Self-consistent Numerical Model Research Articles

One Dimensional Self-consistent Model for Xenon Dielectic Barrier Discharge (DBD)

A one-dimensional self-consistent numerical model for dielectric barrier discharge (DBD) in Xenon is presented. Continuity equations for charged particles, rate equations for excited particles and Poisson's equation are solved. Electrons, ions, excited atoms and excimer density distributions in space and time are simulated in the model. Electrical parameters in a micro-discharge such as electric field, voltage across the gas gap, current density and accumulated charges on both dielectric surfaces are obtained. UV radiation intensities and their efficiencies in a micro-discharge are calculated.

The origin of primeval magnetic fields: Self-consistent simulation of magnetic field generation and amplification

A self-consistent numerical model of self-generation and amplification of magnetic fields in weakly ionized protogalactic matter is presented. This model is based on three-dimensional two-fluid simulations of the dynamics expected for protogalactic plasma–neutral gas clouds characterized by shear flow. Due to the friction between the ionized and neutral gas components self-generated magnetic fields of seed field order, i.e., 10−17 G are created on time scales of 105 yr. Moreover, unstable Kelvin–Helmholtz modes are excited yielding a significant amplification of the field.

Sensitivity of GSM TIP model to the variability of the UV and EUV solar radiation

A self-consistent numerical global model of the coupled thermosphere, ionosphere and protonosphere (GSM TIP) has been used to examine the variations of the upper atmospheric parameters with respect to the changes of the solar extreme ultraviolet/ultraviolet (EUV/UV) flux from solar minimum to solar maximum conditions. Two model runs were executed for equinox and quiet geomagnetic periods for the same initial conditions. In the first case for the given UV flux the amplitude of the EUV flux was changed, whereas in the second case the UV flux was increased at a constant level of the EUV flux. For these cases only the global dynamical structure of the thermosphere has been studied. The model results have shown that in the first case the diurnal mode of the neutral wind increased at an altitude of 300 km and the semidiurnal mode increased at 120 km. In the second case the variation of the neutral wind circulation was opposite. Amplitudes of the variation were 15 m/s at 300 km and 5 m/s at 120 km.

Thermospheric composition changes deduced from geomagnetic storm modeling

To test various hypotheses about positive ionospheric storm development, we numerically simulated the magnetic storm of 24–27 January 1974 to obtain the global pattern of its thermospheric and ionospheric effects. We use a global self‐consistent numerical model of the thermosphere‐ionosphere‐magnetosphere system which calculates all plasma parameters as well as electric fields both of magnetospheric and thermospheric dynamo origin. The predicted neutral composition changes are consistent with observations of the AE‐C and ESRO‐4 satellites. The storm‐to‐quiet density ratio of [O]/[N2] (at a fixed height) does not change significantly at middle and low latitudes while the absolute density of all neutral constituents is enhanced. The density ratio at a fixed pressure level can be slightly enhanced under certain conditions. Positive ionospheric storm effects during the main phase of the storm are shown to be mainly due to the uplifting of the ions along the field lines by an equatorward directed disturbance wind component at middle latitudes and their equatorward (convergent) movement at low latitudes. This is driven by the passage of travelling atmospheric disturbances and by the large‐scale disturbance wind circulation. Under daylight conditions minor contributions arise from the general thermal density enhancement of all constituents favoring positive ionospheric response due to a stronger ion production rather than loss. Height dependent deviations from diffusive equilibrium of minor thermospheric constituents are due to the relatively rapid (in comparison with their diffusion) vertical bulk motion.

Effect of electronegative impurities on the generation of ozone in air

A self-consistent numerical model is used to investigate the effect of electronegative impurities on the ozone yield in a dielectric barrier discharge with a pulsed voltage supply, and the range of impurity concentrations giving a substantial (two-or threefold) increase in the ozone yield is established. Sulfur hexafluoride is considered as a representative component having strong electronegative properties. It is shown that a tiny admixture [SF6]<0.1% can have an appreciable effect on the characteristics of an ozonator. The calculations are compared with published experimental data and given an interpretation.

Self-consistent rolling-hinge model for the evolution of large-offset low-angle normal faults

Research Article| December 01, 1999 Self-consistent rolling-hinge model for the evolution of large-offset low-angle normal faults Luc L. Lavier; Luc L. Lavier 1Lamont-Doherty Earth Observatory of Columbia University, and Department of Earth and Environmental Sciences, Columbia University, Palisades, New York 10964, USA Search for other works by this author on: GSW Google Scholar W. Roger Buck; W. Roger Buck 1Lamont-Doherty Earth Observatory of Columbia University, and Department of Earth and Environmental Sciences, Columbia University, Palisades, New York 10964, USA Search for other works by this author on: GSW Google Scholar Alexei N. B. Poliakov Alexei N. B. Poliakov 2Laboratoire de Géophysique et Tectonique, CNRS UMR 5573, Université de Montpellier Cedex 05, France Search for other works by this author on: GSW Google Scholar Geology (1999) 27 (12): 1127–1130. https://doi.org/10.1130/0091-7613(1999)027<1127:SCRHMF>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Luc L. Lavier, W. Roger Buck, Alexei N. B. Poliakov; Self-consistent rolling-hinge model for the evolution of large-offset low-angle normal faults. Geology 1999;; 27 (12): 1127–1130. doi: https://doi.org/10.1130/0091-7613(1999)027<1127:SCRHMF>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The nature of the physical processes responsible for the formation of continental and oceanic metamorphic core complexes is widely debated. The controversy focuses primarily on whether the low-angle normal faults observed in these environments formed and slipped at low angles or were rotated from an original high-angle orientation after large offsets. We describe a self-consistent numerical model for the extension of a brittle layer that can spontaneously produce normal-fault structures. In our formulation, a fault or faults form because strength is locally reduced with increasing strain. If the reduction in fault strength is <∼10% of the total strength of the layer, then faults lock after an offset smaller than the layer thickness and new faults form. Larger strength reduction leads to single faults that continue to slip no matter how large the fault offset. If the strength reduction occurs by the loss of cohesion, then we see the unlimited offset faults for layers <11–22 km thick for reasonable values of cohesion. The key result of this study is that structures very similar to those observed in both oceanic and continental core complexes are produced by rotation of the inactive part of the model fault after very large offset. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Abyssal hills formed by stretching oceanic lithosphere

Tectonic plates are formed and move apart at mid-ocean ridges. Some portion of this plate-separation process can occur by stretching of the crust, resulting in a complex pattern of extensional faults. Abyssal hills, the most ubiquitous topographic features on Earth1, are thought to be a product of this faulting2,3. Here we report the results of a self-consistent numerical model of lithospheric formation and stretching that includes spontaneous fault creation. In this model, an axial valley develops where the fault activity is most concentrated. The ‘frozen’ fault-generated topography, rafted out of the axial valley, is visually and statistically similar to observed abyssal hills formed at many slower-spreading ridges. Faults appear to be replaced by new faults because their offset changes the local stress field. We accordingly need no temporal variation in magmatism, as required by some previous models4,5,6, to control the spacing or offset of faults. Our model results suggest instead that the irregularity of abyssal hill relief may result from a self-organized critical stress state at spreading centres.

Formulation of a Self-Consistent Model for Quantum Well pin Solar Cells: Dark Behavior

A self-consistent numerical simulation model for a pin single-cell solar cell is formulated. The solar cell device consists of a p–AlGaAs region, an intrinsic i–AlGaAs/GaAs region with several quantum wells, and a n–AlGaAs region. Our simulator solves a field-dependent Schrödinger equation self-consistently with Poisson and drift-diffusion equations. The field-dependent Schrödinger equation is solved using the transfer matrix method. The eigenfunctions and eigenenergies obtained are used to calculate the escape rate of carriers from the quantum wells, the capture rates of carriers by the wells, the absorption spectra in the wells, and the non-radiative recombination rates of carriers in the quantum wells. These rates are then used in a self-consistent finite-difference numerical Poisson-drift-diffusion solver. We believe this is the first such comprehensive model ever reported.

Model for trap filling and avalanche breakdown in semi-insulating Fe:InP

A self-consistent two-carrier numerical model for steady-state current flow in n-semi-insulating-n InP structures allows the treatment of avalanche breakdown in addition to trap filling. Band-to-band impact ionization is included as a source term in the continuity equations. Carrier diffusion, nonlinear velocity field characteristics, and Shockley-Read-Hall recombination through the traps are also included, and the effects of each on the field and trapped carrier distributions are calculated. (The progress of trap filling predicted by the traditional drift-only theory is also calculated.) With impact ionization, hole accumulation near the cathode redistributes the space charge and contributes to positive feedback for avalanche breakdown. The model predictions are consistent with experimentally observed catastrophic breakdown and allow the development of design guidelines for avoiding device failure.

A PARALLEL IMPLEMENTATION OF A TWO-DIMENSIONAL HYDRODYNAMIC MODEL FOR MICROWAVE SEMICONDUCTOR DEVICE INCLUDING INERTIA EFFECTS IN MOMENTUM RELAXATION

A self-consistent numerical transport model based on the hydrodynamic equations obtained from Boltzmann's transport equation (BTE) is presented. The model includes both the temporal and spatial variation in electron velocity. A parallel implementation of the solution method, using FDTD techniques, is illustrated. Numerical results for a GaAs MESFET device are generated using this complete hydrodynamic model (CHM) and compared with results obtained from the more commonly used energy or simplified hydrodynamic model (SHM). The results indicate that for short gate-lengths (less than 0⋅5 μm) the two models lead to different DC steady-state results which in turn lead to different microwave small-signal models for the device. © 1997 by John Wiley & Sons, Ltd.

A PARALLEL IMPLEMENTATION OF A TWO‐DIMENSIONAL HYDRODYNAMIC MODEL FOR MICROWAVE SEMICONDUCTOR DEVICE INCLUDING INERTIA EFFECTS IN MOMENTUM RELAXATION

A self-consistent numerical transport model based on the hydrodynamic equations obtained from Boltzmann's transport equation (BTE) is presented. The model includes both the temporal and spatial variation in electron velocity. A parallel implementation of the solution method, using FDTD techniques, is illustrated. Numerical results for a GaAs MESFET device are generated using this complete hydrodynamic model (CHM) and compared with results obtained from the more commonly used energy or simplified hydrodynamic model (SHM). The results indicate that for short gate-lengths (less than 0⋅5 μm) the two models lead to different DC steady-state results which in turn lead to different microwave small-signal models for the device. © 1997 by John Wiley & Sons, Ltd.

Recombination velocity at oxide–GaAs interfaces fabricated by in situ molecular beam epitaxy

The recombination velocity at oxide–GaAs interfaces fabricated by in situ multiple-chamber molecular beam epitaxy has been investigated. Ga2O3, Al2O3, SiO2, and MgO films have been deposited on clean, atomically ordered n- and p-type (100) GaAs surfaces using molecular beams of Ga–, Al–, Si–, and Mg oxide, respectively. Based on the internal quantum efficiency measured for incident light power densities 1≤P0≤104 W/cm2, the interface recombination velocity S has been inferred using a self-consistent numerical heterostructure device model. While Al2O3–, SiO2–, and MgO–GaAs structures are characterized by an interface recombination velocity which is comparable to that of a bare GaAs surface (≂ 107 cm/s), S observed at Ga2O3–GaAs interfaces is as low as 4000–5000 cm/s. The excellent Ga2O3–GaAs interface recombination velocity is consistent with the previously reported low interface state density in the mid 1010 cm−2 eV−1 range.

Constraints on melt production rate beneath the mid-ocean ridges based on passive flow models

We present a model for computing the total melt production rate from the decompression partial melting region beneath a mid-ocean ridge, and the maximum oceanic crustal thickness created at the ridge axis assuming an ideal melt migration mechanism. The calculations are based on a self-consistent numerical model for the thermal structure and steady-state mantle flow field at a mid-ocean ridge. The model includes the effect of decreasing the melt production rate within the partial melting region by melt extraction as the residual mantle matrix becomes increasingly difficult to melt. Thus the melt fraction depends not only on temperature and pressure determined by the location beneath the ridge axis (the Eulerian description) but also on the accumulated melt extraction since the upwelling mantle matrix enters the partial melting region determined by the location along the flow-line path (the Langrangian description). This effect has been neglected by previous models. The model can predict the size of the melting region and the locations of the boundaries between mantle, residual mantle, and the partial melting region for a given spreading rate, also the distribution of the melt depletion and the mean melting depth. Given the observed average thickness of oceanic crust (∼6 km), which is relatively independent of spreading rate, the model results also provide a constraint on the overall efficiency of melt migration to the ridge axis; the efficiency must decrease from 100% at 10 mm/yr to about 60% at fast spreading rates (>50 mm/yr). Although this reduction may be partially due to the increasing size of the melting region with increasing spreading rate, it still requires less efficient melt migration near the ridge axis at fast spreading rate. We found that the calculated crustal thickness is very sensitive to the mantle temperature. For a normal mantle temperature of 1350°C, the model can generate the observed 6 km oceanic crust over the global range of spreading rates, while the anomalous thicker crusts of the Iceland hotspot and the Reykjanes Ridge are related to higher mantle temperatures associated with the hotspot. Finally, by comparing our model results with previous ones we found that neglecting variations of the melting relations of the residual mantle matrix with melt removal will overestimate the crustal thickness by at least a factor of 1.7.

Experimental and theoretical investigation of high-pressure arcs. II. The magnetically deflected arc (three-dimensional modeling)

While Part I deals with cylindrical arcs, Part II studies the influence of transverse magnetic fields on the arc column for ambient pressures of 0.1-5.0 MPa. If exposed to a magnetic induction of several millitesla, the column of an arc is deflected by the Lorentz forces. In this paper, heat transfer and fluid flow with coupled electromagnetic forces are modeled for the magnetically deflected arc. To verify the predictions, the three-dimensional temperature distributions of the arc column are determined by line and continuum radiation measurements using tomographic methods. These temperature maps are compared with the results of the numerical simulations. To gain insight into the physical professes of the discharge and to make the arc properties available which are not readily measured, a self-consistent numerical model of the arc column is applied to the time-dependent and three-dimensional case. The temperature, velocity, pressure, and current densities are predicted by solving the conservation equations for mass, momentum, and energy, and Ohm's and Biot-Savart's law using material functions of the plasma. A control volume approach facilitates a numerically conservative scheme for solving the coupled partial differential equations. The predictions are in fair agreement with experimental results. A time-dependent fully implicit simulation of the arc was used to investigate the arc instabilities for large magnetic inductions.

Influence of an erosion plasma on the dynamics of a laser absorption wave in a gas

An experimental investigation was made of the influence of an erosion plasma (formed from the target vapour) on the dynamics of a laser-supported detonation wave in the gas surrounding the target. The results confirmed self-consistent numerical model predictions of slowing down of a wave propagating under conditions of partial absorption of laser radiation. The observed effect was attributed to a reduction in the intensity of the radiation, reflected by the target surface and transmitted for the second time by the plasma, because of the absorption in the dense ionised vapour of the target material.

A three-dimensional self-consistent computer simulation of a geomagnetic field reversal

A three-dimensional, self-consistent numerical model of the geodynamo is described, that maintains a magnetic field for over 40,000 years. The model, which incorporates a finitely conducting inner core, undergoes several polarity excursions and then, near the end of the simulation, a successful reversal of the dipole moment. This simulated magnetic field reversal shares some features with real reversals of the geomagnetic field, and may provide insight into the geomagnetic reversal mechanism.

Self-consistent modelling of low-pressure RF discharges in oxygen plasma

A self-consistent numerical model has been developed for an RF plasma discharge in oxygen. The model contains about 100 ion-molecular reactions with 13 neutral and charged species of the RF plasma. The energy distributions of both charged and neutral plasma components with respect to the electrodes have been calculated using a Monte Carlo method. The angular distributions of fast neutral species have also been calculated.

Two-dimensional simulation of constricted-mesa InGaAsP/InP buried-heterostructure lasers

A fully two-dimensional self-consistent numerical model of the steady-state behavior of 1.3 /spl mu/m constricted-mesa InGaAsP/InP buried-heterostructure lasers is presented. Devices operating at this wavelength are very temperature sensitive and therefore the model for the first time includes coupled solutions to the thermal as well as the electrical and optical equation sets. The temperature dependence is included in the Fermi-Dirac statistics, bandgaps, mobilities, densities of states, Auger recombination coefficients, intervalence band absorption, optical gain, and thermal conductivities. The lasing mode profiles, carrier distributions, threshold currents, and temperature characteristics are analyzed and good agreement is found with experimental results, including the temperature dependence of the threshold current and the prediction of a break-point temperature. The optimum design parameters are investigated for reduced threshold currents, and the effect of optical loss in the blocking regions on lateral-mode control is analyzed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Eddy current damping of thin film domain walls

A self-consistent two-dimensional numerical model, is developed to study eddy current damped domain wall motion in conductive, soft thin films. The micromagnetic Landau-Lifshitz equation and Maxwell's equation are solved simultaneously to provide a rigorous description of magnetization dynamics interacting with eddy current, which is relevant to the dynamic response of thin film inductive heads. Simulation results indicate that for Permalloy films thinner than 3000 AA, eddy current damping can be neglected in wall dynamics. For film thickness greater than 1 mu m this damping effect could be the dominating loss mechanism.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Interplanetary shocks generated by expanding magnetic loops

We present a self-consistent numerical model of shock wave formation in the heliosphere by an expanding magnetic loop. In the model a coronal mass ejection is initiated by a loss of magnetohydrostatic equilibrium of the loop as a result of an increase of underlying magnetic field strength. The expanding magnetic loops produce propagating shock waves.The plasma motions are described by a system of two-fluid Navier-Stokes equations taking account of modified coefficients for electron and ion heat conduction, ion viscosity and energy exchange between ions and electrons.We obtain shock wave parameters in the outer heliosphere vs initial perturbations of the magnetic loops, and show that the shocks can be divided into two types, depending on their intensity. In the case of relatively weak shocks a typical feature is formation of a dense and cold layer (“piling-up” of material) near the upper boundary of the loop. In the case of strong shocks large-scale turbulence and viscous heating in the relaxation zone behind the front play an important role, and no appreciable piling-up of plasma occurs.We demonstrate that expanding magnetic loops, which are observed as magnetic clouds in the outer heliosphere, can effectively drive transient shocks ahead.