2D/1D approximations to the 3D neutron transport equation. I: Theory
Kelley, B. W.; Larsen, E. W.
2013-07-01
A new class of '2D/1D' approximations is proposed for the 3D linear Boltzmann equation. These approximate equations preserve the exact transport physics in the radial directions x and y and diffusion physics in the axial direction z. Thus, the 2D/1D equations are more accurate approximations of the 3D Boltzmann equation than the conventional 3D diffusion equation. The 2D/1D equations can be systematically discretized, to yield accurate simulation methods for 3D reactor core problems. The resulting solutions will be more accurate than 3D diffusion solutions, and less expensive to generate than standard 3D transport solutions. In this paper, we (i) show that the simplest 2D/1D equation has certain desirable properties, (ii) systematically discretize this equation, and (iii) derive a stable iteration scheme for solving the discrete system of equations. In a companion paper [1], we give numerical results that confirm the theoretical predictions of accuracy and iterative stability. (authors)
2D/1D approximations to the 3D neutron transport equation. II: Numerical comparisons
Kelley, B. W.; Collins, B.; Larsen, E. W.
2013-07-01
In a companion paper [1], (i) several new '2D/1D equations' are introduced as accurate approximations to the 3D Boltzmann transport equation, (ii) the simplest of these approximate equations is systematically discretized, and (iii) a theoretically stable iteration scheme is developed to solve the discrete equations. In this paper, numerical results are presented that confirm the theoretical predictions made in [1]. (authors)
A 2D/1D coupling neutron transport method based on the matrix MOC and NEM methods
Zhang, H.; Zheng, Y.; Wu, H.; Cao, L.
2013-07-01
A new 2D/1D coupling method based on the matrix MOC method (MMOC) and nodal expansion method (NEM) is proposed for solving the three-dimensional heterogeneous neutron transport problem. The MMOC method, used for radial two-dimensional calculation, constructs a response matrix between source and flux with only one sweep and then solves the linear system by using the restarted GMRES algorithm instead of the traditional trajectory sweeping process during within-group iteration for angular flux update. Long characteristics are generated by using the customization of commercial software AutoCAD. A one-dimensional diffusion calculation is carried out in the axial direction by employing the NEM method. The 2D and ID solutions are coupled through the transverse leakage items. The 3D CMFD method is used to ensure the global neutron balance and adjust the different convergence properties of the radial and axial solvers. A computational code is developed based on these theories. Two benchmarks are calculated to verify the coupling method and the code. It is observed that the corresponding numerical results agree well with references, which indicates that the new method is capable of solving the 3D heterogeneous neutron transport problem directly. (authors)
NASA Astrophysics Data System (ADS)
Moustafa, Salli; Févotte, François; Lathuilière, Bruno; Plagne, Laurent
2014-06-01
The past few years have been marked by a noticeable increase in the interest in 3D whole-core heterogeneous deterministic neutron transport solvers for reference calculations. Due to the extremely large problem sizes tackled by such solvers, they need to use adapted numerical methods and need to be efficiently implemented to take advantage of the full computing power of modern systems. As for numerical methods, one possible approach consists in iterating over resolutions of 2D and 1D MOC problems by taking advantage of prismatic geometries. The MICADO solver, developed at EDF R&D, is a parallel implementation of such a method in distributed and shared memory systems. However it is currently unable to use SIMD vectorization to leverage the full computing power of modern CPUs. In this paper, we describe our first effort to support vectorization in MICADO, typically targeting Intel© SSE CPUs. Both the 2D and 1D algorithms are vectorized, allowing for high expected speedups for the whole spatial solver. We present benchmark computations, which show nearly optimal speedups for our vectorized implementation on the TAKEDA case.
Fevotte, F.; Lathuiliere, B.
2013-07-01
The large increase in computing power over the past few years now makes it possible to consider developing 3D full-core heterogeneous deterministic neutron transport solvers for reference calculations. Among all approaches presented in the literature, the method first introduced in [1] seems very promising. It consists in iterating over resolutions of 2D and ID MOC problems by taking advantage of prismatic geometries without introducing approximations of a low order operator such as diffusion. However, before developing a solver with all industrial options at EDF, several points needed to be clarified. In this work, we first prove the convergence of this iterative process, under some assumptions. We then present our high-performance, parallel implementation of this algorithm in the MICADO solver. Benchmarking the solver against the Takeda case shows that the 2D-1D coupling algorithm does not seem to affect the spatial convergence order of the MOC solver. As for performance issues, our study shows that even though the data distribution is suited to the 2D solver part, the efficiency of the ID part is sufficient to ensure a good parallel efficiency of the global algorithm. After this study, the main remaining difficulty implementation-wise is about the memory requirement of a vector used for initialization. An efficient acceleration operator will also need to be developed. (authors)
2010-02-01
Neutron transport, calculation of multiplication factor and neutron fluxes in 2-D configurations: cell calculations, 2-D diffusion and transport, and burnup. Preparation of a cross section library for the code BOXER from a basic library in ENDF/B format (ETOBOX).
Ion Transport in 2-D Graphene Nanochannels
NASA Astrophysics Data System (ADS)
Xie, Quan; Foo, Elbert; Duan, Chuanhua
2015-11-01
Graphene membranes have recently attracted wide attention due to its great potential in water desalination and selective molecular sieving. Further developments of these membranes, including enhancing their mass transport rate and/or molecular selectivity, rely on the understanding of fundamental transport mechanisms through graphene membranes, which has not been studied experimentally before due to fabrication and measurement difficulties. Herein we report the fabrication of the basic constituent of graphene membranes, i.e. 2-D single graphene nanochannels (GNCs) and the study of ion transport in these channels. A modified bonding technique was developed to form GNCs with well-defined geometry and uniform channel height. Ion transport in such GNCs was studied using DC conductance measurement. Our preliminary results showed that the ion transport in GNCs is still governed by surface charge at low concentrations (10-6M to 10-4M). However, GNCs exhibits much higher ionic conductances than silica nanochannels with the same geometries in the surface-charge-governed regime. This conductance enhancement can be attributed to the pre-accumulation of charges on graphene surfaces. The work is supported by the Faculty Startup Fund (Boston University, USA).
A large 2D PSD for thermal neutron detection
NASA Astrophysics Data System (ADS)
Knott, R. B.; Smith, G. C.; Watt, G.; Boldeman, J. W.
1997-02-01
A 2D PSD based on a MWPC has been constructed for a small angle neutron scattering instrument. The active area of the detector was 640 × 640 mm 2. To meet the specifications for neutron detection efficiency and spatial resolution, and to minimise parallax, the gas mixture was 190 kPa 3He plus 100 kPa CF 4, and the active volume had a thickness of 30 mm. The design maximum neutron count rate of the detector was 10 5 events per secod. The (calculated) neutron detection efficiency was 60% for 2 Å neutrons and the (measured) neutron energy resolution on the anode grid was typically 20% (fwhm). The location of a neutron detection event within the active area was determined using the wire-by-wire method: the spatial resolution (5 × 5 mm 2) was thereby defined by the wire geometry. A 16-channel charge-sensitive preamplifier/amplifier/comparator module has been developed with a channel sensitivity of 0.1 V/fC, noise line width of 0.4 fC (fwhm) and channel-to-channel cross-talk of less than 5%. The Proportional Counter Operating System (PCOS III) (LeCroy Corp, USA) was used for event encoding. The ECL signals produced by the 16 channel modules were latched in PCOS III by a trigger pulse from the anode and the fast encoders produce a position and width for each event. The information was transferred to a UNIX workstation for accumulation and online display.
Grazing incidence neutron diffraction from large scale 2D structures
Toperverg, B. P.; Felcher, G. P.; Metlushko, V. V.; Leiner, V.; Siebrecht, R.; Nikonov, O.
2000-01-13
The distorted wave Born approximation (DWBA) is applied to evaluate the diffraction pattern of neutrons (or X-rays) from a 2D array of dots deposited onto a dissimilar substrate. With the radiation impinging on the surface at a grazing incidence angle {alpha}, the intensities diffracted both in and out the plane of specular reflection are calculated as a function of the periodicity of the array, height and diameter of the dots. The results are presented in the form of diffracted intensity contours in a plane with coordinates {alpha} and {alpha}{prime}, the latter being the glancing angle of scattering. The optimization of the experimental conditions for polarized neutron experiments on submicron dots is discussed. The feasibility of such measurements is confirmed by a test experiment.
Parallel algorithms for 2-D cylindrical transport equations of Eigenvalue problem
Wei, J.; Yang, S.
2013-07-01
In this paper, aimed at the neutron transport equations of eigenvalue problem under 2-D cylindrical geometry on unstructured grid, the discrete scheme of Sn discrete ordinate and discontinuous finite is built, and the parallel computation for the scheme is realized on MPI systems. Numerical experiments indicate that the designed parallel algorithm can reach perfect speedup, it has good practicality and scalability. (authors)
A New 2D-Transport, 1D-Diffusion Approximation of the Boltzmann Transport equation
Larsen, Edward
2013-06-17
The work performed in this project consisted of the derivation, implementation, and testing of a new, computationally advantageous approximation to the 3D Boltz- mann transport equation. The solution of the Boltzmann equation is the neutron flux in nuclear reactor cores and shields, but solving this equation is difficult and costly. The new “2D/1D” approximation takes advantage of a special geometric feature of typical 3D reactors to approximate the neutron transport physics in a specific (ax- ial) direction, but not in the other two (radial) directions. The resulting equation is much less expensive to solve computationally, and its solutions are expected to be sufficiently accurate for many practical problems. In this project we formulated the new equation, discretized it using standard methods, developed a stable itera- tion scheme for solving the equation, implemented the new numerical scheme in the MPACT code, and tested the method on several realistic problems. All the hoped- for features of this new approximation were seen. For large, difficult problems, the resulting 2D/1D solution is highly accurate, and is calculated about 100 times faster than a 3D discrete ordinates simulation.
Transport Experiments on 2D Correlated Electron Physics in Semiconductors
Tsui, Daniel
2014-03-24
This research project was designed to investigate experimentally the transport properties of the 2D electrons in Si and GaAs, two prototype semiconductors, in several new physical regimes that were previously inaccessible to experiments. The research focused on the strongly correlated electron physics in the dilute density limit, where the electron potential energy to kinetic energy ratio rs>>1, and on the fractional quantum Hall effect related physics in nuclear demagnetization refrigerator temperature range on samples with new levels of purity and controlled random disorder.
Parameterising root system growth models using 2D neutron radiography images
NASA Astrophysics Data System (ADS)
Schnepf, Andrea; Felderer, Bernd; Vontobel, Peter; Leitner, Daniel
2013-04-01
Root architecture is a key factor for plant acquisition of water and nutrients from soil. In particular in view of a second green revolution where the below ground parts of agricultural crops are important, it is essential to characterise and quantify root architecture and its effect on plant resource acquisition. Mathematical models can help to understand the processes occurring in the soil-plant system, they can be used to quantify the effect of root and rhizosphere traits on resource acquisition and the response to environmental conditions. In order to do so, root architectural models are coupled with a model of water and solute transport in soil. However, dynamic root architectural models are difficult to parameterise. Novel imaging techniques such as x-ray computed tomography, neutron radiography and magnetic resonance imaging enable the in situ visualisation of plant root systems. Therefore, these images facilitate the parameterisation of dynamic root architecture models. These imaging techniques are capable of producing 3D or 2D images. Moreover, 2D images are also available in the form of hand drawings or from images of standard cameras. While full 3D imaging tools are still limited in resolutions, 2D techniques are a more accurate and less expensive option for observing roots in their environment. However, analysis of 2D images has additional difficulties compared to the 3D case, because of overlapping roots. We present a novel algorithm for the parameterisation of root system growth models based on 2D images of root system. The algorithm analyses dynamic image data. These are a series of 2D images of the root system at different points in time. Image data has already been adjusted for missing links and artefacts and segmentation was performed by applying a matched filter response. From this time series of binary 2D images, we parameterise the dynamic root architecture model in the following way: First, a morphological skeleton is derived from the binary
A velocity-dependent anomalous radial transport model for (2-D, 2-V) kinetic transport codes
NASA Astrophysics Data System (ADS)
Bodi, Kowsik; Krasheninnikov, Sergei; Cohen, Ron; Rognlien, Tom
2008-11-01
Plasma turbulence constitutes a significant part of radial plasma transport in magnetically confined plasmas. This turbulent transport is modeled in the form of anomalous convection and diffusion coefficients in fluid transport codes. There is a need to model the same in continuum kinetic edge codes [such as the (2-D, 2-V) transport version of TEMPEST, NEO, and the code being developed by the Edge Simulation Laboratory] with non-Maxwellian distributions. We present an anomalous transport model with velocity-dependent convection and diffusion coefficients leading to a diagonal transport matrix similar to that used in contemporary fluid transport models (e.g., UEDGE). Also presented are results of simulations corresponding to radial transport due to long-wavelength ExB turbulence using a velocity-independent diffusion coefficient. A BGK collision model is used to enable comparison with fluid transport codes.
Coupling 2-D cylindrical and 3-D x-y-z transport computations
Abu-Shumays, I.K.; Yehnert, C.E.; Pitcairn, T.N.
1998-06-30
This paper describes a new two-dimensional (2-D) cylindrical geometry to three-dimensional (3-D) rectangular x-y-z splice option for multi-dimensional discrete ordinates solutions to the neutron (photon) transport equation. Of particular interest are the simple transformations developed and applied in order to carry out the required spatial and angular interpolations. The spatial interpolations are linear and equivalent to those applied elsewhere. The angular interpolations are based on a high order spherical harmonics representation of the angular flux. Advantages of the current angular interpolations over previous work are discussed. An application to an intricate streaming problem is provided to demonstrate the advantages of the new method for efficient and accurate prediction of particle behavior in complex geometries.
A feasibility study using radiochromic films for fast neutron 2D passive dosimetry
Brady, Samuel L; Gunasingha, Rathnayaka; Yoshizumi, Terry T; Howell, Calvin R; Crowell, Alexander S; Fallin, Brent; Tonchev, Anton P; Dewhirst, Mark W
2013-01-01
The objective of this paper is threefold: (1) to establish sensitivity of XRQA and EBT radiochromic films to fast neutron exposure; (2) to develop a film response to radiation dose calibration curve and (3) to investigate a two-dimensional (2D) film dosimetry technique for use in establishing an experimental setup for a radiobiological irradiation of mice and to assess the dose to the mice in this setup. The films were exposed to a 10 MeV neutron beam via the 2H(d,n)3He reaction. The XRQA film response was a factor of 1.39 greater than EBT film response to the 10 MeV neutron beam when exposed to a neutron dose of 165 cGy. A film response-to-soft tissue dose calibration function was established over a range of 0–10 Gy and had a goodness of fit of 0.9926 with the calibration data. The 2D film dosimetry technique estimated the neutron dose to the mice by measuring the dose using a mouse phantom and by placing a piece of film on the exterior of the experimental mouse setup. The film results were benchmarked using Monte Carlo and aluminum (Al) foil activation measurements. The radiochromic film, Monte Carlo and Al foil dose measurements were strongly correlated, and the film within the mouse phantom agreed to better than 7% of the externally mounted films. These results demonstrated the potential application of radiochromic films for passive 2D neutron dosimetry. PMID:20693612
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.
Active transport and cluster formation on 2D networks.
Greulich, P; Santen, L
2010-06-01
We introduce a model for active transport on inhomogeneous networks embedded in a diffusive environment which is motivated by vesicular transport on actin filaments. In the presence of a hard-core interaction, particle clusters are observed that exhibit an algebraically decaying distribution in a large parameter regime, indicating the existence of clusters on all scales. The scale-free behavior can be understood by a mechanism promoting preferential attachment of particles to large clusters. The results are compared with a diffusion-limited aggregation model and active transport on a regular network. For both models we observe aggregation of particles to clusters which are characterized by a finite size scale if the relevant time scales and particle densities are considered. PMID:20556462
Initial global 2-D shielding analysis for the Advanced Neutron Source core and reflector
Bucholz, J.A.
1995-08-01
This document describes the initial global 2-D shielding analyses for the Advanced Neutron Source (ANS) reactor, the D{sub 2}O reflector, the reflector vessel, and the first 200 mm of light water beyond the reflector vessel. Flux files generated here will later serve as source terms in subsequent shielding analyses. In addition to reporting fluxes and other data at key points of interest, a major objective of this report was to document how these analyses were performed, the phenomena that were included, and checks that were made to verify that these phenomena were properly modeled. In these shielding analyses, the fixed neutron source distribution in the core was based on the `lifetime-averaged` spatial power distribution. Secondary gamma production cross sections in the fuel were modified so as to account intrinsically for delayed fission gammas in the fuel as well as prompt fission gammas. In and near the fuel, this increased the low-energy gamma fluxes by 50 to 250%, but out near the reflector vessel, these same fluxes changed by only a few percent. Sensitivity studies with respect to mesh size were performed, and a new 2-D mesh distribution developed after some problems were discovered with respect to the use of numerous elongated mesh cells in the reflector. All of the shielding analyses were performed sing the ANSL-V 39n/44g coupled library with 25 thermal neutron groups in order to obtain a rigorous representation of the thermal neutron spectrum throughout the reflector. Because of upscatter in the heavy water, convergence was very slow. Ultimately, the fission cross section in the various materials had to be artificially modified in order to solve this fixed source problem as an eigenvalue problem and invoke the Vondy error-mode extrapolation technique which greatly accelerated convergence in the large 2-D RZ DORT analyses. While this was quite effective, 150 outer iterations (over energy) were still required.
Screening and transport in 2D semiconductor systems at low temperatures
Das Sarma, S.; Hwang, E. H.
2015-01-01
Low temperature carrier transport properties in 2D semiconductor systems can be theoretically well-understood within RPA-Boltzmann theory as being limited by scattering from screened Coulomb disorder arising from random quenched charged impurities in the environment. In this work, we derive a number of analytical formula, supported by realistic numerical calculations, for the relevant density, mobility, and temperature range where 2D transport should manifest strong intrinsic (i.e., arising purely from electronic effects) metallic temperature dependence in different semiconductor materials arising entirely from the 2D screening properties, thus providing an explanation for why the strong temperature dependence of the 2D resistivity can only be observed in high-quality and low-disorder 2D samples and also why some high-quality 2D materials manifest much weaker metallicity than other materials. We also discuss effects of interaction and disorder on the 2D screening properties in this context as well as compare 2D and 3D screening functions to comment why such a strong intrinsic temperature dependence arising from screening cannot occur in 3D metallic carrier transport. Experimentally verifiable predictions are made about the quantitative magnitude of the maximum possible low-temperature metallicity in 2D systems and the scaling behavior of the temperature scale controlling the quantum to classical crossover. PMID:26572738
Coupled Neutron Transport for HZETRN
NASA Technical Reports Server (NTRS)
Slaba, Tony C.; Blattnig, Steve R.
2009-01-01
Exposure estimates inside space vehicles, surface habitats, and high altitude aircrafts exposed to space radiation are highly influenced by secondary neutron production. The deterministic transport code HZETRN has been identified as a reliable and efficient tool for such studies, but improvements to the underlying transport models and numerical methods are still necessary. In this paper, the forward-backward (FB) and directionally coupled forward-backward (DC) neutron transport models are derived, numerical methods for the FB model are reviewed, and a computationally efficient numerical solution is presented for the DC model. Both models are compared to the Monte Carlo codes HETC-HEDS, FLUKA, and MCNPX, and the DC model is shown to agree closely with the Monte Carlo results. Finally, it is found in the development of either model that the decoupling of low energy neutrons from the light particle transport procedure adversely affects low energy light ion fluence spectra and exposure quantities. A first order correction is presented to resolve the problem, and it is shown to be both accurate and efficient.
Effects of magnetic impurities on transport in 2D topological insulators
NASA Astrophysics Data System (ADS)
Dang, Xiaoqian; Burton, J. D.; Tsymbal, Evgeny
Understanding the transport properties of topological insulators could bring such materials from fundamental research to potential applications. Here we report on the theoretical investigations of the effects of magnetic impurities on transport properties of model two-dimensional (2D) topological insulators (TIs). We utilize the tight-binding form of the Bernevig-Hughes-Zhang model and investigate the transport properties by employing the Landauer-Büttiker formalism. We explore the current distribution in 2D TIs resulting from scattering by a magnetic impurity which breaks time-reversal symmetry. We find that a magnetic impurity could drive anti-resonant behavior of the conductance, as revealed from full backscattering of the electron current flowing at one of the edges of the TI. This phenomenon occurs due to spin-flip scattering when the Fermi energy matches the impurity state and the magnetic moment of the impurity is aligned along the TI edge. Additionally, we explore the effect of an external magnetic gate attached to the system and show that changing the magnetization orientation within the gate allows the control of conductance. This geometric setup could be realized experimentally providing the opportunity to tune transport properties of 2D TIs by a magnetic gate.
Impact of high speed civil transports on stratospheric ozone: A 2-D model investigation
Kinnison, D.E.; Connell, P.S.
1996-12-01
This study investigates the effect on stratospheric ozone from a fleet of proposed High Speed Civil Transports (HSCTs). The new LLNL 2-D operator-split chemical-radiative-transport model of the troposphere and stratosphere is used for this HSCT investigation. This model is integrated in a diurnal manner, using an implicit numerical solver. Therefore, rate coefficients are not modified by any sort of diurnal average factor. This model also does not make any assumptions on lumping of chemical species into families. Comparisons to previous model-derived HSCT assessment of ozone change are made, both to the previous LLNL 2-D model and to other models from the international assessment modeling community. The sensitivity to the NO{sub x} emission index and sulfate surface area density is also explored.
Assessment of the 2D MOC solver in MPACT: Michigan parallel characteristics transport code
Collins, B.; Kochunas, B.; Downar, T.
2013-07-01
MPACT (Michigan Parallel Characteristics Transport Code) is a new reactor analysis tool being developed by researchers at the University of Michigan as an advanced pin-resolved transport capability within VERA (Virtual Environment for Reactor Analysis). VERA is the end-user reactor simulation tool being developed by the Consortium for the Advanced Simulation of Light Water Reactors (CASL). The MPACT development project is itself unique for the way it is changing how students perform research to achieve the instructional and research goals of an academic institution, while providing immediate value to the industry. One of the major computational pieces in MPACT is the 2D MOC solver. It is critical that the 2D MOC solver provide an efficient, accurate, and robust solution over a broad range of reactor operating conditions. The C5G7 benchmark is first used to test the accuracy of the method with a fixed set of cross-sections. The VERA Core Physics Progression Problems are then used to compare the accuracy of both the 2D transport solver and also the cross-section treatments. (authors)
Wall surface temperature calculation in the SolEdge2D-EIRENE transport code
NASA Astrophysics Data System (ADS)
Denis, J.; Pégourié, B.; Bucalossi, J.; Bufferand, H.; Ciraolo, G.; Gardarein, J.-L.; Gaspar, J.; Grisolia, C.; Hodille, E.; Missirlian, M.; Serre, E.; Tamain, P.
2016-02-01
A thermal wall model is developed for the SolEdge2D-EIRENE edge transport code for calculating the surface temperature of the actively-cooled vessel components in interaction with the plasma. This is a first step towards a self-consistent evaluation of the recycling of particles, which depends on the wall surface temperature. The proposed thermal model is built to match both steady-state temperature and time constant of actively-cooled plasma facing components. A benchmark between this model and the Finite Element Modelling code CAST3M is performed in the case of an ITER-like monoblock. An example of application is presented for a SolEdge2D-EIRENE simulation of a medium-power discharge in the WEST tokamak, showing the steady-state wall temperature distribution and the temperature cycling due to an imposed Edge Localised Mode-like event.
Transport studies in 2D transition metal dichalcogenides and black phosphorus.
Du, Yuchen; Neal, Adam T; Zhou, Hong; Ye, Peide D
2016-07-01
Two-dimensional (2D) materials are a new family of materials with interesting physical properties, ranging from insulating hexagonal boron nitride, semiconducting or semi-metallic transition metal dichalcogenides, to gapless metallic graphene. In this review, we provide a brief discussion of transport studies in transition metal dichalcogenides, including both semiconducting and semi-metallic phases, as well as a discussion of the newly emerged narrow bandgap layered material, black phosphorus, in terms of its electrical and quantum transport properties at room and cryogenic temperatures. Ultra-thin layered channel materials with atomic layer thickness in the cross-plane direction, together with relatively high carrier mobility with appropriate passivation techniques, provide the promise for new scientific discoveries and broad device applications. PMID:27187790
Transport studies in 2D transition metal dichalcogenides and black phosphorus
NASA Astrophysics Data System (ADS)
Du, Yuchen; Neal, Adam T.; Zhou, Hong; Ye, Peide D.
2016-07-01
Two-dimensional (2D) materials are a new family of materials with interesting physical properties, ranging from insulating hexagonal boron nitride, semiconducting or semi-metallic transition metal dichalcogenides, to gapless metallic graphene. In this review, we provide a brief discussion of transport studies in transition metal dichalcogenides, including both semiconducting and semi-metallic phases, as well as a discussion of the newly emerged narrow bandgap layered material, black phosphorus, in terms of its electrical and quantum transport properties at room and cryogenic temperatures. Ultra-thin layered channel materials with atomic layer thickness in the cross-plane direction, together with relatively high carrier mobility with appropriate passivation techniques, provide the promise for new scientific discoveries and broad device applications.
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.
A 2-D Test Problem for CFD Modeling Heat Transfer in Spent Fuel Transfer Cask Neutron Shields
Zigh, Ghani; Solis, Jorge; Fort, James A.
2011-01-14
In the United States, commercial spent nuclear fuel is typically moved from spent fuel pools to outdoor dry storage pads within a transfer cask system that provides radiation shielding to protect personnel and the surrounding environment. The transfer casks are cylindrical steel enclosures with integral gamma and neutron radiation shields. Since the transfer cask system must be passively cooled, decay heat removal from spent nuclear fuel canister is limited by the rate of heat transfer through the cask components, and natural convection from the transfer cask surface. The primary mode of heat transfer within the transfer cask system is conduction, but some cask designs incorporate a liquid neutron shield tank surrounding the transfer cask structural shell. In these systems, accurate prediction of natural convection within the neutron shield tank is an important part of assessing the overall thermal performance of the transfer cask system. The large-scale geometry of the neutron shield tank, which is typically an annulus approximately 2 meters in diameter but only 5-10 cm in thickness, and the relatively small scale velocities (typically less than 5 cm/s) represent a wide range of spatial and temporal scales that contribute to making this a challenging problem for computational fluid dynamics (CFD) modeling. Relevant experimental data at these scales are not available in the literature, but some recent modeling studies offer insights into numerical issues and solutions; however, the geometries in these studies, and for the experimental data in the literature at smaller scales, all have large annular gaps that are not prototypic of the transfer cask neutron shield. This paper presents results for a simple 2-D problem that is an effective numerical analog for the neutron shield application. Because it is 2-D, solutions can be obtained relatively quickly allowing a comparison and assessment of sensitivity to model parameter changes. Turbulence models are considered as
Incorporating a Turbulence Transport Model into 2-D Hybrid Hall Thruster Simulations
NASA Astrophysics Data System (ADS)
Cha, Eunsun; Cappelli, Mark A.; Fernandez, Eduardo
2014-10-01
2-D hybrid simulations of Hall plasma thrusters that do not resolve cross-field transport-generating fluctuations require a model to capture how electrons migrate across the magnetic field. We describe the results of integrating a turbulent electron transport model into simulations of plasma behavior in a plane spanned by the E and B field vectors. The simulations treat the electrons as a fluid and the heavy species (ions/neutrals) as discrete particles. The transport model assumes that the turbulent eddy cascade in the electron fluid to smaller scales is the primary means of electron energy dissipation. Using this model, we compare simulations to experimental measurements made on a laboratory Hall discharge over a range of discharge voltage. Both the current-voltage trends as well as the plasma properties such as plasma temperature, electron density, and ion velocities seem agree favorably with experiments, where a simple Bohm transport model tends to perform poorly in capturing much of the discharge behavior.
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 and analysis of solute transport in 2D fracture/pipe networks: The SOLFRAC program
NASA Astrophysics Data System (ADS)
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 http://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
Neutron imaging of root water uptake, transport and hydraulic redistribution
NASA Astrophysics Data System (ADS)
Warren, J.; Bilheux, H.; Kang, M.; Voisin, S.; Cheng, C.; Horita, J.; Perfect, E.
2012-12-01
Knowledge of plant water fluxes is critical for assessing mechanistic processes linked to biogeochemical cycles, yet resolving root water transport dynamics has been a particularly daunting task. Our objectives were to demonstrate the ability to non-invasively monitor individual root functionality and water fluxes within 1-3-week old Zea mays L. (maize) and Panicum virgatum L. (switchgrass) seedlings using neutron imaging. Seedlings were propagated in a growth chamber adjacent to the HFIR CG1 Beam Line at Oak Ridge National Laboratory in cylindrical or plate-like aluminum chambers containing sand. Seedlings were maintained under fairly dry conditions, with water added only to replace daily evapotranspiration. Plants were placed into the high flux cold neutron beam line and injections of H2O or deuterium oxide (D2O) were tracked through the soil and root systems by collecting consecutive CCD radiographs through time. Water fluxes within the root systems were manipulated by cycling on a growth lamp that altered foliar demand for water and thus internal water potential driving forces. 2D and 3D neutron radiography readily illuminated root structure, root growth, and relative plant and soil water content. 2D pulse-chase irrigation experiments with H2O and D2O, which have different neutron cross sections and thus differences in resulting image contrast, successfully allowed observation of uptake and mass flow of water within the root system. After irrigation there was rapid root water uptake from the newly wetted soil, followed by progressive hydraulic redistribution of water through the root systems to roots terminating in dry soil. Water flux within individual roots responded differentially to foliar illumination based on internal water potential gradients. Using 2D radiography, absolute fluxes of H2O or D2O through the system could not be easily determined since neutron attenuation through the sample was dependent on unknown and dynamic magnitudes of both D and H
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. PMID:12380980
A sequential partly iterative approach for multicomponent reactive transport with CORE2D
Samper, J.; Xu, T.; Yang, C.
2008-11-01
CORE{sup 2D} V4 is a finite element code for modeling partly or fully saturated water flow, heat transport and multicomponent reactive solute transport under both local chemical equilibrium and kinetic conditions. It can handle coupled microbial processes and geochemical reactions such as acid-base, aqueous complexation, redox, mineral dissolution/precipitation, gas dissolution/exsolution, ion exchange, sorption via linear and nonlinear isotherms, sorption via surface complexation. Hydraulic parameters may change due to mineral precipitation/dissolution reactions. Coupled transport and chemical equations are solved by using sequential iterative approaches. A sequential partly-iterative approach (SPIA) is presented which improves the accuracy of the traditional sequential noniterative approach (SNIA) and is more efficient than the general sequential iterative approach (SIA). While SNIA leads to a substantial saving of computing time, it introduces numerical errors which are especially large for cation exchange reactions. SPIA improves the efficiency of SIA because the iteration between transport and chemical equations is only performed in nodes with a large mass transfer between solid and liquid phases. The efficiency and accuracy of SPIA are compared to those of SIA and SNIA using synthetic examples and a case study of reactive transport through the Llobregat Delta aquitard in Spain. SPIA is found to be as accurate as SIA while requiring significantly less CPU time. In addition, SPIA is much more accurate than SNIA with only a minor increase in computing time. A further enhancement of the efficiency of SPIA is achieved by improving the efficiency of the Newton-Raphson method used for solving chemical equations. Such an improvement is obtained by working with increments of log-concentrations and ignoring the terms of the Jacobian matrix containing derivatives of activity coefficients. A proof is given for the symmetry and non-singularity of the Jacobian matrix
Singular perturbation applications in neutron transport
Losey, D.C.; Lee, J.C.
1996-09-01
This is a paper on singular perturbation applications in neutron transport for submission at the next ANS conference. A singular perturbation technique was developed for neutron transport analysis by postulating expansion in terms of a small ordering parameter {eta}. Our perturbation analysis is carried, without approximation, through {Omicron}({eta}{sup 2}) to derive a material interface correction for diffusion theory. Here we present results from an analytical application of the perturbation technique to a fixed source problem and then describe and implementation of the technique in a computational scheme.
A Computer Code for 2-D Transport Calculations in x-y Geometry Using the Interface Current Method.
1990-12-01
Version 00 RICANT performs 2-dimensional neutron transport calculations in x-y geometry using the interface current method. In the interface current method, the angular neutron currents crossing region surfaces are expanded in terms of the Legendre polynomials in the two half-spaces made by the region surfaces.
Quantum transport in neutron-irradiated modulation-doped heterojunctions. I. Fast neutrons
Jin, W.; Zhou, J.; Huang, Y.; Cai, L.
1988-12-15
We have investigated the characteristics of low-temperature quantum transport in Al/sub x/Ga/sub 1-//sub x/As/GaAs modulation-doped heterojunctions irradiated by fast neutrons of about 14 MeV energy. The concentration and the mobility of the two-dimensional electron gas (2D EG) under low magnetic fields decrease with increase in the concentrations of scatterers, such as ionized impurities, lattice defects, and interface roughness. On the other hand, under strong magnetic fields, the Hall plateau broadening associated with the Landau localized states, and the Shubnikov--de Hass (SdH) oscillation enhancement associated with the Landau extended states, increase markedly after fast-neutron irradiation.
Quantum transport in neutron-irradiated modulation-doped heterojunctions. II. Thermal neutrons
Jin, W.; Zhou, J.; Huang, Y.; Cai, L.
1988-12-15
We have investigated the characteristics of the low-temperature quantum transport Al/sub x/Ga/sub 1-//sub x/As/GaAs modulation-doped heterojunctions irradiated by thermal neutrons of about 0.025 eV energy. Time-dependent effects related to nuclear radiation such as ..beta../sup -/ decay and ..gamma.. radiation are discussed in detail. The concentration and the mobility of the two-dimensional electron gas (2D EG) under low magnetic fields, the Hall plateau broadening, and the Shubnikov--de Haas (SdH) oscillation enhancement under strong magnetic fields all increase immediately after the irradiation, and then relax for long times. Above all, parallel conduction without illumination is first observed by us with a higher flux of thermal neutrons.
NASA Astrophysics Data System (ADS)
Duxbury, D.; Heenan, R.; McPhail, D.; Raspino, D.; Rhodes, N.; Rogers, S.; Schooneveld, E.; Spill, E.; Terry, A.
2014-12-01
The performance of the new position sensitive neutron detector arrays of the Small Angle Neutron Scattering (SANS) instrument SANS2d is described. The SANS2d instrument is one of the seven instruments currently available for users on the second target station (TS2) of the ISIS spallation neutron source. Since the instrument became operational in 2009 it has used two one metre square multi-wire proportional detectors (MWPC). However, these detectors suffer from a low count rate capability, are easily damaged by excess beam and are then expensive to repair. The new detector arrays each consist of 120 individual position sensitive detector tubes, filled with 15 bar of 3He. Each of the tubes is one metre long and has a diameter of 8mm giving a detector array with an overall area of one square metre. Two such arrays have been built and installed in the SANS2d vacuum tank where they are currently taking user data. For SANS measurements operation of the detector within a vacuum is essential in order to reduce air scattering. A novel, fully engineered approach has been utilised to ensure that the high voltage connections and preamps are located inside the SANS2d vacuum tank at atmospheric pressure, within air tubes and air boxes respectively. The signal processing electronics and data acquisition system are located remotely in a counting house outside of the blockhouse. This allows easy access for maintenance purposes, without the need to remove the detectors from the vacuum tank. The design will be described in detail. A position resolution of 8mm FWHM or less has been measured along the length of the tubes. The initial measurements taken from a standard sample indicate that whilst the detector arrays themselves only represent a moderate improvement in overall detection efficiency (~ 20%), compared to the previous detector, the count rate capability is increased by a factor of 100. A significant advantage of the new array is the ability to change a single tube in situ
Spin-Orbit Interaction and Related Transport Phenomena in 2d Electron and Hole Systems
NASA Astrophysics Data System (ADS)
Khaetskii, A.
Spin-orbit interaction is responsible for many physical phenomena which are under intensive study currently. Here we discuss several of them. The first phenomenon is the edge spin accumulation, which appears due to spin-orbit interaction in 2D mesoscopic structures in the presence of a charge current. We consider the case of a strong spin-orbit-related splitting of the electron spectrum, i.e. a spin precession length is small compared to the mean free path l. The structure can be either in a ballistic regime (when the mean free path is the largest scale in the problem) or quasi-ballistic regime (when l is much smaller than the sample size). We show how physics of edge spin accumulation in different situations should be understood from the point of view of unitarity of boundary scattering. Using transparent method of scattering states, we are able to explain some previous puzzling theoretical results. We clarify the important role of the form of the spin-orbit Hamiltonian, the role of the boundary conditions, etc., and reveal the wrong results obtained in the field by other researchers. The relation between the edge spin density and the bulk spin current in different regimes is discussed. The detailed comparison with the existing theoretical works is presented. Besides, we consider several new transport phenomena which appear in the presence of spin-orbit interaction, for example, magnetotransport phenomena in an external classical magnetic field. In particular, new mechanism of negative magneto-resistance appears which is due to destruction of spin fluxes by the magnetic field, and which can be really pronounced in 2D systems with strong scatterers.
A plastic scintillator-based 2D thermal neutron mapping system for use in BNCT studies.
Ghal-Eh, N; Green, S
2016-06-01
In this study, a scintillator-based measurement instrument is proposed which is capable of measuring a two-dimensional map of thermal neutrons within a phantom based on the detection of 2.22MeV gamma rays generated via nth+H→D+γ reaction. The proposed instrument locates around a small rectangular water phantom (14cm×15cm×20cm) used in Birmingham BNCT facility. The whole system has been simulated using MCNPX 2.6. The results confirm that the thermal flux peaks somewhere between 2cm and 4cm distance from the system entrance which is in agreement with previous studies. PMID:26986813
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
Ensemble Solute Transport in 2-D Operator-Stable Random Fields
NASA Astrophysics Data System (ADS)
Monnig, N. D.; Benson, D. A.
2006-12-01
The heterogeneous velocity field that exists at many scales in an aquifer will typically cause a dissolved solute plume to grow at a rate faster than Fick's Law predicts. Some statistical model must be adopted to account for the aquifer structure that engenders the velocity heterogeneity. A fractional Brownian motion (fBm) model has been shown to create the long-range correlation that can produce continually faster-than-Fickian plume growth. Previous fBm models have assumed isotropic scaling (defined here by a scalar Hurst coefficient). Motivated by field measurements of aquifer hydraulic conductivity, recent techniques were developed to construct random fields with anisotropic scaling with a self-similarity parameter that is defined by a matrix. The growth of ensemble plumes is analyzed for transport through 2-D "operator- stable" fBm hydraulic conductivity (K) fields. Both the longitudinal and transverse Hurst coefficients are important to both plume growth rates and the timing and duration of breakthrough. Smaller Hurst coefficients in the transverse direction lead to more "continuity" or stratification in the direction of transport. The result is continually faster-than-Fickian growth rates, highly non-Gaussian ensemble plumes, and a longer tail early in the breakthrough curve. Contrary to some analytic stochastic theories for monofractal K fields, the plume growth rate never exceeds Mercado's [1967] purely stratified aquifer growth rate of plume apparent dispersivity proportional to mean distance. Apparent super-Mercado growth must be the result of other factors, such as larger plumes corresponding to either a larger initial plume size or greater variance of the ln(K) field.
An Improved Neutron Transport Algorithm for HZETRN
NASA Technical Reports Server (NTRS)
Slaba, Tony C.; Blattnig, Steve R.; Clowdsley, Martha S.; Walker, Steven A.; Badavi, Francis F.
2010-01-01
Long term human presence in space requires the inclusion of radiation constraints in mission planning and the design of shielding materials, structures, and vehicles. In this paper, the numerical error associated with energy discretization in HZETRN is addressed. An inadequate numerical integration scheme in the transport algorithm is shown to produce large errors in the low energy portion of the neutron and light ion fluence spectra. It is further shown that the errors result from the narrow energy domain of the neutron elastic cross section spectral distributions, and that an extremely fine energy grid is required to resolve the problem under the current formulation. Two numerical methods are developed to provide adequate resolution in the energy domain and more accurately resolve the neutron elastic interactions. Convergence testing is completed by running the code for various environments and shielding materials with various energy grids to ensure stability of the newly implemented method.
NASA Astrophysics Data System (ADS)
Goble, Nicholas; Watson, John; Manfra, Michael; Gao, Xuan
2014-03-01
Understanding the non-monotonic behavior in the temperature dependent resistance, R(T) , of strongly correlated two-dimensional (2D) carriers in clean semiconductors has been a central issue in the studies of 2D metallic states and metal-insulator transitions. We have studied the transport of high mobility 2D holes in 20nm wide GaAs quantum wells with varying interface roughness by changing the Al fraction x in the AlxGa1-xAs barrier. Prior to this work, no comprehensive study of the non-monotonic resistance peak against controlled barrier characteristics has been conducted. We show that the shape of the electronic contribution to R(T) is qualitatively unchanged throughout all of our measurements, regardless of the percentage of Al in the barrier. It is observed that increasing x or short range interface roughness suppresses both the strength and characteristic temperature scale of the 2D metallicity, pointing to the distinct role of short range versus long range disorder in the 2D metallic transport in this 2D hole system with interaction parameter rs ~ 20. N.G. acknowledges the US DOE GAANN fellowship (P200A090276 & P200A070434). M.J.M. is supported by the Miller Family Foundation and the US DOE, Office of Basic Energy Sciences, DMS (DE-SC0006671). X.P.A.G thanks the NSF for funding support (DMR-0906415).
In situ 2D-extraction of DNA wheels by 3D through-solution transport.
Yonamine, Yusuke; Cervantes-Salguero, Keitel; Nakanishi, Waka; Kawamata, Ibuki; Minami, Kosuke; Komatsu, Hirokazu; Murata, Satoshi; Hill, Jonathan P; Ariga, Katsuhiko
2015-12-28
Controlled transfer of DNA nanowheels from a hydrophilic to a hydrophobic surface was achieved by complexation of the nanowheels with a cationic lipid (2C12N(+)). 2D surface-assisted extraction, '2D-extraction', enabled structure-persistent transfer of DNA wheels, which could not be achieved by simple drop-casting. PMID:26583486
2-D Path Corrections for Local and Regional Coda Waves: A Test of Transportability
Mayeda, K M; Malagnini, L; Phillips, W S; Walter, W R; Dreger, D S; Morasca, P
2005-07-13
Reliable estimates of the seismic source spectrum are necessary for accurate magnitude, yield, and energy estimation. In particular, how seismic radiated energy scales with increasing earthquake size has been the focus of recent debate within the community and has direct implications on earthquake source physics studies as well as hazard mitigation. The 1-D coda methodology of Mayeda et al. [2003] has provided the lowest variance estimate of the source spectrum when compared against traditional approaches that use direct S-waves, thus making it ideal for networks that have sparse station distribution. The 1-D coda methodology has been mostly confined to regions of approximately uniform complexity. For larger, more geophysically complicated regions, 2-D path corrections may be required. We will compare performance of 1-D versus 2-D path corrections in a variety of regions. First, the complicated tectonics of the northern California region coupled with high quality broadband seismic data provides for an ideal ''apples-to-apples'' test of 1-D and 2-D path assumptions on direct waves and their coda. Next, we will compare results for the Italian Alps using high frequency data from the University of Genoa. For Northern California, we used the same station and event distribution and compared 1-D and 2-D path corrections and observed the following results: (1) 1-D coda results reduced the amplitude variance relative to direct S-waves by roughly a factor of 8 (800%); (2) Applying a 2-D correction to the coda resulted in up to 40% variance reduction from the 1-D coda results; (3) 2-D direct S-wave results, though better than 1-D direct waves, were significantly worse than the 1-D coda. We found that coda-based moment-rate source spectra derived from the 2-D approach were essentially identical to those from the 1-D approach for frequencies less than {approx}0.7-Hz, however for the high frequencies (0.7 {le} f {le} 8.0-Hz), the 2-D approach resulted in inter-station scatter
Advanced Nodal P_{3}/SP_{3} Axial Transport Solvers for the MPACT 2D/1D Scheme
Stimpson, Shane G; Collins, Benjamin S
2015-01-01
As part of its initiative to provide multiphysics simulations of nuclear reactor cores, the Consortium for Advanced Simulation of Light Water Reactors (CASL) is developing the Virtual Environment for Reactor Applications Core Simulator (VERA-CS). The MPACT code, which is the primary neutron transport solver of VERA-CS, employs the two-dimensional/one-dimensional (2D/1D) method to solve 3-dimensional neutron transport problems and provide sub-pin-level resolution of the power distribution. While 2D method of characteristics is used to solve for the transport effects within each plane, 1D-nodal methods are used axially. There have been extensive studies of the 2D/1D method with a variety nodal methods, and the P_{3}/SP_{3} solver has proved to be an effective method of providing higher-fidelity solutions while maintaining a low computational burden.The current implementation in MPACT wraps a one-node nodal expansion method (NEM) kernel for each moment, iterating between them and performing multiple sweeps to resolve flux distributions. However, it has been observed that this approach is more sensitive to convergence problems. This paper documents the theory and application two new nodal P_{3}/SP_{3} approaches to be used within the 2D/1D method in MPACT. These two approaches aim to provide enhanced stability compared with the pre-existing one-node approach. Results from the HY-NEM-SP_{3} solver show that the accuracy is consistent with the one-node formulations and provides improved convergence for some problems; but the solver has issues with cases in thin planes. Although the 2N-SENM-SP_{3} solver is still under development, it is intended to resolve the issues with HY-NEM-SP_{3} but it will incur some additional computational burden by necessitating an additional 1D-CMFD-P_{3} solver to generate the second moment cell-averaged scalar flux.
Strongly Metallic Electron and Hole 2D Transport in an Ambipolar Si-Vacuum Field Effect Transistor
NASA Astrophysics Data System (ADS)
Hu, Binhui; Yazdanpanah, M. M.; Kane, B. E.; Hwang, E. H.; Das Sarma, S.
2015-07-01
We report experiment and theory on an ambipolar gate-controlled Si(111)-vacuum field effect transistor where we study electron and hole (low-temperature 2D) transport in the same device simply by changing the external gate voltage to tune the system from being a 2D electron system at positive gate voltage to a 2D hole system at negative gate voltage. The electron (hole) conductivity manifests strong (moderate) metallic temperature dependence with the conductivity decreasing by a factor of 8 (2) between 0.3 K and 4.2 K with the peak electron mobility (˜18 m2/V s ) being roughly 20 times larger than the peak hole mobility (in the same sample). Our theory explains the data well using random phase approximation screening of background Coulomb disorder, establishing that the observed metallicity is a direct consequence of the strong temperature dependence of the effective screened disorder.
Electronic Transport Properties of New 2-D Materials GeH and NaSn2As2
NASA Astrophysics Data System (ADS)
He, Bin; Cultrara, Nicholas; Arguilla, Maxx; Goldberger, Joshua; Heremans, Joseph
2-D materials potentially have superior thermoelectric properties compared to traditional 3-D materials due to their layered structure. Here we present electrical and thermoelectric transport properties of 2 types of 2-D materials, GeH and NaSn2As2. GeH is a graphane analog which is prepared using chemical exfoliation of CaGe2 crystals. Intrinsic GeH is proven to be a highly resistive material at room temperature. Resistance and Seebeck coefficient of Ga doped GeH are measured in a cryostat with a gating voltage varying from -100V to 100V. NaSn2As2 is another 2-D system, with Na atom embedded between nearly-2D Sn-As layers. Unlike GeH, NaSn2As2 is a metal based of Hall measurements, with p-type behavior, and with van der Pauw resistances on the order of 5m Ω/square. Thermoelectric transport properties of NaSn2As2 will be reported. This work is support by the NSF EFRI-2DARE project EFRI-1433467.
2D Electrical Resistivity Tomography surveys optimisation of the solutes transports in porous media.
NASA Astrophysics Data System (ADS)
Lekmine, G.; Pessel, M.; Auradou, H.
2009-04-01
Electrical resistivity tomography applied in borehole or cross-borehole is a method often used to follow the invasion process of pollutant [Daily, 1991]. The aim of this work is to test experimentally the electrode arrays and inversion process used to obtain a spatial representation of tracer propagation in porous media. Experiments were conducted in a plexiglas container with glass beads of 166 microns in diameter. The height of the container is 275 mm, its width 85 mm and its thickness 10 mm. 21 electrodes, equally spaced, are placed along each of the lateral sides of the porous medium : these electrodes are used to perform the electrical measurements. The porous medium is lightened from behind and a video camera records the propagation of the fluids. The fluid containing the tracer (i.e the pollutant) is a water solution containing a small amount of dye together with NaCl (0.5g/l up to 2.0g/l). The medium is first saturated by a water solution containing a slight concentration of NaCl so that its density is smaller than the injected fluid. An upward flow is first established, then the denser fluid is injected at the bottom and over the full width of the medium. In this way, the flow is stabilized by gravity avoiding the development of unstable fingers. Still, the fluids are miscible and a mixing front develops during the flow: in the present study, both the determination by optical and electrical imaging of the mean position of the front and its width are of interest. The comparison of the two techniques allows to study the ability of the inversion process to quantify the solute transport. The electrical measurements are acquired by a standard multi electrode system (IRIS Instruments) and the data are inverted with the Res2Dinv software which models the 2D distribution of conductivity contrasts. The obtained bulk conductivity can be related through Archie's law to fluid conductivity by the porosity and the cementation factor which have been experimentally
Li, Yixiang; Qiu, Chunyin; Xu, Shengjun; Ke, Manzhu; Liu, Zhengyou
2015-01-01
Conventional microparticle transports by light or sound are realized along a straight line. Recently, this limit has been overcome in optics as the growing up of the self-accelerating Airy beams, which are featured by many peculiar properties, e.g., bending propagation, diffraction-free and self-healing. However, the bending angles of Airy beams are rather small since they are only paraxial solutions of the two-dimensional (2D) Helmholtz equation. Here we propose a novel micromanipulation by using acoustic Half-Bessel beams, which are strict solutions of the 2D Helmholtz equation. Compared with that achieved by Airy beams, the bending angle of the particle trajectory attained here is much steeper (exceeding 90o). The large-angle bending transport of microparticles, which is robust to complex scattering environment, enables a wide range of applications from the colloidal to biological sciences. PMID:26279478
NASA Astrophysics Data System (ADS)
Li, Yixiang; Qiu, Chunyin; Xu, Shengjun; Ke, Manzhu; Liu, Zhengyou
2015-08-01
Conventional microparticle transports by light or sound are realized along a straight line. Recently, this limit has been overcome in optics as the growing up of the self-accelerating Airy beams, which are featured by many peculiar properties, e.g., bending propagation, diffraction-free and self-healing. However, the bending angles of Airy beams are rather small since they are only paraxial solutions of the two-dimensional (2D) Helmholtz equation. Here we propose a novel micromanipulation by using acoustic Half-Bessel beams, which are strict solutions of the 2D Helmholtz equation. Compared with that achieved by Airy beams, the bending angle of the particle trajectory attained here is much steeper (exceeding 90o). The large-angle bending transport of microparticles, which is robust to complex scattering environment, enables a wide range of applications from the colloidal to biological sciences.
Li, Yixiang; Qiu, Chunyin; Xu, Shengjun; Ke, Manzhu; Liu, Zhengyou
2015-01-01
Conventional microparticle transports by light or sound are realized along a straight line. Recently, this limit has been overcome in optics as the growing up of the self-accelerating Airy beams, which are featured by many peculiar properties, e.g., bending propagation, diffraction-free and self-healing. However, the bending angles of Airy beams are rather small since they are only paraxial solutions of the two-dimensional (2D) Helmholtz equation. Here we propose a novel micromanipulation by using acoustic Half-Bessel beams, which are strict solutions of the 2D Helmholtz equation. Compared with that achieved by Airy beams, the bending angle of the particle trajectory attained here is much steeper (exceeding 90(o)). The large-angle bending transport of microparticles, which is robust to complex scattering environment, enables a wide range of applications from the colloidal to biological sciences. PMID:26279478
Topologically robust transport of entangled photons in a 2D photonic system.
Mittal, Sunil; Orre, Venkata Vikram; Hafezi, Mohammad
2016-07-11
We theoretically study the transport of time-bin entangled photon pairs in a two-dimensional topological photonic system of coupled ring resonators. This system implements the integer quantum Hall model using a synthetic gauge field and exhibits topologically robust edge states. We show that the transport through edge states preserves temporal correlations of entangled photons whereas bulk transport does not preserve these correlations and can lead to significant unwanted temporal bunching or anti-bunching of photons. We study the effect of disorder on the quantum transport properties; while the edge transport remains robust, bulk transport is very susceptible, and in the limit of strong disorder, bulk states become localized. We show that this localization is manifested as an enhanced bunching/anti-bunching of photons. This topologically robust transport of correlations through edge states could enable robust on-chip quantum communication channels and delay lines for information encoded in temporal correlations of photons. PMID:27410836
Crossover from 3D to 2D Quantum Transport in Bi2Se3/In2Se3 Superlattices
NASA Astrophysics Data System (ADS)
Yanfei, Zhao; Haiwen, Liu; Xin, Guo; Ying, Jiang; Yi, Sun; Huichao, Wang; Yong, Wang; Handong, Li; Maohai, Xie; Xincheng, Xie; Jian, Wang
2015-03-01
The topological insulator/normal insulator (TI/NI) superlattices (SLs) with multiple Dirac channels are predicted to offer great opportunity to design novel materials and investigate new quantum phenomena. Here, we report first transport studies on the SLs composed of TI Bi2Se3 layers sandwiched by NI In2Se3 layers artificially grown by molecular beam epitaxy (MBE). The transport properties of two kinds of SL samples show convincing evidence that the transport dimensionality changes from three-dimensional (3D) to two-dimensional (2D) when decreasing the thickness of building block Bi2Se3 layers, corresponding to the crossover from coherent TI transport to separated TI channels. Our findings provide the possibility to realizing 3D surface states in TI/NI SLs.
Crossover from 3D to 2D quantum transport in Bi2Se3/In2Se3 superlattices.
Zhao, Yanfei; Liu, Haiwen; Guo, Xin; Jiang, Ying; Sun, Yi; Wang, Huichao; Wang, Yong; Li, Han-Dong; Xie, Mao-Hai; Xie, Xin-Cheng; Wang, Jian
2014-09-10
The topological insulator/normal insulator (TI/NI) superlattices (SLs) with multiple Dirac channels are predicted to offer great opportunity to design novel materials and investigate new quantum phenomena. Here, we report first transport studies on the SLs composed of TI Bi2Se3 layers sandwiched by NI In2Se3 layers artificially grown by molecular beam epitaxy (MBE). The transport properties of two kinds of SL samples show convincing evidence that the transport dimensionality changes from three-dimensional (3D) to two-dimensional (2D) when decreasing the thickness of building block Bi2Se3 layers, corresponding to the crossover from coherent TI transport to separated TI channels. Our findings provide the possibility to realizing "3D surface states" in TI/NI SLs. PMID:25102289
Spin Hall effect and spin transport in graphene and 2D heterostructures
NASA Astrophysics Data System (ADS)
Oezyilmaz, Barbaros
Semiconducting 2D materials offer new opportunities in both alternative technologies and fundamental discoveries by using the spin degree freedom of electrons. One of the main challenges in this field is to identify new materials which allow the control of spin currents by means of the electric field effect. This requires either a sizeable spin-orbit coupling strength or a sizeable bandgap or both. Unfortunately, pristine graphene has a negligibly small spin-orbit coupling strength. Recently we have addressed this problem in three distinct ways. First we have used chemical functionalization to introduce locally sp3 type bonding. Next we used metal ad-atoms to increase spin-orbit coupling via local enhancement of the spin-orbit coupling strength due to resonant scattering. Finally, I will show that the proximity of graphene on transition metal dichalcogenides can also lead to a significant enhancement of the spin-orbit coupling strength. I will complete my talk with a brief discussion on the possibility of all electrical spin injection into complementary 2D crystals such as WS2, MoS2 or black phosphorus. Membership Pending in the abstract Special Instructions field.
Stable Difference Schemes for the Neutron Transport Equation
Ashyralyev, Allaberen; Taskin, Abdulgafur
2011-09-22
The initial boundary value problem for the neutron transport equation is considered. The first and second orders of accuracy difference schemes for the approximate solution of this problem are presented. In applications, the stability estimates for solutions of difference schemes for the approximate solution of the neutron transport equation are obtained. Numerical techniques are developed and algorithms are tested on an example in MATLAB.
High-field and thermal transport in 2D atomic layer devices
NASA Astrophysics Data System (ADS)
Serov, Andrey; Dorgan, Vincent E.; Behnam, Ashkan; English, Chris D.; Li, Zuanyi; Islam, Sharnali; Pop, Eric
2014-06-01
This paper reviews our recent results of high-field electrical and thermal properties of atomically thin two-dimensional materials. We show how self-heating affects velocity saturation in suspended and supported graphene. We also demonstrate that multi-valley transport must be taken into account to describe high-field transport in MoS2. At the same time we characterized thermal properties of suspended and nanoscale graphene samples over a wide range of temperatures. We uncovered the effects of edge scattering and grain boundaries on thermal transport in graphene, and showed how the thermal conductivity varies between diffusive and ballistic heat flow limits.
NASA Astrophysics Data System (ADS)
Iannaccone, G.; Zhang, Q.; Bruzzone, S.; Fiori, G.
2016-01-01
Different proposals of graphene transistors based on off-plane (i.e., vertical) transport, have recently appeared in the literature, exhibiting experimental current modulation of a factor 104-105 at room temperature. These devices overcome the lack of bandgap that undermines the operation of graphene transistors, and positively exploit graphene's ultimate thinness, high conductivity, and low density of states. However, very little is known about vertical transport through graphene and two-dimensional materials, either in terms of experiments or theory. In this paper we will discuss the physics and the electronics of off-plane transport through hetero-structures of graphene and 2D materials. We investigate transport across vertical heterostructures of 2D materials with multi-scale simulations, including first-principle density functional theory and non-equilibrium Green's functions based on NanoTCAD ViDES. We show that unexpected behaviors emerge, which are not observed in the more familiar semiconductor heterostructures based on III-V and II-VI materials systems, and that are not predicted by simplistic physical models. Such properties have a significant impact on the design and performance of transistors for digital or high frequency operations.
NASA Astrophysics Data System (ADS)
Apruzese, J. P.; Giuliani, J. L.; Hansen, S. B.
2012-09-01
In modeling optically thick, high energy density plasmas (HEDP), radiation transport is of comparable importance to atomic physics, hydrodynamics, and other transport processes. Radiation transport theory is the framework for calculating radiation output based on atomic kinetics, and is thus critical to designing and diagnosing experiments in which radiation production is significant. Starting in the 1960s, the astrophysics community established benchmarks for computational radiation transport, based on a parameterized two-level-atom, and mostly applicable to media with very high optical depths and low collisional quenching of radiative transitions. The purpose of the work reported here is to establish a similar computational radiation transport benchmark that is more relevant to a laboratory HEDP environment. Our model consists of 8 levels of mostly K-shell Al ions, ranging from the ground state of Li-like Al to its bare nucleus. Rates connecting the levels are given by well-known, readily reproducible analytic prescriptions. The results presented consist of level populations as a function of position within the cylindrical medium, and emitted line profiles. For the plasma conditions considered, the magnitudes and spatial variations of the populations are a sensitive indicator of the accuracy of the radiation transport model, and are critical in calculating experimentally relevant quantities such as radiative powers and line ratios.
Neutron Transport Characteristics of a Nuclear Reactor Based Dynamic Neutron Imaging System
Khaial, Anas M.; Harvel, Glenn D.; Chang, Jen-Shih
2006-07-01
An advanced dynamic neutron imaging system has been constructed in the McMaster Nuclear Reactor (MNR) for nondestructive testing and multi-phase flow studies in energy and environmental applications. A high quality neutron beam is required with a thermal neutron flux greater than 5.0 x 10{sup 6} n/cm{sup 2}-s and a collimation ratio of 120 at image plane to promote high-speed neutron imaging up to 2000 frames per second. Neutron source strength and neutron transport have been experimentally and numerically investigated. Neutron source strength at the beam tube entrance was evaluated experimentally by measuring the thermal and fast neutron fluxes, and simple analytical neutron transport calculations were performed based upon these measured neutron fluxes to predict facility components in accordance with high-speed dynamic neutron imaging and operation safety requirements. Monte-Carlo simulations (using MCNP-4B code) with multiple neutron energy groups have also been used to validate neutron beam parameters and to ensure shielding capabilities of facility shutter and cave walls. Neutron flux distributions at the image plane and the neutron beam characteristics were experimentally measured by irradiating a two-dimensional array of Copper foils and using a real-time neutron radiography system. The neutron image characteristics -- such as neutron flux, image size, beam quality -- measured experimentally and predicted numerically for beam tube, beam shutter and radiography cave are compared and discussed in detail in this paper. The experimental results show that thermal neutron flux at image plane is nearly uniform over an imaging area of 20.0-cm diameter and its magnitude ranges from 8.0 x 10{sup 6} - 1.0 x 10{sup 7} n/cm{sup 2}-sec while the neutron-to-gamma ratio is 6.0 x 10{sup 5} n/cm{sup 2}-{mu}Sv. (authors)
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
Pangolin v1.0, a conservative 2-D transport model for large scale parallel calculation
NASA Astrophysics Data System (ADS)
Praga, A.; Cariolle, D.; Giraud, L.
2014-07-01
To exploit the possibilities of parallel computers, we designed a large-scale bidimensional atmospheric transport model named Pangolin. As the basis for a future chemistry-transport model, a finite-volume approach was chosen both for mass preservation and to ease parallelization. To overcome the pole restriction on time-steps for a regular latitude-longitude grid, Pangolin uses a quasi-area-preserving reduced latitude-longitude grid. The features of the regular grid are exploited to improve parallel performances and a custom domain decomposition algorithm is presented. To assess the validity of the transport scheme, its results are compared with state-of-the-art models on analytical test cases. Finally, parallel performances are shown in terms of strong scaling and confirm the efficient scalability up to a few hundred of cores.
Kraloua, B.; Hennad, A.
2008-09-23
The aim of this paper is to determine electric and physical properties by 2D modelling of glow discharge low pressure in continuous regime maintained by term constant source. This electric discharge is confined in reactor plan-parallel geometry. This reactor is filled by Argon monatomic gas. Our continuum model the order two is composed the first three moments the Boltzmann's equations coupled with Poisson's equation by self consistent method. These transport equations are discretized by the finite volumes method. The equations system is resolved by a new technique, it is about the N-BEE explicit scheme using the time splitting method.
NASA Astrophysics Data System (ADS)
Leboeuf, Jean-Noel; Decyk, Viktor; Newman, David; Sanchez, Raul
2012-03-01
The massively parallel, nonlinear, 3D, toroidal, electrostatic, gyrokinetic, PIC, Cartesian geometry UCAN code, with particle ions and adiabatic electrons, has been successfully exercised to identify non-diffusive transport characteristics in DIII-D-like tokamak discharges. The limitation in applying UCAN to larger scale discharges is the 1D domain decomposition in the toroidal (or z-) direction for massively parallel implementation using MPI which has restricted the calculations to a few hundred ion Larmor radii per minor radius. To exceed these sizes, we have implemented 2D domain decomposition in UCAN with the addition of the y-direction to the processor mix. This has been facilitated by use of relevant components in the 2D domain decomposed PLIB2 library of field and particle management routines developed for UCLA's UPIC framework of conventional PIC codes. The gyro-averaging in gyrokinetic codes has necessitated the use of replicated arrays for efficient charge accumulation and particle push. The 2D domain-decomposed UCAN2 code reproduces the original 1D domain results within roundoff. Production calculations at large system sizes have been performed with UCAN2 on 131072 processors of the Cray XE6 at NERSC.
NASA Astrophysics Data System (ADS)
Ivy, D. J.; Rigby, M. L.; Prinn, R. G.; Muhle, J.; Weiss, R. F.
2009-12-01
We present optimized annual global emissions from 1973-2008 of nitrogen trifluoride (NF3), a powerful greenhouse gas which is not currently regulated by the Kyoto Protocol. In the past few decades, NF3 production has dramatically increased due to its usage in the semiconductor industry. Emissions were estimated through the 'pulse-method' discrete Kalman filter using both a simple, flexible 2-D 12-box model used in the Advanced Global Atmospheric Gases Experiment (AGAGE) network and the Model for Ozone and Related Tracers (MOZART v4.5), a full 3-D atmospheric chemistry model. No official audited reports of industrial NF3 emissions are available, and with limited information on production, a priori emissions were estimated using both a bottom-up and top-down approach with two different spatial patterns based on semiconductor perfluorocarbon (PFC) emissions from the Emission Database for Global Atmospheric Research (EDGAR v3.2) and Semiconductor Industry Association sales information. Both spatial patterns used in the models gave consistent results, showing the robustness of the estimated global emissions. Differences between estimates using the 2-D and 3-D models can be attributed to transport rates and resolution differences. Additionally, new NF3 industry production and market information is presented. Emission estimates from both the 2-D and 3-D models suggest that either the assumed industry release rate of NF3 or industry production information is still underestimated.
2D coherent charge transport in highly ordered conducting polymers doped by solid state diffusion
NASA Astrophysics Data System (ADS)
Kang, Keehoon; Watanabe, Shun; Broch, Katharina; Sepe, Alessandro; Brown, Adam; Nasrallah, Iyad; Nikolka, Mark; Fei, Zhuping; Heeney, Martin; Matsumoto, Daisuke; Marumoto, Kazuhiro; Tanaka, Hisaaki; Kuroda, Shin-Ichi; Sirringhaus, Henning
2016-08-01
Doping is one of the most important methods to control charge carrier concentration in semiconductors. Ideally, the introduction of dopants should not perturb the ordered microstructure of the semiconducting host. In some systems, such as modulation-doped inorganic semiconductors or molecular charge transfer crystals, this can be achieved by spatially separating the dopants from the charge transport pathways. However, in conducting polymers, dopants tend to be randomly distributed within the conjugated polymer, and as a result the transport properties are strongly affected by the resulting structural and electronic disorder. Here, we show that in the highly ordered lamellar microstructure of a regioregular thiophene-based conjugated polymer, a small-molecule p-type dopant can be incorporated by solid state diffusion into the layers of solubilizing side chains without disrupting the conjugated layers. In contrast to more disordered systems, this allows us to observe coherent, free-electron-like charge transport properties, including a nearly ideal Hall effect in a wide temperature range, a positive magnetoconductance due to weak localization and the Pauli paramagnetic spin susceptibility.
NASA Astrophysics Data System (ADS)
Zhao, Dongmiao; Tang, Jun; Wu, Xiuguang; Lin, Changning; Liu, Lijun; Chen, Jian
2016-05-01
A 2D vertical (2DV) numerical model, without σ-coordinate transformation in the vertical direction, is developed for the simulation of fl ow and sediment transport in open channels. In the model, time-averaged Reynolds equations are closed by the k-ɛ nonlinear turbulence model. The modifi ed Youngs-VOF method is introduced to capture free surface dynamics, and the free surface slope is simulated using the ELVIRA method. Based on the power-law scheme, the k-ɛ model and the suspended-load transport model are solved numerically with an implicit scheme applied in the vertical plane and an explicit scheme applied in the horizontal plane. Bedload transport is modeled using the Euler-WENO scheme, and the grid-closing skill is adopted to deal with the moving channel bed boundary. Verifi cation of the model using laboratory data shows that the model is able to adequately simulate fl ow and sediment transport in open channels, and is a good starting point for the study of sediment transport dynamics in strong nonlinear fl ow scenarios.
Tupala, E; Hall, H; Bergström, K; Särkioja, T; Räsänen, P; Mantere, T; Callaway, J; Hiltunen, J; Tiihonen, J
2001-05-01
Alcohol acts through mechanisms involving the brain neurotransmitter dopamine (DA) with the nucleus accumbens as the key zone for mediating these effects. We evaluated the densities of DA D(2)/D(3) receptors and transporters in the nucleus accumbens and amygdala of post-mortem human brains by using [(125)l]epidepride and [(125)I]PE2I as radioligands in whole hemispheric autoradiography of Cloninger type 1 and 2 alcoholics and healthy controls. When compared with controls, the mean binding of [(125)I]epidepride to DA D(2)/D(3) receptors was 20% lower in the nucleus accumbens and 41% lower in the amygdala, and [(125)I]PE2I binding to DA transporters in the nucleus accumbens was 39% lower in type 1 alcoholics. These data indicate that dopaminergic functions in these limbic areas may be impaired among type 1 alcoholics, due to the substantially lower number of receptor sites. Our results suggest that such a reduction may result in the chronic overuse of alcohol as an attempt to stimulate DA function. PMID:11326293
Turcksin, Bruno Ragusa, Jean C.
2014-10-01
In this paper, a Diffusion Synthetic Acceleration (DSA) technique applied to the S{sub n} radiation transport equation is developed using Piece-Wise Linear Discontinuous (PWLD) finite elements on arbitrary polygonal grids. The discretization of the DSA equations employs an Interior Penalty technique, as is classically done for the stabilization of the diffusion equation using discontinuous finite element approximations. The penalty method yields a system of linear equations that is Symmetric Positive Definite (SPD). Thus, solution techniques such as Preconditioned Conjugate Gradient (PCG) can be effectively employed. Algebraic MultiGrid (AMG) and Symmetric Gauss–Seidel (SGS) are employed as conjugate gradient preconditioners for the DSA system. AMG is shown to be significantly more efficient than SGS. Fourier analyses are carried out and we show that this discontinuous finite element DSA scheme is always stable and effective at reducing the spectral radius for iterative transport solves, even for grids with high-aspect ratio cells. Numerical results are presented for different grid types: quadrilateral, hexagonal, and polygonal grids as well as grids with local mesh adaptivity.
Coherent heat transport in 2D phononic crystals with acoustic impedance mismatch
NASA Astrophysics Data System (ADS)
Arantes, A.; Anjos, V.
2016-03-01
In this work we have calculated the cumulative thermal conductivities of micro-phononic crystals formed by different combinations of inclusions and matrices at a sub-Kelvin temperature regime. The low-frequency phonon spectra (up to tens of GHz) were obtained by solving the generalized wave equation for inhomogeneous media with the plane wave expansion method. The thermal conductivity was calculated from Boltzmann transport theory highlighting the role of the low-frequency thermal phonons and neglecting phonon-phonon scattering. A purely coherent thermal transport regime was assumed throughout the structures. Our findings show that the cumulative thermal conductivity drops dramatically when compared with their bulk counterpart. Depending on the structural composition this reduction may be attributed to the phonon group velocity due to a flattening of the phonon dispersion relation, the extinction of phonon modes in the density of states or due to the presence of complete band gaps. According to the contrast between the inclusions and the matrices, three types of two dimensional phononic crystals were considered: carbon/epoxy, carbon/polyethylene and tungsten/silicon, which correspond respectively to a moderate, strong and very strong mismatch in the mechanical properties of these materials.
High conductance 2D transport around the Hall mobility peak in electrolyte-gated rubrene crystals.
Xie, Wei; Wang, Shun; Zhang, Xin; Leighton, C; Frisbie, C Daniel
2014-12-12
We report the observation of the Hall effect at hole densities up to 6×10¹³ cm⁻² (0.3 holes/molecule) on the surface of electrolyte-gated rubrene crystals. The perplexing peak in the conductance as a function of gate voltage is confirmed to result from a maximum in mobility, which reaches 4 cm² V⁻¹ s⁻¹ at 2.5×10¹³ cm⁻². Measurements to liquid helium temperatures reveal that this peak is markedly asymmetric, with bandlike and hopping-type transport occurring on the low density side, while unconventional, likely electrostatic-disorder-affected transport dominates the high density side. Most significantly, near the mobility peak the temperature coefficient of the resistance remains positive to as low as 120 K, the low temperature resistance becomes weakly temperature dependent, and the conductance reaches within a factor of 2 of e²/h, revealing conduction unprecedentedly close to a two-dimensional metallic state. PMID:25541790
Transport of aurorally produced N/2D/ by winds in the high latitude thermosphere
NASA Technical Reports Server (NTRS)
Gerard, J.-C.; Roble, R. G.
1982-01-01
A time-dependent, two-dimensional model is developed for describing the meridional circulation of thermospheric odd nitrogen species produced in the auroral zone. The model is based on a previous model by Roble and Gary (1979) extended to upper altitude transport of the nitrogen species. Assumptions made include the existence of a steady neutral wind flowing from low to high latitudes, and an initial background due to scattered Lyman-beta and nightglow emissions. The aurora is also assumed as steady, along with a constant ion production. Predictions made using the model are compared with observations with the Atmosphere Explorer C spacecraft and rocket sounding measurements of the 5200 A distribution near the day-side polar cusp. The model requires thermospheric winds of 100-200 m/sec, flowing from day to nightside. Convective velocities near 1000 m/sec were detected by the Explorer spacecraft, as well as a day-to-nightside flow at the cusp.
Parallel Finite Element Electron-Photon Transport Analysis on 2-D Unstructured Mesh
Drumm, C.R.
1999-01-01
A computer code has been developed to solve the linear Boltzmann transport equation on an unstructured mesh of triangles, from a Pro/E model. An arbitriwy arrangement of distinct material regions is allowed. Energy dependence is handled by solving over an arbitrary number of discrete energy groups. Angular de- pendence is treated by Legendre-polynomial expansion of the particle cross sections and a discrete ordinates treatment of the particle fluence. The resulting linear system is solved in parallel with a preconditioned conjugate-gradients method. The solution method is unique, in that the space-angle dependence is solved si- multaneously, eliminating the need for the usual inner iterations. Electron cross sections are obtained from a Goudsrnit-Saunderson modifed version of the CEPXS code. A one-dimensional version of the code has also been develop@ for testing and development purposes.
Parallel FE Electron-Photon Transport Analysis on 2-D Unstructured Mesh
Drumm, C.R.; Lorenz, J.
1999-03-02
A novel solution method has been developed to solve the coupled electron-photon transport problem on an unstructured triangular mesh. Instead of tackling the first-order form of the linear Boltzmann equation, this approach is based on the second-order form in conjunction with the conventional multi-group discrete-ordinates approximation. The highly forward-peaked electron scattering is modeled with a multigroup Legendre expansion derived from the Goudsmit-Saunderson theory. The finite element method is used to treat the spatial dependence. The solution method is unique in that the space-direction dependence is solved simultaneously, eliminating the need for the conventional inner iterations, a method that is well suited for massively parallel computers.
Design of a transportable high efficiency fast neutron spectrometer
NASA Astrophysics Data System (ADS)
Roecker, C.; Bernstein, A.; Bowden, N. S.; Cabrera-Palmer, B.; Dazeley, S.; Gerling, M.; Marleau, P.; Sweany, M. D.; Vetter, K.
2016-08-01
A transportable fast neutron detection system has been designed and constructed for measuring neutron energy spectra and flux ranging from tens to hundreds of MeV. The transportability of the spectrometer reduces the detector-related systematic bias between different neutron spectra and flux measurements, which allows for the comparison of measurements above or below ground. The spectrometer will measure neutron fluxes that are of prohibitively low intensity compared to the site-specific background rates targeted by other transportable fast neutron detection systems. To measure low intensity high-energy neutron fluxes, a conventional capture-gating technique is used for measuring neutron energies above 20 MeV and a novel multiplicity technique is used for measuring neutron energies above 100 MeV. The spectrometer is composed of two Gd containing plastic scintillator detectors arranged around a lead spallation target. To calibrate and characterize the position dependent response of the spectrometer, a Monte Carlo model was developed and used in conjunction with experimental data from gamma ray sources. Multiplicity event identification algorithms were developed and used with a Cf-252 neutron multiplicity source to validate the Monte Carlo model Gd concentration and secondary neutron capture efficiency. The validated Monte Carlo model was used to predict an effective area for the multiplicity and capture gating analyses. For incident neutron energies between 100 MeV and 1000 MeV with an isotropic angular distribution, the multiplicity analysis predicted an effective area of 500 cm2 rising to 5000 cm2. For neutron energies above 20 MeV, the capture-gating analysis predicted an effective area between 1800 cm2 and 2500 cm2. The multiplicity mode was found to be sensitive to the incident neutron angular distribution.
Impurity transport and radiated power loss estimates in NSTX using 2-d USXR arrays
NASA Astrophysics Data System (ADS)
Stutman, Dan; Finkenthal, Michael; Vero, Robert; Roquemore, Lane; Johnson, David; Kaita, Robert
2000-10-01
Large area, low capacitance, absolute photodiodes have been installed in the three ultrasoft X-ray (USXR) arrays operational on NSTX, for the beginning of the high power operation phase. In addition to bandpass filtered measurements in the USXR range, the absolute diodes enable total radiated power measurements and improve the accuracy of the absolute emissivity estimates. The position of the viewing chords with respect to the NSTX vacuum vessel has been measured using a laser pointing technique and the vignetting of the top array by in-vessel structures calibrated using an in-vessel extended light source. The Granetz-Cormack algorithm with Bessel radial functions is used to derive emissivity maps from the measured brightness profiles. The plasma emission in the spectral ranges defined by the bandpass filters on each array (0.3 μm Ti, 10 μm, 100 μm and 500 μm Be) is modeled using impurity line emission data computed with the HULLAC atomic physics package coupled to a 1-d impurity transport code. The evolution of the USXR emissivity, radiated power, and estimated impurity and plasma profiles during MHD phenomena like the Internal Reconnection Event and sawteeth, as well as emission data for ohmic, auxiliary heated and coaxial helicity injection discharges are presented.
Neutron transport in Eulerian coordinates with bulk material motion
Baker, R. S.; Dahl, J. A.; Fichtl, E. D.; Morel, J. E.
2013-07-01
A consistent, numerically stable algorithm for the solution of the neutron transport equation in the presence of a moving material background is presented for one-dimensional spherical geometry. Manufactured solutions are used to demonstrate the correctness and stability of our numerical algorithm. The importance of including moving material corrections is shown for the r-process in proto-neutron stars. (authors)
NASA Astrophysics Data System (ADS)
Kirnev, G.; Fundamenski, W.; Corrigan, G.
2007-06-01
The scrape-off layer (SOL) of the JET tokamak has been modelled using a two-dimensional plasma/neutral code, EDGE2D/NIMBUS, with variable transport coefficients, chosen according to nine candidate theories for radial heat transport in the SOL. Comparison of the radial power width on the outer divertor plates, λq, predicted by modelling and measured experimentally in L-mode and ELM-averaged H-mode at JET is presented. Transport coefficients based on classical and neo-classical ion conduction are found to offer the best agreement with experimentally measured λq magnitude and scaling with target power, upstream density and toroidal field. These results reinforce the findings of an earlier study, based on a simplified model of the SOL (Chankin 1997 Plasma Phys. Control. Fusion 39 1059), and support the earlier estimate of the power width at the entrance of the outer divertor volume in ITER, λq ap 4 mm mapped to the outer mid-plane (Fundamenski et al 2004 Nucl. Fusion 44 20).
NASA Astrophysics Data System (ADS)
Croissant, T.; Lague, D.; Davy, P.
2014-12-01
Numerical models of floodplain dynamics often use a simplified 1D description of flow hydraulics and sediment transport that cannot fully account for differential friction between vegetated banks and low friction in the main channel. Key parameters of such models are the friction coefficient and the description of the channel bathymetry which strongly influence predicted water depth and velocity, and therefore sediment transport capacity. In this study, we use a newly developed 2D hydrodynamic model, Floodos, whose efficiency is a major advantage for exploring channel morphodynamics from a flood event to millennial time scales. We evaluate the quality of Floodos predictions in the Whataroa river, New Zealand and assess the effect of a spatially distributed friction coefficient (SDFC) on long term sediment transport. Predictions from the model are compared to water depth data from a gauging station located on the Whataroa River in Southern Alps, New Zealand. The Digital Elevation Model (DEM) of the 2.5 km long studied reach is derived from a 2010 LiDAR acquisition with 2 m resolution and an interpolated bathymetry. The several large floods experienced by this river during 2010 allow us to access water depth for a wide range of possible river discharges and to retrieve the scaling between these two parameters. The high resolution DEM used has a non-negligible part of submerged bathymetry that airborne LiDAR was not able to capture. Bathymetry can be reconstructed by interpolation methods that introduce several uncertainties concerning water depth predictions. We address these uncertainties inherent to the interpolation using a simplified channel with a geometry (slope and width) similar to the Whataroa river. We then explore the effect of a SDFC on velocity pattern, water depth and sediment transport capacity and discuss its relevance on long term predictions of sediment transport and channel morphodynamics.
Kim, Young-Keun; Kim, Kyung-Soo
2014-10-15
Maritime transportation demands an accurate measurement system to track the motion of oscillating container boxes in real time. However, it is a challenge to design a sensor system that can provide both reliable and non-contact methods of 6-DOF motion measurements of a remote object for outdoor applications. In the paper, a sensor system based on two 2D laser scanners is proposed for detecting the relative 6-DOF motion of a crane load in real time. Even without implementing a camera, the proposed system can detect the motion of a remote object using four laser beam points. Because it is a laser-based sensor, the system is expected to be highly robust to sea weather conditions.
NASA Astrophysics Data System (ADS)
Kim, Young-Keun; Kim, Kyung-Soo
2014-10-01
Maritime transportation demands an accurate measurement system to track the motion of oscillating container boxes in real time. However, it is a challenge to design a sensor system that can provide both reliable and non-contact methods of 6-DOF motion measurements of a remote object for outdoor applications. In the paper, a sensor system based on two 2D laser scanners is proposed for detecting the relative 6-DOF motion of a crane load in real time. Even without implementing a camera, the proposed system can detect the motion of a remote object using four laser beam points. Because it is a laser-based sensor, the system is expected to be highly robust to sea weather conditions.
NASA Astrophysics Data System (ADS)
Mindur, B.; Alimov, S.; Fiutowski, T.; Schulz, C.; Wilpert, T.
2014-12-01
A two-dimensional (2D) position sensitive detector for neutron scattering applications based on low-pressure gas amplification and micro-strip technology was built and tested with an innovative readout electronics and data acquisition system. This detector contains a thin solid neutron converter and was developed for time- and thus wavelength-resolved neutron detection in single-event counting mode, which improves the image contrast in comparison with integrating detectors. The prototype detector of a Micro-Strip Gas Chamber (MSGC) was built with a solid natGd/CsI thermal neutron converter for spatial resolutions of about 100 μm and counting rates up to 107 neutrons/s. For attaining very high spatial resolutions and counting rates via micro-strip readout with centre-of-gravity evaluation of the signal amplitude distributions, a fast, channel-wise, self-triggering ASIC was developed. The front-end chips (MSGCROCs), which are very first signal processing components, are read out into powerful ADC-FPGA boards for on-line data processing and thereafter via Gigabit Ethernet link into the data receiving PC. The workstation PC is controlled by a modular, high performance dedicated software suite. Such a fast and accurate system is crucial for efficient radiography/tomography, diffraction or imaging applications based on high flux thermal neutron beam. In this paper a brief description of the detector concept with its operation principles, readout electronics requirements and design together with the signals processing stages performed in hardware and software are presented. In more detail the neutron test beam conditions and measurement results are reported. The focus of this paper is on the system integration, two dimensional spatial resolution, the time resolution of the readout system and the imaging capabilities of the overall setup. The detection efficiency of the detector prototype is estimated as well.
Scattered Neutron Tomography Based on A Neutron Transport Inverse Problem
William Charlton
2007-07-01
Neutron radiography and computed tomography are commonly used techniques to non-destructively examine materials. Tomography refers to the cross-sectional imaging of an object from either transmission or reflection data collected by illuminating the object from many different directions.
Transport coefficients in superfluid neutron stars
NASA Astrophysics Data System (ADS)
Tolos, Laura; Manuel, Cristina; Sarkar, Sreemoyee; Tarrus, Jaume
2016-01-01
We study the shear and bulk viscosity coefficients as well as the thermal conductivity as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state and the gap of the system. The shear viscosity due to phonon scattering is compared to calculations of that coming from electron collisions. We also comment on the possible consequences for r-mode damping in superfluid neutron stars. Moreover, we find that phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars. We finally obtain a temperature-independent thermal conductivity from phonon collisions and compare it with the electron-muon thermal conductivity in superfluid neutron stars.
Neutrons and Granite: Transport and Activation
Bedrossian, P J
2004-04-13
In typical ground materials, both energy deposition and radionuclide production by energetic neutrons vary with the incident particle energy in a non-monotonic way. We describe the overall balance of nuclear reactions involving neutrons impinging on granite to demonstrate these energy-dependencies. While granite is a useful surrogate for a broad range of soil and rock types, the incorporation of small amounts of water (hydrogen) does alter the balance of nuclear reactions.
NASA Astrophysics Data System (ADS)
Mani, Ramesh; Kriisa, A.
2015-03-01
Negative diagonal magneto-conductivity/resistivity is a spectacular- and thought provoking- property of driven, far-from-equilibrium, low dimensional electronic systems. The physical response of this exotic electronic state is not yet fully understood since it is rarely encountered in experiment. The microwave-radiation-induced zero-resistance state in the high mobility GaAs/AlGaAs 2D electron system is believed to be an example where negative magneto-conductivity/resistivity is responsible for the observed phenomena. Here, we examine the magneto-transport characteristics of this negative conductivity/resistivity state in the microwave photo-excited two-dimensional electron system (2DES) through a numerical solution of the associated boundary value problem. The results suggest, surprisingly, that a bare negative diagonal conductivity/resistivity state in the 2DES under photo-excitation should yield a positive diagonal resistance with a concomitant sign reversal in the Hall voltage. Transport measurements are supported by the DOE, Office of Basic Energy Sciences, Material Sciences and Engineering Division under DE-SC0001762. Additional support by the ARO under W911NF-07-01-015.
Computation of neutron fluxes in clusters of fuel pins arranged in hexagonal assemblies (2D and 3D)
Prabha, H.; Marleau, G.
2012-07-01
For computations of fluxes, we have used Carvik's method of collision probabilities. This method requires tracking algorithms. An algorithm to compute tracks (in 2D and 3D) has been developed for seven hexagonal geometries with cluster of fuel pins. This has been implemented in the NXT module of the code DRAGON. The flux distribution in cluster of pins has been computed by using this code. For testing the results, they are compared when possible with the EXCELT module of the code DRAGON. Tracks are plotted in the NXT module by using MATLAB, these plots are also presented here. Results are presented with increasing number of lines to show the convergence of these results. We have numerically computed volumes, surface areas and the percentage errors in these computations. These results show that 2D results converge faster than 3D results. The accuracy on the computation of fluxes up to second decimal is achieved with fewer lines. (authors)
Jones, Edward H; Smith, Colin C
2005-12-01
This paper describes an investigation into non-equilibrium partitioning tracer transport and interaction with non-aqueous-phase liquid (NAPL) contaminated water-saturated porous media using a two-dimensional (2-D) physical modelling methodology. A fluorescent partitioning tracer is employed within a transparent porous model which when imaged by a CCD digital camera can provide full spatial tracer concentrations and tracer breakthrough curves. Quasi one-dimensional (1-D) benchmarking tests in models packed with various combinations of clean quartz sand and NAPL are described. These modelled residual NAPL saturations, S(n), of 0-15%. Results demonstrated that the fluorescent partitioning tracer was able to detect and quantify the presence of NAPL at low flow rates. At larger flow rates and/or higher NAPL saturations, the tracer increasingly underpredicted the NAPL volume as expected and this is attributed primarily to non-equilibrium partitioning. Despite little change in permeability, change in NAPL saturations from 4% to 8% resulted in significant NAPL saturation underestimates at the same flow rates implying coalescence of NAPL into wider separated but larger ganglia. A 2-D investigation of an idealised heterogeneous residual NAPL contaminated flow field indicated little permeability change in the NAPL contaminated zone and thus little flow bypassing, leading to reduced underpredictions of NAPL saturations than for equivalent quasi 1-D cases. This was attributed to increased 'sampling' of the NAPL by the tracer. The process is clearly visually identifiable from the experimental images. This rapid and relatively inexpensive experimental method is of value in laboratory studies of partitioning tracer behaviour in porous media; in particular, the ability to observe full field concentrations makes it valuable for the study of complex heterogeneous systems. PMID:16298415
Galián, Carmen; Manon, Florence; Dezi, Manuela; Torres, Cristina; Ebel, Christine; Lévy, Daniel; Jault, Jean-Michel
2011-01-01
Optimized protocols for achieving high-yield expression, purification and reconstitution of membrane proteins are required to study their structure and function. We previously reported high-level expression in Escherichia coli of active BmrC and BmrD proteins from Bacillus subtilis, previously named YheI and YheH. These proteins are half-transporters which belong to the ABC (ATP-Binding Cassette) superfamily and associate in vivo to form a functional transporter able to efflux drugs. In this report, high-yield purification and functional reconstitution were achieved for the heterodimer BmrC/BmrD. In contrast to other detergents more efficient for solubilizing the transporter, dodecyl-ß-D-maltoside (DDM) maintained it in a drug-sensitive and vanadate-sensitive ATPase-competent state after purification by affinity chromatography. High amounts of pure proteins were obtained which were shown either by analytical ultracentrifugation or gel filtration to form a monodisperse heterodimer in solution, which was notably stable for more than one month at 4°C. Functional reconstitution using different lipid compositions induced an 8-fold increase of the ATPase activity (kcat∼5 s−1). We further validated that the quality of the purified BmrC/BmrD heterodimer is suitable for structural analyses, as its reconstitution at high protein densities led to the formation of 2-D crystals. Electron microscopy of negatively stained crystals allowed the calculation of a projection map at 20 Å resolution revealing that BmrC/BmrD might assemble into oligomers in a lipidic environment. PMID:21602923
Galián, Carmen; Manon, Florence; Dezi, Manuela; Torres, Cristina; Ebel, Christine; Lévy, Daniel; Jault, Jean-Michel
2011-01-01
Optimized protocols for achieving high-yield expression, purification and reconstitution of membrane proteins are required to study their structure and function. We previously reported high-level expression in Escherichia coli of active BmrC and BmrD proteins from Bacillus subtilis, previously named YheI and YheH. These proteins are half-transporters which belong to the ABC (ATP-Binding Cassette) superfamily and associate in vivo to form a functional transporter able to efflux drugs. In this report, high-yield purification and functional reconstitution were achieved for the heterodimer BmrC/BmrD. In contrast to other detergents more efficient for solubilizing the transporter, dodecyl-ß-D-maltoside (DDM) maintained it in a drug-sensitive and vanadate-sensitive ATPase-competent state after purification by affinity chromatography. High amounts of pure proteins were obtained which were shown either by analytical ultracentrifugation or gel filtration to form a monodisperse heterodimer in solution, which was notably stable for more than one month at 4°C. Functional reconstitution using different lipid compositions induced an 8-fold increase of the ATPase activity (k(cat)∼5 s(-1)). We further validated that the quality of the purified BmrC/BmrD heterodimer is suitable for structural analyses, as its reconstitution at high protein densities led to the formation of 2-D crystals. Electron microscopy of negatively stained crystals allowed the calculation of a projection map at 20 Å resolution revealing that BmrC/BmrD might assemble into oligomers in a lipidic environment. PMID:21602923
Douard, Veronique; Sabbagh, Yves; Lee, Jacklyn; Patel, Chirag; Kemp, Francis W.; Bogden, John D.; Lin, Sheldon
2013-01-01
We recently discovered that chronic high fructose intake by lactating rats prevented adaptive increases in rates of active intestinal Ca2+ transport and in levels of 1,25-(OH)2D3, the active form of vitamin D. Since sufficient Ca2+ absorption is essential for skeletal growth, our discovery may explain findings that excessive consumption of sweeteners compromises bone integrity in children. We tested the hypothesis that 1,25-(OH)2D3 mediates the inhibitory effect of excessive fructose intake on active Ca2+ transport. First, compared with those fed glucose or starch, growing rats fed fructose for 4 wk had a marked reduction in intestinal Ca2+ transport rate as well as in expression of intestinal and renal Ca2+ transporters that was tightly associated with decreases in circulating levels of 1,25-(OH)2D3, bone length, and total bone ash weight but not with serum parathyroid hormone (PTH). Dietary fructose increased the expression of 24-hydroxylase (CYP24A1) and decreased that of 1α-hydroxylase (CYP27B1), suggesting that fructose might enhance the renal catabolism and impair the synthesis, respectively, of 1,25-(OH)2D3. Serum FGF23, which is secreted by osteocytes and inhibits CYP27B1 expression, was upregulated, suggesting a potential role of bone in mediating the fructose effects on 1,25-(OH)2D3 synthesis. Second, 1,25-(OH)2D3 treatment rescued the fructose effect and normalized intestinal and renal Ca2+ transporter expression. The mechanism underlying the deleterious effect of excessive fructose intake on intestinal and renal Ca2+ transporters is a reduction in serum levels of 1,25-(OH)2D3. This finding is significant because of the large amounts of fructose now consumed by Americans increasingly vulnerable to Ca2+ and vitamin D deficiency. PMID:23571713
The Lattice Boltzmann Method applied to neutron transport
Erasmus, B.; Van Heerden, F. A.
2013-07-01
In this paper the applicability of the Lattice Boltzmann Method to neutron transport is investigated. One of the main features of the Lattice Boltzmann method is the simultaneous discretization of the phase space of the problem, whereby particles are restricted to move on a lattice. An iterative solution of the operator form of the neutron transport equation is presented here, with the first collision source as the starting point of the iteration scheme. A full description of the discretization scheme is given, along with the quadrature set used for the angular discretization. An angular refinement scheme is introduced to increase the angular coverage of the problem phase space and to mitigate lattice ray effects. The method is applied to a model problem to investigate its applicability to neutron transport and the results are compared to a reference solution calculated, using MCNP. (authors)
Hong, Tao; Stock, C.; Cabrera, I.; Broholm, C.; Qiu, Y.; Leao, J. B.; Poulton, S. J.; Copley, J.R.D.
2010-01-01
We report inelastic neutron scattering study of a quasi-two-dimensional S=1/2 dimer system piperazinium hexachlorodicuprate under hydrostatic pressure. The spin gap {Delta} becomes softened with the increase of the hydrostatic pressure up to P = 9.0 kbar. The observed threefold degenerate triplet excitation at P = 6.0 kbar is consistent with the theoretical prediction and the bandwidth of the dispersion relation is unaffected within the experimental uncertainty. At P = 9.0 kbar the spin gap is reduced to {Delta} = 0.55 meV from {Delta} = 1.0 meV at ambient pressure.
Neutron transport study of a beam port based dynamic neutron radiography facility
NASA Astrophysics Data System (ADS)
Khaial, Anas M.
Neutron radiography has the ability to differentiate between gas and liquid in two-phase flow due both to the density difference and the high neutron scattering probability of hydrogen. Previous studies have used dynamic neutron radiography -- in both real-time and high-speed -- for air-water, steam-water and gas-liquid metal two-phase flow measurements. Radiography with thermal neutrons is straightforward and efficient as thermal neutrons are easier to detect with relatively higher efficiency and can be easily extracted from nuclear reactor beam ports. The quality of images obtained using neutron radiography and the imaging speed depend on the neutron beam intensity at the imaging plane. A high quality neutron beam, with thermal neutron intensity greater than 3.0x 10 6 n/cm2-s and a collimation ratio greater than 100 at the imaging plane, is required for effective dynamic neutron radiography up to 2000 frames per second. The primary objectives of this work are: (1) to optimize a neutron radiography facility for dynamic neutron radiography applications and (2) to investigate a new technique for three-dimensional neutron radiography using information obtained from neutron scattering. In this work, neutron transport analysis and experimental validation of a dynamic neutron radiography facility is studied with consideration of real-time and high-speed neutron radiography requirements. A beam port based dynamic neutron radiography facility, for a target thermal neutron flux of 1.0x107 n/cm2-s, has been analyzed, constructed and experimentally verified at the McMaster Nuclear Reactor. The neutron source strength at the beam tube entrance is evaluated experimentally by measuring the thermal and fast neutron fluxes using copper activation flux-mapping technique. The development of different facility components, such as beam tube liner, gamma ray filter, beam shutter and biological shield, is achieved analytically using neutron attenuation and divergence theories. Monte
Computing the moments of the neutron population using deterministic neutron transport
Fichtl, E. D.; Baker, R. S.
2013-07-01
It is important to treat the inherent stochasticity of the fission process in systems where the behavior of the system is stochastic. This occurs when there are few neutrons in the system, or when the neutron source is weak. In order to characterize such systems, the capability to compute the first four moments of the neutron population distribution has been added to the deterministic neutral particle transport code, PARTISN. The moments are then fitted to probability density functions from the Pearson family. PARTISN is compared against MCNP6, with which it agrees well. (authors)
NASA Astrophysics Data System (ADS)
Saadi, S.; Touiza, M.; Guessoum, A.
In this study, we present an implementation on FPGA of 2D signals Encoder/Decoder using dyadic Discrete Wavelet Transform based on quadrature mirror filters, by applying fast wavelet Mallat`s algorithm. The wavelet coefficients will be encoded by Huffman code in order to be transmitted progressively through an Ethernet TCP/IP based connection. The proposed study is implemented and synthesized in VHDL for Xilinx Virtex-IIV2MB1000 FPGA device using ISE 8.1 and simulated on Modelsim PE 6.0d. The synthesis results are presented in detail. The proposed design can substantially accelerate the DWT and the possible reconfiguration can be exploited to reach a higher performance in the future. The system is designed to be integrated as an extension to the nuclear imaging system implemented around our nuclear research reactor. Assuming a Pentium4 processor with clock frequency of 3.3 GHz for the Matlab software implementation, a speed up of over 5 times for a picture size of 256 x 256 was achieved.
Kraidith, Kamonshanok; Svasti, Saovaros; Teerapornpuntakit, Jarinthorn; Vadolas, Jim; Chaimana, Rattana; Lapmanee, Sarawut; Suntornsaratoon, Panan; Krishnamra, Nateetip; Fucharoen, Suthat; Charoenphandhu, Narattaphol
2016-07-01
Previously, β-thalassemia, an inherited anemic disorder with iron overload caused by loss-of-function mutation of β-globin gene, has been reported to induce osteopenia and impaired whole body calcium metabolism, but the pathogenesis of aberrant calcium homeostasis remains elusive. Herein, we investigated how β-thalassemia impaired intestinal calcium absorption and whether it could be restored by administration of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] or hepcidin, the latter of which was the liver-derived antagonist of intestinal iron absorption. The results showed that, in hemizygous β-globin knockout (BKO) mice, the duodenal calcium transport was lower than that in wild-type littermates, and severity was especially pronounced in female mice. Both active and passive duodenal calcium fluxes in BKO mice were found to be less than those in normal mice. This impaired calcium transport could be restored by 7-day 1,25(OH)2D3 treatment. The 1,25(OH)2D3-induced calcium transport was diminished by inhibitors of calcium transporters, e.g., L-type calcium channel, NCX1, and PMCA1b, as well as vesicular transport inhibitors. Interestingly, the duodenal calcium transport exhibited an inverse correlation with transepithelial iron transport, which was markedly enhanced in thalassemic mice. Thus, 3-day subcutaneous hepcidin injection and acute direct hepcidin exposure in the Ussing chamber were capable of restoring the thalassemia-associated impairment of calcium transport; however, the positive effect of hepcidin on calcium transport was completely blocked by proteasome inhibitors MG132 and bortezomib. In conclusion, both 1,25(OH)2D3 and hepcidin could be used to alleviate the β-thalassemia-associated impairment of calcium absorption. Therefore, our study has shed light on the development of a treatment strategy to rescue calcium dysregulation in β-thalassemia. PMID:27245334
3D Multigroup Sn Neutron Transport Code
2001-02-14
ATTILA is a 3D multigroup transport code with arbitrary order ansotropic scatter. The transport equation is solved in first order form using a tri-linear discontinuous spatial differencing on an arbitrary tetrahedral mesh. The overall solution technique is source iteration with DSA acceleration of the scattering source. Anisotropic boundary and internal sources may be entered in the form of spherical harmonics moments. Alpha and k eigenvalue problems are allowed, as well as fixed source problems. Forwardmore » and adjoint solutions are available. Reflective, vacumn, and source boundary conditions are available. ATTILA can perform charged particle transport calculations using slowing down (CSD) terms. ATTILA can also be used to peform infra-red steady-state calculations for radiative transfer purposes.« less
3D Multigroup Sn Neutron Transport Code
McGee, John; Wareing, Todd; Pautz, Shawn
2001-02-14
ATTILA is a 3D multigroup transport code with arbitrary order ansotropic scatter. The transport equation is solved in first order form using a tri-linear discontinuous spatial differencing on an arbitrary tetrahedral mesh. The overall solution technique is source iteration with DSA acceleration of the scattering source. Anisotropic boundary and internal sources may be entered in the form of spherical harmonics moments. Alpha and k eigenvalue problems are allowed, as well as fixed source problems. Forward and adjoint solutions are available. Reflective, vacumn, and source boundary conditions are available. ATTILA can perform charged particle transport calculations using slowing down (CSD) terms. ATTILA can also be used to peform infra-red steady-state calculations for radiative transfer purposes.
In situ quantification and visualization of lithium transport with neutrons.
Liu, Danny X; Wang, Jinghui; Pan, Ke; Qiu, Jie; Canova, Marcello; Cao, Lei R; Co, Anne C
2014-09-01
A real-time quantification of Li transport using a nondestructive neutron method to measure the Li distribution upon charge and discharge in a Li-ion cell is reported. By using in situ neutron depth profiling (NDP), we probed the onset of lithiation in a high-capacity Sn anode and visualized the enrichment of Li atoms on the surface followed by their propagation into the bulk. The delithiation process shows the removal of Li near the surface, which leads to a decreased coulombic efficiency, likely because of trapped Li within the intermetallic material. The developed in situ NDP provides exceptional sensitivity in the temporal and spatial measurement of Li transport within the battery material. This diagnostic tool opens up possibilities to understand rates of Li transport and their distribution to guide materials development for efficient storage mechanisms. Our observations provide important mechanistic insights for the design of advanced battery materials. PMID:25044527
CMFD acceleration of spatial domain-decomposed neutron transport problems
Kelley, B. W.; Larsen, E. W.
2012-07-01
A significant limitation to parallelizing the solution of neutron transport problems is the need for sweeps across the entirety of the problem domain. Angular domain decomposition is common practice, as the equations for each direction are independent aside from their shared scattering/fission source. Accordingly, spatial domain decomposition does not naturally arise in the transport equations and is therefore less frequent in practice. In this paper, we show that a neutron transport domain can be straightforwardly divided into independent, parallelizable sweep regions, globally linked with the standard CMFD method, with an additional update equation. We verify, theoretically (via Fourier analysis) and computationally, that the convergence properties of this method are stable and nominally as rapid as standard CMFD. (authors)
Singular perturbation analysis of the neutron transport equation
Losey, D.C.; Lee, J.C.
1996-07-01
A singular perturbation technique is applied to the one-speed, one- dimensional neutron transport equation with isotropic scattering. Our technique extends previous singular perturbation applications to higher-order and reduces the transport problem to a series of diffusion theory problems in the interior medium and a series of analytically solvable transport problems in the boundary layers. Asymptotic matching links the two solutions, yielding boundary conditions and a composite expansion valid throughout the media. Our formulation generates an accurate correction for the material interface condition used in global diffusion theory calculations.
Graphical User Interface for Simplified Neutron Transport Calculations
Schwarz, Randolph; Carter, Leland L
2011-07-18
A number of codes perform simple photon physics calculations. The nuclear industry is lacking in similar tools to perform simplified neutron physics shielding calculations. With the increased importance of performing neutron calculations for homeland security applications and defense nuclear nonproliferation tasks, having an efficient method for performing simple neutron transport calculations becomes increasingly important. Codes such as Monte Carlo N-particle (MCNP) can perform the transport calculations; however, the technical details in setting up, running, and interpreting the required simulations are quite complex and typically go beyond the abilities of most users who need a simple answer to a neutron transport calculation. The work documented in this report resulted in the development of the NucWiz program, which can create an MCNP input file for a set of simple geometries, source, and detector configurations. The user selects source, shield, and tally configurations from a set of pre-defined lists, and the software creates a complete MCNP input file that can be optionally run and the results viewed inside NucWiz.
A deterministic method for transient, three-dimensional neutron transport
Goluoglu, S.; Bentley, C.; DeMeglio, R.; Dunn, M.; Norton, K.; Pevey, R.; Suslov, I.; Dodds, H.L.
1998-05-01
A deterministic method for solving the time-dependent, three-dimensional Boltzmann transport equation with explicit representation of delayed neutrons has been developed and evaluated. The methodology used in this study for the time variable of the neutron flux is known as the improved quasi-static (IQS) method. The position, energy, and angle-dependent neutron flux is computed deterministically by using the three-dimensional discrete ordinates code TORT. This paper briefly describes the methodology and selected results. The code developed at the University of Tennessee based on this methodology is called TDTORT. TDTORT can be used to model transients involving voided and/or strongly absorbing regions that require transport theory for accuracy. This code can also be used to model either small high-leakage systems, such as space reactors, or asymmetric control rod movements. TDTORT can model step, ramp, step followed by another step, and step followed by ramp type perturbations. It can also model columnwise rod movement. A special case of columnwise rod movement in a three-dimensional model of a boiling water reactor (BWR) with simple adiabatic feedback is also included. TDTORT is verified through several transient one-dimensional, two-dimensional, and three-dimensional benchmark problems. The results show that the transport methodology and corresponding code developed in this work have sufficient accuracy and speed for computing the dynamic behavior of complex multi-dimensional neutronic systems.
TRINIDY: Transport of ions and neutrons in dynamic materials
NASA Astrophysics Data System (ADS)
Spencer, Joshua B.
The TRansport of Ions and Neutrons In DYnamic (TRINIDY) materials code is a new code designed to study the effects of high fluence ion and neutron radiation on solid surfaces. This is done in a quasi-deterministic way, in that the transport of pseudo-particles within target material is accomplished via a Monte Carlo approach while the changes within the target are calculated deterministically by use of a one-dimensional Lagrangian mesh into which each of the tracked pseudo-particles are either deposited or removed. After each cycle the mesh is allowed to relax to a solid state areal density adjusted for its new constituency. As a natural corollary to the change in material compositions in each mesh element comes the resultant change in thickness of the target. Within TRINIDY charged particles are transported by means of a Binary Collision Approximation (BCA) where the elastic nuclear and inelastic electronic stopping forces are decoupled in such a way that the projectile only interacts with one target atom at a time. TRINIDY builds on the legacy of the Transport of Ions in Matter (TRIM), TRIM-SP and TRIDYN codes, in that it uses Biersack's analytic approximation to the quantum scattering integral and a screened coulomb potential as the basic for the charged particle transport. The neutron transport within TRINIDY is based on 32-group elastic scattering and total absorption cross-section data which has been derived from the ENDF7 continuous neutron data sets for each of the naturally occurring elements Hydrogen through Uranium. This work is comprised of essentially three sections. First, there is a detailed technical description of the science behind TRINIDY. Secondly there will be a complete write-up of the validation and verification work done during the development of TRINIDY. Lastly, a series of practical demonstration of particular interest to the semi-conductor industry are presented to exemplify the use of TRINIDY within the realm of applied materials
Neutron transport analysis for nuclear reactor design
Vujic, J.L.
1993-11-30
Replacing regular mesh-dependent ray tracing modules in a collision/transfer probability (CTP) code with a ray tracing module based upon combinatorial geometry of a modified geometrical module (GMC) provides a general geometry transfer theory code in two dimensions (2D) for analyzing nuclear reactor design and control. The primary modification of the GMC module involves generation of a fixed inner frame and a rotating outer frame, where the inner frame contains all reactor regions of interest, e.g., part of a reactor assembly, an assembly, or several assemblies, and the outer frame, with a set of parallel equidistant rays (lines) attached to it, rotates around the inner frame. The modified GMC module allows for determining for each parallel ray (line), the intersections with zone boundaries, the path length between the intersections, the total number of zones on a track, the zone and medium numbers, and the intersections with the outer surface, which parameters may be used in the CTP code to calculate collision/transfer probability and cross-section values. 28 figures.
Neutron transport analysis for nuclear reactor design
Vujic, Jasmina L.
1993-01-01
Replacing regular mesh-dependent ray tracing modules in a collision/transfer probability (CTP) code with a ray tracing module based upon combinatorial geometry of a modified geometrical module (GMC) provides a general geometry transfer theory code in two dimensions (2D) for analyzing nuclear reactor design and control. The primary modification of the GMC module involves generation of a fixed inner frame and a rotating outer frame, where the inner frame contains all reactor regions of interest, e.g., part of a reactor assembly, an assembly, or several assemblies, and the outer frame, with a set of parallel equidistant rays (lines) attached to it, rotates around the inner frame. The modified GMC module allows for determining for each parallel ray (line), the intersections with zone boundaries, the path length between the intersections, the total number of zones on a track, the zone and medium numbers, and the intersections with the outer surface, which parameters may be used in the CTP code to calculate collision/transfer probability and cross-section values.
The AN neutron transport by nodal diffusion
Barbarino, A.; Tomatis, D.
2013-07-01
The two group diffusion model combined to a nodal approach in space is the preferred scheme for the industrial simulation of nuclear water reactors. The main selling point is the speed of computation, allowing a large number of parametric studies. Anyway, the drawbacks of the underlying diffusion equation may arise with highly heterogeneous interfaces, often encountered in modern UO{sub 2} and MO{sub x} fuel loading patterns, and boron less controlled systems. This paper aims at showing how the simplified AN transport model, equivalent to the well known SPN, can be implemented in standard diffusion codes with minor modifications. Some numerical results are illustrated. (authors)
Livnat-Levanon, Nurit; I Gilson, Amy; Ben-Tal, Nir; Lewinson, Oded
2016-01-01
ABC transporters comprise a large and ubiquitous family of proteins. From bacteria to man they translocate solutes at the expense of ATP hydrolysis. Unlike other enzymes that use ATP as an energy source, ABC transporters are notorious for having high levels of basal ATPase activity: they hydrolyze ATP also in the absence of their substrate. It is unknown what are the effects of such prolonged and constant activity on the stability and function of ABC transporters or any other enzyme. Here we report that prolonged ATP hydrolysis is beneficial to the ABC transporter BtuC2D2. Using ATPase assays, surface plasmon resonance interaction experiments, and transport assays we observe that the constantly active transporter remains stable and functional for much longer than the idle one. Remarkably, during extended activity the transporter undergoes a slow conformational change (hysteresis) and gradually attains a hyperactive state in which it is more active than it was to begin with. This phenomenon is different from stabilization of enzymes by ligand binding: the hyperactive state is only reached through ATP hydrolysis, and not ATP binding. BtuC2D2 displays a strong conformational memory for this excited state, and takes hours to return to its basal state after catalysis terminates. PMID:26905293
Livnat-Levanon, Nurit; I. Gilson, Amy; Ben-Tal, Nir; Lewinson, Oded
2016-01-01
ABC transporters comprise a large and ubiquitous family of proteins. From bacteria to man they translocate solutes at the expense of ATP hydrolysis. Unlike other enzymes that use ATP as an energy source, ABC transporters are notorious for having high levels of basal ATPase activity: they hydrolyze ATP also in the absence of their substrate. It is unknown what are the effects of such prolonged and constant activity on the stability and function of ABC transporters or any other enzyme. Here we report that prolonged ATP hydrolysis is beneficial to the ABC transporter BtuC2D2. Using ATPase assays, surface plasmon resonance interaction experiments, and transport assays we observe that the constantly active transporter remains stable and functional for much longer than the idle one. Remarkably, during extended activity the transporter undergoes a slow conformational change (hysteresis) and gradually attains a hyperactive state in which it is more active than it was to begin with. This phenomenon is different from stabilization of enzymes by ligand binding: the hyperactive state is only reached through ATP hydrolysis, and not ATP binding. BtuC2D2 displays a strong conformational memory for this excited state, and takes hours to return to its basal state after catalysis terminates. PMID:26905293
Neutron imaging of ion transport in mesoporous carbon materials.
Sharma, Ketki; Bilheux, Hassina Z; Walker, Lakeisha M H; Voisin, Sophie; Mayes, Richard T; Kiggans, Jim O; Yiacoumi, Sotira; DePaoli, David W; Dai, Sheng; Tsouris, Costas
2013-07-28
Neutron imaging is presented as a tool for quantifying the diffusion of ions inside porous materials, such as carbon electrodes used in the desalination process via capacitive deionization and in electrochemical energy-storage devices. Monolithic mesoporous carbon electrodes of ∼10 nm pore size were synthesized based on a soft-template method. The electrodes were used with an aqueous solution of gadolinium nitrate in an electrochemical flow-through cell designed for neutron imaging studies. Sequences of neutron images were obtained under various conditions of applied potential between the electrodes. The images revealed information on the direction and magnitude of ion transport within the electrodes. From the time-dependent concentration profiles inside the electrodes, the average value of the effective diffusion coefficient for gadolinium ions was estimated to be 2.09 ± 0.17 × 10(-11) m(2) s(-1) at 0 V and 1.42 ± 0.06 × 10(-10) m(2) s(-1) at 1.2 V. The values of the effective diffusion coefficient obtained from neutron imaging experiments can be used to evaluate model predictions of the ion transport rate in capacitive deionization and electrochemical energy-storage devices. PMID:23756558
Exact-to-precision generalized perturbation for neutron transport calculation
Wang, C.; Abdel-Khalik, H. S.
2013-07-01
This manuscript extends the exact-to-precision generalized perturbation theory (E{sub P}GPT), introduced previously, to neutron transport calculation whereby previous developments focused on neutron diffusion calculation only. The E{sub P}GPT collectively denotes new developments in generalized perturbation theory (GPT) that place premium on computational efficiency and defendable accuracy in order to render GPT a standard analysis tool in routine design and safety reactor calculations. EPGPT constructs a surrogate model with quantifiable accuracy which can replace the original neutron transport model for subsequent engineering analysis, e.g. functionalization of the homogenized few-group cross sections in terms of various core conditions, sensitivity analysis and uncertainty quantification. This is achieved by reducing the effective dimensionality of the state variable (i.e. neutron angular flux) by projection onto an active subspace. Confining the state variations to the active subspace allows one to construct a small number of what is referred to as the 'active' responses which are solely dependent on the physics model rather than on the responses of interest, the number of input parameters, or the number of points in the state phase space. (authors)
NASA Astrophysics Data System (ADS)
Barreteau, C.; Michon, B.; Besnard, C.; Giannini, E.
2016-06-01
Silicon and Germanium monopnictides SiP, SiAs, GeP and GeAs form a family of 2D layered semiconductors. We have succeeded in growing bulk single crystals of these compounds by melt-growth under high pressure (0.5-1 GPa) in a cubic anvil hot press. Large (mm-size), shiny, micaceous crystals of GeP, GeAs and SiAs were obtained, and could be exfoliated into 2D flakes. Small and brittle crystals of SiP were yielded by this method. High-pressure sintered polycrystalline SiP and GeAs have also been successfully used as a precursor in the Chemical Vapor Transport growth of these crystals in the presence of I2 as a transport agent. All compounds are found to crystallize in the expected layered structure and do not undergo any structural transition at low temperature, as shown by Raman spectroscopy down to T=5 K. All materials exhibit a semiconducting behavior. The electrical resistivity of GeP, GeAs and SiAs is found to depend on temperature following a 2D-Variable Range Hopping conduction mechanism. The availability of bulk crystals of these compounds opens new perspectives in the field of 2D semiconducting materials for device applications.
Sun, Jianjun; Xu, Jinbin; Cairns, Nigel J.; Perlmutter, Joel S.; Mach, Robert H.
2012-01-01
The dopamine D1, D2, D3 receptors, vesicular monoamine transporter type-2 (VMAT2), and dopamine transporter (DAT) densities were measured in 11 aged human brains (aged 77–107.8, mean: 91 years) by quantitative autoradiography. The density of D1 receptors, VMAT2, and DAT was measured using [3H]SCH23390, [3H]dihydrotetrabenazine, and [3H]WIN35428, respectively. The density of D2 and D3 receptors was calculated using the D3-preferring radioligand, [3H]WC-10 and the D2-preferring radioligand [3H]raclopride using a mathematical model developed previously by our group. Dopamine D1, D2, and D3 receptors are extensively distributed throughout striatum; the highest density of D3 receptors occurred in the nucleus accumbens (NAc). The density of the DAT is 10–20-fold lower than that of VMAT2 in striatal regions. Dopamine D3 receptor density exceeded D2 receptor densities in extrastriatal regions, and thalamus contained a high level of D3 receptors with negligible D2 receptors. The density of dopamine D1 linearly correlated with D3 receptor density in the thalamus. The density of the DAT was negligible in the extrastriatal regions whereas the VMAT2 was expressed in moderate density. D3 receptor and VMAT2 densities were in similar level between the aged human and aged rhesus brain samples, whereas aged human brain samples had lower range of densities of D1 and D2 receptors and DAT compared with the aged rhesus monkey brain. The differential density of D3 and D2 receptors in human brain will be useful in the interpretation of PET imaging studies in human subjects with existing radiotracers, and assist in the validation of newer PET radiotracers having a higher selectivity for dopamine D2 or D3 receptors. PMID:23185343
Mathematical models for volume rendering and neutron transport
Max, N.
1994-09-01
This paper reviews several different models for light interaction with volume densities of absorbing, glowing, reflecting, or scattering material. They include absorption only, glow only, glow and absorption combined, single scattering of external illumination, and multiple scattering. The models are derived from differential equations, and illustrated on a data set representing a cloud. They are related to corresponding models in neutron transport. The multiple scattering model uses an efficient method to propagate the radiation which does not suffer from the ray effect.
Escobar, M.; Meyerovich, A. E.
2014-12-15
We discuss transport of particles along random rough surfaces in quantum size effect conditions. As an intriguing application, we analyze gravitationally quantized ultracold neutrons in rough waveguides in conjunction with GRANIT experiments (ILL, Grenoble). We present a theoretical description of these experiments in the biased diffusion approximation for neutron mirrors with both one- and two-dimensional (1D and 2D) roughness. All system parameters collapse into a single constant which determines the depletion times for the gravitational quantum states and the exit neutron count. This constant is determined by a complicated integral of the correlation function (CF) of surface roughness. The reliable identification of this CF is always hindered by the presence of long fluctuation-driven correlation tails in finite-size samples. We report numerical experiments relevant for the identification of roughness of a new GRANIT waveguide and make predictions for ongoing experiments. We also propose a radically new design for the rough waveguide.
NASA Astrophysics Data System (ADS)
Escobar, M.; Meyerovich, A. E.
2014-12-01
We discuss transport of particles along random rough surfaces in quantum size effect conditions. As an intriguing application, we analyze gravitationally quantized ultracold neutrons in rough waveguides in conjunction with GRANIT experiments (ILL, Grenoble). We present a theoretical description of these experiments in the biased diffusion approximation for neutron mirrors with both one- and two-dimensional (1D and 2D) roughness. All system parameters collapse into a single constant which determines the depletion times for the gravitational quantum states and the exit neutron count. This constant is determined by a complicated integral of the correlation function (CF) of surface roughness. The reliable identification of this CF is always hindered by the presence of long fluctuation-driven correlation tails in finite-size samples. We report numerical experiments relevant for the identification of roughness of a new GRANIT waveguide and make predictions for ongoing experiments. We also propose a radically new design for the rough waveguide.
Benchmarking of Neutron Production of Heavy-Ion Transport Codes
Remec, Igor; Ronningen, Reginald M.; Heilbronn, Lawrence
2012-01-01
Accurate prediction of radiation fields generated by heavy ion interactions is important in medical applications, space missions, and in design and operation of rare isotope research facilities. In recent years, several well-established computer codes in widespread use for particle and radiation transport calculations have been equipped with the capability to simulate heavy ion transport and interactions. To assess and validate these capabilities, we performed simulations of a series of benchmark-quality heavy ion experiments with the computer codes FLUKA, MARS15, MCNPX, and PHITS. We focus on the comparisons of secondary neutron production. Results are encouraging; however, further improvements in models and codes and additional benchmarking are required.
Daniels, J.; Williams, J.; Asherson, P.; McGuffin, P.; Owen, M.
1995-02-27
It has been suggested that the cytochrome P450 mono-oxygenase, debrisoquine 4-hydroxylase, is involved in the catabolism and processing of neurotransmitters subsequent to their reuptake into target cells. It is also thought to be related to the dopamine transporter that acts to take released dopamine back up into presynaptic terminals. The present study used the association approach to test the hypothesis that mutations in the genes for debrisoquine 4-hydroxylase (CYP2D6) and the dopamine transporter (DAT) confer susceptibility to schizophrenia. There were no differences in allele or genotype frequencies between patients and controls in the mutations causing the poor metaboliser phenotype in CYP2D6. In addition there was no association found between schizophrenia and a 48 bp repeat within the 3{prime} untranslated region of DAT. 18 refs., 2 tabs.
Neutron transport in WIMS by the characteristics method
Halsall, M.J. )
1993-01-01
The common methods of solving the neutron transport equation in reactor assembly geometries involve some geometric approximation. The standard differential transport methods and diffusion methods rely on pin-cell smearing, and transmission probability methods make approximations to the boundary fluxes linking pin cells. Integral transport methods (collision probabilities) can cope with pin geometries by numerical integration but require excessive computing times that increase with the square of the number of regions. The characteristics method in WIMS, known as CACTUS, solves the differential transport equation by a numerical tracking technique whose accuracy is limited only by computing resources; in its WIMS implementation it can handle any pin-type geometry without the need for preliminary spatial smearing.
An Improved Neutron Transport Algorithm for Space Radiation
NASA Technical Reports Server (NTRS)
Heinbockel, John H.; Clowdsley, Martha S.; Wilson, John W.
2000-01-01
A low-energy neutron transport algorithm for use in space radiation protection is developed. The algorithm is based upon a multigroup analysis of the straight-ahead Boltzmann equation by using a mean value theorem for integrals. This analysis is accomplished by solving a realistic but simplified neutron transport test problem. The test problem is analyzed by using numerical and analytical procedures to obtain an accurate solution within specified error bounds. Results from the test problem are then used for determining mean values associated with rescattering terms that are associated with a multigroup solution of the straight-ahead Boltzmann equation. The algorithm is then coupled to the Langley HZETRN code through the evaporation source term. Evaluation of the neutron fluence generated by the solar particle event of February 23, 1956, for a water and an aluminum-water shield-target configuration is then compared with LAHET and MCNPX Monte Carlo code calculations for the same shield-target configuration. The algorithm developed showed a great improvement in results over the unmodified HZETRN solution. In addition, a two-directional solution of the evaporation source showed even further improvement of the fluence near the front of the water target where diffusion from the front surface is important.
Mosleh-Shirazi, Mohammad Amin; Zarrini-Monfared, Zinat; Karbasi, Sareh; Zamani, Ali
2014-01-01
Two-dimensional (2D) arrays of thick segmented scintillators are of interest as X-ray detectors for both 2D and 3D image-guided radiotherapy (IGRT). Their detection process involves ionizing radiation energy deposition followed by production and transport of optical photons. Only a very limited number of optical Monte Carlo simulation models exist, which has limited the number of modeling studies that have considered both stages of the detection process. We present ScintSim1, an in-house optical Monte Carlo simulation code for 2D arrays of scintillation crystals, developed in the MATLAB programming environment. The code was rewritten and revised based on an existing program for single-element detectors, with the additional capability to model 2D arrays of elements with configurable dimensions, material, etc., The code generates and follows each optical photon history through the detector element (and, in case of cross-talk, the surrounding ones) until it reaches a configurable receptor, or is attenuated. The new model was verified by testing against relevant theoretically known behaviors or quantities and the results of a validated single-element model. For both sets of comparisons, the discrepancies in the calculated quantities were all <1%. The results validate the accuracy of the new code, which is a useful tool in scintillation detector optimization. PMID:24600168
Mosleh-Shirazi, Mohammad Amin; Zarrini-Monfared, Zinat; Karbasi, Sareh; Zamani, Ali
2014-01-01
Two-dimensional (2D) arrays of thick segmented scintillators are of interest as X-ray detectors for both 2D and 3D image-guided radiotherapy (IGRT). Their detection process involves ionizing radiation energy deposition followed by production and transport of optical photons. Only a very limited number of optical Monte Carlo simulation models exist, which has limited the number of modeling studies that have considered both stages of the detection process. We present ScintSim1, an in-house optical Monte Carlo simulation code for 2D arrays of scintillation crystals, developed in the MATLAB programming environment. The code was rewritten and revised based on an existing program for single-element detectors, with the additional capability to model 2D arrays of elements with configurable dimensions, material, etc., The code generates and follows each optical photon history through the detector element (and, in case of cross-talk, the surrounding ones) until it reaches a configurable receptor, or is attenuated. The new model was verified by testing against relevant theoretically known behaviors or quantities and the results of a validated single-element model. For both sets of comparisons, the discrepancies in the calculated quantities were all <1%. The results validate the accuracy of the new code, which is a useful tool in scintillation detector optimization. PMID:24600168
Beam-transport optimization for cold-neutron spectrometer
NASA Astrophysics Data System (ADS)
Nakajima, Kenji; Ohira-Kawamura, Seiko; Kikuchi, Tatsuya; Kajimoto, Ryoichi; Takahashi, Nobuaki; Nakamura, Mitsutaka; Soyama, Kazuhiko; Osakabe, Toyotaka
2015-01-01
We report the design of the beam-transport system (especially the vertical geometry) for a cold-neutron disk-chopper spectrometer AMATERAS at J-PARC. Based on the elliptical shape, which is one of the most effective geometries for a ballistic mirror, the design was optimized to obtain, at the sample position, a neutron beam with high flux without serious degrading in divergence and spacial homogeneity within the boundary conditions required from actual spectrometer construction. The optimum focal point was examined. An ideal elliptical shape was modified to reduce its height without serious loss of transmission. The final result was adapted to the construction requirements of AMATERAS. Although the ideas studied in this paper are considered for the AMATERAS case, they can be useful also to other spectrometers in similar situations.
Grant, K.E.; Taylor, K.E.; Ellis, J.S.; Wuebbles, D.J.
1987-07-01
The authors have implemented a series of state of the art radiation transport submodels in previously developed one dimensional and two dimensional chemical transport models of the troposphere and stratosphere. These submodels provide the capability of calculating accurate solar and infrared heating rates. They are a firm basis for further radiation submodel development as well as for studying interactions between radiation and model dynamics under varying conditions of clear sky, clouds, and aerosols. 37 refs., 3 figs.
Novel Parallel Numerical Methods for Radiation& Neutron Transport
Brown, P N
2001-03-06
In many of the multiphysics simulations performed at LLNL, transport calculations can take up 30 to 50% of the total run time. If Monte Carlo methods are used, the percentage can be as high as 80%. Thus, a significant core competence in the formulation, software implementation, and solution of the numerical problems arising in transport modeling is essential to Laboratory and DOE research. In this project, we worked on developing scalable solution methods for the equations that model the transport of photons and neutrons through materials. Our goal was to reduce the transport solve time in these simulations by means of more advanced numerical methods and their parallel implementations. These methods must be scalable, that is, the time to solution must remain constant as the problem size grows and additional computer resources are used. For iterative methods, scalability requires that (1) the number of iterations to reach convergence is independent of problem size, and (2) that the computational cost grows linearly with problem size. We focused on deterministic approaches to transport, building on our earlier work in which we performed a new, detailed analysis of some existing transport methods and developed new approaches. The Boltzmann equation (the underlying equation to be solved) and various solution methods have been developed over many years. Consequently, many laboratory codes are based on these methods, which are in some cases decades old. For the transport of x-rays through partially ionized plasmas in local thermodynamic equilibrium, the transport equation is coupled to nonlinear diffusion equations for the electron and ion temperatures via the highly nonlinear Planck function. We investigated the suitability of traditional-solution approaches to transport on terascale architectures and also designed new scalable algorithms; in some cases, we investigated hybrid approaches that combined both.
Current status of the PSG Monte Carlo neutron transport code
Leppaenen, J.
2006-07-01
PSG is a new Monte Carlo neutron transport code, developed at the Technical Research Centre of Finland (VTT). The code is mainly intended for fuel assembly-level reactor physics calculations, such as group constant generation for deterministic reactor simulator codes. This paper presents the current status of the project and the essential capabilities of the code. Although the main application of PSG is in lattice calculations, the geometry is not restricted in two dimensions. This paper presents the validation of PSG against the experimental results of the three-dimensional MOX fuelled VENUS-2 reactor dosimetry benchmark. (authors)
A concurrent, multigroup, discrete ordinates model of neutron transport
Dorr, M.R.; Still, C.H.
1993-10-22
The authors present an algorithm for the concurrent solution of the linear system arising from a multigroup, discrete ordinates model of neutron transport. The target architectures consist of distributed memory computers ranging from workstation clusters to massively parallel computers. Based on an analysis of the memory requirement and floating point complexity of matrix-vector multiplication in the iterative solution of the linear system, the authors propose a data layout and communication strategy designed to achieve scalability with respect to all phase space variables. Numerical results are presented to demonstrate the performance of the algorithm on the nCUBE/2.
A killer micro attack on 3D neutron transport
Dorr, M.R.; Ferguson, J.M.
1990-11-01
We describe the deterministic solution of the neutron transport equation and the computation of the effective criticality of three-dimensional assemblies using the BBN TC2000 killer micros. We observe that the performance of our research code PTRAN running on 48 processors of the TC2000 is competitive with the partially vectorizable version running on a single Cray Y/MP processor. This performance scales well with the number of processors on real problems, including those that are not load balanced a priori. To obtain this performance, we explicitly specify and exploit data locality and data dependence using domain decomposition and dynamic job scheduling. 3 refs., 4 figs., 2 tabs.
Geometric Correction for Diffusive Expansion of Steady Neutron Transport Equation
NASA Astrophysics Data System (ADS)
Wu, Lei; Guo, Yan
2015-06-01
We revisit the diffusive limit of a steady neutron transport equation in a two-dimensional unit disk with one-speed velocity. A classical theorem by Bensoussan et al. (Publ Res Inst Math Sci 15(1):53-157, 1979) states that its solution can be approximated in L ∞ by the leading order interior solution plus the Knudsen layer in the diffusive limit. In this paper, we construct a counterexample to this result via a different boundary layer expansion with geometric correction.
Verbeke, J. M.; Petit, O.
2016-06-01
From nuclear safeguards to homeland security applications, the need for the better modeling of nuclear interactions has grown over the past decades. Current Monte Carlo radiation transport codes compute average quantities with great accuracy and performance; however, performance and averaging come at the price of limited interaction-by-interaction modeling. These codes often lack the capability of modeling interactions exactly: for a given collision, energy is not conserved, energies of emitted particles are uncorrelated, and multiplicities of prompt fission neutrons and photons are uncorrelated. Many modern applications require more exclusive quantities than averages, such as the fluctuations in certain observables (e.g., themore » neutron multiplicity) and correlations between neutrons and photons. In an effort to meet this need, the radiation transport Monte Carlo code TRIPOLI-4® was modified to provide a specific mode that models nuclear interactions in a full analog way, replicating as much as possible the underlying physical process. Furthermore, the computational model FREYA (Fission Reaction Event Yield Algorithm) was coupled with TRIPOLI-4 to model complete fission events. As a result, FREYA automatically includes fluctuations as well as correlations resulting from conservation of energy and momentum.« less
NASA Astrophysics Data System (ADS)
Cappelli, Mark; Young, Chris; Cha, Eusnun; Fernandez, Eduardo; Stanford Plasma Physics Laboratory Collaboration; Eckerd College Collaboration
2015-09-01
We present a simple, zero-equation turbulence model for electron transport across the magnetic field of a plasma Hall thruster and integrate this model into 2-D hybrid particle-in-cell simulations of a 72 mm diameter laboratory thruster operating at 400 W. The turbulent transport model is based on the assumption that the primary means of electron energy dissipation is the turbulent eddy cascade in the electron fluid to smaller scales. Implementing the model into 2-D hybrid simulations is relatively straightforward and leverages the existing framework for solving the electron fluid equations. We find that the model captures the strong axial variation in the mobility seen in experiments. In particular, it predicts the existence of a strong transport barrier which anchors the region of plasma acceleration. The model also captures the time-averaged experimental discharge current and its fluctuations due to ionization instabilities. We observe quantitative agreement with recent laser induced fluorescence measurements of time-averaged xenon ion and neutral velocities along the channel centerline. This work was supported by the Air Force Office of Scientific Research.
Structures of the fractional spaces generated by the difference neutron transport operator
Ashyralyev, Allaberen; Taskin, Abdulgafur
2015-09-18
The initial boundary value problem for the neutron transport equation is considered. The first, second and third order of accuracy difference schemes for the approximate solution of this problem are presented. Highly accurate difference schemes for neutron transport equation based on Padé approximation are constructed. In applications, stability estimates for solutions of difference schemes for the approximate solution of the neutron transport equation are obtained.The positivity of the neutron transport operator in Slobodeckij spaces is proved. Numerical techniques are developed and algorithms are tested on an example in MATLAB.
Dimensionality-dependent charge transport in close-packed nanoparticle arrays: from 2D to 3D
Wang, Ying; Duan, Chao; Peng, Lianmao; Liao, Jianhui
2014-01-01
Charge transport properties in close-packed nanoparticle arrays with thickness crossing over from two dimensions to three dimensions have been studied. The dimensionality transition of nanoparticle arrays was realized by continually printing spatially well-defined nanoparticle monolayers on top of the device in situ. The evolution of charge transport properties depending on the dimensionality has been investigated in both the Efros-Shaklovskii variable-range-hopping (ES-VRH) (low temperature) regime and the sequential hopping (SH) (medium temperature) regime. We find that the energy barriers to transport decrease when the thickness of nanoparticle arrays increases from monolayer to multilayers, but start to level off at the thickness of 4–5 monolayers. The energy barriers are characterized by the coefficient βD at ES-VRH regime and the activation energy Ea at SH regime. Moreover, a turning point for the temperature coefficient of conductance was observed in multilayer nanoparticle arrays at high temperature, which is attributed to the increasing mobility with decreasing temperature of hopping transport in three dimensions. PMID:25523836
Dimensionality-dependent charge transport in close-packed nanoparticle arrays: from 2D to 3D.
Wang, Ying; Duan, Chao; Peng, Lianmao; Liao, Jianhui
2014-01-01
Charge transport properties in close-packed nanoparticle arrays with thickness crossing over from two dimensions to three dimensions have been studied. The dimensionality transition of nanoparticle arrays was realized by continually printing spatially well-defined nanoparticle monolayers on top of the device in situ. The evolution of charge transport properties depending on the dimensionality has been investigated in both the Efros-Shaklovskii variable-range-hopping (ES-VRH) (low temperature) regime and the sequential hopping (SH) (medium temperature) regime. We find that the energy barriers to transport decrease when the thickness of nanoparticle arrays increases from monolayer to multilayers, but start to level off at the thickness of 4-5 monolayers. The energy barriers are characterized by the coefficient βD at ES-VRH regime and the activation energy Ea at SH regime. Moreover, a turning point for the temperature coefficient of conductance was observed in multilayer nanoparticle arrays at high temperature, which is attributed to the increasing mobility with decreasing temperature of hopping transport in three dimensions. PMID:25523836
Dimensionality-dependent charge transport in close-packed nanoparticle arrays: from 2D to 3D
NASA Astrophysics Data System (ADS)
Wang, Ying; Duan, Chao; Peng, Lianmao; Liao, Jianhui
2014-12-01
Charge transport properties in close-packed nanoparticle arrays with thickness crossing over from two dimensions to three dimensions have been studied. The dimensionality transition of nanoparticle arrays was realized by continually printing spatially well-defined nanoparticle monolayers on top of the device in situ. The evolution of charge transport properties depending on the dimensionality has been investigated in both the Efros-Shaklovskii variable-range-hopping (ES-VRH) (low temperature) regime and the sequential hopping (SH) (medium temperature) regime. We find that the energy barriers to transport decrease when the thickness of nanoparticle arrays increases from monolayer to multilayers, but start to level off at the thickness of 4-5 monolayers. The energy barriers are characterized by the coefficient βD at ES-VRH regime and the activation energy Ea at SH regime. Moreover, a turning point for the temperature coefficient of conductance was observed in multilayer nanoparticle arrays at high temperature, which is attributed to the increasing mobility with decreasing temperature of hopping transport in three dimensions.
NASA Astrophysics Data System (ADS)
Hoffman, Adam J.; Lee, John C.
2016-02-01
A new time-dependent Method of Characteristics (MOC) formulation for nuclear reactor kinetics was developed utilizing angular flux time-derivative propagation. This method avoids the requirement of storing the angular flux at previous points in time to represent a discretized time derivative; instead, an equation for the angular flux time derivative along 1D spatial characteristics is derived and solved concurrently with the 1D transport characteristic equation. This approach allows the angular flux time derivative to be recast principally in terms of the neutron source time derivatives, which are approximated to high-order accuracy using the backward differentiation formula (BDF). This approach, called Source Derivative Propagation (SDP), drastically reduces the memory requirements of time-dependent MOC relative to methods that require storing the angular flux. An SDP method was developed for 2D and 3D applications and implemented in the computer code DeCART in 2D. DeCART was used to model two reactor transient benchmarks: a modified TWIGL problem and a C5G7 transient. The SDP method accurately and efficiently replicated the solution of the conventional time-dependent MOC method using two orders of magnitude less memory.
Entin, M. V.; Magarill, L. I.; Olshanetsky, E. B. Kvon, Z. D.; Mikhailov, N. N.; Dvoretsky, S. A.
2013-11-15
The influence of e-h scattering on the conductivity and magnetotransport of 2D semimetallic HgTe is studied both theoretically and experimentally. The presence of e-h scattering leads to the friction between electrons and holes resulting in a large temperature-dependent contribution to the transport coefficients. The coefficient of friction between electrons and holes is determined. The comparison of experimental data with the theory shows that the interaction between electrons and holes based on the long-range Coulomb potential strongly underestimates the e-h friction. The experimental results are in agreement with the model of strong short-range e-h interaction.
Neutron Transport Models and Methods for HZETRN and Coupling to Low Energy Light Ion Transport
NASA Technical Reports Server (NTRS)
Blattnig, S.R.; Slaba, T.C.; Heinbockel, J.H.
2008-01-01
Exposure estimates inside space vehicles, surface habitats, and high altitude aircraft exposed to space radiation are highly influenced by secondary neutron production. The deterministic transport code HZETRN has been identified as a reliable and efficient tool for such studies, but improvements to the underlying transport models and numerical methods are still necessary. In this paper, the forward-backward (FB) and directionally coupled forward-backward (DC) neutron transport models are derived, numerical methods for the FB model are reviewed, and a computationally efficient numerical solution is presented for the DC model. Both models are compared to the Monte Carlo codes HETCHEDS and FLUKA, and the DC model is shown to agree closely with the Monte Carlo results. Finally, it is found in the development of either model that the decoupling of low energy neutrons from the light ion (A<4) transport procedure adversely affects low energy light ion fluence spectra and exposure quantities. A first order correction is presented to resolve the problem, and it is shown to be both accurate and efficient.
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 coherent charge transport in highly ordered conducting polymers doped by solid state diffusion.
Kang, Keehoon; Watanabe, Shun; Broch, Katharina; Sepe, Alessandro; Brown, Adam; Nasrallah, Iyad; Nikolka, Mark; Fei, Zhuping; Heeney, Martin; Matsumoto, Daisuke; Marumoto, Kazuhiro; Tanaka, Hisaaki; Kuroda, Shin-Ichi; Sirringhaus, Henning
2016-08-01
Doping is one of the most important methods to control charge carrier concentration in semiconductors. Ideally, the introduction of dopants should not perturb the ordered microstructure of the semiconducting host. In some systems, such as modulation-doped inorganic semiconductors or molecular charge transfer crystals, this can be achieved by spatially separating the dopants from the charge transport pathways. However, in conducting polymers, dopants tend to be randomly distributed within the conjugated polymer, and as a result the transport properties are strongly affected by the resulting structural and electronic disorder. Here, we show that in the highly ordered lamellar microstructure of a regioregular thiophene-based conjugated polymer, a small-molecule p-type dopant can be incorporated by solid state diffusion into the layers of solubilizing side chains without disrupting the conjugated layers. In contrast to more disordered systems, this allows us to observe coherent, free-electron-like charge transport properties, including a nearly ideal Hall effect in a wide temperature range, a positive magnetoconductance due to weak localization and the Pauli paramagnetic spin susceptibility. PMID:27159015
NASA Astrophysics Data System (ADS)
Eckert, Dominik; Kürzinger, Petra; Bauer, Robert; Griebler, Christian; Cirpka, Olaf A.
2015-01-01
Biodegradation in contaminated aquifers has been shown to be most pronounced at the fringe of contaminant plumes, where mixing of contaminated water and ambient groundwater, containing dissolved electron acceptors, stimulates microbial activity. While physical mixing of contaminant and electron acceptor by transverse dispersion has been shown to be the major bottleneck for biodegradation in steady-state plumes, so far little is known on the effect of flow and transport dynamics (caused, e.g., by a seasonally fluctuating groundwater table) on biodegradation in these systems. Towards this end we performed experiments in quasi-two-dimensional flow-through microcosms on aerobic toluene degradation by Pseudomonas putida F1. Plume dynamics were simulated by vertical alteration of the toluene plume position and experimental results were analyzed by reactive-transport modeling. We found that, even after disappearance of the toluene plume for two weeks, the majority of microorganisms stayed attached to the sediment and regained their full biodegradation potential within two days after reappearance of the toluene plume. Our results underline that besides microbial growth, also maintenance and dormancy are important processes that affect biodegradation performance under transient environmental conditions and therefore deserve increased consideration in future reactive-transport modeling.
Feautrier, D.; Smith, D.L.
1992-03-01
This report describes the development and testing of a deuterium gas target intended for use at a low-energy accelerator facility to produce neutrons for basic research and various nuclear applications. The principle source reaction is H-2(d,n)He-3. It produces a nearly mono-energetic group of neutrons. However, a lower-energy continuum neutron spectrum is produced by the H-2(d;n,p)H-2 reaction and also by deuterons which strike various components in the target assembly. The present target is designed to achieve the following objectives: (1) minimize unwanted background neutron production from the target assembly, (2) provide a relatively low level of residual long-term activity within the target components, (3) have the capacity to dissipate up to 150 watts of beam power with good target longevity, and (4) possess a relatively modest target mass in order to minimize neutron scattering from the target components. The basic physical principles that have to be considered in designing an accelerator target are discussed and the major engineering features of this particular target design are outlined. The results of initial performance tests on this target are documented and some conclusions concerning the viability of the target design are presented.
NASA Astrophysics Data System (ADS)
Hue, V.; Cavalié, T.; Dobrijevic, M.; Hersant, F.; Greathouse, T. K.
2015-09-01
Saturn's axial tilt of 26.7° produces seasons in a similar way as on Earth. Both the stratospheric temperature and composition are affected by this latitudinally varying insolation along Saturn's orbital path. A new time-dependent 2D photochemical model is presented to study the seasonal evolution of Saturn's stratospheric composition. This study focuses on the impact of the seasonally variable thermal field on the main stratospheric C2-hydrocarbon chemistry (C2H2 and C2H6) using a realistic radiative climate model. Meridional mixing and advective processes are implemented in the model but turned off in the present study for the sake of simplicity. The results are compared to a simple study case where a latitudinally and temporally steady thermal field is assumed. Our simulations suggest that, when the seasonally variable thermal field is accounted for, the downward diffusion of the seasonally produced hydrocarbons is faster due to the seasonal compression of the atmospheric column during winter. This effect increases with increasing latitudes which experience the most important thermal changes in the course of the seasons. The seasonal variability of C2H2 and C2H6 therefore persists at higher-pressure levels with a seasonally-variable thermal field. Cassini limb-observations of C2H2 and C2H6 (Guerlet, S. et al. [2009]. Icarus 203, 214-232) are reasonably well-reproduced from the equator to 40° in both hemispheres in the 0.1-1 mbar pressure range. At lower pressure levels, the models only fit the Cassini observations in the northern hemisphere, from the equator to 40°N. Beyond 40° in both hemispheres, deviations from the pure photochemical predictions, mostly in the southern hemisphere, suggest the presence of large-scale stratospheric dynamics.
NASA Astrophysics Data System (ADS)
Baitsch-Ghirardello, Bettina; Stracke, Andreas; Connolly, James A. D.; Nikolaeva, Ksenia M.; Gerya, Taras V.
2014-11-01
Understanding the physical-chemical mechanisms and pathways of geochemical transport in subduction zones remains a long-standing goal of subduction-related research. In this study, we perform fully coupled geochemical-thermo-mechanical (GcTM) numerical simulations to investigate Pb isotopic signatures of the two key "outputs" of subduction zones: (A) serpentinite mélanges and (B) arc basalts. With this approach we analyze three different geodynamic regimes of intra-oceanic subduction systems: (1) retreating subduction with backarc spreading, (2) stable subduction with high fluid-related weakening, and (3) stable subduction with low fluid-related weakening. Numerical results suggest a three-stage Pb geochemical transport in subduction zones: (I) from subducting sediments and oceanic crust to serpentinite mélanges, (II) from subducting serpentinite mélanges to subarc asthenospheric wedge and (III) from the mantle wedge to arc volcanics. Mechanical mixing and fluid-assisted geochemical transport above slabs result in spatially and temporarily variable Pb concentrations in the serpentinized forearc mantle as well as in arc basalts. The Pb isotopic ratios are strongly heterogeneous and show five types of geochemical mixing trends: (i) binary mantle-MORB, (i) binary MORB-sediments, (iii) double binary MORB-mantle and MORB-sediments, (iv) double binary MORB-mantle and mantle-sediments and (v) triple MORB-sediment-mantle. Double binary and triple mixing trends are transient and characterize relatively early stages of subduction. In contrast, steady-state binary mantle-MORB and MORB-sediments trends are typical for mature subduction zones with respectively low and high intensity of sedimentary melange subduction. Predictions from our GcTM models are in agreement with Pb isotopic data from some natural subduction zones.
Bailey, T S; Adams, M L; Chang, J H
2008-10-01
We present a new spatial discretization of the discrete-ordinates transport equation in two-dimensional cylindrical (RZ) geometry for arbitrary polygonal meshes. This discretization is a discontinuous finite element method that utilizes the piecewise linear basis functions developed by Stone and Adams. We describe an asymptotic analysis that shows this method to be accurate for many problems in the thick diffusion limit on arbitrary polygons, allowing this method to be applied to radiative transfer problems with these types of meshes. We also present numerical results for multiple problems on quadrilateral grids and compare these results to the well-known bi-linear discontinuous finite element method.
NASA Astrophysics Data System (ADS)
El Kadi Abderrezzak, Kamal; Die Moran, Andrés; Tassi, Pablo; Ata, Riadh; Hervouet, Jean-Michel
2016-07-01
Bank erosion can be an important form of morphological adjustment in rivers. With the advances made in computational techniques, two-dimensional (2D) depth-averaged numerical models have become valuable tools for resolving many engineering problems dealing with sediment transport. The objective of this research work is to present a simple, new, bank-erosion operator that is integrated into a 2D Saint-Venant-Exner morphodynamic model. The numerical code is based on an unstructured grid of triangular elements and finite-element algorithms. The slope of each element in the grid is compared to the angle of repose of the bank material. Elements for which the slope is too steep are tilted to bring them to the angle of repose along a horizontal axis defined such that the volume loss above the axis is equal to the volume gain below, thus ensuring mass balance. The model performance is assessed using data from laboratory flume experiments and a scale model of the Old Rhine. For the flume experiment case with uniform bank material, relevant results are obtained for bank geometry changes. For the more challenging case (i.e. scale model of the Old Rhine with non-uniform bank material), the numerical model is capable of reproducing the main features of the bank failure, induced by the newly designed groynes, as well as the transport of the mobilized sediment material downstream. Some deviations between the computed results and measured data are, however, observed. They are ascribed to the effects of three-dimensional (3D) flow structures, pore pressure and cohesion, which are not considered in the present 2D model.
NASA Astrophysics Data System (ADS)
Derakhshan, V.; Ketabi, S. A.; Moghaddam, A. G.
2016-09-01
We employed the formalism of bond currents, expressed in terms of non-equilibrium Green’s function to obtain the local currents and transport features of zigzag silicene ribbon in the presence of magnetic impurity. When only intrinsic and Rashba spin–orbit interactions are present, silicene behaves as a two-dimensional topological insulator with gapless edge states. But in the presence of finite intrinsic spin–orbit interaction, the edge states start to penetrate into the bulk of the sample by increasing Rashba interaction strength. The exchange interaction induced by local impurities breaks the time-reversal symmetry of the gapless edge states and influences the topological properties strongly. Subsequently, the singularity of partial Berry curvature disappears and the silicene nanoribbon becomes a trivial insulator. On the other hand, when the concentration of the magnetic impurities is low, the edge currents are not affected significantly. In this case, when the exchange field lies in the x–y plane, the spin mixing around magnetic impurity is more profound rather than the case in which the exchange field is directed along the z-axis. Nevertheless, when the exchange field of magnetic impurities is placed in the x–y plane, a spin-polarized conductance is observed. The resulting conductance polarization can be tuned by the concentration of the impurities and even completely polarized spin transport is achievable.
NASA Astrophysics Data System (ADS)
Olson, Gordon L.
2012-04-01
When using polynomial expansions for the angular variables in the radiation transport equation, the usual procedure is to truncate the series by setting all higher order terms to zero. At low order, such simple closures may not give the optimum solution. This work tests alternate closures that scale either the time- or spatial-derivatives in the highest order equation. These scale factors can be chosen such that waves propagate at exactly the speed of light in optically thin media. Alternatively, they may be chosen to significantly improve the accuracy of low-order solutions with no additional computational cost. The same scaling procedure and scale factors work in one- and multi-dimensions. In multidimensions, reducing the order of a solution can save significant amounts of computer time.
NASA Astrophysics Data System (ADS)
Walker, D. I.; Wolfand, J.; Wang, Y.; Bai, C.; Li, Y.; Abriola, L. M.; Pennell, K. D.
2011-12-01
Understanding the processes governing nanomaterial fate in subsurface environments is important due to their widespread use in commercial and manufacturing settings. To date, the majority of studies on nanoparticle transport in porous media have been conducted under idealized conditions in columns packed with uniform, clean sands. To evaluate the transport of nanoparticles in more representative subsurface systems, column and aquifer cell experiments were completed to investigate the transport of fullerene aggregates (nC60) in unwashed Ottawa sands and in the presence of low permeability lenses. To obtain independent measurements of attachment parameters, nC60 breakthrough and retention profiles were measured in 1-D columns (2.5 dia x 10.8 cm length) with three different size fractions (40-50 mesh, d50=335 μm; 80-100 mesh, d50=165 μm; and 100-140 mesh, d50=125 μm) of unwashed Ottawa sand. A three pore volume pulse of nC60 (ca. 2.5 mg/L) suspension containing 6 mM NaCl resulted in 71, 5 and 3 percent breakthrough in the 40-50, 80-100 and 100-140 mesh unwashed Ottawa sand, respectively. Solid phase retention profiles for all three size fractions exhibited hyper-exponential decline with distance from the column inlet, consistent with a physical straining process. The aquifer cells (63 x 36 x 1.4 cm) were packed with unwashed 40-50 mesh Ottawa sand as the background medium, in which rectangular lenses (2.4 cm x 9.6 cm) of lower permeability (80-100 and 100-140 mesh) were emplaced. Following completion of nonreactive tracer tests, 200-400 mL pulses of nC60 (ca. 2.5 mg/L) suspension were injected through side-ports up-gradient of the lenses. Only trace amounts of nC60 were detected in aqueous samples collected from down-gradient sampling ports. Post-experiment dissection of the aquifer cell demonstrated that solid phase concentrations of nC60 were largest surrounding the injection ports and decreased monotonically with no preferential accumulation observed at the
NASA Astrophysics Data System (ADS)
Thomas, Justin W.
2006-12-01
The Numerical Nuclear Reactor (NNR) is a code suite that is being developed to provide high-fidelity multi-physics capability for the analysis of light water nuclear reactors. The focus of the work here is to extend the capability of the NNR by incorporation of the neutronics module, DeCART, for Boiling Water Reactor (BWR) applications. The DeCART code has been coupled to the NNR fluid mechanics and heat transfer module STAR-CD for light water reactor applications. The coupling has been accomplished via an interface program, which is responsible for mapping the STAR-CD and DeCART meshes, managing communication, and monitoring convergence. DeCART obtains the solution of the 3-D Boltzmann transport equation by performing a series of 2-D modular ray tracing-based method of characteristics problems that are coupled within the framework of 3-D coarse-mesh finite difference. The relatively complex geometry and increased axial heterogeneity found in BWRs are beyond the modeling capability of the original version of DeCART. In this work, DeCART is extended in three primary areas. First, the geometric capability is generalized by extending the modular ray tracing scheme and permitting an unstructured mesh in the global finite difference kernel. Second, numerical instabilities, which arose as a result of the severe axial heterogeneity found in BWR cores, have been resolved. Third, an advanced nodal method has been implemented to improve the accuracy of the axial flux distribution. In this semi-analytic nodal method, the analytic solution to the transverse-integrated neutron diffusion equation is obtained, where the nonhomogeneous neutron source was first approximated by a quartic polynomial. The successful completion of these three tasks has allowed the application of the coupled DeCART/STAR-CD code to practical BWR problems.
2D dual permeability modeling of flow and transport in a two-scale structured lignitic mine soil
NASA Astrophysics Data System (ADS)
Dusek, J.; Gerke, H. H.; Vogel, T.; Maurer, T.; Buczko, U.
2009-04-01
Two-dimensional single- and dual-permeability simulations are used to analyze water and solute fluxes in heterogeneous lignitic mine soil at a forest-reclaimed mine spoil heap. The soil heterogeneity on this experimental site "Bärenbrücker Höhe" resulted from inclined dumping structures and sediment mixtures that consist of sand with lignitic dust and embedded lignitic fragments. Observations on undisturbed field suction-cell lysimeters including tracer experiments revealed funneling-type preferential flow with lateral water and bromide movement along inclined sediment structures. The spatial distribution of soil structures and fragment distributions was acquired by a digital camera and identified by a supervised classification of the digital profile image. First, a classical single-domain modeling approach was used, with spatially variable scaling factors inferred from image analyses. In the next step, a two-continuum scenario was constructed to examine additional effects of nonequilibrium on the flow regime. The scaling factors used for the preferential flow domain are here obtained from the gradient of the grayscale images. So far, the single domain scenarios failed to predict the bromide leaching patterns although water effluent could be described. Dual-permeability model allows the incorporation of structural effects and can be used as a tool to further testing other approaches that account for structure effects. The numerical study suggests that additional experiments are required to obtain better understanding of the highly complex transport processes on this experimental site.
Yaqi Wang; Jean C. Ragusa
2011-02-01
Standard and goal-oriented adaptive mesh refinement (AMR) techniques are presented for the linear Boltzmann transport equation. A posteriori error estimates are employed to drive the AMR process and are based on angular-moment information rather than on directional information, leading to direction-independent adapted meshes. An error estimate based on a two-mesh approach and a jump-based error indicator are compared for various test problems. In addition to the standard AMR approach, where the global error in the solution is diminished, a goal-oriented AMR procedure is devised and aims at reducing the error in user-specified quantities of interest. The quantities of interest are functionals of the solution and may include, for instance, point-wise flux values or average reaction rates in a subdomain. A high-order (up to order 4) Discontinuous Galerkin technique with standard upwinding is employed for the spatial discretization; the discrete ordinates method is used to treat the angular variable.
A killer micro attack on 3D neutron transport
Dorr, M.R.; Ferguson, J.M.
1990-11-16
In this paper, we describe the deterministic solution of the neutron transport equation and the computation of the effective criticality of three-dimensional assemblies using the BBN TC2000 killer micros. We observe that the performance of our research code PTRAN running on 48 processors of the TC2000 is competitive with the partially vectorizable version running on a single Cray Y/MP processor. This performance scales well with the number of processors on real problems, including those that are not load balanced a priori. To obtain this performance, we explicitly specify and exploit data locality and data dependence using domain decomposition and dynamic job scheduling. From the results obtained here, it appears that, at least for this application, a production machine based on the TC2000 architecture with more powerful processors and a commensurate increase in switch speed could yield a significant gain in our design capability. 2 refs., 5 figs., 2 tabs.
On-the-fly Neutron Tomography of Water Transport into Lupine Roots
NASA Astrophysics Data System (ADS)
Zarebanadkouki, Mohsen; Carminati, Andrea; Kaestner, Anders; Mannes, David; Morgano, Manuel; Peetermans, Steven; Lehmann, Eberhard; Trtik, Pavel
Measurement and visualization of water flow in soil and roots is essential for understanding of how roots take up water from soils. Such information would allow for the optimization of irrigation practices and for the identification of the optimal traits for the capture of water, in particular when water is scarce. However, measuring water flow in roots growing in soil is challenging. The previous 2D experiments (Zarebanadkouki et al., 2012) have not been sufficient for understanding the water transport across the root and therefore we employed an on-the-fly tomography technique with temporal resolution of three minutes. In this paper, we show that the series of on-the-fly neutron tomographic experiments performed on the same sample allow for monitoring the three-dimensional spatial distribution of D2O across the root tissue. The obtained data will allow us to calculate the convective and diffusive transport properties across root tissue and to estimate the relative importance of different pathways of water across the root tissue.
Coupled full core neutron transport/CFD simulations of pressurized water reactors
Kochunas, B.; Stimpson, S.; Collins, B.; Downar, T.; Brewster, R.; Baglietto, E.; Yan, J.
2012-07-01
Recently as part of the CASL project, a capability to perform 3D whole-core coupled neutron transport and computational fluid dynamics (CFD) calculations was demonstrated. This work uses the 2D/1D transport code DeCART and the commercial CFD code STAR-CCM+. It builds on previous CASL work demonstrating coupling for smaller spatial domains. The coupling methodology is described along with the problem simulated and results are presented for fresh hot full power conditions. An additional comparison is made to an equivalent model that uses lower order T/H feedback to assess the importance and cost of high fidelity feedback to the neutronics problem. A simulation of a quarter core Combustion Engineering (CE) PWR core was performed with the coupled codes using a Fixed Point Gauss-Seidel iteration technique. The total approximate calculation requirements are nearly 10,000 CPU hours and 1 TB of memory. The problem took 6 coupled iterations to converge. The CFD coupled model and low order T/H feedback model compared well for global solution parameters, with a difference in the critical boron concentration and average outlet temperature of 14 ppm B and 0.94 deg. C, respectively. Differences in the power distribution were more significant with maximum relative differences in the core-wide pin peaking factor (Fq) of 5.37% and average relative differences in flat flux region power of 11.54%. Future work will focus on analyzing problems more relevant to CASL using models with less approximations. (authors)
NASA Astrophysics Data System (ADS)
Maginot, Peter G.; Morel, Jim E.; Ragusa, Jean C.
2012-08-01
We present a new nonlinear spatial finite-element method for the linearized Boltzmann transport equation with Sn angular discretization in 1-D and 2-D Cartesian geometries. This method has two central characteristics. First, it is equivalent to the linear-discontinuous (LD) Galerkin method whenever that method yields a strictly non-negative solution. Second, it always satisfies both the zeroth and first spatial moment equations. Because it yields the LD solution when that solution is non-negative, one might interpret our method as a classical fix-up to the LD scheme. However, fix-up schemes for the LD equations derived in the past have given up solution of the first moment equations when the LD solution is negative in order to satisfy positivity in a simple manner. We present computational results comparing our method in 1-D to the strictly non-negative linear exponential-discontinuous method and to the LD method. We present computational results in 2-D comparing our method to a recently developed LD fix-up scheme and to the LD scheme. It is demonstrated that our method is a valuable alternative to existing methods.
Phenrat, Tanapon; Cihan, Abdullah; Kim, Hye-Jin; Mital, Menka; Illangasekare, Tissa; Lowry, Gregory V
2010-12-01
Concentrated suspensions of polymer-modified Fe(0) nanoparticles (NZVI) are injected into heterogeneous porous media for groundwater remediation. This study evaluated the effect of porous media heterogeneity and the dispersion properties including particle concentration, Fe(0) content, and adsorbed polymer mass and layer thickness which are expected to affect the delivery and emplacement of NZVI in heterogeneous porous media in a two-dimensional (2-D) cell. Heterogeneity in hydraulic conductivity had a significant impact on the deposition of NZVI. Polymer modified NZVI followed preferential flow paths and deposited in the regions where fluid shear is insufficient to prevent NZVI agglomeration and deposition. NZVI transported in heterogeneous porous media better at low particle concentration (0.3 g/L) than at high particle concentrations (3 and 6 g/L) due to greater particle agglomeration at high concentration. High Fe(0) content decreased transport during injection due to agglomeration promoted by magnetic attraction. NZVI with a flat adsorbed polymeric layer (thickness ∼30 nm) could not be transported effectively due to pore clogging and deposition near the inlet, while NZVI with a more extended adsorbed layer thickness (i.e., ∼70 nm) were mobile in porous media. This study indicates the importance of characterizing porous media heterogeneity and NZVI dispersion properties as part of the design of a robust delivery strategy for NZVI in the subsurface. PMID:21058703
Voss, Clifford I.; Provost, A.M.
2002-01-01
SUTRA (Saturated-Unsaturated Transport) is a computer program that simulates fluid movement and the transport of either energy or dissolved substances in a subsurface environment. This upgraded version of SUTRA adds the capability for three-dimensional simulation to the former code (Voss, 1984), which allowed only two-dimensional simulation. The code employs a two- or three-dimensional finite-element and finite-difference method to approximate the governing equations that describe the two interdependent processes that are simulated: 1) fluid density-dependent saturated or unsaturated ground-water flow; and 2) either (a) transport of a solute in the ground water, in which the solute may be subject to: equilibrium adsorption on the porous matrix, and both first-order and zero-order production or decay; or (b) transport of thermal energy in the ground water and solid matrix of the aquifer. SUTRA may also be used to simulate simpler subsets of the above processes. A flow-direction-dependent dispersion process for anisotropic media is also provided by the code and is introduced in this report. As the primary calculated result, SUTRA provides fluid pressures and either solute concentrations or temperatures, as they vary with time, everywhere in the simulated subsurface system. SUTRA flow simulation may be employed for two-dimensional (2D) areal, cross sectional and three-dimensional (3D) modeling of saturated ground-water flow systems, and for cross sectional and 3D modeling of unsaturated zone flow. Solute-transport simulation using SUTRA may be employed to model natural or man-induced chemical-species transport including processes of solute sorption, production, and decay. For example, it may be applied to analyze ground-water contaminant transport problems and aquifer restoration designs. In addition, solute-transport simulation with SUTRA may be used for modeling of variable-density leachate movement, and for cross sectional modeling of saltwater intrusion in
Adams, Robert; Zboray, Robert; Cortesi, Marco; Prasser, Horst-Michael
2014-04-01
A conceptual design optimization of a fast neutron tomography system was performed. The system is based on a compact deuterium-deuterium fast neutron generator and an arc-shaped array of individual neutron detectors. The array functions as a position sensitive one-dimensional detector allowing tomographic reconstruction of a two-dimensional cross section of an object up to 10 cm across. Each individual detector is to be optically isolated and consists of a plastic scintillator and a Silicon Photomultiplier for measuring light produced by recoil protons. A deterministic geometry-based model and a series of Monte Carlo simulations were used to optimize the design geometry parameters affecting the reconstructed image resolution. From this, it is expected that with an array of 100 detectors a reconstructed image resolution of ~1.5mm can be obtained. Other simulations were performed in order to optimize the scintillator depth (length along the neutron path) such that the best ratio of direct to scattered neutron counts is achieved. This resulted in a depth of 6-8 cm and an expected detection efficiency of 33-37%. Based on current operational capabilities of a prototype neutron generator being developed at the Paul Scherrer Institute, planned implementation of this detector array design should allow reconstructed tomograms to be obtained with exposure times on the order of a few hours. PMID:24495568
Study of Transport Behavior and Conversion Efficiency in Pillar Structured Neutron Detectors
Nikolic, R
2007-04-26
Room temperature, high efficiency and scalable radiation detectors can be realized by manipulating materials at the micro scale. With micro-semiconductor-pillars, we will advance the thermal neutron detection efficiency of semiconductor detectors to over 70% with 50 mm in detector thickness. New material science, new transport behavior, neutron to alpha conversion dynamics and their relationship with neutron detection will be discovered with the proposed structures.
Cooperative learning of neutron diffusion and transport theories
Robinson, Michael A.
1999-04-30
A cooperative group instructional strategy is being used to teach a unit on neutron transport and diffusion theory in a first-year-graduate level, Reactor Theory course that was formerly presented in the traditional lecture/discussion style. Students are divided into groups of two or three for the duration of the unit. Class meetings are divided into traditional lecture/discussion segments punctuated by cooperative group exercises. The group exercises were designed to require the students to elaborate, summarize, or practice the material presented in the lecture/discussion segments. Both positive interdependence and individual accountability are fostered by adjusting individual grades on the unit exam by a factor dependent upon group achievement. Group collaboration was also encouraged on homework assignments by assigning each group a single grade on each assignment. The results of the unit exam have been above average in the two classes in which the cooperative group method was employed. In particular, the problem solving ability of the students has shown particular improvement. Further,the students felt that the cooperative group format was both more educationally effective and more enjoyable than the lecture/discussion format.
Multigroup Time-Independent Neutron Transport Code System for Plane or Spherical Geometry.
1986-12-01
Version 00 PALLAS-PL/SP solves multigroup time-independent one-dimensional neutron transport problems in plane or spherical geometry. The problems solved are subject to a variety of boundary conditions or a distributed source. General anisotropic scattering problems are treated for solving deep-penetration problems in which angle-dependent neutron spectra are calculated in detail.
D. W. Nigg; J. K. Hartwell; J. R. Venhuizen; C. A. Wemple; R. Risler; G. E. Laramore; W. Sauerwein; G. Hudepohl; A. Lennox
2006-06-01
The Idaho National Laboratory (INL), the University of Washington (UW) Neutron Therapy Center, the University of Essen (Germany) Neutron Therapy Clinic, and the Northern Illinois University(NIU) Institute for Neutron Therapy at Fermilab have been collaborating in the development of fast-neutron therapy (FNT) with concurrent neutron capture (NCT) augmentation [1,2]. As part of this effort, we have conducted measurements to produce suitable benchmark data as an aid in validation of advanced three-dimensional treatment planning methodologies required for successful administration of FNT/NCT. Free-beam spectral measurements as well as phantom measurements with Lucite{trademark} cylinders using thermal, resonance, and threshold activation foil techniques have now been completed at all three clinical accelerator facilities. The same protocol was used for all measurements to facilitate intercomparison of data. The results will be useful for further detailed characterization of the neutron beams of interest as well as for validation of various charged particle and neutron transport codes and methodologies for FNT/NCT computational dosimetry, such as MCNP [3], LAHET [4], and MINERVA [5].
NASA Technical Reports Server (NTRS)
Singleterry, R. C., Jr.; Wilson, J. W.
1997-01-01
Extension of the high charge and energy (HZE) transport computer program HZETRN for angular transport of neutrons is considered. For this paper, only light ion transport, He4 and lighter, will be analyzed using a pure solar proton source. The angular transport calculator is the ANISN/PC program which is being controlled by the HZETRN program. The neutron flux values are compared for straight-ahead transport and angular transport in one dimension. The shield material is aluminum and the target material is water. The thickness of these materials is varied; however, only the largest model calculated is reported which is 50 gm/sq cm of aluminum and 100 gm/sq cm of water. The flux from the ANISN/PC calculation is about two orders of magnitude lower than the flux from HZETRN for very low energy neutrons. It is only a magnitude lower for the neutrons in the 10 to 20 MeV range in the aluminum and two orders lower in the water. The major reason for this difference is in the transport modes: straight-ahead versus angular. The angular treatment allows a longer path length than the straight-ahead approximation. Another reason is the different cross section sets used by the ANISN/PC-BUGLE-80 mode and the HZETRN mode. The next step is to investigate further the differences between the two codes and isolate the differences to just the angular versus straight-ahead transport mode. Then, create a better coupling between the angular neutron transport and the charged particle transport.
PHISICS multi-group transport neutronic capabilities for RELAP5
Epiney, A.; Rabiti, C.; Alfonsi, A.; Wang, Y.; Cogliati, J.; Strydom, G.
2012-07-01
PHISICS is a neutronic code system currently under development at INL. Its goal is to provide state of the art simulation capability to reactor designers. This paper reports on the effort of coupling this package to the thermal hydraulic system code RELAP5. This will enable full prismatic core and system modeling and the possibility to model coupled (thermal-hydraulics and neutronics) problems with more options for 3D neutron kinetics, compared to the existing diffusion theory neutron kinetics module in RELAP5 (NESTLE). The paper describes the capabilities of the coupling and illustrates them with a set of sample problems. (authors)
1980-10-15
Version 00 PALLAS-2DCY-FX is a code for direct integration of the transport equation in two-dimensional (r,z) geometry. It solves the energy and angular-dependent Boltzmann transport equation with general anisotropic scattering in cylindrical geometry. Its principal applications are to neutron or gamma-ray transport problems in the forward mode. The code is particularly designed for and suited to the solution of deep penetration radiation transport problems with an external (fixed) source.
Cosmic ray heliospheric transport study with neutron monitor data
NASA Astrophysics Data System (ADS)
Ahluwalia, H. S.; Ygbuhay, R. C.; Modzelewska, R.; Dorman, L. I.; Alania, M. V.
2015-10-01
Determining transport coefficients for galactic cosmic ray (GCR) propagation in the turbulent interplanetary magnetic field (IMF) poses a fundamental challenge in modeling cosmic ray modulation processes. GCR scattering in the solar wind involves wave-particle interaction, the waves being Alfven waves which propagate along the ambient field (B). Empirical values at 1 AU are determined for the components of the diffusion tensor for GCR propagation in the heliosphere using neutron monitor (NM) data. At high rigidities, particle density gradients and mean free paths at 1 AU in B can only be computed from the solar diurnal anisotropy (SDA) represented by a vector A (components Ar, Aϕ, and Aθ) in a heliospherical polar coordinate system. Long-term changes in SDA components of NMs (with long track record and the median rigidity of response Rm ~ 20 GV) are used to compute yearly values of the transport coefficients for 1963-2013. We confirm the previously reported result that the product of the parallel (to B) mean free path (λ||) and radial density gradient (Gr) computed from NM data exhibits a weak Schwabe cycle (11y) but strong Hale magnetic cycle (22y) dependence. Its value is most depressed in solar activity minima for positive (p) polarity intervals (solar magnetic field in the Northern Hemisphere points outward from the Sun) when GCRs drift from the polar regions toward the helioequatorial plane and out along the heliospheric current sheet (HCS), setting up a symmetric gradient Gθs pointing away from HCS. Gr drives all SDA components and λ|| Gr contributes to the diffusive component (Ad) of the ecliptic plane anisotropy (A). GCR transport is commonly discussed in terms of an isotropic hard sphere scattering (also known as billiard-ball scattering) in the solar wind plasma. We use it with a flat HCS model and the Ahluwalia-Dorman master equations to compute the coefficients α (=λ⊥/λ∥) and ωτ (a measure of turbulence in the solar wind) and transport
NASA Astrophysics Data System (ADS)
Scheck, L.; Kifonidis, K.; Janka, H.-Th.; Müller, E.
2006-10-01
We study hydrodynamic instabilities during the first seconds of core-collapse supernovae by means of 2D simulations with approximative neutrino transport and boundary conditions that parameterize the effects of the contracting neutron star and allow us to obtain sufficiently strong neutrino heating and, hence, neutrino-driven explosions. Confirming more idealised studies, as well as supernova simulations with spectral transport, we find that random seed perturbations can grow by hydrodynamic instabilities to a globally asymmetric mass distribution in the region between the nascent neutron star and the accretion shock, leading to a dominance of dipole (l=1) and quadrupole (l=2) modes in the explosion ejecta, provided the onset of the supernova explosion is sufficiently slower than the growth time scale of the low-mode instability. By gravitational and hydrodynamic forces, the anisotropic mass distribution causes an acceleration of the nascent neutron star, which lasts for several seconds and can propel the neutron star to velocities of more than 1000 km s-1. Because the explosion anisotropies develop chaotically and change by small differences in the fluid flow, the magnitude of the kick varies stochastically. No systematic dependence of the average neutron star velocity on the explosion energy or the properties of the considered progenitors is found. Instead, the anisotropy of the mass ejection, and hence of the kick, seems to increase when the nascent neutron star contracts more quickly, and thus low-mode instabilities can grow more rapidly. Our more than 70 models separate into two groups, one with high and the other with low neutron star velocities and accelerations after one second of post-bounce evolution, depending on whether the l=1 mode is dominant in the ejecta or not. This leads to a bimodality of the distribution when the neutron star velocities are extrapolated to their terminal values. Establishing a link to the measured distribution of pulsar
NASA Astrophysics Data System (ADS)
Cheng, Wai Chi; Liu, Chun-Ho
2010-05-01
To investigate the detailed momentum and pollutant transports between urban street canyons and the shear layer, a large-eddy simulation (LES) model was developed to calculate the flow and pollutant dispersion in isothermal conditions. The computational domain consisted of three identical two-dimensional (2D) idealized street canyons of unity aspect ratio. The flow field was assumed to be periodic in the horizontal domain boundaries. The subgrid-scale (SGS) stress was calculated by solving the SGS turbulent kinetic energy (TKE) conservation. An area pollutant source with constant pollutant concentration was prescribed on the ground of all streets. Zero pollutant concentration and an open boundary were applied at the domain inflow and outflow, respectively. The quadrant and budget analyses were employed to examine the momentum and pollutant transports at the roof level of the street canyons. Quadrant analyses of the resolved-scale vertical fluxes of momentum and pollutant
Neutron interaction and their transport with bulk materials
NASA Astrophysics Data System (ADS)
Rani, Esther Kalpana; Radhika, K.
2015-05-01
In the current paper an attempt was made to study and provide fundamental information about neutron interactions that are important to nuclear material measurements. The application of this study is explained about macroscopic interactions with bulk compound materials through a program in DEV C++ language which is done by enabling interaction of neutrons in nature. The output of the entire process depends upon the random number (i.e., incident neutron number), thickness of the material and mean free path as input parameters. Further the current study emphasizes on the usage of materials in shielding.
Neutron interaction and their transport with bulk materials
Rani, Esther Kalpana; Radhika, K.
2015-05-15
In the current paper an attempt was made to study and provide fundamental information about neutron interactions that are important to nuclear material measurements. The application of this study is explained about macroscopic interactions with bulk compound materials through a program in DEV C++ language which is done by enabling interaction of neutrons in nature. The output of the entire process depends upon the random number (i.e., incident neutron number), thickness of the material and mean free path as input parameters. Further the current study emphasizes on the usage of materials in shielding.
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
Design studies for a high-resolution, transportable neutron radiography/radioscopy system
Gillespie, G.H.; Micklich, B.J.; McMichael, G.E.
1996-09-30
A preliminary design has been developed for a high-resolution, transportable neutron radiology system (TNRS) concept. The primary system requirement is taken to be a thermal neutron flux of 10[sup 6] n/(cm[sup 2]-sec) with a L/D ratio of 100. The approach is to use an accelerator-driven neutron source, with a radiofrequency quadrupole (RFQ) as the primary accelerator component. Initial concepts for all of the major components of the system have been developed,and selected key parts have been examined further. An overview of the system design is presented, together with brief summaries of the concepts for the ion source, low energy beam transport (LEBT), RFQ, high energy beam transport (HEBT), target, moderator, collimator, image collection, power, cooling, vacuum, structure, robotics, control system, data analysis, transport vehicle, and site support. The use of trade studies for optimizing the TNRS concept are also described.
In situ studies of mass transport in liquid alloys by means of neutron radiography.
Kargl, F; Engelhardt, M; Yang, F; Weis, H; Schmakat, P; Schillinger, B; Griesche, A; Meyer, A
2011-06-29
When in situ techniques became available in recent years this led to a breakthrough in accurately determining diffusion coefficients for liquid alloys. Here we discuss how neutron radiography can be used to measure chemical diffusion in a ternary AlCuAg alloy. Neutron radiography hereby gives complementary information to x-ray radiography used for measuring chemical diffusion and to quasielastic neutron scattering used mainly for determining self-diffusion. A novel Al(2)O(3) based furnace that enables one to study diffusion processes by means of neutron radiography is discussed. A chemical diffusion coefficient of Ag against Al around the eutectic composition Al(68.6)Cu(13.8)Ag(17.6) at.% was obtained. It is demonstrated that the in situ technique of neutron radiography is a powerful means to study mass transport properties in situ in binary and ternary alloys that show poor x-ray contrast. PMID:21654050
Development of deterministic transport methods for low energy neutrons for shielding in space
NASA Technical Reports Server (NTRS)
Ganapol, Barry
1993-01-01
Transport of low energy neutrons associated with the galactic cosmic ray cascade is analyzed in this dissertation. A benchmark quality analytical algorithm is demonstrated for use with BRYNTRN, a computer program written by the High Energy Physics Division of NASA Langley Research Center, which is used to design and analyze shielding against the radiation created by the cascade. BRYNTRN uses numerical methods to solve the integral transport equations for baryons with the straight-ahead approximation, and numerical and empirical methods to generate the interaction probabilities. The straight-ahead approximation is adequate for charged particles, but not for neutrons. As NASA Langley improves BRYNTRN to include low energy neutrons, a benchmark quality solution is needed for comparison. The neutron transport algorithm demonstrated in this dissertation uses the closed-form Green's function solution to the galactic cosmic ray cascade transport equations to generate a source of neutrons. A basis function expansion for finite heterogeneous and semi-infinite homogeneous slabs with multiple energy groups and isotropic scattering is used to generate neutron fluxes resulting from the cascade. This method, called the FN method, is used to solve the neutral particle linear Boltzmann transport equation. As a demonstration of the algorithm coded in the programs MGSLAB and MGSEMI, neutron and ion fluxes are shown for a beam of fluorine ions at 1000 MeV per nucleon incident on semi-infinite and finite aluminum slabs. Also, to demonstrate that the shielding effectiveness against the radiation from the galactic cosmic ray cascade is not directly proportional to shield thickness, a graph of transmitted total neutron scalar flux versus slab thickness is shown. A simple model based on the nuclear liquid drop assumption is used to generate cross sections for the galactic cosmic ray cascade. The ENDF/B V database is used to generate the total and scattering cross sections for neutrons in
Least-squares finite element discretizations of neutron transport equations in 3 dimensions
Manteuffel, T.A; Ressel, K.J.; Starkes, G.
1996-12-31
The least-squares finite element framework to the neutron transport equation introduced in is based on the minimization of a least-squares functional applied to the properly scaled neutron transport equation. Here we report on some practical aspects of this approach for neutron transport calculations in three space dimensions. The systems of partial differential equations resulting from a P{sub 1} and P{sub 2} approximation of the angular dependence are derived. In the diffusive limit, the system is essentially a Poisson equation for zeroth moment and has a divergence structure for the set of moments of order 1. One of the key features of the least-squares approach is that it produces a posteriori error bounds. We report on the numerical results obtained for the minimum of the least-squares functional augmented by an additional boundary term using trilinear finite elements on a uniform tesselation into cubes.
Computational Transport Modeling of High-Energy Neutrons Found in the Space Environment
NASA Technical Reports Server (NTRS)
Cox, Brad; Theriot, Corey A.; Rohde, Larry H.; Wu, Honglu
2012-01-01
The high charge and high energy (HZE) particle radiation environment in space interacts with spacecraft materials and the human body to create a population of neutrons encompassing a broad kinetic energy spectrum. As an HZE ion penetrates matter, there is an increasing chance of fragmentation as penetration depth increases. When an ion fragments, secondary neutrons are released with velocities up to that of the primary ion, giving some neutrons very long penetration ranges. These secondary neutrons have a high relative biological effectiveness, are difficult to effectively shield, and can cause more biological damage than the primary ions in some scenarios. Ground-based irradiation experiments that simulate the space radiation environment must account for this spectrum of neutrons. Using the Particle and Heavy Ion Transport Code System (PHITS), it is possible to simulate a neutron environment that is characteristic of that found in spaceflight. Considering neutron dosimetry, the focus lies on the broad spectrum of recoil protons that are produced in biological targets. In a biological target, dose at a certain penetration depth is primarily dependent upon recoil proton tracks. The PHITS code can be used to simulate a broad-energy neutron spectrum traversing biological targets, and it account for the recoil particle population. This project focuses on modeling a neutron beamline irradiation scenario for determining dose at increasing depth in water targets. Energy-deposition events and particle fluence can be simulated by establishing cross-sectional scoring routines at different depths in a target. This type of model is useful for correlating theoretical data with actual beamline radiobiology experiments. Other work exposed human fibroblast cells to a high-energy neutron source to study micronuclei induction in cells at increasing depth behind water shielding. Those findings provide supporting data describing dose vs. depth across a water-equivalent medium. This
Boyarinov, V. F.; Kondrushin, A. E.; Fomichenko, P. A.
2012-07-01
Finite-difference time-dependent equations of Surface Harmonics method have been obtained for plane geometry. Verification of these equations has been carried out by calculations of tasks from 'Benchmark Problem Book ANL-7416'. The capacity and efficiency of the Surface Harmonics method have been demonstrated by solution of the time-dependent neutron transport equation in diffusion approximation. The results of studies showed that implementation of Surface Harmonics method for full-scale calculations will lead to a significant progress in the efficient solution of the time-dependent neutron transport problems in nuclear reactors. (authors)
Tsechanski, A.; Ofek, R.; Goldfeld, A.; Shani, G.
1989-02-01
The Ben-Gurion University measurements of neutron energy spectra in a graphite stack, resulting from the scattering of 14.7-MeV neutrons streaming through a 6-cm-diam collimator in a 121-cm-thick paraffin wall, have been used as a benchmark for the compatability and accuracy of discrete ordinates, P/sub n/, and transport calculations and as a tool for fusion reactor neutronics. The transport analysis has been carried out with the DOT 4.2 discrete ordinates code and with cross sections processed with the NJOY code. Most of the parameters affecting the accuracy of the flux and L system scattering cross sections in the P/sub n/ approximation, the quadrature set employed, and the energy multigroup structure. First, a spectrum calculated with DOT 4.2, with a detector located on the axis of the system, was compared with a spectrum calculated with the MCNP Monte Carlo code, which was a preliminary verification of the DOT 4.2 results. Both calculated spectra were in good agreement. Next, the DOT 4.2 calculations were compared with the measured spectra. The comparison showed that the discrepancies between the measurements and the calculations increase as the distance between the detector and the system axis increases. This trend indicates that when the flux is determined mainly by multiple scatterings, a more divided multigroup structure should be employed.
Flexible polyvinyl chloride neutron guides for transporting ultracold and very cold neutrons
Arzumanov, S. S. Bondarenko, L. N.; Geltenbort, P.; Morozov, V. I.; Nesvizhevsky, V. V.; Panin, Yu. N.; Strepetov, A. N.; Chuvilin, D. Yu.
2011-12-15
The transmission of ultracold neutrons (UCNs) through flexible polyvinyl chloride (PVC) tubes with lengths of up to 3 m and an internal diameter of 6-8 mm has been studied. High UCN transmission is found even for arbitrarily bent tubes (single bend, double bend, triple bend, figure eight, etc.). The transmission can be improved significantly by coating the inner surface of the tube with a thin layer of liquid fluorine polymer. The prospects of these neutron guides in fundamental and applied research are discussed.
Deterministic methods for time-dependent stochastic neutron transport
Baker, Randal S
2009-01-01
A numerical method is presented for solving the time-dependent survival probability equation in general (lD/2D/3D) geometries using the multi group SNmethod. Although this equation was first formulated by Bell in the early 1960's, it has only been applied to stationary systems (for other than idealized point models) until recently, and detailed descriptions of numerical solution techniques are lacking in the literature. This paper presents such a description and applies it to a dynamic system representative of a figurative criticality accident scenario.
Nonlinear Acceleration Methods for Even-Parity Neutron Transport
W. J. Martin; C. R. E. De Oliveira; H. Park
2010-05-01
Convergence acceleration methods for even-parity transport were developed that have the potential to speed up transport calculations and provide a natural avenue for an implicitly coupled multiphysics code. An investigation was performed into the acceleration properties of the introduction of a nonlinear quasi-diffusion-like tensor in linear and nonlinear solution schemes. Using the tensor reduced matrix as a preconditioner for the conjugate gradients method proves highly efficient and effective. The results for the linear and nonlinear case serve as the basis for further research into the application in a full three-dimensional spherical-harmonics even-parity transport code. Once moved into the nonlinear solution scheme, the implicit coupling of the convergence accelerated transport method into codes for other physics can be done seamlessly, providing an efficient, fully implicitly coupled multiphysics code with high order transport.
L/sub 2/-error estimates for the discrete ordinates method for three-dimensional neutron transport
Asadzadeh, M.
1988-02-01
We prove L/sub 2/-error estimates for the discrete ordinates method for the angular discretization of the three-dimensional neutron transport equation. The analysis is for monoenergetic three-dimensional transport of neutrons in a homogeneous uniform media and isotropic scattering is assumed. A special quadrature rule with relatively uniformly distributed discrete directions is considered.
Quantifying moisture transport in cementitious materials using neutron radiography
NASA Astrophysics Data System (ADS)
Lucero, Catherine L.
A portion of the concrete pavements in the US have recently been observed to have premature joint deterioration. This damage is caused in part by the ingress of fluids, like water, salt water, or deicing salts. The ingress of these fluids can damage concrete when they freeze and expand or can react with the cementitious matrix causing damage. To determine the quality of concrete for assessing potential service life it is often necessary to measure the rate of fluid ingress, or sorptivity. Neutron imaging is a powerful method for quantifying fluid penetration since it can describe where water has penetrated, how quickly it has penetrated and the volume of water in the concrete or mortar. Neutrons are sensitive to light atoms such as hydrogen and thus clearly detect water at high spatial and temporal resolution. It can be used to detect small changes in moisture content and is ideal for monitoring wetting and drying in mortar exposed to various fluids. This study aimed at developing a method to accurately estimate moisture content in mortar. The common practice is to image the material dry as a reference before exposing to fluid and normalizing subsequent images to the reference. The volume of water can then be computed using the Beer-Lambert law. This method can be limiting because it requires exact image alignment between the reference image and all subsequent images. A model of neutron attenuation in a multi-phase cementitious composite was developed to be used in cases where a reference image is not available. The attenuation coefficients for water, un-hydrated cement, and sand were directly calculated from the neutron images. The attenuation coefficient for the hydration products was then back-calculated. The model can estimate the degree of saturation in a mortar with known mixture proportions without using a reference image for calculation. Absorption in mortars exposed to various fluids (i.e., deionized water and calcium chloride solutions) were investigated
Radiation transport calculations for the ANS (Advanced Neutron Source) beam tubes
Engle, W.W., Jr.; Lillie, R.A.; Slater, C.O.
1988-01-01
The Advanced Neutron Source facility (ANS) will incorporate a large number of both radial and no-line-of-sight (NLS) beam tubes to provide very large thermal neutron fluxes to experimental facilities. The purpose of this work was to obtain comparisons for the ANS single- and split-core designs of the thermal and damage neutron and gamma-ray scalar fluxes in these beams tubes. For experimental locations far from the reactor cores, angular flux data are required; however, for close-in experimental locations, the scalar fluxes within each beam tube provide a credible estimate of the various signal to noise ratios. In this paper, the coupled two- and three-dimensional radiation transport calculations employed to estimate the scalar neutron and gamma-ray fluxes will be described and the results from these calculations will be discussed. 6 refs., 2 figs.
Brantley, P S
2006-09-27
We describe an asymptotic analysis of the coupled nonlinear system of equations describing time-dependent three-dimensional monoenergetic neutron transport and isotopic depletion and radioactive decay. The classic asymptotic diffusion scaling of Larsen and Keller [1], along with a consistent small scaling of the terms describing the radioactive decay of isotopes, is applied to this coupled nonlinear system of equations in a medium of specified initial isotopic composition. The analysis demonstrates that to leading order the neutron transport equation limits to the standard time-dependent neutron diffusion equation with macroscopic cross sections whose number densities are determined by the standard system of ordinary differential equations, the so-called Bateman equations, describing the temporal evolution of the nuclide number densities.
Talamo, Alberto
2013-05-01
This study presents three numerical algorithms to solve the time dependent neutron transport equation by the method of the characteristics. The algorithms have been developed taking into account delayed neutrons and they have been implemented into the novel MCART code, which solves the neutron transport equation for two-dimensional geometry and an arbitrary number of energy groups. The MCART code uses regular mesh for the representation of the spatial domain, it models up-scattering, and takes advantage of OPENMP and OPENGL algorithms for parallel computing and plotting, respectively. The code has been benchmarked with the multiplication factor results of a Boiling Water Reactor, with the analytical results for a prompt jump transient in an infinite medium, and with PARTISN and TDTORT results for cross section and source transients. The numerical simulations have shown that only two numerical algorithms are stable for small time steps.
Shafii, Mohammad Ali Meidianti, Rahma Wildian, Fitriyani, Dian; Tongkukut, Seni H. J.; Arkundato, Artoto
2014-09-30
Theoretical analysis of integral neutron transport equation using collision probability (CP) method with quadratic flux approach has been carried out. In general, the solution of the neutron transport using the CP method is performed with the flat flux approach. In this research, the CP method is implemented in the cylindrical nuclear fuel cell with the spatial of mesh being conducted into non flat flux approach. It means that the neutron flux at any point in the nuclear fuel cell are considered different each other followed the distribution pattern of quadratic flux. The result is presented here in the form of quadratic flux that is better understanding of the real condition in the cell calculation and as a starting point to be applied in computational calculation.
Kobayashi, Hiroyuki; Sato, Kazuhiro; Niioka, Takenori; Takeda, Masahide; Okuda, Yuji; Asano, Mariko; Ito, Hiroshi; Miura, Masatomo
2016-06-01
We investigated the effects of polymorphisms in CYP2D6, ABCB1, and ABCG2 and the side effects induced by gefitinib on the pharmacokinetics of O-desmethyl gefitinib, the active metabolite of gefitinib. On day 14 after beginning therapy with gefitinib, plasma concentrations of gefitinib and O-desmethyl gefitinib were measured. Patients were grouped into three groups according to their combination of CYP2D6 alleles: homozygous extensive metabolisers (EMs; *1/*1, *1/*2, and *2/*2; n = 13), heterozygous EMs (*1/*5, *2/*5, *1/*10, and *2/*10; n = 18), and intermediate metabolisers (IMs; *5/*10 and *10/*10; n = 5). The median AUC0-24 of O-desmethyl gefitinib in CYP2D6 IMs was 1460 ng h/mL, whereas that in homozygous EMs was 12,523 ng h/mL (P = 0.021 in univariate analysis). The median AUC ratio of O-desmethyl gefitinib to gefitinib differed among homozygous EMs, heterozygous EMs, and IMs at a ratio of 1.41:0.86:0.24 (P = 0.030). On the other hand, there were no significant differences in the AUC0-24 of O-desmethyl gefitinib between ABCB1 and ABCG2 genotypes. In a multivariate analysis, CYP2D6 homozygous EMs (P = 0.012) were predictive for a higher AUC0-24 of O-desmethyl gefitinib. The side effects of diarrhoea, skin rash, and hepatotoxicity induced by gefitinib were unrelated to the AUC0-24 of O-desmethyl gefitinib. CYP2D6 polymorphisms were associated with the formation of O-desmethyl gefitinib from gefitinib. In CYP2D6 homozygous EMs, the plasma concentrations of O-desmethyl gefitinib were higher over 24 h after taking gefitinib than those of the parent compound; however, side effects induced by gefitinib were unrelated to O-desmethyl gefitinib exposure. PMID:27154635
A/sub n/ method in monokinetic neutron transport theory: Convergence and numerical applications
Coppa, G.; Ravetto, P.; Sumini, M.
1981-10-01
The convergence of the approximate method, referred to as A/sub n/, to study the solution of the monokinetic transport equation is fully investigated, when it is applied to the description of the neutron population in both infinite and finite media.
NASA Astrophysics Data System (ADS)
Dumazert, Jonathan; Coulon, Romain; Carrel, Frédérick; Corre, Gwenolé; Normand, Stéphane; Méchin, Laurence; Hamel, Matthieu
2016-08-01
Neutron detection forms a critical branch of nuclear-related issues, currently driven by the search for competitive alternative technologies to neutron counters based on the helium-3 isotope. The deployment of plastic scintillators shows a high potential for efficient detectors, safer and more reliable than liquids, more easily scalable and cost-effective than inorganic. In the meantime, natural gadolinium, through its 155 and mostly 157 isotopes, presents an exceptionally high interaction probability with thermal neutrons. This paper introduces a dual system including a metal gadolinium core inserted at the center of a high-scale plastic scintillator sphere. Incident fast neutrons are thermalized by the scintillator shell and then may be captured with a significant probability by gadolinium 155 and 157 nuclei in the core. The deposition of a sufficient fraction of the capture high-energy prompt gamma signature inside the scintillator shell will then allow discrimination from background radiations by energy threshold, and therefore neutron detection. The scaling of the system with the Monte Carlo MCNPX2.7 code was carried out according to a tradeoff between the moderation of incident fast neutrons and the probability of slow neutron capture by a moderate-cost metal gadolinium core. Based on the parameters extracted from simulation, a first laboratory prototype for the assessment of the detection method principle has been synthetized. The robustness and sensitivity of the neutron detection principle are then assessed by counting measurement experiments. Experimental results confirm the potential for a stable, highly sensitive, transportable and cost-efficient neutron detector and orientate future investigation toward promising axes.
Anisotropic Elastic Resonance Scattering model for the Neutron Transport equation
Mohamed Ouisloumen; Abderrafi M. Ougouag; Shadi Z. Ghrayeb
2014-11-24
The resonance scattering transfer cross-section has been reformulated to account for anisotropic scattering in the center-of-mass of the neutron-nucleus system. The main innovation over previous implementations is the relaxation of the ubiquitous assumption of isotropic scattering in the center-of-mass and the actual effective use of scattering angle distributions from evaluated nuclear data files in the computation of the angular moments of the resonant scattering kernels. The formulas for the high order anisotropic moments in the laboratory system are also derived. A multi-group numerical formulation is derived and implemented into a module incorporated within the NJOY nuclear data processing code. An ultra-fine energy mesh cross section library was generated using these new theoretical models and then was used for fuel assembly calculations with the PARAGON lattice physics code. The results obtained indicate a strong effect of this new model on reactivity, multi-group fluxes and isotopic inventory during depletion.
Coughlin, P.J.
1989-01-01
The Shippingport Station Decommissioning Project (SSDP) is a US Department of Energy (DOE) project for dismantling the Shippingport atomic power station. One of the more significant and challenging technical aspects of the project, which is being managed for DOE by General Electric-Nuclear Energy, is the marine transport of the reactor pressure vessel (RPV) and its associated neutron shield tank (NST) to the government-owned Hanford Reservation near Richland, Washington. Planning of the transport activity, barge transportation operations, and Hanford transportation operations, are discussed. This work will be the first use of barge transportation in the United States of a radioactive RPV package from a decommissioned land-based nuclear power plant. This extensive transportation operation has been accomplished in a timely, safe, and cost-effective manner.
Radiative or neutron transport modeling using a lattice Boltzmann equation framework
NASA Astrophysics Data System (ADS)
Bindra, H.; Patil, D. V.
2012-07-01
In this paper, the lattice Boltzmann equation (LBE)-based framework is used to obtain the solution for the linear radiative or neutron transport equation. The LBE framework is devised for the integrodifferential forms of these equations which arise due to the inclusion of the scattering terms. The interparticle collisions are neglected, hence omitting the nonlinear collision term. Furthermore, typical representative examples for one-dimensional or two-dimensional geometries and inclusion or exclusion of the scattering term (isotropic and anisotropic) in the Boltzmann transport equation are illustrated to prove the validity of the method. It has been shown that the solution from the LBE methodology is equivalent to the well-known Pn and Sn methods. This suggests that the LBE can potentially provide a more convenient and easy approach to solve the physical problems of neutron and radiation transport.
Wu, Y.; Xie, Z.; Fischer, U.
1999-11-01
A discrete ordinates nodal transport method has been developed for numerical solution of the one-dimensional neutron transport equation in curvilinear geometries. The nodal transport equation is solved by the Green's function method, using the Legendre polynomial expansion for spatial dependence and the discrete ordinates (S{sub N}) approximation for angular dependence. The calculation for various test problems has been performed to verify the method. The numerical results demonstrate that it has very high precision on coarse spatial meshes relative to the standard fine-mesh S{sub N} method with the spatial diamond-differencing scheme.
Transport simulation and image reconstruction for fast-neutron detection of explosives and narcotics
Micklich, B.J.; Fink, C.L.; Sagalovsky, L.
1995-07-01
Fast-neutron inspection techniques show considerable promise for explosive and narcotics detection. A key advantage of using fast neutrons is their sensitivity to low-Z elements (carbon, nitrogen, and oxygen), which are the primary constituents of these materials. We are currently investigating two interrogation methods in detail: Fast-Neutron Transmission Spectroscopy (FNTS) and Pulsed Fast-Neutron Analysis (PFNA). FNTS is being studied for explosives and narcotics detection in luggage and small containers for which the transmission ratio is greater than about 0.01. The Monte-Carlo radiation transport code MCNP is being used to simulate neutron transmission through a series of phantoms for a few (3-5) projection angles and modest (2 cm) resolution. Areal densities along projection rays are unfolded from the transmission data. Elemental abundances are obtained for individual voxels by tomographic reconstruction, and these reconstructed elemental images are combined to provide indications of the presence or absence of explosives or narcotics. PFNA techniques are being investigated for detection of narcotics in cargo containers because of the good penetration of the fast neutrons and the low attenuation of the resulting high-energy gamma-ray signatures. Analytic models and Monte-Carlo simulations are being used to explore the range of capabilities of PFNA techniques and to provide insight into systems engineering issues. Results of studies from both FNTS and PFNA techniques are presented.
Transport simulation and image reconstruction for fast-neutron detection of explosives and narcotics
NASA Astrophysics Data System (ADS)
Micklich, Bradley J.; Fink, Charles L.; Sagalovsky, Leonid
1995-09-01
Fast-neutron inspection techniques show considerable promise for explosive and narcotics detection. A key advantage of using fast neutron is their sensitivity to low-Z elements (carbon, nitrogen, and oxygen), which are the primary constituents of these materials. We are currently investigating two interrogation methods in detail: fast-neutron transmission spectroscopy (FNTS) and pulsed fast-neutron analysis (PFNA). FNTS is being studied for explosives and narcotics detection in luggage and small containers for which the transmission ration is greater than about 0.01. The Monte Carlo radiation transport code MCNP is being used to simulate neutron transmission through a series of phantoms for a few (3-5) projections angles and modest (2 cm) reolution. Areal densities along projection rays are unfolded from the transmission data. Elemental abundances are obtained for individual voxels by tomographic reconstruction, and the reconstructed elemental images are combined to provide indications of the presence or absence of explosives or narcotics. PFNA techniques are being investigated for detection of narcotics in cargo containers because of the good penetration of the fast neutrons and the low attenuation of the resulting high-energy gamma-ray signatures. Analytic models and Monte Carlo simulations are being used to explore the range of capabilities of PFNA techniques and to provide insight into systems engineering issues. Results of studies from both FNTS and PFNA technqiues are presented.
NASA Astrophysics Data System (ADS)
Niranjan, Ram; Rout, R. K.; Srivastava, R.; Kaushik, T. C.; Gupta, Satish C.
2016-03-01
A 17 kJ transportable plasma focus (PF) device with flexible transmission lines is developed and is characterized. Six custom made capacitors are used for the capacitor bank (CB). The common high voltage plate of the CB is fixed to a centrally triggered spark gap switch. The output of the switch is coupled to the PF head through forty-eight 5 m long RG213 cables. The CB has a quarter time-period of 4 μs and an estimated current of 506 kA is delivered to the PF device at 17 kJ (60 μF, 24 kV) energy. The average neutron yield measured using silver activation detector in the radial direction is (7.1 ± 1.4) × 108 neutrons/shot over 4π sr at 5 mbar optimum D2 pressure. The average neutron yield is more in the axial direction with an anisotropy factor of 1.33 ± 0.18. The average neutron energies estimated in the axial as well as in the radial directions are (2.90 ± 0.20) MeV and (2.58 ± 0.20) MeV, respectively. The flexibility of the PF head makes it useful for many applications where the source orientation and the location are important factors. The influence of electromagnetic interferences from the CB as well as from the spark gap on applications area can be avoided by putting a suitable barrier between the bank and the PF head.
Ageing of a neutron shielding used in transport/storage casks
Nizeyiman, Fidele; Alami, Aatif; Issard, Herve; Bellenger, Veronique
2012-07-11
In radioactive materials transport/storage casks, a mineral-filled vinylester composite is used for neutron shielding which relies on its hydrogen and boron atoms content. During cask service life, this composite is mainly subjected to three types of ageing: hydrothermal ageing, thermal oxidation and neutron irradiation. The aim of this study is to investigate the effect of hydrothermal ageing on the properties and chemical composition of this polymer composite. At high temperature (120 Degree-Sign C and 140 Degree-Sign C), the main consequence is the strong decrease of mechanical properties induced by the filler/matrix debonding.
Cascos, V; Martínez-Coronado, R; Alonso, J A; Fernández-Díaz, M T
2014-06-25
Sr0.7Ho0.3CoO3-δ oxide has been recently described as an excellent cathode material (1274 mW cm(-2) at 850 °C with pure H2 as fuel1) for solid oxide fuel cells (SOFCs) with LSGM as electrolyte. In this work, we describe a detailed study of its crystal structure conducted to find out the correlation between the excellent performance as a cathode and the structural features. The tetragonal crystal structure (e.g., I4/mmm) basically contains layers of octahedrally coordinated Co2O6 units alternated with layers of Co1O4 tetrahedra sharing corners. An "in situ" neutron power diffraction (NPD) experiment, between 25 and 800 °C, reveals the presence of a high oxygen deficiency affecting O4 oxygen atoms, with large displacement factors that suggest a large lability and mobility. Difference Fourier maps allow the visualization at high temperatures of the 2D diffusion pathways within the tetrahedral layers, where O3 and O4 oxygens participate. The measured thermal expansion coefficient is 16.61 × 10(-6) K(-1) between 300 and 850 °C, exhibiting an excellent chemical compatibility with the electrolyte. PMID:24873238
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.
Wang, G. B.; Wang, K.; Liu, H. G.; Li, R. D.
2013-07-01
A Monte Carlo tool RSMC (Reaction Sequence Monte Carlo) was developed to simulate deuteron/triton transportation and reaction coupled problem. The 'Forced particle production' variance reduction technique was used to improve the simulation speed, which made the secondary product play a major role. The mono-energy 14 MeV fusion neutron source was employed as a validation. Then the thermal-to-fusion neutron convertor was studied with our tool. Moreover, an in-core conversion efficiency measurement experiment was performed with {sup 6}LiD and {sup 6}LiH converters. Threshold activation foils was used to indicate the fast and fusion neutron flux. Besides, two other pivotal parameters were calculated theoretically. Finally, the conversion efficiency of {sup 6}LiD is obtained as 1.97x10{sup -4}, which matches well with the theoretical result. (authors)
Interfacing MCNPX and McStas for simulation of neutron transport
NASA Astrophysics Data System (ADS)
Klinkby, Esben; Lauritzen, Bent; Nonbøl, Erik; Kjær Willendrup, Peter; Filges, Uwe; Wohlmuther, Michael; Gallmeier, Franz X.
2013-02-01
Simulations of target-moderator-reflector system at spallation sources are conventionally carried out using Monte Carlo codes such as MCNPX (Waters et al., 2007 [1]) or FLUKA (Battistoni et al., 2007; Ferrari et al., 2005 [2,3]) whereas simulations of neutron transport from the moderator and the instrument response are performed by neutron ray tracing codes such as McStas (Lefmann and Nielsen, 1999; Willendrup et al., 2004, 2011a,b [4-7]). The coupling between the two simulation suites typically consists of providing analytical fits of MCNPX neutron spectra to McStas. This method is generally successful but has limitations, as it e.g. does not allow for re-entry of neutrons into the MCNPX regime. Previous work to resolve such shortcomings includes the introduction of McStas inspired supermirrors in MCNPX. In the present paper different approaches to interface MCNPX and McStas are presented and applied to a simple test case. The direct coupling between MCNPX and McStas allows for more accurate simulations of e.g. complex moderator geometries, backgrounds, interference between beam-lines as well as shielding requirements along the neutron guides.
An Algorithm for the Transport of Anisotropic Neutrons
NASA Technical Reports Server (NTRS)
Tweed, J.
2005-01-01
One major obstacle to human space exploration is the possible limitations imposed by the adverse effect of long-term exposure to the space environment. Even before human spaceflight began, the potentially brief exposure of astronauts to the very intense random solar particle events (SPE) were of great concern. A new challenge appears in deep space exploration from exposure to the low-intensity heavy-ion flux of the galactic cosmic rays (GCR) since the missions are of long duration and the accumulated GCR exposures can be high. Because cancer induction rates increase behind low to rather large thicknesses of aluminum shielding, according to available biological data on mammalian exposures to GCR like ions, the shield requirements for a Mars mission are prohibitively expensive in terms of mission launch costs. Therefore, a critical issue in the Human Exploration and Development of Space enterprise is cost effective mitigation of risk associated with ionizing radiation exposure. In order to estimate astronaut risk to GCR exposure and associated cancer risks and health hazards, it is necessary to do shield material studies. To determine an optimum radiation shield material it is necessary to understand nuclear interaction processes such as fragmentation and secondary particle production which is a function of energy dependent cross sections. This requires knowledge of material transmission characteristics either through laboratory testing or improved theoretical modeling. Here ion beam transport theory is of importance in that testing of materials in the laboratory environment generated by particle accelerators is a necessary step in materials development and evaluation for space use. The approximations used in solving the Boltzmann transport equation for the space setting are often not sufficient for laboratory work and those issues are a major emphasis of the present work.
Greg Flach, Frank Smith
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 assigns 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.
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
Discontinuous Galerkin finite element method applied to the 1-D spherical neutron transport equation
Machorro, Eric . E-mail: machorro@amath.washington.edu
2007-04-10
Discontinuous Galerkin finite element methods are used to estimate solutions to the non-scattering 1-D spherical neutron transport equation. Various trial and test spaces are compared in the context of a few sample problems whose exact solution is known. Certain trial spaces avoid unphysical behaviors that seem to plague other methods. Comparisons with diamond differencing and simple corner-balancing are presented to highlight these improvements.
Modular, object-oriented redesign of a large-scale Monte Carlo neutron transport program
Moskowitz, B.S.
2000-02-01
This paper describes the modular, object-oriented redesign of a large-scale Monte Carlo neutron transport program. This effort represents a complete 'white sheet of paper' rewrite of the code. In this paper, the motivation driving this project, the design objectives for the new version of the program, and the design choices and their consequences will be discussed. The design itself will also be described, including the important subsystems as well as the key classes within those subsystems.
NASA Astrophysics Data System (ADS)
Lotsch, Bettina V.
2015-07-01
Graphene's legacy has become an integral part of today's condensed matter science and has equipped a whole generation of scientists with an armory of concepts and techniques that open up new perspectives for the postgraphene area. In particular, the judicious combination of 2D building blocks into vertical heterostructures has recently been identified as a promising route to rationally engineer complex multilayer systems and artificial solids with intriguing properties. The present review highlights recent developments in the rapidly emerging field of 2D nanoarchitectonics from a materials chemistry perspective, with a focus on the types of heterostructures available, their assembly strategies, and their emerging properties. This overview is intended to bridge the gap between two major—yet largely disjunct—developments in 2D heterostructures, which are firmly rooted in solid-state chemistry or physics. Although the underlying types of heterostructures differ with respect to their dimensions, layer alignment, and interfacial quality, there is common ground, and future synergies between the various assembly strategies are to be expected.
NASA Astrophysics Data System (ADS)
Bartesaghi, G.; Gambarini, G.; Negri, A.; Carrara, M.; Burian, J.; Viererbl, L.
2010-04-01
Presently there are no standard protocols for dosimetry in neutron beams for boron neutron capture therapy (BNCT) treatments. Because of the high radiation intensity and of the presence at the same time of radiation components having different linear energy transfer and therefore different biological weighting factors, treatment planning in epithermal neutron fields for BNCT is usually performed by means of Monte Carlo calculations; experimental measurements are required in order to characterize the neutron source and to validate the treatment planning. In this work Monte Carlo simulations in two kinds of tissue-equivalent phantoms are described. The neutron transport has been studied, together with the distribution of the boron dose; simulation results are compared with data taken with Fricke gel dosimeters in form of layers, showing a good agreement.
Hybrid method of deterministic and probabilistic approaches for multigroup neutron transport problem
Lee, D.
2012-07-01
A hybrid method of deterministic and probabilistic methods is proposed to solve Boltzmann transport equation. The new method uses a deterministic method, Method of Characteristics (MOC), for the fast and thermal neutron energy ranges and a probabilistic method, Monte Carlo (MC), for the intermediate resonance energy range. The hybrid method, in case of continuous energy problem, will be able to take advantage of fast MOC calculation and accurate resonance self shielding treatment of MC method. As a proof of principle, this paper presents the hybrid methodology applied to a multigroup form of Boltzmann transport equation and confirms that the hybrid method can produce consistent results with MC and MOC methods. (authors)
Low-energy beam transport studies supporting the Spallation Neutron Source 1-MW beam operationa
Han, Baoxi; Kalvas, T.; Tarvainen, O.; Welton, Robert F; Murray Jr, S N; Pennisi, Terry R; Santana, Manuel; Stockli, Martin P
2012-01-01
The H- injector consisting of a cesium enhanced RF-driven ion source and a 2-lens electrostatic low-energy beam transport (LEBT) system supports the Spallation Neutron Source 1-MW beam operation with ~38 mA beam current in the linac at 60 Hz with a pulse length of up to ~1.0 ms. In this work, two important issues associated with the low-energy beam transport are discussed: 1) inconsistent dependence of the post-RFQ beam current on the ion source tilt angle, and 2) high power beam losses on the LEBT electrodes under some off-nominal conditions compromising their reliability.
Synergism of the method of characteristics and CAD technology for neutron transport calculation
Chen, Z.; Wang, D.; He, T.; Wang, G.; Zheng, H.
2013-07-01
The method of characteristics (MOC) is a very popular methodology in neutron transport calculation and numerical simulation in recent decades for its unique advantages. One of the key problems determining whether the MOC can be applied in complicated and highly heterogeneous geometry is how to combine an effective geometry processing method with MOC. Most of the existing MOC codes describe the geometry by lines and arcs with extensive input data, such as circles, ellipses, regular polygons and combination of them. Thus they have difficulty in geometry modeling, background meshing and ray tracing for complicated geometry domains. In this study, a new idea making use of a CAD solid modeler MCAM which is a CAD/Image-based Automatic Modeling Program for Neutronics and Radiation Transport developed by FDS Team in China was introduced for geometry modeling and ray tracing of particle transport to remove these geometrical limitations mentioned above. The diamond-difference scheme was applied to MOC to reduce the spatial discretization error of the flat flux approximation in theory. Based on MCAM and MOC, a new MOC code was developed and integrated into SuperMC system, which is a Super Multi-function Computational system for neutronics and radiation simulation. The numerical testing results demonstrated the feasibility and effectiveness of the new idea for geometry treatment in SuperMC. (authors)
NASA Technical Reports Server (NTRS)
Wilson, John W. (Inventor); Tripathi, Ram K. (Inventor); Badavi, Francis F. (Inventor); Cucinotta, Francis A. (Inventor)
2012-01-01
An apparatus, method and program storage device for determining high-energy neutron/ion transport to a target of interest. Boundaries are defined for calculation of a high-energy neutron/ion transport to a target of interest; the high-energy neutron/ion transport to the target of interest is calculated using numerical procedures selected to reduce local truncation error by including higher order terms and to allow absolute control of propagated error by ensuring truncation error is third order in step size, and using scaling procedures for flux coupling terms modified to improve computed results by adding a scaling factor to terms describing production of j-particles from collisions of k-particles; and the calculated high-energy neutron/ion transport is provided to modeling modules to control an effective radiation dose at the target of interest.
1985-02-01
Version 00 TP2 is a transport theory code, developed to determine reactivity effects and kinetic parameters such as effective delayed neutron fractions and mean generation time by applying the usual perturbation formalism for two-dimensional geometry.
1985-02-01
Version 00 TP1 is a transport theory code, developed to determine reactivity effects and kinetic parameters such as effective delayed neutron fractions and mean generation time by applying the usual perturbation formalism for one-dimensional geometry.
1995-12-12
Version 00 For a variety of applications (accelerator shielding, the use of neutrons in radiotherapy, radiation damage studies, etc.) It is necessary to carry out transport calculations involving medium-energy neutrons. HILO86R multigroup cross sections are in the form needed for the CCC-254/ANISN-ORNL and CCC-543/TORT-DORT discrete ordinates codes and in the CCC-474/MORSE-CGA Monte Carlo code.
A portable, parallel, object-oriented Monte Carlo neutron transport code in C++
Lee, S.R.; Cummings, J.C.; Nolen, S.D. |
1997-05-01
We have developed a multi-group Monte Carlo neutron transport code using C++ and the Parallel Object-Oriented Methods and Applications (POOMA) class library. This transport code, called MC++, currently computes k and {alpha}-eigenvalues and is portable to and runs parallel on a wide variety of platforms, including MPPs, clustered SMPs, and individual workstations. It contains appropriate classes and abstractions for particle transport and, through the use of POOMA, for portable parallelism. Current capabilities of MC++ are discussed, along with physics and performance results on a variety of hardware, including all Accelerated Strategic Computing Initiative (ASCI) hardware. Current parallel performance indicates the ability to compute {alpha}-eigenvalues in seconds to minutes rather than hours to days. Future plans and the implementation of a general transport physics framework are also discussed.
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
Hoshi, M; Hiraoka, M; Hayakawa, N; Sawada, S; Munaka, M; Kuramoto, A; Oka, T; Iwatani, K; Shizuma, K; Hasai, H
1992-11-01
A benchmark test of the Monte Carlo neutron and photon transport code system (MCNP) was performed using a 252Cf fission neutron source to validate the use of the code for the energy spectrum analyses of Hiroshima atomic bomb neutrons. Nuclear data libraries used in the Monte Carlo neutron and photon transport code calculation were ENDF/B-III, ENDF/B-IV, LASL-SUB, and ENDL-73. The neutron moderators used were granite (the main component of which is SiO2, with a small fraction of hydrogen), Newlight [polyethylene with 3.7% boron (natural)], ammonium chloride (NH4Cl), and water (H2O). Each moderator was 65 cm thick. The neutron detectors were gold and nickel foils, which were used to detect thermal and epithermal neutrons (4.9 eV) and fast neutrons (> 0.5 MeV), respectively. Measured activity data from neutron-irradiated gold and nickel foils in these moderators decreased to about 1/1,000th or 1/10,000th, which correspond to about 1,500 m ground distance from the hypocenter in Hiroshima. For both gold and nickel detectors, the measured activities and the calculated values agreed within 10%. The slopes of the depth-yield relations in each moderator, except granite, were similar for neutrons detected by the gold and nickel foils. From the results of these studies, the Monte Carlo neutron and photon transport code was verified to be accurate enough for use with the elements hydrogen, carbon, nitrogen, oxygen, silicon, chlorine, and cadmium, and for the incident 252Cf fission spectrum neutrons. PMID:1399639
NASA Astrophysics Data System (ADS)
Wanner, Christoph; Zink, Sonja; Eggenberger, Urs; Mäder, Urs
2012-04-01
In Thun, Switzerland, a permeable reactive barrier (PRB) for Cr(VI) reduction by gray cast iron was installed in May 2008. The PRB is composed of a double array of vertical piles containing iron shavings and gravel. The aquifer in Thun is almost saturated with dissolved oxygen and the groundwater flow velocities are ca. 10-15 m/day. Two years after PRB installation Cr(VI) concentrations still permanently exceed the Swiss threshold value for contaminated sites downstream of the barrier at selected localities. Groundwater δ53/52CrSRM979 measurements were used to track Cr(VI) reduction induced by the PRB. δ53/52CrSRM979 values of two samples downstream of the PRB showed a clear fractionation towards more positive values compared to four samples from the hotspot, which is clear evidence of Cr(VI) reduction induced by the PRB. Another downstream sample did not show a shift to more positive δ53/52CrSRM979 values. Because this latter location correlates with the highest downstream Cr(VI) concentration it is proposed that a part of the Cr(VI) plume is bypassing the barrier. Using a Rayleigh fractionation model a minimum present-day overall Cr(VI) reduction efficiency of ca. 15% was estimated. A series of 2D model simulations, including the fractionation of Cr isotopes, confirm that only a PRB bypass of parts of the Cr(VI) plume can lead to the observed values. Additionally, the simulations revealed that the proposed bypass occurs due to an insufficient permeability of the individual PRB piles. It is concluded that with this type of PRB a complete and long-lasting Cr(VI) reduction is extremely difficult to achieve for Cr(VI) contaminations located in nearly oxygen and calcium carbonate saturated aquifer in a regime of high groundwater velocities. Additional remediation action would limit the environmental impact and allow to reach target concentrations.
Calculation of the Local Neutronic Parameters for CANDU Fuel Bundles Using Transport Methods
Balaceanu, Victoria; Rizoiu, Andrei; Hristea, Viorel
2006-07-01
For a realistic neutronic evaluation of the CANDU reactor core it is important to accurately perform the local neutronic parameters (i.e. multigroup macroscopic cross sections for the core materials) calculation. This means using codes that allow a good geometric representation of the CANDU fuel bundle and then solving the transport equation. The paper reported here intends to study in detail the local behavior for two types of CANDU fuel, NU{sub 3}7 (Natural Uranium, 37 elements) and SEU{sub 4}3 (Slightly Enriched Uranium, 43 elements, with 1.1 wt% enrichment). The considered fuel types represent fresh and used bundles. The two types of CANDU super-cells are reference NU{sub 3}7, perturbed NU{sub 3}7, reference SEU{sub 4}3 and perturbed SEU{sub 4}3. The perturbed super-cells contain a Mechanical Control Absorber (a very strong reactivity device). For reaching the proposed objective a methodology is used based on WIMS and PIJXYZ codes. WIMS is a standard lattice-cell code, based on transport theory and it is used for producing fuel cell multigroup macroscopic cross sections. For obtaining the fine local neutronic parameters in the CANDU super-cells (k-eff values, local MCA reactivity worth, flux distributions and reaction rates), the PIJXYZ code is used. PIJXYZ is a 3D integral transport code using the first collision probability method and it has been developed for CANDU cell geometry. It is consistent with WIMS lattice-cell calculations and allows a good geometrical representation of the CANDU bundle in three dimensions. The analysis of the neutronic parameters consists of comparing the obtained results with the similar results calculated with the DRAGON code. This comparison shows a good agreement between these results. (authors)
Wanner, Christoph; Zink, Sonja; Eggenberger, Urs; Mäder, Urs
2012-04-01
In Thun, Switzerland, a permeable reactive barrier (PRB) for Cr(VI) reduction by gray cast iron was installed in May 2008. The PRB is composed of a double array of vertical piles containing iron shavings and gravel. The aquifer in Thun is almost saturated with dissolved oxygen and the groundwater flow velocities are ca. 10-15m/day. Two years after PRB installation Cr(VI) concentrations still permanently exceed the Swiss threshold value for contaminated sites downstream of the barrier at selected localities. Groundwater δ(53/52)Cr(SRM979) measurements were used to track Cr(VI) reduction induced by the PRB. δ(53/52)Cr(SRM979) values of two samples downstream of the PRB showed a clear fractionation towards more positive values compared to four samples from the hotspot, which is clear evidence of Cr(VI) reduction induced by the PRB. Another downstream sample did not show a shift to more positive δ(53/52)Cr(SRM979) values. Because this latter location correlates with the highest downstream Cr(VI) concentration it is proposed that a part of the Cr(VI) plume is bypassing the barrier. Using a Rayleigh fractionation model a minimum present-day overall Cr(VI) reduction efficiency of ca. 15% was estimated. A series of 2D model simulations, including the fractionation of Cr isotopes, confirm that only a PRB bypass of parts of the Cr(VI) plume can lead to the observed values. Additionally, the simulations revealed that the proposed bypass occurs due to an insufficient permeability of the individual PRB piles. It is concluded that with this type of PRB a complete and long-lasting Cr(VI) reduction is extremely difficult to achieve for Cr(VI) contaminations located in nearly oxygen and calcium carbonate saturated aquifer in a regime of high groundwater velocities. Additional remediation action would limit the environmental impact and allow to reach target concentrations. PMID:22343010
An Improved Elastic and Nonelastic Neutron Transport Algorithm for Space Radiation
NASA Technical Reports Server (NTRS)
Clowdsley, Martha S.; Wilson, John W.; Heinbockel, John H.; Tripathi, R. K.; Singleterry, Robert C., Jr.; Shinn, Judy L.
2000-01-01
A neutron transport algorithm including both elastic and nonelastic particle interaction processes for use in space radiation protection for arbitrary shield material is developed. The algorithm is based upon a multiple energy grouping and analysis of the straight-ahead Boltzmann equation by using a mean value theorem for integrals. The algorithm is then coupled to the Langley HZETRN code through a bidirectional neutron evaporation source term. Evaluation of the neutron fluence generated by the solar particle event of February 23, 1956, for an aluminum water shield-target configuration is then compared with MCNPX and LAHET Monte Carlo calculations for the same shield-target configuration. With the Monte Carlo calculation as a benchmark, the algorithm developed in this paper showed a great improvement in results over the unmodified HZETRN solution. In addition, a high-energy bidirectional neutron source based on a formula by Ranft showed even further improvement of the fluence results over previous results near the front of the water target where diffusion out the front surface is important. Effects of improved interaction cross sections are modest compared with the addition of the high-energy bidirectional source terms.
Atmospheric transport of neutrons and gamma rays from near-horizon nuclear detonations
Byrd, R.C.; Heerema, B.D.
1996-03-01
This report continues a study of the transport of neutrons and rays from nuclear detonations at high altitudes to a set of detectors, with an emphasis on the limiting case of sources even beyond the horizon. To improve the calculational efficiency, the standard arrangement of a single source with multiple detectors is transformed to an equivalent one with a single detector and sources at multiple locations. Particular attention is paid to the critical problem of transport at near-horizon angles in an atmosphere whose density decreases exponentially with altitude. As a check, calculations for this region are made using both analytical and Monte Carlo approaches. For sources approaching the horizon, the fluence of gamma rays and neutrons reaching the detector drops gradually as the increasing column density attenuates the direct, unscattered fluence. Near the grazing angle, the direct fluence plummets, but the scattered component continues to decrease slowly and remains observable. Over this range, the timedependent flux of direct-plus-scattered gamma rays changes dramatically in both shape and magnitude, but it probably remains distinct from typical natural backgrounds. The neutron time-of-flight spectrum is dominated by scattering and reflects only the most important aspects of the original source spectrum; its most obvious features are a prominent low-energy tail and the resonance structure produced by nuclear interactions in the atmosphere. In some cases, the fluence of secondary gamma rays produced by these interactions may be larger than that from the source itself.
A hybrid approach to the neutron transport K-eigenvalue problem using NDA-based algorithms
Willert, J. A.; Kelley, C. T.; Knoll, D. A.; Park, H.
2013-07-01
In order to provide more physically accurate solutions to the neutron transport equation it has become increasingly popular to use Monte Carlo simulation to model nuclear reactor dynamics. These Monte Carlo methods can be extremely expensive, so we turn to a class of methods known as hybrid methods, which combine known deterministic and stochastic techniques to solve the transport equation. In our work, we show that we can simulate the action of a transport sweep using a Monte Carlo simulation in order to solve the k-eigenvalue problem. We'll accelerate the solution using nonlinear diffusion acceleration (NDA) as in [1,2]. Our work extends the results in [1] to use Monte Carlo simulation as the high-order solver. (authors)
THE COMMISSIONING PLAN FOR THE SPALLATION NEUTRON SOURCE RING AND TRANSPORT LINES.
RAPARIA,D.BLASKIEWICZ,M.LEE,Y.Y.WEI,J.ET AL.
2004-03-10
The Spallation Neutron Source (SNS) accelerator systems will provide a 1 GeV, 1.44 MW proton beam to a liquid mercury target for neutron production. In order to satisfy the accelerator systems' portion of the Critical Decision 4 (CD-4) commissioning goal (which marks the completion of the construction phase of the project), a beam pulse with intensity greater than 1 x 10{sup 13} protons must be accumulated in the ring, extracted in a single turn and delivered to the target. A commissioning plan has been formulated for bringing into operation and establishing nominal operating conditions for the various ring and transport line subsystems as well as for establishing beam conditions and parameters which meet the commissioning goal.
Application of three-dimensional transport code to the analysis of the neutron streaming experiment
Chatani, K.; Slater, C.O.
1990-01-01
This paper summarized the calculational results of neutron streaming through a Clinch River Breeder Reactor (CRBR) Prototype coolant pipe chaseway. Particular emphasis is placed on results at bends in the chaseway. Calculations were performed with three three-dimensional codes: the discrete ordinates radiation transport code TORT and Monte Carlo radiation transport code MORSE, which were developed by Oak Ridge National Laboratory (ORNL), and the discrete ordinates code ENSEMBLE, which was developed in Japan. The purpose of the calculations is not only to compare the calculational results with the experimental results, but also to compare the results of TORT and MORSE with those of ENSEMBLE. In the TORT calculations, two types of difference methods, weighted-difference method was applied in ENSEMBLE calculation. Both TORT and ENSEMBLE produced nearly the same calculational results, but differed in the number of iterations required for converging each neutron group. Also, the two types of difference methods in the TORT calculations showed no appreciable variance in the number of iterations required. However, a noticeable disparity in the computer times and some variation in the calculational results did occur. The comparisons of the calculational results with the experimental results, showed for the epithermal neutron flux generally good agreement in the first and second legs and at the first bend where the two-dimensional modeling might be difficult. Results were fair to poor along the centerline of the first leg near the opening to the second leg because of discrete ordinates ray effects. Additionally, the agreement was good throughout the first and second legs for the thermal neutron region. Calculations with MORSE were made. These calculational results and comparisons are described also. 8 refs., 4 figs.
Iwatani, K; Hoshi, M; Shizuma, K; Hiraoka, M; Hayakawa, N; Oka, T; Hasai, H
1994-10-01
A benchmark test of the Monte Carlo neutron and photon transport code system (MCNP) was performed using a bare- and energy-moderated 252Cf fission neutron source which was obtained by transmission through 10-cm-thick iron. An iron plate was used to simulate the effect of the Hiroshima atomic bomb casing. This test includes the activation of indium and nickel for fast neutrons and gold, europium, and cobalt for thermal and epithermal neutrons, which were inserted in the moderators. The latter two activations are also to validate 152Eu and 60Co activity data obtained from the atomic bomb-exposed specimens collected at Hiroshima and Nagasaki, Japan. The neutron moderators used were Lucite and Nylon 6 and the total thickness of each moderator was 60 cm or 65 cm. Measured activity data (reaction yield) of the neutron-irradiated detectors in these moderators decreased to about 1/1,000th or 1/10,000th, which corresponds to about 1,500 m ground distance from the hypocenter in Hiroshima. For all of the indium, nickel, and gold activity data, the measured and calculated values agreed within 25%, and the corresponding values for europium and cobalt were within 40%. From this study, the MCNP code was found to be accurate enough for the bare- and energy-moderated 252Cf neutron activation calculations of these elements using moderators containing hydrogen, carbon, nitrogen, and oxygen. PMID:8083048
Iwatani, Kazuo; Shizuma, Kiyoshi; Hasai, Hiromi; Hoshi, Masaharu; Hiraoka, Masayuki; Hayakawa, Norihiko; Oka, Takamitsu
1994-10-01
A benchmark test of the Monte Carlo neutron and photon transport code system (MCNP) was performed using a bare- and energy-moderated {sup 252}Cf fission neutron source which was obtained by transmission through 10-cm-thick iron. An iron plate was used to simulate the effect of the Hiroshima atomic bomb casing. This test includes the activation of indium and nickel for fast neutrons and gold, europium, and cobalt for thermal and epithermal neutrons, which were inserted in the moderators. The latter two activations are also to validate {sup 152}Eu and {sup 60}Co activity data obtained from the atomic bomb-exposed specimens collected at Hiroshima and Nagasaki, Japan. The neutron moderators used were Lucite and Nylon 6 and the total thickness of each moderator was 60 cm or 65 cm. Measured activity data (reaction yield) of the neutron-irradiated detectors in these moderators decreased to about 1/1,000th or 1/10,000th, which corresponds to about 1,500 m ground distance from the hypocenter in Hiroshima. For all of the indium, nickel, and gold activity data, the measured and calculated values agreed within 25%, and the corresponding values for europium and cobalt were within 40%. From this study, the MCNP code was found to be accurate enough for the bare- and energy-moderated {sup 252}Cf neutron activation calculations of these elements using moderators containing hydrogen, carbon, nitrogen, and oxygen. 18 refs., 10 figs., 4 tabs.
Radiation Transport Analysis in Chalcogenide-Based Devices and a Neutron Howitzer Using MCNP
NASA Astrophysics Data System (ADS)
Bowler, Herbert
As photons, electrons, and neutrons traverse a medium, they impart their energy in ways that are analytically difficult to describe. Monte Carlo methods provide valuable insight into understanding this behavior, especially when the radiation source or environment is too complex to simplify. This research investigates simulating various radiation sources using the Monte Carlo N-Particle (MCNP) transport code, characterizing their impact on various materials, and comparing the simulation results to general theory and measurements. A total of five sources were of interest: two photon sources of different incident particle energies (3.83 eV and 1.25 MeV), two electron sources also of different energies (30 keV and 100 keV), and a californium-252 (Cf-252) spontaneous fission neutron source. Lateral and vertical programmable metallization cells (PMCs) were developed by other researchers for exposure to these photon and electron sources, so simplified PMC models were implemented in MCNP to estimate the doses and fluences. Dose rates measured around the neutron source and the predicted maximum activity of activation foils exposed to the neutrons were determined using MCNP and compared to experimental results obtained from gamma-ray spectroscopy. The analytical fluence calculations for the photon and electron cases agreed with MCNP results, and differences are due to MCNP considering particle movements that hand calculations do not. Doses for the photon cases agreed between the analytical and simulated results, while the electron cases differed by a factor of up to 4.8. Physical dose rate measurements taken from the neutron source agreed with MCNP within the 10% tolerance of the measurement device. The activity results had a percent error of up to 50%, which suggests a need to further evaluate the spectroscopy setup.
2013-06-24
Version 07 TART2012 is a coupled neutron-photon Monte Carlo transport code designed to use three-dimensional (3-D) combinatorial geometry. Neutron and/or photon sources as well as neutron induced photon production can be tracked. It is a complete system to assist you with input preparation, running Monte Carlo calculations, and analysis of output results. TART2012 is also incredibly FAST; if you have used similar codes, you will be amazed at how fast this code is compared tomore » other similar codes. Use of the entire system can save you a great deal of time and energy. TART2012 extends the general utility of the code to even more areas of application than available in previous releases by concentrating on improving the physics, particularly with regard to improved treatment of neutron fission, resonance self-shielding, molecular binding, and extending input options used by the code. Several utilities are included for creating input files and displaying TART results and data. TART2012 uses the latest ENDF/B-VI, Release 8, data. New for TART2012 is the use of continuous energy neutron cross sections, in addition to its traditional multigroup cross sections. For neutron interaction, the data are derived using ENDF-ENDL2005 and include both continuous energy cross sections and 700 group neutron data derived using a combination of ENDF/B-VI, Release 8, and ENDL data. The 700 group structure extends from 10-5 eV up to 1 GeV. Presently nuclear data are only available up to 20 MeV, so that only 616 of the groups are currently used. For photon interaction, 701 point photon data were derived using the Livermore EPDL97 file. The new 701 point structure extends from 100 eV up to 1 GeV, and is currently used over this entire energy range. TART2012 completely supersedes all older versions of TART, and it is strongly recommended that one use only the most recent version of TART2012 and its data files. Check authors homepage for related information: http
A Two-Dimensional Monte Carlo Code System for Linear Neutron Transport Calculations.
1980-04-24
Version 00 KIM (k-infinite-Monte Carlo) solves the steady-state linear neutron transport equation for a fixed source problem or, by successive fixed-source runs, for the eigenvalue problem, in a two-dimensional infinite thermal reactor lattice using the Monte Carlo method. In addition to the combinatorial description of domains, the program allows complex configurations to be represented by a discrete set of points whereby the calculation speed is greatly improved. Configurations are described as the result of overlaysmore » of elementary figures over a basic domain.« less
Petrov-galerkin finite element method for solving the neutron transport equation
Greenbaum, A.; Ferguson, J.M.
1986-05-01
A finite element using different trial and test spaces in introduced for solving the neutron transport equation in spherical geometry. It is shown that the widely used discrete ordinates method can also be thought of as such a finite element technique, in which integrals appearing in the difference equations are replaced by one-point Gauss quadrature formulas (midpoint rule). Comparison of accuracy between the new method and the discrete ordinates method is discussed, and numerical examples are given to illustrate the greater accuracy of the new technique.
NASA Astrophysics Data System (ADS)
Colombo, V.; Ravetto, P.; Sumini, M.
1988-08-01
An approximate determination of the critical eigenvalue of the neutron transport equation in integral form, within both the one speed and energy multigroup models, for a homogeneous medium, is achieved by means of a variational technique. The space asymptotic solutions for both the direct and adjoint problems are used as trial functions. A variational procedure is also developed and numerically exploited within the Fourier transformed domain, where noticeable theoretical features can be demonstrated. It is evidenced that excellent results can be obtained with little computational effort, and a set of critical calculations in plane geometry is presented and discussed.
Colombo, V.; Ravetto, P.; Sumini, M.
1988-08-01
An approximate determination of the critical eigenvalue of the neutron transport equation in integral form, within both the one speed and energy multigroup models, for a homogeneous medium, is achieved by means of a variational technique. The space asymptotic solutions for both the direct and adjoint problems are used as trial functions. A variational procedure is also developed and numerically exploited within the Fourier transformed domain, where noticeable theoretical features can be demonstrated. It is evidenced that excellent results can be obtained with little computational effort, and a set of critical calculations in plane geometry is presented and discussed. copyright 1988 Academic Press, Inc.
Hybrid Parallel Programming Models for AMR Neutron Monte-Carlo Transport
NASA Astrophysics Data System (ADS)
Dureau, David; Poëtte, Gaël
2014-06-01
This paper deals with High Performance Computing (HPC) applied to neutron transport theory on complex geometries, thanks to both an Adaptive Mesh Refinement (AMR) algorithm and a Monte-Carlo (MC) solver. Several Parallelism models are presented and analyzed in this context, among them shared memory and distributed memory ones such as Domain Replication and Domain Decomposition, together with Hybrid strategies. The study is illustrated by weak and strong scalability tests on complex benchmarks on several thousands of cores thanks to the petaflopic supercomputer Tera100.
Lee, H.; Lee, D.
2013-07-01
This paper presents a new hybrid method of continuous energy Monte Carlo (MC) and multi-group Method of Characteristics (MOC). For a continuous energy neutron transport analysis, the hybrid method employs a continuous energy MC for resonance energy range to treat the resonances accurately and a multi-group MOC for high and low energy ranges for efficiency. Numerical test with a model problem confirms that the hybrid method can produce consistent results with the reference continuous energy MC-only calculation as well as multi-group MOC-only calculation. (authors)
Willert, Jeffrey; Park, H.; Taitano, William
2015-10-12
High-order/low-order (or moment-based acceleration) algorithms have been used to significantly accelerate the solution to the neutron transport k-eigenvalue problem over the past several years. Recently, the nonlinear diffusion acceleration algorithm has been extended to solve fixed-source problems with anisotropic scattering sources. In this paper, we demonstrate that we can extend this algorithm to k-eigenvalue problems in which the scattering source is anisotropic and a significant acceleration can be achieved. Lastly, we demonstrate that the low-order, diffusion-like eigenvalue problem can be solved efficiently using a technique known as nonlinear elimination.
A Deterministic-Monte Carlo Hybrid Method for Time-Dependent Neutron Transport Problems
Justin Pounders; Farzad Rahnema
2001-10-01
A new deterministic-Monte Carlo hybrid solution technique is derived for the time-dependent transport equation. This new approach is based on dividing the time domain into a number of coarse intervals and expanding the transport solution in a series of polynomials within each interval. The solutions within each interval can be represented in terms of arbitrary source terms by using precomputed response functions. In the current work, the time-dependent response function computations are performed using the Monte Carlo method, while the global time-step march is performed deterministically. This work extends previous work by coupling the time-dependent expansions to space- and angle-dependent expansions to fully characterize the 1D transport response/solution. More generally, this approach represents and incremental extension of the steady-state coarse-mesh transport method that is based on global-local decompositions of large neutron transport problems. An example of a homogeneous slab is discussed as an example of the new developments.
Low-energy beam transport studies supporting the spallation neutron source 1-MW beam operation
Han, B. X.; Welton, R. F.; Murray, S. N. Jr.; Pennisi, T. R.; Santana, M.; Stockli, M. P.; Kalvas, T.; Tarvainen, O.
2012-02-15
The H{sup -} injector consisting of a cesium enhanced RF-driven ion source and a 2-lens electrostatic low-energy beam transport (LEBT) system supports the spallation neutron source 1 MW beam operation with {approx}38 mA beam current in the linac at 60 Hz with a pulse length of up to {approx}1.0 ms. In this work, two important issues associated with the low-energy beam transport are discussed: (1) inconsistent dependence of the post-radio frequency quadrupole accelerator beam current on the ion source tilt angle and (2) high power beam losses on the LEBT electrodes under some off-nominal conditions compromising their reliability.
Low-energy beam transport studies supporting the spallation neutron source 1-MW beam operation
Kalvas, T.; Welton, Robert F; Pennisi, Terry R
2012-01-01
The H{sup -} injector consisting of a cesium enhanced RF-driven ion source and a 2-lens electrostatic low-energy beam transport (LEBT) system supports the spallation neutron source 1 MW beam operation with {approx}38 mA beam current in the linac at 60 Hz with a pulse length of up to {approx}1.0 ms. In this work, two important issues associated with the low-energy beam transport are discussed: (1) inconsistent dependence of the post-radio frequency quadrupole accelerator beam current on the ion source tilt angle and (2) high power beam losses on the LEBT electrodes under some off-nominal conditions compromising their reliability.
NASA Astrophysics Data System (ADS)
Nelson, Adam
Multi-group scattering moment matrices are critical to the solution of the multi-group form of the neutron transport equation, as they are responsible for describing the change in direction and energy of neutrons. These matrices, however, are difficult to correctly calculate from the measured nuclear data with both deterministic and stochastic methods. Calculating these parameters when using deterministic methods requires a set of assumptions which do not hold true in all conditions. These quantities can be calculated accurately with stochastic methods, however doing so is computationally expensive due to the poor efficiency of tallying scattering moment matrices. This work presents an improved method of obtaining multi-group scattering moment matrices from a Monte Carlo neutron transport code. This improved method of tallying the scattering moment matrices is based on recognizing that all of the outgoing particle information is known a priori and can be taken advantage of to increase the tallying efficiency (therefore reducing the uncertainty) of the stochastically integrated tallies. In this scheme, the complete outgoing probability distribution is tallied, supplying every one of the scattering moment matrices elements with its share of data. In addition to reducing the uncertainty, this method allows for the use of a track-length estimation process potentially offering even further improvement to the tallying efficiency. Unfortunately, to produce the needed distributions, the probability functions themselves must undergo an integration over the outgoing energy and scattering angle dimensions. This integration is too costly to perform during the Monte Carlo simulation itself and therefore must be performed in advance by way of a pre-processing code. The new method increases the information obtained from tally events and therefore has a significantly higher efficiency than the currently used techniques. The improved method has been implemented in a code system
Solution and Study of the Two-Dimensional Nodal Neutron Transport Equation
Panta Pazos, Ruben; Biasotto Hauser, Eliete; Tullio de Vilhena, Marco
2002-07-01
In the last decade Vilhena and coworkers reported an analytical solution to the two-dimensional nodal discrete-ordinates approximations of the neutron transport equation in a convex domain. The key feature of these works was the application of the combined collocation method of the angular variable and nodal approach in the spatial variables. By nodal approach we mean the transverse integration of the SN equations. This procedure leads to a set of one-dimensional S{sub N} equations for the average angular fluxes in the variables x and y. These equations were solved by the old version of the LTS{sub N} method, which consists in the application of the Laplace transform to the set of nodal S{sub N} equations and solution of the resulting linear system by symbolic computation. It is important to recall that this procedure allow us to increase N the order of S{sub N} up to 16. To overcome this drawback we step forward performing a spectral painstaking analysis of the nodal S{sub N} equations for N up to 16 and we begin the convergence of the S{sub N} nodal equations defining an error for the angular flux and estimating the error in terms of the truncation error of the quadrature approximations of the integral term. Furthermore, we compare numerical results of this approach with those of other techniques used to solve the two-dimensional discrete approximations of the neutron transport equation. (authors)
NASA Astrophysics Data System (ADS)
Boyarinov, V. F.; Kondrushin, A. E.; Fomichenko, P. A.
2013-12-01
Time-dependent equations of the surface harmonics method (SHM) are obtained for planar one-dimensional geometry. The equations are verified by calculations of test problems from Benchmark Problem Book ANL-7416, and the capabilities and efficiency of applying the SHM for solving the time-dependent neutron transport equation in the diffusion approximation are demonstrated. The results of the work show that the implementation of the SHG for full-scale computations will make possible substantial progress in the efficient solution of time-dependent problems of neutron transport in nuclear reactors.
Monte Carlo Neutrino Transport through Remnant Disks from Neutron Star Mergers
NASA Astrophysics Data System (ADS)
Richers, Sherwood; Kasen, Daniel; O'Connor, Evan; Fernández, Rodrigo; Ott, Christian D.
2015-11-01
We present Sedonu, a new open source, steady-state, special relativistic Monte Carlo (MC) neutrino transport code, available at bitbucket.org/srichers/sedonu. The code calculates the energy- and angle-dependent neutrino distribution function on fluid backgrounds of any number of spatial dimensions, calculates the rates of change of fluid internal energy and electron fraction, and solves for the equilibrium fluid temperature and electron fraction. We apply this method to snapshots from two-dimensional simulations of accretion disks left behind by binary neutron star mergers, varying the input physics and comparing to the results obtained with a leakage scheme for the cases of a central black hole and a central hypermassive neutron star. Neutrinos are guided away from the densest regions of the disk and escape preferentially around 45° from the equatorial plane. Neutrino heating is strengthened by MC transport a few scale heights above the disk midplane near the innermost stable circular orbit, potentially leading to a stronger neutrino-driven wind. Neutrino cooling in the dense midplane of the disk is stronger when using MC transport, leading to a globally higher cooling rate by a factor of a few and a larger leptonization rate by an order of magnitude. We calculate neutrino pair annihilation rates and estimate that an energy of 2.8 × 1046 erg is deposited within 45° of the symmetry axis over 300 ms when a central BH is present. Similarly, 1.9 × 1048 erg is deposited over 3 s when an HMNS sits at the center, but neither estimate is likely to be sufficient to drive a gamma-ray burst jet.
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.
A POD reduced order model for resolving angular direction in neutron/photon transport problems
Buchan, A.G.; Calloo, A.A.; Goffin, M.G.; Dargaville, S.; Fang, F.; Pain, C.C.; Navon, I.M.
2015-09-01
This article presents the first Reduced Order Model (ROM) that efficiently resolves the angular dimension of the time independent, mono-energetic Boltzmann Transport Equation (BTE). It is based on Proper Orthogonal Decomposition (POD) and uses the method of snapshots to form optimal basis functions for resolving the direction of particle travel in neutron/photon transport problems. A unique element of this work is that the snapshots are formed from the vector of angular coefficients relating to a high resolution expansion of the BTE's angular dimension. In addition, the individual snapshots are not recorded through time, as in standard POD, but instead they are recorded through space. In essence this work swaps the roles of the dimensions space and time in standard POD methods, with angle and space respectively. It is shown here how the POD model can be formed from the POD basis functions in a highly efficient manner. The model is then applied to two radiation problems; one involving the transport of radiation through a shield and the other through an infinite array of pins. Both problems are selected for their complex angular flux solutions in order to provide an appropriate demonstration of the model's capabilities. It is shown that the POD model can resolve these fluxes efficiently and accurately. In comparison to high resolution models this POD model can reduce the size of a problem by up to two orders of magnitude without compromising accuracy. Solving times are also reduced by similar factors.
A comparison of acceleration methods for solving the neutron transport k-eigenvalue problem
Willert, Jeffrey; Park, H.; Knoll, D.A.
2014-10-01
Over the past several years a number of papers have been written describing modern techniques for numerically computing the dominant eigenvalue of the neutron transport criticality problem. These methods fall into two distinct categories. The first category of methods rewrite the multi-group k-eigenvalue problem as a nonlinear system of equations and solve the resulting system using either a Jacobian-Free Newton–Krylov (JFNK) method or Nonlinear Krylov Acceleration (NKA), a variant of Anderson Acceleration. These methods are generally successful in significantly reducing the number of transport sweeps required to compute the dominant eigenvalue. The second category of methods utilize Moment-Based Acceleration (or High-Order/Low-Order (HOLO) Acceleration). These methods solve a sequence of modified diffusion eigenvalue problems whose solutions converge to the solution of the original transport eigenvalue problem. This second class of methods is, in our experience, always superior to the first, as most of the computational work is eliminated by the acceleration from the LO diffusion system. In this paper, we review each of these methods. Our computational results support our claim that the choice of which nonlinear solver to use, JFNK or NKA, should be secondary. The primary computational savings result from the implementation of a HOLO algorithm. We display computational results for a series of challenging multi-dimensional test problems.
A comparison of acceleration methods for solving the neutron transport k-eigenvalue problem
NASA Astrophysics Data System (ADS)
Willert, Jeffrey; Park, H.; Knoll, D. A.
2014-10-01
Over the past several years a number of papers have been written describing modern techniques for numerically computing the dominant eigenvalue of the neutron transport criticality problem. These methods fall into two distinct categories. The first category of methods rewrite the multi-group k-eigenvalue problem as a nonlinear system of equations and solve the resulting system using either a Jacobian-Free Newton-Krylov (JFNK) method or Nonlinear Krylov Acceleration (NKA), a variant of Anderson Acceleration. These methods are generally successful in significantly reducing the number of transport sweeps required to compute the dominant eigenvalue. The second category of methods utilize Moment-Based Acceleration (or High-Order/Low-Order (HOLO) Acceleration). These methods solve a sequence of modified diffusion eigenvalue problems whose solutions converge to the solution of the original transport eigenvalue problem. This second class of methods is, in our experience, always superior to the first, as most of the computational work is eliminated by the acceleration from the LO diffusion system. In this paper, we review each of these methods. Our computational results support our claim that the choice of which nonlinear solver to use, JFNK or NKA, should be secondary. The primary computational savings result from the implementation of a HOLO algorithm. We display computational results for a series of challenging multi-dimensional test problems.
Using the transportable, computer-operated, liquid-scintillator fast-neutron spectrometer system
Thorngate, J.H.
1988-11-01
When a detailed energy spectrum is needed for radiation-protection measurements from approximately 1 MeV up to several tens of MeV, organic-liquid scintillators make good neutron spectrometers. However, such a spectrometer requires a sophisticated electronics system and a computer to reduce the spectrum from the recorded data. Recently, we added a Nuclear Instrument Module (NIM) multichannel analyzer and a lap-top computer to the NIM electronics we have used for several years. The result is a transportable fast-neutron spectrometer system. The computer was programmed to guide the user through setting up the system, calibrating the spectrometer, measuring the spectrum, and reducing the data. Measurements can be made over three energy ranges, 0.6--2 MeV, 1.1--8 MeV, or 1.6--16 MeV, with the spectrum presented in 0.1-MeV increments. Results can be stored on a disk, presented in a table, and shown in graphical form. 5 refs., 51 figs.
A demonstration of a whole core neutron transport method in a gas cooled reactor
Connolly, K. J.; Rahnema, F.
2013-07-01
This paper illustrates a capability of the whole core transport method COMET. Building on previous works which demonstrated the accuracy of the method, this work serves to emphasize the robust capability of the method while also accentuating its efficiency. A set of core configurations is presented based on an operating gas-cooled thermal reactor, Japan's HTTR, and COMET determines the eigenvalue and fission density profile throughout each core configuration. Results for core multiplication factors are compared to MCNP for accuracy and also to compare runtimes. In all cases, the values given by COMET differ by those given by MCNP by less than the uncertainty inherent in the stochastic solution procedure, however, COMET requires runtimes shorter on the order of a few hundred. Figures are provided illustrating the whole core fission density profile, with segments of pins explicitly modeled individually, so that pin-level neutron flux behavior can be seen without any approximation due to simplification strategies such as homogenization. (authors)
TART97 a coupled neutron-photon 3-D, combinatorial geometry Monte Carlo transport code
Cullen, D.E.
1997-11-22
TART97 is a coupled neutron-photon, 3 Dimensional, combinatorial geometry, time dependent Monte Carlo transport code. This code can on any modern computer. It is a complete system to assist you with input preparation, running Monte Carlo calculations, and analysis of output results. TART97 is also incredibly FAST; if you have used similar codes, you will be amazed at how fast this code is compared to other similar codes. Use of the entire system can save you a great deal of time and energy. TART97 is distributed on CD. This CD contains on- line documentation for all codes included in the system, the codes configured to run on a variety of computers, and many example problems that you can use to familiarize yourself with the system. TART97 completely supersedes all older versions of TART, and it is strongly recommended that users only use the most recent version of TART97 and its data riles.
NASA Technical Reports Server (NTRS)
Armstrong, T. W.
1972-01-01
Several Monte Carlo radiation transport computer codes are used to predict quantities of interest in the fields of radiotherapy and radiobiology. The calculational methods are described and comparisions of calculated and experimental results are presented for dose distributions produced by protons, neutrons, and negatively charged pions. Comparisons of calculated and experimental cell survival probabilities are also presented.
Wang, Yong; Yue, Wenzheng; Zhang, Mo
2016-01-01
The anisotropic transport of thermal neutron in heterogeneous porous media is of great research interests in many fields. In this paper, it is the first time that a new model based on micron X-ray computed tomography (CT) has been proposed to simultaneously consider both the separation of matrix and pore and the distribution of mineral components. We apply the Monte Carlo method to simulate thermal neutrons transporting through the model along different directions, and meanwhile detect those unreacted thermal neutrons by an array detector on the other side of the model. Therefore, the anisotropy of pore structure can be imaged by the amount of received thermal neutrons, due to the difference of rock matrix and pore-filling fluids in the macroscopic reaction cross section (MRCS). The new model has been verified by the consistent between the simulated data and the pore distribution from X-ray CT. The results show that the evaluation of porosity can be affected by the anisotropy of media. Based on the research, a new formula is developed to describe the correlation between the resolution of array detectors and the quality of imaging. The formula can be further used to analyze the critical resolution and the suitable number of thermal neutrons emitted in each simulation. Unconventionally, we find that a higher resolution cannot always lead to a better image. PMID:27271330
NASA Astrophysics Data System (ADS)
Wang, Yong; Yue, Wenzheng; Zhang, Mo
2016-06-01
The anisotropic transport of thermal neutron in heterogeneous porous media is of great research interests in many fields. In this paper, it is the first time that a new model based on micron X-ray computed tomography (CT) has been proposed to simultaneously consider both the separation of matrix and pore and the distribution of mineral components. We apply the Monte Carlo method to simulate thermal neutrons transporting through the model along different directions, and meanwhile detect those unreacted thermal neutrons by an array detector on the other side of the model. Therefore, the anisotropy of pore structure can be imaged by the amount of received thermal neutrons, due to the difference of rock matrix and pore-filling fluids in the macroscopic reaction cross section (MRCS). The new model has been verified by the consistent between the simulated data and the pore distribution from X-ray CT. The results show that the evaluation of porosity can be affected by the anisotropy of media. Based on the research, a new formula is developed to describe the correlation between the resolution of array detectors and the quality of imaging. The formula can be further used to analyze the critical resolution and the suitable number of thermal neutrons emitted in each simulation. Unconventionally, we find that a higher resolution cannot always lead to a better image.
Wang, Yong; Yue, Wenzheng; Zhang, Mo
2016-01-01
The anisotropic transport of thermal neutron in heterogeneous porous media is of great research interests in many fields. In this paper, it is the first time that a new model based on micron X-ray computed tomography (CT) has been proposed to simultaneously consider both the separation of matrix and pore and the distribution of mineral components. We apply the Monte Carlo method to simulate thermal neutrons transporting through the model along different directions, and meanwhile detect those unreacted thermal neutrons by an array detector on the other side of the model. Therefore, the anisotropy of pore structure can be imaged by the amount of received thermal neutrons, due to the difference of rock matrix and pore-filling fluids in the macroscopic reaction cross section (MRCS). The new model has been verified by the consistent between the simulated data and the pore distribution from X-ray CT. The results show that the evaluation of porosity can be affected by the anisotropy of media. Based on the research, a new formula is developed to describe the correlation between the resolution of array detectors and the quality of imaging. The formula can be further used to analyze the critical resolution and the suitable number of thermal neutrons emitted in each simulation. Unconventionally, we find that a higher resolution cannot always lead to a better image. PMID:27271330
The TORT three-dimensional discrete ordinates neutron/photon transport code (TORT version 3)
Rhoades, W.A.; Simpson, D.B.
1997-10-01
TORT calculates the flux or fluence of neutrons and/or photons throughout three-dimensional systems due to particles incident upon the system`s external boundaries, due to fixed internal sources, or due to sources generated by interaction with the system materials. The transport process is represented by the Boltzman transport equation. The method of discrete ordinates is used to treat the directional variable, and a multigroup formulation treats the energy dependence. Anisotropic scattering is treated using a Legendre expansion. Various methods are used to treat spatial dependence, including nodal and characteristic procedures that have been especially adapted to resist numerical distortion. A method of body overlay assists in material zone specification, or the specification can be generated by an external code supplied by the user. Several special features are designed to concentrate machine resources where they are most needed. The directional quadrature and Legendre expansion can vary with energy group. A discontinuous mesh capability has been shown to reduce the size of large problems by a factor of roughly three in some cases. The emphasis in this code is a robust, adaptable application of time-tested methods, together with a few well-tested extensions.
MCNP: a general Monte Carlo code for neutron and photon transport
Forster, R.A.; Godfrey, T.N.K.
1985-01-01
MCNP is a very general Monte Carlo neutron photon transport code system with approximately 250 person years of Group X-6 code development invested. It is extremely portable, user-oriented, and a true production code as it is used about 60 Cray hours per month by about 150 Los Alamos users. It has as its data base the best cross-section evaluations available. MCNP contains state-of-the-art traditional and adaptive Monte Carlo techniques to be applied to the solution of an ever-increasing number of problems. Excellent user-oriented documentation is available for all facets of the MCNP code system. Many useful and important variants of MCNP exist for special applications. The Radiation Shielding Information Center (RSIC) in Oak Ridge, Tennessee is the contact point for worldwide MCNP code and documentation distribution. A much improved MCNP Version 3A will be available in the fall of 1985, along with new and improved documentation. Future directions in MCNP development will change the meaning of MCNP to Monte Carlo N Particle where N particle varieties will be transported.
DOXCY - A discrete ordinates approximation of neutron transport in heterogeneous rod lattices
Martens, H.D.; Stegemann, D.
1987-08-01
For calculating the fine flux distribution in heterogeneous fuel rod lattices, an exact treatment of the geometry and the use of a high-order approximation of the transport theory is needed. For this purpose, a discrete ordinates solution of the neutron transport equation for mixed geometry has been developed. The discretization of the space is performed in separate one-dimensional cylindrical coordinate systems, imbedded in a two-dimensional rectangular mesh grid. The geometrical link between the cylindrical and the rectangular systems is achieved by approximating the outer circle of each cylindrical system by a polygon with side numbers greater than or equal to8. Thus, each cylindrical geometry is enclosed in a two-dimensional mesh grid consisting of rectangles, trapeziums, and triangles. Because of the different orientation of the angular segmentation in XY and R coordinates, transfer coefficients are derived to calculate the directional flux distribution on the boundary between both systems. A special set of equal-weighted quadrature coefficients (EQ/sub n/) is used to get transfer coefficients, providing a fast and accurate solution. The method is realized in a program called DOXCY, which runs within the nuclear program system RSYST. The program is verified on selected benchmark problems. The numerical results are given, showing the advantage and limits of the method.
On the adequacy of message-passing parallel supercomputers for solving neutron transport problems
Azmy, Y.Y.
1990-01-01
A coarse-grained, static-scheduling parallelization of the standard iterative scheme used for solving the discrete-ordinates approximation of the neutron transport equation is described. The parallel algorithm is based on a decomposition of the angular domain along the discrete ordinates, thus naturally producing a set of completely uncoupled systems of equations in each iteration. Implementation of the parallel code on Intcl's iPSC/2 hypercube, and solutions to test problems are presented as evidence of the high speedup and efficiency of the parallel code. The performance of the parallel code on the iPSC/2 is analyzed, and a model for the CPU time as a function of the problem size (order of angular quadrature) and the number of participating processors is developed and validated against measured CPU times. The performance model is used to speculate on the potential of massively parallel computers for significantly speeding up real-life transport calculations at acceptable efficiencies. We conclude that parallel computers with a few hundred processors are capable of producing large speedups at very high efficiencies in very large three-dimensional problems. 10 refs., 8 figs.
A new paradigm for local-global coupling in whole-core neutron transport.
Lewis, E.; Smith, M.; Palmiotti, G,; Nuclear Engineering Division; Northwestern Univ.; INL
2009-01-01
A new paradigm that increases the efficiency of whole-core neutron transport calculations without lattice homogenization is introduced. Quasi-reflected interface conditions are formulated to partially decouple periodic lattice effects from global flux gradients. The starting point is the finite subelement form of the variational nodal code VARIANT that eliminates fuel-coolant homogenization through the use of heterogeneous nodes. The interface spherical harmonics expansions that couple pin-cell-sized nodes are divided into low-order and high-order terms, and reflected interface conditions are applied to the high-order terms. Combined with an integral transport method within the node, the new approach dramatically reduces both the formation time and the dimensions of the nodal response matrices and leads to sharply reduced memory requirements and computational time. The method is applied to the two-dimensional C5G7 problem, an Organisation for Economic Co-operation and Development/Nuclear Energy Agency pressurized water reactor benchmark containing mixed oxide (MOX) and UO{sub 2} fuel assemblies, as well as to a three-dimensional MOX fuel assembly. Results indicate the new approach results in very little loss of accuracy relative to the corresponding full spherical harmonics expansions while reducing computational times by well over an order of magnitude.
Boyarinov, V. F.; Kondrushin, A. E.; Fomichenko, P. A.
2013-07-01
Time-dependent equations of the Surface Harmonics Method (SHM) have been derived from the time-dependent neutron transport equation with explicit representation of delayed neutrons for solving the two-dimensional time-dependent problems. These equations have been realized in the SUHAM-TD code. The TWIGL benchmark problem has been used for verification of the SUHAM-TD code. The results of the study showed that computational costs required to achieve necessary accuracy of the solution can be an order of magnitude less than with the use of the conventional finite difference method (FDM). (authors)
U{sub N} Method For The Critical Slab Problem In One-Speed Neutron Transport Theory
Oeztuerk, Hakan; Guengoer, Sueleyman
2008-11-11
The Chebyshev polynomial approximation (U{sub N} method) is used to solve the critical slab problem in one-speed neutron transport theory using Marshak boundary condition. The isotropic scattering kernel with the combination of forward and backward scattering is chosen for the neutrons in a uniform finite slab. Numerical results obtained by the U{sub N} method are presented in the tables together with the results obtained by the well-known P{sub N} method for comparison. It is shown that the method converges rapidly with its easily executable equations.
Azmy, Yousry
2014-06-10
We employ the Integral Transport Matrix Method (ITMM) as the kernel of new parallel solution methods for the discrete ordinates approximation of the within-group neutron transport equation. The ITMM abandons the repetitive mesh sweeps of the traditional source iterations (SI) scheme in favor of constructing stored operators that account for the direct coupling factors among all the cells' fluxes and between the cells' and boundary surfaces' fluxes. The main goals of this work are to develop the algorithms that construct these operators and employ them in the solution process, determine the most suitable way to parallelize the entire procedure, and evaluate the behavior and parallel performance of the developed methods with increasing number of processes, P. The fastest observed parallel solution method, Parallel Gauss-Seidel (PGS), was used in a weak scaling comparison with the PARTISN transport code, which uses the source iteration (SI) scheme parallelized with the Koch-baker-Alcouffe (KBA) method. Compared to the state-of-the-art SI-KBA with diffusion synthetic acceleration (DSA), this new method- even without acceleration/preconditioning-is completitive for optically thick problems as P is increased to the tens of thousands range. For the most optically thick cells tested, PGS reduced execution time by an approximate factor of three for problems with more than 130 million computational cells on P = 32,768. Moreover, the SI-DSA execution times's trend rises generally more steeply with increasing P than the PGS trend. Furthermore, the PGS method outperforms SI for the periodic heterogeneous layers (PHL) configuration problems. The PGS method outperforms SI and SI-DSA on as few as P = 16 for PHL problems and reduces execution time by a factor of ten or more for all problems considered with more than 2 million computational cells on P = 4.096.
A Complex-Geometry Validation Experiment for Advanced Neutron Transport Codes
David W. Nigg; Anthony W. LaPorta; Joseph W. Nielsen; James Parry; Mark D. DeHart; Samuel E. Bays; William F. Skerjanc
2013-11-01
The Idaho National Laboratory (INL) has initiated a focused effort to upgrade legacy computational reactor physics software tools and protocols used for support of core fuel management and experiment management in the Advanced Test Reactor (ATR) and its companion critical facility (ATRC) at the INL.. This will be accomplished through the introduction of modern high-fidelity computational software and protocols, with appropriate new Verification and Validation (V&V) protocols, over the next 12-18 months. Stochastic and deterministic transport theory based reactor physics codes and nuclear data packages that support this effort include MCNP5[1], SCALE/KENO6[2], HELIOS[3], SCALE/NEWT[2], and ATTILA[4]. Furthermore, a capability for sensitivity analysis and uncertainty quantification based on the TSUNAMI[5] system has also been implemented. Finally, we are also evaluating the Serpent[6] and MC21[7] codes, as additional verification tools in the near term as well as for possible applications to full three-dimensional Monte Carlo based fuel management modeling in the longer term. On the experimental side, several new benchmark-quality code validation measurements based on neutron activation spectrometry have been conducted using the ATRC. Results for the first four experiments, focused on neutron spectrum measurements within the Northwest Large In-Pile Tube (NW LIPT) and in the core fuel elements surrounding the NW LIPT and the diametrically opposite Southeast IPT have been reported [8,9]. A fifth, very recent, experiment focused on detailed measurements of the element-to-element core power distribution is summarized here and examples of the use of the measured data for validation of corresponding MCNP5, HELIOS, NEWT, and Serpent computational models using modern least-square adjustment methods are provided.
Legrand, Vincent; Merdrignac-Conanec, Odile; Paulus, Werner
2013-03-21
In situ neutron diffraction measurements of the nanocrystalline deuterated oxyhydroxide TiO(OD)(2) compound were performed as a function of time and temperature under NH(3) gas flow in order to study the hydrogen-deuterium exchange mechanism. Data were collected on the instrument D20 at the ILL (France) and the analysis of the kinetics was directly based on the contrast variation of the incoherent neutron cross section of hydrogen and deuterium. The time evolution of the hydrogenated phase fraction was described using the well-known Kolmogorov-Johnson-Mehl-Avrami (KJMA) expression. The H/D exchange reaction is complete within 140 s at 20 °C and within 120 s at 40 °C. The activation energy for the H/D exchange reaction is estimated to be 37 kJ mol(-1). PMID:23328794
Neutron radiography and modelling of water flow and D2O transport in soil and plants
NASA Astrophysics Data System (ADS)
Zare, Mohsen; Carminati, Andrea; Kröner, Eva
2014-05-01
Our understanding of soil and plant water relations is currently limited by the lack of experimental methods to measure the water fluxes in soil and plants. Our study aimed to develop a new non-destructive method to measure the local fluxes of water into roots of plants growing in soil. We injected deuterated water (D2O) near the roots of lupines growing in sandy soils, and we used neutron radiography to image the transport of D2O through the root system. The experiments were performed during day, when plants were transpiring, and at night, when transpiration was reduced. The radiographs showed that: 1) the radial transport of D2O from soil and roots depended similarly from diffusion and convection; and 2) the axial transport of D2O along the root xylem was largely dominated by convection. To determine the convective fluxes from the radiographs, we simulated the D2O transport in soils and roots. A dual porosity model was used to describe the apoplastic and symplastic pathways of water across the root tissue. Other features as the endodermis and the xylem were also included in the model. The D2O transport was modelled solving a convection-diffusion numerical model in soil and plants. The diffusion coefficients of the root tissues were inversely estimated by simulating the experiments at night under the assumption that at night the convective fluxes were negligible. Inverse modelling of the experiment at day gave the profile of water fluxes into the roots, as well as the ration between the apoplastic and symplastic flow. For 24 day-old lupine grown in a sandy soil with uniform water content, our modelling results showed that root water uptake was higher at the proximal parts of the roots near soil surface and it decreased toward the distal parts. The results indicated the water crossed the root cortex mainly through the apoplastic pathway. The method allows the quantification of the root properties and the regions of root water uptake along root systems growing in
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.
Verdu, G.; Capilla, M.; Talavera, C. F.; Ginestar, D.
2012-07-01
PL equations are classical high order approximations to the transport equations which are based on the expansion of the angular dependence of the angular neutron flux and the nuclear cross sections in terms of spherical harmonics. A nodal collocation method is used to discretize the PL equations associated with a neutron source transport problem. The performance of the method is tested solving two 1D problems with analytical solution for the transport equation and a classical 2D problem. (authors)
NASA Astrophysics Data System (ADS)
Ghimire, G. R.
2015-12-01
Sediment deposition is a serious issue in the construction and operation of large reservoir and inland navigation projects in the United States and around the world. Olmsted Locks and Dams in the Ohio River navigation system is facing similar challenges of huge sediment deposition during the ongoing in-wet construction methodology since 1993. HEC-RAS 5.0 integrated with ArcGIS, will be used to yield unsteady 2D hydrodynamic model of Ohio River at Olmsted area. Velocity, suspended sediment, bed sediment and hydrographic survey data acquired from public archives of USGS and USACE Louisville District will be input into the model. Calibration and validation of model will be performed against the measured stage, flow and velocity data. It will be subjected to completely unsteady 1D sediment transport modeling new to HEC-RAS 5.0 which incorporates sediment load and bed gradation via a DSS file, commercial dredging and BSTEM model. Sediment model will be calibrated to replicate the historical bed volume changes. Excavated cross-sections at Olmsted area will also be used to predict the sediment volume trapped inside the ditch over the period between excavations and placement of dam shells at site. Model will attempt to replicate historical dredging volume data and compare with the deposition volume from simulation model to formulate the dredging prediction model. Hence, the results of this research will generate a model that can form a basis for scheduling the dredging event prior to the placement of off-shore cast shells replacing the current as and when required approach of dredging plan. 1 Graduate Student, Department of Civil Engineering, Southern Illinois University Carbondale Carbondale, Illinois, 62901-6603 2 Professor, Department of Civil Engineering, Southern Illinois University Carbondale Carbondale, Illinois, 62901-6603
Giacomelli, L.; Hjalmarsson, A.; Hellesen, C.; Conroy, S.; Sunden, E. Andersson; Ericsson, G.; Johnson, M. Gatu; Sjoestrand, H.; Weiszflog, M.; Kaellne, J.; Tardocchi, M.; Gorini, G.
2008-10-15
The effect of ion cyclotron resonance heating (ICRH) on ({sup 3}He)D plasmas at JET was studied with the time of flight optimized rate (TOFOR) spectrometer dedicated to 2.5 MeV dd neutron measurements. In internal transport barrier (ITB) plasma experiments with large {sup 3}He concentrations (X({sup 3}He)>15%) an increase in neutron yield was observed after the ITB disappeared but with the auxiliary neutral beam injection and ICRH power still applied. The analysis of the TOFOR data revealed the formation of a high energy (fast) D population in this regime. The results were compared to other mode conversion experiments with similar X({sup 3}He) but slightly different heating conditions. In this study we report on the high energy neutron tails originating from the fast D ions and their correlation with X({sup 3}He) and discuss the light it can shed on ICRH-plasma power coupling mechanisms.
NASA Astrophysics Data System (ADS)
Sunil, C.; Tyagi, Mohit; Biju, K.; Shanbhag, A. A.; Bandyopadhyay, T.
2015-12-01
The scarcity and the high cost of 3He has spurred the use of various detectors for neutron monitoring. A new lithium yttrium borate scintillator developed in BARC has been studied for its use in a neutron rem counter. The scintillator is made of natural lithium and boron, and the yield of reaction products that will generate a signal in a real time detector has been studied by FLUKA Monte Carlo radiation transport code. A 2 cm lead introduced to enhance the gamma rejection shows no appreciable change in the shape of the fluence response or in the yield of reaction products. The fluence response when normalized at the average energy of an Am-Be neutron source shows promise of being used as rem counter.
Liu, Yingzi; Koltick, David; Byrne, Patrick; Wang, Haoyu; Zheng, Wei; Nie, Linda H
2014-01-01
This study was conducted to investigate the methodology and feasibility of developing a transportable neutron activation analysis (NAA) system to quantify manganese (Mn) in bone using a portable deuterium–deuterium (DD) neutron generator as the neutron source. Since a DD neutron generator was not available in our laboratory, a deuterium–tritium (DT) neutron generator was used to obtain experimental data and validate the results from Monte Carlo (MC) simulations. After validation, MC simulations using a DD generator as the neutron source were then conducted. Different types of moderators and reflectors were simulated, and the optimal thicknesses for the moderator and reflector were determined. To estimate the detection limit (DL) of the system, and to observe the interference of the magnesium (Mg) γ line at 844 keV to the Mn γ line at 847 keV, three hand phantoms with Mn concentrations of 30 parts per million (ppm), 150 ppm, and 500 ppm were made and irradiated by the DT generator system. The Mn signals in these phantoms were then measured using a 50% high-efficiency high-purity germanium (HPGe) detector. The DL was calculated to be about 4.4 ppm for the chosen irradiation, decay, and measurement time. This was calculated to be equivalent to a DL of about 3.3 ppm for the DD generator system. To achieve this DL with one 50% high-efficiency HPGe detector, the dose to the hand was simulated to be about 37 mSv, with the total body equivalent dose being about 23μSv. In conclusion, it is feasible to develop a transportable NAA system to quantify Mn in bone in vivo with an acceptable radiation exposure to the subject. PMID:24165395
Tomkiewicz, Alex C.; Tamimi, Mazin; Huq, Ashfia; McIntosh, Steven
2015-09-21
Ruddlesden-Popper structured oxides, general form An+1BnO3n+1, consist of n-layers of the perovskite structure stacked in between rock-salt layers, and have potential application in solid oxide electrochemical cells and ion transport membrane reactors. Three materials with constant Co/Fe ratio, LaSrCo0.5Fe0.5O4-δ (n = 1), La0.3Sr2.7CoFeO7-δ (n = 2), and LaSr3Co1.5Fe1.5O10-δ (n = 3) were synthesized and studied via in situ neutron powder diffraction between 765 K and 1070 K at a pO2 of 10-1 atm. Then, the structures were fit to a tetragonal I4/mmm space group, and were found to have increased total oxygen vacancy concentration in the order La0.3Sr2.7CoFeO7-δ > LaSr3Co1.5Fe1.5O10-δmore » > LaSrCo0.5Fe0.5O4-δ, following the trend predicted for charge compensation upon increasing Sr2+/La3+ ratio. The oxygen vacancies within the material were almost exclusively located within the perovskite layers for all of the crystal structures with only minimal vacancy formation in the rock-salt layer. Finally, analysis of the concentration of these vacancies at each distinct crystallographic site and the anisotropic atomic displacement parameters for the oxygen sites reveals potential preferred oxygen transport pathways through the perovskite layers.« less
Filippone, W.L.; Baker, R.S.
1990-12-31
The neutron transport equation is solved by a hybrid method that iteratively couples regions where deterministic (S{sub N}) and stochastic (Monte Carlo) methods are applied. Unlike previous hybrid methods, the Monte Carlo and S{sub N} regions are fully coupled in the sense that no assumption is made about geometrical separation or decoupling. The hybrid method provides a new means of solving problems involving both optically thick and optically thin regions that neither Monte Carlo nor S{sub N} is well suited for by themselves. The fully coupled Monte Carlo/S{sub N} technique consists of defining spatial and/or energy regions of a problem in which either a Monte Carlo calculation or an S{sub N} calculation is to be performed. The Monte Carlo region may comprise the entire spatial region for selected energy groups, or may consist of a rectangular area that is either completely or partially embedded in an arbitrary S{sub N} region. The Monte Carlo and S{sub N} regions are then connected through the common angular boundary fluxes, which are determined iteratively using the response matrix technique, and volumetric sources. The hybrid method has been implemented in the S{sub N} code TWODANT by adding special-purpose Monte Carlo subroutines to calculate the response matrices and volumetric sources, and linkage subrountines to carry out the interface flux iterations. The common angular boundary fluxes are included in the S{sub N} code as interior boundary sources, leaving the logic for the solution of the transport flux unchanged, while, with minor modifications, the diffusion synthetic accelerator remains effective in accelerating S{sub N} calculations. The special-purpose Monte Carlo routines used are essentially analog, with few variance reduction techniques employed. However, the routines have been successfully vectorized, with approximately a factor of five increase in speed over the non-vectorized version.
3D Neutron Transport PWR Full-core Calculation with RMC code
NASA Astrophysics Data System (ADS)
Qiu, Yishu; She, Ding; Fan, Xiao; Wang, Kan; Li, Zeguang; Liang, Jingang; Leroyer, Hadrien
2014-06-01
Nowadays, there are more and more interests in the use of Monte Carlo codes to calculate the detailed power density distributions in full-core reactors. With the Inspur TS1000 HPC Server of Tsinghua University, several calculations have been done based on the EDF 3D Neutron Transport PWR Full-core benchmark through large-scale parallelism. To investigate and compare the results of the deterministic method and Monte Carlo method, EDF R&D and Department of Engineering Physics of Tsinghua University are having a collaboration to make code to code verification. So in this paper, two codes are used. One is the code COCAGNE developed by the EDF R&D, a deterministic core code, and the other is the Monte Carlo code RMC developed by Department of Engineering Physics in Tsinghua University. First, the full-core model is described and a 26-group calculation was performed by these two codes using the same 26-group cross-section library provided by EDF R&D. Then the parallel and tally performance of RMC is discussed. RMC employs a novel algorithm which can cut down most of the communications. It can be seen clearly that the speedup ratio almost linearly increases with the nodes. Furthermore the cell-mapping method applied by RMC consumes little time to tally even millions of cells. The results of the codes COCAGNE and RMC are compared in three ways. The results of these two codes agree well with each other. It can be concluded that both COCAGNE and RMC are able to provide 3D-transport solutions associated with detailed power density distributions calculation in PWR full-core reactors. Finally, to investigate how many histories are needed to obtain a given standard deviation for a full 3D solution, the non-symmetrized condensed 2-group fluxes of RMC are discussed.
DeHart, M.D.
1992-12-01
A method for applying the discrete ordinates method for solution of the neutron transport equation in arbitary two-dimensional meshes has been developed. The finite difference approach normally used to approximate spatial derivatives in extrapolating angular fluxes across a cell is replaced by direct solution of the characteristic form of the transport equation for each discrete direction. Thus, computational cells are not restricted to the traditional shape of a mesh element within a given coordinate system. However, in terms of the treatment of energy and angular dependencies, this method resembles traditional discrete ordinates techniques. Using the method developed here, a general two-dimensional space can be approximated by an irregular mesh comprised of arbitrary polygons. The present work makes no assumptions about the orientations or the number of sides in a given cell, and computes all geometric relationships between each set of sides in each cell for each discrete direction. A set of non-reentrant polygons can therefore be used to represent any given two dimensional space. Results for a number of test problems have been compared to solutions obtained from traditional methods, with good agreement. Comparisons include benchmarks against analytical results for problems with simple geometry, as well numerical results obtained from traditional discrete ordinates methods by applying the ANISN and TWOTRAN computer programs. Numerical results were obtained for problems ranging from simple one-dimensional geometry to complicated multidimensional configurations. These results have demonstrated the ability of the developed method to closely approximate complex geometrical configurations and to obtain accurate results for problems that are extremely difficult to model using traditional methods.
A Coupled Neutron-Photon 3-D Combinatorial Geometry Monte Carlo Transport Code
1998-06-12
TART97 is a coupled neutron-photon, 3 dimensional, combinatorial geometry, time dependent Monte Carlo transport code. This code can run on any modern computer. It is a complete system to assist you with input preparation, running Monte Carlo calculations, and analysis of output results. TART97 is also incredibly fast: if you have used similar codes, you will be amazed at how fast this code is compared to other similar codes. Use of the entire system canmore » save you a great deal of time and energy. TART 97 is distributed on CD. This CD contains on-line documentation for all codes included in the system, the codes configured to run on a variety of computers, and many example problems that you can use to familiarize yourself with the system. TART97 completely supersedes all older versions of TART, and it is strongly recommended that users only use the most recent version of TART97 and ist data files.« less
Inversion of Source and Transport Parameters of Relativistic SEPs from Neutron Monitor Data
NASA Astrophysics Data System (ADS)
Agueda, Neus; Bütikofer, Rolf; Vainio, Rami; Heber, Bernd; Afanasiev, Alexander; Malandraki, Olga E.
2016-04-01
We present a new methodology to study the release processes of relativistic solar energetic particles (SEPs) based on the direct inversion of Ground Level Enhancements (GLEs) observed by the worldwide network of neutron monitors (NMs). The new approach makes use of several models, including: the propagation of relativistic SEPs from the Sun to the Earth, their transport in the Earth's magnetosphere and atmosphere, as well as the detection of the nucleon component of the secondary cosmic rays by ground based NMs. The combination of these models allows us to compute the expected ground-level NM counting rates for a series of instantaneous releases from the Sun. The amplitudes of the source components are then inferred by fitting the NM observations with the modeled NM counting rate increases. Within the HESPERIA project, we will develop the first software package for the direct inversion of GLEs and we will make it freely available for the solar and heliospheric communities. Acknowledgement: This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 637324.
NASA Astrophysics Data System (ADS)
Chauvet, Yves
1985-07-01
This paper summarized two improvements of a real production code by using vectorization and multitasking techniques. After a short description of Monte Carlo algorithms employed in our neutron transport problems, we briefly describe the work we have done in order to get a vector code. Vectorization principles will be presented and measured performances on the CRAY 1S, CYBER 205 and CRAY X-MP compared in terms of vector lengths. The second part of this work is an adaptation to multitasking on the CRAY X-MP using exclusively standard multitasking tools available with FORTRAN under the COS 1.13 system. Two examples will be presented. The goal of the first one is to measure the overhead inherent to multitasking when tasks become too small and to define a granularity threshold that is to say a minimum size for a task. With the second example we propose a method that is very X-MP oriented in order to get the best speedup factor on such a computer. In conclusion we prove that Monte Carlo algorithms are very well suited to future vector and parallel computers.
NASA Astrophysics Data System (ADS)
Meyer, Andreas; Kargl, Florian; Horbach, Jürgen
The application of quasielastic neutron scattering and molecular dynamics simulation to the study of mass transport in silicate melts is outlined. It is shown how the knowledge of atomic dynamics and structure reveals the mechanisms of mass transport. Peculiar properties of atomic diffusion and viscous flow behaviour as a function of melt composition are discussed in terms of the formation of alkali diffusion channels in the static structure. This non-homogeneous distribution of alkali ions in a disrupted tetrahedral Si-O network is investigated in binary lithium, sodium and potassium silicate melts and in ternary sodium aluminosilicates and sodium ironsilicates representing the main compositions of natural volcanic rocks.
Metastable states of a flux-line lattice studied by transport and small-angle neutron scattering
Pautrat, A.; Scola, J.; Simon, Ch.; Brulet, A.; Bhattacharya, S.
2005-02-01
Flux-line lattice (FLL) states have been studied using transport measurements and small-angle neutron scattering in low-T{sub c} materials. In Pb-In, the bulk dislocations in the FLL do not influence the transport properties. In Fe-doped NbSe{sub 2}, transport properties can differ after a field cooling (FC) or a zero field cooling (ZFC) procedure, as previously reported. The ZFC FLL is found ordered with narrow Bragg peaks and is linked to a linear V(I) curve and to a superficial critical current. The FC FLL pattern exhibits two Bragg peaks and the corresponding V(I) curve shows an S-shape. This can be explained by the coexistence of two ordered FLLs slightly tilted from the applied field direction by different superficial currents. These currents are wiped out when the transport current is increased.
Metastable states of a flux-line lattice studied by transport and small-angle neutron scattering
NASA Astrophysics Data System (ADS)
Pautrat, A.; Scola, J.; Simon, Ch.; Mathieu, P.; Brûlet, A.; Goupil, C.; Higgins, M. J.; Bhattacharya, S.
2005-02-01
Flux-line lattice (FLL) states have been studied using transport measurements and small-angle neutron scattering in low- Tc materials. In Pb-In , the bulk dislocations in the FLL do not influence the transport properties. In Fe -doped NbSe2 , transport properties can differ after a field cooling (FC) or a zero field cooling (ZFC) procedure, as previously reported. The ZFC FLL is found ordered with narrow Bragg peaks and is linked to a linear V(I) curve and to a superficial critical current. The FC FLL pattern exhibits two Bragg peaks and the corresponding V(I) curve shows an S -shape. This can be explained by the coexistence of two ordered FLLs slightly tilted from the applied field direction by different superficial currents. These currents are wiped out when the transport current is increased.
Niranjan, Ram; Rout, R K; Srivastava, R; Kaushik, T C; Gupta, Satish C
2016-03-01
A 17 kJ transportable plasma focus (PF) device with flexible transmission lines is developed and is characterized. Six custom made capacitors are used for the capacitor bank (CB). The common high voltage plate of the CB is fixed to a centrally triggered spark gap switch. The output of the switch is coupled to the PF head through forty-eight 5 m long RG213 cables. The CB has a quarter time-period of 4 μs and an estimated current of 506 kA is delivered to the PF device at 17 kJ (60 μF, 24 kV) energy. The average neutron yield measured using silver activation detector in the radial direction is (7.1 ± 1.4) × 10(8) neutrons/shot over 4π sr at 5 mbar optimum D2 pressure. The average neutron yield is more in the axial direction with an anisotropy factor of 1.33 ± 0.18. The average neutron energies estimated in the axial as well as in the radial directions are (2.90 ± 0.20) MeV and (2.58 ± 0.20) MeV, respectively. The flexibility of the PF head makes it useful for many applications where the source orientation and the location are important factors. The influence of electromagnetic interferences from the CB as well as from the spark gap on applications area can be avoided by putting a suitable barrier between the bank and the PF head. PMID:27036774
NASA Astrophysics Data System (ADS)
Mayor, Louise
2016-05-01
Graphene might be the most famous example, but there are other 2D materials and compounds too. Louise Mayor explains how these atomically thin sheets can be layered together to create flexible “van der Waals heterostructures”, which could lead to a range of novel applications.
Tomkiewicz, Alex C.; Tamimi, Mazin; Huq, Ashfia; McIntosh, Steven
2015-09-21
Ruddlesden-Popper structured oxides, general form A_{n+1}B_{n}O_{3n+1}, consist of n-layers of the perovskite structure stacked in between rock-salt layers, and have potential application in solid oxide electrochemical cells and ion transport membrane reactors. Three materials with constant Co/Fe ratio, LaSrCo_{0.5}Fe_{0.5}O_{4-δ} (n = 1), La_{0.3}Sr_{2.7}CoFeO_{7-δ} (n = 2), and LaSr_{3}Co_{1.5}Fe_{1.5}O_{10-δ} (n = 3) were synthesized and studied via in situ neutron powder diffraction between 765 K and 1070 K at a pO_{2} of 10^{-1} atm. Then, the structures were fit to a tetragonal I4/mmm space group, and were found to have increased total oxygen vacancy concentration in the order La_{0.3}Sr_{2.7}CoFeO_{7-δ} > LaSr_{3}Co_{1.5}Fe_{1.5}O_{10-δ} > LaSrCo_{0.5}Fe_{0.5}O_{4-δ}, following the trend predicted for charge compensation upon increasing Sr^{2+}/La^{3+} ratio. The oxygen vacancies within the material were almost exclusively located within the perovskite layers for all of the crystal structures with only minimal vacancy formation in the rock-salt layer. Finally, analysis of the concentration of these vacancies at each distinct crystallographic site and the anisotropic atomic displacement parameters for the oxygen sites reveals potential preferred oxygen transport pathways through the perovskite layers.
NASA Astrophysics Data System (ADS)
Bergmann, Ryan
Graphics processing units, or GPUs, have gradually increased in computational power from the small, job-specific boards of the early 1990s to the programmable powerhouses of today. Compared to more common central processing units, or CPUs, GPUs have a higher aggregate memory bandwidth, much higher floating-point operations per second (FLOPS), and lower energy consumption per FLOP. Because one of the main obstacles in exascale computing is power consumption, many new supercomputing platforms are gaining much of their computational capacity by incorporating GPUs into their compute nodes. Since CPU-optimized parallel algorithms are not directly portable to GPU architectures (or at least not without losing substantial performance), transport codes need to be rewritten to execute efficiently on GPUs. Unless this is done, reactor simulations cannot take full advantage of these new supercomputers. WARP, which can stand for ``Weaving All the Random Particles,'' is a three-dimensional (3D) continuous energy Monte Carlo neutron transport code developed in this work as to efficiently implement a continuous energy Monte Carlo neutron transport algorithm on a GPU. WARP accelerates Monte Carlo simulations while preserving the benefits of using the Monte Carlo Method, namely, very few physical and geometrical simplifications. WARP is able to calculate multiplication factors, flux tallies, and fission source distributions for time-independent problems, and can run in both criticality or fixed source modes. WARP can transport neutrons in unrestricted arrangements of parallelepipeds, hexagonal prisms, cylinders, and spheres. WARP uses an event-based algorithm, but with some important differences. Moving data is expensive, so WARP uses a remapping vector of pointer/index pairs to direct GPU threads to the data they need to access. The remapping vector is sorted by reaction type after every transport iteration using a high-efficiency parallel radix sort, which serves to keep the
Zarebanadkouki, Mohsen; Kroener, Eva; Kaestner, Anders; Carminati, Andrea
2014-10-01
Our understanding of soil and plant water relations is limited by the lack of experimental methods to measure water fluxes in soil and plants. Here, we describe a new method to noninvasively quantify water fluxes in roots. To this end, neutron radiography was used to trace the transport of deuterated water (D2O) into roots. The results showed that (1) the radial transport of D2O from soil to the roots depended similarly on diffusive and convective transport and (2) the axial transport of D2O along the root xylem was largely dominated by convection. To quantify the convective fluxes from the radiographs, we introduced a convection-diffusion model to simulate the D2O transport in roots. The model takes into account different pathways of water across the root tissue, the endodermis as a layer with distinct transport properties, and the axial transport of D2O in the xylem. The diffusion coefficients of the root tissues were inversely estimated by simulating the experiments at night under the assumption that the convective fluxes were negligible. Inverse modeling of the experiment at day gave the profile of water fluxes into the roots. For a 24-d-old lupine (Lupinus albus) grown in a soil with uniform water content, root water uptake was higher in the proximal parts of lateral roots and decreased toward the distal parts. The method allows the quantification of the root properties and the regions of root water uptake along the root systems. PMID:25189533
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.
1993-08-09
Version 00 This data base was developed for use in Monte Carlo or discrete ordinate transport codes, for example, the general Monte Carlo code MCNP. Various modules of the NJOY processing code system have been enhanced to permit processing of the ENDF/B-VI formatted evaluations into both continuous-energy and multi-group format. The transport data files for all 18 projectile-plus-target systems have been processed through NJOY, and coupled multi-particle, multi-group transport libraries for MCNP now exist. Inmore » addition, pointwise MCNP libraries to 100 MeV for incident neutrons have been prepared for the nine targets. The production version of the MCNP code is being modified to handle the new pointwise libraries. The production version of MCNP already supports the use of coupled multi-group libraries.« less
Thomas, Sarah; Uhoya, Walter; Tsoi, Georgiy; Wenger, Lowell E; Vohra, Yogesh; Chesnut, Gary Neal; Weir, S. T.; Tulk, Christopher A; Moreira Dos Santos, Antonio F
2012-01-01
Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Neel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.
Nanoimprint lithography: 2D or not 2D? A review
NASA Astrophysics Data System (ADS)
Schift, Helmut
2015-11-01
Nanoimprint lithography (NIL) is more than a planar high-end technology for the patterning of wafer-like substrates. It is essentially a 3D process, because it replicates various stamp topographies by 3D displacement of material and takes advantage of the bending of stamps while the mold cavities are filled. But at the same time, it keeps all assets of a 2D technique being able to pattern thin masking layers like in photon- and electron-based traditional lithography. This review reports about 20 years of development of replication techniques at Paul Scherrer Institut, with a focus on 3D aspects of molding, which enable NIL to stay 2D, but at the same time enable 3D applications which are "more than Moore." As an example, the manufacturing of a demonstrator for backlighting applications based on thermally activated selective topography equilibration will be presented. This technique allows generating almost arbitrary sloped, convex and concave profiles in the same polymer film with dimensions in micro- and nanometer scale.
Morgan C. White
2000-07-01
The fundamental motivation for the research presented in this dissertation was the need to development a more accurate prediction method for characterization of mixed radiation fields around medical electron accelerators (MEAs). Specifically, a model is developed for simulation of neutron and other particle production from photonuclear reactions and incorporated in the Monte Carlo N-Particle (MCNP) radiation transport code. This extension of the capability within the MCNP code provides for the more accurate assessment of the mixed radiation fields. The Nuclear Theory and Applications group of the Los Alamos National Laboratory has recently provided first-of-a-kind evaluated photonuclear data for a select group of isotopes. These data provide the reaction probabilities as functions of incident photon energy with angular and energy distribution information for all reaction products. The availability of these data is the cornerstone of the new methodology for state-of-the-art mutually coupled photon-neutron transport simulations. The dissertation includes details of the model development and implementation necessary to use the new photonuclear data within MCNP simulations. A new data format has been developed to include tabular photonuclear data. Data are processed from the Evaluated Nuclear Data Format (ENDF) to the new class ''u'' A Compact ENDF (ACE) format using a standalone processing code. MCNP modifications have been completed to enable Monte Carlo sampling of photonuclear reactions. Note that both neutron and gamma production are included in the present model. The new capability has been subjected to extensive verification and validation (V&V) testing. Verification testing has established the expected basic functionality. Two validation projects were undertaken. First, comparisons were made to benchmark data from literature. These calculations demonstrate the accuracy of the new data and transport routines to better than 25 percent. Second, the ability to
Filho, J. F. P.
2013-07-01
In this work, an analytical discrete ordinates method is used to solve a nodal formulation of a neutron transport problem in x, y-geometry. The proposed approach leads to an important reduction in the order of the associated eigenvalue systems, when combined with the classical level symmetric quadrature scheme. Auxiliary equations are proposed, as usually required for nodal methods, to express the unknown fluxes at the boundary introduced as additional unknowns in the integrated equations. Numerical results, for the problem defined by a two-dimensional region with a spatially constant and isotropically emitting source, are presented and compared with those available in the literature. (authors)
Dworak, D; Loskiewicz, J; Janik, M
2001-05-01
The diffusion approximation solution for neutron transport has been used in well-logging geophysics for calculating tool responses in boreholes, sometimes with success. The problem of the dimension of different materials to which it can be applied with success is important for the borehole environment. The results obtained show that the diffusion approximation can be used for distances greater than a few millimetre in some rock types. For iron, barium, and other highly absorbing media the use of the diffusion approximation is inappropriate even for large distances. PMID:11258535
Wongthai, Printip; Hagiwara, Kohei; Miyoshi, Yurika; Wiriyasermkul, Pattama; Wei, Ling; Ohgaki, Ryuichi; Kato, Itsuro; Hamase, Kenji; Nagamori, Shushi; Kanai, Yoshikatsu
2015-03-01
The efficacy of boron neutron capture therapy relies on the selective delivery of boron carriers to malignant cells. p-Boronophenylalanine (BPA), a boron delivery agent, has been proposed to be localized to cells through transporter-mediated mechanisms. In this study, we screened aromatic amino acid transporters to identify BPA transporters. Human aromatic amino acid transporters were functionally expressed in Xenopus oocytes and examined for BPA uptake and kinetic parameters. The roles of the transporters in BPA uptake were characterized in cancer cell lines. For the quantitative assessment of BPA uptake, HPLC was used throughout the study. Among aromatic amino acid transporters, ATB(0,+), LAT1 and LAT2 were found to transport BPA with Km values of 137.4 ± 11.7, 20.3 ± 0.8 and 88.3 ± 5.6 μM, respectively. Uptake experiments in cancer cell lines revealed that the LAT1 protein amount was the major determinant of BPA uptake at 100 μM, whereas the contribution of ATB(0,+) became significant at 1000 μM, accounting for 20-25% of the total BPA uptake in MCF-7 breast cancer cells. ATB(0,+), LAT1 and LAT2 transport BPA at affinities comparable with their endogenous substrates, suggesting that they could mediate effective BPA uptake in vivo. The high and low affinities of LAT1 and ATB(0,+), respectively, differentiate their roles in BPA uptake. ATB(0,+), as well as LAT1, could contribute significantly to the tumor accumulation of BPA at clinical dose. PMID:25580517
NASA Technical Reports Server (NTRS)
Bogart, D. D.; Shook, D. F.; Fieno, D.
1973-01-01
Integral tests of evaluated ENDF/B high-energy cross sections have been made by comparing measured and calculated neutron leakage flux spectra from spheres of various materials. An Am-Be (alpha,n) source was used to provide fast neutrons at the center of the test spheres of Be, CH2, Pb, Nb, Mo, Ta, and W. The absolute leakage flux spectra were measured in the energy range 0.5 to 12 MeV using a calibrated NE213 liquid scintillator neutron spectrometer. Absolute calculations of the spectra were made using version 3 ENDF/B cross sections and an S sub n discrete ordinates multigroup transport code. Generally excellent agreement was obtained for Be, CH2, Pb, and Mo, and good agreement was observed for Nb although discrepancies were observed for some energy ranges. Poor comparative results, obtained for Ta and W, are attributed to unsatisfactory nonelastic cross sections. The experimental sphere leakage flux spectra are tabulated and serve as possible benchmarks for these elements against which reevaluated cross sections may be tested.
1991-08-01
Version: 00 The original MORSE code was a multipurpose neutron and gamma-ray transport Monte Carlo code. It was designed as a tool for solving most shielding problems. Through the use of multigroup cross sections, the solution of neutron, gamma-ray, or coupled neutron-gamma-ray problems could be obtained in either the forward or adjoint mode. Time dependence for both shielding and criticality problems is provided. General three-dimensional geometry could be used with an albedo option available atmore » any material surface. Isotropic or anisotropic scattering up to a P16 expansion of the angular distribution was allowed. MORSE-CG incorporated the Mathematical Applications, Inc. (MAGI) combinatorial geometry routines. MORSE-B modifies the Monte Carlo neutron and photon transport computer code MORSE-CG by adding routines which allow various flexible options.« less
Photocurrent spectroscopy of 2D materials
NASA Astrophysics Data System (ADS)
Cobden, David
Confocal photocurrent measurements provide a powerful means of studying many aspects of the optoelectronic and electrical properties of a 2D device or material. At a diffraction-limited point they can provide a detailed absorption spectrum, and they can probe local symmetry, ultrafast relaxation rates and processes, electron-electron interaction strengths, and transport coefficients. We illustrate this with several examples, once being the photo-Nernst effect. In gapless 2D materials, such as graphene, in a perpendicular magnetic field a photocurrent antisymmetric in the field is generated near to the free edges, with opposite sign at opposite edges. Its origin is the transverse thermoelectric current associated with the laser-induced electron temperature gradient. This effect provides an unambiguous demonstration of the Shockley-Ramo nature of long-range photocurrent generation in gapless materials. It also provides a means of investigating quasiparticle properties. For example, in the case of graphene on hBN, it can be used to probe the Lifshitz transition that occurs due to the minibands formed by the Moire superlattice. We also observe and discuss photocurrent generated in other semimetallic (WTe2) and semiconducting (WSe2) monolayers. Work supported by DoE BES and NSF EFRI grants.
Košťál, Michal; Cvachovec, František; Milčák, Ján; Mravec, Filip
2013-05-01
The paper is intended to show the effect of a biological shielding simulator on fast neutron and photon transport in its vicinity. The fast neutron and photon fluxes were measured by means of scintillation spectroscopy using a 45×45 mm(2) and a 10×10 mm(2) cylindrical stilbene detector. The neutron spectrum was measured in the range of 0.6-10 MeV and the photon spectrum in 0.2-9 MeV. The results of the experiment are compared with calculations. The calculations were performed with various nuclear data libraries. PMID:23434890
Gleicher, Frederick N.; Williamson, Richard L.; Ortensi, Javier; Wang, Yaqi; Spencer, Benjamin W.; Novascone, Stephen R.; Hales, Jason D.; Martineau, Richard C.
2014-10-01
The MOOSE neutron transport application RATTLESNAKE was coupled to the fuels performance application BISON to provide a higher fidelity tool for fuel performance simulation. This project is motivated by the desire to couple a high fidelity core analysis program (based on the self-adjoint angular flux equations) to a high fidelity fuel performance program, both of which can simulate on unstructured meshes. RATTLESNAKE solves self-adjoint angular flux transport equation and provides a sub-pin level resolution of the multigroup neutron flux with resonance treatment during burnup or a fast transient. BISON solves the coupled thermomechanical equations for the fuel on a sub-millimeter scale. Both applications are able to solve their respective systems on aligned and unaligned unstructured finite element meshes. The power density and local burnup was transferred from RATTLESNAKE to BISON with the MOOSE Multiapp transfer system. Multiple depletion cases were run with one-way data transfer from RATTLESNAKE to BISON. The eigenvalues are shown to agree well with values obtained from the lattice physics code DRAGON. The one-way data transfer of power density is shown to agree with the power density obtained from an internal Lassman-style model in BISON.
Competing coexisting phases in 2D water
Zanotti, Jean-Marc; Judeinstein, Patrick; Dalla-Bernardina, Simona; Creff, Gaëlle; Brubach, Jean-Blaise; Roy, Pascale; Bonetti, Marco; Ollivier, Jacques; Sakellariou, Dimitrios; Bellissent-Funel, Marie-Claire
2016-01-01
The properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules. PMID:27185018
Competing coexisting phases in 2D water
NASA Astrophysics Data System (ADS)
Zanotti, Jean-Marc; Judeinstein, Patrick; Dalla-Bernardina, Simona; Creff, Gaëlle; Brubach, Jean-Blaise; Roy, Pascale; Bonetti, Marco; Ollivier, Jacques; Sakellariou, Dimitrios; Bellissent-Funel, Marie-Claire
2016-05-01
The properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules.
Competing coexisting phases in 2D water.
Zanotti, Jean-Marc; Judeinstein, Patrick; Dalla-Bernardina, Simona; Creff, Gaëlle; Brubach, Jean-Blaise; Roy, Pascale; Bonetti, Marco; Ollivier, Jacques; Sakellariou, Dimitrios; Bellissent-Funel, Marie-Claire
2016-01-01
The properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules. PMID:27185018
3-D Deep Penetration Neutron Imaging of Thick Absorgin and Diffusive Objects Using Transport Theory
Ragusa, Jean; Bangerth, Wolfgang
2011-08-01
here explores the inverse problem of optical tomography applied to heterogeneous domains. The neutral particle transport equation was used as the forward model for how neutral particles stream through and interact within these heterogeneous domains. A constrained optimization technique that uses Newtons method served as the basis of the inverse problem. Optical tomography aims at reconstructing the material properties using (a) illuminating sources and (b) detector readings. However, accurate simulations for radiation transport require that the particle (gamma and/or neutron) energy be appropriate discretize in the multigroup approximation. This, in turns, yields optical tomography problems where the number of unknowns grows (1) about quadratically with respect to the number of energy groups, G, (notably to reconstruct the scattering matrix) and (2) linearly with respect to the number of unknown material regions. As pointed out, a promising approach could rely on algorithms to appropriately select a material type per material zone rather than G2 values. This approach, though promising, still requires further investigation: (a) when switching from cross-section values unknowns to material type indices (discrete integer unknowns), integer programming techniques are needed since derivative information is no longer available; and (b) the issue of selecting the initial material zoning remains. The work reported here proposes an approach to solve the latter item, whereby a material zoning is proposed using one-group or few-groups transport approximations. The capabilities and limitations of the presented method were explored; they are briefly summarized next and later described in fuller details in the Appendices. The major factors that influenced the ability of the optimization method to reconstruct the cross sections of these domains included the locations of the sources used to illuminate the domains, the number of separate experiments used in the reconstruction, the
NASA Astrophysics Data System (ADS)
Arapov, Yu. G.; Yakunin, M. V.; Gudina, S. V.; Harus, G. I.; Neverov, V. N.; Shelushinina, N. G.; Podgornyh, S. M.; Uskova, E. A.; Zvonkov, B. N.
2007-04-01
The resistivity ρ of low mobility dilute 2D-elecron gas in a InGaAs/GaAs double quantum well (DQW) exhibits the monotonic "insulating-like" temperature dependence (dρ/dT < 0) at T = 1.8-70K in zero magnetic field. This temperature interval corresponds to a ballistic regime (kBTτ/ℏ > 0.1) for our samples. We observed the coexistence of both the quantum Hall (QH) effect for the filling factors v = 2, 4 and the low magnetic field insulator — QH liquid (with v = 10) transition.
NASA Astrophysics Data System (ADS)
Bergmann, Ryan
Graphics processing units, or GPUs, have gradually increased in computational power from the small, job-specific boards of the early 1990s to the programmable powerhouses of today. Compared to more common central processing units, or CPUs, GPUs have a higher aggregate memory bandwidth, much higher floating-point operations per second (FLOPS), and lower energy consumption per FLOP. Because one of the main obstacles in exascale computing is power consumption, many new supercomputing platforms are gaining much of their computational capacity by incorporating GPUs into their compute nodes. Since CPU-optimized parallel algorithms are not directly portable to GPU architectures (or at least not without losing substantial performance), transport codes need to be rewritten to execute efficiently on GPUs. Unless this is done, reactor simulations cannot take full advantage of these new supercomputers. WARP, which can stand for ``Weaving All the Random Particles,'' is a three-dimensional (3D) continuous energy Monte Carlo neutron transport code developed in this work as to efficiently implement a continuous energy Monte Carlo neutron transport algorithm on a GPU. WARP accelerates Monte Carlo simulations while preserving the benefits of using the Monte Carlo Method, namely, very few physical and geometrical simplifications. WARP is able to calculate multiplication factors, flux tallies, and fission source distributions for time-independent problems, and can run in both criticality or fixed source modes. WARP can transport neutrons in unrestricted arrangements of parallelepipeds, hexagonal prisms, cylinders, and spheres. WARP uses an event-based algorithm, but with some important differences. Moving data is expensive, so WARP uses a remapping vector of pointer/index pairs to direct GPU threads to the data they need to access. The remapping vector is sorted by reaction type after every transport iteration using a high-efficiency parallel radix sort, which serves to keep the
An Intercomparison of 2-D Models Within a Common Framework
NASA Technical Reports Server (NTRS)
Weisenstein, Debra K.; Ko, Malcolm K. W.; Scott, Courtney J.; Jackman, Charles H.; Fleming, Eric L.; Considine, David B.; Kinnison, Douglas E.; Connell, Peter S.; Rotman, Douglas A.; Bhartia, P. K. (Technical Monitor)
2002-01-01
A model intercomparison among the Atmospheric and Environmental Research (AER) 2-D model, the Goddard Space Flight Center (GSFC) 2-D model, and the Lawrence Livermore National Laboratory 2-D model allows us to separate differences due to model transport from those due to the model's chemical formulation. This is accomplished by constructing two hybrid models incorporating the transport parameters of the GSFC and LLNL models within the AER model framework. By comparing the results from the native models (AER and e.g. GSFC) with those from the hybrid model (e.g. AER chemistry with GSFC transport), differences due to chemistry and transport can be identified. For the analysis, we examined an inert tracer whose emission pattern is based on emission from a High Speed Civil Transport (HSCT) fleet; distributions of trace species in the 2015 atmosphere; and the response of stratospheric ozone to an HSCT fleet. Differences in NO(y) in the upper stratosphere are found between models with identical transport, implying different model representations of atmospheric chemical processes. The response of O3 concentration to HSCT aircraft emissions differs in the models from both transport-dominated differences in the HSCT-induced perturbations of H2O and NO(y) as well as from differences in the model represent at ions of O3 chemical processes. The model formulations of cold polar processes are found to be the most significant factor in creating large differences in the calculated ozone perturbations
NASA Technical Reports Server (NTRS)
Jordan, T. M.
1970-01-01
The theory used in FASTER-III, a Monte Carlo computer program for the transport of neutrons and gamma rays in complex geometries, is outlined. The program includes the treatment of geometric regions bounded by quadratic and quadric surfaces with multiple radiation sources which have specified space, angle, and energy dependence. The program calculates, using importance sampling, the resulting number and energy fluxes at specified point, surface, and volume detectors. It can also calculate minimum weight shield configuration meeting a specified dose rate constraint. Results are presented for sample problems involving primary neutron, and primary and secondary photon, transport in a spherical reactor shield configuration.
Rahnema, Farzad; Garimeela, Srinivas; Ougouag, Abderrafi; Zhang, Dingkang
2013-11-29
This project will develop a 3D, advanced coarse mesh transport method (COMET-Hex) for steady- state and transient analyses in advanced very high-temperature reactors (VHTRs). The project will lead to a coupled neutronics and thermal hydraulic (T/H) core simulation tool with fuel depletion capability. The computational tool will be developed in hexagonal geometry, based solely on transport theory without (spatial) homogenization in complicated 3D geometries. In addition to the hexagonal geometry extension, collaborators will concurrently develop three additional capabilities to increase the code’s versatility as an advanced and robust core simulator for VHTRs. First, the project team will develop and implement a depletion method within the core simulator. Second, the team will develop an elementary (proof-of-concept) 1D time-dependent transport method for efficient transient analyses. The third capability will be a thermal hydraulic method coupled to the neutronics transport module for VHTRs. Current advancements in reactor core design are pushing VHTRs toward greater core and fuel heterogeneity to pursue higher burn-ups, efficiently transmute used fuel, maximize energy production, and improve plant economics and safety. As a result, an accurate and efficient neutron transport, with capabilities to treat heterogeneous burnable poison effects, is highly desirable for predicting VHTR neutronics performance. This research project’s primary objective is to advance the state of the art for reactor analysis.
Study of water distribution and transport in a polymer electrolyte fuel cell using neutron imaging
NASA Astrophysics Data System (ADS)
Pekula, N.; Heller, K.; Chuang, P. A.; Turhan, A.; Mench, M. M.; Brenizer, J. S.; Ünlü, K.
2005-04-01
A procedure to utilize neutron imaging for the visualization of two-phase flow within an operating polymer electrolyte fuel cell has been developed at the Penn State Breazeale Nuclear Reactor. Neutron images allow us to visualize the liquid water inside the flow channel (˜0.5 mm deep) and gas diffusion media (˜200 μm thick) in real operating conditions. The current temporal and spatial resolution for radioscopy is approximately 30 frames/s and 129 μm/pixel in a 50 cm 2 image area. Continuous digital radioscopy can be recorded for 45 min. The determination of water volume within the cell has been enabled by referencing a calibration look-up table that correlates neutron attenuation to an equivalent liquid water thickness. It was found that liquid water tends to accumulate at specific locations within the fuel cell, depending on operating conditions. Anode flow channel blockage was observed to occur at low power, while higher power conditions resulted in more dispersed distribution of liquid droplets. Under high-power conditions, liquid water tended to accumulate along or under the channel walls at 180° turns, and radioscopy revealed that individual liquid droplet velocities were several orders of magnitude less than that of the reactant flow, indicating a slug-flow regime up to at least 1 A/cm 2.
Boillat, P; Oberholzer, P; Seyfang, B C; Kästner, A; Perego, R; Scherer, G G; Lehmann, E H; Wokaun, A
2011-06-15
A method combining (2)H labeling of different sources of H atoms (hydrogen, water vapor) with neutron imaging for the analysis of transport parameters in the bulk and at the interfaces of Nafion polymer electrolyte membranes is proposed. The use of different isotope compositions in the steady state allows evaluation of the relation between bulk and interface transport parameters, but relies on literature data for evaluating absolute values. By using transients of isotope composition, absolute values of these parameters including the self-diffusion coefficient of H can be extracted, making this method an attractive alternative to self-diffusion measurements using nuclear magnetic resonance (NMR), allowing measurements in precisely controlled conditions in real fuel cell structures. First measurements were realized on samples with and without electrodes and we report values of the self-diffusion coefficient of the same order of magnitude as values measured using NMR, although with slightly higher numbers. In our particular case, lower interfacial exchange rates for water transport were observed for samples with an electrode. PMID:21613688
Biondo, Elliott D; Ibrahim, Ahmad M; Mosher, Scott W; Grove, Robert E
2015-01-01
Detailed radiation transport calculations are necessary for many aspects of the design of fusion energy systems (FES) such as ensuring occupational safety, assessing the activation of system components for waste disposal, and maintaining cryogenic temperatures within superconducting magnets. Hybrid Monte Carlo (MC)/deterministic techniques are necessary for this analysis because FES are large, heavily shielded, and contain streaming paths that can only be resolved with MC. The tremendous complexity of FES necessitates the use of CAD geometry for design and analysis. Previous ITER analysis has required the translation of CAD geometry to MCNP5 form in order to use the AutomateD VAriaNce reducTion Generator (ADVANTG) for hybrid MC/deterministic transport. In this work, ADVANTG was modified to support CAD geometry, allowing hybrid (MC)/deterministic transport to be done automatically and eliminating the need for this translation step. This was done by adding a new ray tracing routine to ADVANTG for CAD geometries using the Direct Accelerated Geometry Monte Carlo (DAGMC) software library. This new capability is demonstrated with a prompt dose rate calculation for an ITER computational benchmark problem using both the Consistent Adjoint Driven Importance Sampling (CADIS) method an the Forward Weighted (FW)-CADIS method. The variance reduction parameters produced by ADVANTG are shown to be the same using CAD geometry and standard MCNP5 geometry. Significant speedups were observed for both neutrons (as high as a factor of 7.1) and photons (as high as a factor of 59.6).
NASA Technical Reports Server (NTRS)
Ghorai, S. K.
1983-01-01
The purpose of this project was to use a one-dimensional discrete coordinates transport code called ANISN in order to determine the energy-angle-spatial distribution of neutrons in a 6-feet cube rock box which houses a D-T neutron generator at its center. The project was two-fold. The first phase of the project involved adaptation of the ANISN code written for an IBM 360/75/91 computer to the UNIVAC system at JSC. The second phase of the project was to use the code with proper geometry, source function and rock material composition in order to determine the neutron flux distribution around the rock box when a 14.1 MeV neutron generator placed at its center is activated.
NASA Astrophysics Data System (ADS)
Košťál, Michal; Milčák, Ján; Cvachovec, František; Jánský, Bohumil; Rypar, Vojtěch; Juříček, Vlastimil; Novák, Evžen; Egorov, Alexander; Zaritskiy, Sergey
2016-02-01
A set of benchmark experiments was carried out in the full scale VVER-1000 mock-up on the reactor LR-0 in order to validate neutron transport calculation methodologies and to perform the optimization of the shape and locations of neutron flux operation monitors channels inside the shielding of the new VVER-1000 type reactors. Compared with previous experiments on the VVER-1000 mock-up on the reactor LR-0, the fast neutron spectra were measured in the extended neutron energy interval (0.1-10 MeV) and new calculations were carried out with the MCNPX code using various nuclear data libraries (ENDF/B VII.0, JEFF 3.1, JENDL 3.3, JENDL 4, ROSFOND 2009, and CENDL 3.1). Measurements and calculations were carried out at different points in the mock-up. The calculation and experimental data are compared.
NASA Astrophysics Data System (ADS)
Ghorai, S. K.
1983-09-01
The purpose of this project was to use a one-dimensional discrete coordinates transport code called ANISN in order to determine the energy-angle-spatial distribution of neutrons in a 6-feet cube rock box which houses a D-T neutron generator at its center. The project was two-fold. The first phase of the project involved adaptation of the ANISN code written for an IBM 360/75/91 computer to the UNIVAC system at JSC. The second phase of the project was to use the code with proper geometry, source function and rock material composition in order to determine the neutron flux distribution around the rock box when a 14.1 MeV neutron generator placed at its center is activated.
2008-02-29
Version 00 (1) Problems to be solved: MVP/GMVP II can solve eigenvalue and fixed-source problems. The multigroup code GMVP can solve forward and adjoint problems for neutron, photon and neutron-photon coupled transport. The continuous-energy code MVP can solve only the forward problems. Both codes can also perform time-dependent calculations. (2) Geometry description: MVP/GMVP employs combinatorial geometry to describe the calculation geometry. It describes spatial regions by the combination of the 3-dimensional objects (BODIes). Currently, themore » following objects (BODIes) can be used. - BODIes with linear surfaces : half space, parallelepiped, right parallelepiped, wedge, right hexagonal prism - BODIes with quadratic surface and linear surfaces : cylinder, sphere, truncated right cone, truncated elliptic cone, ellipsoid by rotation, general ellipsoid - Arbitrary quadratic surface and torus The rectangular and hexagonal lattice geometry can be used to describe the repeated geometry. Furthermore, the statistical geometry model is available to treat coated fuel particles or pebbles for high temperature reactors. (3) Particle sources: The various forms of energy-, angle-, space- and time-dependent distribution functions can be specified. See Abstract for more detail.« less
Thomas, Sarah; Montgomery, Jeffrey M; Tsoi, Georgiy; Vohra, Yogesh; Chesnut, Gary Neal; Weir, S. T.; Tulk, Christopher A; Moreira Dos Santos, Antonio F
2013-01-01
Neutron diffraction and electrical transport measurements have been carried out on the heavy rare-earth metal terbium at high pressures and low temperatures in order to elucidate the onset of ferromagnetic (FM) order as a function of pressure. The electrical resistance measurements show a change in slope as the temperature is lowered through the FM Curie temperature. The temperature of this FM transition decreases at a rate of-16.7 K/GPa up to a pressure of 3.6 GPa, at which point the onset of FM order is suppressed. The neutron diffraction measurements as a function of pressure at temperatures ranging from 90 to 290 K confirm that the change of slope in the resistance is associated with the FM ordering, since this occurs at pressures similar to those determined from the resistance results at these temperatures. A disappearance of FM ordering was observed as the pressure is increased above 3.6 GPa and is correlated with the phase transition from the ambient hexagonal close packed structure to an -Sm-type structure at high pressures.
Thomas, Sarah A.; Montgomery, Jeffrey M.; Tsoi, Georgiy M.; Vohra, Yogesh K.; Chesnut, Gary N.; Weir, Samuel T.; Tulk, Christopher A.; dos Santos, Antonio M.
2013-06-11
Neutron diffraction and electrical transport measurements have been carried out on the heavy rare earth metal terbium at high pressures and low temperatures in order to elucidate the onset of ferromagnetic order as a function of pressure. The electrical resistance measurements show a change in slope as the temperature is lowered through the ferromagnetic Curie temperature. The temperature of this ferromagnetic transition decreases from approximately 240 K at ambient pressure at a rate of –16.7 K/GPa up to a pressure of 3.6 GPa, at which point the onset of ferromagnetic order is suppressed. Neutron diffraction measurements as a function of pressure at temperatures ranging from 90 K to 290 K confirm that the change of slope in the resistance is associated with the ferromagnetic ordering, since this occurs at pressures similar to those determined from the resistance results at these temperatures. Furthermore, a change in ferromagnetic ordering as the pressure is increased above 3.6 GPa is correlated with the phase transition from the ambient hexagonal close packed (hcp) structure to an α-Sm type structure at high pressures.
Chatani, K. )
1992-08-01
This report summarizes the calculational results from analyses of a Clinch River Breeder Reactor (CRBR) prototypic coolant pipe chaseway neutron streaming experiment Comparisons of calculated and measured results are presented, major emphasis being placed on results at bends in the chaseway. Calculations were performed with three three-dimensional radiation transport codes: the discrete ordinates code TORT and the Monte Carlo code MORSE, both developed by the Oak Ridge National Laboratory (ORNL), and the discrete ordinates code ENSEMBLE, developed by Japan. The calculated results from the three codes are compared (1) with previously-calculated DOT3.5 two-dimensional results, (2) among themselves, and (3) with measured results. Calculations with TORT used both the weighted-difference and nodal methods. Only the weighted-difference method was used in ENSEMBLE. When the calculated results were compared to measured results, it was found that calculation-to-experiment (C/E) ratios were good in the regions of the chaseway where two-dimensional modeling might be difficult and where there were no significant discrete ordinates ray effects. Excellent agreement was observed for responses dominated by thermal neutron contributions. MORSE-calculated results and comparisons are described also, and detailed results are presented in an appendix.
Thomas, Sarah A.; Montgomery, Jeffrey M.; Tsoi, Georgiy M.; Vohra, Yogesh K.; Chesnut, Gary N.; Weir, Samuel T.; Tulk, Christopher A.; dos Santos, Antonio M.
2013-06-11
Neutron diffraction and electrical transport measurements have been carried out on the heavy rare earth metal terbium at high pressures and low temperatures in order to elucidate the onset of ferromagnetic order as a function of pressure. The electrical resistance measurements show a change in slope as the temperature is lowered through the ferromagnetic Curie temperature. The temperature of this ferromagnetic transition decreases from approximately 240 K at ambient pressure at a rate of –16.7 K/GPa up to a pressure of 3.6 GPa, at which point the onset of ferromagnetic order is suppressed. Neutron diffraction measurements as a function ofmore » pressure at temperatures ranging from 90 K to 290 K confirm that the change of slope in the resistance is associated with the ferromagnetic ordering, since this occurs at pressures similar to those determined from the resistance results at these temperatures. Furthermore, a change in ferromagnetic ordering as the pressure is increased above 3.6 GPa is correlated with the phase transition from the ambient hexagonal close packed (hcp) structure to an α-Sm type structure at high pressures.« less
NASA Astrophysics Data System (ADS)
McClanahan, Timothy; Mirofanov, Igor; Boynton, William; Chin, Gordon; Livengood, Timothy; Su, Jiao Jang; Sagdeev, Raold; Parsons, Ann; Evans, Larry; Starr, Richard; Hamara, Dave; Bodnarik, Julia; Williams, Jeane-Pierre; Mazarico, Erwan; Litvak, Maxim; Sanin, Anton; Murray, Joseph
2016-04-01
We report evidence that the Moon's diurnally modulating neutron flux is being forced by a latitude dependent mix of 1) transient hydrogen-bearing volatiles near the surface in the upper latitudes and 2) regolith temperature variation in lower latitudes. In this study we investigate diurnally varying neutron flux measurements from the Lunar Reconnaissance Orbiter's (LRO) Lunar Exploration Neutron Detector's Collimated Sensor for Epithermal Neutrons (LEND CSETN) and surface temperature observations from the Diviner radiometer poleward of >±45°. Our presentation shows that the modulating neutron flux is not consistent with a regolith temperature control for latitudes >70°. The anticorrelation may be evidence for transported lunar hydrogen volatiles or highly non-uniform regolith compositional dynamics. Observational evidence is consistent with regolith temperature being the source of the neutron flux modulation in the northern mare (45° to 60°) and may be related to its mafic composition and fast neutron contributions. Predictions for hypothesized regolith temperature effects are evaluated using insolation inferred from the Lunar Observing Laser Altimeter (LOLA) topography.
Cullen, D E
1998-11-22
TART98 is a coupled neutron-photon, 3 Dimensional, combinatorial geometry, time dependent Monte Carlo radiation transport code. This code can run on any modern computer. It is a complete system to assist you with input preparation, running Monte Carlo calculations, and analysis of output results. TART98 is also incredibly FAST; if you have used similar codes, you will be amazed at how fast this code is compared to other similar codes. Use of the entire system can save you a great deal of time and energy. TART98 is distributed on CD. This CD contains on-line documentation for all codes included in the system, the codes configured to run on a variety of computers, and many example problems that you can use to familiarize yourself with the system. TART98 completely supersedes all older versions of TART, and it is strongly recommended that users only use the most recent version of TART98 and its data files.
NKG2D ligands as therapeutic targets
Spear, Paul; Wu, Ming-Ru; Sentman, Marie-Louise; Sentman, Charles L.
2013-01-01
The Natural Killer Group 2D (NKG2D) receptor plays an important role in protecting the host from infections and cancer. By recognizing ligands induced on infected or tumor cells, NKG2D modulates lymphocyte activation and promotes immunity to eliminate ligand-expressing cells. Because these ligands are not widely expressed on healthy adult tissue, NKG2D ligands may present a useful target for immunotherapeutic approaches in cancer. Novel therapies targeting NKG2D ligands for the treatment of cancer have shown preclinical success and are poised to enter into clinical trials. In this review, the NKG2D receptor and its ligands are discussed in the context of cancer, infection, and autoimmunity. In addition, therapies targeting NKG2D ligands in cancer are also reviewed. PMID:23833565
Chang, B
2004-03-22
This paper contains three analytical solutions of transport problems which can be used to test ray-effect errors in the numerical solutions of the Boltzmann Transport Equation (BTE). We derived the first two solutions and the third was shown to us by M. Prasad. Since this paper is intended to be an internal LLNL report, no attempt was made to find the original derivations of the solutions in the literature in order to cite the authors for their work.
Prototype Neutron Energy Spectrometer
Stephen Mitchell, Sanjoy Mukhopadhyay, Richard Maurer, Ronald Wolff
2010-06-16
The project goals are: (1) Use three to five pressurized helium tubes with varying polyethylene moderators to build a neutron energy spectrometer that is most sensitive to the incident neutron energy of interest. Neutron energies that are of particular interest are those from the fission neutrons (typically around 1-2 MeV); (2) Neutron Source Identification - Use the neutron energy 'selectivity' property as a tool to discriminate against other competing processes by which neutrons are generated (viz. Cosmic ray induced neutron production [ship effect], [a, n] reactions); (3) Determine the efficiency as a function of neutron energy (response function) of each of the detectors, and thereby obtain the composite neutron energy spectrum from the detector count rates; and (4) Far-field data characterization and effectively discerning shielded fission source. Summary of the presentation is: (1) A light weight simple form factor compact neutron energy spectrometer ready to be used in maritime missions has been built; (2) Under laboratory conditions, individual Single Neutron Source Identification is possible within 30 minutes. (3) Sources belonging to the same type of origin viz., (a, n), fission, cosmic cluster in the same place in the 2-D plot shown; and (4) Isotopes belonging to the same source origin like Cm-Be, Am-Be (a, n) or Pu-239, U-235 (fission) do have some overlap in the 2-D plot.
2d PDE Linear Symmetric Matrix Solver
1983-10-01
ICCG2 (Incomplete Cholesky factorized Conjugate Gradient algorithm for 2d symmetric problems) was developed to solve a linear symmetric matrix system arising from a 9-point discretization of two-dimensional elliptic and parabolic partial differential equations found in plasma physics applications, such as resistive MHD, spatial diffusive transport, and phase space transport (Fokker-Planck equation) problems. These problems share the common feature of being stiff and requiring implicit solution techniques. When these parabolic or elliptic PDE''s are discretized withmore » finite-difference or finite-element methods,the resulting matrix system is frequently of block-tridiagonal form. To use ICCG2, the discretization of the two-dimensional partial differential equation and its boundary conditions must result in a block-tridiagonal supermatrix composed of elementary tridiagonal matrices. The incomplete Cholesky conjugate gradient algorithm is used to solve the linear symmetric matrix equation. Loops are arranged to vectorize on the Cray1 with the CFT compiler, wherever possible. Recursive loops, which cannot be vectorized, are written for optimum scalar speed. For matrices lacking symmetry, ILUCG2 should be used. Similar methods in three dimensions are available in ICCG3 and ILUCG3. A general source containing extensions and macros, which must be processed by a pre-compiler to obtain the standard FORTRAN source, is provided along with the standard FORTRAN source because it is believed to be more readable. The pre-compiler is not included, but pre-compilation may be performed by a text editor as described in the UCRL-88746 Preprint.« less
NASA Astrophysics Data System (ADS)
Zarebanadkouki, M.; Kroener, E.; Ahmed, M. A.; Carminati, A.
2014-12-01
Our understanding of soil and plant water relations is currently limited by the lack of experimental methods to measure the water fluxes in soil and plants. Our study aimed to develop a new non-destructive method to measure the local fluxes of water into roots of plants growing in soils. We injected deuterated water (D2O) near the roots of lupines growing in sandy soils, and we used neutron radiography to image the transport of D2O through the root system. The experiments were performed during day, when plants were transpiring, and at night, when transpiration was reduced. The radiographs showed that: 1) the radial transport of D2O from soil and roots depended similarly to diffusion and convection; and 2) the axial transport of D2O along the root xylem was largely dominated by convection. To determine the convective fluxes from the radiographs, we simulated the D2O transport in soils and roots. A dual porosity model was used to describe the apoplastic and symplastic pathways of water across the root tissue. Other features such as the endodermis and the xylem were also included in the model. The D2O transport was modelled solving a convection-diffusion numerical model in soil and plants. The diffusion coefficients of the root tissues were inversely estimated by simulating the experiments at night under the assumption that at night the convective fluxes were negligible. Inverse modelling of the experiment at day gave the profile of water fluxes into the roots. For 24 day-old lupine grown in a sandy soil with uniform water content, our modelling results showed that root water uptake was higher at the proximal parts of the roots near soil surface and it decreased toward the distal parts. The method allows the quantification of the root properties and the regions of root water uptake along root systems growing in soils. Future applications of this method include the characterization of varying root systems, the radial and axial hydraulic conductivity of different root
Kramer, K J; Latkowski, J F; Abbott, R P; Boyd, J K; Powers, J J; Seifried, J E
2008-10-24
Lawrence Livermore National Laboratory is currently developing a hybrid fusion-fission nuclear energy system, called LIFE, to generate power and burn nuclear waste. We utilize inertial confinement fusion to drive a subcritical fission blanket surrounding the fusion chamber. It is composed of TRISO-based fuel cooled by the molten salt flibe. Low-yield (37.5 MJ) targets and a repetition rate of 13.3 Hz produce a 500 MW fusion source that is coupled to the subcritical blanket, which provides an additional gain of 4-8, depending on the fuel. In the present work, we describe the neutron transport and nuclear burnup analysis. We utilize standard analysis tools including, the Monte Carlo N-Particle (MCNP) transport code, ORIGEN2 and Monteburns to perform the nuclear design. These analyses focus primarily on a fuel composed of depleted uranium not requiring chemical reprocessing or enrichment. However, other fuels such as weapons grade plutonium and highly-enriched uranium are also under consideration. In addition, we have developed a methodology using {sup 6}Li as a burnable poison to replace the tritium burned in the fusion targets and to maintain constant power over the lifetime of the engine. The results from depleted uranium analyses suggest up to 99% burnup of actinides is attainable while maintaining full power at 2GW for more than five decades.
Perspectives for spintronics in 2D materials
NASA Astrophysics Data System (ADS)
Han, Wei
2016-03-01
The past decade has been especially creative for spintronics since the (re)discovery of various two dimensional (2D) materials. Due to the unusual physical characteristics, 2D materials have provided new platforms to probe the spin interaction with other degrees of freedom for electrons, as well as to be used for novel spintronics applications. This review briefly presents the most important recent and ongoing research for spintronics in 2D materials.
Design of a high-current low-energy beam transport line for an intense D-T/D-D neutron generator
NASA Astrophysics Data System (ADS)
Lu, Xiaolong; Wang, Junrun; Zhang, Yu; Li, Jianyi; Xia, Li; Zhang, Jie; Ding, Yanyan; Jiang, Bing; Huang, Zhiwu; Ma, Zhanwen; Wei, Zheng; Qian, Xiangping; Xu, Dapeng; Lan, Changlin; Yao, Zeen
2016-03-01
An intense D-T/D-D neutron generator is currently being developed at the Lanzhou University. The Cockcroft-Walton accelerator, as a part of the neutron generator, will be used to accelerate and transport the high-current low-energy beam from the duoplasmatron ion source to the rotating target. The design of a high-current low-energy beam transport (LEBT) line and the dynamics simulations of the mixed beam were carried out using the TRACK code. The results illustrate that the designed beam line facilitates smooth transportation of a deuteron beam of 40 mA, and the number of undesired ions can be reduced effectively using two apertures.
Frankel, J.I.
1997-09-01
This investigation used sysmbolic manipulation in developing analytical methods and general computational strategies for solving both linear and nonlinear, regular and singular integral and integro-differential equations which appear in radiative and mixed-mode energy transport. Contained in this report are seven papers which present the technical results as individual modules.
Phosphorene: A New High-Mobility 2D Semiconductor
NASA Astrophysics Data System (ADS)
Liu, Han; Neal, Adam; Zhu, Zhen; Tomanek, David; Ye, Peide
2014-03-01
The rise of 2D crystals has opened various possibilities for future electrical and optical applications. MoS2 n-type transistors are showing great potential in ultra-scaled and low-power electronics. Here, we introduce phosphorene, a name we coined for 2D few-layer black phosphorus, a new 2D material with layered structure. We perform ab initio band structure calculations and show that the fundamental band gap depends sensitively on the number of layers. We observe transport behavior, which shows a mobility variation in the 2D plane. High on-current of 194 mA/mm, high hole mobility up to 286 cm2/V .s and on/off ratio up to 104 was achieved with phosphorene transistors at room temperature. Schottky barrier height at the metal/phosphorene interface was also measured as a function of temperature. We demonstrate a CMOS inverter with combination to MoS2 NMOS transistors, which shows great potential for semiconducting 2D crystals in future electronic, optoelectronic and flexible electronic devices.
Validation and testing of the VAM2D computer code
Kool, J.B.; Wu, Y.S. )
1991-10-01
This document describes two modeling studies conducted by HydroGeoLogic, Inc. for the US NRC under contract no. NRC-04089-090, entitled, Validation and Testing of the VAM2D Computer Code.'' VAM2D is a two-dimensional, variably saturated flow and transport code, with applications for performance assessment of nuclear waste disposal. The computer code itself is documented in a separate NUREG document (NUREG/CR-5352, 1989). The studies presented in this report involve application of the VAM2D code to two diverse subsurface modeling problems. The first one involves modeling of infiltration and redistribution of water and solutes in an initially dry, heterogeneous field soil. This application involves detailed modeling over a relatively short, 9-month time period. The second problem pertains to the application of VAM2D to the modeling of a waste disposal facility in a fractured clay, over much larger space and time scales and with particular emphasis on the applicability and reliability of using equivalent porous medium approach for simulating flow and transport in fractured geologic media. Reflecting the separate and distinct nature of the two problems studied, this report is organized in two separate parts. 61 refs., 31 figs., 9 tabs.
Updated version of the DOT 4 one- and two-dimensional neutron/photon transport code
Rhoades, W.A.; Childs, R.L.
1982-07-01
DOT 4 is designed to allow very large transport problems to be solved on a wide range of computers and memory arrangements. Unusual flexibilty in both space-mesh and directional-quadrature specification is allowed. For example, the radial mesh in an R-Z problem can vary with axial position. The directional quadrature can vary with both space and energy group. Several features improve performance on both deep penetration and criticality problems. The program has been checked and used extensively.
Pillar Structured Thermal Neutron Detector
Nikolic, R; Conway, A; Reinhardt, C; Graff, R; Wang, T; Deo, N; Cheung, C
2008-06-10
This work describes an innovative solid state device structure that leverages advanced semiconductor fabrication technology to produce an efficient device for thermal neutron detection which we have coined the 'Pillar Detector'. State-of-the-art thermal neutron detectors have shortcomings in simultaneously achieving high efficiency, low operating voltage while maintaining adequate fieldability performance. By using a three dimensional silicon PIN diode pillar array filled with isotopic {sup 10}boron ({sup 10}B), a high efficiency device is theoretically possible. Here we review the design considerations for going from a 2-D to 3-D device and discuss the materials trade-offs. The relationship between the geometrical features and efficiency within our 3-D device is investigated by Monte Carlo radiation transport method coupled with finite element drift-diffusion carrier transport simulations. To benchmark our simulations and validate the predicted efficiency scaling, experimental results of a prototype device are illustrated. The fabricated pillar structures reported in this work are composed of 2 {micro}m diameter silicon pillars with a 2 {micro}m spacing and pillar height of 12 {micro}m. The pillar detector with a 12 {micro}m height achieved a thermal neutron detection efficiency of 7.3% at a reverse bias of -2 V.
Annotated Bibliography of EDGE2D Use
J.D. Strachan and G. Corrigan
2005-06-24
This annotated bibliography is intended to help EDGE2D users, and particularly new users, find existing published literature that has used EDGE2D. Our idea is that a person can find existing studies which may relate to his intended use, as well as gain ideas about other possible applications by scanning the attached tables.
Staring 2-D hadamard transform spectral imager
Gentry, Stephen M.; Wehlburg, Christine M.; Wehlburg, Joseph C.; Smith, Mark W.; Smith, Jody L.
2006-02-07
A staring imaging system inputs a 2D spatial image containing multi-frequency spectral information. This image is encoded in one dimension of the image with a cyclic Hadamarid S-matrix. The resulting image is detecting with a spatial 2D detector; and a computer applies a Hadamard transform to recover the encoded image.
1991-05-01
Version 00 MORSE-CGA was developed to add the capability of modelling rectangular lattices for nuclear reactor cores or for multipartitioned structures. It thus enhances the capability of the MORSE code system. The MORSE code is a multipurpose neutron and gamma-ray transport Monte Carlo code. It has been designed as a tool for solving most shielding problems. Through the use of multigroup cross sections, the solution of neutron, gamma-ray, or coupled neutron-gamma-ray problems may be obtainedmore » in either the forward or adjoint mode. Time dependence for both shielding and criticality problems is provided. General three-dimensional geometry may be used with an albedo option available at any material surface. Isotropic or anisotropic scattering up to a P16 expansion of the angular distribution is allowed.« less
A Posteriori Error Estimation for a Nodal Method in Neutron Transport Calculations
Azmy, Y.Y.; Buscaglia, G.C.; Zamonsky, O.M.
1999-11-03
An a posteriori error analysis of the spatial approximation is developed for the one-dimensional Arbitrarily High Order Transport-Nodal method. The error estimator preserves the order of convergence of the method when the mesh size tends to zero with respect to the L{sup 2} norm. It is based on the difference between two discrete solutions that are available from the analysis. The proposed estimator is decomposed into error indicators to allow the quantification of local errors. Some test problems with isotropic scattering are solved to compare the behavior of the true error to that of the estimated error.
2d PDE Linear Asymmetric Matrix Solver
1983-10-01
ILUCG2 (Incomplete LU factorized Conjugate Gradient algorithm for 2d problems) was developed to solve a linear asymmetric matrix system arising from a 9-point discretization of two-dimensional elliptic and parabolic partial differential equations found in plasma physics applications, such as plasma diffusion, equilibria, and phase space transport (Fokker-Planck equation) problems. These equations share the common feature of being stiff and requiring implicit solution techniques. When these parabolic or elliptic PDE''s are discretized with finite-difference or finite-elementmore » methods, the resulting matrix system is frequently of block-tridiagonal form. To use ILUCG2, the discretization of the two-dimensional partial differential equation and its boundary conditions must result in a block-tridiagonal supermatrix composed of elementary tridiagonal matrices. A generalization of the incomplete Cholesky conjugate gradient algorithm is used to solve the matrix equation. Loops are arranged to vectorize on the Cray1 with the CFT compiler, wherever possible. Recursive loops, which cannot be vectorized, are written for optimum scalar speed. For problems having a symmetric matrix ICCG2 should be used since it runs up to four times faster and uses approximately 30% less storage. Similar methods in three dimensions are available in ICCG3 and ILUCG3. A general source, containing extensions and macros, which must be processed by a pre-compiler to obtain the standard FORTRAN source, is provided along with the standard FORTRAN source because it is believed to be more readable. The pre-compiler is not included, but pre-compilation may be performed by a text editor as described in the UCRL-88746 Preprint.« less
Light field morphing using 2D features.
Wang, Lifeng; Lin, Stephen; Lee, Seungyong; Guo, Baining; Shum, Heung-Yeung
2005-01-01
We present a 2D feature-based technique for morphing 3D objects represented by light fields. Existing light field morphing methods require the user to specify corresponding 3D feature elements to guide morph computation. Since slight errors in 3D specification can lead to significant morphing artifacts, we propose a scheme based on 2D feature elements that is less sensitive to imprecise marking of features. First, 2D features are specified by the user in a number of key views in the source and target light fields. Then the two light fields are warped view by view as guided by the corresponding 2D features. Finally, the two warped light fields are blended together to yield the desired light field morph. Two key issues in light field morphing are feature specification and warping of light field rays. For feature specification, we introduce a user interface for delineating 2D features in key views of a light field, which are automatically interpolated to other views. For ray warping, we describe a 2D technique that accounts for visibility changes and present a comparison to the ideal morphing of light fields. Light field morphing based on 2D features makes it simple to incorporate previous image morphing techniques such as nonuniform blending, as well as to morph between an image and a light field. PMID:15631126
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.
Inertial solvation in femtosecond 2D spectra
NASA Astrophysics Data System (ADS)
Hybl, John; Albrecht Ferro, Allison; Farrow, Darcie; Jonas, David
2001-03-01
We have used 2D Fourier transform spectroscopy to investigate polar solvation. 2D spectroscopy can reveal molecular lineshapes beneath ensemble averaged spectra and freeze molecular motions to give an undistorted picture of the microscopic dynamics of polar solvation. The transition from "inhomogeneous" to "homogeneous" 2D spectra is governed by both vibrational relaxation and solvent motion. Therefore, the time dependence of the 2D spectrum directly reflects the total response of the solvent-solute system. IR144, a cyanine dye with a dipole moment change upon electronic excitation, was used to probe inertial solvation in methanol and propylene carbonate. Since the static Stokes' shift of IR144 in each of these solvents is similar, differences in the 2D spectra result from solvation dynamics. Initial results indicate that the larger propylene carbonate responds more slowly than methanol, but appear to be inconsistent with rotational estimates of the inertial response. To disentangle intra-molecular vibrations from solvent motion, the 2D spectra of IR144 will be compared to the time-dependent 2D spectra of the structurally related nonpolar cyanine dye HDITCP.
Internal Photoemission Spectroscopy of 2-D Materials
NASA Astrophysics Data System (ADS)
Nguyen, Nhan; Li, Mingda; Vishwanath, Suresh; Yan, Rusen; Xiao, Shudong; Xing, Huili; Cheng, Guangjun; Hight Walker, Angela; Zhang, Qin
Recent research has shown the great benefits of using 2-D materials in the tunnel field-effect transistor (TFET), which is considered a promising candidate for the beyond-CMOS technology. The on-state current of TFET can be enhanced by engineering the band alignment of different 2D-2D or 2D-3D heterostructures. Here we present the internal photoemission spectroscopy (IPE) approach to determine the band alignments of various 2-D materials, in particular SnSe2 and WSe2, which have been proposed for new TFET designs. The metal-oxide-2-D semiconductor test structures are fabricated and characterized by IPE, where the band offsets from the 2-D semiconductor to the oxide conduction band minimum are determined by the threshold of the cube root of IPE yields as a function of photon energy. In particular, we find that SnSe2 has a larger electron affinity than most semiconductors and can be combined with other semiconductors to form near broken-gap heterojunctions with low barrier heights which can produce a higher on-state current. The details of data analysis of IPE and the results from Raman spectroscopy and spectroscopic ellipsometry measurements will also be presented and discussed.
Sippel, K. H.; Bacik, J.; Quiocho, F. A.; Fisher, S. Z.
2014-01-01
Inorganic phosphate is an essential molecule for all known life. Organisms have developed many mechanisms to ensure an adequate supply, even in low-phosphate conditions. In prokaryotes phosphate transport is instigated by the phosphate-binding protein (PBP), the initial receptor for the ATP-binding cassette (ABC) phosphate transporter. In the crystal structure of the PBP–phosphate complex, the phosphate is completely desolvated and sequestered in a deep cleft and is bound by 13 hydrogen bonds: 12 to protein NH and OH donor groups and one to a carboxylate acceptor group. The carboxylate plays a key recognition role by accepting a phosphate hydrogen. PBP phosphate affinity is relatively consistent across a broad pH range, indicating the capacity to bind monobasic (H2PO4 −) and dibasic (HPO4 2−) phosphate; however, the mechanism by which it might accommodate the second hydrogen of monobasic phosphate is unclear. To answer this question, neutron diffraction studies were initiated. Large single crystals with a volume of 8 mm3 were grown and subjected to hydrogen/deuterium exchange. A 2.5 Å resolution data set was collected on the Protein Crystallography Station at the Los Alamos Neutron Science Center. Initial refinement of the neutron data shows significant nuclear density, and refinement is ongoing. This is the first report of a neutron study from this superfamily. PMID:24915101
Whole-core neutron transport calculations without fuel-coolant homogenization
Smith, M. A.; Tsoulfanidis, N.; Lewis, E. E.; Palmiotti, G.; Taiwo, T. A.
2000-02-10
The variational nodal method implemented in the VARIANT code is generalized to perform full core transport calculations without spatial homogenization of cross sections at either the fuel-pin cell or fuel assembly level. The node size is chosen to correspond to one fuel-pin cell in the radial plane. Each node is divided into triangular finite subelements, with the interior spatial flux distribution represented by piecewise linear trial functions. The step change in the cross sections at the fuel-coolant interface can thus be represented explicitly in global calculations while retaining the fill spherical harmonics capability of VARIANT. The resulting method is applied to a two-dimensional seven-group representation of a LWR containing MOX fuel assemblies. Comparisons are made of the accuracy of various space-angle approximations and of the corresponding CPU times.
Gheisari, R.; Firoozabadi, M. M.; Mohammadi, H.
2014-01-15
A new idea to calculate ultracold neutron (UCN) production by using Monte Carlo simulation method to calculate the cold neutron (CN) flux and an analytical approach to calculate the UCN production from the simulated CN flux was given. A super-thermal source (UCN source) was modeled based on an arrangement of D{sub 2}O and solid D{sub 2} (sD{sub 2}). The D{sub 2}O was investigated as the neutron moderator, and sD{sub 2} as the converter. In order to determine the required parameters, a two-dimensional (2D) neutron balance equation written in Matlab was combined with the MCNPX simulation code. The 2D neutron-transport equation in cylindrical (ρ − z) geometry was considered for 330 neutron energy groups in the sD{sub 2}. The 2D balance equation for UCN and CN was solved using simulated CN flux as boundary value. The UCN source dimensions were calculated for the development of the next UCN source. In the optimal condition, the UCN flux and the UCN production rate (averaged over the sD{sub 2} volume) equal to 6.79 × 10{sup 6} cm{sup −2}s{sup −1} and 2.20 ×10{sup 5} cm{sup −3}s{sup −1}, respectively.
Johnson, J.O.
2000-10-23
The Department of Energy (DOE) has given the Spallation Neutron Source (SNS) project approval to begin Title I design of the proposed facility to be built at Oak Ridge National Laboratory (ORNL) and construction is scheduled to commence in FY01 . The SNS initially will consist of an accelerator system capable of delivering an {approximately}0.5 microsecond pulse of 1 GeV protons, at a 60 Hz frequency, with 1 MW of beam power, into a single target station. The SNS will eventually be upgraded to a 2 MW facility with two target stations (a 60 Hz station and a 10 Hz station). The radiation transport analysis, which includes the neutronic, shielding, activation, and safety analyses, is critical to the design of an intense high-energy accelerator facility like the proposed SNS, and the Monte Carlo method is the cornerstone of the radiation transport analyses.
D. Scott Lucas; D. S. Lucas
2005-09-01
An LDRD (Laboratory Directed Research and Development) project is underway at the Idaho National Laboratory (INL) to apply the three-dimensional multi-group deterministic neutron transport code (Attila®) to criticality, flux and depletion calculations of the Advanced Test Reactor (ATR). This paper discusses the development of Attila models for ATR, capabilities of Attila, the generation and use of different cross-section libraries, and comparisons to ATR data, MCNP, MCNPX and future applications.
Brittle damage models in DYNA2D
Faux, D.R.
1997-09-01
DYNA2D is an explicit Lagrangian finite element code used to model dynamic events where stress wave interactions influence the overall response of the system. DYNA2D is often used to model penetration problems involving ductile-to-ductile impacts; however, with the advent of the use of ceramics in the armor-anti-armor community and the need to model damage to laser optics components, good brittle damage models are now needed in DYNA2D. This report will detail the implementation of four brittle damage models in DYNA2D, three scalar damage models and one tensor damage model. These new brittle damage models are then used to predict experimental results from three distinctly different glass damage problems.
Ginsparg, P.
1991-01-01
These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.
Ginsparg, P.
1991-12-31
These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.
2D electronic materials for army applications
NASA Astrophysics Data System (ADS)
O'Regan, Terrance; Perconti, Philip
2015-05-01
The record electronic properties achieved in monolayer graphene and related 2D materials such as molybdenum disulfide and hexagonal boron nitride show promise for revolutionary high-speed and low-power electronic devices. Heterogeneous 2D-stacked materials may create enabling technology for future communication and computation applications to meet soldier requirements. For instance, transparent, flexible and even wearable systems may become feasible. With soldier and squad level electronic power demands increasing, the Army is committed to developing and harnessing graphene-like 2D materials for compact low size-weight-and-power-cost (SWAP-C) systems. This paper will review developments in 2D electronic materials at the Army Research Laboratory over the last five years and discuss directions for future army applications.
2-d Finite Element Code Postprocessor
1996-07-15
ORION is an interactive program that serves as a postprocessor for the analysis programs NIKE2D, DYNA2D, TOPAZ2D, and CHEMICAL TOPAZ2D. ORION reads binary plot files generated by the two-dimensional finite element codes currently used by the Methods Development Group at LLNL. Contour and color fringe plots of a large number of quantities may be displayed on meshes consisting of triangular and quadrilateral elements. ORION can compute strain measures, interface pressures along slide lines, reaction forcesmore » along constrained boundaries, and momentum. ORION has been applied to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.« less
Chemical Approaches to 2D Materials.
Samorì, Paolo; Palermo, Vincenzo; Feng, Xinliang
2016-08-01
Chemistry plays an ever-increasing role in the production, functionalization, processing and applications of graphene and other 2D materials. This special issue highlights a selection of enlightening chemical approaches to 2D materials, which nicely reflect the breadth of the field and convey the excitement of the individuals involved in it, who are trying to translate graphene and related materials from the laboratory into a real, high-impact technology. PMID:27478083
Extended 2D generalized dilaton gravity theories
NASA Astrophysics Data System (ADS)
de Mello, R. O.
2008-09-01
We show that an anomaly-free description of matter in (1+1) dimensions requires a deformation of the 2D relativity principle, which introduces a non-trivial centre in the 2D Poincaré algebra. Then we work out the reduced phase space of the anomaly-free 2D relativistic particle, in order to show that it lives in a noncommutative 2D Minkowski space. Moreover, we build a Gaussian wave packet to show that a Planck length is well defined in two dimensions. In order to provide a gravitational interpretation for this noncommutativity, we propose to extend the usual 2D generalized dilaton gravity models by a specific Maxwell component, which guages the extra symmetry associated with the centre of the 2D Poincaré algebra. In addition, we show that this extension is a high energy correction to the unextended dilaton theories that can affect the topology of spacetime. Further, we couple a test particle to the general extended dilaton models with the purpose of showing that they predict a noncommutativity in curved spacetime, which is locally described by a Moyal star product in the low energy limit. We also conjecture a probable generalization of this result, which provides strong evidence that the noncommutativity is described by a certain star product which is not of the Moyal type at high energies. Finally, we prove that the extended dilaton theories can be formulated as Poisson Sigma models based on a nonlinear deformation of the extended Poincaré algebra.
Uranium Neutron Capture Gamma Cascade Generation and Transport Simulation for Capture Tank Response
NASA Astrophysics Data System (ADS)
Rosener, Thomas Jay
1992-01-01
A computer analysis has been performed to evaluate the energy dependent response of a capture tank to the gamma-ray cascades emitted from excited ^ {239}U. The GAMINT code was developed to simulate the decay of the ^{239 }U nucleus, formed in the ^{238}U(n,gamma)^{239 }U reaction, in order to provide the source spectrum for the complete analysis of the capture tank efficiency. This model determines the energies of the gamma-ray cascades, the order of emission of the gamma rays in a cascade, and the gamma-ray multiplicities by Monte Carlo techniques. A gamma-ray emission spectrum for the excited ^{239}U nucleus is generated. In the GAMINT code, known level data for ^{239}U is used below 1 MeV. A statistical approach based on the back-shifted Fermi gas model is used for the continuum level density. A single -particle model description for transition rates, with hindrance factors applied, is used to determine the gamma ray transition probabilities. Internal conversion probabilities are determined and the inclusion of this competing process suppresses the low energy portion of the gamma spectrum. A capture tank responds to the combined effect of the gamma rays of various energies from a cascade, after being transported through the material between the sample and the capture tank. Examined is the energy deposition, in a capture tank, by the cascades generated from resonant and off-resonant capture in a ^{238 }U sample. Internal conversion has a negligible effect on the average cascade energy deposited in the tank. Off -resonant (volumetric) capture deposits, on the average, less energy than resonant (surface) capture in the capture tank as a result of self-shielding of the gamma rays in the capture sample.
Spatial homogenization methods for pin-by-pin neutron transport calculations
NASA Astrophysics Data System (ADS)
Kozlowski, Tomasz
For practical reactor core applications low-order transport approximations such as SP3 have been shown to provide sufficient accuracy for both static and transient calculations with considerably less computational expense than the discrete ordinate or the full spherical harmonics methods. These methods have been applied in several core simulators where homogenization was performed at the level of the pin cell. One of the principal problems has been to recover the error introduced by pin-cell homogenization. Two basic approaches to treat pin-cell homogenization error have been proposed: Superhomogenization (SPH) factors and Pin-Cell Discontinuity Factors (PDF). These methods are based on well established Equivalence Theory and Generalized Equivalence Theory to generate appropriate group constants. These methods are able to treat all sources of error together, allowing even few-group diffusion with one mesh per cell to reproduce the reference solution. A detailed investigation and consistent comparison of both homogenization techniques showed potential of PDF approach to improve accuracy of core calculation, but also reveal its limitation. In principle, the method is applicable only for the boundary conditions at which it was created, i.e. for boundary conditions considered during the homogenization process---normally zero current. Therefore, there exists a need to improve this method, making it more general and environment independent. The goal of proposed general homogenization technique is to create a function that is able to correctly predict the appropriate correction factor with only homogeneous information available, i.e. a function based on heterogeneous solution that could approximate PDFs using homogeneous solution. It has been shown that the PDF can be well approximated by least-square polynomial fit of non-dimensional heterogeneous solution and later used for PDF prediction using homogeneous solution. This shows a promise for PDF prediction for off
Burns, Kimberly A.
2009-08-01
The accurate and efficient simulation of coupled neutron-photon problems is necessary for several important radiation detection applications. Examples include the detection of nuclear threats concealed in cargo containers and prompt gamma neutron activation analysis for nondestructive determination of elemental composition of unknown samples.
Thermal conductivity measurements in a 2D Yukawa system
NASA Astrophysics Data System (ADS)
Nosenko, V.; Ivlev, A.; Zhdanov, S.; Morfill, G.; Goree, J.; Piel, A.
2007-03-01
Thermal conductivity was measured for a 2D Yukawa system. First, we formed a monolayer suspension of microspheres in a plasma, i.e., a dusty plasma, which is like a colloidal suspension, but with an extremely low volume fraction and a partially-ionized rarefied gas instead of solvent. In the absence of manipulation, the suspension forms a 2D triangular lattice. To melt this lattice and form a liquid, we used a laser-heating method. Two focused laser beams were moved rapidly around in the monolayer. The kinetic temperature of the particles increased with the laser power applied, and above a threshold a melting transition occurred. We used digital video microscopy for direct imaging and particle tracking. The spatial profiles of the particle kinetic temperature were calculated. Using the heat transport equation with an additional term to account for the energy dissipation due to the gas drag, we analyzed the temperature distribution to derive the thermal conductivity.
NASA Technical Reports Server (NTRS)
Olinto, Angela V.; Haensel, Pawel; Frieman, Joshua A.
1991-01-01
The effects are studied of H-dibaryons on the structure of neutron stars. It was found that H particles could be present in neutron stars for a wide range of dibaryon masses. The appearance of dibaryons softens the equations of state, lowers the maximum neutron star mass, and affects the transport properties of dense matter. The parameter space is constrained for dibaryons by requiring that a 1.44 solar mass neutron star be gravitationally stable.
Half-metallicity in 2D organometallic honeycomb frameworks.
Sun, Hao; Li, Bin; Zhao, Jin
2016-10-26
Half-metallic materials with a high Curie temperature (T C) have many potential applications in spintronics. Magnetic metal free two-dimensional (2D) half-metallic materials with a honeycomb structure contain graphene-like Dirac bands with π orbitals and show excellent aspects in transport properties. In this article, by investigating a series of 2D organometallic frameworks with a honeycomb structure using first principles calculations, we study the origin of forming half-metallicity in this kind of 2D organometallic framework. Our analysis shows that charge transfer and covalent bonding are two crucial factors in the formation of half-metallicity in organometallic frameworks. (i) Sufficient charge transfer from metal atoms to the molecules is essential to form the magnetic centers. (ii) These magnetic centers need to be connected through covalent bonding, which guarantee the strong ferromagnetic (FM) coupling. As examples, the organometallic frameworks composed by (1,3,5)-benzenetricarbonitrile (TCB) molecules with noble metals (Au, Ag, Cu) show half-metallic properties with T C as high as 325 K. In these organometallic frameworks, the strong electronegative cyano-groups (CN groups) drive the charge transfer from metal atoms to the TCB molecules, forming the local magnetic centers. These magnetic centers experience strong FM coupling through the d-p covalent bonding. We propose that most of the 2D organometallic frameworks composed by molecule-CN-noble metal honeycomb structures contain similar half metallicity. This is verified by replacing TCB molecules with other organic molecules. Although the TCB-noble metal organometallic framework has not yet been synthesized, we believe the development of synthesizing techniques and facility will enable the realization of them. Our study provides new insight into the 2D half-metallic material design for the potential applications in nanotechnology. PMID:27541575
2D numerical modelling of meandering channel formation
NASA Astrophysics Data System (ADS)
XIAO, Y.; ZHOU, G.; YANG, F. S.
2016-03-01
A 2D depth-averaged model for hydrodynamic sediment transport and river morphological adjustment was established. The sediment transport submodel takes into account the influence of non-uniform sediment with bed surface armoring and considers the impact of secondary flow in the direction of bed-load transport and transverse slope of the river bed. The bank erosion submodel incorporates a simple simulation method for updating bank geometry during either degradational or aggradational bed evolution. Comparison of the results obtained by the extended model with experimental and field data, and numerical predictions validate that the proposed model can simulate grain sorting in river bends and duplicate the characteristics of meandering river and its development. The results illustrate that by using its control factors, the improved numerical model can be applied to simulate channel evolution under different scenarios and improve understanding of patterning processes.
Optical modulators with 2D layered materials
NASA Astrophysics Data System (ADS)
Sun, Zhipei; Martinez, Amos; Wang, Feng
2016-04-01
Light modulation is an essential operation in photonics and optoelectronics. With existing and emerging technologies increasingly demanding compact, efficient, fast and broadband optical modulators, high-performance light modulation solutions are becoming indispensable. The recent realization that 2D layered materials could modulate light with superior performance has prompted intense research and significant advances, paving the way for realistic applications. In this Review, we cover the state of the art of optical modulators based on 2D materials, including graphene, transition metal dichalcogenides and black phosphorus. We discuss recent advances employing hybrid structures, such as 2D heterostructures, plasmonic structures, and silicon and fibre integrated structures. We also take a look at the future perspectives and discuss the potential of yet relatively unexplored mechanisms, such as magneto-optic and acousto-optic modulation.
Large Area Synthesis of 2D Materials
NASA Astrophysics Data System (ADS)
Vogel, Eric
Transition metal dichalcogenides (TMDs) have generated significant interest for numerous applications including sensors, flexible electronics, heterostructures and optoelectronics due to their interesting, thickness-dependent properties. Despite recent progress, the synthesis of high-quality and highly uniform TMDs on a large scale is still a challenge. In this talk, synthesis routes for WSe2 and MoS2 that achieve monolayer thickness uniformity across large area substrates with electrical properties equivalent to geological crystals will be described. Controlled doping of 2D semiconductors is also critically required. However, methods established for conventional semiconductors, such as ion implantation, are not easily applicable to 2D materials because of their atomically thin structure. Redox-active molecular dopants will be demonstrated which provide large changes in carrier density and workfunction through the choice of dopant, treatment time, and the solution concentration. Finally, several applications of these large-area, uniform 2D materials will be described including heterostructures, biosensors and strain sensors.
2D microwave imaging reflectometer electronics
Spear, A. G.; Domier, C. W. Hu, X.; Muscatello, C. M.; Ren, X.; Luhmann, N. C.; Tobias, B. J.
2014-11-15
A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.
2D microwave imaging reflectometer electronics
NASA Astrophysics Data System (ADS)
Spear, A. G.; Domier, C. W.; Hu, X.; Muscatello, C. M.; Ren, X.; Tobias, B. J.; Luhmann, N. C.
2014-11-01
A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.
2D microwave imaging reflectometer electronics.
Spear, A G; Domier, C W; Hu, X; Muscatello, C M; Ren, X; Tobias, B J; Luhmann, N C
2014-11-01
A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program. PMID:25430247
2D-Crystal-Based Functional Inks.
Bonaccorso, Francesco; Bartolotta, Antonino; Coleman, Jonathan N; Backes, Claudia
2016-08-01
The possibility to produce and process graphene, related 2D crystals, and heterostructures in the liquid phase makes them promising materials for an ever-growing class of applications as composite materials, sensors, in flexible optoelectronics, and energy storage and conversion. In particular, the ability to formulate functional inks with on-demand rheological and morphological properties, i.e., lateral size and thickness of the dispersed 2D crystals, is a step forward toward the development of industrial-scale, reliable, inexpensive printing/coating processes, a boost for the full exploitation of such nanomaterials. Here, the exfoliation strategies of graphite and other layered crystals are reviewed, along with the advances in the sorting of lateral size and thickness of the exfoliated sheets together with the formulation of functional inks and the current development of printing/coating processes of interest for the realization of 2D-crystal-based devices. PMID:27273554
The 2D lingual appliance system.
Cacciafesta, Vittorio
2013-09-01
The two-dimensional (2D) lingual bracket system represents a valuable treatment option for adult patients seeking a completely invisible orthodontic appliance. The ease of direct or simplified indirect bonding of 2D lingual brackets in combination with low friction mechanics makes it possible to achieve a good functional and aesthetic occlusion, even in the presence of a severe malocclusion. The use of a self-ligating bracket significantly reduces chair-side time for the orthodontist, and the low-profile bracket design greatly improves patient comfort. PMID:24005953
Inkjet printing of 2D layered materials.
Li, Jiantong; Lemme, Max C; Östling, Mikael
2014-11-10
Inkjet printing of 2D layered materials, such as graphene and MoS2, has attracted great interests for emerging electronics. However, incompatible rheology, low concentration, severe aggregation and toxicity of solvents constitute critical challenges which hamper the manufacturing efficiency and product quality. Here, we introduce a simple and general technology concept (distillation-assisted solvent exchange) to efficiently overcome these challenges. By implementing the concept, we have demonstrated excellent jetting performance, ideal printing patterns and a variety of promising applications for inkjet printing of 2D layered materials. PMID:25169938
Measurement of 2D birefringence distribution
NASA Astrophysics Data System (ADS)
Noguchi, Masato; Ishikawa, Tsuyoshi; Ohno, Masahiro; Tachihara, Satoru
1992-10-01
A new measuring method of 2-D birefringence distribution has been developed. It has not been an easy job to get a birefringence distribution in an optical element with conventional ellipsometry because of its lack of scanning means. Finding an analogy between the rotating analyzer method in ellipsometry and the phase-shifting method in recently developed digital interferometry, we have applied the phase-shifting algorithm to ellipsometry, and have developed a new method that makes the measurement of 2-D birefringence distribution easy and possible. The system contains few moving parts, assuring reliability, and measures a large area of a sample at one time, making the measuring time very short.
NASA Astrophysics Data System (ADS)
Joung Lim, Mi; Maeng, Young Jae; Fero, Arnold H.; Anderson, Stanwood L.
2016-02-01
The 2D/1D synthesis methodology has been used to calculate the fast neutron (E > 1.0 MeV) exposure to the beltline region of the reactor pressure vessel. This method uses the DORT 3.1 discrete ordinates code and the BUGLE-96 cross-section library based on ENDF/B-VI. RAPTOR-M3G (RApid Parallel Transport Of Radiation-Multiple 3D Geometries) which performs full 3D calculations was developed and is based on domain decomposition algorithms, where the spatial and angular domains are allocated and processed on multi-processor computer architecture. As compared to traditional single-processor applications, this approach reduces the computational load as well as the memory requirement per processor. Both methods are applied to surveillance test results for the Korea Standard Nuclear Plant (KSNP)-OPR (Optimized Power Reactor) 1000 MW. The objective of this paper is to compare the results of the KSNP surveillance program between 2D/1D synthesis and RAPTOR-M3G. Each operating KSNP has a reactor vessel surveillance program consisting of six surveillance capsules located between the core and the reactor vessel in the downcomer region near the reactor vessel wall. In addition to the In-Vessel surveillance program, an Ex-Vessel Neutron Dosimetry (EVND) program has been implemented. In order to estimate surveillance test results, cycle-specific forward transport calculations were performed by 2D/1D synthesis and by RAPTOR-M3G. The ratio between measured and calculated (M/C) reaction rates will be discussed. The current plan is to install an EVND system in all of the Korea PWRs including the new reactor type, APR (Advanced Power Reactor) 1400 MW. This work will play an important role in establishing a KSNP-specific database of surveillance test results and will employ RAPTOR-M3G for surveillance dosimetry location as well as positions in the KSNP reactor vessel.
Parallel stitching of 2D materials
Ling, Xi; Wu, Lijun; Lin, Yuxuan; Ma, Qiong; Wang, Ziqiang; Song, Yi; Yu, Lili; Huang, Shengxi; Fang, Wenjing; Zhang, Xu; et al
2016-01-27
Diverse parallel stitched 2D heterostructures, including metal–semiconductor, semiconductor–semiconductor, and insulator–semiconductor, are synthesized directly through selective “sowing” of aromatic molecules as the seeds in the chemical vapor deposition (CVD) method. Lastly, the methodology enables the large-scale fabrication of lateral heterostructures, which offers tremendous potential for its application in integrated circuits.
Parallel Stitching of 2D Materials.
Ling, Xi; Lin, Yuxuan; Ma, Qiong; Wang, Ziqiang; Song, Yi; Yu, Lili; Huang, Shengxi; Fang, Wenjing; Zhang, Xu; Hsu, Allen L; Bie, Yaqing; Lee, Yi-Hsien; Zhu, Yimei; Wu, Lijun; Li, Ju; Jarillo-Herrero, Pablo; Dresselhaus, Mildred; Palacios, Tomás; Kong, Jing
2016-03-01
Diverse parallel stitched 2D heterostructures, including metal-semiconductor, semiconductor-semiconductor, and insulator-semiconductor, are synthesized directly through selective "sowing" of aromatic molecules as the seeds in the chemical vapor deposition (CVD) method. The methodology enables the large-scale fabrication of lateral heterostructures, which offers tremendous potential for its application in integrated circuits. PMID:26813882
Baby universes in 2d quantum gravity
NASA Astrophysics Data System (ADS)
Ambjørn, Jan; Jain, Sanjay; Thorleifsson, Gudmar
1993-06-01
We investigate the fractal structure of 2d quantum gravity, both for pure gravity and for gravity coupled to multiple gaussian fields and for gravity coupled to Ising spins. The roughness of the surfaces is described in terms of baby universes and using numerical simulations we measure their distribution which is related to the string susceptibility exponent γstring.
Quantum Oscillations in an Interfacial 2D Electron Gas.
Zhang, Bingop; Lu, Ping; Liu, Henan; Lin, Jiao; Ye, Zhenyu; Jaime, Marcelo; Balakirev, Fedor F.; Yuan, Huiqiu; Wu, Huizhen; Pan, Wei; Zhang, Yong
2016-01-01
Recently, it has been predicted that topological crystalline insulators (TCIs) may exist in SnTe and Pb_{1-x}Sn_{x}Te thin films [1]. To date, most studies on TCIs were carried out either in bulk crystals or thin films, and no research activity has been explored in heterostructures. We present here the results on electronic transport properties of the 2D electron gas (2DEG) realized at the interfaces of PbTe/ CdTe (111) heterostructures. Evidence of topological state in this interfacial 2DEG was observed.
Characterization of the high-energy neutron beam of the PRISMA beamline using a diamond detector
NASA Astrophysics Data System (ADS)
Cazzaniga, C.; Frost, C. D.; Minniti, T.; Schooneveld, E.; Perelli Cippo, E.; Tardocchi, M.; Rebai, M.; Gorini, G.
2016-07-01
The high-energy neutron component (En > 10 MeV) of the neutron spectrum of PRISMA, a beam-line at the ISIS spallation source, has been characterized for the first time. Neutron measurements using a Single-crystal Diamond Detector at a short-pulse source are obtained by a combination of pulse height and time of flight analysis. An XY scan provides a 2D map of the high-energy neutron beam which has a diameter of about 40 mm. The high neutron flux, that has been found to be (3.8 ± 0.7) · 105 cm‑2s‑1 for En > 10 MeV in the centre, opens up for a possible application of the beam-line as a high-energy neutron irradiation position. Results are of interest for the development of the ChipIR beam-line, which will feature an atmospheric-like neutron spectrum for chip irradiation experiment. Furthermore, these results demonstrate that diamond detectors can be used at spallation sources to investigate the transport of high-energy neutrons down instruments which is of interest in general to designers as high-energy neutrons are a source of background in thermal beamlines.
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. PMID:26861346
Rubinson, Kenneth A; Faraone, Antonio
2016-05-14
X-ray and neutron scattering have been used to provide insight into the structures of ionic solutions for over a century, but the probes have covered distances shorter than 8 Å. For the non-hydrolyzing salt SrI2 in aqueous solution, a locally ordered lattice of ions exists that scatters slow neutrons coherently down to at least 0.1 mol L(-1) concentration, where the measured average distance between scatterers is over 18 Å. To investigate the motions of these scatterers, coherent quasielastic neutron scattering (CQENS) data on D2O solutions with SrI2 at 1, 0.8, 0.6, and 0.4 mol L(-1) concentrations was obtained to provide an experimental measure of the diffusive transport rate for the motion between pairs of ions relative to each other. Because CQENS measures the motion of one ion relative to another, the frame of reference is centered on an ion, which is unique among all diffusion measurement methods. We call the measured quantity the pairwise diffusive transport rate Dp. In addition to this ion centered frame of reference, the diffusive transport rate can be measured as a function of the momentum transfer q, where q = (4π/λ)sin θ with a scattering angle of 2θ. Since q is related to the interion distance (d = 2π/q), for the experimental range 0.2 Å(-1)≤q≤ 1.0 Å(-1), Dp is, then, measured over interion distances from 40 Å to ≈6 Å. We find the measured diffusional transport rates increase with increasing distance between scatterers over the entire range covered and interpret this behavior to be caused by dynamic coupling among the ions. Within the model of Fickian diffusion, at the longer interionic distances Dp is greater than the Nernst-Hartley value for an infinitely dilute solution. For these nm-distance diffusional transport rates to conform with the lower, macroscopically measured diffusion coefficients, we propose that local, coordinated counter motion of at least pairs of ions is part of the transport process. PMID:27096293
NASA Technical Reports Server (NTRS)
Jordan, T. M.
1970-01-01
A description of the FASTER-III program for Monte Carlo Carlo calculation of photon and neutron transport in complex geometries is presented. Major revisions include the capability of calculating minimum weight shield configurations for primary and secondary radiation and optimal importance sampling parameters. The program description includes a users manual describing the preparation of input data cards, the printout from a sample problem including the data card images, definitions of Fortran variables, the program logic, and the control cards required to run on the IBM 7094, IBM 360, UNIVAC 1108 and CDC 6600 computers.
Report of the 1988 2-D Intercomparison Workshop, chapter 3
NASA Technical Reports Server (NTRS)
Jackman, Charles H.; Brasseur, Guy; Soloman, Susan; Guthrie, Paul D.; Garcia, Rolando; Yung, Yuk L.; Gray, Lesley J.; Tung, K. K.; Ko, Malcolm K. W.; Isaken, Ivar
1989-01-01
Several factors contribute to the errors encountered. With the exception of the line-by-line model, all of the models employ simplifying assumptions that place fundamental limits on their accuracy and range of validity. For example, all 2-D modeling groups use the diffusivity factor approximation. This approximation produces little error in tropospheric H2O and CO2 cooling rates, but can produce significant errors in CO2 and O3 cooling rates at the stratopause. All models suffer from fundamental uncertainties in shapes and strengths of spectral lines. Thermal flux algorithms being used in 2-D tracer tranport models produce cooling rates that differ by as much as 40 percent for the same input model atmosphere. Disagreements of this magnitude are important since the thermal cooling rates must be subtracted from the almost-equal solar heating rates to derive the net radiative heating rates and the 2-D model diabatic circulation. For much of the annual cycle, the net radiative heating rates are comparable in magnitude to the cooling rate differences described. Many of the models underestimate the cooling rates in the middle and lower stratosphere. The consequences of these errors for the net heating rates and the diabatic circulation will depend on their meridional structure, which was not tested here. Other models underestimate the cooling near 1 mbar. Suchs errors pose potential problems for future interactive ozone assessment studies, since they could produce artificially-high temperatures and increased O3 destruction at these levels. These concerns suggest that a great deal of work is needed to improve the performance of thermal cooling rate algorithms used in the 2-D tracer transport models.
VAM2D: Variably saturated analysis model in two dimensions
Huyakorn, P.S.; Kool, J.B.; Wu, Y.S. )
1991-10-01
This report documents a two-dimensional finite element model, VAM2D, developed to simulate water flow and solute transport in variably saturated porous media. Both flow and transport simulation can be handled concurrently or sequentially. The formulation of the governing equations and the numerical procedures used in the code are presented. The flow equation is approximated using the Galerkin finite element method. Nonlinear soil moisture characteristics and atmospheric boundary conditions (e.g., infiltration, evaporation and seepage face), are treated using Picard and Newton-Raphson iterations. Hysteresis effects and anisotropy in the unsaturated hydraulic conductivity can be taken into account if needed. The contaminant transport simulation can account for advection, hydrodynamic dispersion, linear equilibrium sorption, and first-order degradation. Transport of a single component or a multi-component decay chain can be handled. The transport equation is approximated using an upstream weighted residual method. Several test problems are presented to verify the code and demonstrate its utility. These problems range from simple one-dimensional to complex two-dimensional and axisymmetric problems. This document has been produced as a user's manual. It contains detailed information on the code structure along with instructions for input data preparation and sample input and printed output for selected test problems. Also included are instructions for job set up and restarting procedures. 44 refs., 54 figs., 24 tabs.
Topological phase transition in 2D porous media flows
NASA Astrophysics Data System (ADS)
Waisbord, Nicolas; Stoop, Norbert; Kantsler, Vasily; Guasto, Jeffrey S.; Dunkel, Jorn; Guasto Team; Dunkel Team; Kantsler Team
2015-11-01
Since the establishment of Darcy's law, analysis of porous-media flows has focused primarily on linking macroscopic transport properties, such as mean flow rate and dispersion, to the pore statistics of the material matrix. Despite intense efforts to understand the fluid velocity statistics from the porous-media structure, a qualitative and quantitative connection remains elusive. Here, we combine precisely controlled experiments with theory to quantify how geometric disorder in the matrix affects the flow statistics and transport in a quasi-2D microfluidic channel. Experimentally measured velocity fields for a range of different microstructure configurations are found to be in excellent agreement with large-scale numerical simulations. By successively increasing the matrix disorder, we study the transition from periodic flow structures to transport networks consisting of extended high-velocity channels. Morse-Smale complex analysis of the flow patterns reveals a topological phase transition that is linked to a qualitative change in the physical transport properties. This work demonstrates that topological flow analysis provides a mathematically well-defined, broadly applicable framework for understanding and quantifying fluid transport in complex geometries.
Interpretive 2-D treatment of scrape-off-layer plasmas
Umansky, M.; Allen, A.; Daughton, W.
1996-12-31
The width of the scrape-off-layer in a tokamak is determined by cross field transport. In Alcator C-mod the plasma parameters in the scrape-off-layer are measured at upstream and divertor plate locations. We solve a 2-D scrape-off-layer heat conduction equation in the flux geometry (as determined by EFIT) of the C-mod experiment. Bolometric measurements are utilized for the radiative loss term. We use the end wall probe measurements of electron temperature as a boundary condition and the fast scanning probe measurements of upstream temperature are treated as constraints to determine the cross field transport and thermal conductivity. Results are compared with 1-D onion-skin-model predictions.
2-D soft x-ray arrays in the EAST.
Chen, Kaiyun; Xu, Liqing; Hu, Liqun; Duan, Yanmin; Li, Xueqin; Yuan, Yi; Mao, Songtao; Sheng, Xiuli; Zhao, Jinlong
2016-06-01
A high spatial and temporal resolution soft x-ray (SXR) imaging diagnostic has been installed in EAST for the study of magnetohydrodynamics activities and core high-Z impurity transport. Up to 122 lines of sight view the poloidal plasma from three directions (two up-down symmetrical horizontal arrays and one vertical array), which renders the diagnostic able to provide detailed tomographic reconstructions under various conditions. Fourier-Bessel method based on flux coordinates was employed for 2-D SXR tomographic reconstruction. Examples of several events measured by SXR diagnostic in EAST are shown, namely the crash patterns of sawtooth, periodical burst of edge localized modes, and the transport of high-Z intrinsic impurities. PMID:27370451
2-D soft x-ray arrays in the EAST
NASA Astrophysics Data System (ADS)
Chen, Kaiyun; Xu, Liqing; Hu, Liqun; Duan, Yanmin; Li, Xueqin; Yuan, Yi; Mao, Songtao; Sheng, Xiuli; Zhao, Jinlong
2016-06-01
A high spatial and temporal resolution soft x-ray (SXR) imaging diagnostic has been installed in EAST for the study of magnetohydrodynamics activities and core high-Z impurity transport. Up to 122 lines of sight view the poloidal plasma from three directions (two up-down symmetrical horizontal arrays and one vertical array), which renders the diagnostic able to provide detailed tomographic reconstructions under various conditions. Fourier-Bessel method based on flux coordinates was employed for 2-D SXR tomographic reconstruction. Examples of several events measured by SXR diagnostic in EAST are shown, namely the crash patterns of sawtooth, periodical burst of edge localized modes, and the transport of high-Z intrinsic impurities.
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
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
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
Explicit 2-D Hydrodynamic FEM Program
1996-08-07
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. Themore » 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.« less
Schottky diodes from 2D germanane
NASA Astrophysics Data System (ADS)
Sahoo, Nanda Gopal; Esteves, Richard J.; Punetha, Vinay Deep; Pestov, Dmitry; Arachchige, Indika U.; McLeskey, James T.
2016-07-01
We report on the fabrication and characterization of a Schottky diode made using 2D germanane (hydrogenated germanene). When compared to germanium, the 2D structure has higher electron mobility, an optimal band-gap, and exceptional stability making germanane an outstanding candidate for a variety of opto-electronic devices. One-atom-thick sheets of hydrogenated puckered germanium atoms have been synthesized from a CaGe2 framework via intercalation and characterized by XRD, Raman, and FTIR techniques. The material was then used to fabricate Schottky diodes by suspending the germanane in benzonitrile and drop-casting it onto interdigitated metal electrodes. The devices demonstrate significant rectifying behavior and the outstanding potential of this material.
Wongthai, Printip; Hagiwara, Kohei; Miyoshi, Yurika; Wiriyasermkul, Pattama; Wei, Ling; Ohgaki, Ryuichi; Kato, Itsuro; Hamase, Kenji; Nagamori, Shushi; Kanai, Yoshikatsu
2015-01-01
The efficacy of boron neutron capture therapy relies on the selective delivery of boron carriers to malignant cells. p-Boronophenylalanine (BPA), a boron delivery agent, has been proposed to be localized to cells through transporter-mediated mechanisms. In this study, we screened aromatic amino acid transporters to identify BPA transporters. Human aromatic amino acid transporters were functionally expressed in Xenopus oocytes and examined for BPA uptake and kinetic parameters. The roles of the transporters in BPA uptake were characterized in cancer cell lines. For the quantitative assessment of BPA uptake, HPLC was used throughout the study. Among aromatic amino acid transporters, ATB0,+, LAT1 and LAT2 were found to transport BPA with Km values of 137.4 ± 11.7, 20.3 ± 0.8 and 88.3 ± 5.6 μM, respectively. Uptake experiments in cancer cell lines revealed that the LAT1 protein amount was the major determinant of BPA uptake at 100 μM, whereas the contribution of ATB0,+ became significant at 1000 μM, accounting for 20–25% of the total BPA uptake in MCF-7 breast cancer cells. ATB0,+, LAT1 and LAT2 transport BPA at affinities comparable with their endogenous substrates, suggesting that they could mediate effective BPA uptake in vivo. The high and low affinities of LAT1 and ATB0,+, respectively, differentiate their roles in BPA uptake. ATB0,+, as well as LAT1, could contribute significantly to the tumor accumulation of BPA at clinical dose. PMID:25580517
Layer Engineering of 2D Semiconductor Junctions.
He, Yongmin; Sobhani, Ali; Lei, Sidong; Zhang, Zhuhua; Gong, Yongji; Jin, Zehua; Zhou, Wu; Yang, Yingchao; Zhang, Yuan; Wang, Xifan; Yakobson, Boris; Vajtai, Robert; Halas, Naomi J; Li, Bo; Xie, Erqing; Ajayan, Pulickel
2016-07-01
A new concept for junction fabrication by connecting multiple regions with varying layer thicknesses, based on the thickness dependence, is demonstrated. This type of junction is only possible in super-thin-layered 2D materials, and exhibits similar characteristics as p-n junctions. Rectification and photovoltaic effects are observed in chemically homogeneous MoSe2 junctions between domains of different thicknesses. PMID:27136275
NASA Astrophysics Data System (ADS)
Smith, Greg; Lankshear, Allan
1998-07-01
2dF is a multi-object instrument mounted at prime focus at the AAT capable of spectroscopic analysis of 400 objects in a single 2 degree field. It also prepares a second 2 degree 400 object field while the first field is being observed. At its heart is a high precision robotic positioner that places individual fiber end magnetic buttons on one of two field plates. The button gripper is carried on orthogonal gantries powered by linear synchronous motors and contains a TV camera which precisely locates backlit buttons to allow placement in user defined locations to 10 (mu) accuracy. Fiducial points on both plates can also be observed by the camera to allow repeated checks on positioning accuracy. Field plates rotate to follow apparent sky rotation. The spectrographs both analyze light from the 200 observing fibers each and back- illuminate the 400 fibers being re-positioned during the observing run. The 2dF fiber position and spectrograph system is a large and complex instrument located at the prime focus of the Anglo Australian Telescope. The mechanical design has departed somewhat from the earlier concepts of Gray et al, but still reflects the audacity of those first ideas. The positioner is capable of positioning 400 fibers on a field plate while another 400 fibers on another plate are observing at the focus of the telescope and feeding the twin spectrographs. When first proposed it must have seemed like ingenuity unfettered by caution. Yet now it works, and works wonderfully well. 2dF is a system which functions as the result of the combined and coordinated efforts of the astronomers, the mechanical designers and tradespeople, the electronic designers, the programmers, the support staff at the telescope, and the manufacturing subcontractors. The mechanical design of the 2dF positioner and spectrographs was carried out by the mechanical engineering staff of the AAO and the majority of the manufacture was carried out in the AAO workshops.
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.
Compact 2-D graphical representation of DNA
NASA Astrophysics Data System (ADS)
Randić, Milan; Vračko, Marjan; Zupan, Jure; Novič, Marjana
2003-05-01
We present a novel 2-D graphical representation for DNA sequences which has an important advantage over the existing graphical representations of DNA in being very compact. It is based on: (1) use of binary labels for the four nucleic acid bases, and (2) use of the 'worm' curve as template on which binary codes are placed. The approach is illustrated on DNA sequences of the first exon of human β-globin and gorilla β-globin.
2D materials: Graphene and others
NASA Astrophysics Data System (ADS)
Bansal, Suneev Anil; Singh, Amrinder Pal; Kumar, Suresh
2016-05-01
Present report reviews the recent advancements in new atomically thick 2D materials. Materials covered in this review are Graphene, Silicene, Germanene, Boron Nitride (BN) and Transition metal chalcogenides (TMC). These materials show extraordinary mechanical, electronic and optical properties which make them suitable candidates for future applications. Apart from unique properties, tune-ability of highly desirable properties of these materials is also an important area to be emphasized on.
Mason, W.E.
1983-03-01
A set of finite element codes for the solution of nonlinear, two-dimensional (TACO2D) and three-dimensional (TACO3D) heat transfer problems. Performs linear and nonlinear analyses of both transient and steady state heat transfer problems. Has the capability to handle time or temperature dependent material properties. Materials may be either isotropic or orthotropic. A variety of time and temperature dependent boundary conditions and loadings are available including temperature, flux, convection, radiation, and internal heat generation.
FOREWORD: Neutron metrology Neutron metrology
NASA Astrophysics Data System (ADS)
Thomas, David J.; Nolte, Ralf; Gressier, Vincent
2011-12-01
industry, from the initial fuel enrichment and fabrication processes right through to storage or reprocessing, and neutron metrology is clearly important in this area. Neutron fields do, however, occur in other areas, for example where neutron sources are used in oil well logging and moisture measurements. They also occur around high energy accelerators, including photon linear accelerators used for cancer therapy, and are expected to be a more serious problem around the new hadron radiation therapy facilities. Roughly 50% of the cosmic ray doses experienced by fliers at the flight altitudes of commercial aircraft are due to neutrons. Current research on fusion presents neutron metrology with a whole new range of challenges because of the very high fluences expected. One of the most significant features of neutron fields is the very wide range of possible neutron energies. In the nuclear industry, for example, neutrons occur with energies from those of thermal neutrons at a few meV to the upper end of the fission spectrum at perhaps 10 MeV. For cosmic ray dosimetry the energy range extends into the GeV region. This enormous range sets a challenge for designing measuring devices and a parallel challenge of developing measurement standards for characterizing these devices. One of the major considerations when deciding on topics for this special issue was agreeing on what not to include. Modelling, i.e. the use of radiation transport codes, is now a very important aspect of neutron measurements. These calculations are vital for shielding and for instrument design; nevertheless, the topic has only been included here where it has a direct bearing on metrology and the development of standards. Neutron spectrometry is an increasingly important technique for unravelling some of the problems of dose equivalent measurements and for plasma diagnostics in fusion research. However, this topic is at least one step removed from primary metrology and so it was felt that it should not be
Magnetic gating of a 2D topological insulator.
Dang, Xiaoqian; Burton, J D; Tsymbal, Evgeny Y
2016-09-28
Deterministic control of transport properties through manipulation of spin states is one of the paradigms of spintronics. Topological insulators offer a new playground for exploring interesting spin-dependent phenomena. Here, we consider a ferromagnetic 'gate' representing a magnetic adatom coupled to the topologically protected edge state of a two-dimensional (2D) topological insulator to modulate the electron transmission of the edge state. Due to the locked spin and wave vector of the transport electrons the transmission across the magnetic gate depends on the mutual orientation of the adatom magnetic moment and the current. If the Fermi energy matches an exchange-split bound state of the adatom, the electron transmission can be blocked due to the full back scattering of the incident wave. This antiresonance behavior is controlled by the adatom magnetic moment orientation so that the transmission of the edge state can be changed from 1 to 0. Expanding this consideration to a ferromagnetic gate representing a 1D chain of atoms shows a possibility to control the spin-dependent current of a strip of a 2D topological insulator by magnetization orientation of the ferromagnetic gate. PMID:27437829
Magnetic gating of a 2D topological insulator
NASA Astrophysics Data System (ADS)
Dang, Xiaoqian; Burton, J. D.; Tsymbal, Evgeny Y.
2016-09-01
Deterministic control of transport properties through manipulation of spin states is one of the paradigms of spintronics. Topological insulators offer a new playground for exploring interesting spin-dependent phenomena. Here, we consider a ferromagnetic ‘gate’ representing a magnetic adatom coupled to the topologically protected edge state of a two-dimensional (2D) topological insulator to modulate the electron transmission of the edge state. Due to the locked spin and wave vector of the transport electrons the transmission across the magnetic gate depends on the mutual orientation of the adatom magnetic moment and the current. If the Fermi energy matches an exchange-split bound state of the adatom, the electron transmission can be blocked due to the full back scattering of the incident wave. This antiresonance behavior is controlled by the adatom magnetic moment orientation so that the transmission of the edge state can be changed from 1 to 0. Expanding this consideration to a ferromagnetic gate representing a 1D chain of atoms shows a possibility to control the spin-dependent current of a strip of a 2D topological insulator by magnetization orientation of the ferromagnetic gate.
Tomosynthesis imaging with 2D scanning trajectories
NASA Astrophysics Data System (ADS)
Khare, Kedar; Claus, Bernhard E. H.; Eberhard, Jeffrey W.
2011-03-01
Tomosynthesis imaging in chest radiography provides volumetric information with the potential for improved diagnostic value when compared to the standard AP or LAT projections. In this paper we explore the image quality benefits of 2D scanning trajectories when coupled with advanced image reconstruction approaches. It is intuitively clear that 2D trajectories provide projection data that is more complete in terms of Radon space filling, when compared with conventional tomosynthesis using a linearly scanned source. Incorporating this additional information for obtaining improved image quality is, however, not a straightforward problem. The typical tomosynthesis reconstruction algorithms are based on direct inversion methods e.g. Filtered Backprojection (FBP) or iterative algorithms that are variants of the Algebraic Reconstruction Technique (ART). The FBP approach is fast and provides high frequency details in the image but at the same time introduces streaking artifacts degrading the image quality. The iterative methods can reduce the image artifacts by using image priors but suffer from a slow convergence rate, thereby producing images lacking high frequency details. In this paper we propose using a fast converging optimal gradient iterative scheme that has advantages of both the FBP and iterative methods in that it produces images with high frequency details while reducing the image artifacts. We show that using favorable 2D scanning trajectories along with the proposed reconstruction method has the advantage of providing improved depth information for structures such as the spine and potentially producing images with more isotropic resolution.
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.
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. PMID:25602462
Zhu, Jinlong; Wang, Yonggang; Li, Shuai; Howard, John W; Neuefeind, Jörg; Ren, Yang; Wang, Hui; Liang, Chengdu; Yang, Wenge; Zou, Ruqiang; Jin, Changqing; Zhao, Yusheng
2016-06-20
Na-rich antiperovskites are recently developed solid electrolytes with enhanced sodium ionic conductivity and show promising functionality as a novel solid electrolyte in an all solid-state battery. In this work, the sodium ionic transport pathways of the parent compound Na3OBr, as well as the modified layered antiperovskite Na4OI2, were studied and compared through temperature-dependent neutron diffraction combined with the maximum entropy method. In the cubic Na3OBr antiperovskite, the nuclear density distribution maps at 500 K indicate that sodium ions hop within and among oxygen octahedra, and Br(-) ions are not involved. In the tetragonal Na4OI2 antiperovskite, Na ions, which connect octahedra in the ab plane, have the lowest activation energy barrier. The transport of sodium ions along the c axis is assisted by I(-) ions. PMID:27251879
2D superconductivity by ionic gating
NASA Astrophysics Data System (ADS)
Iwasa, Yoshi
2D superconductivity is attracting a renewed interest due to the discoveries of new highly crystalline 2D superconductors in the past decade. Superconductivity at the oxide interfaces triggered by LaAlO3/SrTiO3 has become one of the promising routes for creation of new 2D superconductors. Also, the MBE grown metallic monolayers including FeSe are also offering a new platform of 2D superconductors. In the last two years, there appear a variety of monolayer/bilayer superconductors fabricated by CVD or mechanical exfoliation. Among these, electric field induced superconductivity by electric double layer transistor (EDLT) is a unique platform of 2D superconductivity, because of its ability of high density charge accumulation, and also because of the versatility in terms of materials, stemming from oxides to organics and layered chalcogenides. In this presentation, the following issues of electric filed induced superconductivity will be addressed; (1) Tunable carrier density, (2) Weak pinning, (3) Absence of inversion symmetry. (1) Since the sheet carrier density is quasi-continuously tunable from 0 to the order of 1014 cm-2, one is able to establish an electronic phase diagram of superconductivity, which will be compared with that of bulk superconductors. (2) The thickness of superconductivity can be estimated as 2 - 10 nm, dependent on materials, and is much smaller than the in-plane coherence length. Such a thin but low resistance at normal state results in extremely weak pinning beyond the dirty Boson model in the amorphous metallic films. (3) Due to the electric filed, the inversion symmetry is inherently broken in EDLT. This feature appears in the enhancement of Pauli limit of the upper critical field for the in-plane magnetic fields. In transition metal dichalcogenide with a substantial spin-orbit interactions, we were able to confirm the stabilization of Cooper pair due to its spin-valley locking. This work has been supported by Grant-in-Aid for Specially
FOREWORD: Neutron metrology Neutron metrology
NASA Astrophysics Data System (ADS)
Thomas, David J.; Nolte, Ralf; Gressier, Vincent
2011-12-01
industry, from the initial fuel enrichment and fabrication processes right through to storage or reprocessing, and neutron metrology is clearly important in this area. Neutron fields do, however, occur in other areas, for example where neutron sources are used in oil well logging and moisture measurements. They also occur around high energy accelerators, including photon linear accelerators used for cancer therapy, and are expected to be a more serious problem around the new hadron radiation therapy facilities. Roughly 50% of the cosmic ray doses experienced by fliers at the flight altitudes of commercial aircraft are due to neutrons. Current research on fusion presents neutron metrology with a whole new range of challenges because of the very high fluences expected. One of the most significant features of neutron fields is the very wide range of possible neutron energies. In the nuclear industry, for example, neutrons occur with energies from those of thermal neutrons at a few meV to the upper end of the fission spectrum at perhaps 10 MeV. For cosmic ray dosimetry the energy range extends into the GeV region. This enormous range sets a challenge for designing measuring devices and a parallel challenge of developing measurement standards for characterizing these devices. One of the major considerations when deciding on topics for this special issue was agreeing on what not to include. Modelling, i.e. the use of radiation transport codes, is now a very important aspect of neutron measurements. These calculations are vital for shielding and for instrument design; nevertheless, the topic has only been included here where it has a direct bearing on metrology and the development of standards. Neutron spectrometry is an increasingly important technique for unravelling some of the problems of dose equivalent measurements and for plasma diagnostics in fusion research. However, this topic is at least one step removed from primary metrology and so it was felt that it should not be
GBL-2D Version 1.0: a 2D geometry boolean library.
McBride, Cory L. (Elemental Technologies, American Fort, UT); Schmidt, Rodney Cannon; Yarberry, Victor R.; Meyers, Ray J.
2006-11-01
This report describes version 1.0 of GBL-2D, a geometric Boolean library for 2D objects. The library is written in C++ and consists of a set of classes and routines. The classes primarily represent geometric data and relationships. Classes are provided for 2D points, lines, arcs, edge uses, loops, surfaces and mask sets. The routines contain algorithms for geometric Boolean operations and utility functions. Routines are provided that incorporate the Boolean operations: Union(OR), XOR, Intersection and Difference. A variety of additional analytical geometry routines and routines for importing and exporting the data in various file formats are also provided. The GBL-2D library was originally developed as a geometric modeling engine for use with a separate software tool, called SummitView [1], that manipulates the 2D mask sets created by designers of Micro-Electro-Mechanical Systems (MEMS). However, many other practical applications for this type of software can be envisioned because the need to perform 2D Boolean operations can arise in many contexts.
Interparticle Attraction in 2D Complex Plasmas
NASA Astrophysics Data System (ADS)
Kompaneets, Roman; Morfill, Gregor E.; Ivlev, Alexei V.
2016-03-01
Complex (dusty) plasmas allow experimental studies of various physical processes occurring in classical liquids and solids by directly observing individual microparticles. A major problem is that the interaction between microparticles is generally not molecularlike. In this Letter, we propose how to achieve a molecularlike interaction potential in laboratory 2D complex plasmas. We argue that this principal aim can be achieved by using relatively small microparticles and properly adjusting discharge parameters. If experimentally confirmed, this will make it possible to employ complex plasmas as a model system with an interaction potential resembling that of conventional liquids.
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.
ENERGY LANDSCAPE OF 2D FLUID FORMS
Y. JIANG; ET AL
2000-04-01
The equilibrium states of 2D non-coarsening fluid foams, which consist of bubbles with fixed areas, correspond to local minima of the total perimeter. (1) The authors find an approximate value of the global minimum, and determine directly from an image how far a foam is from its ground state. (2) For (small) area disorder, small bubbles tend to sort inwards and large bubbles outwards. (3) Topological charges of the same sign repel while charges of opposite sign attract. (4) They discuss boundary conditions and the uniqueness of the pattern for fixed topology.
A scalable 2-D parallel sparse solver
Kothari, S.C.; Mitra, S.
1995-12-01
Scalability beyond a small number of processors, typically 32 or less, is known to be a problem for existing parallel general sparse (PGS) direct solvers. This paper presents a parallel general sparse PGS direct solver for general sparse linear systems on distributed memory machines. The algorithm is based on the well-known sequential sparse algorithm Y12M. To achieve efficient parallelization, a 2-D scattered decomposition of the sparse matrix is used. The proposed algorithm is more scalable than existing parallel sparse direct solvers. Its scalability is evaluated on a 256 processor nCUBE2s machine using Boeing/Harwell benchmark matrices.
2D stepping drive for hyperspectral systems
NASA Astrophysics Data System (ADS)
Endrödy, Csaba; Mehner, Hannes; Grewe, Adrian; Sinzinger, Stefan; Hoffmann, Martin
2015-07-01
We present the design, fabrication and characterization of a compact 2D stepping microdrive for pinhole array positioning. The miniaturized solution enables a highly integrated compact hyperspectral imaging system. Based on the geometry of the pinhole array, an inch-worm drive with electrostatic actuators was designed resulting in a compact (1 cm2) positioning system featuring a step size of about 15 µm in a 170 µm displacement range. The high payload (20 mg) as required for the pinhole array and the compact system design exceed the known electrostatic inch-worm-based microdrives.
ERIC Educational Resources Information Center
Crank, Ron
This instructional unit is one of 10 developed by students on various energy-related areas that deals specifically with transportation and energy use. Its objective is for the student to be able to discuss the implication of energy usage as it applies to the area of transportation. Some topics covered are efficiencies of various transportation…
Frascati neutron generator (FNG)
NASA Astrophysics Data System (ADS)
Martone, M.; Angelone, M.; Pillon, Mario
1995-03-01
The 14 MeV neutron generator (FNG), in operation at the ENEA Energy Center of Frascati, Italy, is described. It produces up to 1 X 1011 neutrons per second and consists essentially of a deuterium-ion accelerator, a beam transport system, and a target of titanium tritide, where neutrons are produced by the T(d,n)4He fusion reactions. An application of FNG in the context of research activity on controlled thermonuclear fusion research is also briefly described.
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.
Microwave Assisted 2D Materials Exfoliation
NASA Astrophysics Data System (ADS)
Wang, Yanbin
Two-dimensional materials have emerged as extremely important materials with applications ranging from energy and environmental science to electronics and biology. Here we report our discovery of a universal, ultrafast, green, solvo-thermal technology for producing excellent-quality, few-layered nanosheets in liquid phase from well-known 2D materials such as such hexagonal boron nitride (h-BN), graphite, and MoS2. We start by mixing the uniform bulk-layered material with a common organic solvent that matches its surface energy to reduce the van der Waals attractive interactions between the layers; next, the solutions are heated in a commercial microwave oven to overcome the energy barrier between bulk and few-layers states. We discovered the minutes-long rapid exfoliation process is highly temperature dependent, which requires precise thermal management to obtain high-quality inks. We hypothesize a possible mechanism of this proposed solvo-thermal process; our theory confirms the basis of this novel technique for exfoliation of high-quality, layered 2D materials by using an as yet unknown role of the solvent.
Multienzyme Inkjet Printed 2D Arrays.
Gdor, Efrat; Shemesh, Shay; Magdassi, Shlomo; Mandler, Daniel
2015-08-19
The use of printing to produce 2D arrays is well established, and should be relatively facile to adapt for the purpose of printing biomaterials; however, very few studies have been published using enzyme solutions as inks. Among the printing technologies, inkjet printing is highly suitable for printing biomaterials and specifically enzymes, as it offers many advantages. Formulation of the inkjet inks is relatively simple and can be adjusted to a variety of biomaterials, while providing nonharmful environment to the enzymes. Here we demonstrate the applicability of inkjet printing for patterning multiple enzymes in a predefined array in a very straightforward, noncontact method. Specifically, various arrays of the enzymes glucose oxidase (GOx), invertase (INV) and horseradish peroxidase (HP) were printed on aminated glass surfaces, followed by immobilization using glutardialdehyde after printing. Scanning electrochemical microscopy (SECM) was used for imaging the printed patterns and to ascertain the enzyme activity. The successful formation of 2D arrays consisting of enzymes was explored as a means of developing the first surface confined enzyme based logic gates. Principally, XOR and AND gates, each consisting of two enzymes as the Boolean operators, were assembled, and their operation was studied by SECM. PMID:26214072
NASA Astrophysics Data System (ADS)
Ding, M.; Hartl, M.; Wang, Y.; Hjelm, R.
2013-12-01
In nuclear waste management, clays are canonical materials in the construction of engineered barriers. They are also naturally occurring reactive minerals which play an important role in retention and colloidal facilitated reactive transport in subsurface systems. Knowledge of total and accessible porosity in clays is crucial in determining fluids transport behavior in clays. It will provide fundamental insight on the performance efficiency of specific clays as a barrier material and their role in regulating radionuclide transport in subsurface environments. The aim of the present work is to experimentally investigate the change in pore characteristics of clays as function of moisture content, and to determine their pore character in relation to their water retention capacity. Recent developments in small-angle neutron scattering (SANS) techniques allow quantitative measurement of pore morphology and size distribution of various materials in their pristine state under various sample environments (exposure to solution, high temperature, and so on). Furthermore, due to dramatic different neutron scattering properties of hydrogen and deuterium, one can readily use contrast variation, which is the isotopic labeling with various ratios of H and D (e.g. mixture of H2O/D2O) to highlight or suppress features of the sample. This is particularly useful in the study of complex pore system such as clays. In this study, we have characterized the pore structures for a number of clays including clay minerals and field samples which are relevant to high-level waste systems under various sample environments (e.g., humidity, temperature and pressure) using SANS. Our results suggest that different clays show unique pore features under various sample environments. To distinguish between accessible/non-accessible pores and the nature of pore filling (e.g. the quantity of H2O adsorbed by clays, and the distribution of H2O in relation to pore character) to water, clays were exposed for
2-D or not 2-D, that is the question: A Northern California test
Mayeda, K; Malagnini, L; Phillips, W S; Walter, W R; Dreger, D
2005-06-06
Reliable estimates of the seismic source spectrum are necessary for accurate magnitude, yield, and energy estimation. In particular, how seismic radiated energy scales with increasing earthquake size has been the focus of recent debate within the community and has direct implications on earthquake source physics studies as well as hazard mitigation. The 1-D coda methodology of Mayeda et al. has provided the lowest variance estimate of the source spectrum when compared against traditional approaches that use direct S-waves, thus making it ideal for networks that have sparse station distribution. The 1-D coda methodology has been mostly confined to regions of approximately uniform complexity. For larger, more geophysically complicated regions, 2-D path corrections may be required. The complicated tectonics of the northern California region coupled with high quality broadband seismic data provides for an ideal ''apples-to-apples'' test of 1-D and 2-D path assumptions on direct waves and their coda. Using the same station and event distribution, we compared 1-D and 2-D path corrections and observed the following results: (1) 1-D coda results reduced the amplitude variance relative to direct S-waves by roughly a factor of 8 (800%); (2) Applying a 2-D correction to the coda resulted in up to 40% variance reduction from the 1-D coda results; (3) 2-D direct S-wave results, though better than 1-D direct waves, were significantly worse than the 1-D coda. We found that coda-based moment-rate source spectra derived from the 2-D approach were essentially identical to those from the 1-D approach for frequencies less than {approx}0.7-Hz, however for the high frequencies (0.7{le} f {le} 8.0-Hz), the 2-D approach resulted in inter-station scatter that was generally 10-30% smaller. For complex regions where data are plentiful, a 2-D approach can significantly improve upon the simple 1-D assumption. In regions where only 1-D coda correction is available it is still preferable over 2
NASA Astrophysics Data System (ADS)
Lucero, Catherine L.; Bentz, Dale P.; Hussey, Daniel S.; Jacobson, David L.; Weiss, W. Jason
Air entrainment is commonly added to concrete to help in reducing the potential for freeze thaw damage. It is hypothesized that the entrained air voids remain unsaturated or partially saturated long after the smaller pores fill with water. Small gel and capillary pores in the cement matrix fill quickly on exposure to water, but larger pores (entrapped and entrained air voids) require longer times or other methods to achieve saturation. As such, it is important to quantitatively determine the water content and degree of saturation in air entrained cementitious materials. In order to further investigate properties of cement-based mortar, a model based on Beer's Law has been developed to interpret neutron radiographs. This model is a powerful tool for analyzing images acquired from neutron radiography. A mortar with a known volume of aggregate, water to cement ratio and degree of hydration can be imaged and the degree of saturation can be estimated.
Numerical Evaluation of 2D Ground States
NASA Astrophysics Data System (ADS)
Kolkovska, Natalia
2016-02-01
A ground state is defined as the positive radial solution of the multidimensional nonlinear problem
Canard configured aircraft with 2-D nozzle
NASA Technical Reports Server (NTRS)
Child, R. D.; Henderson, W. P.
1978-01-01
A closely-coupled canard fighter with vectorable two-dimensional nozzle was designed for enhanced transonic maneuvering. The HiMAT maneuver goal of a sustained 8g turn at a free-stream Mach number of 0.9 and 30,000 feet was the primary design consideration. The aerodynamic design process was initiated with a linear theory optimization minimizing the zero percent suction drag including jet effects and refined with three-dimensional nonlinear potential flow techniques. Allowances were made for mutual interference and viscous effects. The design process to arrive at the resultant configuration is described, and the design of a powered 2-D nozzle model to be tested in the LRC 16-foot Propulsion Wind Tunnel is shown.
2D Electrostatic Actuation of Microshutter Arrays
NASA Technical Reports Server (NTRS)
Burns, Devin E.; Oh, Lance H.; Li, Mary J.; Jones, Justin S.; Kelly, Daniel P.; Zheng, Yun; Kutyrev, Alexander S.; Moseley, Samuel H.
2015-01-01
An electrostatically actuated microshutter array consisting of rotational microshutters (shutters that rotate about a torsion bar) were designed and fabricated through the use of models and experiments. Design iterations focused on minimizing the torsional stiffness of the microshutters, while maintaining their structural integrity. Mechanical and electromechanical test systems were constructed to measure the static and dynamic behavior of the microshutters. The torsional stiffness was reduced by a factor of four over initial designs without sacrificing durability. Analysis of the resonant behavior of the microshutter arrays demonstrates that the first resonant mode is a torsional mode occurring around 3000 Hz. At low vacuum pressures, this resonant mode can be used to significantly reduce the drive voltage necessary for actuation requiring as little as 25V. 2D electrostatic latching and addressing was demonstrated using both a resonant and pulsed addressing scheme.
2D Electrostatic Actuation of Microshutter Arrays
NASA Technical Reports Server (NTRS)
Burns, Devin E.; Oh, Lance H.; Li, Mary J.; Kelly, Daniel P.; Kutyrev, Alexander S.; Moseley, Samuel H.
2015-01-01
Electrostatically actuated microshutter arrays consisting of rotational microshutters (shutters that rotate about a torsion bar) were designed and fabricated through the use of models and experiments. Design iterations focused on minimizing the torsional stiffness of the microshutters, while maintaining their structural integrity. Mechanical and electromechanical test systems were constructed to measure the static and dynamic behavior of the microshutters. The torsional stiffness was reduced by a factor of four over initial designs without sacrificing durability. Analysis of the resonant behavior of the microshutters demonstrates that the first resonant mode is a torsional mode occurring around 3000 Hz. At low vacuum pressures, this resonant mode can be used to significantly reduce the drive voltage necessary for actuation requiring as little as 25V. 2D electrostatic latching and addressing was demonstrated using both a resonant and pulsed addressing scheme.
Graphene suspensions for 2D printing
NASA Astrophysics Data System (ADS)
Soots, R. A.; Yakimchuk, E. A.; Nebogatikova, N. A.; Kotin, I. A.; Antonova, I. V.
2016-04-01
It is shown that, by processing a graphite suspension in ethanol or water by ultrasound and centrifuging, it is possible to obtain particles with thicknesses within 1-6 nm and, in the most interesting cases, 1-1.5 nm. Analogous treatment of a graphite suspension in organic solvent yields eventually thicker particles (up to 6-10 nm thick) even upon long-term treatment. Using the proposed ink based on graphene and aqueous ethanol with ethylcellulose and terpineol additives for 2D printing, thin (~5 nm thick) films with sheet resistance upon annealing ~30 MΩ/□ were obtained. With the ink based on aqueous graphene suspension, the sheet resistance was ~5-12 kΩ/□ for 6- to 15-nm-thick layers with a carrier mobility of ~30-50 cm2/(V s).
Chaotic advection in 2D anisotropic porous media
NASA Astrophysics Data System (ADS)
Varghese, Stephen; Speetjens, Michel; Trieling, Ruben; Toschi, Federico
2015-11-01
Traditional methods for heat recovery from underground geothermal reservoirs employ a static system of injector-producer wells. Recent studies in literature have shown that using a well-devised pumping scheme, through actuation of multiple injector-producer wells, can dramatically enhance production rates due to the increased scalar / heat transport by means of chaotic advection. However the effect of reservoir anisotropy on kinematic mixing and heat transport is unknown and has to be incorporated and studied for practical deployment in the field. As a first step, we numerically investigate the effect of anisotropy (both magnitude and direction) on (chaotic) advection of passive tracers in a time-periodic Darcy flow within a 2D circular domain driven by periodically reoriented diametrically opposite source-sink pairs. Preliminary results indicate that anisotropy has a significant impact on the location, shape and size of coherent structures in the Poincare sections. This implies that the optimal operating parameters (well spacing, time period of well actuation) may vary strongly and must be carefully chosen so as to enhance subsurface transport. This work is part of the research program of the Foundation for Fundamental Research on Matter (FOM), which is part of Netherlands Organisation for Scientific Research (NWO). This research program is co-financed by Shell Global Solutions International B.V.
Metrology for graphene and 2D materials
NASA Astrophysics Data System (ADS)
Pollard, Andrew J.
2016-09-01
The application of graphene, a one atom-thick honeycomb lattice of carbon atoms with superlative properties, such as electrical conductivity, thermal conductivity and strength, has already shown that it can be used to benefit metrology itself as a new quantum standard for resistance. However, there are many application areas where graphene and other 2D materials, such as molybdenum disulphide (MoS2) and hexagonal boron nitride (h-BN), may be disruptive, areas such as flexible electronics, nanocomposites, sensing and energy storage. Applying metrology to the area of graphene is now critical to enable the new, emerging global graphene commercial world and bridge the gap between academia and industry. Measurement capabilities and expertise in a wide range of scientific areas are required to address this challenge. The combined and complementary approach of varied characterisation methods for structural, chemical, electrical and other properties, will allow the real-world issues of commercialising graphene and other 2D materials to be addressed. Here, examples of metrology challenges that have been overcome through a multi-technique or new approach are discussed. Firstly, the structural characterisation of defects in both graphene and MoS2 via Raman spectroscopy is described, and how nanoscale mapping of vacancy defects in graphene is also possible using tip-enhanced Raman spectroscopy (TERS). Furthermore, the chemical characterisation and removal of polymer residue on chemical vapour deposition (CVD) grown graphene via secondary ion mass spectrometry (SIMS) is detailed, as well as the chemical characterisation of iron films used to grow large domain single-layer h-BN through CVD growth, revealing how contamination of the substrate itself plays a role in the resulting h-BN layer. In addition, the role of international standardisation in this area is described, outlining the current work ongoing in both the International Organization of Standardization (ISO) and the
Electron Energy Levels in the 1D-2D Transition
NASA Astrophysics Data System (ADS)
Pepper, Michael; Sanjeev, Kumar; Thomas, Kalarikad; Creeth, Graham; English, David; Ritchie, David; Griffiths, Jonathan; Farrer, Ian; Jones, Geraint
Using GaAs-AlGaAs heterostructures we have investigated the behaviour of electron energy levels with relaxation of the potential confining a 2D electron gas into a 1D configuration. In the ballistic regime of transport, when the conductance shows quantized plateaux, different types of behaviour are found according to the spins of interacting levels, whether a magnetic field is applied and lifting of the momentum degeneracy with a source-drain voltage. We have observed both crossing and anti-crossing of levels and have investigated the manner in which they can be mutually converted. In the presence of a magnetic field levels can cross and lock together as the confinement is altered in a way which is characteristic of parallel channels. The overall behaviour is discussed in terms of electron interactions and the wavefunction flexibility allowed by the increasing two dimensionality of the electron distribution as the confinement is weakened. Work supported by UK EPSRC.
Enhancement of biomixing by swimming cells in 2D films
NASA Astrophysics Data System (ADS)
Gollub, Jerry; Kurtuldu, Huseyin; Guasto, Jeffrey; Johnson, Karl
2011-11-01
Fluid mixing in active suspensions of microorganisms is important to ecological phenomena and shows surprising statistical behavior. We investigate the mixing produced by swimming unicellular algal cells (Chlamydomonas) in quasi-2D films by tracking the motions of cells and of microscopic passive tracer particles advected by the fluid. The reduced spatial dimension of the system leads to long-range flows and a surprisingly strong dependence of tracer transport on the swimmer concentration. The mean square displacements are well described by a stochastic Langevin model, with an effective diffusion coefficient D growing as the 3/2 power of the swimmer concentration, due to the interaction of tracer particles with multiple swimmers. We also discuss the anomalous probability distributions of tracer displacements, which become Gaussian at high concentration, but show strong power-law tails at low concentration. Supported by NSF Grant DMR-0803153.
A 2D channel-clogging biofilm model.
Winstanley, H F; Chapwanya, M; Fowler, A C; O'Brien, S B G
2015-09-01
We present a model of biofilm growth in a long channel where the biomass is assumed to have the rheology of a viscous polymer solution. We examine the competition between growth and erosion-like surface detachment due to the flow. A particular focus of our investigation is the effect of the biofilm growth on the fluid flow in the pores, and the issue of whether biomass can grow sufficiently to shut off fluid flow through the pores, thus clogging the pore space. Net biofilm growth is coupled along the pore length via flow rate and nutrient transport in the pore flow. Our 2D model extends existing results on stability of 1D steady state biofilm thicknesses to show that, in the case of flows driven by a fixed pressure drop, full clogging of the pore can indeed happen in certain cases dependent on the functional form of the detachment term. PMID:25240390
Hirobe, Tomohisa; Ito, Shosuke; Wakamatsu, Kazumasa
2013-09-01
The novel mutation named ru2(d) /Hps5(ru2-d) , characterized by light-colored coats and ruby-eyes, prohibits differentiation of melanocytes by inhibiting tyrosinase (Tyr) activity, expression of Tyr, Tyr-related protein 1 (Tyrp1), Tyrp2, and Kit. However, it is not known whether the ru2(d) allele affects pheomelanin synthesis in recessive yellow (e/Mc1r(e) ) or in pheomelanic stage in agouti (A) mice. In this study, effects of the ru2(d) allele on pheomelanin synthesis were investigated by chemical analysis of melanin present in dorsal hairs of 5-week-old mice from F2 generation between C57BL/10JHir (B10)-co-isogenic ruby-eye 2(d) and B10-congenic recessive yellow or agouti. Eumelanin content was decreased in ruby-eye 2(d) and ruby-eye 2(d) agouti mice, whereas pheomelanin content in ruby-eye 2(d) recessive yellow and ruby-eye 2(d) agouti mice did not differ from the corresponding Ru2(d) /- mice, suggesting that the ru2(d) allele inhibits eumelanin but not pheomelanin synthesis. PMID:23672590
Magnetoresistance in Co/2D MoS2/Co and Ni/2D MoS2/Ni junctions.
Zhang, Han; Ye, Meng; Wang, Yangyang; Quhe, Ruge; Pan, Yuanyuan; Guo, Ying; Song, Zhigang; Yang, Jinbo; Guo, Wanlin; Lu, Jing
2016-06-28
Semiconducting single-layer (SL) and few-layer MoS2 have a flat surface, free of dangling bonds. Using density functional theory coupled with non-equilibrium Green's function method, we investigate the spin-polarized transport properties of Co/2D MoS2/Co and Ni/2D MoS2/Ni junctions with MoS2 layer numbers of N = 1, 3, and 5. Well-defined interfaces are formed between MoS2 and metal electrodes. The junctions with a SL MoS2 spacer are almost metallic owing to the strong coupling between MoS2 and the ferromagnets, while those are tunneling with a few layer MoS2 spacer. Both large magnetoresistance and tunneling magnetoresistance are found when fcc or hcp Co is used as an electrode. Therefore, flat single- and few-layer MoS2 can serve as an effective nonmagnetic spacer in a magnetoresistance or tunneling magnetoresistance device with a well-defined interface. PMID:27257639
Surface delta interaction in the g7/2 - d5/2 model space
NASA Astrophysics Data System (ADS)
Yu, Xiaofei; Zamick, Larry
2016-05-01
Using an attractive surface delta interaction we obtain wave functions for 2 neutrons (or neutron holes) in the g7/2 -d5/2 model space. If we take the single particle energies to be degenerate we find that the g factors for I = 2 , 4 and 6 are all the same G (J) =gl, the orbital g factor of the nucleon. For a free neutron gl = 0, so in this case all 2 particles or 2 holes' g factors are equal to zero. Only the orbital part of the g-factors contributes - the spin part cancels out. We then consider the effects of introducing a single energy splitting between the 2 orbits. We make a linear approximation for all other n values.
Measurements of Schottky barrier heights formed from metals and 2D transition metal dichalcogedides
NASA Astrophysics Data System (ADS)
Kim, Changsik; Moon, Inyong; Nam, Seunggeol; Cho, Yeonchoo; Shin, Hyeon-Jin; Park, Seongjun; Yoo, Won Jong
Schottky barrier height (SBH) is an important parameter that needs to be considered for designing electronic devices. However, for two dimensional (2D) materials based devices, SBH control is limited by 2D structure induced quantum confinement and 2D surface induced Fermi level pinning. In this work, we explore differences in measuring SBH between 2D and 3D materials. Recently, low temperature I-V measurement has been reported to extract SBH based on thermionic emission equation for Schottky diode. However, 2D devices are not real Schottky diode in that both source and drain metal electrodes make Schottky contact. According to our experimental results, SBH extracted from linear slope of ln (I/T3/2) against 1/T show widely diverse values, dependent on applied voltage bias and tested temperature which affect carrier transport including tunneling or thermionic emission across the metal-2D material interface. In this work, we wish to demonstrate the method to determine SBH and Fermi level pinning which are attributed to 2D transition metal dichalcogedides, differently from conventional 3D materials. .
Few-layer III-VI and IV-VI 2D semiconductor transistors
NASA Astrophysics Data System (ADS)
Sucharitakul, Sukrit; Liu, Mei; Kumar, Rajesh; Sankar, Raman; Chou, Fang C.; Chen, Yit-Tsong; Gao, Xuan
Since the discovery of atomically thin graphene, a large variety of exfoliable 2D materials have been thoroughly explored for their exotic transport behavior and promises in technological breakthroughs. While most attention on 2D materials beyond graphene is focused on transition metal-dichalcogenides, relatively less attention is paid to layered III-VI and IV-VI semiconductors such as InSe, SnSe etc which bear stronger potential as 2D materials with high electron mobility or thermoelectric figure of merit. We will discuss our recent work on few-layer InSe 2D field effect transistors which exhibit carrier mobility approaching 1000 cm2/Vs and ON-OFF ratio exceeding 107 at room temperature. In addition, the fabrication and device performance of transistors made of mechanically exfoliated multilayer IV-VI semiconductor SnSe and SnSe2 will be discussed.
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.
Hoffman, A. J.; Lee, J. C.
2013-07-01
A new time-dependent neutron transport method based on the method of characteristics (MOC) has been developed. Whereas most spatial kinetics methods treat time dependence through temporal discretization, this new method treats time dependence by defining the characteristics to span space and time. In this implementation regions are defined in space-time where the thickness of the region in time fulfills an analogous role to the time step in discretized methods. The time dependence of the local source is approximated using a truncated Taylor series expansion with high order derivatives approximated using backward differences, permitting the solution of the resulting space-time characteristic equation. To avoid a drastic increase in computational expense and memory requirements due to solving many discrete characteristics in the space-time planes, the temporal variation of the boundary source is similarly approximated. This allows the characteristics in the space-time plane to be represented analytically rather than discretely, resulting in an algorithm comparable in implementation and expense to one that arises from conventional time integration techniques. Furthermore, by defining the boundary flux time derivative in terms of the preceding local source time derivative and boundary flux time derivative, the need to store angularly-dependent data is avoided without approximating the angular dependence of the angular flux time derivative. The accuracy of this method is assessed through implementation in the neutron transport code DeCART. The method is employed with variable-order local source representation to model a TWIGL transient. The results demonstrate that this method is accurate and more efficient than the discretized method. (authors)
NASA Astrophysics Data System (ADS)
Cheng, Chingyun; Kangara, Jayampathi; Arakelyan, Ilya; Thomas, John
2016-05-01
We tune the dimensionality of a strongly interacting degenerate 6 Li Fermi gas from 2D to quasi-2D, by adjusting the radial confinement of pancake-shaped clouds to control the radial chemical potential. In the 2D regime with weak radial confinement, the measured pair binding energies are in agreement with 2D-BCS mean field theory, which predicts dimer pairing energies in the many-body regime. In the qausi-2D regime obtained with increased radial confinement, the measured pairing energy deviates significantly from 2D-BCS theory. In contrast to the pairing energy, the measured radii of the cloud profiles are not fit by 2D-BCS theory in either the 2D or quasi-2D regimes, but are fit in both regimes by a beyond mean field polaron-model of the free energy. Supported by DOE, ARO, NSF, and AFOSR.
Quantum Diffusion on Molecular Tubes: Universal Scaling of the 1D to 2D Transition
NASA Astrophysics Data System (ADS)
Chuang, Chern; Lee, Chee Kong; Moix, Jeremy M.; Knoester, Jasper; Cao, Jianshu
2016-05-01
The transport properties of disordered systems are known to depend critically on dimensionality. We study the diffusion coefficient of a quantum particle confined to a lattice on the surface of a tube, where it scales between the 1D and 2D limits. It is found that the scaling relation is universal and independent of the temperature, disorder, and noise parameters, and the essential order parameter is the ratio between the localization length in 2D and the circumference of the tube. Phenomenological and quantitative expressions for transport properties as functions of disorder and noise are obtained and applied to real systems: In the natural chlorosomes found in light-harvesting bacteria the exciton transfer dynamics is predicted to be in the 2D limit, whereas a family of synthetic molecular aggregates is found to be in the homogeneous limit and is independent of dimensionality.
Quantum Diffusion on Molecular Tubes: Universal Scaling of the 1D to 2D Transition.
Chuang, Chern; Lee, Chee Kong; Moix, Jeremy M; Knoester, Jasper; Cao, Jianshu
2016-05-13
The transport properties of disordered systems are known to depend critically on dimensionality. We study the diffusion coefficient of a quantum particle confined to a lattice on the surface of a tube, where it scales between the 1D and 2D limits. It is found that the scaling relation is universal and independent of the temperature, disorder, and noise parameters, and the essential order parameter is the ratio between the localization length in 2D and the circumference of the tube. Phenomenological and quantitative expressions for transport properties as functions of disorder and noise are obtained and applied to real systems: In the natural chlorosomes found in light-harvesting bacteria the exciton transfer dynamics is predicted to be in the 2D limit, whereas a family of synthetic molecular aggregates is found to be in the homogeneous limit and is independent of dimensionality. PMID:27232033
2D Radiative Processes Near Cloud Edges
NASA Technical Reports Server (NTRS)
Varnai, T.
2012-01-01
Because of the importance and complexity of dynamical, microphysical, and radiative processes taking place near cloud edges, the transition zone between clouds and cloud free air has been the subject of intense research both in the ASR program and in the wider community. One challenge in this research is that the one-dimensional (1D) radiative models widely used in both remote sensing and dynamical simulations become less accurate near cloud edges: The large horizontal gradients in particle concentrations imply that accurate radiative calculations need to consider multi-dimensional radiative interactions among areas that have widely different optical properties. This study examines the way the importance of multidimensional shortwave radiative interactions changes as we approach cloud edges. For this, the study relies on radiative simulations performed for a multiyear dataset of clouds observed over the NSA, SGP, and TWP sites. This dataset is based on Microbase cloud profiles as well as wind measurements and ARM cloud classification products. The study analyzes the way the difference between 1D and 2D simulation results increases near cloud edges. It considers both monochromatic radiances and broadband radiative heating, and it also examines the influence of factors such as cloud type and height, and solar elevation. The results provide insights into the workings of radiative processes and may help better interpret radiance measurements and better estimate the radiative impacts of this critical region.
Simulation of Yeast Cooperation in 2D.
Wang, M; Huang, Y; Wu, Z
2016-03-01
Evolution of cooperation has been an active research area in evolutionary biology in decades. An important type of cooperation is developed from group selection, when individuals form spatial groups to prevent them from foreign invasions. In this paper, we study the evolution of cooperation in a mixed population of cooperating and cheating yeast strains in 2D with the interactions among the yeast cells restricted to their small neighborhoods. We conduct a computer simulation based on a game theoretic model and show that cooperation is increased when the interactions are spatially restricted, whether the game is of a prisoner's dilemma, snow drifting, or mutual benefit type. We study the evolution of homogeneous groups of cooperators or cheaters and describe the conditions for them to sustain or expand in an opponent population. We show that under certain spatial restrictions, cooperator groups are able to sustain and expand as group sizes become large, while cheater groups fail to expand and keep them from collapse. PMID:26988702
Phase Engineering of 2D Tin Sulfides.
Mutlu, Zafer; Wu, Ryan J; Wickramaratne, Darshana; Shahrezaei, Sina; Liu, Chueh; Temiz, Selcuk; Patalano, Andrew; Ozkan, Mihrimah; Lake, Roger K; Mkhoyan, K A; Ozkan, Cengiz S
2016-06-01
Tin sulfides can exist in a variety of phases and polytypes due to the different oxidation states of Sn. A subset of these phases and polytypes take the form of layered 2D structures that give rise to a wide host of electronic and optical properties. Hence, achieving control over the phase, polytype, and thickness of tin sulfides is necessary to utilize this wide range of properties exhibited by the compound. This study reports on phase-selective growth of both hexagonal tin (IV) sulfide SnS2 and orthorhombic tin (II) sulfide SnS crystals with diameters of over tens of microns on SiO2 substrates through atmospheric pressure vapor-phase method in a conventional horizontal quartz tube furnace with SnO2 and S powders as the source materials. Detailed characterization of each phase of tin sulfide crystals is performed using various microscopy and spectroscopy methods, and the results are corroborated by ab initio density functional theory calculations. PMID:27099950
Parallel map analysis on 2-D grids
Berry, M.; Comiskey, J.; Minser, K.
1993-12-31
In landscape ecology, computer modeling is used to assess habitat fragmentation and its ecological iMPLications. Specifically, maps (2-D grids) of habitat clusters must be analyzed to determine number, sizes and geometry of clusters. Models prior to this study relied upon sequential Fortran-77 programs which limited the sizes of maps and densities of clusters which could be analyzed. In this paper, we present more efficient computer models which can exploit recursion or parallelism. Significant improvements over the original Fortran-77 programs have been achieved using both recursive and nonrecursive C implementations on a variety of workstations such as the Sun Sparc 2, IBM RS/6000-350, and HP 9000-750. Parallel implementations on a 4096-processor MasPar MP-1 and a 32-processor CM-5 are also studied. Preliminary experiments suggest that speed improvements for the parallel model on the MasPar MP-1 (written in MPL) and on the CM-5 (written in C using CMMD) can be as much as 39 and 34 times faster, respectively, than the most efficient sequential C program on a Sun Sparc 2 for a 512 map. An important goal in this research effort is to produce a scalable map analysis algorithm for the identification and characterization of clusters for relatively large maps on massively-parallel computers.
2D Turbulence with Complicated Boundaries
NASA Astrophysics Data System (ADS)
Roullet, G.; McWilliams, J. C.
2014-12-01
We examine the consequences of lateral viscous boundary layers on the 2D turbulence that arises in domains with complicated boundaries (headlands, bays etc). The study is carried out numerically with LES. The numerics are carefully designed to ensure all global conservation laws, proper boundary conditions and a minimal range of dissipation scales. The turbulence dramatically differs from the classical bi-periodic case. Boundary layer separations lead to creation of many small vortices and act as a continuing energy source exciting the inverse cascade of energy throughout the domain. The detachments are very intermittent in time. In free decay, the final state depends on the effective numerical resolution: laminar with a single dominant vortex for low Re and turbulent with many vortices for large enough Re. After very long time, the turbulent end-state exhibits a striking tendency for the emergence of shielded vortices which then interact almost elastically. In the forced case, the boundary layers allow the turbulence to reach a statistical steady state without any artificial hypo-viscosity or other large-scale dissipation. Implications are discussed for the oceanic mesoscale and submesoscale turbulence.
2-D wavelet with position controlled resolution
NASA Astrophysics Data System (ADS)
Walczak, Andrzej; Puzio, Leszek
2005-09-01
Wavelet transformation localizes all irregularities in the scene. It is most effective in the case when intensities in the scene have no sharp details. It is the case often present in a medical imaging. To identify the shape one has to extract it from the scene as typical irregularity. When the scene does not contain sharp changes then common differential filters are not efficient tool for a shape extraction. The new 2-D wavelet for such task has been proposed. Described wavelet transform is axially symmetric and has varied scale in dependence on the distance from the centre of the wavelet symmetry. The analytical form of the wavelet has been presented as well as its application for details extraction in the scene. Most important feature of the wavelet transform is that it gives a multi-scale transformation, and if zoom is on the wavelet selectivity varies proportionally to the zoom step. As a result, the extracted shape does not change during zoom operation. What is more the wavelet selectivity can be fit to the local intensity gradient properly to obtain best extraction of the irregularities.
2-D Animation's Not Just for Mickey Mouse.
ERIC Educational Resources Information Center
Weinman, Lynda
1995-01-01
Discusses characteristics of two-dimensional (2-D) animation; highlights include character animation, painting issues, and motion graphics. Sidebars present Silicon Graphics animations tools and 2-D animation programs for the desktop computer. (DGM)
Merging of RVR meander with CONCEPTS: Simplified 2D model for long-term meander evolution
Technology Transfer Automated Retrieval System (TEKTRAN)
RVR Meander is a simplified two-dimensional (2D) hydrodynamic and migration model (Abad and Garcia, 2006) while CONCEPTS (CONservational Channel Evolution and Pollutant Transport System) is a one-dimensional (1D) hydrodynamic and morphodynamic model (Langendoen and Alonso, 2008; Langendoen and Simon...
Global small solutions of 2-D incompressible MHD system
NASA Astrophysics Data System (ADS)
Lin, Fanghua; Xu, Li; Zhang, Ping
2015-11-01
In this paper, we consider the global wellposedness of 2-D incompressible magneto-hydrodynamical system with smooth initial data which is close to some non-trivial steady state. It is a coupled system between the Navier-Stokes equations and a free transport equation with a universal nonlinear coupling structure. The main difficulty of the proof lies in exploring the dissipative mechanism of the system. To achieve this and to avoid the difficulty of propagating anisotropic regularity for the free transport equation, we first reformulate our system (1.1) in the Lagrangian coordinates (2.19). Then we employ anisotropic Littlewood-Paley analysis to establish the key a prioriL1 (R+ ; Lip (R2)) estimate for the Lagrangian velocity field Yt. With this estimate, we can prove the global wellposedness of (2.19) with smooth and small initial data by using the energy method. We emphasize that the algebraic structure of (2.19) is crucial for the proofs to work. The global wellposedness of the original system (1.1) then follows by a suitable change of variables.
Effects of Agent's Repulsion in 2d Flocking Models
NASA Astrophysics Data System (ADS)
Moussa, Najem; Tarras, Iliass; Mazroui, M'hammed; Boughaleb, Yahya
In nature many animal groups, such as fish schools or bird flocks, clearly display structural order and appear to move as a single coherent entity. In order to understand the complex behavior of these systems, many models have been proposed and tested so far. This paper deals with an extension of the Vicsek model, by including a second zone of repulsion, where each agent attempts to maintain a minimum distance from the others. The consideration of this zone in our study seems to play an important role during the travel of agents in the two-dimensional (2D) flocking models. Our numerical investigations show that depending on the basic ingredients such as repulsion radius (R1), effect of density of agents (ρ) and noise (η), our nonequilibrium system can undergo a kinetic phase transition from no transport to finite net transport. For different values of ρ, kinetic phase diagrams in the plane (η ,R1) are found. Implications of these findings are discussed.
What carries heat in novel 2D semiconductors?
NASA Astrophysics Data System (ADS)
Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Mauri, Francesco; Marzari, Nicola
When materials are scaled down to the microscopic scale, or when dimensionality is reduced, thermal transport exhibits new intriguing behaviors that are not present in conventional bulk crystals. While phonons are typically considered to be the excitations responsible for carrying heat through a crystal, as dimensionality is reduced, the motion of phonons driven by a temperature perturbation becomes correlated, and collective excitations of many phonons arise. This leads to a wealth of complex phenomena, such as very high thermal conductivity (the highest known conductivities are indeed found in 2D materials), or wave-like heat diffusion, with second sound, hitherto found only in a few exotic materials at cryogenic temperatures, routinely present at room temperature. In this contribution, we show that heat transport in crystals can be described exactly with the kinetic theory of a gas of collective phonon excitations, termed relaxons. In this way, it is possible to recover a microscopic interpretation based on mean free paths and relaxation times without any simplification of the linearised phonon Boltzmann equation.
MAZE96. Generates 2D Input for DYNA NIKE & TOPAZ
Sanford, L.; Hallquist, J.O.
1992-02-24
MAZE is an interactive program that serves as an input and two-dimensional mesh generator for DYNA2D, NIKE2D, TOPAZ2D, and CHEMICAL TOPAZ2D. MAZE also generates a basic template for ISLAND input. MAZE has been applied to the generation of input data to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.
On 2D graphical representation of DNA sequence of nondegeneracy
NASA Astrophysics Data System (ADS)
Zhang, Yusen; Liao, Bo; Ding, Kequan
2005-08-01
Some two-dimensional (2D) graphical representations of DNA sequences have been given by Gates, Nandy, Leong and Mogenthaler, Randić, and Liao et al., which give visual characterizations of DNA sequences. In this Letter, we introduce a nondegeneracy 2D graphical representation of DNA sequence, which is different from Randić's novel 2D representation and Liao's 2D representation. We also present the nondegeneracy forms corresponding to the representations of Gates, Nandy, Leong and Mogenthaler.
Generates 2D Input for DYNA NIKE & TOPAZ
1996-07-15
MAZE is an interactive program that serves as an input and two-dimensional mesh generator for DYNA2D, NIKE2D, TOPAZ2D, and CHEMICAL TOPAZ2D. MAZE also generates a basic template for ISLAND input. MAZE has been applied to the generation of input data to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.
Ultrasonic 2D matrix PVDF transducer
NASA Astrophysics Data System (ADS)
Ptchelintsev, A.; Maev, R. Gr.
2000-05-01
During the past decade a substantial amount of work has been done in the area of ultrasonic imaging technology using 2D arrays. The main problems arising for the two-dimensional matrix transducers at megahertz frequencies are small size and huge count of the elements, high electrical impedance, low sensitivity, bad SNR and slower data acquisition rate. The major technological difficulty remains the high density of the interconnect. To solve these problems numerous approaches have been suggested. In the present work, a 24×24 elements (24 transmit+24 receive) matrix and a switching board were developed. The transducer consists of two 52 μm PVDF layers each representing a linear array of 24 elements placed one on the top of the other. Electrodes in these two layers are perpendicular and form the grid of 0.5×0.5 mm pitch. The layers are bonded together with the ground electrode being monolithic and located between the layers. The matrix is backed from the rear surface with an epoxy composition. During the emission, a linear element from the emitting layer generates a longitudinal wave pulse propagating inside the test object. Reflected pulses are picked-up by the receiving layer. During one transmit-receive cycle one transmit element and one receive element are selected by corresponding multiplexers. These crossed elements emulate a small element formed by their intersection. The present design presents the following advantages: minimizes number of active channels and density of the interconnect; reduces the electrical impedance of the element improving electrical matching; enables the transmit-receive mode; due to the efficient backing provides bandwidth and good time resolution; and, significantly reduces the electronics complexity. The matrix can not be used for the beam steering and focusing. Owing to this impossibility of focusing, the penetration depth is limited as well by the diffraction phenomena.
Neutron Imaging of Archaeological Bronzes
Ryzewski, Krysta; Herringer, Susan; Bilheux, Hassina Z; Walker, Lakeisha MH; Sheldon, Brian; Voisin, Sophie; Bilheux, Jean-Christophe; Finocchiaro, Vincenzo
2013-01-01
This article presents the initial results of 2-D and 3-D neutron imaging of bronze artifacts using the CG-1D prototype beamline at the High Flux Isotope Reactor (HFIR) located at the Oak Ridge National Laboratory (ORNL). Neutron imaging is a non-destructive technique capable of producing unprecedented three-dimensional information on archaeomaterials, including qualitative, quantitative, and visual data on impurities, composition change, voids, and c
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.
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.
Correlated Electron Phenomena in 2D Materials
NASA Astrophysics Data System (ADS)
Lambert, Joseph G.
In this thesis, I present experimental results on coherent electron phenomena in layered two-dimensional materials: single layer graphene and van der Waals coupled 2D TiSe2. Graphene is a two-dimensional single-atom thick sheet of carbon atoms first derived from bulk graphite by the mechanical exfoliation technique in 2004. Low-energy charge carriers in graphene behave like massless Dirac fermions, and their density can be easily tuned between electron-rich and hole-rich quasiparticles with electrostatic gating techniques. The sharp interfaces between regions of different carrier densities form barriers with selective transmission, making them behave as partially reflecting mirrors. When two of these interfaces are set at a separation distance within the phase coherence length of the carriers, they form an electronic version of a Fabry-Perot cavity. I present measurements and analysis of multiple Fabry-Perot modes in graphene with parallel electrodes spaced a few hundred nanometers apart. Transition metal dichalcogenide (TMD) TiSe2 is part of the family of materials that coined the term "materials beyond graphene". It contains van der Waals coupled trilayer stacks of Se-Ti-Se. Many TMD materials exhibit a host of interesting correlated electronic phases. In particular, TiSe2 exhibits chiral charge density waves (CDW) below TCDW ˜ 200 K. Upon doping with copper, the CDW state gets suppressed with Cu concentration, and CuxTiSe2 becomes superconducting with critical temperature of T c = 4.15 K. There is still much debate over the mechanisms governing the coexistence of the two correlated electronic phases---CDW and superconductivity. I will present some of the first conductance spectroscopy measurements of proximity coupled superconductor-CDW systems. Measurements reveal a proximity-induced critical current at the Nb-TiSe2 interfaces, suggesting pair correlations in the pure TiSe2. The results indicate that superconducting order is present concurrently with CDW in
CYP2D7 Sequence Variation Interferes with TaqMan CYP2D6*15 and *35 Genotyping
Riffel, Amanda K.; Dehghani, Mehdi; Hartshorne, Toinette; Floyd, Kristen C.; Leeder, J. Steven; Rosenblatt, Kevin P.; Gaedigk, Andrea
2016-01-01
TaqMan™ genotyping assays are widely used to genotype CYP2D6, which encodes a major drug metabolizing enzyme. Assay design for CYP2D6 can be challenging owing to the presence of two pseudogenes, CYP2D7 and CYP2D8, structural and copy number variation and numerous single nucleotide polymorphisms (SNPs) some of which reflect the wild-type sequence of the CYP2D7 pseudogene. The aim of this study was to identify the mechanism causing false-positive CYP2D6*15 calls and remediate those by redesigning and validating alternative TaqMan genotype assays. Among 13,866 DNA samples genotyped by the CompanionDx® lab on the OpenArray platform, 70 samples were identified as heterozygotes for 137Tins, the key SNP of CYP2D6*15. However, only 15 samples were confirmed when tested with the Luminex xTAG CYP2D6 Kit and sequencing of CYP2D6-specific long range (XL)-PCR products. Genotype and gene resequencing of CYP2D6 and CYP2D7-specific XL-PCR products revealed a CC>GT dinucleotide SNP in exon 1 of CYP2D7 that reverts the sequence to CYP2D6 and allows a TaqMan assay PCR primer to bind. Because CYP2D7 also carries a Tins, a false-positive mutation signal is generated. This CYP2D7 SNP was also responsible for generating false-positive signals for rs769258 (CYP2D6*35) which is also located in exon 1. Although alternative CYP2D6*15 and *35 assays resolved the issue, we discovered a novel CYP2D6*15 subvariant in one sample that carries additional SNPs preventing detection with the alternate assay. The frequency of CYP2D6*15 was 0.1% in this ethnically diverse U.S. population sample. In addition, we also discovered linkage between the CYP2D7 CC>GT dinucleotide SNP and the 77G>A (rs28371696) SNP of CYP2D6*43. The frequency of this tentatively functional allele was 0.2%. Taken together, these findings emphasize that regardless of how careful genotyping assays are designed and evaluated before being commercially marketed, rare or unknown SNPs underneath primer and/or probe regions can impact
CYP2D7 Sequence Variation Interferes with TaqMan CYP2D6 (*) 15 and (*) 35 Genotyping.
Riffel, Amanda K; Dehghani, Mehdi; Hartshorne, Toinette; Floyd, Kristen C; Leeder, J Steven; Rosenblatt, Kevin P; Gaedigk, Andrea
2015-01-01
TaqMan™ genotyping assays are widely used to genotype CYP2D6, which encodes a major drug metabolizing enzyme. Assay design for CYP2D6 can be challenging owing to the presence of two pseudogenes, CYP2D7 and CYP2D8, structural and copy number variation and numerous single nucleotide polymorphisms (SNPs) some of which reflect the wild-type sequence of the CYP2D7 pseudogene. The aim of this study was to identify the mechanism causing false-positive CYP2D6 (*) 15 calls and remediate those by redesigning and validating alternative TaqMan genotype assays. Among 13,866 DNA samples genotyped by the CompanionDx® lab on the OpenArray platform, 70 samples were identified as heterozygotes for 137Tins, the key SNP of CYP2D6 (*) 15. However, only 15 samples were confirmed when tested with the Luminex xTAG CYP2D6 Kit and sequencing of CYP2D6-specific long range (XL)-PCR products. Genotype and gene resequencing of CYP2D6 and CYP2D7-specific XL-PCR products revealed a CC>GT dinucleotide SNP in exon 1 of CYP2D7 that reverts the sequence to CYP2D6 and allows a TaqMan assay PCR primer to bind. Because CYP2D7 also carries a Tins, a false-positive mutation signal is generated. This CYP2D7 SNP was also responsible for generating false-positive signals for rs769258 (CYP2D6 (*) 35) which is also located in exon 1. Although alternative CYP2D6 (*) 15 and (*) 35 assays resolved the issue, we discovered a novel CYP2D6 (*) 15 subvariant in one sample that carries additional SNPs preventing detection with the alternate assay. The frequency of CYP2D6 (*) 15 was 0.1% in this ethnically diverse U.S. population sample. In addition, we also discovered linkage between the CYP2D7 CC>GT dinucleotide SNP and the 77G>A (rs28371696) SNP of CYP2D6 (*) 43. The frequency of this tentatively functional allele was 0.2%. Taken together, these findings emphasize that regardless of how careful genotyping assays are designed and evaluated before being commercially marketed, rare or unknown SNPs underneath primer
Comparison of unstable water infiltration in porous media in 2D and 3D experiments
NASA Astrophysics Data System (ADS)
Schütz, C.; Neuweiler, I.; Lehmann, P.; Papafotiou, A.; Vontobel, P.; Hartmann, S.
2010-05-01
Water infiltration into unsaturated soil is an important process for groundwater recharge and thus for water balance of natural hydrosystems. The characteristics of infiltration patterns depend on porous media properties and initial moisture content. Infiltration fronts into soil can be unstable in layered media with fine over dry coarse material. To predict arrival times of infiltration fronts and average water content in upscaled models, it is necessary to understand occurrence of instabilities. The unstable flow behavior is not captured by standard models and finger characteristics have mostly been investigated experimentally. Most experiments in the past were carried out in 2D setups and it is not clear how the results of such studies relate to real 3D systems. The aim of this study is to compare development and finger characteristics of unstable infiltration in 2D and 3D setups. We carried out laboratory experiments on fast infiltration in 2D and 3D setups and measured water content in porous media with neutron transmission technology at the NEUTRA beam line at the Paul Scherrer Institute, Switzerland. The 2D experiments were carried out in a glass sandbox (260 mm high, 75 mm wide and 11 mm deep). For the 3D experiments aluminum cylindrical column (150 mm in height and 100 mm in diameter) were used. Both columns were filled homogeneously with coarse quartz sand (grain size 0.7 - 1.2 mm) below fine sand layer (0.1 - 0.3 mm) of 20 - 30 mm thickness. Two dimensional projection images of water content with spatial resolution of 125 microns were deduced from neutron images every 2 second. For the 3D setup water content distribution was reconstructed in 3D to monitor water content inside the fingers over time. Water content and finger-width (15 - 23 mm) were similar for 2D and 3D setups. In both cases water content was maximum when the front passes and was decreasing afterwards (indicating "overshoot" behavior). Also the water content difference between values after
Wende, Charles W. J.; Babcock, Dale F.; Menegus, Robert L.
1983-01-01
A nuclear reactor includes an active portion with fissionable fuel and neutron moderating material surrounded by neutron reflecting material. A control element in the active portion includes a group of movable rods constructed of neutron-absorbing material. Each rod is movable with respect to the other rods to vary the absorption of neutrons and effect control over neutron flux.
Thomae, R.; Gough, R.; Keller, R.; Leung, K.N.; Schenkel, T.; Aleksandrov, A.; Stockli, M.; Welton, R.
2001-09-01
The ion source and Low Energy Beam Transport section of the front-end systems presently being built by Berkeley Lab are required to provide 50 mA of H - beam current at 6% duty factor (1 ms pulses at 60 Hz) with a normalized rms emittance of less than 0.20 p-mm-mrad. Experimental results, including emittance, chopping, and steering measurements, on the performance of the ion source and LEBT system operated at the demanded beam parameters will be discussed.
Differential CYP 2D6 Metabolism Alters Primaquine Pharmacokinetics
Potter, Brittney M. J.; Xie, Lisa H.; Vuong, Chau; Zhang, Jing; Zhang, Ping; Duan, Dehui; Luong, Thu-Lan T.; Bandara Herath, H. M. T.; Dhammika Nanayakkara, N. P.; Tekwani, Babu L.; Walker, Larry A.; Nolan, Christina K.; Sciotti, Richard J.; Zottig, Victor E.; Smith, Philip L.; Paris, Robert M.; Read, Lisa T.; Li, Qigui; Pybus, Brandon S.; Sousa, Jason C.; Reichard, Gregory A.
2015-01-01
Primaquine (PQ) metabolism by the cytochrome P450 (CYP) 2D family of enzymes is required for antimalarial activity in both humans (2D6) and mice (2D). Human CYP 2D6 is highly polymorphic, and decreased CYP 2D6 enzyme activity has been linked to decreased PQ antimalarial activity. Despite the importance of CYP 2D metabolism in PQ efficacy, the exact role that these enzymes play in PQ metabolism and pharmacokinetics has not been extensively studied in vivo. In this study, a series of PQ pharmacokinetic experiments were conducted in mice with differential CYP 2D metabolism characteristics, including wild-type (WT), CYP 2D knockout (KO), and humanized CYP 2D6 (KO/knock-in [KO/KI]) mice. Plasma and liver pharmacokinetic profiles from a single PQ dose (20 mg/kg of body weight) differed significantly among the strains for PQ and carboxy-PQ. Additionally, due to the suspected role of phenolic metabolites in PQ efficacy, these were probed using reference standards. Levels of phenolic metabolites were highest in mice capable of metabolizing CYP 2D6 substrates (WT and KO/KI 2D6 mice). PQ phenolic metabolites were present in different quantities in the two strains, illustrating species-specific differences in PQ metabolism between the human and mouse enzymes. Taking the data together, this report furthers understanding of PQ pharmacokinetics in the context of differential CYP 2D metabolism and has important implications for PQ administration in humans with different levels of CYP 2D6 enzyme activity. PMID:25645856
2D to 3D to 2D Dimensionality Crossovers in Thin BSCCO Films
NASA Astrophysics Data System (ADS)
Williams, Gary A.
2003-03-01
With increasing temperature the superfluid fraction in very thin BSCCO films undergoes a series of dimensionality crossovers. At low temperatures the strong anisotropy causes the thermal excitations to be 2D pancake-antipancake pairs in uncoupled layers. At higher temperatures where the c-axis correlation length becomes larger than a layer there is a crossover to 3D vortex loops. These are initially elliptical, but as the 3D Tc is approached they become more circular as the anisotropy scales away, as modeled by Shenoy and Chattopadhyay [1]. Close to Tc when the correlation length becomes comparable to the film thickness there is a further crossover to a 2D Kosterlitz-Thouless transition, with a drop of the superfluid fraction to zero at T_KT which can be of the order of 1 K below T_c. Good agreement with this model is found for experiments on thin BSCCO 2212 films [2]. 1. S. R. Shenoy and B. Chattopadhyay, Phys. Rev. B 51, 9129 (1995). 2. K. Osborn et al., cond-mat/0204417.
Mechanical characterization of 2D, 2D stitched, and 3D braided/RTM materials
NASA Technical Reports Server (NTRS)
Deaton, Jerry W.; Kullerd, Susan M.; Portanova, Marc A.
1993-01-01
Braided composite materials have potential for application in aircraft structures. Fuselage frames, floor beams, wing spars, and stiffeners are examples where braided composites could find application if cost effective processing and damage tolerance requirements are met. Another important consideration for braided composites relates to their mechanical properties and how they compare to the properties of composites produced by other textile composite processes being proposed for these applications. Unfortunately, mechanical property data for braided composites do not appear extensively in the literature. Data are presented in this paper on the mechanical characterization of 2D triaxial braid, 2D triaxial braid plus stitching, and 3D (through-the-thickness) braid composite materials. The braided preforms all had the same graphite tow size and the same nominal braid architectures, (+/- 30 deg/0 deg), and were resin transfer molded (RTM) using the same mold for each of two different resin systems. Static data are presented for notched and unnotched tension, notched and unnotched compression, and compression after impact strengths at room temperature. In addition, some static results, after environmental conditioning, are included. Baseline tension and compression fatigue results are also presented, but only for the 3D braided composite material with one of the resin systems.
Lagrangian statistics in laboratory 2D turbulence
NASA Astrophysics Data System (ADS)
Xia, Hua; Francois, Nicolas; Punzmann, Horst; Shats, Michael
2014-05-01
Turbulent mixing in liquids and gases is ubiquitous in nature and industrial flows. Understanding statistical properties of Lagrangian trajectories in turbulence is crucial for a range of problems such as spreading of plankton in the ocean, transport of pollutants, etc. Oceanic data on trajectories of the free-drifting instruments, indicate that the trajectory statistics can often be described by a Lagrangian integral scale. Turbulence however is a state of a flow dominated by a hierarchy of scales, and it is not clear which of these scales mostly affect particle dispersion. Moreover, coherent structures often coexist with turbulence in laboratory experiments [1]. The effect of coherent structures on particle dispersion in turbulent flows is not well understood. Recent progress in scientific imaging and computational power made it possible to tackle this problem experimentally. In this talk, we report the analysis of the higher order Lagrangian statistics in laboratory two-dimensional turbulence. Our results show that fluid particle dispersion is diffusive and it is determined by a single measurable Lagrangian scale related to the forcing scale [2]. Higher order moments of the particle dispersion show strong self-similarity in fully developed turbulence [3]. Here we introduce a new dispersion law that describes single particle dispersion during the turbulence development [4]. These results offer a new way of predicting dispersion in turbulent flows in which one of the low energy scales are persistent. It may help better understanding of drifter Lagrangian statistics in the regions of the ocean where small scale coherent eddies are present [5]. Reference: 1. H. Xia, H. Punzmann, G. Falkovich and M. Shats, Physical Review Letters, 101, 194504 (2008) 2. H. Xia, N. Francois, H. Punzmann, and M. Shats, Nature Communications, 4, 2013 (2013) 3. R. Ferrari, A.J. Manfroi , W.R. Young, Physica D 154 111 (2001) 4. H. Xia, N. Francois, H. Punzmann and M. Shats, submitted (2014
Synthesis and characterization of 2D molybdenum carbide (MXene)
Halim, Joseph; Kota, Sankalp; Lukatskaya, Maria R.; Naguib, Michael; Zhao, Meng -Qiang; Moon, Eun Ju; Pitock, Jeremy; Nanda, Jagjit; May, Steven J.; Gogotsi, Yury; et al
2016-02-17
Large scale synthesis and delamination of 2D Mo2CT x (where T is a surface termination group) has been achieved by selectively etching gallium from the recently discovered nanolaminated, ternary transition metal carbide Mo2Ga2C. Different synthesis and delamination routes result in different flake morphologies. The resistivity of free-standing Mo2CT x films increases by an order of magnitude as the temperature is reduced from 300 to 10 K, suggesting semiconductor-like behavior of this MXene, in contrast to Ti3C2T x which exhibits metallic behavior. At 10 K, the magnetoresistance is positive. Additionally, changes in electronic transport are observed upon annealing of the films.more » When 2 μm thick films are tested as electrodes in supercapacitors, capacitances as high as 700 F cm–3 in a 1 m sulfuric acid electrolyte and high capacity retention for at least 10,000 cycles at 10 A g–1 are obtained. Free-standing Mo2CT x films, with ≈8 wt% carbon nanotubes, perform well when tested as an electrode material for Li-ions, especially at high rates. In conclusion, at 20 and 131 C cycling rates, stable reversible capacities of 250 and 76 mAh g–1, respectively, are achieved for over 1000 cycles.« less
2-D Inhomogeneous Modeling of the Solar CO Bands
NASA Astrophysics Data System (ADS)
Ayres, T. R.
1996-05-01
The recent discovery of off-limb emissions in the mid-IR ( ~ 5 mu m) vibration-rotation bands of solar carbon monoxide (CO) has sparked new interest in the formation of the molecular lines, and their ability to diagnose thermal conditions at high altitudes. The off-limb extensions of the strong CO lines indicate the penetration of cool material (T ~ 3500 K) several hundred kilometers into the otherwise hot (T ~ 6000 K) chromosphere. The origin of the cool gas, and its role in the thermal energy balance, remain controversial. The interpretation of the CO observations must rely heavily upon numerical modeling, in particular highly-inhomogeneous thermal structures arrayed in a 2-D scheme that can properly treat the geometry of the grazing rays at the solar limb. The radiation transport, itself, is especially simple for the CO off-limb emissions, because the fundamental bands form quite close to LTE (high collision rates; low spontaneous decay rates) and the background continuum is purely thermal as well (f--f transitions in H(-) and H). Thus, the geometrical aspects of the problem can be treated in considerably more detail than would be practical for typical NLTE scattering lines. I describe the recent modeling efforts, and the diagnostic potential of the CO bands for future observational studies of inhomogeneous surface structure on the Sun, and on other stars of late spectral type. This work was supported by NSF grant AST-9218063 to the University of Colorado.
Gravitational Wave Signals from 2D and 3D Core Collapse Supernova Explosions
NASA Astrophysics Data System (ADS)
Yakunin, Konstantin; Mezzacappa, Anthony; Marronetti, Pedro; Bruenn, Stephen; Hix, W. Raphael; Lentz, Eric J.; Messer, O. E. Bronson; Harris, J. Austin; Endeve, Eirik; Blondin, John
2016-03-01
We study two- and three-dimensional (2D and 3D) core-collapse supernovae (CCSN) using our first-principles CCSN simulations performed with the neutrino hydrodynamics code CHIMERA. The following physics is included: Newtonian hydrodynamics with a nuclear equation of state capable of describing matter in both NSE and non-NSE, MGFLD neutrino transport with realistic neutrino interactions, an effective GR gravitational potential, and a nuclear reaction network. Both our 2D and 3D models achieve explosion, which in turn enables us to determine their complete gravitational wave signals. In this talk, we present them, and we analyze the similarities and differences between the 2D and 3D signals.
Differential Cytochrome P450 2D Metabolism Alters Tafenoquine Pharmacokinetics
Vuong, Chau; Xie, Lisa H.; Potter, Brittney M. J.; Zhang, Jing; Zhang, Ping; Duan, Dehui; Nolan, Christina K.; Sciotti, Richard J.; Zottig, Victor E.; Nanayakkara, N. P. Dhammika; Tekwani, Babu L.; Walker, Larry A.; Smith, Philip L.; Paris, Robert M.; Read, Lisa T.; Li, Qigui; Pybus, Brandon S.; Sousa, Jason C.; Reichard, Gregory A.; Smith, Bryan
2015-01-01
Cytochrome P450 (CYP) 2D metabolism is required for the liver-stage antimalarial efficacy of the 8-aminoquinoline molecule tafenoquine in mice. This could be problematic for Plasmodium vivax radical cure, as the human CYP 2D ortholog (2D6) is highly polymorphic. Diminished CYP 2D6 enzyme activity, as in the poor-metabolizer phenotype, could compromise radical curative efficacy in humans. Despite the importance of CYP 2D metabolism for tafenoquine liver-stage efficacy, the exact role that CYP 2D metabolism plays in the metabolism and pharmacokinetics of tafenoquine and other 8-aminoquinoline molecules has not been extensively studied. In this study, a series of tafenoquine pharmacokinetic experiments were conducted in mice with different CYP 2D metabolism statuses, including wild-type (WT) (reflecting extensive metabolizers for CYP 2D6 substrates) and CYPmouse 2D knockout (KO) (reflecting poor metabolizers for CYP 2D6 substrates) mice. Plasma and liver pharmacokinetic profiles from a single 20-mg/kg of body weight dose of tafenoquine differed between the strains; however, the differences were less striking than previous results obtained for primaquine in the same model. Additionally, the presence of a 5,6-ortho-quinone tafenoquine metabolite was examined in both mouse strains. The 5,6-ortho-quinone species of tafenoquine was observed, and concentrations of the metabolite were highest in the WT extensive-metabolizer phenotype. Altogether, this study indicates that CYP 2D metabolism in mice affects tafenoquine pharmacokinetics and could have implications for human tafenoquine pharmacokinetics in polymorphic CYP 2D6 human populations. PMID:25870069
Simulation of the full-core pin-model by JMCT Monte Carlo neutron-photon transport code
Li, D.; Li, G.; Zhang, B.; Shu, L.; Shangguan, D.; Ma, Y.; Hu, Z.
2013-07-01
Since the large numbers of cells over a million, the tallies over a hundred million and the particle histories over ten billion, the simulation of the full-core pin-by-pin model has become a real challenge for the computers and the computational methods. On the other hand, the basic memory of the model has exceeded the limit of a single CPU, so the spatial domain and data decomposition must be considered. JMCT (J Monte Carlo Transport code) has successful fulfilled the simulation of the full-core pin-by-pin model by the domain decomposition and the nested parallel computation. The k{sub eff} and flux of each cell are obtained. (authors)
Salles, Fabrice; Jobic, Hervé; Devic, Thomas; Llewellyn, Philip L; Serre, Christian; Férey, Gérard; Maurin, Guillaume
2010-01-26
Quasi-elastic neutron scattering measurements are combined with molecular dynamics simulations to determine the self-diffusivity, corrected diffusivity, and transport diffusivity of CO(2) in the metal-organic framework MIL-47(V) (MIL = Materials Institut Lavoisier) over a wide range of loading. The force field used for describing the host/guest interactions is first validated on the thermodynamics of the MIL-47(V)/CO(2) system, prior to being transferred to the investigations of the dynamics. A decreasing profile is then deduced for D(s) and D(o) whereas D(t) presents a non monotonous evolution with a slight decrease at low loading followed by a sharp increase at higher loading. Such decrease of D(t) which has never been evidenced in any microporous systems comes from the atypical evolution of the thermodynamic correction factor that reaches values below 1 at low loading. This implies that, due to intermolecular interactions, the CO(2) molecules in MIL-47(V) do not behave like an ideal gas. Further, molecular simulations enabled us to elucidate unambiguously a 3D diffusion mechanism within the pores of MIL-47(V). PMID:19957953
NASA Astrophysics Data System (ADS)
Owens, A. R.; Welch, J. A.; Kópházi, J.; Eaton, M. D.
2016-06-01
In this paper two discontinuous Galerkin isogeometric analysis methods are developed and applied to the first-order form of the neutron transport equation with a discrete ordinate (SN) angular discretisation. The discontinuous Galerkin projection approach was taken on both an element level and the patch level for a given Non-Uniform Rational B-Spline (NURBS) patch. This paper describes the detailed dispersion analysis that has been used to analyse the numerical stability of both of these schemes. The convergence of the schemes for both smooth and non-smooth solutions was also investigated using the method of manufactured solutions (MMS) for multidimensional problems and a 1D semi-analytical benchmark whose solution contains a strongly discontinuous first derivative. This paper also investigates the challenges posed by strongly curved boundaries at both the NURBS element and patch level with several algorithms developed to deal with such cases. Finally numerical results are presented both for a simple pincell test problem as well as the C5G7 quarter core MOX/UOX small Light Water Reactor (LWR) benchmark problem. These numerical results produced by the isogeometric analysis (IGA) methods are compared and contrasted against linear and quadratic discontinuous Galerkin finite element (DGFEM) SN based methods.
Latent heat induced rotation limited aggregation in 2D ice nanocrystals
NASA Astrophysics Data System (ADS)
Bampoulis, Pantelis; Siekman, Martin H.; Kooij, E. Stefan; Lohse, Detlef; Zandvliet, Harold J. W.; Poelsema, Bene
2015-07-01
The basic science responsible for the fascinating shapes of ice crystals and snowflakes is still not understood. Insufficient knowledge of the interaction potentials and the lack of relevant experimental access to the growth process are to blame for this failure. Here, we study the growth of fractal nanostructures in a two-dimensional (2D) system, intercalated between mica and graphene. Based on our scanning tunneling spectroscopy data, we provide compelling evidence that these fractals are 2D ice. They grow while they are in material contact with the atmosphere at 20 °C and without significant thermal contact to the ambient. The growth is studied in situ, in real time and space at the nanoscale. We find that the growing 2D ice nanocrystals assume a fractal shape, which is conventionally attributed to Diffusion Limited Aggregation (DLA). However, DLA requires a low mass density mother phase, in contrast to the actual currently present high mass density mother phase. Latent heat effects and consequent transport of heat and molecules are found to be key ingredients for understanding the evolution of the snow (ice) flakes. We conclude that not the local availability of water molecules (DLA), but rather them having the locally required orientation is the key factor for incorporation into the 2D ice nanocrystal. In combination with the transport of latent heat, we attribute the evolution of fractal 2D ice nanocrystals to local temperature dependent rotation limited aggregation. The ice growth occurs under extreme supersaturation, i.e., the conditions closely resemble the natural ones for the growth of complex 2D snow (ice) flakes and we consider our findings crucial for solving the "perennial" snow (ice) flake enigma.
Latent heat induced rotation limited aggregation in 2D ice nanocrystals.
Bampoulis, Pantelis; Siekman, Martin H; Kooij, E Stefan; Lohse, Detlef; Zandvliet, Harold J W; Poelsema, Bene
2015-07-21
The basic science responsible for the fascinating shapes of ice crystals and snowflakes is still not understood. Insufficient knowledge of the interaction potentials and the lack of relevant experimental access to the growth process are to blame for this failure. Here, we study the growth of fractal nanostructures in a two-dimensional (2D) system, intercalated between mica and graphene. Based on our scanning tunneling spectroscopy data, we provide compelling evidence that these fractals are 2D ice. They grow while they are in material contact with the atmosphere at 20 °C and without significant thermal contact to the ambient. The growth is studied in situ, in real time and space at the nanoscale. We find that the growing 2D ice nanocrystals assume a fractal shape, which is conventionally attributed to Diffusion Limited Aggregation (DLA). However, DLA requires a low mass density mother phase, in contrast to the actual currently present high mass density mother phase. Latent heat effects and consequent transport of heat and molecules are found to be key ingredients for understanding the evolution of the snow (ice) flakes. We conclude that not the local availability of water molecules (DLA), but rather them having the locally required orientation is the key factor for incorporation into the 2D ice nanocrystal. In combination with the transport of latent heat, we attribute the evolution of fractal 2D ice nanocrystals to local temperature dependent rotation limited aggregation. The ice growth occurs under extreme supersaturation, i.e., the conditions closely resemble the natural ones for the growth of complex 2D snow (ice) flakes and we consider our findings crucial for solving the "perennial" snow (ice) flake enigma. PMID:26203037
A Geometric Boolean Library for 2D Objects
2006-01-05
The 2D Boolean Library is a collection of C++ classes -- which primarily represent 2D geometric data and relationships, and routines -- which contain algorithms for 2D geometric Boolean operations and utility functions. Classes are provided for 2D points, lines, arcs, edgeuses, loops, surfaces and mask sets. Routines are provided that incorporate the Boolean operations Union(OR), XOR, Intersection and Difference. Various analytical geometry routines and routines for importing and exporting the data in various filemore » formats, are also provided in the library.« less
A Geometric Boolean Library for 2D Objects
McBride, Corey L.; Yarberry, Victor; Jorgensen, Craig
2006-01-05
The 2D Boolean Library is a collection of C++ classes -- which primarily represent 2D geometric data and relationships, and routines -- which contain algorithms for 2D geometric Boolean operations and utility functions. Classes are provided for 2D points, lines, arcs, edgeuses, loops, surfaces and mask sets. Routines are provided that incorporate the Boolean operations Union(OR), XOR, Intersection and Difference. Various analytical geometry routines and routines for importing and exporting the data in various file formats, are also provided in the library.
AnisWave2D: User's Guide to the 2d Anisotropic Finite-DifferenceCode
Toomey, Aoife
2005-01-06
This document describes a parallel finite-difference code for modeling wave propagation in 2D, fully anisotropic materials. The code utilizes a mesh refinement scheme to improve computational efficiency. Mesh refinement allows the grid spacing to be tailored to the velocity model, so that fine grid spacing can be used in low velocity zones where the seismic wavelength is short, and coarse grid spacing can be used in zones with higher material velocities. Over-sampling of the seismic wavefield in high velocity zones is therefore avoided. The code has been implemented to run in parallel over multiple processors and allows large-scale models and models with large velocity contrasts to be simulated with ease.
Klassifikation von Standardebenen in der 2D-Echokardiographie mittels 2D-3D-Bildregistrierung
NASA Astrophysics Data System (ADS)
Bergmeir, Christoph; Subramanian, Navneeth
Zum Zweck der Entwicklung eines Systems, das einen unerfahrenen Anwender von Ultraschall (US) zur Aufnahme relevanter anatomischer Strukturen leitet, untersuchen wir die Machbarkeit von 2D-US zu 3D-CT Registrierung. Wir verwenden US-Aufnahmen von Standardebenen des Herzens, welche zu einem 3D-CT-Modell registriert werden. Unser Algorithmus unterzieht sowohl die US-Bilder als auch den CT-Datensatz Vorverarbeitungsschritten, welche die Daten durch Segmentierung auf wesentliche Informationen in Form von Labein für Muskel und Blut reduzieren. Anschließend werden diese Label zur Registrierung mittels der Match-Cardinality-Metrik genutzt. Durch mehrmaliges Registrieren mit verschiedenen Initialisierungen ermitteln wir die im US-Bild sichtbare Standardebene. Wir evaluierten die Methode auf sieben US-Bildern von Standardebenen. Fünf davon wurden korrekt zugeordnet.
Multiyear Statistics of 2-D Shortwave Radiative Effects at Three ARM Sites
NASA Technical Reports Server (NTRS)
Varnai, Tamas
2010-01-01
This study examines the importance of horizontal photon transport effects, which are not considered in the 1-D calculations of solar radiative heating used by most atmospheric dynamical models. In particular, the paper analyzes the difference between 2-D and 1-D radiative calculations for 2-D vertical cross-sections of clouds that were observed at three sites over 2- to 3-year periods. The results show that 2-D effects increase multiyear 24-hour average total solar absorption by about 4.1 W/sq m, 1.2 W/sq m, and 0.3 W/sq m at a tropical, mid-latitude, and arctic site, respectively. However, 2-D effects are often much larger than these average values, especially for high sun and for convective clouds. The results also reveal a somewhat unexpected behavior, that horizontal photon transport often enhances solar heating even for oblique sun. These findings underscore the need for fast radiation calculation methods that can allow atmospheric dynamical simulations to consider the inherently multidimensional nature of shortwave radiative processes.
Functional characterization of CYP2D6 enhancer polymorphisms
Wang, Danxin; Papp, Audrey C.; Sun, Xiaochun
2015-01-01
CYP2D6 metabolizes nearly 25% of clinically used drugs. Genetic polymorphisms cause large inter-individual variability in CYP2D6 enzyme activity and are currently used as biomarker to predict CYP2D6 metabolizer phenotype. Previously, we had identified a region 115 kb downstream of CYP2D6 as enhancer for CYP2D6, containing two completely linked single nucleotide polymorphisms (SNPs), rs133333 and rs5758550, associated with enhanced transcription. However, the enhancer effect on CYP2D6 expression, and the causative variant, remained to be ascertained. To characterize the CYP2D6 enhancer element, we applied chromatin conformation capture combined with the next-generation sequencing (4C assays) and chromatin immunoprecipitation with P300 antibody, in HepG2 and human primary culture hepatocytes. The results confirmed the role of the previously identified enhancer region in CYP2D6 expression, expanding the number of candidate variants to three highly linked SNPs (rs133333, rs5758550 and rs4822082). Among these, only rs5758550 demonstrated regulating enhancer activity in a reporter gene assay. Use of clustered regularly interspaced short palindromic repeats mediated genome editing in HepG2 cells targeting suspected enhancer regions decreased CYP2D6 mRNA expression by 70%, only upon deletion of the rs5758550 region. These results demonstrate robust effects of both the enhancer element and SNP rs5758550 on CYP2D6 expression, supporting consideration of rs5758550 for CYP2D6 genotyping panels to yield more accurate phenotype prediction. PMID:25381333
NASA Astrophysics Data System (ADS)
Chae, Dongho; Constantin, Peter; Wu, Jiahong
2014-09-01
We give an example of a well posed, finite energy, 2D incompressible active scalar equation with the same scaling as the surface quasi-geostrophic equation and prove that it can produce finite time singularities. In spite of its simplicity, this seems to be the first such example. Further, we construct explicit solutions of the 2D Boussinesq equations whose gradients grow exponentially in time for all time. In addition, we introduce a variant of the 2D Boussinesq equations which is perhaps a more faithful companion of the 3D axisymmetric Euler equations than the usual 2D Boussinesq equations.
Sagua, A.; Lescano, Gabriela M.; Alonso, J.A.; Martínez-Coronado, R.; Fernández-Díaz, M.T.; Morán, E.
2012-06-15
Graphical abstract: A pure specimen has been synthesized by the hydroxide route. This spinel, studied by NPD, shows an important inversion degree, λ = 0.80. A bond-valence study shows that the tetrahedral Mn ions are divalent whereas the octahedral Mn and Ni are slightly oxidized from the expected 3+ and 2+ values, respectively. The mixed valence Mn{sup 3+}/Mn{sup 4+} accounts for a hopping mechanism between adjacent octahedral sites, leading to a significant conductivity. Highlights: ► A low-temperature hydroxide route allowed preparing almost pure specimens of NiMn{sub 2}O{sub 4}. ► NPD essential to determine inversion degree; contrasting Ni and Mn for neutrons. ► Bond valence establishes valence state of octahedral and tetrahedral Ni and Mn ions. ► Thermal analysis, transport measurements complement characterization of this oxide. ► A structure–properties relationship is established. -- Abstract: The title compound has been synthesized by the hydroxide route. The crystal structure has been investigated at room temperature from high-resolution neutron powder diffraction (NPD) data. It crystallizes in a cubic spinel structure, space group Fd3{sup ¯}m, Z = 8, with a = 8.3940(2) Å at 295 K. The crystallographic formula is (Ni{sub 0.202(1)}Mn{sub 0.798(1)}){sub 8a}(Ni{sub 0.790(1)}Mn{sub 1.210(1)}){sub 16d}O{sub 4} where 8a and 16d stand for the tetrahedral and octahedral sites of the spinel structure, respectively. There is a significant inversion degree of the spinel structure, λ = 0.80. In fact, the variable parameter for the oxygen position, u = 0.2636(4), is far from that expected (u = 0.25) for normal spinels. From a bond-valence study, it seems that the valence distribution in NiMn{sub 2}O{sub 4} spinel is not as trivial as expected (Ni{sup 2+} and Mn{sup 3+}), but clearly the tetrahedral Mn ions are divalent whereas the octahedral Mn and Ni are slightly oxidized from the expected +3 and +2 values, respectively. The mixed valence observed at
Efficient Visible Quasi-2D Perovskite Light-Emitting Diodes.
Byun, Jinwoo; Cho, Himchan; Wolf, Christoph; Jang, Mi; Sadhanala, Aditya; Friend, Richard H; Yang, Hoichang; Lee, Tae-Woo
2016-09-01
Efficient quasi-2D-structure perovskite light-emitting diodes (4.90 cd A(-1) ) are demonstrated by mixing a 3D-structured perovskite material (methyl ammonium lead bromide) and a 2D-structured perovskite material (phenylethyl ammonium lead bromide), which can be ascribed to better film uniformity, enhanced exciton confinement, and reduced trap density. PMID:27334788
Integrating Mobile Multimedia into Textbooks: 2D Barcodes
ERIC Educational Resources Information Center
Uluyol, Celebi; Agca, R. Kagan
2012-01-01
The major goal of this study was to empirically compare text-plus-mobile phone learning using an integrated 2D barcode tag in a printed text with three other conditions described in multimedia learning theory. The method examined in the study involved modifications of the instructional material such that: a 2D barcode was used near the text, the…
Liu, T.; Ding, A.; Ji, W.; Xu, X. G.; Carothers, C. D.; Brown, F. B.
2012-07-01
Monte Carlo (MC) method is able to accurately calculate eigenvalues in reactor analysis. Its lengthy computation time can be reduced by general-purpose computing on Graphics Processing Units (GPU), one of the latest parallel computing techniques under development. The method of porting a regular transport code to GPU is usually very straightforward due to the 'embarrassingly parallel' nature of MC code. However, the situation becomes different for eigenvalue calculation in that it will be performed on a generation-by-generation basis and the thread coordination should be explicitly taken care of. This paper presents our effort to develop such a GPU-based MC code in Compute Unified Device Architecture (CUDA) environment. The code is able to perform eigenvalue calculation under simple geometries on a multi-GPU system. The specifics of algorithm design, including thread organization and memory management were described in detail. The original CPU version of the code was tested on an Intel Xeon X5660 2.8 GHz CPU, and the adapted GPU version was tested on NVIDIA Tesla M2090 GPUs. Double-precision floating point format was used throughout the calculation. The result showed that a speedup of 7.0 and 33.3 were obtained for a bare spherical core and a binary slab system respectively. The speedup factor was further increased by a factor of {approx}2 on a dual GPU system. The upper limit of device-level parallelism was analyzed, and a possible method to enhance the thread-level parallelism was proposed. (authors)
Solares, G.R.; Zamenhof, R.G. |
1995-10-01
A novel approach to the microdosimetry of neutron capture therapy has been developed using high-resolution quantitative autoradiography (HRQAR) and two-dimensional Monte Carlo simulation. This approach has been applied using actual cell morophology (nuclear and cytoplasmic cell structures) and the measured microdistribution of boron-10 in a transplanted murine brain tumor (GL261) containing p-boronophenylalanine (BPA) as the boron compound. The 2D Monte Carlo transport code for the {alpha} and {sup 7}Li charged particles from the {sup 10}B(n,{alpha}){sup 7}Li reactions has been developed as a surrogate to a full 3D approach to calculate a variety of different microdosimetric parameters. The HRQAR method and the surrogate 2D Monte Carlo approach are described in detail and examples of their use are presented. 27 refs., 11 figs., 1 tab.
Van der Waals stacked 2D layered materials for optoelectronics
NASA Astrophysics Data System (ADS)
Zhang, Wenjing; Wang, Qixing; Chen, Yu; Wang, Zhuo; Wee, Andrew T. S.
2016-06-01
The band gaps of many atomically thin 2D layered materials such as graphene, black phosphorus, monolayer semiconducting transition metal dichalcogenides and hBN range from 0 to 6 eV. These isolated atomic planes can be reassembled into hybrid heterostructures made layer by layer in a precisely chosen sequence. Thus, the electronic properties of 2D materials can be engineered by van der Waals stacking, and the interlayer coupling can be tuned, which opens up avenues for creating new material systems with rich functionalities and novel physical properties. Early studies suggest that van der Waals stacked 2D materials work exceptionally well, dramatically enriching the optoelectronics applications of 2D materials. Here we review recent progress in van der Waals stacked 2D materials, and discuss their potential applications in optoelectronics.