybrid travel-time predictions and uncertainty models. For ease of use, model-based and empirical corrections are combined to produce one travel-time correction surface (per seismic station) and uncertainty model that is applied on top of the iasp91 global Earth model in our location algorithm. Such 3-D models and uncertainty characterizations help to achieve location accuracy and computation of representative location error ellipses in a regional monitoring environment, particularly for small events not recorded teleseismically. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48, Contribution UCRL-JC-155079-ABS.

Flanagan, M. P.; Myers, S. C.

2003-12-01

132

Application of the Dual Fermion-Dynamical Cluster Approach to the 1D Falicov Kimball Model  

NASA Astrophysics Data System (ADS)

The Falicov Kimball model is the simplest model for correlated electrons. It was introduced to study metal-insulator transitions. In one dimension, it is known to possess a charge density wave (CDW) instability at zero transition temperature (Tc). However, finite cluster methods like Dynamical Mean Field Theory (DMFT), Dynamical Cluster Approximation (DCA), Cellular Dynamical Mean Field Theory (CDMFT) , etc. show finite temperature CDW transition. In this paper, we study the model using the recently developed Dual Fermion-Dynamical Cluster approach that takes into account large length scale correlations through the auxiliary particles known as dual Fermions. We find that Tc obtained from this method is lower than that obtained from the cluster methods. In particular, we study the scaling behavior of Tc with the linear cluster size and also the scaling of other one-particle and two-particle quantities near the criticality.

Pathak, Sandeep; Meng, Zi Yang; Yang, S.-X.; Jarrell, Mark; Moreno, Juana

2012-02-01

133

Radon exhalation from uranium mill tailings: experimental validation of a 1-D model.  

PubMed

TRACI, a model based on the physical mechanisms governing the migration of radon in unsaturated soils, has been developed to evaluate the radon flux density at the surface of uranium mill tailings. To check the validity of the TRACI model and the effectiveness of cover layers, an in situ study was launched in 1997 with the French uranium mining company, COGEMA. The study consisted of continuous measurements of moisture content, suction, radon concentration at various depths inside a UMT cover, and flux density at its surface. An initial analysis has shown that radon concentration and flux density, as calculated with a steady-state diffusion model using monthly averaged moisture contents, are in good agreement with measured monthly averaged concentrations and flux densities. PMID:11379078

Ferry, C; Richon, P; Beneito, A; Robé, M C

2001-01-01

134

A turbulent inflow model based on velocity modulation  

NASA Astrophysics Data System (ADS)

This article presents a novel turbulent inflow model based on modulation of the velocity field for use with time-domain propulsor calculations. Given an experimental mean and rms turbulent inflow, a model can be constructed by modulating the velocity field over a range of frequencies. Assuming the turbulence is homogeneous, the inflow can be constructed as a Fourier series where the frequencies can also be modulated to smooth the broadband output. To demonstrate the effectiveness of the model, experimental inflow velocity data were acquired for an upstream stator, downstream rotor configuration mounted on an undersea vehicle afterbody. Two main sources of turbulence originated from the vorticity shed from the stator wakes and the boundary layer vorticity produced on the hull body. Three-dimensional, unsteady velocity data were acquired using hot-wire anemometry and reduced to provide mean and rms velocity values. Time-series data were processed to provide velocity power spectra used to calibrate the model. Simulations were performed using a modified version of the propulsor unsteady flow code capable of computing fully turbulent inflows. This solver models the propulsor blade as a vortex lattice and sheds the vorticity into the wake to solve the unsteady potential flow. The no-flux boundary conditions are satisfied at the lattice control points and the resulting unsteady circulation is a function of the instantaneous inflow velocity field over the blade. Vorticity is shed into the wake to account for the full time history of the inflow velocity field. To demonstrate the full effectiveness of the model, computed surface pressure data were exported to a code to compute the far-field radiated noise (both tonal and broadband). Simulated data were compared with experimentally obtained noise data with favorable results. Applications of this methodology in the incompressible flow domain include broadband analysis of propulsor-radiated noise on undersea vehicles and radiator fan noise in cars.

Huyer, Stephen A.; Beal, David

2007-11-01

135

Modeling Bioenhanced DNAPL Dissolution in 1-D and 2-D Flow systems  

NASA Astrophysics Data System (ADS)

Chlorinated ethenes, such as tetrachloroethene (PCE), released into the environment can form dense non-aqueous phase liquids (DNAPLs), which can act as persistent sources of contamination to groundwater. Due to their low aqueous solubility, these DNAPL contaminant sources can persist for up to hundreds of years under natural conditions. Several methods have been investigated to enhance the rate of dissolution of DNAPLs, including bioenhanced dissolution, which consists of stimulating the growth of a microbial population that biodegrades the contaminant, thereby reducing its concentration at the DNAPL-water interface, and creating a greater driving force for contaminant dissolution. This phenomenon has been studied at length in batch reactors and column studies. The hypothesis of this research is that, in modeling DNAPL dissolution bioenhancement via dehalorespiration, it is important to include the effects of microbial competition, as well as spatial effects. A two-dimensional coupled flow-transport model was developed using the finite-volume method (FVM), which includes a DNAPL pool source, and the effects of multiple microbial species. The model has been confirmed to maintain mass balance and has been validated by comparison to an analytical solution for pool dissolution. The model will be used to simulate a pseudo one-dimensional system and a two-dimensional system under multiple microbial competition scenarios and varying hydrodynamic conditions. The results of these simulations will be compared to determine differences in estimations of dissolution bioenhancement, and analyzed for spatial effects that are captured by a two-dimensional model, but not by a pseudo one-dimensional FVM model. Preliminary two-dimensional simulations have shown the effects of large biomass growth near the NAPL source, which could lead to bioclogging and change the flow field. Further simulations are underway and the results will be presented.

Wesseldyke, E. S.; Becker, J. G.; Seagren, E. A.; Mayer, A. S.

2011-12-01

136

Space-based Observational Constraints for 1-D Plume Rise Models.  

National Technical Information Service (NTIS)

We use a space-based plume height climatology derived from observations made by the Multi-angle Imaging SpectroRadiometer (MISR) instrument aboard the NASA Terra satellite to evaluate the ability of a plume-rise model currently embedded in several atmosph...

C. Ichoku J. A. Logan M. Wooster M. V. Martin R. Paguam R. A. Kahn

2012-01-01

137

Modeling 1D structures on semiconductor surfaces: synergy of theory and experiment.  

PubMed

Atomic scale nanowires attract enormous interest in a wide range of fields. On the one hand, due to their quasi-one-dimensional nature, they can act as an experimental testbed for exotic physics: Peierls instability, charge density waves, and Luttinger liquid behavior. On the other hand, due to their small size, they are of interest not only for future device applications in the micro-electronics industry, but also for applications regarding molecular electronics. This versatile nature makes them interesting systems to produce and study, but their size and growth conditions push both experimental production and theoretical modeling to their limits. In this review, modeling of atomic scale nanowires on semiconductor surfaces is discussed, focusing on the interplay between theory and experiment. The current state of modeling efforts on Pt- and Au-induced nanowires on Ge(001) is presented, indicating their similarities and differences. Recently discovered nanowire systems (Ir, Co, Sr) on the Ge(001) surface are also touched upon. The importance of scanning tunneling microscopy as a tool for direct comparison of theoretical and experimental data is shown, as is the power of density functional theory as an atomistic simulation approach. It becomes clear that complementary strengths of theoretical and experimental investigations are required for successful modeling of the atomistic nanowires, due to their complexity. PMID:24599293

Vanpoucke, Danny E P

2014-04-01

138

A versatile compact model for ballistic 1D transistor: Applications to GNRFET and CNTFET  

Microsoft Academic Search

This paper presents a versatile compact model dedicated to ballistic ID transistors that are fabricated in very advanced technologies, in order to predict the ultimate performances of novel nano-device-based circuits. The results presented here after are related to MOS like CNTFET and GNRFET thanks to a unified expression of the non parabolic energy dispersion relation NPEDR which enhances other tentative

Sebastien Fregonese; Cristell Maneux; Thomas Zimmer

2009-01-01

139

Modeling 1D structures on semiconductor surfaces: synergy of theory and experiment  

NASA Astrophysics Data System (ADS)

Atomic scale nanowires attract enormous interest in a wide range of fields. On the one hand, due to their quasi-one-dimensional nature, they can act as an experimental testbed for exotic physics: Peierls instability, charge density waves, and Luttinger liquid behavior. On the other hand, due to their small size, they are of interest not only for future device applications in the micro-electronics industry, but also for applications regarding molecular electronics. This versatile nature makes them interesting systems to produce and study, but their size and growth conditions push both experimental production and theoretical modeling to their limits. In this review, modeling of atomic scale nanowires on semiconductor surfaces is discussed, focusing on the interplay between theory and experiment. The current state of modeling efforts on Pt- and Au-induced nanowires on Ge(001) is presented, indicating their similarities and differences. Recently discovered nanowire systems (Ir, Co, Sr) on the Ge(001) surface are also touched upon. The importance of scanning tunneling microscopy as a tool for direct comparison of theoretical and experimental data is shown, as is the power of density functional theory as an atomistic simulation approach. It becomes clear that complementary strengths of theoretical and experimental investigations are required for successful modeling of the atomistic nanowires, due to their complexity.

Vanpoucke, Danny E. P.

2014-04-01

140

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.o3/ each output from the run at u=N km/s. - chemistry.in: the chemical network used - species.in: the pre-shock chemical composition. - inputmhdrun.u.template : the template with all physical parameters used to sample the grid of velocities * The fourth level contains for each run the following ascii files: - cooling.out : local total emission from a number of species. - energetics.out : various energy fluxes - err_cool.out : a few error messages whichi have occurred during the run. - excit.out : H2 excitation diagram throughout the shock - fe_lines.out: zero (we discarded Fe emission) - fe_pops.out: zero as well - H2_lev.out: integrated column densities of each H2 level - H2_line.out: integrated emission of 200 H2 lines - info_mhd.out: an ascii file which describes the parameters used in the run. - intensity.out: integrated intensities of several atomic lines. - jlb.out: a specific output file for J.L.B. - mhd_coldens.out: column densities of all species along the shock - mhd_phys.out: various physical quantities of interest along the shock - mhd_speci.out: the chemical profile (abundances) - populations.out: local populations of some atomic levels - species.out: post-shock temperature and composition Each ascii file has a self-explanatory first line which contains the names of each quantities in the column below. (3 data files).

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

2012-11-01

141

Reactive Transport Modeling of Microbially-Mediated Chromate Reduction in 1-D Soil Columns  

NASA Astrophysics Data System (ADS)

Cr(VI) reduction tests were performed with the well known metal reducing bacterium Shewanella oneidensis MR-1 in liquid phase batch reactors and continuous flow soil columns under anaerobic conditions. In the batch tests, the cultures were grown with fumarate as the terminal electron acceptor and lactate as the electron donor in a simulated groundwater medium to determine yield coefficients and specific growth rates. The bench-scale soil column experiments were carried out with MR-1 to test the hypothesis that the kinetic parameters obtained in batch studies, combined with microbial attachment /detachment processes, will accurately predict reactive transport of Cr(VI) during bacterial Cr(VI) reduction in a soil matrix. Cr(VI)-free simulated groundwater media containing fumarate as the limiting substrate and lactate was supplied to a 2.1cm (ID) x 15 cm soil column inoculated with MR-1 for a duration of 9 residence times to allow for biomass to build-up in the column. Thereafter the column was supplied with both Cr(VI) and substrate. The concentrations of effluent substrate, biomass and Cr(VI) were monitored on a periodic basis and attached biomass in the column was measured in the termination of each column test. A reactive transport model was developed in which 6 governing equations deal with Cr(VI) bioreaction, fumarate (as electron donor) consumption, aqueous biomass growth and transport, solid biomass detachment and attachment kinetics, aqueous and solid phase enzyme reaction and transport, respectively. The model incorporating the enzyme reaction kinetics for Cr(VI) reduction, Monod kinetic expressions for substrate depletion, nonlinear attachment and detachment kinetics for aqueous and solid phase microorganism concentration, was solved by a fully implicit, finite-difference procedure using RT3D (A Modular Computer Code for Reactive Multi-species Transport in 3-Dimensional Groundwater Systems) platform in one dimension. Cr(VI)-free column data was used to calibrate the biomass attachment and detachment terms used in the model. Column data collected with Cr(VI) in the influent was used to calibrate the model. The modeling results indicate that the Cr(VI) and substrate predictions match closely with the column data. The calibrated model was also able to match attached biomass profiles within the column as well as aqueous biomass in the effluent.

Qiu, H.; Viamajala, S.; Alam, M. M.; Peyton, B. M.; Petersen, J. N.; Yonge, D. R.

2002-12-01

142

A 1D coupled Schrödinger drift-diffusion model including collisions  

Microsoft Academic Search

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

143

First-order phase transition in 1d Potts model with long-range interactions  

Microsoft Academic Search

The first-order phase transition in the one-dimensional q-state Potts model with long-range interactions decaying with distance as 1\\/r1+s, has been studied by Monte Carlo numerical simulations for 0 2. On the basis of the finite-size scaling analysis of interface free energy DFL, specific heat and Binder's fourth order cumulant, we obtain the first-order transition which occurs for s below a

Katarina Uzelac; Zvonko Glumac

1997-01-01

144

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

Microsoft Academic Search

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

145

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

Microsoft Academic Search

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.,

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

2009-01-01

146

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

147

A Simplified 1-D Model for Calculating CO2 Leakage through Conduits  

SciTech Connect

In geological CO{sub 2} storage projects, a cap rock is generally needed to prevent CO{sub 2} from leaking out of the storage formation. However, the injected CO{sub 2} may still encounter some discrete flow paths such as a conductive well or fault (here referred to as conduits) through the cap rock allowing escape of CO{sub 2} from the storage formation. As CO{sub 2} migrates upward, it may migrate into the surrounding formations. The amount of mass that is lost to the formation is called attenuation. This report describes a simplified model to calculate the CO{sub 2} mass flux at different locations of the conduit and the amount of attenuation to the surrounding formations. From the comparison among the three model results, we can conclude that the steady-state conduit model (SSCM) provides a more accurate solution than the PMC at a given discretization. When there is not a large difference between the permeability of the surrounding formation and the permeability of the conduits, and there is leak-off at the bottom formation (the formation immediately above the CO{sub 2} plume), a fine discretization is needed for an accurate solution. Based on this comparison, we propose to use the SSCM in the rapid prototype for now given it does not produce spurious oscillations, and is already in FORTRAN and therefore can be easily made into a dll for use in GoldSim.

Zhang, Y.; Oldenburg, C.M.

2011-02-15

148

An improved Doppler model for obtaining accurate maximum blood velocities.  

PubMed

Maximum blood velocity estimates are frequently required in diagnostic applications, including carotid stenosis evaluation, arteriovenous fistula inspection, and maternal-fetal examinations. However, the currently used methods for ultrasound measurements are inaccurate and often rely on applying heuristic thresholds to a Doppler power spectrum. A new method that uses a mathematical model to predict the correct threshold that should be used for maximum velocity measurements has recently been introduced. Although it is a valuable and deterministic tool, this method is limited to parabolic flows insonated by uniform pressure fields. In this work, a more generalized technique that overcomes such limitations is presented. The new approach, which uses an extended Doppler spectrum model, has been implemented in an experimental set-up based on a linear array probe that transmits defocused steered waves. The improved model has been validated by Field II simulations and phantom experiments on tubes with diameters between 2mm and 8mm. Using the spectral threshold suggested by the new model significantly higher accuracy estimates of the peak velocity can be achieved than are now clinically attained, including for narrow beams and non-parabolic velocity profiles. In particular, an accuracy of +1.2±2.5cm/s has been obtained in phantom measurements for velocities ranging from 20 to 80cm/s. This result represents an improvement that can significantly affect the way maximum blood velocity is investigated today. PMID:24934798

Ricci, Stefano; Matera, Riccardo; Tortoli, Piero

2014-09-01

149

Constraining the temporal evolution of a deep hypersaline anoxic basin by 1D geochemical modelling  

NASA Astrophysics Data System (ADS)

Deep hypersaline anoxic basins (DHABs) are seafloor features of the accretionary prism of the Mediterranean Ridge. They have formed by the dissolution of exhumed shallow Messinian evaporites and subsequent concentration of the ultra-saline solutions in depressions on the seafloor. As an example, the horseshoe-shaped Urania basin is a DHAB south of the Peloponnese peninsula contains one of the most saline (about six times higher than Mediterranean seawater) and sulfidic (up to 15mM) water bodies of the Earth. Furthermore, its deepest part is underlain by a mud volcano that is responsible for the injection of fluid mud beneath the brine lake, with exceptionally sharp chemoclines between water column, brine, and mud layer. We here present a model approach to reconstruct the temporal aspects of the formation, dynamics and persistence of the brine-mud-system in the deep pit of the Urania Basin. Based on data from a sampling campaign with RV Meteor (Cruise M84/1 in February 2011), we set up a one-dimensional geochemical model that integrates diffusion, reaction and advective transport and mixing. Using a set of model preconditions, we aimed to answer (1) which processes are required to maintain the current situation of steep chemical gradients of the brine-mud-system, (2) how fast the current situation could have developed under different scenarios, and (3) how long such extraordinary conditions could have persisted through Earth's history. We further discuss the consequences of the temporal framework for the evolution of prokaryotic life in this extreme habitat.

Goldhammer, Tobias; Aiello, Ivano; Zabel, Matthias

2014-05-01

150

First-order phase transition in $1d$ Potts model with long-range interactions  

Microsoft Academic Search

The first-order phase transition in the one-dimensional $q$-state Potts model\\u000awith long-range interactions decaying with distance as $1\\/r^{1+\\\\sigma}$ has\\u000abeen studied by Monte Carlo numerical simulations for $0 < \\\\sigma \\\\le 1$ and\\u000ainteger values of $q > 2$. On the basis of finite-size scaling analysis of\\u000ainterface free energy $\\\\Delta F_L$, specific heat and Binder's fourth order\\u000acumulant, we

K. Uzelac; Z. Glumac

1998-01-01

151

Conformally exact results for SL(2, R) ? SO(1, 1) d-2/ SO(1, 1) coset models  

NASA Astrophysics Data System (ADS)

Using the conformal invariance of the SL(2, R)? SO(1, 1) d-2/ SO(1, 1) coset models we calculate the conformally exact metric and dilaton, to all orders in the 1/ k expansion. We consider both vector and axial gauging. We find that these cosets represent two different space-time geometries: (2d black hole) ? Rd-2 for the vector gauging and (3d bllck string) ? Rd-3 for the axial one. In particular for d = 3 and for the axial gauging one obtains the exact metric and dilaton of the charged black string model introduced by Horne and Horowitz. If the value of k is finite we find two curvature singularities which degenerate to one in the semi-classical k ?? limit. We also calculate the reflection and transmission coefficients for the scattering of a tachyon wave and using the Bogoliubov transformation we find the Hawking temperature.

Sfetsos, Konstadinos

1993-01-01

152

Nonlinear inverse model for velocity estimation from an image sequence  

NASA Astrophysics Data System (ADS)

Velocity estimation from an image sequence is one of the most challenging inverse problems in computer vision, geosciences, and remote sensing applications. In this paper a nonlinear model has been created for estimating motion field under the constraint of conservation of intensity. A linear differential form of heat or optical flow equation is replaced by a nonlinear temporal integral form of the intensity conservation constraint equation. Iterative equations with Gauss-Newton and Levenberg-Marguardt algorithms are formulated based on the nonlinear equations, velocity field modeling, and a nonlinear least squares model. An algorithm with progressive relaxation of the overconstraint to improve the performance of the velocity estimation is also proposed. The new estimator is benchmarked using a numerical simulation model. Both angular and magnitude error measurements based on the synthetic surface heat flow from the numerical model demonstrate that the performance of the new approach with the nonlinear model is much better than the results of using a linear model of heat or optical flow equation. Four sequences of NOAA Advanced Very High Resolution Radiometer (AVHRR) images taken in the New York Bight fields is also used to demonstrate the performance of the nonlinear inverse model, and the estimated velocity fields are compared with those measured with the Coastal Ocean Dynamics Radar array. The experimental results indicate that the nonlinear inverse model provides significant improvement over the linear inverse model for real AVHRR data sets.

Chen, Wei

2011-06-01

153

Hyperbolic reformulation of a 1D viscoelastic blood flow model and ADER finite volume schemes  

NASA Astrophysics Data System (ADS)

The applicability of ADER finite volume methods to solve hyperbolic balance laws with stiff source terms in the context of well-balanced and non-conservative schemes is extended to solve a one-dimensional blood flow model for viscoelastic vessels, reformulated as a hyperbolic system, via a relaxation time. A criterion for selecting relaxation times is found and an empirical convergence rate assessment is carried out to support this result. The proposed methodology is validated by applying it to a network of viscoelastic vessels for which experimental and numerical results are available. The agreement between the results obtained in the present paper and those available in the literature is satisfactory. Key features of the present formulation and numerical methodologies, such as accuracy, efficiency and robustness, are fully discussed in the paper.

Montecinos, Gino I.; Müller, Lucas O.; Toro, Eleuterio F.

2014-06-01

154

Point Defects in 3D and 1D Nanomaterials: The Model Case of Titanium Dioxide  

NASA Astrophysics Data System (ADS)

Titanium dioxide is one of the most important oxides for applications in energy and environment, such as solar cells, photocatalysis, lithium-ion batteries. In recent years, new forms of titanium dioxide with unusual structure and/or morphology have been developed, including nanocrystals, nanotubes or nanowires. We have studied in detail the point defect chemistry in nanocrystalline TiO2 powders and ceramics. There can be a change from predominant Frenkel to Schottky disorder, depending on the experimental conditions, e.g. temperature and oxygen partial pressure. We have also studied the local environment of various dopants with similar ion radius, but different ion charge (Zn2+, Y3+, Sn4+, Zr4+, Nb5+) in TiO2 nanopowders and nanoceramics by Extended X-Ray Absorption Fine Structure (EXAFS) Spectroscopy. Interfacial segregation of acceptors was demonstrated, but donors and isovalent ions do not segregate. An electrostatic "space charge" segregation model is applied, which explains well the observed phenomena.

Knauth, Philippe

2010-11-01

155

Construction of a 3D seismic velocity model for the Barents Sea region using sediment vs. crystalline crust thickness relationships  

NASA Astrophysics Data System (ADS)

We present a 3D seismic velocity model for the extended Barents Sea region, including Svalbard, Novaya Zemlya, the Kara Sea and the Kola-Karelia Regions. The purpose of developing a higher-resolution velocity model is to improve generally the seismic event localization in the target region. The model should improve the future monitoring facilities and the accompanied travel-time modeling. Initial testing of the model will base on the modeling of a series of seismic ground-truth events recorded by the surrounding stations. The model has a spatial resolution of 50x50 km and includes 1490 nodes. Each node is filled with a 5-layer crustal model (plus water/ice- and additional mantle layers): Nodes within the oceanic and continental domains bear two sedimentary layers (low/high vp) and three "crystalline" crustal layers (low/intermediate/high vp). Basis of this model is a recent compilation of seismic velocities taken from published wide-angle profiles, unpublished ESP profiles and additional gravity modeling along deep MSC-profiles. Over 700 1D velocity profiles are collected. In order to interpolate the velocity/depth-information from the randomly distributed 1D profiles on the equal-spaced grid, the following technique was applied: Analyzing the database, we found a strong linear trend between the total thickness of the sediment layers and the remaining crystalline crust within pre-defined continental provinces (e.g. distinct sedimentary basins, plateaus, basement highs, etc.). Area-wide depth-to-basement information, based on the integrated analysis of seismic, gravity and magnetic data is used to calculate the crystalline and total crustal thicknesses as functions of sediment thickness. The mean seismic velocities and thickness-rates for each of the 5 crustal layers are calculated from the compiled database. Analysis of the regressions show that about 75-90% of the data input is fitted by the calculated functions with a maximum of 20% deviation relative to its total thickness. The compiled database provides further excellent statistical background for composition of crystalline crustal rocks in the target region. The overall distribution of seismic velocities within crystalline crust shows a clear bimodal structure with velocity peaks at 6.4 and 6.8 km/s. First modeling tests along four selected transects were carried out to evaluate the constructed 3D seismic model. According to the tests travel-time deviations can exceed 2 s at distances of 300-800 km (by comparison to a standard 1D model).

Ritzmann, O.; Faleide, J.; Bungum, H.; Maercklin, N.; Schweitzer, J.; Mooney, W. D.; Detweiler, S. T.; Leith, W. S.

2004-12-01

156

Short time-scale analysis of the NW Mediterranean ecosystem during summer-autumn transition: A 1D modelling approach  

NASA Astrophysics Data System (ADS)

Modelling was used as a tool to better understand the physical and biological processes observed during the multidisciplinary cruise DYNAPROC 2 (DYNAmic of rapid PROCesses in the water column), which took place in the Ligurian Sea in September-October 2004. The aim of the cruise was to study the short time-scale physical and biological processes that occur when the ecosystem switches from summer oligotrophy to autumnal mesotrophy. In this study, we have tested two 1D physical-biological coupled models. The first was a classical model in which surface layer dynamics were obtained using the turbulent kinetic energy model of Gaspar [Gaspar et al., 1990]. The simulated food-web took into account ten state variables: three nutrients, three classes of phytoplankton, two classes of zooplankton and two types of detritus. The second model (called IDA, Isopycnals Depth Adjustment) was based on the initial one but it took into account the measured variations of isopycnals depths. The results showed that the IDA model most efficiently reproduced the observed ecosystem dynamics. We have therefore used the IDA model to show that physical processes observed during the cruise had a major effect on biological compartment, mainly on nano- and picophytoplankton.

Raybaud, V.; Nival, P.; Prieur, L.

2011-01-01

157

Three-dimensional green water velocity on a model structure  

NASA Astrophysics Data System (ADS)

Flow kinematics of green water due to plunging breaking waves impinging on a simplified, 3D model structure was investigated in the laboratory. Two breaking wave conditions were tested: one with waves impinging on the vertical wall of the model at still water level, and the other with waves impinging on the horizontal deck surface. The bubble image velocimetry (BIV) technique was used to measure flow velocities. Measurements were taken on both vertical and horizontal planes. Evolution of green water flow kinematics in time and space was revealed and was found to be quite different between the two wave conditions, even though the incoming waves are essentially identical. The time history of maximum velocity is demonstrated and compared. In both cases, the maximum velocity occurs near the green water front and beneath the free surface. The maximum horizontal velocity for the deck impinging case is 1.44 C with C being the wave phase speed, which is greater than 1.24 C for the wall impingement case. The overall turbulence level is about 0.3 of the corresponding maximum velocity in each wave condition. The results were also compared with 2D experimental results to examine the 3D effect. It was found that the magnitude of the maximum vertical velocity during the runup process is 1.7 C in the 3D model study and 2.9 C in the 2D model study, whereas the maximum horizontal velocity on the deck is similar, 1.2 C in both 3D and 2D model studies.

Chang, Kuang-An; Ariyarathne, Kusalika; Mercier, Richard

2011-08-01

158

Geometric and frequency EMI sounding of estuarine earthen flood defence embankments in Ireland using 1D inversion models  

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

159

Spontaneous formation of vorticity staircase and multiple jets in a 1D barotropic model with parameterized eddy mixing  

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

160

Giant Fluctuations of Local Magnetoresistance of Organic Spin Valves and the Non-Hermitian 1D Anderson Model.  

PubMed

Motivated by recent experiments, where the tunnel magnetoresitance (TMR) of a spin valve was measured locally, we theoretically study the distribution of TMR along the surface of magnetized electrodes. We show that, even in the absence of interfacial effects (like hybridization due to donor and acceptor molecules), this distribution is very broad, and the portion of area with negative TMR is appreciable even if on average the TMR is positive. The origin of the local sign reversal is quantum interference of subsequent spin-rotation amplitudes in the course of incoherent transport of carriers between the source and the drain. We find the distribution of local TMR exactly by drawing upon formal similarity between evolution of spinors in time and of the reflection coefficient along a 1D chain in the Anderson model. The results obtained are confirmed by the numerical simulations. PMID:24949781

Roundy, R C; Nemirovsky, D; Kagalovsky, V; Raikh, M E

2014-06-01

161

Giant Fluctuations of Local Magnetoresistance of Organic Spin Valves and the Non-Hermitian 1D Anderson Model  

NASA Astrophysics Data System (ADS)

Motivated by recent experiments, where the tunnel magnetoresitance (TMR) of a spin valve was measured locally, we theoretically study the distribution of TMR along the surface of magnetized electrodes. We show that, even in the absence of interfacial effects (like hybridization due to donor and acceptor molecules), this distribution is very broad, and the portion of area with negative TMR is appreciable even if on average the TMR is positive. The origin of the local sign reversal is quantum interference of subsequent spin-rotation amplitudes in the course of incoherent transport of carriers between the source and the drain. We find the distribution of local TMR exactly by drawing upon formal similarity between evolution of spinors in time and of the reflection coefficient along a 1D chain in the Anderson model. The results obtained are confirmed by the numerical simulations.

Roundy, R. C.; Nemirovsky, D.; Kagalovsky, V.; Raikh, M. E.

2014-06-01

162

Is flow velocity a significant parameter in flood damage modelling?  

NASA Astrophysics Data System (ADS)

Flow velocity is generally presumed to influence flood damage. However, this influence is hardly quantified and virtually no damage models take it into account. Therefore, the influences of flow velocity, water depth and combinations of these two impact parameters on various types of flood damage were investigated in five communities affected by the Elbe catchment flood in Germany in 2002. 2-D hydraulic models with high to medium spatial resolutions were used to calculate the impact parameters at the sites in which damage occurred. A significant influence of flow velocity on structural damage, particularly on roads, could be shown in contrast to a minor influence on monetary losses and business interruption. Forecasts of structural damage to road infrastructure should be based on flow velocity alone. The energy head is suggested as a suitable flood impact parameter for reliable forecasting of structural damage to residential buildings above a critical impact level of 2 m of energy head or water depth. However, general consideration of flow velocity in flood damage modelling, particularly for estimating monetary loss, cannot be recommended.

Kreibich, H.; Piroth, K.; Seifert, I.; Maiwald, H.; Kunert, U.; Schwarz, J.; Merz, B.; Thieken, A. H.

2009-10-01

163

An analytical 1-D model for vertical momentum and energy flux through a fully developed wind farm  

NASA Astrophysics Data System (ADS)

Wind farms capture momentum from the atmospheric boundary layer (ABL) both at the leading edge and from the atmosphere above. Momentum is advected into the wind farm and wake turbulence draws excess momentum in from between turbines until momentum is only available from above the wind farm. This distance can be described by the so-called drag development length scale, which arises from the canopy drag force term in the momentum equation. At this point the flow can be considered fully developed. The horizontally-averaged velocity profile for a fully developed wind farm flow exhibits a characteristic inflection point near the top of the wind farm, similar to that of sparse canopy-type flows (Markfort et al., JoT, 2012). The inflected vertical velocity profile is associated with the presence of a dominant characteristic turbulence scale, which may be responsible for a significant portion of the vertical momentum flux. We evaluate an analytical canopy-type flow model for wind farm-atmosphere interaction by testing it against wind-tunnel experimental data of flow through a model wind farm. The model is adapted to predict the mean flow, vertical momentum flux, and the mean kinetic energy flux as well as kinetic energy dissipation within the wind farm. This model is particularly useful for wind farm configuration optimization, considering wind turbine spacing and surface roughness and can also be useful to represent wind farms in regional scale atmospheric simulations.

Markfort, Corey D.; Zhang, Wei; Porté-Agel, Fernando

2014-05-01

164

Velocity model of the Hronov-Po?í?í Fault Zone from Rayleigh wave dispersion  

NASA Astrophysics Data System (ADS)

The Hronov-Po?í?í Fault Zone (HPFZ) is an active tectonic area with regularly occurring shallow earthquakes up to magnitude 5. For their exact locations, at least an average velocity model of the area is needed. A method of measuring local phase velocities of surface waves using the array of stations deployed permanently in the HPFZ is introduced. Seven regional and teleseismic events are selected to represent different backazimuths of propagation. Applicable range of periods is estimated for each event. The coherency of the waves reaching the array is constraining the short period range. The dimension of the array is a limiting factor for the long-periods. A dispersion curve of Rayleigh wave phase velocity measured at the vertical component and characterizing 1D properties of the target area is determined using the seven measurements for the interval from 1 to 40 s. An isometric method is used to invert the determined dispersion curve for shear and longitudinal velocity distribution from the surface to the depth of 65 km.

Kolínský, Petr; Valenta, Jan; Málek, Ji?í

2014-07-01

165

Evaluation of six fracture models in high velocity perforation  

Microsoft Academic Search

A systematic evaluation of six ductile fracture models is performed to identify the most suitable fracture criterion for high velocity perforation problems. Included in the paper are the Wilkins, the Johnson–Cook, the maximum shear stress, the modified Cockcroft–Latham, the constant fracture strain, and the Bao–Wierzbicki fracture models. These six fracture models are implemented into ABAQUS\\/Explicit by means of a user

X. Teng; T. Wierzbicki

2006-01-01

166

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

167

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

168

Limb darkening laws for two exoplanet host stars derived from 3D stellar model atmospheres. Comparison with 1D models and HST light curve observations  

NASA Astrophysics Data System (ADS)

We compare limb darkening laws derived from 3D hydrodynamical model atmospheres and 1D hydrostatic MARCS models for the host stars of two well-studied transiting exoplanet systems, the late-type dwarfs HD 209458 and HD 189733. The surface brightness distribution of the stellar disks is calculated for a wide spectral range using 3D LTE spectrum formation and opacity sampling?. We test our theoretical predictions using least-squares fits of model light curves to wavelength-integrated primary eclipses that were observed with the Hubble Space Telescope (HST). The limb darkening law derived from the 3D model of HD 209458 in the spectral region between 2900 Å and 5700 Å produces significantly better fits to the HST data, removing systematic residuals that were previously observed for model light curves based on 1D limb darkening predictions. This difference arises mainly from the shallower mean temperature structure of the 3D model, which is a consequence of the explicit simulation of stellar surface granulation where 1D models need to rely on simplified recipes. In the case of HD 189733, the model atmospheres produce practically equivalent limb darkening curves between 2900 Å and 5700 Å, partly due to obstruction by spectral lines, and the data are not sufficient to distinguish between the light curves. We also analyze HST observations between 5350 Å and 10 500 Å for this star; the 3D model leads to a better fit compared to 1D limb darkening predictions. The significant improvement of fit quality for the HD 209458 system demonstrates the higher degree of realism of 3D hydrodynamical models and the importance of surface granulation for the formation of the atmospheric radiation field of late-type stars. This result agrees well with recent investigations of limb darkening in the solar continuum and other observational tests of the 3D models. The case of HD 189733 is no contradiction as the model light curves are less sensitive to the temperature stratification of the stellar atmosphere and the observed data in the 2900-5700 Å region are not sufficient to distinguish more clearly between the 3D and 1D limb darkening predictions. Full theoretical spectra for both stars are 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/539/A102, as well as at www.astro.ex.ac.uk/people/sing.

Hayek, W.; Sing, D.; Pont, F.; Asplund, M.

2012-03-01

169

A reduced-order model based on the coupled 1D-3D finite element simulations for an efficient analysis of hemodynamics problems  

NASA Astrophysics Data System (ADS)

A reduced-order model for an efficient analysis of cardiovascular hemodynamics problems using multiscale approach is presented in this work. Starting from a patient-specific computational mesh obtained by medical imaging techniques, an analysis methodology based on a two-step automatic procedure is proposed. First a coupled 1D-3D Finite Element Simulation is performed and the results are used to adjust a reduced-order model of the 3D patient-specific area of interest. Then, this reduced-order model is coupled with the 1D model. In this way, three-dimensional effects are accounted for in the 1D model in a cost effective manner, allowing fast computation under different scenarios. The methodology proposed is validated using a patient-specific aortic coarctation model under rest and non-rest conditions.

Soudah, Eduardo; Rossi, Riccardo; Idelsohn, Sergio; Oñate, Eugenio

2014-05-01

170

Regulatory Roles of CD1d-Restricted NKT Cells in the Induction of Toxic Shock-Like Syndrome in an Animal Model of Fatal Ehrlichiosis  

Microsoft Academic Search

CD1d-restricted NKT cells are key players in host defense against various microbial infections. Using a murine model of fatal ehrlichiosis, we investigated the role of CD1d-restricted NKT cells in induction of toxic shock-like syndrome caused by gram-negative, lipopolysaccharide-lacking, monocytotropic Ehrlichia. Our previous studies showed that intraperitoneal infection of wild-type (WT) mice with virulent Ehrlichia (Ixodes ovatus Ehrlichia (IOE)) results in

H. L. Stevenson; E. C. Crossley; N. Thirumalapura; D. H. Walker; N. Ismail

2008-01-01

171

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

172

Testing models of the oculomotor velocity-to-position transformation.  

PubMed

1. Do neural computations in premotor circuits mirror the physical properties of the systems they control? In 1987, Tweed and Vilis showed that oculomotor theories where a neural integrator converts eye angular velocity commands into position commands cannot be correct, because angular position is not the integral of angular velocity. Recently Schnabolk and Raphan proposed that an angular velocity integrator is nevertheless used to generate tonic commands in the oculomotor system. Here we test the Schnabolk-Raphan (S-R) model against Tweed and Vilis's quaternion (Q) model of the velocity to position transformation. 2. The S-R model predicts large (up to 7 degrees) transient (approximately 700 ms) deviations ("blips") in torsional eye position during attempted horizontal and vertical saccades. The Q model predicts no blips. Search coil recordings of saccades by 7 normal human subjects showed no large blips. 3. For approximately 200 saccades by each subject, we plotted the area under the torsional blip versus the product of saccade eccentricity and magnitude. According to the S-R model, this graph should form a straight line with slope 1.00. According to the Q model, the slope should be zero. Measured slopes averaged 0.016 (range -0.073 to 0.061) for saccade targets at 20 degrees eccentricity and 0.040 (range 0.004-0.076) for targets at 40 degrees. 4. No parameter change can significantly improve the S-R model, but lowering one parameter eradicates the tiny inaccuracy in the Q model. We show that the fundamental reason for the S-R model's failure is its use of a commutative controller to steer a noncommutative plant. PMID:7807223

Tweed, D; Misslisch, H; Fetter, M

1994-09-01

173

Modeling and comparative study of fluid velocities in heterogeneous rocks  

NASA Astrophysics Data System (ADS)

Detailed knowledge of the distribution of effective porosity and fluid velocities in heterogeneous rock samples is crucial for understanding and predicting spatially resolved fluid residence times and kinetic reaction rates of fluid-rock interactions. The applicability of conventional MRI techniques to sedimentary rocks is limited by internal magnetic field gradients and short spin relaxation times. The approach developed at the UNB MRI Centre combines the 13-interval Alternating-Pulsed-Gradient Stimulated-Echo (APGSTE) scheme and three-dimensional Single Point Ramped Imaging with T1 Enhancement (SPRITE). These methods were designed to reduce the errors due to effects of background gradients and fast transverse relaxation. SPRITE is largely immune to time-evolution effects resulting from background gradients, paramagnetic impurities and chemical shift. Using these techniques quantitative 3D porosity maps as well as single-phase fluid velocity fields in sandstone core samples were measured. Using a new Magnetic Resonance Imaging technique developed at the MRI Centre at UNB, we created 3D maps of porosity distributions as well as single-phase fluid velocity distributions of sandstone rock samples. Then, we evaluated the applicability of the Kozeny-Carman relationship for modeling measured fluid velocity distributions in sandstones samples showing meso-scale heterogeneities using two different modeling approaches. The MRI maps were used as reference points for the modeling approaches. For the first modeling approach, we applied the Kozeny-Carman relationship to the porosity distributions and computed respective permeability maps, which in turn provided input for a CFD simulation - using the Stanford CFD code GPRS - to compute averaged velocity maps. The latter were then compared to the measured velocity maps. For the second approach, the measured velocity distributions were used as input for inversely computing permeabilities using the GPRS CFD code. The computed permeabilities were then correlated with the ones based on the porosity maps and the Kozeny-Carman relationship. The findings of the comparative modeling study are discussed and its potential impact on the modeling of fluid residence times and kinetic reaction rates of fluid-rock interactions in rocks containing meso-scale heterogeneities are reviewed.

Hingerl, Ferdinand F.; Romanenko, Konstantin; Pini, Ronny; Balcom, Bruce; Benson, Sally

2013-04-01

174

Scale up tools in reactive extrusion and compounding processes. Could 1D-computer modeling be helpful?  

NASA Astrophysics Data System (ADS)

Industrial scale-up (or scale down) in Compounding and Reactive Extrusion processes is one of the most critical R&D challenges. Indeed, most of High Performances Polymers are obtained within a reactive compounding involving chemistry: free radical grafting, in situ compatibilization, rheology control... but also side reactions: oxidation, branching, chain scission... As described by basic Arrhenius and kinetics laws, the competition between all chemical reactions depends on residence time distribution and temperature. Then, to ensure the best possible scale up methodology, we need tools to match thermal history of the formulation along the screws from a lab scale twin screw extruder to an industrial one. This paper proposes a comparison between standard scale-up laws and the use of Computer modeling Software such as Ludovic® applied and compared to experimental data. Scaling data from a compounding line to another one, applying general rules (for example at constant specific mechanical energy), shows differences between experimental and computed data, and error depends on the screw speed range. For more accurate prediction, 1D-Computer Modeling could be used to optimize the process conditions to ensure the best scale-up product, especially in temperature sensitive reactive extrusion processes. When the product temperature along the screws is the key, Ludovic® software could help to compute the temperature profile along the screws and extrapolate conditions, even screw profile, on industrial extruders.

Pradel, J.-L.; David, C.; Quinebèche, S.; Blondel, P.

2014-05-01

175

Improving three dimensional velocity model for Puerto Rico - Virgin Islands for rapid earthquake re-locations  

NASA Astrophysics Data System (ADS)

Puerto Rico and the Virgin Islands (PRVI) block lie on the northeastern boundary of the Caribbean plate, where active transpressional tectonics result in the deformation of the boundaries of this block. Every year hundreds of earthquakes occur within and around PRVI region and at least four destructive earthquakes after 1700 are documented in the historical records. The mission of the Puerto Rico Seismic Network (PRSN), Department of Geology of the University of Puerto Rico in Mayagüez is to detect, analyze, disseminate earthquake/tsunami messages and investigate the seismicity in the PR/VI. Currently the PRSN operates 30 seismic stations and receive real time stream from over 75 station installed around the Caribbean. 25 years worth of data recorded by the PRSN has been quality checked and compiled to constrain a new velocity structure using the tomographic package TomoDD. Currently at PRSN, the velocity structure to perform real-time determination of hypocenters consists of a 1-D model. Therefore, this ambitious tomographic study seek to produce a more comprehensive velocity model to be implemented at the PRSN for the daily earthquake locations. Results from this study are a collaborative effort between the University of Miami and the University of Puerto Rico - Mayaguez.

Huerfano, V. A.; Lopez, A. M.; Castillo, L.; Baez-Sanchez, G.; Soto-Cordero, L.; Lin, G.; Zhang, Q.

2010-12-01

176

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

177

Thirteen-velocity three-dimensional lattice Boltzmann model  

Microsoft Academic Search

A thirteen-velocity three-dimensional lattice Boltzmann model on a cubic grid is presented. The transport coefficients derived from the standard Chapman-Enskog expansion are given together with the conditions for isotropy and Galilean invariance. The different invariants of the model are discussed. The results of measurements of drag and torque on a free falling sphere in a cylinder are in good agreement

Dominique d’Humières; M’hamed Bouzidi; Pierre Lallemand

2001-01-01

178

Treg cells in pancreatic lymph nodes: the possible role in diabetogenesis and ? cell regeneration in a T1D model.  

PubMed

Previously, we established a model in which physiologically adequate function of the autologous ? cells was recovered in non-obese diabetic (NOD) mice after the onset of hyperglycemia by rendering them hemopoietic chimera. These mice were termed antea-diabetic. In the current study, we addressed the role of T regulatory (Treg) cells in the mechanisms mediating the restoration of euglycemia in the antea-diabetic NOD model. The data generated in this study demonstrated that the numbers of Treg cells were decreased in unmanipulated NOD mice, with the most profound deficiency detected in the pancreatic lymph nodes (PLNs). The impaired retention of the Treg cells in the PLNs correlated with the locally compromised profile of the chemokines involved in their trafficking, with the most prominent decrease observed in SDF-1. The amelioration of autoimmunity and restoration of euglycemia observed in the antea-diabetic mice was associated with restoration of the Treg cell population in the PLNs. These data indicate that the function of the SDF-1/CXCR4 axis and the retention of Treg cells in the PLNs have a potential role in diabetogenesis and in the amelioration of autoimmunity and ? cell regeneration in the antea-diabetic model. We have demonstrated in the antea-diabetic mouse model that lifelong recovery of the ? cells has a strong correlation with normalization of the Treg cell population in the PLNs. This finding offers new opportunities for testing the immunomodulatory regimens that promote accumulation of Treg cells in the PLNs as a therapeutic approach for type 1 diabetes (T1D). PMID:23042535

Nti, Benjamin K; Markman, Janet L; Bertera, Suzanne; Styche, Alexis J; Lakomy, Robert J; Subbotin, Vladimir M; Trucco, Massimo; Zorina, Tatiana D

2012-11-01

179

Developing a Low-Velocity Collision Model Based on the Nasa Standard Breakup Model  

Microsoft Academic Search

We have conducted a series of low-velocity impact experiments to understand the dispersion properties of fragments newly created by low-velocity impacts possible in space, especially in geostationary Earth orbit. The test results are utilized to establish a mathematical prediction model to be used in debris generation and propagation codes. Since the expected collision velocity between catalogued objects in geostationary Earth

Toshiya Hanada; Mail Code SX; Lyndon B. Johnson

2000-01-01

180

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

SciTech Connect

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

181

Thirteen-velocity three-dimensional lattice Boltzmann model  

NASA Astrophysics Data System (ADS)

A thirteen-velocity three-dimensional lattice Boltzmann model on a cubic grid is presented. The transport coefficients derived from the standard Chapman-Enskog expansion are given together with the conditions for isotropy and Galilean invariance. The different invariants of the model are discussed. The results of measurements of drag and torque on a free falling sphere in a cylinder are in good agreement with solutions of the Navier-Stokes equation. Comparison of the time evolution of a freely decaying Taylor-Green vortex computed by fast Fourier transform and by the present model is presented.

D'humières, Dominique; Bouzidi, M.'hamed; Lallemand, Pierre

2001-06-01

182

Thirteen-velocity three-dimensional lattice Boltzmann model.  

PubMed

A thirteen-velocity three-dimensional lattice Boltzmann model on a cubic grid is presented. The transport coefficients derived from the standard Chapman-Enskog expansion are given together with the conditions for isotropy and Galilean invariance. The different invariants of the model are discussed. The results of measurements of drag and torque on a free falling sphere in a cylinder are in good agreement with solutions of the Navier-Stokes equation. Comparison of the time evolution of a freely decaying Taylor-Green vortex computed by fast Fourier transform and by the present model is presented. PMID:11415253

d'Humières, D; Bouzidi, M; Lallemand, P

2001-06-01

183

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

184

Electric structure of the Copahue Volcano (Neuquén Province, Argentina), from magnetotelluric soundings: 1D and 2D modellings  

NASA Astrophysics Data System (ADS)

Four magnetotelluric soundings were carried out in 1993 in the region of the Copahue active volcano located at the border between Chile and Argentina (37°45'S, 71°18'W). Three soundings were located inside the caldera of the ancient stratovolcano (east of Copahue) and the fourth outside it. The soundings inside the caldera were situated at about 6, 11, and 14 km from the volcano. Digital data were obtained covering the range of periods from 1 sec to 10,000 sec using induction coils and a flux-gate magnetometer to obtain the magnetic data and Cu-SO 4Cu electrodes for electric field measurements. The apparent resistivity curves corresponding to principal directions were analyzed in conjunction with the geological background in order to eliminate distortion — which is very important in this hot volcanic region. Then, 1D modellings were performed using the "normal" curves — i.e., curves without distortions. Using the apparent resistivity curves with distortions, 2D modelling was also performed along a profile perpendicular to the regional tectonic trend suggested by MT soundings into the caldera. Results show low resistivity values of about 3-15 ?m between 9 km to 20 km depth in the crust, suggesting high temperatures, with minimum values of about 700°C with partially melted zones in the upper crust between 9 km to 20 km depth under the caldera. The presence of a possible sulphide-carbonaceous layer (SC layer) in the upper basement could play an important role in lowering the electrical resistivities because of its high electronic conductivity.

Mamaní, M. J.; Borzotta, E.; Venencia, J. E.; Maidana, A.; Moyano, C. E.; Castiglione, B.

2000-05-01

185

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

186

Model for the relation between shock velocity and particle velocity in weak shock waves in metals  

SciTech Connect

The weak-shock theory of D. C. Wallace (Phys. Rev. B {bold 22}, 1487 (1980)) is used to calculate shock velocities as a function of particle velocity. The calculated shock velocities are based on thermoelastic behavior, plasticity behavior, and precursor behavior. The results are calculated and compared with data for 6061T6 Al, Be, Cu, Fe, 21-6-9 stainless steel, and U. Except for Fe, the agreement is reasonable. The contributions to the shock velocity from material strength and precursor behavior are rather small but, nevertheless, are calculated fairly well with the present theory.

Tonks, D.L. (Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico (USA))

1991-10-15

187

Stochastic optimal velocity model and its long-lived metastability.  

PubMed

In this paper, we propose a stochastic cellular automaton model of traffic flow extending two exactly solvable stochastic models, i.e., the asymmetric simple exclusion process and the zero range process. Moreover, it is regarded as a stochastic extension of the optimal velocity model. In the fundamental diagram (flux-density diagram), our model exhibits several regions of density where more than one stable state coexists at the same density in spite of the stochastic nature of its dynamical rule. Moreover, we observe that two long-lived metastable states appear for a transitional period, and that the dynamical phase transition from a metastable state to another metastable/stable state occurs sharply and spontaneously. PMID:16241502

Kanai, Masahiro; Nishinari, Katsuhiro; Tokihiro, Tetsuji

2005-09-01

188

Spectral modification of seismic waves propagating through solids exhibiting a resonance frequency: a 1-D coupled wave propagation-oscillation model  

Microsoft Academic Search

A 1-D model is presented that couples the microscale oscillations of non-wetting fluid blobs in a partially saturated poroelastic medium with the macroscale wave propagation through the elastic skeleton. The fluid oscillations are caused by surface tension forces that act as the restoring forces driving the oscillations. The oscillations are described mathematically with the equation for a linear oscillator and

Marcel Frehner; Stefan M. Schmalholz; Yuri Podladchikov

2009-01-01

189

A 1-D model evaluation of OH regeneration mechanisms from isoprene oxidation for use in global models.  

NASA Astrophysics Data System (ADS)

Hydroxyl radical (OH) is one of the main oxidants in the troposphere. It drives photochemistry and thus cleaning the troposphere from ubiquitous reactive compounds that impact on the environment and the ecosystems. Due to the high reactivity of OH, both its atmospheric measurements and the simulations of its concentrations remain challenging. Recent measurements have shown significant mismatch with atmospheric simulations based on current knowledge of organic atmospheric chemistry. New degradations pathways in the oxidation chemistry of isoprene, initiated by OH radical, have been proposed based on chamber experiments and theoretical calculations. These pathways regenerate OH and are actually missing from global chemistry and transport models (CTMs) that show an underestimation of OH when compared to the limited number of observations. In this study we use the 1-dimensional model Wageningen University Single Column Model (WUSCM) to investigate, evaluate and reduce for use in global CTMs, isoprene oxidation pathways that are leading to OH regeneration and were recently proposed in literature applied on the PEGASOS 2012 campaign over Cabauw, Netherlands. The WUSCM simulates boundary layer meteorology (radiation, land-atmosphere interaction and mixing) and can support different chemistry schemes coupled with the KPP solver. The chemistry scheme used in the TM4-ECPL global model chemical scheme is the basis for the development and testing of the new pathways of isoprene chemistry.

Daskalakis, Nikos; Krol, Maarten; Kanakidou, Maria

2014-05-01

190

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

191

Traveling waves in an optimal velocity model of freeway traffic.  

PubMed

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

2001-03-01

192

A priori testing of subgrid-scale models for the velocity-pressure and vorticity-velocity formulations  

NASA Technical Reports Server (NTRS)

Subgrid-scale models for Large Eddy Simulation (LES) in both the velocity-pressure and the vorticity-velocity formulations were evaluated and compared in a priori tests using spectral Direct Numerical Simulation (DNS) databases of isotropic turbulence: 128(exp 3) DNS of forced turbulence (Re(sub(lambda))=95.8) filtered, using the sharp cutoff filter, to both 32(exp 3) and 16(exp 3) synthetic LES fields; 512(exp 3) DNS of decaying turbulence (Re(sub(Lambda))=63.5) filtered to both 64(exp 3) and 32(exp 3) LES fields. Gaussian and top-hat filters were also used with the 128(exp 3) database. Different LES models were evaluated for each formulation: eddy-viscosity models, hyper eddy-viscosity models, mixed models, and scale-similarity models. Correlations between exact versus modeled subgrid-scale quantities were measured at three levels: tensor (traceless), vector (solenoidal 'force'), and scalar (dissipation) levels, and for both cases of uniform and variable coefficient(s). Different choices for the 1/T scaling appearing in the eddy-viscosity were also evaluated. It was found that the models for the vorticity-velocity formulation produce higher correlations with the filtered DNS data than their counterpart in the velocity-pressure formulation. It was also found that the hyper eddy-viscosity model performs better than the eddy viscosity model, in both formulations.

Winckelmans, G. S.; Lund, T. S.; Carati, D.; Wray, A. A.

1996-01-01

193

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

Microsoft Academic Search

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

194

Sensitivity of long-period ground motion simulations to seismic velocity perturbations in the Wasatch Front community velocity model  

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

195

Independent scattering model and velocity dispersion in trabecular bone: comparison with a multiple scattering model.  

PubMed

Speed of sound measurements are used clinically to assess bone strength. Trabecular bone is an attenuating composite material in which negative values of velocity dispersion have been measured; this behavior remaining poorly explained physically. The aim of this work is to describe the ultrasonic propagation in trabecular bone modeled by infinite cylinders immersed in a saturating matrix and to derive the physical determinants of velocity dispersion. An original homogenization model accounting for the coupling of independent scattering and absorption phenomena allows the computation of phase velocity and of dispersion while varying bone properties. The first step of the model consists in the computation of the attenuation coefficient at all frequencies. The second step of the model corresponds to the application of the general Kramers-Krönig relationship to derive the frequency dependence of phase velocity. The model predicts negative values of velocity dispersion in agreement with experimental results obtained in phantoms mimicking trabecular bone. In trabecular bone, only negative values of velocity dispersion are predicted by the model, which span within the range of values measured experimentally. However, the comparison of the present results with results obtained in Haiat et al. (J Acoust Soc Am 124:4047-4058, 2008) assuming multiple scattering indicates that accounting for multiple scattering phenomena leads to a better prediction of velocity dispersion in trabecular bone. PMID:20490887

Haïat, G; Naili, S

2011-02-01

196

The proteasome function reporter GFPu accumulates in young brains of the APPswe/PS1dE9 Alzheimer's disease mouse model.  

PubMed

Alzheimer's disease (AD), the most common cause of dementia, is neuropathologically characterized by accumulation of insoluble fibrous inclusions in the brain in the form of intracellular neurofibrillary tangles and extracellular senile plaques. Perturbation of the ubiquitin-proteasome system (UPS) has long been considered an attractive hypothesis to explain the pathogenesis of AD. However, studies on UPS functionality with various methods and AD models have achieved non-conclusive results. To get further insight into UPS functionality in AD, we have crossed a well-documented APPswe/PS1dE9 AD mouse model with a UPS functionality reporter, GFPu, mouse expressing green fluorescence protein (GFP) fused to a constitutive degradation signal (CL-1) that facilitates its rapid turnover in conditions of a normal UPS. Our western blot results indicate that GFPu reporter protein was accumulated in the cortex and hippocampus, but not striatum in the APPswe/PS1dE9 AD mouse model at 4 weeks of age, which is confirmed by fluorescence microscopy and elevated levels of p53, an endogenous UPS substrate. In accordance with this, the levels of ubiquitinated proteins were elevated in the AD mouse model. These results suggest that UPS is either impaired or functionally insufficient in specific brain regions in the APPswe/PS1dE9 AD mouse model at a very young age, long before senile plaque formation and the onset of memory loss. These observations may shed new light on the pathogenesis of AD. PMID:24363091

Liu, Yanying; Hettinger, Casey L; Zhang, Dong; Rezvani, Khosrow; Wang, Xuejun; Wang, Hongmin

2014-04-01

197

The proteasome function reporter GFPu accumulates in young brains of the APPswe/PS1dE9 Alzheimer's disease mouse model  

PubMed Central

Alzheimer’s disease (AD), the most common cause of dementia, is neuropathologically characterized by accumulation of insoluble fibrous inclusions in the brain in the form of intracellular neurofibrillary tangles and extracellular senile plaques. Perturbation of the ubiquitin-proteasome system (UPS) has long been considered an attractive hypothesis to explain the pathogenesis of AD. However, studies on UPS functionality with various methods and AD models have achieved non-conclusive results. To get further insight into UPS functionality in AD, we have crossed a well-documented APPswe/PS1dE9 AD mouse model with a UPS functionality reporter, GFPu, mouse expressing green fluorescence protein (GFP) fused to a constitutive degradation signal (CL-1) that facilitates its rapid turnover in conditions of a normal UPS. Our western blot results indicate that GFPu reporter protein was accumulated in the cortex and hippocampus but not striatum in the APPswe/PS1dE9 AD mouse model at 4 weeks of age, which is confirmed by fluorescence microscopy and elevated levels of p53, an endogenous UPS substrate. In accordance with this, the levels of ubiquitinated proteins were elevated in the AD mouse model. These results suggest that UPS is either impaired or functionally insufficient in specific brain regions in the APPswe/PS1dE9 AD mouse model at a very young age, long before senile plaque formation and the onset of memory loss. These observations may shed new light on the pathogenesis of AD.

Liu, Yanying; Hettinger, Casey L.; Zhang, Dong; Rezvani, Khosrow; Wang, Xuejun; Wang, Hongmin

2014-01-01

198

BANG1D  

Microsoft Academic Search

BANG1D simulates the mechanics of a subaqueous, turbid surge, a seafloor-failure-induced turbidity current that behaves like a snow avalanche or a pyroclastic burst. BANG1D uses the one-dimensional, layer-averaged equations for the conservation of fluid, sediment, momentum and turbulent kinetic energy in a turbidity current. The Lagrangian forms of these equations are solved explicitly at nodes within the turbid surge as

Lincoln F. Pratson; Jasim Imran; Eric W. H. Hutton; Gary Parker; James P. M. Syvitski

2001-01-01

199

'A Civil Action' 1-D Transport Game  

NSDL National Science Digital Library

The 'A Civil Action' 1-D Contaminant Transport Game is an EXCEL spreadsheet that enables students to compute concentrations of TCE traveling in the groundwater flow system toward well H that emanate from the W.R. Grace site. The idea of the game is to draw students into learning some of the fundamental concepts about (1) how contaminants move in the subsurface and (2) how models can be used to test hypotheses. These concepts are taught within the context of the famous 'A Civil Action' trial described in the book by Jonathan Harr (1996) and the movie starring John Travolta (1998). The spreadsheet computes values of hydraulic head, advective flow velocities and traveltimes, contaminant velocities, and contaminant concentrations at 20 locations along the flowpath from W.R. Grace to the Aberjona River. Breakthrough curves showing changes in concentration versus distance and changes in concentration versus time pop-up automatically (see below). The spreadsheet also creates graphs of advective and contaminant velocities versus distance.

Bair, Scott

200

Simple 1D Fokker-Planck modelling of ion cyclotron resonance frequency heating at arbitrary cyclotron harmonics accounting for Coulomb relaxation on non-Maxwellian populations  

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

201

Do4Models: Performance of current climate model dust emission schemes from a 1D box model perspective using field campaign data to constrain the simulated dust emission flux  

NASA Astrophysics Data System (ADS)

Dust emission schemes in climate models are relatively simple and are often tuned to represent observed background aerosol concentrations many of which are thousands of kilometres from source regions. Parameterisations of dust emission in numerical models were developed from idealised experiments such as those conducted in wind tunnels. Improvement of current model dust emission schemes has been difficult to achieve because of the paucity of observations from key dust sources. The Dust Observations for Models project (DO4Models) aims to gather data from source regions at a scale appropriate to climate model grid box resolution. Here we present the results of 1D box model simulations in which three commonly used parameterisations for the horizontal and vertical dust emission flux (Marticorena and Bergametti 1995, Alfaro and Gomez 2001, Shao et al. 2004) are applied and compared with Do4Models field campaign data retrieved over a typical salt pan dust source (Sua Pan, Botswana). The sensitivity of the schemes to input parameters such as soil moisture content, aerodynamic surface roughness length, shear velocity, soil texture class, and particle size is tested with particular regard to the representation of horizontal-to-vertical-mass-flux ratio. The effects of spatial averaging over 11 field sites is evaluated as is the average dust emission flux of a typical 12x12km model grid box. It is analysed whether the full range of surface processes (temporal changes in roughness, moisture, and soil conditions) is represented sufficiently well after averaging yet. Furthermore, the application of the dispersed soil size distribution on the performance of the emission schemes compared to the typically used undisturbed soil size distribution provided from soil databases is examined. Preliminary results suggest that the current schemes do not describe the observed emission process well. The scheme after Shao et al. (2004) provides the most accurate horizontal flux estimate so far. However, as our observed horizontal-to-vertical-dust-flux ratio is fairly variable compared to other field sites (e.g. Owens Lake), an accurate representation of the saltating flux does not assure a good simulation of the vertical emission flux. The simpler scheme after Marticorena and Bergametti (1995) can therefore compete in terms of total vertical dust flux despite its deficiencies in representing the full range of physics involved. We show that the moisture correction strongly affects the simulated dust flux and that the drag partition correction after Marticorena and Bergametti (1997) needs a little revision to be applicable to the whole range of observed roughness lengths. The dispersed soil texture data allow for a better representation of the deflatable dust fraction which controls the horizontal flux. It is more consistently constrained with regard to the measured saltating flux.

Haustein, Karsten; King, James; Wiggs, Giles; Washington, Richard

2013-04-01

202

Authentication Based on Pole-zero Models of Signature Velocity  

PubMed Central

With the increase of communication and financial transaction through internet, on-line signature verification is an accepted biometric technology for access control and plays a significant role in authenticity and authorization in modernized society. Therefore, fast and precise algorithms for the signature verification are very attractive. The goal of this paper is modeling of velocity signal that pattern and properties is stable for persons. With using pole-zero models based on discrete cosine transform, precise method is proposed for modeling and then features is founded from strokes. With using linear, parzen window and support vector machine classifiers, the signature verification technique was tested with a large number of authentic and forgery signatures and has demonstrated the good potential of this technique. The signatures are collected from three different database include a proprietary database, the SVC2004 and the Sabanci University signature database benchmark databases. Experimental results based on Persian, SVC2004 and SUSIG databases show that our method achieves an equal error rate of 5.91%, 5.62% and 3.91% in the skilled forgeries, respectively.

Rashidi, Saeid; Fallah, Ali; Towhidkhah, Farzad

2013-01-01

203

A transport model of the turbulent scalar-velocity  

NASA Technical Reports Server (NTRS)

Performance tests of the third-order turbulence closure for predictions of separating and recirculating flows in backward-facing steps were studied. Computations of the momentum and temperature fields in the flow domain being considered entail the solution of time-averaged transport equations containing the second-order turbulent fluctuating products. The triple products, which are responsible for the diffusive transport of the second-order products, attain greater significance in separating and reattaching flows. The computations are compared with several algebraic models and with the experimental data. The prediction was improved considerably, particularly in the separated shear layer. Computations are further made for the temperature-velocity double products and triple products. Finally, several advantages were observed in the usage of the transport equations for the evaluation of the turbulence triple products; one of the most important features is that the transport model can always take the effects of convection and diffusion into account in strong convective shear flows such as reattaching separated layers while conventional algebraic models cannot account for these effects in the evaluation of turbulence variables.

Amano, R. S.; Goel, P.; Chai, J. C.

1987-01-01

204

Hydrodynamic Model for the Superfluid Helium Critical Velocity in Rough Channels.  

National Technical Information Service (NTIS)

A simple model for a Feynman type critical velocity is presented which explicitly involves surface roughness as well as channel size, and can be fitted to most low temperature critical velocities in small, rough channels. (Author)

J. C. Weaver

1973-01-01

205

Comparison of CME radial velocities from a flux rope model and an ice cream cone model  

NASA Astrophysics Data System (ADS)

Coronal Mass Ejections (CMEs) on the Sun are the largest energy release process in the solar system and act as the primary driver of geomagnetic storms and other space weather phenomena on the Earth. So it is very important to infer their directions, velocities and three-dimensional structures. In this study, we choose two different models to infer radial velocities of halo CMEs since 2008 : (1) an ice cream cone model by Xue et al (2005) using SOHO/LASCO data, (2) a flux rope model by Thernisien et al. (2009) using the STEREO/SECCHI data. In addition, we use another flux rope model in which the separation angle of flux rope is zero, which is morphologically similar to the ice cream cone model. The comparison shows that the CME radial velocities from among each model have very good correlations (R>0.9). We will extending this comparison to other partial CMEs observed by STEREO and SOHO.

Kim, T.; Moon, Y.; Na, H.

2011-12-01

206

3-D Velocity Structure Modeling and Source Process Inversion: The 2003 Miyagi-ken Hokubu, Japan, Earthquake Sequence  

NASA Astrophysics Data System (ADS)

At 7:13 a.m. on July 26, 2003 (JST), an M6.4 earthquake occurred in the northern part of the Miyagi prefecture, northeastern Japan. This mainshock was associated with a distinct foreshock (M5.6) and vital aftershock activities (M5.5 for the largest). They form the earthquake sequence called `the 2003 Miyagi-ken Hokubu earthquake sequence.' The results of seismic tomography and reflection surveys carried out after the sequence suggest a complex crustal structure in and around the source region of the earthquakes (Okada et al., 2004; Kato et al., 2004). This implies that the modeling of a 3-D velocity structure is crucial for waveform analyses such as a source process inversion and they should be greatly influenced by the choice of Green's functions. We first compiled the results of various explorations and constructed the initial model of the crustal velocity structure. 1-D and 2-D inversions of aftershock seismograms were performed for the velocity structure using this initial model and a similar method to that in Ichinose et al. (2003). We then combined the results into the final 3-D velocity model. The Green's functions for the source process inversion were calculated by finite difference codes with the reciprocity theorem and the 3-D model discretized at intervals of 200m. Since the detailed distribution of aftershocks indicates a curved fault plane (Okada et al., 2003), we modeled it with flexible triangular subfaults. The source process inversion of KiK-net and K-NET seismograms with the 3-D Green's functions indicates the primary asperity to be located in the middle of the northern half of the fault plane, though the inversion with Green's functions for 1-D velocity models recovered it in a shallow part above the center of the fault plane (Hikima and Koketsu, 2004). The agreement between the observed and simulated seismograms has significantly been improved in the 3-D result, which is consistent with the result of an inversion of geodetic data (Miura et al., 2004).

Hikima, K.; Koketsu, K.

2004-12-01

207

Accurate numerical modeling of 1D flow in channels with arbitrary shape. Application of the energy balanced property  

NASA Astrophysics Data System (ADS)

This work focuses on the numerical treatment of 1D flow in channels with arbitrary shape using energy balanced arguments. The system of equations is defined using the mass and momentum conservation equations, allowing the resolution of hydraulic jumps where energy conservation arguments are not valid. When necessary, conservation of mechanical energy takes part actively in the numerical scheme when evaluating the source terms. The numerical scheme is based on an augmented Roe solver that involves the presence of source terms by adding an extra stationary wave. The characteristics of the numerical scheme include the energy balanced property, and being only first order accurate in time and space, leads to exact numerical solutions for steady solutions with independence of the grid refinement in channels with general geometries. Riemann problems considered here involve non-prismatic channels, bed variations and the resonance regime, including the limiting situation when the Riemann data belong to the resonance hypersurface. Numerical results point out that the finite volume numerical scheme with nonconservative terms presented here, converges to the exact solution. The well balanced property is ensured, as it is a particular case of the energy balanced property in cases of quiescent equilibrium.

Murillo, J.; García-Navarro, P.

2014-03-01

208

An Intriguing Shift Occurs in the Novel Protein Phosphatase 1 Binding Partner, TCTEX1D4: Evidence of Positive Selection in a Pika Model  

PubMed Central

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

209

Flow of Cars Crossing with Unequal Velocities in a Two-Dimensional Cellular Automaton Model  

Microsoft Academic Search

Simulation has been performed for traffic flow in two-dimensional cellular automaton models including cars with unequal velocities: the northbound cars with a normal speed and the eastbound cars with a high speed. For the eastbound high speed cars, two models are considered. In the model I, the intrinsic velocity is defined for all eastbound cars. In the model II, the

Minoru Fukui; Hirokazu Oikawa; Yoshihiro Ishibashi

1996-01-01

210

Numerical modeling of probe velocity effects for electromagnetic NDE methods  

NASA Astrophysics Data System (ADS)

The present discussion of magnetic flux (MLF) leakage inspection introduces the behavior of motion-induced currents. The results obtained indicate that velocity effects exist at even low probe speeds for magnetic materials, compelling the inclusion of velocity effects in MLF testing of oil pipelines, where the excitation level and pig speed are much higher than those used in the present work. Probe velocity effect studies should influence probe design, defining suitable probe speed limits and establishing training guidelines for defect-characterization schemes.

Shin, Y. K.; Lord, W.

211

Investigation of D1 Receptor-Agonist Interactions and D1/D2 Agonist Selectivity Using a Combination of Pharmacophore and Receptor Homology Modeling  

PubMed Central

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

212

1-D model for forced flow-thermal gradient chemical vapor infiltration process for carbon\\/carbon composites  

Microsoft Academic Search

A one-dimensional model was developed for the forced flow-thermal gradient chemical vapor infiltration of carbon\\/carbon composites. The infiltration time predicted by the model agreed very well with experiments, where propylene and propane were used as the hydrocarbon source. The model was also validated by interrupting the infiltration and comparing predicted with observed densities.

S. Vaidyaraman; W. J. Lackey; P. K. Agrawal; T. L. Starr

1996-01-01

213

A simple model to predict residual velocities of thick composite laminates subjected to high velocity impact  

Microsoft Academic Search

A punch curve was used as the “structural constitutive model” that captures the highly nonlinear behavior of the laminate in the penetration process. This model in conjunction with a special two-noded ring element based on the Mindlin thick plate theory was employed to model damage processes during static and dynamic penetration. Different criteria for initiation of damage and plug formation

C. T. Sun; S. V. Potti

1996-01-01

214

(abstract) Modeling the Critical Velocity Ionization Experiment Interaction  

NASA Technical Reports Server (NTRS)

Proper interpretation of critical velocity ionization experiments depends upon understanding the expected results from in-situ or remote sensors. In particular, the 1991 shuttle based CIV experiment had diagnostics.

Wang, J.; Murphy, G.; Biasca, R.

1993-01-01

215

Exact realization of integer and fractional quantum Hall phases in U(1)×U(1) models in (2+1)d  

SciTech Connect

In this work we present a set of microscopic U(1)×U(1) models which realize insulating phases with a quantized Hall conductivity ?{sub xy}. The models are defined in terms of physical degrees of freedom, and can be realized by local Hamiltonians. For one set of these models, we find that ?{sub xy} is quantized to be an even integer. The origin of this effect is a condensation of objects made up of bosons of one species bound to a single vortex of the other species. For other models, the Hall conductivity can be quantized as a rational number times two. For these systems, the condensed objects contain bosons of one species bound to multiple vortices of the other species. These systems have excitations carrying fractional charges and non-trivial mutual statistics. We present sign-free reformulations of these models which can be studied in Monte Carlo, and we use such reformulations to numerically detect a gapless boundary between the quantum Hall and trivial insulator states. We also present the broader phase diagrams of the models. -- Highlights: •We present a set of models of two species of bosons which realize topological phases. •The models exist on a lattice, and can be realized by local Hamiltonians. •These models exhibit both integer and fractional bosonic Hall effects. •The models can be studied in sign-free Monte Carlo.

Geraedts, Scott D., E-mail: sgeraedt@caltech.edu; Motrunich, Olexei I.

2013-07-15

216

Monte Carlo solution of the Boltzmann equation via a discrete velocity model  

NASA Astrophysics Data System (ADS)

A new discrete velocity scheme for solving the Boltzmann equation is described. Directly solving the Boltzmann equation is computationally expensive because, in addition to working in physical space, the nonlinear collision integral must also be evaluated in a velocity space. Collisions between each point in velocity space with all other points in velocity space must be considered in order to compute the collision integral most accurately, but this is expensive. The computational costs in the present method are reduced by randomly sampling a set of collision partners for each point in velocity space analogous to the Direct Simulation Monte Carlo (DSMC) method. The present method has been applied to a traveling 1D shock wave. The jump conditions across the shock wave match the Rankine-Hugoniot jump conditions. The internal shock wave structure was compared to DSMC solutions, and good agreement was found for Mach numbers ranging from 1.2 to 10. Since a coarse velocity discretization is required for efficient calculation, the effects of different velocity grid resolutions are examined. Additionally, the new scheme's performance is compared to DSMC and it was found that upstream of the shock wave the new scheme performed nearly an order of magnitude faster than DSMC for the same upstream noise. The noise levels are comparable for the same computational effort downstream of the shock wave.

Morris, A. B.; Varghese, P. L.; Goldstein, D. B.

2011-02-01

217

An empirical model to forecast solar wind velocity through statistical modeling  

NASA Astrophysics Data System (ADS)

The accurate prediction of the solar wind velocity has been a major challenge in the space weather community. Previous studies proposed many empirical and semi-empirical models to forecast the solar wind velocity based on either the historical observations, e.g. the persistence model, or the instantaneous observations of the sun, e.g. the Wang-Sheeley-Arge model. In this study, we use the one-minute WIND data from January 1995 to August 2012 to investigate and compare the performances of 4 models often used in literature, here referred to as the null model, the persistence model, the one-solar-rotation-ago model, and the Wang-Sheeley-Arge model. It is found that, measured by root mean square error, the persistence model gives the most accurate predictions within two days. Beyond two days, the Wang-Sheeley-Arge model serves as the best model, though it only slightly outperforms the null model and the one-solar-rotation-ago model. Finally, we apply the least-square regression to linearly combine the null model, the persistence model, and the one-solar-rotation-ago model to propose a 'general persistence model'. By comparing its performance against the 4 aforementioned models, it is found that the accuracy of the general persistence model outperforms the other 4 models within five days. Due to its great simplicity and superb performance, we believe that the general persistence model can serve as a benchmark in the forecast of solar wind velocity and has the potential to be modified to arrive at better models.

Gao, Y.; Ridley, A. J.

2013-12-01

218

Modeling and simulation for microscopic traffic flow based on multiple headway, velocity and acceleration difference  

Microsoft Academic Search

A new car-following model termed as multiple headway, velocity, and acceleration difference (MHVAD) is proposed to describe\\u000a the traffic phenomenon, which is a further extension of the existing model of full velocity difference (FVD) and full velocity\\u000a and acceleration difference (FVAD). Based on the stability analysis, it is shown that the critical value of the sensitivity\\u000a in the MHVAD model

Yongfu Li; Dihua Sun; Weining Liu; Min Zhang; Min Zhao; Xiaoyong Liao; Liang Tang

219

Scale-similarity model for Lagrangian velocity correlations in isotropic and stationary turbulence  

NASA Astrophysics Data System (ADS)

A scale-similarity model for Lagrangian two-point, two-time velocity correlations (LVCs) in isotropic turbulence is developed from the Kolmogorov similarity hypothesis. It is a second approximation to the isocontours of LVCs, while the Smith-Hay model is only a first approximation. This model expresses the LVC by its space correlation and a dispersion velocity. We derive the analytical expression for the dispersion velocity from the Navier-Stokes equations using the quasinormality assumption. The dispersion velocity is dependent on enstrophy spectra and shown to be smaller than the sweeping velocity for the Eulerian velocity correlation. Therefore, the Lagrangian decorrelation process is slower than the Eulerian decorrelation process. The data from direct numerical simulation of isotropic turbulence support the scale-similarity model: the LVCs for different space separations collapse into a universal form when plotted against the separation axis defined by the model.

He, Guo-Wei; Jin, Guodong; Zhao, Xin

2009-12-01

220

Integrating models to simulate emergent behaviour: effects of organic matter on soil hydraulics in the ICZ-1D soil-vegetation model  

NASA Astrophysics Data System (ADS)

Soil develops as a result of interacting processes, many of which have been described in more or less detailed models. A key challenge in developing predictive models of soil function is to integrate processes that operate across a wide range of temporal and spatial scales. Many soil functions could be classified as "emergent", since they result from the interaction of subsystems. For example, soil organic matter (SOM) dynamics are commonly considered in relation to carbon storage, but can have profound effects on soil hydraulic properties that are conventionally considered to be static. Carbon fixed by plants enters the soil as litterfall, root turnover or via mycorrhizae. Plants need water and nutrients to grow, and an expanding root system provides access to a larger volume of soil for uptake of water and nutrients. Roots also provide organic exudates, such as oxalate, which increase nutrient availability. Carbon inputs are transformed at various rates into soil biota, CO2, and more persistent forms of organic matter. The SOM is partly taken up into soil aggregates of variable sizes, which slows down degradation. Water availability is an important factor as both plant growth and SOM degradation can be limited by shortage of water. Water flow is the main driver for transport of nutrients and other solutes. The flow of water in turn is influenced by the presence of SOM as this influences soil water retention and hydraulic conductivity. Towards the top of the unsaturated zone, bioturbation by the soil fauna transports both solid material and solutes. Weathering rates of minerals determine the availability of many nutrients and are in turn dependent on parameters such as pH, water content, CO2 pressure and oxalate concentration. Chemical reactions between solutes, dissolution and precipitation, and exchange on adsorption sites further influence solute concentrations. Within the FP7 SoilTrEC project, we developed a model that incorporates all of these processes, to explore the complex interactions involved in soil development and change. We were unable to identify appropriately-detailed existing models for plant productivity and for the dynamics of soil aggregation and porosity, and so developed the PROSUM and CAST models, respectively, to simulate these subsystems. Moreover, we applied the BRNS generator to obtain a chemical equilibrium model. These were combined with HYDRUS-1D (water and solute transport), a weathering model (derived from the SAFE model) and a simple bioturbation model. The model includes several feedbacks, such as the effect of soil organic matter on water retention and hydraulic conductivity. We encountered several important challenges when building the integrated model. First, a mechanism was developed that initiates the execution of a single time step for an individual sub-model and accounts for the relevant mass transfers between sub-models. This allows for different and sometimes variable time step duration in the submodels. Secondly, we removed duplicated processes and identified and included relevant solute production terms that had been neglected. The model is being tested against datasets obtained from several Soil Critical Zone Observatories in Europe. This contribution focuses on the design strategy for the model.

Valstar, Johan; Rowe, Ed; Konstantina, Moirogiorgou; Giannakis, Giorgos; Nikolaidis, Nikolaos

2014-05-01

221

Status of the solar and infrared radiation submodels in the LLNL 1-D and 2-D chemical-transport models  

SciTech Connect

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

222

Shuttle data book: SRM fragment velocity model. Presented to the SRB Fragment Model Review Panel  

NASA Technical Reports Server (NTRS)

This study was undertaken to determine the velocity of fragments generated by the range safety destruction (RSD) or random failure of a Space Transportation System (STS) Solid Rocket Motor (SRM). The specific requirement was to provide a fragment model for use in those Galileo and Ulysses RTG safety analyses concerned with possible fragment impact on the spacecraft radioisotope thermoelectric generators (RTGS). Good agreement was obtained between predictions and observations for fragment velocity, velocity distributions, azimuths, and rotation rates. Based on this agreement with the entire data base, the model was used to predict the probable fragment environments which would occur in the event of an STS-SRM RSD or randon failure at 10, 74, 84 and 110 seconds. The results of these predictions are the basis of the fragment environments presented in the Shuttle Data Book (NSTS-08116). The information presented here is in viewgraph form.

1989-01-01

223

Detailed P- and S-wave Velocity Models Along the LARSE II Transect, Southern California  

NASA Astrophysics Data System (ADS)

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 gathers of the Los Angeles Region Seismic Experiment, Phase II (LARSE II), and we developed refraction velocity models from these picks using two different inversion algorithms. Vp/Vs ratios were calculated from the resulting P- and S-wave models where both models are constrained by ray coverage. The two P-wave velocity models are compared to each other and to results from forward modeling. Generally, the P-wave inverse and forward models agree well for velocities lower than 5.0 km/s but only broadly agree with each other for velocities above 5.0 km/s. Similarly, the S-wave inverse models agree well with each other for velocities lower than 2.5 km/s but only broadly agree for velocities higher than 2.5 km/s. The most prominent structures in our S-wave models are two north-dipping low-velocity zones in the Central Transverse Ranges that we interpret as faults. These low-velocity zones differ somewhat between the two inversion models, but the Vp/Vs models (one model for each technique) show these features to be remarkably similar. Interestingly, both Vp/Vs models have several features that are not visible in either the P- or S-wave models alone. Two of these features (relatively high Vp/Vs ratios) occur in the vicinity of wells that bottom in "granitic" rocks and we interpret these high Vp/Vs ratios to indicate that the granitic rocks are highly fractured or even brecciated. Finally, to evaluate the Southern California Earthquake Center (SCEC) Community Velocity Model (CVM), which predicts Vs based on the Vp model, we compare data from our Vp and Vp/Vs models to empirical formulas that relate P- to S-wave velocities (see Brocher, 2005). These empirical curves provide an adequate average relationship between Vp and Vs, but our model Vs varies as much as ± 20 % for Vp ? 5.0 km/s and as much as ± 35 % for Vp ? 5.0 km/s. This large variation in the predicted S- wave velocity demonstrates the value of determining Vs independently from Vp.

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

2008-12-01

224

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

225

Modeling students' conceptual understanding of force, velocity, and acceleration  

NASA Astrophysics Data System (ADS)

We have developed a multiple choice test designed to probe students' 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 ``partially correct'' 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.

2009-11-01

226

Age-related changes in visual acuity, learning and memory in the APPswe/PS1dE9 mouse model of Alzheimer's disease.  

PubMed

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

2012-05-16

227

Analysis of Hook Formation Mechanism in Ultra Low Carbon Steel using CON1D Heat Flow - Solidification Model  

Microsoft Academic Search

Subsurface hook formation at the meniscus during the continuous casting of steel slabs is an important cause of surface defects, owing to their easy entrapment of mold flux and inclusion-laden gas bubbles. This work investigates the fundamentals of meniscus solidification and how hooks form by a combination of advanced computational models and plant measurements. From experimental results, the pitch deviation

Ho-Jung Shin; Brian G. Thomas; Go-Gi Lee; Chang-Hyun Lee

2004-01-01

228

Study of fog characteristics by using the 1-D COBEL model at the airport of Thessaloniki, Greece  

NASA Astrophysics Data System (ADS)

An attempt is made to couple the one dimensional COBEL - ISBA (COuche Brouillard Eau Liquide - Interactions Soil Biosphere Atmosphere) model with the WRF (Weather Research and Forecasting) numerical weather prediction model. This accomplishment will improve the accuracy on the short-term forecasting of fog events, which is of paramount importance -mainly to the airway companies, the airports functioning and the community as well- and will provide the means for the implementation of extensive studies of fog events formed at the "Macedonia" airport of Thessaloniki. Numerical experiments have been performed to study in depth the thermodynamic structure and the microphysical characteristics of the fog event that was formed on 06/01/2010. Moreover, the meteorological conditions -under the influence of which- the fog event was formed are also investigated. Sensitivity tests with respect to the initial conditions of temperature, relative humidity and geostrophic wind speed profiles have been performed to illustrate the model’s performance. Dew deposition rates have also been examined in order to test the importance of it on controlling the fog formation. The numerical results have been compared with actual measurements and the findings have been evaluated and discussed.

Stolaki, S.; Pytharoulis, I.; Karacostas, T.

2010-07-01

229

Short time-scale analysis of the NW Mediterranean ecosystem during summer–autumn transition: A 1D modelling approach  

Microsoft Academic Search

Modelling was used as a tool to better understand the physical and biological processes observed during the multidisciplinary cruise DYNAPROC 2 (DYNAmic of rapid PROCesses in the water column), which took place in the Ligurian Sea in September–October 2004. The aim of the cruise was to study the short time-scale physical and biological processes that occur when the ecosystem switches

V. Raybaud; P. Nival; L. Prieur

2011-01-01

230

Estimation of flow velocity for a debris flow via the two-phase fluid model  

NASA Astrophysics Data System (ADS)

The two-phase fluid model is applied in this study to calculate the steady velocity of a debris flow along a channel bed. By using the momentum equations of the solid and liquid phases in the debris flow together with an empirical formula to describe the interaction between two phases, the steady velocities of the solid and liquid phases are obtained theoretically. The comparison of those velocities obtained by the proposed method with the observed velocities of two real-world debris flows shows that the proposed method can estimate accurately the velocity for a debris flow.

Guo, S.; Xu, P.; Zheng, Z.; Gao, Y.

2014-06-01

231

Creating Flood Inundation Maps Using 1D Hydrologic Model and GIS for Lower Meric River Basin, Turkey  

NASA Astrophysics Data System (ADS)

In Turkey, one of the areas facing the danger of flooding is Lower Meric River basin, the part between Edirne and Enos, Turkey. Despite being in the flood zone, the region is used widely as an agricultural and settlement land. The State Hydraulic Works (DSI) has built levees to prevent flood damages on the Lower Evros River Basin. However, having floods in the region reaching areas behind levees, clearly showed the need for reviewing and updating the cross-sections of the critical areas in the river bed. In this study, determination of floodplains for various stream-flow values in any cross sections of the river is aimed. The study area is divided into two sections (Study Area 1 & Study Area 2). Available stream flow gauging station data, which is located in study areas, are used in model. Model created using HEC-RAS, is calibrated with 2006 flood which occurred in the study area. After calibration, floodplain maps are created for 1000 m3/s flows from 1000 to6000 m3/s flows for Study Area1. For Study Area 2, floodplain maps are created for 2, 5, 10, 50, 100 years return periods. The models can illustrate the extent of flooding under different conditions allowing residents in the area to see how predicted flood levels could affect their property, and help them make informed decisions.

Sonmez, O.; Dogan, E.; Demir, I.

2012-12-01

232

Analysis of peripheral artery velocity tracing in a porcine model  

PubMed Central

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

233

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

234

Comparison of ground-based UV irradiance measurements with satellite-derived values and 1-D- and 3-D-radiative transfer model calculations in mountainous terrain  

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

235

Evaluation of Bulk Charging in Geostationary Transfer Orbit and Earth Escape Trajectories Using the Numit 1-D Charging Model  

NASA Technical Reports Server (NTRS)

The NUMIT 1-dimensional bulk charging model is used as a screening to ol for evaluating time-dependent bulk internal or deep dielectric) ch arging of dielectrics exposed to penetrating electron environments. T he code is modified to accept time dependent electron flux time serie s along satellite orbits for the electron environment inputs instead of using the static electron flux environment input originally used b y the code and widely adopted in bulk charging models. Application of the screening technique ts demonstrated for three cases of spacecraf t exposure within the Earth's radiation belts including a geostationa ry transfer orbit and an Earth-Moon transit trajectory for a range of orbit inclinations. Electric fields and charge densities are compute d for dielectric materials with varying electrical properties exposed to relativistic electron environments along the orbits. Our objectiv e is to demonstrate a preliminary application of the time-dependent e nvironments input to the NUMIT code for evaluating charging risks to exposed dielectrics used on spacecraft when exposed to the Earth's ra diation belts. The results demonstrate that the NUMIT electric field values in GTO orbits with multiple encounters with the Earth's radiat ion belts are consistent with previous studies of charging in GTO orb its and that potential threat conditions for electrostatic discharge exist on lunar transit trajectories depending on the electrical proper ties of the materials exposed to the radiation environment.

Minow, Joseph I.; Coffey, Victoria N.; Parker, Linda N.; Blackwell, William C., Jr.; Jun, Insoo; Garrett, Henry B.

2007-01-01

236

Simulation of marine boundary layer characteristics using a 1-D PBL model over the Bay of Bengal during BOBMEX-99  

NASA Astrophysics Data System (ADS)

The characteristic features of the marine boundary layer (MBL) over the Bay of Bengal during the southwest monsoon and the factors influencing it are investigated. The Bay of Bengal and Monsoon Experiment (BOBMEX) carried out during July-August 1999 is the first observational experiment under the Indian Climate Research Programme (ICRP). A very high-resolution data in the vertical was obtained during this experiment, which was used to study the MBL characteristics off the east coast of India in the north and south Bay of Bengal. Spells of active and suppressed convection over the Bay were observed, of which, three representative convective episodes were considered for the study. For this purpose a one-dimensional multi-level PBL model with a TKE-? closure scheme was used. The soundings, viz., the vertical profiles of temperature, humidity, zonal and meridional component of wind, obtained onboard ORV Sagar Kanya and from coastal stations along the east coast are used for the study. The temporal evolution of turbulent kinetic energy, marine boundary layer height (MBLH), sensible and latent heat fluxes and drag coefficient of momentum are simulated for different epochs of monsoon and monsoon depressions during BOBMEX-99.The model also generates the vertical profiles of potential temperature, specific humidity, zonal and meridional wind. These simulated values compared reasonably well with the observations available from BOBMEX.

Sam, N. V.; Mohanty, U. C.; Satyanarayana, A. N. V.

2003-06-01

237

Dimuon radiation at relativistic energies available at the CERN Super Proton Synchrotron within a (3 + 1)D hydrodynamic + cascade model  

SciTech Connect

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

238

Absence of finite-temperature ballistic charge (and spin) transport in the 1D Hubbard model at half filling (and zero spin density)  

NASA Astrophysics Data System (ADS)

Finite-temperature T > 0 transport properties of integrable and nonintegrable one-dimensional (1D) many-particle quantum systems are rather different, showing ballistic and diffusive behavior, respectively. The repulsive 1D Hubbard model is a prominent example of an integrable correlated system. For electronic densities n ? 1 (and spin densities m ? 0) it is an ideal charge (and spin) conductor, with ballistic charge (and spin) transport for T ? 0. In spite of the fact that it is solvable by the Bethe ansatz, at n = 1 (and m = 0) its T > 0 charge (and spin) transport properties are an issue that remains poorly understood. Here we combine this solution with symmetry and the explicit calculation of current-operator matrix elements between energy eigenstates to show that for on-site repulsion U > 0 and at n = 1 the charge stiffness D?(T) vanishes for T > 0 in the thermodynamic limit. A similar behavior is found by such methods for the spin stiffness Ds(T) for U > 0 and T > 0, which vanishes at m = 0. This absence of finite temperature n = 1 ballistic charge transport and m = 0 ballistic spin transport are exact results that clarify long-standing open problems.

Carmelo, J. M. P.; Gu, Shi-Jian; Sampaio, M. J.

2014-06-01

239

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

240

Two-band model description of electroabsorption and third-harmonic generation in 1-D MX linear chains  

SciTech Connect

Within a two-band model, the authors investigate the electroabsorption (EA) and third-harmonic generation (THG) processes in halogen-bridged mixed-valence Pt complexes: PtCl, PtBr and Ptl. For PtCl, the theoretical THG spectrum shows three peaks, corresponding to (i) a three-photon resonance at 0.83 eV originating in a M(etal)-M(etal) transition; (ii) a two-photon resonance at 1.5 eV from an M-M band-edge transition; and (iii) a three-photon resonance at 1.6 eV from an M-X transition. The latter two peaks account well for the twin-peak structure seen experimentally. They show that the twin-peak intensity strongly decreases from PtCl to PtBr and disappears for PtI. They also discuss the theoretical EA spectra due to localized defects (polarons, bipolarons, kinks, and excitons).

Shuai, Z.; Bredas, J.L. [Universite de Mons-Hainaut (Belgium); Saxena, A.; Gammel, J.T.; Bishop, A.R. [Los Alamos National Lab., NM (United States)

1994-10-01

241

Impact of river bed morphology on discharge and water levels simulated by a 1D Saint-Venant hydraulic model at regional scale  

NASA Astrophysics Data System (ADS)

SummaryRiver cross-sections data are required to represent channel geometry in hydrodynamic models. In the absence of accurate data at regional scale, simplified or parameterized cross sections are often used, which might affect the performance of the hydrodynamic model. In this study we assess the sensitivity of a 1D Saint-Venant hydraulic model to different types of river morphological data. The question is addressed using a 1D unsteady hydraulic model (HEC-RAS), with lateral inflows provided by the hydro(geo)logical model Eau-Dyssée, to explore a wide spectrum of river geometry scenarios, regarding river bed slopes and cross-sectional shapes. The target scale is the one of the Seine River (France). As a gateway for larger and more complex regional hydro(geo)logical applications, our case-study covers a well-described 89-km reach in a sub-tributary of the Seine River. River morphology is described by high-resolution cross-sections, and Manning's roughness coefficient (n) is used for calibration against observed discharges and river stages in a mid-reach control point, with satisfactory performances over the 8-year simulation period. The resulting model still simulates realistic discharge hydrographs when forced with degraded channel geometry data, using either fewer cross-sections or approximated ones. In such cases, however, the hydraulic model does not always satisfactorily predict the associated water levels when compared to observations. In certain geometry scenarios, the RMSE between simulated water levels using degraded geometry and observations may go up to 0.3 m. The study confirms that the accuracy of predicted water levels and maximum water depths simulated by a Saint-Venant model relies on an accurate representation of channel geometry and bed level slopes along the river reach. From the various scenarios, it appears that the longitudinal description of the bed level profiles has a larger impact on the simulation of water levels than the cross-sectional shapes. This offers interesting implications for flood forecast mapping applications and regional scale models that often use simplified river geometry and Digital Elevation Models (DEMs) built by remote sensing technologies to simulate the water levels.

Saleh, F.; Ducharne, A.; Flipo, N.; Oudin, L.; Ledoux, E.

2013-01-01

242

A Velocity Distribution Model for Steady State Heat Transfer  

NASA Technical Reports Server (NTRS)

Consider a box that is filled with an ideal gas and that is aligned along Cartesian coordinates (x, y, z) having until length in the 'y' direction and unspecified length in the 'x' and 'z' directions. Heat is applied uniformly over the 'hot' end of the box (y = 1) and is removed uniformly over the 'cold' end (y = O) at a constant rate such that the ends of the box are maintained at temperatures T(sub 0) at y = O and T(sub 1) at y = 1. Let U, V, and W denote the respective velocity components of a molecule inside the box selected at some random time and at some location (x, y, z). If T(sub 0) = T(sub 1), then U, Y, and W are mutually independent and Gaussian, each with mean zero and variance RT(sub 0), where R is the gas constant. When T(sub 0) does not equal T(sub 1) the velocity components are not independent and are not Gaussian. Our objective is to characterize the joint distribution of the velocity components U, Y, and W as a function of y, and, in particular, to characterize the distribution of V given y. It is hoped that this research will lead to an increased physical understanding of the nature of turbulence.

Hall, Eric B.

1996-01-01

243

Linear velocity fields in non-Gaussian models for large-scale structure  

NASA Technical Reports Server (NTRS)

Linear velocity fields in two types of physically motivated non-Gaussian models are examined for large-scale structure: seed models, in which the density field is a convolution of a density profile with a distribution of points, and local non-Gaussian fields, derived from a local nonlinear transformation on a Gaussian field. The distribution of a single component of the velocity is derived for seed models with randomly distributed seeds, and these results are applied to the seeded hot dark matter model and the global texture model with cold dark matter. An expression for the distribution of a single component of the velocity in arbitrary local non-Gaussian models is given, and these results are applied to such fields with chi-squared and lognormal distributions. It is shown that all seed models with randomly distributed seeds and all local non-Guassian models have single-component velocity distributions with positive kurtosis.

Scherrer, Robert J.

1992-01-01

244

Modeling point velocity and depth statistical distributions in steep tropical and alpine stream reaches  

NASA Astrophysics Data System (ADS)

Statistical hydraulic models predict the frequency distributions of point hydraulic variables, relative to their reach-averaged values, in a stream reach based on its average characteristics (e.g., discharge, depth, width, average particle size). The models initially developed in Europe have not been tested for steeper streams (>4%) with coarse grain size. We recorded water velocities and depths in 44 reaches of steep streams in tropical islands and the Alps during 69 surveys. We fitted the observed distributions of velocities and depths using a mixture of two distributions, one with low variance and the other with a high variance. Then, we predicted the mixing parameter on the basis of the reach-averaged characteristics. We compared the observed and predicted frequencies for five classes of velocities, including a class of negative velocities, and four classes of water depths. The predictions of class frequencies have a bias of ?5%. Our statistical model of velocity distribution predicts the frequencies of velocity classes with an explained variance between 33 and 72% for four classes of velocity and null for a class of intermediate velocity. The statistical model of depth distributions was less efficient with an explained variance between 25 and 38% for three classes of depth and null for large depths. The average Froude number, the total height of large drops relative to the reach length and the average slope are the main explanatory variables of velocity and depth distributions.

Girard, V.; Lamouroux, N.; Mons, R.

2014-01-01

245

Mw5.5 Aftershock of the 2009 L'Aquila, Italy, Earthquake: Broadband Composite Source Modeling with 1D Deterministic Green's Functions  

NASA Astrophysics Data System (ADS)

We perform an extended study of the largest aftershock of the Mw6.3 2009 L'Aquila, Italy, earthquake, based on low-frequency inversion and broadband simulation of strong-motion data. The Mw5.5 aftershock occurred on April 7 and was recorded by ~30 permanent and temporal accelerometric stations located within 50km from the epicenter. Using ISOLA software we perform a CMT inversion, finding the centroid at 15km depth in agreement with previous studies. Distribution of relocated small aftershocks by Valoroso et al. (2013) suggests that the event ruptured a normal fault dipping NE at 60 degrees, antithetic to the major L'Aquila fault. To better constrain the source model, we invert strong-motion data in the frequency range 0.1-0.5 Hz, considering a finite-extent fault with homogenous slip and radial propagation at constant speed. We estimate fault dimension of 6x6km, static stress drop of 10 MPa (relatively low with respect to other studies), and find a weak indication of bilateral rupture propagation. These features are used to setup a broadband (0-10Hz) composite source model with fractal number-size distribution of overlapping subsources. The Green's functions are calculated in 1D layered medium in the full frequency range, assuming shallow site-specific structure, wherever available, and an average profile for generic rock stations; no stochastic Green's functions are used. At stations with not very strong site effects, the fit between synthetic and observed waveforms is generally good. Careful analysis of S-wave group polarization at high frequencies reveals that while some stations retain the predominantly linear polarization in accordance with the 1D modeling, other stations show a peculiar mismatch. The high-frequency mismatch appears either as the occurrence of random circular polarization, or as a variation of the angle characterizing the linear polarization. We discuss these observations in terms of crustal heterogeneity and azimuthally dependent site amplification.

Gallovic, Frantisek; Pacor, Francesca; Zahradnik, Jiri; Luzi, Lucia; Puglia, Rodolfo; D'Amico, Maria

2014-05-01

246

Current plate velocities relative to the hotspots incorporating the NUVEL-1 global plate motion model  

Microsoft Academic Search

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

247

Full velocity difference and acceleration model for a car-following theory  

NASA Astrophysics Data System (ADS)

In order to describe the car-following behavior more actually in real traffic, a full velocity difference and acceleration model (for short, FVDAM) is proposed by synthetically taking into account headway, velocity difference and acceleration of the leading car on the basis of full velocity difference model. The analytical method and numerical simulation results show that the proposed model can describe the phase transition of traffic flow and estimate the evolution of traffic congestion, that incorporating the acceleration of the leading car into car-following model can stabilize traffic flow, suppress the traffic jam and increase capacity, and that the following car in FVDAM can accelerate more quickly than in FVDM.

Yu, Shaowei; Liu, Qingling; Li, Xiuhai

2013-05-01

248

A transient two-phase velocity difference model for drift calculation in CANDU thermohydraulic codes  

SciTech Connect

A realistic velocity difference scheme has been developed for calculating the drift parameters in both horizontally and vertically oriented sections of the primary heat transport systems of CANDU reactors. This model predicts the unequal velocity effects, spatially and temporally. It can be used to describe the slip in transient and multipurpose thermohydraulic codes. The transient velocity difference equation of this model is an arrangement of the two-fluid model equations. This equation describes the time-dependent relation between the phase velocities. This is a function of the pressure gradient, phase inertias, volume fraction, flow regime, inerfacial forces, and additional constitutive relations. In addition, the model includes a package of momentum exchange constitutive laws to calculate the interphase momentum exchange parameters and virtual mass coefficients. The parameters necessary for the integration of this model into CANDU thermohydraulic codes (SOPHT, FIREBIRD) are expressed in terms of the dynamic difference velocity. These parameters are the drift mass flow rate, drift velocity, distribution parameter, flow quality, effective density, and flow enthalpy. Numerical results revealed that the velocity difference model fairly predicted the drift flux parameters when compared with those calculated by existing slipdrift correlations in the SOPHT and FIREBIRD codes, other drift flux models, and with certain experimental data reported in the literature.

Sami, S.M.

1986-12-01

249

Hypocenter relocation using a fast grid search method and a 3-D seismic velocity model for the Sumatra region  

SciTech Connect

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 [Study Program of Earth Sciences, Faculty of Earth Sciences and Technology, Institute of Technology Bandung, Jl. Ganesha No. 10, Bandung 40132, Indonesia and Meteorological, Climatological, and Geophysical Agency, Jl. Angkasa 1 No. 2, Kemayoran, Jakar (Indonesia)] [Study Program of Earth Sciences, Faculty of Earth Sciences and Technology, Institute of Technology Bandung, Jl. Ganesha No. 10, Bandung 40132, Indonesia and Meteorological, Climatological, and Geophysical Agency, Jl. Angkasa 1 No. 2, Kemayoran, Jakar (Indonesia); Widiyantoro, Sri [Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institute of Technology Bandung, Jl. Ganesha No. 10, Bandung 40132 (Indonesia)] [Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institute of Technology Bandung, Jl. Ganesha No. 10, Bandung 40132 (Indonesia); Nugraha, Andri Dian [Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institute of Technologyc Bandung, Jl. Ganesha No. 10, Bandung 40132 (Indonesia)] [Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institute of Technologyc Bandung, Jl. Ganesha No. 10, Bandung 40132 (Indonesia)

2013-09-09

250

Impacts of Leads on the Wintertime Sea-ice Environment Using 1D and 3D Models Validated with In-Situ Observations  

NASA Astrophysics Data System (ADS)

Though leads only represent a small portion of the Arctic sea-ice area, their contribution to the surface turbulent energy and momentum fluxes can be significant. Numerous modeling studies presented in the literature have been conducted examining these effects. The results of such studies have indicated the importance of the environmental large-scale stability, the environmental humidity, the lead width, the ice (lead) concentration, the lead size distribution, the character of the leads (open water, refrozen), etc. Because global climate models (GCMs) show significant sensitivity to the large-scale net energy flux from the heterogeneous sea-ice surface, and because thinner ice in the projected future Arctic climate will likely result in increasing lead fractions, the appropriate GCM representation of this complex system is important. This study presents modeling results based on observations from the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment, for which the mid-winter sea-ice was greatly heterogeneous. In mid-January, the 100x100 km region surrounding the SHEBA ice camp consisted of a lead fraction of ~16-33% as revealed by SAR data. This included primarily older refrozen lead areas that were generated at least a month earlier (~16-25% areal coverage), with a smaller fraction of newly opened leads (~4-9% areal coverage). Utilizing the sequence of SAR images, the atmospheric observations at the SHEBA site, and a 1-D snow and ice model, the spatial distribution of sea-ice thickness, snow depth, and surface temperatures within this domain were estimated over a 6-week period, revealing the significant impact of leads in all stages on GCM-scale temperatures and fluxes. This combined observational/model data series is used to evaluate a variety of one-dimensional turbulent flux aggregation techniques (e.g., mosaic) that use different assumptions. Furthermore, by using the spatial distribution of these surface characteristics, three-dimensional large eddy simulations (LES) have been done to a) validate the 1D aggregation techniques and b) to assess how mesoscale circulations generated by the surface heterogeneity impact net surface fluxes. Initially, the LES modeling uses very simple idealized surface conditions and progressively moves towards the much more complex conditions revealed by the SHEBA observations. Our LES studies both validate previous results and address issues not covered in the previous studies in an effort to understand and represent the SHEBA surface fluxes on scales from local point measurements to the GCM grid-box size.

Persson, O. P.; Solomon, A.

2013-12-01

251

An Innovative Model-Based Velocity Integration Procedure with an Application in Eastern Saudi Arabia  

NASA Astrophysics Data System (ADS)

During the workflow of seismic data processing, approximately one third of the processing time is allocated to estimate initial stacking velocity functions. The precision of the current available methods of estimating stacking velocity is limited in vertical and horizontal velocity resolution, especially in cases involving multiples and limited-offset data sets. A new procedure is proposed in this study to effectively build initial stacking velocity functions for processing new seismic lines with improved productivity, increased accuracy and interpretation consistency. The procedure builds a 3-D velocity model from previous surface and borehole seismic surveys as well as interpretation data for seven key horizons. A common-model platform has been used to allow for integration of otherwise independent data types. Results show that using the estimated integrated velocity model has allowed velocity picking in seismic data sets with poor signal-to-noise ratio due to excessive ambient noise or karsting. The model also helped in discriminating stacking velocities in areas with stretched or poor semblance peaks.

Al-Moqbel, Abdulaziz Mohammed Saleh

252

SH velocity and compositional models near the 660-km discontinuity beneath South America and northeast Asia  

Microsoft Academic Search

We constrain SH wave velocity structures near the 660-km discontinuity beneath South America and northeast Asia, using triplicated phases near the discontinuity recorded in the epicentral distance range of 10°-35° for three deep events. We then explore mineralogical and compositional models appropriate for explaining the inferred seismic structures between the two regions. SH velocity structures near the 660-km discontinuity are

Yi Wang; Lianxing Wen; Donald Weidner; Yumei He

2006-01-01

253

Vibration measurements using continuous scanning laser vibrometry: velocity sensitivity model experimental validation  

Microsoft Academic Search

This paper builds on a previous study in which the theoretical description of the velocity sensed by a single laser beam incident in an arbitrary direction on a rotating target undergoing arbitrary vibration was extended to continuous scanning laser vibrometer measurements on targets with flexible cross sections. The velocity sensitivity model was written in terms of either laser beam orientation

B. J. Halkon; S. R. Frizzel; S. J. Rothberg

2003-01-01

254

Self-healing slip pulses in dynamic rupture models due to velocity-dependent strength  

USGS Publications Warehouse

Seismological observations of short slip duration on faults (short rise time on seismograms) during earthquakes are not consistent with conventional crack models of dynamic rupture and fault slip. In these models, the leading edge of rupture stops only when a strong region is encountered, and slip at an interior point ceases only when waves from the stopped edge of slip propagate back to that point. In contrast, some seismological evidence suggests that the duration of slip is too short for waves to propagate from the nearest edge of the ruptured surface, perhaps even if the distance used is an asperity size instead of the entire rupture dimension. What controls slip duration, if not dimensions of the fault or of asperities? In this study, dynamic earthquake rupture and slip are represented by a propagating shear crack. For all propagating shear cracks, slip velocity is highest near the rupture front, and at a small distance behind the rupture front, the slip velocity decreases. As pointed out by Heaton (1990), if the crack obeys a negative slip-rate-dependent strength relation, the lower slip velocity behind the rupture front will lead to strengthening that further reduces the velocity, and under certain circumstances, healing of slip can occur. The boundary element method of Hamano (1974) is used in a program adapted from Andrews (1985) for numerical simulations of mode II rupture with two different velocity-dependent strength functions. For the first function, after a slip-weakening displacement, the crack follows an exponential velocity-weakening relation. The characteristic velocity V0 of the exponential determines the magnitude of the velocity-dependence at dynamic velocities. The velocity-dependence at high velocity is essentially zero when V0 is small and the resulting slip velocity distribution is similar to slip weakening. If V0 is larger, rupture propagation initially resembles slip-weakening, but spontaneous healing occurs behind the rupture front. The rise time and rupture propagation velocity depend on the choice of constitutive parameters. The second strength function is a natural log velocity-dependent form similar to constitutive laws that fit experimental rock friction data at lower velocities. Slip pulses also arise with this function. For a reasonable choice of constitutive parameters, slip pulses with this function do not propagate at speeds greater than the Raleighwave velocity. The calculated slip pulses are similar in many aspects to seismic observations of short rise time. In all cases of self-healing slip pulses, the residual stress increases with distance behind the trailing edge of the pulse so that the final stress drop is much less than the dynamic stress drop, in agreement with the model of Brune (1976) and some recent seismological observations of rupture.

Beeler, N. M.; Tullis, T. E.

1996-01-01

255

Linking bed surface characteristics, near-bed flow hydraulics and sediment transport in pool-riffle sequences using a simple 1D morphodynamic model.  

NASA Astrophysics Data System (ADS)

Many gravel bed streams have a typical bed morphology consisting of pool-riffle sequences, which provides important habitat diversity both in terms of flow and substrate. Here we use a 1D unsteady multi-fraction morphodynamic model to explain the formation, self maintenance and degradation of pool-riffle sequences. Previous research has focussed almost exclusively on understanding self-maintenance on existing pool-riffle sequences, leaving formation and degradation at a speculative level. Spontaneous formation of pools and riffles has not been attempted before, even though other similar stable bedforms have been generated numerically and in the laboratory through the interaction of flow and sediment transport, like alternate bars in meanders and central bars in braided rivers. While this previous research substantially simplified flow (constant discharge), geometry (sinusoidal description of curvature or channel width) and sediment (uniform material) it showed the forcing effects of either curvature or width on the location of bedforms. For the formation of pools and riffles we use elements of the previous approach (width forcing) but we also incorporate a much more detailed geometry, flow and sediment description, since our intent is to study driving mechanisms for both the morphology and the sediment composition of the bed in a more realistic setting. We tested two hypotheses using our model. The first hypothesis states that the dynamic interaction of 1D flow and sediment processes can not only maintain but also generate a stable pool-riffle morphology with the corresponding longitudinal sorting on a stream with a non uniform bed material, variations in width and subjected to a variable flow regime. The second hypothesis we investigated is that the two key forming sediment processes of erosion/deposition and sorting have different time scales, which interact with the flow time scales to produce a feedback mechanism that reinforces the pool-riffle morphology, including bed geometry and composition. We performed both variable flow and constant flow simulation imposing the width variations observed in an existing river reach and did experiments starting from both a flat bed (to study formation) and from a pool-riffle sequence (to study degradation). Using measured flows on a stream in which we have removed initial bedforms and sediment sorting our model spontaneously generates pools with finer substrate at narrow sections and riffles with coarser sediment at wider sections, closely resembling the natural bed morphology. Additional experiments show that under our modelling assumptions a variable flow regime is fundamental for development and self-maintenance of the longitudinal grain sorting characteristic of pool-riffle sequences, which could not be obtained or maintained with constant discharges.

de Almeida, Gustavo; Rodriguez, Jose

2013-04-01

256

Velocity prediction errors related to flow model calibration uncertainty  

Microsoft Academic Search

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

D. E. Stephenson; G. M. Duffield; D. R. Buss

1990-01-01

257

A ceramic fracture model for high velocity impact  

Microsoft Academic Search

The objectives of this research program were to develop, implement, and demonstrate a failure model for aluminum oxide ceramic under impact loading. A comprehensive test program for Coors AD-85 was conducted. Four types of experiments provided a basis for the development of the ceramic failure model. A phenomenological damage-based failure model for compressive fracture of impacted aluminum oxide was developed

William H. Cook

1993-01-01

258

Discrete set of kink velocities in Josephson structures: The nonlocal double sine-Gordon model  

NASA Astrophysics Data System (ADS)

We study a model of Josephson layered structure which is characterized by two peculiarities: (i) superconducting layers are thin; (ii) the current-phase relation is non-sinusoidal and is described by two sine harmonics. The governing equation is a nonlocal generalization of double sine-Gordon (NDSG) equation. We argue that the dynamics of fluxons in the NDSG model is unusual. Specifically, we show that there exists a set of particular constant velocities (called "sliding" velocities) for non-radiating stationary fluxon propagation. In dynamics, the presence of this set results in quantization of fluxon velocities: in numerical experiments a traveling kink-like excitation radiates energy and slows down to one of these particular constant velocities, taking the shape of predicted 2?-kink. We conjecture that the set of these stationary velocities is infinite and present an asymptotic formula for them.

Alfimov, G. L.; Malishevskii, A. S.; Medvedeva, E. V.

2014-07-01

259

Near-surface ocean velocity from infrared images: Global Optimal Solution to an inverse model  

NASA Astrophysics Data System (ADS)

We address the problem of obtaining ocean surface velocities from sequences of thermal (AVHRR) space-borne images by inverting the heat conservation equation (including sources of surface heat fluxes and vertical entrainment). We demonstrate the utility of the technique by deriving surface velocities from (1) The motion of a synthetic surface tracer in a numerical model and (2) a sequence of five actual AVHRR images from 1 day. Typical formulations of this tracer inversion problem yield too few equations at each pixel, which is often remedied by imposing additional constraints (e.g., horizontal divergence, vorticity, and energy). In contrast, we propose an alternate strategy to convert the underdetermined equation set to an overdetermined one. We divide the image scene into many subarrays and define velocities and sources within each subarray using bilinear expressions in terms of the corner points (called knots). In turn, all velocities and sources on the knots can be determined by seeking an optimum solution to these linear equations over the large scale, which we call the Global Optimal Solution (GOS). We test the accuracy of the GOS by contaminating the model output with up to 10% white noise but find that filtering the data with a Gaussian convolution filter yields velocities nearly indistinguishable from those without the added noise. We compare the GOS velocity fields with those from the numerical model and from the Maximum Cross Correlation (MCC) technique. A histogram of the difference between GOS and numerical model velocities is narrower and more peaked than the similar comparison with MCC, irrespective of the time interval (?t = 2 or 4 h) between images. The calculation of the root mean square error difference between the GOS (and MCC) results and the model velocities indicates that the GOS/model error is only half that of the MCC/model error irrespective of the time interval (?t = 2 or 4 h) between images. Finally, the application of the technique to a sequence of five NOAA AVHRR images yields a velocity field, which we compare with that from a Coastal Ocean Dynamics Radar (CODAR) array. We find that the GOS velocities generally agree more closely with those from the CODAR than they do with those from the MCC. Specifically, the root mean square error obtained by differencing GOS and CODAR velocities is smaller than that from the similar calculation with MCC velocities. The magnitude of the complex correlation between GOS and CODAR is larger than that between MCC and CODAR. The phase of the complex correlation indicates that both MCC and GOS on average yield velocity vectors biased in the clockwise direction relative to the CODAR vectors for the period examined.

Chen, Wei; Mied, Richard P.; Shen, Colin Y.

2008-10-01

260

High-Resolution Seismic Velocity and Attenuation Models of Eastern Tibet and Adjacent Regions (Post Print).  

National Technical Information Service (NTIS)

High-resolution seismic velocity and attenuation models of the Tibetan Plateau and adjacent regions of western China are critical to monitoring seismology efforts in Eurasia. Our waveform data are collected from new deployed seismic networks including NET...

E. A. Sandvol J. Ni S. Ceylan T. Hearn X. Bao

2012-01-01

261

Examining Applicability of the NASA Standard Breakup Model to Low-Velocity Collisions  

Microsoft Academic Search

The data from a series of low-velocity collision experiments performed at Kyushu University will be re-analyzed based on the method used in the National Aeronautics and Space Administration (NASA) standard breakup model 2000 revision to be compared with the hypervelocity collision model adopted in the NASA standard breakup model. The results will indicate that the NASA hypervelocity collision model can

Hidehiro Hata; Yasuo Kurakazu; Toshiya Hanada; Yasuhiro Akahoshi; Tetsuo Yasaka; Shoji Harada

2004-01-01

262

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

263

Estimating V??s(30) (or NEHRP site classes) from shallow velocity models (depths < 30 m)  

USGS Publications Warehouse

The average velocity to 30 m [V??s(30)] is a widely used parameter for classifying sites to predict their potential to amplify seismic shaking. In many cases, however, models of shallow shear-wave velocities, from which V??s(30) can be computed, do not extend to 30 m. If the data for these cases are to be used, some method of extrapolating the velocities must be devised. Four methods for doing this are described here and are illustrated using data from 135 boreholes in California for which the velocity model extends to at least 30 m. Methods using correlations between shallow velocity and V??s(30) result in significantly less bias for shallow models than the simplest method of assuming that the lowermost velocity extends to 30 m. In addition, for all methods the percent of sites misclassified is generally less than 10% and falls to negligible values for velocity models extending to at least 25 m. Although the methods using correlations do a better job on average of estimating V??s(30), the simplest method will generally result in a lower value of V??s(30) and thus yield a more conservative estimate of ground motion [which generally increases as V??s(30) decreases].

Boore, D. M.

2004-01-01

264

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

265

Forearc structure beneath southwestern British Columbia: A three-dimensional tomographic velocity model  

Microsoft Academic Search

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

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

2005-01-01

266

1-D fluid model of atmospheric-pressure rf He+O{sub 2} cold plasmas: Parametric study and critical evaluation  

SciTech Connect

In this paper atmospheric-pressure rf He+O{sub 2} cold plasmas are studied by means of a 1-D fluid model. 17 species and 60 key reactions selected from a study of 250+ reactions are incorporated in the model. O{sub 2}{sup +}, O{sub 3}{sup -}, and O are the dominant positive ion, negative ion, and reactive oxygen species, respectively. Ground state O is mainly generated by electron induced reactions and quenching of atomic and molecular oxygen metastables, while three-body reactions leading to the formation of O{sub 2} and O{sub 3} are the main mechanisms responsible for O destruction. The fraction of input power dissipated by ions is {approx}20%. For the conditions considered in the study {approx}6% of the input power is coupled to ions in the bulk and this amount will increase with increasing electronegativity. Radial and electrode losses of neutral species are in most cases negligible when compared to gas phase processes as these losses are diffusion limited due to the large collisionality of the plasma. The electrode loss rate of neutral species is found to be nearly independent of the surface adsorption probability p for p > 0.001 and therefore plasma dosage can be quantified even if p is not known precisely.

Yang Aijun; Wang Xiaohua; Rong Mingzhe; Liu Dingxin [State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an 710049 (China); Iza, Felipe [School of Electronic, Electrical and Systems Engineering, Loughborough University, Loughborough LE11 3TU (United Kingdom); Kong, Michael G. [State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an 710049 (China); School of Electronic, Electrical and Systems Engineering, Loughborough University, Loughborough LE11 3TU (United Kingdom)

2011-11-15

267

Butyrylcholinesterase is Associated with ?-Amyloid Plaques in the Transgenic APPSWE/PSEN1dE9 Mouse Model of Alzheimer Disease  

PubMed Central

Histochemical analysis of Alzheimer disease (AD) brain tissues indicates that butyrylcholinesterase (BuChE) is present in ?-amyloid (A?) plaques. The role of BuChE in AD pathology is unknown but an animal model developing similar BuChE-associated A? plaques could provide insights. The APPSWE/PSEN1dE9 mouse (ADTg), which develops A? plaques, was examined to determine if BuChE associates with these plaques, as in AD. We found that in mature ADTg mice, BuChE activity associated with A? plaques. A?-, thioflavin-S- and BuChE-positive plaques mainly accumulated in olfactory structures, cerebral cortex, hippocampal formation, amygdala and cerebellum. No plaques were stained for acetylcholinesterase activity. The distribution and abundance of plaque staining in ADTg closely resembled many aspects of plaque staining in AD. BuChE staining consistently showed fewer plaques than were detected with A? immunostaining but a greater number of plaques than were visualized with thioflavin-S. Double-labelling experiments demonstrated that all BuChE-positive plaques were A?-positive while only some BuChE-positive plaques were thioflavin-S-positive. These observations suggest that BuChE is associated with a subpopulation of A? plaques and may play a role in AD plaque maturation. Further study of this animal model could clarify the role of BuChE in AD pathology.

Darvesh, Sultan; Cash, Meghan K.; Reid, G. Andrew; Martin, Earl; Mitnitski, Arnold; Geula, Changiz

2011-01-01

268

Velocity Modeling of Land 3-D Surface Seismic Data for Prestack Depth Migration  

NASA Astrophysics Data System (ADS)

Since the early 1990's prestack depth migrations (PSDM) have been routinely applied to 3-D seismic data. Using current methods building an accurate velocity model is dependent on the quality of the seismic data. Data quality is a reason why PSDM have been applied nearly exclusively to marine data. To apply the power of PSDM to land 3-D surface seismic data deriving an initial sediment velocity model that overcomes limitations of data quality associated with land 3-D seismic data is essential. In this study I use a non-seismic approach to generate an initial sediment velocity model for PSDM of land 3-D surface seismic data. Differences in data quality between marine and land 3-D seismic data provided the motivation to investigate innovative velocity modeling techniques for land 3-D surface seismic data. In this study current practices primarily for marine data were reviewed and problems with land 3-D surface seismic data were identified. An approach that integrates the efficiency and accuracy of current methods and overcomes the limitations imposed by data quality was implemented. Data were acquired over Vinton Dome in southwest Louisiana and used in this case study to derive an initial sediment velocity model using sonic logs. Comparing the results with a prestack time migration (PSTM) and a PSDM that had been migrated using a seismically derived velocity model demonstrated that this approach enhanced the fidelity of the Vinton Dome 3-D surface seismic data.

Duncan, W. S.; Zhou, H.

2005-05-01

269

Subgrid scale updraft velocity in km-scale models: implication for the aerosol indirect effect  

NASA Astrophysics Data System (ADS)

Aerosol-cloud-interactions (ACI) span a large range of spatial and temporal scales. The coarse resolution used in Global Circulation Models and Earth System models is unable to resolve the fine scale processes (e.g. vertical velocity, turbulent mixing) or the microphysical and dynamic feedbacks that are important for ACI, which leads to important uncertainties. The microphysical link between aerosols and clouds is activation, which is a strong function of the cloud-scale updraft velocity. To bridge the gap between the cloud scale and the global scale, a potential approach is using high-resolution large-scale models such as those from operational Numerical Weather Prediction (NWP). However, even for non-hydrostatic km-scale NWP models, vertical velocities are only partially resolved. This work focuses on the parameterisation of the sub-grid vertical velocity and aerosol activation in such models. In order to estimate the contribution of the unresolved sub-grid variability, we analyse the updraft velocity at cloud resolving scales. Our strategy relies on running Large Eddy Simulation (LES) models and analysing hi-resolution aircraft observations of stratocumulus and shallow cumulus clouds to devise the scale-linking partition function of the total updraft velocity variability. To construct such a function, the resolved and sub-grid parts of the variables at coarser grid sizes are deduced after coarse graining the initial high resolution datasets. On this basis, we have developed and tested a framework for a parameterization that represents the sub-grid variability of updraft velocity in UK-Met Office NWP model, the Unified Model (UM), which is applicable to resolutions up to a few km. We show that without correction, the variability of updraft velocity decreases with decreasing model resolution. Applying our parameterization leads to consistent estimates of vertical velocity variability across the different resolutions. The contribution of the sub-grid variability to the vertical velocity standard deviation is factor of ~4-8 increase in simulations at a 1 km horizontal grid resolution. Offline calculations of CCN activated fraction using two activation schemes have been performed to investigate the sensitivity of the activation processes when the sub-grid scale vertical velocity variability is accounted for. These tests show significant increases in the CCN activated fraction, from +20% up to +100% depending on CCN concentration and the scheme considered. This highlights important implications for future ACI simulations at km-scale.

Malavelle, F.; Haywood, J.; Field, P.; Hill, A.; Abel, S.; Lock, A.; Shipway, B.; McBeath, K.

2013-12-01

270

Intercomparison of Eight Forward 1D Vector Radiative Transfer Models, with the Performance of Satellite Aerosol Remote Sensing Algorithms in Mind  

NASA Astrophysics Data System (ADS)

Quantification and characterization of the omnipresent atmospheric aerosol by remote sensing methods is key to answering many challenging questions in atmospheric science, in climate modeling and in air quality monitoring foremost. In recent years, accurate measurement of the state of polarization of photon fluxes at optical sensors in the visible and near-IR spectrum has been hailed as a very promising approach to aerosol remote sensing. Consequently, there has been a flurry of activity in polarized or 'vector' radiative transfer (vRT) model development. This covers the multiple scattering and ground reflection aspects of sensor signal prediction that complement single-particle scattering computation, and lies at the core of all physics-based retrieval algorithms. One can legitimately ask: What level of model fidelity (representativeness of natural scenes) and what computational accuracy should be achieved for this task in view of the practical constraints that apply? These constraints are, at a minimum: (i) the desired accuracy of the retrieved aerosol properties, (ii) observational uncertainties, and (iii) operational efficiency requirements as determined by throughput. We offer a rational and balanced approach to address these questions and illustrate it with a systematic inter-comparison of the performance of a diverse set of 1D vRT models using a small but representative set of test cases. This 'JPL' benchmarking suite of cases is naturally divided into two parts. First the emphasis is on stratified atmospheres with a continuous mixture of molecular and aerosol scattering and absorption over a black surface, with the corresponding pure cases treated for diagnostic purposes. Then the emphasis shifts to the variety of surfaces, both polarizing and not, that can be encountered in real observations and may confuse the aerosol retrieval algorithm if not properly treated.

Davis, Anthony B.; Kalashnikova, Olga V.; Diner, David J.; Garay, Michael J.; Lyapustin, Alexei I.; Korkin, Sergey V.; Martonchik, John V.; Natraj, Vijay; Sanghavi, Suniti V.; Xu, Feng; Zhai, Pengwang; Rozanov, Vladimir V.; Kokhanovsky, Alexander A.

2014-05-01

271

A subgrid-scale model based on the second-order velocity structure function  

NASA Astrophysics Data System (ADS)

A series of tests were performed to help extend the use of a subgrid-scale model to compressible and wall-bounded flows. A priori tests were done in the case of the incompressible turbulent channel flow. They showed that a 1-D formulation of the structure-function model is more appropriate, leading to a satisfactory behavior of the model at the walls without requiring any damping function. This model is consistent with the original formulation of Metais & Lesieur (1990). In large-eddy simulations of compressible isotropic turbulence, both models performed well up to an initial rms Mach number of 0.6.

Comte, P.; Lee, Sangsan; Cabot, William H.

1990-12-01

272

A subgrid-scale model based on the second-order velocity structure function  

NASA Technical Reports Server (NTRS)

A series of tests were performed to help extend the use of a subgrid-scale model to compressible and wall-bounded flows. A priori tests were done in the case of the incompressible turbulent channel flow. They showed that a 1-D formulation of the structure-function model is more appropriate, leading to a satisfactory behavior of the model at the walls without requiring any damping function. This model is consistent with the original formulation of Metais & Lesieur (1990). In large-eddy simulations of compressible isotropic turbulence, both models performed well up to an initial rms Mach number of 0.6.

Comte, P.; Lee, Sangsan; Cabot, William H.

1990-01-01

273

Diurnal variation of stratospheric and lower mesospheric HOCl, ClO and HO2 at the equator: comparison of 1-D model calculations with measurements by satellite instruments  

NASA Astrophysics Data System (ADS)

The diurnal variation of HOCl and the related species ClO, HO2 and HCl measured by satellites has been compared with the results of a one-dimensional photochemical model. The study compares the data from various limb-viewing instruments with model simulations from the middle stratosphere to the lower mesosphere. Data from three sub-millimetre instruments and two infrared spectrometers are used, namely from the Sub-Millimetre Radiometer (SMR) on board Odin, the Microwave Limb Sounder (MLS) on board Aura, the Superconducting Submillimeter-wave Limb-Emission Sounder (SMILES) on the International Space Station, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board ENVISAT, and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on board SCISAT. Inter-comparison of the measurements from instruments on sun-synchronous satellites (SMR, MLS, MIPAS) and measurements from solar occultation instruments (ACE-FTS) is challenging since the measurements correspond to different solar zenith angles (or local times). However, using a model which covers all solar zenith angles and data from the SMILES instrument which measured at all local times over a period of several months provides the possibility to verify the model and to indirectly compare the diurnally variable species. The satellite data were averaged for latitudes of 20° S to 20° N for the SMILES observation period from November 2009 to April 2010 and were compared at three altitudes: 35, 45 and 55 km. Besides presenting the SMILES data, the study also shows a first comparison of the latest MLS data (version 3.3) of HOCl, ClO, and HO2 with other satellite observations, as well as a first evaluation of HO2 observations made by Odin/SMR. The MISU-1D model has been carefully initialised and run for conditions and locations of the observations. The diurnal cycle features for the species investigated here are generally well reproduced by the model. The satellite observations and the model agree well in terms of absolute mixing ratios. The differences between the day and night values of the model are in good agreement with the observations although the amplitude of the HO2 diurnal variation is 10-20% lower in the model than in the observations. In particular, the data offered the opportunity to study the reaction ClO+HO2 ? HOCl+O2 in the lower mesosphere at 55 km. At this altitude the HOCl night-time variation depends only on this reaction. The result of this analysis points towards a value of the rate constant within the range of the JPL 2006 recommendation and the upper uncertainty limit of the JPL 2011 recommendation at 55 km.

Khosravi, M.; Baron, P.; Urban, J.; Froidevaux, L.; Jonsson, A. I.; Kasai, Y.; Kuribayashi, K.; Mitsuda, C.; Murtagh, D. P.; Sagawa, H.; Santee, M. L.; Sato, T. O.; Shiotani, M.; Suzuki, M.; von Clarmann, T.; Walker, K. A.; Wang, S.

2013-08-01

274

Current plate velocities relative to the hotspots incorporating the NUVEL-1 global plate motion model  

NASA Technical Reports Server (NTRS)

The NUVEL-1 model of current global relative plate velocities is presently incorporated into HS2-NUVEL1, a global model for plate velocities relative to hotspots; the results thus obtained are compared with those of the AM1-2 model of hotspot-relative plate velocities. While there are places in which plate velocities relative to the hotspots differ between HS2-NUVEL1 and AM1-2 by tens of degrees in direction and 15 mm/yr in speed, the hotspot Euler vectors differ with 95 percent confidence only for the Arabian and Indian plates. Plates attached to subducting slabs move faster relative to the hotspots than do plates without slabs.

Gripp, Alice E.; Gordon, Richard G.

1990-01-01

275

Measurements and a model for convective velocities in the turbulent boundary layer  

NASA Technical Reports Server (NTRS)

A physical model is presented which describes convective velocities within a flat plate turbulent boundary layer. A production zone concept is used as a basis for the physical model. The production zone concept employs the idea that packets of turbulent fluid are generated near the viscous sublayer. These packets are found to be discernible from the mean motion and may move either outward from the production zone or inward depending on their circulation relative to the fluid surrounding the packet. The packets are predicted to travel with a convective velocity different from the local mean velocity throughout most of the boundary layer. The model also predicts that the convective velocities will be functions of wave number outside the production zone.

Cliff, W. C.; Sandborn, V. A.

1973-01-01

276

Comparison of vertical velocities analyzed by a numerical model and measured by a VHF wind profiler  

NASA Technical Reports Server (NTRS)

The use of wind profilers for measuring vertical velocities in the troposphere and lower stratosphere is potentially of great interest for verification of forecasts, diagnosis of mesoscale circulations, and studies of wave motions. The studies of profiler vertical velocities to date have shown that the observed patterns of ascent and subsidence are reasonable when compared to the synoptic conditions. However, difficulties arise when a direct verification of the profiler vertical winds is sought. Since no other technique can measure the vertical velocities over the same height range and with the same claimed accuracy as the profilers, direct comparisons are impossible. The only alternative is to compare the measurements to analyzed vertical velocity fields. Here, researchers compare vertical measurements made with the SOUSY VHF radar over a period of 11 days at the beginning of November 1981 to the analyzed vertical velocities produced by the European Center for Medium-range Weather Forecasting (ECMWF) model for grid points near the radar site.

Larsen, M. F.; Rottger, J.; Dennis, T. S.

1986-01-01

277

A multifractal model for linking Lagrangian and Eulerian velocity structure functions  

NASA Astrophysics Data System (ADS)

A multifractal model is developed to connect the Lagrangian multifractal dimensions with their Eulerian counterparts. We propose that the characteristic time scale of a Lagrangian quantity should be the Lagrangian time scale, and it should not be the Eulerian time scale which was widely used in previous studies on Lagrangian statistics. Using the present model, we can obtain the scaling exponents of Lagrangian velocity structure functions from the existing data or models of scaling exponents of Eulerian velocity structure functions. This model is validated by comparing its prediction with the results of experiments, direct numerical simulations, and the previous theoretical models. The comparison shows that the proposed model can better predict the scaling exponents of Lagrangian velocity structure functions, especially for orders larger than 6.

Dong, Yu-Feng; Jin, Guo-Dong

2014-05-01

278

Sensitivity testing of a 1-D calving criterion numerical model constrained by observations of post-LIA fluctuations of Kangiata Nunaata Sermia, SW Greenland  

NASA Astrophysics Data System (ADS)

The ability to successfully model the behaviour of Greenlandic tidewater glaciers is pivotal for the prediction of future behaviour and potential impact on global sea level. However, to have confidence in the results of numerical models, they must be capable of replicating the full range of observed glacier behaviour (i.e. both advance and retreat) when realistic forcings are applied. Due to the paucity of observational records recording this behaviour, it is therefore necessary to verify calving models against reconstructions of glacier dynamics. The dynamics of Kangiata Nunaata Sermia (KNS) can be reconstructed with a high degree of detail using a combination of sedimentological and geomorphological evidence, photographs, historical sources and satellite imagery. Since the LIA-maximum KNS has retreated a total of 21 km with multiple phases of rapid retreat evident between topographic pinning points. A readvance attaining a position 9 km from the current terminus associated with the '1920 stade' is also identified. KNS therefore represents an ideal test location for calving models since it has both advanced and retreated over known timescales, while the scale of fluctuations implies KNS is sensitive to parameter(s) controlling terminus stability. Using the known stable positions for verification, we present the results of an array of sensitivity tests conducted on KNS using the 1-D flowband calving model of Nick et al (2009). The model is initially tuned to an historically stable position where the glacier configuration is accurately known (in this case 1985), and forced by varying surface mass balance, crevasse water depth, submarine melt rate at the calving front, in addition to the strength and pervasiveness of sikussak in the fjord. Successive series of experiments were run using each parameter to test model sensitivity to the initial conditions of each variable. Results indicate that the model is capable of stabilising at locations that are in agreement with the geomorphic/historical record. Reference: Nick FM, Vieli A, Howat IM, Joughin I. 2009. Large-scale changes in Greenland outlet glaciers triggered at the terminus. Nature Geoscience 2 : 110-114

Lea, J. M.; Mair, D.; Nick, F. M.; Rea, B. R.; Schofield, E.; Nienow, P. W.

2012-12-01

279

A three-dimensional P wave velocity model for the Charlevoix seismic zone, Quebec, Canada  

NASA Astrophysics Data System (ADS)

A three-dimensional P wave velocity model has been developed for the Charlevoix seismic zone (CSZ). The CSZ is located along the St. Lawrence River ˜100 km northeast of Quebec City, Canada, and is one of the most active seismic zones in eastern North America. Five earthquakes with magnitudes equal to or exceeding 6.0 have occurred in the CSZ in historic time, and around 200 earthquakes occur annually. Hypocenters are located in Precambrian basement rocks. Basement rocks have been affected by numerous tectonic events including Grenvillian collision, Iapetan rifting, and meteor impact. We performed a sequential, tomographic inversion for P wave velocity structure based upon 3093 P wave arrivals from 489 earthquakes recorded by 12 stations. High velocity is associated with the center of the impact crater. The region of high velocity is surrounded by low velocities interpreted to be highly disrupted rocks. An elongated, high-velocity region is present at midcrustal depths that trends parallel to the St. Lawrence River. Earthquakes avoid the high-velocity body and separate into two bands, one on either side of the feature. Larger earthquakes (magnitude ? 4) have occurred along the northern edges of the high-velocity region.

Vlahovic, Gordana; Powell, Christine; Lamontagne, Maurice

2003-09-01

280

Actinometric and radiometric measurement and modeling of the photolysis rate coefficient of ozone to O(1D) during Mauna Loa Observatory Photochemistry Experiment 2  

Microsoft Academic Search

The in situ photolysis rate coefficient of O3 to O(1D) has been measured at Mauna Loa Observatory using a new actinometric instrument based on the reaction of O(1D) with N2O and with a hemispherical radiometer. One minute averaged photolysis rate coefficients were determined with an overall uncertainty of approximately +\\/-11% at the 1sigma level for the actinometer and +\\/-15% at

Richard E. Shetter; Christopher A. Cantrell; Kathleen O. Lantz; Siri J. Flocke; John J. Orlando; Geoffrey S. Tyndall; Timothy M. Gilpin; Chris A. Fischer; Sasha Madronich; Jack G. Calvert; Wolfgang Junkermann

1996-01-01

281

Electron Density and Two-Channel Neutron Emission Measurements in Steady-State Spherical Inertial-Electrostatically Confined Plasmas, with Review of the 1-D Kinetic Model  

NASA Technical Reports Server (NTRS)

Electron density measurements have been made in steady-state plasmas in a spherical inertial electrostatic confinement (IEC) discharge using microwave interferometry. Plasma cores interior to two cathodes, having diameters of 15 and 23 cm, respectively, were probed over a transverse range of 10 cm with a spatial resolution of about 1.4 cm for buffer gas pressures from 0.2 to 6 Pa in argon and deuterium. The transverse profiles are generally flat, in some cases with eccentric symmetric minima, and give mean densities of from approx. = 0.4 to 7x 10(exp 10)/cu cm, the density generally increasing with the neutral gas pressure. Numerical solutions of the 1-D Poisson equation for EC plasmas are reviewed and energy distribution functions are identified which give flat transverse profiles. These functions are used with the plasma approximation to obtain solutions which also give densities consistent with the measurements, and a double potential well solution is obtained which has minima qualitatively similar to those observed. Explicit consideration is given to the compatibility of the solutions interior and exterior to the cathode, and to grid transparency. Deuterium fusion neutron emission rates were also measured and found to be isotropic, to within the measurement error, over two simultaneous directions. Anisotropy was observed in residual emissions during operation with non-fusing hydrogen-1. The deuterium rates are consistent with predictions from the model.

Dobson, Chris C.; Hrbud, Ivana

2004-01-01

282

Focal mechanisms of earthquake multiplets in the western part of the Corinth Rift (Greece): influence of the velocity model and constraints on the geometry of the active faults  

NASA Astrophysics Data System (ADS)

The composite fault plane solutions for 24 large multiplets recorded in the western part of the Corinth Rift between 2000 and 2007 are computed by jointly inverting P polarities and Sv/P, Sh/P, Sv/Sh amplitude ratios of the direct waves. The fault plane solutions are determined using 1-D and 3-D velocity models. Solutions computed with the 3-D velocity model are preferred to the ones computed with the 1-D model because overall, 3-D solutions have a better score function. They correspond essentially to E-NE/W-SW and W-NW/E-SE striking normal faults, which is consistent with the N-S extensional/vertical shortening tectonic regime of the area. For 15 multiplets, one of the nodal planes is similar to the plane delineated by the earthquakes. It is then possible to determine which nodal plane is the fault plane. The analysis of the fault plane solutions highlights a clear decrease of their dip with depth and towards the north. Several multiplets with steeply dipping fault planes (50°-60°) located at depths of 7-8 km are clearly located at the base of onshore and offshore faults that crop out close to the south border of the Corinth Gulf, indicating that these faults are steep down to 7-8 km depth. To the north, multiplets underline a low angle north-dipping structure (20°-30°) on which steep north-dipping faults could take root.

Godano, Maxime; Deschamps, Anne; Lambotte, Sophie; Lyon-Caen, Hélène; Bernard, Pascal; Pacchiani, Francesco

2014-06-01

283

Potential of high resolution satellite imagery, remote weather data and 1D hydraulic modeling to evaluate flood areas in Gonaives, Haiti  

NASA Astrophysics Data System (ADS)

We present a feasibility study to explore potential of high-resolution imagery, coupled with hydraulic flood modeling to predict flooding risks, applied to the case study of Gonaives basins (585 km²), Haiti. We propose a methodology working at different scales, providing accurate results and a faster intervention during extreme flood events. The 'Hispaniola' island, in the Caribbean tropical zone, is often affected by extreme floods events. Floods are caused by tropical springs and hurricanes, and may lead to several damages, including cholera epidemics, as recently occurred, in the wake of the earthquake upon January 12th 2010 (magnitude 7.0). Floods studies based upon hydrological and hydraulic modeling are hampered by almost complete lack of ground data. Thenceforth, and given the noticeable cost involved in the organization of field measurement campaigns, the need for exploitation of remote sensing images data. HEC-RAS 1D modeling is carried out under different scenarios of available Digital Elevation Models. The DEMs are generated using optical remote sensing satellite (WorldView-1) and SRTM, combined with information from an open source database (Open Street Map). We study two recent flood episodes, where flood maps from remote sensing were available. Flood extent and land use have been assessed by way of data from SPOT-5 satellite, after hurricane Jeanne in 2004 and hurricane Hanna in 2008. A semi-distributed, DEM based hydrological model is used to simulate flood flows during the hurricanes. Precipitation input is taken from daily rainfall data derived from TRMM satellite, plus proper downscaling. The hydraulic model is calibrated using floodplain friction as tuning parameters against the observed flooded area. We compare different scenarios of flood simulation, and the predictive power of model calibration. The method provide acceptable results in depicting flooded areas, especially considering the tremendous lack of ground data, and show the potential of remote sensing information in prediction of flood events in this area, for the purpose of risk assessment and land use planning, and possibly for flood forecast during extreme events.

Bozza, Andrea; Durand, Arnaud; Allenbach, Bernard; Confortola, Gabriele; Bocchiola, Daniele

2013-04-01

284

Quantum Gravity and Maximum Attainable Velocities in the Standard Model  

SciTech Connect

A main difficulty in the quantization of the gravitational field is the lack of experiments that discriminate among the theories proposed to quantize gravity. Recently we showed that the Standard Model(SM) itself contains tiny Lorentz invariance violation(LIV) terms coming from QG. All terms depend on one arbitrary parameter {alpha} that set the scale of QG effects. In this talk we review the LIV for mesons nucleons and leptons and apply it to study several effects, including the GZK anomaly.

Alfaro, Jorge [Facultad de Fisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile)

2007-06-19

285

One-velocity model of a heterogeneous medium with a hyperbolic adiabatic kernel  

NASA Astrophysics Data System (ADS)

The one-velocity model equations for a heterogeneous medium are presented that take into account the internal forces of interfractional interactions and heat and mass exchange. The shock adiabat obtained for the mixture agrees with the one-velocity model equations. For one-dimensional unsteady adiabatic flows, the characteristic equations are found and relations along characteristic directions are determined. It is shown that the model equations with allowance for interfractional interaction forces are hyperbolic. Several finite-difference and finite-volume schemes designed for integrating the model equations are discussed.

Surov, V. S.

2008-06-01

286

Seismic traveltime inversion of 3D velocity model with triangulated interfaces  

NASA Astrophysics Data System (ADS)

Seismic traveltime tomographic inversion has played an important role in detecting the internal structure of the solid earth. We use a set of blocks to approximate geologically complex media that cannot be well described by layered models or cells. The geological body is described as an aggregate of arbitrarily shaped blocks, which are separated by triangulated interfaces. We can describe the media as homogenous or heterogeneous in each block. We define the velocities at the given rectangle grid points for each block, and the heterogeneous velocities in each block can be calculated by a linear interpolation algorithm. The parameters of the velocity grid positions are independent of the model parameterization, which is advantageous in the joint inversion of the velocities and the node depths of an interface. We implement a segmentally iterative ray tracer to calculate traveltimes in the 3D heterogeneous block models. The damped least squares method is employed in seismic traveltime inversion, which includes the partial derivatives of traveltime with respect to the depths of nodes in the triangulated interfaces and velocities defined in rectangular grids. The numerical tests indicate that the node depths of a triangulated interface and homogeneous velocity distributions can be well inverted in a stratified model.

Li, Fei; Xu, Tao; Zhang, Minghui; Wu, Zhenbo; Wu, Chenglong; Zhang, Zhongjie; Teng, Jiwen

2014-04-01

287

Asymptotics of conduction velocity restitution in models of electrical excitation in the heart.  

PubMed

We extend a non-Tikhonov asymptotic embedding, proposed earlier, for calculation of conduction velocity restitution curves in ionic models of cardiac excitability. Conduction velocity restitution is the simplest non-trivial spatially extended problem in excitable media, and in the case of cardiac tissue it is an important tool for prediction of cardiac arrhythmias and fibrillation. An idealized conduction velocity restitution curve requires solving a non-linear eigenvalue problem with periodic boundary conditions, which in the cardiac case is very stiff and calls for the use of asymptotic methods. We compare asymptotics of restitution curves in four examples, two generic excitable media models, and two ionic cardiac models. The generic models include the classical FitzHugh-Nagumo model and its variation by Barkley. They are treated with standard singular perturbation techniques. The ionic models include a simplified "caricature" of Noble (J. Physiol. Lond. 160:317-352, 1962) model and Beeler and Reuter (J. Physiol. Lond. 268:177-210, 1977) model, which lead to non-Tikhonov problems where known asymptotic results do not apply. The Caricature Noble model is considered with particular care to demonstrate the well-posedness of the corresponding boundary-value problem. The developed method for calculation of conduction velocity restitution is then applied to the Beeler-Reuter model. We discuss new mathematical features appearing in cardiac ionic models and possible applications of the developed method. PMID:20204709

Simitev, R D; Biktashev, V N

2011-01-01

288

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

USGS Publications Warehouse

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

289

a Modified Cellular Automaton Model for Ring Road Traffic with Velocity Guidance  

NASA Astrophysics Data System (ADS)

We present a modified cellular automaton model to study the traffic flow on a signal controlled ring road with velocity guidance. The velocity guidance is such a strategy that when vehicles approach the traffic light, suggested velocities are provided for avoiding the vehicles' sharp brakes in front of red light. Simulation results show that this strategy may significantly reduce the vehicles' stopping rate and the effect size is dependent upon the traffic density, the detector position, the signal's cycle time and the obedience rate of vehicles to the guidance.

Mei, C. Q.; Huang, H. J.; Tang, T. Q.

290

Aperiodic stepwise growth model for the velocity and orientation dependence of solute trapping  

SciTech Connect

An atomistic model for the dependence on interface orientation and velocity v of the solute partition coefficient k during rapid solidification is developed in detail. Starting with a simple stepwise growth model, the simple continuous growth model result is obtained for k(v) when the growth steps are assumed to pass at random intervals rather than periodically. The model is applied to rapid solidification of silicon. Crystal growth at all orientations is assumed to occur by the rapid lateral passage of (111) steps at speeds determined by the interface velocity and orientation. Solute escape is parametrized by a diffusion coefficient at the edge of the moving step and a diffusion coefficient at the terrace, far from the step edge. The model results in an excellent fit to data for the velocity and orientation dependence of k of Bi in Si.

Goldman, L.M.; Aziz, M.J.

1987-07-01

291

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

SciTech Connect

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

292

Gaussian diffusion sphere model to predict deposition velocities under the combined effects of electrophoresis and thermophoresis  

NASA Astrophysics Data System (ADS)

The Gaussian diffusion sphere model (GDSM) is proposed to predict the average deposition velocity of particles onto a flat plate exposed to parallel airflow after considering the combined effects of electrophoresis and thermophoresis. This model can account for convection, Brownian diffusion, gravitational settling, thermophoresis, and electrophoresis, and it provides fast calculation times and accurate predictions. Using the GDSM, the effects of the deposition surface size on the deposition velocity are analyzed. When the gravitational effect is dominant for a face-up surface or the attractive electrophoresis effect is dominant, the deposition velocity is estimated to be independent of the deposition surface size. Deposition under the influence of thermophoresis depends on the deposition surface size due to the formation of a thermal boundary layer. Deposition velocities for a 450-mm-long surface are studied under a temperature difference of 40 K and for electric field strengths ranging from 0 to 1000 V/cm.

Kang, Soojin; Yook, Se-Jin; Lee, Kwan-Soo

2014-03-01

293

Diurnal variation of stratospheric HOCl, ClO and HO2 at the equator: comparison of 1-D model calculations with measurements of satellite instruments  

NASA Astrophysics Data System (ADS)

The diurnal variation of HOCl and the related species ClO, HO2 and HCl measured by satellites has been compared with the results of a one-dimensional photochemical model. The study compares the data from various limb-viewing instruments with model simulations from the middle stratosphere to the lower mesosphere. Data from three sub-millimeter instruments and two infrared spectrometers are used, namely from the Sub-Millimeter Radiometer (SMR) on board Odin, the Microwave Limb Sounder (MLS) on board Aura, the Superconducting Submillimeter-wave Limb-Emission Sounder (SMILES) on the International Space Station, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board ENVISAT, and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on board SCISAT. Inter-comparison of the measurements from instruments on sun-synchronous satellites (SMR, MLS, MIPAS) and measurements from solar occultation instruments (ACE-FTS) is challenging since the measurements correspond to different solar zenith angles (or local times). However, using a model which covers all solar zenith angles and the new SMILES instrument which measures at all local times over a period of several months provides the possibility to indirectly compare the diurnally variable species. The satellite data were averaged for latitudes of 20° S to 20° N for the SMILES observation period from November 2009 to April 2010 and were compared at three altitudes: 35, 45 and 55 km. This study presents the first evaluation of HO2 Odin/SMR data and also the first comparison of the new SMILES data and the latest version of MLS (version 3.3) with other satellite observations. The MISU-1D model has been run for conditions and locations of the observations. The diurnal cycle features for the species investigated here are generally well reproduced by the model. The satellite observations and the model generally agree well in terms of absolute mixing ratios as well as differences between the day and night values. This confirms that gas phase chemistry of these species based on latest recommendations of reaction rate constants is fairly well understood.

Khosravi, M.; Baron, P.; Urban, J.; Froidevaux, L.; Jonsson, A. I.; Kasai, Y.; Kuribayashi, K.; Mitsuda, C.; Murtagh, D. P.; Sagawa, H.; Santee, M. L.; Sato, T. O.; Shiotani, M.; Suzuki, M.; von Clarmann, T.; Walker, K. A.; Wang, S.

2012-08-01

294

3-D Depth Interval Velocity Model Analysis and Interpretation of the Nankai Trough Margin (Southwest Japan).  

NASA Astrophysics Data System (ADS)

The 3-D Muroto seismic transect images the Nankai Trough margin south of Shikoku island, Japan, where the Philippine Sea plate subducts at a rate of 2-4 cm/y beneath the accretionary prism. The ODP drill sites of Legs 190-196 show the basaltic basement of the incoming plate overlain by the Shikoku Basin Lower Miocene-Lower Pleistocene hemipelagic mudstone, and the Pleistocene-Recent Nankai Trough turbidites. A geological meaningful interval velocity volume has been modeled using 3-D pre-stack depth migration (PSDM) calibrating the seismic volume with known depths at the drill sites, and extended to the entire seaward part of the Muroto transect. Our final PSDM velocity gradients closely resemble the drill holes logging and core velocities. Hence, the PSDM velocity field is representative of the "in-situ" velocities. In the trench area, the velocities increase with depth within the turbidites (1525-1580 m/s), as expected for a section with a normal compaction trend (decreasing porosity with depth). In the Upper Shikoku Basin Facies (USBF) hemipelagic unit (1580-1860 m/s), the P-wave velocity increases downhole although the porosity remains approximately constant within the entire unit. A conclusion of Leg 190 is that velocity in this interval can be controlled by cementation. In the upper part of the Lower Shikoku Basin Facies (LSBF) hemipelagic unit (1860-1920 m/s) the velocity increases until about 50-60 m below the top of LSBF, where a velocity inversion of about 50 m/s is recorded. The velocity inversion can be connected to an anomalously high fluid content at that level in the LSBF unit. We interpret this depth (5200 m below the sea level) as the stratigraphic equivalent of the decollement that occurs landward in the imbricate thrust zone. Below the velocity inversion zone, the PSDM velocities increase again with depth in the rest of the LSBF and the Volcaniclastic units (1870-2160 m/s). This is in agreement with a decrease in porosity versus depth in the underthrusting sediments. At about 5500 m, the velocity sharply increases to 3500-3800 m/s at the top of the oceanic crust. Landward in the accretionary prism, the PSDM vertical gradient maintains a similar trend to the one described in the trench, though the velocity values are slightly higher. The average PSDM vertical gradient above the decollement decreases from 0.99 s-1 seaward of the trench axis to 0.87 s-1 landward near the frontal thrust. The velocity inversion described in the trench extends almost to the first 30 km of the decollement (first 1200 cdps). The velocity inversion is about 150 m/s at the 808 drill site location, and it increases landward to 200-300 m/s (cdps interval 800-1600). The vertical gradient in the underthrusting section decreases from 0.97 s-1 in the basin to 0.72 s-1 beneath the frontal thrust. In this unit, the lateral velocity gradient between the basin and the deformation front is 0.02 s-1, corresponding to a 10% thinning in the direction of the subduction. This has been related to dewatering processes due to compaction of the underthrusting sediments. Velocity variations occurring along strike of the Muroto transect are generally negligible and a similar velocity field pattern is observed all along the data set. More in detail, the southwest sector of the Muroto transect around inline 215, shows lower velocities in the underthrusting section than the northeast sector around inline 284, on the order of 100 to 200 m/s.

Costa Pisani, P.; Kramer, G.; Moore, G. F.; Tobin, H. J.

2005-12-01

295

Velocity field measurements in oblique static divergent vocal fold models  

NASA Astrophysics Data System (ADS)

During normal phonation, the vocal fold cycle is characterized by the glottal opening transitioning from a convergent to a divergent passage and then closing before the cycle is repeated. Under ordinary phonatory conditions, both vocal folds, which form the glottal passage, move in phase with each other, creating a time-varying symmetric opening. However, abnormal pathological conditions, such as unilateral paralysis, and polyps, can result in geometrical asymmetries between the vocal folds throughout the phonatory cycle. This study investigates pulsatile flow fields through 7.5 times life-size vocal fold models with included divergence angles of 5 to 30 degrees, and obliquities between the vocal folds of up to 15 degrees. Flow conditions were scaled to match physiological parameters. Data were taken at the anterior posterior mid-plane using phase-averaged Particle Image Velocimetry (PIV). Viscous flow phenomena including the Coanda effect, flow separation points, and jet "flapping" were investigated. The results are compared to previously reported work of flow through symmetric divergent vocal fold models.

Erath, Byron

2005-11-01

296

Shear wave velocity model in Iceland from ambient noise and teleseismic Rayleigh wave tomography  

NASA Astrophysics Data System (ADS)

Iceland is a place of great geophysical interest due to its location at a hotspot and in the Mid-Atlantic spreading ridge. Despite numerous geophysics studies, disagreements still exist on crustal and mantle structure beneath Iceland. This research aims to construct a new shear wave model of Iceland by combining Rayleigh wave tomography from ambient seismic noise and teleseismic data recorded at the HOTSPOT experiment. Rayleigh wave phase velocities at periods from 5 to 25 s were obtained from ambient noise tomography. These short period phase velocities were combined with the longer period maps from teleseismic data by Li and Detrick [2006] for inverting 3-D SV wave velocities. Shear wave velocity in the shallow and mid crust shows a broad distribution of low velocity anomalies in central and southern Iceland and the lower crust map presents a more concentrated low velocity anomaly mainly beneath the Iceland hotspot. The low velocities in the crust are largely due to partial melt and high temperature associated with the hotspot activity. The variation of low velocity anomaly implies that melt is produced or accumulated in the lower crust under the hotspot and transported to nearby volcanic and rift zones at shallow depths. In the mantle, low velocity anomalies are present in areas that correlate well with the current and past spreading ridge locations rather than beneath the hotspot. In contrast, a relative high velocity anomaly is imaged below 80 km at the hotspot, which could reflect mantle residual after melt extraction or anisotropy caused by vertical flow in the plume conduit.

Li, A.; Azevedo, L. C.; Fu, Y. V.; Yuan, D.

2013-12-01

297

No-net-rotation model of current plate velocities incorporating plate motion model NUVEL-1  

NASA Technical Reports Server (NTRS)

NNR-NUVEL1 is presented which is a model of plate velocities relative to the unique reference frame defined by requiring no-net-rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model NUVEL-1 (DeMets et al., 1990). In NNR-NUVEL1, the Pacific plate rotates in a right-handed sense relative to the no-net-rotation reference frame at 0.67 deg/m.y. about 63 deg S, 107 deg E. At Hawaii the Pacific plate moves relative to the no-net-rotation reference frame at 70 mm/yr, which is 25 mm/yr slower than the Pacific plate moves relative to the hotspots. Differences between NNR-NUVEL1 and HS2-NUVEL1 are described. The no-net-rotation reference frame differs significantly from the hotspot reference frame. If the difference between reference frames is caused by motion of the hotspots relative to a mean-mantle reference frame, then hotspots beneath the Pacific plate move with coherent motion towards the east-southeast. Alternatively, the difference between reference frames can show that the uniform drag, no-net-torque reference frame, which is kinematically equivalent to the no-net-rotation reference frame, is based on a dynamically incorrect premise.

Argus, Donald F.; Gordon, Richard G.

1991-01-01

298

SALSA3D: Validating a Global 3D P-Velocity Model of the Earth's Crust and Mantle for Improved Event Location  

NASA Astrophysics Data System (ADS)

We are developing a global 3D P wave velocity model of the Earth's crust and mantle using seismic tomography to assess improvement to seismic event locations obtained using high quality 3D Earth models in lieu of 1D and 2/2.5D models. We present the most recent version of SALSA3D (SAndia LoS Alamos 3D) version 1.9, 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. Our model is derived from the latest version of the GT catalog of P/Pn travel-time picks assembled by Los Alamos National Laboratory. For this current version, we employ more robust data quality control measures than previously used, as well as additional global GT data sources. To prevent over-weighting due to ray path redundancy and to reduce the computational burden, we cluster rays into representative rays. 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 everywhere else, overlying 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 such a refinement. In previous versions, we based this refinement on velocity changes from previous model iterations. For the current version, 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. In addition to the changes in grid refinement, we also employ a more robust convergence criterion between successive grid refinements, allowing a better fit to first broader model features, then progressively to finer ones. 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 ~400 processors. We compare the travel-time prediction and location capabilities 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. For the current version of the model, we test using the full 3D covariance matrix to calculate path-dependent travel time uncertainty rather than standard 1D, distance-dependent uncertainty. The SALSA3D model reduces mislocation over the standard 1D ak135 model regardless of Pn to P ratio, with the improvement being most pronounced at higher azimuthal gaps. SALSA3D also reduces mislocation compared to the combined RSTT/ak135 model (2.5D - RSTT for regional phases), with SALSA3D and RSTT performing about the same when using only Pn arrivals in location tests.

Begnaud, M. L.; Ballard, S.; Young, C. J.; Hipp, J. R.; Encarnacao, A.; Phillips, W. S.; Chael, E. P.; Rowe, C. A.

2012-12-01

299

Diurnal Evolution of Organic Aerosols over Paris: Insights from the Combination of Measurements during the MEGAPOLI campaign with a 1D Model  

NASA Astrophysics Data System (ADS)

In spite of rapid developments in our understanding of organic aerosol (OA) physicochemical properties, representing the OA composition and evolution over urban areas remains a challenge. This study addresses the diurnal evolution of OA over Paris during the MEGAPOLI campaign. We analyze the observations with a model that aims at a balanced representation of the various processes that contribute to the diurnal variation of the organic aerosol budget. It is a 1D Eulerian model of the atmospheric boundary layer that contains advanced modules for gas-phase chemistry, gas/particle partitioning, and dry deposition. The model represents a computationally efficient framework for the accurate description of OA formation and photochemical evolution in the boundary layer. Semi-volatile organic components are distributed into volatility bins based on their saturation concentration and are allowed to partition into the aerosol phase. Furthermore, the semi-volatile organics in the gas phase continue to react with OH radical leading to compounds with lower volatility and hence continued OA formation. Model results are evaluated against available observations of OA, gas-phase chemistry and boundary layer dynamics. The model results are used along with the Aerosol Mass Spectrometer (AMS) dataset from the MEGAPOLI campaign to give new insights into the sources and diurnal production of OA over Paris. Furthermore, budget calculations are performed to show the contribution of the various processes (i.e., photochemistry, aerosol thermodynamics, boundary layer dynamics, etc.) to the calculated OA mass. Finally, the influence of uncertainties in several processes that determine the OA budget on the calculated OA properties is systematically analyzed through a series of sensitivity analyses. These include emission fractions of semivolatile and intermediate volatile compounds (SVOC/IVOC), secondary OA yields for the various gas-phase precursors, gas-phase aging of SVOC and IVOC during several generations of oxidation, dry deposition of OA and its gas-phase precursors, the temperature dependence of gas/particle partitioning, and assumptions on the volatility and entrainment of the background OA concentration.

Janssen, Ruud H. H.; Tsimpidi, Alexandra P.; Karydis, Vlassis A.; Lelieveld, Jos

2014-05-01

300

From Anti-greenhouse Effect of Solar Absorbers to Cooling Effect of Greenhouse Gases: A 1-D Radiative Convective Model Study  

NASA Astrophysics Data System (ADS)

The haze layer in Titan's upper atmosphere absorbs 90% of the solar radiation, but is inefficient for trapping infrared radiation generated by the surface. Its existence partially compensates for the greenhouse warming and keeps the surface approximately 9°C cooler than would otherwise be expected from the greenhouse effect alone. This is the so called anti-greenhouse effect (McKay et al., 1991). This effect can be used to alleviate the warming caused by the increasing level of greenhouse gases in the Earth's atmosphere. A one-dimensional radiative convective model (Kasting et al., 2009 and references listed there) is used to investigate the anti-greenhouse effect in the Earth atmosphere. Increasing of solar absorbers, e.g. aerosols and ozone, in the stratosphere reduces the surface solar flux and cool the surface. However, the absorption of the solar flux also increases the temperature in the upper atmosphere, while reduces the temperature at the surface. Thus, the temperature profile of the atmosphere changes and the regions with positive vertical temperature gradient are expanded. According to Shia (2010) the radiative forcing of greenhouse gases is directly related to the vertical temperature gradient. Under the new temperature profile increases of greenhouse gases should have less warming effect. When the solar absorbers keep increasing, eventually most of the atmosphere has positive temperature gradient and increasing greenhouse gases would cool the surface (Shia, 2011). The doubling CO2 scenario in the Earth atmosphere is simulated for different levels of solar absorbers using the 1-D RC model. The model results show that if the solar absorber increases to a certain level that less than 50% solar flux reaching the surface, doubling CO2 cools the surface by about 2 C. This means if the snowball Earth is generated by solar absorbers in the stratosphere, increasing greenhouse gases would make it freeze even more (Shia, 2011). References: Kasting, J. et al. 2009, http://vpl.astro.washington.edu/sci/AntiModels/models09.html McKay, C.P. et al. 1991, Titan: Greenhouse and Anti-greenhouse Effects on Titan. Science 253 (5024), 1118-21 Shia, R. 2011, Climate Effect of Greenhouse Gas: Warming or Cooling is Determined by Temperature Gradient, American Geophysical Union, Fall Meeting 2012, abstract #A51A-0274 Shia, R. 2010, Mechanism of Radiative Forcing of Greenhouse Gas and its Implication to the Global Warming, American Geophysical Union, Fall Meeting 2010, abstract #A11J-02

Shia, R.

2012-12-01

301

Distribution Parameter and Drift Velocity of Drift-Flux Model in Bubbly Flow  

SciTech Connect

In view of the practical importance of the drift-flux model for two-phase flow analysis in general and in the analysis of nuclear-reactor transients and accidents in particular, the distribution parameter and the drift velocity have been studied for bubbly-flow regime. The constitutive equation that specifies the distribution parameter in the bubbly flow has been derived by taking into account the effect of the bubble size on the phase distribution, since the bubble size would govern the distribution of the void fraction. A comparison of the newly developed model with various fully-developed bubbly-flow data over a wide range of flow parameters shows a satisfactory agreement. The constitutive equation for the drift velocity developed by Ishii has been reevaluated by the drift velocity obtained from local flow parameters such as void fraction, gas velocity and liquid velocity measured under steady fully-developed bubbly flow conditions. It has been confirmed that the newly developed model of the distribution parameter and the drift velocity correlation developed by Ishii can also be applicable to developing bubbly flows. (authors)

Takashi Hibiki [Kyoto University, Kumatori, Sennan, Osaka 590-0494 (Japan); Mamoru Ishii [Purdue University, West Lafayette, IN 47907 (United States)

2002-07-01

302

Hill-type muscle model with serial damping and eccentric force-velocity relation.  

PubMed

Hill-type muscle models are commonly used in biomechanical simulations to predict passive and active muscle forces. Here, a model is presented which consists of four elements: a contractile element with force-length and force-velocity relations for concentric and eccentric contractions, a parallel elastic element, a series elastic element, and a serial damping element. With this, it combines previously published effects relevant for muscular contraction, i.e. serial damping and eccentric force-velocity relation. The model is exemplarily applied to arm movements. The more realistic representation of the eccentric force-velocity relation results in human-like elbow-joint flexion. The model is provided as ready to use Matlab and Simulink code. PMID:24612719

Haeufle, D F B; Günther, M; Bayer, A; Schmitt, S

2014-04-11

303

Waveform Simulations For TAIGER Data Sets From Taiwan 3D Reference Velocity And Moho Boundary Models  

NASA Astrophysics Data System (ADS)

Studying seismic waveform variations in space and time is an important issue to investigate structural heterogeneities and ground motion responses for seismic hazard mitigation. The available 3D reference velocity models from transmission tomography studies are mainly limited by depth resolution, refraction arrival picks without explicit considering later phases and the spatial distribution of earthquakes and stations. Seismic data collected from the TAIGER (TAiwan Integrated GEodynamics Research) project can provide a valuable opportunity for studying deep crust structures. Evaluation of 3D reference models and update their shallow velocity structure is presented through travel-time and waveforms studies. Even though a well-defined multi-scaled reference velocity model of Taiwan is being debated, existing models are still important to study the structural heterogeneities and path effects through parallel computation of 4th-order staggered grid FD 3D waveform simulation. Simulation utilizes both far-field point and finite-dimensional moment tensor sources to investigate effects on Moho reflections and lateral velocity variations. Constraints on Moho reference boundary obtained from receiver function studies is discussed and compared with data collected from TAIGER project. For controlled source experiments, synthetic simulations show clear and focused Moho reflections in the 3-C data. Simultaneous 3D simulation of all available seismic records provides unique constraints on reference velocity model known so far. The waveform simulation will provide a fundamental research platform for future full 3D waveform inversion.

Hsieh, M.; Chen, H.; Zhao, L.

2008-12-01

304

Developing a Crustal and Upper Mantle Velocity Model for the Brazilian Northeast  

NASA Astrophysics Data System (ADS)

Development of 3D models for the earth's crust and upper mantle is important for accurately predicting travel times for regional phases and to improve seismic event location. The Brazilian Northeast is a tectonically active area within stable South America and displays one of the highest levels of seismicity in Brazil, with earthquake swarms containing events up to mb 5.2. Since 2011, seismic activity is routinely monitored through the Rede Sismográfica do Nordeste (RSisNE), a permanent network supported by the national oil company PETROBRAS and consisting of 15 broadband stations with an average spacing of ~200 km. Accurate event locations are required to correctly characterize and identify seismogenic areas in the region and assess seismic hazard. Yet, no 3D model of crustal thickness and crustal and upper mantle velocity variation exists. The first step in developing such models is to refine crustal thickness and depths to major seismic velocity boundaries in the crust and improve on seismic velocity estimates for the upper mantle and crustal layers. We present recent results in crustal and uppermost mantle structure in NE Brazil that will contribute to the development of a 3D model of velocity variation. Our approach has consisted of: (i) computing receiver functions to obtain point estimates of crustal thickness and Vp/Vs ratio and (ii) jointly inverting receiver functions and surface-wave dispersion velocities from an independent tomography study to obtain S-velocity profiles at each station. This approach has been used at all the broadband stations of the monitoring network plus 15 temporary, short-period stations that reduced the inter-station spacing to ~100 km. We expect our contributions will provide the basis to produce full 3D velocity models for the Brazilian Northeast and help determine accurate locations for seismic events in the region.

Julia, J.; Nascimento, R.

2013-05-01

305

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

SciTech Connect

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

306

Fluid velocity distribution in nitrifying trickling filters: mathematical model and NMR calibration  

Microsoft Academic Search

Modeling trickling filter performance requires knowledge of the distribution of flow velocities within the packed column. A probability density function (PDF) is developed for the likelihood of finding a given flow (Reynolds number) over a point on the packing material surface.The model predicts an exponential relationship between the Reynolds number and the probability of finding that flow rate. Wetted area,

Valdis Krumins; Michael Line; Fred Wheaton

2000-01-01

307

Nested-squares Discrete Boltzmann Models with arbitrary number of velocities satisfying a continuous theory relation  

Microsoft Academic Search

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

308

Comparison of the velocity distribution between the adhesion approximation and the Euler-Jeans-Newton model  

SciTech Connect

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

309

Compensation for relative velocity between needle and soft tissue for friction modeling in needle insertion.  

PubMed

Percutaneous therapies and in particular needle insertion treatments require an accurate model of needle-tissue interaction. Friction is a major interaction force component during needle insertion, and force-velocity mapping is an indicator of the interaction characteristics. However, soft tissue deformation is an inevitable and complex phenomenon that should be taken into account in order to correct the friction-velocity cycle. The main purpose of this study is to provide a means of compensating for the velocity of tissue with respect to a moving needle in the insertion direction. A high-gain observer is presented which can track this relative motion in a simple manner with no need for computer vision that may pose further challenges. To evaluate the performance of the velocity observer, experiments were carried out on gelatin and agar phantoms. PMID:23366053

Asadian, Ali; Patel, Rajni V; Kermani, Mehrdad R

2012-01-01

310

Using the International Monitoring System to Validate SALSA3D: A Global 3D P-Velocity Model of the Crust and Mantle for Improved Seismic Event Location  

NASA Astrophysics Data System (ADS)

We demonstrate the ability of SALSA3D (SAndia LoS Alamos 3D) version 2.1, a global 3D P-wave velocity model of the Earth's crust and mantle, to reduce mislocations compared to those derived from standard 1D and 2-2.5D models, for a set of realizations using only IMS stations - an example of a sparse network whose locations depend heavily on the velocity model employed - and a carefully chosen group of globally-distributed ground truth (GT) events. Our model is derived from the latest version of the GT catalog of P/Pn travel-time picks assembled by Los Alamos National Laboratory. The model uses the GeoTess triangular tessellation system described by Ballard et al. (2009; www.sandia.gov/geotess), which incorporates variable resolution both laterally and radially. For our starting model, we use a simplified version of the NNSA Unified model in Eurasia and the Crust 2.0 model elsewhere. Damping reduces velocity adjustments so that ray path changes between iterations are small. We obtain proper model smoothness via progressive grid refinement using the diagonal of the model resolution matrix to determine where the data warrant such a refinement. Our approach provides more consistent and continuous areas of refinement, producing 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 of ~400 processors. The global IMS network consists of approximately 150 primary and auxiliary stations, forming a pre-defined, sparse network with which to locate seismic events. 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. Using Pn and P picks from IMS stations only, 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 accuracy and precision of relocation. We test using the full 3D covariance matrix of the current model to calculate path-dependent travel time uncertainty, rather than applying standard, 1D, distance-dependent uncertainty. SALSA3D reduces mislocation over the standard 1D ak135 model regardless of Pn to P ratio, with the most pronounced improvement at higher azimuthal gaps. SALSA3D also reduces mislocation compared to the combined RSTT/ak135 model (2.5D - RSTT for regional phases), with minimal improvement over RSTT when only regional Pn phases are used to compute locations.

Begnaud, M. L.; Ballard, S.; Young, C. J.; Hipp, J. R.; Encarnacao, A.; Phillips, W.; Chael, E. P.; Rowe, C. A.

2013-12-01

311

Investigation of the radiation brightness of gases around a burning model moving at supersonic velocity  

NASA Astrophysics Data System (ADS)

Experimental results are presented on the ablation and shape change of burning models made of a pyrotechnic composition moving in air at supersonic velocity. A radiometer was used to measure the radiation brightness at a wavelength of 0.63 micron in the shock layer and wake of the burning models. The glow characteristics are determined as a function of the initial air pressure in the path of motion; and a theoretical model for the motion and ablation of burning bodies flying at supersonic velocity is developed which satisfactorily describes the experimental results. The present study is of interest in connection with the aerodynamic heating of vehicles flying at hypersonic velocity in planetary atmospheres.

Baulin, N. N.; Kuvalkin, D. G.; Piliugin, N. N.; Taganov, O. K.; Tikhomirov, S. G.

1987-01-01

312

A Community Velocity Model (CVM) for the Sichuan basin and Longmen Shan, China  

NASA Astrophysics Data System (ADS)

We present a new three-dimensional velocity model of the crust and upper mantle for the eastern margin of the Tibetan Plateau, developed using the concept of a Community Velocity Model (CVM) (Magistrale et al., 2000; Süss and Shaw, 2003). The model extends from 27.5°-34.5°N and 100°-110°E, and describes the velocity structure of the Sichuan basin and surrounding fold-and-thrust belt systems (including the Longmen Shan, Micang Shan, Daba Shan, Eastern Sichuan and Kangdian), as well as the Kunlun and Xianshuihe-Anninghe strike fault systems in the eastern Tibetan Plateau. The model consists of 3D surfaces representing major geologic unit contacts and faults, and is parameterized with velocity-depth curves (Boore and Joyner, 1997) calibrated using sonic logs from wells. The model incorporates data from 1166 oil wells, industry isopach maps, surface geological maps and digital elevation models. The model was developed in the program GoCAD, a geological computer-aided design application (Mallet, 1992). The geological surfaces were modeled based on industry isopach maps for various units augmented by stratigraphic picks in oil and gas wells and regional seismic reflection profiles. These surfaces include base Quaternary, Cretaceous, Jurassic, Triassic, and Paleozoic horizons. These surface are locally cut by major faults, which are compatible with the locations and displacements of major faults systems in the Sichuan Community Fault Model (CFM) (Hubbard et al., 2012). The velocity profiles for each layer are calibrated with high-resolution sonic log as well as stacking velocities from seismic reflection profiles and vertical seismic profiles. This upper crustal model extends down to ~10-15 km depth, and is embedded into a regional tomographic model (Xu and Song, 2010). The Sichuan basin is an atypical basin in terms of its velocity structure. The rocks exposed at the surface are primarily Mesozoic in age, with limited patch of Cenozoic rocks in the southwestern part of the basin. As a consequence, the velocities (Vp) in the basin are generally fast. They range from about 3000 to ~7500 m/s, exhibiting increasing velocities with age and depth. We divide the rock in the Sichuan basin and Longmen Shan region into five basic types: (1) Cenozoic alluvium; (2) Mesozoic sedimentary and metamorphic rocks; (3) Paleozoic sedimentary and metamorphic rocks; (4) Proterozoic sedimentary and metamorphic rocks and (5) granite. Cenozoic alluvium is thin (0~500 m) and limited primarily to the southwestern basin. Mesozoic sedimentary rocks are thick (2600-9800 m) and widely exposed at the surface and in boreholes in the basin. Their velocities vary from about 3000-6000 m/s. Paleozoic sedimentary and metamorphic rocks are also common, exposed primarily in the Longmen Shan and in regions to the north, east, and south of the basin. These units vary in thickness from 400-4100 m, and have velocities from about 5000-7000 m/s. Proterozoic sedimentary and metamorphic rocks crop out in narrow regions around the boundary of the basin, but are disturbed within the basin. Two exploration wells penetrate the base of Sinian, giving a velocity of about 6500-7500 m/s. The model will serve as a basic community resource for strong ground motion prediction and seismic hazard assessments in the densely populated Sichuan basin.

Wang, M.; Hubbard, J.; Shaw, J. H.; Plesch, A.; Jia, D.

2012-12-01

313

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

314

MAMPOSSt: Modelling Anisotropy and Mass Profiles of Observed Spherical Systems - I. Gaussian 3D velocities  

NASA Astrophysics Data System (ADS)

Mass modelling of spherical systems through internal kinematics is hampered by the mass-velocity anisotropy degeneracy inherent in the Jeans equation, as well as the lack of techniques that are both fast and adaptable to realistic systems. A new fast method, called Modelling Anisotropy and Mass Profiles of Observed Spherical Systems (MAMPOSSt), is developed and thoroughly tested. MAMPOSSt performs a maximum-likelihood fit of the distribution of observed tracers in projected phase space (projected radius and line-of-sight velocity). As in other methods, MAMPOSSt assumes a shape for the gravitational potential (or equivalently the total mass profile). However, instead of postulating a shape for the distribution function in terms of energy and angular momentum, or supposing Gaussian line-of-sight velocity distributions, MAMPOSSt assumes a velocity anisotropy profile and a shape for the 3D velocity distribution. The formalism is presented for the case of a Gaussian 3D velocity distribution. In contrast to most methods based on moments, MAMPOSSt requires no binning, differentiation, nor extrapolation of the observables. Tests on cluster-mass haloes from ?CDM dissipationless cosmological simulations indicate that, with 500 tracers, MAMPOSSt is able to jointly recover the virial radius, tracer scale radius, dark matter scale radius and outer or constant velocity anisotropy with small bias (<10 per cent on scale radii and <2 per cent on the two other quantities) and inefficiencies of 10, 27, 48 and 20 per cent, respectively. MAMPOSSt does not perform better when some parameters are frozen, and even particularly worse when the virial radius is set to its true value, which appears to be the consequence of halo triaxiality. The accuracy of MAMPOSSt depends weakly on the adopted interloper removal scheme, including an efficient iterative Bayesian scheme that we introduce here, which can directly obtain the virial radius with as good precision as MAMPOSSt. Additional tests are made on the number of tracers, the stacking of haloes, the chosen aperture, and the density and velocity anisotropy models. Our tests show that MAMPOSSt with Gaussian 3D velocities is very competitive with other methods that are either currently restricted to constant velocity anisotropy or 3 orders of magnitude slower. These tests suggest that MAMPOSSt can be a very powerful and rapid method for the mass and anisotropy modelling of systems such as clusters and groups of galaxies, elliptical and dwarf spheroidal galaxies.

Mamon, Gary A.; Biviano, Andrea; Boué, Gwenaël

2013-03-01

315

Lattice Botlzmann Solution to the 1D MHD-Burgers Equation  

NASA Astrophysics Data System (ADS)

Recently, Fleischer & Diamond [2000] have considered the 1D MHD-Burgers equation as a paradigm for the spatio-temporal intermittency involving coherent structures. This is the simplest model to exhibit Alvenization - the exchange of fluid and magnetic energies. In the limit B 0, the equations reduce to the familiar Burgers equation, which exbibits shocks. Our lattice Boltzmann solution introduces two scalar distribution functions - one for the velocity field and one for the magnetic field. The coupled BGK equations require only a simple phase space velocity lattice of (+1,-1,+2,-2). A linear stability analysis is performed and simulation results are presented. The need for adaptive grids is discussed.

Vahala, Linda; Vahala, George

2002-11-01

316

Elastoacoustic model with uncertain mechanical properties for ultrasonic wave velocity prediction: application to cortical bone evaluation.  

PubMed

The axial transmission technique can measure the longitudinal wave velocity of an immersed solid. An elementary model of the technique is developed with a set of source and receivers placed in a semi-infinite fluid coupled at a plane interface with a semi-infinite solid. The acoustic fluid is homogeneous. The solid is homogeneous, isotropic, and linearly elastic. The work is focused on the prediction of the measured velocity (apparent velocity) when the solid is considered to have random material properties. The probability density functions of the random variables modeling each mechanical parameter of the solid are derived following the maximum entropy principle. Specific attention is paid to the modeling of Poisson's ratio so that the second-order moments of the velocities remain finite. The stochastic solver is based on a Monte Carlo numerical simulation and uses an exact semianalytic expression of the acoustic response derived with the Cagniard-de Hoop method. Results are presented for a solid with the material properties of cortical bone. The estimated mean values and confidence regions of the apparent velocity are presented for various dispersion levels of the random parameters. A sensibility analysis with respect to the source and receivers locations is presented. PMID:16521733

Macocco, Karina; Grimal, Quentin; Naili, Salah; Soize, Christian

2006-02-01

317

A universal framework for modelling measured velocity in laser vibrometry with applications  

NASA Astrophysics Data System (ADS)

This paper presents a novel, universally applicable framework for modelling measured velocity in laser vibrometry systems. The framework is introduced generically before demonstration of its application to three scanning vibrometer systems, each configured to measure vibration of a tracked point on a rotating target. The novelty in this vectorial framework lies in the combination of its elements, which include vector descriptions of target velocity, optical device velocity at deflection points, laser beam orientations, incorporating reflection and refraction, and surface normals. Initial alignment and a full set of inevitable misalignments are incorporated by the modification of position vectors and the use of rotation matrices. Inclusion of components of measured velocity associated with moving optical devices is an important feature of the framework. The models derived and their validation against published data demonstrate how this versatile framework can be applied to any optical configuration measuring target motions with any level of complexity. The individual models are explored extensively and quantitatively through simulation. Small but inevitable misalignments are shown to generate measurable low order velocity components and their effects on the sensitivities to in-plane and out-of-plane components of target vibration are quantified.

Rothberg, Steve J.; Tirabassi, Mario

2012-01-01

318

A California statewide three-dimensional seismic velocity model from both absolute and differential times  

USGS Publications Warehouse

We obtain a seismic velocity model of the California crust and uppermost mantle using a regional-scale double-difference tomography algorithm. We begin by using absolute arrival-time picks to solve for a coarse three-dimensional (3D) P velocity (VP) model with a uniform 30 km horizontal node spacing, which we then use as the starting model for a finer-scale inversion using double-difference tomography applied to absolute and differential pick times. For computational reasons, we split the state into 5 subregions with a grid spacing of 10 to 20 km and assemble our final statewide VP model by stitching together these local models. We also solve for a statewide S-wave model using S picks from both the Southern California Seismic Network and USArray, assuming a starting model based on the VP results and a VP=VS ratio of 1.732. Our new model has improved areal coverage compared with previous models, extending 570 km in the SW-NE directionand 1320 km in the NW-SE direction. It also extends to greater depth due to the inclusion of substantial data at large epicentral distances. Our VP model generally agrees with previous separate regional models for northern and southern California, but we also observe some new features, such as high-velocity anomalies at shallow depths in the Klamath Mountains and Mount Shasta area, somewhat slow velocities in the northern Coast Ranges, and slow anomalies beneath the Sierra Nevada at midcrustal and greater depths. This model can be applied to a variety of regional-scale studies in California, such as developing a unified statewide earthquake location catalog and performing regional waveform modeling.

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

2010-01-01

319

New upper mantle P-velocity model of Eurasia resolves connections to main regional tectonic structures  

NASA Astrophysics Data System (ADS)

We present a new model of P-velocity anomalies in the upper mantle beneath Eurasia constructed by merging several existing models and by computing new results for a number of gap areas. The models were computed based on tomographic inversions of travel-time data from the worldwide catalogues (ISC, 2001). The calculations were performed in a series of overlapping circular areas of 700-1000 km size. All data with rays corresponding to sources and/or stations in the areas traveling through the target volume were, at least partly, used in the inversions. In case of lack of stations and events, the calculations were based on PP-rays with reflection points in the target area. The new model of Eurasia resolves connections between upper mantle structures and main tectonic units. Cratonic blocks in Eurasia, such as the East-European, Siberian, Indian and Arabian cratons are detected in terms of high-velocity patterns down to 250-300 km depth. The subduction zones in the western Pacific, Burma and the Mediterranean are robustly resolved, consistent with previous studies. In zones of continental collision, we observe traces of mantle delamination as drops of high-velocity material in the mantle. Sites of intraplate volcanism in Europe, Siberia, Mongolia and Yakutia coincide with low-velocity areas, interpreted as overheated upper mantle. Digital version of the model can be downloaded at www.ivan-art.com/temp/vis_eurasia.zip. P-velocity anomalies beneath Eurasia at 100 km depth from regional tomographic inversion. Polygons indicate possible locations of cratonic lithosphere blocks; stars mark the areas of Cenozoic volcanism. P-velocity anomalies beneath Eurasia at 300 km depth from regional tomographic inversion. Polygons indicate possible locations of cratonic lithosphere blocks.

Koulakov, I.; Kaban, M. K.; Cloetingh, S.

2012-12-01

320

Cellular automaton model considering the velocity effect of a car on the successive car  

NASA Astrophysics Data System (ADS)

In this paper we present a cellular automata model for one-lane traffic flow. The update rules of velocity of a car depend not only on the positions of this car and the car ahead of it, but also on the velocities of the two cars. Using computer simulations we obtain some basic qualitative results and the fundamental diagram of the proposed model. In comparison with those of the existing models in the literature, we find that the fundamental diagram of the proposed model is more consistent with the results measured in the real traffic, and the model is able to reproduce some relevant macroscopic states that are found in the real traffic flow but cannot be predicted by the existing models.

Li, Xiaobai; Wu, Qingsong; Jiang, Rui

2001-12-01

321

Shallow-velocity models at the Kilauea Volcano, Hawaii, determined from array analyses of tremor wavefields  

USGS Publications Warehouse

The properties of the surface wavefield at Kilauea Volcano are analysed using data from small-aperture arrays of short-period seismometers deployed in and around the Kilauea caldera. Tremor recordings were obtained during two Japan-US cooperative experiments conducted in 1996 and 1997. The seismometers were deployed in three semi-circular arrays with apertures of 300, 300 and 400 m, and a linear array with length of 1680 m. Data are analysed using a spatio-temporal correlation technique well suited for the study of the stationary stochastic wavefields of Rayleigh and Love waves associated with volcanic activity and scattering sources distributed in and around the summit caldera. Spatial autocorrelation coefficients are obtained as a function of frequency and are inverted for the dispersion characteristics of Rayleigh and Love waves using a grid search that seeks phase velocities for which the L-2 norm between data and forward modelling operators is minimized. Within the caldera, the phase velocities of Rayleigh waves range from 1400 to 1800 m s-1 at 1 Hz down to 300-400 m s-1 at 10 Hz, and the phase velocities of Love waves range from 2600 to 400 m s-1 within the same frequency band. Outside the caldera, Rayleigh wave velocities range from 1800 to 1600 m s-1 at 1 Hz down to 260-360 m s-1 at 10 Hz, and Love wave velocities range from 600 to 150 m s-1 within the same frequency band. The dispersion curves are inverted for velocity structure beneath each array, assuming these dispersions represent the fundamental modes of Rayleigh and Love waves. The velocity structures observed at different array sites are consistent with results from a recent 3-D traveltime tomography of the caldera region, and point to a marked velocity discontinuity associated with the southern caldera boundary.

Saccorotti, G.; Chouet, B.; Dawson, P.

2003-01-01

322

Creating and coupling a high-resolution DEM with a 1-D hydraulic model in a GIS for scenario-based assessment of avulsion hazard in a gravel bed river  

Microsoft Academic Search

This paper explores the development and assimilation of a high resolution topographic surface with a one- dimensional hydraulic model for investigation of avulsion hazard potential on a gravel bed river. A detailed LiDAR- based channel and floodplain surface model is created to define the geometry parameter required by the 1D hydraulic model HEC-RAS. The ability to extract dense and optimally

G. R. Aggett

2007-01-01

323

Creating and coupling a high-resolution DTM with a 1-D hydraulic model in a GIS for scenario-based assessment of avulsion hazard in a gravel-bed river  

Microsoft Academic Search

In this paper we explore the development and assimilation of a high resolution topographic surface with a one-dimensional hydraulic model for investigation of avulsion hazard potential on a gravel-bed river. A detailed channel and floodplain digital terrain model (DTM) is created to define the geometry parameter required by the 1D hydraulic model HEC-RAS. The ability to extract dense and optimally

G. R. Aggett; J. P. Wilson

2009-01-01

324

STP Random Walk 1D Program  

NSDL National Science Digital Library

The RandomWalk1D program simulates a random walk in one dimension for steps of unit length and equal time intervals. The default number of steps is N = 16 and the probability of going right or left at any step is the same (the probability p of going to the right for a single step is 0.5). RandomWalk1D is part of a suite of Open Source Physics programs that model aspects of Statistical and Thermal Physics (STP). The program is distributed as a ready-to-run (compiled) Java archive. Double clicking the stp RandomWalk1D.jar file will run the program if Java is installed on your computer. Additional programs can be found by searching ComPADRE for Open Source Physics, STP, or Statistical and Thermal Physics.

Gould, Harvey; Tobochnik, Jan; Christian, Wolfgang; Cox, Anne

2008-10-10

325

Phase-field model: Boundary layer, velocity of propagation, and the stability spectrum  

Microsoft Academic Search

We present a study of a phase-field model for diffusion-limited growth. A boundary-layer approximation is used to show that for sharp interface, the first approximation to the phase-field model is the free boundary model, which includes surface tension and a linear kinetic term. The velocity of propagation and the stability spectrum are calculated for a steady-state flat interface. In the

Raz Kupferman; Ofer Shochet; Eshel Ben-Jacob; Zeev Schuss

1992-01-01

326

Muscle-joint models incorporating activation dynamics, moment-angle, and moment-velocity properties  

Microsoft Academic Search

Muscle input\\/output models incorporating activation dynamics, moment-angle, and moment-velocity factors are commonly used to predict the moment produced by muscle during nonisometric contractions: the three factors are generally assumed to be independent. The authors examined the ability of models with independent factors, as well as models with coupled factors, to fit input\\/output data measured during simultaneous modulation of the fraction

Guayhaur Shue; Patrick E. Crago; Howard Jay Chizeck

1995-01-01

327

Isotropic and anisotropic shear velocity model of the NA upper mantle using EarthScope data  

NASA Astrophysics Data System (ADS)

The EarthScope TA deployment has provided dense array coverage across the continental US and with it, the opportunity for high resolution 3D seismic velocity imaging of both lithosphere and asthenosphere in the continent. Building upon our previous work, we present a new 3D isotropic, radially and azimuthally anisotropic shear wave model of the North American (NA) lithospheric mantle, using full waveform tomography and shorter-period (40 s) waveform data. Our isotropic velocity model exhibits pronounced spatial correlation between major tectonic localities of the eastern NA continent, as evidenced in the geology, and seismic anomalies, suggesting recurring episodes of tectonic events not only are well exposed at the surface, but also leave persistent scars in the continental lithosphere mantle, marked by isotropic and radially anisotropic velocity anomalies that reach as deep as 100-150 km. In eastern North America, our Vs images distinguish the fast velocity cratonic NA from the deep rooted large volume high velocity blocks which are east of the continent rift margin and extend 200-300 km offshore into Atlantic. In between is a prominent narrow band of low velocities that roughly follows the south and eastern Laurentia rift margin and extends into New England. The lithosphere associated with this low velocity band is thinned likely due to combined effects of repeated rifting processes along the rift margin and northward extension of the Bermuda low-velocity channel across the New England region. Deep rooted high velocity blocks east of the Laurentia margin are proposed to represent the Proterozoic Gondwanian terranes of pan-African affinity, which were captured during the Rodinia formation but left behind during the opening of the Atlantic Ocean. The anisotropy model takes advantage of the up-to-date SKS compilation in the continent and new splitting results from Greenland. The new joint waveform and SKS splitting data inversion is carried out with a 2° horizontal resolution throughout the continental US, and 4° in Canada and northwestern Atlantic. Our preliminary results confirm prevailing depth dependent layering in azimuthal anisotropy observed in our previous work, and show also in greater details anisotropy lateral variations in the craton and across the margins. Tectonic implications of the new model are discussed in light of regional tectonics.

Leiva, J.; Clouzet, P.; French, S. W.; Yuan, H.; Romanowicz, B. A.

2013-12-01

328

Comparison of P-, SV- and SH-wave velocity models below Japan and northeast China  

NASA Astrophysics Data System (ADS)

The recent deployment of the NECESSArray seismic network in northeast China has allowed new insights on the velocity structure of this formerly poorly resolved area. This experiment has brought new data to debate about the geodynamical context in this region (stagnant slab, origin of intraplate volcanism, etc...). We use an efficient method for the measurement of travel time residuals by cross-correlating observed and synthetic waveforms. Synthetic seismograms are convolved with high-frequency source-time functions inverted along with focal depths, following a simulated annealing approach. Thus, resulting modeled waveforms take more accurately account for the source effects. The method is used to perform measurements on direct P, SV and SH phases extracted from, respectively, vertical, radial and transverse band-pass-filtered records from NECESSArray and F-NET seismological networks. We finally invert the resulting datasets in order to obtain P-, SV- and SH-wave velocity models. To do so, we use a fast and efficient inversion method using ray theory. Observed structures in the three tomographic models show a very good geographical coherency. Nevertheless, some differences are observed below Songliao basin and Changbaishan volcano between P and SV models and SH model. By measuring velocity ratios, we discuss anisotropy and thermal/compositional origin of these velocity anomalies.

Kawakatsu, H.; Schardong, L.; Takeuchi, N.; Tanaka, S.; Obayashi, M.; Chen, Y. J.; Ning, J.; Niu, F.; Grand, S. P.; Ni, J.

2013-12-01

329

Crustal velocities near Coalinga, California, modeled from a combined earthquake/explosion refraction profile  

USGS Publications Warehouse

Crustal velocity structure for the region near Coalinga, California, has been derived from both earthquake and explosion seismic phase data recorded along a NW-SE seismic-refraction profile on the western flank of the Great Valley east of the Diablo Range. Comparison of the two data sets reveals P-wave phases in common which can be correlated with changes in the velocity structure below the earthquake hypocenters. In addition, the earthquake records reveal secondary phases at station ranges of less than 20 km that could be the result of S- to P-wave conversions at velocity interfaces above the earthquake hypocenters. Two-dimensional ray-trace modeling of the P-wave travel times resulted in a P-wave velocity model for the western flank of the Great Valley comprised of: 1) a 7- to 9-km thick section of sedimentary strata with velocities similar to those found elsewhere in the Great Valley (1.6 to 5.2 km s-1); 2) a middle crust extending to about 14 km depth with velocities comparable to those reported for the Franciscan assemblage in the Diablo Range (5.6 to 5.9 km s-1); and 3) a 13- to 14-km thick lower crust with velocities similar to those reported beneath the Diablo Range and the Great Valley (6.5 to 7.30 km s-1). This lower crust may have been derived from subducted oceanic crust that was thickened by accretionary underplating or crustal shortening. -Authors

Macgregor-Scott, N.; Walter, A.

1988-01-01

330

Agradient velocity, vortical motion and gravity waves in a rotating shallow-water model  

NASA Astrophysics Data System (ADS)

A new approach to modelling slow vortical motion and fast inertia-gravity waves is suggested within the rotating shallow-water primitive equations with arbitrary topography. The velocity is exactly expressed as a sum of the gradient wind, described by the Bernoulli function,B, and the remaining agradient part, proportional to the velocity tendency. Then the equation for inverse potential vorticity,Q, as well as momentum equations for agradient velocity include the same source of intrinsic flow evolution expressed as a single term J (B, Q), where J is the Jacobian operator (for any steady state J (B, Q) = 0). Two components of agradient velocity are responsible for the fast inertia-gravity wave propagation similar to the traditionally used divergence and ageostrophic vorticity. This approach allows for the construction of balance relations for vortical dynamics and potential vorticity inversion schemes even for moderate Rossby and Froude numbers assuming the characteristic value of |J(B, Q)| = to be small. The components of agradient velocity are used as the fast variables slaved to potential vorticity that allows for diagnostic estimates of the velocity tendency, the direct potential vorticity inversion with the accuracy of 2 and the corresponding potential vorticity-conserving agradient velocity balance model (AVBM). The ultimate limitations of constructing the balance are revealed in the form of the ellipticity condition for balanced tendency of the Bernoulli function which incorporates both known criteria of the formal stability: the gradient wind modified by the characteristic vortical Rossby wave phase speed should be subcritical. The accuracy of the AVBM is illustrated by considering the linear normal modes and coastal Kelvin waves in the f-plane channel with topography.

Sutyrin Georgi, G.

2004-07-01

331

The impact of Bdnf gene deficiency to the memory impairment and brain pathology of APPswe/PS1dE9 mouse model of Alzheimer's disease.  

PubMed

Brain-derived neurotrophic factor (BDNF) importantly regulates learning and memory and supports the survival of injured neurons. Reduced BDNF levels have been detected in the brains of Alzheimer's disease (AD) patients but the exact role of BDNF in the pathophysiology of the disorder remains obscure. We have recently shown that reduced signaling of BDNF receptor TrkB aggravates memory impairment in APPswe/PS1dE9 (APdE9) mice, a model of AD. The present study examined the influence of Bdnf gene deficiency (heterozygous knockout) on spatial learning, spontaneous exploratory activity and motor coordination/balance in middle-aged male and female APdE9 mice. We also studied brain BDNF protein levels in APdE9 mice in different ages showing progressive amyloid pathology. Both APdE9 and Bdnf mutations impaired spatial learning in males and showed a similar trend in females. Importantly, the effect was additive, so that double mutant mice performed the worst. However, APdE9 and Bdnf mutations influenced spontaneous locomotion in contrasting ways, such that locomotor hyperactivity observed in APdE9 mice was normalized by Bdnf deficiency. Obesity associated with Bdnf deficiency did not account for the reduced hyperactivity in double mutant mice. Bdnf deficiency did not alter amyloid plaque formation in APdE9 mice. Before plaque formation (3 months), BDNF protein levels where either reduced (female) or unaltered (male) in the APdE9 mouse cortex. Unexpectedly, this was followed by an age-dependent increase in mature BDNF protein. Bdnf mRNA and phospho-TrkB levels remained unaltered in the cortical tissue samples of middle-aged APdE9 mice. Immunohistological studies revealed increased BDNF immunoreactivity around amyloid plaques indicating that the plaques may sequester BDNF protein and prevent it from activating TrkB. If similar BDNF accumulation happens in human AD brains, it would suggest that functional BDNF levels in the AD brains are even lower than reported, which could partially contribute to learning and memory problems of AD patients. PMID:23844236

Rantamäki, Tomi; Kemppainen, Susanna; Autio, Henri; Stavén, Saara; Koivisto, Hennariikka; Kojima, Masami; Antila, Hanna; Miettinen, Pasi O; Kärkkäinen, Elisa; Karpova, Nina; Vesa, Liisa; Lindemann, Lothar; Hoener, Marius C; Tanila, Heikki; Castrén, Eero

2013-01-01

332

The Impact of Bdnf Gene Deficiency to the Memory Impairment and Brain Pathology of APPswe/PS1dE9 Mouse Model of Alzheimer's Disease  

PubMed Central

Brain-derived neurotrophic factor (BDNF) importantly regulates learning and memory and supports the survival of injured neurons. Reduced BDNF levels have been detected in the brains of Alzheimer’s disease (AD) patients but the exact role of BDNF in the pathophysiology of the disorder remains obscure. We have recently shown that reduced signaling of BDNF receptor TrkB aggravates memory impairment in APPswe/PS1dE9 (APdE9) mice, a model of AD. The present study examined the influence of Bdnf gene deficiency (heterozygous knockout) on spatial learning, spontaneous exploratory activity and motor coordination/balance in middle-aged male and female APdE9 mice. We also studied brain BDNF protein levels in APdE9 mice in different ages showing progressive amyloid pathology. Both APdE9 and Bdnf mutations impaired spatial learning in males and showed a similar trend in females. Importantly, the effect was additive, so that double mutant mice performed the worst. However, APdE9 and Bdnf mutations influenced spontaneous locomotion in contrasting ways, such that locomotor hyperactivity observed in APdE9 mice was normalized by Bdnf deficiency. Obesity associated with Bdnf deficiency did not account for the reduced hyperactivity in double mutant mice. Bdnf deficiency did not alter amyloid plaque formation in APdE9 mice. Before plaque formation (3 months), BDNF protein levels where either reduced (female) or unaltered (male) in the APdE9 mouse cortex. Unexpectedly, this was followed by an age-dependent increase in mature BDNF protein. Bdnf mRNA and phospho-TrkB levels remained unaltered in the cortical tissue samples of middle-aged APdE9 mice. Immunohistological studies revealed increased BDNF immunoreactivity around amyloid plaques indicating that the plaques may sequester BDNF protein and prevent it from activating TrkB. If similar BDNF accumulation happens in human AD brains, it would suggest that functional BDNF levels in the AD brains are even lower than reported, which could partially contribute to learning and memory problems of AD patients.

Rantamaki, Tomi; Kemppainen, Susanna; Autio, Henri; Staven, Saara; Koivisto, Hennariikka; Kojima, Masami; Antila, Hanna; Miettinen, Pasi O.; Karkkainen, Elisa; Karpova, Nina; Vesa, Liisa; Lindemann, Lothar; Hoener, Marius C.; Tanila, Heikki; Castren, Eero

2013-01-01

333

A new GNSS velocity field for Fennoscandia and comparison to GIA models (Invited)  

NASA Astrophysics Data System (ADS)

In Fennoscandia, the process of Glacial Isostatic Adjustment (GIA) causes ongoing crustal deformation. The vertical and horizontal movements of the Earth can be measured to a high degree of precision using Global Navigation Satellite System (GNSS). The GNSS network in Fennoscandia has gradually been established since the early 1990s and today contains a dense network well suited for geophysical studies and especially GIA. We will present new velocity estimates for the Fennoscandian and North-European GNSS network using the processing package GAMIT/GLOBK. GNSS measurements have proved to be a good tool to constrain and validate GIA models. However, reference frame uncertainties, plate tectonics as well as intra-plate deformations might decontaminate the results. Different ITRFs have had large discrepancies, especially in the TZ-component, which have made the geophysical interpretation of GNSS results difficult. In GIA areas the uncertainties in the TZ component almost directly affect the height component which makes constraining of GIA models less reliable. Plate tectonics introduces large horizontal velocities which are hard to distinguish from horizontal GIA-induced velocities. We will present a new approach where our GNSS velocity field is directly realized in a GIA frame. With this approach, the effect of systematic errors in the reference frames and 'biasing' signal from the plate tectonics will be reduced to a minimum for our GIA results. Moreover, we are able to provide consistent GIA-free plate velocities for the Eurasian plate.

Kierulf, H. P.; Simpson, M. J.; Steffen, H.; Lidberg, M.

2013-12-01

334

Size-Distribution Analysis of Macromolecules by Sedimentation Velocity Ultracentrifugation and Lamm Equation Modeling  

Microsoft Academic Search

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

335

An analytical model for composite sandwich panels with honeycomb core subjected to high-velocity impact  

Microsoft Academic Search

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

336

Empirical model to compute the velocity histories of flyers driven by electrically exploding foils  

Microsoft Academic Search

A modification of the gas gun (Gurney) formulation is used to compute the velocity and position histories of flyers driven by electrically exploded metal foils. The model is based on a numerical time integration of an energy conservation statement for the flyer and the expanding high-pressure metal vapor. Empirically altered, experimental power curves are used for the time-dependent energy term

S. C. Schmidt; W. L. Seitz; J. Wackerle

1977-01-01

337

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

Microsoft Academic Search

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

338

Profiles of stationary shock waves for hexagonal discrete velocity model with all triple collisions  

Microsoft Academic Search

Stationary shock wave profiles are investigated for the hexagonal discrete velocity model with binary and all triple collisions. The singular points corresponding to equilibrium limit states are studied analytically in the phase space of the relevant dynamical systems. The influence of triple collisions on various macroscopic quantities which characterize the shock profiles is investigated. The infinite Mach number case is

T. Platkowski

1992-01-01

339

On the velocity covariance and transport modeling in heterogeneous anisotropic porous formations 2. Unsaturated flow  

Microsoft Academic Search

Velocity covariances, and the resultant macrodispersion coefficient tensor, derived by Russo (this issue) for saturated flow conditions, are applied for unsaturated flow conditions, employing the assumption that for a given mean capillary pressure head, water saturation is a deterministic constant and log conductivity is a multivariate normal, stationary random space function. The applicability of the approach for modeling flow and

David Russo

1995-01-01

340

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

Microsoft Academic Search

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

341

Improved Near-surface Velocity Models from Waveform Tomography Applied to Vibroseis MCS Reflection Data  

Microsoft Academic Search

Multichannel vibroseis reflection surveys are prevalent in the land exploration seismic industry because of benefits in speed and cost, along with reduced environmental impact when compared to explosive sources. Since the downgoing energy must travel through the shallow subsurface, an improved model of near-surface velocity can in theory substantially improve the resolution of deeper reflections. We describe techniques aimed at

B. Smithyman; R. M. Clowes

2009-01-01

342

Complete regional waveform modeling to estimate seismic velocity structure and source parameters for CTBT monitoring  

Microsoft Academic Search

The velocity structures and source parameters estimated by waveform modeling provide valuable information for CTBT monitoring. The inferred crustal and uppermost mantle structures advance understanding of tectonics and guides regionalization for event location and identification efforts. Estimation of source parameters such as seismic moment, depth and mechanism (whether earthquake, explosion or collapse) is crucial to event identification. In this paper

T Bredbeck; A Rodgers; W Walter

1999-01-01

343

Models for Gas Hydrate-Bearing Sediments Inferred from Hydraulic Permeability and Elastic Velocities  

USGS Publications Warehouse

Elastic velocities and hydraulic permeability of gas hydrate-bearing sediments strongly depend on how gas hydrate accumulates in pore spaces and various gas hydrate accumulation models are proposed to predict physical property changes due to gas hydrate concentrations. Elastic velocities and permeability predicted from a cementation model differ noticeably from those from a pore-filling model. A nuclear magnetic resonance (NMR) log provides in-situ water-filled porosity and hydraulic permeability of gas hydrate-bearing sediments. To test the two competing models, the NMR log along with conventional logs such as velocity and resistivity logs acquired at the Mallik 5L-38 well, Mackenzie Delta, Canada, were analyzed. When the clay content is less than about 12 percent, the NMR porosity is 'accurate' and the gas hydrate concentrations from the NMR log are comparable to those estimated from an electrical resistivity log. The variation of elastic velocities and relative permeability with respect to the gas hydrate concentration indicates that the dominant effect of gas hydrate in the pore space is the pore-filling characteristic.

Lee, Myung W.

2008-01-01

344

Modeling the spatiotemporal organization of velocity storage in the vestibuloocular reflex by optokinetic studies  

NASA Technical Reports Server (NTRS)

1. A generalized three-dimensional state space model of visual vestibular interaction was developed. Matrix and dynamical system operators associated with inputs from the semicircular canals, otolith velocity estimator, and the visual system have been incorporated into the model, which focus on their relationship to the velocity storage integrator. 2. A relationship was postulated between the eigenvalues and the direction of the eigenvectors of the system matrix and the orientation of the spatial vertical. It was assumed that the system matrix for a tilted position was a composition of two linear transformations of the system matrix for the upright position. One transformation modifies the eigenvalues of the system matrix, whereas another rotates the eigenvectors of the system matrix. The pitch and roll eigenvectors rotate with the head, whereas the yaw axis eigenvector remains approximately spatially invariant. 3. Based on the three-dimensional model, a computational procedure was formulated to identify the eigenvalues and eigenvectors of the system matrix with the use of a modification of the marquardt algorithm. With the use of data obtained from a monkey, it was shown that the three-dimensional behavior of velocity storage cannot be predicted solely in terms of its time constants, i.e., the inverse of its eigenvalues. With the use of the same eigenvalues the data could either be fit or not fit, depending on the eigenvector directions. Therefore, it is necessary to specify eigenvector directions when characterizing velocity storage in three dimensions. 4. Parameters found with the use of the Marquardt algorithm were incorporated into the model. Diagonal matrices in a head coordinate frame were introduced for coupling the visual system to the integrator and to the direct optokinetic pathway. Simulations of optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN) were run. The model predicted the behavior of yaw and pitch OKN and OKAN when the animal is upright. It also predicted the cross-coupling in the side down position. The trajectories in velocity space were also accurately simulated. 5. One of the predictions of the model is that when the stimulus direction is along an eigenvector, the trajectory in velocity space is a straight line. Using the "spectral width" of the residuals from a straight line sequence during OKAN, we developed a methodology to estimate how close the OKAN decay was to an eigenvector trajectory. 6. Thus we have developed a model-based approach for studying and interpreting the response characteristics of velocity storage in three dimensions.(ABSTRACT TRUNCATED AT 400 WORDS).

Raphan, T.; Sturm, D.; Cohen, B. (Principal Investigator)

1991-01-01

345

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

346

Elastic-wave velocity in marine sediments with gas hydrates: Effective medium modeling  

USGS Publications Warehouse

We offer a first-principle-based effective medium model for elastic-wave velocity in unconsolidated, high porosity, ocean bottom sediments containing gas hydrate. The dry sediment frame elastic constants depend on porosity, elastic moduli of the solid phase, and effective pressure. Elastic moduli of saturated sediment are calculated from those of the dry frame using Gassmann's equation. To model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions: (a) hydrate modifies the pore fluid elastic properties without affecting the frame; (b) hydrate becomes a component of the solid phase, modifying the elasticity of the frame. The goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data. We apply the model to sonic and VSP data from ODP Hole 995 and obtain hydrate concentration estimates from assumption (b) consistent with estimates obtained from resistivity, chlorinity and evolved gas data. Copyright 1999 by the American Geophysical Union.

Helgerud, M. B.; Dvorkin, J.; Nur, A.; Sakai, A.; Collett, T.

1999-01-01

347

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

NASA Astrophysics Data System (ADS)

An isothermal experimental investigation of the three-dimensional flowfield 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 by measuring the cross-plane velocities. These were found to consist of large radial flows, of order 15 percent of the mean axial velocities at the lobe inlet, with changing sign depending on location. The cross-plane flow is consistent with a large-scale axial vortex pair (per lobe) which persists throughout the downstream duct and enhances mixing in this region.

Koutmos, P.; McGuirk, J. J.

1989-12-01

348

Nowcasting convection velocity in the high-latitude ionosphere using statistical models  

NASA Astrophysics Data System (ADS)

The Weimer and IZMEM statistical convection models are driven with a time series of interplanetary magnetic field (IMF) measurements made onboard the Wind spacecraft. The model outputs are used to infer the ionospheric convection velocity at Casey, Antarctica (80.8°S geomagnetic latitude), and then compared with measurements of Doppler velocity made using a Digisonde, and measurements of F-region convection implied by a collocated magnetometer. During a single, representative campaign interval, 13-17 February 1996, the Weimer model explained 19% (42%) of the variation in Doppler speed (direction) observed by the Digisonde, and 21% (14%) of the equivalent convection components observed by the magnetometer. This compares with IZMEM which explained 16% (46%) of the variation in Doppler speed (direction) observed by the Digisonde, and 34% (32%) of the equivalent convection components observed by the magnetometer. In general, there was better agreement between convection direction than convection speed. Some of the disagreement was probably due to differences between the IMF measured by Wind located ~170 RE upstream in the solar wind and the IMF actually arriving at the magnetopause. However, the results of this study do show that measurements of ionospheric velocity using different experimental techniques need heavy averaging to identify a common component of velocity controlled by the IMF vector. The present time series approach was also used to estimate 16+/-5 min as the time required for the ionospheric convection to reconfigure in response to IMF changes occurring at the magnetopause.

Parkinson, M. L.; Smith, P. R.; Dyson, P. L.; Morris, R. J.

1999-07-01

349

Probabilistic Earthquake Relocation in Three-Dimensional Velocity Models for the Yellowstone National Park Region, Wyoming  

Microsoft Academic Search

Recorded seismicity for the Yellowstone National Park region, com- prising 25,267 earthquakes from November 1972 to December 2002, has been re- located using three-dimensional velocity models and probabilistic earthquake loca- tion. In addition, new coda magnitudes for earthquakes between 1984 and 2002 were computed by using an improved coda magnitude equation. Three-dimensional ve- locity models for earthquake location were computed

Stephan Husen; Robert B. Smith

2004-01-01

350

Quasi-static modeling of delamination crack propagation in laminates subjected to low-velocity impact  

Microsoft Academic Search

The quasi-static characteristics of impact responses and impact-induced delamination crack propagation in [905\\/05\\/905] graphite\\/epoxy laminates subjected to low-velocity heavy mass impact have been investigated. A one-degree-of-freedom spring-mass model was used to predict the contact force history. The peak contact force was then used in conjunction with a linear beam model to calculate the strain-energy release rate. The delamination size was

C. T. Sun; C. J. Jih

1995-01-01

351

Numerical modelling of perforation failure in fibre metal laminates subjected to low velocity impact loading  

Microsoft Academic Search

Low velocity impact tests have been conducted on fibre metal laminates (FMLs). The resulting load–displacement traces and deformation\\/failure modes were then used to validate a series of numerical models. Here, finite element (FE) models were developed to simulate the impact response of the 2\\/1, 3\\/2 and 4\\/3 FMLs, focussing, in particular on the perforation threshold and the associated failure mechanisms.

J. Fan; Z. W. Guan; W. J. Cantwell

2011-01-01

352

Ab initio calculation of the sound velocity of dense hydrogen: implications for models of Jupiter.  

PubMed

First-principles molecular dynamics simulations were used to calculate the sound velocity of dense hydrogen, and the results were compared with extrapolations of experimental data that currently conflict with either astrophysical models or data obtained from recent global oscillation measurements of Jupiter. Excellent agreement with the extrapolated experimental data was obtained. These results strongly support the notion that the existing models for the jovian interior need to be revised. PMID:7652571

Alavi, A; Parrinello, M; Frenkel, D

1995-09-01

353

Elastic-wave velocity in marine sediments with gas hydrates: Effective medium modeling  

Microsoft Academic Search

We offer a first-principle-based effective medium model for elastic-wave velocity in unconsolidated, high porosity, ocean bottom sediments containing gas hydrate. The dry sediment frame elastic constants depend on porosity, elastic moduli of the solid phase, and effective pressure. Elastic moduli of saturated sediment are calculated from those of the dry frame using Gassmann's equation. To model the effect of gas

M. B. Helgerud; J. Dvorkin; A. Nur; A. Sakai; T. Collett

1999-01-01

354

Global plate motion models incorporating the velocity field of ITRF96  

Microsoft Academic Search

In this paper, incorporating the ITRF96 velocity field that is free of any tectonic plate model assumption, a new present-day plate motion model relative to the ITRF96 reference frame, called the ITRF96VEL, is determined. The total angular momentum of all tectonic plates with regards to the ITRF96VEL shows that the ITRF96 rotates in a right-handed sense relative to the no-net-rotation

Zhang Qiang; Zhu Wenyao; Xiong Yongqin

1999-01-01

355

Velocity Measurements Near the Empennage of a SmallScale Helicopter Model  

NASA Technical Reports Server (NTRS)

A test program was conducted in the NASA Langley 14- by 22-Foot Subsonic Tunnel to measure the flow near the empennage of a small-scale powered helicopter model with an operating tail fan. Three-component velocity profiles were measured with Laser Velocimetry (LV) one chord forward of the horizontal tail for four advance ratios to evaluate the effect of the rotor wake impingement on the horizontal tail angle of attack. These velocity data indicate the horizontal tail can experience unsteady downwash angle variations of over 30 degrees due to the rotor wake influence. The horizontal tail is most affected by the rotor wake above advance ratios of 0.10. Velocity measurements of the flow on the inlet side of the fan were made for a low-speed flight condition using both conventional LV techniques and a promising, non-intrusive, global, three-component velocity measurement technique called Doppler Global Velocimetry (DGV). The velocity data show an accelerated flow near the fan duct, and vorticity calculations track the passage of main rotor wake vortices through the measurement plane. DGV shows promise as an evolving tool for rotor flowfield diagnostics.

Gorton, Susan Althoff; Meyers, James F.; Berry, John D.

1996-01-01

356

Modeling Compressional and Shear Wave Velocities of Unconsolidated Sediments in the Vadose Zone  

NASA Astrophysics Data System (ADS)

Recent advances in seismic surveys have provided ways to image shallow structure in highly attenuating soils and near-surface rock. Applications include using surface wave methods to find tunnels; mapping landfills with seismic refraction methods; finding faults, the water table, or other strong heterogeneities using seismic reflection surveys. Recent improvements in laboratory ultrasonic measurement techniques have provided reliable data on compressional and shear wave velocities in soils at low pressures analogous to the top few meters to tens of meters of the subsurface. The availability of these data points the way for development of interpretation methods that may allow seismologists to obtain more information from their data in the future. For environmental applications, improvements to interpretation methods could lead to reliable detection of second-order features such as changes in soil saturation, presence of dense non-aqueous phase liquids, or changes in clay content. Traditional modeling techniques developed in the oil industry are optimized for consolidated materials at pressures and depths greater than those typical for environmental applications. The shallow subsurface velocities are highly nonlinear and the soils are highly attenuating, and these characteristics must be considered when modeling velocities (and also when processing seismic data). Various factors, including grain contact roughness, location of clay with respect to sand grains, location of fluid in the partially-saturated case, loose vs. dense packing, all affect the compressional and shear wave velocities and attenuation and their pressure (depth) dependence. Care must be taken when applying effective medium theories or grain-contact theories to model shallow soil velocity behavior. Unconsolidated materials at low pressures show much greater variation in compressional vs. shear wave properties than consolidated materials and high-pressure applications would show. Despite the modeling difficulties, progress in seismic interpretation may be made if data are available for both compressional and shear waves. Examples of pitfalls and methods for successful soil velocity modeling will be presented using lab and field velocity data from the literature, for sands, silty sands, and other unconsolidated materials. The goal is to develop techniques to improve interpretation of seismic data from the vadose zone. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract W-7405-ENG-48 and supported specifically by the DOE Environmental Management Science Program. >http://www.llnl.gov/ees/esd/expgeoph/Berge/EMSP/

Berge, P. A.

2001-12-01

357

Comparison of solar wind velocity measurements with a theoretical acceleration model  

SciTech Connect

Interplanetary radio scintillation (IPS) measurements of the solar wind velocity were made using the receiving antennas of the European Incoherent Scatter Facility (EISCAT) radar system in northern Scandinavia from June through October 1990. The observations, which cover the distance range from 11 to 90 R{sub s} from Sun center, were taken with sufficient density to measure the same stream at two (or more) different distances. The deduced velocities are in the range 100 {approx lt} U {approx lt} 540 km s{sup {minus}1}. The authors selected from 192 observations, 16 examples of streams observed with good radial alignment, of which 12 were observed unchanged for several days. The measured velocities are compared with calculations based on a two-fluid solar wind model with Alfven waves. In eight cases the measurements are in good agreement with the model when a moderate amount of wave energy is added to the flow. In four cases the observed streams show low or moderate velocities below, say, 20 R{sub s} but then accelerate fast at larger distances from the Sun. This delayed acceleration is much steeper than the acceleration in the model at these distances. In the remaining four cases the streams seem to reach their final velocities much closer to the base than in other cases, and they are not observed to accelerate much between 10 and 90 R{sub s}. At these distances all related solar wind models they have seen give the same results; they all fit half the data, and none can fit the other half.

Coles, W.A. (Univ. of California, La Jolla (United States)); Esser, R. (Univ. of Tromsoe (Norway)); Loevhaug, U.P. (EISCAT, Ramfjordbotn (Norway)); Markkanen, J. (Geophysical Observatory, Sodankyla (Finland))

1991-08-01

358

Estimation of ground surface topography and velocity model by SAR-GPR and its application to landmine detection  

NASA Astrophysics Data System (ADS)

The height variation of ground surface and incorrect velocity will affect imaging processing of landmine. To eliminate these effects, ground surface topography and velocity model are needed. For effective detection of landmines, a stepped-frequency continuous-wave array antenna ground penetrating radar system, called SAR-GPR, was developed. Based on multi-offset common middle point (CMP) data acquired by SAR-GPR, we describe a velocity model estimation method using velocity spectrum technique. Also after pre-stack migration, the ground surface can be identified clearly. To compensate landmine imaging for the effect created by height variation, the ground surface displacement, a kind of static correction technique, is used based on the information of ground surface topography and velocity model. To solve the problem of incorrect velocity, we present a continuous variable root-mean-square velocity based on the velocity model. The velocity is used in normal moveout correction (NMO) to adjust the time delay of multi-offset data, and also applied to migration for reconstruction of landmine image. After the application of ground surface topography and velocity model to data processing, we could obtain good landmine images in experiment.

Feng, Xuan; Zhou, Zheng-shu; Kobayashi, Takao; Savelyev, Timofei G.; Fujiwara, Jun; Sato, Motoyuki

2005-06-01

359

Modeling a Material's Instantaneous Velocity during Acceleration Driven by a Detonation's Gas-Push Process  

NASA Astrophysics Data System (ADS)

This paper will describe both the scientific findings and the model developed in order to quantfy a material's instantaneous velocity versus position, time, or the expansion ratio of an explosive's gaseous products while its gas pressure is accelerating the material. The formula derived to represent this gas-push process for the 2nd stage of the BRIGS Two-Step Detonation Propulsion Model was found to fit very well the published experimental data available for twenty explosives. When the formula's two key parameters (the ratio Vinitial / Vfinal and ExpansionRatioFinal) were adjusted slightly from the average values describing closely many explosives to values representing measured data for a particular explosive, the formula's representation of that explosive's gas-push process was improved. The time derivative of the velocity formula representing acceleration and/or pressure compares favorably to Jones-Wilkins-Lee equation-of-state model calculations performed using published JWL parameters.

Backofen, Joseph E.

2005-07-01

360

A numerical study on finding an optimum model in velocity tomography by using the Extended Information Criterion  

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

361

Comparative Experimental and Modeling Study of Fluid Velocities in Heterogeneous Rocks  

NASA Astrophysics Data System (ADS)

Understanding the spatial distribution of fluid velocities and effective porosities in rocks is crucial for predicting kinetic reaction rates and fluid-rock interactions in a plethora of geo-engineering applications, ranging from geothermal systems, Enhanced Oil Recovery to Carbon Capture and Storage. Magnetic Resonance Imaging can be used to measure spatially resolved porosities and fluid velocities in porous media. Large internal field gradients and short spin relaxation times, however, constrain the usability of the conventional MRI technique in natural rock samples. The combination of three-dimensional Single Point Ramped Imaging with T1 Enhancement (SPRITE) and the 13-interval Alternating-Pulsed-Gradient Stimulated-Echo (APGSTE) scheme - a method developed at the UNB MRI Center - is able to compensate for those challenges and quantitative 3 dimensional maps of porosities and fluid velocities can be obtained. In this study we measured velocities and porosities using MRI in a sandstone rock sample showing meso-scale heterogeneities. Then we generated permeabilities using three independent approaches, employed them to model single-phase fluid flow in the measured rock sample and compared the generated velocity maps with the respective MRI measurements. For the first modeling approach, we applied the Kozeny-Carman relationship to create a permeability map based on porosities measured using MRI. For the second approach we used permeabilities derived from CO2-H2O multi-phase experiments performed in the same rock sample assuming the validity of the J-Leverett function. The permeabilities in the third approach were generated by applying a new inverse iterative-updating technique. The resulting three permeability maps were then used as input for a CFD simulation - using the Stanford CFD code AD-GPRS - to create a respective velocity map, which in turn was then compared to the measured velocity map. The results of the different independent methods for generating permeability maps as well as their correlation with the measured velocity maps are evaluated. Furthermore the implication of this study on understanding kinetic reaction rates and fluid-rock interaction is discussed.

Hingerl, F.; Romanenko, K.; Pini, R.; Balcom, B.; Benson, S. M.

2013-12-01

362

A Velocity Shear Driven Turbulence Model for Recent ACE Magnetometer Observations  

NASA Astrophysics Data System (ADS)

Recent magnetometer measurements from the ACE spacecraft show magnetic fluctuation enhancements above the normal Kolmogorov cascade levels adjacent the Doppler-shifted proton gyro-scales. It has been suggested that enhanced wave activity associated with a large solar wind structure, such as glancing passage of a CME, could explain the observations; however to date, a physical process has not been explored aside from conjectures that velocity shear-based Kelvin-Helmholtz (KH) instabilities may be present. Here we use a two-and-one-half dimensional compressible MHD code, initialized with plasma parameters and initial conditions consistent with the observations, to show that large-scale velocity shears can lead to spectral enhancements adjacent the proton gyro-scales for appropriate orientations of the solar wind magnetic field and the normal plane of the velocity shears. Our model includes finite frequency (Hall) and finite wavenumber (Finite Larmor Radius) effects. The development of spectral anisotropies due to velocity shears appears as a natural consequence of wave advection and does not depend on threshold conditions of the KH instability. Thus, the range of applicability for our model is somewhat broader than the KH instability.

Ghosh, S.; Roelof, E. C.; Smith, C. W.

2012-12-01

363

Prediction of Critical Velocity During Cold Spraying Based on a Coupled Thermomechanical Eulerian Model  

NASA Astrophysics Data System (ADS)

In cold spraying (CS), critical velocity of particles is one of the most important parameters. The impacting particle and substrate inevitably undergo a strong thermomechanical coupling process at the contacting interface and serious plastic deformation in a very short time. In this paper, a coupled thermomechanical Eulerian (CTM-Eulerian) model was, for the first time, developed for CS particles to investigate plastic deformation and heat conduction within the bulk, and to predict the critical velocity. Results show that heat conduction has a significant effect on the temperature distribution within the particle which will influence the atom diffusion at the impacting interface, while a little influence on plastic deformation. Moreover, based on the deformed particle shapes and plastic strain analysis, a calculated critical velocity of about 300 m/s for copper is obtained. Finally, this CTM-Eulerian model is extended to other commonly sprayed materials and the predicted critical velocities of Fe, Ni, SS304, Al, In718, and TC4 are about 350, 380, 395, 410, 490, and 500 m/s, respectively.

Wang, F. F.; Li, W. Y.; Yu, M.; Liao, H. L.

2014-01-01

364

Evaluation of an imputed pitch velocity model of the auditory kappa effect.  

PubMed

Three experiments evaluated an imputed pitch velocity model of the auditory kappa effect. Listeners heard 3-tone sequences and judged the timing of the middle (target) tone relative to the timing of the 1st and 3rd (bounding) tones. Experiment 1 held pitch constant but varied the time (T) interval between bounding tones (T = 728, 1,000, or 1,600 ms) in order to establish baseline performance levels for the 3 values of T. Experiments 2 and 3 combined the values of T tested in Experiment 1 with a pitch manipulation in order to create fast (8 semitones/728 ms), medium (8 semitones/1,000 ms), and slow (8 semitones/1,600 ms) velocity conditions. Consistent with an auditory motion hypothesis, distortions in perceived timing were larger for fast than for slow velocity conditions for both ascending sequences (Experiment 2) and descending sequences (Experiment 3). Overall, results supported the proposed imputed pitch velocity model of the auditory kappa effect. PMID:19331507

Henry, Molly J; McAuley, J Devin

2009-04-01

365

Muscle-joint models incorporating activation dynamics, moment-angle, and moment-velocity properties.  

PubMed

Muscle input/output models incorporating activation dynamics, moment-angle, and moment-velocity factors are commonly used to predict the moment produced by muscle during nonisometric contractions; the three factors are generally assumed to be independent. We examined the ability of models with independent factors, as well as models with coupled factors, to fit input/output data measured during simultaneous modulation of the fraction of muscle stimulated (recruitment) and joint angle inputs. The models were evaluated in stimulated cat soleus muscles producing ankle extension moment, with regard to their potential applications in neuroprostheses with either fixed parameters or parameter adaptation. Both uncoupled and coupled models predicted the output moment well for random angle perturbation sizes ranging from 10 degrees to 30 degrees. For the uncoupled model, the best parameter values depended on the range of perturbations and the mean angle. Introducing coupling between activation and velocity in the model reduced this parameter sensitivity; one set of model parameter values fit the data for all perturbation sizes and also fit the data under isometric or constant stimulation conditions. Thus, the coupled model would be the most appropriate for applications requiring fixed parameter values. In contrast, with continuous parameter adaptation, errors due to changing test conditions decreased more quickly for the uncoupled model, suggesting that it would perform well in adaptive control of neuroprostheses. PMID:7868149

Shue, G; Crago, P E; Chizeck, H J

1995-02-01

366

Three-dimensional modeling of shallow shear-wave velocities for Las Vegas, Nevada, using sediment type  

Microsoft Academic Search

A three-dimensional model of near-surface shear-wave velocity in the deep alluvial basin underlying the metropolitan area\\u000a of Las Vegas, Nevada (USA), is being developed for earthquake site response projections. The velocity dataset, which includes\\u000a 230 measurements, is interpolated across the model using depth-dependent correlations of velocity with sediment type. The\\u000a sediment-type database contains more than 1 400 well and borehole

Barbara Luke; Helena Murvosh; Wanda Taylor; Jeff Wagoner

2009-01-01

367

Density, Shear and Compressional Velocity Models of the Vrancea Seismogenic Zone  

NASA Astrophysics Data System (ADS)

Additional constraints on the geodynamic models for the origin of the intermediate depth Vrancea Seismogenic Zone are given by three-dimensional P and S-wave velocity and density images. The reconstructed physical parameters aim to substantiate or eliminate two contrasting models which explain the Vrancea seismicity: the subduction model and the active continental lithospheric delamination model. For our goal, we apply the tomographic inversion method of sequential integrated inversion proposed by Tondi and de Franco (2006) to shot data collected during the VRANCEA99 (Hauser et al., 2001) and VRANCEA2001 (Landes et al., 2004) seismic refraction experiments, to local earthquake data collected during the CALIXTO (EOS, 1998) experiment and to recent gravity measurements of the studied area. We first locate P and S wave sources of local events with the NonLinLoc location program (Lomax et al., 2000) and then we consider these events as those originated from shots points. The mathematical formulation of the seismic travel time inversion algorithm, which regularizes the solution with the minimization of the first and the second partial derivatives of the functionals describing the velocity parameters, enables us to control the proliferation of caustics and arrivals during iterations, which is a common problem when using ray-tracing techniques with realistic and extensive heterogeneous velocity models. This increases the robustness and efficiency of the method and efficiently handles a seismic data set which is severely affected by scattering effects. Furthermore, the density model parametrization, which uses polyhedral bodies whose density is linearly dependent on the three coordinates (Pohànka, 1998), leads to a perfect match between the density and the velocity model parametrization and takes into account the presence of geological structures characterized by a gradual increase in density with depth. After each iteration, the events are relocated with the updated velocity model until the discrepancies between two subsequent localizations are sufficiently small. The reliability of the reconstructed models, which explain equally well both travel times and gravity data, is quantified through a restoring test and the estimation of travel times and gravity residuals.

Tondi, R.; Achauer, U.; Besutiu, L.

2007-05-01

368

Towards a Rational Model for the Triple Velocity Correlations of Turbulence  

NASA Technical Reports Server (NTRS)

This paper presents a rational approach to modelling the triple velocity correlations that appear in the transport equations for the Reynolds stresses. All existing models of these correlations have largely been formulated on phenomenological grounds and are defective in one important aspect: they all neglect to allow for the dependence of these correlations on the local gradients of mean velocity. The mathematical necessity for this dependence will be demonstrated in the paper. The present contribution lies in the novel use of Group Representation Theory to determine the most general tensorial form of these correlations in terms of all the second- and third-order tensor quantities that appear in the exact equations that govern their evolution. The requisite representation did not exist in the literature and therefore had to be developed specifically for this purpose by Professor G. F. Smith. The outcome of this work is a mathematical framework for the construction of algebraic, explicit, and rational models for the triple velocity correlations that are theoretically consistent and include all the correct dependencies. Previous models are reviewed, and all are shown to be an incomplete subset of this new representation, even to lowest order.

Younis, B. A.; Gatski, T. B.; Speziale, C. G.