Mixed-RKDG Finite Element Methods for the 2-D Hydrodynamic Model for Semiconductor Device Simulation
Chen, Zhangxin; Cockburn, Bernardo; Jerome, Joseph W.; Shu, Chi-Wang
1995-01-01
In this paper we introduce a new method for numerically solving the equations of the hydrodynamic model for semiconductor devices in two space dimensions. The method combines a standard mixed finite element method, used to obtain directly an approximation to the electric field, with the so-called Runge-Kutta Discontinuous Galerkin (RKDG) method, originally devised for numerically solving multi-dimensional hyperbolic systems of conservation laws, which is applied here to the convective part of the equations. Numerical simulations showing the performance of the new method are displayed, and the results compared with those obtained by using Essentially Nonoscillatory (ENO) finite difference schemes. Frommore » the perspective of device modeling, these methods are robust, since they are capable of encompassing broad parameter ranges, including those for which shock formation is possible. The simulations presented here are for Gallium Arsenide at room temperature, but we have tested them much more generally with considerable success.« less
A mathematical model for a didactic device able to simulate a 2D Newtonian gravitational field
NASA Astrophysics Data System (ADS)
De Marchi, Fabrizio
2015-01-01
In this paper we propose a mathematical model to describe a theoretical device able to simulate an inverse-square force on a test mass moving on a horizontal plane. We use two pulleys, a counterweight, a wire and a smooth rail, in addition to the test mass. The tension of the wire (i.e. the attractive force on the test mass) is determined by the position of a counterweight free to move on a rail placed under the plane. The profile of the rail is calculated in order to obtain the required Newtonian force. Details of this calculation are reported in the paper, and numerical simulations are provided in order to investigate the stability of the orbits under the effect of the main friction forces and other perturbative effects. This work points out that there are some criticalities intrinsic to the apparatus and gives some suggestions about how to minimize their impact.
2D materials for nanophotonic devices
NASA Astrophysics Data System (ADS)
Xu, Renjing; Yang, Jiong; Zhang, Shuang; Pei, Jiajie; Lu, Yuerui
2015-12-01
Two-dimensional (2D) materials have become very important building blocks for electronic, photonic, and phononic devices. The 2D material family has four key members, including the metallic graphene, transition metal dichalcogenide (TMD) layered semiconductors, semiconducting black phosphorous, and the insulating h-BN. Owing to the strong quantum confinements and defect-free surfaces, these atomically thin layers have offered us perfect platforms to investigate the interactions among photons, electrons and phonons. The unique interactions in these 2D materials are very important for both scientific research and application engineering. In this talk, I would like to briefly summarize and highlight the key findings, opportunities and challenges in this field. Next, I will introduce/highlight our recent achievements. We demonstrated atomically thin micro-lens and gratings using 2D MoS2, which is the thinnest optical component around the world. These devices are based on our discovery that the elastic light-matter interactions in highindex 2D materials is very strong. Also, I would like to introduce a new two-dimensional material phosphorene. Phosphorene has strongly anisotropic optical response, which creates 1D excitons in a 2D system. The strong confinement in phosphorene also enables the ultra-high trion (charged exciton) binding energies, which have been successfully measured in our experiments. Finally, I will briefly talk about the potential applications of 2D materials in energy harvesting.
Simulating MEMS Chevron Actuator for Strain Engineering 2D Materials
NASA Astrophysics Data System (ADS)
Vutukuru, Mounika; Christopher, Jason; Bishop, David; Swan, Anna
2D materials pose an exciting paradigm shift in the world of electronics. These crystalline materials have demonstrated high electric and thermal conductivities and tensile strength, showing great potential as the new building blocks of basic electronic circuits. However, strain engineering 2D materials for novel devices remains a difficult experimental feat. We propose the integration of 2D materials with MEMS devices to investigate the strain dependence on material properties such as electrical and thermal conductivity, refractive index, mechanical elasticity, and band gap. MEMS Chevron actuators, provides the most accessible framework to study strain in 2D materials due to their high output force displacements for low input power. Here, we simulate Chevron actuators on COMSOL to optimize actuator design parameters and accurately capture the behavior of the devices while under the external force of a 2D material. Through stationary state analysis, we analyze the response of the device through IV characteristics, displacement and temperature curves. We conclude that the simulation precisely models the real-world device through experimental confirmation, proving that the integration of 2D materials with MEMS is a viable option for constructing novel strain engineered devices. The authors acknowledge support from NSF DMR1411008.
NASA Astrophysics Data System (ADS)
Kangliang, Wei; Xiaoyan, Liu; Gang, Du; Ruqi, Han
2010-08-01
We demonstrate a two-dimensional (2D) full-band ensemble Monte-Carlo simulator for heterostructures, which deals with carrier transport in two different semiconductor materials simultaneously as well as at the boundary by solving self-consistently the 2D Poisson and Boltzmann transport equations (BTE). The infrastructure of this simulator, including the energy bands obtained from the empirical pseudo potential method, various scattering mechanics employed, and the appropriate treatment of the carrier transport at the boundary between two different semiconductor materials, is also described. As verification and calibration, we have performed a simulation on two types of silicon-germanium (Si-Ge) heterojunctions with different doping profiles—the p-p homogeneous type and the n-p inhomogeneous type. The current-voltage characteristics are simulated, and the distributions of potential and carrier density are also plotted, which show the validity of our simulator.
Realistic and efficient 2D crack simulation
NASA Astrophysics Data System (ADS)
Yadegar, Jacob; Liu, Xiaoqing; Singh, Abhishek
2010-04-01
Although numerical algorithms for 2D crack simulation have been studied in Modeling and Simulation (M&S) and computer graphics for decades, realism and computational efficiency are still major challenges. In this paper, we introduce a high-fidelity, scalable, adaptive and efficient/runtime 2D crack/fracture simulation system by applying the mathematically elegant Peano-Cesaro triangular meshing/remeshing technique to model the generation of shards/fragments. The recursive fractal sweep associated with the Peano-Cesaro triangulation provides efficient local multi-resolution refinement to any level-of-detail. The generated binary decomposition tree also provides efficient neighbor retrieval mechanism used for mesh element splitting and merging with minimal memory requirements essential for realistic 2D fragment formation. Upon load impact/contact/penetration, a number of factors including impact angle, impact energy, and material properties are all taken into account to produce the criteria of crack initialization, propagation, and termination leading to realistic fractal-like rubble/fragments formation. The aforementioned parameters are used as variables of probabilistic models of cracks/shards formation, making the proposed solution highly adaptive by allowing machine learning mechanisms learn the optimal values for the variables/parameters based on prior benchmark data generated by off-line physics based simulation solutions that produce accurate fractures/shards though at highly non-real time paste. Crack/fracture simulation has been conducted on various load impacts with different initial locations at various impulse scales. The simulation results demonstrate that the proposed system has the capability to realistically and efficiently simulate 2D crack phenomena (such as window shattering and shards generation) with diverse potentials in military and civil M&S applications such as training and mission planning.
THz devices based on 2D electron systems
NASA Astrophysics Data System (ADS)
Xing, Huili Grace; Yan, Rusen; Song, Bo; Encomendero, Jimy; Jena, Debdeep
2015-05-01
In two-dimensional electron systems with mobility on the order of 1,000 - 10,000 cm2/Vs, the electron scattering time is about 1 ps. For the THz window of 0.3 - 3 THz, the THz photon energy is in the neighborhood of 1 meV, substantially smaller than the optical phonon energy of solids where these 2D electron systems resides. These properties make the 2D electron systems interesting as a platform to realize THz devices. In this paper, I will review 3 approaches investigated in the past few years in my group toward THz devices. The first approach is the conventional high electron mobility transistor based on GaN toward THz amplifiers. The second approach is to employ the tunable intraband absorption in 2D electron systems to realize THz modulators, where I will use graphene as a model material system. The third approach is to exploit plasma wave in these 2D electron systems that can be coupled with a negative differential conductance element for THz amplifiers/sources/detectors.
2D numerical simulation of the MEP energy-transport model with a finite difference scheme
Romano, V. . E-mail: romano@dmi.unict.it
2007-02-10
A finite difference scheme of Scharfetter-Gummel type is used to simulate a consistent energy-transport model for electron transport in semiconductors devices, free of any fitting parameters, formulated on the basis of the maximum entropy principle. Simulations of silicon n{sup +}-n-n{sup +} diodes, 2D-MESFET and 2D-MOSFET and comparisons with the results obtained by a direct simulation of the Boltzmann transport equation and with other energy-transport models, known in the literature, show the validity of the model and the robustness of the numerical scheme.
Simulation of 2D Fields of Raindrop Size Distributions
NASA Astrophysics Data System (ADS)
Berne, A.; Schleiss, M.; Uijlenhoet, R.
2008-12-01
The raindrop size distribution (DSD hereafter) is of primary importance for quantitative applications of weather radar measurements. The radar reflectivity~Z (directly measured by radar) is related to the power backscattered by the ensemble of hydrometeors within the radar sampling volume. However, the rain rate~R (the flux of water to the surface) is the variable of interest for many applications (hydrology, weather forecasting, air traffic for example). Usually, radar reflectivity is converted into rain rate using a power law such as Z=aRb. The coefficients a and b of the Z-R relationship depend on the DSD. The variability of the DSD in space and time has to be taken into account to improve radar rain rate estimates. Therefore, the ability to generate a large number of 2D fields of DSD which are statistically homogeneous provides a very useful simulation framework that nicely complements experimental approaches based on DSD data, in order to investigate radar beam propagation through rain as well as radar retrieval techniques. The proposed approach is based on geostatistics for structural analysis and stochastic simulation. First, the DSD is assumed to follow a gamma distribution. Hence a 2D field of DSDs can be adequately described as a 2D field of a multivariate random function consisting of the three DSD parameters. Such fields are simulated by combining a Gaussian anamorphosis and a multivariate Gaussian random field simulation algorithm. Using the (cross-)variogram models fitted on data guaranties that the spatial structure of the simulated fields is consistent with the observed one. To assess its validity, the proposed method is applied to data collected during intense Mediterranean rainfall. As only time series are available, Taylor's hypothesis is assumed to convert time series in 1D range profile. Moreover, DSD fields are assumed to be isotropic so that the 1D structure can be used to simulate 2D fields. A large number of 2D fields of DSD parameters are
TMD 2D Materials: Defects, Passivation, Functionalization and Device Impact
NASA Astrophysics Data System (ADS)
Wallace, Robert
Transition metal dichalcogenides (TMDs) such as MoS2 have become popular in ``beyond CMOS'' device concepts and research due to their band structure in two-dimensional layers - viz. a significant band gap. Various device demonstrations have been reported utilizing exfoliated and synthesized single/few layer TMDs for possible electronic and photonic applications. The performance of such devices will also necessarily depend upon the TMD layer quality. The impact of defects and impurities on device transport characteristics is of interest, as well as methods to passivate and minimize their effects. The interaction of the TMDs with component materials, such as dielectrics and contacts, is also an important aspect. This talk will present our recent work using in-situ and ex-situ methods to understand the physics and chemistry of TMDs and their associated interfaces. This work was supported in part by the LEAST Center, one of the six SRC STARnet Centers, sponsored by MARCO and DARPA; the SWAN Center sponsored by the SRC NRI and NIST, and the NSF under Award ECCS-1407765.
Numerical simulation of rock cutting using 2D AUTODYN
NASA Astrophysics Data System (ADS)
Woldemichael, D. E.; Rani, A. M. Abdul; Lemma, T. A.; Altaf, K.
2015-12-01
In a drilling process for oil and gas exploration, understanding of the interaction between the cutting tool and the rock is important for optimization of the drilling process using polycrystalline diamond compact (PDC) cutters. In this study the finite element method in ANSYS AUTODYN-2D is used to simulate the dynamics of cutter rock interaction, rock failure, and fragmentation. A two-dimensional single PDC cutter and rock model were used to simulate the orthogonal cutting process and to investigate the effect of different parameters such as depth of cut, and back rake angle on two types of rocks (sandstone and limestone). In the simulation, the cutting tool was dragged against stationary rock at predetermined linear velocity and the depth of cut (1,2, and 3 mm) and the back rake angles(-10°, 0°, and +10°) were varied. The simulation result shows that the +10° back rake angle results in higher rate of penetration (ROP). Increasing depth of cut leads to higher ROP at the cost of higher cutting force.
Quantum Simulation with 2D Arrays of Trapped Ions
NASA Astrophysics Data System (ADS)
Richerme, Philip
2016-05-01
The computational difficulty of solving fully quantum many-body spin problems is a significant obstacle to understanding the behavior of strongly correlated quantum matter. This work proposes the design and construction of a 2D quantum spin simulator to investigate the physics of frustrated materials, highly entangled states, mechanisms potentially underpinning high-temperature superconductivity, and other topics inaccessible to current 1D systems. The effective quantum spins will be encoded within the well-isolated electronic levels of trapped ions, confined in a two-dimensional planar geometry, and made to interact using phonon-mediated optical dipole forces. The system will be scalable to 100+ quantum particles, far beyond the realm of classical intractability, while maintaining individual-ion control, long quantum coherence times, and site-resolved projective spin measurements. Once constructed, the two-dimensional quantum simulator will implement a broad range of spin models on a variety of reconfigurable lattices and characterize their behavior through measurements of spin-spin correlations and entanglement. This versatile tool will serve as an important experimental resource for exploring difficult quantum many-body problems in a regime where classical methods fail.
Device and methods for "gold standard" registration of clinical 3D and 2D cerebral angiograms
NASA Astrophysics Data System (ADS)
Madan, Hennadii; Likar, Boštjan; Pernuš, Franjo; Å piclin, Žiga
2015-03-01
Translation of any novel and existing 3D-2D image registration methods into clinical image-guidance systems is limited due to lack of their objective validation on clinical image datasets. The main reason is that, besides the calibration of the 2D imaging system, a reference or "gold standard" registration is very difficult to obtain on clinical image datasets. In the context of cerebral endovascular image-guided interventions (EIGIs), we present a calibration device in the form of a headband with integrated fiducial markers and, secondly, propose an automated pipeline comprising 3D and 2D image processing, analysis and annotation steps, the result of which is a retrospective calibration of the 2D imaging system and an optimal, i.e., "gold standard" registration of 3D and 2D images. The device and methods were used to create the "gold standard" on 15 datasets of 3D and 2D cerebral angiograms, whereas each dataset was acquired on a patient undergoing EIGI for either aneurysm coiling or embolization of arteriovenous malformation. The use of the device integrated seamlessly in the clinical workflow of EIGI. While the automated pipeline eliminated all manual input or interactive image processing, analysis or annotation. In this way, the time to obtain the "gold standard" was reduced from 30 to less than one minute and the "gold standard" of 3D-2D registration on all 15 datasets of cerebral angiograms was obtained with a sub-0.1 mm accuracy.
NASA Astrophysics Data System (ADS)
Bezzeccheri, E.; Colasanti, S.; Falco, A.; Liguori, R.; Rubino, A.; Lugli, P.
2016-05-01
Vertical Organic Transistors and Phototransistors have been proven to be promising technologies due to the advantages of reduced channel length and larger sensitive area with respect to planar devices. Nevertheless, a real improvement of their performance is subordinate to the quantitative description of their operation mechanisms. In this work, we present a comparative study on the modeling of vertical and planar Organic Phototransistor (OPT) structures. Computer-based simulations of the devices have been carried out with Synopsys Sentaurus TCAD in a 2D Drift-Diffusion framework. The photoactive semiconductor material has been modeled using the virtual semiconductor approach as the archetypal P3HT:PC61BM bulk heterojunction. It has been found that both simulated devices have comparable electrical and optical characteristics, accordingly to recent experimental reports on the subject.
Nano-scale electronic and optoelectronic devices based on 2D crystals
NASA Astrophysics Data System (ADS)
Zhu, Wenjuan
In the last few years, the research community has been rapidly growing interests in two-dimensional (2D) crystals and their applications. The properties of these 2D crystals are diverse -- ranging from semi-metal such as graphene, semiconductors such as MoS2, to insulator such as boron nitride. These 2D crystals have many unique properties as compared to their bulk counterparts due to their reduced dimensionality and symmetry. A key difference is the band structures, which lead to distinct electronic and photonic properties. The 2D nature of the material also plays an important role in defining their exceptional properties of mechanical strength, surface sensitivity, thermal conductivity, tunable band-gap and their interaction with light. These unique properties of 2D crystals open up a broad territory of applications in computing, communication, energy, and medicine. In this talk, I will present our work on understanding the electrical properties of graphene and MoS2, in particular current transport and band-gap engineering in graphene, interface between gate dielectrics and graphene, and gap states in MoS2. I will also present our work on the nano-scale electronic devices (RF and logic devices) and photonic devices (plasmonic devices and photo-detectors) based on these 2D crystals.
A 2D simulation model for urban flood management
NASA Astrophysics Data System (ADS)
Price, Roland; van der Wielen, Jonathan; Velickov, Slavco; Galvao, Diogo
2014-05-01
The European Floods Directive, which came into force on 26 November 2007, requires member states to assess all their water courses and coast lines for risk of flooding, to map flood extents and assets and humans at risk, and to take adequate and coordinated measures to reduce the flood risk in consultation with the public. Flood Risk Management Plans are to be in place by 2015. There are a number of reasons for the promotion of this Directive, not least because there has been much urban and other infrastructural development in flood plains, which puts many at risk of flooding along with vital societal assets. In addition there is growing awareness that the changing climate appears to be inducing more frequent extremes of rainfall with a consequent increases in the frequency of flooding. Thirdly, the growing urban populations in Europe, and especially in the developing countries, means that more people are being put at risk from a greater frequency of urban flooding in particular. There are urgent needs therefore to assess flood risk accurately and consistently, to reduce this risk where it is important to do so or where the benefit is greater than the damage cost, to improve flood forecasting and warning, to provide where necessary (and possible) flood insurance cover, and to involve all stakeholders in decision making affecting flood protection and flood risk management plans. Key data for assessing risk are water levels achieved or forecasted during a flood. Such levels should of course be monitored, but they also need to be predicted, whether for design or simulation. A 2D simulation model (PriceXD) solving the shallow water wave equations is presented specifically for determining flood risk, assessing flood defense schemes and generating flood forecasts and warnings. The simulation model is required to have a number of important properties: -Solve the full shallow water wave equations using a range of possible solutions; -Automatically adjust the time step and
2D and 3D Numerical Simulations of Flux Cancellation
NASA Technical Reports Server (NTRS)
Karpen, Judith T.; DeVore, C.; Antiochos, S. K.; Linton, M. G.
2009-01-01
Cancellation of magnetic flux in the solar photosphere and chromosphere has been linked observationally and theoretically to a broad range of solar activity, from filament channel formation to CME initiation. Because this phenomenon is typically measured at only a single layer in the atmosphere, in the radial (line of sight) component of the magnetic field, the actual processes behind this observational signature are ambiguous. It is clear that reconnection is involved in some way, but the location of the reconnection sites and associated connectivity changes remain uncertain in most cases. We are using numerical modeling to demystify flux cancellation, beginning with the simplest possible configuration: a subphotospheric Lundquist flux tube surrounded by a potential field, immersed in a gravitationally stratified atmosphere, spanning many orders of magnitude in plasma beta. In this system, cancellation is driven slowly by a 2-cell circulation pattern imposed in the convection zone, such that the tops of the cells are located around the beta=1 level (i.e., the photosphere) and the flows converge and form a downdraft at the polarity inversion line; note however that no flow is imposed along the neutral line. We will present the results of 2D and 3D MHD-AMR simulations of flux cancellation, in which the flux at the photosphere begins in either an unsheared or sheared state. In all cases, a low-lying flux rope is formed by reconnection at the polarity inversion line within a few thousand seconds. The flux rope remains stable and does not rise, however, in contrast to models which do not include the presence of significant mass loading.
2D radiation-magnetohydrodynamic simulations of SATURN imploding Z-pinches
Hammer, J.H.; Eddleman, J.L.; Springer, P.T.
1995-11-06
Z-pinch implosions driven by the SATURN device at Sandia National Laboratory are modeled with a 2D radiation magnetohydrodynamic (MHD) code, showing strong growth of magneto-Rayleigh Taylor (MRT) instability. Modeling of the linear and nonlinear development of MRT modes predicts growth of bubble-spike structures that increase the time span of stagnation and the resulting x-ray pulse width. Radiation is important in the pinch dynamics keeping the sheath relatively cool during the run-in and releasing most of the stagnation energy. The calculations give x-ray pulse widths and magnitudes in reasonable agreement with experiments, but predict a radiating region that is too dense and radially localized at stagnation. We also consider peaked initial density profiles with constant imploding sheath velocity that should reduce MRT instability and improve performance. 2D krypton simulations show an output x-ray power > 80 TW for the peaked profile.
Simulations of two-particle interactions with 2D quantum walks in time
Schreiber, A.; Laiho, K.; Silberhorn, C.; Rohde, P. P.; Štefaňak, M.; Potoček, V.; Hamilton, C.; Jex, I.
2014-12-04
We present the experimental implementation of a quantum walk on a two-dimensional lattice and show how to employ the optical system to simulate the quantum propagation of two interacting particles. Our quantum walk in time transfers the spatial spread of a quantum walk into the time domain, which guarantees a high stability and scalability of the setup. We present with our device quantum walks over 12 steps on a 2D lattice. By changing the properties of the driving quantum coin, we investigate different kinds of two-particle interactions and reveal their impact on the occurring quantum propagation.
A 2D simulation model for urban flood management
NASA Astrophysics Data System (ADS)
Price, Roland; van der Wielen, Jonathan; Velickov, Slavco; Galvao, Diogo
2014-05-01
The European Floods Directive, which came into force on 26 November 2007, requires member states to assess all their water courses and coast lines for risk of flooding, to map flood extents and assets and humans at risk, and to take adequate and coordinated measures to reduce the flood risk in consultation with the public. Flood Risk Management Plans are to be in place by 2015. There are a number of reasons for the promotion of this Directive, not least because there has been much urban and other infrastructural development in flood plains, which puts many at risk of flooding along with vital societal assets. In addition there is growing awareness that the changing climate appears to be inducing more frequent extremes of rainfall with a consequent increases in the frequency of flooding. Thirdly, the growing urban populations in Europe, and especially in the developing countries, means that more people are being put at risk from a greater frequency of urban flooding in particular. There are urgent needs therefore to assess flood risk accurately and consistently, to reduce this risk where it is important to do so or where the benefit is greater than the damage cost, to improve flood forecasting and warning, to provide where necessary (and possible) flood insurance cover, and to involve all stakeholders in decision making affecting flood protection and flood risk management plans. Key data for assessing risk are water levels achieved or forecasted during a flood. Such levels should of course be monitored, but they also need to be predicted, whether for design or simulation. A 2D simulation model (PriceXD) solving the shallow water wave equations is presented specifically for determining flood risk, assessing flood defense schemes and generating flood forecasts and warnings. The simulation model is required to have a number of important properties: -Solve the full shallow water wave equations using a range of possible solutions; -Automatically adjust the time step and
Nanohole-array-based device for 2D snapshot multispectral imaging
Najiminaini, Mohamadreza; Vasefi, Fartash; Kaminska, Bozena; Carson, Jeffrey J. L.
2013-01-01
We present a two-dimensional (2D) snapshot multispectral imager that utilizes the optical transmission characteristics of nanohole arrays (NHAs) in a gold film to resolve a mixture of input colors into multiple spectral bands. The multispectral device consists of blocks of NHAs, wherein each NHA has a unique periodicity that results in transmission resonances and minima in the visible and near-infrared regions. The multispectral device was illuminated over a wide spectral range, and the transmission was spectrally unmixed using a least-squares estimation algorithm. A NHA-based multispectral imaging system was built and tested in both reflection and transmission modes. The NHA-based multispectral imager was capable of extracting 2D multispectral images representative of four independent bands within the spectral range of 662 nm to 832 nm for a variety of targets. The multispectral device can potentially be integrated into a variety of imaging sensor systems. PMID:24005065
Simulation of Ultra-Small MOSFETs Using a 2-D Quantum-Corrected Drift-Diffusion Model
NASA Technical Reports Server (NTRS)
Biegal, Bryan A.; Rafferty, Connor S.; Yu, Zhiping; Ancona, Mario G.; Dutton, Robert W.; Saini, Subhash (Technical Monitor)
1998-01-01
The continued down-scaling of electronic devices, in particular the commercially dominant MOSFET, will force a fundamental change in the process of new electronics technology development in the next five to ten years. The cost of developing new technology generations is soaring along with the price of new fabrication facilities, even as competitive pressure intensifies to bring this new technology to market faster than ever before. To reduce cost and time to market, device simulation must become a more fundamental, indeed dominant, part of the technology development cycle. In order to produce these benefits, simulation accuracy must improve markedly. At the same time, device physics will become more complex, with the rapid increase in various small-geometry and quantum effects. This work describes both an approach to device simulator development and a physical model which advance the effort to meet the tremendous electronic device simulation challenge described above. The device simulation approach is to specify the physical model at a high level to a general-purpose (but highly efficient) partial differential equation solver (in this case PROPHET, developed by Lucent Technologies), which then simulates the model in 1-D, 2-D, or 3-D for a specified device and test regime. This approach allows for the rapid investigation of a wide range of device models and effects, which is certainly essential for device simulation to catch up with, and then stay ahead of, electronic device technology of the present and future. The physical device model used in this work is the density-gradient (DG) quantum correction to the drift-diffusion model [Ancona, Phys. Rev. B 35(5), 7959 (1987)]. This model adds tunneling and quantum smoothing of carrier density profiles to the drift-diffusion model. We used the DG model in 1-D and 2-D (for the first time) to simulate both bipolar and unipolar devices. Simulations of heavily-doped, short-base diodes indicated that the DG quantum
Simulating nanoscale semiconductor devices.
Salinger, Andrew Gerhard; Zhao, P.; Woolard, D. L.; Kelley, C. Tim; Lasater, Matthew S.
2005-03-01
The next generation of electronic devices will be developed at the nanoscale and molecular level, where quantum mechanical effects are observed. These effects must be accounted for in the design process for such small devices. One prototypical nanoscale semiconductor device under investigation is a resonant tunneling diode (RTD). Scientists are hopeful the quantum tunneling effects present in an RTD can be exploited to induce and sustain THz frequency current oscillations. To simulate the electron transport within the RTD, the Wigner-Poisson equations are used. These equations describe the time evolution of the electrons distribution within the device. In this paper, this model and a parameter study using this model will be presented. The parameter study involves calculating the steady-state current output from the RTD as a function of an applied voltage drop across the RTD and also calculating the stability of that solution. To implement the parameter study, the computational model was connected to LOCA (Library of Continuation Algorithms), a part of Sandia National Laboratories parallel solver project, Trilinos. Numerical results will be presented.
A microfluidic device for 2D to 3D and 3D to 3D cell navigation
NASA Astrophysics Data System (ADS)
Shamloo, Amir; Amirifar, Leyla
2016-01-01
Microfluidic devices have received wide attention and shown great potential in the field of tissue engineering and regenerative medicine. Investigating cell response to various stimulations is much more accurate and comprehensive with the aid of microfluidic devices. In this study, we introduced a microfluidic device by which the matrix density as a mechanical property and the concentration profile of a biochemical factor as a chemical property could be altered. Our microfluidic device has a cell tank and a cell culture chamber to mimic both 2D to 3D and 3D to 3D migration of three types of cells. Fluid shear stress is negligible on the cells and a stable concentration gradient can be obtained by diffusion. The device was designed by a numerical simulation so that the uniformity of the concentration gradients throughout the cell culture chamber was obtained. Adult neural cells were cultured within this device and they showed different branching and axonal navigation phenotypes within varying nerve growth factor (NGF) concentration profiles. Neural stem cells were also cultured within varying collagen matrix densities while exposed to NGF concentrations and they experienced 3D to 3D collective migration. By generating vascular endothelial growth factor concentration gradients, adult human dermal microvascular endothelial cells also migrated in a 2D to 3D manner and formed a stable lumen within a specific collagen matrix density. It was observed that a minimum absolute concentration and concentration gradient were required to stimulate migration of all types of the cells. This device has the advantage of changing multiple parameters simultaneously and is expected to have wide applicability in cell studies.
Reactor2D: A tool for simulation of shock deformation
NASA Astrophysics Data System (ADS)
Kraus, Eugeny I.; Shabalin, Ivan I.
2016-10-01
The basic steps for creating a numerical tool to simulate the deformation and failure processes of complex technical objects (CTO) are presented. Calculations of shock loading of CTO both at low and high speeds, showing the efficiency of the numerical tools created are carried out.
COYOTE: A computer program for 2-D reactive flow simulations
Cloutman, L.D.
1990-04-01
We describe the numerical algorithm used in the COYOTE two- dimensional, transient, Eulerian hydrodynamics program for reactive flows. The program has a variety of options that provide capabilities for a wide range of applications, and it is designed to be robust and relatively easy to use while maintaining adequate accuracy and efficiency to solve realistic problems. It is based on the ICE method, and it includes a general species and chemical reaction network for simulating reactive flows. It also includes swirl, turbulence transport models, and a nonuniform mesh capability. We describe several applications of the program. 33 refs., 4 figs.
Simulation of subgrid orographic precipitation with an embedded 2-D cloud-resolving model
NASA Astrophysics Data System (ADS)
Jung, Joon-Hee; Arakawa, Akio
2016-03-01
By explicitly resolving cloud-scale processes with embedded two-dimensional (2-D) cloud-resolving models (CRMs), superparameterized global atmospheric models have successfully simulated various atmospheric events over a wide range of time scales. Up to now, however, such models have not included the effects of topography on the CRM grid scale. We have used both 3-D and 2-D CRMs to simulate the effects of topography with prescribed "large-scale" winds. The 3-D CRM is used as a benchmark. The results show that the mean precipitation can be simulated reasonably well by using a 2-D representation of topography as long as the statistics of the topography such as the mean and standard deviation are closely represented. It is also shown that the use of a set of two perpendicular 2-D grids can significantly reduce the error due to a 2-D representation of topography.
Simulations of Quantum Spin Models on 2D Frustrated Lattices
NASA Astrophysics Data System (ADS)
Melko, Roger
2006-03-01
Algorithmic advances in quantum Monte Carlo techniques have opened up the possibility of studying models in the general class of the S=1/2 XXZ model (equivalent to hard-core bosons) on frustrated lattices. With an antiferromagnetic diagonal interaction (Jz), these models can be solved exactly with QMC, albeit with some effort required to retain ergodicity in the near-degenerate manifold of states that exists for large Jz. The application of the quantum (ferromagnetic off-diagonal) interaction to this classically degenerate manifold produces a variety of intriguing physics, including an order-by-disorder supersolid phase, novel insulating states, and possible exotic quantum critical phenomena. We discuss numerical results for the triangular and kagome lattices with nearest and next-nearest neighbor exchange interactions, and focus on the relevance of the simulations to related areas of physics, such as experiments of cold trapped atomic gasses and the recent theory of deconfined quantum criticality.
A droplet-to-digital (D2D) microfluidic device for single cell assays.
Shih, Steve C C; Gach, Philip C; Sustarich, Jess; Simmons, Blake A; Adams, Paul D; Singh, Seema; Singh, Anup K
2015-01-01
We have developed a new hybrid droplet-to-digital microfluidic platform (D2D) that integrates droplet-in-channel microfluidics with digital microfluidics (DMF) for performing multi-step assays. This D2D platform combines the strengths of the two formats-droplets-in-channel for facile generation of droplets containing single cells, and DMF for on-demand manipulation of droplets including control of different droplet volumes (pL-μL), creation of a dilution series of ionic liquid (IL), and parallel single cell culturing and analysis for IL toxicity screening. This D2D device also allows for automated analysis that includes a feedback-controlled system for merging and splitting of droplets to add reagents, an integrated Peltier element for parallel cell culture at optimum temperature, and an impedance sensing mechanism to control the flow rate for droplet generation and preventing droplet evaporation. Droplet-in-channel is well-suited for encapsulation of single cells as it allows the careful manipulation of flow rates of aqueous phase containing cells and oil to optimize encapsulation. Once single cell containing droplets are generated, they are transferred to a DMF chip via a capillary where they are merged with droplets containing IL and cultured at 30 °C. The DMF chip, in addition to permitting cell culture and reagent (ionic liquid/salt) addition, also allows recovery of individual droplets for off-chip analysis such as further culturing and measurement of ethanol production. The D2D chip was used to evaluate the effect of IL/salt type (four types: NaOAc, NaCl, [C2mim] [OAc], [C2mim] [Cl]) and concentration (four concentrations: 0, 37.5, 75, 150 mM) on the growth kinetics and ethanol production of yeast and as expected, increasing IL concentration led to lower biomass and ethanol production. Specifically, [C2mim] [OAc] had inhibitory effects on yeast growth at concentrations 75 and 150 mM and significantly reduced their ethanol production compared to cells grown
Distributed and coupled 2D electro-thermal model of power semiconductor devices
NASA Astrophysics Data System (ADS)
Belkacem, Ghania; Lefebvre, Stéphane; Joubert, Pierre-Yves; Bouarroudj-Berkani, Mounira; Labrousse, Denis; Rostaing, Gilles
2014-05-01
The development of power electronics in the field of transportations (automotive, aeronautics) requires the use of power semiconductor devices providing protection and diagnostic functions. In the case of series protections power semiconductor devices which provide protection may operate in shortcircuit and act as a current limiting device. This mode of operations is very constraining due to the large dissipation of power. In these particular conditions of operation, electro-thermal models of power semiconductor devices are of key importance in order to optimize their thermal design and increase their reliability. The development of such an electro-thermal model for power MOSFET transistors based on the coupling between two computation softwares (Matlab and Cast3M) is described in this paper. The 2D electro-thermal model is able to predict (i) the temperature distribution on chip surface well as in the volume under short-circuit operations, (ii) the effect of the temperature on the distribution of the current flowing within the die and (iii) the effects of the ageing of the metallization layer on the current density and the temperature. In this paper, the electrical and thermal models are described as well as the implemented coupling scheme.
2-D simulation of a waveguide free electron laser having a helical undulator
Kim, S.K.; Lee, B.C.; Jeong, Y.U.
1995-12-31
We have developed a 2-D simulation code for the calculation of output power from an FEL oscillator having a helical undulator and a cylindrical waveguide. In the simulation, the current and the energy of the electron beam is 2 A and 400 keV, respectively. The parameters of the permanent-magnet helical undulator are : period = 32 mm, number of periods = 20, magnetic field = 1.3 kG. The gain per pass is 10 and the output power is calculated to be higher than 10 kW The results of the 2-D simulation are compared with those of 1-D simulation.
Silicon nanoscale 2D donor devices fabricated by UHV-STM lithography
NASA Astrophysics Data System (ADS)
Kline, J. S.; Shen, T.-C.; Yang, C.; Liu, Y.
2005-03-01
We developed a scheme to fabricate nanoscale electronic devices by patterning 2D shallow donors into single crystal silicon. The goal of this approach is to seamlessly integrate nano- and microelectronics. In this approach, we pattern the devices on H terminated Si(100)-2x1 surfaces via UHV-STM. Phosphine molecules selectively adsorb onto the patterned areas to define conduction pathways. Low temperature Si MBE is used to encapsulate the dopants in the Si lattice. Two-terminal electrical connection to the outside-world is provided by a template structure formed by conventional microfabrication. A third terminal used for gate modulation of the device is formed by silicon nitride jet vapor deposition and metallization. Low temperature electrical characterization of conducting wires show significant departure from Ohmic conduction for width < 50nm. Electro and magnetotransport properties will be discussed. Tunnel junction and single electron transistor fabrication are currently underway. The low charged-defect density provided by complete encapsulation could allow the fabrication of a solid state quantum computer.
Development of an ab-initio calculation method for 2D layered materials-based optoelectronic devices
NASA Astrophysics Data System (ADS)
Kim, Han Seul; Kim, Yong-Hoon
We report on the development of a novel first-principles method for the calculation of non-equilibrium nanoscale device operation process. Based on region-dependent Δ self-consistent field method beyond the standard density functional theory (DFT), we will introduce a novel method to describe non-equilibrium situations such as external bias and simultaneous optical excitations. In particular, we will discuss the limitation of conventional method and advantage of our scheme in describing 2D layered materials-based devices operations. Then, we investigate atomistic mechanism of optoelectronic effects from 2D layered materials-based devices and suggest the optimal material and architecture for such devices.
2D numerical simulation of passive autocatalytic recombiner for hydrogen mitigation
NASA Astrophysics Data System (ADS)
Gera, B.; Sharma, P. K.; Singh, R. K.
2012-04-01
Resolving hydrogen related safety issues, pertaining to nuclear reactor safety has been an important area of research world over for the past decade. The studies on hydrogen transport behavior and development of hydrogen mitigation systems are still being pursued actively in various research labs, including Bhabha Atomic Research Centre (BARC), in India. The passive autocatalytic recombiner (PAR) is one of such hydrogen mitigating device consisting of catalyst surfaces arranged in an open-ended enclosure. In the plate type recombiner design sheets made of stainless steel and coated with platinum catalyst material are arranged in parallel inside a flow channel. The catalyst elements are exposed to a constant flow of a mixture of air, hydrogen and steam, a catalytic reaction occurs spontaneously at the catalyst surfaces and the heat of reaction produces natural convection flow through the enclosure. Numerical simulation and experiments are required for an in-depth knowledge of such plate type PAR. Specific finite volume based in-house 2D computational fluid dynamics (CFD) code has been developed to model and analyse the working of these recombiners and has been used to simulate one literature quoted experiment. The validation results were in good agreement against literature quoted German REKO experiments. Parametric study has been performed for particular recombiner geometry for various inlet conditions. Salient features of the simplified CFD model developed at BARC and results of the present model calculations are presented in this paper.
Linking 3D and 2D binding kinetics of membrane proteins by multiscale simulations
Xie, Zhong-Ru; Chen, Jiawen; Wu, Yinghao
2014-01-01
Membrane proteins are among the most functionally important proteins in cells. Unlike soluble proteins, they only possess two translational degrees of freedom on cell surfaces, and experience significant constraints on their rotations. As a result, it is currently challenging to characterize the in situ binding of membrane proteins. Using the membrane receptors CD2 and CD58 as a testing system, we developed a multiscale simulation framework to study the differences of protein binding kinetics between 3D and 2D environments. The association and dissociation processes were implemented by a coarse-grained Monte-Carlo algorithm, while the dynamic properties of proteins diffusing on lipid bilayer were captured from all-atom molecular dynamic simulations. Our simulations show that molecular diffusion, linker flexibility and membrane fluctuations are important factors in adjusting binding kinetics. Moreover, by calibrating simulation parameters to the measurements of 3D binding, we derived the 2D binding constant which is quantitatively consistent with the experimental data, indicating that the method is able to capture the difference between 3D and 2D binding environments. Finally, we found that the 2D dissociation between CD2 and CD58 is about 100-fold slower than the 3D dissociation. In summary, our simulation framework offered a generic approach to study binding mechanisms of membrane proteins. PMID:25271078
The simulation of 3D microcalcification clusters in 2D digital mammography and breast tomosynthesis
Shaheen, Eman; Van Ongeval, Chantal; Zanca, Federica; Cockmartin, Lesley; Marshall, Nicholas; Jacobs, Jurgen; Young, Kenneth C.; Dance, David R.; Bosmans, Hilde
2011-12-15
Purpose: This work proposes a new method of building 3D models of microcalcification clusters and describes the validation of their realistic appearance when simulated into 2D digital mammograms and into breast tomosynthesis images. Methods: A micro-CT unit was used to scan 23 breast biopsy specimens of microcalcification clusters with malignant and benign characteristics and their 3D reconstructed datasets were segmented to obtain 3D models of microcalcification clusters. These models were then adjusted for the x-ray spectrum used and for the system resolution and simulated into 2D projection images to obtain mammograms after image processing and into tomographic sequences of projection images, which were then reconstructed to form 3D tomosynthesis datasets. Six radiologists were asked to distinguish between 40 real and 40 simulated clusters of microcalcifications in two separate studies on 2D mammography and tomosynthesis datasets. Receiver operating characteristic (ROC) analysis was used to test the ability of each observer to distinguish between simulated and real microcalcification clusters. The kappa statistic was applied to assess how often the individual simulated and real microcalcification clusters had received similar scores (''agreement'') on their realistic appearance in both modalities. This analysis was performed for all readers and for the real and the simulated group of microcalcification clusters separately. ''Poor'' agreement would reflect radiologists' confusion between simulated and real clusters, i.e., lesions not systematically evaluated in both modalities as either simulated or real, and would therefore be interpreted as a success of the present models. Results: The area under the ROC curve, averaged over the observers, was 0.55 (95% confidence interval [0.44, 0.66]) for the 2D study, and 0.46 (95% confidence interval [0.29, 0.64]) for the tomosynthesis study, indicating no statistically significant difference between real and simulated
An efficient simulation method of a cyclotron sector-focusing magnet using 2D Poisson code
NASA Astrophysics Data System (ADS)
Gad Elmowla, Khaled Mohamed M.; Chai, Jong Seo; Yeon, Yeong H.; Kim, Sangbum; Ghergherehchi, Mitra
2016-10-01
In this paper we discuss design simulations of a spiral magnet using 2D Poisson code. The Independent Layers Method (ILM) is a new technique that was developed to enable the use of two-dimensional simulation code to calculate a non-symmetric 3-dimensional magnetic field. In ILM, the magnet pole is divided into successive independent layers, and the hill and valley shape around the azimuthal direction is implemented using a reference magnet. The normalization of the magnetic field in the reference magnet produces a profile that can be multiplied by the maximum magnetic field in the hill magnet, which is a dipole magnet made of the hills at the same radius. Both magnets are then calculated using the 2D Poisson SUPERFISH code. Then a fully three-dimensional magnetic field is produced using TOSCA for the original spiral magnet, and the comparison of the 2D and 3D results shows a good agreement between both.
Low frequency 2D Raman-THz spectroscopy of ionic solution: A simulation study
NASA Astrophysics Data System (ADS)
Pan, Zhijun; Wu, Tianmin; Jin, Tan; Liu, Yong; Nagata, Yuki; Zhang, Ruiting; Zhuang, Wei
2015-06-01
The 2D Raman-THz spectrum of the MgCl2 solution was simulated using the molecular dynamics simulation and the stability matrix method and compared with that of the pure water. The 2D Raman-THz signal provides more information on the ion effects on the collective water motion than the conventional 1D signal. The presence of MgCl2 suppresses the cross peak of water between the hydrogen bond bending and the other intermolecular vibrational mode, which clearly illustrates that the water hydrogen bending motion is affected by the confining effect of the ions. Our theoretical work thus demonstrates that the 2D Raman-THz technique can become a valuable nonlinear vibrational probe for the molecular dynamics in the ionic solutions.
Numerical simulation of ( T 2, T 1) 2D NMR and fluid responses
NASA Astrophysics Data System (ADS)
Tan, Mao-Jin; Zou, You-Long; Zhang, Jin-Yan; Zhao, Xin
2012-12-01
One-dimensional nuclear magnetic resonance (1D NMR) logging technology is limited for fluid typing, while two-dimensional nuclear magnetic resonance (2D NMR) logging can provide more parameters including longitudinal relaxation time ( T 1) and transverse relaxation time ( T 2) relative to fluid types in porous media. Based on the 2D NMR relaxation mechanism in a gradient magnetic field, echo train simulation and 2D NMR inversion are discussed in detail. For 2D NMR inversion, a hybrid inversion method is proposed based on the damping least squares method (LSQR) and an improved truncated singular value decomposition (TSVD) algorithm. A series of spin echoes are first simulated with multiple waiting times ( T W s) in a gradient magnetic field for given fluid models and these synthesized echo trains are inverted by the hybrid method. The inversion results are consistent with given models. Moreover, the numerical simulation of various fluid models such as the gas-water, light oil-water, and vicious oil-water models were carried out with different echo spacings ( T E s) and T W s by this hybrid method. Finally, the influences of different signal-to-noise ratios (SNRs) on inversion results in various fluid models are studied. The numerical simulations show that the hybrid method and optimized observation parameters are applicable to fluid typing of gas-water and oil-water models.
NASA Astrophysics Data System (ADS)
Sirait, S. H.; Edison, R. E.; Baidillah, M. R.; Taruno, W. P.; Haryanto, F.
2016-08-01
The aim of this study is to simulate the potential distribution of 2D brain geometry based on two electrodes ECVT. ECVT (electrical capacitance tomography) is a tomography modality which produces dielectric distribution image of a subject from several capacitance electrodes measurements. This study begins by producing the geometry of 2D brain based on MRI image and then setting the boundary conditions on the boundaries of the geometry. The values of boundary conditions follow the potential values used in two electrodes brain ECVT, and for this reason the first boundary is set to 20 volt and 2.5 MHz signal and another boundary is set to ground. Poisson equation is implemented as the governing equation in the 2D brain geometry and finite element method is used to solve the equation. Simulated Hodgkin-Huxley action potential is applied as disturbance potential in the geometry. We divide this study into two which comprises simulation without disturbance potential and simulation with disturbance potential. From this study, each of time dependent potential distributions from non-disturbance and disturbance potential of the 2D brain geometry has been generated.
2-D MHD numerical simulations of EML plasma armatures with ablation
NASA Astrophysics Data System (ADS)
Boynton, G. C.; Huerta, M. A.; Thio, Y. C.
1993-01-01
We use a 2-D) resistive MHD code to simulate an EML plasma armature. The energy equation includes Ohmic heating, radiation heat transport and the ideal gas equation of state, allowing for variable ionization using the Saha equations. We calculate rail ablation taking into account the flow of heat into the interior of the rails. Our simulations show the development of internal convective flows and secondary arcs. We use an explicit Flux Corrected Transport algorithm to advance all quantities in time.
The simulation of 3D mass models in 2D digital mammography and breast tomosynthesis
Shaheen, Eman De Keyzer, Frederik; Bosmans, Hilde; Ongeval, Chantal Van; Dance, David R.; Young, Kenneth C.
2014-08-15
Purpose: This work proposes a new method of building 3D breast mass models with different morphological shapes and describes the validation of the realism of their appearance after simulation into 2D digital mammograms and breast tomosynthesis images. Methods: Twenty-five contrast enhanced MRI breast lesions were collected and each mass was manually segmented in the three orthogonal views: sagittal, coronal, and transversal. The segmented models were combined, resampled to have isotropic voxel sizes, triangularly meshed, and scaled to different sizes. These masses were referred to as nonspiculated masses and were then used as nuclei onto which spicules were grown with an iterative branching algorithm forming a total of 30 spiculated masses. These 55 mass models were projected into 2D projection images to obtain mammograms after image processing and into tomographic sequences of projection images, which were then reconstructed to form 3D tomosynthesis datasets. The realism of the appearance of these mass models was assessed by five radiologists via receiver operating characteristic (ROC) analysis when compared to 54 real masses. All lesions were also given a breast imaging reporting and data system (BIRADS) score. The data sets of 2D mammography and tomosynthesis were read separately. The Kendall's coefficient of concordance was used for the interrater observer agreement assessment for the BIRADS scores per modality. Further paired analysis, using the Wilcoxon signed rank test, of the BIRADS assessment between 2D and tomosynthesis was separately performed for the real masses and for the simulated masses. Results: The area under the ROC curves, averaged over all observers, was 0.54 (95% confidence interval [0.50, 0.66]) for the 2D study, and 0.67 (95% confidence interval [0.55, 0.79]) for the tomosynthesis study. According to the BIRADS scores, the nonspiculated and the spiculated masses varied in their degrees of malignancy from normal (BIRADS 1) to highly
2D-3D hybrid stabilized finite element method for tsunami runup simulations
NASA Astrophysics Data System (ADS)
Takase, S.; Moriguchi, S.; Terada, K.; Kato, J.; Kyoya, T.; Kashiyama, K.; Kotani, T.
2016-09-01
This paper presents a two-dimensional (2D)-three-dimensional (3D) hybrid stabilized finite element method that enables us to predict a propagation process of tsunami generated in a hypocentral region, which ranges from offshore propagation to runup to urban areas, with high accuracy and relatively low computational costs. To be more specific, the 2D shallow water equation is employed to simulate the propagation of offshore waves, while the 3D Navier-Stokes equation is employed for the runup in urban areas. The stabilized finite element method is utilized for numerical simulations for both of the 2D and 3D domains that are independently discretized with unstructured meshes. The multi-point constraint and transmission methods are applied to satisfy the continuity of flow velocities and pressures at the interface between the resulting 2D and 3D meshes, since neither their spatial dimensions nor node arrangements are consistent. Numerical examples are presented to demonstrate the performance of the proposed hybrid method to simulate tsunami behavior, including offshore propagation and runup to urban areas, with substantially lower computation costs in comparison with full 3D computations.
2D and 3D simulations of damage in 5-grain copper gas gun samples
Tonks, Davis L; Cerreta, Ellen K; Dennis - Koller, Darcie; Escobedo - Diaz, Juan P; Trujillo, Carl P; Luo, Shengian; Bingert, John F
2010-12-16
2D and 3D Hydrocode simulations were done of a gas gun damage experiment involving a 5 grain sample with a polycrystalline flyer with a velocity of about 140 m/s. The simulations were done with the Flag hydrocode and involved explicit meshing of the 5 grains with a single crystal plasticity model and a pressure based damage model. The calculated fields were compared with two cross sections from the recovered sample. The sample exhibited grain boundary cracks at high angle and tilt grain boundaries in the sample but not at a sigma 3 twin boundary. However, the calculation showed large gradients in stress and strain at only the twin boundary, contrary to expectation. This indicates that the twin boundary is quite strong to resist the predicted high gradients and that the calculation needs the addition of a grain boundary fracture mode. The 2D and 3D simulations were compared.
2D MHD test-particle simulations in modeling geomagnetic storms
NASA Astrophysics Data System (ADS)
Li, Z.; Elkington, S. R.; Hudson, M. K.; Murphy, J. J.; Schmitt, P.; Wiltberger, M. J.
2012-12-01
The effects of magnetic storms on the evolution of the electron radiation belts are studied using MHD test-particle simulations. The 2D guiding center code developed by Elkington et al. (2002) has been used to simulate particle motion in the Solar Magnetic equatorial plane in the MHD fields calculated from the Lyon-Fedder-Mobarry global MHD code. However, our study shows that the B-minimum plane is well off the SM equatorial plane during solstice events. Since 3D test-particle simulation is computationally expensive, we improve the 2D model by pushing particles in the B-minimum surface instead of the SM equatorial plane. Paraview software is used to visualize the LFM data file and to find the B-minimum surface. Magnetic and electric fields on B-minimum surface are projected to the equatorial plane for particle pushing.
FRANC2D: A two-dimensional crack propagation simulator. Version 2.7: User's guide
NASA Technical Reports Server (NTRS)
Wawrzynek, Paul; Ingraffea, Anthony
1994-01-01
FRANC 2D (FRacture ANalysis Code, 2 Dimensions) is a menu driven, interactive finite element computer code that performs fracture mechanics analyses of 2-D structures. The code has an automatic mesh generator for triangular and quadrilateral elements. FRANC2D calculates the stress intensity factor using linear elastic fracture mechanics and evaluates crack extension using several methods that may be selected by the user. The code features a mesh refinement and adaptive mesh generation capability that is automatically developed according to the predicted crack extension direction and length. The code also has unique features that permit the analysis of layered structure with load transfer through simulated mechanical fasteners or bonded joints. The code was written for UNIX workstations with X-windows graphics and may be executed on the following computers: DEC DecStation 3000 and 5000 series, IBM RS/6000 series, Hewlitt-Packard 9000/700 series, SUN Sparc stations, and most Silicon Graphics models.
Simulation of Cardiac Arrhythmias Using a 2D Heterogeneous Whole Heart Model.
Balakrishnan, Minimol; Chakravarthy, V Srinivasa; Guhathakurta, Soma
2015-01-01
Simulation studies of cardiac arrhythmias at the whole heart level with electrocardiogram (ECG) gives an understanding of how the underlying cell and tissue level changes manifest as rhythm disturbances in the ECG. We present a 2D whole heart model (WHM2D) which can accommodate variations at the cellular level and can generate the ECG waveform. It is shown that, by varying cellular-level parameters like the gap junction conductance (GJC), excitability, action potential duration (APD) and frequency of oscillations of the auto-rhythmic cell in WHM2D a large variety of cardiac arrhythmias can be generated including sinus tachycardia, sinus bradycardia, sinus arrhythmia, sinus pause, junctional rhythm, Wolf Parkinson White syndrome and all types of AV conduction blocks. WHM2D includes key components of the electrical conduction system of the heart like the SA (Sino atrial) node cells, fast conducting intranodal pathways, slow conducting atriovenctricular (AV) node, bundle of His cells, Purkinje network, atrial, and ventricular myocardial cells. SA nodal cells, AV nodal cells, bundle of His cells, and Purkinje cells are represented by the Fitzhugh-Nagumo (FN) model which is a reduced model of the Hodgkin-Huxley neuron model. The atrial and ventricular myocardial cells are modeled by the Aliev-Panfilov (AP) two-variable model proposed for cardiac excitation. WHM2D can prove to be a valuable clinical tool for understanding cardiac arrhythmias.
Simulation of Cardiac Arrhythmias Using a 2D Heterogeneous Whole Heart Model
Balakrishnan, Minimol; Chakravarthy, V. Srinivasa; Guhathakurta, Soma
2015-01-01
Simulation studies of cardiac arrhythmias at the whole heart level with electrocardiogram (ECG) gives an understanding of how the underlying cell and tissue level changes manifest as rhythm disturbances in the ECG. We present a 2D whole heart model (WHM2D) which can accommodate variations at the cellular level and can generate the ECG waveform. It is shown that, by varying cellular-level parameters like the gap junction conductance (GJC), excitability, action potential duration (APD) and frequency of oscillations of the auto-rhythmic cell in WHM2D a large variety of cardiac arrhythmias can be generated including sinus tachycardia, sinus bradycardia, sinus arrhythmia, sinus pause, junctional rhythm, Wolf Parkinson White syndrome and all types of AV conduction blocks. WHM2D includes key components of the electrical conduction system of the heart like the SA (Sino atrial) node cells, fast conducting intranodal pathways, slow conducting atriovenctricular (AV) node, bundle of His cells, Purkinje network, atrial, and ventricular myocardial cells. SA nodal cells, AV nodal cells, bundle of His cells, and Purkinje cells are represented by the Fitzhugh-Nagumo (FN) model which is a reduced model of the Hodgkin-Huxley neuron model. The atrial and ventricular myocardial cells are modeled by the Aliev-Panfilov (AP) two-variable model proposed for cardiac excitation. WHM2D can prove to be a valuable clinical tool for understanding cardiac arrhythmias. PMID:26733873
NASA Technical Reports Server (NTRS)
Tang, H. T.; Hofmann, R.; Yee, G.; Vaughan, D. K.
1980-01-01
Transient, nonlinear soil-structure interaction simulations of an Electric Power Research Institute, SIMQUAKE experiment were performed using the large strain, time domain STEALTH 2D code and a cyclic, kinematically hardening cap soil model. Results from the STEALTH simulations were compared to identical simulations performed with the TRANAL code and indicate relatively good agreement between all the STEALTH and TRANAL calculations. The differences that are seen can probably be attributed to: (1) large (STEALTH) vs. small (TRANAL) strain formulation and/or (2) grid discretization differences.
Momentum Transport: 2D and 3D Cloud Resolving Model Simulations
NASA Technical Reports Server (NTRS)
Tao, Wei-Kuo
2001-01-01
The major objective of this study is to investigate the momentum budgets associated with several convective systems that developed during the TOGA COARE IOP (west Pacific warm pool region) and GATE (east Atlantic region). The tool for this study is the improved Goddard Cumulas Ensemble (GCE) model which includes a 3-class ice-phase microphysical scheme, explicit cloud radiative interactive processes and air-sea interactive surface processes. The model domain contains 256 x 256 grid points (with 2 km resolution) in the horizontal and 38 grid points (to a depth of 22 km) in the vertical. The 2D domain has 1024 grid points. The simulations were performed over a 7-day time period (December 19-26, 1992, for TOGA COARE and September 1-7, 1994 for GATE). Cyclic literal boundary conditions are required for this type of long-term integration. Two well organized squall systems (TOGA, COARE February 22, 1993, and GATE September 12, 1994) were also simulated using the 3D GCE model. Only 9 h simulations were required to cover the life time of the squall systems. the lateral boundary conditions were open for these two squall systems simulations. the following will be examined: (1) the momentum budgets in the convective and stratiform regions, (2) the relationship between momentum transport and cloud organization (i.e., well organized squall lines versus less organized convective), (3) the differences and similarities in momentum transport between 2D and 3D simulated convective systems, and (4) the differences and similarities in momentum budgets between cloud systems simulated with open and cyclic lateral boundary conditions. Preliminary results indicate that there are only small differences between 2D and 3D simulated momentum budgets. Major differences occur, however, between momentum budgets associated with squall systems simulated using different lateral boundary conditions.
Fast 2-D soft X-ray imaging device based on micro pattern gas detector
NASA Astrophysics Data System (ADS)
Pacella, D.; Bellazzini, R.; Brez, A.; Pizzicaroli, G.
2003-09-01
An innovative fast system for X-ray imaging has been developed at ENEA Frascati (Italy) to be used as diagnostic of magnetic plasmas for thermonuclear fusion. It is based on a pinhole camera coupled to a Micro Pattern Gas Detector (MPGD) having a Gas Electron Multiplier (GEM) as amplifying stage. This detector (2.5 cm × 2.5 cm active area) is equipped with a 2-D read-out printed circuit board with 144 pixels (12 × 12), with an electronic channel for each pixel (charge conversion, shaping, discrimination and counting). Working in photon counting mode, in proportional regime, it is able to get X-ray images of the plasma in a selectable X-ray energy range, at very high photon fluxes (106 ph s-̊1mm-2 all over the detector) and high framing rate (up to 100 kHz). It has very high dynamic range, high signal to noise ratio (statistical) and large flexibility in the optical configurations (magnification and views on the plasma). The system has been tested successfully on the Frascati Tokamak Upgrade (FTU), having central electron temperature of a few keV and density of 1020 m-3, during the summer 2001, with a one-dimensional perpendicular view of the plasma. In collaboration with ENEA, the Johns Hopkins University (JHU) and Princeton Plasma Physics (PPPL), this system has been set up and calibrated in the X-ray energy range 2-8 keV and it has been installed, with a two-dimensional tangential view, on the spherical tokamak NSTX at Princeton. Time resolved X-ray images of the NSTX plasma core have been obtained. Fast acquisitions, performed up to 50 kHz of framing rate, allow the study of the plasma evolution and its magneto-hydrodynamic instabilities, while with a slower sampling (a few kHz) the curvature of the magnetic surfaces can be measured. All these results reveal the good imaging properties of this device at high time resolution, despite of the low number of pixels, and the effectiveness of the fine controlled energy discrimination.
2D Quantum Simulation of MOSFET Using the Non Equilibrium Green's Function Method
NASA Technical Reports Server (NTRS)
Svizhenko, Alexel; Anantram, M. P.; Govindan, T. R.; Yan, Jerry (Technical Monitor)
2000-01-01
The objectives this viewgraph presentation summarizes include: (1) the development of a quantum mechanical simulator for ultra short channel MOSFET simulation, including theory, physical approximations, and computer code; (2) explore physics that is not accessible by semiclassical methods; (3) benchmarking of semiclassical and classical methods; and (4) study other two-dimensional devices and molecular structure, from discretized Hamiltonian to tight-binding Hamiltonian.
Penetration of tungsten-alloy rods into composite ceramic targets: Experiments and 2-D simulations
Rosenberg, Z.; Dekel, E.; Hohler, V.; Stilp, A. J.; Weber, K.
1998-07-10
A series of terminal ballistics experiments, with scaled tungsten-alloy penetrators, was performed on composite targets consisting of ceramic tiles glued to thick steel backing plates. Tiles of silicon-carbide, aluminum nitride, titanium-dibroide and boron-carbide were 20-80 mm thick, and impact velocity was 1.7 km/s. 2-D numerical simulations, using the PISCES code, were performed in order to simulate these shots. It is shown that a simplified version of the Johnson-Holmquist failure model can account for the penetration depths of the rods but is not enough to capture the effect of lateral release waves on these penetrations.
Quantum simulation of 2D topological physics in a 1D array of optical cavities.
Luo, Xi-Wang; Zhou, Xingxiang; Li, Chuan-Feng; Xu, Jin-Shi; Guo, Guang-Can; Zhou, Zheng-Wei
2015-07-06
Orbital angular momentum of light is a fundamental optical degree of freedom characterized by unlimited number of available angular momentum states. Although this unique property has proved invaluable in diverse recent studies ranging from optical communication to quantum information, it has not been considered useful or even relevant for simulating nontrivial physics problems such as topological phenomena. Contrary to this misconception, we demonstrate the incredible value of orbital angular momentum of light for quantum simulation by showing theoretically how it allows to study a variety of important 2D topological physics in a 1D array of optical cavities. This application for orbital angular momentum of light not only reduces required physical resources but also increases feasible scale of simulation, and thus makes it possible to investigate important topics such as edge-state transport and topological phase transition in a small simulator ready for immediate experimental exploration.
NASA Astrophysics Data System (ADS)
Wagner, Martin G.; Strother, Charles M.; Mistretta, Charles A.
2016-03-01
Recent efforts to perform a 3D reconstruction of interventional devices such as guidewires from monoplane and biplane fluoroscopic images require the segmentation of the exact device path in the respective 2D projection images. The segmentation of the device in low dose fluoroscopy images can be challenging since noise and motion artifacts degrade the image quality. Additionally, extracting the device path from the segmented region may result in ambiguous results due to overlapping device parts or discontinuities in the device segmentation. The purpose of this work is to present a novel guidewire tracking and segmentation algorithm, which segments the device region based on three different features based on a ridge detection filter, noise reduction for curvilinear structures as well as an a priori probability map. The features are calculated from background subtracted as well as unsubtracted fluoroscopic images. The device path extraction is based on a topology preserving thinning algorithm followed by a path search, which minimizes a cost function based on distance and directional difference between adjacent segments as well as the similarity to the device path extracted from the previous frame. The quantitative evaluation was performed using 7 data sets acquired from a canine study. Device shapes with different complexities are compared to semi-automatic segmentations. An average segmentation accuracy of 0.50 0.41 mm was achieved where each point along the device was compared to the point on the reference device centerline with the same distance to the device tip. In all cases the device path could be resolved correctly, which would allow a more accurate and reliable reconstruction of the 3D path of the device.
Comparison between 2D and 3D Numerical Modelling of a hot forging simulative test
Croin, M.; Ghiotti, A.; Bruschi, S.
2007-04-07
The paper presents the comparative analysis between 2D and 3D modelling of a simulative experiment, performed in laboratory environment, in which operating conditions approximate hot forging of a turbine aerofoil section. The plane strain deformation was chosen as an ideal case to analyze the process because of the thickness variations in the final section and the consequent distributions of contact pressure and sliding velocity at the interface that are closed to the conditions of the real industrial process. In order to compare the performances of 2D and 3D approaches, two different analyses were performed and compared with the experiments in terms of loads and temperatures peaks at the interface between the dies and the workpiece.
Spatially Resolved Synthetic Spectra from 2D Simulations of Stainless Steel Wire Array Implosions
Clark, R. W.; Giuliani, J. L.; Thornhill, J. W.; Chong, Y. K.; Dasgupta, A.; Davis, J.
2009-01-21
A 2D radiation MHD model has been developed to investigate stainless steel wire array implosion experiments on the Z and refurbished Z machines. This model incorporates within the Mach2 MHD code a self-consistent calculation of the non-LTE kinetics and ray trace based radiation transport. Such a method is necessary in order to account for opacity effects in conjunction with ionization kinetics of K-shell emitting plasmas. Here the model is used to investigate multi-dimensional effects of stainless steel wire implosions. In particular, we are developing techniques to produce non-LTE, axially and/or radially resolved synthetic spectra based upon snapshots of our 2D simulations. Comparisons between experimental spectra and these synthetic spectra will allow us to better determine the state of the experimental pinches.
Simulation of the flow and mass transfer for KDP crystals undergoing 2D translation during growth
NASA Astrophysics Data System (ADS)
Zhou, Chuan; Li, Mingwei; Hu, Zhitao; Yin, Huawei; Wang, Bangguo; Cui, Qidong
2016-09-01
In this study, a novel motion mode for crystals during growth, i.e., 2D translation, is proposed. Numerical simulations of flow and mass transfer are conducted for the growth of large-scale potassium dihydrogen phosphate (KDP) crystals subjected to the new motion mode. Surface supersaturation and shear stress are obtained as functions of the translational velocity, distance, size, orientation of crystals. The dependence of these two parameters on the flow fields around the crystals is also discussed. The thicknesses of the solute boundary layer varied with translational velocity are described. The characteristics of solution flow and surface supersaturation distribution are summarized, where it suggests that the morphological stability of a crystal surface can be enhanced if the proposed 2D translation is applied to crystal growth.
Application of 2-D simulations to hollow z-pinch implosions
Peterson, D.L.; Bowers, R.L.; Brownell, J.H.
1997-12-01
The application of simulations of z-pinch implosions should have at least two goals: first, to properly model the most important physical processes occurring in the pinch allowing for a better understanding of the experiments and second, provide a design capability for future experiments. Beginning with experiments fielded at Los Alamos on the Pegasus 1 and Pegasus 2 capacitor banks, the authors have developed a methodology for simulating hollow z-pinches in two dimensions which has reproduced important features of the measured experimental current drive, spectrum, radiation pulse shape, peak power and total radiated energy. This methodology employs essentially one free parameter, the initial level of the random density perturbations imposed at the beginning of the 2-D simulation, but in general no adjustments to other parameters are required. Currently the authors are applying this capability to the analysis of recent Saturn and PBFA-Z experiments. The code results provide insight into the nature of the pinch plasma prior to arrival on-axis, during thermalization and development after peak pinch time. Among other things, the simulation results provide an explanation for the production of larger amounts of radiated energy than would be expected from a simple slug-model kinetic energy analysis and the appearance of multiple peaks in the radiation power. The 2-D modeling has also been applied to the analysis of Saturn dynamic hohlraum experiments and is being used in the design of this and other Z-Pinch applications on PBFA-Z.
Epitaxial MoS2/GaN structures to enable vertical 2D/3D semiconductor heterostructure devices
NASA Astrophysics Data System (ADS)
Ruzmetov, D.; Zhang, K.; Stan, G.; Kalanyan, B.; Eichfeld, S.; Burke, R.; Shah, P.; O'Regan, T.; Crowne, F.; Birdwell, A. G.; Robinson, J.; Davydov, A.; Ivanov, T.
MoS2/GaN structures are investigated as a building block for vertical 2D/3D semiconductor heterostructure devices that utilize a 3D substrate (GaN) as an active component of the semiconductor device without the need of mechanical transfer of the 2D layer. Our CVD-grown monolayer MoS2 has been shown to be epitaxially aligned to the GaN lattice which is a pre-requisite for high quality 2D/3D interfaces desired for efficient vertical transport and large area growth. The MoS2 coverage is nearly 50 % including isolated triangles and monolayer islands. The GaN template is a double-layer grown by MOCVD on sapphire and allows for measurement of transport perpendicular to the 2D layer. Photoluminescence, Raman, XPS, Kelvin force probe microscopy, and SEM analysis identified high quality monolayer MoS2. The MoS2/GaN structures electrically conduct in the out-of-plane direction and across the van der Waals gap, as measured with conducting AFM (CAFM). The CAFM current maps and I-V characteristics are analyzed to estimate the MoS2/GaN contact resistivity to be less than 4 Ω-cm2 and current spreading in the MoS2 monolayer to be approx. 1 μm in diameter. Epitaxial MoS2/GaN heterostructures present a promising platform for the design of energy-efficient, high-speed vertical devices incorporating 2D layered materials with 3D semiconductors.
Two-dimensional B-C-O alloys: a promising class of 2D materials for electronic devices.
Zhou, Si; Zhao, Jijun
2016-04-28
Graphene, a superior 2D material with high carrier mobility, has limited application in electronic devices due to zero band gap. In this regard, boron and nitrogen atoms have been integrated into the graphene lattice to fabricate 2D semiconducting heterostructures. It is an intriguing question whether oxygen can, as a replacement of nitrogen, enter the sp2 honeycomb lattice and form stable B-C-O monolayer structures. Here we explore the atomic structures, energetic and thermodynamic stability, and electronic properties of various 2D B-C-O alloys using first-principles calculations. Our results show that oxygen can be stably incorporated into the graphene lattice by bonding with boron. The B and O species favor forming alternate patterns into the chain- or ring-like structures embedded in the pristine graphene regions. These B-C-O hybrid sheets can be either metals or semiconductors depending on the B : O ratio. The semiconducting (B2O)nCm and (B6O3)nCm phases exist under the B- and O-rich conditions, and possess a tunable band gap of 1.0-3.8 eV and high carrier mobility, retaining ∼1000 cm2 V(-1) s(-1) even for half coverage of B and O atoms. These B-C-O alloys form a new class of 2D materials that are promising candidates for high-speed electronic devices.
NASA Astrophysics Data System (ADS)
Christopher, Jason; Vutukuru, Mounika; Bishop, David; Swan, Anna; Goldberg, Bennett
Straining 2D materials can dramatically change electrical, thermal and optical properties and can even cause unconventional behavior such as generating pseudo-magnetic fields. However attempts at probing these effects have been hindered by the difficulty involved with precisely straining these materials. Here we present micro-electromechanical systems (MEMS) as an ideal platform for straining 2D materials because they are readily compatible with existing electronics and their size makes them compatible with 2D materials. Additionally the MEMS platform does more than facilitate experimentation; by freeing us to think of strain as dynamical it makes a whole new class of devices practical for next generation technology. To demonstrate the power of this platform we have for the first time measured the strain response of the Raman and photoluminescence spectra of suspended MoS2, and measured the friction force between MoS2 and the MEMS structure. This talk will touch on the basics of designing MEMS structures for straining 2D materials, how to transfer 2D materials onto MEMS without break either, proof of concept experimental results, and next steps in developing the MEMS platform. This work is supported by NSF DMR Grant 1411008, and author J. Christopher thanks the NDSEG program for its support.
NASA Astrophysics Data System (ADS)
Chowdhury, Rup K.; Maiti, Rishi; Ghorai, Arup; Midya, Anupam; Ray, Samit K.
2016-07-01
We report for the first time, the fabrication of novel two-dimensional (2D) p-WS2/n-Si vertical heterostructures with superior junction and photoresponse characteristics. Few layer WS2 has been synthesized by a lithium-ion intercalation technique in hexane and coated on Si substrates for realization of CMOS compatible devices. Atomic force microscopy and Raman spectroscopy have been used to confirm the 2D nature of WS2 layers. Sharp band-edge absorption and emission peaks have indicated the formation of mono-to-few-layers thick direct band gap WS2 films. The electrical and optical responses of the heterostructures have exhibited superior properties revealing the formation of an abrupt heterojunction. The fabricated photodetector device depicts a peak responsivity of 1.11 A W-1 at -2 V with a broadband spectral response of 400-1100 nm and a moderate photo-to-dark current ratio of ~103. The optical switching characteristics have been studied as a function of applied bias and illuminated power density. A comparative study of the reported results on 2D transition metal chalcogenides indicates the superior characteristics of WS2/n-Si heterostructures for future photonic devices.
Fast acceleration of 2D wave propagation simulations using modern computational accelerators.
Wang, Wei; Xu, Lifan; Cavazos, John; Huang, Howie H; Kay, Matthew
2014-01-01
Recent developments in modern computational accelerators like Graphics Processing Units (GPUs) and coprocessors provide great opportunities for making scientific applications run faster than ever before. However, efficient parallelization of scientific code using new programming tools like CUDA requires a high level of expertise that is not available to many scientists. This, plus the fact that parallelized code is usually not portable to different architectures, creates major challenges for exploiting the full capabilities of modern computational accelerators. In this work, we sought to overcome these challenges by studying how to achieve both automated parallelization using OpenACC and enhanced portability using OpenCL. We applied our parallelization schemes using GPUs as well as Intel Many Integrated Core (MIC) coprocessor to reduce the run time of wave propagation simulations. We used a well-established 2D cardiac action potential model as a specific case-study. To the best of our knowledge, we are the first to study auto-parallelization of 2D cardiac wave propagation simulations using OpenACC. Our results identify several approaches that provide substantial speedups. The OpenACC-generated GPU code achieved more than 150x speedup above the sequential implementation and required the addition of only a few OpenACC pragmas to the code. An OpenCL implementation provided speedups on GPUs of at least 200x faster than the sequential implementation and 30x faster than a parallelized OpenMP implementation. An implementation of OpenMP on Intel MIC coprocessor provided speedups of 120x with only a few code changes to the sequential implementation. We highlight that OpenACC provides an automatic, efficient, and portable approach to achieve parallelization of 2D cardiac wave simulations on GPUs. Our approach of using OpenACC, OpenCL, and OpenMP to parallelize this particular model on modern computational accelerators should be applicable to other computational models of
NASA Astrophysics Data System (ADS)
Mendoza-Torres, F.; Diaz-Viera, M. A.
2015-12-01
In many natural fractured porous media, such as aquifers, soils, oil and geothermal reservoirs, fractures play a crucial role in their flow and transport properties. An approach that has recently gained popularity for modeling fracture systems is the Discrete Fracture Network (DFN) model. This approach consists in applying a stochastic boolean simulation method, also known as object simulation method, where fractures are represented as simplified geometric objects (line segments in 2D and polygons in 3D). One of the shortcomings of this approach is that it usually does not consider the dependency relationships that may exist between the geometric properties of fractures (direction, length, aperture, etc), that is, each property is simulated independently. In this work a method for modeling such dependencies by copula theory is introduced. In particular, a nonparametric model using Bernstein copulas for direction-length fracture dependency in 2D is presented. The application of this method is illustrated in a case study for a fractured rock sample from a carbonate reservoir outcrop.
Multipacting Simulation Study for 56 MHz Quarter Wave Resonator using 2D Code
Naik,D.; Ben-Zvi, I.
2009-01-02
A beam excited 56 MHz Radio Frequency (RF) Niobium Quarter Wave Resonator (QWR) has been proposed to enhance RHIC beam luminosity and bunching. Being a RF cavity, multipacting is expected; therefore an extensive study was carried out with the Multipac 2.1 2D simulation code. The study revealed that multipacting occurs in various bands up to peak surface electric field 50 kV/m and is concentrated mostly above the beam gap and on the outer conductor. To suppress multipacting, a ripple structure was introduced to the outer conductor and the phenomenon was successfully eliminated from the cavity.
Tuning and simulating a 193-nm resist for 2D applications
NASA Astrophysics Data System (ADS)
Howard, William B.; Wiaux, Vincent; Ercken, Monique; Bui, Bang; Byers, Jeff D.; Pochkowski, Mike
2002-07-01
For some applications, the usefulness of lithography simulation results depends strongly on the matching between experimental conditions and the simulation input parameters. If this matching is optimized and other sources of error are minimized, then the lithography model can be used to explain printed wafer experimental results. Further, simulation can be useful in predicting the results or in choosing the correct set of experiments. In this paper, PROLITH and ProDATA AutoTune were used to systematically vary simulation input parameters to match measured results on printed wafers used in a 193 nm process. The validity of the simulation parameters was then checked using 3D simulation compared to 2D top-down SEM images. The quality of matching was evaluated using the 1D metrics of average gate CD and Line End Shortening (LES). To ensure the most accurate simulation, a new approach was taken to create a compound mask from GDSII contextual information surrounding an accurate SEM image of the reticle region of interest. Corrections were made to account for all metrology offsets.
A Novel 2-D Programmable Photonic Time Delay Device for MM-Wave Signal Processing Applications
NASA Technical Reports Server (NTRS)
Yao, X.; Maleki, L.
1994-01-01
We describe a novel programmable photonic true time delay device that has the properties of low loss, inherent two dimensionality with a packing density exceeding 25 lines/cm super 2, virtually infinite bandwidth, and is easy to manufacture.
GMC COLLISIONS AS TRIGGERS OF STAR FORMATION. I. PARAMETER SPACE EXPLORATION WITH 2D SIMULATIONS
Wu, Benjamin; Loo, Sven Van; Tan, Jonathan C.; Bruderer, Simon
2015-09-20
We utilize magnetohydrodynamic (MHD) simulations to develop a numerical model for giant molecular cloud (GMC)–GMC collisions between nearly magnetically critical clouds. The goal is to determine if, and under what circumstances, cloud collisions can cause pre-existing magnetically subcritical clumps to become supercritical and undergo gravitational collapse. We first develop and implement new photodissociation region based heating and cooling functions that span the atomic to molecular transition, creating a multiphase ISM and allowing modeling of non-equilibrium temperature structures. Then in 2D and with ideal MHD, we explore a wide parameter space of magnetic field strength, magnetic field geometry, collision velocity, and impact parameter and compare isolated versus colliding clouds. We find factors of ∼2–3 increase in mean clump density from typical collisions, with strong dependence on collision velocity and magnetic field strength, but ultimately limited by flux-freezing in 2D geometries. For geometries enabling flow along magnetic field lines, greater degrees of collapse are seen. We discuss observational diagnostics of cloud collisions, focussing on {sup 13}CO(J = 2–1), {sup 13}CO(J = 3–2), and {sup 12}CO(J = 8–7) integrated intensity maps and spectra, which we synthesize from our simulation outputs. We find that the ratio of J = 8–7 to lower-J emission is a powerful diagnostic probe of GMC collisions.
Strain hardening in 2D discrete dislocation dynamics simulations: A new '2.5D' algorithm
NASA Astrophysics Data System (ADS)
Keralavarma, S. M.; Curtin, W. A.
2016-10-01
The two-dimensional discrete dislocation dynamics (2D DD) method, consisting of parallel straight edge dislocations gliding on independent slip systems in a plane strain model of a crystal, is often used to study complicated boundary value problems in crystal plasticity. However, the absence of truly three dimensional mechanisms such as junction formation means that forest hardening cannot be modeled, unless additional so-called '2.5D' constitutive rules are prescribed for short-range dislocation interactions. Here, results from three dimensional dislocation dynamics (3D DD) simulations in an FCC material are used to define new constitutive rules for short-range interactions and junction formation between dislocations on intersecting slip systems in 2D. The mutual strengthening effect of junctions on preexisting obstacles, such as precipitates or grain boundaries, is also accounted for in the model. The new '2.5D' DD model, with no arbitrary adjustable parameters beyond those obtained from lower scale simulation methods, is shown to predict athermal hardening rates, differences in flow behavior for single and multiple slip, and latent hardening ratios. All these phenomena are well-established in the plasticity of crystals and quantitative results predicted by the model are in good agreement with experimental observations.
2D PIC simulations for an EN discharge with magnetized electrons and unmagnetized ions
NASA Astrophysics Data System (ADS)
Lieberman, Michael A.; Kawamura, Emi; Lichtenberg, Allan J.
2009-10-01
We conducted 2D particle-in-cell (PIC) simulations for an electronegative (EN) discharge with magnetized electrons and unmagnetized ions, and compared the results to a previously developed 1D (radial) analytical model of an EN plasma with strongly magnetized electrons and weakly magnetized ions [1]. In both cases, there is a static uniform applied magnetic field in the axial direction. The 1D radial model mimics the wall losses of the particles in the axial direction by introducing a bulk loss frequency term νL. A special (desired) solution was found in which only positive and negative ions but no electrons escaped radially. The 2D PIC results show good agreement with the 1D model over a range of parameters and indicate that the analytical form of νL employed in [1] is reasonably accurate. However, for the PIC simulations, there is always a finite flux of electrons to the radial wall which is about 10 to 30% of the negative ion flux.[4pt] [1] G. Leray, P. Chabert, A.J. Lichtenberg and M.A. Lieberman, J. Phys. D, accepted for publication 2009.
Ion acoustic wave collapse via two-ion wave decay: 2D Vlasov simulation and theory
NASA Astrophysics Data System (ADS)
Chapman, Thomas; Berger, Richard; Banks, Jeffrey; Brunner, Stephan
2015-11-01
The decay of ion acoustic waves (IAWs) via two-ion wave decay may transfer energy from the electric field of the IAWs to the particles, resulting in a significant heating of resonant particles. This process has previously been shown in numerical simulations to decrease the plasma reflectivity due to stimulated Brillouin scattering. Two-ion wave decay is a fundamental property of ion acoustic waves that occurs over most if not all of the parameter space of relevance to inertial confinement fusion experiments, and can lead to a sudden collapse of IAWs. The treatment of all species kinetically, and in particular the electrons, is required to describe the decay process correctly. We present fully kinetic 2D+2V Vlasov simulations of IAWs undergoing decay to a highly nonlinear turbulent state using the code LOKI. The scaling of the decay rate with characteristic plasma parameters and wave amplitude is shown. A new theory describing two-ion wave decay in 2D, that incorporates key kinetic properties of the electrons, is presented and used to explain quantitatively for the first time the observed decay of IAWs. Work performed under auspices of U.S. DoE by LLNL, Contract DE-AC52-07NA2734. Funded by LDRD 15-ERD-038 and supported by LLNL Grand Challenge allocation.
Calibration and simulation of ASM2d at different temperatures in a phosphorus removal pilot plant.
García-Usach, F; Ferrer, J; Bouzas, A; Seco, A
2006-01-01
In this work, an organic and nutrient removal pilot plant was used to study the temperature influence on phosphorus accumulating organisms. Three experiments were carried out at 13, 20 and 24.5 degrees C, achieving a high phosphorus removal percentage in all cases. The ASM2d model was calibrated at 13 and 20 degrees C and the Arrhenius equation constant was obtained for phosphorus removal processes showing that the temperature influences on the biological phosphorus removal subprocesses in a different degree. The 24.5 degrees C experiment was simulated using the model parameters obtained by means of the Arrhenius equation. The simulation results for the three experiments showed good correspondence with the experimental data, demonstrating that the model and the calibrated parameters were able to predict the pilot plant behaviour.
Superclusters of galaxies from the 2dF redshift survey. 2. Comparison with simulations
Einasto, Jaan; Einasto, M.; Saar, E.; Tago, E.; Liivamagi, L.J.; Joeveer, M.J; Suhhonenko, I.; Hutsi, G.; Jaaniste, J.; Heinamaki, P.; Muller, V.; Knebe, A.; Tucker, D.; /Fermilab
2006-04-01
We investigate properties of superclusters of galaxies found on the basis of the 2dF Galaxy Redshift Survey, and compare them with properties of superclusters from the Millennium Simulation.We study the dependence of various characteristics of superclusters on their distance from the observer, on their total luminosity, and on their multiplicity. The multiplicity is defined by the number of Density Field (DF) clusters in superclusters. Using the multiplicity we divide superclusters into four richness classes: poor, medium, rich and extremely rich.We show that superclusters are asymmetrical and have multi-branching filamentary structure, with the degree of asymmetry and filamentarity being higher for the more luminous and richer superclusters. The comparison of real superclusters with Millennium superclusters shows that most properties of simulated superclusters agree very well with real data, the main differences being in the luminosity and multiplicity distributions.
Highly-resolved 2D HYDRA simulations of Double-Shell Ignition Designs
Milovich, J L; Amendt, P; Hamza, A; Marinak, M; Robey, H
2006-06-30
Double-shell (DS) targets (Amendt, P. A. et al., 2002) offer a complementary approach to the cryogenic baseline design (Lindl, J. et al., 2004) for achieving ignition on the National Ignition Facility (NIF). Among the expected benefits are the ease of room temperature preparation and fielding, the potential for lower laser backscatter and the reduced need for careful shock timing. These benefits are offset, however, by demanding fabrication tolerances, e.g., shell concentricity and shell surface smoothness. In particular, the latter is of paramount importance since DS targets are susceptible to the growth of interface perturbations from impulsive and time-dependent accelerations. Previous work (Milovich, J. L. et al., 2004) has indicated that the growth of perturbations on the outer surface of the inner shell is potentially disruptive. To control this instability new designs have been proposed requiring bimetallic inner shells and material-matching mid-Z nanoporous foam. The challenges in manufacturing such exotic foams have led to a further evaluation of the densities and pore sizes needed to reduce the seeding of perturbations on the outer surface of the inner shell, thereby guiding the ongoing material science research efforts. Highly-resolved 2D simulations of porous foams have been performed to establish an upper limit on the allowable pore sizes for instability growth. Simulations indicate that foams with higher densities than previously thought are now possible. Moreover, while at the present time we are only able to simulate foams with average pore sizes larger than 1 micron (due to computational limitations), we can conclude that these pore sizes are potentially problematic. Furthermore, the effect of low-order hohlraum radiation asymmetries on the growth of intrinsic surface perturbations is also addressed. Highly-resolved 2D simulations indicate that the transverse flows that are set up by these low-order mode features (which can excite Kelvin
Reynolds-Averaged Navier-Stokes Simulation of a 2D Circulation Control Wind Tunnel Experiment
NASA Technical Reports Server (NTRS)
Allan, Brian G.; Jones, Greg; Lin, John C.
2011-01-01
Numerical simulations are performed using a Reynolds-averaged Navier-Stokes (RANS) flow solver for a circulation control airfoil. 2D and 3D simulation results are compared to a circulation control wind tunnel test conducted at the NASA Langley Basic Aerodynamics Research Tunnel (BART). The RANS simulations are compared to a low blowing case with a jet momentum coefficient, C(sub u), of 0:047 and a higher blowing case of 0.115. Three dimensional simulations of the model and tunnel walls show wall effects on the lift and airfoil surface pressures. These wall effects include a 4% decrease of the midspan sectional lift for the C(sub u) 0.115 blowing condition. Simulations comparing the performance of the Spalart Allmaras (SA) and Shear Stress Transport (SST) turbulence models are also made, showing the SST model compares best to the experimental data. A Rotational/Curvature Correction (RCC) to the turbulence model is also evaluated demonstrating an improvement in the CFD predictions.
Spot size variation FCS in simulations of the 2D Ising model
NASA Astrophysics Data System (ADS)
Burns, Margaret C.; Nouri, Mariam; Veatch, Sarah L.
2016-06-01
Spot variation fluorescence correlation spectroscopy (svFCS) was developed to study the movement and organization of single molecules in plasma membranes. This experimental technique varies the size of an illumination area while measuring correlations in time using standard fluorescence correlation methods. Frequently, this data is interpreted using the assumption that correlation measurements reflect the dynamics of single molecule motions, and not motions of the average composition. Here, we explore how svFCS measurements report on the dynamics of components diffusing within simulations of a 2D Ising model with a conserved order parameter. Simulated correlation functions report on both the fast dynamics of single component mobility and the slower dynamics of the average composition. Over a range of simulation conditions, a conventional svFCS analysis suggests the presence of anomalous diffusion even though single molecule motions are nearly Brownian in these simulations. This misinterpretation is most significant when the surface density of the fluorescent label is elevated, therefore we suggest future measurements be made over a range of tracer densities. Some simulation conditions reproduce qualitative features of published svFCS experimental data. Overall, this work emphasizes the need to probe membranes using multiple complimentary experimental methodologies in order to draw conclusions regarding the nature of spatial and dynamical heterogeneity in these systems.
Tropical Oceanic Precipitation Processes over Warm Pool: 2D and 3D Cloud Resolving Model Simulations
NASA Technical Reports Server (NTRS)
Tao, W.- K.; Johnson, D.
1998-01-01
Rainfall is a key link in the hydrologic cycle as well as the primary heat source for the atmosphere, The vertical distribution of convective latent-heat release modulates the large-scale circulations of the tropics, Furthermore, changes in the moisture distribution at middle and upper levels of the troposphere can affect cloud distributions and cloud liquid water and ice contents. How the incoming solar and outgoing longwave radiation respond to these changes in clouds is a major factor in assessing climate change. Present large-scale weather and climate models simulate cloud processes only crudely, reducing confidence in their predictions on both global and regional scales. One of the most promising methods to test physical parameterizations used in General Circulation Models (GCMS) and climate models is to use field observations together with Cloud Resolving Models (CRMs). The CRMs use more sophisticated and physically realistic parameterizations of cloud microphysical processes, and allow for their complex interactions with solar and infrared radiative transfer processes. The CRMs can reasonably well resolve the evolution, structure, and life cycles of individual clouds and cloud systems, The major objective of this paper is to investigate the latent heating, moisture and momenti,im budgets associated with several convective systems developed during the TOGA COARE IFA - westerly wind burst event (late December, 1992). The tool for this study is the Goddard Cumulus Ensemble (CCE) model which includes a 3-class ice-phase microphysical scheme, The model domain contains 256 x 256 grid points (using 2 km resolution) in the horizontal and 38 grid points (to a depth of 22 km depth) in the vertical, The 2D domain has 1024 grid points. The simulations are performed over a 7 day time period. We will examine (1) the precipitation processes (i.e., condensation/evaporation) and their interaction with warm pool; (2) the heating and moisture budgets in the convective and
Two-dimensional B-C-O alloys: a promising class of 2D materials for electronic devices
NASA Astrophysics Data System (ADS)
Zhou, Si; Zhao, Jijun
2016-04-01
Graphene, a superior 2D material with high carrier mobility, has limited application in electronic devices due to zero band gap. In this regard, boron and nitrogen atoms have been integrated into the graphene lattice to fabricate 2D semiconducting heterostructures. It is an intriguing question whether oxygen can, as a replacement of nitrogen, enter the sp2 honeycomb lattice and form stable B-C-O monolayer structures. Here we explore the atomic structures, energetic and thermodynamic stability, and electronic properties of various 2D B-C-O alloys using first-principles calculations. Our results show that oxygen can be stably incorporated into the graphene lattice by bonding with boron. The B and O species favor forming alternate patterns into the chain- or ring-like structures embedded in the pristine graphene regions. These B-C-O hybrid sheets can be either metals or semiconductors depending on the B : O ratio. The semiconducting (B2O)nCm and (B6O3)nCm phases exist under the B- and O-rich conditions, and possess a tunable band gap of 1.0-3.8 eV and high carrier mobility, retaining ~1000 cm2 V-1 s-1 even for half coverage of B and O atoms. These B-C-O alloys form a new class of 2D materials that are promising candidates for high-speed electronic devices.Graphene, a superior 2D material with high carrier mobility, has limited application in electronic devices due to zero band gap. In this regard, boron and nitrogen atoms have been integrated into the graphene lattice to fabricate 2D semiconducting heterostructures. It is an intriguing question whether oxygen can, as a replacement of nitrogen, enter the sp2 honeycomb lattice and form stable B-C-O monolayer structures. Here we explore the atomic structures, energetic and thermodynamic stability, and electronic properties of various 2D B-C-O alloys using first-principles calculations. Our results show that oxygen can be stably incorporated into the graphene lattice by bonding with boron. The B and O species favor
Owen, Kevin; Fuller, Michael I.; Hossack, John A.
2015-01-01
Two-dimensional arrays present significant beamforming computational challenges because of their high channel count and data rate. These challenges are even more stringent when incorporating a 2-D transducer array into a battery-powered hand-held device, placing significant demands on power efficiency. Previous work in sonar and ultrasound indicates that 2-D array beamforming can be decomposed into two separable line-array beamforming operations. This has been used in conjunction with frequency-domain phase-based focusing to achieve fast volume imaging. In this paper, we analyze the imaging and computational performance of approximate near-field separable beamforming for high-quality delay-and-sum (DAS) beamforming and for a low-cost, phaserotation-only beamforming method known as direct-sampled in-phase quadrature (DSIQ) beamforming. We show that when high-quality time-delay interpolation is used, separable DAS focusing introduces no noticeable imaging degradation under practical conditions. Similar results for DSIQ focusing are observed. In addition, a slight modification to the DSIQ focusing method greatly increases imaging contrast, making it comparable to that of DAS, despite having a wider main lobe and higher side lobes resulting from the limitations of phase-only time-delay interpolation. Compared with non-separable 2-D imaging, up to a 20-fold increase in frame rate is possible with the separable method. When implemented on a smart-phone-oriented processor to focus data from a 60 × 60 channel array using a 40 × 40 aperture, the frame rate per C-mode volume slice increases from 16 to 255 Hz for DAS, and from 11 to 193 Hz for DSIQ. Energy usage per frame is similarly reduced from 75 to 4.8 mJ/ frame for DAS, and from 107 to 6.3 mJ/frame for DSIQ. We also show that the separable method outperforms 2-D FFT-based focusing by a factor of 1.64 at these data sizes. This data indicates that with the optimal design choices, separable 2-D beamforming can
Owen, Kevin; Fuller, Michael; Hossack, John
2012-07-01
Two-dimensional arrays present significant beamforming computational challenges because of their high channel count and data rate. These challenges are even more stringent when incorporating a 2-D transducer array into a battery-powered hand-held device, placing significant demands on power efficiency. Previous work in sonar and ultrasound indicates that 2-D array beamforming can be decomposed into two separable line-array beamforming operations. This has been used in conjunction with frequency-domain phase-based focusing to achieve fast volume imaging. In this paper, we analyze the imaging and computational performance of approximate near-field separable beamforming for high-quality delay-and-sum (DAS) beamforming and for a low-cost, phase-rotation-only beamforming method known as direct-sampled in-phase quadrature (DSIQ) beamforming. We show that when high-quality time-delay interpolation is used, separable DAS focusing introduces no noticeable imaging degradation under practical conditions. Similar results for DSIQ focusing are observed. In addition, a slight modification to the DSIQ focusing method greatly increases imaging contrast, making it comparable to that of DAS, despite having a wider main lobe and higher side lobes resulting from the limitations of phase-only time-delay interpolation. Compared with non-separable 2-D imaging, up to a 20-fold increase in frame rate is possible with the separable method. When implemented on a smart-phone-oriented processor to focus data from a 60 x 60 channel array using a 40 x 40 aperture, the frame rate per C-mode volume slice increases from 16 to 255 Hz for DAS, and from 11 to 193 Hz for DSIQ. Energy usage per frame is similarly reduced from 75 to 4.8 mJ/ frame for DAS, and from 107 to 6.3 mJ/frame for DSIQ. We also show that the separable method outperforms 2-D FFT-based focusing by a factor of 1.64 at these data sizes. This data indicates that with the optimal design choices, separable 2-D beamforming can
Numerical simulation of 2D buoyant jets in ice-covered and temperature-stratified water
NASA Astrophysics Data System (ADS)
Gu, Ruochuan
A two-dimensional (2D) unsteady simulation model is applied to the problem of a submerged warm water discharge into a stratified lake or reservoir with an ice cover. Numerical simulations and analyses are conducted to gain insight into large-scale convective recirculation and flow processes in a cold waterbody induced by a buoyant jet. Jet behaviors under various discharge temperatures are captured by directly modeling flow and thermal fields. Flow structures and processes are described by the simulated spatial and temporal distributions of velocity and temperature in various regions: deflection, recirculation, attachment, and impingement. Some peculiar hydrothermal and dynamic features, e.g. reversal of buoyancy due to the dilution of a warm jet by entraining cold ambient water, are identified and examined. Simulation results show that buoyancy is the most important factor controlling jet behavior and mixing processes. The inflow boundary is treated as a liquid wall from which the jet is offset. Similarity and difference in effects of boundaries perpendicular and parallel to flow, and of buoyancy on jet attachment and impingement, are discussed. Symmetric flow configuration is used to de-emphasize the Coanda effect caused by offset.
Rise characteristics of gas bubbles in a 2D rectangular column: VOF simulations vs experiments
Krishna, R.; Baten, J.M. van
1999-10-01
About five centuries ago, Leonardo da Vinci described the sinuous motion of gas bubbles rising in water. The authors have attempted to simulate the rise trajectories of bubbles of 4, 5, 7, 8, 9, 12, and 20 mm in diameter rising in a 2D rectangular column filled with water. The simulations were carried out using the volume-of-fluid (VOF) technique developed by Hirt and Nichols (J. Computational Physics, 39, 201--225 (1981)). To solve the Navier-Stokes equations of motion the authors used a commercial solver, CFX 4.1c of AEA Technology, UK. They developed their own bubble-tracking algorithm to capture sinuous bubble motions. The 4 and 5 mm bubbles show large lateral motions observed by Da Vinci. The 7, 8 and 9 mm bubble behave like jellyfish. The 12 mm bubble flaps its wings like a bird. The extent of lateral motion of the bubbles decreases with increasing bubble size. Bubbles larger than 20 mm in size assume a spherical cap form and simulations of the rise characteristics match experiments exactly. VOF simulations are powerful tools for a priori determination of the morphology and rise characteristics of bubbles rising in a liquid. Bubble-bubble interactions are also properly modeled by the VOF technique.
Simulation of growth normal fault sandbox tests using the 2D discrete element method
NASA Astrophysics Data System (ADS)
Chu, Sheng-Shin; Lin, Ming-Lang; Huang, Wen-Chao; Nien, Wei-Tung; Liu, Huan-Chi; Chan, Pei-Chen
2015-01-01
A fault slip can cause the deformation of shallow soil layers and destroy infrastructures. The Shanchiao Fault on the west side of the Taipei Basin is one such fault. The activities of the Shanchiao Fault have caused the quaternary sediment beneath the Taipei Basin to become deformed, damaging structures, traffic construction, and utility lines in the area. Data on geological drilling and dating have been used to determine that a growth fault exists in the Shanchiao Fault. In an experiment, a sandbox model was built using noncohesive sandy soil to simulate the existence of a growth fault in the Shanchiao Fault and forecast the effect of the growth fault on shear-band development and ground differential deformation. The experimental results indicated that when a normal fault contains a growth fault at the offset of the base rock, the shear band develops upward beside the weak side of the shear band of the original-topped soil layer, and surfaces considerably faster than that of the single-topped layer. The offset ratio required is approximately one-third that of the single-cover soil layer. In this study, a numerical simulation of the sandbox experiment was conducted using a discrete element method program, PFC2D, to simulate the upper-covering sand layer shear-band development pace and the scope of a growth normal fault slip. The simulation results indicated an outcome similar to that of the sandbox experiment, which can be applied to the design of construction projects near fault zones.
2-D LSP Simulations of the Self Magnetic Pinch Radiographic Diode
NASA Astrophysics Data System (ADS)
Threadgold, J.; Crotch, I.; Rose, D. V.
2003-10-01
The Atomic Weapons Establishment (AWE) UK has a number of Pulsed Power driven flash X-ray machines which are used to take transmission radiographs of hydrodynamic experiments. Some of the lower voltage x-ray machines (< 2 MV) use the Self Magnetic (SM) Pinch diode for their source. The SM pinch diode has proved to be a reliable source for providing small diameter radiographic spot sizes. With an emphasis on reduction of the x-ray spot size at higher voltages, one part of the diode research project has been to field SM pinch diodes at higher voltages. The SM pinch diode relies upon the magnitude of its own electron current (> 50 kA) to pinch the electron beam to a small diameter onto a high Z converter target. An electromagnetic PIC code, LSP, has been used to carry out 2-D simulations of the diode to support this project. The code has been used to investigate the effect of different target materials within the diode and to investigate the resultant electron trajectories onto the target. Results of these code simulations will be compared to experimental data The simulations show good agreement with measured experimental data on diode performance. The simulations suggest further improvements in spot size reduction could be achieved with changes in the diode geometry.
2D/3D Monte Carlo Feature Profile Simulator FPS-3D
NASA Astrophysics Data System (ADS)
Moroz, Paul
2010-11-01
Numerical simulation of etching/deposition profiles is important for semiconductor industry, as it allows analysis and prediction of the outcome of materials processing on a micron and sub-micron scale. The difficulty, however, is in making such a simulator a reliable, general, and easy to use tool applicable to different situations, for example, with different ratios of ion to neutral fluxes, different chemistries, different energies of incoming particles, and different angular and energy dependencies for surface reactions, without recompiling the code each time when the parameters change. The FPS-3D simulator [1] does not need recompilation when the features, materials, gases, or plasma are changed -- modifications to input, chemistry, and flux files are enough. The code allows interaction of neutral low-energy species with the surface mono-layer, while considering finite penetration depth into the volume for fast particles and ions. The FPS-3D code can simulate etching and deposition processes, both for 2D and 3D geometries. FPS-3D is using an advanced graphics package from HFS for presenting real-time process and profile evolution. The presentation will discuss the FPS-3D code with examples for different process conditions. The author is thankful to Drs. S.-Y. Kang of TEL TDC and P. Miller of HFS for valuable discussions. [4pt] [1] P. Moroz, URP.00101, GEC, Saratoga, NY, 2009.
2D array transducers for real-time 3D ultrasound guidance of interventional devices
NASA Astrophysics Data System (ADS)
Light, Edward D.; Smith, Stephen W.
2009-02-01
We describe catheter ring arrays for real-time 3D ultrasound guidance of devices such as vascular grafts, heart valves and vena cava filters. We have constructed several prototypes operating at 5 MHz and consisting of 54 elements using the W.L. Gore & Associates, Inc. micro-miniature ribbon cables. We have recently constructed a new transducer using a braided wiring technology from Precision Interconnect. This transducer consists of 54 elements at 4.8 MHz with pitch of 0.20 mm and typical -6 dB bandwidth of 22%. In all cases, the transducer and wiring assembly were integrated with an 11 French catheter of a Cook Medical deployment device for vena cava filters. Preliminary in vivo and in vitro testing is ongoing including simultaneous 3D ultrasound and x-ray fluoroscopy.
NASA Astrophysics Data System (ADS)
Cao, Jiang; Cresti, Alessandro; Esseni, David; Pala, Marco
2016-02-01
We simulate a band-to-band tunneling field-effect transistor based on a vertical heterojunction of single-layer MoS2 and WTe2, by exploiting the non-equilibrium Green's function method and including electron-phonon scattering. For both in-plane and out-of-plane transport, we attempt to calibrate out models to the few available experimental results. We focus on the role of chemical doping and back-gate biasing, and investigate the off-state physics of this device by analyzing the influence of the top-gate geometrical alignment on the device performance. The device scalability as a function of gate length is also studied. Finally, we present two metrics for the switching delay and energy of the device. Our simulations indicate that vertical field-effect transistors based on transition metal dichalcogenides can provide very small values of sub-threshold swing when properly designed in terms of doping concentration and top-gate extension length.
NASA Astrophysics Data System (ADS)
Dessart, L.; Owocki, S. P.
2005-07-01
We present initial attempts to include the multi-dimensional nature of radiation transport in hydrodynamical simulations of the small-scale structure that arises from the line-driven instability in hot-star winds. Compared to previous 1D or 2D models that assume a purely radial radiation force, we seek additionally to treat the lateral momentum and transport of diffuse line-radiation, initially here within a 2D context. A key incentive is to study the damping effect of the associated diffuse line-drag on the dynamical properties of the flow, focusing particularly on whether this might prevent lateral break-up of shell structures at scales near the lateral Sobolev angle of ca. 1^o. Based on 3D linear perturbation analyses that show a viscous diffusion character for the damping at these scales, we first explore nonlinear simulations that cast the lateral diffuse force in the simple, local form of a parallel viscosity. We find, however, that the resulting strong damping of lateral velocity fluctuations only further isolates azimuthal zones, leading again to azimuthal incoherence down to the grid scale. To account then for the further effect of lateral mixing of radiation associated with the radial driving, we next explore models in which the radial force is azimuthally smoothed over a chosen scale, and thereby show that this does indeed translate to a similar scale for the resulting density and velocity structure. Accounting for both the lateral line-drag and the lateral mixing in a more self-consistent way thus requires a multi-ray computation of the radiation transport. As a first attempt, we explore further a method first proposed by Owocki (1999), which uses a restricted 3-ray approach that combines a radial ray with two oblique rays set to have an impact parameter p < Rast within the stellar core. From numerical simulations with various grid resolutions (and p), we find that, compared to equivalent 1-ray simulations, the high-resolution 3-ray models show
NASA Astrophysics Data System (ADS)
Li, Jinghe; Song, Linping; Liu, Qing Huo
2016-02-01
A simultaneous multiple frequency contrast source inversion (CSI) method is applied to reconstructing hydrocarbon reservoir targets in a complex multilayered medium in two dimensions. It simulates the effects of a salt dome sedimentary formation in the context of reservoir monitoring. In this method, the stabilized biconjugate-gradient fast Fourier transform (BCGS-FFT) algorithm is applied as a fast solver for the 2D volume integral equation for the forward computation. The inversion technique with CSI combines the efficient FFT algorithm to speed up the matrix-vector multiplication and the stable convergence of the simultaneous multiple frequency CSI in the iteration process. As a result, this method is capable of making quantitative conductivity image reconstruction effectively for large-scale electromagnetic oil exploration problems, including the vertical electromagnetic profiling (VEP) survey investigated here. A number of numerical examples have been demonstrated to validate the effectiveness and capacity of the simultaneous multiple frequency CSI method for a limited array view in VEP.
Catalog of velocity distributions around a reconnection site in 2D PIC simulations
NASA Astrophysics Data System (ADS)
Lechner, Lukas; Bourdin, Philippe-A.; Nakamura, Takuma K. M.; Nakamura, Rumi; Narita, Yasuhito
2016-04-01
The velocity distribution of electrons and ions are known to be a marker for regions where magnetic reconnection develops. Past theoretical and computational works demonstrated that non-gyrotropic and anisotropic distributions depending on particle meandering motions and accelerations are seen around the reconnection point. The Magnetospheric Multiscale (MMS) mission is expected to resolve such kinetic scale reconnection regions. We present a catalog of velocity distribution functions that can give hints on the location within the current sheet relative to the reconnection point, which is sometimes unclear from pure spacecraft observations. We use 2D PIC simulations of anti-parallel magnetic reconnection to obtain velocity distributions at different locations, like in the center of the reconnection site, the ion and electron diffusion regions, or the reconnection inflow and outflow regions. With sufficiently large number of particles we resolve the distribution functions also in rather small regions. Such catalog may be compared with future MMS observations of the Earth's magnetotail.
Relaxation of ferroelectric states in 2D distributions of quantum dots: EELS simulation
NASA Astrophysics Data System (ADS)
Cortés, C. M.; Meza-Montes, L.; Moctezuma, R. E.; Carrillo, J. L.
2016-06-01
The relaxation time of collective electronic states in a 2D distribution of quantum dots is investigated theoretically by simulating EELS experiments. From the numerical calculation of the probability of energy loss of an electron beam, traveling parallel to the distribution, it is possible to estimate the damping time of ferroelectric-like states. We generate this collective response of the distribution by introducing a mean field interaction among the quantum dots, and then, the model is extended incorporating effects of long-range correlations through a Bragg-Williams approximation. The behavior of the dielectric function, the energy loss function, and the relaxation time of ferroelectric-like states is then investigated as a function of the temperature of the distribution and the damping constant of the electronic states in the single quantum dots. The robustness of the trends and tendencies of our results indicate that this scheme of analysis can guide experimentalists to develop tailored quantum dots distributions for specific applications.
NASA Astrophysics Data System (ADS)
Khuat Duy, B.; Archambeau, P.; Dewals, B. J.; Erpicum, S.; Pirotton, M.
2009-04-01
Following recurrent inundation problems on the Berwinne catchment, in Belgium, a combined hydrologic and hydrodynamic study has been carried out in order to find adequate solutions for the floods mitigation. Thanks to detailed 2D simulations, the effectiveness of the solutions can be assessed not only in terms of discharge and height reductions in the river, but also with other aspects such as the inundated surfaces reduction and the decrease of inundated buildings and roads. The study is carried out in successive phases. First, the hydrological runoffs are generated using a physically based and spatially distributed multi-layer model solving depth-integrated equations for overland flow, subsurface flow and baseflow. Real floods events are simulated using rainfall series collected at 8 stations (over 20 years of available data). The hydrological inputs are routed through the river network (and through the sewage network if relevant) with the 1D component of the modelling system, which solves the Saint-Venant equations for both free-surface and pressurized flows in a unified way. On the main part of the river, the measured river cross-sections are included in the modelling, and existing structures along the river (such as bridges, sluices or pipes) are modelled explicitely with specific cross sections. Two gauging stations with over 15 years of continuous measurements allow the calibration of both the hydrologic and hydrodynamic models. Second, the flood mitigation solutions are tested in the simulations in the case of an extreme flooding event, and their effects are assessed using detailed 2D simulations on a few selected sensitive areas. The digital elevation model comes from an airborne laser survey with a spatial resolution of 1 point per square metre and is completed in the river bed with a bathymetry interpolated from cross-section data. The upstream discharge is extracted from the 1D simulation for the selected rainfall event. The study carried out with this
A new model for two-dimensional numerical simulation of pseudo-2D gas-solids fluidized beds
Li, Tingwen; Zhang, Yongmin
2013-10-11
Pseudo-two dimensional (pseudo-2D) fluidized beds, for which the thickness of the system is much smaller than the other two dimensions, is widely used to perform fundamental studies on bubble behavior, solids mixing, or clustering phenomenon in different gas-solids fluidization systems. The abundant data from such experimental systems are very useful for numerical model development and validation. However, it has been reported that two-dimensional (2D) computational fluid dynamic (CFD) simulations of pseudo-2D gas-solids fluidized beds usually predict poor quantitative agreement with the experimental data, especially for the solids velocity field. In this paper, a new model is proposed to improve the 2D numerical simulations of pseudo-2D gas-solids fluidized beds by properly accounting for the frictional effect of the front and back walls. Two previously reported pseudo-2D experimental systems were simulated with this model. Compared to the traditional 2D simulations, significant improvements in the numerical predictions have been observed and the predicted results are in better agreement with the available experimental data.
Hall-Effect Thruster Simulations with 2-D Electron Transport and Hydrodynamic Ions
NASA Technical Reports Server (NTRS)
Mikellides, Ioannis G.; Katz, Ira; Hofer, Richard H.; Goebel, Dan M.
2009-01-01
A computational approach that has been used extensively in the last two decades for Hall thruster simulations is to solve a diffusion equation and energy conservation law for the electrons in a direction that is perpendicular to the magnetic field, and use discrete-particle methods for the heavy species. This "hybrid" approach has allowed for the capture of bulk plasma phenomena inside these thrusters within reasonable computational times. Regions of the thruster with complex magnetic field arrangements (such as those near eroded walls and magnets) and/or reduced Hall parameter (such as those near the anode and the cathode plume) challenge the validity of the quasi-one-dimensional assumption for the electrons. This paper reports on the development of a computer code that solves numerically the 2-D axisymmetric vector form of Ohm's law, with no assumptions regarding the rate of electron transport in the parallel and perpendicular directions. The numerical challenges related to the large disparity of the transport coefficients in the two directions are met by solving the equations in a computational mesh that is aligned with the magnetic field. The fully-2D approach allows for a large physical domain that extends more than five times the thruster channel length in the axial direction, and encompasses the cathode boundary. Ions are treated as an isothermal, cold (relative to the electrons) fluid, accounting for charge-exchange and multiple-ionization collisions in the momentum equations. A first series of simulations of two Hall thrusters, namely the BPT-4000 and a 6-kW laboratory thruster, quantifies the significance of ion diffusion in the anode region and the importance of the extended physical domain on studies related to the impact of the transport coefficients on the electron flow field.
Simulation of Pyroclastic Flows of Colima Volcano, Mexico, Using the TITAN2D Program
NASA Astrophysics Data System (ADS)
Rupp, B.; Bursik, M.; Patra, A.; Pitman, B.; Bauer, A.; Nichita, C.; Saucedo, R.; Macias, J.
2003-04-01
A new numerical code for simulating granular avalanches, TITAN2D, was used to model block-and-ash flows from the 1991-1999 eruptions of Colima Volcano, Mexico. The block-and-ash flows were simulated on a gridded Digital Elevation Model(DEM), which was prepared and imported using a standard GIS function library (GRASS). The TITAN2D program is based upon a model for an incompressible Coulomb continuum, a 'shallow-water' granular flow. The conservation equations for mass and momentum are solved with a Coulomb-type friction term at the interface between the granular material and the basal surface. It is assumed that conservation of energy can be neglected to first order because the coarse grain size typical of the basal avalanche results in minimal thermal effects on avalanche propagation. The resulting hyperbolic system of equations is solved using a parallel, adaptive mesh, Godunov scheme. The Message Passing Interface (MPI) API allows for computing on multiple processors, which increases computational power, decreases computing time, and allows the use of large data sets. Adaptive gridding allows for the concentration of computing power on regions of special interest. Mesh refinement captures the leading edge of the avalanche, as well as locations where the topography changes rapidly. Mesh unrefinement is applied where solution values are relatively constant or small. There were thousands of rockfalls and numerous block-and-ash flows during the 1991-1999 eruptions of Colima Volcano, with volumes ranging from a few cubic meters to 10^6 m^3. We have records of numerous flows, which include volume, run out distance, deposit area, and in some cases a videotape record of flow propagation. The flows originated from a vent plugging dome, lava flows or minor column collapse. All flows followed cross-slope concavities on the upper edifice, and channels or relative topographic lows on the lower edifice. The flows propagated for distances up to 4 km from the source. We are
NASA Astrophysics Data System (ADS)
Simmons, Daniel; Cools, Kristof; Sewell, Phillip
2016-11-01
Time domain electromagnetic simulation tools have the ability to model transient, wide-band applications, and non-linear problems. The Boundary Element Method (BEM) and the Transmission Line Modeling (TLM) method are both well established numerical techniques for simulating time-varying electromagnetic fields. The former surface based method can accurately describe outwardly radiating fields from piecewise uniform objects and efficiently deals with large domains filled with homogeneous media. The latter volume based method can describe inhomogeneous and non-linear media and has been proven to be unconditionally stable. Furthermore, the Unstructured TLM (UTLM) enables modelling of geometrically complex objects by using triangular meshes which removes staircasing and unnecessary extensions of the simulation domain. The hybridization of BEM and UTLM which is described in this paper is named the Boundary Element Unstructured Transmission-line (BEUT) method. It incorporates the advantages of both methods. The theory and derivation of the 2D BEUT method is described in this paper, along with any relevant implementation details. The method is corroborated by studying its correctness and efficiency compared to the traditional UTLM method when applied to complex problems such as the transmission through a system of Luneburg lenses and the modelling of antenna radomes for use in wireless communications.
Simulation of abrasive flow machining process for 2D and 3D mixture models
NASA Astrophysics Data System (ADS)
Dash, Rupalika; Maity, Kalipada
2015-12-01
Improvement of surface finish and material removal has been quite a challenge in a finishing operation such as abrasive flow machining (AFM). Factors that affect the surface finish and material removal are media viscosity, extrusion pressure, piston velocity, and particle size in abrasive flow machining process. Performing experiments for all the parameters and accurately obtaining an optimized parameter in a short time are difficult to accomplish because the operation requires a precise finish. Computational fluid dynamics (CFD) simulation was employed to accurately determine optimum parameters. In the current work, a 2D model was designed, and the flow analysis, force calculation, and material removal prediction were performed and compared with the available experimental data. Another 3D model for a swaging die finishing using AFM was simulated at different viscosities of the media to study the effects on the controlling parameters. A CFD simulation was performed by using commercially available ANSYS FLUENT. Two phases were considered for the flow analysis, and multiphase mixture model was taken into account. The fluid was considered to be a
NASA Astrophysics Data System (ADS)
Eichenlaub, Jesse B.
1995-03-01
Mounting a lenticular lens in front of a flat panel display is a well known, inexpensive, and easy way to create an autostereoscopic system. Such a lens produces half resolution 3D images because half the pixels on the LCD are seen by the left eye and half by the right eye. This may be acceptable for graphics, but it makes full resolution text, as displayed by common software, nearly unreadable. Very fine alignment tolerances normally preclude the possibility of removing and replacing the lens in order to switch between 2D and 3D applications. Lenticular lens based displays are therefore limited to use as dedicated 3D devices. DTI has devised a technique which removes this limitation, allowing switching between full resolution 2D and half resolution 3D imaging modes. A second element, in the form of a concave lenticular lens array whose shape is exactly the negative of the first lens, is mounted on a hinge so that it can be swung down over the first lens array. When so positioned the two lenses cancel optically, allowing the user to see full resolution 2D for text or numerical applications. The two lenses, having complementary shapes, naturally tend to nestle together and snap into perfect alignment when pressed together--thus obviating any need for user operated alignment mechanisms. This system represents an ideal solution for laptop and notebook computer applications. It was devised to meet the stringent requirements of a laptop computer manufacturer including very compact size, very low cost, little impact on existing manufacturing or assembly procedures, and compatibility with existing full resolution 2D text- oriented software as well as 3D graphics. Similar requirements apply to high and electronic calculators, several models of which now use LCDs for the display of graphics.
2D Waveguides as spin devices: spin-orbit and lead effects
NASA Astrophysics Data System (ADS)
Meza-Montes, Lilia
2011-03-01
Straight waveguides with different shapes have been proposed as devices to control the spin polarized transport, with Rahsba spin-orbit interaction as the mechanism to induce spin mixing. Several theoretical approaches have been applied, mostly based on transfer-matrix method. Here, the Schroedinger equation is solved by means of the Finite-Element Method,finding good agreement with previous calculations. It is known that positions of the leads influence the ballistic transport in this sort of cavities due to changes in the spatial symmetry. The role of the lead positions on the transmission and, in turn on the spin polarization, will be discussed for several geometries. The linear Dresselhaus interaction is taken into account to consider zincblende structure. Implications for quantum dots is also addresed. Partially supported by VIEP-BUAP.
Development of 2D soft X-ray measurement system in the large helical device.
Takemura, Y; Ohdachi, S; Watanabe, K Y; Du, X D
2014-11-01
A fast two-dimensional soft X-ray camera using silicon photo diode array is being developed in order to investigate high frequency MHD instability with high mode number. The advantage of the adopted diode is a large sensor area of 10 mm × 10 mm and small diode capacitance which enable us to measure signals with the short response time. The characteristic of the prototype is summarized as follows: Channel number is 6 × 8 = 48, detection range 1∼10 keV, the spatial resolution 128 mm at the plasma location, and frequency range DC∼100 kHz. Synthetic image of the prototype in the Large Helical Device is estimated by using perturbation model of MHD mode. PMID:25430317
NASA Astrophysics Data System (ADS)
Yamada, Susumu; Kitamura, Akihiro; Kurikami, Hiroshi; Machida, Masahiko
2015-04-01
Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on March 2011 released significant quantities of radionuclides to atmosphere. The most significant nuclide is radioactive cesium isotopes. Therefore, the movement of the cesium is one of the critical issues for the environmental assessment. Since the cesium is strongly sorbed by soil particles, the cesium transport can be regarded as the sediment transport which is mainly brought about by the aquatic system such as a river and a lake. In this research, our target is the sediment transport on Ogaki dam reservoir which is located in about 16 km northwest from FDNPP. The reservoir is one of the principal irrigation dam reservoirs in Fukushima Prefecture and its upstream river basin was heavily contaminated by radioactivity. We simulate the sediment transport on the reservoir using 2-D river simulation code named Nays2D originally developed by Shimizu et al. (The latest version of Nays2D is available as a code included in iRIC (http://i-ric.org/en/), which is a river flow and riverbed variation analysis software package). In general, a 2-D simulation code requires a huge amount of calculation time. Therefore, we parallelize the code and execute it on a parallel computer. We examine the relationship between the behavior of the sediment transport and the height of the reservoir exit. The simulation result shows that almost all the sand that enter into the reservoir deposit close to the entrance of the reservoir for any height of the exit. The amounts of silt depositing within the reservoir slightly increase by raising the height of the exit. However, that of the clay dramatically increases. Especially, more than half of the clay deposits, if the exit is sufficiently high. These results demonstrate that the water level of the reservoir has a strong influence on the amount of the clay discharged from the reservoir. As a result, we conclude that the tuning of the water level has a possibility for controlling the
Resistive MHD and kinetic simulations of 2D magnetotail equilibria leading to reconnection onset
NASA Astrophysics Data System (ADS)
Merkin, V. G.; Sitnov, M. I.; Lyon, J.; Cassak, P.
2013-12-01
Recent progress in theory and fully kinetic particle-in-cell simulations of 2D magnetotail-like configurations has revealed an important class of equilibria, which can be unstable to ion tearing instability and eventually result in explosive dissipation of energy, fast plasma sheet flows, dipolarizations and changes in initial magnetic topology (reconnection). Such configurations are characterized by an increase of magnetic flux at the tailward end of the equilibrium state. While the instability and subsequent reconfiguration of the initial state exhibit kinetic signatures, the question remains, which parts of the process can be reproduced using reduced plasma models, e.g., resistive and Hall MHD. In this presentation we explore the stability of the new class of magnetotail equilibria to the resistive tearing mode and investigate its properties as a function of equilibrium parameters, e.g., the current sheet thickness and the amount of flux accumulation at the tailward end of the equilibrium, as well as other system parameters, e.g., resistivity and Lundquist number. We discuss comparative aspects of the system behavior in kinetic and resistive MHD simulations, in particular, what, if any, parameters of the MHD system lead to similar growth rates of the instability. Since the theoretical onset condition of the kinetic tearing mode can be expressed fully in MHD terms, we also investigate the effects of including this criterion as an additional constraint on the tearing onset in our resistive MHD simulations. This work is a first step toward inclusion of a kinetically-motivated description of reconnection onset in global MHD simulations of the magnetosphere.
Simulation and analysis of solute transport in 2D fracture/pipe networks: the SOLFRAC program.
Bodin, Jacques; Porel, Gilles; Delay, Fred; Ubertosi, Fabrice; Bernard, Stéphane; de Dreuzy, Jean-Raynald
2007-01-01
The Time Domain Random Walk (TDRW) method has been recently developed by Delay and Bodin [Delay, F. and Bodin, J., 2001. Time domain random walk method to simulate transport by advection-dispersion and matrix diffusion in fracture networks. Geophys. Res. Lett., 28(21): 4051-4054.] and Bodin et al. [Bodin, J., Porel, G. and Delay, F., 2003c. Simulation of solute transport in discrete fracture networks using the time domain random walk method. Earth Planet. Sci. Lett., 6566: 1-8.] for simulating solute transport in discrete fracture networks. It is assumed that the fracture network can reasonably be represented by a network of interconnected one-dimensional pipes (i.e. flow channels). Processes accounted for are: (1) advection and hydrodynamic dispersion in the channels, (2) matrix diffusion, (3) diffusion into stagnant zones within the fracture planes, (4) sorption reactions onto the fracture walls and in the matrix, (5) linear decay, and (6) mass sharing at fracture intersections. The TDRW method is handy and very efficient in terms of computation costs since it allows for the one-step calculation of the particle residence time in each bond of the network. This method has been programmed in C++, and efforts have been made to develop an efficient and user-friendly software, called SOLFRAC. This program is freely downloadable at the URL (labo.univ-poitiers.fr/hydrasa/intranet/telechargement.htm). It calculates solute transport into 2D pipe networks, while considering different types of injections and different concepts of local dispersion within each flow channel. Post-simulation analyses are also available, such as the mean velocity or the macroscopic dispersion at the scale of the entire network. The program may be used to evaluate how a given transport mechanism influences the macroscopic transport behaviour of fracture networks. It may also be used, as is the case, e.g., with analytical solutions, to interpret laboratory or field tracer test experiments performed
2-D Three Fluid Simulation of Upstreaming Ions Above Auroral Precipitation
NASA Astrophysics Data System (ADS)
Danielides, M. A.; Lummerzheim, D.; Otto, A.; Stevens, R. J.
2006-12-01
The ionosphere is a rich reservoir of charged particles from which a variable fraction is transported to the magnetosphere. An important transport phenomena is the formation of upward ion flow above auroral structure. A primary region of the outflow is not known, but contributions come from polar cap, dayside cusp/cleft region, auroral oval, or even from mid-latitudes. In the past global magnetospheric models and fluid codes were used to simulate large scale ion outflow above, e.g., the polar-cap aurora. However, satellites orbiting at low- altitudes have repeatingly detected localized ion outflow above the auroral oval. Ionosphere-magnetosphere coupling simulations gave first insides into the small-scale dynamics of aurora. The aim of this study is the investigation of coupled plasma and neutral dynamics in smaller scale aurora to explain the generation, structure, and dynamics of vertical ion upstream. We consider auroral electron precipitation at ionospheric heights in a 2-D three fluid ionospheric-magnetospheric coupling code (Otto and Zhu, 2003). Specially we examine the effects of the electron precipitation, heat conduction and heating in field- aligned current through coulomb collisions or turbulence causing: i) electron heating, ii) electron pressure gradients, and iii) upstreaming of ions through a resulting ambipolar electric field. Our first case studies are performed for different boundary conditions and for different auroral electron precipitation parameters (variation in characteristic auroral energy, auroral energy flux and horizontal scale). The results shall clarify how auroral precipitation can drive ions upwards. Finally we discuss the effect of ion drag and the interaction of the upstreaming ions with a stable neutral constituent. Otto, O. and H. Zhu, Fluid plasma simulation of coupled systems: Ionosphere and magnetosphere, Space Plasma Simulation. Edited by J. Buechner, C. Dum, and M. Scholer., Lecture Notes in Physics, vol. 615, p.193
2D IR spectra of cyanide in water investigated by molecular dynamics simulations
Lee, Myung Won; Carr, Joshua K.; Göllner, Michael; Hamm, Peter; Meuwly, Markus
2013-01-01
Using classical molecular dynamics simulations, the 2D infrared (IR) spectroscopy of CN− solvated in D2O is investigated. Depending on the force field parametrizations, most of which are based on multipolar interactions for the CN− molecule, the frequency-frequency correlation function and observables computed from it differ. Most notably, models based on multipoles for CN− and TIP3P for water yield quantitatively correct results when compared with experiments. Furthermore, the recent finding that T 1 times are sensitive to the van der Waals ranges on the CN− is confirmed in the present study. For the linear IR spectrum, the best model reproduces the full widths at half maximum almost quantitatively (13.0 cm−1 vs. 14.9 cm−1) if the rotational contribution to the linewidth is included. Without the rotational contribution, the lines are too narrow by about a factor of two, which agrees with Raman and IR experiments. The computed and experimental tilt angles (or nodal slopes) α as a function of the 2D IR waiting time compare favorably with the measured ones and the frequency fluctuation correlation function is invariably found to contain three time scales: a sub-ps, 1 ps, and one on the 10-ps time scale. These time scales are discussed in terms of the structural dynamics of the surrounding solvent and it is found that the longest time scale (≈10 ps) most likely corresponds to solvent exchange between the first and second solvation shell, in agreement with interpretations from nuclear magnetic resonance measurements.
Observed and simulated power spectra of kinetic and magnetic energy retrieved with 2D inversions
NASA Astrophysics Data System (ADS)
Danilovic, S.; Rempel, M.; van Noort, M.; Cameron, R.
2016-10-01
Context. Information on the origin of internetwork magnetic field is hidden at the smallest spatial scales. Aims: We try to retrieve the power spectra with certainty to the highest spatial frequencies allowed by current instrumentation. Methods: To accomplish this, we use a 2D inversion code that is able to recover information up to the instrumental diffraction limit. Results: The retrieved power spectra have shallow slopes that extend further down to much smaller scales than has been found before. They do not seem to show any power law. The observed slopes at subgranular scales agree with those obtained from recent local dynamo simulations. Small differences are found for the vertical component of kinetic energy that suggest that observations suffer from an instrumental effect that is not taken into account. Conclusions: Local dynamo simulations quantitatively reproduce the observed magnetic energy power spectra on the scales of granulation down to the resolution limit of Hinode/SP, within the error bars inflicted by the method used and the instrumental effects replicated.
Some features of auroral electric fields as seen in 2D numerical simulations
NASA Technical Reports Server (NTRS)
Thiemann, H.; Singh, N.; Schunk, R. W.
1984-01-01
Results of 2D plasma simulations are presented and related to auroral observations. The formation of V-shaped potentials is studied with a 2 1/2 dimensional electrostatic particle-in-cell code for a magnetized plasma. It is shown that amplitudes for perpendicular electric fields are larger than for parallel electric fields, and for Te less than 100 eV, the amplitudes are comparable to the electric fields associated with the electrostatic shocks observed from the S3-3 satellite. The excitation of electrostatic ion-cyclotron EIC waves which occurs in the region below the parallel potential drop is discussed. In auroral plasmas EIC waves are observed above the V-shaped double layers in association with ion beams and field-aligned currents. The results also show that oppositely directed electric fields in the center and at the edges of the simulation region produce oppositely directed currents. Precipitating auroral ions in association with electron inverted-V events are seen by the DMSP-F6 satellite.
2D simulation of transport and degradation in the River Rhine.
Teichmann, L; Reuschenbach, P; Müller, B; Horn, H
2002-01-01
A simple 2D model has been developed for the simulation of mass transport and degradation of substances in the river Rhine. The model describes mass transport in the flow direction with a convective and a dispersive term. Transversal transport is described by segmenting the river and formulating a transversal exchange coefficient between the segments. Degradation can be formulated with any kinetics from first order to complex enzyme kinetics. The model was verified with monitoring data from the river Rhine. The hydrodynamic parameters such as dispersion coefficients and exchange coefficients were fitted to the conductivity, which was assumed to be non-degradable. The degradation term was fitted to ammonia values. The model was used to simulate measured concentrations of a readily (Aniline) and a poorly biodegradable substance (1,4-Dioxan) 10 m from the left river bank. It was the objective of this research program to develop a model which allows a realistic estimation of the locally and regionally predicted environmental concentration of chemical substances in the EU risk assessment scheme.
A Comparison of 2D to 3D Hydro Simulations of Asteroid Mitigation by a Strong Surface Explosion
NASA Astrophysics Data System (ADS)
Weaver, R.; Dearholdt, W.
2011-12-01
Disruption of a potentially hazardous object (PHO) by an energetic surface or subsurface burst is considered as one possible method of impact-hazard mitigation. This technique of employing surface or subsurface explosions has been popularized in the media but is probably one of the lower priority deflection/disruption methods, unless the warning time is short. In all of our current simulation we use realistic RADAR shape models for the initial geometry, not merely spherical objects. The non-sphericity of the geometry is very important in the resultant shock hydrodynamic evolution. This work is a follow-on to previous 2D simulations with the RAGE hydrocode to simulate the imparted momentum as a function of depth-of-burial (DOB) on a non-spherical "rubble pile" composition. Specifically, here, we have started a full 3D simulation of a 1 Mt surface explosion on a porous (~40% porosity) "rubble pile" model in the shape of asteroid 25143 Itokawa. This simulation has progressed far enough to start comparisons between the 2D and 3D runs of this model. There are significant changes in the 3D geometry that reduce the momentum imparted to the asteroid in these RAGE simulations. I will discuss this set of simulations, give some background results from previous 2D simulations and indicate the differences between 2D and 3D simulations.
2-D spectral element simulations of destructive ground shaking in Catania (Italy)
NASA Astrophysics Data System (ADS)
Priolo, Enrico
This study wants to estimate the strong ground motion in the municipal area of Catania (Italy) for a catastrophic earthquake scenario. It is part of a larger research program funded by the National Research Council - National Group for the Defence Against Earthquakes (CNR-GNDT), The Catania Project, devoted to evaluating the seismic risk of a highly urbanised area, such as that of Catania, located in a seismically active region. The reference earthquake simulates the catastrophic event (M 7.2) of 1693. The ground shaking is computed solving the 2-D full-wave equation by the Chebyshev spectral element method (SPEM). Particular emphasis is given to the construction of realistic structural models, also including the finest local detail, obtained from the geophysical, geological and geotechnical data available. Simulations are performed for several sources, to account for both a change in source position and orientation, and the finite extension of the fault along its dip. Synthetic seismograms and peak ground acceleration (PGA) envelopes, calculated at the surface for four transects across the Catania area, constitute the main result of this study which can be used for practical purposes. Simulations show that ground motion is strongly influenced by both source characteristics and crustal structure. We have found that PGA values range between 0.1 g and 0.5 g, although particular site conditions strongly affect these values locally. For example, the frequencies of maximum interest in civil engineering (1.5-4 Hz) are enhanced selectively by a thick portion of surface sediments (i.e., 30-100 m for an average shear wave velocity of 500-600 m/s). An unexpected feature is the appreciable increase of PGA at large epicentral distances, which contradicts classical attenuation relations. All the results are examined through an analysis of the propagating wavefield.
Using high resolution bathymetric lidar data for a Telemac2D simulation
NASA Astrophysics Data System (ADS)
Dobler, Wolfgang; Baran, Ramona; Steinbacher, Frank; Ritter, Marcel; Aufleger, Markus
2014-05-01
Knowledge about the hydraulic situation in a mountain torrent is relevant to quantify flood risks, to study sediment transport and to assess the waterbodies' ecology. To conduct reliable calculations, high-quality terrain data of riverbeds, riverbanks and floodplains are required. Typically, digital terrain models (DTMs) of floodplains are derived from classical airborne laserscanning (red wavelength) together with terrestrial surveys along riverbeds and riverbanks. Usually, these are restricted to a limited number of cross sections. Terrestrial surveys are required since laser measurement systems cannot penetrate the water column of the observed waterbodies. Consequently, data describing the geometry of riverbeds and bank structures are hardly available at high spatial resolutions and extents, comparable to the airborne-laser scanning derived data for river floodplains. In this study, a newly available, water-penetrating airborne laser system (green wavelength, FFG research project between the University of Innsbruck and Riegl LMS) was used to survey a mountain torrent. Detailed and extensive data (~30 points/m² on topo-bathy side) of the riverbed and the riverbanks were acquired with this single sensor. In order to construct a 2D-Telemac simulation, the point cloud was down-sampled to an appropriate resolution required for the simulation. The creation of the mesh was carried out with the Software HydroVish and imported into Blue Kenue for further boundary treatment. On one hand the calibration of the numerical model was based on a known water discharge-rate and on the other on abundant data points of the water surface. The green laser system demonstrates its great potential for such an analysis. The final results of the numerical simulation show clearly the supremacy of using such a high resolution data basis in contrast to the traditional way of terrestrial surveying of cross sections along riverbeds.
Simulation of bootstrap current in 2D and 3D ideal magnetic fields in tokamaks
NASA Astrophysics Data System (ADS)
Raghunathan, M.; Graves, J. P.; Cooper, W. A.; Pedro, M.; Sauter, O.
2016-09-01
We aim to simulate the bootstrap current for a MAST-like spherical tokamak using two approaches for magnetic equilibria including externally caused 3D effects such as resonant magnetic perturbations (RMPs), the effect of toroidal ripple, and intrinsic 3D effects such as non-resonant internal kink modes. The first approach relies on known neoclassical coefficients in ideal MHD equilibria, using the Sauter (Sauter et al 1999 Phys. Plasmas 6 2834) expression valid for all collisionalities in axisymmetry, and the second approach being the quasi-analytic Shaing–Callen (Shaing and Callen 1983 Phys. Fluids 26 3315) model in the collisionless regime for 3D. Using the ideal free-boundary magnetohydrodynamic code VMEC, we compute the flux-surface averaged bootstrap current density, with the Sauter and Shaing–Callen expressions for 2D and 3D ideal MHD equilibria including an edge pressure barrier with the application of resonant magnetic perturbations, and equilibria possessing a saturated non-resonant 1/1 internal kink mode with a weak internal pressure barrier. We compare the applicability of the self-consistent iterative model on the 3D applications and discuss the limitations and advantages of each bootstrap current model for each type of equilibrium.
Simulation of bootstrap current in 2D and 3D ideal magnetic fields in tokamaks
NASA Astrophysics Data System (ADS)
Raghunathan, M.; Graves, J. P.; Cooper, W. A.; Pedro, M.; Sauter, O.
2016-09-01
We aim to simulate the bootstrap current for a MAST-like spherical tokamak using two approaches for magnetic equilibria including externally caused 3D effects such as resonant magnetic perturbations (RMPs), the effect of toroidal ripple, and intrinsic 3D effects such as non-resonant internal kink modes. The first approach relies on known neoclassical coefficients in ideal MHD equilibria, using the Sauter (Sauter et al 1999 Phys. Plasmas 6 2834) expression valid for all collisionalities in axisymmetry, and the second approach being the quasi-analytic Shaing-Callen (Shaing and Callen 1983 Phys. Fluids 26 3315) model in the collisionless regime for 3D. Using the ideal free-boundary magnetohydrodynamic code VMEC, we compute the flux-surface averaged bootstrap current density, with the Sauter and Shaing-Callen expressions for 2D and 3D ideal MHD equilibria including an edge pressure barrier with the application of resonant magnetic perturbations, and equilibria possessing a saturated non-resonant 1/1 internal kink mode with a weak internal pressure barrier. We compare the applicability of the self-consistent iterative model on the 3D applications and discuss the limitations and advantages of each bootstrap current model for each type of equilibrium.
Hasanzadeh, Mohammad; Shadjou, Nasrin; Mokhtarzadeh, Ahad; Ramezani, Mohammad
2016-11-01
Graphene is a 2-D carbon nanomaterial with many distinctive properties that are electrochemically beneficial, such as large surface-to-volume ratio, lowered power usage, high conductivity and electron mobility. Graphene-based electrochemical immune-devices have recently gained much importance for detecting antigens and biomarkers responsible for cancer diagnosis. This review describes fabrication and chemical modification of the surfaces of graphene for immunesensing applications. We also present a comprehensive overview of current developments and key issues in the determination of some biological molecules with particular emphasis on evaluating the models. This review focuses mostly on new developments in the last 5years in development of chip architecture and integration, different sensing modes that can be used in conjunction with microfluidics, and new applications that have emerged or have been demonstrated; it also aims to point out where future research can be directed to in these areas. PMID:27524045
Towards Simulating the Transverse Ising Model in a 2D Array of Trapped Ions
NASA Astrophysics Data System (ADS)
Sawyer, Brian
2013-05-01
Two-dimensional Coulomb crystals provide a useful platform for large-scale quantum simulation. Penning traps enable confinement of large numbers of ions (>100) and allow for the tunable-range spin-spin interactions demonstrated in linear ion strings, facilitating simulation of quantum magnetism at a scale that is currently intractable on classical computers. We readily confine hundreds of Doppler laser-cooled 9Be+ within a Penning trap, producing a planar array of ions with self-assembled triangular order. The transverse ``drumhead'' modes of our 2D crystal along with the valence electron spin of Be+ serve as a resource for generating spin-motion and spin-spin entanglement. Applying a spin-dependent optical dipole force (ODF) to the ion array, we perform spectroscopy and thermometry of individual drumhead modes. This ODF also allows us to engineer long-range Ising spin couplings of either ferromagnetic or anti-ferromagnetic character whose approximate power-law scaling with inter-ion distance, d, may be varied continuously from 1 /d0 to 1 /d3. An effective transverse magnetic field is applied via microwave radiation at the ~124-GHz spin-flip frequency, and ground states of the effective Ising Hamiltonian may in principle be prepared adiabatically by slowly decreasing this transverse field in the presence of the induced Ising coupling. Long-range anti-ferromagnetic interactions are of particular interest due to their inherent spin frustration and resulting large, near-degenerate manifold of ground states. We acknowledge support from NIST and the DARPA-OLE program.
Icarus: A 2-D Direct Simulation Monte Carlo (DSMC) Code for Multi-Processor Computers
BARTEL, TIMOTHY J.; PLIMPTON, STEVEN J.; GALLIS, MICHAIL A.
2001-10-01
Icarus is a 2D Direct Simulation Monte Carlo (DSMC) code which has been optimized for the parallel computing environment. The code is based on the DSMC method of Bird[11.1] and models from free-molecular to continuum flowfields in either cartesian (x, y) or axisymmetric (z, r) coordinates. Computational particles, representing a given number of molecules or atoms, are tracked as they have collisions with other particles or surfaces. Multiple species, internal energy modes (rotation and vibration), chemistry, and ion transport are modeled. A new trace species methodology for collisions and chemistry is used to obtain statistics for small species concentrations. Gas phase chemistry is modeled using steric factors derived from Arrhenius reaction rates or in a manner similar to continuum modeling. Surface chemistry is modeled with surface reaction probabilities; an optional site density, energy dependent, coverage model is included. Electrons are modeled by either a local charge neutrality assumption or as discrete simulational particles. Ion chemistry is modeled with electron impact chemistry rates and charge exchange reactions. Coulomb collision cross-sections are used instead of Variable Hard Sphere values for ion-ion interactions. The electro-static fields can either be: externally input, a Langmuir-Tonks model or from a Green's Function (Boundary Element) based Poison Solver. Icarus has been used for subsonic to hypersonic, chemically reacting, and plasma flows. The Icarus software package includes the grid generation, parallel processor decomposition, post-processing, and restart software. The commercial graphics package, Tecplot, is used for graphics display. All of the software packages are written in standard Fortran.
Debris Flow Hazard Map Simulation using FLO-2D For Selected Areas in the Philippines
NASA Astrophysics Data System (ADS)
Khallil Ferrer, Peter; Llanes, Francesca; dela Resma, Marvee; Realino, Victoriano, II; Obrique, Julius; Ortiz, Iris Jill; Aquino, Dakila; Narod Eco, Rodrigo; Mahar Francisco Lagmay, Alfredo
2014-05-01
On December 4, 2012, Super Typhoon Bopha wreaked havoc in the southern region of Mindanao, leaving 1,067 people dead and causing USD 800 million worth of damage. Classified as a Category 5 typhoon by the Joint Typhoon Warning Center (JTWC), Bopha brought intense rainfall and strong winds that triggered landslides and debris flows, particularly in Barangay (village) Andap, New Bataan municipality, in the southern Philippine province of Compostela Valley. The debris flow destroyed school buildings and covered courts and an evacuation center. Compostela Valley also suffered the most casualties of any province: 612 out of a total of 1,067. In light of the disaster in Compostela, measures were immediately devised to improve available geohazard maps to raise public awareness about landslides and debris flows. A debris flow is a very rapid to extremely rapid flow of saturated non-plastic debris in a steep channel. They are generated when heavy rainfall saturates sediments, causing them to flow down river channels within an alluvial fan situated at the base of the slope of a mountain drainage network. Many rural communities in the Philippines, such as Barangay Andap, are situated at the apex of alluvial fans and in the path of potential debris flows. In this study, we conducted simulations of debris flows to assess the risks in inhabited areas throughout the Philippines and validated the results in the field, focusing on the provinces of Pangasinan and Aurora as primary examples. Watersheds that drain in an alluvial fan using a 10-m resolution Synthetic Aperture Radar (SAR)-derived Digital Elevation Model (DEM) was first delineated, and then a 1 in 100-year rain return rainfall scenario for the watershed was used to simulate debris flows using FLO-2D, a flood-routing software. The resulting simulations were used to generate debris flow hazard maps which are consistent with danger zones in alluvial fans delineated previously from satellite imagery and available DEMs. The
Library Analog Semiconductor Devices SPICE Simulators
Deveney, Michael F.; Archer, Wendel; Bogdan, Carolyn W.
1996-07-23
SPICE-SANDIA.LIB is a library of parameter sets and macromodels of semiconductor devices. They are used with Spice-based (SPICE is a program for electronic circuit analysis) simulators to simulate electronic circuits.
NASA Technical Reports Server (NTRS)
Shie, Chung-Lin; Tao, Wei-Kuo; Simpson, Joanne
2003-01-01
The 1999 Kwajalein Atoll field experiment (KWAJEX), one of several major TRMM (Tropical Rainfall Measuring Mission) field experiments, has successfully obtained a wealth of information and observation data on tropical convective systems over the western Central Pacific region. In this paper, clouds and convective systems that developed during three active periods (Aug 7-12, Aug 17-21, and Aug 29-Sep 13) around Kwajalein Atoll site are simulated using both 2D and 3D Goddard Cumulus Ensemble (GCE) models. Based on numerical results, the clouds and cloud systems are generally unorganized and short lived. These features are validated by radar observations that support the model results. Both the 2D and 3D simulated rainfall amounts and their stratiform contribution as well as the heat, water vapor, and moist static energy budgets are examined for the three convective episodes. Rainfall amounts are quantitatively similar between the two simulations, but the stratiform contribution is considerably larger in the 2D simulation. Regardless of dimension, fo all three cases, the large-scale forcing and net condensation are the two major physical processes that account for the evolution of the budgets with surface latent heat flux and net radiation solar and long-wave radiation)being secondary processes. Quantitative budget differences between 2D and 3D as well as between various episodes will be detailed.Morover, simulated radar signatures and Q1/Q2 fields from the three simulations are compared to each other and with radar and sounding observations.
NASA Technical Reports Server (NTRS)
Kapoor, Kamlesh; Anderson, Bernhard H.; Shaw, Robert J.
1994-01-01
A two-dimensional computational code, PRLUS2D, which was developed for the reactive propulsive flows of ramjets and scramjets, was validated for two-dimensional shock-wave/turbulent-boundary-layer interactions. The problem of compression corners at supersonic speeds was solved using the RPLUS2D code. To validate the RPLUS2D code for hypersonic speeds, it was applied to a realistic hypersonic inlet geometry. Both the Baldwin-Lomax and the Chien two-equation turbulence models were used. Computational results showed that the RPLUS2D code compared very well with experimentally obtained data for supersonic compression corner flows, except in the case of large separated flows resulting from the interactions between the shock wave and turbulent boundary layer. The computational results compared well with the experiment results in a hypersonic NASA P8 inlet case, with the Chien two-equation turbulence model performing better than the Baldwin-Lomax model.
Stability and accuracy of 3D neutron transport simulations using the 2D/1D method in MPACT
Collins, Benjamin; Stimpson, Shane; Kelley, Blake W.; Young, Mitchell T. H.; Kochunas, Brendan; Graham, Aaron; Larsen, Edward W.; Downar, Thomas; Godfrey, Andrew
2016-08-25
We derived a consistent “2D/1D” neutron transport method from the 3D Boltzmann transport equation, to calculate fuel-pin-resolved neutron fluxes for realistic full-core Pressurized Water Reactor (PWR) problems. The 2D/1D method employs the Method of Characteristics to discretize the radial variables and a lower order transport solution to discretize the axial variable. Our paper describes the theory of the 2D/1D method and its implementation in the MPACT code, which has become the whole-core deterministic neutron transport solver for the Consortium for Advanced Simulations of Light Water Reactors (CASL) core simulator VERA-CS. We also performed several applications on both leadership-class and industry-classmore » computing clusters. Results are presented for whole-core solutions of the Watts Bar Nuclear Power Station Unit 1 and compared to both continuous-energy Monte Carlo results and plant data.« less
NASA Astrophysics Data System (ADS)
Suzuki, Y.; KOYAGUCHI, T.; OGAWA, M.; Hachisu, I.
2001-05-01
Mixing of eruption cloud and air is one of the most important processes for eruption cloud dynamics. The critical condition of eruption types (eruption column or pyroclastic flow) depends on efficiency of mixing of eruption cloud and the ambient air. However, in most of the previous models (e.g., Sparks,1986; Woods, 1988), the rate of mixing between cloud and air is taken into account by introducing empirical parameters such as entrainment coefficient or turbulent diffusion coefficient. We developed a numerical model of 2-D (axisymmetrical) eruption columns in order to simulate the turbulent mixing between eruption column and air. We calculated the motion of an eruption column from a circular vent on the flat surface of the earth. Supposing that relative velocity of gas and ash particles is sufficiently small, we can treat eruption cloud as a single gas. Equation of state (EOS) for the mixture of the magmatic component (i.e. volcanic gas plus pyroclasts) and air can be expressed by EOS for an ideal gas, because volume fraction of the gas phase is very large. The density change as a function of mixing ratio between air and the magmatic component has a strong non-linear feature, because the density of the mixture drastically decreases as entrained air expands by heating. This non-linear feature can be reproduced by changing the gas constant and the ratio of specific heat in EOS for ideal gases; the molecular weight increases and the ratio of specific heat approaches 1 as the magmatic component increases. It is assumed that the dynamics of eruption column follows the Euler equation, so that no viscous effect except for the numerical viscosity is taken into account. Roe scheme (a general TVD scheme for compressible flow) is used in order to simulate the generation of shock waves inside and around the eruption column. The results show that many vortexes are generated around the boundary between eruption cloud and air, which results in violent mixing. When the size of
NASA Astrophysics Data System (ADS)
Wang, X.; Cai, M.
2016-11-01
A nonlinear velocity model that considers the influence of confinement and rock mass failure on wave velocity is developed. A numerical method, which couples FLAC and SPECFEM2D, is developed for ground motion modeling near excavation boundaries in underground mines. The motivation of developing the FLAC/SPECFEM2D coupled approach is to take merits of each code, such as the stress analysis capability in FLAC and the powerful wave propagation analysis capability in SPECFEM2D. Because stress redistribution and failure of the rock mass around an excavation are considered, realistic non-uniform velocity fields for the SPECFEM2D model can be obtained, and this is a notable feature of this study. Very large differences in wavefields and ground motion are observed between the results from the non-uniform and the uniform velocity models. If the non-uniform velocity model is used, the ground motion around a stope can be amplified up to five times larger than that given by the design scaling law. If a uniform velocity model is used, the amplification factor is only about three. Using the FLAC/SPECFEM2D coupled modeling approach, accurate velocity models can be constructed and this in turn will assist in predicting ground motions accurately around underground excavations.
2D fluid simulations of discharges at atmospheric pressure in reactive gas mixtures
NASA Astrophysics Data System (ADS)
Bourdon, Anne
2015-09-01
Since a few years, low-temperature atmospheric pressure discharges have received a considerable interest as they efficiently produce many reactive chemical species at a low energy cost. This potential is of great interest for a wide range of applications as plasma assisted combustion or biomedical applications. Then, in current simulations of atmospheric pressure discharges, there is the need to take into account detailed kinetic schemes. It is interesting to note that in some conditions, the kinetics of the discharge may play a role on the discharge dynamics itself. To illustrate this, we consider the case of the propagation of He-N2 discharges in long capillary tubes, studied for the development of medical devices for endoscopic applications. Simulation results put forward that the discharge dynamics and structure depend on the amount of N2 in the He-N2 mixture. In particular, as the amount of N2 admixture increases, the discharge propagation velocity in the tube increases, reaches a maximum for about 0 . 1 % of N2 and then decreases, in agreement with experiments. For applications as plasma assisted combustion with nanosecond repetitively pulsed discharges, there is the need to handle the very different timescales of the nanosecond discharge with the much longer (micro to millisecond) timescales of combustion processes. This is challenging from a computational point of view. It is also important to better understand the coupling of the plasma induced chemistry and the gas heating. To illustrate this, we present the simulation of the flame ignition in lean mixtures by a nanosecond pulsed discharge between two point electrodes. In particular, among the different discharge regimes of nanosecond repetitively pulsed discharges, a ``spark'' regime has been put forward in the experiments, with an ultra-fast local heating of the gas. For other discharge regimes, the gas heating is much weaker. We have simulated the nanosecond spark regime and have observed shock waves
2-D and 3-D numerical simulation of a supersonic inlet flowfield
NASA Astrophysics Data System (ADS)
Enomoto, Shunji; Arakawa, Chuichi
The 2-D and 3-D steady, Reynolds-averaged Navier-Stokes equations were numerically solved for the flowfields in an experimentally tested inlet model with bleed through a cavity. In the 2-D analysis, a normal shock was located at diffuser inlet instead of the position below the cavity. The normal shock in the middle of the diffuser caused a massive separation of the boundary layer and a large total pressure loss. In the 3-D analysis, the shock wave was distorted by the side wall boundary layer separation, and the complex flow structure was established. The result of the 3-D analysis agreed well with the experiment.
Improved physics for simulating submicron bipolar devices
NASA Astrophysics Data System (ADS)
Bennett, H. S.; Fuoss, D. E.
1985-10-01
The conventional device physics in most numerical simulations of bipolar transistors may not predict the measured electrical performance of shallow heavily doped emitters and bases. This paper summarizes improved device physics for numerical simulations of solid state devices with dopant densities up to aobut 3 x 10 to the 20th/cu cm and with junction depths as small as 0.1 micron. This improved device physics pertains to bandgap narrowing, effective intrinsic carrier concentrations, carrier mobilities, and lifetimes. When this improved physics is incorporated into device analysis codes such as SEDAN and then used to compute the electrical performance of n-p-n transistors, the predicted values agree very well with the measured values of the current-voltage characteristics and dc common emitter gains for devices with emitter-base junction depths between 10-0.16 microns.
Zhang, Xiaotao; He, Yudong; Li, Rongjin; Dong, Huanli; Hu, Wenping
2016-05-01
R. Li, H. Dong, and co-workers describe the exfoliation of cheap and abundant minerals, such as mica, into nanometer-thick 2D crystals with atomically flat surfaces. As described on page 3755, the application of the 2D electret in organic field-effect transistors is well-suited for flexible nonvolatile memory devices. Stored information can be retrieved even after power cycling. Moreover, the devices can be used as full-function transistors with a low-resistance and a high-resistance state.
NASA Technical Reports Server (NTRS)
Proffitt, M. H.; Solomon, S.; Loewenstein, M.
1992-01-01
A linear reference relationship between O3 and N2O has been used to estimate polar winter O3 loss from aircraft data taken in the lower stratosphere. Here, this relationship is evaluated at high latitudes by comparing it with a 2D model simulation and with NIMBUS 7 satellite measurements. Although comparisons with satellite measurements are limited to January through May, the model simulations are compared during other seasons. The model simulations and the satellite data are found to be consistent with the winter O3 loss analysis. It is shown that such analyses are likely to be inappropriate during other seasons.
Justification for a 2D versus 3D fingertip finite element model during static contact simulations.
Harih, Gregor; Tada, Mitsunori; Dolšak, Bojan
2016-10-01
The biomechanical response of a human hand during contact with various products has not been investigated in details yet. It has been shown that excessive contact pressure on the soft tissue can result in discomfort, pain and also cumulative traumatic disorders. This manuscript explores the benefits and limitations of a simplified two-dimensional vs. an anatomically correct three-dimensional finite element model of a human fingertip. Most authors still use 2D FE fingertip models due to their simplicity and reduced computational costs. However we show that an anatomically correct 3D FE fingertip model can provide additional insight into the biomechanical behaviour. The use of 2D fingertip FE models is justified when observing peak contact pressure values as well as displacement during the contact for the given studied cross-section. On the other hand, an anatomically correct 3D FE fingertip model provides a contact pressure distribution, which reflects the fingertip's anatomy.
Simulation of multi-steps thermal transition in 2D spin-crossover nanoparticles
NASA Astrophysics Data System (ADS)
Jureschi, Catalin-Maricel; Pottier, Benjamin-Louis; Linares, Jorge; Richard Dahoo, Pierre; Alayli, Yasser; Rotaru, Aurelian
2016-04-01
We have used an Ising like model to study the thermal behavior of a 2D spin crossover (SCO) system embedded in a matrix. The interaction parameter between edge SCO molecules and its local environment was included in the standard Ising like model as an additional term. The influence of the system's size and the ratio between the number of edge molecules and the other molecules were also discussed.
EDGE2D Simulations of JET{sup 13}C Migration Experiments
J.D. Strachan; J.P. Coad; G. Corrigan; G.F. Matthews; J. Spence
2004-06-16
Material migration has received renewed interest due to tritium retention associated with carbon transport to remote vessel locations. Those results influence the desirability of carbon usage on ITER. Subsequently, additional experiments have been performed, including tracer experiments attempting to identify material migration from specific locations. In this paper, EDGE2D models a well-diagnosed JET{sup 13}C tracer migration experiment. The role of SOL flows upon the migration patterns is identified.
Special nuclear material simulation device
Leckey, John H.; DeMint, Amy; Gooch, Jack; Hawk, Todd; Pickett, Chris A.; Blessinger, Chris; York, Robbie L.
2014-08-12
An apparatus for simulating special nuclear material is provided. The apparatus typically contains a small quantity of special nuclear material (SNM) in a configuration that simulates a much larger quantity of SNM. Generally the apparatus includes a spherical shell that is formed from an alloy containing a small quantity of highly enriched uranium. Also typically provided is a core of depleted uranium. A spacer, typically aluminum, may be used to separate the depleted uranium from the shell of uranium alloy. A cladding, typically made of titanium, is provided to seal the source. Methods are provided to simulate SNM for testing radiation monitoring portals. Typically the methods use at least one primary SNM spectral line and exclude at least one secondary SNM spectral line.
NASA Astrophysics Data System (ADS)
Das, Saptarshi
2016-10-01
This article proposes a disruptive device concept which meets both low power and high performance criterion for post-CMOS computing and at the same time enables aggressive channel length scaling. This device, hereafter refer to as two-dimensional electrostrictive field effect transistor or 2D-EFET, allows sub-60 mV/decade subthreshold swing and considerably higher ON current compared to any state of the art FETs. Additionally, by the virtue of its ultra-thin body nature and electrostatic integrity, the 2D-EFET enjoys scaling beyond 10 nm technology node. The 2D-EFET works on the principle of voltage induced strain transduction. It uses an electrostrictive material as gate oxide which expands in response to an applied gate bias and thereby transduces an out-of-plane stress on the 2D channel material. This stress reduces the inter-layer distance between the consecutive layers of the semiconducting 2D material and dynamically reduces its bandgap to zero i.e. converts it into a semi-metal. Thus the device operates with a large bandgap in the OFF state and a small or zero bandgap in the ON state. As a consequence of this transduction mechanism, internal voltage amplification takes place which results in sub-60 mV/decade subthreshold swing (SS).
Das, Saptarshi
2016-01-01
This article proposes a disruptive device concept which meets both low power and high performance criterion for post-CMOS computing and at the same time enables aggressive channel length scaling. This device, hereafter refer to as two-dimensional electrostrictive field effect transistor or 2D-EFET, allows sub-60 mV/decade subthreshold swing and considerably higher ON current compared to any state of the art FETs. Additionally, by the virtue of its ultra-thin body nature and electrostatic integrity, the 2D-EFET enjoys scaling beyond 10 nm technology node. The 2D-EFET works on the principle of voltage induced strain transduction. It uses an electrostrictive material as gate oxide which expands in response to an applied gate bias and thereby transduces an out-of-plane stress on the 2D channel material. This stress reduces the inter-layer distance between the consecutive layers of the semiconducting 2D material and dynamically reduces its bandgap to zero i.e. converts it into a semi-metal. Thus the device operates with a large bandgap in the OFF state and a small or zero bandgap in the ON state. As a consequence of this transduction mechanism, internal voltage amplification takes place which results in sub-60 mV/decade subthreshold swing (SS). PMID:27721489
NASA Astrophysics Data System (ADS)
Elangovan, Premkumar; Warren, Lucy M.; Mackenzie, Alistair; Rashidnasab, Alaleh; Diaz, Oliver; Dance, David R.; Young, Kenneth C.; Bosmans, Hilde; Strudley, Celia J.; Wells, Kevin
2014-08-01
Planar 2D x-ray mammography is generally accepted as the preferred screening technique used for breast cancer detection. Recently, digital breast tomosynthesis (DBT) has been introduced to overcome some of the inherent limitations of conventional planar imaging, and future technological enhancements are expected to result in the introduction of further innovative modalities. However, it is crucial to understand the impact of any new imaging technology or methodology on cancer detection rates and patient recall. Any such assessment conventionally requires large scale clinical trials demanding significant investment in time and resources. The concept of virtual clinical trials and virtual performance assessment may offer a viable alternative to this approach. However, virtual approaches require a collection of specialized modelling tools which can be used to emulate the image acquisition process and simulate images of a quality indistinguishable from their real clinical counterparts. In this paper, we present two image simulation chains constructed using modelling tools that can be used for the evaluation of 2D-mammography and DBT systems. We validate both approaches by comparing simulated images with real images acquired using the system being simulated. A comparison of the contrast-to-noise ratios and image blurring for real and simulated images of test objects shows good agreement ( < 9% error). This suggests that our simulation approach is a promising alternative to conventional physical performance assessment followed by large scale clinical trials.
Elangovan, Premkumar; Warren, Lucy M; Mackenzie, Alistair; Rashidnasab, Alaleh; Diaz, Oliver; Dance, David R; Young, Kenneth C; Bosmans, Hilde; Strudley, Celia J; Wells, Kevin
2014-08-01
Planar 2D x-ray mammography is generally accepted as the preferred screening technique used for breast cancer detection. Recently, digital breast tomosynthesis (DBT) has been introduced to overcome some of the inherent limitations of conventional planar imaging, and future technological enhancements are expected to result in the introduction of further innovative modalities. However, it is crucial to understand the impact of any new imaging technology or methodology on cancer detection rates and patient recall. Any such assessment conventionally requires large scale clinical trials demanding significant investment in time and resources. The concept of virtual clinical trials and virtual performance assessment may offer a viable alternative to this approach. However, virtual approaches require a collection of specialized modelling tools which can be used to emulate the image acquisition process and simulate images of a quality indistinguishable from their real clinical counterparts. In this paper, we present two image simulation chains constructed using modelling tools that can be used for the evaluation of 2D-mammography and DBT systems. We validate both approaches by comparing simulated images with real images acquired using the system being simulated. A comparison of the contrast-to-noise ratios and image blurring for real and simulated images of test objects shows good agreement ( < 9% error). This suggests that our simulation approach is a promising alternative to conventional physical performance assessment followed by large scale clinical trials.
Simulator scene display evaluation device
NASA Technical Reports Server (NTRS)
Haines, R. F. (Inventor)
1986-01-01
An apparatus for aligning and calibrating scene displays in an aircraft simulator has a base on which all of the instruments for the aligning and calibrating are mounted. Laser directs beam at double right prism which is attached to pivoting support on base. The pivot point of the prism is located at the design eye point (DEP) of simulator during the aligning and calibrating. The objective lens in the base is movable on a track to follow the laser beam at different angles within the field of vision at the DEP. An eyepiece and a precision diopter are movable into a position behind the prism during the scene evaluation. A photometer or illuminometer is pivotable about the pivot into and out of position behind the eyepiece.
Multi-layered coarse grid modelling in 2D urban flood simulations
NASA Astrophysics Data System (ADS)
Chen, Albert S.; Evans, Barry; Djordjević, Slobodan; Savić, Dragan A.
2012-11-01
SummaryRegular grids are commonly used in 2D flood modelling due to wide availability of terrain models and low pre-processing required for input preparation. Despite advances in both computing software and hardware, high resolution flood modelling remains computationally demanding when applied to a large study area when the available time and resources are limited. Traditional grid coarsening approach may reduce not only the computing demands, but also the accuracy of results due to the loss of detailed information. To keep key features that affect flow propagation within coarse grid, the approach proposed and tested in this paper adopts multiple layers in flood modelling to reflect individual flow paths separated by buildings within a coarse grid cell. The cell in each layer has its own parameters (elevation, roughness, building coverage ratio, and conveyance reduction factors) to describe itself and the conditions at boundaries with neighbourhood cells. Results of tests on the synthetic case study and the real world urban area show that the proposed multi-layered approach greatly improves the accuracy of coarse grid modelling with an insignificant additional computing cost. The proposed approach has been tested in conjunction with the UIM model by taking the high resolution results as the benchmark. The implementation of the proposed multi-layered methodology to any regular grid based 2D model would be straightforward.
Karavitis, G.A.
1984-01-01
The SIMSYS2D two-dimensional water-quality simulation system is a large-scale digital modeling software system used to simulate flow and transport of solutes in freshwater and estuarine environments. Due to the size, processing requirements, and complexity of the system, there is a need to easily move the system and its associated files between computer sites when required. A series of job control language (JCL) procedures was written to allow transferability between IBM and IBM-compatible computers. (USGS)
SEM simulation for 2D and 3D inspection metrology and defect review
NASA Astrophysics Data System (ADS)
Levi, Shimon; Schwartsband, Ishai; Khristo, Sergey; Ivanchenko, Yan; Adan, Ofer
2014-03-01
Advanced SEM simulation has become a key element in the ability of SEM inspection, metrology and defect review to meet the challenges of advanced technologies. It grants additional capabilities to the end user, such as 3D height measurements, accurate virtual metrology, and supports Design Based Metrology to bridge the gap between design layout and SEM image. In this paper we present SEM simulations capabilities, which take into consideration all parts of the SEM physical and electronic path, interaction between Electron beam and material, multi perspective SEM imaging and shadowing derived from proximity effects caused by the interaction of the Secondary Electrons signal with neighboring pattern edges. Optimizing trade-off between simulation accuracy, calibration procedures and computational complexity, the simulation is running in real-time with minimum impact on throughput. Experiment results demonstrate Height measurement capacities, and CAD based simulated pattern is compared with SEM image to evaluate simulated pattern fidelity.
Direct MD Simulations of Terahertz Absorption and 2D Spectroscopy Applied to Explosive Crystals.
Katz, G; Zybin, S; Goddard, W A; Zeiri, Y; Kosloff, R
2014-03-01
A direct molecular dynamics simulation of the THz spectrum of a molecular crystal is presented. A time-dependent electric field is added to a molecular dynamics simulation of a crystal slab. The absorption spectrum is composed from the energy dissipated calculated from a series of applied pulses characterized by a carrier frequency. The spectrum of crystalline cyclotrimethylenetrinitramine (RDX) and triacetone triperoxide (TATP) were simulated with the ReaxFF force field. The proposed direct method avoids the linear response and harmonic approximations. A multidimensional extension of the spectroscopy is suggested and simulated based on the nonlinear response to a single polarized pulse of radiation in the perpendicular polarization direction. PMID:26274066
NASA Astrophysics Data System (ADS)
Kawamura, E.; Lieberman, M. A.; Graves, D. B.
2014-12-01
A fast 2D axisymmetric fluid-analytical plasma reactor model using the finite elements simulation tool COMSOL is interfaced with a 1D particle-in-cell (PIC) code to study ion energy distributions (IEDs) in multi-frequency capacitive argon discharges. A bulk fluid plasma model, which solves the time-dependent plasma fluid equations for the ion continuity and electron energy balance, is coupled with an analytical sheath model, which solves for the sheath parameters. The time-independent Helmholtz equation is used to solve for the fields and a gas flow model solves for the steady-state pressure, temperature and velocity of the neutrals. The results of the fluid-analytical model are used as inputs to a PIC simulation of the sheath region of the discharge to obtain the IEDs at the target electrode. Each 2D fluid-analytical-PIC simulation on a moderate 2.2 GHz CPU workstation with 8 GB of memory took about 15-20 min. The multi-frequency 2D fluid-analytical model was compared to 1D PIC simulations of a symmetric parallel-plate discharge, showing good agreement. We also conducted fluid-analytical simulations of a multi-frequency argon capacitively coupled plasma (CCP) with a typical asymmetric reactor geometry at 2/60/162 MHz. The low frequency 2 MHz power controlled the sheath width and sheath voltage while the high frequencies controlled the plasma production. A standing wave was observable at the highest frequency of 162 MHz. We noticed that adding 2 MHz power to a 60 MHz discharge or 162 MHz to a dual frequency 2 MHz/60 MHz discharge can enhance the plasma uniformity. We found that multiple frequencies were not only useful for controlling IEDs but also plasma uniformity in CCP reactors.
Numerical Simulations of 2-D Phase-Field Model with Convection
NASA Astrophysics Data System (ADS)
Xu, Ying; McDonough, J. M.; Tagavi, K. A.
2003-11-01
We present a 2-D isotropic phase-field model with convection induced by a flow field applied to freezing into a supercooled melt of pure substance, nickle. Numerical procedures and details of numerical parameters employed are provided, and the convergence of the numerical method is demonstrated by conducting grid-function convergence tests. Dendrite structures, temperature fields, pressure fields, streamlines and velocity vector fields are presented at several different times during the dendrite growth process. Comparisons of dendrites and temperature fields with and without convection indicate that the flow field has a significant effect on the growth rate of the dendrites; in particular, it inhibits the growth. In addition, the flow field influences the dendritic structural morphologies and thickness of the interface. Moreover, the dendrites behave as a solid body in the flow leading to stagnation points and other interesting flow features.
Fractal electronic devices: simulation and implementation.
Fairbanks, M S; McCarthy, D N; Scott, S A; Brown, S A; Taylor, R P
2011-09-01
Many natural structures have fractal geometries that exhibit useful functional properties. These properties, which exploit the recurrence of patterns at increasingly small scales, are often desirable in applications and, consequently, fractal geometry is increasingly employed in diverse technologies ranging from radio antennae to storm barriers. In this paper, we explore the application of fractal geometry to electrical devices. First, we lay the foundations for the implementation of fractal devices by considering diffusion-limited aggregation (DLA) of atomic clusters. Under appropriate growth conditions, atomic clusters of various elements form fractal patterns driven by DLA. We perform a fractal analysis of both simulated and physical devices to determine their spatial scaling properties and demonstrate their potential as fractal circuit elements. Finally, we simulate conduction through idealized and DLA fractal devices and show that their fractal scaling properties generate novel, nonlinear conduction properties in response to depletion by electrostatic gates. PMID:21841218
Fractal electronic devices: simulation and implementation
NASA Astrophysics Data System (ADS)
Fairbanks, M. S.; McCarthy, D. N.; Scott, S. A.; Brown, S. A.; Taylor, R. P.
2011-09-01
Many natural structures have fractal geometries that exhibit useful functional properties. These properties, which exploit the recurrence of patterns at increasingly small scales, are often desirable in applications and, consequently, fractal geometry is increasingly employed in diverse technologies ranging from radio antennae to storm barriers. In this paper, we explore the application of fractal geometry to electrical devices. First, we lay the foundations for the implementation of fractal devices by considering diffusion-limited aggregation (DLA) of atomic clusters. Under appropriate growth conditions, atomic clusters of various elements form fractal patterns driven by DLA. We perform a fractal analysis of both simulated and physical devices to determine their spatial scaling properties and demonstrate their potential as fractal circuit elements. Finally, we simulate conduction through idealized and DLA fractal devices and show that their fractal scaling properties generate novel, nonlinear conduction properties in response to depletion by electrostatic gates.
NASA Astrophysics Data System (ADS)
Hahn, Herwig; Reuters, Benjamin; Geipel, Sascha; Schauerte, Meike; Benkhelifa, Fouad; Ambacher, Oliver; Kalisch, Holger; Vescan, Andrei
2015-03-01
GaN-based heterostructure FETs (HFETs) featuring a 2-D electron gas (2DEG) can offer very attractive device performance for power-switching applications. This performance can be assessed by evaluation of the dynamic on-resistance Ron,dyn vs. the breakdown voltage Vbd. In literature, it has been shown that with a high Vbd, Ron,dyn is deteriorated. The impairment of Ron,dyn is mainly driven by electron injection into surface, barrier, and buffer traps. Electron injection itself depends on the electric field which typically peaks at the gate edge towards the drain. A concept suitable to circumvent this issue is the charge-balancing concept which employs a 2-D hole gas (2DHG) on top of the 2DEG allowing for the electric field peak to be suppressed. Furthermore, the 2DEG concentration in the active channel cannot decrease by a change of the surface potential. Hence, beside an improvement in breakdown voltage, also an improvement in dynamic behaviour can be expected. Whereas the first aspect has already been demonstrated, the second one has not been under investigation so far. Hence, in this report, the effect of charge-balancing is discussed and its impact on the dynamic characteristics of HFETs is evaluated. It will be shown that with appropriate device design, the dynamic behaviour of HFETs can be improved by inserting an additional 2DHG.
Hahn, Herwig Reuters, Benjamin; Geipel, Sascha; Schauerte, Meike; Kalisch, Holger; Vescan, Andrei; Benkhelifa, Fouad; Ambacher, Oliver
2015-03-14
GaN-based heterostructure FETs (HFETs) featuring a 2-D electron gas (2DEG) can offer very attractive device performance for power-switching applications. This performance can be assessed by evaluation of the dynamic on-resistance R{sub on,dyn} vs. the breakdown voltage V{sub bd}. In literature, it has been shown that with a high V{sub bd}, R{sub on,dyn} is deteriorated. The impairment of R{sub on,dyn} is mainly driven by electron injection into surface, barrier, and buffer traps. Electron injection itself depends on the electric field which typically peaks at the gate edge towards the drain. A concept suitable to circumvent this issue is the charge-balancing concept which employs a 2-D hole gas (2DHG) on top of the 2DEG allowing for the electric field peak to be suppressed. Furthermore, the 2DEG concentration in the active channel cannot decrease by a change of the surface potential. Hence, beside an improvement in breakdown voltage, also an improvement in dynamic behaviour can be expected. Whereas the first aspect has already been demonstrated, the second one has not been under investigation so far. Hence, in this report, the effect of charge-balancing is discussed and its impact on the dynamic characteristics of HFETs is evaluated. It will be shown that with appropriate device design, the dynamic behaviour of HFETs can be improved by inserting an additional 2DHG.
Simulations of the infrared, Raman, and 2D-IR photon echo spectra of water in nanoscale silica pores
Burris, Paul C.; Laage, Damien; Thompson, Ward H.
2016-05-20
Vibrational spectroscopy is frequently used to characterize nanoconfined liquids and probe the effect of the confining framework on the liquid structure and dynamics relative to the corresponding bulk fluid. However, it is still unclear what molecular-level information can be obtained from such measurements. In this Paper, we address this question by using molecular dynamics (MD) simulations to reproduce the linear infrared (IR), Raman, and two-dimensional IR (2D-IR) photon echo spectra for water confined within hydrophilic (hydroxyl-terminated) silica mesopores. To simplify the spectra the OH stretching region of isotopically dilute HOD in D2O is considered. An empirical mapping approach is usedmore » to obtain the OH vibrational frequencies, transition dipoles, and transition polarizabilities from the MD simulations. The simulated linear IR and Raman spectra are in good general agreement with measured spectra of water in mesoporous silica reported in the literature. The key effect of confinement on the water spectrum is a vibrational blueshift for OH groups that are closest to the pore interface. The blueshift can be attributed to the weaker hydrogen bonds (H-bonds) formed between the OH groups and silica oxygen acceptors. Non-Condon effects greatly diminish the contribution of these OH moieties to the linear IR spectrum, but these weaker H-bonds are readily apparent in the Raman spectrum. The 2D-IR spectra have not yet been measured and thus the present results represent a prediction. Lastly, the simulated spectra indicate that it should be possible to probe the slower spectral diffusion of confined water compared to the bulk liquid by analysis of the 2D-IR spectra.« less
Radar Reflectivity Simulated by a 2-D Spectra Bin Model: Sensitivity of Cloud-aerosol Interaction
NASA Technical Reports Server (NTRS)
Li, Kiaowen; Tao, Wei-Kuo; Khain, Alexander; Simpson, Joanne; Johnson, Daniel
2003-01-01
The Goddard Cumulus Ensemble (GCE) model with bin spectra microphysics is used to simulate mesoscale convective systems.The model uses explicit bins to represent size spectra of cloud nuclei, water drops, ice crystals, snow and graupel. Each hydrometeorite category is described by 33 mass bins. The simulations provide a unique data set of simulated raindrop size distribution in a realistic dynamic frame. Calculations of radar parameters using simulated drop size distribution serve as an evaluation of numerical model performance. In addition, the GCE bin spectra modes is a very useful tool to study uncertainties related to radar observations; all the environmental parameters are precisely known. In this presentation, we concentrate on the discussion of Z-R (ZDR-R) relation in the simulated systems. Due to computational limitations, the spectra bin model has been run in two dimensions with 31 stretched vertical layers and 1026 horizontal grid points (1 km resolution). Two different cases, one in midlatitude continent, the other in tropical ocean, have been simulated. The continental case is a strong convection which lasted for two hours. The oceanic case is a persistent system with more than 10 hours' life span. It is shown that the simulated Z-R (ZDR-R) relations generally agree with observations using radar and rain gauge data. The spatial and temporal variations of Z-R relation in different locations are also analyzed. Impact of aerosols on cloud formation and raindrop size distribution was studied. Both clean (low CCN) and dirty (high CCN) cases are simulated. The Z-R relation is shown to vary considerable in the initial CCN concentrations.
Monte Carlo Simulations of Charge Transport in 2D Organic Photovoltaics.
Gagorik, Adam G; Mohin, Jacob W; Kowalewski, Tomasz; Hutchison, Geoffrey R
2013-01-01
The effect of morphology on charge transport in organic photovoltaics is assessed using Monte Carlo. In isotopic two-phase morphologies, increasing the domain size from 6.3 to 18.3 nm improves the fill factor by 11.6%, a result of decreased tortuosity and relaxation of Coulombic barriers. Additionally, when small aggregates of electron acceptors are interdispersed into the electron donor phase, charged defects form in the system, reducing fill factors by 23.3% on average, compared with systems without aggregates. In contrast, systems with idealized connectivity show a 3.31% decrease in fill factor when domain size was increased from 4 to 64 nm. We attribute this to a decreased rate of exciton separation at donor-acceptor interfaces. Finally, we notice that the presence of Coulomb interactions increases device performance as devices become smaller. The results suggest that for commonly found isotropic morphologies the Coulomb interactions between charge carriers dominates exciton separation effects.
In vitro construction of 2D and 3D simulations of the murine hematopoietic niche.
Chitteti, Brahmananda Reddy; Bethel, Monique; Voytik-Harbin, Sherry L; Kacena, Melissa A; Srour, Edward F
2013-01-01
Hematopoietic stem cells (HSC) undergo multilineage differentiation or self-renewal to maintain normal hematopoiesis and to sustain the size of the HSC pool throughout life. These processes are determined by a complex interplay of molecular signals between HSC and other cellular components such as osteoblasts (OB), stromal cells, endothelial cells, and a number of extracellular matrix (ECM) proteins. Through changes in its physical properties within the bone marrow (BM) microenvironment, collagen, which is one of the most critical ECM proteins, can modulate HSC function and maintenance of the competence of the hematopoietic niche (HN). At present, there is no consensus as to how different cellular elements of the niche collaborate and interact to promote HSC self-renewal or differentiation to maintain hematopoiesis. Deciphering these interactions and the impact of mechanical properties of the collagen microstructures within the HN has critical clinical implications in the areas of stem cell homing, engraftment, and maintenance of HSC function. In this chapter, we describe several of the in vitro methodologies for establishing and maintaining HSC in vitro including the isolation of OB, stromal cells, and hematopoietic progenitor cells, as well as the establishment of both two-dimensional (2D) and three-dimensional (3D) coculture systems.
Fourier based methodology for simulating 2D-random shapes in heterogeneous materials
NASA Astrophysics Data System (ADS)
Mattrand, C.; Béakou, A.; Charlet, K.
2015-08-01
Gaining insights into the effects of microstructural details on materials behavior may be achieved by incorporating their attributes into numerical modeling. This requires us to make considerable efforts to feature heterogeneity morphology distributions and their spatial arrangement. This paper focuses on modeling the scatter observed in materials heterogeneity geometry. The proposed strategy is based on the development of a 1D-shape signature function representing the 2D-section of a given shape, on Fourier basis functions. The Fourier coefficients are then considered as random variables. This methodology has been applied to flax fibers which are gradually introduced into composite materials as a potential alternative to synthetic reinforcements. In this contribution, the influence of some underlying assumptions regarding the choice of one 1D-shape signature function, its discretization scheme and truncation level, and the best way of modeling the associated random variables is also investigated. Some configurations coming from the combination of these tuning parameters are found to be sufficiently relevant to render efficiently the morphometric factors of the observed fibers statistically speaking.
Monte Carlo simulations of a novel Micromegas 2D array for proton dosimetry.
Dolney, D; Ainsley, C; Hollebeek, R; Maughan, R
2016-02-21
Modern proton therapy affords control of the delivery of radiotherapeutic dose on fine length and temporal scales. The authors have developed a novel detector technology based on Micromesh Gaseous Structure (Micromegas) that is uniquely tailored for applications using therapeutic proton beams. An implementation of a prototype Micromegas detector for Monte Carlo using Geant4 is presented here. Comparison of simulation results with measurements demonstrates agreement in relative dose along the proton longitudinal dose profile to be 1%. The effect of a radioactive calibration source embedded in the chamber gas is demonstrated by measurements and reproduced by simulations, also at the 1% level. Our Monte Carlo simulations are shown to reproduce the time structure of ionization pulses produced by a double-scattering delivery system.
Monte Carlo simulations of a novel Micromegas 2D array for proton dosimetry
NASA Astrophysics Data System (ADS)
Dolney, D.; Ainsley, C.; Hollebeek, R.; Maughan, R.
2016-02-01
Modern proton therapy affords control of the delivery of radiotherapeutic dose on fine length and temporal scales. The authors have developed a novel detector technology based on Micromesh Gaseous Structure (Micromegas) that is uniquely tailored for applications using therapeutic proton beams. An implementation of a prototype Micromegas detector for Monte Carlo using Geant4 is presented here. Comparison of simulation results with measurements demonstrates agreement in relative dose along the proton longitudinal dose profile to be 1%. The effect of a radioactive calibration source embedded in the chamber gas is demonstrated by measurements and reproduced by simulations, also at the 1% level. Our Monte Carlo simulations are shown to reproduce the time structure of ionization pulses produced by a double-scattering delivery system.
NASA Astrophysics Data System (ADS)
Michelson, Sara; Bao, Jian-Wen; Grell, Evelyn
2016-04-01
In this study, numerical model simulations of an idealized 2-D squall line are investigated using microphysics budget analysis. Four commonly-used microphysics schemes of various complexity are used in the simulations. Diagnoses of the source and sink terms of the hydrometeor budget equations reveal that the differences related to the assumptions of hydrometeor size-distributions between the schemes lead to the differences in the simulations due to the net effect of various microphysical processes on the interaction between latent heating/evaporative cooling and flow dynamics as the squall line develops. Results from this study also highlight the possibility that the advantage of double-moment formulations can be overshadowed by the uncertainties in the spectral definition of individual hydrometeor categories and spectrum-dependent microphysical processes.
Using FPGA Devices to Accelerate Biomolecular Simulations
Alam, Sadaf R; Agarwal, Pratul K; Smith, Melissa C; Vetter, Jeffrey S; Caliga, David E
2007-03-01
A field-programmable gate array implementation of the particle-mesh Ewald a molecular dynamics simulation method reduces the microprocessor time-to-solution by a factor of three while using only high-level languages. The application speedup on FPGA devices increases with the problem size. The authors use a performance model to analyze the potential of simulating large-scale biological systems faster than many cluster-based supercomputing platforms.
NASA Astrophysics Data System (ADS)
Darvini, G.; Salandin, P.
2009-12-01
To analyze the impact of the hydraulic conductivity K spatial variability in a real field case (as an example to delimitate a well catchment), numerical simulations can be reasonably developed in a two-dimensional vertical average context. Nevertheless the plume evolution is a consequence of a more complex three-dimensional heterogeneous structure whose vertical variability dominates the dispersion phenomena at local scale. In larger domains, the effect of the vertical heterogeneity combines itself with that one due to the horizontal variability of K, and only when the plume has travelled a large number of (horizontal) integral scales, its evolution can be analyzed in a regional context, under the hypothesis that the transmissivity spatial distribution prevails. Until this limit is reached, the vertical and horizontal variability of K are combined to give a fully 3-D dispersion process. In all these situations, to successfully accomplish the 3-D heterogeneous structure of the aquifer in 2-D simulations, more than the planimetric depth-averaged variability of K must be accounted for. To define the uncertainty related to the use of different planimetric schematizations of the real hydraulic conductivity spatial distribution, we present here the results of some numerical experiments that compare the 3-D plume evolution with 2-D simulations developed by tacking into account different hydraulic conductivity distribution schematization, by considering a hierarchical architecture of media also. This description of a sedimentary formation combined with the finite size of the plume requires theoretical and numerical tools able to take into account the flow field inhomogeneity and the ergodicity lack that characterize the transport phenomena. Following this way it will be possible to quantify / reduce the uncertainty related to a 2-D schematization in a large number of real cases where the domain spans between the local and the regional scale and whose dimension may lead to
14 CFR 121.921 - Training devices and simulators.
Code of Federal Regulations, 2014 CFR
2014-01-01
... devices and simulators. (a) Each flight training device or airplane simulator that will be used in an AQP... 14 Aeronautics and Space 3 2014-01-01 2014-01-01 false Training devices and simulators. 121.921... device or flight simulator qualification level: (1) Required evaluation of individual or crew...
14 CFR 121.921 - Training devices and simulators.
Code of Federal Regulations, 2010 CFR
2010-01-01
... devices and simulators. (a) Each flight training device or airplane simulator that will be used in an AQP... 14 Aeronautics and Space 3 2010-01-01 2010-01-01 false Training devices and simulators. 121.921... device or flight simulator qualification level: (1) Required evaluation of individual or crew...
14 CFR 121.921 - Training devices and simulators.
Code of Federal Regulations, 2012 CFR
2012-01-01
... devices and simulators. (a) Each flight training device or airplane simulator that will be used in an AQP... 14 Aeronautics and Space 3 2012-01-01 2012-01-01 false Training devices and simulators. 121.921... device or flight simulator qualification level: (1) Required evaluation of individual or crew...
14 CFR 121.921 - Training devices and simulators.
Code of Federal Regulations, 2013 CFR
2013-01-01
... devices and simulators. (a) Each flight training device or airplane simulator that will be used in an AQP... 14 Aeronautics and Space 3 2013-01-01 2013-01-01 false Training devices and simulators. 121.921... device or flight simulator qualification level: (1) Required evaluation of individual or crew...
Kaiglová, Jana; Langhammer, Jakub; Jiřinec, Petr; Janský, Bohumír; Chalupová, Dagmar
2015-03-01
This article used various hydrodynamic and sediment transport models to analyze the potential and the limits of different channel schematizations. The main aim was to select and evaluate the most suitable simulation method for fine-grained sediment remobilization assessment. Three types of channel schematization were selected to study the flow potential for remobilizing fine-grained sediment in artificially modified channels. Schematization with a 1D cross-sectional horizontal plan, a 1D+ approach, splitting the riverbed into different functional zones, and full 2D mesh, adopted in MIKE by the DHI modeling suite, was applied to the study. For the case study, a 55-km stretch of the Bílina River, in the Czech Republic, Central Europe, which has been heavily polluted by the chemical and coal mining industry since the mid-twentieth century, was selected. Long-term exposure to direct emissions of toxic pollutants including heavy metals and persistent organic pollutants (POPs) resulted in deposits of pollutants in fine-grained sediments in the riverbed. Simulations, based on three hydrodynamic model schematizations, proved that for events not exceeding the extent of the riverbed profile, the 1D schematization can provide comparable results to a 2D model. The 1D+ schematization can improve accuracy while keeping the benefits of high-speed simulation and low requirements of input DEM data, but the method's suitability is limited by the channel properties. PMID:25687259
Simulations of chemotaxis and random motility in 2D random porous domains.
Jabbarzadeh, Ehsan; Abrams, Cameron F
2007-02-01
We discuss a generic computational model of eukariotic chemotaxis in 2D random porous domains. The model couples the fully time-dependent finite-difference solution of a reaction-diffusion equation for the concentration field of a chemoattractant to biased random walks representing individual chemotactic cells. We focus in particular on the influence of consumption of chemoattractant by the boundaries of obstacles with irregular shapes which are distributed randomly in the domain on the chemotactic response of the cells. Cells are stimulated to traverse a field of obstacles by a line source of chemoattractant. We find that the reactivity of the obstacle boundaries with respect to the chemoattractant strongly determines the transit time of cells through two primary mechanisms. The channeling effect arises because cells are effectively repelled from surfaces which consume chemoattractant, and opposing surfaces therefore act to keep cells in the middle of channels. This reduces traversal times relative to the case with unreactive boundaries, provided that the appropriate Péclet number relating the strength of reactivity to diffusion in governing chemoattractant transport is neither too low nor too high. The dead-zone effect arises due to a realistic threshold on the chemotactic response, which at steady state results in portions of the domain having no detectable gradient. Of these two, the channeling effect is responsible for 90% of the sensitivity of transit times to boundary reactivity. Based on these results, we speculate that it may be possible to tune the rates of cellular penetration into porous domains by engineering the reactivity of the internal surfaces to cytokines.
Treatment of LBCs in 2D simulation of convection over hills
NASA Astrophysics Data System (ADS)
Tian, Wenshou; Guo, Zhenhai; Yu, Rucong
2004-08-01
A series of idealized model simulations are analyzed to determine the sensitivity of model results to different configurations of the lateral boundary conditions (LBCs) in simulating mesoscale shallow convection over hilly terrain. In the simulations with steady thermal forcing at the model surface, a radiation condition at both boundaries is the best choice under high wind conditions, and the best results are produced when both the normal velocities and the temperature are treated with the radiation scheme in which the phase speed is the same for different variables. When the background wind speed is reasonably small, the LBC configuration with either the radiation or the zero gradient condition at both boundaries tends to make the numerical solution unstable. The choice of a constant condition at the inflow boundary and a radiation outflow boundary condition is appropriate in most cases. In the simulations with diurnal thermal forcing at the model surface, different LBC schemes are combined together to reduce spurious signals induced by the outflow boundary. A specification inflow boundary condition, in which the velocity fields at the inflow boundary are provided using the time-dependent results of a simulation with periodic LBCs over a flat domain, is tested and the results indicate that the specification condition at the inflow boundary makes it possible to use a smaller model domain to obtain reasonable results. The model horizontal domain length should be greater than a critical length, which depends on the domain depth H and the angle between gravity wave phase lines and the vertical. An estimate of minimum domain length is given by[(H - z_i )/π U]sqrt {N^2 L_x^2 - 4π ^2 U^2 } , where N and U are the background stability and wind speed, respectively, L x is the typical gravity wavelength scale, and z i is the convective boundary layer (CBL) depth.
Heat transfer simulation of composite devices
NASA Astrophysics Data System (ADS)
Imre, L.
Composite devices are built from elements of various sizes, shapes, materials, and functions. The present investigation is concerned with composite devices in which, during their normal operation, heat is produced that has to be dissipated in some suitable way. In connection with this requirement, a cooling agent can be made to flow through the system by means of a pump or by an exploitation of the thermosyphon effect. Simultaneous processes in composite devices are considered along with a physical mathematical modelling conception, network models, and hierarchic and mixed models. Attention is given to the simulation of thermohydrodynamical systems, the application of simultaneous heat and mass flow network models, and the simulation of thermomechanical systems.
2D simulations based on general time-dependent reciprocal relation for LFEIT.
Karadas, Mursel; Gencer, Nevzat Guneri
2015-08-01
Lorentz field electrical impedance tomography (LFEIT) is a newly proposed technique for imaging the conductivity of the tissues by measuring the electromagnetic induction under the ultrasound pressure field. In this paper, the theory and numerical simulations of the LFEIT are reported based on the general time dependent formulation. In LFEIT, a phased array ultrasound probe is used to introduce a current distribution inside a conductive body. The velocity current occurs, due to the movement of the conductive particles under a static magnetic field. In order to sense this current, a receiver coil configuration that surrounds the volume conductor is utilized. Finite Element Method (FEM) is used to carry out the simulations of LFEIT. It is shown that, LFEIT can be used to reconstruct the conductivity even up to 50% perturbation in the initial conductivity distribution. PMID:26736569
The ideal tearing mode: 2D MHD simulations in the linear and nonlinear regimes
NASA Astrophysics Data System (ADS)
Landi, Simone; Del Zanna, Luca; Pucci, Fulvia; Velli, Marco; Papini, Emanuele
2015-04-01
We present compressible, resistive MHD numerical simulations of the linear and nonlinear evolution of the tearing instability, for both Harris sheet and force-free initial equilibrium configurations. We analyze the behavior of a current sheet with aspect ratio S1/3, where S is the Lundquist number. This scaling has been recently recognized to be the threshold for fast reconnection occurring on the ideal Alfvenic timescale, with a maximum growth rate that becomes asymptotically independent on S. Our simulations clearly confirm that the tearing instability maximum growth rate and the full dispersion relation are exactly those predicted by the linear theory, at least for the values of S explored here. In the nonlinear stage, we notice the rapid onset and subsequent coalescence of plasmoids, as observed in previous simulations of the Sweet-Parker reconnection scenario. These findings strongly support the idea that in a fully dynamic regime, as soon as current sheets develop and reach the critical threshold in their aspect ratio of S1/3 (occurring well before the Sweet-Parker configuration is able to form), the tearing mode is able to trigger fast reconnection and plasmoids formation on Alfvenic timescales, as required to explain the violent flare activity often observed in solar and astrophysical plasmas.
Zhou, Y. L.; Wang, Z. H.; Xu, X. Q.; Li, H. D.; Feng, H.; Sun, W. G.
2015-01-15
Plasma fueling with high efficiency and deep injection is very important to enable fusion power performance requirements. It is a powerful and efficient way to study neutral transport dynamics and find methods of improving the fueling performance by doing large scale simulations. Two basic fueling methods, gas puffing (GP) and supersonic molecular beam injection (SMBI), are simulated and compared in realistic divertor geometry of the HL-2A tokamak with a newly developed module, named trans-neut, within the framework of BOUT++ boundary plasma turbulence code [Z. H. Wang et al., Nucl. Fusion 54, 043019 (2014)]. The physical model includes plasma density, heat and momentum transport equations along with neutral density, and momentum transport equations. Transport dynamics and profile evolutions of both plasma and neutrals are simulated and compared between GP and SMBI in both poloidal and radial directions, which are quite different from one and the other. It finds that the neutrals can penetrate about four centimeters inside the last closed (magnetic) flux surface during SMBI, while they are all deposited outside of the LCF during GP. It is the radial convection and larger inflowing flux which lead to the deeper penetration depth of SMBI and higher fueling efficiency compared to GP.
Zhou, Y. L.; Wang, Z. H.; Xu, X. Q.; Li, H. D.; Feng, H.; Sun, W. G.
2015-01-09
Plasma fueling with high efficiency and deep injection is very important to enable fusion power performance requirements. It is a powerful and efficient way to study neutral transport dynamics and find methods of improving the fueling performance by doing large scale simulations. Furthermore, two basic fueling methods, gas puffing (GP) and supersonic molecular beam injection (SMBI), are simulated and compared in realistic divertor geometry of the HL-2A tokamak with a newly developed module, named trans-neut, within the framework of BOUT++ boundary plasma turbulence code [Z. H. Wang et al., Nucl. Fusion 54, 043019 (2014)]. The physical model includes plasma density, heat and momentum transport equations along with neutral density, and momentum transport equations. In transport dynamics and profile evolutions of both plasma and neutrals are simulated and compared between GP and SMBI in both poloidal and radial directions, which are quite different from one and the other. It finds that the neutrals can penetrate about four centimeters inside the last closed (magnetic) flux surface during SMBI, while they are all deposited outside of the LCF during GP. Moreover, it is the radial convection and larger inflowing flux which lead to the deeper penetration depth of SMBI and higher fueling efficiency compared to GP.
Zhou, Y. L.; Wang, Z. H.; Xu, X. Q.; Li, H. D.; Feng, H.; Sun, W. G.
2015-01-09
Plasma fueling with high efficiency and deep injection is very important to enable fusion power performance requirements. It is a powerful and efficient way to study neutral transport dynamics and find methods of improving the fueling performance by doing large scale simulations. Furthermore, two basic fueling methods, gas puffing (GP) and supersonic molecular beam injection (SMBI), are simulated and compared in realistic divertor geometry of the HL-2A tokamak with a newly developed module, named trans-neut, within the framework of BOUT++ boundary plasma turbulence code [Z. H. Wang et al., Nucl. Fusion 54, 043019 (2014)]. The physical model includes plasma density,more » heat and momentum transport equations along with neutral density, and momentum transport equations. In transport dynamics and profile evolutions of both plasma and neutrals are simulated and compared between GP and SMBI in both poloidal and radial directions, which are quite different from one and the other. It finds that the neutrals can penetrate about four centimeters inside the last closed (magnetic) flux surface during SMBI, while they are all deposited outside of the LCF during GP. Moreover, it is the radial convection and larger inflowing flux which lead to the deeper penetration depth of SMBI and higher fueling efficiency compared to GP.« less
A GPU Simulation Tool for Training and Optimisation in 2D Digital X-Ray Imaging
Gallio, Elena; Rampado, Osvaldo; Gianaria, Elena; Bianchi, Silvio Diego; Ropolo, Roberto
2015-01-01
Conventional radiology is performed by means of digital detectors, with various types of technology and different performance in terms of efficiency and image quality. Following the arrival of a new digital detector in a radiology department, all the staff involved should adapt the procedure parameters to the properties of the detector, in order to achieve an optimal result in terms of correct diagnostic information and minimum radiation risks for the patient. The aim of this study was to develop and validate a software capable of simulating a digital X-ray imaging system, using graphics processing unit computing. All radiological image components were implemented in this application: an X-ray tube with primary beam, a virtual patient, noise, scatter radiation, a grid and a digital detector. Three different digital detectors (two digital radiography and a computed radiography systems) were implemented. In order to validate the software, we carried out a quantitative comparison of geometrical and anthropomorphic phantom simulated images with those acquired. In terms of average pixel values, the maximum differences were below 15%, while the noise values were in agreement with a maximum difference of 20%. The relative trends of contrast to noise ratio versus beam energy and intensity were well simulated. Total calculation times were below 3 seconds for clinical images with pixel size of actual dimensions less than 0.2 mm. The application proved to be efficient and realistic. Short calculation times and the accuracy of the results obtained make this software a useful tool for training operators and dose optimisation studies. PMID:26545097
2D simulations of transport dynamics during tokamak fuelling by supersonic molecular beam injection
NASA Astrophysics Data System (ADS)
Wang, Z. H.; Xu, X. Q.; Xia, T. Y.; Rognlien, T. D.
2014-04-01
Time-dependent transport of both plasma and neutrals is simulated during supersonic molecular beam injection (SMBI) yielding the evolution of edge plasma and neutral profiles. The SMBI model is included as a module, called trans-neut, within the original BOUT++ boundary plasma turbulence code. Results of calculations are reported for the realistic divertor geometry of the HL-2A tokamak. The model can also be used to study the effect of gas puffing. A seven-field fluid model couples plasma density, heat, and momentum transport equations together with neutral density and momentum transport equations for both molecules and atoms. Collisional interactions between molecules, atoms, and plasma include dissociation, ionization, recombination and charge-exchange effects. Sheath boundary conditions and particle recycling are applied at both the wall and the divertor plates. A localized boundary condition of constant molecular flux (product of density times speed) is applied at the outermost flux surface to model the SMBI. Steady state profiles with and without particle recycling are achieved before SMBI. During SMBI, the simulation shows that neutrals can penetrate several centimetres inside the last closed (magnetic) flux surface (LCFS). Along the SMBI path, plasma density increases while plasma temperature decreases. The molecule penetration depth depends on both the SMBI flux and the initial plasma density and temperature along its path. As the local plasma density increases substantially, molecule and atom penetration depths decrease due to their higher dissociation and ionization rates if the electron temperature does not drop too low. Dynamic poloidal spreading of the enhanced plasma density region is observed due to rapid ion flow along the magnetic field (parallel) driven by a parallel pressure asymmetry during SMBI. Profile relaxation in the radial and poloidal directions is simulated after SMBI termination, showing that the plasma returns to pre-SMBI conditions on
A GPU Simulation Tool for Training and Optimisation in 2D Digital X-Ray Imaging.
Gallio, Elena; Rampado, Osvaldo; Gianaria, Elena; Bianchi, Silvio Diego; Ropolo, Roberto
2015-01-01
Conventional radiology is performed by means of digital detectors, with various types of technology and different performance in terms of efficiency and image quality. Following the arrival of a new digital detector in a radiology department, all the staff involved should adapt the procedure parameters to the properties of the detector, in order to achieve an optimal result in terms of correct diagnostic information and minimum radiation risks for the patient. The aim of this study was to develop and validate a software capable of simulating a digital X-ray imaging system, using graphics processing unit computing. All radiological image components were implemented in this application: an X-ray tube with primary beam, a virtual patient, noise, scatter radiation, a grid and a digital detector. Three different digital detectors (two digital radiography and a computed radiography systems) were implemented. In order to validate the software, we carried out a quantitative comparison of geometrical and anthropomorphic phantom simulated images with those acquired. In terms of average pixel values, the maximum differences were below 15%, while the noise values were in agreement with a maximum difference of 20%. The relative trends of contrast to noise ratio versus beam energy and intensity were well simulated. Total calculation times were below 3 seconds for clinical images with pixel size of actual dimensions less than 0.2 mm. The application proved to be efficient and realistic. Short calculation times and the accuracy of the results obtained make this software a useful tool for training operators and dose optimisation studies. PMID:26545097
A GPU Simulation Tool for Training and Optimisation in 2D Digital X-Ray Imaging.
Gallio, Elena; Rampado, Osvaldo; Gianaria, Elena; Bianchi, Silvio Diego; Ropolo, Roberto
2015-01-01
Conventional radiology is performed by means of digital detectors, with various types of technology and different performance in terms of efficiency and image quality. Following the arrival of a new digital detector in a radiology department, all the staff involved should adapt the procedure parameters to the properties of the detector, in order to achieve an optimal result in terms of correct diagnostic information and minimum radiation risks for the patient. The aim of this study was to develop and validate a software capable of simulating a digital X-ray imaging system, using graphics processing unit computing. All radiological image components were implemented in this application: an X-ray tube with primary beam, a virtual patient, noise, scatter radiation, a grid and a digital detector. Three different digital detectors (two digital radiography and a computed radiography systems) were implemented. In order to validate the software, we carried out a quantitative comparison of geometrical and anthropomorphic phantom simulated images with those acquired. In terms of average pixel values, the maximum differences were below 15%, while the noise values were in agreement with a maximum difference of 20%. The relative trends of contrast to noise ratio versus beam energy and intensity were well simulated. Total calculation times were below 3 seconds for clinical images with pixel size of actual dimensions less than 0.2 mm. The application proved to be efficient and realistic. Short calculation times and the accuracy of the results obtained make this software a useful tool for training operators and dose optimisation studies.
Real-time 2D floating-point fast Fourier transforms for seeker simulation
NASA Astrophysics Data System (ADS)
Chamberlain, Richard; Lord, Eric; Shand, David J.
2002-07-01
The floating point Fast Fourier Transform (FFT) is one of the most useful basic functions available to the image and signal processing engineer allowing many complex and detailed special functions to be implemented more simply in the frequency domain. In the Hardware-in-the-Loop field an image transformed using FFT would allow the designer to think about accurate frequency based simulation of seeker lens effects, motion blur, detector transfer functions and much more. Unfortunately, the transform requires many hundreds of thousands or millions of floating point operations on a single modest sized image making it impractical for realtime Hardware-in-the-Loop systems. .until now. This paper outlines the development, by Nallatech, of an FPGA based IEEE floating point core. It traces the subsequent use of this core to develop a full 256 X 256 FFT and filter process implemented on COTS hardware at frame rates up to 150Hz. This transform can be demonstrated to model optical transfer functions at a far greater accuracy than the current spatial models. Other applications and extensions of this technique will be discussed such as filtering for image tracking algorithms and in the simulation of radar processing in the frequency domain.
Yielding in a strongly aggregated colloidal gel: 2D simulations and theory
NASA Astrophysics Data System (ADS)
Roy, Saikat; Tirumkudulu, Mahesh
2015-11-01
We investigated the micro-structural details and the mechanical response under uniaxial compression of the strongly aggregating gel starting from low to high packing fraction.The numerical simulations account for short-range inter-particle attractions, normal and tangential deformation at particle contacts,sliding and rolling friction, and preparation history. It is observed that in the absence of rolling resistance(RR),the average coordination number varies only slightly with compaction whereas it is significant in the presence of RR. The particle contact distribution is isotropic throughout the consolidation process. In both cases, the yield strain is constant with the volume fraction. The modulus values are very similar at different attraction, and with and without RR implying that the elastic modulus does not scale with attraction.The modulus was found to be a weak function of the preparation history. The increase in yield stress with volume fraction is a consequence of the increased elastic modulus of the network. However, the yield stress scales similarly both with and without RR. The power law exponent of 5.4 is in good agreement with previous simulation results. A micromechanical theory is also proposed to describe the stress versus strain relation for the gelled network.
NASA Astrophysics Data System (ADS)
Pérez-Corona, M.; García, J. A.; Taller, G.; Polgár, D.; Bustos, E.; Plank, Z.
2016-02-01
The purpose of geophysical electrical surveys is to determine the subsurface resistivity distribution by making measurements on the ground surface. From these measurements, the true resistivity of the subsurface can be estimated. The ground resistivity is related to various geological parameters, such as the mineral and fluid content, porosity and degree of water saturation in the rock. Electrical resistivity surveys have been used for many decades in hydrogeological, mining and geotechnical investigations. More recently, they have been used for environmental surveys. To obtain a more accurate subsurface model than is possible with a simple 1-D model, a more complex model must be used. In a 2-D model, the resistivity values are allowed to vary in one horizontal direction (usually referred to as the x direction) but are assumed to be constant in the other horizontal (the y) direction. A more realistic model would be a fully 3-D model where the resistivity values are allowed to change in all three directions. In this research, a simulation of the cone penetration test and 2D imaging resistivity are used as tools to simulate the distribution of hydrocarbons in soil.
A hierarchical lattice spring model to simulate the mechanics of 2-D materials-based composites
NASA Astrophysics Data System (ADS)
Brely, Lucas; Bosia, Federico; Pugno, Nicola
2015-07-01
In the field of engineering materials, strength and toughness are typically two mutually exclusive properties. Structural biological materials such as bone, tendon or dentin have resolved this conflict and show unprecedented damage tolerance, toughness and strength levels. The common feature of these materials is their hierarchical heterogeneous structure, which contributes to increased energy dissipation before failure occurring at different scale levels. These structural properties are the key to exceptional bioinspired material mechanical properties, in particular for nanocomposites. Here, we develop a numerical model in order to simulate the mechanisms involved in damage progression and energy dissipation at different size scales in nano- and macro-composites, which depend both on the heterogeneity of the material and on the type of hierarchical structure. Both these aspects have been incorporated into a 2-dimensional model based on a Lattice Spring Model, accounting for geometrical nonlinearities and including statistically-based fracture phenomena. The model has been validated by comparing numerical results to continuum and fracture mechanics results as well as finite elements simulations, and then employed to study how structural aspects impact on hierarchical composite material properties. Results obtained with the numerical code highlight the dependence of stress distributions on matrix properties and reinforcement dispersion, geometry and properties, and how failure of sacrificial elements is directly involved in the damage tolerance of the material. Thanks to the rapidly developing field of nanocomposite manufacture, it is already possible to artificially create materials with multi-scale hierarchical reinforcements. The developed code could be a valuable support in the design and optimization of these advanced materials, drawing inspiration and going beyond biological materials with exceptional mechanical properties.
KEEN and KEEPN wave simulations from 2D to 4D
NASA Astrophysics Data System (ADS)
Mehrenberger, Michel; Afeyan, Bedros; Larson, David; Crouseilles, Nicolas; Casas, Fernando; Faou, Erwan; Dodhy, Adila; Sonnendrucker, Eric; Shoucri, Magdi
2015-11-01
We show for well-driven KEEN (Kinetic Electrostatic Electron Nonlinear) waves and their analogs in pair plasmas KEEPN (Positron) waves, how the dynamics is captured in a variety of complimentary numerical approaches. Symplectic integration and quadrature node based techniques are deployed to achieve satisfactory results in the long time evolution of highly nonlinear, kinetic, non-stationary, self-organized structures in phase space. Fixed and composite velocity grid arbitrary-order interpolation approaches have advantages we highlight. Adaptivity to local phase space density morphological structures will be discussed starting within the framework of the Shape Function Kinetics (SFK) approach. Fine resolution in velocity only in the range affected by KEEN waves makes for more efficient simulations, especially in higher dimensions. We explore the parameter space of unequal electron and positron temperatures as well as the effects of a relative drift velocity in their initial conditions. Ponderomotively driven KEEPN waves have many novelties when compared to KEEN waves, such as double, staggered, vortex structures, which we highlight. Work supported by the AFOSR and OFES.
NASA Technical Reports Server (NTRS)
Zimmerman, Michael I.; Farrell, W. M.; Snubbs, T. J.; Halekas, J. S.
2011-01-01
Anticipating the plasma and electrical environments in permanently shadowed regions (PSRs) of the moon is critical in understanding local processes of space weathering, surface charging, surface chemistry, volatile production and trapping, exo-ion sputtering, and charged dust transport. In the present study, we have employed the open-source XOOPIC code [I] to investigate the effects of solar wind conditions and plasma-surface interactions on the electrical environment in PSRs through fully two-dimensional pattic1e-in-cell simulations. By direct analogy with current understanding of the global lunar wake (e.g., references) deep, near-terminator, shadowed craters are expected to produce plasma "mini-wakes" just leeward of the crater wall. The present results (e.g., Figure I) are in agreement with previous claims that hot electrons rush into the crater void ahead of the heavier ions, fanning a negative cloud of charge. Charge separation along the initial plasma-vacuum interface gives rise to an ambipolar electric field that subsequently accelerates ions into the void. However, the situation is complicated by the presence of the dynamic lunar surface, which develops an electric potential in response to local plasma currents (e.g., Figure Ia). In some regimes, wake structure is clearly affected by the presence of the charged crater floor as it seeks to achieve current balance (i.e. zero net current to the surface).
Ion Dynamics at a Rippled Quasi-parallel Shock: 2D Hybrid Simulations
NASA Astrophysics Data System (ADS)
Hao, Yufei; Lu, Quanming; Gao, Xinliang; Wang, Shui
2016-05-01
In this paper, two-dimensional hybrid simulations are performed to investigate ion dynamics at a rippled quasi-parallel shock. The results show that the ripples around the shock front are inherent structures of a quasi-parallel shock, and the re-formation of the shock is not synchronous along the surface of the shock front. By following the trajectories of the upstream ions, we find that these ions behave differently when they interact with the shock front at different positions along the shock surface. The upstream particles are transmitted more easily through the upper part of a ripple, and the corresponding bulk velocity downstream is larger, where a high-speed jet is formed. In the lower part of the ripple, the upstream particles tend to be reflected by the shock. Ions reflected by the shock may suffer multiple-stage acceleration when moving along the shock surface or trapped between the upstream waves and the shock front. Finally, these ions may escape further upstream or move downstream; therefore, superthermal ions can be found both upstream and downstream.
Origin of energetic ions observed in the terrestrial ion foreshock : 2D full-particle simulations
NASA Astrophysics Data System (ADS)
Savoini, Philippe; Lembege, bertrand
2016-04-01
Collisionless shocks are well-known structures in astrophysical environments which dissipate bulk flow kinetic energy and accelerate large fraction of particle. Spacecrafts have firmly established the existence of the so-called terrestrial foreshock region magnetically connected to the shock and filled by two distinct populations in the quasi-perpendicular shock region (i.e. for 45r{ } ≤ quad θ Bn quad ≤ 90r{ }, where θ Bn is the angle between the shock normal and the upstream magnetic field) : (i) the field-aligned ion beams or `` FAB '' characterized by a gyrotropic distributionsout{,} and (ii) the gyro-phase bunched ions or `` GPB '' characterized by a NON gyrotropic distribution. The present work is based on the use of two dimensional PIC simulation of a curved shock and associated foreshock region where full curvature effects, time of flight effects and both electrons and ions dynamics are fully described by a self consistent approach. Our previous analysis (Savoini et Lembège, 2015) has evidenced that these two types of backstreaming populations can originate from the shock front itself without invoking any local diffusion by ion beam instabilities. Present results are focussed on individual ion trajectories and evidence that "FAB" population is injected into the foreshock mainly along the shock front whereas the "GPB" population penetrates more deeply the shock front. Such differences explain why the "FAB" population loses their gyro-phase coherency and become gyrotropic which is not the case for the "GPB". The impact of these different injection features on the energy gain for each ion population will be presented in détails. Savoini, P. and B. Lembège (2015), `` Production of nongyrotropic and gyrotropic backstreaming ion distributions in the quasi-perpendicular ion foreshock région '', J. Geophys. Res., 120, pp 7154-7171, doi = 10.1002/2015JA021018.
2D conditional simulation of channels on wells using a random walk approach
NASA Astrophysics Data System (ADS)
Wang, Jiahua; Wang, Xiangbo; Ren, Changlin
2009-03-01
Channel modeling is one of the popular topics in the application of geostatistics to fluvial reservoir modeling. This paper presents an approach to designing channels which have a general flow direction through sand well locations and which avoid shale well locations. This approach is named the random walk on graphs of well locations, and is applied to model channel reservoirs. This modeling process consists of two parts: one direction walk modeling and two direction walk modeling. The first model aims to determine each channel location by the use of a transition probability with a random walk essentially in the main flow direction, say the north-south direction, while the second model simulates different channels that can be oriented in both directions, either from north to south or from south to north. In both parts of the model, the transition probability is estimated based on two coefficients: one is the correlation coefficient of channel observations; the other is the obstacle coefficient of non-channel observations. A case study with a dense array of 332 wells is presented using the proposed random walk model. For the purpose of model verification, channel maps created by the random walk are compared to the hand-drawn channel maps made by geologists. The results show a good agreement in both types of maps, but in contrast to the single map supplied by geologists, the random walk model is capable of generating many realizations of channel configuration, hence allowing for uncertainty evaluation. A limitation of this approach, related to the influence of the number of wells, is discussed.
NASA Astrophysics Data System (ADS)
Dages, Cecile; Samouelian, Anatja; Lanoix, Marthe; Dollinger, Jeanne; Chakkour, Sara; Chovelon, Gabrielle; Trabelsi, Khouloud; Voltz, Marc
2015-04-01
Ditches are involved in the transfer of pesticide to surface and groundwaters (e.g. Louchart et al., 2001). Soil horizons underlying ditch beds may present specific soil characteristics compared to neighbouring field soils due to erosion/deposition processes, to the specific biological activities (rooting dynamic and animal habitat) in the ditches (e.g. Vaughan et al., 2008) and to management practices (burning, dredging, mowing,...). Moreover, in contrast to percolation processes in field soils that can be assumed to be mainly 1D vertical, those occurring in the ditch beds are by essence 2D or even 3D. Nevertheless, due to a lake of knowledge, these specific aspects of transfer within ditch beds are generally omitted for hydrological simulation at the catchment scale (Mottes et al., 2014). Accordingly, the aims of this study were i) to characterize subsurface solute transfer through ditch beds and ii) to determine equivalent hydraulic parameters of the ditch beds for use in catchment scale hydrological simulations. A complementary aim was to evaluate the error in predictions performed when percolation in ditches is assumed to be similar to that in the neighbouring field soil. First, bromide transfer experiments were performed on undisturbed soil column (15 cm long with a 15 cm inner-diameter), horizontally and vertically sampled within each soil horizon underlying a ditch bed and within the neighboring field. Columns were sampled at the Roujan catchment (Hérault, France), which belongs to the long term Mediterranean hydrological observatory OMERE (Voltz and Albergel, 2002). Second, for each column, a set of parameters was determined by inverse optimization with mobile-immobile or dual permeability models, with CXTFIT (Toride et al., 1999) or with HYDRUS (Simunek et al., 1998). Third, infiltration and percolation in the ditch was simulated by a 2D flow domain approach considering the 2D variation in hydraulic properties of the cross section of a ditch bed. Last
NASA Astrophysics Data System (ADS)
Campforts, Benjamin; Vanacker, Veerle; Vanderborght, Jan; Baken, Stijn; Smolders, Erik; Govers, Gerard
2016-04-01
Meteoric 10Be allows for the quantification of vertical and lateral soil fluxes over long time scales (103-105 yr). However, the mobility of meteoric 10Be in the soil system makes a translation of meteoric 10Be inventories into erosion and deposition rates complex. Here, we present a spatially explicit 2D model simulating the behaviour of meteoric 10Be on a hillslope. The model consists of two parts. The first component deals with advective and diffusive mobility of meteoric 10Be within the soil profile, and the second component describes lateral soil and meteoric 10Be fluxes over the hillslope. Soil depth is calculated dynamically, accounting for soil production through weathering as well as downslope fluxes of soil due to creep, water and tillage erosion. Synthetic model simulations show that meteoric 10Be inventories can be related to erosion and deposition across a wide range of geomorphological and pedological settings. Our results also show that meteoric 10Be can be used as a tracer to detect human impact on soil fluxes for soils with a high affinity for meteoric 10Be. However, the quantification of vertical mobility is essential for a correct interpretation of the observed variations in meteoric 10Be profiles and inventories. Application of the Be2D model to natural conditions using data sets from the Southern Piedmont (Bacon et al., 2012) and Appalachian Mountains (Jungers et al., 2009; West et al., 2013) allows to reliably constrain parameter values. Good agreement between simulated and observed meteoric 10Be concentrations and inventories is obtained with realistic parameter values. Furthermore, our results provide detailed insights into the processes redistributing meteoric 10Be at the soil-hillslope scale.
Simulations of the C-2/C-2U Field Reversed Configurations with the Q2D code
NASA Astrophysics Data System (ADS)
Onofri, Marco; Dettrick, Sean; Barnes, Daniel; Tajima, Toshiki; TAE Team
2015-11-01
C-2U was built to sustain advanced beam-driven FRCs for 5 + ms. The Q2D transport code is used to simulate the evolution of C-2U discharges and to study sustainment via fast ion current and pressure, with the latter comparable to the thermal plasma pressure. The code solves the MHD equations together with source terms due to neutral beams, which are calculated by a Monte Carlo method. We compare simulations with experimental results obtained in the HPF14 regime of C-2 (6 neutral beams with energy of 20 keV and total power of 4.2 MW). All simulations start from an initial equilibrium and transport coefficients are chosen to match experimental data. The best agreement is obtained when utilizing an enhanced energy transfer between fast ions and the plasma, which may be an indication of anomalous heating due to beneficial beam-plasma instabilities. Similar simulations of C-2U (neutral beam power increased to 10 + MW and angled beam injection) are compared with experimental results, where a steady state has been obtained for 5 + ms, correlated with the neutral beam pulse and limited by engineering constraints.
FireStem2D--a two-dimensional heat transfer model for simulating tree stem injury in fires.
Chatziefstratiou, Efthalia K; Bohrer, Gil; Bova, Anthony S; Subramanian, Ravishankar; Frasson, Renato P M; Scherzer, Amy; Butler, Bret W; Dickinson, Matthew B
2013-01-01
FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. We present the results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees. We also conducted a set of virtual sensitivity analysis experiments to test the effects of unevenness of heating around the stem and with aboveground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes.
FireStem2D – A Two-Dimensional Heat Transfer Model for Simulating Tree Stem Injury in Fires
Chatziefstratiou, Efthalia K.; Bohrer, Gil; Bova, Anthony S.; Subramanian, Ravishankar; Frasson, Renato P. M.; Scherzer, Amy; Butler, Bret W.; Dickinson, Matthew B.
2013-01-01
FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. We present the results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees. We also conducted a set of virtual sensitivity analysis experiments to test the effects of unevenness of heating around the stem and with aboveground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes. PMID:23894599
NASA Astrophysics Data System (ADS)
Humair, F.; Matasci, B.; Carrea, D.; Pedrazzini, A.; Loye, A.; Pedrozzi, G.; Nicolet, P.; Jaboyedoff, M.
2012-04-01
account the results of the experimental testing are performed and compared with the a-priori simulations. 3D simulations were performed using a software that takes into account the effect of the forest cover in the blocky trajectory (RockyFor 3D) and an other that neglects this aspect (Rotomap; geo&soft international). 2D simulation (RocFall; Rocscience) profiles were located in the blocks paths deduced from 3D simulations. The preliminary results show that: (1) high speed movies are promising and allow us to track the blocks using video software, (2) the a-priori simulations tend to overestimate the runout distance which is certainly due to an underestimation of the obstacles as well as the breaking of the failing rocks which is not taken into account in the models, (3) the trajectories deduced from both a-priori simulation and real size experiment highlights the major influence of the channelized slope morphology on rock paths as it tends to follow the flow direction. This indicates that the 2D simulation have to be performed along the line of flow direction.
NASA Astrophysics Data System (ADS)
Peng, Zezhong
1992-01-01
A generalized energy transport (G-ET) model is introduced. This model incorporates the effects of non -analytic carrier distribution functions and the dominant scattering process on the formulation of the energy transport model, also includes effects of the electron transfer between the lower valley occurs in multivalley semi-conductors. A path-integration and slope-weighting Monte Carlo (PSMC) method is introduced to speed up the conventional MC method, and to improve its accuracy and smoothness. A stable extended S-G discretization algorithm was developed for the G-ET model. Further, many numerical techniques, including methods of mesh auto generation, updating and scaling, trial solution with 2D extrapolation, a global convergence test, a convergence refining, a forced -damping and residual-current filtering, were developed to improve the convergence and the computation efficiency. UMDFET2, a general submicron device simulator, was implemented with G-ET model, an efficient hot electron injection model, a Fowler-Nordheim tunneling model, an impact ionization model, and a model for band-to-band tunneling have also been added. A discretized gate capacitor (DGC) EPROM model and post-processing quasi-transient (PPQT) method has been introduced to efficiently and accurately simulate EPROM devices. Deep submicron NMOS devices have been simulated to study velocity overshoot and hot electron effects. UMDFET2 has been successfully used to predict the V_{t}, I_{ds}, I_{sub}, I_{g}, the programming and erasing characteristics V_ {t}(t) of submicron EPROM/Flash devices. A "Virtual Fab", which consists of statistics analysis tool for experimental design and data analysis, SUPREM3/4 for process simulation, and UMDFET2 for device simulation, has been used successfully for EPROM device design and optimization, and has demonstrated a good predicting ability with excellent overall accuracy. The correlation of the ET models and MC models has been studied, and it has been found that
Analysis of Highly-Resolved Simulations of 2-D Humps Toward Improvement of Second-Moment Closures
NASA Technical Reports Server (NTRS)
Jeyapaul, Elbert; Rumsey Christopher
2013-01-01
Fully resolved simulation data of flow separation over 2-D humps has been used to analyze the modeling terms in second-moment closures of the Reynolds-averaged Navier- Stokes equations. Existing models for the pressure-strain and dissipation terms have been analyzed using a priori calculations. All pressure-strain models are incorrect in the high-strain region near separation, although a better match is observed downstream, well into the separated-flow region. Near-wall inhomogeneity causes pressure-strain models to predict incorrect signs for the normal components close to the wall. In a posteriori computations, full Reynolds stress and explicit algebraic Reynolds stress models predict the separation point with varying degrees of success. However, as with one- and two-equation models, the separation bubble size is invariably over-predicted.
Walking simulator for evaluation of ophthalmic devices
NASA Astrophysics Data System (ADS)
Barabas, James; Woods, Russell L.; Peli, Eli
2005-03-01
Simulating mobility tasks in a virtual environment reduces risk for research subjects, and allows for improved experimental control and measurement. We are currently using a simulated shopping mall environment (where subjects walk on a treadmill in front of a large projected video display) to evaluate a number of ophthalmic devices developed at the Schepens Eye Research Institute for people with vision impairment, particularly visual field defects. We have conducted experiments to study subject's perception of "safe passing distance" when walking towards stationary obstacles. The subject's binary responses about potential collisions are analyzed by fitting a psychometric function, which gives an estimate of the subject's perceived safe passing distance, and the variability of subject responses. The system also enables simulations of visual field defects using head and eye tracking, enabling better understanding of the impact of visual field loss. Technical infrastructure for our simulated walking environment includes a custom eye and head tracking system, a gait feedback system to adjust treadmill speed, and a handheld 3-D pointing device. Images are generated by a graphics workstation, which contains a model with photographs of storefronts from an actual shopping mall, where concurrent validation experiments are being conducted.
NASA Astrophysics Data System (ADS)
Pang, Liping; Close, Murray E.; Watt, James P. C.; Vincent, Keith W.
2000-06-01
Two 15 m×15 m field plots, a Te Awa silt loam and a Twyford fine sandy loam, located in Hawkes Bay, New Zealand, were applied with bromide, picloram, atrazine, and simazine. The Te Awa subsoil was a heterogeneous coarse sand and sandy gravel, and the Twyford subsoil was a more homogenous fine sandy loam. The underlying aquifers were composed of alluvial gravels at both sites with the water tables generally between 4-5 m below ground level. The sites were monitored for 2.2-3.5 years at approximately monthly intervals using suction cups in the unsaturated zone and monitoring wells in groundwater. HYDRUS-2D was used to simulate water movement and solute transport in soil and groundwater in a domain with a depth of 10 m and length of 68 m, including a 4.5-m unsaturated zone. The model simulated well the general trend of field observations for soil water content ( θ) and potential ( ψs), and the values matched better for the soils with less heterogeneity. For the soils with significant surface cracks, the simulated θ values were overestimated. On the other hand, for the soil layer perching on top of a less permeable layer, the simulated θ values were underestimated. Simulated pesticide concentrations using the "best available literature values" (BALVs) of organic carbon distribution coefficient ( Koc) and half-life ( T1/2) were generally lower than those observed. At early times in the trails, most simulations using BALVs were still within the same order of magnitude as observed concentrations for the shallow depths. However, at greater depths and later times, there were major differences between observed and simulated concentrations. The model was then calibrated for Koc and T1/2 values using observed data with an aid of the PEST optimisation package. Despite higher organic contents found in the topsoil, optimised Koc values for pesticides were consistently lower for the topsoil than for the subsoil, and were also lower than the BALVs except for picloram, possibly
Simulation of Ultra-Small MOSFETs Using a 2-D Quantum-Corrected Drift-Diffusion Model
NASA Technical Reports Server (NTRS)
Biegel, Bryan A.; Rafferty, Conor S.; Yu, Zhiping; Dutton, Robert W.; Ancona, Mario G.; Saini, Subhash (Technical Monitor)
1998-01-01
We describe an electronic transport model and an implementation approach that respond to the challenges of device modeling for gigascale integration. We use the density-gradient (DG) transport model, which adds tunneling and quantum smoothing of carrier density profiles to the drift-diffusion model. We present the current implementation of the DG model in PROPHET, a partial differential equation solver developed by Lucent Technologies. This implementation approach permits rapid development and enhancement of models, as well as run-time modifications and model switching. We show that even in typical bulk transport devices such as P-N diodes and BJTs, DG quantum effects can significantly modify the I-V characteristics. Quantum effects are shown to be even more significant in small, surface transport devices, such as sub-0.1 micron MOSFETs. In thin-oxide MOS capacitors, we find that quantum effects may reduce gate capacitance by 25% or more. The inclusion of quantum effects in simulations dramatically improves the match between C-V simulations and measurements. Significant quantum corrections also occur in the I-V characteristics of short-channel MOSFETs due to the gate capacitance correction.
NASA Astrophysics Data System (ADS)
Simão Ferreira, C. J.; Bijl, H.; van Bussel, G.; van Kuik, G.
2007-07-01
The implementation of wind energy conversion systems in the built environment renewed the interest and the research on Vertical Axis Wind Turbines (VAWT), which in this application present several advantages over Horizontal Axis Wind Turbines (HAWT). The VAWT has an inherent unsteady aerodynamic behavior due to the variation of angle of attack with the angle of rotation, perceived velocity and consequentially Reynolds number. The phenomenon of dynamic stall is then an intrinsic effect of the operation of a Vertical Axis Wind Turbine at low tip speed ratios, having a significant impact in both loads and power. The complexity of the unsteady aerodynamics of the VAWT makes it extremely attractive to be analyzed using Computational Fluid Dynamics (CFD) models, where an approximation of the continuity and momentum equations of the Navier-Stokes equations set is solved. The complexity of the problem and the need for new design approaches for VAWT for the built environment has driven the authors of this work to focus the research of CFD modeling of VAWT on: •comparing the results between commonly used turbulence models: URANS (Spalart-Allmaras and k-epsilon) and large eddy models (Large Eddy Simulation and Detached Eddy Simulation) •verifying the sensitivity of the model to its grid refinement (space and time), •evaluating the suitability of using Particle Image Velocimetry (PIV) experimental data for model validation. The 2D model created represents the middle section of a single bladed VAWT with infinite aspect ratio. The model simulates the experimental work of flow field measurement using Particle Image Velocimetry by Simão Ferreira et al for a single bladed VAWT. The results show the suitability of the PIV data for the validation of the model, the need for accurate simulation of the large eddies and the sensitivity of the model to grid refinement.
NASA Astrophysics Data System (ADS)
Jia, Xiaojie; Ai, Bin; Deng, Youjun; Xu, Xinxiang; Peng, Hua; Shen, Hui
2015-08-01
On the basis of perfect PC2D simulation to the measured current density vs voltage (J-V) curve of the best selective emitter (SE) solar cell fabricated by the CSG Company using the screen printing phosphoric paste method, we systematically investigated the effect of the parameters of gridline, base, selective emitter, back surface field (BSF) layer and surface recombination rate on performance of the SE solar cell. Among these parameters, we identified that the base minority carrier lifetime, the front and back surface recombination rate and the ratio of the sheet-resistance of heavily and lightly doped region are the four largest efficiency-affecting factors. If all the parameters have ideal values, the SE solar cell fabricated on a p-type monocrystalline silicon wafer can even obtain the efficiency of 20.45%. In addition, the simulation also shows that fine gridline combining dense gridline and increasing bus bar number while keeping the lower area ratio can offer the other ways to improve the efficiency.
2D simulation of active species and ozone production in a multi-tip DC air corona discharge
NASA Astrophysics Data System (ADS)
Meziane, M.; Eichwald, O.; Sarrette, J. P.; Ducasse, O.; Yousfi, M.
2011-11-01
The present paper shows for the first time in the literature a complete 2D simulation of the ozone production in a DC positive multi-tip to plane corona discharge reactor crossed by a dry air flow at atmospheric pressure. The simulation is undertaken until 1 ms and involves tens of successive discharge and post-discharge phases. The air flow is stressed by several monofilament corona discharges generated by a maximum of four anodic tips distributed along the reactor. The nonstationary hydrodynamics model for reactive gas mixture is solved using the commercial FLUENT software. During each discharge phase, thermal and vibrational energies as well as densities of radical and metastable excited species are locally injected as source terms in the gas medium surrounding each tip. The chosen chemical model involves 10 neutral species reacting following 24 reactions. The obtained results allow us to follow the cartography of the temperature and the ozone production inside the corona reactor as a function of the number of high voltage anodic tips.
NASA Astrophysics Data System (ADS)
Vanzo, Davide; Siviglia, Annunziato; Zolezzi, Guido
2014-05-01
In last decades, pushed by an increasing interest in environmental problems and supported by an exponential growth of computational capability, novel numerical methods and models have been developed. Despite the progress in parallel computing, computational time is still one of the main bottlenecks when dealing with long term environmental simulations. To overcome such time constraint in morphodynamic models, artificial acceleration of bed evolution has been implemented with different strategies (e.g. Roelvink 2006). The key idea is to accelerate the morphological evolution increasing the discrete bottom variations of a given "morphological factor" during numerical integration thus considerably speeding up computational time. On the other hand, an artificial alteration of the governing equations is put forward, for which related numerical and physical consequences are not completely known. The present work investigates the role of the morphological factor in numerical simulations of a well-defined, 2D reach-scale process in river morphodynamics, which can be taken as a benchmark for the established knowledge made available from theoretical and physical scale models developed in the past decades. The chosen process is the evolution of free migrating bars in a straight channel. The numerical morphodynamic model used in this work is GIAMT2D (Siviglia et al. 2013), which solves the governing system of shallow water and Exner equations following a fully coupled approach with a finite volume method on unstructured triangular grids. By processing numerical outcomes also through Continuous Wavelet Transform, the differences in free migrating bars properties (temporal evolution and equilibrium values of wavelength, amplitude, celerity) are investigated in simple test cases with different values of the morphological factor. Numerical results are compared with available analytical theories for free bars. The outcomes highlight the consequences of using the morphological
NASA Astrophysics Data System (ADS)
Wang, Z. J.; Ming, T. F.; Gao, X.; Du, X. D.; Ohdachi, S.
2016-11-01
A high-speed tangentially viewing vacuum ultraviolet (VUV) telescope system, using an inverse Schwarzschild-type optic system was developed to study fluctuations in the Large Helical Device (LHD). However, for the original system, the sampling rate was restricted to below 2000 Hz due to the low signal to noise (S/N) ratio in the experiment. In order to improve the S/N ratio, upgrade of the system was made. With this upgraded optical system, the maximum framing rate is improved to 6000 fps with a similar spatial resolution. Rotation of the m = 2 structure caused by the magnetohydrodynamic (MHD) instability is measured by the upgraded system. The spatial structure of the image is consistent with the synthetic image assuming the interchange mode type displacement of the flux surfaces.
Falvo, Cyril; Zhuang, Wei; Kim, Yung Sam; Axelsen, Paul H.; Hochstrasser, Robin M.; Mukamel, Shaul
2012-01-01
The infrared optical response of Amyloid Fibrils Aβ1–40 is investigated. Simulations of two models corresponding to different protonation states are compared with experiment. The simulations reveal that vibrational frequency distributions inside the fibrils are dominated by sidechain fluctuations. We further confirm earlier suggestions based on 2D-IR measurements that water molecules can be trapped inside the fibrils. PMID:22338639
NASA Technical Reports Server (NTRS)
Li, Xiaofan; Sui, C.-H.; Lau, K.-M.
1999-01-01
The phase relation between the perturbation kinetic energy (K') associated with the tropical convection and the horizontal-mean moist available potential energy (bar-P) associated with environmental conditions is investigated by an energetics analysis of a numerical experiment. This experiment is performed using a 2-D cloud resolving model forced by the TOGA-COARE derived vertical velocity. The imposed upward motion leads to a decrease of bar-P directly through the associated vertical advective cooling, and to an increase of K' directly through cloud related processes, feeding the convection. The maximum K' and its maximum growth rate lags and leads, respectively, the maximum imposed large-scale upward motion by about 1-2 hours, indicating that convection is phase locked with large-scale forcing. The dominant life cycle of the simulated convection is about 9 hours, whereas the time scales of the imposed large-scale forcing are longer than the diurnal cycle. In the convective events, maximum growth of K' leads maximum decay of the perturbation moist available potential energy (P') by about 3 hours through vertical heat transport by perturbation circulation, and perturbation cloud heating. Maximum decay of P' leads maximum decay of bar-P by about one hour through the perturbation radiative, processes, the horizontal-mean cloud heating, and the large-scale vertical advective cooling. Therefore, maximum gain of K' occurs about 4-5 hours before maximum decay of bar-P.
Design optimization of pixel sensors using device simulations for the phase-II CMS tracker upgrade
NASA Astrophysics Data System (ADS)
Jain, G.; Bhardwaj, A.; Dalal, R.; Eber, R.; Eichorn, T.; Fernandez, M.; Lalwani, K.; Messineo, A.; Palomo, F. R.; Peltola, T.; Printz, M.; Ranjan, K.; Villa, I.; Hidalgo, S.
2016-07-01
In order to address the problems caused by the harsh radiation environment during the high luminosity phase of the LHC (HL-LHC), all silicon tracking detectors (pixels and strips) in the CMS experiment will undergo an upgrade. And so to develop radiation hard pixel sensors, simulations have been performed using the 2D TCAD device simulator, SILVACO, to obtain design parameters. The effect of various design parameters like pixel size, pixel depth, implant width, metal overhang, p-stop concentration, p-stop depth and bulk doping density on the leakage current and critical electric field are studied for both non-irradiated as well as irradiated pixel sensors. These 2D simulation results of planar pixels are useful for providing insight into the behaviour of non-irradiated and irradiated silicon pixel sensors and further work on 3D simulation is underway.
A 2-D FEM thermal model to simulate water flow in a porous media: Campi Flegrei caldera case study
NASA Astrophysics Data System (ADS)
Romano, V.; Tammaro, U.; Capuano, P.
2012-05-01
Volcanic and geothermal aspects both exist in many geologically young areas. In these areas the heat transfer process is of fundamental importance, so that the thermal and fluid-dynamic processes characterizing a viscous fluid in a porous medium are very important to understand the complex dynamics of the these areas. The Campi Flegrei caldera, located west of the city of Naples, within the central-southern sector of the large graben of Campanian plain, is a region where both volcanic and geothermal phenomena are present. The upper part of the geothermal system can be considered roughly as a succession of volcanic porous material (tuff) saturated by a mixture formed mainly by water and carbon dioxide. We have implemented a finite elements approach in transient conditions to simulate water flow in a 2-D porous medium to model the changes of temperature in the geothermal system due to magmatic fluid inflow, accounting for a transient phase, not considered in the analytical solutions and fluid compressibility. The thermal model is described by means of conductive/convective equations, in which we propose a thermal source represented by a parabolic shape function to better simulate an increase of temperature in the central part (magma chamber) of a box, simulating the Campi Flegrei caldera and using more recent evaluations, from literature, for the medium's parameters (specific heat capacity, density, thermal conductivity, permeability). A best-fit velocity for the permeant is evaluated by comparing the simulated temperatures with those measured in wells drilled by Agip (Italian Oil Agency) in the 1980s in the framework of geothermal exploration. A few tens of days are enough to reach the thermal steady state, showing the quick response of the system to heat injection. The increase in the pressure due to the heat transport is then used to compute ground deformation, in particular the vertical displacements characteristics of the Campi Flegrei caldera behaviour. The
TITAN2D simulations of pyroclastic flows at Cerro Machín Volcano, Colombia: Hazard implications
NASA Astrophysics Data System (ADS)
Murcia, H. F.; Sheridan, M. F.; Macías, J. L.; Cortés, G. P.
2010-03-01
Cerro Machín is a dacitic tuff ring located in the central part of the Colombian Andes. It lies at the southern end of the Cerro Bravo-Cerro Machín volcanic belt. This volcano has experienced at least six major explosive eruptions during the last 5000 years. These eruptions have generated pyroclastic flows associated with Plinian activity that have traveled up to 8 km from the crater, and pyroclastic flows associated with Vulcanian activity with shorter runouts of 5 km from the source. Today, some 21,000 people live within a 8 km radius of Cerro Machín. The volcano is active with fumaroles and has shown increasing seismic activity since 2004, and therefore represents a potentially increasing threat to the local population. To evaluate the possible effects of future eruptions that may generate pyroclastic density currents controlled by granular flow dynamics we performed flow simulations with the TITAN2D code. These simulations were run in all directions around the volcano, using the input parameters of the largest eruption reported. The results show that an eruption of 0.3 km 3 of pyroclastic flows from a collapsing Plinian column would travel up to 9 km from the vent, emplacing a deposit thicker than 60 m within the Toche River valley. Deposits >45 m thick can be expected in the valleys of San Juan, Santa Marta, and Azufral creeks, while 30 m thick deposits could accumulate within the drainages of the Tochecito, Bermellón, and Coello Rivers. A minimum area of 56 km 2 could be affected directly by this kind of eruption. In comparison, Vulcanian column-collapse pyroclastic flows of 0.1 km 3 would travel up to 6 km from the vent depositing >45 m thick debris inside the Toche River valley and more than 30 m inside the valleys of San Juan, Santa Marta, and Azufral creeks. The minimum area that could be affected directly by this kind of eruption is 33 km 2. The distribution and thickness of the deposits obtained by these simulations are consistent with the hazard
First principles simulations of nanoelectronic devices
NASA Astrophysics Data System (ADS)
Maassen, Jesse
As the miniaturization of devices begins to reveal the atomic nature of materials, where chemical bonding and quantum effects are important, one must resort to a parameter-free theory for predictions. This thesis theoretically investigates the quantum transport properties of nanoelectronic devices using atomistic first principles. Our theoretical formalism employs density functional theory (DFT) in combination with Keldysh nonequilibrium Green's functions (NEGF). Self-consistently solving the DFT Hamiltonian with the NEGF charge density provides a way to simulate nonequilibrium systems without phenomenological parameters. This state-of-the-art technique was used to study three problems related to the field of nanoelectronics. First, we investigated the role of metallic contacts (Cu, Ni and Co) on the transport characteristics of graphene devices. With Cu, the graphene is simply electron-doped (Fermi level shift of ≈ -0.7 eV) which creates a unique signature in the conduction profile allowing one to extract the doping level. With Ni and Co, spin-dependent band gaps are formed in graphene's linear dispersion bands, thus leading to the prediction of high spin injection efficiencies reaching 60% and 80%, respectively. Second, we studied how controlled doping distributions in nano-scale Si transistors could suppress OFF-state leakage currents. By assuming the dopants (B and P) are confined in ≈ 1.1 nm regions in the channel, we discovered large conductance variations (GMAX/G MIN ˜ 105) as a function of the doping location. The largest fluctuations arise when the dopants are in the vicinity of the electrodes. Our results indicate that if the dopants are located away from the leads, a distance equal to 20% of the channel length, the tunneling current can be suppressed by a factor of 2 when compared to the case of uniform doping. Thus, controlled doping engineering is found to suppress device-to-device variations and lower the undesirable leakage current. Finally, we
NASA Astrophysics Data System (ADS)
Fediai, Artem; Ryndyk, Dmitry A.; Cuniberti, Gianaurelio
2016-10-01
Up to now, the electrical properties of the contacts between 3D metals and 2D materials have never been computed at a fully ab initio level due to the huge number of atomic orbitals involved in a current path from an electrode to a pristine 2D material. As a result, there are still numerous open questions and controversial theories on the electrical properties of systems with 3D/2D interfaces—for example, the current path and the contact length scalability. Our work provides a first-principles solution to this long-standing problem with the use of the modular approach, a method which rigorously combines a Green function formalism with the density functional theory (DFT) for this particular contact type. The modular approach is a general approach valid for any 3D/2D contact. As an example, we apply it to the most investigated among 3D/2D contacts—metal/graphene contacts—and show its abilities and consistency by comparison with existing experimental data. As it is applicable to any 3D/2D interface, the modular approach allows the engineering of 3D/2D contacts with the pre-defined electrical properties.
Fediai, Artem; Ryndyk, Dmitry A; Cuniberti, Gianaurelio
2016-10-01
Up to now, the electrical properties of the contacts between 3D metals and 2D materials have never been computed at a fully ab initio level due to the huge number of atomic orbitals involved in a current path from an electrode to a pristine 2D material. As a result, there are still numerous open questions and controversial theories on the electrical properties of systems with 3D/2D interfaces-for example, the current path and the contact length scalability. Our work provides a first-principles solution to this long-standing problem with the use of the modular approach, a method which rigorously combines a Green function formalism with the density functional theory (DFT) for this particular contact type. The modular approach is a general approach valid for any 3D/2D contact. As an example, we apply it to the most investigated among 3D/2D contacts-metal/graphene contacts-and show its abilities and consistency by comparison with existing experimental data. As it is applicable to any 3D/2D interface, the modular approach allows the engineering of 3D/2D contacts with the pre-defined electrical properties.
NASA Astrophysics Data System (ADS)
Sato, Haruo; Fehler, Michael C.
2016-10-01
The envelope broadening and the peak delay of the S-wavelet of a small earthquake with increasing travel distance are results of scattering by random velocity inhomogeneities in the earth medium. As a simple mathematical model, Sato proposed a new stochastic synthesis of the scalar wavelet envelope in 3-D von Kármán type random media when the centre wavenumber of the wavelet is in the power-law spectral range of the random velocity fluctuation. The essential idea is to split the random medium spectrum into two components using the centre wavenumber as a reference: the long-scale (low-wavenumber spectral) component produces the peak delay and the envelope broadening by multiple scattering around the forward direction; the short-scale (high-wavenumber spectral) component attenuates wave amplitude by wide angle scattering. The former is calculated by the Markov approximation based on the parabolic approximation and the latter is calculated by the Born approximation. Here, we extend the theory for the envelope synthesis of a wavelet in 2-D random media, which makes it easy to compare with finite difference (FD) simulation results. The synthetic wavelet envelope is analytically written by using the random medium parameters in the angular frequency domain. For the case that the power spectral density function of the random velocity fluctuation has a steep roll-off at large wavenumbers, the envelope broadening is small and frequency independent, and scattering attenuation is weak. For the case of a small roll-off, however, the envelope broadening is large and increases with frequency, and the scattering attenuation is strong and increases with frequency. As a preliminary study, we compare synthetic wavelet envelopes with the average of FD simulation wavelet envelopes in 50 synthesized random media, which are characterized by the RMS fractional velocity fluctuation ε = 0.05, correlation scale a = 5 km and the background wave velocity V0 = 4 km s-1. We use the radiation
NASA Astrophysics Data System (ADS)
Sato, Haruo; Fehler, Michael C.
2016-07-01
The envelope broadening and the peak delay of the S-wavelet of a small earthquake with increasing travel distance are results of scattering by random velocity inhomogeneities in the earth medium. As a simple mathematical model, Sato (2016) proposed a new stochastic synthesis of the scalar wavelet envelope in 3-D von Kármán type random media when the center wavenumber of the wavelet is in the power-law spectral range of the random velocity fluctuation. The essential idea is to split the random medium spectrum into two components using the center wavenumber as a reference: the long-scale (low-wavenumber spectral) component produces the peak delay and the envelope broadening by multiple scattering around the forward direction; the short-scale (high-wavenumber spectral) component attenuates wave amplitude by wide angle scattering. The former is calculated by the Markov approximation based on the parabolic approximation and the latter is calculated by the Born approximation. Here, we extend the theory for the envelope synthesis of a wavelet in 2-D random media, which makes it easy to compare with finite difference (FD) simulation results. The synthetic wavelet envelope is analytically written by using the random medium parameters in the angular frequency domain. For the case that the power spectral density function of the random velocity fluctuation has a steep roll-off at large wavenumbers, the envelope broadening is small and frequency independent, and scattering attenuation is weak. For the case of a small roll-off, however, the envelope broadening is large and increases with frequency, and the scattering attenuation is strong and increases with frequency. As a preliminary study, we compare synthetic wavelet envelopes with the average of FD simulation wavelet envelopes in 50 synthesized random media, which are characterized by the RMS fractional velocity fluctuation ε=0.05, correlation scale a =5 km and the background wave velocity V0=4 km/s. We use the radiation
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Stolarski, Richard S.
1999-01-01
In this study, we examine the sensitivity of long lived tracers to changes in the base transport components in our 2-D model. Changes to the strength of the residual circulation in the upper troposphere and stratosphere and changes to the lower stratospheric K(sub zz) had similar effects in that increasing the transport rates decreased the overall stratospheric mean age, and increased the rate of removal of material from the stratosphere. Increasing the stratospheric K(sub yy) increased the mean age due to the greater recycling of air parcels through the middle atmosphere, via the residual circulation, before returning to the troposphere. However, increasing K(sub yy) along with self-consistent increases in the corresponding planetary wave drive, which leads to a stronger residual circulation, more than compensates for the K(sub yy)-effect, and produces significantly younger ages throughout the stratosphere. Simulations with very small tropical stratospheric K(sub yy) decreased the globally averaged age of air by as much as 25% in the middle and upper stratosphere, and resulted in substantially weaker vertical age gradients above 20 km in the extratropics. We found only very small stratospheric tracer sensitivity to the magnitude of the horizontal mixing across the tropopause, and to the strength of the mesospheric gravity wave drag and diffusion used in the model. We also investigated the transport influence on chemically active tracers and found a strong age-tracer correlation, both in concentration and calculated lifetimes. The base model transport gives the most favorable overall comparison with a variety of inert tracer observations, and provides a significant improvement over our previous 1995 model transport. Moderate changes to the base transport were found to provide modest agreement with some of the measurements. Transport scenarios with residence times ranging from moderately shorter to slightly longer relative to the base case simulated N2O lifetimes
Mennemann, Jan-Frederik Jüngel, Ansgar
2014-10-15
Discrete transparent boundary conditions (DTBC) and the Perfectly Matched Layers (PML) method for the realization of open boundary conditions in quantum device simulations are compared, based on the stationary and time-dependent Schrödinger equation. The comparison includes scattering state, wave packet, and transient scattering state simulations in one and two space dimensions. The Schrödinger equation is discretized by a second-order Crank–Nicolson method in case of DTBC. For the discretization with PML, symmetric second-, fourth-, and sixth-order spatial approximations as well as Crank–Nicolson and classical Runge–Kutta time-integration methods are employed. In two space dimensions, a ring-shaped quantum waveguide device is simulated in the stationary and transient regime. As an application, a simulation of the Aharonov–Bohm effect in this device is performed, showing the excitation of bound states localized in the ring region. The numerical experiments show that the results obtained from PML are comparable to those obtained using DTBC, while keeping the high numerical efficiency and flexibility as well as the ease of implementation of the former method. -- Highlights: •In-depth comparison between discrete transparent boundary conditions (DTBC) and PML. •First 2-D transient scattering state simulations using DTBC. •First 2-D transient scattering state simulations of the Aharonov–Bohm effect.
NASA Astrophysics Data System (ADS)
Fernández-Pato, Javier; Caviedes-Voullième, Daniel; García-Navarro, Pilar
2016-05-01
One of the most difficult issues in the development of hydrologic models is to find a rigorous source of data and specific parameters to a given problem, on a given location that enable reliable calibration. In this paper, a distributed and physically based model (2D Shallow Water Equations) is used for surface flow and runoff calculations in combination with two infiltration laws (Horton and Green-Ampt) for estimating infiltration in a watershed. This technique offers the capability of assigning a local and time-dependent infiltration rate to each computational cell depending on the available surface water, soil type or vegetation. We investigate how the calibration of parameters is affected by transient distributed Shallow Water model and the complexity of the problem. In the first part of this work, we calibrate the infiltration parameters for both Horton and Green-Ampt models under flat ponded soil conditions. Then, by means of synthetic test cases, we perform a space-distributed sensitivity analysis in order to show that this calibration can be significantly affected by the introduction of topography or rainfall. In the second part, parameter calibration for a real catchment is addressed by comparing the numerical simulations with two different sets of experimental data, corresponding to very different events in terms of the rainfall volume. We show that the initial conditions of the catchment and the rainfall pattern have a special relevance in the quality of the adjustment. Hence, it is shown that the topography of the catchment and the storm characteristics affect the calibration of infiltration parameters.
NASA Astrophysics Data System (ADS)
Lee, Khil-Ha; Kim, Sung-Wook; Kim, Sang-Hyun
2014-05-01
model, called FLO-2D runs to simulate channel routing downstream to give the maximum water level. Once probable inundation areas are identified by the huge volume of water in the caldera lake, the unique geography, and the limited control capability, a potential hazard assessment can be represented. The study will contribute to build a geohazard map for the decision-makers and practitioners. Keywords: Volcanic flood, Caldera lake, Hazard assessment, Magma effusion Acknowledgement This research was supported by a grant [NEMA-BAEKDUSAN-2012-1-2] from the Volcanic Disaster Preparedness Research Center sponsored by National Emergency Management Agency of Korea.
Allain, Ariane; Chauvot de Beauchêne, Isaure; Langenfeld, Florent; Guarracino, Yann; Laine, Elodie; Tchertanov, Luba
2014-01-01
Allostery is a universal phenomenon that couples the information induced by a local perturbation (effector) in a protein to spatially distant regulated sites. Such an event can be described in terms of a large scale transmission of information (communication) through a dynamic coupling between structurally rigid (minimally frustrated) and plastic (locally frustrated) clusters of residues. To elaborate a rational description of allosteric coupling, we propose an original approach - MOdular NETwork Analysis (MONETA) - based on the analysis of inter-residue dynamical correlations to localize the propagation of both structural and dynamical effects of a perturbation throughout a protein structure. MONETA uses inter-residue cross-correlations and commute times computed from molecular dynamics simulations and a topological description of a protein to build a modular network representation composed of clusters of residues (dynamic segments) linked together by chains of residues (communication pathways). MONETA provides a brand new direct and simple visualization of protein allosteric communication. A GEPHI module implemented in the MONETA package allows the generation of 2D graphs of the communication network. An interactive PyMOL plugin permits drawing of the communication pathways between chosen protein fragments or residues on a 3D representation. MONETA is a powerful tool for on-the-fly display of communication networks in proteins. We applied MONETA for the analysis of communication pathways (i) between the main regulatory fragments of receptors tyrosine kinases (RTKs), KIT and CSF-1R, in the native and mutated states and (ii) in proteins STAT5 (STAT5a and STAT5b) in the phosphorylated and the unphosphorylated forms. The description of the physical support for allosteric coupling by MONETA allowed a comparison of the mechanisms of (a) constitutive activation induced by equivalent mutations in two RTKs and (b) allosteric regulation in the activated and non
SPICE-SANDIA.LIB. Library Analog Semiconductor Devices SPICE Simulators
Deveney, M.F.; Archer, W.; Bogdan, C.
1996-06-06
SPICE-SANDIA.LIB is a library of parameter sets and macromodels of semiconductor devices. They are used with Spice-based (SPICE is a program for electronic circuit analysis) simulators to simulate electronic circuits.
SIMULATIONS OF 2D AND 3D THERMOCAPILLARY FLOWS BY A LEAST-SQUARES FINITE ELEMENT METHOD. (R825200)
Numerical results for time-dependent 2D and 3D thermocapillary flows are presented in this work. The numerical algorithm is based on the Crank-Nicolson scheme for time integration, Newton's method for linearization, and a least-squares finite element method, together with a matri...
Simulation and Modeling of Submicron Semiconductor Devices by a New Hydrodynamic Method.
NASA Astrophysics Data System (ADS)
Lin, Qi.
Robust numerical methods for the solution of the hydrodynamic model are developed and implemented for the simulation of submicron semiconductor devices. The hydrodynamic equations are reformulated into readily solvable self-adjoint forms with the aid of newly defined HD-Slotboom state variables. A new discretization strategy is developed to resolve the rapid variation in the carrier densities and carrier temperatures. The approach also yields a coefficient matrix for each discretized hydrodynamic equation, which is guaranteed to be diagonally dominant. The hydrodynamic equations are decoupled by using a Gummel block iteration method. A fixed-point iteration technique is employed to solve the discretized equations, which guarantees that each decoupled equation converges for any starting value. Furthermore, the decoupling of equations and use of the fixed-point iteration scheme obviate the need for direct solutions of large matrix equations, and thereby eliminate the need for large memory allocations. The algorithm is inherently parallel, so it can be readily implemented on parallel machines to increase computation speed. Using these methods, several simulation packages are developed for the analysis of one-dimensional (1-D) n^+-n-n^+ devices, and square electric fields, two-dimensional (2-D) & three-dimensional (3-D) MOSFET's, and two-dimensional SOI MOSFET's. Various simulation results for these devices are presented. Some one-dimensional simulation results are compared with Monte Carlo calculations, and a good agreement is observed. Also convergence, stability, and efficiency of the methods are examined by a set of numerical experiments. The device simulators are applied to investigate the hot-electron induced degradation in submicron SOI devices and EPROM's. The impact of localized interface charge on device characteristics is studied. Some measured results are used to calibrate the process parameters in the simulators so that the simulators can predict device
SEMICONDUCTOR DEVICES: Simulation for signal charge transfer of charge coupled devices
NASA Astrophysics Data System (ADS)
Zujun, Wang; Yinong, Liu; Wei, Chen; Benqi, Tang; Zhigang, Xiao; Shaoyan, Huang; Minbo, Liu; Yong, Zhang
2009-12-01
Physical device models and numerical processing methods are presented to simulate a linear buried channel charge coupled devices (CCDs). The dynamic transfer process of CCD is carried out by a three-phase clock pulse driver. By using the semiconductor device simulation software MEDICI, dynamic transfer pictures of signal charges cells, electron concentration and electrostatic potential are presented. The key parameters of CCD such as charge transfer efficiency (CTE) and dark electrons are numerically simulated. The simulation results agree with the theoretic and experimental results.
Simulating FinFET Self-Heating for Device Reliability
NASA Astrophysics Data System (ADS)
Ham, James; Carr, Lincoln; Graas, Carole
2014-03-01
The continual scaling of transistors has led to sharp gradients in temperature (from ballistic transport of carriers) that result in new difficulties modeling device reliability. Current device-level thermal simulations do not track phonon populations, which are necessary to understand damage from high temperatures in scaled devices. A model for simulating highly localized hot spots due to an optical phonon bottle-neck near the channel/drain interface of a device operating in a ballistic transport regime will be presented. Various expansions of the Boltzmann transport equation (spherical harmonic expansion and methods of moments) are compared to a hydrodynamic model for device thermal simulations. We will discuss the post-processing technique for arriving at phonon populations from technology computer aided design (TCAD) simulations.
NASA Technical Reports Server (NTRS)
Tao, W.-K.; Shie, C.-H.; Simpson, J.; Starr, D.; Johnson, D.; Sud, Y.
2003-01-01
Real clouds and clouds systems are inherently three dimensional (3D). Because of the limitations in computer resources, however, most cloud-resolving models (CRMs) today are still two-dimensional (2D). A few 3D CRMs have been used to study the response of clouds to large-scale forcing. In these 3D simulations, the model domain was small, and the integration time was 6 hours. Only recently have 3D experiments been performed for multi-day periods for tropical cloud system with large horizontal domains at the National Center for Atmospheric Research. The results indicate that surface precipitation and latent heating profiles are very similar between the 2D and 3D simulations of these same cases. The reason for the strong similarity between the 2D and 3D CRM simulations is that the observed large-scale advective tendencies of potential temperature, water vapor mixing ratio, and horizontal momentum were used as the main forcing in both the 2D and 3D models. Interestingly, the 2D and 3D versions of the CRM used in CSU and U.K. Met Office showed significant differences in the rainfall and cloud statistics for three ARM cases. The major objectives of this project are to calculate and axamine: (1)the surface energy and water budgets, (2) the precipitation processes in the convective and stratiform regions, (3) the cloud upward and downward mass fluxes in the convective and stratiform regions; (4) cloud characteristics such as size, updraft intensity and lifetime, and (5) the entrainment and detrainment rates associated with clouds and cloud systems that developed in TOGA COARE, GATE, SCSMEX, ARM and KWAJEX. Of special note is that the analyzed (model generated) data sets are all produced by the same current version of the GCE model, i.e. consistent model physics and configurations. Trajectory analyse and inert tracer calculation will be conducted to identify the differences and similarities in the organization of convection between simulated 2D and 3D cloud systems.
NASA Astrophysics Data System (ADS)
Bilski, Bartosz; Frenner, Karsten; Osten, Wolfgang
2010-05-01
Scatterometry is a method commonly used in semiconductor metrology for measuring critical dimension (CD). It relies on measurement of light diffracted on a periodic structure and using it to derive the actual profile by running complex simulations. As CD is getting smaller with next lithography nodes, the Line-Edge Roughness/Line Width Roughness (LER/LWR) are becoming significant fraction of its overall size - therefore there is a need to include them in the simulations. Simulation of the LER/LWR's influence, in its random nature, calls for simulating relatively large fields. These large fields, if treated with rigorous electromagnetic simulations, are either very time-extensive or impossible to conduct, therefore computationally bearable, approximate approach needs to be applied. Our approximate method is "Field-Stitching Method" (FSM). We present its 2D version with varying parameter called "overlap region". We simulate the line grating structure with CD disturbed by LER/LWR and apply Rigorous Coupled Wave Analysis (RCWA) supported by the 2D FSM. We also generate the results obtained exclusively by RCWA, to which we compare the results of the approximate approach. Based on the comparison we discuss the benefits FSM brings and its limitations.
NASA Astrophysics Data System (ADS)
Ito, Y.; Noborio, K.
2015-12-01
In Japan, soil disinfection with hot water has been popular since the use of methyl bromide was restricted in 2005. Decreasing the amount of hot water applied may make farmers reduce the operation cost. To determine the appropriate amount of hot water needed for soil disinfection, HYDRUS-2D was evaluated. A field experiment was conducted and soil water content and soil temperature were measured at 5, 10, 20, 40, 60, 80 and 100 cm deep when 95oC hot water was applied. Irrigation tubing equipped with drippers every 30 cm were laid at the soil surface, z=0 cm. An irrigation rate for each dripper was 0.83 cm min-1 between t=0 and 120 min, and thereafter it was zero. Temperature of irrigation water was 95oC. Total simulation time with HYDRUS-2D was 720 min for a homogeneous soil. A simulating domain was selected as x=60 cm and z=100 cm. A potential evaporation rate was assumed to be 0 cm min-1 because the soil surface was covered with a plastic sheet. The boundary condition at the bottom was free drainage and those of both sides were no-flux conditions. Hydraulic properties and bulk densities measured at each depth were used for simulation. It was assumed that there was no organic matter contained. Soil thermal properties were adopted from previous study and HYDRUS 2D. Simulated temperatures at 5, 10, 20 and 40 cm deep agreed well with those measured although simulated temperatures at 60, 80, and 100 cm deep were overly estimated. Estimates of volumetric water content at 5 cm deep agreed well with measured values. Simulated values at 10 to 100 cm deep were overly estimated by 0.1 to 0.3 (m3 m-3). The deeper the soil became, the more the simulated wetting front lagged behind the measured one. It was speculated that water viscosity estimated smaller at high temperature might attributed to the slower advances of wetting front simulated with HYDRUS 2-D.
NASA Astrophysics Data System (ADS)
Kim, Kyeong-Hyeon; Kim, Dong-Su; Kim, Tae-Ho; Kang, Seong-Hee; Cho, Min-Seok; Suh, Tae Suk
2015-11-01
The phantom-alignment error is one of the factors affecting delivery quality assurance (QA) accuracy in intensity-modulated radiation therapy (IMRT). Accordingly, a possibility of inadequate use of spatial information in gamma evaluation may exist for patient-specific IMRT QA. The influence of the phantom-alignment error on gamma evaluation can be demonstrated experimentally by using the gamma passing rate and the gamma value. However, such experimental methods have a limitation regarding the intrinsic verification of the influence of the phantom set-up error because experimentally measuring the phantom-alignment error accurately is impossible. To overcome this limitation, we aimed to verify the effect of the phantom set-up error within the gamma evaluation formula by using a Monte Carlo simulation. Artificial phantom set-up errors were simulated, and the concept of the true point (TP) was used to represent the actual coordinates of the measurement point for the mathematical modeling of these effects on the gamma. Using dose distributions acquired from the Monte Carlo simulation, performed gamma evaluations in 2D and 3D. The results of the gamma evaluations and the dose difference at the TP were classified to verify the degrees of dose reflection at the TP. The 2D and the 3D gamma errors were defined by comparing gamma values between the case of the imposed phantom set-up error and the TP in order to investigate the effect of the set-up error on the gamma value. According to the results for gamma errors, the 3D gamma evaluation reflected the dose at the TP better than the 2D one. Moreover, the gamma passing rates were higher for 3D than for 2D, as is widely known. Thus, the 3D gamma evaluation can increase the precision of patient-specific IMRT QA by applying stringent acceptance criteria and setting a reasonable action level for the 3D gamma passing rate.
NASA Astrophysics Data System (ADS)
Wang, Jin; Ma, Jianyong; Zhou, Changhe
2014-11-01
A 3×3 high divergent 2D-grating with period of 3.842μm at wavelength of 850nm under normal incidence is designed and fabricated in this paper. This high divergent 2D-grating is designed by the vector theory. The Rigorous Coupled Wave Analysis (RCWA) in association with the simulated annealing (SA) is adopted to calculate and optimize this 2D-grating.The properties of this grating are also investigated by the RCWA. The diffraction angles are more than 10 degrees in the whole wavelength band, which are bigger than the traditional 2D-grating. In addition, the small period of grating increases the difficulties of fabrication. So we fabricate the 2D-gratings by direct laser writing (DLW) instead of traditional manufacturing method. Then the method of ICP etching is used to obtain the high divergent 2D-grating.
Numerical simulation of carpet cloaking device in terahertz frequency range
NASA Astrophysics Data System (ADS)
Gill, V. V.; Vozianova, A. V.; Khodzitsky, M. K.
2015-11-01
This work is devoted to the numerical calculation of the effective constitutive parameters of the carpet cloaking device and to the numerical simulation of this cloak using finite element method (FEM) for the terahertz frequency range.
Electronic device simulates respiration rate and depth
NASA Technical Reports Server (NTRS)
Thomas, J. A.
1964-01-01
An oscillator circuit and a thermistor, in close proximity to a light bulb, periodically alter the heat output of the bulb by varying the voltage across its filament. Use of this simulator permits checkout tests on pneumographs.
Modeling and Simulation of Marine Hydrokinetic Devices
NASA Astrophysics Data System (ADS)
Shoele, K.; Previsic, M.
2012-12-01
To accurately design a wave energy conversion system, the time domain numerical model is necessary. This is due to nonlinearities in the system from different sources such as hydrodynamic forces, device dynamics, control mechanisms, and mooring lines. Combining model accuracy with efficient and fast calculation of hydrodynamic forces in time domain is challenging and time-consuming. This article describes an easy to use and unified computational framework that handles those challenges efficiently for different types of wave energy converters. The framework has been generated as a Matlab toolbox that contains the key components of a wave to wire model. It can be used for initial performance evaluation of wave energy converters as well as detailed nonlinear analysis in the time domain. The preprocessing, post-processing, and standard modeling procedure are among the unique capabilities of the toolbox that enable users to check different device concepts and optimize device performance without dealing with modeling troubles. The hydrodynamic parameters are initially computed using the three-dimensional panel method and transformed to time domain by systematic identification techniques to accelerate computation of the hydrodynamic radiation forces. The dynamics of the whole system including nonlinear viscous forces, multi-body dynamics, mooring lines, and power takeoff units is then modeled in Matlab Simulink interface. Validation of the model with experimental studies is described and the responses of different wave energy conversion systems, especially their converted power, are presented.
NASA Astrophysics Data System (ADS)
Wu, C.; Chang, T.
2010-12-01
A new method in describing the multifractal characteristics of intermittent events was introduced by Cheng and Wu [Chang T. and Wu C.C., Physical Rev, E77, 045401(R), 2008]. The procedure provides a natural connection between the rank-ordered spectrum and the idea of one-parameter scaling for monofractals. This technique has been demonstrated using results obtained from a 2D MHD simulation. It has also been successfully applied to in-situ solar wind observations [Chang T., Wu, C.C. and Podesta, J., AIP Conf Proc. 1039, 75, 2008], and the broadband electric field oscillations from the auroral zone [Tam, S.W.Y. et al., Physical Rev, E81, 036414, 2010]. We take the next step in this procedure. By using the ROMA spectra and the scaled probability distribution functions (PDFs), raw PDFs can be calculated, which can be compared directly with PDFs from observations or simulation results. In addition to 2D MHD simulation results and in-situ solar wind observation, we show clearly using the ROMA analysis the multifractal character of the 3D fluid simulation data obtained from the JHU turbulence database cluster at http://turbulence.pha.jhu.edu. In particular, we show the scaling of the non-symmetrical PDF for the parallel-velocity fluctuations of this 3D fluid data.
Device simulation of cuprous oxide heterojunction solar cells
NASA Astrophysics Data System (ADS)
Takiguchi, Yuki; Miyajima, Shinsuke
2015-11-01
We developed a device simulation model of cuprous oxide (Cu2O)-based heterojunction solar cells. The developed model well reproduces the reported experimental current density-voltage characteristics and the external quantum efficiency results. By using the model, we explored structures for high-efficiency Cu2O-based heterojunction solar cells. It was found that the electron affinity of the buffer layer between transparent conducting oxide and Cu2O significantly affects solar cell performance. Surface recombination on the rear side of the device can be suppressed by employing a highly doped back surface layer. Our device simulation demonstrates a conversion efficiency of 16% without any optical confinement structure.
Device for simulating anterior segment surgery.
Otto, Clifton S
2005-07-01
To provide a more realistic method for practicing anterior segment surgery, a device was designed that incorporates aspects of currently available cadaver globe fixation methods. A Styrofoam head was fitted with a funnel and tubing system that allows for direct application of variable external suction to a globe placed in an artificial socket. Prototypes were tested in a wet lab environment, which demonstrated that this method provides reliable globe fixation and allows for variable control of intraocular pressure during a variety of anterior and posterior segment surgical techniques.
NASA Astrophysics Data System (ADS)
Wendling, A.; Daniel, J. L.; Hivet, G.; Vidal-Sallé, E.; Boisse, P.
2015-12-01
Numerical simulation is a powerful tool to predict the mechanical behavior and the feasibility of composite parts. Among the available numerical approaches, as far as woven reinforced composites are concerned, 3D finite element simulation at the mesoscopic scale leads to a good compromise between realism and complexity. At this scale, the fibrous reinforcement is modeled by an interlacement of yarns assumed to be homogeneous that have to be accurately represented. Among the numerous issues induced by these simulations, the first one consists in providing a representative meshed geometrical model of the unit cell at the mesoscopic scale. The second one consists in enabling a fast data input in the finite element software (contacts definition, boundary conditions, elements reorientation, etc.) so as to obtain results within reasonable time. Based on parameterized 3D CAD modeling tool of unit-cells of dry fabrics already developed, this paper presents an efficient strategy which permits an automated meshing of the models with 3D hexahedral elements and to accelerate of several orders of magnitude the simulation data input. Finally, the overall modeling strategy is illustrated by examples of finite element simulation of the mechanical behavior of fabrics.
CONFIG: Qualitative simulation tool for analyzing behavior of engineering devices
NASA Technical Reports Server (NTRS)
Malin, Jane T.; Basham, Bryan D.; Harris, Richard A.
1987-01-01
To design failure management expert systems, engineers mentally analyze the effects of failures and procedures as they propagate through device configurations. CONFIG is a generic device modeling tool for use in discrete event simulation, to support such analyses. CONFIG permits graphical modeling of device configurations and qualitative specification of local operating modes of device components. Computation requirements are reduced by focussing the level of component description on operating modes and failure modes, and specifying qualitative ranges of variables relative to mode transition boundaries. Simulation processing occurs only when modes change or variables cross qualitative boundaries. Device models are built graphically, using components from libraries. Components are connected at ports by graphical relations that define data flow. The core of a component model is its state transition diagram, which specifies modes of operation and transitions among them.
NASA Technical Reports Server (NTRS)
Scalapino, D. J.; Sugar, R. L.; White, S. R.; Bickers, N. E.; Scalettar, R. T.
1989-01-01
Numerical simulations on the half-filled three-dimensional Hubbard model clearly show the onset of Neel order. Simulations of the two-dimensional electron-phonon Holstein model show the competition between the formation of a Peierls-CDW state and a superconducting state. However, the behavior of the partly filled two-dimensional Hubbard model is more difficult to determine. At half-filling, the antiferromagnetic correlations grow as T is reduced. Doping away from half-filling suppresses these correlations, and it is found that there is a weak attractive pairing interaction in the d-wave channel. However, the strength of the pair field susceptibility is weak at the temperatures and lattice sizes that have been simulated, and the nature of the low-temperature state of the nearly half-filled Hubbard model remains open.
NASA Astrophysics Data System (ADS)
Suzuki, Akihiro; Maeda, Keiichi; Shigeyama, Toshikazu
2016-07-01
A two-dimensional special relativistic radiation-hydrodynamics code is developed and applied to numerical simulations of supernova shock breakout in bipolar explosions of a blue supergiant. Our calculations successfully simulate the dynamical evolution of a blast wave in the star and its emergence from the surface. Results of the model with spherical energy deposition show a good agreement with previous simulations. Furthermore, we calculate several models with bipolar energy deposition and compare their results with the spherically symmetric model. The bolometric light curves of the shock breakout emission are calculated by a ray-tracing method. Our radiation-hydrodynamic models indicate that the early part of the shock breakout emission can be used to probe the geometry of the blast wave produced as a result of the gravitational collapse of the iron core.
NASA Astrophysics Data System (ADS)
Kononenko, O.; Lopes, N. C.; Cole, J. M.; Kamperidis, C.; Mangles, S. P. D.; Najmudin, Z.; Osterhoff, J.; Poder, K.; Rusby, D.; Symes, D. R.; Warwick, J.; Wood, J. C.; Palmer, C. A. J.
2016-09-01
In this work, two-dimensional (2D) hydrodynamic simulations of a variable length gas cell were performed using the open source fluid code OpenFOAM. The gas cell was designed to study controlled injection of electrons into a laser-driven wakefield at the Astra Gemini laser facility. The target consists of two compartments: an accelerator and an injector section connected via an aperture. A sharp transition between the peak and plateau density regions in the injector and accelerator compartments, respectively, was observed in simulations with various inlet pressures. The fluid simulations indicate that the length of the down-ramp connecting the sections depends on the aperture diameter, as does the density drop outside the entrance and the exit cones. Further studies showed, that increasing the inlet pressure leads to turbulence and strong fluctuations in density along the axial profile during target filling, and consequently, is expected to negatively impact the accelerator stability.
NASA Astrophysics Data System (ADS)
Chen, J.-C.; Chuang, M.-R.; Jeng, C.-J.; Wang, J.-S.
2012-04-01
Taiwan is an island located in the subtropical zone where typhoons often bring heavy rainfall. Heavy rainfall, stream having steep slope, and weak geological condition resulted in a high susceptibility to debris flow. Especially, Typhoon Morakot struck southern Taiwan on August 8, 2009 with high rainfall intensity and accumulated rainfall as high as 2860 mm for 72 hours. Severe landslides and debris flow hazards were induced. In this work, debris-flow events caused by Typhoon Morakot in Shinfa Village of Liouguei District, where resulted in severe impacts to local communities, in southern Taiwan were selected for case study. A two-dimensional model (FLO-2D software) was used to simulate a debris flow, and the accuracy of the simulation, including flow depth, velocity, sediment, and inundation area, was analyzed in the case study. This study consists of three phases. In the first phase, debris flow data, including information on topography, rainfall and rheological parameters were compiled to establish a database of factors that influence debris flow. For the second phase, a numerical simulation was performed using FLO-2D with the results presented as area of debris-flow inundation, maximum deposit depth, and deposit volume. The simulation results were then compared with the aerial photos and the micro geomorphological study. Finally, suitable conditions for using this model and reasonable parameters needed for simulation are presented. In this study, parameters and processes needed for a numerical simulation method for debris flow routing and depositions are formulated to provide a reference for hazard zone mapping or debris-flow hazard mitigation.
Chukalovsky, A. A.; Rakhimova, T. V.; Klopovsky, K. S.; Mankelevich, Yu. A.; Proshina, O. V.
2011-03-15
The kinetic processes occurring in an electric-discharge oxygen-iodine laser are analyzed with the help of a 2D (r, z) gasdynamic model taking into account transport of excited oxygen, singlet oxygen, and radicals from the electric discharge and their mixing with the iodine-containing gas. The main processes affecting the dynamics of the gas temperature and gain are revealed. The simulation results obtained using the 2D model agree well with the experimental data on the mixture gain. A subsonic oxygen-iodine laser in which singlet oxygen is generated by a 350 W transverse RF discharge excited in an oxygen flow at a pressure P = 10 Torr and the discharge tube wall is covered with mercury oxide is simulated. The simulated mixing system is optimized in terms of the flow rate and the degree of preliminary dissociation of the iodine flow. The optimal regime of continuous operation of a subsonic electric-discharge oxygen-iodine laser is found.
Fan, D.; Geng, C.; Chen, L.Q.
1997-03-01
The local kinetics and topological phenomena during normal grain growth were studied in two dimensions by computer simulations employing a continuum diffuse-interface field model. The relationships between topological class and individual grain growth kinetics were examined, and compared with results obtained previously from analytical theories, experimental results and Monte Carlo simulations. It was shown that both the grain-size and grain-shape (side) distributions are time-invariant and the linear relationship between the mean radii of individual grains and topological class n was reproduced. The moments of the shape distribution were determined, and the differences among the data from soap froth. Potts model and the present simulation were discussed. In the limit when the grain size goes to zero, the average number of grain edges per grain is shown to be between 4 and 5, implying the direct vanishing of 4- and 5-sided grains, which seems to be consistent with recent experimental observations on thin films. Based on the simulation results, the conditions for the applicability of the familiar Mullins-Von Neumann law and the Hillert`s equation were discussed.
User`s guide for the casting process simulator software CaPS-2D, Version 1.0
Domanus, H.M.; Schmitt, R.C.; Ahuja, S.
1993-07-01
Most casting defects occur during initial pouring and therefore the design of the running system, which guides the metal from the ladle into the mold, is crucial. Traditionally, the running system and mold filling are designed by trial and error, which is tedious, time consuming. and expensive. The uncertainties that remain can be overcome by a computer simulation that demonstrates the actual process of mold filling and subsequent solidification. Computer simulation of various processes has become more and more common in recent years. The cost-effectiveness of making flawless castings has made the foundry worker more aware of the process of mold filling, identification of hot spots, etc. The macroscopic Casting Process Simulator (CaPS) software combines heat transfer and fluid flow aspects and can describe a variety of solidification aspects, including mold filling. CaPS is a two-dimensional time-dependent computer code involving a finite-volume formulation for the mass, momentum. and energy equations. CaPS has the following characteristics: CaPS uses the PATRAN geometric modeling package for constructing the geometry, generating a neutral file consisting of a list of named components, and post-processing of the simulation results; building the geometry independently of the mesh is a time-saving procedure. A structured mesh generator of structured regular cells is included and is interfaced with the neutral-file output of the solid geometric package. Visual user interfaces have been developed on the basis of the HOOPS package, which contains a hierarchical database of geometric information. The CaPS shell scripts interactively provide a step-by-step procedure to simulate the solidification process, thus making the software very user-friendly.
3D numerical simulation of laser-generated Lamb waves propagation in 2D acoustic black holes
NASA Astrophysics Data System (ADS)
Yan, Shiling; Lomonosov, Alexey M.; Shen, Zhonghua; Han, Bing
2015-05-01
Acoustic black holes have been widely used in damping structural vibration. In this work, the Lamb waves are utilized to evaluate the specified structure. The three-dimensional numerical model of acoustic black holes with parabolic profile was established. The propagation of laser-generated Lamb wave in two-dimensional acoustic black holes was numerically simulated using the finite element method. The results indicated that the incident wave was trapped by the structure obviously.
2D hybrid simulations of super-diffusion at the magnetopause driven by Kelvin-Helmholtz instability
Cowee, Misa M; Winske, Dan; Gary, S Peter
2009-01-01
This manuscript describes the self-consistent simulation of diffusion at the magnetopause driven by Kelvin-Helmholtz (KH) instability. Two-dimensional hybrid (kinetic ions, fluid electrons) simulations of the most KH-unstable configuration where the shear flow is oriented perpendicular to the uniform magnetic field are carried out. The motion of the simulation particles are tracked during the run and their mean-square displacement normal to the magnetopause is calculated from which diffusion coefficients are determined. The diffusion coefficients are found to be time dependent, with D{sub x} {proportional_to} t{sup {alpha}}, where {alpha} > 1. Additionally, the probability distribution functions (PDF) of the 'jump lengths' the particles make over time are found to be non-gaussian. Such time-dependent diffusion coefficients and non-gaussian PDF's have been associated with so-called 'super-diffusion', in which diffusive mixing of particles is enhanced over classical diffusion. The results indicate that while turbulence associated with the break-down of vortices contributes to this enhanced diffusion, it is the growth of large-scale, coherent vortices is the more important process in facilitating it.
NASA Astrophysics Data System (ADS)
Amaya-Ventura, Gilberto; Rodríguez-Romo, Suemi
2011-09-01
This paper deals with the computational simulation of the reaction-diffusion-advection phenomena emerging in Rayleigh-Bénard (RB) and Poiseuille-Bénard reactive convection systems. We use the Boussinesq's approximation for buoyancy forces and the Lattice Boltzmann method (LBM). The first kinetic mesoscopic model proposed here is based on the discrete Boltzmann equation needed to solve the momentum balance coupled with buoyancy forces. Then, a second lattice Boltzmann algorithm is applied to solve the reaction-diffusion-advection equation to calculate the evolution of the chemical species concentration. We use a reactive system composed by nitrous oxide (so call laughing gas) in air as an example; its spatio-temporal decomposition is calculated. Two cases are considered, a rectangular enclosed cavity and an open channel. The simulations are performed at low Reynolds numbers and in a steady state between the first and second thermo-hydrodynamic instabilities. The results presented here, for the thermo-hydrodynamic behavior, are in good agreement with experimental data; while our| chemical kinetics simulation yields expected results. Some applications of our approach are related to chemical reactors and atmospheric phenomena, among others.
NASA Astrophysics Data System (ADS)
Uchino, H.; Machida, S.
2012-12-01
A physical process of the substorm triggering in the Earth's Magnetotail is thought to be closely related to the magnetic reconnection and the tearing instability. Recently we proposed a new scheme of the substorm onset called "Catapult Current Sheet Relaxation (CCSR) Model " to physically understand the results from GEOTAIL and THEMIS data. The CCSR Model has characters that are the decrease of the total pressure and thinning of the current sheet at the distance about -12Re in the magnetotail a few minutes before the substorm onset, and the simultaneous occurrence of the dipolarization at X~-10Re and the magnetic reconnection at X~-20Re at the time of the onset. In this study, we investigate a stability of the current sheet and the particle acceleration via particle simulation in order to assess the validity of the CCSR model and to clarify the mechanism of substorm onset. We give an initial magnetic field structure which is akin to the Earth's dipole magnetic field together with a stretched magnetic field by thin current sheet, and further add a weak northward magnetic field at the place where Near-Earth Neutral Line is expected to be formed. The results of simulation contain similar features that characterize the CCSR Model. A physically interpretation of the simulation result with the linear instability theory as well as comparison with observations will be given.
NASA Astrophysics Data System (ADS)
Matos, J. R.; Welty, C.; Packman, A.
2005-12-01
The main purpose of the simulations in this research is the analysis of three-dimensional surface-groundwater interchange in heterogeneous systems. The effects of channel pattern, bed forms and aquifer heterogeneity on flow interactions between stream and groundwater systems are examined in order to contribute for a better understanding of the hyporheic process. A two-dimensional approach was also adopted to allow comparisons with the three-dimensional results. The grid was designed using the correlation scales of the heterogeneous fields and the scale of the stream meanders. MODFLOW and MODPATH were used to evaluate magnitude, direction and spatial distribution of the exchange flow. PMWIN and PMPATH were used as pre and post-processors during the construction of the models and analysis of results. Gaining and losing streams as well as parallel flow and flow across streams were simulated as idealized cases intended to describe how properties of the streambed and aquifer in low-gradient lowland streams contribute to hyporheic exchange. At first a straight river was analyzed then meandering streams were created with a sine curve and variations on wavelength and amplitude. Bed forms were simulated assuming a sinusoidal distribution of pressure head in the bed surface. Aspects of the influence of bedforms on mechanisms such as "pumping" and "turnover" are expected to be addressed with simulations. Flow velocities between 20 and 40 cm/s in the channel were tested with the objective of showing the influence of river morphology and natural bed forms on the flow exchange in the hyporheic zone. Several meander cycles and four levels of hydraulic conductivity variance were analyzed. Results of flow variances along the cross-sections and wetted perimeter show the increasing on hyporheic exchange as the degree of heterogeneity increases. Particle tracking was performed to define hyporheic residence time distributions. When comparing the homogeneous fields with all degrees of
NASA Astrophysics Data System (ADS)
Alvarado, M. J.; Prinn, R. G.
2007-12-01
The growth of aerosol particles and production of ozone in young smoke plumes is the result of a complex interaction between the mean flow in the smoke plume, turbulent diffusion, gas-phase oxidation, coagulation, and mass transfer between phases. Models allow us to separate the effects of these processes and predict their impact on the global environment. We present the results of two and three-dimensional Eulerian simulations of the dynamics and chemistry of the smoke plume formed by the Timbavati savannah fire studied during SAFARI 2000 (Hobbs et al., 2003, JGR, doi:10.1029/2002JD002352). The dynamical model is an extension of an Eulerian cloud-resolving model that has previously been used to study the role of deep convective clouds on tropospheric chemistry (Wang and Prinn, 2000, JGR, 105(D17) 22,269-22,297). The model includes a source of sensible heat, gases, and particles at the surface to simulate the savannah fire. The new gas and aerosol chemistry model includes heterogeneous chemistry, kinetic mass transfer, coagulation and the formation of secondary organic and inorganic aerosol. Photolysis rates are calculated based on the solution of the radiative transfer equation within the plume, including the scattering and absorption of radiation by the smoke aerosols. Our preliminary 2D Eulerian results using standard chemistry and UV fluxes show that the model can simulate the lower but not the higher levels of O3 observed. Also, the simulated 2D O3 field shows a wave-like pattern in the downwind direction, even though the emissions from the fire are held constant. This suggests that plume heterogeneity in the downwind direction may account for some of the observed variability in O3. We will present results of runs incorporating higher resolution calculation of photolysis rates, heterogeneous HONO formation, and gas phase reactions involving the uncharacterized organic compounds observed in the gas phase of the Timbavati plume in order to better simulate these
Schaffranek, Raymond W.
2004-01-01
A numerical model for simulation of surface-water integrated flow and transport in two (horizontal-space) dimensions is documented. The model solves vertically integrated forms of the equations of mass and momentum conservation and solute transport equations for heat, salt, and constituent fluxes. An equation of state for salt balance directly couples solution of the hydrodynamic and transport equations to account for the horizontal density gradient effects of salt concentrations on flow. The model can be used to simulate the hydrodynamics, transport, and water quality of well-mixed bodies of water, such as estuaries, coastal seas, harbors, lakes, rivers, and inland waterways. The finite-difference model can be applied to geographical areas bounded by any combination of closed land or open water boundaries. The simulation program accounts for sources of internal discharges (such as tributary rivers or hydraulic outfalls), tidal flats, islands, dams, and movable flow barriers or sluices. Water-quality computations can treat reactive and (or) conservative constituents simultaneously. Input requirements include bathymetric and topographic data defining land-surface elevations, time-varying water level or flow conditions at open boundaries, and hydraulic coefficients. Optional input includes the geometry of hydraulic barriers and constituent concentrations at open boundaries. Time-dependent water level, flow, and constituent-concentration data are required for model calibration and verification. Model output consists of printed reports and digital files of numerical results in forms suitable for postprocessing by graphical software programs and (or) scientific visualization packages. The model is compatible with most mainframe, workstation, mini- and micro-computer operating systems and FORTRAN compilers. This report defines the mathematical formulation and computational features of the model, explains the solution technique and related model constraints, describes the
2D/3D quench simulation using ANSYS for epoxy impregnated Nb3Sn high field magnets
Ryuji Yamada et al.
2002-09-19
A quench program using ANSYS is developed for the high field collider magnet for three-dimensional analysis. Its computational procedure is explained. The quench program is applied to a one meter Nb{sub 3}Sn high field model magnet, which is epoxy impregnated. The quench simulation program is used to estimate the temperature and mechanical stress inside the coil as well as over the whole magnet. It is concluded that for the one meter magnet with the presented cross section and configuration, the thermal effects due to the quench is tolerable. But we need much more quench study and improvements in the design for longer magnets.
2D photonic-crystal optomechanical nanoresonator.
Makles, K; Antoni, T; Kuhn, A G; Deléglise, S; Briant, T; Cohadon, P-F; Braive, R; Beaudoin, G; Pinard, L; Michel, C; Dolique, V; Flaminio, R; Cagnoli, G; Robert-Philip, I; Heidmann, A
2015-01-15
We present the optical optimization of an optomechanical device based on a suspended InP membrane patterned with a 2D near-wavelength grating (NWG) based on a 2D photonic-crystal geometry. We first identify by numerical simulation a set of geometrical parameters providing a reflectivity higher than 99.8% over a 50-nm span. We then study the limitations induced by the finite value of the optical waist and lateral size of the NWG pattern using different numerical approaches. The NWG grating, pierced in a suspended InP 265-nm thick membrane, is used to form a compact microcavity involving the suspended nanomembrane as an end mirror. The resulting cavity has a waist size smaller than 10 μm and a finesse in the 200 range. It is used to probe the Brownian motion of the mechanical modes of the nanomembrane. PMID:25679837
Numerical simulations in the development of propellant management devices
NASA Astrophysics Data System (ADS)
Gaulke, Diana; Winkelmann, Yvonne; Dreyer, Michael
Propellant management devices (PMDs) are used for positioning the propellant at the propel-lant port. It is important to provide propellant without gas bubbles. Gas bubbles can inflict cavitation and may lead to system failures in the worst case. Therefore, the reliable operation of such devices must be guaranteed. Testing these complex systems is a very intricate process. Furthermore, in most cases only tests with downscaled geometries are possible. Numerical sim-ulations are used here as an aid to optimize the tests and to predict certain results. Based on these simulations, parameters can be determined in advance and parts of the equipment can be adjusted in order to minimize the number of experiments. In return, the simulations are validated regarding the test results. Furthermore, if the accuracy of the numerical prediction is verified, then numerical simulations can be used for validating the scaling of the experiments. This presentation demonstrates some selected numerical simulations for the development of PMDs at ZARM.
Electronic simulation of a multiterminal quantum Hall effect device
NASA Astrophysics Data System (ADS)
Sosso, A.; Capra, P. P.
1999-04-01
A circuit with only resistors and unity gain amplifiers can be proven to be equivalent to the Ricketts and Kemeny electrical model of multiterminal quantum Hall effect (QHE) devices. By means of the new equivalent circuit, commercial software for electronic circuit analysis can be used to study a QHE measurement system. Moreover, it can be easily implemented, and we were able to build a circuit that simulates the electrical behavior of a QHE device. Particular care was taken in the design to reduce the effect of parasitic capacitances, which act as loads connected to the device terminals. Bootstrap buffers have been adopted to significantly reduce the capacitance of input stage. The small residual loading effect can be calculated and eliminated, allowing simulation of a QHE device with good accuracy.
NASA Astrophysics Data System (ADS)
de Garis, Hugo; Korkin, Michael; Guttikonda, Padma; Cooley, Donald
2000-11-01
This paper presents some simulation results of the evolution of 2D visual pattern recognizers to be implemented very shortly on real hardware, namely the 'CAM-Brain Machine' (CBM), an FPGA based piece of evolvable hardware which implements a genetic algorithm (GA) to evolve a 3D cellular automata (CA) based neural network circuit module, of approximately 1,000 neurons, in about a second, i.e. a complete run of a GA, with 10,000s of circuit growths and performance evaluations. Up to 65,000 of these modules, each of which is evolved with a humanly specified function, can be downloaded into a large RAM space, and interconnected according to humanly specified gvdvips -o SPIE-2000.ps SPIE-2000 artificial brain architectures. This RAM, containing an artificial brain with up to 75 million neurons, is then updated by the CBM at a rate of 130 billion CA cells per second. Such speeds will enable real time control of robots and hopefully the birth of a new research field that we call 'brain building.' The first such artificial brain, to be built at STARLAB in 2000 and beyond, will be used to control the behaviors of a life sized kitten robot called 'Robokitty.' This kitten robot will need 2D pattern recognizers in the visual section of its artificial brain. This paper presents simulation results on the evolvability and generalization properties of such recognizers.
Kasinathan, N.; Rajakumar, A.; Vaidyanathan, G.; Chetal, S.C.
1995-09-01
Post shutdown decay heat removal is an important safety requirement in any nuclear system. In order to improve the reliability of this function, Liquid metal (sodium) cooled fast breeder reactors (LMFBR) are equipped with redundant hot pool dipped immersion coolers connected to natural draught air cooled heat exchangers through intermediate sodium circuits. During decay heat removal, flow through the core, immersion cooler primary side and in the intermediate sodium circuits are also through natural convection. In order to establish the viability and validate computer codes used in making predictions, a 1:20 scale experimental model called RAMONA with water as coolant has been built and experimental simulation of decay heat removal situation has been performed at KfK Karlsruhe. Results of two such experiments have been compiled and published as benchmarks. This paper brings out the results of the numerical simulation of one of the benchmark case through a 1D/2D coupled code system, DHDYN-1D/THYC-2D and the salient features of the comparisons. Brief description of the formulations of the codes are also included.
Design, modelling and simulation aspects of an ankle rehabilitation device
NASA Astrophysics Data System (ADS)
Racu, C. M.; Doroftei, I.
2016-08-01
Ankle injuries are amongst the most common injuries of the lower limb. Besides initial treatment, rehabilitation of the patients plays a crucial role for future activities and proper functionality of the foot. Traditionally, ankle injuries are rehabilitated via physiotherapy, using simple equipment like elastic bands and rollers, requiring intensive efforts of therapists and patients. Thus, the need of robotic devices emerges. In this paper, the design concept and some modelling and simulation aspects of a novel ankle rehabilitation device are presented.
NASA Technical Reports Server (NTRS)
Gnoffo, Peter A.; Berry, Scott A.; VanNorman, John W.
2011-01-01
This paper is one of a series of five papers in a special session organized by the NASA Fundamental Aeronautics Program that addresses uncertainty assessments for CFD simulations in hypersonic flow. Simulations of a shock emanating from a compression corner and interacting with a fully developed turbulent boundary layer are evaluated herein. Mission relevant conditions at Mach 7 and Mach 14 are defined for a pre-compression ramp of a scramjet powered vehicle. Three compression angles are defined, the smallest to avoid separation losses and the largest to force a separated flow engaging more complicated flow physics. The Baldwin-Lomax and the Cebeci-Smith algebraic models, the one-equation Spalart-Allmaras model with the Catrix-Aupoix compressibility modification and two-equation models including Menter SST, Wilcox k-omega 98, and Wilcox k-omega 06 turbulence models are evaluated. Each model is fully defined herein to preclude any ambiguity regarding model implementation. Comparisons are made to existing experimental data and Van Driest theory to provide preliminary assessment of model form uncertainty. A set of coarse grained uncertainty metrics are defined to capture essential differences among turbulence models. Except for the inability of algebraic models to converge for some separated flows there is no clearly superior model as judged by these metrics. A preliminary metric for the numerical component of uncertainty in shock-turbulent-boundary-layer interactions at compression corners sufficiently steep to cause separation is defined as 55%. This value is a median of differences with experimental data averaged for peak pressure and heating and for extent of separation captured in new, grid-converged solutions presented here. This value is consistent with existing results in a literature review of hypersonic shock-turbulent-boundary-layer interactions by Roy and Blottner and with more recent computations of MacLean.
2004-08-01
AnisWave2D is a 2D finite-difference code for a simulating seismic wave propagation in fully anisotropic materials. The code is implemented to run in parallel over multiple processors and is fully portable. A mesh refinement algorithm has been utilized to allow the grid-spacing to be tailored to the velocity model, avoiding the over-sampling of high-velocity materials that usually occurs in fixed-grid schemes.
Comparison of Non-Parabolic Hydrodynamic Simulations for Semiconductor Devices
NASA Technical Reports Server (NTRS)
Smith, A. W.; Brennan, K. F.
1996-01-01
Parabolic drift-diffusion simulators are common engineering level design tools for semiconductor devices. Hydrodynamic simulators, based on the parabolic band approximation, are becoming more prevalent as device dimensions shrink and energy transport effects begin to dominate device characteristic. However, band structure effects present in state-of-the-art devices necessitate relaxing the parabolic band approximation. This paper presents simulations of ballistic diodes, a benchmark device, of Si and GaAs using two different non-parabolic hydrodynamic formulations. The first formulation uses the Kane dispersion relationship in the derivation of the conservation equations. The second model uses a power law dispersion relation {(hk)(exp 2)/2m = xW(exp Y)}. Current-voltage relations show that for the ballistic diodes considered. the non-parabolic formulations predict less current than the parabolic case. Explanations of this will be provided by examination of velocity and energy profiles. At low bias, the simulations based on the Kane formulation predict greater current flow than the power law formulation. As the bias is increased this trend changes and the power law predicts greater current than the Kane formulation. It will be shown that the non-parabolicity and energy range of the hydrodynamic model based on the Kane dispersion relation are limited due to the binomial approximation which was utilized in the derivation.
Multiscale quantum mechanics/electromagnetics simulation for electronic devices.
Yam, ChiYung; Meng, Lingyi; Chen, GuanHua; Chen, Quan; Wong, Ngai
2011-08-28
The continuous downsizing of modern electronic devices implies the increasing importance of quantum phenomena. As the feature sizes of transistors inch towards 10 nanometer, simulations including quantum effects and atomistic details are inevitable. Here we report a novel hybrid quantum mechanics and electromagnetics (QM/EM) method to model individual electronic components at the nanoscale. QM and EM models are solved in different regions of the system in a self-consistent manner. As a demonstration, we study a carbon nanotube based electronic device embedded in a silicon block. Good agreement is obtained between simulation by QM/EM method and full QM treatment of the entire system.
Simulation of neutron radiation damage in silicon semiconductor devices.
Shadid, John Nicolas; Hoekstra, Robert John; Hennigan, Gary Lee; Castro, Joseph Pete Jr.; Fixel, Deborah A.
2007-10-01
A code, Charon, is described which simulates the effects that neutron damage has on silicon semiconductor devices. The code uses a stabilized, finite-element discretization of the semiconductor drift-diffusion equations. The mathematical model used to simulate semiconductor devices in both normal and radiation environments will be described. Modeling of defect complexes is accomplished by adding an additional drift-diffusion equation for each of the defect species. Additionally, details are given describing how Charon can efficiently solve very large problems using modern parallel computers. Comparison between Charon and experiment will be given, as well as comparison with results from commercially-available TCAD codes.
Performance issues for iterative solvers in device simulation
NASA Technical Reports Server (NTRS)
Fan, Qing; Forsyth, P. A.; Mcmacken, J. R. F.; Tang, Wei-Pai
1994-01-01
Due to memory limitations, iterative methods have become the method of choice for large scale semiconductor device simulation. However, it is well known that these methods still suffer from reliability problems. The linear systems which appear in numerical simulation of semiconductor devices are notoriously ill-conditioned. In order to produce robust algorithms for practical problems, careful attention must be given to many implementation issues. This paper concentrates on strategies for developing robust preconditioners. In addition, effective data structures and convergence check issues are also discussed. These algorithms are compared with a standard direct sparse matrix solver on a variety of problems.
Techniques utilized in the simulated altitude testing of a 2D-CD vectoring and reversing nozzle
NASA Technical Reports Server (NTRS)
Block, H. Bruce; Bryant, Lively; Dicus, John H.; Moore, Allan S.; Burns, Maureen E.; Solomon, Robert F.; Sheer, Irving
1988-01-01
Simulated altitude testing of a two-dimensional, convergent-divergent, thrust vectoring and reversing exhaust nozzle was accomplished. An important objective of this test was to develop test hardware and techniques to properly operate a vectoring and reversing nozzle within the confines of an altitude test facility. This report presents detailed information on the major test support systems utilized, the operational performance of the systems and the problems encountered, and test equipment improvements recommended for future tests. The most challenging support systems included the multi-axis thrust measurement system, vectored and reverse exhaust gas collection systems, and infrared temperature measurement systems used to evaluate and monitor the nozzle. The feasibility of testing a vectoring and reversing nozzle of this type in an altitude chamber was successfully demonstrated. Supporting systems performed as required. During reverser operation, engine exhaust gases were successfully captured and turned downstream. However, a small amount of exhaust gas spilled out the collector ducts' inlet openings when the reverser was opened more than 60 percent. The spillage did not affect engine or nozzle performance. The three infrared systems which viewed the nozzle through the exhaust collection system worked remarkably well considering the harsh environment.
NASA Astrophysics Data System (ADS)
Westerhof, E.; de Blank, H. J.; Pratt, J.
2016-03-01
Two dimensional reduced MHD simulations of neoclassical tearing mode growth and suppression by ECCD are performed. The perturbation of the bootstrap current density and the EC drive current density perturbation are assumed to be functions of the perturbed flux surfaces. In the case of ECCD, this implies that the applied power is flux surface averaged to obtain the EC driven current density distribution. The results are consistent with predictions from the generalized Rutherford equation using common expressions for Δ \\text{bs}\\prime and Δ \\text{ECCD}\\prime . These expressions are commonly perceived to describe only the effect on the tearing mode growth of the helical component of the respective current perturbation acting through the modification of Ohm’s law. Our results show that they describe in addition the effect of the poloidally averaged current density perturbation which acts through modification of the tearing mode stability index. Except for modulated ECCD, the largest contribution to the mode growth comes from this poloidally averaged current density perturbation.
NASA Astrophysics Data System (ADS)
Nikitin, Sergey; Khokhlova, Tatiana; Pelivanov, Ivan
2012-02-01
Dependencies of the optoacoustic (OA) transformation efficiency on tissue temperature were obtained for the application in OA temperature monitoring during thermal therapies. Accurate measurement of the OA signal amplitude versus temperature was performed in different ex-vivo tissues in the temperature range 25°C - 80°C. The investigated tissues were selected to represent different structural components: chicken breast (skeletal muscle), porcine lard (fatty tissue) and porcine liver (richly perfused tissue). Backward mode of the OA signal detection and a narrow probe laser beam were used in the experiments to avoid the influence of changes in light scattering with tissue coagulation on the OA signal amplitude. Measurements were performed in heating and cooling regimes. Characteristic behavior of the OA signal amplitude temperature dependences in different temperature ranges were described in terms of changes in different structural components of the tissue samples. Finally, numerical simulation of the OA temperature monitoring with a linear transducers array was performed to demonstrate the possibility of real-time temperature mapping.
Arnal, B; Pinton, G; Garapon, P; Pernot, M; Fink, M; Tanter, M
2013-10-01
Shear wave imaging (SWI) maps soft tissue elasticity by measuring shear wave propagation with ultrafast ultrasound acquisitions (10 000 frames s(-1)). This spatiotemporal data can be used as an input for an inverse problem that determines a shear modulus map. Common inversion methods are local: the shear modulus at each point is calculated based on the values of its neighbour (e.g. time-of-flight, wave equation inversion). However, these approaches are sensitive to the information loss such as noise or the lack of the backscattered signal. In this paper, we evaluate the benefits of a global approach for elasticity inversion using a least-squares formulation, which is derived from full waveform inversion in geophysics known as the adjoint method. We simulate an acoustic waveform in a medium with a soft and a hard lesion. For this initial application, full elastic propagation and viscosity are ignored. We demonstrate that the reconstruction of the shear modulus map is robust with a non-uniform background or in the presence of noise with regularization. Compared to regular local inversions, the global approach leads to an increase of contrast (∼+3 dB) and a decrease of the quantification error (∼+2%). We demonstrate that the inversion is reliable in the case when there is no signal measured within the inclusions like hypoechoic lesions which could have an impact on medical diagnosis.
NASA Astrophysics Data System (ADS)
Lyra, W.; Johansen, A.; Zsom, A.; Klahr, H.; Piskunov, N.
2009-04-01
Context: As accretion in protoplanetary disks is enabled by turbulent viscosity, the border between active and inactive (dead) zones constitutes a location where there is an abrupt change in the accretion flow. The gas accumulation that ensues triggers the Rossby wave instability, which in turn saturates into anticyclonic vortices. It has been suggested that the trapping of solids within them leads to a burst of planet formation on very short timescales. Aims: We study in the formation and evolution of the vortices in greater detail, focusing on the implications for the dynamics of embedded solid particles and planet formation. Methods: We performed two-dimensional global simulations of the dynamics of gas and solids in a non-magnetized thin protoplanetary disk with the Pencil code. We used multiple particle species of radius 1, 10, 30, and 100 cm. We computed the particles' gravitational interaction by a particle-mesh method, translating the particles' number density into surface density and computing the corresponding self-gravitational potential via fast Fourier transforms. The dead zone is modeled as a region of low viscosity. Adiabatic and locally isothermal equations of state are used. Results: The Rossby wave instability is triggered under a variety of conditions, thus making vortex formation a robust process. Inside the vortices, fast accumulation of solids occurs and the particles collapse into objects of planetary mass on timescales as short as five orbits. Because the drag force is size-dependent, aerodynamical sorting ensues within the vortical motion, and the first bound structures formed are composed primarily of similarly-sized particles. In addition to erosion due to ram pressure, we identify gas tides from the massive vortices as a disrupting agent of formed protoplanetary embryos. We find evidence that the backreaction of the drag force from the particles onto the gas modifies the evolution of the Rossby wave instability, with vortices being
Nibedita, R; Kumar, R A; Majumdar, A; Hosur, R V; Govil, G; Majumder, K; Chauhan, V S
1993-09-01
Solution conformation of a self-complementary 14-mer DNA duplex (d-GGATTGGCCAATCC) containing the GCCAAT recognition motif of several transcription factors has been investigated by NMR spectroscopy. Complete resonance assignment of all the protons (except H5',H5'' protons) has been obtained following standard procedures based on two-dimensional NMR techniques. Three-bond coupling constants have been determined by spectral simulation procedures. New strategies have been described and employed for quantifying NOE intensities from the structural point of view. Approximate ranges of gamma torsion angles have been obtained from a selective NOESY experiment, by estimating the J(4'-5'), J(4'-5''), or their sum in the H1'-H4' cross peaks of the spectrum. Likewise, ranges of epsilon torsion angles have been obtained by monitoring the H3' multiplicities in the H8/H6-H3' cross peaks in selective NOESY spectra. With the help of such a total of 73 coupling constraints, 79 NOE intensity constraints, and 108 H-bond constraints, model building has been carried out to obtain a structure which satisfies the constraints. Starting from such a structure, an expanded distance constraint set has been created which has been used for the distance geometry calculations using the program TANDY. In the best structure thus derived, interesting irregularities similar to a BI-BII transition have been observed in the center. The molecule exhibits a bend. The overall base stacking is different from that in either B- or A-DNA models. The base pairs are tilted with respect to the local helix axes. The observed structural features are likely to have important implications for the recognition mechanism of the GCCAAT motif.
NASA Astrophysics Data System (ADS)
Constantinescu, R.; Thouret, J. C.; Sandri, L.; Irimus, I. A.; Stefanescu, R.
2012-04-01
Pyroclastic density currents, which include pyroclastic surges and pyroclastic flows (PFs), are among the most dangerous volcanic phenomena. We present a probabilistic hazard assessment of the PFs generated from eruptive column collapse at El Misti volcano (5822 m) in South Peru. The high relief of the cone, the location of the city of Arequipa (~1,000,000 people) on two large volcanoclastic fans and the H (3.5 km)/L (17 km) ratio (0.2) between the summit and the city center, make PFs a direct threat. We consider three eruption scenario sizes: small Vulcanian/Phreatomagmatic (VEI 2), medium Sub-Plinian (VEI 3-4), and large Plinian (VEI 4+). We use the Event-Tree approach in a Bayesian scheme with BET_VH (Bayesian Event Tree for Volcanic Hazard) software. Quantitative data that stem from numerical simulations from TITAN2D (termed prior models) and from stratigraphic record (termed past data) are input to BET_VH, which enables us to compute the probabilities (in a 1-year time window) of (i) having an eruption (ii) in a selected location/vent (iii) of a specific size, (iv) and that this eruption will produce PFs (v) that will reach a location of interest around El Misti. TITAN2D simulation runs, expressed as color-coded thicknesses of PDC deposits, fit well the extent of past PFs deposits, including thick confined deposits (0.5-7 m) in the Rio Chili canyon and its tributary ravines (Quebradas San Lazaro, Huarangal and Agua Salada).The unconfined, thinner (≤10cm) deposits, as displayed by simulation runs on the interfluves, is attributed to ash-cloud surges. Such thin, fine ash deposits have not been emphasized in geological maps either because they have been removed away or remain yet unrecognized. The simulated Vulcanian flows, restricted to the upper part of the cone, become confined (0.1-1m thick) in the ravines which converge towards each of the three Quebradas. The simulated Subplinian PF deposits reach 0.1 to 1 m thick in the Quebradas and 1-4 m WNW of El
Sidler, Rolf; Carcione, José M.; Holliger, Klaus
2013-02-15
We present a novel numerical approach for the comprehensive, flexible, and accurate simulation of poro-elastic wave propagation in 2D polar coordinates. An important application of this method and its extensions will be the modeling of complex seismic wave phenomena in fluid-filled boreholes, which represents a major, and as of yet largely unresolved, computational problem in exploration geophysics. In view of this, we consider a numerical mesh, which can be arbitrarily heterogeneous, consisting of two or more concentric rings representing the fluid in the center and the surrounding porous medium. The spatial discretization is based on a Chebyshev expansion in the radial direction and a Fourier expansion in the azimuthal direction and a Runge–Kutta integration scheme for the time evolution. A domain decomposition method is used to match the fluid–solid boundary conditions based on the method of characteristics. This multi-domain approach allows for significant reductions of the number of grid points in the azimuthal direction for the inner grid domain and thus for corresponding increases of the time step and enhancements of computational efficiency. The viability and accuracy of the proposed method has been rigorously tested and verified through comparisons with analytical solutions as well as with the results obtained with a corresponding, previously published, and independently benchmarked solution for 2D Cartesian coordinates. Finally, the proposed numerical solution also satisfies the reciprocity theorem, which indicates that the inherent singularity associated with the origin of the polar coordinate system is adequately handled.
Physical model for characterizing and simulating a FLOTOX EEPROM device
NASA Astrophysics Data System (ADS)
Wu, Ching-Yuan; Chen, Chiou-Feng
1992-05-01
A physical model has been developed to analyze the dynamic characteristics of a FLOTOX EEPROM device. The effects of the structural parameters such as the area and thickness of the tunneling-oxide and interpoly-oxide layers are characterized by a coupling ratio to describe the discrete programming or erasing operation. The physical parameters including the electron trapping and positive-charge generation effects are used to describe the endurance and retention operations of an EEPROM device. Computer simulations based on this model have been performed to analyze the operations of an EEPROM device, including the effects of three different programming/erasing input voltage waveforms (pulse, exponential rise and triangular). A method for protecting an EEPROM device from overshooting or undershooting during programming or erasing operation is proposed. Therefore, the proposed model can be used as a computer-aided-design (CAD) tool for device design and an efficient simulation tool for describing the dynamic operation and reliability of an EEPROM device.
14 CFR 121.921 - Training devices and simulators.
Code of Federal Regulations, 2011 CFR
2011-01-01
... device or flight simulator qualification level: (1) Required evaluation of individual or crew proficiency. (2) Training to proficiency or training activities that determine if an individual or crew is ready for an evaluation of proficiency. (3) Activities used to meet recency of experience requirements....
NASA Astrophysics Data System (ADS)
Gürleme, Beran; Tarık Meriç, Hakan; Ulutaş, Ergin; Anunziato, Alessandro
2016-04-01
The aim of this study is the simulation and visualization of the initial and maximum tsunami wave heights in 2D and 3D along the Mediterranean coasts inferred from the five largest earthquakes in history in this region. The earthquakes considered in the study are 21 July 365 Crete, 8 August 1303 Crete, 3 May 1481 Rhodes, 28 December Messina and 21 May 2003 Algeria. All these earthquakes spawned tsunamis and inflicted damage in coastal regions. The study was conducted to explain which could be the potential Tsunami consequences caused by similar earthquakes occurring in the region in the future. The methodology used for the calculation of tsunami wave heights from the earthquakes includes the determination of earthquake parameters, modeling of the initial wave height, simulation of the wave propagation and calculation of the maximum wave heights near coastal areas. The parameters of the earthquakes are based on previously published fault mechanism solutions and known tectonic features of the regions. Static dislocation algorithm for the initial wave height is used from the parameters of focal mechanism solutions. The study was conducted also to understand the reliability of the previously published focal mechanism solutions for the earthquakes by using the principal stress axis in the regions. The 2D and 3D visualized models of tsunamis from the earthquakes include isometric grid representing the sea surface for the purpose of a better understanding of the initial tsunami mechanism compared to 1D visualizations. In many studies, the earthquake locations, tectonic features of the regions, initial heights and tsunami simulations are shown on maps as bird's eye in 1D visualization. However these kinds of features are related in depths and bathymetric features. For that reason, our approaches will contribute to have better understanding where the uplift- subsidence of initial heights and crests-troughs of simulated wave heights and thus provide a better insight of the
NASA Astrophysics Data System (ADS)
Rank, Christopher M.; Heußer, Thorsten; Flach, Barbara; Brehm, Marcus; Kachelrieß, Marc
2015-03-01
We propose a new method for PET/MR respiratory motion compensation, which is based on a 3D-2D registration of strongly undersampled MR data and a) runs in parallel with the PET acquisition, b) can be interlaced with clinical MR sequences, and c) requires less than one minute of the total MR acquisition time per bed position. In our simulation study, we applied a 3D encoded radial stack-of-stars sampling scheme with 160 radial spokes per slice and an acquisition time of 38 s. Gated 4D MR images were reconstructed using a 4D iterative reconstruction algorithm. Based on these images, motion vector fields were estimated using our newly-developed 3D-2D registration framework. A 4D PET volume of a patient with eight hot lesions in the lungs and upper abdomen was simulated and MoCo 4D PET images were reconstructed based on the motion vector fields derived from MR. For evaluation, average SUVmean values of the artificial lesions were determined for a 3D, a gated 4D, a MoCo 4D and a reference (with ten-fold measurement time) gated 4D reconstruction. Compared to the reference, 3D reconstructions yielded an underestimation of SUVmean values due to motion blurring. In contrast, gated 4D reconstructions showed the highest variation of SUVmean due to low statistics. MoCo 4D reconstructions were only slightly affected by these two sources of uncertainty resulting in a significant visual and quantitative improvement in terms of SUVmean values. Whereas temporal resolution was comparable to the gated 4D images, signal-to-noise ratio and contrast-to-noise ratio were close to the 3D reconstructions.
SIERRA - A 3-D device simulator for reliability modeling
NASA Astrophysics Data System (ADS)
Chern, Jue-Hsien; Arledge, Lawrence A., Jr.; Yang, Ping; Maeda, John T.
1989-05-01
SIERRA is a three-dimensional general-purpose semiconductor-device simulation program which serves as a foundation for investigating integrated-circuit (IC) device and reliability issues. This program solves the Poisson and continuity equations in silicon under dc, transient, and small-signal conditions. Executing on a vector/parallel minisupercomputer, SIERRA utilizes a matrix solver which uses an incomplete LU (ILU) preconditioned conjugate gradient square (CGS, BCG) method. The ILU-CGS method provides a good compromise between memory size and convergence rate. The authors have observed a 5x to 7x speedup over standard direct methods in simulations of transient problems containing highly coupled Poisson and continuity equations such as those found in reliability-oriented simulations. The application of SIERRA to parasitic CMOS latchup and dynamic random-access memory single-event-upset studies is described.
NASA Astrophysics Data System (ADS)
Orlić, Ivica; Mekterović, Darko; Mekterović, Igor; Ivošević, Tatjana
2015-11-01
VIBA-Lab is a computer program originally developed by the author and co-workers at the National University of Singapore (NUS) as an interactive software package for simulation of Particle Induced X-ray Emission and Rutherford Backscattering Spectra. The original program is redeveloped to a VIBA-Lab 3.0 in which the user can perform semi-quantitative analysis by comparing simulated and measured spectra as well as simulate 2D elemental maps for a given 3D sample composition. The latest version has a new and more versatile user interface. It also has the latest data set of fundamental parameters such as Coster-Kronig transition rates, fluorescence yields, mass absorption coefficients and ionization cross sections for K and L lines in a wider energy range than the original program. Our short-term plan is to introduce routine for quantitative analysis for multiple PIXE and XRF excitations. VIBA-Lab is an excellent teaching tool for students and researchers in using PIXE and RBS techniques. At the same time the program helps when planning an experiment and when optimizing experimental parameters such as incident ions, their energy, detector specifications, filters, geometry, etc. By "running" a virtual experiment the user can test various scenarios until the optimal PIXE and BS spectra are obtained and in this way save a lot of expensive machine time.
A Review of Simulators with Haptic Devices for Medical Training.
Escobar-Castillejos, David; Noguez, Julieta; Neri, Luis; Magana, Alejandra; Benes, Bedrich
2016-04-01
Medical procedures often involve the use of the tactile sense to manipulate organs or tissues by using special tools. Doctors require extensive preparation in order to perform them successfully; for example, research shows that a minimum of 750 operations are needed to acquire sufficient experience to perform medical procedures correctly. Haptic devices have become an important training alternative and they have been considered to improve medical training because they let users interact with virtual environments by adding the sense of touch to the simulation. Previous articles in the field state that haptic devices enhance the learning of surgeons compared to current training environments used in medical schools (corpses, animals, or synthetic skin and organs). Consequently, virtual environments use haptic devices to improve realism. The goal of this paper is to provide a state of the art review of recent medical simulators that use haptic devices. In particular we focus on stitching, palpation, dental procedures, endoscopy, laparoscopy, and orthopaedics. These simulators are reviewed and compared from the viewpoint of used technology, the number of degrees of freedom, degrees of force feedback, perceived realism, immersion, and feedback provided to the user. In the conclusion, several observations per area and suggestions for future work are provided. PMID:26888655
A Review of Simulators with Haptic Devices for Medical Training.
Escobar-Castillejos, David; Noguez, Julieta; Neri, Luis; Magana, Alejandra; Benes, Bedrich
2016-04-01
Medical procedures often involve the use of the tactile sense to manipulate organs or tissues by using special tools. Doctors require extensive preparation in order to perform them successfully; for example, research shows that a minimum of 750 operations are needed to acquire sufficient experience to perform medical procedures correctly. Haptic devices have become an important training alternative and they have been considered to improve medical training because they let users interact with virtual environments by adding the sense of touch to the simulation. Previous articles in the field state that haptic devices enhance the learning of surgeons compared to current training environments used in medical schools (corpses, animals, or synthetic skin and organs). Consequently, virtual environments use haptic devices to improve realism. The goal of this paper is to provide a state of the art review of recent medical simulators that use haptic devices. In particular we focus on stitching, palpation, dental procedures, endoscopy, laparoscopy, and orthopaedics. These simulators are reviewed and compared from the viewpoint of used technology, the number of degrees of freedom, degrees of force feedback, perceived realism, immersion, and feedback provided to the user. In the conclusion, several observations per area and suggestions for future work are provided.
Fluid Structure Interaction Simulations of Pediatric Ventricular Assist Device Operation
NASA Astrophysics Data System (ADS)
Long, Chris; Marsden, Alison; Bazilevs, Yuri
2011-11-01
Pediatric ventricular assist devices (PVADs) are used for mechanical circulatory support in children with failing hearts. They can be used to allow the heart to heal naturally or to extend the life of the patient until transplant. A PVAD has two chambers, blood and air, separated by a flexible membrane. The air chamber is pressurized, which drives the membrane and pumps the blood. The primary risk associated with these devices is stroke or embolism from thrombogenesis. Simulation of these devices is difficult due to a complex coupling of two fluid domains and a thin membrane, requiring fluid-structure interaction modeling. The goal of this work is to accurately simulate the hemodynamics of a PVAD. We perform FSI simulations using an Arbitrary Lagrangian-Eulerian (ALE) finite element framework to account for large motions of the membrane and the fluid domains. The air, blood, and membrane are meshed as distinct subdomains, and a method for non-matched discretizations at the fluid-structure interface is presented. The use of isogeometric analysis to model the membrane mechanics is also discussed, and the results of simulations are presented.
Simulation and training of lumbar punctures using haptic volume rendering and a 6DOF haptic device
NASA Astrophysics Data System (ADS)
Färber, Matthias; Heller, Julika; Handels, Heinz
2007-03-01
The lumbar puncture is performed by inserting a needle into the spinal chord of the patient to inject medicaments or to extract liquor. The training of this procedure is usually done on the patient guided by experienced supervisors. A virtual reality lumbar puncture simulator has been developed in order to minimize the training costs and the patient's risk. We use a haptic device with six degrees of freedom (6DOF) to feedback forces that resist needle insertion and rotation. An improved haptic volume rendering approach is used to calculate the forces. This approach makes use of label data of relevant structures like skin, bone, muscles or fat and original CT data that contributes information about image structures that can not be segmented. A real-time 3D visualization with optional stereo view shows the punctured region. 2D visualizations of orthogonal slices enable a detailed impression of the anatomical context. The input data consisting of CT and label data and surface models of relevant structures is defined in an XML file together with haptic rendering and visualization parameters. In a first evaluation the visible human male data has been used to generate a virtual training body. Several users with different medical experience tested the lumbar puncture trainer. The simulator gives a good haptic and visual impression of the needle insertion and the haptic volume rendering technique enables the feeling of unsegmented structures. Especially, the restriction of transversal needle movement together with rotation constraints enabled by the 6DOF device facilitate a realistic puncture simulation.
NASA Astrophysics Data System (ADS)
Tea, E.; Hin, C.
In this work, we provide a detailed analysis of phosphorene performance as n-type and p-type active materials. The study is based on first principles calculation of phosphorene electronic structure, and resulting electron and hole scattering rates and lifetimes. Emphasis is put on extreme regimes commonly found in semiconductor devices, i.e. high electric fields and heavy doping, where impact ionization and Auger recombination can occur. We found that electron-initiated impact ionization is weaker than the hole-initiated process, when compared to carrier-phonon interaction rates, suggesting resilience to impact ionization initiated breakdown. Moreover, calculated minority electron lifetimes are limited by radiative recombination only, not by Auger processes, suggesting that phosphorene could achieve good quantum efficiencies in optoelectronic devices. The provided scattering rates and lifetimes are critical input data for the modeling and understanding of phosphorene-based device physics.
Tea, E; Hin, C
2016-08-10
In this work, we provide a detailed analysis of phosphorene's performance as an n-type and p-type active material. This study is based on first principles calculations of the phosphorene electronic structure, and the resulting electron and hole scattering rates and lifetimes. Emphasis is put on extreme regimes commonly found in semiconductor devices, i.e. high electric fields and heavy doping, where impact ionization and Auger recombination can occur. We found that electron-initiated impact ionization is weaker than the hole-initiated process, when compared to carrier-phonon interaction rates, suggesting resilience to impact ionization initiated breakdown. Moreover, calculated minority electron lifetimes are limited by radiative recombination only, not by Auger processes, suggesting that phosphorene could achieve good quantum efficiencies in optoelectronic devices. The provided scattering rates and lifetimes are critical input data for the modeling and understanding of phosphorene-based device physics.
Tea, E; Hin, C
2016-08-10
In this work, we provide a detailed analysis of phosphorene's performance as an n-type and p-type active material. This study is based on first principles calculations of the phosphorene electronic structure, and the resulting electron and hole scattering rates and lifetimes. Emphasis is put on extreme regimes commonly found in semiconductor devices, i.e. high electric fields and heavy doping, where impact ionization and Auger recombination can occur. We found that electron-initiated impact ionization is weaker than the hole-initiated process, when compared to carrier-phonon interaction rates, suggesting resilience to impact ionization initiated breakdown. Moreover, calculated minority electron lifetimes are limited by radiative recombination only, not by Auger processes, suggesting that phosphorene could achieve good quantum efficiencies in optoelectronic devices. The provided scattering rates and lifetimes are critical input data for the modeling and understanding of phosphorene-based device physics. PMID:27479904
NASA Astrophysics Data System (ADS)
Tierz, Pablo; Ramona Stefanescu, Elena; Sandri, Laura; Patra, Abani; Marzocchi, Warner; Sulpizio, Roberto
2014-05-01
Probabilistic hazard assessments of Pyroclastic Density Currents (PDCs) are of great interest for decision-making purposes. However, there is a limited number of published works available on this topic. Recent advances in computation and statistical methods are offering new opportunities beyond the classical Monte Carlo (MC) sampling which is known as a simple and robust method but it usually turns out to be slow and computationally intractable. In this work, Titan2D numerical simulator has been coupled to Polynomial Chaos Quadrature (PCQ) to propagate the simulator parametric uncertainty and compute VEI-based probabilistic hazard maps of dense PDCs formed as a result of column collapse at Vesuvius volcano, Italy. Due to the lack of knowledge about the exact conditions under which these PDCs will form, Probability Distribution Functions (PDFs) are assigned to the simulator input parameters (Bed Friction Angle and Volume) according to three VEI sizes. Uniform distributions were used for both parameters since there is insufficient information to assume that any value in the range is more likely that any other value. Reasonable (and compatible) ranges for both variables were constrained according to past eruptions at Vesuvius volcanic system. On the basis of reasoning above a number of quadrature points were taken within those ranges, which resulted in one execution of the TITAN2D code at each quadrature point. With a computational cost several orders of magnitude smaller than MC, exceedance probabilities for a given threshold of flow depth (and conditional to the occurrence of VEI3, VEI4 and VEI5 eruptions) were calculated using PCQ. Moreover, PCQ can be run at different threshold values of the same output variable (flow depth, speed, kinetic energy, …) and, therefore, it can serve to compute Exceedance Probability curves (aka hazard curves) at singular points inside the hazard domain, representing the most important and useful scientific input to quantitative risk
NASA Astrophysics Data System (ADS)
Wyseure, Guido; Chou, Po-Yi
2010-05-01
All hydrological handbooks contain methods for direct runoff and base-flow separation. The semi-log separation method is the most classical one. One can, however, question the physical base for such method. In addition, the water fluxes in the riverbed are important for ecology and water quality. In our study an 2-D cross-section including the river and the surrounding aquifer was set-up in HYDRUS 2D/3D. Initial conditions were a steady-state subsurface flow feeding the river with a recharge from the soil surface. A surface runoff event was simulated by a rise and recession of the water level in the river. Differences between summer and winter situation were explored by given representative temperatures to the different components of the river-aquifer system. The simulations show that the fluxes are very different along the riverbed. Even during steady state baseflow we see that the fluxes through the bottom were 2 to 3 times smaller as compared to the side banks. During the hydrographs the proportion can become up to 5 times. Another interesting result is that within the time frame of the hydrograph and its immediate recession relatively little water, which pentetrated in the aquifer, returns to the river. Most of the water replenishes the aquifer and there is only a very small rise of baseflow. In our simulation we returned to the original level as before the hydrograph, so in reality even less or no rise in baseflow may occur immediately after a hydrograph. Of course, in a longer time-frame the recharge of the aquifer will give a rise to the actual subsurface drainage. The change in seasonal temperatures within the river-aquifer system has a substantial effect. For identical river stage hydrograph changes the hyporheic exchange fluxes are more intense in summer than in winter. If we define the hyporheic zone as the extedn to which the water fluxes from the river can penetrate, then we see that this zone is wider on the sides as compared to the bottom of the
NASA Technical Reports Server (NTRS)
Li, Xiaofan; Sui, C.-H.; Lau, K-M.; Adamec, D.
1999-01-01
A two-dimensional coupled ocean-cloud resolving atmosphere model is used to investigate possible roles of convective scale ocean disturbances induced by atmospheric precipitation on ocean mixed-layer heat and salt budgets. The model couples a cloud resolving model with an embedded mixed layer-ocean circulation model. Five experiment are performed under imposed large-scale atmospheric forcing in terms of vertical velocity derived from the TOGA COARE observations during a selected seven-day period. The dominant variability of mixed-layer temperature and salinity are simulated by the coupled model with imposed large-scale forcing. The mixed-layer temperatures in the coupled experiments with 1-D and 2-D ocean models show similar variations when salinity effects are not included. When salinity effects are included, however, differences in the domain-mean mixed-layer salinity and temperature between coupled experiments with 1-D and 2-D ocean models could be as large as 0.3 PSU and 0.4 C respectively. Without fresh water effects, the nocturnal heat loss over ocean surface causes deep mixed layers and weak cooling rates so that the nocturnal mixed-layer temperatures tend to be horizontally-uniform. The fresh water flux, however, causes shallow mixed layers over convective areas while the nocturnal heat loss causes deep mixed layer over convection-free areas so that the mixed-layer temperatures have large horizontal fluctuations. Furthermore, fresh water flux exhibits larger spatial fluctuations than surface heat flux because heavy rainfall occurs over convective areas embedded in broad non-convective or clear areas, whereas diurnal signals over whole model areas yield high spatial correlation of surface heat flux. As a result, mixed-layer salinities contribute more to the density differences than do mixed-layer temperatures.
Zhang, Y; Yang, J; Liu, H; Liu, D
2014-06-01
Purpose: The purpose of this work is to compare the verification results of three solutions (2D/3D ionization chamber arrays measurement and Monte Carlo simulation), the results will help make a clinical decision as how to do our cervical IMRT verification. Methods: Seven cervical cases were planned with Pinnacle 8.0m to meet the clinical acceptance criteria. The plans were recalculated in the Matrixx and Delta4 phantom with the accurate plans parameters. The plans were also recalculated by Monte Carlo using leaf sequences and MUs for individual plans of every patient, Matrixx and Delta4 phantom. All plans of Matrixx and Delta4 phantom were delivered and measured. The dose distribution of iso slice, dose profiles, gamma maps of every beam were used to evaluate the agreement. Dose-volume histograms were also compared. Results: The dose distribution of iso slice and dose profiles from Pinnacle calculation were in agreement with the Monte Carlo simulation, Matrixx and Delta4 measurement. A 95.2%/91.3% gamma pass ratio was obtained between the Matrixx/Delta4 measurement and Pinnacle distributions within 3mm/3% gamma criteria. A 96.4%/95.6% gamma pass ratio was obtained between the Matrixx/Delta4 measurement and Monte Carlo simulation within 2mm/2% gamma criteria, almost 100% gamma pass ratio within 3mm/3% gamma criteria. The DVH plot have slightly differences between Pinnacle and Delta4 measurement as well as Pinnacle and Monte Carlo simulation, but have excellent agreement between Delta4 measurement and Monte Carlo simulation. Conclusion: It was shown that Matrixx/Delta4 and Monte Carlo simulation can be used very efficiently to verify cervical IMRT delivery. In terms of Gamma value the pass ratio of Matrixx was little higher, however, Delta4 showed more problem fields. The primary advantage of Delta4 is the fact it can measure true 3D dosimetry while Monte Carlo can simulate in patients CT images but not in phantom.
A quantum energy transport model for semiconductor device simulation
Sho, Shohiro; Odanaka, Shinji
2013-02-15
This paper describes numerical methods for a quantum energy transport (QET) model in semiconductors, which is derived by using a diffusion scaling in the quantum hydrodynamic (QHD) model. We newly drive a four-moments QET model similar with a classical ET model. Space discretization is performed by a new set of unknown variables. Numerical stability and convergence are obtained by developing numerical schemes and an iterative solution method with a relaxation method. Numerical simulations of electron transport in a scaled MOSFET device are discussed. The QET model allows simulations of quantum confinement transport, and nonlocal and hot-carrier effects in scaled MOSFETs.
Fukuyoshi, Shuichi; Kometani, Masaharu; Watanabe, Yurie; Hiratsuka, Masahiro; Yamaotsu, Noriyuki; Hirono, Shuichi; Manabe, Noriyoshi; Takahashi, Ohgi; Oda, Akifumi
2016-01-01
Many natural mutants of the drug metabolizing enzyme cytochrome P450 (CYP) 2D6 have been reported. Because the enzymatic activities of many mutants are different from that of the wild type, the genetic polymorphism of CYP2D6 plays an important role in drug metabolism. In this study, the molecular dynamics simulations of the wild type and mutants of CYP2D6, CYP2D6.1, 2, 10, 14A, 51, and 62 were performed, and the predictions of static and dynamic structures within them were conducted. In the mutant CYP2D6.10, 14A, and 61, dynamic properties of the F-G loop, which is one of the components of the active site access channel of CYP2D6, were different from that of the wild type. The F-G loop acted as the "hatch" of the channel, which was closed in those mutants. The structure of CYP2D6.51 was not converged by the simulation, which indicated that the three-dimensional structure of CYP2D6.51 was largely different from that of the wild type. In addition, the intramolecular interaction network of CYP2D6.10, 14A, and 61 was different from that of the wild type, and it is considered that these structural changes are the reason for the decrease or loss of enzymatic activities. On the other hand, the static and dynamic properties of CYP2D6.2, whose activity was normal, were not considerably different from those of the wild type.
Watanabe, Yurie; Hiratsuka, Masahiro; Yamaotsu, Noriyuki; Hirono, Shuichi; Manabe, Noriyoshi; Takahashi, Ohgi; Oda, Akifumi
2016-01-01
Many natural mutants of the drug metabolizing enzyme cytochrome P450 (CYP) 2D6 have been reported. Because the enzymatic activities of many mutants are different from that of the wild type, the genetic polymorphism of CYP2D6 plays an important role in drug metabolism. In this study, the molecular dynamics simulations of the wild type and mutants of CYP2D6, CYP2D6.1, 2, 10, 14A, 51, and 62 were performed, and the predictions of static and dynamic structures within them were conducted. In the mutant CYP2D6.10, 14A, and 61, dynamic properties of the F-G loop, which is one of the components of the active site access channel of CYP2D6, were different from that of the wild type. The F-G loop acted as the “hatch” of the channel, which was closed in those mutants. The structure of CYP2D6.51 was not converged by the simulation, which indicated that the three-dimensional structure of CYP2D6.51 was largely different from that of the wild type. In addition, the intramolecular interaction network of CYP2D6.10, 14A, and 61 was different from that of the wild type, and it is considered that these structural changes are the reason for the decrease or loss of enzymatic activities. On the other hand, the static and dynamic properties of CYP2D6.2, whose activity was normal, were not considerably different from those of the wild type. PMID:27046024
A compact inflow control device for simulating flight fan noise
NASA Astrophysics Data System (ADS)
Homyak, L.; McArdle, J. G.; Heidelberg, L. J.
Inflow control device (ICD's) of various shapes and sizes have been used to simulate inflight fan tone noise during ground static tests. A small, simple inexpensive ICD design was optimized from previous design and fabrication techniques. This compact two-fan-diameter ICD exhibits satisfactory acoustic performance characteristics without causing noise attenuation or redirection. In addition, it generates no important new noise sources. Design and construction details of the compact ICD are discussed and acoustic performance test results are presented.
A compact inflow control device for simulating flight fan noise
NASA Astrophysics Data System (ADS)
Homyak, L.; McArdle, J. G.; Heidelberg, L. J.
1983-04-01
Inflow control device (ICD's) of various shapes and sizes have been used to simulate inflight fan tone noise during ground static tests. A small, simple inexpensive ICD design was optimized from previous design and fabrication techniques. This compact two-fan-diameter ICD exhibits satisfactory acoustic performance characteristics without causing noise attenuation or redirection. In addition, it generates no important new noise sources. Design and construction details of the compact ICD are discussed and acoustic performance test results are presented.
A compact inflow control device for simulating flight fan noise
NASA Technical Reports Server (NTRS)
Homyak, L.; Mcardle, J. G.; Heidelberg, L. J.
1983-01-01
Inflow control device (ICD's) of various shapes and sizes have been used to simulate inflight fan tone noise during ground static tests. A small, simple inexpensive ICD design was optimized from previous design and fabrication techniques. This compact two-fan-diameter ICD exhibits satisfactory acoustic performance characteristics without causing noise attenuation or redirection. In addition, it generates no important new noise sources. Design and construction details of the compact ICD are discussed and acoustic performance test results are presented.
NASA Astrophysics Data System (ADS)
Martelloni, Gianluca; Bagnoli, Franco; Di Cintio, Pierfrancesco
2015-04-01
We integrate existing soil infiltration modeling with particle based methods in order to simulate two and three-dimensional setups of triggered landslides. Commonly, the infiltration models are based on continuum schemes (e.g. Eulerian approach) by means of which it is possible to define the field of the pore pressure within a soil. By contrast, the particle based methods follow a Lagrangian scheme that allows one to identify the particle trajectories and their dynamical properties. In this work, in order to simulate the triggering mechanism, we apply the classical, fractal and fractional Richards equations and the Mohr-Coulomb failure criterion, adapted to the molecular dynamics technique. In our scheme the (local) positive pore pressure is simply implemented as a perturbation of the rest state of each grain. Therefore, the pore pressure function can be interpreted as a time-space dependent scalar field acting on each particle. To initialize the system we generate, using a molecular dynamics based algorithm, a mechanically stable disk (2D) or sphere (3D) packing simulating the consolidated soil. In this way, we can built the micro and macro pore structure related to different infiltration time scales. The inter-particle interactions are modeled with a Lennard-Jones like potential. The particle positions are updated in time, after and during a rainfall, with standard molecular dynamics. We analyze the sensitivity of the model with respect to the variation of some parameters such as hydraulic conductivity, cohesion, slope and friction angle, soil depth and fractional order of the generalized infiltration model. In addition, we consider both regular and random particle configurations. The results of our simulations are found to be in agreement with real landslides. In particular, the mean velocity patterns of the simulated landslides appear extremely similar to the observed ones. Moreover, it is possible to apply the method of the inverse surface displacement
NASA Astrophysics Data System (ADS)
Hao, Yufei; Lu, Quanming; Lembege, Bertrand; Huang, Can; Wu, Mingyu; Guo, Fan; Shan, Lican; Zheng, Jian; Wang, Shui
2015-04-01
Experimental observations from space missions (including Cluster more recently) have clearly revealed the existence of high speed jets (HSJ) in the downstream region of the quasi-parallel terrestrial bow shock. Presently, two-dimensional (2-D) hybrid simulations are performed to reproduce and investigate the formation of such HSJ through a rippled quasi-parallel shock front. The simulation results show (i) that such shock fronts are strongly nonstationary (self reformation) along the shock normal, and (ii) that ripples are evidenced along the shock front as the upstream ULF waves (excited by interaction between incoming and reflected ions) are convected back to the front by the solar wind and contribute to the rippling formation. Then, these ripples are inherent structures of a quasi-parallel shock and the self reformation of the shock is not synchronous along the surface of the shock front. As a consequence, new incoming solar wind ions interact differently at different locations along the shock surface, and some can be only deflected (instead of being decelerated) at locations where ripples are large enough to play the role of local « secondary » shock. Therefore, the ion bulk velocity is also different locally after ions are transmitted dowstream, and local high-speed jets patterns are formed somewhere downstream. After a short reminder of main quasi-parallel shock features, this presentation will focus (i) on experimental observations of HSJ, (ii) on our preliminary simulation results obtained on HSJ, (iii) on their relationship with local bursty patterns of (turbulent) magnetic field evidenced at the front, and (iv) on the spatial and time scales of HSJ to be compared later on with experimental observations. Such downstream HSJ are shown to be generated by the nonstationary shock front itself and do not require any upstream perturbations (such as tangential/rotational discontinuity, HFA, etc..) to be convected by the solar wind and to interact with the shock
Gargett, Maegan Rosenfeld, Anatoly; Oborn, Brad; Metcalfe, Peter
2015-02-15
Purpose: MRI-guided radiation therapy systems (MRIgRT) are being developed to improve online imaging during treatment delivery. At present, the operation of single point dosimeters and an ionization chamber array have been characterized in such systems. This work investigates a novel 2D diode array, named “magic plate,” for both single point calibration and 2D positional performance, the latter being a key element of modern radiotherapy techniques that will be delivered by these systems. Methods: GEANT4 Monte Carlo methods have been employed to study the dose response of a silicon diode array to 6 MV photon beams, in the presence of in-line and perpendicularly aligned uniform magnetic fields. The array consists of 121 silicon diodes (dimensions 1.5 × 1.5 × 0.38 mm{sup 3}) embedded in kapton substrate with 1 cm pitch, spanning a 10 × 10 cm{sup 2} area in total. A geometrically identical, water equivalent volume was simulated concurrently for comparison. The dose response of the silicon diode array was assessed for various photon beam field shapes and sizes, including an IMRT field, at 1 T. The dose response was further investigated at larger magnetic field strengths (1.5 and 3 T) for a 4 × 4 cm{sup 2} photon field size. Results: The magic plate diode array shows excellent correspondence (< ± 1%) to water dose in the in-line orientation, for all beam arrangements and magnetic field strengths investigated. The perpendicular orientation, however, exhibits a dose shift with respect to water at the high-dose-gradient beam edge of jaw-defined fields [maximum (4.3 ± 0.8)% over-response, maximum (1.8 ± 0.8)% under-response on opposing side for 1 T, uncertainty 1σ]. The trend is not evident in areas with in-field dose gradients typical of IMRT dose maps. Conclusions: A novel 121 pixel silicon diode array detector has been characterized by Monte Carlo simulation for its performance inside magnetic fields representative of current prototype and proposed MRI
NASA Astrophysics Data System (ADS)
Leterme, Bertrand; Beerten, Koen
2013-04-01
Climate, soils and vegetation are known to exert strong controls on the water balance in a given area. The role of geomorphological processes, however, is generally overlooked in hydrological studies. In this study, the impact of landscape evolution, including geomorphological processes, is being assessed using HYDRUS 2-D simulations. A realistic sequence of consecutive landscape development stages during the last millennium in the Campine area was taken to investigate the potential role of changing landscapes on the water balance. The sequence is based on a detailed landscape reconstruction of a small interfluve in the Nete basin (Campine area, northern Belgium), following a study of sediment-soil profiles using classical geomorphological techniques, optically stimulated luminescence dating, palynology and historical archives. At least four distinctive phases in the topography-soil-vegetation system have been identified: around ca. 1000 a BP, 500 a BP, 250 a BP and 150 a BP. The sequence is characterised by progressive destruction of the soil catena (podzol profile) and vegetation, and an overall increase in relief intensity due to heavy use of land, until the landscape became stabilized ca. 150 a BP. In parallel, soil hydraulic properties were measured and used for parameterization of the HYDRUS simulations. For each stage of the sequence, a two-dimensional landscape was drawn in HYDRUS-2D using the reconstructed information on vegetation, topography, soil horizons and soil hydraulic properties. The impact of changes in this geomorphological system on water balance was then evaluated by applying a 30-year time series of climate observations. Using the same recent climate data for the different stages allows to focus on the effect of geomorphological and land use changes on evapotranspiration, runoff and groundwater recharge. In general, the results show that soil development and/or erosion alone would have had only very limited impact on the water balance during
Utama, M. Iqbal Bakti; Lu, Xin; Yuan, Yanwen; Xiong, Qihua
2014-12-22
Seed catalyst such as perylene-3,4,9,10-tetracarboxylic acid tetrapotassium (PTAS) salt has been used for promoting the growth of atomically thin layered materials in chemical vapor deposition (CVD) synthesis. However, the ramifications from the usage of such catalyst are not known comprehensively. Here, we report the influence of PTAS seeding on the transistor device performance from few-layered CVD-grown molybdenum diselenide (MoSe{sub 2}) flakes. While better repeatability and higher yield can be obtained with the use of PTAS seeds in synthesis, we observed that PTAS-seeded flakes contain particle impurities. Moreover, devices from PTAS-seeded MoSe{sub 2} flakes consistently displayed poorer field-effect mobility, current on-off ratio, and subthreshold swing as compared to unseeded flakes.
NASA Astrophysics Data System (ADS)
Prins, Steven L.; Blatchford, James; Olubuyide, Oluwamuyiwa; Riley, Deborah; Chang, Simon; Hong, Qi-Zhong; Kim, T. S.; Borges, Ricardo; Lin, Li
2009-03-01
As design rules and corresponding logic standard cell layouts continue to shrink node-on-node in accordance with Moore's law, complex 2D interactions, both intra-cell and between cells, become much more prominent. For example, in lithography, lack of scaling of λ/NA implies aggressive use of resolution enhancement techniques to meet logic scaling requirements-resulting in adverse effects such as 'forbidden pitches'-and also implies an increasing range of optical influence relative to cell size. These adverse effects are therefore expected to extend well beyond the cell boundary, leading to lithographic marginalities that occur only when a given cell is placed "in context" with other neighboring cells in a variable design environment [1]. This context dependence is greatly exacerbated by increased use of strain engineering techniques such as SiGe and dual-stress liners (DSL) to enhance transistor performance, both of which also have interaction lengths on the order of microns. The use of these techniques also breaks the formerly straightforward connection between lithographic 'shapes' and end-of-line electrical performance, thus making the formulation of design rules that are robust to process variations and complex 2D interactions more difficult. To address these issues, we have developed a first-principles-based simulation flow to study contextdependent electrical effects in layout, arising not only from lithography, but also from stress and interconnect parasitic effects. This flow is novel in that it can be applied to relatively large layout clips- required for context-dependent analysis-without relying on semi-empirical or 'black-box' models for the fundamental electrical effects. The first-principles-based approach is ideal for understanding contextdependent effects early in the design phase, so that they can be mitigated through restrictive design rules. The lithographic simulations have been discussed elsewhere [1] and will not be presented in detail. The
A multiscale quantum mechanics/electromagnetics method for device simulations.
Yam, ChiYung; Meng, Lingyi; Zhang, Yu; Chen, GuanHua
2015-04-01
Multiscale modeling has become a popular tool for research applying to different areas including materials science, microelectronics, biology, chemistry, etc. In this tutorial review, we describe a newly developed multiscale computational method, incorporating quantum mechanics into electronic device modeling with the electromagnetic environment included through classical electrodynamics. In the quantum mechanics/electromagnetics (QM/EM) method, the regions of the system where active electron scattering processes take place are treated quantum mechanically, while the surroundings are described by Maxwell's equations and a semiclassical drift-diffusion model. The QM model and the EM model are solved, respectively, in different regions of the system in a self-consistent manner. Potential distributions and current densities at the interface between QM and EM regions are employed as the boundary conditions for the quantum mechanical and electromagnetic simulations, respectively. The method is illustrated in the simulation of several realistic systems. In the case of junctionless field-effect transistors, transfer characteristics are obtained and a good agreement between experiments and simulations is achieved. Optical properties of a tandem photovoltaic cell are studied and the simulations demonstrate that multiple QM regions are coupled through the classical EM model. Finally, the study of a carbon nanotube-based molecular device shows the accuracy and efficiency of the QM/EM method.
Simulation of devices based on carbon nanotubes and graphene
NASA Astrophysics Data System (ADS)
Abramov, I. I.; Labunov, V. A.; Kolomejtseva, N. V.; Romanova, I. A.
2014-12-01
The simulation results of different devices based on carbon nanotubes (CNT) and graphene are described in the paper. The combined numerical model of hybrid integrated structures including resonant tunneling diode and field-effect transistor (RTD-FET) is proposed. Simulation of RTD-FET based on CNT of different types (chirality) was realized with the use of the developed model. The technique of express simulation of nanoradio based on CNT of the type I (based on only single CNT) and of the type II (hybrid radio) is developed. Proposed models can be used for calculation of nanoradio characteristics such as: 1) resonant frequency of CNT; 2) oscillation amplitude of CNT; 3) CNT IV-characteristics depending on different factors. Results of device simulation based on single-wall and multi-wall CNT are given in the paper. IV-characteristics of nanoscale resonant tunneling structure based on graphene-on-SiC were calculated. As well as it was investigated the influence of different parameters on the electrical characteristic of graphene-based nanostructures.
Simulation of magnetic active polymers for versatile microfluidic devices
NASA Astrophysics Data System (ADS)
Gusenbauer, Markus; Özelt, Harald; Fischbacher, Johann; Reichel, Franz; Exl, Lukas; Bance, Simon; Kataeva, Nadezhda; Binder, Claudia; Brückl, Hubert; Schreﬂ, Thomas
2013-01-01
We propose to use a compound of magnetic nanoparticles (20-100 nm) embedded in a flexible polymer (Polydimethylsiloxane PDMS) to filter circulating tumor cells (CTCs). The analysis of CTCs is an emerging tool for cancer biology research and clinical cancer management including the detection, diagnosis and monitoring of cancer. The combination of experiments and simulations lead to a versatile microfluidic lab-on-chip device. Simulations are essential to understand the influence of the embedded nanoparticles in the elastic PDMS when applying a magnetic gradient field. It combines finite element calculations of the polymer, magnetic simulations of the embedded nanoparticles and the fluid dynamic calculations of blood plasma and blood cells. With the use of magnetic active polymers a wide range of tunable microfluidic structures can be created. The method can help to increase the yield of needed isolated CTCs.
NASA Astrophysics Data System (ADS)
Babbick, M.; Dijkstra, C.; Larkin, O. J.; Anthony, P.; Davey, M. R.; Power, J. B.; Lowe, K. C.; Cogoli-Greuter, M.; Hampp, R.
Gravity is an important environmental factor that controls plant growth and development. Studies have shown that the perception of gravity is not only a property of specialized cells, but can also be performed by undifferentiated cultured cells. In this investigation, callus of Arabidopsis thaliana cv. Columbia was used to investigate the initial steps of gravity-related signalling cascades, through altered expression of transcription factors (TFs). TFs are families of small proteins that regulate gene expression by binding to specific promoter sequences. Based on microarray studies, members of the gene families WRKY, MADS-box, MYB, and AP2/EREBP were selected for investigation, as well as members of signalling chains, namely IAA 19 and phosphoinositol-4-kinase. Using qRT-PCR, transcripts were quantified within a period of 30 min in response to hypergravity (8 g), clinorotation [2-D clinostat and 3-D random positioning machine (RPM)] and magnetic levitation (ML). The data indicated that (1) changes in gravity induced stress-related signalling, and (2) exposure in the RPM induced changes in gene expression which resemble those of magnetic levitation. Two dimensional clinorotation resulted in responses similar to those caused by hypergravity. It is suggested that RPM and ML are preferable to simulate microgravity than clinorotation.
NASA Astrophysics Data System (ADS)
Zhao, Yi; Fu, Ceji
2016-10-01
Tailoring the spectrum of thermal emission from the emitter is important for improving the performance of a thermophotovoltaic (TPV) system. In this work, a two-dimensional (2D) layered grating structure made of SiO2 and tungsten (W), which can realize wavelength-selective control of thermal emission, was proposed for a potential emitter in TPV applications. Numerical simulations of the spectral emissivity of the structure from the ultraviolet (UV) to the mid-infrared region reveals that the spectral-normal emissivity of the structure is enhanced to above 0.95 in the wavelength region from 0.55 μm to 1.9 μm for both TE and TM waves, but drops sharply at wavelength larger than 2 μm. Physical mechanisms responsible for the wavelength-selective emissivity were elucidated as due to resonance of magnetic polaritons (MPs) in the SiO2 spacer and in the grooves of the tungsten grating, Wood's anomaly (WA), excitation of surface plasmon polaritons (SPPs) and wave interference. Furthermore, the structure was found to exhibit quasi-diffuse and polarization-insensitive features of thermal emission, suggesting that the proposed structure can serve as the emitter in the design of high performance TPV systems.
NASA Astrophysics Data System (ADS)
Rockwood, Matthew; Green, Melissa
2012-11-01
In experimental, three-dimensional vortex-dominated flows, common particle image velocimetry (PIV) data is often collected in only the plane of interest due to equipment constraints. For flows with significant out of plane velocities or velocity gradients, this can create large discrepancies in Lagrangian analyses that require accurate particle trajectories. A Finite Time Lyapunov Exponent (FTLE) analysis is one such example, and has been shown to be very powerful at examining vortex dynamics and interactions in a variety of aperiodic flows. In this work, FTLE analysis of a turbulent channel simulation was conducted using both full three-dimensional velocity data and modified planar data extracted from the same computational domain. When the out of plane velocity component is neglected the difference in FTLE fields is non-trivial. A quantitative comparison and computation of error is presented for several planes across the width of the channel to determine the efficacy of using 2D analyses on the inherently 3D flows.
Icarus: A 2D direct simulation Monte Carlo (DSMC) code for parallel computers. User`s manual - V.3.0
Bartel, T.; Plimpton, S.; Johannes, J.; Payne, J.
1996-10-01
Icarus is a 2D Direct Simulation Monte Carlo (DSMC) code which has been optimized for the parallel computing environment. The code is based on the DSMC method of Bird and models from free-molecular to continuum flowfields in either cartesian (x, y) or axisymmetric (z, r) coordinates. Computational particles, representing a given number of molecules or atoms, are tracked as they have collisions with other particles or surfaces. Multiple species, internal energy modes (rotation and vibration), chemistry, and ion transport are modelled. A new trace species methodology for collisions and chemistry is used to obtain statistics for small species concentrations. Gas phase chemistry is modelled using steric factors derived from Arrhenius reaction rates. Surface chemistry is modelled with surface reaction probabilities. The electron number density is either a fixed external generated field or determined using a local charge neutrality assumption. Ion chemistry is modelled with electron impact chemistry rates and charge exchange reactions. Coulomb collision cross-sections are used instead of Variable Hard Sphere values for ion-ion interactions. The electrostatic fields can either be externally input or internally generated using a Langmuir-Tonks model. The Icarus software package includes the grid generation, parallel processor decomposition, postprocessing, and restart software. The commercial graphics package, Tecplot, is used for graphics display. The majority of the software packages are written in standard Fortran.
NASA Astrophysics Data System (ADS)
Ocłoń, Paweł; Łopata, Stanisław; Nowak, Marzena
2014-09-01
This study presents a novel, simplified model for the time-efficient simulation of transient conjugate heat transfer in round tubes. The flow domain and the tube wall are modeled in 1D and 2D, respectively and empirical correlations are used to model the flow domain in 1D. The model is particularly useful when dealing with complex physics, such as flow boiling, which is the main focus of this study. The tube wall is assumed to have external fins. The flow is vertical upwards. Note that straightforward computational fluid dynamics (CFD) analysis of conjugate heat transfer in a system of tubes, leads to 3D modeling of fluid and solid domains. Because correlation is used and dimensionality reduced, the model is numerically more stable and computationally more time-efficient compared to the CFD approach. The benefit of the proposed approach is that it can be applied to large systems of tubes as encountered in many practical applications. The modeled equations are discretized in space using the finite volume method, with central differencing for the heat conduction equation in the solid domain, and upwind differencing of the convective term of the enthalpy transport equation in the flow domain. An explicit time discretization with forward differencing was applied to the enthalpy transport equation in the fluid domain. The conduction equation in the solid domain was time discretized using the Crank-Nicholson scheme. The model is applied in different boundary conditions and the predicted boiling patterns and temperature fields are discussed.
NASA Astrophysics Data System (ADS)
Ocłoń, Paweł; Łopata, Stanisław; Nowak, Marzena
2015-04-01
This study presents a novel, simplified model for the time-efficient simulation of transient conjugate heat transfer in round tubes. The flow domain and the tube wall are modeled in 1D and 2D, respectively and empirical correlations are used to model the flow domain in 1D. The model is particularly useful when dealing with complex physics, such as flow boiling, which is the main focus of this study. The tube wall is assumed to have external fins. The flow is vertical upwards. Note that straightforward computational fluid dynamics (CFD) analysis of conjugate heat transfer in a system of tubes, leads to 3D modeling of fluid and solid domains. Because correlation is used and dimensionality reduced, the model is numerically more stable and computationally more time-efficient compared to the CFD approach. The benefit of the proposed approach is that it can be applied to large systems of tubes as encountered in many practical applications. The modeled equations are discretized in space using the finite volume method, with central differencing for the heat conduction equation in the solid domain, and upwind differencing of the convective term of the enthalpy transport equation in the flow domain. An explicit time discretization with forward differencing was applied to the enthalpy transport equation in the fluid domain. The conduction equation in the solid domain was time discretized using the Crank-Nicholson scheme. The model is applied in different boundary conditions and the predicted boiling patterns and temperature fields are discussed.
NASA Astrophysics Data System (ADS)
Tirupathi, S.; Schiemenz, A. R.; Liang, Y.; Parmentier, E.; Hesthaven, J.
2013-12-01
The style and mode of melt migration in the mantle are important to the interpretation of basalts erupted on the surface. Both grain-scale diffuse porous flow and channelized melt migration have been proposed. To better understand the mechanisms and consequences of melt migration in a heterogeneous mantle, we have undertaken a numerical study of reactive dissolution in an upwelling and viscously deformable mantle where solubility of pyroxene increases upwards. Our setup is similar to that described in [1], except we use a larger domain size in 2D and 3D and a new numerical method. To enable efficient simulations in 3D through parallel computing, we developed a high-order accurate numerical method for the magma dynamics problem using discontinuous Galerkin methods and constructed the problem using the numerical library deal.II [2]. Linear stability analyses of the reactive dissolution problem reveal three dynamically distinct regimes [3] and the simulations reported in this study were run in the stable regime and the unstable wave regime where small perturbations in porosity grows periodically. The wave regime is more relevant to melt migration beneath the mid-ocean ridges but computationally more challenging. Extending the 2D simulations in the stable regime in [1] to 3D using various combinations of sustained perturbations in porosity at the base of the upwelling column (which may result from a viened mantle), we show the geometry and distribution of dunite channel and high-porosity melt channels are highly correlated with inflow perturbation through superposition. Strong nonlinear interactions among compaction, dissolution, and upwelling give rise to porosity waves and high-porosity melt channels in the wave regime. These compaction-dissolution waves have well organized but time-dependent structures in the lower part of the simulation domain. High-porosity melt channels nucleate along nodal lines of the porosity waves, growing downwards. The wavelength scales
Ut-Minimos a Hierarchical Transport Model Based Simulator for Deep Submicron Silicon Devices
NASA Astrophysics Data System (ADS)
Yeap, Choh-Fei
1995-01-01
The challenge of Ultra Large Scale Integration (ULSI) of integrated circuits reinforces the need for accurate and efficient simulations to speed development and reduce cost. The predictive power of conventional simulation based on the drift-diffusion (DD) model has diminished to a critically low level. An improved transport model must now replace, what has been the foundation of semiconductor device simulation, the DD model. The hydrodynamic (HD) transport model, that addresses non-local effects such as velocity overshoot and carrier heating, is an attractive candidate. The true viability of the HD models in replacing the DD model rests on their availability in well-accepted device simulators, physical accuracy and ease of solution. This work is an attempt to hasten and facilitate this replacement. The focus of this dissertation is an effort towards implementing a hierarchy of promising HD transport model candidates in an established and well-accepted device simulator using robust and efficient discretization and solution methods. Thus, UT-MiniMOS 3.0, a 2-D two -carrier integrated simulator for deep submicron silicon devices, has been developed to include a hierarchy of transport models and to construct a programming environment for easy implementation and maintenance of the physical models and numerical techniques. The hierarchy of transport models includes the DD model, post-processing current contour HD model, parabolic HD model, Stratton's energy balance model, Chen's energy transport model, Lee's HD model, Stettler's HD model, Bordelon's non-parabolic HD (NPHD) model, lattice temperature model, and Monte Carlo (MC) model. Each of these HD models is cast into a generalized HD formulation with four controlling parameters. This generalized HD formulation allows a unified discretization for all HD models. The NPHD model has been shown to provide the best overall agreement to MC energy, velocity and concentration. HD simulation in UT-MiniMOS for a bias point
UNIPIC code for simulations of high power microwave devices
Wang Jianguo; Zhang Dianhui; Wang Yue; Qiao Hailiang; Li Xiaoze; Liu Chunliang; Li Yongdong; Wang Hongguang
2009-03-15
In this paper, UNIPIC code, a new member in the family of fully electromagnetic particle-in-cell (PIC) codes for simulations of high power microwave (HPM) generation, is introduced. In the UNIPIC code, the electromagnetic fields are updated using the second-order, finite-difference time-domain (FDTD) method, and the particles are moved using the relativistic Newton-Lorentz force equation. The convolutional perfectly matched layer method is used to truncate the open boundaries of HPM devices. To model curved surfaces and avoid the time step reduction in the conformal-path FDTD method, CP weakly conditional-stable FDTD (WCS FDTD) method which combines the WCS FDTD and CP-FDTD methods, is implemented. UNIPIC is two-and-a-half dimensional, is written in the object-oriented C++ language, and can be run on a variety of platforms including WINDOWS, LINUX, and UNIX. Users can use the graphical user's interface to create the geometric structures of the simulated HPM devices, or input the old structures created before. Numerical experiments on some typical HPM devices by using the UNIPIC code are given. The results are compared to those obtained from some well-known PIC codes, which agree well with each other.
NASA Astrophysics Data System (ADS)
López-Venegas, Alberto M.; Horrillo, Juan; Pampell-Manis, Alyssa; Huérfano, Victor; Mercado, Aurelio
2015-06-01
The most recent tsunami observed along the coast of the island of Puerto Rico occurred on October 11, 1918, after a magnitude 7.2 earthquake in the Mona Passage. The earthquake was responsible for initiating a tsunami that mostly affected the northwestern coast of the island. Runup values from a post-tsunami survey indicated the waves reached up to 6 m. A controversy regarding the source of the tsunami has resulted in several numerical simulations involving either fault rupture or a submarine landslide as the most probable cause of the tsunami. Here we follow up on previous simulations of the tsunami from a submarine landslide source off the western coast of Puerto Rico as initiated by the earthquake. Improvements on our previous study include: (1) higher-resolution bathymetry; (2) a 3D-2D coupled numerical model specifically developed for the tsunami; (3) use of the non-hydrostatic numerical model NEOWAVE (non-hydrostatic evolution of ocean WAVE) featuring two-way nesting capabilities; and (4) comprehensive energy analysis to determine the time of full tsunami wave development. The three-dimensional Navier-Stokes model tsunami solution using the Navier-Stokes algorithm with multiple interfaces for two fluids (water and landslide) was used to determine the initial wave characteristic generated by the submarine landslide. Use of NEOWAVE enabled us to solve for coastal inundation, wave propagation, and detailed runup. Our results were in agreement with previous work in which a submarine landslide is favored as the most probable source of the tsunami, and improvement in the resolution of the bathymetry yielded inundation of the coastal areas that compare well with values from a post-tsunami survey. Our unique energy analysis indicates that most of the wave energy is isolated in the wave generation region, particularly at depths near the landslide, and once the initial wave propagates from the generation region its energy begins to stabilize.
Simulating Pediatric Ventricular Assist Device Operation Using Fluid Structure Interaction
NASA Astrophysics Data System (ADS)
Long, Chris; Bazilevs, Yuri; Marsden, Alison
2012-11-01
Ventricular Assist Devices (VADs) provide mechanical circulatory support to patients in heart failure. They are primarily used to extend life until cardiac transplant, but also show promise as a ``bridge-to-recovery'' device in pediatric patients. Commercially available pediatric pumps are pulsatile displacement pumps, with two distinct chambers for air and blood separated by a thin, flexible membrane. The air chamber pneumatically drives the membrane, which drives blood through the other chamber via displacement. The primary risk factor associated with these devices is stroke or embolism due to thrombogenesis in the blood chamber, occurring in as many as 40% of patients. Our goal is to perform simulations that accurately model the hemodynamics of the device, as well as the non-linear membrane buckling. We apply a finite-element based fluid solver, with an Arbitrary Lagrangian-Eulerian (ALE) framework to account for mesh motion. Isogeometric Analysis with a Kirchhoff-Love shell formulation is used on the membrane, and two distinct fluid subdomains are used for the air and blood chambers. The Fluid Structure Interaction (FSI) problem is solved simultaneously, using a Matrix Free method to model the interactions at the fluid-structure boundary. Methods and results are presented.
Determination of LDD MOSFET drain resistance from device simulation
NASA Astrophysics Data System (ADS)
Samudra, G. S.; Seah, B. P.; Ling, C. H.
1996-05-01
A simple, efficient and accurate technique for the determination of the drain resistance of LDD MOSFETs, using a two-dimensional device simulator, is presented. This method does not require the artificial introduction of constraints that would alter the normal operating conditions and geometry of the device. Comparison is made with a more elaborate technique, where the drain region is modelled as a network of resistances. For an appropriately chosen mesh size, good agreement to within 10% has been achieved for the two techniques. In terms of computational labour, the simple technique enjoys at least an order of magnitude advantage compared with the more elaborate model. The two techniques have also been used to study the dependence of the drain resistance on the gate and the drain bias, and to establish the accuracy over a broad bias range. An estimate is also made of the degradation of the drain resistance due to hot-carrier stress.
TID Simulation of Advanced CMOS Devices for Space Applications
NASA Astrophysics Data System (ADS)
Sajid, Muhammad
2016-07-01
This paper focuses on Total Ionizing Dose (TID) effects caused by accumulation of charges at silicon dioxide, substrate/silicon dioxide interface, Shallow Trench Isolation (STI) for scaled CMOS bulk devices as well as at Buried Oxide (BOX) layer in devices based on Silicon-On-Insulator (SOI) technology to be operated in space radiation environment. The radiation induced leakage current and corresponding density/concentration electrons in leakage current path was presented/depicted for 180nm, 130nm and 65nm NMOS, PMOS transistors based on CMOS bulk as well as SOI process technologies on-board LEO and GEO satellites. On the basis of simulation results, the TID robustness analysis for advanced deep sub-micron technologies was accomplished up to 500 Krad. The correlation between the impact of technology scaling and magnitude of leakage current with corresponding total dose was established utilizing Visual TCAD Genius program.
Simulation of Carbon Production from Material Surfaces in Fusion Devices
NASA Astrophysics Data System (ADS)
Marian, J.; Verboncoeur, J.
2005-10-01
Impurity production at carbon surfaces by plasma bombardment is a key issue for fusion devices as modest amounts can lead to excessive radiative power loss and/or hydrogenic D-T fuel dilution. Here results of molecular dynamics (MD) simulations of physical and chemical sputtering of hydrocarbons are presented for models of graphite and amorphous carbon, the latter formed by continuous D-T impingement in conditions that mimic fusion devices. The results represent more extensive simulations than we reported last year, including incident energies in the 30-300 eV range for a variety of incident angles that yield a number of different hydrocarbon molecules. The calculated low-energy yields clarify the uncertainty in the complex chemical sputtering rate since chemical bonding and hard-core repulsion are both included in the interatomic potential. Also modeled is hydrocarbon break-up by electron-impact collisions and transport near the surface. Finally, edge transport simulations illustrate the sensitivity of the edge plasma properties arising from moderate changes in the carbon content. The models will provide the impurity background for the TEMPEST kinetic edge code.
Shimizu, A. Ido, T.; Kato, S.; Hamada, Y.; Kurachi, M.; Makino, R.; Nishiura, M.; Nishizawa, A.
2014-11-15
Two-dimensional potential profiles in the Large Helical Device (LHD) were measured with heavy ion beam probe (HIBP). To measure the two-dimensional profile, the probe beam energy has to be changed. However, this task is not easy, because the beam transport line of LHD-HIBP system is very long (∼20 m), and the required beam adjustment consumes much time. To reduce the probe beam energy adjustment time, an automatic beam adjustment system has been developed. Using this system, required time to change the probe beam energy is dramatically reduced, such that two-dimensional potential profiles were able to be successfully measured with HIBP by changing the probe beam energy shot to shot.
Jia, Mingjie; Kim, Taesung
2014-10-21
Microfluidic devices utilize ion concentration polarization (ICP) phenomena for a variety of applications, but a comprehensive understanding of the generation of ICP is still necessary. Recently, the emergence of a novel single channel ICP (SC-ICP) device has stimulated further research on the mechanism of ICP generation, so that we developed a 2-D model of an SC-ICP device that integrates a nanoporous membrane on the bottom surface of the channel, allowing bulk flow over the membrane. We solved a set of coupled governing equations with appropriate boundary conditions to explore ICP numerically. As a result, we not only showed that the simulation results held a strong qualitative agreement with experimental results, but also found the distribution of ion concentrations in the SC-ICP device that has never been reported in previous studies. We confirmed again that the electrophoretic mobility (EPM) of counterions in the membrane is the most dominant factor determining the generation and strength of ICP, whereas the charge density of the membrane was dominant to the ICP strength only when a high EPM value was assumed. From the viewpoint of practical applications, an SC-ICP device with a long membrane under low buffer strength showed enhanced performance in the preconcentration of charged molecules. Therefore, we believe that the simulation results could not only provide sharp insight into ICP phenomena but also predict and optimize the performance of SC-ICP devices in various microfluidic applications.
14 CFR 121.407 - Training program: Approval of airplane simulators and other training devices.
Code of Federal Regulations, 2014 CFR
2014-01-01
... Program § 121.407 Training program: Approval of airplane simulators and other training devices. Link to an amendment published at 78 FR 67836, Nov. 12, 2013. (a) Each airplane simulator and other training device... training or check flight. (b) A particular airplane simulator or other training device may be approved...
NASA Astrophysics Data System (ADS)
Mitsui, Y.; Hirahara, K.
2006-12-01
There have been a lot of studies that simulate large earthquakes occurring quasi-periodically at a subduction zone, based on the laboratory-derived rate-and-state friction law [eg. Kato and Hirasawa (1997), Hirose and Hirahara (2002)]. All of them assume that pore fluid pressure in the fault zone is constant. However, in the fault zone, pore fluid pressure changes suddenly, due to coseismic pore dilatation [Marone (1990)] and thermal pressurization [Mase and Smith (1987)]. If pore fluid pressure drops and effective normal stress rises, fault slip is decelerated. Inversely, if pore fluid pressure rises and effective normal stress drops, fault slip is accelerated. The effect of pore fluid may cause slow slip events and low-frequency tremor [Kodaira et al. (2004), Shelly et al. (2006)]. For a simple spring model, how pore dilatation affects slip instability was investigated [Segall and Rice (1995), Sleep (1995)]. When the rate of the slip becomes high, pore dilatation occurs and pore pressure drops, and the rate of the slip is restrained. Then the inflow of pore fluid recovers the pore pressure. We execute 2D earthquake cycle simulations at a subduction zone, taking into account such changes of pore fluid pressure following Segall and Rice (1995), in addition to the numerical scheme in Kato and Hirasawa (1997). We do not adopt hydrostatic pore pressure but excess pore pressure for initial condition, because upflow of dehydrated water seems to exist at a subduction zone. In our model, pore fluid is confined to the fault damage zone and flows along the plate interface. The smaller the flow rate is, the later pore pressure recovers. Since effective normal stress keeps larger, the fault slip is decelerated and stress drop becomes smaller. Therefore the smaller flow rate along the fault zone leads to the shorter earthquake recurrence time. Thus, not only the frictional parameters and the subduction rate but also the fault zone permeability affects the recurrence time of
DEM simulation of granular flow in a Couette device
NASA Astrophysics Data System (ADS)
Vidyapati, Vidyapati; Kheripour Langrudi, M.; Tardos, Gabriel; Sun, Jin; Sundaresan, Sankaran; Subramaniam, Shankar
2009-11-01
We study the shear motion of granular material in an annular shear cell operated in batch and continuous modes. In order to quantitatively simulate shear behavior of granular material composed of spherical shaped grains, a 3D discrete element method (DEM) is used. The ultimate goal of the present work is to compare DEM results for the normal and shear stresses in stationary and moving granular beds confined in Couette device with experimental results. The DEM captures the experimental observation of transition behavior from quasi-- static (in batch mode operation) to rapid flow (in continuous mode operation) regime of granular flows. Although there are quantitative differences between DEM model predictions and experiments, the qualitative features are nicely reproduced. It is observed (both in experiments and in simulations) that the intermediate regime is broad enough to require a critical assessment of continuum models for granular flows.
NASA Technical Reports Server (NTRS)
Tao, W-K.
2003-01-01
Real clouds and cloud systems are inherently three-dimensional (3D). Because of the limitations in computer resources, however, most cloud-resolving models (CRMs) today are still two-dimensional (2D). A few 3D CRMs have been used to study the response of clouds to large-scale forcing. In these 3D simulations, the model domain was small, and the integration time was 6 hours. Only recently have 3D experiments been performed for multi-day periods for tropical cloud systems with large horizontal domains at the National Center for Atmospheric Research (NACAR) and at NASA Goddard Space Flight Center . At Goddard, a 3D Goddard Cumulus Ensemble (GCE) model was used to simulate periods during TOGA COARE, SCSMEX and KWAJEX using 512 by 512 km domain (with 2 km resolution). The results indicate that surface precipitation and latent heating profiles are very similar between the 2D and 3D GCE model simulations. The reason for the strong similarity between the 2D and 3D CRM simulations is that the same observed large-scale advective tendencies of potential temperature, water vapor mixing ratio, and horizontal momentum were used as the main focusing in both the 2D and 3D models. Interestingly, the 2D and 3D versions of the CRM used at CSU showed significant differences in the rainfall and cloud statistics for three ARM cases. The major objectives of this paper are: (1) to assess the performance of the super-parameterization technique, (2) calculate and examine the surface energy (especially radiation) and water budgets, and (3) identify the differences and similarities in the organization and entrainment rates of convection between simulated 2D and 3D cloud systems.
NASA Astrophysics Data System (ADS)
Biswas, A.; Sharma, S. P.
2012-12-01
best result without any ambiguity and smaller uncertainty. Keywords: SP anomaly, inclined sheet, 2D structure, forward problems, VFSA Optimization,
Becker, Kathrin; Stauber, Martin; Schwarz, Frank; Beißbarth, Tim
2015-09-01
We propose a novel 3D-2D registration approach for micro-computed tomography (μCT) and histology (HI), constructed for dental implant biopsies, that finds the position and normal vector of the oblique slice from μCT that corresponds to HI. During image pre-processing, the implants and the bone tissue are segmented using a combination of thresholding, morphological filters and component labeling. After this, chamfer matching is employed to register the implant edges and fine registration of the bone tissues is achieved using simulated annealing. The method was tested on n=10 biopsies, obtained at 20 weeks after non-submerged healing in the canine mandible. The specimens were scanned with μCT 100 and processed for hard tissue sectioning. After registration, we assessed the agreement of bone to implant contact (BIC) using automated and manual measurements. Statistical analysis was conducted to test the agreement of the BIC measurements in the registered samples. Registration was successful for all specimens and agreement of the respective binary images was high (median: 0.90, 1.-3. Qu.: 0.89-0.91). Direct comparison of BIC yielded that automated (median 0.82, 1.-3. Qu.: 0.75-0.85) and manual (median 0.61, 1.-3. Qu.: 0.52-0.67) measures from μCT were significant positively correlated with HI (median 0.65, 1.-3. Qu.: 0.59-0.72) between μCT and HI groups (manual: R(2)=0.87, automated: R(2)=0.75, p<0.001). The results show that this method yields promising results and that μCT may become a valid alternative to assess osseointegration in three dimensions.
NASA Technical Reports Server (NTRS)
Zimmerman, M. I.; Farrell, W. M.; Poppe, A. R.
2014-01-01
We present results from a new grid-free 2D plasma simulation code applied to a small, unmagnetized body immersed in the streaming solar wind plasma. The body was purposely modeled as an irregular shape in order to examine photoemission and solar wind plasma flow in high detail on the dayside, night-side, terminator and surface-depressed 'pocket' regions. Our objective is to examine the overall morphology of the various plasma interaction regions that form around a small body like a small near-Earth asteroid (NEA). We find that the object obstructs the solar wind flow and creates a trailing wake region downstream, which involves the interplay between surface charging and ambipolar plasma expansion. Photoemission is modeled as a steady outflow of electrons from illuminated portions of the surface, and under direct illumination the surface forms a non-monotonic or ''double-sheath'' electric potential upstream of the body, which is important for understanding trajectories and equilibria of lofted dust grains in the presence of a complex asteroid geometry. The largest electric fields are found at the terminators, where ambipolar plasma expansion in the body-sized night-side wake merges seamlessly with the thin photoelectric sheath on the dayside. The pocket regions are found to be especially complex, with nearby sunlit regions of positive potential electrically connected to unlit negative potentials and forming adjacent natural electric dipoles. For objects near the surface, we find electrical dissipation times (through collection of local environmental solar wind currents) that vary over at least 5 orders of magnitude: from 39 Micro(s) inside the near-surface photoelectron cloud under direct sunlight to less than 1 s inside the particle-depleted night-side wake and shadowed pocket regions
New simulation and measurement results on gateable DEPFET devices
NASA Astrophysics Data System (ADS)
Bähr, Alexander; Aschauer, Stefan; Hermenau, Katrin; Herrmann, Sven; Lechner, Peter H.; Lutz, Gerhard; Majewski, Petra; Miessner, Danilo; Porro, Matteo; Richter, Rainer H.; Schaller, Gerhard; Sandow, Christian; Schnecke, Martina; Schopper, Florian; Stefanescu, Alexander; Strüder, Lothar; Treis, Johannes
2012-07-01
To improve the signal to noise level, devices for optical and x-ray astronomy use techniques to suppress background events. Well known examples are e.g. shutters or frame-store Charge Coupled Devices (CCDs). Based on the DEpleted P-channel Field Effect Transistor (DEPFET) principle a so-called Gatebale DEPFET detector can be built. Those devices combine the DEPFET principle with a fast built-in electronic shutter usable for optical and x-ray applications. The DEPFET itself is the basic cell of an active pixel sensor build on a fully depleted bulk. It combines internal amplification, readout on demand, analog storage of the signal charge and a low readout noise with full sensitivity over the whole bulk thickness. A Gatebale DEPFET has all these benefits and obviates the need for an external shutter. Two concepts of Gatebale DEPFET layouts providing a built-in shutter will be introduced. Furthermore proof of principle measurements for both concepts are presented. Using recently produced prototypes a shielding of the collection anode up to 1 • 10-4 was achieved. Predicted by simulations, an optimized geometry should result in values of 1 • 10-5 and better. With the switching electronic currently in use a timing evaluation of the shutter opening and closing resulted in rise and fall times of 100ns.
2D Quantum Transport Modeling in Nanoscale MOSFETs
NASA Technical Reports Server (NTRS)
Svizhenko, Alexei; Anantram, M. P.; Govindan, T. R.; Biegel, Bryan
2001-01-01
With the onset of quantum confinement in the inversion layer in nanoscale MOSFETs, behavior of the resonant level inevitably determines all device characteristics. While most classical device simulators take quantization into account in some simplified manner, the important details of electrostatics are missing. Our work addresses this shortcoming and provides: (a) a framework to quantitatively explore device physics issues such as the source-drain and gate leakage currents, DIBL, and threshold voltage shift due to quantization, and b) a means of benchmarking quantum corrections to semiclassical models (such as density- gradient and quantum-corrected MEDICI). We have developed physical approximations and computer code capable of realistically simulating 2-D nanoscale transistors, using the non-equilibrium Green's function (NEGF) method. This is the most accurate full quantum model yet applied to 2-D device simulation. Open boundary conditions, oxide tunneling and phase-breaking scattering are treated on equal footing. Electrons in the ellipsoids of the conduction band are treated within the anisotropic effective mass approximation. Quantum simulations are focused on MIT 25, 50 and 90 nm "well- tempered" MOSFETs and compared to classical and quantum corrected models. The important feature of quantum model is smaller slope of Id-Vg curve and consequently higher threshold voltage. These results are quantitatively consistent with I D Schroedinger-Poisson calculations. The effect of gate length on gate-oxide leakage and sub-threshold current has been studied. The shorter gate length device has an order of magnitude smaller current at zero gate bias than the longer gate length device without a significant trade-off in on-current. This should be a device design consideration.
2D Quantum Mechanical Study of Nanoscale MOSFETs
NASA Technical Reports Server (NTRS)
Svizhenko, Alexei; Anantram, M. P.; Govindan, T. R.; Biegel, B.; Kwak, Dochan (Technical Monitor)
2000-01-01
With the onset of quantum confinement in the inversion layer in nanoscale MOSFETs, behavior of the resonant level inevitably determines all device characteristics. While most classical device simulators take quantization into account in some simplified manner, the important details of electrostatics are missing. Our work addresses this shortcoming and provides: (a) a framework to quantitatively explore device physics issues such as the source-drain and gate leakage currents, DIBL, and threshold voltage shift due to quantization, and b) a means of benchmarking quantum corrections to semiclassical models (such as density-gradient and quantum-corrected MEDICI). We have developed physical approximations and computer code capable of realistically simulating 2-D nanoscale transistors, using the non-equilibrium Green's function (NEGF) method. This is the most accurate full quantum model yet applied to 2-D device simulation. Open boundary conditions and oxide tunneling are treated on an equal footing. Electrons in the ellipsoids of the conduction band are treated within the anisotropic effective mass approximation. We present the results of our simulations of MIT 25, 50 and 90 nm "well-tempered" MOSFETs and compare them to those of classical and quantum corrected models. The important feature of quantum model is smaller slope of Id-Vg curve and consequently higher threshold voltage. Surprisingly, the self-consistent potential profile shows lower injection barrier in the channel in quantum case. These results are qualitatively consistent with ID Schroedinger-Poisson calculations. The effect of gate length on gate-oxide leakage and subthreshold current has been studied. The shorter gate length device has an order of magnitude smaller current at zero gate bias than the longer gate length device without a significant trade-off in on-current. This should be a device design consideration.
NASA Technical Reports Server (NTRS)
Tao, Wei-Kuo; Hou, A.; Atlas, R.; Starr, D.; Sud, Y.
2003-01-01
Real clouds and cloud systems are inherently three-dimensional (3D). Because of the limitations in computer resources, however, most cloud-resolving models (CRMs) today are still two-dimensional (2D). A few 3D CRMs have been used to study the response of clouds to large-scale forcing. In these 3D simulations, the model domain was small, and the integration time was 6 hours. The major objectives of this paper are: (1) to assess the performance of the super-parameterization technique (i.e. is 2D or semi-3D CRM appropriate for the super-parameterization?); (2) calculate and examine the surface energy (especially radiation) and water budgets; (3) identify the differences and similarities in the organization and entrainment rates of convection between simulated 2D and 3D cloud systems.
NASA Astrophysics Data System (ADS)
Castro, Maria Clara; Patriarche, Delphine; Goblet, Patrick
2005-09-01
Because helium and heat production results from a common source, a continental 4He crustal flux of 4.65 * 10 - 14 mol m - 2 s - 1 has been estimated based on heat flow considerations. In addition, because the observed mantle He / heat flux ratio at the proximity of mid-ocean ridges (6.6 * 10 - 14 mol J - 1 ) is significantly lower than the radiogenic production ratio (1.5 * 10 - 12 mol J - 1 ), the presence of a terrestrial helium-heat imbalance was suggested. The latter could be explained by the presence of a layered mantle in which removal of He is impeded from the lower mantle [R.K. O'Nions, E.R. Oxburgh, Heat and helium in the Earth, Nature 306 (1983) 429-431; E.R. Oxburgh, R.K. O'Nions, Helium loss, tectonics, and the terrestrial heat budget, Science 237 (1987) 1583-1588]. van Keken et al. [P.E. van Keken, C.J. Ballentine, D. Porcelli, A dynamical investigation of the heat and helium imbalance, Earth Planet, Sci. Lett. 188 (2001) 421-434] have recently claimed that the helium-heat imbalance remains a robust observation. Such conclusions, however, were reached under the assumption that a steady-state regime was in place for both tracers and that their transport properties are similar at least in the upper portion of the crust. Here, through 2-D simulations of groundwater flow, heat transfer and 4He transport carried out simultaneously in the Carrizo aquifer and surrounding formations in southwest Texas, we assess the legitimacy of earlier assumptions. Specifically, we show that the driving transport mechanisms for He and heat are of a fundamentally different nature for a high range of permeabilities ( k ≤ 10 - 16 m 2) found in metamorphic and volcanic rocks at all depths in the crust. The assumption that transport properties for these two tracers are similar in the crust is thus unsound. We also show that total 4He / heat flux ratios lower than radiogenic production ratios do not reflect a He deficit in the crust or mantle original reservoir. Instead, they
NASA Astrophysics Data System (ADS)
Savoini, P.; Lembege, B.
2014-12-01
The ion foreshock located upstream of the Earth's bow shock is populated with ions reflected back by the shock front. In-situ spacecraft measurements have clearly established the existence of two distinct populations in the upstream of the quasi-perpendicular shock region (i.e. for 45o ≤ ΘBn≤ 90o, where ΘBn is the angle between the shock normal and the upstream magnetostatic field): (i) field-aligned ion beams (or 'FAB') characterized by a gyrotropic distribution, and (ii) gyro-phase bunched ions (or 'GPB') characterized by a NON gyrotropic distribution, which exhibits a non-vanishing perpendicular bulk velocity. The use of 2D PIC simulations where full curvature effects, time of flight effects and both electrons and ions dynamics are fully described, has evidenced that the shock front itself can be the possible source of these two characteristic populations. A recent analysis has evidenced that both populations can be discriminated in terms of interaction time (Δtinter) with the shock front. 'GPB' and 'FAB' populations are characterized by a short (Δtinter ~ 1 τci) and much larger (Δtinter ≥ 2 τci) interaction time respectively, where τci is the ion upstream gyroperiod. In addition, present statistical results evidence that: (i) backstreaming ions are splitted into 'FAB' and 'GPB' populations depending on their injection angle when hitting the shock front (defined between the local normal to the shock front and the gyration velocity vector). (ii) As a consequence, ion trajectories strongly differ between the 'FAB' and 'GPB' populations at the shock front. In particular, 'FAB' ions suffer multi-bounces along the curved front whereas 'GPB' ions make only one bounce. Such differences may explain why the 'FAB' population loses their gyro-phase coherency and become gyrotropic which is not the case for the 'GPB'. Then, the differences observed between 'FAB' and 'GPB' populations do not involve some distinct reflection processes as often claimed in the
2005-07-01
Aniso2d is a two-dimensional seismic forward modeling code. The earth is parameterized by an X-Z plane in which the seismic properties Can have monoclinic with x-z plane symmetry. The program uses a user define time-domain wavelet to produce synthetic seismograms anrwhere within the two-dimensional media.
NASA Astrophysics Data System (ADS)
Jang, Hyun-Sook; Yu, Changqian; Hayes, Robert; Granick, Steve
2015-03-01
Polymer vesicles (``polymersomes'') are an intriguing class of soft materials, commonly used to encapsulate small molecules or particles. Here we reveal they can also effectively incorporate nanoparticles inside their polymer membrane, leading to novel ``2D nanocomposites.'' The embedded nanoparticles alter the capacity of the polymersomes to bend and to stretch upon external stimuli.
A dynamic model for the simulation of induction heating devices
Nerg, J.; Tolsa, K.; Silventoinen, P.; Partanen, J.; Pyrhoenen, J.
1999-09-01
Induction heating is an efficient, easily controlled method for the heating of electrically conductive objects in processes such as metal hardening or annealing. Here, a simulation procedure designed for the dynamic analysis of induction heating systems is described. The procedure starts from the FEM based evaluation of the load impedance. This, as a function of the heating time is transferred to the dynamic model describing the whole induction heating device, i.e., the power supply, its control system, the load and the impedance matching circuit. With the developed model the start-up of the heating process as well as quick transients, e.g., fault situations can be examined. The applicability of the model was tested in the design of the induction heating installation developed for the annealing of aluminium plates. Temperature error less than 5% has been achieved.
Simulations of charge transfer in Electron Multiplying Charge Coupled Devices
NASA Astrophysics Data System (ADS)
Bush, N.; Stefanov, K.; Hall, D.; Jordan, D.; Holland, A.
2014-12-01
Electron Multiplying Charge Coupled Devices (EMCCDs) are a variant of traditional CCD technology well suited to applications that demand high speed operation in low light conditions. On-chip signal amplification allows the sensor to effectively suppress the noise introduced by readout electronics, permitting sub-electron read noise at MHz pixel rates. The devices have been the subject of many detailed studies concerning their operation, however there has not been a study into the transfer and multiplication process within the EMCCD gain register. Such an investigation has the potential to explain certain observed performance characteristics, as well as inform further optimisations to their operation. In this study, the results from simulation of charge transfer within an EMCCD gain register element are discussed with a specific focus on the implications for serial charge transfer efficiency (CTE). The effects of operating voltage and readout speed are explored in context with typical operating conditions. It is shown that during transfer, a small portion of signal charge may become trapped at the semiconductor-insulator interface that could act to degrade the serial CTE in certain operating conditions.
A generalized Poisson solver for first-principles device simulations
NASA Astrophysics Data System (ADS)
Bani-Hashemian, Mohammad Hossein; Brück, Sascha; Luisier, Mathieu; VandeVondele, Joost
2016-01-01
Electronic structure calculations of atomistic systems based on density functional theory involve solving the Poisson equation. In this paper, we present a plane-wave based algorithm for solving the generalized Poisson equation subject to periodic or homogeneous Neumann conditions on the boundaries of the simulation cell and Dirichlet type conditions imposed at arbitrary subdomains. In this way, source, drain, and gate voltages can be imposed across atomistic models of electronic devices. Dirichlet conditions are enforced as constraints in a variational framework giving rise to a saddle point problem. The resulting system of equations is then solved using a stationary iterative method in which the generalized Poisson operator is preconditioned with the standard Laplace operator. The solver can make use of any sufficiently smooth function modelling the dielectric constant, including density dependent dielectric continuum models. For all the boundary conditions, consistent derivatives are available and molecular dynamics simulations can be performed. The convergence behaviour of the scheme is investigated and its capabilities are demonstrated.
A generalized Poisson solver for first-principles device simulations.
Bani-Hashemian, Mohammad Hossein; Brück, Sascha; Luisier, Mathieu; VandeVondele, Joost
2016-01-28
Electronic structure calculations of atomistic systems based on density functional theory involve solving the Poisson equation. In this paper, we present a plane-wave based algorithm for solving the generalized Poisson equation subject to periodic or homogeneous Neumann conditions on the boundaries of the simulation cell and Dirichlet type conditions imposed at arbitrary subdomains. In this way, source, drain, and gate voltages can be imposed across atomistic models of electronic devices. Dirichlet conditions are enforced as constraints in a variational framework giving rise to a saddle point problem. The resulting system of equations is then solved using a stationary iterative method in which the generalized Poisson operator is preconditioned with the standard Laplace operator. The solver can make use of any sufficiently smooth function modelling the dielectric constant, including density dependent dielectric continuum models. For all the boundary conditions, consistent derivatives are available and molecular dynamics simulations can be performed. The convergence behaviour of the scheme is investigated and its capabilities are demonstrated. PMID:26827208
Modelling RF sources using 2-D PIC codes
Eppley, K.R.
1993-03-01
In recent years, many types of RF sources have been successfully modelled using 2-D PIC codes. Both cross field devices (magnetrons, cross field amplifiers, etc.) and pencil beam devices (klystrons, gyrotrons, TWT`S, lasertrons, etc.) have been simulated. All these devices involve the interaction of an electron beam with an RF circuit. For many applications, the RF structure may be approximated by an equivalent circuit, which appears in the simulation as a boundary condition on the electric field (``port approximation``). The drive term for the circuit is calculated from the energy transfer between beam and field in the drift space. For some applications it may be necessary to model the actual geometry of the structure, although this is more expensive. One problem not entirely solved is how to accurately model in 2-D the coupling to an external waveguide. Frequently this is approximated by a radial transmission line, but this sometimes yields incorrect results. We also discuss issues in modelling the cathode and injecting the beam into the PIC simulation.
Modelling RF sources using 2-D PIC codes
Eppley, K.R.
1993-03-01
In recent years, many types of RF sources have been successfully modelled using 2-D PIC codes. Both cross field devices (magnetrons, cross field amplifiers, etc.) and pencil beam devices (klystrons, gyrotrons, TWT'S, lasertrons, etc.) have been simulated. All these devices involve the interaction of an electron beam with an RF circuit. For many applications, the RF structure may be approximated by an equivalent circuit, which appears in the simulation as a boundary condition on the electric field ( port approximation''). The drive term for the circuit is calculated from the energy transfer between beam and field in the drift space. For some applications it may be necessary to model the actual geometry of the structure, although this is more expensive. One problem not entirely solved is how to accurately model in 2-D the coupling to an external waveguide. Frequently this is approximated by a radial transmission line, but this sometimes yields incorrect results. We also discuss issues in modelling the cathode and injecting the beam into the PIC simulation.
2D Quantum Transport Modeling in Nanoscale MOSFETs
NASA Technical Reports Server (NTRS)
Svizhenko, Alexei; Anantram, M. P.; Govindan, T. R.; Biegel, B.
2001-01-01
We have developed physical approximations and computer code capable of realistically simulating 2-D nanoscale transistors, using the non-equilibrium Green's function (NEGF) method. This is the most accurate full quantum model yet applied to 2-D device simulation. Open boundary conditions, oxide tunneling and phase-breaking scattering are treated on an equal footing. Electron bandstructure is treated within the anisotropic effective mass approximation. We present the results of our simulations of MIT 25 and 90 nm "well-tempered" MOSFETs and compare them to those of classical and quantum corrected models. The important feature of quantum model is smaller slope of Id-Vg curve and consequently higher threshold voltage. These results are consistent with 1D Schroedinger-Poisson calculations. The effect of gate length on gate-oxide leakage and subthreshold current has been studied. The shorter gate length device has an order of magnitude smaller leakage current than the longer gate length device without a significant trade-off in on-current.
Advanced Simulation Technology to Design Etching Process on CMOS Devices
NASA Astrophysics Data System (ADS)
Kuboi, Nobuyuki
2015-09-01
Prediction and control of plasma-induced damage is needed to mass-produce high performance CMOS devices. In particular, side-wall (SW) etching with low damage is a key process for the next generation of MOSFETs and FinFETs. To predict and control the damage, we have developed a SiN etching simulation technique for CHxFy/Ar/O2 plasma processes using a three-dimensional (3D) voxel model. This model includes new concepts for the gas transportation in the pattern, detailed surface reactions on the SiN reactive layer divided into several thin slabs and C-F polymer layer dependent on the H/N ratio, and use of ``smart voxels''. We successfully predicted the etching properties such as the etch rate, polymer layer thickness, and selectivity for Si, SiO2, and SiN films along with process variations and demonstrated the 3D damage distribution time-dependently during SW etching on MOSFETs and FinFETs. We confirmed that a large amount of Si damage was caused in the source/drain region with the passage of time in spite of the existing SiO2 layer of 15 nm in the over etch step and the Si fin having been directly damaged by a large amount of high energy H during the removal step of the parasitic fin spacer leading to Si fin damage to a depth of 14 to 18 nm. By analyzing the results of these simulations and our previous simulations, we found that it is important to carefully control the dose of high energy H, incident energy of H, polymer layer thickness, and over-etch time considering the effects of the pattern structure, chamber-wall condition, and wafer open area ratio. In collaboration with Masanaga Fukasawa and Tetsuya Tatsumi, Sony Corporation. We thank Mr. T. Shigetoshi and Mr. T. Kinoshita of Sony Corporation for their assistance with the experiments.
2011-12-31
Mesh2d is a Fortran90 program designed to generate two-dimensional structured grids of the form [x(i),y(i,j)] where [x,y] are grid coordinates identified by indices (i,j). The x(i) coordinates alone can be used to specify a one-dimensional grid. Because the x-coordinates vary only with the i index, a two-dimensional grid is composed in part of straight vertical lines. However, the nominally horizontal y(i,j0) coordinates along index i are permitted to undulate or otherwise vary. Mesh2d also assignsmore » an integer material type to each grid cell, mtyp(i,j), in a user-specified manner. The complete grid is specified through three separate input files defining the x(i), y(i,j), and mtyp(i,j) variations.« less
14 CFR 121.407 - Training program: Approval of airplane simulators and other training devices.
Code of Federal Regulations, 2013 CFR
2013-01-01
... Program § 121.407 Training program: Approval of airplane simulators and other training devices. (a) Each airplane simulator and other training device that is used in a training course permitted under § 121.409... or check airman at the end of each training or check flight. (b) A particular airplane simulator...
14 CFR 61.64 - Use of a flight simulator and flight training device.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 14 Aeronautics and Space 2 2013-01-01 2013-01-01 false Use of a flight simulator and flight... Ratings and Pilot Authorizations § 61.64 Use of a flight simulator and flight training device. (a) Use of a flight simulator or flight training device. If an applicant for a certificate or rating uses...
14 CFR 61.64 - Use of a flight simulator and flight training device.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 14 Aeronautics and Space 2 2014-01-01 2014-01-01 false Use of a flight simulator and flight... Ratings and Pilot Authorizations § 61.64 Use of a flight simulator and flight training device. (a) Use of a flight simulator or flight training device. If an applicant for a certificate or rating uses...
14 CFR 121.407 - Training program: Approval of airplane simulators and other training devices.
Code of Federal Regulations, 2012 CFR
2012-01-01
... Program § 121.407 Training program: Approval of airplane simulators and other training devices. (a) Each airplane simulator and other training device that is used in a training course permitted under § 121.409... or check airman at the end of each training or check flight. (b) A particular airplane simulator...
14 CFR 121.409 - Training courses using airplane simulators and other training devices.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 14 Aeronautics and Space 3 2010-01-01 2010-01-01 false Training courses using airplane simulators... Program § 121.409 Training courses using airplane simulators and other training devices. (a) Training courses utilizing airplane simulators and other training devices may be included in the certificate...
14 CFR 121.409 - Training courses using airplane simulators and other training devices.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 14 Aeronautics and Space 3 2013-01-01 2013-01-01 false Training courses using airplane simulators... Program § 121.409 Training courses using airplane simulators and other training devices. (a) Training courses utilizing airplane simulators and other training devices may be included in the certificate...
14 CFR 121.407 - Training program: Approval of airplane simulators and other training devices.
Code of Federal Regulations, 2010 CFR
2010-01-01
... Program § 121.407 Training program: Approval of airplane simulators and other training devices. (a) Each airplane simulator and other training device that is used in a training course permitted under § 121.409... or check airman at the end of each training or check flight. (b) A particular airplane simulator...
14 CFR 61.64 - Use of a flight simulator and flight training device.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 14 Aeronautics and Space 2 2012-01-01 2012-01-01 false Use of a flight simulator and flight... Ratings and Pilot Authorizations § 61.64 Use of a flight simulator and flight training device. (a) Use of a flight simulator or flight training device. If an applicant for a certificate or rating uses...
14 CFR 121.409 - Training courses using airplane simulators and other training devices.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 14 Aeronautics and Space 3 2012-01-01 2012-01-01 false Training courses using airplane simulators... Program § 121.409 Training courses using airplane simulators and other training devices. (a) Training courses utilizing airplane simulators and other training devices may be included in the certificate...
14 CFR 125.297 - Approval of flight simulators and flight training devices.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 14 Aeronautics and Space 3 2010-01-01 2010-01-01 false Approval of flight simulators and flight... Flight Crewmember Requirements § 125.297 Approval of flight simulators and flight training devices. (a) Flight simulators and flight training devices approved by the Administrator may be used in...
14 CFR 121.409 - Training courses using airplane simulators and other training devices.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 14 Aeronautics and Space 3 2011-01-01 2011-01-01 false Training courses using airplane simulators... Program § 121.409 Training courses using airplane simulators and other training devices. (a) Training courses utilizing airplane simulators and other training devices may be included in the certificate...
NASA Astrophysics Data System (ADS)
Lacava, C.; Carrol, L.; Bozzola, A.; Marchetti, R.; Minzioni, P.; Cristiani, I.; Fournier, M.; Bernabe, S.; Gerace, D.; Andreani, L. C.
2016-03-01
We present the characterization of Silicon-on-insulator (SOI) photonic-crystal based 2D grating-couplers (2D-GCs) fabricated by CEA-Leti in the frame of the FP7 Fabulous project, which is dedicated to the realization of devices and systems for low-cost and high-performance passives-optical-networks. On the analyzed samples different test structures are present, including 2D-GC connected to another 2D-GC by different waveguides (in a Mach-Zehnder like configuration), and 2D-GC connected to two separate 2D-GCs, so as to allow a complete assessment of different parameters. Measurements were carried out using a tunable laser source operating in the extended telecom bandwidth and a fiber-based polarization controlling system at the input of device-under-test. The measured data yielded an overall fiber-to-fiber loss of 7.5 dB for the structure composed by an input 2D-GC connected to two identical 2D-GCs. This value was obtained at the peak wavelength of the grating, and the 3-dB bandwidth of the 2D-GC was assessed to be 43 nm. Assuming that the waveguide losses are negligible, so as to make a worst-case analysis, the coupling efficiency of the single 2D-GC results to be equal to -3.75 dB, constituting, to the best of our knowledge, the lowest value ever reported for a fully CMOS compatible 2D-GC. It is worth noting that both the obtained values are in good agreement with those expected by the numerical simulations performed using full 3D analysis by Lumerical FDTD-solutions.
Advanced Numerical Methods and Software Approaches for Semiconductor Device Simulation
Carey, Graham F.; Pardhanani, A. L.; Bova, S. W.
2000-01-01
In this article we concisely present several modern strategies that are applicable to driftdominated carrier transport in higher-order deterministic models such as the driftdiffusion, hydrodynamic, and quantum hydrodynamic systems. The approaches include extensions of “upwind” and artificial dissipation schemes, generalization of the traditional Scharfetter – Gummel approach, Petrov – Galerkin and streamline-upwind Petrov Galerkin (SUPG), “entropy” variables, transformations, least-squares mixed methods and other stabilized Galerkin schemes such as Galerkin least squares and discontinuous Galerkin schemes. The treatment is representative rather than an exhaustive review and several schemes are mentioned only briefly with appropriate reference to the literature. Some of themore » methods have been applied to the semiconductor device problem while others are still in the early stages of development for this class of applications. We have included numerical examples from our recent research tests with some of the methods. A second aspect of the work deals with algorithms that employ unstructured grids in conjunction with adaptive refinement strategies. The full benefits of such approaches have not yet been developed in this application area and we emphasize the need for further work on analysis, data structures and software to support adaptivity. Finally, we briefly consider some aspects of software frameworks. These include dial-an-operator approaches such as that used in the industrial simulator PROPHET, and object-oriented software support such as those in the SANDIA National Laboratory framework SIERRA.« less
Advanced numerical methods and software approaches for semiconductor device simulation
CAREY,GRAHAM F.; PARDHANANI,A.L.; BOVA,STEVEN W.
2000-03-23
In this article the authors concisely present several modern strategies that are applicable to drift-dominated carrier transport in higher-order deterministic models such as the drift-diffusion, hydrodynamic, and quantum hydrodynamic systems. The approaches include extensions of upwind and artificial dissipation schemes, generalization of the traditional Scharfetter-Gummel approach, Petrov-Galerkin and streamline-upwind Petrov Galerkin (SUPG), entropy variables, transformations, least-squares mixed methods and other stabilized Galerkin schemes such as Galerkin least squares and discontinuous Galerkin schemes. The treatment is representative rather than an exhaustive review and several schemes are mentioned only briefly with appropriate reference to the literature. Some of the methods have been applied to the semiconductor device problem while others are still in the early stages of development for this class of applications. They have included numerical examples from the recent research tests with some of the methods. A second aspect of the work deals with algorithms that employ unstructured grids in conjunction with adaptive refinement strategies. The full benefits of such approaches have not yet been developed in this application area and they emphasize the need for further work on analysis, data structures and software to support adaptivity. Finally, they briefly consider some aspects of software frameworks. These include dial-an-operator approaches such as that used in the industrial simulator PROPHET, and object-oriented software support such as those in the SANDIA National Laboratory framework SIERRA.
NASA Astrophysics Data System (ADS)
Thuillier, Sandrine; Le Port, Alban; Manach, Pierre-Yves
2011-08-01
Surface defects are small concave imperfections that can develop during forming on outer convex panels of automotive parts like doors. They occur during springback steps, after drawing in the vicinity of bending over a curved line and flanging/hemming in the vicinity of the upper corner of a door. They can alter significantly the final quality of the automobile and it is of primary importance to deal with them as early as possible in the design of the forming tools. The aim of this work is to reproduce at the laboratory scale such a defect, in the case of the flanging along a curved edge, made of two orthogonal straight part of length 50 mm and joint by a curved line. A dedicated device has been designed and steel samples were tested. Each sample was measured initially (after laser cutting) and after flanging, with a 3D measuring machine. 2D profiles were extracted and the curvature was calculated. Surface defects were defined between points where the curvature sign changed. Isovalues of surface defect depth could then be plotted, thus displaying also the spatial geometry on the part surface. An experimental database has been created on the influence of process parameters like the flanging height and the flanging radius. Numerical simulations have been performed with the finite element code Abaqus to predict the occurrence of such surface defects and to analyze stress and strain distribution within the defect area.
NASA Astrophysics Data System (ADS)
Peters, C. A.; Crandell, L. E.; Um, W.; Jones, K. W.; Lindquist, W. B.
2011-12-01
Geochemical reactions in the subsurface can alter the porosity and permeability of a porous medium through mineral precipitation and dissolution. While effects on porosity are relatively well understood, changes in permeability are more difficult to estimate. In this work, pore-network modeling is used to estimate the permeability of a porous medium using pore and throat size distributions. These distributions can be determined from 2D Scanning Electron Microscopy (SEM) images of thin sections or from 3D X-ray Computed Tomography (CT) images of small cores. Each method has unique advantages as well as unique sources of error. 3D CT imaging has the advantage of reconstructing a 3D pore network without the inherent geometry-based biases of 2D images but is limited by resolutions around 1 μm. 2D SEM imaging has the advantage of higher resolution, and the ability to examine sub-grain scale variations in porosity and mineralogy, but is limited by the small size of the sample of pores that are quantified. A pore network model was created to estimate flow permeability in a sand-packed experimental column investigating reaction of sediments with caustic radioactive tank wastes in the context of the Hanford, WA site. Before, periodically during, and after reaction, 3D images of the porous medium in the column were produced using the X2B beam line facility at the National Synchrotron Light Source (NSLS) at Brookhaven National Lab. These images were interpreted using 3DMA-Rock to characterize the pore and throat size distributions. After completion of the experiment, the column was sectioned and imaged using 2D SEM in backscattered electron mode. The 2D images were interpreted using erosion-dilation to estimate the pore and throat size distributions. A bias correction was determined by comparison with the 3D image data. A special image processing method was developed to infer the pore space before reaction by digitally removing the precipitate. The different sets of pore
NASA Astrophysics Data System (ADS)
Takeshita, Toshihiro; Makimoto, Natsumi; Nogami, Hirofumi; Sawada, Renshi; Kobayashi, Takeshi
2016-10-01
We fabricated a MEMS actuator device that is used as an actuator component of an optical scanning device without deflection of the device using finite element method (FEM) software. When Pt/Ti/PZT/Pt/Ti/SiO2 multilayers were deposited on a silicon-on-insulator (SOI) wafer in order to fabricate the MEMS actuator device, the wafer was deflected because of inner stress generated by thin-film deposition, and as a result, the MEMS actuator device using the deflected wafer was also deflected. We aimed to define the relationship between the deflection of the SOI wafer and the deflection of the MEMS actuator device by simulation. Moreover, by using this relationship, we determined the optimal deflection of the SOI wafer after the deposition of thin films, enabling the fabrication of a MEMS actuator device without deflection, by simulation. From the simulation result, when the changes in the deflection of SOI wafers were 14.1 and 7.4 µm, the displacements of the MEMS actuator device were 1.1 and 5.7 µm, respectively. The simulation results were in good agreement with the experimental results. From the simulation results, the optimal wafer deflection for preventing the deflection of the MEMS actuator device was 15.6 µm. This value was close to the experimental value, 14.1 µm. This method enables easy simulation of any MEMS device that is complicated in design and which uses multilayer thin films.
Simulation of electron transport in quantum well devices
NASA Technical Reports Server (NTRS)
Miller, D. R.; Gullapalli, K. K.; Reddy, V. R.; Neikirk, D. P.
1992-01-01
Double barrier resonant tunneling diodes (DBRTD) have received much attention as possible terahertz devices. Despite impressive experimental results, the specifics of the device physics (i.e., how the electrons propagate through the structure) are only qualitatively understood. Therefore, better transport models are warranted if this technology is to mature. In this paper, the Lattice Wigner function is used to explain the important transport issues associated with DBRTD device behavior.
ERIC Educational Resources Information Center
Ward, Ted; Levine, S. Joseph
The SimulaR, a portable tabletop instructional simulator and response recording device has been designed to aid research in development of programed instruction and is scheduled for a field test involving instructional simulation of remedial reading. Major components consist of a two channel audio playback device, a visual component incorporating…
14 CFR 121.407 - Training program: Approval of airplane simulators and other training devices.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 14 Aeronautics and Space 3 2011-01-01 2011-01-01 false Training program: Approval of airplane... Program § 121.407 Training program: Approval of airplane simulators and other training devices. (a) Each airplane simulator and other training device that is used in a training course permitted under §...
NASA Technical Reports Server (NTRS)
Ko, Malcolm K. W.; Sze, Nien-Dak; Weisenstein, Debra K.; Rodriguez, Jose M.
1988-01-01
Satellite borne instruments, the Total Ozone Mapping Spectrometer (TOMS) and the Solar Backscatter Ultraviolet spectrometer (SBUV), show that total column ozone has decreased by more than 5 percent in the neighborhood of 60 S at all seasons since 1979. This is considerably larger than the decrease calculated by 2-D models which take into account solar flux variation and increases of trace gas concentrations over the same period. The meteorological conditions (warmer temperature and the apparent lack of polar stratospheric clouds) at these latitudes do not seem to favor heterogeneous chemistry as the direct cause for the observed ozone reduction. A mechanism involving the seasonal transport of ozone-poor air mass from within the polar vortex to lower latitudes (the so-called dilution effect) is proposed as a possible explanation for the observed year-round ozone reduction in regions away from the vortex.
NASA Technical Reports Server (NTRS)
Mikellides, Ioannis G.; Katz, Ira; Goebel, Dan M.; Jameson, Kristina K.
2006-01-01
Numerical simulations with the time-dependent Orificed Cathode (OrCa2D-II) computer code show that classical enhancements of the plasma resistivity can not account for the elevated electron temperatures and steep plasma potential gradients measured in the plume of a 25-27.5 A discharge hollow cathode. The cathode, which employs a 0.11-in diameter orifice, was operated at 5.5 sccm without an applied magnetic field using two different anode geometries. It is found that anomalous resistivity based on electron-driven instabilities improves the comparison between theory and experiment. It is also estimated that other effects such as the Hall-effect from the self-induced magnetic field, not presently included in OrCa2D-II, may contribute to the constriction of the current density streamlines thus explaining the higher plasma densities observed along the centerline.
NASA Astrophysics Data System (ADS)
Duan, Taizhong; Griffiths, Cedric M.; Johnsen, Sverre O.
1999-07-01
An attributed controlled grammar (ACG) has been formally used to represent the parasequences of a clastic shallow-marine system. The lithofacies distribution has been conditionally simulated in two dimensions using the ACG. In knowledge representation, the ACG has been shown to have several advantages over context-free, programmed and attributed grammars. The ACG for the parasequences is manually constructed by domain experts based on a conditioning dataset, combined with related sedimentological knowledge. The dataset includes several geological sections measured from outcrops and interpreted from boreholes. A parasequence is decomposed into coastal plain, foreshore, upper shoreface, lower shoreface and offshore facies tracts and their boundaries. Within each tract, lithofacies distribution is described by the facies transition relationship, which can be constructed directly from the dataset and adjusted in terms of related sedimentological knowledge. The boundaries between the tracts are represented by point chains, whereas the facies transitions are controlled by a transitional probability matrix and both vertical and horizontal extensions of the corresponding lithofacies. The simulation results show the following features: (1) the simulation honors the conditioning dataset, (2) the lithofacies distribution simulated from the ACG shows increased variability compared to traditional interpolations between geological sections and (3) the simulated lithofacies distribution is controlled mainly by the uncertainty of the vertical and horizontal extension of each lithofacies, which cannot usually be obtained directly from the conditional dataset, and is not formally considered in traditional geological correlation and interpretation. Work is underway to quantify such lateral and vertical extension in present-day systems.
Yang, Li-Ming; Dornfeld, Matthew; Frauenheim, Thomas; Ganz, Eric
2015-10-21
We predict a highly stable and robust atomically thin gold monolayer with a hexagonal close packed lattice stabilized by metallic bonding with contributions from strong relativistic effects and aurophilic interactions. We have shown that the framework of the Au monolayer can survive 10 ps MD annealing simulations up to 1400 K. The framework is also able to survive large motions out of the plane. Due to the smaller number of bonds per atom in the 2D layer compared to the 3D bulk we observe significantly enhanced energy per bond (0.94 vs. 0.52 eV per bond). This is similar to the increase in bond strength going from 3D diamond to 2D graphene. It is a non-magnetic metal, and was found to be the global minima in the 2D space. Phonon dispersion calculations demonstrate high kinetic stability with no negative modes. This 2D gold monolayer corresponds to the top monolayer of the bulk Au(111) face-centered cubic lattice. The close-packed lattice maximizes the aurophilic interactions. We find that the electrons are completely delocalized in the plane and behave as 2D nearly free electron gas. We hope that the present work can inspire the experimental fabrication of novel free standing 2D metal systems.
NASA Astrophysics Data System (ADS)
Rafiee Dastjerdi, S.; Ghanaatshoar, M.
2013-08-01
A finite difference time domain method based on regular Yee's algorithm in an orthogonal coordinate system is utilized to calculate the band structure of a two-dimensional square-lattice photonic crystal comprising dielectric cylinders in air background and to simulate the image formation of mentioned structure incorporating the perfectly matched layer boundary condition. By analyzing the photonic band diagram of this system, we find that the frequency region of effective negative refraction exists in the second band in near-infrared domain. In this case, electromagnetic wave propagates with a negative phase velocity and the evanescent waves can be supported to perform higher image resolution.
Ghorbani-Asl, Mahdi; Juarez-Mosqueda, Rosalba; Kuc, Agnieszka; Heine, Thomas
2012-08-14
Molecular dynamics simulations using quantum mechanics for the electronic system, i.e., within the Born-Oppenheimer or related Car-Parrinello approximation, became feasible and popular in recent years for very large systems. The most common setup for these simulations is the supercell method in conjunction with the Γ-point approximation. Here we provide a tool which is useful to choose the supercell of the considered system such that it makes it appear to have either an as large as possible band gap (optimized for Car-Parrinello setup) or the metallic character reflected at the Γ point (e.g., fold the Dirac point to the Γ point for graphene and carbon nanotubes) in order to monitor the metallic character in a trajectory. We address carbon nanotubes, graphene, and inorganic TS2 analogues with T = Re, Nb. We further provide a simple Hückel code, which allows checking the electronic states close to the Fermi level within the Γ-point approximation, and we test its predictions against the density-functional-based tight-binding approach.
Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology
Shavanova, Kateryna; Bakakina, Yulia; Burkova, Inna; Shtepliuk, Ivan; Viter, Roman; Ubelis, Arnolds; Beni, Valerio; Starodub, Nickolaj; Yakimova, Rositsa; Khranovskyy, Volodymyr
2016-01-01
The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct “beyond graphene” domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical). A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials. PMID:26861346
Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology.
Shavanova, Kateryna; Bakakina, Yulia; Burkova, Inna; Shtepliuk, Ivan; Viter, Roman; Ubelis, Arnolds; Beni, Valerio; Starodub, Nickolaj; Yakimova, Rositsa; Khranovskyy, Volodymyr
2016-01-01
The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct "beyond graphene" domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical). A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials.
NASA Astrophysics Data System (ADS)
Savoini, P.; Lembege, B.
2015-12-01
The ion foreshock located upstream of the Earth's shock wave is populated with ions having interacted with the shock, and then, reflected back with an high energy gain. Spacecrafts have clearly established the existence of two distinct populations in the quasi-perpendicular shock region (i.e. for 45° ≤ ΘBn ≤ 90°, where ΘBn is the angle between the shock normal and the upstream magnetic field) : (i) field-aligned ion beams or « FAB » characterized by a gyrotropic distribution, and (ii) gyro-phase bunched ions or « GPB » characterized by a NON gyrotropic distribution. One of the important unresolved problem is the exact origin of the particles contributing to these two populations. To our knowledge, it was the first time that full-particle simulations have been performed including self-consistently the shock front curvature and nonstationarity, and the time-of-flight effects. Our analysis evidences that these two backstreaming populations may be reflected by the front itself and can be differentiated both in terms of interaction time and trajectory within the shock front. In particular, simulations evidence that "GPB" population is characterized by a short interaction time (ΔTinter = 1 to 2 τci) while the "FAB" population corresponds to a much larger time range (from 1 τci to 10 τci), where tci is the upstream ion gyroperiod. Present individual ion trajectories evidence that "FAB" population shows a strong perpendicular drift at the shock front (i.e. strong dependence of the pitch angle to the perpendicular velocity) whereas the "GPB" population shows no perpendicular drift (i.e. its pitch angle is mainly driven by the parallel velocity). Such differences explain why the "FAB" population loses their gyro-phase coherency and become gyrotropic which is not the case for the "GPB". This important result was not expected and greatly simplifies the question of their origin.
Knowledge system and method for simulating chemical controlled release device performance
Cowan, Christina E.; Van Voris, Peter; Streile, Gary P.; Cataldo, Dominic A.; Burton, Frederick G.
1991-01-01
A knowledge system for simulating the performance of a controlled release device is provided. The system includes an input device through which the user selectively inputs one or more data parameters. The data parameters comprise first parameters including device parameters, media parameters, active chemical parameters and device release rate; and second parameters including the minimum effective inhibition zone of the device and the effective lifetime of the device. The system also includes a judgemental knowledge base which includes logic for 1) determining at least one of the second parameters from the release rate and the first parameters and 2) determining at least one of the first parameters from the other of the first parameters and the second parameters. The system further includes a device for displaying the results of the determinations to the user.
2D materials and van der Waals heterostructures.
Novoselov, K S; Mishchenko, A; Carvalho, A; Castro Neto, A H
2016-07-29
The physics of two-dimensional (2D) materials and heterostructures based on such crystals has been developing extremely fast. With these new materials, truly 2D physics has begun to appear (for instance, the absence of long-range order, 2D excitons, commensurate-incommensurate transition, etc.). Novel heterostructure devices--such as tunneling transistors, resonant tunneling diodes, and light-emitting diodes--are also starting to emerge. Composed from individual 2D crystals, such devices use the properties of those materials to create functionalities that are not accessible in other heterostructures. Here we review the properties of novel 2D crystals and examine how their properties are used in new heterostructure devices.
Note: Device for underwater laboratory simulation of unconfined blast waves
NASA Astrophysics Data System (ADS)
Courtney, Elijah; Courtney, Amy; Courtney, Michael
2015-06-01
Shock tubes simulate blast waves to study their effects in air under laboratory conditions; however, few experimental models exist for simulating underwater blast waves that are needed for facilitating experiments in underwater blast transmission, determining injury thresholds in marine animals, validating numerical models, and exploring mitigation strategies for explosive well removals. This method incorporates an oxy-acetylene driven underwater blast simulator which creates peak blast pressures of about 1860 kPa. Shot-to-shot consistency was fair, with an average standard deviation near 150 kPa. Results suggest that peak blast pressures from 460 kPa to 1860 kPa are available by adjusting the distance from the source.
Note: Device for underwater laboratory simulation of unconfined blast waves.
Courtney, Elijah; Courtney, Amy; Courtney, Michael
2015-06-01
Shock tubes simulate blast waves to study their effects in air under laboratory conditions; however, few experimental models exist for simulating underwater blast waves that are needed for facilitating experiments in underwater blast transmission, determining injury thresholds in marine animals, validating numerical models, and exploring mitigation strategies for explosive well removals. This method incorporates an oxy-acetylene driven underwater blast simulator which creates peak blast pressures of about 1860 kPa. Shot-to-shot consistency was fair, with an average standard deviation near 150 kPa. Results suggest that peak blast pressures from 460 kPa to 1860 kPa are available by adjusting the distance from the source. PMID:26133878
NASA Technical Reports Server (NTRS)
Woolley, C. T.; Groom, N. J.
1981-01-01
A description of a digital computer simulation of an Annular Momentum Control Device (AMCD) laboratory model is presented. The AMCD is a momentum exchange device which is under development as an advanced control effector for spacecraft attitude control systems. The digital computer simulation of this device incorporates the following models: six degree of freedom rigid body dynamics; rim warp; controller dynamics; nonlinear distributed element axial bearings; as well as power driver and power supply current limits. An annotated FORTRAN IV source code listing of the computer program is included.
Simulating Ideal Assistive Devices to Reduce the Metabolic Cost of Running
Uchida, Thomas K.; Seth, Ajay; Pouya, Soha; Dembia, Christopher L.; Hicks, Jennifer L.; Delp, Scott L.
2016-01-01
Tools have been used for millions of years to augment the capabilities of the human body, allowing us to accomplish tasks that would otherwise be difficult or impossible. Powered exoskeletons and other assistive devices are sophisticated modern tools that have restored bipedal locomotion in individuals with paraplegia and have endowed unimpaired individuals with superhuman strength. Despite these successes, designing assistive devices that reduce energy consumption during running remains a substantial challenge, in part because these devices disrupt the dynamics of a complex, finely tuned biological system. Furthermore, designers have hitherto relied primarily on experiments, which cannot report muscle-level energy consumption and are fraught with practical challenges. In this study, we use OpenSim to generate muscle-driven simulations of 10 human subjects running at 2 and 5 m/s. We then add ideal, massless assistive devices to our simulations and examine the predicted changes in muscle recruitment patterns and metabolic power consumption. Our simulations suggest that an assistive device should not necessarily apply the net joint moment generated by muscles during unassisted running, and an assistive device can reduce the activity of muscles that do not cross the assisted joint. Our results corroborate and suggest biomechanical explanations for similar effects observed by experimentalists, and can be used to form hypotheses for future experimental studies. The models, simulations, and software used in this study are freely available at simtk.org and can provide insight into assistive device design that complements experimental approaches. PMID:27656901
NASA Astrophysics Data System (ADS)
Tackley, P. J.
2014-12-01
Here we extend the numerical convection models of Venus models of [1], which included melting, magmatism, decaying heat-producing elements, core cooling, realistic temperature-dependent viscosity and either stagnant lid or episodic lithospheric overturn. In [1] it was found that for stagnant lid convection the dominant mode of heat loss is magmatic heat pipe, which requires massive magmatism and produces very thick, cold crust, inconsistent with observations. In contrast, episodic lid overturn interspersed by periods of quiescence effectively loses Venus's heat while giving lower rates of volcanism and a thinner crust. Calculations predict 5-8 overturn events over Venus's history, each lasting ˜150 Myr, initiating in one place and then spreading globally. Venus-like amplitudes of topography and geoid can be produced in either stagnant or episodic modes, with a viscosity profile that is Earth-like but shifted to higher values. Here we extend [1] by considering intrusive magmatism as an alternative to the purely extrusive magmatism previously assumed. Intrusive magmatism warms and weakens the crust, resulting in substantial surface deformation and a thinner crust. This is further enhanced by using a basaltic rheology for the crust instead of assuming the same rheological parameters as for the mantle. In some cases massive intrusive magmatism can even lead to episodic lithospheric overturn events without plastic yielding. Here we quantitatively analyse the resulting surface deformation and other signatures, and compare to observations in order to constrain the likely ratio of intrusive to extrusive magmatism. [1] Armann, M., and P. J. Tackley (2012), Simulating the thermochemical magmatic and tectonic evolution of Venus's mantle and lithosphere: Two-dimensional models, J. Geophys. Res., 117, E12003, doi:10.1029/2012JE004231.
NASA Astrophysics Data System (ADS)
Tackley, Paul
2015-04-01
Here we extend the numerical convection models of Venus models of [1], which included melting, magmatism, decaying heat-producing elements, core cooling, realistic temperature-dependent viscosity and either stagnant lid or episodic lithospheric overturn. In [1] it was found that for stagnant lid convection the dominant mode of heat loss is magmatic heat pipe, which requires massive magmatism and produces very thick, cold crust, inconsistent with observations. In contrast, episodic lid overturn interspersed by periods of quiescence effectively loses Venus's heat while giving lower rates of volcanism and a thinner crust. Calculations predict 5-8 overturn events over Venus's history, each lasting ˜150 Myr, initiating in one place and then spreading globally. Venus-like amplitudes of topography and geoid can be produced in either stagnant or episodic modes, with a viscosity profile that is Earth-like but shifted to higher values. Here we extend [1] by considering intrusive magmatism as an alternative to the purely extrusive magmatism previously assumed. Intrusive magmatism warms and weakens the crust, resulting in substantial surface deformation and a thinner crust. This is further enhanced by using a basaltic rheology for the crust instead of assuming the same rheological parameters as for the mantle. In some cases massive intrusive magmatism can even lead to episodic lithospheric overturn events without plastic yielding. Here we quantitatively analyse the resulting surface deformation and other signatures, and compare to observations in order to constrain the likely ratio of intrusive to extrusive magmatism. [1] Armann, M., and P. J. Tackley (2012), Simulating the thermochemical magmatic and tectonic evolution of Venus's mantle and lithosphere: Two-dimensional models, J. Geophys. Res., 117, E12003, doi:10.1029/2012JE004231.
NASA Technical Reports Server (NTRS)
Monta, William J.
1992-01-01
A pitot-rake survey of the simulated exhaust of a half-span scramjet nozzle model was conducted in the Langley 20-Inch Mach 6 Tunnel to provide an additional data set for computational fluid dynamics (CFD) code comparisons. A wind-tunnel model was tested with a 26-tube pitot rake that could be manually positioned along the mid-semispan plane of the model. The model configuration had an external expansion surface of 20 degrees and an internal cowl expansion of 12 degrees; tests were also performed with a flow fence. Tests were conducted at a free-stream Reynolds number of approximately 6.5 x 10(exp 6) per foot and a model angle of attack of -0.75 degrees. The two exhaust gas mediums that were tested were air and a Freon 12-argon mixture. Each medium was tested at two jet total pressures at approximately 28 and 14 psia. This document presents the flow-field survey results in graphical as well as tabular form, and several observations concerning the results are discussed. The surveys reveal the major expected flow-field characteristics for each test configuration. For a 50-percent freon 12 and 50-percent argon mixture by volume (Fr-Ar), the exhaust jet pressures were slightly higher than those for air. The addition of a flow fence slightly raised the pitot pressure for the Fr-Ar mixture, but it produced little change for air. For the Fr-Ar exhaust, the plume was larger and the region between the shock wave and plume was smaller.
WFR-2D: an analytical model for PWAS-generated 2D ultrasonic guided wave propagation
NASA Astrophysics Data System (ADS)
Shen, Yanfeng; Giurgiutiu, Victor
2014-03-01
This paper presents WaveFormRevealer 2-D (WFR-2D), an analytical predictive tool for the simulation of 2-D ultrasonic guided wave propagation and interaction with damage. The design of structural health monitoring (SHM) systems and self-aware smart structures requires the exploration of a wide range of parameters to achieve best detection and quantification of certain types of damage. Such need for parameter exploration on sensor dimension, location, guided wave characteristics (mode type, frequency, wavelength, etc.) can be best satisfied with analytical models which are fast and efficient. The analytical model was constructed based on the exact 2-D Lamb wave solution using Bessel and Hankel functions. Damage effects were inserted in the model by considering the damage as a secondary wave source with complex-valued directivity scattering coefficients containing both amplitude and phase information from wave-damage interaction. The analytical procedure was coded with MATLAB, and a predictive simulation tool called WaveFormRevealer 2-D was developed. The wave-damage interaction coefficients (WDICs) were extracted from harmonic analysis of local finite element model (FEM) with artificial non-reflective boundaries (NRB). The WFR-2D analytical simulation results were compared and verified with full scale multiphysics finite element models and experiments with scanning laser vibrometer. First, Lamb wave propagation in a pristine aluminum plate was simulated with WFR-2D, compared with finite element results, and verified by experiments. Then, an inhomogeneity was machined into the plate to represent damage. Analytical modeling was carried out, and verified by finite element simulation and experiments. This paper finishes with conclusions and suggestions for future work.
14 CFR 142.59 - Flight simulators and flight training devices.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 14 Aeronautics and Space 3 2011-01-01 2011-01-01 false Flight simulators and flight training... TRANSPORTATION (CONTINUED) SCHOOLS AND OTHER CERTIFICATED AGENCIES TRAINING CENTERS Personnel and Flight Training Equipment Requirements § 142.59 Flight simulators and flight training devices. (a) An applicant for,...
14 CFR 142.59 - Flight simulators and flight training devices.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 14 Aeronautics and Space 3 2012-01-01 2012-01-01 false Flight simulators and flight training... TRANSPORTATION (CONTINUED) SCHOOLS AND OTHER CERTIFICATED AGENCIES TRAINING CENTERS Personnel and Flight Training Equipment Requirements § 142.59 Flight simulators and flight training devices. (a) An applicant for,...
14 CFR 142.59 - Flight simulators and flight training devices.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 14 Aeronautics and Space 3 2014-01-01 2014-01-01 false Flight simulators and flight training... TRANSPORTATION (CONTINUED) SCHOOLS AND OTHER CERTIFICATED AGENCIES TRAINING CENTERS Personnel and Flight Training Equipment Requirements § 142.59 Flight simulators and flight training devices. (a) An applicant for,...
14 CFR 125.297 - Approval of flight simulators and flight training devices.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 14 Aeronautics and Space 3 2014-01-01 2014-01-01 false Approval of flight simulators and flight... OPERATIONS CERTIFICATION AND OPERATIONS: AIRPLANES HAVING A SEATING CAPACITY OF 20 OR MORE PASSENGERS OR A... Flight Crewmember Requirements § 125.297 Approval of flight simulators and flight training devices....
14 CFR 125.297 - Approval of flight simulators and flight training devices.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 14 Aeronautics and Space 3 2013-01-01 2013-01-01 false Approval of flight simulators and flight... OPERATIONS CERTIFICATION AND OPERATIONS: AIRPLANES HAVING A SEATING CAPACITY OF 20 OR MORE PASSENGERS OR A... Flight Crewmember Requirements § 125.297 Approval of flight simulators and flight training devices....
14 CFR 125.297 - Approval of flight simulators and flight training devices.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 14 Aeronautics and Space 3 2012-01-01 2012-01-01 false Approval of flight simulators and flight... OPERATIONS CERTIFICATION AND OPERATIONS: AIRPLANES HAVING A SEATING CAPACITY OF 20 OR MORE PASSENGERS OR A... Flight Crewmember Requirements § 125.297 Approval of flight simulators and flight training devices....
14 CFR 142.59 - Flight simulators and flight training devices.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 14 Aeronautics and Space 3 2013-01-01 2013-01-01 false Flight simulators and flight training... TRANSPORTATION (CONTINUED) SCHOOLS AND OTHER CERTIFICATED AGENCIES TRAINING CENTERS Personnel and Flight Training Equipment Requirements § 142.59 Flight simulators and flight training devices. (a) An applicant for,...
NASA Astrophysics Data System (ADS)
Tackley, Paul
2014-05-01
magmatism as an alternative to the purely extrusive magmatism assumed in [1]. Intrusive magmatism warms and weakens the crust, resulting in substantial surface deformation and a thinner crust. This is further enhanced by using a basaltic rheology for the crust instead of assuming the same rheological parameters as for the mantle. Here we quantitatively analyse the resulting surface deformation and other signatures, and compare to observations in order to constrain the likely ratio of intrusive to extrusive magmatism. [1] Armann, M., and P. J. Tackley (2012), Simulating the thermochemical magmatic and tectonic evo- lution of Venus's mantle and lithosphere: Two-dimensional models, J. Geophys. Res., 117, E12003, doi:10.1029/2012JE004231.
Modeling and Simulation of a Helicopter Slung Load Stabilization Device
NASA Technical Reports Server (NTRS)
Cicolani, Luigi S.; Ehlers, George E.
2002-01-01
This paper addresses the problem of simulation and stabilization of the yaw motions of a cargo container slung load. The study configuration is a UH-60 helicopter carrying a 6ft x 6 ft x 8 ft CONEX container. This load is limited to 60 KIAS in operations and flight testing indicates that it starts spinning in hover and that spin rate increases with airspeed. The simulation reproduced the load yaw motions seen in the flight data after augmenting the load model with terms representing unsteady load yaw moment effects acting to reinforce load oscillations, and augmenting the hook model to include yaw resistance at the hook. The use of a vertical fin to stabilize the load is considered. Results indicate that the CONEX airspeed can be extended to 110 kts using a 3x5 ft fin.
Atomistic simulation of transport phenomena in nanoelectronic devices.
Luisier, Mathieu
2014-07-01
Computational chemistry deals with the first-principles calculation of electronic and crystal structures, phase diagrams, charge distributions, vibrational frequencies, or ion diffusivity in complex molecules and solids. Typically, none of these numerical experiments allows for the calculation of electrical currents under the influence of externally applied voltages. To address this issue, there is an imperative need for an advanced simulation approach capable of treating all kind of transport phenomena (electron, energy, momentum) at a quantum mechanical level. The goal of this tutorial review is to give an overview of the "quantum transport" (QT) research activity, introduce specific techniques such as the Non-equilibrium Green's Function (NEGF) formalism, describe their basic features, and underline their strengths and weaknesses. Three examples from the nanoelectronics field have been selected to illustrate the insight provided by quantum transport simulations. Details are also given about the numerical algorithms to solve the NEGF equations and about strategies to parallelize the workload on supercomputers. PMID:24728143
Atomistic simulation of transport phenomena in nanoelectronic devices.
Luisier, Mathieu
2014-07-01
Computational chemistry deals with the first-principles calculation of electronic and crystal structures, phase diagrams, charge distributions, vibrational frequencies, or ion diffusivity in complex molecules and solids. Typically, none of these numerical experiments allows for the calculation of electrical currents under the influence of externally applied voltages. To address this issue, there is an imperative need for an advanced simulation approach capable of treating all kind of transport phenomena (electron, energy, momentum) at a quantum mechanical level. The goal of this tutorial review is to give an overview of the "quantum transport" (QT) research activity, introduce specific techniques such as the Non-equilibrium Green's Function (NEGF) formalism, describe their basic features, and underline their strengths and weaknesses. Three examples from the nanoelectronics field have been selected to illustrate the insight provided by quantum transport simulations. Details are also given about the numerical algorithms to solve the NEGF equations and about strategies to parallelize the workload on supercomputers.
Simulation of Enhanced-Explosive Devices in Chambers and Tunnels
Bell, J B; Kuhl, A L; Beckner, V E
2007-06-05
Introduction: Shock-dispersed fuel (SDF) explosives use a small chemical charge to disperse a combustible fuel that burns in the post-detonation environment. The energy released in the combustion process has the potential for generating higher pressures and temperatures than conventional explosives. However, the development of these types of novel explosive systems requires a detailed understanding of all of the modes of energy release. Objective: The objective of this project is develop a simulation capability for predicting explosion and combustion phase of SDF charges and apply that capability to quantifying the behavior of these types of explosives. Methodology: We approximate the dynamics of an SDF charge using high Reynolds number, fast chemistry model that effectively captures the thermodynamic behavior of SDF charges and accurately models the key modes of energy release. The overall computational model is combined with Adaptive Mesh Refinement (AMR) , implemented in a parallel adaptive framework suited to the massively parallel computer systems. Results: We have developed a multiphase version of the model and used it to simulate an SDF charge in which the dispersed fuel is aluminum flakes. Flow visualizations show that the combustion field is turbulent for the chamber and tunnel cases studied. During the 3 milli-seconds of simulation, over 90% of the Al fuel was consumed for the chamber case, while about 40% was consumed in the tunnel case in agreement with Al-SDF experiments. Significance to DoD: DoD has a requirement to develop enhanced energetic materials to support future military systems. The SDF charges described here utilize the combustion mechanism to increase energy per gram of fuel by a factor of 7 to 10 over conventional (detonating) charges, and increase the temperature of the explosion cloud to 2,000-4,000 K (depending on the SDF fuel). Accurate numerical simulation of such SDF explosions allows one to understand the energy release mechanism
Electron Transport Simulations of 4-Terminal Crossed Graphene Nanoribbons Devices
NASA Astrophysics Data System (ADS)
Brandimarte, Pedro; Papior, Nick R.; Engelund, Mads; Garcia-Lekue, Aran; Frederiksen, Thomas; Sánchez-Portal, Daniel
Recently, it has been reported theoretically a current switching mechanism by voltage control in a system made by two perpendicular 14-armchair graphene nanoribbons (GNRs). In order to investigate the possibilities of using crossed GNRs as ON/OFF devices, we have studied their electronic and transport properties as function structural parameters determining the crossing. Our calculations were performed with TranSIESTA code, which has been recently generalized to consider N >= 1 arbitrarily distributed electrodes at finite bias. We find that the transmission along each individual GNR and among them strongly depends on the stacking. For a 60° rotation angle, the lattice matching in the crossing region provokes a strong scattering effect that translates into an increased interlayer transmission. FP7 FET-ICT PAMS-project (European Commission, contract 610446), MINECO (Grant MAT2013-46593-C6-2-P) and Basque Dep. de Educación, UPV/EHU (Grant IT-756-13).
Simulating ecological changes caused by marine energy devices
NASA Astrophysics Data System (ADS)
Schuchert, Pia; Elsaesser, Bjoern; Pritchard, Daniel; Kregting, Louise
2015-04-01
Marine renewable energy from wave and tidal technology has the potential to contribute significantly globally to energy security for future generations. However common to both tidal and wave energy extraction systems is concern regarding the potential environmental consequences of the deployment of the technology as environmental and ecological effects are so far poorly understood. Ecological surveys and studies to investigate the environmental impacts are time consuming and costly and are generally reactive; a more efficient approach is to develop 2 and 3D linked hydrodynamic-ecological modelling which has the potential to be proactive and to allow forecasting of the effects of array installation. The objective of the study was to explore tools which can help model and evaluate possible far- and near field changes in the environment and ecosystem caused by the introduction of arrays of marine energy devices. Using the commercial software, MIKE by DHI, we can predict and model possible changes in the ecosystem. MIKE21 and ECOLab modelling software provide the opportunity to couple high level hydrodynamic models with process based ecological models and/or agent based models (ABM). The flow solutions of the model were determined in an idealised tidal basin with the dimensions similar to that of Strangford Lough, Northern Ireland, a body of water renowned for the location of the first grid-connected tidal turbine, SeaGen. In the first instance a simple process oriented ecological NPZD model was developed which are used to model marine and freshwater systems describing four state variables, Nutrient, Phytoplankton, Zooplankton and Detritus. The ecological model was run and evaluated under two hydrodynamic scenarios of the idealised basin. This included no tidal turbines (control) and an array of 55 turbines, an extreme scenario. Whilst an array of turbines has an effect on the hydrodynamics of the Lough, it is unlikely to see an extreme effect on the NPZD model
Development of a multi-physics simulation framework for semiconductor materials and devices
NASA Astrophysics Data System (ADS)
Almeida, Nuno Sucena
Modern day semiconductor technology devices face the ever increasing issue of accounting for quantum mechanics effects on their modeling and performance assessment. The objective of this work is to create a user-friendly, extensible and powerful multi-physics simulation blackbox for nano-scale semiconductor devices. By using a graphical device modeller this work will provide a friendly environment were a user without deep knowledge of device physics can create a device, simulate it and extract optical and electrical characteristics deemed of interest to his engineering occupation. Resorting to advanced template C++ object-oriented design from the start, this work was able to implement algorithms to simulate 1,2 and 3D devices which along with scripting using the well known Python language enables the user to create batch simulations, to better optimize device performance. Higher-dimensional semiconductors, like wires and dots, require a huge computational cost. MPI parallel libraries enable the software to tackle complex geometries which otherwise would be unfeasible on a small single-CPU computer. Quantum mechanical phenomena is described by Schrodinger's equation which must be solved self-consistently with Poisson's equation for the electrostatic charge and, if required, make use of piezoelectric charge terms from elasticity constraints. Since the software implements a generic n-dimensional FEM engine, virtually any kind of Partial Differential Equation can be solved and in the future, other required solvers besides the ones already implemented will also be included for easy of use. In particular for the semiconductor device physics, we solve the quantum mechanics effective mass conduction-valence band k·p approximation to the Schrodinger-Poisson, in any crystal growth orientation (C,polar M,A and semi-polar planes or any user defined angle) and also include Piezoelectric effects caused by strain in lattice mismatched layers, where the implemented software
Device performance simulations of multilayer black phosphorus tunneling transistors
NASA Astrophysics Data System (ADS)
Liu, Fei; Shi, Qing; Wang, Jian; Guo, Hong
2015-11-01
We report a theoretical investigation of ballistic transport in multilayer black phosphorus (BP) tunneling transistors (TFETs) with HfO2 as the gate oxide. First-principles calculations show that monolayer BP can be preserved well on HfO2 (111) surface. For a better device performance, the optimum layer and transport direction at different channel lengths are investigated. It is shown that BP TFETs have larger drain current in the armchair direction (AD) than in the zigzag direction, and the current difference can be several orders of magnitude. On-state current can be enhanced in the BP TFETs using thicker BP film, while the minimal leakage current is increased at the same time. To reduce the leakage current and subthreshold swing in the multilayer BP TFETs, lower source/drain doping concentration and smaller drain voltage should be applied. Compared to monolayer MoS2, MoSe2, and MoTe2 TFETs monolayer BP TFETs in AD can reach larger on-state current at the same Ion/Ioff ratio.
Vertical Drop Testing and Simulation of Anthropomorphic Test Devices
NASA Technical Reports Server (NTRS)
Polanco, Michael A.; Littell, Justin D.
2011-01-01
A series of 14 vertical impact tests were conducted using Hybrid III 50th Percentile and Hybrid II 50th Percentile Anthropomorphic Test Devices (ATDs) at NASA Langley Research Center. The purpose of conducting these tests was threefold: to compare and contrast the impact responses of Hybrid II and Hybrid III ATDs under two different loading conditions, to compare the impact responses of the Hybrid III configured with a nominal curved lumbar spine to that of a Hybrid III configured with a straight lumbar spine, and to generate data for comparison with predicted responses from two commercially available ATD finite element models. The two loading conditions examined were a high magnitude, short duration acceleration pulse, and a low magnitude, long duration acceleration pulse, each created by using different paper honeycomb blocks as pulse shape generators in the drop tower. The test results show that the Hybrid III results differ from the Hybrid II results more for the high magnitude, short duration pulse case. The comparison of the lumbar loads for each ATD configuration show drastic differences in the loads seen in the spine. The analytical results show major differences between the responses of the two finite element models. A detailed discussion of possible sources of the discrepancies between the two analytical models is also provided.
Baiz, Carlos R.; Schach, Denise; Tokmakoff, Andrei
2014-01-01
We describe a microscope for measuring two-dimensional infrared (2D IR) spectra of heterogeneous samples with μm-scale spatial resolution, sub-picosecond time resolution, and the molecular structure information of 2D IR, enabling the measurement of vibrational dynamics through correlations in frequency, time, and space. The setup is based on a fully collinear “one beam” geometry in which all pulses propagate along the same optics. Polarization, chopping, and phase cycling are used to isolate the 2D IR signals of interest. In addition, we demonstrate the use of vibrational lifetime as a contrast agent for imaging microscopic variations in molecular environments. PMID:25089490
Grid FriendlyTM Device Model Development and Simulation
Lu, Ning; Hammerstrom, Donald J.; Patrick, Stasha N.
2009-12-30
In late 2007, the Bonneville Power Administration (BPA) contracted Pacific Northwest National Laboratory (PNNL) to complete a research project titled Grid-Responsive Demand-Side Control Using Grid Friendly Appliance Technologies [Hammerstrom 2009, DeSteese and Hammerstrom 2009]. Cosponsors included Portland General Electric (PGE) and Puget Sound Energy (PSE). The project focused on applications of the Grid Friendly Appliance (GFA) controller, which is an autonomous controller that was designed to advise devices like appliances concerning valuable demand-side grid services that should be conducted. The controller bases its advice on observations it makes from the ac voltage signal. Electric tank water heaters were selected to be controlled by the GFA controller in this project. Two autonomous responses are addressed herein. First, an under-voltage-responsive water heater is able to recognize sudden reductions in feeder circuit voltage at each water heater and may curtail any electric load that is being consumed by the water heater. These under-voltage events are usually induced by nearby electrical faults. An under-voltage response is necessarily specified by the set of voltage thresholds at which the responsive water heaters would respond. The set of voltages at which the curtailment would be released must also be specified. Additionally, any delays prior to the water heater load becoming curtailed or again released must be specified. For example, a delay may be intentionally imposed prior to curtailing water heater loads to avoid responses during the fault itself. Much longer and randomized delays should be imposed prior to the release of curtailments in order to re-establish diversity of the water heater loads and soften what could otherwise be an abrupt reintroduction of a large aggregated electrical load into the already stressed grid region.
Cebral, Juan R; Löhner, Rainald
2005-04-01
The simulation of blood flow past endovascular devices such as coils and stents is a challenging problem due to the complex geometry of the devices. Traditional unstructured grid computational fluid dynamics relies on the generation of finite element grids that conform to the boundary of the computational domain. However, the generation of such grids for patient-specific modeling of cerebral aneurysm treatment with coils or stents is extremely difficult and time consuming. This paper describes the application of an adaptive grid embedding technique previously developed for complex fluid structure interaction problems to the simulation of endovascular devices. A hybrid approach is used: the vessel walls are treated with body conforming grids and the endovascular devices with an adaptive mesh embedding technique. This methodology fits naturally in the framework of image-based computational fluid dynamics and opens the door for exploration of different therapeutic options and personalization of endovascular procedures. PMID:15822805
NASA Astrophysics Data System (ADS)
Leiner, Claude; Nemitz, Wolfgang; Schweitzer, Susanne; Wenzl, Franz P.; Peharz, Gerhard; Sommer, Christian
2015-09-01
The development of photonic multi-scale devices with tailor-made optical properties requires the control and the manipulation of light propagation within structures of different length scales, ranging from sub-wavelength to macroscopic dimensions. Unfortunately, applications of common optical simulation methods are usually restricted to particular size regimes. For this reason, a complete optical simulation of multi-scale devices can only be conducted by combining different simulation methods. In our previous work we already introduced an interface method that uses the Poynting vector to bridge between classical Ray-Tracing and the Finite-Difference-Time-Domain method to enable the simulation of suchlike devices. In this contribution we present and discuss a method to reduce the simulation effort and time consumption of this interface simulation process. This approach is based on an FDTD simulation concept for creating the matrices containing probability density distributions that are needed for the FDTD-RT interface simulations by using broadband frequency sources. With this new FDTD simulation concept, the number of simulations needed to create these matrices can be significantly decreased.
NASA Technical Reports Server (NTRS)
Kwak, Dochan
2000-01-01
Over three million Americans and 20 million people worldwide suffer from some form of heart failure. Mechanical heart assist devices are being used as a temporary support to sick ventricle and valves as a bridge-to-transplant or bridge-to-recovery. This viewgraph presentation gives an overview of the development of NASA-DeBakey Ventricular Assist Device (VAD) using numerical aerospace simulation technology.
Simulation and Comparison of Various Gamma-Ray Imaging Detector Configurations for IPRL Devices
Manini, H A
2006-12-27
Simulations are performed for seven different geometrical configurations of CdZnTe (CZT) detector arrays for Intelligent Personal Radiation Locator (IPRL) devices. IPRL devices are portable radiation detectors that have gamma-ray imaging capability. The detector performance is analyzed for each type of IPRL configuration, and the intrinsic photopeak efficiency, intrinsic photopeak count rate, detector image resolution, imaging efficiency, and imaging count rate are determined.
NASA Astrophysics Data System (ADS)
Chicea, Anca-Lucia
2015-09-01
The paper presents the process of building geometric and kinematic models of a technological equipment used in the process of manufacturing devices. First, the process of building the model for a six axes industrial robot is presented. In the second part of the paper, the process of building the model for a five-axis CNC milling machining center is also shown. Both models can be used for accurate cutting processes simulation of complex parts, such as prosthetic devices.
Simulation of ion beam induced current in radiation detectors and microelectronic devices.
Vizkelethy, Gyorgy
2009-10-01
Ionizing radiation is known to cause Single Event Effects (SEE) in a variety of electronic devices. The mechanism that leads to these SEEs is current induced by the radiation in these devices. While this phenomenon is detrimental in ICs, this is the basic mechanism behind the operation of semiconductor radiation detectors. To be able to predict SEEs in ICs and detector responses we need to be able to simulate the radiation induced current as the function of time. There are analytical models, which work for very simple detector configurations, but fail for anything more complex. On the other end, TCAD programs can simulate this process in microelectronic devices, but these TCAD codes costs hundreds of thousands of dollars and they require huge computing resources. In addition, in certain cases they fail to predict the correct behavior. A simulation model based on the Gunn theorem was developed and used with the COMSOL Multiphysics framework.
Simulation and Reliability Study of Cu/Low-k Devices in Flip-chip Packages
Zhao, J.-H.; Wilkerson, Brett; Uehling, Trent
2004-12-08
The package impact to the mechanical integrity of the low dielectric constant (low-k) dielectrics back end of the line (BEOL) structure has been proven to be significant in recent publications. This work reports a simulation study of the package-induced delamination in low-k structures by interfacial fracture mechanics combined with multi-scale finite element method. The numerical simulation is validated by reliability test results of low-k devices in different flip-chip package configurations. The modeling result is compared to reliability test data of low-k devices in organic, ceramic flip-chip packages, and good correlation is found. Feasibility of flip-chip packaging for low-k devices is demonstrated. The risk of low-k delamination on different package configurations is rated based on both reliability data and numerical simulations.
Non-parabolic hydrodynamic formulations for the simulation of inhomogeneous semiconductor devices
NASA Technical Reports Server (NTRS)
Smith, Arlynn W.; Brennan, Kevin F.
1995-01-01
Hydrodynamic models are becoming prevalent design tools for small scale devices and other devices in which high energy effects can dominate transport. Most current hydrodynamic models use a parabolic band approximation to obtain fairly simple conservation equations. Interest in accounting for band structure effects in hydrodynamic device simulation has begun to grow since parabolic models can not fully describe the transport in state of the art devices due to the distribution populating non-parabolic states within the band. This paper presents two different non-parabolic formulations of the hydrodynamic model suitable for the simulation of inhomogeneous semiconductor devices. The first formulation uses the Kane dispersion relationship (hk)(exp 2)/2m = W(1 + alpha(W)). The second formulation makes use of a power law ((hk)(exp 2)/2m = xW(sup y)) for the dispersion relation. Hydrodynamic models which use the first formulation rely on the binomial expansion to obtain moment equations with closed form coefficients. This limits the energy range over which the model is valid. The power law formulation readily produces closed form coefficients similar to those obtained using the parabolic band approximation. However, the fitting parameters (x,y) are only valid over a limited energy range. The physical significance of the band non-parabolicity is discussed as well as the advantages/disadvantages and approximations of the two non-parabolic models. A companion paper describes device simulations based on the three dispersion relationships: parabolic, Kane dispersion, and power low dispersion.
Non-Parabolic Hydrodynamic Formulations for the Simulation of Inhomogeneous Semiconductor Devices
NASA Technical Reports Server (NTRS)
Smith, A. W.; Brennan, K. F.
1996-01-01
Hydrodynamic models are becoming prevalent design tools for small scale devices and other devices in which high energy effects can dominate transport. Most current hydrodynamic models use a parabolic band approximation to obtain fairly simple conservation equations. Interest in accounting for band structure effects in hydrodynamic device simulation has begun to grow since parabolic models cannot fully describe the transport in state of the art devices due to the distribution populating non-parabolic states within the band. This paper presents two different non-parabolic formulations or the hydrodynamic model suitable for the simulation of inhomogeneous semiconductor devices. The first formulation uses the Kane dispersion relationship ((hk)(exp 2)/2m = W(1 + alphaW). The second formulation makes use of a power law ((hk)(exp 2)/2m = xW(exp y)) for the dispersion relation. Hydrodynamic models which use the first formulation rely on the binomial expansion to obtain moment equations with closed form coefficients. This limits the energy range over which the model is valid. The power law formulation readily produces closed form coefficients similar to those obtained using the parabolic band approximation. However, the fitting parameters (x,y) are only valid over a limited energy range. The physical significance of the band non-parabolicity is discussed as well as the advantages/disadvantages and approximations of the two non-parabolic models. A companion paper describes device simulations based on the three dispersion relationships; parabolic, Kane dispersion and power law dispersion.
Ginestra, Paola Serena; Ceretti, Elisabetta; Fiorentino, Antonio
2016-07-01
Modeling and simulation of prosthetic devices are the new tools investigated for the production of total customized prostheses. Computational simulations are used to evaluate the geometrical and material designs of a device while assessing its mechanical behavior. Data acquisition through magnetic resonance imaging, computed tomography or laser scanning is the first step that gives information about the human anatomical structures; a file format has to be elaborated through computer-aided design software. Computer-aided design tools can be used to develop a device that respects the design requirements as, for instance, the human anatomy. Moreover, through finite element analysis software and the knowledge of loads and conditions the prostheses are supposed to face in vivo, it is possible to simulate, analyze and predict the mechanical behavior of the prosthesis and its effects on the surrounding tissues. Moreover, the simulations are useful to eventually improve the design (as geometry, materials, features) before the actual production of the device. This article presents an extensive analysis on the use of finite element modeling for the design, testing and development of prosthesis and orthosis devices. PMID:27095509
Simulation of scalp cooling by external devices for prevention of chemotherapy-induced alopecia.
Pliskow, Bradley; Mitra, Kunal; Kaya, Mehmet
2016-02-01
Hypothermia of the scalp tissue during chemotherapy treatment (scalp cooling) has been shown to reduce or prevent chemotherapy-induced hair loss. In this study, numerical models are developed to investigate the interaction between different types of external scalp cooling devices and the human scalp tissue. This work focuses on improving methods of modeling scalp cooling devices as it relates specifically to the prevention of chemotherapy-induced alopecia. First, the cooling power needed for any type of device to achieve therapeutic levels of scalp hypothermia is investigated. Subsequently, two types of scalp cooling devices are simulated: a pre-cooled/frozen cap design and a liquid-cooled cap design. For an average patient, simulations show that 38.5W of heat must be extracted from the scalp tissue for this therapy in order to cool the hair follicle to 22°C. In practice, the cooling power must be greater than this amount to account for thermal losses of the device. Simulations show that pre-cooled and liquid-cooled cap designs result in different tissue temperatures over the course of the procedure. However, it is the temperature of the coolant that largely determines the resulting tissue temperature. Simulations confirm that the thermal resistance of the hair/air layer has a large impact on the resulting tissue temperatures. The results should be correlated with experimental data as an effort to determine the optimal parameter choices for this model.
Alloyed 2D Metal-Semiconductor Atomic Layer Junctions.
Kim, Ah Ra; Kim, Yonghun; Nam, Jaewook; Chung, Hee-Suk; Kim, Dong Jae; Kwon, Jung-Dae; Park, Sang Won; Park, Jucheol; Choi, Sun Young; Lee, Byoung Hun; Park, Ji Hyeon; Lee, Kyu Hwan; Kim, Dong-Ho; Choi, Sung Mook; Ajayan, Pulickel M; Hahm, Myung Gwan; Cho, Byungjin
2016-03-01
Heterostructures of compositionally and electronically variant two-dimensional (2D) atomic layers are viable building blocks for ultrathin optoelectronic devices. We show that the composition of interfacial transition region between semiconducting WSe2 atomic layer channels and metallic NbSe2 contact layers can be engineered through interfacial doping with Nb atoms. WxNb1-xSe2 interfacial regions considerably lower the potential barrier height of the junction, significantly improving the performance of the corresponding WSe2-based field-effect transistor devices. The creation of such alloyed 2D junctions between dissimilar atomic layer domains could be the most important factor in controlling the electronic properties of 2D junctions and the design and fabrication of 2D atomic layer devices.
Alloyed 2D Metal-Semiconductor Atomic Layer Junctions.
Kim, Ah Ra; Kim, Yonghun; Nam, Jaewook; Chung, Hee-Suk; Kim, Dong Jae; Kwon, Jung-Dae; Park, Sang Won; Park, Jucheol; Choi, Sun Young; Lee, Byoung Hun; Park, Ji Hyeon; Lee, Kyu Hwan; Kim, Dong-Ho; Choi, Sung Mook; Ajayan, Pulickel M; Hahm, Myung Gwan; Cho, Byungjin
2016-03-01
Heterostructures of compositionally and electronically variant two-dimensional (2D) atomic layers are viable building blocks for ultrathin optoelectronic devices. We show that the composition of interfacial transition region between semiconducting WSe2 atomic layer channels and metallic NbSe2 contact layers can be engineered through interfacial doping with Nb atoms. WxNb1-xSe2 interfacial regions considerably lower the potential barrier height of the junction, significantly improving the performance of the corresponding WSe2-based field-effect transistor devices. The creation of such alloyed 2D junctions between dissimilar atomic layer domains could be the most important factor in controlling the electronic properties of 2D junctions and the design and fabrication of 2D atomic layer devices. PMID:26839956
A demonstration device to simulate the radial velocity method for exoplanet detection
NASA Astrophysics Data System (ADS)
Choopan, W.; Liewrian, W.; Ketpichainarong, W.; Panijpan, B.
2016-07-01
A device for simulating exoplanet detection by the radial method based on the Doppler principle has been constructed. The spectral shift of light from a distant star, mutually revolving with the exoplanet, is simulated by the spectral shift of the sound wave emitted by the device’s star approaching and receding relative to the static frequency detector. The detected sound frequency shift reflects the relative velocity of the ‘star’ very well. Both teachers and students benefit from the radial velocity method and the transit method (published by us previously) provided by this device.
A Neural-FEM tool for the 2-D magnetic hysteresis modeling
NASA Astrophysics Data System (ADS)
Cardelli, E.; Faba, A.; Laudani, A.; Lozito, G. M.; Riganti Fulginei, F.; Salvini, A.
2016-04-01
The aim of this work is to present a new tool for the analysis of magnetic field problems considering 2-D magnetic hysteresis. In particular, this tool makes use of the Finite Element Method to solve the magnetic field problem in real device, and fruitfully exploits a neural network (NN) for the modeling of 2-D magnetic hysteresis of materials. The NS has as input the magnetic inductions components B at the k-th simulation step and returns as output the corresponding values of the magnetic field H corresponding to the input pattern. It is trained by vector measurements performed on the magnetic material to be modeled. This input/output scheme is directly implemented in a FEM code employing the magnetic potential vector A formulation. Validations through measurements on a real device have been performed.
Friedel, Michael J.
2001-01-01
This report describes a model for simulating transient, Variably Saturated, coupled water-heatsolute Transport in heterogeneous, anisotropic, 2-Dimensional, ground-water systems with variable fluid density (VST2D). VST2D was developed to help understand the effects of natural and anthropogenic factors on quantity and quality of variably saturated ground-water systems. The model solves simultaneously for one or more dependent variables (pressure, temperature, and concentration) at nodes in a horizontal or vertical mesh using a quasi-linearized general minimum residual method. This approach enhances computational speed beyond the speed of a sequential approach. Heterogeneous and anisotropic conditions are implemented locally using individual element property descriptions. This implementation allows local principal directions to differ among elements and from the global solution domain coordinates. Boundary conditions can include time-varying pressure head (or moisture content), heat, and/or concentration; fluxes distributed along domain boundaries and/or at internal node points; and/or convective moisture, heat, and solute fluxes along the domain boundaries; and/or unit hydraulic gradient along domain boundaries. Other model features include temperature and concentration dependent density (liquid and vapor) and viscosity, sorption and/or decay of a solute, and capability to determine moisture content beyond residual to zero. These features are described in the documentation together with development of the governing equations, application of the finite-element formulation (using the Galerkin approach), solution procedure, mass and energy balance considerations, input requirements, and output options. The VST2D model was verified, and results included solutions for problems of water transport under isohaline and isothermal conditions, heat transport under isobaric and isohaline conditions, solute transport under isobaric and isothermal conditions, and coupled water
Novel Approach to Simulate Sleep Apnea Patients for Evaluating Positive Pressure Therapy Devices
Isetta, Valentina; Montserrat, Josep M.; Santano, Raquel; Wimms, Alison J.; Ramanan, Dinesh; Woehrle, Holger; Navajas, Daniel; Farré, Ramon
2016-01-01
Bench testing is a useful method to characterize the response of different automatic positive airway pressure (APAP) devices under well-controlled conditions. However, previous models did not consider the diversity of obstructive sleep apnea (OSA) patients’ characteristics and phenotypes. The objective of this proof-of-concept study was to design a new bench test for realistically simulating an OSA patient’s night, and to implement a one-night example of a typical female phenotype for comparing responses to several currently-available APAP devices. We developed a novel approach aimed at replicating a typical night of sleep which includes different disturbed breathing events, disease severities, sleep/wake phases, body postures and respiratory artefacts. The simulated female OSA patient example that we implemented included periods of wake, light sleep and deep sleep with positional changes and was connected to ten different APAP devices. Flow and pressure readings were recorded; each device was tested twice. The new approach for simulating female OSA patients effectively combined a wide variety of disturbed breathing patterns to mimic the response of a predefined patient type. There were marked differences in response between devices; only three were able to overcome flow limitation to normalize breathing, and only five devices were associated with a residual apnea-hypopnea index of <5/h. In conclusion, bench tests can be designed to simulate specific patient characteristics, and typical stages of sleep, body position, and wake. Each APAP device behaved differently when exposed to this controlled model of a female OSA patient, and should lead to further understanding of OSA treatment. PMID:26978077
Novel Approach to Simulate Sleep Apnea Patients for Evaluating Positive Pressure Therapy Devices.
Isetta, Valentina; Montserrat, Josep M; Santano, Raquel; Wimms, Alison J; Ramanan, Dinesh; Woehrle, Holger; Navajas, Daniel; Farré, Ramon
2016-01-01
Bench testing is a useful method to characterize the response of different automatic positive airway pressure (APAP) devices under well-controlled conditions. However, previous models did not consider the diversity of obstructive sleep apnea (OSA) patients' characteristics and phenotypes. The objective of this proof-of-concept study was to design a new bench test for realistically simulating an OSA patient's night, and to implement a one-night example of a typical female phenotype for comparing responses to several currently-available APAP devices. We developed a novel approach aimed at replicating a typical night of sleep which includes different disturbed breathing events, disease severities, sleep/wake phases, body postures and respiratory artefacts. The simulated female OSA patient example that we implemented included periods of wake, light sleep and deep sleep with positional changes and was connected to ten different APAP devices. Flow and pressure readings were recorded; each device was tested twice. The new approach for simulating female OSA patients effectively combined a wide variety of disturbed breathing patterns to mimic the response of a predefined patient type. There were marked differences in response between devices; only three were able to overcome flow limitation to normalize breathing, and only five devices were associated with a residual apnea-hypopnea index of <5/h. In conclusion, bench tests can be designed to simulate specific patient characteristics, and typical stages of sleep, body position, and wake. Each APAP device behaved differently when exposed to this controlled model of a female OSA patient, and should lead to further understanding of OSA treatment. PMID:26978077
NASA Astrophysics Data System (ADS)
Onofrio, Nicolas; Guzman, David; Strachan, Alejandro
2016-07-01
We describe a new method that enables reactive molecular dynamics (MD) simulations of electrochemical processes and apply it to study electrochemical metallization cells (ECMs). The model, called EChemDID, extends the charge equilibration method to capture the effect of external electrochemical potential on partial atomic charges and describes its equilibration over connected metallic structures, on-the-fly, during the MD simulation. We use EChemDID to simulate resistance switching in nanoscale ECMs; these devices consist of an electroactive metal separated from an inactive electrode by an insulator and can be reversibly switched to a low-resistance state by the electrochemical formation of a conducting filament between electrodes. Our structures use Cu as the active electrode and SiO2 as the dielectric and have dimensions at the foreseen limit of scalability of the technology, with a dielectric thickness of approximately 1 nm. We explore the effect of device geometry on switching timescales and find that nanowires with an electroactive shell, where ions migrate towards a smaller inactive electrode core, result in faster switching than planar devices. We observe significant device-to-device variability in switching timescales and intermittent switching for these nanoscale devices. To characterize the evolution in the electronic structure of the dielectric as dissolved metallic ions switch the device, we perform density functional theory calculations on structures obtained from an EChemDID MD simulation. These results confirm the appearance of states around the Fermi energy as the metallic filament bridges the electrodes and show that the metallic ions and not defects in the dielectric contribute to the majority of those states.
Advanced simulation technology for etching process design for CMOS device applications
NASA Astrophysics Data System (ADS)
Kuboi, Nobuyuki; Fukasawa, Masanaga; Tatsumi, Tetsuya
2016-07-01
Plasma etching is a critical process for the realization of high performance in the next generation of CMOS devices. To predict and control fluctuations in the etching properties accurately during mass production, it is essential that etching process simulation technology considers fluctuations in the plasma chamber wall conditions, the effects of by-products on the critical dimensions, the Si recess dependence on the wafer open area ratio and local pattern structure, and the time-dependent plasma-induced damage distribution associated with the three-dimensional feature scale profile at the 100 nm level. This consideration can overcome the issues with conventional simulations performed under the assumed ideal conditions, which are not accurate enough for practical process design. In this article, these advanced process simulation technologies are reviewed, and, from the results of suitable process simulations, a new etching system that automatically controls the etching properties is proposed to enable stable CMOS device fabrication with high yields.
Large-eddy simulation of a turbulent flow over a heavy vehicle with drag reduction devices
NASA Astrophysics Data System (ADS)
Lee, Sangseung; Kim, Myeongkyun; You, Donghyun
2015-11-01
Aerodynamic drag contributes to a considerable amount of energy loss of heavy vehicles. To reduce the energy loss, drag reduction devices such as side skirts and boat tails, are often installed to the side and the rear of a heavy vehicle. In the present study, turbulent flow around a heavy vehicle with realistic geometric details is simulated using large-eddy simulation (LES), which is capable of providing unsteady flow physics responsible for aerodynamic in sufficient detail. Flow over a heavy vehicle with and without a boat tail and side skirts as drag reduction devices is simulated. The simulation results are validated against accompanying in-house experimental measurements. Effects of a boat tail and side skirts on drag reduction are discussed in detail. Supported by the Korea Agency for Infrastructure Technology Advancement (KAIA) Grant NTIS 1615007940.
Interactive 2D to 3D stereoscopic image synthesis
NASA Astrophysics Data System (ADS)
Feldman, Mark H.; Lipton, Lenny
2005-03-01
Advances in stereoscopic display technologies, graphic card devices, and digital imaging algorithms have opened up new possibilities in synthesizing stereoscopic images. The power of today"s DirectX/OpenGL optimized graphics cards together with adapting new and creative imaging tools found in software products such as Adobe Photoshop, provide a powerful environment for converting planar drawings and photographs into stereoscopic images. The basis for such a creative process is the focus of this paper. This article presents a novel technique, which uses advanced imaging features and custom Windows-based software that utilizes the Direct X 9 API to provide the user with an interactive stereo image synthesizer. By creating an accurate and interactive world scene with moveable and flexible depth map altered textured surfaces, perspective stereoscopic cameras with both visible frustums and zero parallax planes, a user can precisely model a virtual three-dimensional representation of a real-world scene. Current versions of Adobe Photoshop provide a creative user with a rich assortment of tools needed to highlight elements of a 2D image, simulate hidden areas, and creatively shape them for a 3D scene representation. The technique described has been implemented as a Photoshop plug-in and thus allows for a seamless transition of these 2D image elements into 3D surfaces, which are subsequently rendered to create stereoscopic views.
14 CFR 141.41 - Flight simulators, flight training devices, and training aids.
Code of Federal Regulations, 2013 CFR
2013-01-01
..., and training aids. 141.41 Section 141.41 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... aids. An applicant for a pilot school certificate or a provisional pilot school certificate must show that its flight simulators, flight training devices, training aids, and equipment meet the...
14 CFR 141.41 - Flight simulators, flight training devices, and training aids.
Code of Federal Regulations, 2011 CFR
2011-01-01
..., and training aids. 141.41 Section 141.41 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... aids. An applicant for a pilot school certificate or a provisional pilot school certificate must show that its flight simulators, flight training devices, training aids, and equipment meet the...
14 CFR 141.41 - Flight simulators, flight training devices, and training aids.
Code of Federal Regulations, 2010 CFR
2010-01-01
..., and training aids. 141.41 Section 141.41 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... aids. An applicant for a pilot school certificate or a provisional pilot school certificate must show that its flight simulators, flight training devices, training aids, and equipment meet the...
14 CFR 141.41 - Flight simulators, flight training devices, and training aids.
Code of Federal Regulations, 2012 CFR
2012-01-01
..., and training aids. 141.41 Section 141.41 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... aids. An applicant for a pilot school certificate or a provisional pilot school certificate must show that its flight simulators, flight training devices, training aids, and equipment meet the...
14 CFR 141.41 - Flight simulators, flight training devices, and training aids.
Code of Federal Regulations, 2014 CFR
2014-01-01
..., and training aids. 141.41 Section 141.41 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... aids. An applicant for a pilot school certificate or a provisional pilot school certificate must show that its flight simulators, flight training devices, training aids, and equipment meet the...
NASA Astrophysics Data System (ADS)
Do, Van-Nam
2014-09-01
We review fundamental aspects of the non-equilibrium Green function method in the simulation of nanometer electronic devices. The method is implemented into our recently developed computer package OPEDEVS to investigate transport properties of electrons in nano-scale devices and low-dimensional materials. Concretely, we present the definition of the four real-time Green functions, the retarded, advanced, lesser and greater functions. Basic relations among these functions and their equations of motion are also presented in detail as the basis for the performance of analytical and numerical calculations. In particular, we review in detail two recursive algorithms, which are implemented in OPEDEVS to solve the Green functions defined in finite-size opened systems and in the surface layer of semi-infinite homogeneous ones. Operation of the package is then illustrated through the simulation of the transport characteristics of a typical semiconductor device structure, the resonant tunneling diodes.
Engineering light outcoupling in 2D materials.
Lien, Der-Hsien; Kang, Jeong Seuk; Amani, Matin; Chen, Kevin; Tosun, Mahmut; Wang, Hsin-Ping; Roy, Tania; Eggleston, Michael S; Wu, Ming C; Dubey, Madan; Lee, Si-Chen; He, Jr-Hau; Javey, Ali
2015-02-11
When light is incident on 2D transition metal dichalcogenides (TMDCs), it engages in multiple reflections within underlying substrates, producing interferences that lead to enhancement or attenuation of the incoming and outgoing strength of light. Here, we report a simple method to engineer the light outcoupling in semiconducting TMDCs by modulating their dielectric surroundings. We show that by modulating the thicknesses of underlying substrates and capping layers, the interference caused by substrate can significantly enhance the light absorption and emission of WSe2, resulting in a ∼11 times increase in Raman signal and a ∼30 times increase in the photoluminescence (PL) intensity of WSe2. On the basis of the interference model, we also propose a strategy to control the photonic and optoelectronic properties of thin-layer WSe2. This work demonstrates the utilization of outcoupling engineering in 2D materials and offers a new route toward the realization of novel optoelectronic devices, such as 2D LEDs and solar cells.
Chen, Duan; Wei, Guo-Wei
2010-01-01
The miniaturization of nano-scale electronic devices, such as metal oxide semiconductor field effect transistors (MOSFETs), has given rise to a pressing demand in the new theoretical understanding and practical tactic for dealing with quantum mechanical effects in integrated circuits. Modeling and simulation of this class of problems have emerged as an important topic in applied and computational mathematics. This work presents mathematical models and computational algorithms for the simulation of nano-scale MOSFETs. We introduce a unified two-scale energy functional to describe the electrons and the continuum electrostatic potential of the nano-electronic device. This framework enables us to put microscopic and macroscopic descriptions in an equal footing at nano scale. By optimization of the energy functional, we derive consistently-coupled Poisson-Kohn-Sham equations. Additionally, layered structures are crucial to the electrostatic and transport properties of nano transistors. A material interface model is proposed for more accurate description of the electrostatics governed by the Poisson equation. Finally, a new individual dopant model that utilizes the Dirac delta function is proposed to understand the random doping effect in nano electronic devices. Two mathematical algorithms, the matched interface and boundary (MIB) method and the Dirichlet-to-Neumann mapping (DNM) technique, are introduced to improve the computational efficiency of nano-device simulations. Electronic structures are computed via subband decomposition and the transport properties, such as the I-V curves and electron density, are evaluated via the non-equilibrium Green's functions (NEGF) formalism. Two distinct device configurations, a double-gate MOSFET and a four-gate MOSFET, are considered in our three-dimensional numerical simulations. For these devices, the current fluctuation and voltage threshold lowering effect induced by the discrete dopant model are explored. Numerical convergence
Chen, Duan; Wei, Guo-Wei
2010-06-20
The miniaturization of nano-scale electronic devices, such as metal oxide semiconductor field effect transistors (MOSFETs), has given rise to a pressing demand in the new theoretical understanding and practical tactic for dealing with quantum mechanical effects in integrated circuits. Modeling and simulation of this class of problems have emerged as an important topic in applied and computational mathematics. This work presents mathematical models and computational algorithms for the simulation of nano-scale MOSFETs. We introduce a unified two-scale energy functional to describe the electrons and the continuum electrostatic potential of the nano-electronic device. This framework enables us to put microscopic and macroscopic descriptions in an equal footing at nano scale. By optimization of the energy functional, we derive consistently-coupled Poisson-Kohn-Sham equations. Additionally, layered structures are crucial to the electrostatic and transport properties of nano transistors. A material interface model is proposed for more accurate description of the electrostatics governed by the Poisson equation. Finally, a new individual dopant model that utilizes the Dirac delta function is proposed to understand the random doping effect in nano electronic devices. Two mathematical algorithms, the matched interface and boundary (MIB) method and the Dirichlet-to-Neumann mapping (DNM) technique, are introduced to improve the computational efficiency of nano-device simulations. Electronic structures are computed via subband decomposition and the transport properties, such as the I-V curves and electron density, are evaluated via the non-equilibrium Green's functions (NEGF) formalism. Two distinct device configurations, a double-gate MOSFET and a four-gate MOSFET, are considered in our three-dimensional numerical simulations. For these devices, the current fluctuation and voltage threshold lowering effect induced by the discrete dopant model are explored. Numerical convergence
Design, simulation and testing on a light modulating thermal image device
NASA Astrophysics Data System (ADS)
Zhang, Liuqiang; Yang, Genqing
2001-03-01
In this paper, a novel thermal image device working on a light modulating principle is devised, which promises to have a high sensitivity and to eliminate cryogenic coolers while keeping costs low. This device incorporates the functions of infrared image conversion and image intensification together, on the basis of light modulating micromachined arrays. The design and modelling of the device are presented. Theoretical calculations on the sensitivity, minimum detectable power and response time are carried out using a simple beam theory, and the design is optimized for the sake of high sensitivity and low minimum detectable power. Finite-element simulation using the ANSYS 5.4 program is performed and compared with that of the theoretical calculations. Light modulating thermal image device (LMTID) samples were prepared and infrared radiation sensing was performed, of which the primary results demonstrated the potential of LMTID in infrared imaging.
Stochastic Inversion of 2D Magnetotelluric Data
Chen, Jinsong
2010-07-01
The algorithm is developed to invert 2D magnetotelluric (MT) data based on sharp boundary parametrization using a Bayesian framework. Within the algorithm, we consider the locations and the resistivity of regions formed by the interfaces are as unknowns. We use a parallel, adaptive finite-element algorithm to forward simulate frequency-domain MT responses of 2D conductivity structure. Those unknown parameters are spatially correlated and are described by a geostatistical model. The joint posterior probability distribution function is explored by Markov Chain Monte Carlo (MCMC) sampling methods. The developed stochastic model is effective for estimating the interface locations and resistivity. Most importantly, it provides details uncertainty information on each unknown parameter. Hardware requirements: PC, Supercomputer, Multi-platform, Workstation; Software requirements C and Fortan; Operation Systems/version is Linux/Unix or Windows
Stochastic Inversion of 2D Magnetotelluric Data
2010-07-01
The algorithm is developed to invert 2D magnetotelluric (MT) data based on sharp boundary parametrization using a Bayesian framework. Within the algorithm, we consider the locations and the resistivity of regions formed by the interfaces are as unknowns. We use a parallel, adaptive finite-element algorithm to forward simulate frequency-domain MT responses of 2D conductivity structure. Those unknown parameters are spatially correlated and are described by a geostatistical model. The joint posterior probability distribution function ismore » explored by Markov Chain Monte Carlo (MCMC) sampling methods. The developed stochastic model is effective for estimating the interface locations and resistivity. Most importantly, it provides details uncertainty information on each unknown parameter. Hardware requirements: PC, Supercomputer, Multi-platform, Workstation; Software requirements C and Fortan; Operation Systems/version is Linux/Unix or Windows« less
Static & Dynamic Response of 2D Solids
1996-07-15
NIKE2D is an implicit finite-element code for analyzing the finite deformation, static and dynamic response of two-dimensional, axisymmetric, plane strain, and plane stress solids. The code is fully vectorized and available on several computing platforms. A number of material models are incorporated to simulate a wide range of material behavior including elasto-placicity, anisotropy, creep, thermal effects, and rate dependence. Slideline algorithms model gaps and sliding along material interfaces, including interface friction, penetration and single surfacemore » contact. Interactive-graphics and rezoning is included for analyses with large mesh distortions. In addition to quasi-Newton and arc-length procedures, adaptive algorithms can be defined to solve the implicit equations using the solution language ISLAND. Each of these capabilities and more make NIKE2D a robust analysis tool.« less
Static & Dynamic Response of 2D Solids
Lin, Jerry
1996-07-15
NIKE2D is an implicit finite-element code for analyzing the finite deformation, static and dynamic response of two-dimensional, axisymmetric, plane strain, and plane stress solids. The code is fully vectorized and available on several computing platforms. A number of material models are incorporated to simulate a wide range of material behavior including elasto-placicity, anisotropy, creep, thermal effects, and rate dependence. Slideline algorithms model gaps and sliding along material interfaces, including interface friction, penetration and single surface contact. Interactive-graphics and rezoning is included for analyses with large mesh distortions. In addition to quasi-Newton and arc-length procedures, adaptive algorithms can be defined to solve the implicit equations using the solution language ISLAND. Each of these capabilities and more make NIKE2D a robust analysis tool.
Panizzolo, Fausto A.; Marcolin, Giuseppe; Petrone, Nicola
2013-01-01
The aims of this study were to examine two ski simulators, Skimagic and Skier’s Edge, and to evaluate their efficacy as functional training devices for skiers. Vertical ground reaction forces, knee flexion angle kinematics and muscles activity were recorded on these devices and compared with those measured in similar condition while skiing on snow. Five ski instructors performed three randomized testing sessions (snow, Skimagic and Skier’s Edge). During the testing sessions, vertical ground reaction forces were recorded by means of pressure insoles in synchronisation with a portable data logger that collected values of knee flexion-extension and EMG activation of rectus femoris and vastus medialis. EMG activations and ground reaction forces measured while skiing on simulators were lower than on snow. Although less overall EMG activation was present on the simulators, the pattern of EMG activity was closer to real snow on Skimagic than on Skiers’ Edge. Results of the present study suggested that the two devices are not effectively applicable for strength training. However, based on the recorded EMG patterns, the Skimagic treadmill is potentially suitable to act as a functional training device for recreational skiers provided that an increase of speed and slope on Skimagic could induce a closer matching of the studied biomechanical parameters with the snow skiing conditions. Key points EMG activation and ground reaction forces were lower on both simulators with respect to snow. Both simulators were not able to provide an effective contribution to strength development for skiers. In term of functional training Skier’s Edge showed a predominance of concentric action over eccentric which is in contrast with competitive skiing. Skimagic treadmill could be potentially suitable to act as a functional training device for recreational skiers only if an increase of speed and slope will induce a closer matching of the studied biomechanical parameters with the snow
DYNA2D96. Explicit 2-D Hydrodynamic FEM Program
Whirley, R.G.
1992-04-01
DYNA2D is a vectorized, explicit, two-dimensional, axisymmetric and plane strain finite element program for analyzing the large deformation dynamic and hydrodynamic response of inelastic solids. DYNA2D contains 13 material models and 9 equations of state (EOS) to cover a wide range of material behavior. The material models implemented in all machine versions are: elastic, orthotropic elastic, kinematic/isotropic elastic plasticity, thermoelastoplastic, soil and crushable foam, linear viscoelastic, rubber, high explosive burn, isotropic elastic-plastic, temperature-dependent elastic-plastic. The isotropic and temperature-dependent elastic-plastic models determine only the deviatoric stresses. Pressure is determined by one of 9 equations of state including linear polynomial, JWL high explosive, Sack Tuesday high explosive, Gruneisen, ratio of polynomials, linear polynomial with energy deposition, ignition and growth of reaction in HE, tabulated compaction, and tabulated.
2D Four-Channel Perfect Reconstruction Filter Bank Realized with the 2D Lattice Filter Structure
NASA Astrophysics Data System (ADS)
Sezen, S.; Ertüzün, A.
2006-12-01
A novel orthogonal 2D lattice structure is incorporated into the design of a nonseparable 2D four-channel perfect reconstruction filter bank. The proposed filter bank is obtained by using the polyphase decomposition technique which requires the design of an orthogonal 2D lattice filter. Due to constraint of perfect reconstruction, each stage of this lattice filter bank is simply parameterized by two coefficients. The perfect reconstruction property is satisfied regardless of the actual values of these parameters and of the number of the lattice stages. It is also shown that a separable 2D four-channel perfect reconstruction lattice filter bank can be constructed from the 1D lattice filter and that this is a special case of the proposed 2D lattice filter bank under certain conditions. The perfect reconstruction property of the proposed 2D lattice filter approach is verified by computer simulations.
Atomistic methodologies for material properties of 2D materials at the nanoscale
NASA Astrophysics Data System (ADS)
Zhang, Zhen
Research on two dimensional (2D) materials, such as graphene and MoS2, now involves thousands of researchers worldwide cutting across physics, chemistry, engineering and biology. Due to the extraordinary properties of 2D materials, research extends from fundamental science to novel applications of 2D materials. From an engineering point of view, understanding the material properties of 2D materials under various conditions is crucial for tailoring the electrical and mechanical properties of 2D-material-based devices at the nanoscale. Even at the nanoscale, molecular systems typically consist of a vast number of atoms. Molecular dynamics (MD) simulations enable us to understand the properties of assemblies of molecules in terms of their structure and the microscopic interactions between them. From a continuum approach, mechanical properties and thermal properties, such as strain, stress, and heat capacity, are well defined and experimentally measurable. In MD simulations, material systems are considered to be discrete, and only interatomic potential, interatomic forces, and atom positions are directly obtainable. Besides, most of the fracture mechanics concepts, such as stress intensity factors, are not applicable since there is no singularity in MD simulations. However, energy release rate still remains to be a feasible and crucial physical quantity to characterize the fracture mechanical property of materials at the nanoscale. Therefore, equivalent definition of a physical quantity both in atomic scale and macroscopic scale is necessary in order to understand molecular and continuum scale phenomena concurrently. This work introduces atomistic simulation methodologies, based on interatomic potential and interatomic forces, as a tool to unveil the mechanical properties, thermal properties and fracture mechanical properties of 2D materials at the nanoscale. Among many 2D materials, graphene and MoS2 have attracted intense interest. Therefore, we applied our
Generating a 2D Representation of a Complex Data Structure
NASA Technical Reports Server (NTRS)
James, Mark
2006-01-01
A computer program, designed to assist in the development and debugging of other software, generates a two-dimensional (2D) representation of a possibly complex n-dimensional (where n is an integer >2) data structure or abstract rank-n object in that other software. The nature of the 2D representation is such that it can be displayed on a non-graphical output device and distributed by non-graphical means.
A simultaneous 2D/3D autostereo workstation
NASA Astrophysics Data System (ADS)
Chau, Dennis; McGinnis, Bradley; Talandis, Jonas; Leigh, Jason; Peterka, Tom; Knoll, Aaron; Sumer, Aslihan; Papka, Michael; Jellinek, Julius
2012-03-01
We present a novel immersive workstation environment that scientists can use for 3D data exploration and as their everyday 2D computer monitor. Our implementation is based on an autostereoscopic dynamic parallax barrier 2D/3D display, interactive input devices, and a software infrastructure that allows client/server software modules to couple the workstation to scientists' visualization applications. This paper describes the hardware construction and calibration, software components, and a demonstration of our system in nanoscale materials science exploration.
2001-01-31
This software reduces the data from two-dimensional kSA MOS program, k-Space Associates, Ann Arbor, MI. Initial MOS data is recorded without headers in 38 columns, with one row of data per acquisition per lase beam tracked. The final MOSS 2d data file is reduced, graphed, and saved in a tab-delimited column format with headers that can be plotted in any graphing software.
A new inversion method for (T2, D) 2D NMR logging and fluid typing
NASA Astrophysics Data System (ADS)
Tan, Maojin; Zou, Youlong; Zhou, Cancan
2013-02-01
One-dimensional nuclear magnetic resonance (1D NMR) logging technology has some significant limitations in fluid typing. However, not only can two-dimensional nuclear magnetic resonance (2D NMR) provide some accurate porosity parameters, but it can also identify fluids more accurately than 1D NMR. In this paper, based on the relaxation mechanism of (T2, D) 2D NMR in a gradient magnetic field, a hybrid inversion method that combines least-squares-based QR decomposition (LSQR) and truncated singular value decomposition (TSVD) is examined in the 2D NMR inversion of various fluid models. The forward modeling and inversion tests are performed in detail with different acquisition parameters, such as magnetic field gradients (G) and echo spacing (TE) groups. The simulated results are discussed and described in detail, the influence of the above-mentioned observation parameters on the inversion accuracy is investigated and analyzed, and the observation parameters in multi-TE activation are optimized. Furthermore, the hybrid inversion can be applied to quantitatively determine the fluid saturation. To study the effects of noise level on the hybrid method and inversion results, the numerical simulation experiments are performed using different signal-to-noise-ratios (SNRs), and the effect of different SNRs on fluid typing using three fluid models are discussed and analyzed in detail.
2D Spinodal Decomposition in Forced Turbulence
NASA Astrophysics Data System (ADS)
Fan, Xiang; Diamond, Patrick; Chacon, Luis; Li, Hui
2015-11-01
Spinodal decomposition is a second order phase transition for binary fluid mixture, from one thermodynamic phase to form two coexisting phases. The governing equation for this coarsening process below critical temperature, Cahn-Hilliard Equation, is very similar to 2D MHD Equation, especially the conserved quantities have a close correspondence between each other, so theories for MHD turbulence are used to study spinodal decomposition in forced turbulence. Domain size is increased with time along with the inverse cascade, and the length scale can be arrested by a forced turbulence with direct cascade. The two competing mechanisms lead to a stabilized domain size length scale, which can be characterized by Hinze Scale. The 2D spinodal decomposition in forced turbulence is studied by both theory and simulation with ``pixie2d.'' This work focuses on the relation between Hinze scale and spectra and cascades. Similarities and differences between spinodal decomposition and MHD are investigated. Also some transport properties are studied following MHD theories. This work is supported by the Department of Energy under Award Number DE-FG02-04ER54738.
MAGNUM-2D computer code: user's guide
England, R.L.; Kline, N.W.; Ekblad, K.J.; Baca, R.G.
1985-01-01
Information relevant to the general use of the MAGNUM-2D computer code is presented. This computer code was developed for the purpose of modeling (i.e., simulating) the thermal and hydraulic conditions in the vicinity of a waste package emplaced in a deep geologic repository. The MAGNUM-2D computer computes (1) the temperature field surrounding the waste package as a function of the heat generation rate of the nuclear waste and thermal properties of the basalt and (2) the hydraulic head distribution and associated groundwater flow fields as a function of the temperature gradients and hydraulic properties of the basalt. MAGNUM-2D is a two-dimensional numerical model for transient or steady-state analysis of coupled heat transfer and groundwater flow in a fractured porous medium. The governing equations consist of a set of coupled, quasi-linear partial differential equations that are solved using a Galerkin finite-element technique. A Newton-Raphson algorithm is embedded in the Galerkin functional to formulate the problem in terms of the incremental changes in the dependent variables. Both triangular and quadrilateral finite elements are used to represent the continuum portions of the spatial domain. Line elements may be used to represent discrete conduits. 18 refs., 4 figs., 1 tab.
Periodically sheared 2D Yukawa systems
Kovács, Anikó Zsuzsa; Hartmann, Peter; Donkó, Zoltán
2015-10-15
We present non-equilibrium molecular dynamics simulation studies on the dynamic (complex) shear viscosity of a 2D Yukawa system. We have identified a non-monotonic frequency dependence of the viscosity at high frequencies and shear rates, an energy absorption maximum (local resonance) at the Einstein frequency of the system at medium shear rates, an enhanced collective wave activity, when the excitation is near the plateau frequency of the longitudinal wave dispersion, and the emergence of significant configurational anisotropy at small frequencies and high shear rates.
NASA Technical Reports Server (NTRS)
Warren, Gary
1988-01-01
The SOS code is used to compute the resonance modes (frequency-domain information) of sample devices and separately to compute the transient behavior of the same devices. A code, DOT, is created to compute appropriate dot products of the time-domain and frequency-domain results. The transient behavior of individual modes in the device is then plotted. Modes in a coupled-cavity traveling-wave tube (CCTWT) section excited beam in separate simulations are analyzed. Mode energy vs. time and mode phase vs. time are computed and it is determined whether the transient waves are forward or backward waves for each case. Finally, the hot-test mode frequencies of the CCTWT section are computed.
Development of FDTD simulation tool for designing micro-nanostructured based optical devices
NASA Astrophysics Data System (ADS)
Shrestha, Anil; Mizuno, Genki; Oduor, Patrick; Islam, Saif; Dutta, Achyut K.; Dhar, Nibir K.
2016-05-01
The use of Graphics Processing Unit (GPU) for computational work has revolutionized how complex electromagnetic problems are solved. Complex problems which required supercomputers in the past for analysis can now be tackled and solved using personal computers by channeling the computational work towards GPUs instead of the traditional computer Central Processing Unit (CPU). Finite-Difference Time-Domain (FDTD) analysis, which is a computationally expensive method of solving electromagnetic problems is highly parallel in nature and can be readily executed in a GPU. We have developed an algorithm for three dimensional FDTD analysis of optical devices with micro and nano-structures using Compute Unified Device Architecture (CUDA). The developed algorithm exploits the benefits of multiple cores of GPU chips and boosts the speed of simulation without sacrificing its accuracy. We achieved a 25-fold speed up of simulation using CUDA compared to MATLAB code in CPU.
Yoshiyasu, Yusuke; Ayusawa, Ko; Yoshida, Eiichi; Matsumoto, Yoshio; Endo, Yui
2015-01-01
We present a forward dynamics (FD) simulation technique for human figures when they are supported by assistive devices. By incorporating a geometric skin deformation model, called linear blend skinning (skinning), into rigid-body skeleton dynamics, we can model a time-varying geometry of body surface plausibly and efficiently. Based on the skinning model, we also derive a Jacobian (a linear mapping) that maps contact forces exerted on the skin to joint torques, which is the main technical contribution of this paper. This algorithm allows us to efficiently simulate dynamics of human body that interacts with assistive devices. Experimental results showed that the proposed approach can generate plausible motions and can estimate pressure distribution that is roughly comparable to the tactile sensor data.
Wang, Qin; Wang, Xiang-Bin
2014-01-01
We present a model on the simulation of the measurement-device independent quantum key distribution (MDI-QKD) with phase randomized general sources. It can be used to predict experimental observations of a MDI-QKD with linear channel loss, simulating corresponding values for the gains, the error rates in different basis, and also the final key rates. Our model can be applicable to the MDI-QKDs with arbitrary probabilistic mixture of different photon states or using any coding schemes. Therefore, it is useful in characterizing and evaluating the performance of the MDI-QKD protocol, making it a valuable tool in studying the quantum key distributions. PMID:24728000
Numerical simulation of 3D boundary-driven acoustic streaming in microfluidic devices.
Lei, Junjun; Hill, Martyn; Glynne-Jones, Peter
2014-02-01
This article discusses three-dimensional (3D) boundary-driven streaming in acoustofluidic devices. Firstly, the 3D Rayleigh streaming pattern in a microchannel is simulated and its effect on the movement of microparticles of various sizes is demonstrated. The results obtained from this model show good comparisons with 3D experimental visualisations and demonstrate the fully 3D nature of the acoustic streaming field and the associated acoustophoretic motion of microparticles in acoustofluidic devices. This method is then applied to another acoustofluidic device in order to gain insights into an unusual in-plane streaming pattern. The origin of this streaming has not been fully described and its characteristics cannot be explained from the classical theory of Rayleigh streaming. The simulated in-plane streaming pattern was in good agreement with the experimental visualisation. The mechanism behind it is shown to be related to the active sound intensity field, which supports our previous findings on the mechanism of the in-plane acoustic streaming pattern visualised and modelled in a thin-layered capillary device.
An efficient method-of-lines simulation procedure for organic semiconductor devices.
Rogel-Salazar, J; Bradley, D D C; Cash, J R; Demello, J C
2009-03-14
We describe an adaptive grid method-of-lines (MOL) solution procedure for modelling charge transport and recombination in organic semiconductor devices. The procedure we describe offers an efficient, robust and versatile means of simulating semiconductor devices that allows for much simpler coding of the underlying equations than alternative simulation procedures. The MOL technique is especially well-suited to modelling the extremely stiff (and hence difficult to solve) equations that arise during the simulation of organic-and some inorganic-semiconductor devices. It also has wider applications in other areas, including reaction kinetics, combustion and aero- and fluid dynamics, where its ease of implementation also makes it an attractive choice. The MOL procedure we use converts the underlying semiconductor equations into a series of coupled ordinary differential equations (ODEs) that can be integrated forward in time using an appropriate ODE solver. The time integration is periodically interrupted, the numerical solution is interpolated onto a new grid that is better matched to the solution profile, and the time integration is then resumed on the new grid. The efficacy of the simulation procedure is assessed by considering a single layer device structure, for which exact analytical solutions are available for the electric potential, the charge distributions and the current-voltage characteristics. Two separate state-of-the-art ODE solvers are tested: the single-step Runge-Kutta solver Radau5 and the multi-step solver ODE15s, which is included as part of the Matlab ODE suite. In both cases, the numerical solutions show excellent agreement with the exact analytical solutions, yielding results that are accurate to one part in 1 x 10(4). The single-step Radau5 solver, however, is found to provide faster convergence since its efficiency is not compromised by the periodic interruption of the time integration when the grid is updated.
Recent advances in computational methodology for simulation of mechanical circulatory assist devices
Marsden, Alison L.; Bazilevs, Yuri; Long, Christopher C.; Behr, Marek
2014-01-01
Ventricular assist devices (VADs) provide mechanical circulatory support to offload the work of one or both ventricles during heart failure. They are used in the clinical setting as destination therapy, as bridge to transplant, or more recently as bridge to recovery to allow for myocardial remodeling. Recent developments in computational simulation allow for detailed assessment of VAD hemodynamics for device design and optimization for both children and adults. Here, we provide a focused review of the recent literature on finite element methods and optimization for VAD simulations. As VAD designs typically fall into two categories, pulsatile and continuous flow devices, we separately address computational challenges of both types of designs, and the interaction with the circulatory system with three representative case studies. In particular, we focus on recent advancements in finite element methodology that has increased the fidelity of VAD simulations. We outline key challenges, which extend to the incorporation of biological response such as thrombosis and hemolysis, as well as shape optimization methods and challenges in computational methodology. PMID:24449607
Three-dimensional parallel UNIPIC-3D code for simulations of high-power microwave devices
Wang Jianguo; Chen Zaigao; Wang Yue; Zhang Dianhui; Qiao Hailiang; Fu Meiyan; Yuan Yuan; Liu Chunliang; Li Yongdong; Wang Hongguang
2010-07-15
This paper introduces a self-developed, three-dimensional parallel fully electromagnetic particle simulation code UNIPIC-3D. In this code, the electromagnetic fields are updated using the second-order, finite-difference time-domain method, and the particles are moved using the relativistic Newton-Lorentz force equation. The electromagnetic field and particles are coupled through the current term in Maxwell's equations. Two numerical examples are used to verify the algorithms adopted in this code, numerical results agree well with theoretical ones. This code can be used to simulate the high-power microwave (HPM) devices, such as the relativistic backward wave oscillator, coaxial vircator, and magnetically insulated line oscillator, etc. UNIPIC-3D is written in the object-oriented C++ language and can be run on a variety of platforms including WINDOWS, LINUX, and UNIX. Users can use the graphical user's interface to create the complex geometric structures of the simulated HPM devices, which can be automatically meshed by UNIPIC-3D code. This code has a powerful postprocessor which can display the electric field, magnetic field, current, voltage, power, spectrum, momentum of particles, etc. For the sake of comparison, the results computed by using the two-and-a-half-dimensional UNIPIC code are also provided for the same parameters of HPM devices, the numerical results computed from these two codes agree well with each other.
2-D Modeling of Nanoscale MOSFETs: Non-Equilibrium Green's Function Approach
NASA Technical Reports Server (NTRS)
Svizhenko, Alexei; Anantram, M. P.; Govindan, T. R.; Biegel, Bryan
2001-01-01
We have developed physical approximations and computer code capable of realistically simulating 2-D nanoscale transistors, using the non-equilibrium Green's function (NEGF) method. This is the most accurate full quantum model yet applied to 2-D device simulation. Open boundary conditions and oxide tunneling are treated on an equal footing. Electrons in the ellipsoids of the conduction band are treated within the anisotropic effective mass approximation. Electron-electron interaction is treated within Hartree approximation by solving NEGF and Poisson equations self-consistently. For the calculations presented here, parallelization is performed by distributing the solution of NEGF equations to various processors, energy wise. We present simulation of the "benchmark" MIT 25nm and 90nm MOSFETs and compare our results to those from the drift-diffusion simulator and the quantum-corrected results available. In the 25nm MOSFET, the channel length is less than ten times the electron wavelength, and the electron scattering time is comparable to its transit time. Our main results are: (1) Simulated drain subthreshold current characteristics are shown, where the potential profiles are calculated self-consistently by the corresponding simulation methods. The current predicted by our quantum simulation has smaller subthreshold slope of the Vg dependence which results in higher threshold voltage. (2) When gate oxide thickness is less than 2 nm, gate oxide leakage is a primary factor which determines off-current of a MOSFET (3) Using our 2-D NEGF simulator, we found several ways to drastically decrease oxide leakage current without compromising drive current. (4) Quantum mechanically calculated electron density is much smaller than the background doping density in the poly silicon gate region near oxide interface. This creates an additional effective gate voltage. Different ways to. include this effect approximately will be discussed.
NASA Astrophysics Data System (ADS)
Ishizawa, Akihiro; Watanabe, Tomo-Hiko; Sugama, Hideo; Maeyama, Shinya; Nunami, Masanori; Nakajima, Noriyoshi
2014-10-01
Turbulent transport in a high ion temperature discharge of Large Helical Device (LHD) is investigated by means of electromagnetic gyrokinetic simulations including kinetic electrons. A new electromagnetic gyrokinetic simulation code GKV+enables us to examine electron heat and particle fluxes as well as ion heat flux in finite beta heliotron/stellarator plasmas. This problem has not been previously explored because of numerical difficulties associated with complex three-dimensional magnetic structures as well as multiple spatio-temporal scales related to electromagnetic ion and electron dynamics. The turbulent fluxes, which are evaluated through a nonlinear simulation carried out in the K-super computer system, will be reported. This research uses computational resources of K at RIKEN Advanced Institute for Computational Science through the HPCI System Research project (Project ID: hp140044).
Development and evaluation of a device to simulate a sonic boom
NASA Technical Reports Server (NTRS)
Rash, L. C.; Barrett, R. F.; Hart, F. D.
1972-01-01
A device to simulate the vibrational and acoustical properties of a sonic boom was developed and evaluated. The design employed a moving circular diaphragm which produced pressure variations by altering the volume of an air-tight enclosure that was located adjacent to an acoustical test chamber. A review of construction oriented problems, along with their solutions, is presented. The simulator is shown to produce the effects of sonic booms having pressure signatures with rise times as low as 5 milliseconds, durations as short as 80 milliseconds, and overpressures as high as 2.5 pounds per square foot. Variations in the signatures are possible by independent adjustments of the simulator. The energy spectral density is also shown to be in agreement with theory and with actual measurements for aircraft.
Yoganandan, Narayan; Pintar, Frank A; Schlick, Michael; Humm, John R; Voo, Liming; Merkle, Andrew; Kleinberger, Michael
2015-09-18
The objective of the study was to develop a simple device, Vertical accelerator (Vertac), to apply vertical impact loads to Post Mortem Human Subject (PMHS) or dummy surrogates because injuries sustained in military conflicts are associated with this vector; example, under-body blasts from explosive devices/events. The two-part mechanically controlled device consisted of load-application and load-receiving sections connected by a lever arm. The former section incorporated a falling weight to impact one end of the lever arm inducing a reaction at the other/load-receiving end. The "launch-plate" on this end of the arm applied the vertical impact load/acceleration pulse under different initial conditions to biological/physical surrogates, attached to second section. It is possible to induce different acceleration pulses by using varying energy absorbing materials and controlling drop height and weight. The second section of Vertac had the flexibility to accommodate different body regions for vertical loading experiments. The device is simple and inexpensive. It has the ability to control pulses and flexibility to accommodate different sub-systems/components of human surrogates. It has the capability to incorporate preloads and military personal protective equipment (e.g., combat helmet). It can simulate vehicle roofs. The device allows for intermittent specimen evaluations (x-ray and palpation, without changing specimen alignment). The two free but interconnected sections can be used to advance safety to military personnel. Examples demonstrating feasibilities of the Vertac device to apply vertical impact accelerations using PMHS head-neck preparations with helmet and booted Hybrid III dummy lower leg preparations under in-contact and launch-type impact experiments are presented.
Emerging and potential opportunities for 2D flexible nanoelectronics
NASA Astrophysics Data System (ADS)
Zhu, Weinan; Park, Saungeun; Akinwande, Deji
2016-05-01
The last 10 years have seen the emergence of two-dimensional (2D) nanomaterials such as graphene, transition metal dichalcogenides (TMDs), and black phosphorus (BP) among the growing portfolio of layered van der Waals thin films. Graphene, the prototypical 2D material has advanced rapidly in device, circuit and system studies that has resulted in commercial large-area applications. In this work, we provide a perspective of the emerging and potential translational applications of 2D materials including semiconductors, semimetals, and insulators that comprise the basic material set for diverse nanosystems. Applications include RF transceivers, smart systems, the so-called internet of things, and neurotechnology. We will review the DC and RF electronic performance of graphene and BP thin film transistors. 2D materials at sub-um channel length have so far enabled cut-off frequencies from baseband to 100GHz suitable for low-power RF and sub-THz concepts.
Integrated devices for quantum information and quantum simulation with polarization encoded qubits
NASA Astrophysics Data System (ADS)
Sansoni, Linda; Sciarrino, Fabio; Mataloni, Paolo; Crespi, Andrea; Ramponi, Roberta; Osellame, Roberto
2012-06-01
The ability to manipulate quantum states of light by integrated devices may open new perspectives both for fundamental tests of quantum mechanics and for novel technological applications. The technology for handling polarization-encoded qubits, the most commonly adopted approach, was still missing in quantum optical circuits until the ultrafast laser writing (ULW) technique was adopted for the first time to realize integrated devices able to support and manipulate polarization encoded qubits.1 Thanks to this method, polarization dependent and independent devices can be realized. In particular the maintenance of polarization entanglement was demonstrated in a balanced polarization independent integrated beam splitter1 and an integrated CNOT gate for polarization qubits was realized and carachterized.2 We also exploited integrated optics for quantum simulation tasks: by adopting the ULW technique an integrated quantum walk circuit was realized3 and, for the first time, we investigate how the particle statistics, either bosonic or fermionic, influences a two-particle discrete quantum walk. Such experiment has been realized by adopting two-photon entangled states and an array of integrated symmetric directional couplers. The polarization entanglement was exploited to simulate the bunching-antibunching feature of non interacting bosons and fermions. To this scope a novel three-dimensional geometry for the waveguide circuit is introduced, which allows accurate polarization independent behaviour, maintaining a remarkable control on both phase and balancement of the directional couplers.
Georgi, Howard; Kats, Yevgeny
2008-09-26
We discuss what can be learned about unparticle physics by studying simple quantum field theories in one space and one time dimension. We argue that the exactly soluble 2D theory of a massless fermion coupled to a massive vector boson, the Sommerfield model, is an interesting analog of a Banks-Zaks model, approaching a free theory at high energies and a scale-invariant theory with nontrivial anomalous dimensions at low energies. We construct a toy standard model coupling to the fermions in the Sommerfield model and study how the transition from unparticle behavior at low energies to free particle behavior at high energies manifests itself in interactions with the toy standard model particles.
Graphene based 2D-materials for supercapacitors
NASA Astrophysics Data System (ADS)
Palaniselvam, Thangavelu; Baek, Jong-Beom
2015-09-01
Ever-increasing energy demands and the depletion of fossil fuels are compelling humanity toward the development of suitable electrochemical energy conversion and storage devices to attain a more sustainable society with adequate renewable energy and zero environmental pollution. In this regard, supercapacitors are being contemplated as potential energy storage devices to afford cleaner, environmentally friendly energy. Recently, a great deal of attention has been paid to two-dimensional (2D) nanomaterials, including 2D graphene and its inorganic analogues (transition metal double layer hydroxides, chalcogenides, etc), as potential electrodes for the development of supercapacitors with high electrochemical performance. This review provides an overview of the recent progress in using these graphene-based 2D materials as potential electrodes for supercapacitors. In addition, future research trends including notable challenges and opportunities are also discussed.
Kim, Young Yong; Kang, Gu Hyun; Kim, Won Hee; Choi, Hyun Young; Jang, Yong Soo; Lee, Young Jae; Kim, Jae Guk; Kim, Hyeongtae; Kim, Gyoung Yong
2016-01-01
Objective This study aimed to compare intubation performance between blind intubation through supraglottic airway devices and direct laryngoscopy by novices under manikin simulation. We hypothesized that the intubation time by novices using supraglottic airway devices was superior to that with the Macintosh laryngoscope (MCL). Methods A prospective, randomized crossover study was conducted with 95 participants, to evaluate i-gel, air-Q, LMA Fastrach, and MCL devices. Primary outcomes were the intubation time and the success rate for intubation. Results The i-gel showed the shortest insertion and tube passing time among the four devices; the i-gel and air-Q also showed the shortest total intubation time (all P<0.0083; i-gel vs. air-Q, P=0.03). The i-gel and MCL showed the highest cumulative success rate (all P<0.0083; i-gel vs. MCL, P=0.12). Conclusion Blind intubation through the i-gel showed almost equal intubation performance compared to direct laryngoscopy. PMID:27752621
2D Mica Crystal as Electret in Organic Field-Effect Transistors for Multistate Memory.
Zhang, Xiaotao; He, Yudong; Li, Rongjin; Dong, Huanli; Hu, Wenping
2016-05-01
Organic nonvolatile multistate storage devices based on organic field-effect transistors using mica as the 2D single-crystal electrets are developed. A4-paper-sized 2D mica crystals with flat surface are prepared successfully. Devices with mica electrets exhibit a typical memory effect and show ideal output curves on both the on and the off states.
Modeling and simulation of floating gate nanocrystal FET devices and circuits
NASA Astrophysics Data System (ADS)
Hasaneen, El-Sayed A. M.
The nonvolatile memory market has been growing very fast during the last decade, especially for mobile communication systems. The Semiconductor Industry Association International Technology Roadmap for Semiconductors states that the difficult challenge for nonvolatile semiconductor memories is to achieve reliable, low power, low voltage performance and high-speed write/erase. This can be achieved by aggressive scaling of the nonvolatile memory cells. Unfortunately, scaling down of conventional nonvolatile memory will further degrade the retention time due to the charge loss between the floating gate and drain/source contacts and substrate which makes conventional nonvolatile memory unattractive. Using nanocrystals as charge storage sites reduces dramatically the charge leakage through oxide defects and drain/source contacts. Floating gate nanocrystal nonvolatile memory, FG-NCNVM, is a candidate for future memory because it is advantageous in terms of high-speed write/erase, small size, good scalability, low-voltage, low-power applications, and the capability to store multiple bits per cell. Many studies regarding FG-NCNVMs have been published. Most of them have dealt with fabrication improvements of the devices and device characterizations. Due to the promising FG-NCNVM applications in integrated circuits, there is a need for circuit a simulation model to simulate the electrical characteristics of the floating gate devices. In this thesis, a FG-NCNVM circuit simulation model has been proposed. It is based on the SPICE BSIM simulation model. This model simulates the cell behavior during normal operation. Model validation results have been presented. The SPICE model shows good agreement with experimental results. Current-voltage characteristics, transconductance and unity gain frequency (fT) have been studied showing the effect of the threshold voltage shift (DeltaVth) due to nanocrystal charge on the device characteristics. The threshold voltage shift due to
The Simulation of AN Imaging Gamma-Ray Compton Backscattering Device Using GEANT4
NASA Astrophysics Data System (ADS)
Flechas, D.; Sarmiento, L. G.; Cristancho, F.; Fajardo, E.
2014-02-01
A gamma-backscattering imaging device dubbed Compton Camera, developed at GSI (Darmstadt, Germany) and modified and studied at the Nuclear Physics Group of the National University of Colombia in Bogotá, uses the back-to-back emission of two gamma rays in the positron annihilation to construct a bidimensional image that represents the distribution of matter in the field-of-view of the camera. This imaging capability can be used in a host of different situations, for example, to identify and study deposition and structural defects, and to help locating concealed objects, to name just two cases. In order to increase the understanding of the response of the Compton Camera and, in particular, its image formation process, and to assist in the data analysis, a simulation of the camera was developed using the GEANT4 simulation toolkit. In this work, the images resulting from different experimental conditions are shown. The simulated images and their comparison with the experimental ones already suggest methods to improve the present experimental device
Issues on utility management simulation system for miscellaneous airborne electromechanical devices
NASA Astrophysics Data System (ADS)
Chen, Juan; Liu, Qiaozhen; Wang, Zhanlin
2006-11-01
UMS for miscellaneous airborne electromechanical devices is the part and parcel of VMS. The object of utility management is airborne electromechanical devices which ensure that air engine, avionics and other systems work in order. This paper works over several items about UMS by introducing advanced simulation and its correlative technologies. Firstly, message transmission software of 1553B bus is designed and the bus characteristics are tested. Also, the problem of time synchronization is solved by testing network delay. Secondly, in order to obtain high performance of distributed process ability, heuristic job dispatching algorithm and hydrodynamic load balancing strategy are adopted, which solve the static job dispatch and dynamic job scheduling respectively. The hydrodynamic load balancing strategy is aiming to fulfill the resources usage in the whole system and accomplishes best resources sharing. Thirdly, this paper establishes and realizes the demo environment for visual simulation of the electromechanical subsystems. Adopting tree-mode during the software design makes the system scalable and reconstruction. As multithreading synchronization is resolved, real-time performance of simulation. is ensured during.
A Planar Quantum Transistor Based on 2D-2D Tunneling in Double Quantum Well Heterostructures
Baca, W.E.; Blount, M.A.; Hafich, M.J.; Lyo, S.K.; Moon, J.S.; Reno, J.L.; Simmons, J.A.; Wendt, J.R.
1998-12-14
We report on our work on the double electron layer tunneling transistor (DELTT), based on the gate-control of two-dimensional -- two-dimensional (2D-2D) tunneling in a double quantum well heterostructure. While previous quantum transistors have typically required tiny laterally-defined features, by contrast the DELTT is entirely planar and can be reliably fabricated in large numbers. We use a novel epoxy-bond-and-stop-etch (EBASE) flip-chip process, whereby submicron gating on opposite sides of semiconductor epitaxial layers as thin as 0.24 microns can be achieved. Because both electron layers in the DELTT are 2D, the resonant tunneling features are unusually sharp, and can be easily modulated with one or more surface gates. We demonstrate DELTTs with peak-to-valley ratios in the source-drain I-V curve of order 20:1 below 1 K. Both the height and position of the resonant current peak can be controlled by gate voltage over a wide range. DELTTs with larger subband energy offsets ({approximately} 21 meV) exhibit characteristics that are nearly as good at 77 K, in good agreement with our theoretical calculations. Using these devices, we also demonstrate bistable memories operating at 77 K. Finally, we briefly discuss the prospects for room temperature operation, increases in gain, and high-speed.
Simulation of time-dispersion spectral device with sample spectra accumulation
NASA Astrophysics Data System (ADS)
Zhdanov, Arseny; Khansuvarov, Ruslan; Korol, Georgy
2014-09-01
This research is conducted in order to design a spectral device for light sources power spectrum analysis. The spectral device should process radiation from sources, direct contact with radiation of which is either impossible or undesirable. Such sources include jet blast of an aircraft, optical radiation in metallurgy and textile industry. In proposed spectral device optical radiation is guided out of unfavorable environment via a piece of optical fiber with high dispersion. It is necessary for analysis to make samples of analyzed radiation as short pulses. Dispersion properties of such optical fiber cause spectral decomposition of input optical pulses. The faster time of group delay vary the stronger the spectral decomposition effect. This effect allows using optical fiber with high dispersion as a major element of proposed spectral device. Duration of sample must be much shorter than group delay time difference of a dispersive system. In the given frequency range this characteristic has to be linear. The frequency range is 400 … 500 THz for typical optical fiber. Using photonic-crystal fiber (PCF) gives much wider spectral range for analysis. In this paper we propose simulation of single pulse transmission through dispersive system with linear dispersion characteristic and quadratic-detected output responses accumulation. During simulation we propose studying influence of optical fiber dispersion characteristic angle on spectral measurement results. We also consider pulse duration and group delay time difference impact on output pulse shape and duration. Results show the most suitable dispersion characteristic that allow choosing the structure of PCF - major element of time-dispersion spectral analysis method and required number of samples for reliable assessment of measured spectrum.
Epitaxial 2D SnSe2/ 2D WSe2 van der Waals Heterostructures.
Aretouli, Kleopatra Emmanouil; Tsoutsou, Dimitra; Tsipas, Polychronis; Marquez-Velasco, Jose; Aminalragia Giamini, Sigiava; Kelaidis, Nicolaos; Psycharis, Vassilis; Dimoulas, Athanasios
2016-09-01
van der Waals heterostructures of 2D semiconductor materials can be used to realize a number of (opto)electronic devices including tunneling field effect devices (TFETs). It is shown in this work that high quality SnSe2/WSe2 vdW heterostructure can be grown by molecular beam epitaxy on AlN(0001)/Si(111) substrates using a Bi2Se3 buffer layer. A valence band offset of 0.8 eV matches the energy gap of SnSe2 in such a way that the VB edge of WSe2 and the CB edge of SnSe2 are lined up, making this materials combination suitable for (nearly) broken gap TFETs. PMID:27537619
Simulated workplace protection factors for half-facepiece respiratory protective devices.
Duling, Matthew G; Lawrence, Robert B; Slaven, James E; Coffey, Christopher C
2007-06-01
This study investigates two different methods (random effects model and 5th percentile) for determining the performance of three types of respiratory protective devices (elastomeric N95 respirators, N95 filtering-facepiece respirators, and surgical masks) during a simulated workplace test. This study recalculated the protection level of three types of respiratory protective devices using the random effects model, compared the two methods with each other and the APF of 10 for half-facepiece respirators, and determined the value of each of the fit test protocols in attaining the desired level of simulated workplace protection factor (SWPF). Twenty-five test subjects with varying face sizes tested 15 models of elastomeric N95 respirators, 15 models of N95 filtering-facepiece respirators, and 6 models of surgical masks. Simulated workplace testing was conducted using a TSI PORTACOUNT Plus model 8020 and consisted of a series of seven exercises. Six simulated workplace tests were performed with redonning of the respirator/mask occurring between each test. Each of the six tests produced an SWPF. To determine the level of protection provided by the respiratory protective devices, a 90% lower confidence limit for the simulated workplace protection factor (SWPF(LCL90%)) and the 5th percentile of simulated workplace protection factor were computed. The 5th percentile method values could be up to seven times higher than the SWPF(LCL90%) values. Without fit testing, all half-facepiece N95 respirators had a 5th percentile of 4.6 and an SWPF(LCL90%) value of 2.7. N95 filtering-facepiece respirators as a class had values of 3.3 and 2.0, respectively, whereas N95 elastomeric respirators had values of 7.3 and 4.6, respectively. Surgical masks did not provide any protection, with values of 1.2 and 1.4, respectively. Passing either the Bitrex, saccharin, or Companion fit test resulted in the respirators providing the expected level of protection with 5th percentiles greater than or
Three-dimensional two-fluid Braginskii simulations of the large plasma device
Fisher, Dustin M. Rogers, Barrett N.; Rossi, Giovanni D.; Guice, Daniel S.; Carter, Troy A.
2015-09-15
The Large Plasma Device (LAPD) is modeled using the 3D Global Braginskii Solver code. Comparisons to experimental measurements are made in the low-bias regime in which there is an intrinsic E × B rotation of the plasma. In the simulations, this rotation is caused primarily by sheath effects and may be a likely mechanism for the intrinsic rotation seen in LAPD. Simulations show strong qualitative agreement with the data, particularly the radial dependence of the density fluctuations, cross-correlation lengths, radial flux dependence outside of the cathode edge, and camera imagery. Kelvin Helmholtz (KH) turbulence at relatively large scales is the dominant driver of cross-field transport in these simulations with smaller-scale drift waves and sheath modes playing a secondary role. Plasma holes and blobs arising from KH vortices in the simulations are consistent with the scale sizes and overall appearance of those in LAPD camera images. The addition of ion-neutral collisions in the simulations at previously theorized values reduces the radial particle flux by about a factor of two, from values that are somewhat larger than the experimentally measured flux to values that are somewhat lower than the measurements. This reduction is due to a modest stabilizing contribution of the collisions on the KH-modes driving the turbulent transport.
Pulsed Laser System to Simulate Effects of Cosmic Rays in Semiconductor Devices
NASA Technical Reports Server (NTRS)
Aveline, David C.; Adell, Philippe C.; Allen, Gregory R.; Guertin, Steven M.; McClure, Steven S.
2011-01-01
Spaceflight system electronic devices must survive a wide range of radiation environments with various particle types including energetic protons, electrons, gamma rays, x-rays, and heavy ions. High-energy charged particles such as heavy ions can pass straight through a semiconductor material and interact with a charge-sensitive region, generating a significant amount of charge (electron-hole pairs) along their tracks. These excess charges can damage the device, and the response can range from temporary perturbations to permanent changes in the state or performance. These phenomena are called single event effects (SEE). Before application in flight systems, electronic parts need to be qualified and tested for performance and radiation sensitivity. Typically, their susceptibility to SEE is tested by exposure to an ion beam from a particle accelerator. At such facilities, the device under test (DUT) is irradiated with large beams so there is no fine resolution to investigate particular regions of sensitivity on the parts. While it is the most reliable approach for radiation qualification, these evaluations are time consuming and costly. There is always a need for new cost-efficient strategies to complement accelerator testing: pulsed lasers provide such a solution. Pulsed laser light can be utilized to simulate heavy ion effects with the advantage of being able to localize the sensitive region of an integrated circuit. Generally, a focused laser beam of approximately picosecond pulse duration is used to generate carrier density in the semiconductor device. During irradiation, the laser pulse is absorbed by the electronic medium with a wavelength selected accordingly by the user, and the laser energy can ionize and simulate SEE as would occur in space. With a tightly focused near infrared (NIR) laser beam, the beam waist of about a micrometer can be achieved, and additional scanning techniques are able to yield submicron resolution. This feature allows mapping of all
NASA Astrophysics Data System (ADS)
Tran, Nguyen The
In this study, three dimensional ray tracing simulations are used as a tool for the design and manufacturing of optical sensors and white LED devices. Key experimental results and independent experimental results are used to verify the simulation results and a satisfactory agreement is obtained. In the optical sensor technology, it is required to understand the pattern of propagation of light and the relationship between the collected signal and the detected objects. The Monte Carlo simulation results show for the first time that the response of the optical sensor for detecting particles in suspension depends not only on the concentration but also on the particle size, optical path length, and the optical properties of a particle. Sensor performance limit greatly depends on particle size and optical path length. Simulation results show that the sensor response is more sensitive to the concentration of smaller particle sizes than particle sizes. Single expression for the sensor response to the change of particle concentration of different sizes is presented. The simulation results are compared with individual experimental results to verify the accuracy of the simulations and a satisfactory agreement is obtained. Light propagation in an LED package experiences similar phenomena as in an optical sensor for sediment-concentration measurement: reflection, scattering, and absorption. In the LED packaging, the LED device should have high external quantum efficiency and should provide different patterns of the output light so that it can serve for different applications. The efficiency of an LED device depends on many factors: LED chip structures (size, shapes, and surface types), types of the reflector cup (specular or diffuse), cup geometries, lens geometries and dimension, and optical properties of encapsulant such as refractive indices and transmittance. The simulation results show that the high negative deformed angle chip (HNDA-chip) has a higher light output than
Delays in Admittance-Controlled Haptic Devices Make Simulated Masses Feel Heavier
Kuling, Irene A.; Smeets, Jeroen B. J.; Lammertse, Piet; Onneweer, Bram; Mugge, Winfred
2015-01-01
In an admittance-controlled haptic device, input forces are used to calculate the movement of the device. Although developers try to minimize delays, there will always be delays between the applied force and the corresponding movement in such systems, which might affect what the user of the device perceives. In this experiment we tested whether these delays in a haptic human-robot interaction influence the perception of mass. In the experiment an admittance-controlled manipulator was used to simulate various masses. In a staircase design subjects had to decide which of two virtual masses was heavier after gently pushing them leftward with the right hand in mid-air (no friction, no gravity). The manipulator responded as quickly as possible or with an additional delay (25 or 50 ms) to the forces exerted by the subject on the handle of the haptic device. The perceived mass was ~10% larger for a delay of 25 ms and ~20% larger for a delay of 50 ms. Based on these results, we estimated that the delays that are present in nowadays admittance-controlled haptic devices (up to 20ms) will give an increase in perceived mass which is smaller than the Weber fraction for mass (~10% for inertial mass). Additional analyses showed that the subjects’ decision on mass when the perceptual differences were small did not correlate with intuitive variables such as force, velocity or a combination of these, nor with any other measured variable, suggesting that subjects did not have a consistent strategy during guessing or used other sources of information, for example the efference copy of their pushes. PMID:26361353
Delays in Admittance-Controlled Haptic Devices Make Simulated Masses Feel Heavier.
Kuling, Irene A; Smeets, Jeroen B J; Lammertse, Piet; Onneweer, Bram; Mugge, Winfred
2015-01-01
In an admittance-controlled haptic device, input forces are used to calculate the movement of the device. Although developers try to minimize delays, there will always be delays between the applied force and the corresponding movement in such systems, which might affect what the user of the device perceives. In this experiment we tested whether these delays in a haptic human-robot interaction influence the perception of mass. In the experiment an admittance-controlled manipulator was used to simulate various masses. In a staircase design subjects had to decide which of two virtual masses was heavier after gently pushing them leftward with the right hand in mid-air (no friction, no gravity). The manipulator responded as quickly as possible or with an additional delay (25 or 50 ms) to the forces exerted by the subject on the handle of the haptic device. The perceived mass was ~10% larger for a delay of 25 ms and ~20% larger for a delay of 50 ms. Based on these results, we estimated that the delays that are present in nowadays admittance-controlled haptic devices (up to 20ms) will give an increase in perceived mass which is smaller than the Weber fraction for mass (~10% for inertial mass). Additional analyses showed that the subjects' decision on mass when the perceptual differences were small did not correlate with intuitive variables such as force, velocity or a combination of these, nor with any other measured variable, suggesting that subjects did not have a consistent strategy during guessing or used other sources of information, for example the efference copy of their pushes.
Physiologically Modulating Videogames or Simulations which use Motion-Sensing Input Devices
NASA Technical Reports Server (NTRS)
Pope, Alan T. (Inventor); Stephens, Chad L. (Inventor); Blanson, Nina Marie (Inventor)
2014-01-01
New types of controllers allow players to make inputs to a video game or simulation by moving the entire controller itself. This capability is typically accomplished using a wireless input device having accelerometers, gyroscopes, and an infrared LED tracking camera. The present invention exploits these wireless motion-sensing technologies to modulate the player's movement inputs to the videogame based upon physiological signals. Such biofeedback-modulated video games train valuable mental skills beyond eye-hand coordination. These psychophysiological training technologies enhance personal improvement, not just the diversion, of the user.
Simulation study of x-ray backscatter imaging of pressure-plate improvised explosive devices
NASA Astrophysics Data System (ADS)
van den Heuvel, Johan; Fiore, Franco
2012-06-01
Improvised Explosive Devices (IEDs) triggered by pressure-plates are a serious threat in current theatres of operation. X-ray backscatter imaging (XBI) is a potential method for detecting buried pressure-plates. Monte-Carlo simulation code was developed in-house and has been used to study the potential of XBI for pressure-plate detection. It is shown that pressure-plates can be detected at depths up to 7 cm with high photon energies of 350 keV with reasonable speeds of 1 to 10 km/h. However, spatial resolution is relatively low due to multiple scattering.
NASA Astrophysics Data System (ADS)
Ozaki, T.; Goncharov, P.; Veschev, E.; Sudo, S.; Tamura, N.; ,
2008-03-01
It is very important to investigate the confinement of α particle, which is produced by the nuclear reaction in ITER or fusion reactor. The pellet charge exchange measurement (PCX) is one of the most powerful methods because it can directly provide the profile of α particle energy spectra in plasma. In Large Helical Device (LHD), it is possible to confine the high energetic particle (helium) accelerated by using the ion cyclotron resonance heating (ICH). Therefore it is possible to perform the simulation experiment of α particle diagnostic in LHD.
Modified Dirac Hamiltonian for efficient quantum mechanical simulations of micron sized devices
NASA Astrophysics Data System (ADS)
Habib, K. M. Masum; Sajjad, Redwan N.; Ghosh, Avik W.
2016-03-01
Representing massless Dirac fermions on a spatial lattice poses a potential challenge known as the Fermion Doubling problem. Addition of a quadratic term to the Dirac Hamiltonian provides a possible way to circumvent this problem. We show that the modified Hamiltonian with the additional term results in a very small Hamiltonian matrix when discretized on a real space square lattice. The resulting Hamiltonian matrix is considerably more efficient for numerical simulations without sacrificing on accuracy and is several orders of magnitude faster than the atomistic tight binding model. Using this Hamiltonian and the non-equilibrium Green's function formalism, we show several transport phenomena in graphene, such as magnetic focusing, chiral tunneling in the ballistic limit, and conductivity in the diffusive limit in micron sized graphene devices. The modified Hamiltonian can be used for any system with massless Dirac fermions such as Topological Insulators, opening up a simulation domain that is not readily accessible otherwise.
Jung, Eun-Young; Park, Dong Kyun; Lee, Young Ho; Jo, Hyun Sook; Lim, Yong Su; Park, Rae Woong
2012-05-01
This study confirmed the educational effectiveness of practical exercises (PE) using intravenous (IV) simulators incorporating virtual reality (VR)/haptics (based on the sense of touch) device technologies. First-year nursing students (n=114) were randomly divided into three PE groups: Group A, utilizing a conventional arm model (IV arm); Group B, utilizing a VR/Haptics IV Simulator (IV sim); and Group C, utilizing both the IV arm and IV sim. Group C scored highest on procedures for conducting venipuncture. Group B was more successful in performing injections than Groups A and C. Group C required significantly less time than Group B to complete a venipuncture injection and was faster than Group A, although this difference was not significant. In conclusion, a new paradigm of PE is suggested using both IV sim and IV arm.
Teymurazyan, A.; Pang, G.
2012-03-15
Purpose: Most electronic portal imaging devices (EPIDs) developed so far use a thin Cu plate/phosphor screen to convert x-ray energies into light photons, while maintaining a high spatial resolution. This results in a low x-ray absorption and thus a low quantum efficiency (QE) of approximately 2-4% for megavoltage (MV) x-rays. A significant increase of QE is desirable for applications such as MV cone-beam computed tomography (MV-CBCT). Furthermore, the Cu plate/phosphor screen contains high atomic number (high-Z) materials, resulting in an undesirable over-response to low energy x-rays (due to photoelectric effect) as well as high energy x-rays (due to pair production) when used for dosimetric verification. Our goal is to develop a new MV x-ray detector that has a high QE and uses low-Z materials to overcome the obstacles faced by current MV x-ray imaging technologies. Methods: A new high QE and low-Z EPID is proposed. It consists of a matrix of plastic scintillating fibers embedded in a water-equivalent medium and coupled to an optically sensitive 2D active matrix flat panel imager (AMFPI) for image readout. It differs from the previous approach that uses segmented crystalline scintillators made of higher density and higher atomic number materials to detect MV x-rays. The plastic scintillating fibers are focused toward the x-ray source to avoid image blurring due to oblique incidence of off-axis x-rays. When MV x-rays interact with the scintillating fibers in the detector, scintillation light will be produced. The light photons produced in a fiber core and emitted within the acceptance angle of the fiber will be guided toward the AMFPI by total internal reflection. A Monte Carlo simulation has been used to investigate imaging and dosimetric characteristics of the proposed detector under irradiation of MV x-rays. Results: Properties, such as detection efficiency, modulation transfer function, detective quantum efficiency (DQE), energy dependence of detector
Noise Characteristics of a Four-Jet Impingement Device Inside a Broadband Engine Noise Simulator
NASA Technical Reports Server (NTRS)
Brehm, Christoph; Housman, Jeffrey A.; Kiris, Cetin C.; Hutcheson, Florence V.
2015-01-01
The noise generation mechanisms for four directly impinging supersonic jets are investigated employing implicit large eddy simulations with a higher-order accurate weighted essentially non-oscillatory shock-capturing scheme. Impinging jet devices are often used as an experimental apparatus to emulate a broadband noise source. Although such devices have been used in many experiments, a detailed investigation of the noise generation mechanisms has not been conducted before. Thus, the underlying physical mechanisms that are responsible for the generation of sound waves are not well understood. The flow field is highly complex and contains a wide range of temporal and spatial scales relevant for noise generation. Proper orthogonal decomposition of the flow field is utilized to characterize the unsteady nature of the flow field involving unsteady shock oscillations, large coherent turbulent flow structures, and the sporadic appearance of vortex tubes in the center of the impingement region. The causality method based on Lighthill's acoustic analogy is applied to link fluctuations of flow quantities inside the source region to the acoustic pressure in the far field. It will be demonstrated that the entropy fluctuation term in the Lighthill's stress tensor plays a vital role in the noise generation process. Consequently, the understanding of the noise generation mechanisms is employed to develop a reduced-order linear acoustic model of the four-jet impingement device. Finally, three linear acoustic FJID models are used as broadband noise sources inside an engine nacelle and the acoustic scattering results are validated against far-field acoustic experimental data.
Proposal of tunneling- and diffusion-current hybrid MOSFET: A device simulation study
NASA Astrophysics Data System (ADS)
Furukawa, Kiichi; Teramoto, Akinobu; Kuroda, Rihito; Suwa, Tomoyuki; Hashimoto, Keiichi; Kojiri, Takashi; Sugawa, Shigetoshi
2016-04-01
Transistors with low-power operation and sufficient signal processing speed have been widely required especially for mobile applications. To meet these requirements, we propose a novel tunneling- and diffusion-current hybrid MOSFETs which utilize both a small S-factor of tunneling-current and a high current drivability of diffusion-current. On the basis of the device concept and the working principle that we propose, device structures and parameters of the hybrid MOSFET were examined in detail with device simulation. We investigated the optimum structure of the tunneling and diffusion parts, and the effects of various structural parameters. In particular, we found that the threshold voltage adjustment of each current and the suppression of leakage current were the most important to maximize the characteristics of the hybrid MOSFET. From the result of structural parameter optimization, a minimum S-factor of 20 mV/decade and a high current drivability of 500 µA/µm were obtained simultaneously. In addition, a process flow idea to fabricate three-dimensional structure hybrid MOSFETs with tunneling-current side channels and diffusion-current top channel is presented.
Simulation of the scrape-off layer region of tokamak devices
NASA Astrophysics Data System (ADS)
Ricci, Paolo
2015-04-01
Understanding the key processes occurring in the tokamak scrape-off layer (SOL) is becoming of the outmost importance while we enter the ITER era and we move towards the conception of future fusion reactors. By controlling the heat exhaust, by playing an important role in determining the overall plasma confinement, and by regulating the impurity level in tokamak core, the dynamics of the fusion fuel in the SOL is, in fact, related to some of the most crucial issues that the fusion program is facing today. Because of the limited diagnostic access and in view of predicting the SOL dynamics in future devices, simulations are becoming crucial to address the physics of this region. The present paper, which summarizes the lecture on SOL simulations that was given during the 7th ITER international school (August 25-29, 2014, Aix-en-Provence, France), provides a brief overview of the simulation approaches to the SOL dynamics. First, disentangling the complexity of the system, the key physics processes occurring in the SOL are described. Then, the different simulation approaches to the SOL dynamics are presented, from first-principles kinetic and fluid models, to the phenomenological analysis.
Rieben, Robert N.
2004-01-01
The goal of this dissertation is two-fold. The first part concerns the development of a numerical method for solving Maxwell's equations on unstructured hexahedral grids that employs both high order spatial and high order temporal discretizations. The second part involves the use of this method as a computational tool to perform high fidelity simulations of various electromagnetic devices such as optical transmission lines and photonic crystal structures to yield a level of accuracy that has previously been computationally cost prohibitive. This work is based on the initial research of Daniel White who developed a provably stable, charge and energy conserving method for solving Maxwell's equations in the time domain that is second order accurate in both space and time. The research presented here has involved the generalization of this procedure to higher order methods. High order methods are capable of yielding far more accurate numerical results for certain problems when compared to corresponding h-refined first order methods , and often times at a significant reduction in total computational cost. The first half of this dissertation presents the method as well as the necessary mathematics required for its derivation. The second half addresses the implementation of the method in a parallel computational environment, its validation using benchmark problems, and finally its use in large scale numerical simulations of electromagnetic transmission devices.
Practical Algorithm For Computing The 2-D Arithmetic Fourier Transform
NASA Astrophysics Data System (ADS)
Reed, Irving S.; Choi, Y. Y.; Yu, Xiaoli
1989-05-01
Recently, Tufts and Sadasiv [10] exposed a method for computing the coefficients of a Fourier series of a periodic function using the Mobius inversion of series. They called this method of analysis the Arithmetic Fourier Transform(AFT). The advantage of the AFT over the FN 1' is that this method of Fourier analysis needs only addition operations except for multiplications by scale factors at one stage of the computation. The disadvantage of the AFT as they expressed it originally is that it could be used effectively only to compute finite Fourier coefficients of a real even function. To remedy this the AFT developed in [10] is extended in [11] to compute the Fourier coefficients of both the even and odd components of a periodic function. In this paper, the improved AFT [11] is extended to a two-dimensional(2-D) Arithmetic Fourier Transform for calculating the Fourier Transform of two-dimensional discrete signals. This new algorithm is based on both the number-theoretic method of Mobius inversion of double series and the complex conjugate property of Fourier coefficients. The advantage of this algorithm over the conventional 2-D FFT is that the corner-turning problem needed in a conventional 2-D Discrete Fourier Transform(DFT) can be avoided. Therefore, this new 2-D algorithm is readily suitable for VLSI implementation as a parallel architecture. Comparing the operations of 2-D AFT of a MxM 2-D data array with the conventional 2-D FFT, the number of multiplications is significantly reduced from (2log2M)M2 to (9/4)M2. Hence, this new algorithm is faster than the FFT algorithm. Finally, two simulation results of this new 2-D AFT algorithm for 2-D artificial and real images are given in this paper.
Lee, Cheng-Han; Hsieh, Chih-Chen
2013-01-01
We examined the performance of three microfluidic devices for stretching DNA. The first device is a microchannel with a contraction, and the remaining two are the modifications to the first. The modified designs were made with the help of computer simulations [C. C. Hsieh and T. H. Lin, Biomicrofluidics 5(4), 044106 (2011) and C. C. Hsieh, T. H. Lin, and C. D. Huang, Biomicrofluidics 6, 044105 (2012)] and they were optimized for operating with electric field. In our experiments, we first used DC electric field to stretch DNA. However, the experimental results were not even in qualitative agreement with our simulations. More detailed investigation revealed that DNA molecules adopt a globular conformation in high DC field and therefore become more difficult to stretch. Owing to the similarity between flow field and electric field, we turned to use flow field to stretch DNA with the same devices. The evolution patterns of DNA conformation in flow field were found qualitatively the same as our prediction based on electric field. We analyzed the maximum values, the evolution and the distributions of DNA extension at different Deborah number in each device. We found that the shear and the hydrodynamic interaction have significant influence on the performance of the devices. PMID:24404001
Optical fiber poling by induction: analysis by 2D numerical modeling.
De Lucia, F; Huang, D; Corbari, C; Healy, N; Sazio, P J A
2016-04-15
Since their first demonstration some 25 years ago, thermally poled silica fibers have been used to realize device functions such as electro-optic modulation, switching, polarization-entangled photons, and optical frequency conversion with a number of advantages over bulk free-space components. We have recently developed an innovative induction poling technique that could allow for the development of complex microstructured fiber geometries for highly efficient χ(2)-based device applications. To systematically implement these more advanced poled fiber designs, we report here the development of comprehensive numerical models of the induction poling mechanism itself via two-dimensional (2D) simulations of ion migration and space-charge region formation using finite element analysis. PMID:27082323
2D-2D tunneling field-effect transistors using WSe2/SnSe2 heterostructures
NASA Astrophysics Data System (ADS)
Roy, Tania; Tosun, Mahmut; Hettick, Mark; Ahn, Geun Ho; Hu, Chenming; Javey, Ali
2016-02-01
Two-dimensional materials present a versatile platform for developing steep transistors due to their uniform thickness and sharp band edges. We demonstrate 2D-2D tunneling in a WSe2/SnSe2 van der Waals vertical heterojunction device, where WSe2 is used as the gate controlled p-layer and SnSe2 is the degenerately n-type layer. The van der Waals gap facilitates the regulation of band alignment at the heterojunction, without the necessity of a tunneling barrier. ZrO2 is used as the gate dielectric, allowing the scaling of gate oxide to improve device subthreshold swing. Efficient gate control and clean interfaces yield a subthreshold swing of ˜100 mV/dec for >2 decades of drain current at room temperature, hitherto unobserved in 2D-2D tunneling devices. The subthreshold swing is independent of temperature, which is a clear signature of band-to-band tunneling at the heterojunction. A maximum switching ratio ION/IOFF of 107 is obtained. Negative differential resistance in the forward bias characteristics is observed at 77 K. This work bodes well for the possibilities of two-dimensional materials for the realization of energy-efficient future-generation electronics.
Simulation of electrical discharge in a 3.6 Joule miniature plasma focus device using SIMULINK
NASA Astrophysics Data System (ADS)
Jafari, Hossein; Habibi, Morteza
2014-08-01
A novel technique has been developed and studied in this paper to simulate the electrical discharge circuit of a 3.6 J miniature plasma focus device (PFD) and investigate the effect of inductance variation on voltage spike and current dip. The technique is based on a correlation between the electrical discharge circuit and plasma dynamics in a very small PFD that operates at the energy of 3.6 J. The simulation inputs include the charging voltage, capacitor bank capacitance, current limiter resistance, by-pass resistance as well as the time-dependent inductance and resistance of the plasma sheath which are calculated by assuming the plasma dynamics as transit times in going from one phase to the next. The variations of the most important elements in the circuit (i.e. the constant and breakdown inductances) and their effects on the current dip are studied in PFDs with low and high constant inductance. The model demonstrated for achieving a good pinch in the PFD, although the total inductance of the system should be low; however there is always an optimum inductance which causes an appropriate pinch. Furthermore, the electrical power produced by the pulsed power supply, the mechanical energy as well as the magnetic energy which are transferred into the plasma tube were obtained from simulation. The graph of electrical power demonstrated a high instantaneous increment in the power transferred into the plasma as one of the greatest advantages of the pulsed power supply. The simulation was performed using software tools within the MATLAB/SIMULINK simulation environment.
Efficient Multi-Dimensional Simulation of Quantum Confinement Effects in Advanced MOS Devices
NASA Technical Reports Server (NTRS)
Biegel, Bryan A.; Ancona, Mario G.; Rafferty, Conor S.; Yu, Zhiping
2000-01-01
We investigate the density-gradient (DG) transport model for efficient multi-dimensional simulation of quantum confinement effects in advanced MOS devices. The formulation of the DG model is described as a quantum correction ot the classical drift-diffusion model. Quantum confinement effects are shown to be significant in sub-100nm MOSFETs. In thin-oxide MOS capacitors, quantum effects may reduce gate capacitance by 25% or more. As a result, the inclusion of quantum effects may reduce gate capacitance by 25% or more. As a result, the inclusion of quantum effects in simulations dramatically improves the match between C-V simulations and measurements for oxide thickness down to 2 nm. Significant quantum corrections also occur in the I-V characteristics of short-channel (30 to 100 nm) n-MOSFETs, with current drive reduced by up to 70%. This effect is shown to result from reduced inversion charge due to quantum confinement of electrons in the channel. Also, subthreshold slope is degraded by 15 to 20 mV/decade with the inclusion of quantum effects via the density-gradient model, and short channel effects (in particular, drain-induced barrier lowering) are noticeably increased.
Efficient Multi-Dimensional Simulation of Quantum Confinement Effects in Advanced MOS Devices
NASA Technical Reports Server (NTRS)
Biegel, Bryan A.; Rafferty, Conor S.; Ancona, Mario G.; Yu, Zhi-Ping
2000-01-01
We investigate the density-gradient (DG) transport model for efficient multi-dimensional simulation of quantum confinement effects in advanced MOS devices. The formulation of the DG model is described as a quantum correction to the classical drift-diffusion model. Quantum confinement effects are shown to be significant in sub-100nm MOSFETs. In thin-oxide MOS capacitors, quantum effects may reduce gate capacitance by 25% or more. As a result, the inclusion or quantum effects in simulations dramatically improves the match between C-V simulations and measurements for oxide thickness down to 2 nm. Significant quantum corrections also occur in the I-V characteristics of short-channel (30 to 100 nm) n-MOSFETs, with current drive reduced by up to 70%. This effect is shown to result from reduced inversion charge due to quantum confinement of electrons in the channel. Also, subthreshold slope is degraded by 15 to 20 mV/decade with the inclusion of quantum effects via the density-gradient model, and short channel effects (in particular, drain-induced barrier lowering) are noticeably increased.
A multicomb variance reduction scheme for Monte Carlo semiconductor simulators
Gray, M.G.; Booth, T.E.; Kwan, T.J.T.; Snell, C.M.
1998-04-01
The authors adapt a multicomb variance reduction technique used in neutral particle transport to Monte Carlo microelectronic device modeling. They implement the method in a two-dimensional (2-D) MOSFET device simulator and demonstrate its effectiveness in the study of hot electron effects. The simulations show that the statistical variance of hot electrons is significantly reduced with minimal computational cost. The method is efficient, versatile, and easy to implement in existing device simulators.
Schulz-Wendtland, R; Bani, M; Lux, M P; Schwab, S; Loehberg, C R; Jud, S M; Rauh, C; Bayer, C M; Beckmann, M W; Uder, M; Fasching, P A; Adamietz, B; Meier-Meitinger, M
2012-05-01
Purpose: Experimental study of a new system for digital 2D and 3D full-field mammography (FFDM) using a high resolution detector based on two shifts of a-Se. Material and Methods: Images were acquired using the new FFDM system Amulet® (FujiFilm, Tokio, Japan), an a-Se detector (receptor 24 × 30 cm(2), pixel size 50 µm, memory depth 12 bit, spatial resolution 10 lp/mm, DQE > 0.50). Integrated in the detector is a new method for data transfer, based on optical switch technology. The object of investigation was the Wisconsin Mammographic Random Phantom, Model 152A (Radiation Measurement Inc., Middleton, WI, USA) and the same parameters and exposure data (Tungsten, 100 mAs, 30 kV) were consistently used. We acquired 3 different pairs of images in the c-c and ml planes (2D) and in the c-c and c-c planes with an angle of 4 degrees (3D). Five radiologists experienced in mammography (experience ranging from 3 months to more than 5 years) analyzed the images (monitoring) which had been randomly encoded (random generator) with regard to the recognition of details such as specks of aluminum oxide (200-740 µm), nylon fibers (0.4-1.6 mm) and round lesions/masses (diameters 5-14 mm), using special linear glasses for 3D visualization, and compared the results. Results: A total of 225 correct positive decisions could be detected: we found 222 (98.7 %) correct positive results for 2D and 3D visualization in each case. Conclusion: The results of this phantom study showed the same detection rates for both 2D and 3D imaging using full field digital mammography. Our results must be confirmed in further clinical trials.
QED-1 device and measurements of gettering efficiency for a simulated divertor plasma
Owens, D.K.; Yamada, M.
1980-03-01
The QED-1 device at PPL has provided gettering efficiency data for neutralized hydrogen plasma on titanium. The hollow-anode arcjet produces a plasma column 1 cm in diameter with 10/sup 12/ < n/s