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Sample records for simulated electronic structures

  1. The CECAM Electronic Structure Library: community-driven development of software libraries for electronic structure simulations

    NASA Astrophysics Data System (ADS)

    Oliveira, Micael

    The CECAM Electronic Structure Library (ESL) is a community-driven effort to segregate shared pieces of software as libraries that could be contributed and used by the community. Besides allowing to share the burden of developing and maintaining complex pieces of software, these can also become a target for re-coding by software engineers as hardware evolves, ensuring that electronic structure codes remain at the forefront of HPC trends. In a series of workshops hosted at the CECAM HQ in Lausanne, the tools and infrastructure for the project were prepared, and the first contributions were included and made available online (http://esl.cecam.org). In this talk I will present the different aspects and aims of the ESL and how these can be useful for the electronic structure community.

  2. Modeling and simulation of electronic structure, material interface and random doping in nano electronic devices

    PubMed Central

    Chen, Duan; Wei, Guo-Wei

    2010-01-01

    The miniaturization of nano-scale electronic devices, such as metal oxide semiconductor field effect transistors (MOSFETs), has given rise to a pressing demand in the new theoretical understanding and practical tactic for dealing with quantum mechanical effects in integrated circuits. Modeling and simulation of this class of problems have emerged as an important topic in applied and computational mathematics. This work presents mathematical models and computational algorithms for the simulation of nano-scale MOSFETs. We introduce a unified two-scale energy functional to describe the electrons and the continuum electrostatic potential of the nano-electronic device. This framework enables us to put microscopic and macroscopic descriptions in an equal footing at nano scale. By optimization of the energy functional, we derive consistently-coupled Poisson-Kohn-Sham equations. Additionally, layered structures are crucial to the electrostatic and transport properties of nano transistors. A material interface model is proposed for more accurate description of the electrostatics governed by the Poisson equation. Finally, a new individual dopant model that utilizes the Dirac delta function is proposed to understand the random doping effect in nano electronic devices. Two mathematical algorithms, the matched interface and boundary (MIB) method and the Dirichlet-to-Neumann mapping (DNM) technique, are introduced to improve the computational efficiency of nano-device simulations. Electronic structures are computed via subband decomposition and the transport properties, such as the I-V curves and electron density, are evaluated via the non-equilibrium Green's functions (NEGF) formalism. Two distinct device configurations, a double-gate MOSFET and a four-gate MOSFET, are considered in our three-dimensional numerical simulations. For these devices, the current fluctuation and voltage threshold lowering effect induced by the discrete dopant model are explored. Numerical convergence

  3. Modeling and simulation of electronic structure, material interface and random doping in nano electronic devices.

    PubMed

    Chen, Duan; Wei, Guo-Wei

    2010-06-20

    The miniaturization of nano-scale electronic devices, such as metal oxide semiconductor field effect transistors (MOSFETs), has given rise to a pressing demand in the new theoretical understanding and practical tactic for dealing with quantum mechanical effects in integrated circuits. Modeling and simulation of this class of problems have emerged as an important topic in applied and computational mathematics. This work presents mathematical models and computational algorithms for the simulation of nano-scale MOSFETs. We introduce a unified two-scale energy functional to describe the electrons and the continuum electrostatic potential of the nano-electronic device. This framework enables us to put microscopic and macroscopic descriptions in an equal footing at nano scale. By optimization of the energy functional, we derive consistently-coupled Poisson-Kohn-Sham equations. Additionally, layered structures are crucial to the electrostatic and transport properties of nano transistors. A material interface model is proposed for more accurate description of the electrostatics governed by the Poisson equation. Finally, a new individual dopant model that utilizes the Dirac delta function is proposed to understand the random doping effect in nano electronic devices. Two mathematical algorithms, the matched interface and boundary (MIB) method and the Dirichlet-to-Neumann mapping (DNM) technique, are introduced to improve the computational efficiency of nano-device simulations. Electronic structures are computed via subband decomposition and the transport properties, such as the I-V curves and electron density, are evaluated via the non-equilibrium Green's functions (NEGF) formalism. Two distinct device configurations, a double-gate MOSFET and a four-gate MOSFET, are considered in our three-dimensional numerical simulations. For these devices, the current fluctuation and voltage threshold lowering effect induced by the discrete dopant model are explored. Numerical convergence

  4. Modeling and simulation of electronic structure, material interface and random doping in nano-electronic devices

    NASA Astrophysics Data System (ADS)

    Chen, Duan; Wei, Guo-Wei

    2010-06-01

    The miniaturization of nano-scale electronic devices, such as metal oxide semiconductor field effect transistors (MOSFETs), has given rise to a pressing demand in the new theoretical understanding and practical tactic for dealing with quantum mechanical effects in integrated circuits. Modeling and simulation of this class of problems have emerged as an important topic in applied and computational mathematics. This work presents mathematical models and computational algorithms for the simulation of nano-scale MOSFETs. We introduce a unified two-scale energy functional to describe the electrons and the continuum electrostatic potential of the nano-electronic device. This framework enables us to put microscopic and macroscopic descriptions in an equal footing at nano-scale. By optimization of the energy functional, we derive consistently coupled Poisson-Kohn-Sham equations. Additionally, layered structures are crucial to the electrostatic and transport properties of nano-transistors. A material interface model is proposed for more accurate description of the electrostatics governed by the Poisson equation. Finally, a new individual dopant model that utilizes the Dirac delta function is proposed to understand the random doping effect in nano-electronic devices. Two mathematical algorithms, the matched interface and boundary (MIB) method and the Dirichlet-to-Neumann mapping (DNM) technique, are introduced to improve the computational efficiency of nano-device simulations. Electronic structures are computed via subband decomposition and the transport properties, such as the I- V curves and electron density, are evaluated via the non-equilibrium Green's functions (NEGF) formalism. Two distinct device configurations, a double-gate MOSFET and a four-gate MOSFET, are considered in our three-dimensional numerical simulations. For these devices, the current fluctuation and voltage threshold lowering effect induced by the discrete dopant model are explored. Numerical

  5. Atomistic Simulation and Electronic Structure of Lithium Doped Ionic Liquids: Structure, Transport, and Electrochemical Stability

    NASA Technical Reports Server (NTRS)

    Haskins, Justin B.; Bauschlicher, Charles W.; Lawson, John W.

    2015-01-01

    Zero-temperature density functional theory (DFT), density functional theory molecular dynamics (DFT-MD), and classical molecular dynamics using polarizable force fields (PFF-MD) are employed to evaluate the influence of Lithium ion on the structure, transport, and electrochemical stability of three potential ionic liquid electrolytes: N--methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([pyr14][TFSI]), N--methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide ([pyr13][FSI]), and 1-ethyl-3--methylimidazolium boron tetrafluoride ([EMIM][BF4]). We characterize the Lithium ion solvation shell through zero-temperature DFT simulations of [Li(Anion)sub n](exp n-1) -clusters, DFT-MD simulations of isolated lithium ions in small ionic liquid systems, and PFF-MD simulations with high Li-doping levels in large ionic liquid systems. At low levels of Li-salt doping, highly stable solvation shells having 2-3 anions are seen in both [pyr14][TFSI] and [pyr13][FSI], while solvation shells with 4 anions dominate in [EMIM][BF sub 4]. At higher levels of doping, we find the formation of complex Li-network structures that increase the frequency of 4 anion-coordinated solvation shells. A comparison of computational and experimental Raman spectra for a wide range of [Li(Anion) sub n](exp n -1) - clusters shows that our proposed structures are consistent with experiment. We estimate the ion diffusion coefficients and quantify both size and simulation time effects. We find estimates of lithium ion diffusion are a reasonable order of magnitude and can be corrected for simulation time effects. Simulation size, on the other hand, is also important, with diffusion coefficients from long PFF-MD simulations of small cells having 20-40% error compared to large-cell values. Finally, we compute the electrochemical window using differences in electronic energy levels of both isolated cation/anion pairs and small ionic liquid systems with Li-salt doping. The single pair and liquid

  6. Transverse instability and the structure of two-dimensional electron holes: particle-in-cell simulations

    NASA Astrophysics Data System (ADS)

    Lu, Q.; Wu, M.; Huang, C.; Wang, S.

    2011-12-01

    A multi-dimensional electron phase-space hole (electron hole) is considered to be unstable to the transverse instability. We perform two-dimensional (2D) particle-in-cell (PIC) simulations to study the evolution of electron holes at different plasma conditions; we find that the evolution is determined by combined actions between the transverse instability and the stabilization by the ackground magnetic field. In very weakly magnetized plasma, the transverse instability dominates the evolution of the electron holes. The parallel cut of the perpendicular electric field has bipolar structures, accompanied by the kinking of the electron holes. Such structures last for only tens of electron plasma periods. With the increase of the background magnetic field, the evolution of the electron holes becomes slower. The bipolar structures of the parallel cut of the perpendicular electric field in the electron holes can evolve into unipolar structures. In very strongly magnetized plasma, the unipolar structures of the parallel cut of the perpendicular electric field can last for thousands of electron plasma periods. At the same time, the perpendicular electric field in the electron holes can also influence electron trajectories passing through the electron holes, which results in variations of charge density along the direction perpendicular to the background magnetic field outside of the electron holes. When the amplitude of the electron hole is sufficiently strong, streaked structures of the perpendicular electric field can be formed outside of the electron holes, which then emit electrostatic whistler waves because of the interactions between the streaked structures of the perpendicular electric field and vibrations of the kinked electron holes.

  7. FEMSIM + HRMC: Simulation of and structural refinement using fluctuation electron microscopy for amorphous materials

    NASA Astrophysics Data System (ADS)

    Maldonis, Jason J.; Hwang, Jinwoo; Voyles, Paul M.

    2017-04-01

    FEMSIM, a Fortran code, is used to simulate the fluctuation electron microscopy signal, the variance, V(k) , from a model atomic structure. FEMSIM has been incorporated into a hybrid-reverse Monte Carlo code that combines an embedded atom or Finnis-Sinclair potential with the deviation between simulated and experimental V(k) data to refine an atomic model with structure constrained by both the potential and experimental data. The resulting models have experimentally-derived medium-range order.

  8. Electronic Structure, Statistical Mechanical Simulations, and EXAFS Spectroscopy of Aqueous Potassium

    SciTech Connect

    Glezakou, Vanda A.; Chen, Yongsheng; Fulton, John L.; Schenter, Gregory K.; Dang, Liem X.

    2006-03-01

    We investigate the solvation structure of aqueous potassium ions, using a combination of electronic structure calculations, statistical mechanical simulations with a derived polarizable empirical potential and experimental measurement of the Extended X-ray Absorption Fine Structure (EXAFS) spectra. The potassium K-edge (at 3608 eV) EXAFS spectra were acquired on the bending magnet of sector 20 at the Advanced Photon source, at ambient conditions and for the concentrations of 1m and 4m KCl. We focus on the coordination distances and the degree of disorder of the first hydration shell as determined by electronic structure calculations, molecular dynamics simulations and experimental measurement. Finally, we characterize the changes of the structure in the first hydration shell with increasing temperature as predicted by molecular simulation.

  9. Electronic and atomic structure and dynamics of electrode-electrolyte interfaces by computer simulation

    NASA Astrophysics Data System (ADS)

    Walbran, Sean Michael

    We have carried out simulation studies of the electrode electrolyte interface using quantum mechanical electronic structure direct dynamics and classical molecular dynamics methods. We have obtained a complete description of the electrostatic response of the copper/water interface including electronic structure of the electrode, molecular structure of the Stern layer, and a continuum treatment of the electrolyte ions. We have furthered the investigation of chlorine adsorbtion and electron transfer reactions at the interface by refining and exploring electronic structure techniques. While these techniques are currently too expensive for use in electron transfer studies, we were able to study the cuprous/cupric reaction at a copper electrode in water by incorporating features of more detailed simulations into classical molecular dynamics models. In contrast with earlier studies of ferrous/ferric electron transfer, we find that the cuprous/cupric reaction proceeds adiabatically. Results on the electron transfer rates are in reasonable agreement with new experiments carried out by out collaborators at Argonne National Laboratory.

  10. Fully kinetic simulations of collisionless, mesothermal plasma emission: Macroscopic plume structure and microscopic electron characteristics

    NASA Astrophysics Data System (ADS)

    Hu, Yuan; Wang, Joseph

    2017-03-01

    This paper presents a fully kinetic particle particle-in-cell simulation study on the emission of a collisionless plasma plume consisting of cold beam ions and thermal electrons. Results are presented for both the two-dimensional macroscopic plume structure and the microscopic electron kinetic characteristics. We find that the macroscopic plume structure exhibits several distinctive regions, including an undisturbed core region, an electron cooling expansion region, and an electron isothermal expansion region. The properties of each region are determined by microscopic electron kinetic characteristics. The division between the undisturbed region and the cooling expansion region approximately matches the Mach line generated at the edge of the emission surface, and that between the cooling expansion region and the isothermal expansion region approximately matches the potential well established in the beam. The interactions between electrons and the potential well lead to a new, near-equilibrium state different from the initial distribution for the electrons in the isothermal expansion region. The electron kinetic characteristics in the plume are also very anisotropic. As the electron expansion process is mostly non-equilibrium and anisotropic, the commonly used assumption that the electrons in a collisionless, mesothermal plasma plume may be treated as a single equilibrium fluid in general is not valid.

  11. A distributed approach to verification and validation of electronic structure simulation data using ESTEST

    NASA Astrophysics Data System (ADS)

    Yuan, Gary; Gygi, François

    2012-08-01

    We present a Verification and Validation (V&V) approach for electronic structure computations based on a network of distributed servers running the ESTEST (Electronic Structure TEST) software. This network-based infrastructure enables remote verification, validation, comparison and sharing of electronic structure data obtained with different simulation codes. The implementation and configuration of the distributed framework is described. ESTEST features are enhanced by server communication and data sharing, minimizing the duplication of effort by separate research groups. We discuss challenges that arise from the use of a distributed network of ESTEST servers and outline possible solutions. A community web portal called ESTEST Discovery is introduced for the purpose of facilitating the collection and annotation of contents from multiple ESTEST servers. We describe examples of use of the framework using two currently running servers at the University of California Davis and at the Centre Européen de Calcul Atomique et Moléculaire (CECAM).

  12. Simulation of NMR data reveals that proteins' local structures are stabilized by electronic polarization.

    PubMed

    Tong, Yan; Ji, Chang G; Mei, Ye; Zhang, John Z H

    2009-06-24

    Molecular dynamics simulations of NMR backbone relaxation order parameters have been carried out to investigate the polarization effect on the protein's local structure and dynamics for five benchmark proteins (bovine pancreatic trypsin inhibitor, immunoglobulin-binding domain (B1) of streptococcal protein G, bovine apo-calbindin D9K, human interleukin-4 R88Q mutant, and hen egg white lysozyme). In order to isolate the polarization effect from other interaction effects, our study employed both the standard AMBER force field (AMBER03) and polarized protein-specific charges (PPCs) in the MD simulations. The simulated order parameters, employing both the standard nonpolarizable and polarized force fields, are directly compared with experimental data. Our results show that residue-specific order parameters at some specific loop and turn regions are significantly underestimated by the MD simulations using the standard AMBER force field, indicating hyperflexibility of these local structures. Detailed analysis of the structures and dynamic motions of individual residues reveals that the hyperflexibility of these local structures is largely related to the breaking or weakening of relevant hydrogen bonds. In contrast, the agreement with the experimental results is significantly improved and more stable local structures are observed in the MD simulations using the polarized force field. The comparison between theory and experiment provides convincing evidence that intraprotein hydrogen bonds in these regions are stabilized by electronic polarization, which is critical to the dynamical stability of these local structures in proteins.

  13. Quantum implementation of the unitary coupled cluster for simulating molecular electronic structure

    NASA Astrophysics Data System (ADS)

    Shen, Yangchao; Zhang, Xiang; Zhang, Shuaining; Zhang, Jing-Ning; Yung, Man-Hong; Kim, Kihwan

    2017-02-01

    In classical computational chemistry, the coupled-cluster ansatz is one of the most commonly used ab initio methods, which is critically limited by its nonunitary nature. The unitary modification as an ideal solution to the problem is, however, extremely inefficient in classical conventional computation. Here, we provide experimental evidence that indeed the unitary version of the coupled-cluster ansatz can be reliably performed in a physical quantum system, a trapped-ion system. We perform a simulation on the electronic structure of a molecular ion (HeH+), where the ground-state energy surface curve is probed, the energies of the excited states are studied, and bond dissociation is simulated nonperturbatively. Our simulation takes advantages from quantum computation to overcome the intrinsic limitations in classical computation, and our experimental results indicate that the method is promising for preparing molecular ground states for quantum simulations.

  14. Photoisomerization mechanism of 4-methylpyridine explored by electronic structure calculations and nonadiabatic dynamics simulations

    SciTech Connect

    Cao Jun; Fang Weihai; Fang Qiu

    2011-01-28

    In the present paper, different electronic structure methods have been used to determine stationary and intersection structures on the ground (S{sub 0}) and {sup 1}{pi}{pi}* (S{sub 2}) states of 4-methylpyridine, which is followed by adiabatic and nonadiabatic dynamics simulations to explore the mechanistic photoisomerization of 4-methylpyridine. Photoisomerization starts from the S{sub 2}({sup 1}{pi}{pi}*) state and overcomes a small barrier, leading to formation of the prefulvene isomer in the S{sub 0} state via a S{sub 2}/S{sub 0} conical intersection. The ultrafast S{sub 2}{yields} S{sub 0} nonradiative decay and low quantum yield for the photoisomerization reaction were well reproduced by the combined electronic structure calculation and dynamics simulation. The prefulvene isomer was assigned as a long-lived intermediate and suggested to isomerize to 4-methylpyridine directly in the previous study, which is not supported by the present calculation. The nonadiabatic dynamics simulation and electronic structure calculation reveal that the prefulvene isomer is a short-lived intermediate and isomerizes to benzvalene form very easily. The benzvalene form was predicted as the stable isomer in the present study and is probably the long-lived intermediate observed experimentally. A consecutive light and thermal isomerization cycle via Dewar isomer was determined and this cycle mechanism is different from that reported in the previous study. It should be pointed out that formation of Dewar isomer from the S{sub 2}({sup 1}{pi}{pi}*) state is not in competition with the isomerization to the prefulvene form. The Dewar structure observed experimentally may originate from other excited states.

  15. ELECTROMAGNETIC SIMULATIONS OF DIELECTRIC WALL ACCELERATOR STRUCTURES FOR ELECTRON BEAM ACCELERATION

    SciTech Connect

    Nelson, S D; Poole, B R

    2005-05-05

    Dielectric Wall Accelerator (DWA) technology incorporates the energy storage mechanism, the switching mechanism, and the acceleration mechanism for electron beams. Electromagnetic simulations of DWA structures includes these effects and also details of the switch configuration and how that switch time affects the electric field pulse which accelerates the particle beam. DWA structures include both bi-linear and bi-spiral configurations with field gradients on the order of 20MV/m and the simulations include the effects of the beampipe, the beampipe walls, the DWA High Gradient Insulator (HGI) insulating stack, wakefield impedance calculations, and test particle trajectories with low emittance gain. Design trade-offs include the transmission line impedance (typically a few ohms), equilibration ring optimization, driving switch inductances, and layer-to-layer coupling effects and the associated affect on the acceleration pulse's peak value.

  16. Effect of Eshelby twist on core structure of screw dislocations in molybdenum: atomic structure and electron microscope image simulations

    NASA Astrophysics Data System (ADS)

    Gröger, R.; Dudeck, K. J.; Nellist, P. D.; Vitek, V.; Hirsch, P. B.; Cockayne, D. J. H.

    2011-06-01

    This paper addresses the question as to whether the core structure of screw dislocations in Mo in the bulk can be obtained from high-resolution electron microscopy (HREM) images of such dislocations viewed end-on in a thin foil. Atomistic simulations of the core structure of screw dislocations in elastically anisotropic Mo were carried out using bond order potentials. These simulations take account automatically of the effects of the surface relaxation displacements (anisotropic Eshelby twist). They show that the differential displacements of the atoms at the surface are different with components perpendicular to the Burgers vector about five times larger than those in the middle of the foil, the latter being characteristic of the bulk. Nye tensor plots show that the surface relaxation stresses strongly affect the incompatible distortions. HREM simulations of the computed structure reflect the displacements at the exit surface, modified by interband scattering and the microscope transfer function. Nye tensor plots obtained from the HREM images show that interband scattering also affects the incompatible distortions. It is concluded that it would be very difficult to obtain information on the core structure of screw dislocations in the bulk Mo from HREM images, even under ideal experimental conditions, and that quantitative comparisons between experimental and simulated images from assumed model structures would be essential.

  17. DFT simulation, quantum chemical electronic structure, spectroscopic and structure-activity investigations of 2-benzothiazole acetonitrile

    NASA Astrophysics Data System (ADS)

    Arjunan, V.; Thillai Govindaraja, S.; Jose, Sujin P.; Mohan, S.

    2014-07-01

    The Fourier transform infrared and FT-Raman spectra of 2-benzothiazole acetonitrile (BTAN) have been recorded in the range 4000-450 and 4000-100 cm-1 respectively. The conformational analysis of the compound has been carried out to obtain the stable geometry of the compound. The complete vibrational assignment and analysis of the fundamental modes of the compound are carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The experimental vibrational frequencies are compared with the wavenumbers derived theoretically by B3LYP gradient calculations employing the standard 6-31G**, high level 6-311++G** and cc-pVTZ basis sets. The structural parameters, thermodynamic properties and vibrational frequencies of the normal modes obtained from the B3LYP methods are in good agreement with the experimental data. The 1H (400 MHz; CDCl3) and 13C (100 MHz; CDCl3) nuclear magnetic resonance (NMR) spectra are also recorded. The electronic properties, the energies of the highest occupied and lowest unoccupied molecular orbitals are measured by DFT approach. The kinetic stability of the molecule has been determined from the frontier molecular orbital energy gap. The charges of the atoms and the structure-chemical reactivity relations of the compound are determined by its chemical potential, global hardness, global softness, electronegativity, electrophilicity and local reactivity descriptors by conceptual DFT methods. The non-linear optical properties of the compound have been discussed by measuring the polarisability and hyperpolarisability tensors.

  18. Statistical Exploration of Electronic Structure of Molecules from Quantum Monte-Carlo Simulations

    SciTech Connect

    Prabhat, Mr; Zubarev, Dmitry; Lester, Jr., William A.

    2010-12-22

    In this report, we present results from analysis of Quantum Monte Carlo (QMC) simulation data with the goal of determining internal structure of a 3N-dimensional phase space of an N-electron molecule. We are interested in mining the simulation data for patterns that might be indicative of the bond rearrangement as molecules change electronic states. We examined simulation output that tracks the positions of two coupled electrons in the singlet and triplet states of an H2 molecule. The electrons trace out a trajectory, which was analyzed with a number of statistical techniques. This project was intended to address the following scientific questions: (1) Do high-dimensional phase spaces characterizing electronic structure of molecules tend to cluster in any natural way? Do we see a change in clustering patterns as we explore different electronic states of the same molecule? (2) Since it is hard to understand the high-dimensional space of trajectories, can we project these trajectories to a lower dimensional subspace to gain a better understanding of patterns? (3) Do trajectories inherently lie in a lower-dimensional manifold? Can we recover that manifold? After extensive statistical analysis, we are now in a better position to respond to these questions. (1) We definitely see clustering patterns, and differences between the H2 and H2tri datasets. These are revealed by the pamk method in a fairly reliable manner and can potentially be used to distinguish bonded and non-bonded systems and get insight into the nature of bonding. (2) Projecting to a lower dimensional subspace ({approx}4-5) using PCA or Kernel PCA reveals interesting patterns in the distribution of scalar values, which can be related to the existing descriptors of electronic structure of molecules. Also, these results can be immediately used to develop robust tools for analysis of noisy data obtained during QMC simulations (3) All dimensionality reduction and estimation techniques that we tried seem to

  19. Electronic Driver Education Simulator.

    ERIC Educational Resources Information Center

    Spence, Keith R.

    1980-01-01

    Describes the collision avoidance simulator, which provides both a hands-on prolect for digital electronics students and a motivation device for driver education students. Gives details of the electrical construction and operation of the simulator. (JOW)

  20. Efficient preconditioning of the electronic structure problem in large scale ab initio molecular dynamics simulations

    SciTech Connect

    Schiffmann, Florian; VandeVondele, Joost

    2015-06-28

    We present an improved preconditioning scheme for electronic structure calculations based on the orbital transformation method. First, a preconditioner is developed which includes information from the full Kohn-Sham matrix but avoids computationally demanding diagonalisation steps in its construction. This reduces the computational cost of its construction, eliminating a bottleneck in large scale simulations, while maintaining rapid convergence. In addition, a modified form of Hotelling’s iterative inversion is introduced to replace the exact inversion of the preconditioner matrix. This method is highly effective during molecular dynamics (MD), as the solution obtained in earlier MD steps is a suitable initial guess. Filtering small elements during sparse matrix multiplication leads to linear scaling inversion, while retaining robustness, already for relatively small systems. For system sizes ranging from a few hundred to a few thousand atoms, which are typical for many practical applications, the improvements to the algorithm lead to a 2-5 fold speedup per MD step.

  1. Excited-state dynamics of oxazole: A combined electronic structure calculations and dynamic simulations study

    NASA Astrophysics Data System (ADS)

    Cao, Jun; Xie, Zhi-Zhong; Yu, Xiaodong

    2016-08-01

    In the present work, the combined electronic structure calculations and surface hopping simulations have been performed to investigate the excited-state decay of the parent oxazole in the gas phase. Our calculations show that the S2 state decay of oxazole is an ultrafast process characterized by the ring-opening and ring-closure of the five-membered oxazole ring, in which the triplet contribution is minor. The ring-opening involves the Osbnd C bond cleavage affording the nitrile ylide and airine intermediates, while the ring-closure gives rise to a bicyclic species through a 2sbnd 5 bond formation. The azirine and bicyclic intermediates in the S0 state are very likely involved in the phototranspositions of oxazoles. This is different from the previous mechanism in which these intermediates in the T1 state have been proposed for these phototranspositions.

  2. Efficient preconditioning of the electronic structure problem in large scale ab initio molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Schiffmann, Florian; VandeVondele, Joost

    2015-06-01

    We present an improved preconditioning scheme for electronic structure calculations based on the orbital transformation method. First, a preconditioner is developed which includes information from the full Kohn-Sham matrix but avoids computationally demanding diagonalisation steps in its construction. This reduces the computational cost of its construction, eliminating a bottleneck in large scale simulations, while maintaining rapid convergence. In addition, a modified form of Hotelling's iterative inversion is introduced to replace the exact inversion of the preconditioner matrix. This method is highly effective during molecular dynamics (MD), as the solution obtained in earlier MD steps is a suitable initial guess. Filtering small elements during sparse matrix multiplication leads to linear scaling inversion, while retaining robustness, already for relatively small systems. For system sizes ranging from a few hundred to a few thousand atoms, which are typical for many practical applications, the improvements to the algorithm lead to a 2-5 fold speedup per MD step.

  3. Ab Initio Simulations and Electronic Structure of Lithium-Doped Ionic Liquids: Structure, Transport, and Electrochemical Stability.

    PubMed

    Haskins, Justin B; Bauschlicher, Charles W; Lawson, John W

    2015-11-19

    Density functional theory (DFT), density functional theory molecular dynamics (DFT-MD), and classical molecular dynamics using polarizable force fields (PFF-MD) are employed to evaluate the influence of Li(+) on the structure, transport, and electrochemical stability of three potential ionic liquid electrolytes: N-methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([pyr14][TFSI]), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide ([pyr13][FSI]), and 1-ethyl-3-methylimidazolium boron tetrafluoride ([EMIM][BF4]). We characterize the Li(+) solvation shell through DFT computations of [Li(Anion)n]((n-1)-) clusters, DFT-MD simulations of isolated Li(+) in small ionic liquid systems, and PFF-MD simulations with high Li-doping levels in large ionic liquid systems. At low levels of Li-salt doping, highly stable solvation shells having two to three anions are seen in both [pyr14][TFSI] and [pyr13][FSI], whereas solvation shells with four anions dominate in [EMIM][BF4]. At higher levels of doping, we find the formation of complex Li-network structures that increase the frequency of four anion-coordinated solvation shells. A comparison of computational and experimental Raman spectra for a wide range of [Li(Anion)n]((n-1)-) clusters shows that our proposed structures are consistent with experiment. We then compute the ion diffusion coefficients and find measures from small-cell DFT-MD simulations to be the correct order of magnitude, but influenced by small system size and short simulation length. Correcting for these errors with complementary PFF-MD simulations, we find DFT-MD measures to be in close agreement with experiment. Finally, we compute electrochemical windows from DFT computations on isolated ions, interacting cation/anion pairs, and liquid-phase systems with Li-doping. For the molecular-level computations, we generally find the difference between ionization energy and electron affinity from isolated ions and interacting cation/anion pairs to

  4. Photochromic Mechanism of a Bridged Diarylethene: Combined Electronic Structure Calculations and Nonadiabatic Dynamics Simulations.

    PubMed

    Wang, Ya-Ting; Gao, Yuan-Jun; Wang, Qian; Cui, Ganglong

    2017-02-02

    Intramolecularly bridged diarylethenes exhibit improved photocyclization quantum yields because the anti-syn isomerization that originally suppresses photocyclization in classical diarylethenes is blocked. Experimentally, three possible channels have been proposed to interpret experimental observation, but many details of photochromic mechanism remain ambiguous. In this work we have employed a series of electronic structure methods (OM2/MRCI, DFT, TDDFT, RI-CC2, DFT/MRCI, and CASPT2) to comprehensively study excited state properties, photocyclization, and photoreversion dynamics of 1,2-dicyano[2,2]metacyclophan-1-ene. On the basis of optimized stationary points and minimum-energy conical intersections, we have refined experimentally proposed photochromic mechanism. Only an S1/S0 minimum-energy conical intersection is located; thus, we can exclude the third channel experimentally proposed. In addition, we find that both photocyclization and photoreversion processes use the same S1/S0 conical intersection to decay the S1 system to the S0 state, so we can unify the remaining two channels into one. These new insights are verified by our OM2/MRCI nonadiabatic dynamics simulations. The S1 excited-state lifetimes of photocyclization and photoreversion are estimated to be 349 and 453 fs, respectively, which are close to experimentally measured values: 240 ± 60 and 250 fs in acetonitrile solution. The present study not only interprets experimental observations and refines previously proposed mechanism but also provides new physical insights that are valuable for future experiments.

  5. Propagation of localized structures in relativistic magnetized electron-positron plasmas using particle-in-cell simulations

    SciTech Connect

    López, Rodrigo A.; Muñoz, Víctor; Viñas, Adolfo F.; Valdivia, Juan A.

    2015-09-15

    We use a particle-in-cell simulation to study the propagation of localized structures in a magnetized electron-positron plasma with relativistic finite temperature. We use as initial condition for the simulation an envelope soliton solution of the nonlinear Schrödinger equation, derived from the relativistic two fluid equations in the strongly magnetized limit. This envelope soliton turns out not to be a stable solution for the simulation and splits in two localized structures propagating in opposite directions. However, these two localized structures exhibit a soliton-like behavior, as they keep their profile after they collide with each other due to the periodic boundary conditions. We also observe the formation of localized structures in the evolution of a spatially uniform circularly polarized Alfvén wave. In both cases, the localized structures propagate with an amplitude independent velocity.

  6. Xyce parallel electronic simulator.

    SciTech Connect

    Keiter, Eric R; Mei, Ting; Russo, Thomas V.; Rankin, Eric Lamont; Schiek, Richard Louis; Thornquist, Heidi K.; Fixel, Deborah A.; Coffey, Todd S; Pawlowski, Roger P; Santarelli, Keith R.

    2010-05-01

    This document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users Guide. The focus of this document is (to the extent possible) exhaustively list device parameters, solver options, parser options, and other usage details of Xyce. This document is not intended to be a tutorial. Users who are new to circuit simulation are better served by the Xyce Users Guide.

  7. Time-efficient simulations of tight-binding electronic structures with Intel Xeon PhiTM many-core processors

    NASA Astrophysics Data System (ADS)

    Ryu, Hoon; Jeong, Yosang; Kang, Ji-Hoon; Cho, Kyu Nam

    2016-12-01

    Modelling of multi-million atomic semiconductor structures is important as it not only predicts properties of physically realizable novel materials, but can accelerate advanced device designs. This work elaborates a new Technology-Computer-Aided-Design (TCAD) tool for nanoelectronics modelling, which uses a sp3d5s∗ tight-binding approach to describe multi-million atomic structures, and simulate electronic structures with high performance computing (HPC), including atomic effects such as alloy and dopant disorders. Being named as Quantum simulation tool for Advanced Nanoscale Devices (Q-AND), the tool shows nice scalability on traditional multi-core HPC clusters implying the strong capability of large-scale electronic structure simulations, particularly with remarkable performance enhancement on latest clusters of Intel Xeon PhiTM coprocessors. A review of the recent modelling study conducted to understand an experimental work of highly phosphorus-doped silicon nanowires, is presented to demonstrate the utility of Q-AND. Having been developed via Intel Parallel Computing Center project, Q-AND will be open to public to establish a sound framework of nanoelectronics modelling with advanced HPC clusters of a many-core base. With details of the development methodology and exemplary study of dopant electronics, this work will present a practical guideline for TCAD development to researchers in the field of computational nanoelectronics.

  8. Simulating Policy Processes through Electronic Mail.

    ERIC Educational Resources Information Center

    Flynn, John P.

    1987-01-01

    Focuses on the use of electronic mail for teaching and learning about social welfare policy processes and compares electronic mail as a simulation medium to more structured computer applications. (Author)

  9. Ab initio calculations on twisted graphene/hBN: Electronic structure and STM image simulation

    NASA Astrophysics Data System (ADS)

    Correa, J. D.; Cisternas, E.

    2016-09-01

    By performing ab initio calculations we obtained theoretical scanning tunneling microscopy (STM) images and studied the electronic properties of graphene on a hexagonal boron-nitrite (hBN) layer. Three different stack configurations and four twisted angles were considered. All calculations were performed using density functional theory, including van der Waals interactions as implemented in the SIESTA ab initio package. Our results show that the electronic structure of graphene is preserved, although some small changes are induced by the interaction with the hBN layer, particularly in the total density of states at 1.5 eV under the Fermi level. When layers present a twisted angle, the density of states shows several van Hove singularities under the Fermi level, which are associated to moiré patterns observed in theoretical STM images.

  10. The VENUS/NWChem Software Package. Tight Coupling Between Chemical Dynamics Simulations and Electronic Structure Theory

    SciTech Connect

    Lourderaj, Upakarasamy; Sun, Rui; De Jong, Wibe A.; Windus, Theresa L.; Hase, William L.

    2014-03-01

    The interface for VENUS and NWChem, and the resulting software package for direct dynamics simulations are described. The coupling of the two codes is considered to be a tight coupling. The two codes are compiled and linked together and act as one executable with data being passed between the two codes through routine calls. The advantages of this type of coupling are discussed. The interface has been designed to have as little interference as possible with the core codes of both VENUS and NWChem. VENUS is the code that propagates the direct dynamics trajectories and, therefore, is the program that drives the overall execution of VENUS/NWChem. VENUS has remained an essentially sequential code, which uses the highly parallel structure of NWChem. Subroutines of the interface which accomplish the data transmission and communication between the two computer programs are described. Recent examples of the use of VENUS/NWChem for direct dynamics simulations are summarized.

  11. Electronic structure and mesoscopic simulations of nonylphenol ethoxylate surfactants. a combined DFT and DPD study.

    PubMed

    Valencia, Diego; Aburto, Jorge; García-Cruz, Isidoro

    2013-08-07

    The aim of this work was to gain insight into the effect of ethylene oxide (EO) chains on the properties of a series of nonylphenol ethoxylate (NPE) surfactants. We performed a theoretical study of NPE surfactants by means of density functional theory (DFT) and dissipative particle dynamics (DPD). Both approximations were used separately to obtain different properties. Four NPEs were selected for this purpose (EO = 4, 7, 11 and 15 length chains). DFT methods provided some electronic properties that are related to the EO units. One of them is the solvation Gibbs energy, which exhibited a linear trend with EO chain length. DPD calculations allow us to observe the dynamic behavior in water of the NPE surfactants. We propose a coarse-grained model which properly simulates the mesophases of each surfactant. This model can be used in other NPEs applications.

  12. Simulation of the β-voltaic effect in silicon pin structures irradiated with electrons from a nickel-63 β source

    SciTech Connect

    Nagornov, Yu. S.; Murashev, V. N.

    2016-01-15

    The prospects of β voltaics as electric-power sources for semiconductor circuits are considered. Experimental studies show that charging of the surface and a decrease in the electrovoltaic power are important. Simulation of the β-voltaic effect induced by electrons from a nickel-63 source on silicon pin structures is performed; it is shown that the coefficient of the collection of generated charge carriers can be as high as 13%. The dose dependences of the performance efficiency of silicon β-voltaic structures are determined for the case of irradiation with α particles and γ-ray photons; it is shown that 1.3 × 10{sup 14} and 10{sup 20} cm{sup –2}, respectively, are the threshold doses, above which a rapid decrease in efficiency occurs. The optimal parameters of microchannel structures in β-voltaic electronics, in which the width of the channels and the distance between them correspond to 3 and 10 μm, are determined.

  13. Ensemble Monte Carlo simulation of electron transport in GaAs/AlAs quantum wire structure under the effect of terahertz electric field

    NASA Astrophysics Data System (ADS)

    Borzdov, Andrei V.; Borzdov, Vladimir M.; V'yurkov, Vladimir V.

    2016-12-01

    Ensemble Monte Carlo simulation of electron transport in GaAs/AlAs quantum wire transistor structure is performed. The response of electron drift velocity on the action of harmonic longitudinal electric field is calculated for several values of electric field strength amplitude and gate bias at 77 and 300 K. The periodical electric field has a 1 THz frequency. The nonlinear behaviour of electron drift velocity due to scattering processes is observed.

  14. Electron hole tracking PIC simulation

    NASA Astrophysics Data System (ADS)

    Zhou, Chuteng; Hutchinson, Ian

    2016-10-01

    An electron hole is a coherent BGK mode solitary wave. Electron holes are observed to travel at high velocities relative to bulk plasmas. The kinematics of a 1-D electron hole is studied using a novel Particle-In-Cell simulation code with fully kinetic ions. A hole tracking technique enables us to follow the trajectory of a fast-moving solitary hole and study quantitatively hole acceleration and coupling to ions. The electron hole signal is detected and the simulation domain moves by a carefully designed feedback control law to follow its propagation. This approach has the advantage that the length of the simulation domain can be significantly reduced to several times the hole width, which makes high resolution simulations tractable. We observe a transient at the initial stage of hole formation when the hole accelerates to several times the cold-ion sound speed. Artificially imposing slow ion speed changes on a fully formed hole causes its velocity to change even when the ion stream speed in the hole frame greatly exceeds the ion thermal speed, so there are no reflected ions. The behavior that we observe in numerical simulations agrees very well with our analytic theory of hole momentum conservation and energization effects we call ``jetting''. The work was partially supported by the NSF/DOE Basic Plasma Science Partnership under Grant DE-SC0010491. Computer simulations were carried out on the MIT PSFC parallel AMD Opteron/Infiniband cluster Loki.

  15. Electron Structure of Francium

    NASA Astrophysics Data System (ADS)

    Koufos, Alexander

    2012-02-01

    This talk presents the first calculations of the electronic structure of francium for the bcc, fcc and hcp structures, using the Augmented Plane Wave (APW) method in its muffin-tin and linearized general potential forms. Both the Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA), were used to calculate the electronic structure and total energy of francium (Fr). The GGA and LDA both found the total energy of the hcp structure slightly below that of the fcc and bcc structure, respectively. This is in agreement with similar results for the other alkali metals using the same methodology. The equilibrium lattice constant, bulk modulus and superconductivity parameters were calculated. We found that under pressures, in the range of 1-5 GPa, Fr could be a superconductor at a critical temperature of about 4K.

  16. Developments in electron gun simulation

    SciTech Connect

    Herrmannsfeldt, W.B.

    1994-05-01

    This paper will discuss the developments in the electron gun simulation programs that are based on EGUN and its derivatives and supporting programs. Much of the code development has been inspired by technology changes in computer hardware; the implications on EGN2 of this evolution will be discussed. Some examples and a review of the capabilities of the EGUN family will be described.

  17. Terrestrial gamma ray flashes from electron avalanches in thunderstorms - the detailed structure and time evolution of electron, photon, optical and radio emission - results from a new simulation software package

    NASA Astrophysics Data System (ADS)

    Connell, P. H.

    2013-12-01

    To design the MXGS coded mask imager of the ASIM mission to the ISS, to detect and locate TGF gamma-rays, a first order software package was written at UV to simulate the vertical expansion of gamma-ray photons from 15-20 km altitudes up to 300-600 km orbital altitudes, to make some estimate of the probable TGF spectra and diffuse beam structure that might be observed by MXGS. A new software package includes the simulation of the Runaway Electron Avalanche (REA) origin of TGFs by electron ionization and Bremsstrahlung scattering and photon emission. It uses the standard KeV-MeV scattering physics of electron and photon interactions, close range Moller electron ionization, Binary-Electron-Bethe models of electron scattering, positron Bhabha scattering and annihilation, electron excitation and photon emission. It also uses a super particle spatial mesh system to control particle-momentum flux densities, electric field evolution and exponential avalanche growth and falloff. The package takes care of all high energy scattering physics, leaving the user free to concentrate on defining the three components of scattering medium, electric-magnetic field geometry, and free electron flux field geometry whose details are the main unknown in TGF research. Results will be presented from TGF simulations using realistic electric fields expected within and above storm clouds, and will include video displays showing the evolving ionization structure of electron trajectories, the time evolution of photon flux fields, electron-positron flux fields, their important circular feedback movement in the local earth magnetic field, local molecular ion densities, and the dielectric effect of induced local electric fields. The second aim of the package is as a step in creating open source software which could evolve into a standard research software package approved by the REA-TGF research community to correctly simulate all the relevant physical processes involved in the complex phenomenon

  18. Structural mechanics simulations

    NASA Technical Reports Server (NTRS)

    Biffle, Johnny H.

    1992-01-01

    Sandia National Laboratory has a very broad structural capability. Work has been performed in support of reentry vehicles, nuclear reactor safety, weapons systems and components, nuclear waste transport, strategic petroleum reserve, nuclear waste storage, wind and solar energy, drilling technology, and submarine programs. The analysis environment contains both commercial and internally developed software. Included are mesh generation capabilities, structural simulation codes, and visual codes for examining simulation results. To effectively simulate a wide variety of physical phenomena, a large number of constitutive models have been developed.

  19. Extended electron energy loss fine structure simulation of the local boron environment in sodium aluminoborosilicate glasses containing gadolinium

    SciTech Connect

    Qian, Morris; Li, Hong; Li, Liyu ); Strachan, Denis M. )

    2003-12-01

    Phase separation in sodium-aluminoborosilicate glasses was systematically studied as a function of Gd2O3 concentration with transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS) methods. Gadolinium-induced phase separation in the three systems can be consistently explained by proposing that Gd cations partition to the borate-rich environments and subsequent agglomeration of the Gd-borate moieties, or short-range ordered structural groups, in the glass. Agglomeration of the Gd-borate rich environments is further discussed within the context of excess metal oxides,[Na2O]ex or[Al2O3]ex=|Na2O - Al2O3|, and excess B2O3,[B2O3]ex, available for incorporating Gd cations. Results showed that agglomeration of the Gd-borate rich environments occurred at a much lower Gd2O3 concentration in the glass without[Na2O]ex or[Al2O3]ex and at a significantly higher Gd2O3 concentration in the glass with either[Na2O]ex or[Al2O3]ex. Assuming 1BO4 : 1Gd : 2BO3 (based on literature-reported Gd-metaborate structure) as a local Gd-borate environment in glass, we introduced the saturation index of boron, SI[B]= Gd2O3/(1/3[B2O3]ex), to examine the glass susceptibility to Gd-induced phase separation for all three alkali-aluminoborosilicate systems. While our results have provided some insight to the glass structure, they also provide insight to the mechanism by which the metal oxide is dissolved into the melt. This appears to occur predominantly through boron complexation of the metal oxide.

  20. Extended electron energy loss fine structure simulation of the local boron environment in sodium aluminoborosilicate glasses containing gadolinium

    SciTech Connect

    Qian, Morris; Li, Hong; Li, Liyu ); Strachan, Denis M. )

    2003-10-15

    Gadolinium can be dissolved in sodium-alumino-borosilicate glasses up to 47 wt% in a baseline borosilicate glass (mol%) 20 B2O3, 5 Al2O3, 60 SiO2,and 20 Na2O. Understanding of Gd dissolution in borosilicate melts is important in glass formulation optimization. Electron energy loss fine structure (ELFS) spectroscopy is chosen, which provides well resolved local atomic structure information for both amorphous and crystalline materials with high sensitivity to low Z elements such as Al, B, Na, O, and Si where the x-ray absorption fine structure (XAFS) technique faces experimental difficulty. In this study, we report our results of boron K-edge ELFS study. Two borosilicate glass samples with 30 and 47 mass% Gd2O3, B20Gd30 and B20Gd47were chosen for B K-edge ELFS study. EEL spectra were acquired on a Philips 430 TEM equipped with Gatan PEELS system 666 and EL/P 2.1 software with Custom function AcqLong. The ELFS data analysis was performed using UWELFS, UWXAFS and FEFF software. From our Gd solubility study, the local structure of Gd in the borate environment possibly resembles double chain structure found in crystalline Gd(BO2)3 as proposed by Chakraborty et al. The B/Gd ratio's in both glasses are smaller then 3, which means the excess Gd atoms in the Si-sites would be 17 and 60 mol% of the total Gd atoms, respectively according to the model, yet the local environment of borate sites saturated with Gd should be remained. To verity above hypothesis, the double chain structure model was applied to fit boron K-edge. The model was shown to well fit experimental boron K-edge EELS spectra for both glasses with some degree of distance distortion which is understandable in amorphous structure. Therefore, it is very likely that Gd stabilized in borate sites has a local structure resembling the double chain Gd(BO2)3 structure as proposed by our solubility study and literature.

  1. Xyce parallel electronic simulator design.

    SciTech Connect

    Thornquist, Heidi K.; Rankin, Eric Lamont; Mei, Ting; Schiek, Richard Louis; Keiter, Eric Richard; Russo, Thomas V.

    2010-09-01

    This document is the Xyce Circuit Simulator developer guide. Xyce has been designed from the 'ground up' to be a SPICE-compatible, distributed memory parallel circuit simulator. While it is in many respects a research code, Xyce is intended to be a production simulator. As such, having software quality engineering (SQE) procedures in place to insure a high level of code quality and robustness are essential. Version control, issue tracking customer support, C++ style guildlines and the Xyce release process are all described. The Xyce Parallel Electronic Simulator has been under development at Sandia since 1999. Historically, Xyce has mostly been funded by ASC, the original focus of Xyce development has primarily been related to circuits for nuclear weapons. However, this has not been the only focus and it is expected that the project will diversify. Like many ASC projects, Xyce is a group development effort, which involves a number of researchers, engineers, scientists, mathmaticians and computer scientists. In addition to diversity of background, it is to be expected on long term projects for there to be a certain amount of staff turnover, as people move on to different projects. As a result, it is very important that the project maintain high software quality standards. The point of this document is to formally document a number of the software quality practices followed by the Xyce team in one place. Also, it is hoped that this document will be a good source of information for new developers.

  2. Simulations of Gaussian electron guns for RHIC electron lens

    SciTech Connect

    Pikin, A.

    2014-02-28

    Simulations of two versions of the electron gun for RHIC electron lens are presented. The electron guns have to generate an electron beam with Gaussian radial profile of the electron beam density. To achieve the Gaussian electron emission profile on the cathode we used a combination of the gun electrodes and shaping of the cathode surface. Dependence of electron gun performance parameters on the geometry of electrodes and the margins for electrodes positioning are presented.

  3. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: The effects of current-path patterns on magnetotransport in spatially-confined structures by Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Wu, Jian-Chun; Sun, Hua; Li, Zhen-Ya

    2009-11-01

    Simulations are performed on clusters of finite size to study the effects of size and current-path structure on magnetotransport in spatially-confined samples. Magnetotransport networks are established and calculated based on fractal structures including Koch curves and percolation backbones extracted from regular lattices. The structure pattern of clusters is shown to play an important role in the magnetotransport behaviours by affecting the magnetoresistance fluctuations due to spin disorder in the systems of small size, which suggests the possibility of controlling the magnetotransport by the design of current-path configurations.

  4. Simulation of phase structures

    SciTech Connect

    Lawson, J.

    1995-04-20

    This memo outlines a procedure developed by the author to extract information from phase measurements and produce a simulated phase structure for use in modeling optical systems, including characteristic optics for the Beamlet and NIF laser systems. The report includes an IDL program listing.

  5. P3HT:DiPBI bulk heterojunction solar cells: morphology and electronic structure probed by multiscale simulation and UV/vis spectroscopy.

    PubMed

    Winands, Thorsten; Böckmann, Marcus; Schemme, Thomas; Ly, Phong-Minh Timmy; de Jong, Djurre H; Wang, Zhaohui; Denz, Cornelia; Heuer, Andreas; Doltsinis, Nikos L

    2016-02-17

    Coarse grained molecular dynamics simulations are performed for a mixture of poly(3-hexylthiophene) (P3HT) and diperylene bisimide (DiPBI). The effect of different annealing and cooling protocols on the morphology is investigated and the resulting domain structures are analyzed. In particular, π-stacked clusters of DiPBI molecules are observed whose size decreases with increasing temperature. Domain structure and diffusivity data suggest that the DiPBI subsystem undergoes an order → disorder phase transition between 700 and 900 K. Electronic structure calculations based on density functional theory are carried out after backmapping the coarse grained model onto an atomistic force field representation built upon first principles. UV/vis absorption spectra of the P3HT:DiPBI mixture are computed using time-dependent density functional linear response theory and recorded experimentally for a spin-coated thin film. It is demonstrated that the absorption spectrum depends sensitively on the details of the amorphous structure, thus providing valuable insight into the morphology. In particular, the results show that the tempering procedure has a significant influence on the material's electronic properties. This knowledge may help to develop effective processing routines to enhance the performance of bulk heterojunction solar cells.

  6. Atomic and electronic structure of Pd{sub 40}Ni{sub 40}P{sub 20} bulk metallic glass from ab initio simulations

    SciTech Connect

    Kumar, Vijay; Fujita, T.; Chen, M. W.; Inoue, A.; Konno, K.; Matsuura, M.; Kawazoe, Y.

    2011-10-01

    The atomic structure of Pd{sub 40}Ni{sub 40}P{sub 20} bulk metallic glass has been simulated using an ab initio molecular dynamics method with projector-augmented wave pseudopotentials for electron-ion interaction and generalized gradient approximation for exchange-correlation energy. The calculated extended x-ray absorption fine structure (EXAFS) spectra of Pd-K and Ni-K edges, the mass density, and the electronic structure agree remarkably well with the available experimental data and the EXAFS spectra measured at the SPring-8 synchrotron radiation facility. Our results show that the atomic structure can be described in terms of P-centered polyhedra. There are no two P atoms that are nearest neighbors at this composition, and this could be a reason for the observed optimal P concentration of about 20 at.%. The neighboring polyhedra share metal (M) atoms and form a polar covalently bonded random network of P-M-P favoring certain angles. The remaining M atoms act as metallic glue with a tendency of nanoscale clustering of Pd-Pd and Ni-Ni atoms.

  7. Simulation of planar channeling-radiation spectra of relativistic electrons and positrons channeled in a diamond-structure or tungsten single crystal (classical approach)

    NASA Astrophysics Data System (ADS)

    Azadegan, B.; Wagner, W.

    2015-01-01

    We present a Mathematica package for simulation of spectral-angular distributions and energy spectra of planar channeling radiation of relativistic electrons and positrons channeled along major crystallographic planes of a diamond-structure or tungsten single crystal. The program is based on the classical theory of channeling radiation which has been successfully applied to study planar channeling of light charged particles at energies higher than 100 MeV. Continuous potentials for different planes of diamond, Si, Ge and W single crystals are calculated using the Doyle-Turner approximation to the atomic scattering factor and taking thermal vibrations of the crystal atoms into account. Numerical methods are applied to solve the classical one-dimensional equation of motion. The code is designed to calculate the trajectories, velocities and accelerations of electrons (positrons) channeled by the planar continuous potential. In the framework of classical electrodynamics, these data allow realistic simulations of spectral-angular distributions and energy spectra of planar channeling radiation. Since the generated output is quantitative, the results of calculation may be useful, e.g., for setup configuration and crystal alignment in channeling experiments, for the study of the dependence of channeling radiation on the input parameters of particle beams with respect to the crystal orientation, but also for the simulation of positron production by means of pair creation what is mandatory for the design of efficient positron sources necessary in high-energy and collider physics. Although the classical theory of channeling is well established for long time, there is no adequate library program for simulation of channeling radiation up to now, which is commonly available, sufficiently simple and effective to employ and, therefore, of benefit as for special investigations as for a quick overview of basic features of this type of radiation.

  8. Classification of projection images of proteins with structural polymorphism by manifold: a simulation study for x-ray free-electron laser diffraction imaging.

    PubMed

    Yoshidome, Takashi; Oroguchi, Tomotaka; Nakasako, Masayoshi; Ikeguchi, Mitsunori

    2015-09-01

    Coherent x-ray diffraction imaging (CXDI) enables us to visualize noncrystalline sample particles with micrometer to submicrometer dimensions. Using x-ray free-electron laser (XFEL) sources, two-dimensional diffraction patterns are collected from fresh samples supplied to the irradiation area in the "diffraction-before-destruction" scheme. A recent significant increase in the intensity of the XFEL pulse is promising and will allow us to visualize the three-dimensional structures of proteins using XFEL-CXDI in the future. For the protocol proposed for molecular structure determination using future XFEL-CXDI [T. Oroguchi and M. Nakasako, Phys. Rev. E 87, 022712 (2013)10.1103/PhysRevE.87.022712], we require an algorithm that can classify the data in accordance with the structural polymorphism of proteins arising from their conformational dynamics. However, most of the algorithms proposed primarily require the numbers of conformational classes, and then the results are biased by the numbers. To improve this point, here we examine whether a method based on the manifold concept can classify simulated XFEL-CXDI data with respect to the structural polymorphism of a protein that predominantly adopts two states. After random sampling of the conformations of the two states and in-between states from the trajectories of molecular dynamics simulations, a diffraction pattern is calculated from each conformation. Classification was performed by using our custom-made program suite named enma, in which the diffusion map (DM) method developed based on the manifold concept was implemented. We successfully classify most of the projection electron density maps phase retrieved from diffraction patterns into each of the two states and in-between conformations without the knowledge of the number of conformational classes. We also examined the classification of the projection electron density maps of each of the three states with respect to the Euler angle. The present results suggest that

  9. Simulation study of electron response amplification in coherent electron cooling

    SciTech Connect

    Hao Y.; Litvinenko, V.N.

    2012-05-20

    In Coherent Electron Cooling (CEC), it is essential to study the amplification of electron response to a single ion in the FEL process, in order to proper align the electron beam and the ion beam in the kicker to maximize the cooling effect. In this paper, we use Genesis to simulate the amplified electron beam response of single ion in FEL amplification process, which acts as Green's function of the FEL amplifier.

  10. Electronic structure quantum Monte Carlo

    NASA Astrophysics Data System (ADS)

    Bajdich, Michal; Mitas, Lubos

    2009-04-01

    Quantum Monte Carlo (QMC) is an advanced simulation methodology for studies of manybody quantum systems. The QMC approaches combine analytical insights with stochastic computational techniques for efficient solution of several classes of important many-body problems such as the stationary Schrödinger equation. QMC methods of various flavors have been applied to a great variety of systems spanning continuous and lattice quantum models, molecular and condensed systems, BEC-BCS ultracold condensates, nuclei, etc. In this review, we focus on the electronic structure QMC, i.e., methods relevant for systems described by the electron-ion Hamiltonians. Some of the key QMC achievements include direct treatment of electron correlation, accuracy in predicting energy differences and favorable scaling in the system size. Calculations of atoms, molecules, clusters and solids have demonstrated QMC applicability to real systems with hundreds of electrons while providing 90-95% of the correlation energy and energy differences typically within a few percent of experiments. Advances in accuracy beyond these limits are hampered by the so-called fixed-node approximation which is used to circumvent the notorious fermion sign problem. Many-body nodes of fermion states and their properties have therefore become one of the important topics for further progress in predictive power and efficiency of QMC calculations. Some of our recent results on the wave function nodes and related nodal domain topologies will be briefly reviewed. This includes analysis of few-electron systems and descriptions of exact and approximate nodes using transformations and projections of the highly-dimensional nodal hypersurfaces into the 3D space. Studies of fermion nodes offer new insights into topological properties of eigenstates such as explicit demonstrations that generic fermionic ground states exhibit the minimal number of two nodal domains. Recently proposed trial wave functions based on Pfaffians with

  11. Electronic Neural-Network Simulator

    NASA Technical Reports Server (NTRS)

    Moopenn, Alex W.; Thakoor, Anilkumar P.; Lambe, John J.

    1988-01-01

    Experimental circuits faster than simulation programs run on digital computers. Serial shift register routes clock pulses C1 to neurons in sequence. Clock pulses C2 interrogate neurons. Neuron interconnection information stored in simulated synapses. Can be expanded to greater complexity.

  12. Electronic transport in nanoscale structures

    NASA Astrophysics Data System (ADS)

    Lagerqvist, Johan

    In this dissertation electronic transport in nanoscale structures is discussed. An expression for the shot noise, a fluctuation in current due to the discreteness of charge, is derived directly from the wave functions of a nanoscale system. Investigation of shot noise is of particular interest due to the rich fundamental physics involved. For example, the study of shot noise can provide fundamental insight on the nature of electron transport in a nanoscale junction. We report calculations of the shot noise properties of parallel wires in the regime in which the interwire distance is much smaller than the inelastic mean free path. The validity of quantized transverse momenta in a nanoscale structure and its effect on shot noise is also discussed. We theoretically propose and show the feasibility of a novel protocol for DNA sequencing based on the electronic signature of single-stranded DNA while it translocates through a nanopore. We find that the currents for the bases are sufficiently different to allow for efficient sequencing. Our estimates reveal that sequencing of an entire human genome could be done with very high accuracy in a matter of hours, e.g., orders of magnitude faster than present techniques. We also find that although the overall magnitude of the current may change dramatically with different detection conditions, the intrinsic distinguishability of the bases is not significantly affected by pore size and transverse field strength. Finally, we study the ability of water to screen charges in nanopores by using all-atom molecular dynamics simulations coupled to electrostatic calculations. Due to the short length scales of the nanopore geometry and the large local field gradient of a single ion, the energetics of transporting an ion through the pore is strongly dependent on the microscopic details of the electric field. We show that as long as the pore allows the first hydration shell to stay intact, e.g., ˜6 nearby water molecules, the electric field

  13. Electron Beam IEMP Simulation Development

    DTIC Science & Technology

    1975-08-01

    Effect of Injected Current Pulse Width Variation Upon Transmittfed Current Pulse 69 4.10 Open Shutter Photograph of Surface Flashover on Dielectric Tube...occurred, presumably by electrical breakdown In volume. However it was no+ observed In all cases. Surface flashover Is another electrical failure mode...early in the Injected pulse 71 TDIELECTRIC TUBE ELECTRON BEAM oil~ Flgu--e 4.10 Open Shutter Photograph of Surface Flashover on Dielectric Tube 7

  14. ELECTRON COOLING SIMULATION FOR ARBITRARY DISTRIBUTION OF ELECTRONS

    SciTech Connect

    SIDORIN,A.; SMIRNOV, A.; FEDOTOV, A.; BEN-ZVI, I.; KAYRAN, D.

    2007-09-10

    Typically, several approximations are being used in simulation of electron cooling process, for example, density distribution of electrons is calculated using an analytical expression and distribution in the velocity space is assumed to be Maxwellian in all degrees of freedom. However, in many applications, accurate description of the cooling process based on realistic distribution of electrons is very useful. This is especially true for a high-energy electron cooling system which requires bunched electron beam produced by an Energy Recovery Linac (Em). Such systems are proposed, for instance, for RHIC and electron - ion collider. To address unique features of the RHIC-I1 cooler, new algorithms were introduced in BETACOOL code which allow us to take into account local properties of electron distribution as well as calculate friction force for an arbitrary velocity distribution. Here, we describe these new numerical models. Results based on these numerical models are compared with typical approximations using electron distribution produced by simulations of electron bunch through ERL of RHIC-II cooler.

  15. Track-Structure Simulations for Charged Particles

    PubMed Central

    Dingfelder, Michael

    2013-01-01

    Monte-Carlo track-structure simulations provide a detailed and accurate picture of radiation transport of charged particles through condensed matter of biological interest. Liquid water serves as surrogate for soft tissue and is used in most Monte-Carlo track-structure codes. Basic theories of radiation transport and track-structure simulations are discussed and differences to condensed history codes highlighted. Interaction cross sections for electrons, protons, alpha particles, light and heavy ions are required input data for track-structure simulations. Different calculation methods, including the plane-wave Born approximation, the dielectric theory, and semi-empirical approaches are presented using liquid water as a target. Low-energy electron transport and light ion transport are discussed as areas of special interest. PMID:23032889

  16. Simulated electron holography of PSD particles

    NASA Astrophysics Data System (ADS)

    Conbhuí, Pádraig Ó.; Williams, Wyn; Nagy, Les

    2016-04-01

    Electron holography is an experimental technique that is capable of observing magnetic microstructures on the same scale as can be determined using numerical modeling and thus bridge the gap between experimental measurements and theory. I will present a technique for simulating holographic images from the results of micromagnetic models and demonstrate an easily used tool for generating holograms on the fly in an interactive environment (ie in ParaView). Since holography flattens 3D information onto a 2D image, some useful information can be lost. By looking at some examples of holograms of interesting 3D magnetizations (ie PSD structures), particularly how they change as they're rotated, along with comparisons of different structures, I will examine what information can be retrieved and what might be lost. The existance of an external dipole can be indicative of an in-plane component of a seemingly out-of-plane vortex core. It is also seen, however, that two quite different structures (in this case a [111] vortex core and a [111] uniform magnetization) can sometimes be quite indistinguishable.

  17. Photoinduced reactions of both 2-formyl-2H-azirine and isoxazole: A theoretical study based on electronic structure calculations and nonadiabatic dynamics simulations

    SciTech Connect

    Cao, Jun

    2015-06-28

    In the present work, the combined electronic structure calculations and dynamics simulations have been performed to explore photocleavages of 2-formyl-2H-azirine and isoxazole in the gas phase and the subsequent rearrangement reactions. The carbonyl n → π{sup *} transition induces a cleavage of the C—N single bond of 2-formyl-2H-azirine to yield β-formylvinylnitrene in open-shell singlet state. However, the n → π{sup *} excitation of the imine chromophore results in a cleavage of the C—C single bond, producing a nitrile ylide intermediate through an internal conversion to the ground state. β-formylvinylnitrene and nitrile ylide with the carbonyl group are easily transformed into 2-formyl-2H-azirine and oxazole, respectively. The N—O bond cleavages on both S{sub 1}({sup 1}ππ{sup *}) and S{sub 2}({sup 1}n{sub N}π{sup *}) of isoxazole are ultrafast processes, and they give products of 2-formyl-2H-azirine, 3-formylketenimine, HCN + CHCHO, and HCO + CHCHN. Both 2H-azirines and ketenimines were suggested to be formed from the triplet vinylnitrenes by intersystem crossing in the previous studies. However, our calculations show that the singlet β-formylvinylnitrene is responsible for the formation of 2-formyl-2H-azirine and 3-formylketenimine, and the singlet vinylnitrenes can play a key role in the photoinduced reactions of both 2H-azirines and isoxazoles.

  18. Combining MOSCED with molecular simulation free energy calculations or electronic structure calculations to develop an efficient tool for solvent formulation and selection

    NASA Astrophysics Data System (ADS)

    Cox, Courtney E.; Phifer, Jeremy R.; Ferreira da Silva, Larissa; Gonçalves Nogueira, Gabriel; Ley, Ryan T.; O'Loughlin, Elizabeth J.; Pereira Barbosa, Ana Karolyne; Rygelski, Brett T.; Paluch, Andrew S.

    2017-02-01

    Solubility parameter based methods have long been a valuable tool for solvent formulation and selection. Of these methods, the MOdified Separation of Cohesive Energy Density (MOSCED) has recently been shown to correlate well the equilibrium solubility of multifunctional non-electrolyte solids. However, before it can be applied to a novel solute, a limited amount of reference solubility data is required to regress the necessary MOSCED parameters. Here we demonstrate for the solutes methylparaben, ethylparaben, propylparaben, butylparaben, lidocaine and ephedrine how conventional molecular simulation free energy calculations or electronic structure calculations in a continuum solvent, here the SMD or SM8 solvation model, can instead be used to generate the necessary reference data, resulting in a predictive flavor of MOSCED. Adopting the melting point temperature and enthalpy of fusion of these compounds from experiment, we are able to predict equilibrium solubilities. We find the method is able to well correlate the (mole fraction) equilibrium solubility in non-aqueous solvents over four orders of magnitude with good quantitative agreement.

  19. Photoinduced reactions of both 2-formyl-2H-azirine and isoxazole: A theoretical study based on electronic structure calculations and nonadiabatic dynamics simulations

    NASA Astrophysics Data System (ADS)

    Cao, Jun

    2015-06-01

    In the present work, the combined electronic structure calculations and dynamics simulations have been performed to explore photocleavages of 2-formyl-2H-azirine and isoxazole in the gas phase and the subsequent rearrangement reactions. The carbonyl n → π* transition induces a cleavage of the C—N single bond of 2-formyl-2H-azirine to yield β-formylvinylnitrene in open-shell singlet state. However, the n → π* excitation of the imine chromophore results in a cleavage of the C—C single bond, producing a nitrile ylide intermediate through an internal conversion to the ground state. β-formylvinylnitrene and nitrile ylide with the carbonyl group are easily transformed into 2-formyl-2H-azirine and oxazole, respectively. The N—O bond cleavages on both S1(1ππ*) and S2(1nNπ*) of isoxazole are ultrafast processes, and they give products of 2-formyl-2H-azirine, 3-formylketenimine, HCN + CHCHO, and HCO + CHCHN. Both 2H-azirines and ketenimines were suggested to be formed from the triplet vinylnitrenes by intersystem crossing in the previous studies. However, our calculations show that the singlet β-formylvinylnitrene is responsible for the formation of 2-formyl-2H-azirine and 3-formylketenimine, and the singlet vinylnitrenes can play a key role in the photoinduced reactions of both 2H-azirines and isoxazoles.

  20. An electronic notebook for physical system simulation

    NASA Astrophysics Data System (ADS)

    Kelsey, Robert L.

    2003-09-01

    A scientist who sets up and runs experiments typically keeps notes of this process in a lab notebook. A scientist who runs computer simulations should be no different. Experiments and simulations both require a set-up process which should be documented along with the results of the experiment or simulation. The documentation is important for knowing and understanding what was attempted, what took place, and how to reproduce it in the future. Modern simulations of physical systems have become more complex due in part to larger computational resources and increased understanding of physical systems. These simulations may be performed by combining the results from multiple computer codes. The machines that these simulations are executed on are often massively parallel/distributed systems. The output result of one of these simulations can be a terabyte of data and can require months of computing. All of these things contribute to the difficulty of keeping a useful record of the process of setting up and executing a simulation for a physical system. An electronic notebook for physical system simulations has been designed to help document the set up and execution process. Much of the documenting is done automatically by the simulation rather than the scientist running the simulation. The simulation knows what codes, data, software libraries, and versions thereof it is drawing together. All of these pieces of information become documented in the electronic notebook. The electronic notebook is designed with and uses the eXtensible Markup Language (XML). XML facilitates the representation, storage, interchange, and further use of the documented information.

  1. Theoretical electronic structure of structurally modified graphene

    NASA Astrophysics Data System (ADS)

    Dvorak, Marc David

    Graphene has emerged as a promising replacement for silicon in next-generation electronics and optoelectronic devices. If graphene is to be used in semiconductor devices, however, it must acquire an electronic band gap. Numerous approaches have been proposed to control the band gap of graphene, including the periodic patterning of defects. However, the mechanism for band gap opening and the associated physics in graphene patterned with defects remain unclear. Using both analytic theory and first-principles calculations, we show that periodic patterning of defects on graphene can open a large and tunable band gap, induce strong absorption peaks at optical wavelengths, and host a giant band gap quantum spin Hall phase. First, a geometric rule is analytically derived for the arrangements of defects that open a band gap in graphene, with one ninth of all possible patterns opening a band gap. Next, we perform ab-initio density functional calculations to compare the effects of structural vacancies, hexagonal BN dopants, and passivants on the electronic structure of graphene. Qualitatively, these three types of structural defects behave the same, with only slight differences in their resulting band structures. By adjusting the shape of structural defects, we show how to move the Dirac cones in reciprocal space in accordance with the tight-binding model for the anisotropic honeycomb lattice, while the fundamental mechanism for band gap opening remains the same. To quantitatively predict the band gap and optical properties of these materials, we employ many-body perturbation theory with Green's functions (GW/Bethe-Salpeter equation) to directly include electron-electron and electron-hole interactions. Structurally modified graphene shows a strong renormalization of the fundamental band gap over single particle descriptions, and a strong electron-hole interaction as indicated by strong exciton binding energies (> 0.5 eV). Finally, we show that structurally modified graphene

  2. Electronic Structure Principles and Aromaticity

    ERIC Educational Resources Information Center

    Chattaraj, P. K.; Sarkar, U.; Roy, D. R.

    2007-01-01

    The relationship between aromaticity and stability in molecules on the basis of quantities such as hardness and electrophilicity is explored. The findings reveal that aromatic molecules are less energetic, harder, less polarizable, and less electrophilic as compared to antiaromatic molecules, as expected from the electronic structure principles.

  3. Electron Scattering and Nuclear Structure

    ERIC Educational Resources Information Center

    Trower, W. P.; Ficenec, J. R.

    1971-01-01

    Presents information about the nucleus gained by studies of electron scattering. Discusses what can be implied about the shape of the charge distribution, the nucleus positions, the vibrational modes of the nucleus, the momentum of the nucleus, and the granularity and core structures of the nucleus. (DS)

  4. Structural basis for the temperature-induced transition of D-amino acid oxidase from pig kidney revealed by molecular dynamic simulation and photo-induced electron transfer.

    PubMed

    Nueangaudom, Arthit; Lugsanangarm, Kiattisak; Pianwanit, Somsak; Kokpol, Sirirat; Nunthaboot, Nadtanet; Tanaka, Fumio

    2012-02-28

    The structural basis for the temperature-induced transition in the D-amino acid oxidase (DAAO) monomer from pig kidney was studied by means of molecular dynamic simulations (MDS). The center to center (Rc) distances between the isoalloxazine ring (Iso) and all aromatic amino acids (Trp and Tyr) were calculated at 10 °C and 30 °C. Rc was shortest in Tyr224 (0.82 and 0.88 nm at 10 and 30 °C, respectively), and then in Tyr228. Hydrogen bonding (H-bond) formed between the Iso N1 and Gly315 N (peptide), between the Iso N3H and Leu51 O (peptide) and between the Iso N5 and Ala49 N (peptide) at 10 °C, whilst no H-bond was formed at the Iso N1 and Iso N3H at 30 °C. The H-bond of Iso O4 with Leu51 N (peptide) at 10 °C switched to that with Ala49 N (peptide) at 30 °C. The reported fluorescence lifetimes (228 and 182 ps at 10 and 30 °C, respectively) of DAAO were analyzed with Kakitani and Mataga (KM) ET theory. The calculated fluorescence lifetimes displayed an excellent agreement with the observed lifetimes. The ET rate was fastest from Tyr224 to the excited Iso (Iso*) at 10 °C and from Tyr314 at 30 °C, despite the fact that the Rc was shortest between Iso and Tyr224 at both temperatures. This was explained by the electrostatic energy in the protein. The differences in the observed fluorescence lifetimes at 10 and 30 °C were ascribed to the differences in electron affinity of the Iso* at both temperatures, in which the free energies of the electron affinity of Iso* at 10 and 30 °C were -8.69 eV and -8.51 eV respectively. The other physical quantities related to ET did not differ appreciably at both temperatures. The electron affinities at both temperatures were calculated with a semi-empirical molecular orbital method (MO) of PM6. Mean calculated electron affinities over 100 snapshots with 0.1 ps intervals were -7.69 eV at 10 °C and -7.59 eV at 30 °C. The difference in the calculated electron affinities, -0.11 eV, was close to the observed difference in the

  5. Single Pass Electron Cooling Simulations for MEIC

    SciTech Connect

    Bell, G. I.; Pogorelov, I. V.; Schwartz, B. T.; Zhang, Yuhong; Zhang, He

    2013-12-01

    Cooling of medium energy protons is critical for the proposed Jefferson Lab Medium Energy Ion Collider (MEIC). We present simulations of electron cooling of protons up to 60 GeV. In the beam frame in which the proton and electrons are co-propagating, their motion is non-relativistic. We use a binary collision model which treats the cooling process as the sum of a large number of two-body collisions which are calculated exactly. This model can treat even very close collisions between an electron and ion with high accuracy. We also calculate dynamical friction using a delta-f PIC model. The code VSim (formerly Vorpal) is used to perform the simulations. We compare the friction rates with that obtained by a 3D integral over electron velocities which is used by BETACOOL.

  6. Electric fields in Scanning Electron Microscopy simulations

    NASA Astrophysics Data System (ADS)

    Arat, K. T.; Bolten, J.; Klimpel, T.; Unal, N.

    2016-03-01

    The electric field distribution and charging effects in Scanning Electron Microscopy (SEM) were studied by extending a Monte-Carlo based SEM simulator by a fast and accurate multigrid (MG) based 3D electric field solver. The main focus is on enabling short simulation times with maintaining sufficient accuracy, so that SEM simulation can be used in practical applications. The implementation demonstrates a gain in computation speed, when compared to a Gauss-Seidel based reference solver is roughly factor of 40, with negligible differences in the result (~10-6 𝑉). In addition, the simulations were compared with experimental SEM measurements using also complex 3D sample, showing that i) the modelling of e-fields improves the simulation accuracy, and ii) multigrid method provide a significant benefit in terms of simulation time.

  7. Graph-based linear scaling electronic structure theory

    NASA Astrophysics Data System (ADS)

    Niklasson, Anders M. N.; Mniszewski, Susan M.; Negre, Christian F. A.; Cawkwell, Marc J.; Swart, Pieter J.; Mohd-Yusof, Jamal; Germann, Timothy C.; Wall, Michael E.; Bock, Nicolas; Rubensson, Emanuel H.; Djidjev, Hristo

    2016-06-01

    We show how graph theory can be combined with quantum theory to calculate the electronic structure of large complex systems. The graph formalism is general and applicable to a broad range of electronic structure methods and materials, including challenging systems such as biomolecules. The methodology combines well-controlled accuracy, low computational cost, and natural low-communication parallelism. This combination addresses substantial shortcomings of linear scaling electronic structure theory, in particular with respect to quantum-based molecular dynamics simulations.

  8. Graph-based linear scaling electronic structure theory.

    PubMed

    Niklasson, Anders M N; Mniszewski, Susan M; Negre, Christian F A; Cawkwell, Marc J; Swart, Pieter J; Mohd-Yusof, Jamal; Germann, Timothy C; Wall, Michael E; Bock, Nicolas; Rubensson, Emanuel H; Djidjev, Hristo

    2016-06-21

    We show how graph theory can be combined with quantum theory to calculate the electronic structure of large complex systems. The graph formalism is general and applicable to a broad range of electronic structure methods and materials, including challenging systems such as biomolecules. The methodology combines well-controlled accuracy, low computational cost, and natural low-communication parallelism. This combination addresses substantial shortcomings of linear scaling electronic structure theory, in particular with respect to quantum-based molecular dynamics simulations.

  9. Understanding Cellulose Through Molecular Simulation and Electron Tomography

    SciTech Connect

    Matthews, J.

    2013-01-01

    High-resolution cellulose crystal structures have been determined from diffraction experiments using large diameter microfibrils as the sample material. However, cellulose microfibrils in plants are much smaller in diameter, and are more difficult to directly examine experimentally. Molecular dynamics simulation combined with quantum chemical calculations can help to elucidate the structure and dynamics of small diameter cellulose microfibrils. These simulation techniques also aid in the interpretation of electron tomography volumetric structural data from maize cell walls, where pretreatment with dilute acid or ammonia reveals microfibril geometry.

  10. Electronic and structural properties of functional nanostructures

    NASA Astrophysics Data System (ADS)

    Yang, Teng

    In this Thesis, I present a study of electronic and structural properties of functional nanostructures such as MoSxIy nanowires, self-assembled monolayer on top of metallic surfaces and structural changes induced in graphite by photo excitations. MoSxI y nanowires, which can be easily synthesized in one step, show many advantages over conventional carbon nanotubes in molecular electronics and many other applications. But how to self-assemble them into desired pattern for practical electronic network? Self-assembled monolayers of polymers on metallic surfaces may help to guide pattern formation of some nanomaterials such as MoSxIy nanowires. I have investigated the physical properties of these nanoscale wires and microscopic self-assembly mechanisms of patterns by total energy calculations combined with molecular dynamics simulations and structure optimization. First, I studied the stability of novel Molybdenum chaicohalide nanowires, a candidate for molecular electronics applications. Next, I investigated the self-assembly of nanoparticles into ordered arrays with the aid of a template. Such templates, I showed, can be formed by polymer adsorption on surfaces such as highly ordered pyrolytic graphite and Ag(111). Finally, I studied the physical origin of of structural changes induced in graphite by light in form of a femtosecond laser pulse.

  11. Exposure simulation of electron beam microcolumn lithography

    NASA Astrophysics Data System (ADS)

    Kim, Sang-Kon; Oh, Hye-Keun

    2004-05-01

    We propose an improved method to describe the electron-resist interaction based on Dill"s model for exposure simulation. For this purpose, Monte Carlo simulation was performed to obtain the energy intensity distribution in the chemically amplified resist. Tabulated Mott data for elastic scattering, Moller and Vriens cross sections for inelastic scattering, and Modified Bethe equation plus discrete energy loss for energy loss are used for the calculation of the energy intensity distribution. Through the electron-resist interaction, the energy intensity distribution changes resist components into the exposure production such as the photoacid concentration or the photoacid generator inside resists with various pattern shapes by using the modified Dill"s model. Our simulation profiles show a good agreement with experimental profiles.

  12. Xyce(™) Parallel Electronic Simulator

    SciTech Connect

    2013-10-03

    The Xyce Parallel Electronic Simulator simulates electronic circuit behavior in DC, AC, HB, MPDE and transient mode using standard analog (DAE) and/or device (PDE) device models including several age and radiation aware devices. It supports a variety of computing platforms (both serial and parallel) computers. Lastly, it uses a variety of modern solution algorithms dynamic parallel load-balancing and iterative solvers.! ! Xyce is primarily used to simulate the voltage and current behavior of a circuit network (a network of electronic devices connected via a conductive network). As a tool, it is mainly used for the design and analysis of electronic circuits.! ! Kirchoff's conservation laws are enforced over a network using modified nodal analysis. This results in a set of differential algebraic equations (DAEs). The resulting nonlinear problem is solved iteratively using a fully coupled Newton method, which in turn results in a linear system that is solved by either a standard sparse-direct solver or iteratively using Trilinos linear solver packages, also developed at Sandia National Laboratories.

  13. Structural Dynamics of Electronic Systems

    NASA Astrophysics Data System (ADS)

    Suhir, E.

    2013-03-01

    The published work on analytical ("mathematical") and computer-aided, primarily finite-element-analysis (FEA) based, predictive modeling of the dynamic response of electronic systems to shocks and vibrations is reviewed. While understanding the physics of and the ability to predict the response of an electronic structure to dynamic loading has been always of significant importance in military, avionic, aeronautic, automotive and maritime electronics, during the last decade this problem has become especially important also in commercial, and, particularly, in portable electronics in connection with accelerated testing of various surface mount technology (SMT) systems on the board level. The emphasis of the review is on the nonlinear shock-excited vibrations of flexible printed circuit boards (PCBs) experiencing shock loading applied to their support contours during drop tests. At the end of the review we provide, as a suitable and useful illustration, the exact solution to a highly nonlinear problem of the dynamic response of a "flexible-and-heavy" PCB to an impact load applied to its support contour during drop testing.

  14. Electronic structure investigations of quasicrystals

    NASA Astrophysics Data System (ADS)

    Rotenberg, E.; Theis, W.; Horn, K.

    2004-08-01

    We present a review of the determination of density of states (DOS) of quasicrystals using valence band photoemission spectroscopy. The absence of fine or spiky structure in the angle-integrated DOS of quasicrystals suggests the possibility of delocalized electronic states. These were confirmed with angle-resolved photoemission studies, which clearly establish the presence of dispersing features attributed to momentum-dependent bandstructure. Such dispersing states are observed not only for deeper-lying sp states, but also for d-derived bands near the Fermi level. Data from three different high symmetry surfaces of decagonal Al-Ni-Co, an ideal model system, are presented. We find that only a few dominant reciprocal lattice vectors are sufficient to describe the quasiperiodic potential, and the implications for electronic properties are discussed.

  15. Electronic instrumentation for smart structures

    NASA Astrophysics Data System (ADS)

    Blanar, George J.

    1995-04-01

    The requirements of electronic instrumentation for smart structures are similar to those of data acquisition systems at our national particle physics laboratories. Modern high energy and heavy ion physics experiments may have tens of thousands of channels of data sources producing data that must be converted to digital form, compacted, stored and interpreted. In parallel, multiple sensors distributed in and around smart structures generate either binary or analog signals that are voltage, charge, or time like in their information content. In all cases, they must be transmitted, converted and preserved into a unified digital format for real-time processing. This paper will review the current status of practical large scale electronic measurement systems with special attention to architectures and physical organization. Brief surveys of the current state of the art will include preamplifiers and amplifiers, comparators and discriminators, voltage or charge analog-to-digital converters, time internal meters or time-to-digital converters, and finally, counting or scalar systems. The paper will conclude by integrating all of these ideas in a concept for an all-digital readout of a smart structure using the latest techniques used in physics research today.

  16. Xyce parallel electronic simulator release notes.

    SciTech Connect

    Keiter, Eric R; Hoekstra, Robert John; Mei, Ting; Russo, Thomas V.; Schiek, Richard Louis; Thornquist, Heidi K.; Rankin, Eric Lamont; Coffey, Todd S; Pawlowski, Roger P; Santarelli, Keith R.

    2010-05-01

    The Xyce Parallel Electronic Simulator has been written to support, in a rigorous manner, the simulation needs of the Sandia National Laboratories electrical designers. Specific requirements include, among others, the ability to solve extremely large circuit problems by supporting large-scale parallel computing platforms, improved numerical performance and object-oriented code design and implementation. The Xyce release notes describe: Hardware and software requirements New features and enhancements Any defects fixed since the last release Current known defects and defect workarounds For up-to-date information not available at the time these notes were produced, please visit the Xyce web page at http://www.cs.sandia.gov/xyce.

  17. The electronic structure of Lu

    NASA Astrophysics Data System (ADS)

    Tibbetts, T. A.; Harmon, B. N.

    1982-12-01

    The electronic structure of hcp Lu has been calculated using a linearized augmented plane wave (LAPW) method and the Hedin-Lundqvist local density approximation for exchange and correlation. Although complete self-consistency was hindered by the proximity of the 4f levels to the Fermi energy, the valence bands were converged and the calculation yielded a Fermi surface remarkably similar to that calculated by Keeton and Loucks. Comparison is made with recent de Haas-van Alphen and neutron magnetic form factor experiments.

  18. Simulation of plasma double-layer structures

    NASA Technical Reports Server (NTRS)

    Borovsky, J. E.; Joyce, G.

    1982-01-01

    Electrostatic plasma double layers are numerically simulated by means of a magnetized 2 1/2 dimensional particle in cell method. The investigation of planar double layers indicates that these one dimensional potential structures are susceptible to periodic disruption by instabilities in the low potential plasmas. Only a slight increase in the double layer thickness with an increase in its obliqueness to the magnetic field is observed. Weak magnetization results in the double layer electric field alignment of accelerated particles and strong magnetization results in their magnetic field alignment. The numerical simulations of spatially periodic two dimensional double layers also exhibit cyclical instability. A morphological invariance in two dimensional double layers with respect to the degree of magnetization implies that the potential structures scale with Debye lengths rather than with gyroradii. Electron beam excited electrostatic electron cyclotron waves and (ion beam driven) solitary waves are present in the plasmas adjacent to the double layers.

  19. Xyce parallel electronic simulator : reference guide.

    SciTech Connect

    Mei, Ting; Rankin, Eric Lamont; Thornquist, Heidi K.; Santarelli, Keith R.; Fixel, Deborah A.; Coffey, Todd Stirling; Russo, Thomas V.; Schiek, Richard Louis; Warrender, Christina E.; Keiter, Eric Richard; Pawlowski, Roger Patrick

    2011-05-01

    This document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users Guide. The focus of this document is (to the extent possible) exhaustively list device parameters, solver options, parser options, and other usage details of Xyce. This document is not intended to be a tutorial. Users who are new to circuit simulation are better served by the Xyce Users Guide. The Xyce Parallel Electronic Simulator has been written to support, in a rigorous manner, the simulation needs of the Sandia National Laboratories electrical designers. It is targeted specifically to run on large-scale parallel computing platforms but also runs well on a variety of architectures including single processor workstations. It also aims to support a variety of devices and models specific to Sandia needs. This document is intended to complement the Xyce Users Guide. It contains comprehensive, detailed information about a number of topics pertinent to the usage of Xyce. Included in this document is a netlist reference for the input-file commands and elements supported within Xyce; a command line reference, which describes the available command line arguments for Xyce; and quick-references for users of other circuit codes, such as Orcad's PSpice and Sandia's ChileSPICE.

  20. Xyce parallel electronic simulator : users' guide.

    SciTech Connect

    Mei, Ting; Rankin, Eric Lamont; Thornquist, Heidi K.; Santarelli, Keith R.; Fixel, Deborah A.; Coffey, Todd Stirling; Russo, Thomas V.; Schiek, Richard Louis; Warrender, Christina E.; Keiter, Eric Richard; Pawlowski, Roger Patrick

    2011-05-01

    This manual describes the use of the Xyce Parallel Electronic Simulator. Xyce has been designed as a SPICE-compatible, high-performance analog circuit simulator, and has been written to support the simulation needs of the Sandia National Laboratories electrical designers. This development has focused on improving capability over the current state-of-the-art in the following areas: (1) Capability to solve extremely large circuit problems by supporting large-scale parallel computing platforms (up to thousands of processors). Note that this includes support for most popular parallel and serial computers; (2) Improved performance for all numerical kernels (e.g., time integrator, nonlinear and linear solvers) through state-of-the-art algorithms and novel techniques. (3) Device models which are specifically tailored to meet Sandia's needs, including some radiation-aware devices (for Sandia users only); and (4) Object-oriented code design and implementation using modern coding practices that ensure that the Xyce Parallel Electronic Simulator will be maintainable and extensible far into the future. Xyce is a parallel code in the most general sense of the phrase - a message passing parallel implementation - which allows it to run efficiently on the widest possible number of computing platforms. These include serial, shared-memory and distributed-memory parallel as well as heterogeneous platforms. Careful attention has been paid to the specific nature of circuit-simulation problems to ensure that optimal parallel efficiency is achieved as the number of processors grows. The development of Xyce provides a platform for computational research and development aimed specifically at the needs of the Laboratory. With Xyce, Sandia has an 'in-house' capability with which both new electrical (e.g., device model development) and algorithmic (e.g., faster time-integration methods, parallel solver algorithms) research and development can be performed. As a result, Xyce is a unique

  1. Interchain impacts on electronic structures of heterocyclic oligomers and polymers containing group 14, 15, and 16 heteroatoms: quantum chemical calculations in combination with molecular dynamics simulations.

    PubMed

    Zhang, Guiling; Ma, Jing; Wen, Jin

    2007-10-11

    The packing structures and packing effects on excitation energies of oligomers of polyfuran (PFu), polypyrrole (PPy), polycyclopentidene (PCp), polythiophene (PTh), polyphosphole (PPh), and polysilole (PSi) are comparatively studied by employing molecular dynamics (MD) simulations and time-dependent density functional theory (TDDFT) calculations. The dependence of packing structures on the main group of heteroatoms in the five-membered heterocyclic oligomers is exhibited from MD simulations. The planarity of backbones and the population of pi-stacked structures increase with the heteroatoms going from group 14 to group 16; i.e., PCp < PPy < PFu; PSi < PPh < PTh. The polymers with the third row elements, PSi and PPh, tend to have larger chain flexibilities in the packing systems than those with the second row elements, PCp and PPy, respectively. On the basis of the second-order Møller-Plesset perturbation (MP2) and natural bond orbital (NBO) calculations of the pi-stacked pairs, the difference in pi-stack orientations, head-to-tail vs head-to-head, between various packing systems is rationalized by individual interchain bond orbital interactions involved with heteroatoms. The packing systems with higher row elements tend to have narrower band gaps. The band gaps are closely related to the chain torsions driven by interchain interactions. The noticeable chain distortions in the packing systems of PCp, PSi, and PPh lead to the significant increase of band gaps in comparison with those appraised from periodic boundary conditions (PBC) calculations on their planar isolated chains.

  2. Aircraft Electronics Maintenance Training Simulator. Curriculum Outlines.

    ERIC Educational Resources Information Center

    Blackhawk Technical Coll., Janesville, WI.

    Instructional materials are provided for nine courses in an aircraft electronics maintenance training program. Courses are as follows: aviation basic electricity, direct current and alternating current electronics, basic avionic installations, analog electronics, digital electronics, microcomputer electronics, radio communications, aircraft…

  3. Nonlinearity in structural and electronic materials

    SciTech Connect

    Bishop, A.R.; Beardmore, K.M.; Ben-Naim, E.

    1997-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project strengthens a nonlinear technology base relevant to a variety of problems arising in condensed matter and materials science, and applies this technology to those problems. In this way the controlled synthesis of, and experiments on, novel electronic and structural materials provide an important focus for nonlinear science, while nonlinear techniques help advance the understanding of the scientific principles underlying the control of microstructure and dynamics in complex materials. This research is primarily focused on four topics: (1) materials microstructure: growth and evolution, and porous media; (2) textures in elastic/martensitic materials; (3) electro- and photo-active polymers; and (4) ultrafast photophysics in complex electronic materials. Accomplishments included the following: organization of a ``Nonlinear Materials`` seminar series and international conferences including ``Fracture, Friction and Deformation,`` ``Nonequilibrium Phase Transitions,`` and ``Landscape Paradigms in Physics and Biology``; invited talks at international conference on ``Synthetic Metals,`` ``Quantum Phase Transitions,`` ``1996 CECAM Euroconference,`` and the 1995 Fall Meeting of the Materials Research Society; large-scale simulations and microscopic modeling of nonlinear coherent energy storage at crack tips and sliding interfaces; large-scale simulation and microscopic elasticity theory for precursor microstructure and dynamics at solid-solid diffusionless phase transformations; large-scale simulation of self-assembling organic thin films on inorganic substrates; analysis and simulation of smoothing of rough atomic surfaces; and modeling and analysis of flux pattern formation in equilibrium and nonequilibrium Josephson junction arrays and layered superconductors.

  4. The Xyce Parallel Electronic Simulator - An Overview

    SciTech Connect

    HUTCHINSON,SCOTT A.; KEITER,ERIC R.; HOEKSTRA,ROBERT J.; WATTS,HERMAN A.; WATERS,ARLON J.; SCHELLS,REGINA L.; WIX,STEVEN D.

    2000-12-08

    The Xyce{trademark} Parallel Electronic Simulator has been written to support the simulation needs of the Sandia National Laboratories electrical designers. As such, the development has focused on providing the capability to solve extremely large circuit problems by supporting large-scale parallel computing platforms (up to thousands of processors). In addition, they are providing improved performance for numerical kernels using state-of-the-art algorithms, support for modeling circuit phenomena at a variety of abstraction levels and using object-oriented and modern coding-practices that ensure the code will be maintainable and extensible far into the future. The code is a parallel code in the most general sense of the phrase--a message passing parallel implementation--which allows it to run efficiently on the widest possible number of computing platforms. These include serial, shared-memory and distributed-memory parallel as well as heterogeneous platforms. Furthermore, careful attention has been paid to the specific nature of circuit-simulation problems to ensure that optimal parallel efficiency is achieved even as the number of processors grows.

  5. Characterization of electron temperature by simulating a multicusp ion source

    NASA Astrophysics Data System (ADS)

    Yeon, Yeong Heum; Ghergherehchi, Mitra; Kim, Sang Bum; Jun, Woo Jung; Lee, Jong Chul; Mohamed Gad, Khaled Mohamed; Namgoong, Ho; Chai, Jong Seo

    2016-12-01

    Multicusp ion sources are used in cyclotrons and linear accelerators to produce high beam currents. The structure of a multicusp ion source consists of permanent magnets, filaments, and an anode body. The configuration of the array of permanent magnets, discharge voltage of the plasma, extraction bias voltage, and structure of the multicusp ion source body decide the quality of the beam. The electrons are emitted from the filament by thermionic emission. The emission current can be calculated from thermal information pertaining to the filament, and from the applied voltage and current. The electron trajectories were calculated using CST Particle Studio to optimize the plasma. The array configuration of the permanent magnets decides the magnetic field inside the ion source. The extraction bias voltage and the structure of the multicusp ion source body decide the electric field. Optimization of the electromagnetic field was performed with these factors. CST Particle Studio was used to calculate the electron temperature with a varying permanent magnet array. Four types of permanent magnet array were simulated to optimize the electron temperature. It was found that a 2-layer full line cusp field (with inverse field) produced the best electron temperature control behavior.

  6. Simulations and measurements in scanning electron microscopes at low electron energy.

    PubMed

    Walker, Christopher G H; Frank, Luděk; Müllerová, Ilona

    2016-11-01

    The advent of new imaging technologies in Scanning Electron Microscopy (SEM) using low energy (0-2 keV) electrons has brought about new ways to study materials at the nanoscale. It also brings new challenges in terms of understanding electron transport at these energies. In addition, reduction in energy has brought new contrast mechanisms producing images that are sometimes difficult to interpret. This is increasing the push for simulation tools, in particular for low impact energies of electrons. The use of Monte Carlo calculations to simulate the transport of electrons in materials has been undertaken by many authors for several decades. However, inaccuracies associated with the Monte Carlo technique start to grow as the energy is reduced. This is not simply associated with inaccuracies in the knowledge of the scattering cross-sections, but is fundamental to the Monte Carlo technique itself. This is because effects due to the wave nature of the electron and the energy band structure of the target above the vacuum energy level become important and these are properties which are difficult to handle using the Monte Carlo method. In this review we briefly describe the new techniques of scanning low energy electron microscopy and then outline the problems and challenges of trying to understand and quantify the signals that are obtained. The effects of charging and spin polarised measurement are also briefly explored. SCANNING 38:802-818, 2016. © 2016 Wiley Periodicals, Inc.

  7. Electronic processes in multilayer memory structures

    NASA Astrophysics Data System (ADS)

    Plotnikov, A. F.

    The papers presented in this volume contain results of recent theoretical and experimental research related to electron processes in optoelectronic memory media based on structures consisting of a metal, an amorphous insulating layer, and a semiconductor. Topics discussed include photostimulated electron processes in metal-insulator-semiconductor structures, electron transfer phenomena in amorphous dielectric layers, degradation phenomena in MNOS memory elements under prolonged charge injection into the dielectric layer, and characteristics of charge relaxation in MNOS structures following multiple reprogramming.

  8. Simulation of the electronic structure of simple oxides BeO and SiO2 and complex oxides Be2SiO4 and Be2Si x Ge1 - x O4 with the phenacite structure

    NASA Astrophysics Data System (ADS)

    Mazurenko, V. V.; Rudenko, A. N.; Kvashnin, Ya. O.; Mazurenko, V. G.; Novoselov, Yu. N.; Pustovarov, V. A.; Kukharenko, A. I.; Cholakh, S. O.

    2011-05-01

    The ab initio numerical calculations of the electronic structure of simple oxides BeO and SiO2 and complex oxides Be2SiO4 and Be2Si x Ge1 - x O4 with the phenacite structure have been performed using the electron density functional theory. The calculations indicate that the main feature of the systems under investigation is the presence of oxygen states in both the valence and conduction bands. The splitting of the bottom of the conduction band has been revealed in the electronic structure of the Be2Si x Ge1 - x O4 system. The splitting width is about 1.5 eV. The main contribution to the formation of a narrow subband of the conduction band comes from the 2 s and 2 p states of oxygen and the 4 d state of germanium. Microscopic models of the spatial localization of the electron density on lower energy states of the conduction band of oxide crystals have been developed using the Wannier function technique. The reflection spectra of BeO, SiO2, and Be2SiO4 have been analyzed. The reported calculations of the electronic structure imply the exciton nature of the 9.7-eV reflection peak in the Be2SiO4 crystal.

  9. Stochastic simulation of electron avalanches on supercomputers

    SciTech Connect

    Rogasinsky, S. V.; Marchenko, M. A.

    2014-12-09

    In the paper, we present a three-dimensional parallel Monte Carlo algorithm named ELSHOW which is developed for simulation of electron avalanches in gases. Parallel implementation of the ELSHOW was made on supercomputers with different architectures (massive parallel and hybrid ones). Using the ELSHOW, calculations of such integral characteristics as the number of particles in an avalanche, the coefficient of impact ionization, the drift velocity, and the others were made. Also, special precise computations were made to select an appropriate size of the time step using the technique of dependent statistical tests. Particularly, the algorithm consists of special methods of distribution modeling, a lexicographic implementation scheme for “branching” of trajectories, justified estimation of functionals. A comparison of the obtained results for nitrogen with previously published theoretical and experimental data was made.

  10. Theory and simulations of electron vortices generated by magnetic pushing

    SciTech Connect

    Richardson, A. S.; Angus, J. R.; Swanekamp, S. B.; Schumer, J. W.; Ottinger, P. F.

    2013-08-15

    Vortex formation and propagation are observed in kinetic particle-in-cell (PIC) simulations of magnetic pushing in the plasma opening switch. These vortices are studied here within the electron-magnetohydrodynamic (EMHD) approximation using detailed analytical modeling. PIC simulations of these vortices have also been performed. Strong v×B forces in the vortices give rise to significant charge separation, which necessitates the use of the EMHD approximation in which ions are fixed and the electrons are treated as a fluid. A semi-analytic model of the vortex structure is derived, and then used as an initial condition for PIC simulations. Density-gradient-dependent vortex propagation is then examined using a series of PIC simulations. It is found that the vortex propagation speed is proportional to the Hall speed v{sub Hall}≡cB{sub 0}/4πn{sub e}eL{sub n}. When ions are allowed to move, PIC simulations show that the electric field in the vortex can accelerate plasma ions, which leads to dissipation of the vortex. This electric field contributes to the separation of ion species that has been observed to occur in pulsed-power experiments with a plasma-opening switch.

  11. Electronic correlation contributions to structural energies

    NASA Astrophysics Data System (ADS)

    Haydock, Roger

    2015-03-01

    The recursion method is used to calculate electronic excitation spectra including electron-electron interactions within the Hubbard model. The effects of correlation on structural energies are then obtained from these spectra and applied to stacking faults. http://arxiv.org/abs/1405.2288 Supported by the Richmond F. Snyder Fund and Gifts.

  12. Electron vortex magnetic holes: A nonlinear coherent plasma structure

    SciTech Connect

    Haynes, Christopher T. Burgess, David; Sundberg, Torbjorn; Camporeale, Enrico

    2015-01-15

    We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.

  13. Electron vortex magnetic holes: A nonlinear coherent plasma structure

    NASA Astrophysics Data System (ADS)

    Haynes, Christopher T.; Burgess, David; Camporeale, Enrico; Sundberg, Torbjorn

    2015-01-01

    We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.

  14. Electronic structure of lithium tetraborate

    NASA Astrophysics Data System (ADS)

    Wooten, David J.

    Due to many of its attributes, Li2B4O7 provides a possible material for incorporation as either a primary or companion material in future solid state neutron detectors. There is however a lack of fundamental characterization information regarding this useful material, particularly its electronic configuration. To address this, an investigation of Li2B4O7(110) and Li2B 4O7(100) was undertaken, utilizing photoemission and inverse photoemission spectroscopic techniques. The measured band gap depended on crystallographic direction with the band gaps ranging from 8.9+/-0.5 eV to 10.1+/-0.5 eV. The measurement yielded a density of states that qualitatively agreed with the theoretical results from model bulk band structure calculations for Li2B4O7; albeit with a larger band gap than predicted, but consistent with the known deficiencies of Local Density Approximation and Density Functional Theory calculations. The occupied states of both surfaces were extremely flat; to the degree that resolving periodic dispersion of the occupied states was inconclusive, within the resolution of the system. However, both surfaces demonstrated clear periodic dispersion within the empty states very close to theoretical Brillouin zone values. These attributes also translated to a lighter charge carrier effective mass in the unoccupied states. Of the two surfaces, Li2B4O 7(110) yielded the more consistent values in orthogonal directions for energy states. The presence of a bulk band gap surface state and image potential state in Li2B4O7(110) was indicative of a defect-free surface. The absence of both in the more polar, more dielectric Li2B4O7(100) was attributed to the presence of defects determined to be O vacancies. The results from Li2B 4O7(110) were indicative of a more stable surface than Li 2B4O7(100). In addition, Li 1s bulk and surface core level components were determined at the binding energies of -56.5+0.4 and -53.7+0.5 eV. Resonance features were observed along the [001

  15. Electronic-structure calculation for metals by local optimization

    NASA Astrophysics Data System (ADS)

    Woodward, C.; Min, B. I.; Benedek, R.; Garner, J.

    1989-03-01

    Recent work by Car and Parrinello has generated considerable interest in the calculation of electronic structure by nonlinear optimization. The technique introduced by these authors, dynamical simulated annealing, is designed for problems that involve energy barriers. When local optimization suffices to determine the energy minimum, more direct methods are available. In this paper we apply the algorithm suggested by Williams and Soler to calculate the electronic structure of metals, using a plane-wave expansion for the electronic orbitals and an electron-ion pseudopotential of the Kleinman-Bylander form. Radial pseudopotentials were taken from the compilation of Bachelet, Hamann, and Schlüter. Calculations are performed to optimize the electronic structure (i) with fixed atomic configuration, or (ii) with the atomic volume being optimized simultaneously. It is found that the dual optimization (ii) converges in essentially the same number of steps as the static lattice optimization (i). Numerical results are presented for Li, K, Al, and simple-cubic P.

  16. Electronic Structure of Lithium Tetraborate

    DTIC Science & Technology

    2010-06-01

    binding energies of -56.5+0.4 and -53.7+0.5 eV. Resonance features were observed along the [001] direction and were attributed to a Coster- Kronig ...could be theoretically explained as an Auger electron [12] or Coster- Kronig process [13] of a Li 1s electron photoexcitation to an unoccupied 2p...Coster Kronig , which requires only one Li atom. Such a Coster Kronig mechanism is pictorially displayed below in Figure 7.9. 128 Figure 7.9

  17. Electron tomography of dislocation structures

    SciTech Connect

    Liu, G.S.; House, S.D.; Kacher, J.; Tanaka, M.; Higashida, K.; Robertson, I.M.

    2014-01-15

    Recent developments in the application of electron tomography for characterizing microstructures in crystalline solids are described. The underlying principles for electron tomography are presented in the context of typical challenges in adapting the technique to crystalline systems and in using diffraction contrast imaging conditions. Methods for overcoming the limitations associated with the angular range, the number of acquired images, and uniformity of image contrast are introduced. In addition, a method for incorporating the real space coordinate system into the tomogram is presented. As the approach emphasizes development of experimental solutions to the challenges, the solutions developed and implemented are presented in the form of examples.

  18. Electron gun controlled smart structure

    DOEpatents

    Martin, Jeffrey W.; Main, John Alan; Redmond, James M.; Henson, Tammy D.; Watson, Robert D.

    2001-01-01

    Disclosed is a method and system for actively controlling the shape of a sheet of electroactive material; the system comprising: one or more electrodes attached to the frontside of the electroactive sheet; a charged particle generator, disposed so as to direct a beam of charged particles (e.g. electrons) onto the electrode; a conductive substrate attached to the backside of the sheet; and a power supply electrically connected to the conductive substrate; whereby the sheet changes its shape in response to an electric field created across the sheet by an accumulation of electric charge within the electrode(s), relative to a potential applied to the conductive substrate. Use of multiple electrodes distributed across on the frontside ensures a uniform distribution of the charge with a single point of e-beam incidence, thereby greatly simplifying the beam scanning algorithm and raster control electronics, and reducing the problems associated with "blooming". By placing a distribution of electrodes over the front surface of a piezoelectric film (or other electroactive material), this arrangement enables improved control over the distribution of surface electric charges (e.g. electrons) by creating uniform (and possibly different) charge distributions within each individual electrode. Removal or deposition of net electric charge can be affected by controlling the secondary electron yield through manipulation of the backside electric potential with the power supply. The system can be used for actively controlling the shape of space-based deployable optics, such as adaptive mirrors and inflatable antennae.

  19. Complex structures of dense lithium: Electronic origin

    NASA Astrophysics Data System (ADS)

    Degtyareva, V. F.

    2016-11-01

    Lithium—the lightest alkali metal exhibits unexpected structures and electronic behavior at high pressures. Like the heavier alkali metals, Li is bcc at ambient pressure and transforms first to fcc (at 7.5 GPa). The post-fcc high-pressure form Li-cI 16 (at 40-60 GPa) is similar to Na-cI 16 and related to more complex structures of heavy alkalis Rb-oC52 and Cs- oC84. The other high pressure phases for Li (oC88, oC40, oC24) observed at pressures up to 130 GPa are found only in Li. The different route of Li high-pressure structures correlates with its special electronic configuration containing the only 3 electrons (at 1s and 2s levels). Crystal structures for Li are analyzed within the model of Fermi sphere-Brillouin zone interactions. Stability of post-fcc structures for Li are supported by the Hume-Rothery arguments when new diffraction plains appear close to the Fermi level producing pseudogaps near the Fermi level and decreasing the crystal energy. The filling of Brillouin-Jones zones by electron states for a given structure defines the physical properties as optical reflectivity, electrical resistivity and superconductivity. To understand the complexity of structural and physical properties of Li above 60 GPa it is necessary to assume the valence electron band overlap with the core electrons and increase the valence electron count under compression.

  20. Electronic Structure of Small Lanthanide Containing Molecules

    NASA Astrophysics Data System (ADS)

    Kafader, Jared O.; Ray, Manisha; Topolski, Josey E.; Chick Jarrold, Caroline

    2016-06-01

    Lanthanide-based materials have unusual electronic properties because of the high number of electronic degrees of freedom arising from partial occupation of 4f orbitals, which make these materials optimal for their utilization in many applications including electronics and catalysis. Electronic spectroscopy of small lanthanide molecules helps us understand the role of these 4f electrons, which are generally considered core-like because of orbital contraction, but are energetically similar to valence electrons. The spectroscopy of small lanthanide-containing molecules is relatively unexplored and to broaden this understanding we have completed the characterization of small cerium, praseodymium, and europium molecules using photoelectron spectroscopy coupled with DFT calculations. The characterization of PrO, EuH, EuO/EuOH, and CexOy molecules have allowed for the determination of their electron affinity, the assignment of numerous anion to neutral state transitions, modeling of anion/neutral structures and electron orbital occupation.

  1. Structural physiology based on electron crystallography

    PubMed Central

    Fujiyoshi, Yoshinori

    2011-01-01

    There are many questions in brain science, which are extremely interesting but very difficult to answer. For example, how do education and other experiences during human development influence the ability and personality of the adult? The molecular mechanisms underlying such phenomena are still totally unclear. However, technological and instrumental advancements of electron microscopy have facilitated comprehension of the structures of biological components, cells, and organelles. Electron crystallography is especially good for studying the structure and function of membrane proteins, which are key molecules of signal transduction in neural and other cells. Electron crystallography is now an established technique to analyze the structures of membrane proteins in lipid bilayers, which are close to their natural biological environment. By utilizing cryo-electron microscopes with helium cooled specimen stages, which were developed through a personal motivation to understand functions of neural systems from a structural point of view, structures of membrane proteins were analyzed at a resolution higher than 3 Å. This review has four objectives. First, it is intended to introduce the new research field of structural physiology. Second, it introduces some of the personal struggles, which were involved in developing the cryo-electron microscope. Third, it discusses some of the technology for the structural analysis of membrane proteins based on cryo-electron microscopy. Finally, it reviews structural and functional analyses of membrane proteins. PMID:21416541

  2. Probing the bonding and electronic structure of single atom dopants in graphene with electron energy loss spectroscopy.

    PubMed

    Ramasse, Quentin M; Seabourne, Che R; Kepaptsoglou, Despoina-Maria; Zan, Recep; Bangert, Ursel; Scott, Andrew J

    2013-10-09

    A combination of scanning transmission electron microscopy, electron energy loss spectroscopy, and ab initio calculations reveal striking electronic structure differences between two distinct single substitutional Si defect geometries in graphene. Optimised acquisition conditions allow for exceptional signal-to-noise levels in the spectroscopic data. The near-edge fine structure can be compared with great accuracy to simulations and reveal either an sp(3)-like configuration for a trivalent Si or a more complicated hybridized structure for a tetravalent Si impurity.

  3. Including the Effects of Electronic Excitations and Electron-Phonon Coupling in Cascade Simulations

    SciTech Connect

    Duffy, Dorothy |

    2008-07-01

    Radiation damage has traditionally been modeled using cascade simulations however such simulations generally neglect the effects of electron-ion interactions, which may be significant in high energy cascades. A model has been developed which includes the effects of electronic stopping and electron-phonon coupling in Molecular Dynamics simulations by means of an inhomogeneous Langevin thermostat. The energy lost by the atoms to electronic excitations is gained by the electronic system and the energy evolution of the electronic system is modeled by the heat diffusion equation. Energy is exchanged between the electronic system and the atoms in the Molecular Dynamics simulation by means of a Langevin thermostat, the temperature of which is the local electronic temperature. The model is applied to a 10 keV cascade simulation for Fe. (authors)

  4. Efficient numerical simulation of electron states in quantum wires

    NASA Technical Reports Server (NTRS)

    Kerkhoven, Thomas; Galick, Albert T.; Ravaioli, Umberto; Arends, John H.; Saad, Youcef

    1990-01-01

    A new algorithm is presented for the numerical simulation of electrons in a quantum wire as described by a two-dimensional eigenvalue problem for Schroedinger's equation coupled with Poisson's equation. Initially, the algorithm employs an underrelaxed fixed point iteration to generate an approximation which is reasonably close to the solution. Subsequently, this approximate solution is employed as an initial guess for a Jacobian-free implementation of an approximate Newton method. In this manner the nonlinearity in the model is dealt with effectively. The effectiveness of this approach is demonstrated in a set of numerical experiments which study the electron states on the cross section of a quantum wire structure based on III-V semiconductors at 4.2 and 77 K.

  5. Electronic and Thermal Properties of Graphene and Carbon Structures

    NASA Astrophysics Data System (ADS)

    Anthony, Gilmore; Khatun, Mahfuza

    2011-10-01

    We will present the general properties of carbon structures. The research involves the study of carbon structures: Graphene, Graphene nanoribbons (GNRs), and Carbon Nanotubes (CNTs). A review of electrical and thermal conduction phenomena of the structures will be discussed. Particularly carbon nanoribbons and CNTs have many interesting physical properties, and have the potential for device applications. Our research interests include the study of electronic structures, electrical and thermal transport properties of the carbon structures. Results are produced analytically as well as by simulation. The numerical simulations are conducted using various tools such as Visual Molecular Dynamics (VMD), Large Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS), NanoHub at Purdue University and the Beowulf Cluster at Ball State University.

  6. An arbitrary wavelength solver for global gyrokinetic simulations. Application to the study of fine radial structures on microturbulence due to non-adiabatic passing electron dynamics

    NASA Astrophysics Data System (ADS)

    Dominski, J.; McMillan, B. F.; Brunner, S.; Merlo, G.; Tran, T.-M.; Villard, L.

    2017-02-01

    The influence of the fine layers of the non-adiabatic passing electron response on electrostatic turbulent transport, previously studied systematically in flux tube geometry [Dominski et al., Phys. Plasmas 22, 062303 (2015)], is pursued in global geometry in conditions relevant for the TCV tokamak with a deuterium plasma (mi/me = 3672). The spectral organization of the passing electron turbulent flux and its dependence on the radial profile of the safety factor are revealed. A radially dependent toroidal spectral analysis of the turbulent fluxes led to the key result that the particle and heat diffusivities of passing-electrons are proportional to the local density of low-order mode rational surfaces. To permit this study of the short radial scales associated with the passing electron dynamics, a new field solver valid at an arbitrary wavelength is implemented in ORB5, for the gyrokinetic quasi-neutrality equation. A benchmark is conducted against the global version of the gyrokinetic code GENE, showing very good agreement.

  7. Instructional Approach to Molecular Electronic Structure Theory

    ERIC Educational Resources Information Center

    Dykstra, Clifford E.; Schaefer, Henry F.

    1977-01-01

    Describes a graduate quantum mechanics projects in which students write a computer program that performs ab initio calculations on the electronic structure of a simple molecule. Theoretical potential energy curves are produced. (MLH)

  8. Computational Chemistry Using Modern Electronic Structure Methods

    ERIC Educational Resources Information Center

    Bell, Stephen; Dines, Trevor J.; Chowdhry, Babur Z.; Withnall, Robert

    2007-01-01

    Various modern electronic structure methods are now days used to teach computational chemistry to undergraduate students. Such quantum calculations can now be easily used even for large size molecules.

  9. High resolution simulation of beam dynamics in electron linacs for x-ray free electron lasers

    NASA Astrophysics Data System (ADS)

    Qiang, J.; Ryne, R. D.; Venturini, M.; Zholents, A. A.; Pogorelov, I. V.

    2009-10-01

    In this paper we report on large-scale high resolution simulations of beam dynamics in electron linacs for the next-generation x-ray free electron lasers (FELs). We describe key features of a parallel macroparticle simulation code including three-dimensional (3D) space-charge effects, short-range structure wakefields, coherent synchrotron radiation (CSR) wakefields, and treatment of radio-frequency (rf) accelerating cavities using maps obtained from axial field profiles. We present a study of the microbunching instability causing severe electron beam fragmentation in the longitudinal phase space which is a critical issue for future FELs. Using parameters for a proposed FEL linac at Lawrence Berkeley National Laboratory (LBNL), we show that a large number of macroparticles (beyond 100 million) is generally needed to control the numerical macroparticle shot noise and avoid overestimating the microbunching instability. We explore the effect of the longitudinal grid on simulation results. We also study the effect of initial uncorrelated energy spread on the final uncorrelated energy spread of the beam for the FEL linac.

  10. Teaching Behavioral Modeling and Simulation Techniques for Power Electronics Courses

    ERIC Educational Resources Information Center

    Abramovitz, A.

    2011-01-01

    This paper suggests a pedagogical approach to teaching the subject of behavioral modeling of switch-mode power electronics systems through simulation by general-purpose electronic circuit simulators. The methodology is oriented toward electrical engineering (EE) students at the undergraduate level, enrolled in courses such as "Power…

  11. Controlling the Electronic Structure of Bilayer Graphene

    NASA Astrophysics Data System (ADS)

    Ohta, Taisuke; Bostwick, Aaron; Seyller, Thomas; Horn, Karsten; Rotenberg, Eli

    2006-08-01

    We describe the synthesis of bilayer graphene thin films deposited on insulating silicon carbide and report the characterization of their electronic band structure using angle-resolved photoemission. By selectively adjusting the carrier concentration in each layer, changes in the Coulomb potential led to control of the gap between valence and conduction bands. This control over the band structure suggests the potential application of bilayer graphene to switching functions in atomic-scale electronic devices.

  12. Computational complexity in electronic structure.

    PubMed

    Whitfield, James Daniel; Love, Peter John; Aspuru-Guzik, Alán

    2013-01-14

    In quantum chemistry, the price paid by all known efficient model chemistries is either the truncation of the Hilbert space or uncontrolled approximations. Theoretical computer science suggests that these restrictions are not mere shortcomings of the algorithm designers and programmers but could stem from the inherent difficulty of simulating quantum systems. Extensions of computer science and information processing exploiting quantum mechanics has led to new ways of understanding the ultimate limitations of computational power. Interestingly, this perspective helps us understand widely used model chemistries in a new light. In this article, the fundamentals of computational complexity will be reviewed and motivated from the vantage point of chemistry. Then recent results from the computational complexity literature regarding common model chemistries including Hartree-Fock and density functional theory are discussed.

  13. Structural and electronic properties of a tetrahedral amorphous carbon surface

    NASA Astrophysics Data System (ADS)

    Dong, Jianjun; Drabold, D. A.

    1997-03-01

    We present ab initio studies of a model of tetrahedral amorphous carbon (ta-C) surface. Our methodology is LDA (with Harris functional and local basis) molecular dynamics simulations. The surface is modeled by a 216 atom slab supercell. Several candidate slabs are constructed by starting with the DTW model (B.R. Djordjevic, M.F. Thorpe and F. Wooten, Phys. Rev. B 52) 5685 (1995) and applying various simulated heating/quenching cycles. We analyze the structural and electronic properties of the surface , with special attention forcused on the electronic signatures of surface structural defects. Preliminary results indicate that the surface layer significantly graphitizes, and many surface gap states are present in the electronic density of states.

  14. Electron-cloud measurements and simulations for the APS

    SciTech Connect

    Furman, M.A.; Pivi, M.; Harkay, K.C.; Rosenberg, R.A.

    2001-06-26

    We compare experimental results with simulations of the electron cloud effect induced by a positron beam at the APS synchrotron light source at ANL, where the electron cloud effect has been observed and measured with dedicated probes. We find good agreement between simulations and measurements for reasonable values of certain secondary electron yield (SEY) parameters, most of which were extracted from recent bench measurements at SLAC.

  15. A GPU Accelerated Simulation Program for Electron Cooling Process

    NASA Astrophysics Data System (ADS)

    Zhang, He; Huang, He; Li, Rui; Chen, Jie; Luo, Li-Shi

    2015-04-01

    Electron cooling is essential to achieve high luminosity in the medium energy electron ion collider (MIEC) project at Jefferson Lab. Bunched electron beam with energy above 50 MeV is used to cool coasting and/or bunched ion beams. Although the conventional electron cooling technique has been widely used, such an implementation in MEIC is still challenging. We are developing a simulation program for the electron cooling process to fulfill the need of the electron cooling system design for MEIC. The program simulates the evolution of the ion beam under the intrabeam scattering (IBS) effect and the electron cooling effect using Monte Carlo method. To accelerate the calculation, the program is developed on a GPU platform. We will present some preliminary simulation results. Work supported by the Department of Energy, Laboratory Directed Research and Development Funding, under Contract No. DE-AC05-06OR23177.

  16. Foil support structure for large electron guns

    SciTech Connect

    Brucker, J.P.; Rose, E.A.

    1993-08-01

    This paper describes a novel support structure for a vacuum diode used to pump a gaseous laser with an electron beam. Conventional support structures are designed to hold a foil flat and rigid. This new structure takes advantage of the significantly greater strength of metals in pure tension, utilizing curved shapes for both foil and support structure. The shape of the foil is comparable to the skin of a balloon, and the shape of the support structures is comparable to the cables of a suspension bridge. This design allows a significant reduction in foil thickness and support structure mass, resulting in a lower electron-beam loss between diode and laser gas. In addition, the foil is pre-formed in the support structure at pressures higher than operating pressure. Therefore, the foil is operated far from the yield point. Increased reliability is anticipated.

  17. Multimode Simulations of Free Electron Lasers

    DTIC Science & Technology

    2002-03-01

    the Novosibirsk racetrack microtron [50]. The three-stage FEL klystron oscillator consists of three identical undulators separated by two...mode radius 0 Lλ π= 2500= 1 1.9= W . The microtron provides an electron beam with current density and radius . The electron beam can be given an

  18. The Electron Transport Chain: An Interactive Simulation

    ERIC Educational Resources Information Center

    Romero, Chris; Choun, James

    2014-01-01

    This activity provides students an interactive demonstration of the electron transport chain and chemiosmosis during aerobic respiration. Students use simple, everyday objects as hydrogen ions and electrons and play the roles of the various proteins embedded in the inner mitochondrial membrane to show how this specific process in cellular…

  19. Effects of inverse degree on electronic structure and electron energy-loss spectrum in zinc ferrites

    NASA Astrophysics Data System (ADS)

    Sun, D.; Wang, M. X.; Zhang, Z. H.; Tao, H. L.; He, M.; Song, B.; Li, Q.

    2015-12-01

    First-principles calculations were performed to study the effects of inverse degree in zinc ferrite on electronic structure and properties. The electron energy-loss near-edge fine structure (ELNES) were simulated, and the splitting of peak and intensities of the oxygen K-edges can be used to identify the inversion of zinc ferrite. More Fe3+ transferring from the octahedral sites to the tetrahedral sites lead to the changing of the ligand shells surrounding the absorbing atom, accounting for the observed changing in ELNES. The standard criterion for determining the reversal extent of the cations in zinc ferrite by ELNES was given.

  20. Linear-scaling density functional simulations of the effect of crystallographic structure on the electronic and optical properties of fullerene solvates.

    PubMed

    Xue, Hong-Tao; Boschetto, Gabriele; Krompiec, Michal; Morse, Graham E; Tang, Fu-Ling; Skylaris, Chris-Kriton

    2017-02-15

    In this work, the crystal properties, HOMO and LUMO energies, band gaps, density of states, as well as the optical absorption spectra of fullerene C60 and its derivative phenyl-C61-butyric-acid-methyl-ester (PCBM) co-crystallised with various solvents such as benzene, biphenyl, cyclohexane, and chlorobenzene were investigated computationally using linear-scaling density functional theory with plane waves as implemented in the ONETEP program. Such solvates are useful materials as electron acceptors for organic photovoltaic (OPV) devices. We found that the fullerene parts contained in the solvates are unstable without solvents, and the interactions between fullerene and solvent molecules in C60 and PCBM solvates make a significant contribution to the cohesive energies of solvates, indicating that solvent molecules are essential to keep C60 and PCBM solvates stable. Both the band gap (Eg) and the HOMO and LUMO states of C60 and PCBM solvates are mainly determined by the fullerene parts contained in solvates. Chlorobenzene- and ortho-dichlorobenzene-solvated PCBM are the most promising electron-accepting materials among these solvates for increasing the driving force for charge separation in OPVs due to their relatively high LUMO energies. The UV-Vis absorption spectra of solvent-free C60 and PCBM crystals in the present work are similar to those of C60 and PCBM thin films shown in the literature. Changes in the absorption spectra of C60 solvates relative to the solvent-free C60 crystal are more significant than those of PCBM solvates due to the weaker effect of solvents on the π-stacking interactions between fullerene molecules in the latter solvates. The main absorptions for all C60 and PCBM crystals are located in the ultraviolet (UV) region.

  1. Image simulation for electron energy loss spectroscopy

    SciTech Connect

    Oxley, Mark P.; Pennycook, Stephen J.

    2007-10-22

    In this paper, aberration correction of the probe forming optics of the scanning transmission electron microscope has allowed the probe-forming aperture to be increased in size, resulting in probes of the order of 1 Å in diameter. The next generation of correctors promise even smaller probes. Improved spectrometer optics also offers the possibility of larger electron energy loss spectrometry detectors. The localization of images based on core-loss electron energy loss spectroscopy is examined as function of both probe-forming aperture and detector size. The effective ionization is nonlocal in nature, and two common local approximations are compared to full nonlocal calculations. Finally, the affect of the channelling of the electron probe within the sample is also discussed.

  2. Image simulation for electron energy loss spectroscopy

    DOE PAGES

    Oxley, Mark P.; Pennycook, Stephen J.

    2007-10-22

    In this paper, aberration correction of the probe forming optics of the scanning transmission electron microscope has allowed the probe-forming aperture to be increased in size, resulting in probes of the order of 1 Å in diameter. The next generation of correctors promise even smaller probes. Improved spectrometer optics also offers the possibility of larger electron energy loss spectrometry detectors. The localization of images based on core-loss electron energy loss spectroscopy is examined as function of both probe-forming aperture and detector size. The effective ionization is nonlocal in nature, and two common local approximations are compared to full nonlocal calculations.more » Finally, the affect of the channelling of the electron probe within the sample is also discussed.« less

  3. Gyrokinetic particle simulation of fast-electron driven beta-induced Aflvén eigenmode

    NASA Astrophysics Data System (ADS)

    Cheng, Junyi; Zhang, Wenlu; Lin, Zhihong; Holod, Ihor; Li, Ding; Chen, Yang; Cao, Jintao

    2016-05-01

    The fast-electron driven beta-induced Alfvén eigenmode (e-BAE) in toroidal plasmas is investigated for the first time using global gyrokinetic particle simulations, where the fast electron is described by the drift kinetic equation. The simulation shows that the e-BAE propagates in the fast electron diamagnetic direction and its polarization is close to an ideal MHD mode. The phase space structure shows that only the fast electron processional resonance is responsible for the e-BAE excitations while fast-ion driven BAE can be excited through all the channels, including transit, bounce, and processional resonance.

  4. Electronic device simulates respiration rate and depth

    NASA Technical Reports Server (NTRS)

    Thomas, J. A.

    1964-01-01

    An oscillator circuit and a thermistor, in close proximity to a light bulb, periodically alter the heat output of the bulb by varying the voltage across its filament. Use of this simulator permits checkout tests on pneumographs.

  5. Geant4-DNA simulation of electron slowing-down spectra in liquid water

    NASA Astrophysics Data System (ADS)

    Incerti, S.; Kyriakou, I.; Tran, H. N.

    2017-04-01

    This work presents the simulation of monoenergetic electron slowing-down spectra in liquid water by the Geant4-DNA extension of the Geant4 Monte Carlo toolkit (release 10.2p01). These spectra are simulated for several incident energies using the most recent Geant4-DNA physics models, and they are compared to literature data. The influence of Auger electron production is discussed. For the first time, a dedicated Geant4-DNA example allowing such simulations is described and is provided to Geant4 users, allowing further verification of Geant4-DNA track structure simulation capabilities.

  6. Hydrated Electron Transfer to Nucleobases in Aqueous Solutions Revealed by Ab Initio Molecular Dynamics Simulations.

    PubMed

    Zhao, Jing; Wang, Mei; Fu, Aiyun; Yang, Hongfang; Bu, Yuxiang

    2015-08-03

    We present an ab initio molecular dynamics (AIMD) simulation study into the transfer dynamics of an excess electron from its cavity-shaped hydrated electron state to a hydrated nucleobase (NB)-bound state. In contrast to the traditional view that electron localization at NBs (G/A/C/T), which is the first step for electron-induced DNA damage, is related only to dry or prehydrated electrons, and a fully hydrated electron no longer transfers to NBs, our AIMD simulations indicate that a fully hydrated electron can still transfer to NBs. We monitored the transfer dynamics of fully hydrated electrons towards hydrated NBs in aqueous solutions by using AIMD simulations and found that due to solution-structure fluctuation and attraction of NBs, a fully hydrated electron can transfer to a NB gradually over time. Concurrently, the hydrated electron cavity gradually reorganizes, distorts, and even breaks. The transfer could be completed in about 120-200 fs in four aqueous NB solutions, depending on the electron-binding ability of hydrated NBs and the structural fluctuation of the solution. The transferring electron resides in the π*-type lowest unoccupied molecular orbital of the NB, which leads to a hydrated NB anion. Clearly, the observed transfer of hydrated electrons can be attributed to the strong electron-binding ability of hydrated NBs over the hydrated electron cavity, which is the driving force, and the transfer dynamics is structure-fluctuation controlled. This work provides new insights into the evolution dynamics of hydrated electrons and provides some helpful information for understanding the DNA-damage mechanism in solution.

  7. Electronic structure and polarizability of metallic nanoshells

    NASA Astrophysics Data System (ADS)

    Prodan, E.; Nordlander, P.

    2002-01-01

    An efficient method for the calculation of the electronic structure of metallic nanoshells is developed. The method is applied to a large nanoshell (of 10 nm in diameter) containing more than 2.5×10 4 conduction electrons. The calculations show that the density of states of the nanoshell is relatively bulk-like. The frequency dependent polarizability is calculated and shown to display strong confinement effects and features similar to what is predicted by semi-classical electrodynamic theory.

  8. Effective in silico prediction of new oxazolidinone antibiotics: force field simulations of the antibiotic–ribosome complex supervised by experiment and electronic structure methods

    PubMed Central

    2016-01-01

    Summary We propose several new and promising antibacterial agents for the treatment of serious Gram-positive infections. Our predictions rely on force field simulations, supervised by first principle calculations and available experimental data. Different force fields were tested in order to reproduce linezolid's conformational space in terms of a) the isolated and b) the ribosomal bound state. In a first step, an all-atom model of the bacterial ribosome consisting of nearly 1600 atoms was constructed and evaluated. The conformational space of 30 different ribosomal/oxazolidinone complexes was scanned by stochastic methods, followed by an evaluation of their enthalpic penalties or rewards and the mechanical strengths of the relevant hydrogen bonds (relaxed force constants; compliance constants). The protocol was able to reproduce the experimentally known enantioselectivity favoring the S-enantiomer. In a second step, the experimentally known MIC values of eight linezolid analogues were used in order to crosscheck the robustness of our model. In a final step, this benchmarking led to the prediction of several new and promising lead compounds. Synthesis and biological evaluation of the new compounds are on the way. PMID:27340438

  9. Structural and electronic properties for atomic clusters

    NASA Astrophysics Data System (ADS)

    Sun, Yan

    We have studied the structural and electronic properties for different groups of atomic clusters by doing a global search on the potential energy surface using the Taboo Search in Descriptors Space (TSDS) method and calculating the energies with Kohn-Sham Density Functional Theory (KS-DFT). Our goal was to find the structural and electronic principles for predicting the structure and stability of clusters. For Ben (n = 3--20), we have found that the evolution of geometric and electronic properties with size reflects a change in the nature of the bonding from van der Waals to metallic and then bulk-like. The cluster sizes with extra stability agree well with the predictions of the jellium model. In the 4d series of transition metal (TM) clusters, as the d-type bonding becomes more important, the preferred geometric structure changes from icosahedral (Y, Zr), to distorted compact structures (Nb, Mo), and FCC or simple cubic crystal fragments (Tc, Ru, Rh) due to the localized nature of the d-type orbital. Analysis of relative isomer energies and their electronic density of states suggest that these clusters tend to follow a maximum hardness principle (MHP). For A4B12 clusters (A is divalent, B is monovalent), we found unusually large (on average 1.95 eV) HOMO-LUMO gap values. This shows the extra stability at an electronic closed shell (20 electrons) predicted by the jellium model. The importance of symmetry, closed electronic and ionic shells in stability is shown by the relative stability of homotops of Mg4Ag12 which also provides support for the hypothesis that clusters that satisfy more than one stability criterion ("double magic") should be particularly stable.

  10. High Resolution Simulation of Beam Dynamics in Electron Linacs for Free Electron Lasers

    SciTech Connect

    Ryne, R.D.; Venturini, M.; Zholents, A.A.; Qiang, J.

    2009-01-05

    In this paper we report on large scale multi-physics simulation of beam dynamics in electron linacs for next generation free electron lasers (FELs). We describe key features of a parallel macroparticle simulation code including three-dimensional (3D) space-charge effects, short-range structure wake fields, longitudinal coherent synchrotron radiation (CSR) wake fields, and treatment of radiofrequency (RF) accelerating cavities using maps obtained from axial field profiles. A macroparticle up-sampling scheme is described that reduces the shot noise from an initial distribution with a smaller number of macroparticles while maintaining the global properties of the original distribution. We present a study of the microbunching instability which is a critical issue for future FELs due to its impact on beam quality at the end of the linac. Using parameters of a planned FEL linac at Lawrence Berkeley National Laboratory (LBNL), we show that a large number of macroparticles (beyond 100 million) is needed to control numerical shot noise that drives the microbunching instability. We also explore the effect of the longitudinal grid on simulation results. We show that acceptable results are obtained with around 2048 longitudinal grid points, and we discuss this in view of the spectral growth rate predicted from linear theory. As an application, we present results from simulations using one billion macroparticles of the FEL linac under design at LBNL. We show that the final uncorrelated energy spread of the beam depends not only on the initial uncorrelated energy spread but also depends strongly on the shape of the initial current profile. By using a parabolic initial current profile, 5 keV initial uncorrelated energy spread at 40 MeV injection energy, and improved linac design, those simulations demonstrate that a reasonable beam quality can be achieved at the end of the linac, with the final distribution having about 100 keV energy spread, 2.4 GeV energy, and 1.2 kA peak

  11. Defect Induced Electronic Structure of Uranofullerene

    PubMed Central

    Dai, Xing; Cheng, Cheng; Zhang, Wei; Xin, Minsi; Huai, Ping; Zhang, Ruiqin; Wang, Zhigang

    2013-01-01

    The interaction between the inner atoms/cluster and the outer fullerene cage is the source of various novel properties of endohedral metallofullerenes. Herein, we introduce an adatom-type spin polarization defect on the surface of a typical endohedral stable U2@C60 to predict the associated structure and electronic properties of U2@C61 based on the density functional theory method. We found that defect induces obvious changes in the electronic structure of this metallofullerene. More interestingly, the ground state of U2@C61 is nonet spin in contrast to the septet of U2@C60. Electronic structure analysis shows that the inner U atoms and the C ad-atom on the surface of the cage contribute together to this spin state, which is brought about by a ferromagnetic coupling between the spin of the unpaired electrons of the U atoms and the C ad-atom. This discovery may provide a possible approach to adapt the electronic structure properties of endohedral metallofullerenes. PMID:23439318

  12. PGOPHER: A program for simulating rotational, vibrational and electronic spectra

    NASA Astrophysics Data System (ADS)

    Western, Colin M.

    2017-01-01

    The PGOPHER program is a general purpose program for simulating and fitting molecular spectra, particularly the rotational structure. The current version can handle linear molecules, symmetric tops and asymmetric tops and many possible transitions, both allowed and forbidden, including multiphoton and Raman spectra in addition to the common electric dipole absorptions. Many different interactions can be included in the calculation, including those arising from electron and nuclear spin, and external electric and magnetic fields. Multiple states and interactions between them can also be accounted for, limited only by available memory. Fitting of experimental data can be to line positions (in many common formats), intensities or band contours and the parameters determined can be level populations as well as rotational constants. PGOPHER is provided with a powerful and flexible graphical user interface to simplify many of the tasks required in simulating, understanding and fitting molecular spectra, including Fortrat diagrams and energy level plots in addition to overlaying experimental and simulated spectra. The program is open source, and can be compiled with open source tools. This paper provides a formal description of the operation of version 9.1.

  13. Simulations of the runaway electron distributions

    SciTech Connect

    Wiley, J.C.; Choi, D.; Horton, W.

    1980-11-01

    The time evolution of the electron distribution function is followed from an initial Maxwellian to the quasi-steady-state runaway distribution as a function of E/E/sub D/ and Z using a new two-dimensional Fokker--Planck code. The electron distributions are used to determine the runaway production rate, the current density along with the fraction of Ohmic power directed to the runaways, and the perpendicular and parallel temperatures of the high energy distributions. A simple parameterization of the high energy distribution is given and used to investigate the high frequency runaway instability for the infinite uniform plasma.

  14. Simulations of the runaway electron distributions

    SciTech Connect

    Wiley, J. C.; Choi, D. I.; Horton, W.

    1980-03-01

    The time evolution of the electron distribution function is followed from an initial Maxwellian to the quasi-steady state runaway distribution as a function of E/E/sub D/ and Z using a new two-dimensional Fokker-Planck code. The electron distributions are used to determine the runaway production rate, the current density along with the fraction of Ohmic power directed to the runaways, and the perpendicular and parallel temperatures of the high energy distributions. A simple parameterization of the high energy distribution is given and used to investigate the high frequency runaway instability for the infinite uniform plasma.

  15. Structured building model reduction toward parallel simulation

    SciTech Connect

    Dobbs, Justin R.; Hencey, Brondon M.

    2013-08-26

    Building energy model reduction exchanges accuracy for improved simulation speed by reducing the number of dynamical equations. Parallel computing aims to improve simulation times without loss of accuracy but is poorly utilized by contemporary simulators and is inherently limited by inter-processor communication. This paper bridges these disparate techniques to implement efficient parallel building thermal simulation. We begin with a survey of three structured reduction approaches that compares their performance to a leading unstructured method. We then use structured model reduction to find thermal clusters in the building energy model and allocate processing resources. Experimental results demonstrate faster simulation and low error without any interprocessor communication.

  16. Boron Fullerenes: An Electronic Structure Study

    NASA Astrophysics Data System (ADS)

    Sadrzadeh, Arta; Pupysheva, Olga; Boustani, Ihsan; Yakobson, Boris

    2008-03-01

    Using ab initio calculations, we study electronic structure and frequency modes of B80, a member of boron fullerene family made from boron isomorphs of carbon fullerenes with additional atoms in the centers of hexagons. We also investigate geometrical and electronic structural properties of double-rings with various diameters, which are important as building blocks of boron nanotubes, and as the most stable clusters among the studied isomers with no more than 36 atoms. Double-rings also appear as building blocks of B80. Furthermore, we investigate the possibility of further stabilizing some of fullerenes by depleting them.

  17. The Electronic Structure of Heavy Element Complexes

    SciTech Connect

    Bursten, Bruce E.

    2000-07-25

    The area of study is the bonding in heavy element complexes, and the application of more sophisticated electronic structure theories. Progress is recounted in several areas: (a) technological advances and current methodologies - Relativistic effects are extremely important in gaining an understanding of the electronic structure of compounds of the actinides, transactinides, and other heavy elements. Therefore, a major part of the continual benchmarking was the proper inclusion of the appropriate relativistic effects for the properties under study. (b) specific applications - These include organoactinide sandwich complexes, CO activation by actinide atoms, and theoretical studies of molecules of the transactinide elements. Finally, specific directions in proposed research are described.

  18. Digital simulation of the SIR-C sensor electronics

    NASA Technical Reports Server (NTRS)

    Klein, Jeffrey D.; Curlander, John C.

    1987-01-01

    In this paper software for simulation of the response of the SIR-C sensor to a point target is described. Synthetic SAR data is generated by passing successive chirps through a simulation of the transmitter electronics, propagation path and receiver electronics. This result is then processed with a digital correlator to yield the point target response of the system. This allows an accurate assessment of the effect of the radar design on the final image product.

  19. Electron-cloud simulation results for the PSR and SNS

    SciTech Connect

    Pivi, M.; Furman, M.A.

    2002-07-08

    We present recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and updated results for the Proton Storage Ring (PSR) at Los Alamos. In particular, a complete refined model for the secondary emission process including the so called true secondary, rediffused and backscattered electrons has been included in the simulation code.

  20. Electron Energization in Reconnection Outflows with Kinetic Riemann Simulations

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Drake, J. F.; Swisdak, M.

    2015-12-01

    How electrons are heated during magnetic reconnection in the corona has been a basic puzzle for a long time. Here we carry out PIC Riemann simulations to explore electron energization including its dependence on parameters. One-dimensional Riemann simulations, with its simple magnetic geometry, facilitate the study of the reconnection outflow far downstream of x-line in much more detail than is possible with conventional reconnection simulations. We examine the behavior of the electron temperature in this configuration. We find that the electron temperature in the exhaust increases and approaches a constant. Since the heating is independent of the x-line in the Riemann model, these results suggest that electron heating in the exhausts can extend to macroscopic scales in the corona. In runs with guide field, such heating only weakly depends on the proton-to-electron mass ratio used in the simulation. The scaling of the electron temperature increment with the available magnetic energy is discussed and comparisons with conventional reconnection simulations are made.

  1. Quantum Monte Carlo finite temperature electronic structure of quantum dots

    NASA Astrophysics Data System (ADS)

    Leino, Markku; Rantala, Tapio T.

    2002-08-01

    Quantum Monte Carlo methods allow a straightforward procedure for evaluation of electronic structures with a proper treatment of electronic correlations. This can be done even at finite temperatures [1]. We test the Path Integral Monte Carlo (PIMC) simulation method [2] for one and two electrons in one and three dimensional harmonic oscillator potentials and apply it in evaluation of finite temperature effects of single and coupled quantum dots. Our simulations show the correct finite temperature excited state populations including degeneracy in cases of one and three dimensional harmonic oscillators. The simulated one and two electron distributions of a single and coupled quantum dots are compared to those from experiments and other theoretical (0 K) methods [3]. Distributions are shown to agree and the finite temperature effects are discussed. Computational capacity is found to become the limiting factor in simulations with increasing accuracy. Other essential aspects of PIMC and its capability in this type of calculations are also discussed. [1] R.P. Feynman: Statistical Mechanics, Addison Wesley, 1972. [2] D.M. Ceperley, Rev.Mod.Phys. 67, 279 (1995). [3] M. Pi, A. Emperador and M. Barranco, Phys.Rev.B 63, 115316 (2001).

  2. Simulation of runaway electrons in tokamak

    NASA Astrophysics Data System (ADS)

    Guo, Zehua; Tang, Xianzhu; McDevitt, Chris

    2015-11-01

    Runaway electrons with relativisitc energy (>Mev) are generated in tokamaks when the acceleration by parallel electric field exceeds the drag due to Coulomb collisions with the bulk plasma. Carrying about 70% of the ITER thermal current (15MA), they can possibly cause severe damage to tokamak facing components. Here we report the development of a solver for computing the evolution of runaway electron distribution in tokamak geometries. Essential effects from Coulomb collisions, radiation losses, toroidal effects and the radial transport are included on the same footings. Numerical techniques (implicit-explicit time-stepping, KT/NT central schemes) to overcome the difficulties arising from the wide spread of time scales in runaway electron dynamics and the hyperbolic nature of the relativistic Fokker-Planck equation will be discussed. We will use the solver to study two important physics: 1) the presence of stable point in the phase space and its relation to the electric field threshold; 2) the radial transport of runaways in tokamak geometry and its effects on the distribution function. Work supported by DOE via LANL-LDRD.

  3. Atomic and electronic structure of exfoliated black phosphorus

    SciTech Connect

    Wu, Ryan J.; Topsakal, Mehmet; Jeong, Jong Seok; Wentzcovitch, Renata M.; Mkhoyan, K. Andre; Low, Tony; Robbins, Matthew C.; Haratipour, Nazila; Koester, Steven J.

    2015-11-15

    Black phosphorus, a layered two-dimensional crystal with tunable electronic properties and high hole mobility, is quickly emerging as a promising candidate for future electronic and photonic devices. Although theoretical studies using ab initio calculations have tried to predict its atomic and electronic structure, uncertainty in its fundamental properties due to a lack of clear experimental evidence continues to stymie our full understanding and application of this novel material. In this work, aberration-corrected scanning transmission electron microscopy and ab initio calculations are used to study the crystal structure of few-layer black phosphorus. Directly interpretable annular dark-field images provide a three-dimensional atomic-resolution view of this layered material in which its stacking order and all three lattice parameters can be unambiguously identified. In addition, electron energy-loss spectroscopy (EELS) is used to measure the conduction band density of states of black phosphorus, which agrees well with the results of density functional theory calculations performed for the experimentally determined crystal. Furthermore, experimental EELS measurements of interband transitions and surface plasmon excitations are also consistent with simulated results. Finally, the effects of oxidation on both the atomic and electronic structure of black phosphorus are analyzed to explain observed device degradation. The transformation of black phosphorus into amorphous PO{sub 3} or H{sub 3}PO{sub 3} during oxidation may ultimately be responsible for the degradation of devices exposed to atmosphere over time.

  4. NASCAP simulation of laboratory charging tests using multiple electron guns

    NASA Technical Reports Server (NTRS)

    Mandell, M. J.; Katz, I.; Parks, D. E.

    1981-01-01

    NASCAP calculations have been performed simulating exposure of a spacecraft-like model to multiple electron guns. The results agree well with experiment. It is found that magnetic field effects are fairly small, but substantial differential charging can result from electron gun placement. Conditions for surface flashover are readily achieved.

  5. Simulating Electron Clouds in Heavy-Ion Accelerators

    SciTech Connect

    Cohen, R.H.; Friedman, A.; Kireeff Covo, M.; Lund, S.M.; Molvik,A.W.; Bieniosek, F.M.; Seidl, P.A.; Vay, J-L.; Stoltz, P.; Veitzer, S.

    2005-04-07

    Contaminating clouds of electrons are a concern for most accelerators of positive-charged particles, but there are some unique aspects of heavy-ion accelerators for fusion and high-energy density physics which make modeling such clouds especially challenging. In particular, self-consistent electron and ion simulation is required, including a particle advance scheme which can follow electrons in regions where electrons are strongly-, weakly-, and un-magnetized. They describe their approach to such self-consistency, and in particular a scheme for interpolating between full-orbit (Boris) and drift-kinetic particle pushes that enables electron time steps long compared to the typical gyro period in the magnets. They present tests and applications: simulation of electron clouds produced by three different kinds of sources indicates the sensitivity of the cloud shape to the nature of the source; first-of-a-kind self-consistent simulation of electron-cloud experiments on the High-Current Experiment (HCX) at Lawrence Berkeley National Laboratory, in which the machine can be flooded with electrons released by impact of the ion beam and an end plate, demonstrate the ability to reproduce key features of the ion-beam phase space; and simulation of a two-stream instability of thin beams in a magnetic field demonstrates the ability of the large-timestep mover to accurately calculate the instability.

  6. Numerical simulations of runaway electron generation in pressurized gases

    SciTech Connect

    Levko, D.; Yatom, S.; Vekselman, V.; Gleizer, J. Z.; Gurovich, V. Tz.; Krasik, Ya. E.

    2012-01-01

    The results of a numerical simulation of the generation of runaway electrons in pressurized nitrogen and helium gases are presented. It was shown that runaway electrons generation occurs in two stages. In the first stage, runaway electrons are composed of the electrons emitted by the cathode and produced in gas ionization in the vicinity of the cathode. This stage is terminated with the formation of the virtual cathode, which becomes the primary source of runaway electrons in the second stage. Also, it was shown that runaway electrons current is limited by both the shielding of the field emission by the space charge of the emitted electrons and the formation of a virtual cathode. In addition, the influence of the initial conditions, such as voltage rise time and amplitude, gas pressure, and the type of gas, on the processes that accompany runaway electrons generation is presented.

  7. Structure refinement from precession electron diffraction data.

    PubMed

    Palatinus, Lukáš; Jacob, Damien; Cuvillier, Priscille; Klementová, Mariana; Sinkler, Wharton; Marks, Laurence D

    2013-03-01

    Electron diffraction is a unique tool for analysing the crystal structures of very small crystals. In particular, precession electron diffraction has been shown to be a useful method for ab initio structure solution. In this work it is demonstrated that precession electron diffraction data can also be successfully used for structure refinement, if the dynamical theory of diffraction is used for the calculation of diffracted intensities. The method is demonstrated on data from three materials - silicon, orthopyroxene (Mg,Fe)(2)Si(2)O(6) and gallium-indium tin oxide (Ga,In)(4)Sn(2)O(10). In particular, it is shown that atomic occupancies of mixed crystallographic sites can be refined to an accuracy approaching X-ray or neutron diffraction methods. In comparison with conventional electron diffraction data, the refinement against precession diffraction data yields significantly lower figures of merit, higher accuracy of refined parameters, much broader radii of convergence, especially for the thickness and orientation of the sample, and significantly reduced correlations between the structure parameters. The full dynamical refinement is compared with refinement using kinematical and two-beam approximations, and is shown to be superior to the latter two.

  8. Multi-million atom electronic structure calculations for quantum dots

    NASA Astrophysics Data System (ADS)

    Usman, Muhammad

    Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In the past decade or so, these nanostructures have attracted significant experimental and theoretical attention in the field of nanoscience. The new and tunable optical and electrical properties of these artificial atoms have been proposed in a variety of different fields, for example in communication and computing systems, medical and quantum computing applications. Predictive and quantitative modeling and simulation of these structures can help to narrow down the vast design space to a range that is experimentally affordable and move this part of nanoscience to nano-Technology. Modeling of such quantum dots pose a formidable challenge to theoretical physicists because: (1) Strain originating from the lattice mismatch of the materials penetrates deep inside the buffer surrounding the quantum dots and require large scale (multi-million atom) simulations to correctly capture its effect on the electronic structure, (2) The interface roughness, the alloy randomness, and the atomistic granularity require the calculation of electronic structure at the atomistic scale. Most of the current or past theoretical calculations are based on continuum approach such as effective mass approximation or k.p modeling capturing either no or one of the above mentioned effects, thus missing some of the essential physics. The Objectives of this thesis are: (1) to model and simulate the experimental quantum dot topologies at the atomistic scale; (2) to theoretically explore the essential physics i.e. long range strain, linear and quadratic piezoelectricity, interband optical transition strengths, quantum confined

  9. Electronic structure of Mn and Fe oxides

    NASA Astrophysics Data System (ADS)

    Harrison, Walter

    2008-03-01

    We present a clear, simple tight-binding representation of the electronic structure and cohesive energy (energy of atomization) of MnO, Mn2O3, and MnO2, in which the formal charge states Mn^2+, Mn^3+, and Mn^4+, respectively, occur. It is based upon localized cluster orbitals for each Mn and its six oxygen neighbors. This approach is fundamentally different from local-density theory (or LDA+U), and perhaps diametrically opposite to Dynamical Mean Field Theory. Electronic states were calculated self-consistently using existing parameters [1], but it is found that the charge density is quite insensitive to charge state, so that the starting parameters are adequate. The cohesive energy per Mn is dominated by the transfer of two s electrons to oxygen p states, the same for all three compounds. The differing transfer of majority d electrons to oxygen p states, and the coupling between them, accounts for the observed variation in cohesion in the series. The same description applies to the perovskites, such as LaxSr1-xMnO3, and can be used for FeO, Fe2O3 (and FeO2), Because the formulation is local, it is equally applicable to impurities, defects and surfaces. [1] Walter A. Harrison, Elementary Electronic Structure, World Scientific (Singapore, 1999), revised edition (2004).

  10. Computational study on structural modification of single-walled carbon nanotubes by electron irradiation

    SciTech Connect

    Yasuda, Masaaki; Mimura, Ryosuke; Kawata, Hiroaki; Hirai, Yoshihiko

    2011-03-01

    Molecular dynamics simulation is carried out to investigate structural modifications of single-walled carbon nanotubes by electron irradiation. Electron irradiation effects are introduced by the Monte Carlo method using an elastic collision cross section. We demonstrate the applicability of the method to the analysis of structural modifications with electron beam such as cutting, shrinking, and bending. The behavior of the carbon atoms in the nanotube during the structural modification is revealed. The simulation results also show the variation of the mechanical properties of carbon nanotubes by electron irradiation.

  11. Local atomic order, electronic structure and electron transport properties of Cu-Zr metallic glasses

    NASA Astrophysics Data System (ADS)

    Antonowicz, J.; Pietnoczka, A.; Pekała, K.; Latuch, J.; Evangelakis, G. A.

    2014-05-01

    We studied atomic and electronic structures of binary Cu-Zr metallic glasses (MGs) using combined experimental and computational methods including X-ray absorption fine structure spectroscopy, electrical resistivity, thermoelectric power (TEP) measurements, molecular dynamics (MD) simulations, and ab-initio calculations. The results of MD simulations and extended X-ray absorption fine structure analysis indicate that atomic order of Cu-Zr MGs and can be described in terms of interpenetrating icosahedral-like clusters involving five-fold symmetry. MD configurations were used as an input for calculations of theoretical electronic density of states (DOS) functions which exhibits good agreement with the experimental X-ray absorption near-edge spectra. We found no indication of minimum of DOS at Fermi energy predicted by Mott's nearly free electron (NFE) model for glass-forming alloys. The theoretical DOS was subsequently used to test Mott's model describing the temperature variation of electrical resistivity and thermoelectric power of transition metal-based MGs. We demonstrate that the measured temperature variations of electrical resistivity and TEP remain in a contradiction with this model. On the other hand, the experimental temperature dependence of electrical resistivity can be explained by incipient localization of conduction electrons. It is shown that weak localization model works up to relatively high temperatures when localization is destroyed by phonons. Our results indicate that electron transport properties of Cu-Zr MGs are dominated by localization effects rather than by electronic structure. We suggest that NFE model fails to explain a relatively high glass-forming ability of binary Cu-Zr alloys.

  12. Local atomic order, electronic structure and electron transport properties of Cu-Zr metallic glasses

    SciTech Connect

    Antonowicz, J. Pietnoczka, A.; Pękała, K.; Latuch, J.; Evangelakis, G. A.

    2014-05-28

    We studied atomic and electronic structures of binary Cu-Zr metallic glasses (MGs) using combined experimental and computational methods including X-ray absorption fine structure spectroscopy, electrical resistivity, thermoelectric power (TEP) measurements, molecular dynamics (MD) simulations, and ab-initio calculations. The results of MD simulations and extended X-ray absorption fine structure analysis indicate that atomic order of Cu-Zr MGs and can be described in terms of interpenetrating icosahedral-like clusters involving five-fold symmetry. MD configurations were used as an input for calculations of theoretical electronic density of states (DOS) functions which exhibits good agreement with the experimental X-ray absorption near-edge spectra. We found no indication of minimum of DOS at Fermi energy predicted by Mott's nearly free electron (NFE) model for glass-forming alloys. The theoretical DOS was subsequently used to test Mott's model describing the temperature variation of electrical resistivity and thermoelectric power of transition metal-based MGs. We demonstrate that the measured temperature variations of electrical resistivity and TEP remain in a contradiction with this model. On the other hand, the experimental temperature dependence of electrical resistivity can be explained by incipient localization of conduction electrons. It is shown that weak localization model works up to relatively high temperatures when localization is destroyed by phonons. Our results indicate that electron transport properties of Cu-Zr MGs are dominated by localization effects rather than by electronic structure. We suggest that NFE model fails to explain a relatively high glass-forming ability of binary Cu-Zr alloys.

  13. Electronic structure engineering of various structural phases of phosphorene.

    PubMed

    Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Tankeshwar, K

    2016-07-21

    We report the tailoring of the electronic structures of various structural phases of phosphorene (α-P, β-P, γ-P and δ-P) based homo- and hetero-bilayers through in-plane mechanical strains, vertical pressure and transverse electric field by employing density functional theory. In-plane biaxial strains have considerably modified the electronic bandgap of both homo- and hetero-bilayers while vertical pressure induces metallization in the considered structures. The γ-P homo-bilayer structure showed the highest ultimate tensile strength (UTS ∼ 6.21 GPa) upon in-plane stretching. Upon application of a transverse electric field, the variation in the bandgap of hetero-bilayers was found to be strongly dependent on the polarity of the applied field which is attributed to the counterbalance between the external electric field and the internal field induced by different structural phases and heterogeneity in the arrangements of atoms of each surface of the hetero-bilayer system. Our results demonstrate that the electronic structures of the considered hetero- and homo-bilayers of phosphorene could be modified by biaxial strain, pressure and electric field to achieve the desired properties for future nano-electronic devices.

  14. [Structured electronic consultation letter for shoulder disorders].

    PubMed

    Paloneva, Juha; Oikari, Marjo; Ylinen, Jari; Ingalsuo, Minna; Ilkka, Kunnamo; Ilkka, Kiviranta

    2012-01-01

    Referral to a specialist has a significant influence on management of the patient and costs associated with the treatments. However, development and research of the process by which patients are referred has been almost neglected. Expectations considering the purpose, contents, and timing of the referral of the consulting physician and the consultant do not always meet. A structured, electronic consultation letter was developed to respond this need. Functionality and interactivity are the key elements of the referral, including (1) an electronic referral letter to a specialist, (2) interactive education in clinical examination and management of shoulder disorders, and (3) an instrument of clinical examination and documentation of shoulder disorders.

  15. Development of the electron cooling simulation program for JLEIC

    SciTech Connect

    Zhang, He; Chen, Jie; Li, Rui; Zhang, Yuhong; Huang, He; Luo, Li-Shi

    2016-05-01

    In the JLab Electron Ion Collider (JLEIC) project the traditional electron cooling technique is used to reduce the ion beam emittance at the booster ring, and to compensate the intrabeam scattering effect and maintain the ion beam emittance during collision at the collider ring. A new electron cooling process simulation program has been developed to fulfill the requirements of the JLEIC electron cooler design. The new program allows the users to calculate the electron cooling rate and simulate the cooling process with either DC or bunched electron beam to cool either coasting or bunched ion beam. It has been benchmarked with BETACOOL in aspect of accuracy and efficiency. In typical electron cooling process of JLEIC, the two programs agree very well and we have seen a significant improvement of computational speed using the new one. Being adaptive to the modern multicore hardware makes it possible to further enhance the efficiency for computationally intensive problems. The new program is being actively used in the electron cooling study and cooler design for JLEIC. We will present our models and some simulation results in this paper.

  16. The electronic structure of nonpolyhex carbon nanotubes.

    PubMed

    László, István

    2004-01-01

    Generalizing the folding method to any periodic two-dimensional planar carbon structures we have calculated the corresponding electronic structures in the framework of the one orbital one site tight-binding (Bloch-Hückel) method by solving the eigenvalue problems in a numerical way. We discussed the metallic or the nonmetallic behavior of the nanotubes by applying the folding vectors of parameters (m, n). We extended the topological coordinate method to two-dimensional periodic planar structures as well. Nearly regular hexagonal, pentagonal, and heptagonal polygons were obtained. The curvatures of the final relaxed structures can be read from the sizes of the polygons. Thus relying only on the topological information we could describe the shape of the tubular structures and their conductivity behaviors.

  17. Probing Structural and Electronic Dynamics with Ultrafast Electron Microscopy

    SciTech Connect

    Plemmons, DA; Suri, PK; Flannigan, DJ

    2015-05-12

    In this Perspective, we provide an overview,of the field of ultrafast electron microscopy (UEM). We begin by briefly discussing the emergence of methods for probing ultrafast structural dynamics and the information that can be obtained. Distinctions are drawn between the two main types a probes for femtosecond (fs) dynamics fast electrons and X-ray photons and emphasis is placed on hour the nature of charged particles is exploited in ultrafast electron-based' experiments:. Following this, we describe the versatility enabled by the ease with which electron trajectories and velocities can be manipulated with transmission electron microscopy (TEM): hardware configurations, and we emphasize how this is translated to the ability to measure scattering intensities in real, reciprocal, and energy space from presurveyed and selected rianoscale volumes. Owing to decades of ongoing research and development into TEM instrumentation combined with advances in specimen holder technology, comprehensive experiments can be conducted on a wide range of materials in various phases via in situ methods. Next, we describe the basic operating concepts, of UEM, and we emphasize that its development has led to extension of several of the formidable capabilities of TEM into the fs domain, dins increasing the accessible temporal parameter spade by several orders of magnitude. We then divide UEM studies into those conducted in real (imaging), reciprocal (diffraction), and energy (spectroscopy) spate. We begin each of these sections by providing a brief description of the basic operating principles and the types of information that can be gathered followed by descriptions of how these approaches are applied in UM, the type of specimen parameter space that can be probed, and an example of the types of dynamics that can be resolved. We conclude with an Outlook section, wherein we share our perspective on some future directions of the field pertaining to continued instrument development and

  18. Molecular Dynamics Simulations of Shocks Including Electronic Heat Conduction and Electron-Phonon Coupling

    NASA Astrophysics Data System (ADS)

    Ivanov, Dmitriy S.; Zhigilei, Leonid V.; Bringa, Eduardo M.; De Koning, Maurice; Remington, Bruce A.; Caturla, Maria Jose; Pollaine, Stephen M.

    2004-07-01

    Shocks are often simulated using the classical molecular dynamics (MD) method in which the electrons are not included explicitly and the interatomic interaction is described by an effective potential. As a result, the fast electronic heat conduction in metals and the coupling between the lattice vibrations and the electronic degrees of freedom can not be represented. Under conditions of steep temperature gradients that can form near the shock front, however, the electronic heat conduction can play an important part in redistribution of the thermal energy in the shocked target. We present the first atomistic simulation of a shock propagation including the electronic heat conduction and electron-phonon coupling. The computational model is based on the two-temperature model (TTM) that describes the time evolution of the lattice and electron temperatures by two coupled non-linear differential equations. In the combined TTM-MD method, MD substitutes the TTM equation for the lattice temperature. Simulations are performed with both MD and TTM-MD models for an EAM Al target shocked at 300 kbar. The target includes a tilt grain boundary, which provides a region where shock heating is more pronounced and, therefore, the effect of the electronic heat conduction is expected to be more important. We find that the differences between the predictions of the MD and TTM-MD simulations are significantly smaller as compared to the hydrodynamics calculations performed at similar conditions with and without electronic heat conduction.

  19. Electron antineutrino detection from simulated supernovae

    NASA Astrophysics Data System (ADS)

    Luoma, Steffon Jon

    Supernova 1987A demonstrated that neutrinos from a nearby supernova could be detected terrestrially. The partition of events between the neutrino flavours generated by stellar collapse can provide details about supernova dynamics and by using Monte Carlo simulations we can prepare for the analysis of data from the next such supernova. Through its sensitivity to the charged current, neutral current and elastic scattering interactions in both the heavy and light waters, the Sudbury Neutrino Observatory (SNO) is able to measure this partition. The unique signal of the charged current [Special characters omitted.] interactions with deuterium nuclei ([Special characters omitted.] + d [arrow right] n + n + e + ) allows a direct count of the number of [Special characters omitted.] 's to be made. With the addition of NaCl to the heavy water the efficiency of detecting neutrons was increased, which in turn increased the sensitivity for the detection of [Special characters omitted.] 's. This work explores methods of identifying [Special characters omitted.] 's in the high flux environment of a modeled supernova source in SNO during the salt phase. The differences in energy spectrum and in PMT hit pattern of positrons and neutrons allow for distinction between the two, and thus permits classification. Association of these particles to the [Special characters omitted.] interaction is made possible by measuring the time and space between detection of the positron and each neutron generated from the same [Special characters omitted.] . A [Special characters omitted.] is considered to be identified when the correct final state particles generated from the interaction with a deuterium nucleus are associated with each other. Because the expected data rate may be very high and may have a large dynamic range, causing some improper particle association, a pivotal component of this analysis is understanding the rate dependencies. To accomplish this, datasets were generated at several

  20. Boltzmann electron PIC simulation of the E-sail effect

    NASA Astrophysics Data System (ADS)

    Janhunen, P.

    2015-12-01

    The solar wind electric sail (E-sail) is a planned in-space propulsion device that uses the natural solar wind momentum flux for spacecraft propulsion with the help of long, charged, centrifugally stretched tethers. The problem of accurately predicting the E-sail thrust is still somewhat open, however, due to a possible electron population trapped by the tether. Here we develop a new type of particle-in-cell (PIC) simulation for predicting E-sail thrust. In the new simulation, electrons are modelled as a fluid, hence resembling hybrid simulation, but in contrast to normal hybrid simulation, the Poisson equation is used as in normal PIC to calculate the self-consistent electrostatic field. For electron-repulsive parts of the potential, the Boltzmann relation is used. For electron-attractive parts of the potential we employ a power law which contains a parameter that can be used to control the number of trapped electrons. We perform a set of runs varying the parameter and select the one with the smallest number of trapped electrons which still behaves in a physically meaningful way in the sense of producing not more than one solar wind ion deflection shock upstream of the tether. By this prescription we obtain thrust per tether length values that are in line with earlier estimates, although somewhat smaller. We conclude that the Boltzmann PIC simulation is a new tool for simulating the E-sail thrust. This tool enables us to calculate solutions rapidly and allows to easily study different scenarios for trapped electrons.

  1. Structural Reliability and Monte Carlo Simulation.

    ERIC Educational Resources Information Center

    Laumakis, P. J.; Harlow, G.

    2002-01-01

    Analyzes a simple boom structure and assesses its reliability using elementary engineering mechanics. Demonstrates the power and utility of Monte-Carlo simulation by showing that such a simulation can be implemented more readily with results that compare favorably to the theoretical calculations. (Author/MM)

  2. Elements of Regolith Simulant's Cost Structure

    NASA Technical Reports Server (NTRS)

    Rickman, Douglas L.

    2009-01-01

    The cost of lunar regolith simulants is much higher than many users anticipate. After all, it is nothing more than broken rock. This class will discuss the elements which make up the cost structure for simulants. It will also consider which elements can be avoided under certain circumstances and which elements might be altered by the application of additional research and development.

  3. Electronic structure of worm-eaten graphene

    NASA Astrophysics Data System (ADS)

    Negishi, Hayato; Takeda, Kyozaburo

    2017-02-01

    We theoretically study the electronic structure of graphenes having several kinds of imperfections such as atomic vacancies and heteroatom replacements. We consider 12 different configurations of vacancies and 39 different geometries of heteroatom replacements in order to approximately take into account the random conformations of imperfections. To systematically provide a perspective understanding of the defect π and σ states caused by atomistic voids and/or vacancies and heteroatom replacements, we have carried out a tight-binding (TB) calculation. We study the orbital hybridization to clarify the origin and formation of π and σ defect states arising from such imperfections. We also discuss the electronic structure around the Fermi level through the TB band calculation.

  4. Electronic origin of structural transition in 122 Fe based superconductors

    NASA Astrophysics Data System (ADS)

    Ghosh, Haranath; Sen, Smritijit; Ghosh, Abyay

    2017-03-01

    Direct quantitative correlations between the orbital order and orthorhombicity is achieved in a number of Fe-based superconductors of 122 family. The former (orbital order) is calculated from first principles simulations using experimentally determined doping and temperature dependent structural parameters while the latter (the orthorhombicity) is taken from already established experimental studies; when normalized, both the above quantities quantitatively corresponds to each other in terms of their doping as well as temperature variations. This proves that the structural transition in Fe-based materials is electronic in nature due to orbital ordering. An universal correlations among various structural parameters and electronic structure are also obtained. Most remarkable among them is the mapping of two Fe-Fe distances in the low temperature orthorhombic phase, with the band energies Edxz, Edyz of Fe at the high symmetry points of the Brillouin zone. The fractional co-ordinate zAs of As which essentially determines anion height is inversely (directly) proportional to Fe-As bond distances (with exceptions of K doped BaFe2As2) for hole (electron) doped materials as a function of doping. On the other hand, Fe-As bond-distance is found to be inversely (directly) proportional to the density of states at the Fermi level for hole (electron) doped systems. Implications of these results to current issues of Fe based superconductivity are discussed.

  5. Electronic structure investigation of biphenylene films

    NASA Astrophysics Data System (ADS)

    Totani, R.; Grazioli, C.; Zhang, T.; Bidermane, I.; Lüder, J.; de Simone, M.; Coreno, M.; Brena, B.; Lozzi, L.; Puglia, C.

    2017-02-01

    Photoelectron Spectroscopy (PS) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy have been used to investigate the occupied and empty density of states of biphenylene films of different thicknesses, deposited onto a Cu(111) crystal. The obtained results have been compared to previous gas phase spectra and single molecule Density Functional Theory (DFT) calculations to get insights into the possible modification of the molecular electronic structure in the film induced by the adsorption on a surface. Furthermore, NEXAFS measurements allowed characterizing the variation of the molecular arrangement with the film thickness and helped to clarify the substrate-molecule interaction.

  6. Atomic and Electronic Structure of Solids

    NASA Astrophysics Data System (ADS)

    Kaxiras, Efthimios

    2003-01-01

    Preface; Acknowledgements; Part I. Crystalline Solids: 1. Atomic structure of crystals; 2. The single-particle approximation; 3. Electrons in crystal potential; 4. Band structure of crystals; 5. Applications of band theory; 6. Lattice vibrations; 7. Magnetic behaviour of solids; 8. Superconductivity; Part II. Defects, Non-Crystalline Solids and Finite Structures: 9. Defects I: point defects; 10. Defects II: line defects; 11. Defects III: surfaces and interfaces; 12. Non-crystalline solids; 13. Finite structures; Part III. Appendices: A. Elements of classical electrodynamics; B. Elements of quantum mechanics; C. Elements of thermodynamics; D. Elements of statistical mechanics; E. Elements of elasticity theory; F. The Madelung energy; G. Mathematical tools; H. Nobel Prize citations; I. Units and symbols; References; Index.

  7. Controlling the Electronic Structure of Bilayer Graphene

    NASA Astrophysics Data System (ADS)

    Ohta, Taisuke; Bostwick, Aaron; McChesney, Jessica; Seyller, Thomas; Horn, Karsten; Rotenberg, Eli

    2007-03-01

    Carbon-based materials such as carbon nanotubes, graphite intercalation compounds, fullerenes, and ultrathin graphite films exhibit many exotic phenomena such as superconductivity and an anomalous quantum Hall effect. These findings have caused renewed interest in the electronic structure of ultrathin layers of graphene: a single honeycomb carbon layer that is the building block for these materials. There is a strong motivation to incorporate graphene multilayers into atomic-scale devices, spurred on by rapid progress in their fabrication and manipulation. We have synthesized bilayer graphene thin films deposited on insulating silicon carbide and characterized their electronic band structure using angle-resolved photoemission. By selectively adjusting the carrier concentration in each layer, changes in the Coulomb potential led to control of the gap between valence and conduction bands [1]. This control over the band structure suggests the potential application of bilayer graphene to switching functions in atomic scale electronic devices. [1] T. Ohta, A. Bostwick, T. Seyller, K. Horn, E. Rotenberg, Science, 313, 951 (2006).

  8. Simulation Of Electron Cloud Effects On Electron Beam At ERL With Pipelined QuickPIC

    SciTech Connect

    Feng, B.; Muggli, P.; Huang, C.; Decyk, V.; Mori, W. B.; Hoffstaetter, G. H.; Katsouleas, T.

    2009-01-22

    With the successful implementation of pipelining algorithm to the QuickPIC code, the number of processors used is increased by 2 to 3 orders of magnitude, and the speed of the simulation is improved by a similar factor. The pipelined QuickPIC is used to simulate the electron cloud effect on electron beam in the Cornell Energy Recovery Linac (ERL) due to extremely small emittance and high peak currents anticipated in the machine. A tune shift is found due to electron cloud on electron beams, which is of equal magnitude to that on positron beams but in an opposite direction; however, emittance growth of the electron beam in an electron cloud is not observed for ERL parameters.

  9. Update of the Electron Cloud Simulations for DAFNE

    SciTech Connect

    Demma, Theo; Pivi, Mauro T.F.; /SLAC

    2012-04-12

    A strong horizontal instability, limiting the positron current at I {approx} 500mA, has been observed at DAFNE since the installation of the FINUDA detector in 2003. Experiments and simulations seem to provide evidence that the electron cloud build-up in the wigglers and bending magnets of the DAFNE positron ring induces coupled bunch instability with features compatible with observations. Recently the installation of a new horizontal feedback system allowed to control the instability for value of the positron current as high as possible (I {approx} 1000mA). To better understand the electron cloud effects and possibly to find a remedy, a detailed simulation study is undergoing. In this communication we present recent simulation results relative to the single bunch instability induced by an electron cloud interacting with the beam.

  10. Simulation of the nonlinear evolution of electron plasma waves

    NASA Technical Reports Server (NTRS)

    Nishikawa, K.-I.; Cairns, I. H.

    1991-01-01

    Electrostatic waves driven by an electron beam in an ambient magnetized plasma were studied using a quasi-1D PIC simulation of electron plasma waves (i.e., Langmuir waves). The results disclose the presence of a process for moving wave energy from frequencies and wavenumbers predicted by linear theory to the Langmuir-like frequencies during saturation of the instability. A decay process for producing backward propagating Langmuir-like waves, along with low-frequency waves, is observed. The simulation results, however, indicate that the backscattering process is not the conventional Langmuir wave decay. Electrostatic waves near multiples of the electron plasma frequency are generated by wave-wave coupling during the nonlinear stage of the simulations, confirming the suggestion of Klimas (1983).

  11. Terahertz Free Electron Laser: Design, Simulation and Analysis

    DTIC Science & Technology

    2014-12-01

    general principal is that a “pump” light pulse (usually a high peak power laser ) is incident upon a sample and causes an excitation . A certain time...light in free electron lasers , x-ray sources, and THz sources, and neutron production. Niowave also builds radio frequency ( RF ) guns, superconducting...FREE ELECTRON LASER : DESIGN, SIMULATION AND ANALYSIS by Conor M. Pogue December 2014 Dissertation Supervisor William B. Colson THIS PAGE

  12. Simulating electron clouds in heavy-ion acceleratorsa)

    NASA Astrophysics Data System (ADS)

    Cohen, R. H.; Friedman, A.; Covo, M. Kireeff; Lund, S. M.; Molvik, A. W.; Bieniosek, F. M.; Seidl, P. A.; Vay, J.-L.; Stoltz, P.; Veitzer, S.

    2005-05-01

    Contaminating clouds of electrons are a concern for most accelerators of positively charged particles, but there are some unique aspects of heavy-ion accelerators for fusion and high-energy density physics which make modeling such clouds especially challenging. In particular, self-consistent electron and ion simulation is required, including a particle advance scheme which can follow electrons in regions where electrons are strongly magnetized, weakly magnetized, and unmagnetized. The approach to such self-consistency is described, and in particular a scheme for interpolating between full-orbit (Boris) and drift-kinetic particle pushes that enables electron time steps long compared to the typical gyroperiod in the magnets. Tests and applications are presented: simulation of electron clouds produced by three different kinds of sources indicates the sensitivity of the cloud shape to the nature of the source; first-of-a-kind self-consistent simulation of electron-cloud experiments on the high-current experiment [L. R. Prost, P. A. Seidl, F. M. Bieniosek, C. M. Celata, A. Faltens, D. Baca, E. Henestroza, J. W. Kwan, M. Leitner, W. L. Waldron, R. Cohen, A. Friedman, D. Grote, S. M. Lund, A. W. Molvik, and E. Morse, "High current transport experiment for heavy ion inertial fusion," Physical Review Special Topics, Accelerators and Beams 8, 020101 (2005)], at Lawrence Berkeley National Laboratory, in which the machine can be flooded with electrons released by impact of the ion beam on an end plate, demonstrate the ability to reproduce key features of the ion-beam phase space; and simulation of a two-stream instability of thin beams in a magnetic field demonstrates the ability of the large-time-step mover to accurately calculate the instability.

  13. Electronic structure theory of the superheavy elements

    NASA Astrophysics Data System (ADS)

    Eliav, Ephraim; Fritzsche, Stephan; Kaldor, Uzi

    2015-12-01

    High-accuracy calculations of atomic properties of the superheavy elements (SHE) up to element 122 are reviewed. The properties discussed include ionization potentials, electron affinities and excitation energies, which are associated with the spectroscopic and chemical behavior of these elements, and are therefore of considerable interest. Accurate predictions of these quantities require high-order inclusion of relativity and electron correlation, as well as large, converged basis sets. The Dirac-Coulomb-Breit Hamiltonian, which includes all terms up to second order in the fine-structure constant α, serves as the framework for the treatment; higher-order Lamb shift terms are considered in some selected cases. Electron correlation is treated by either the multiconfiguration self-consistent-field approach or by Fock-space coupled cluster theory. The latter is enhanced by the intermediate Hamiltonian scheme, allowing the use of larger model (P) spaces. The quality of the calculations is assessed by applying the same methods to lighter homologs of the SHEs and comparing with available experimental information. Very good agreement is obtained, within a few hundredths of an eV, and similar accuracy is expected for the SHEs. Many of the properties predicted for the SHEs differ significantly from what may be expected by straightforward extrapolation of lighter homologs, demonstrating that the structure and chemistry of SHEs are strongly affected by relativity. The major scientific challenge of the calculations is to find the electronic structure and basic atomic properties of the SHE and assign its proper place in the periodic table. Significant recent developments include joint experimental-computational studies of the excitation spectrum of Fm and the ionization energy of Lr, with excellent agreement of experiment and theory, auguring well for the future of research in the field.

  14. SIMPLEX: simulator and postprocessor for free-electron laser experiments.

    PubMed

    Tanaka, Takashi

    2015-09-01

    SIMPLEX is a computer program developed for simulating the amplification process of free-electron lasers (FELs). It numerically solves the so-called FEL equations describing the evolution of the radiation field and growth of microbunching while the electron beam travels along the undulator. In order to reduce the numerical cost, the FEL equations have been reduced to more convenient forms for numerical implementation by applying reasonable approximations. SIMPLEX is equipped with a postprocessor to facilitate the retrieval of desired information from the simulation results, which is crucial for practical applications such as designing the beamline and analyzing the experimental results.

  15. SIMPLEX: simulator and postprocessor for free-electron laser experiments

    PubMed Central

    Tanaka, Takashi

    2015-01-01

    SIMPLEX is a computer program developed for simulating the amplification process of free-electron lasers (FELs). It numerically solves the so-called FEL equations describing the evolution of the radiation field and growth of microbunching while the electron beam travels along the undulator. In order to reduce the numerical cost, the FEL equations have been reduced to more convenient forms for numerical implementation by applying reasonable approximations. SIMPLEX is equipped with a postprocessor to facilitate the retrieval of desired information from the simulation results, which is crucial for practical applications such as designing the beamline and analyzing the experimental results. PMID:26289287

  16. Electronic structure and magnetic properties of doped Al1- x Ti x N ( x = 0.03, 0.25) compositions based on cubic aluminum nitride from ab initio simulation data

    NASA Astrophysics Data System (ADS)

    Bannikov, V. V.; Beketov, A. R.; Baranov, M. V.; Elagin, A. A.; Kudyakova, V. S.; Shishkin, R. A.

    2016-05-01

    The phase stability, electronic structure, and magnetic properties of Al1- x Ti x N compositions based on the metastable aluminum nitride modification with the rock-salt structure at low ( x = 0.03) and high ( x = 0.25) concentrations of titanium in the system have been investigated using the results of ab initio band calculations. It has been shown that, at low values of x, the partial substitution is characterized by a positive enthalpy, which, however, changes sign with an increase in the titanium concentration. According to the results of the band structure calculations, the doped compositions have electronic conductivity. For x = 0.03, titanium impurity atoms have local magnetic moments (˜0.6 μB), and the electronic spectrum is characterized by a 100% spin polarization of near-Fermi states. Some of the specific features of the chemical bonding in Al1- x Ti x N cubic phases have been considered.

  17. Actinide electronic structure and atomic forces

    NASA Astrophysics Data System (ADS)

    Albers, R. C.; Rudin, Sven P.; Trinkle, Dallas R.; Jones, M. D.

    2000-07-01

    We have developed a new method[1] of fitting tight-binding parameterizations based on functional forms developed at the Naval Research Laboratory.[2] We have applied these methods to actinide metals and report our success using them (see below). The fitting procedure uses first-principles local-density-approximation (LDA) linear augmented plane-wave (LAPW) band structure techniques[3] to first calculate an electronic-structure band structure and total energy for fcc, bcc, and simple cubic crystal structures for the actinide of interest. The tight-binding parameterization is then chosen to fit the detailed energy eigenvalues of the bands along symmetry directions, and the symmetry of the parameterization is constrained to agree with the correct symmetry of the LDA band structure at each eigenvalue and k-vector that is fit to. By fitting to a range of different volumes and the three different crystal structures, we find that the resulting parameterization is robust and appears to accurately calculate other crystal structures and properties of interest.

  18. Xyce Parallel Electronic Simulator : reference guide, version 2.0.

    SciTech Connect

    Hoekstra, Robert John; Waters, Lon J.; Rankin, Eric Lamont; Fixel, Deborah A.; Russo, Thomas V.; Keiter, Eric Richard; Hutchinson, Scott Alan; Pawlowski, Roger Patrick; Wix, Steven D.

    2004-06-01

    This document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users' Guide. The focus of this document is (to the extent possible) exhaustively list device parameters, solver options, parser options, and other usage details of Xyce. This document is not intended to be a tutorial. Users who are new to circuit simulation are better served by the Xyce Users' Guide.

  19. Free-electron laser simulations on the MPP

    NASA Technical Reports Server (NTRS)

    Vonlaven, Scott A.; Liebrock, Lorie M.

    1987-01-01

    Free electron lasers (FELs) are of interest because they provide high power, high efficiency, and broad tunability. FEL simulations can make efficient use of computers of the Massively Parallel Processor (MPP) class because most of the processing consists of applying a simple equation to a set of identical particles. A test version of the KMS Fusion FEL simulation, which resides mainly in the MPPs host computer and only partially in the MPP, has run successfully.

  20. Xyce parallel electronic simulator reference guide, version 6.0.

    SciTech Connect

    Keiter, Eric R; Mei, Ting; Russo, Thomas V.; Schiek, Richard Louis; Thornquist, Heidi K.; Verley, Jason C.; Fixel, Deborah A.; Coffey, Todd S; Pawlowski, Roger P; Warrender, Christina E.; Baur, David Gregory.

    2013-08-01

    This document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users Guide [1] . The focus of this document is (to the extent possible) exhaustively list device parameters, solver options, parser options, and other usage details of Xyce. This document is not intended to be a tutorial. Users who are new to circuit simulation are better served by the Xyce Users Guide [1] .

  1. Xyce™ Parallel Electronic Simulator: Reference Guide, Version 5.1

    SciTech Connect

    Keiter, Eric R.; Mei, Ting; Russo, Thomas V.; Rankin, Eric Lamont; Schiek, Richard Louis; Santarelli, Keith R.; Thornquist, Heidi K.; Fixel, Deborah A.; Coffey, Todd S.; Pawlowski, Roger P.

    2009-11-01

    This document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users’ Guide. The focus of this document is (to the extent possible) exhaustively list device parameters, solver options, parser options, and other usage details of Xyce. This document is not intended to be a tutorial. Users who are new to circuit simulation are better served by the Xyce Users’ Guide.

  2. Xyce parallel electronic simulator reference guide, version 6.1

    SciTech Connect

    Keiter, Eric R; Mei, Ting; Russo, Thomas V.; Schiek, Richard Louis; Sholander, Peter E.; Thornquist, Heidi K.; Verley, Jason C.; Baur, David Gregory

    2014-03-01

    This document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users Guide [1] . The focus of this document is (to the extent possible) exhaustively list device parameters, solver options, parser options, and other usage details of Xyce. This document is not intended to be a tutorial. Users who are new to circuit simulation are better served by the Xyce Users Guide [1] .

  3. Xyce Parallel Electronic Simulator : reference guide, version 4.1.

    SciTech Connect

    Mei, Ting; Rankin, Eric Lamont; Thornquist, Heidi K.; Santarelli, Keith R.; Fixel, Deborah A.; Coffey, Todd Stirling; Russo, Thomas V.; Schiek, Richard Louis; Keiter, Eric Richard; Pawlowski, Roger Patrick

    2009-02-01

    This document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users Guide. The focus of this document is (to the extent possible) exhaustively list device parameters, solver options, parser options, and other usage details of Xyce. This document is not intended to be a tutorial. Users who are new to circuit simulation are better served by the Xyce Users Guide.

  4. Electronic Structure Rearrangements in Hybrid Ribozyme/Protein Catalysis

    NASA Astrophysics Data System (ADS)

    Kang, Jiyoung; Kino, Hiori; Field, Martin J.; Tateno, Masaru

    2017-04-01

    We analyzed the electronic structural changes that occur in the reaction cycle of a biological catalyst composed of RNA and protein, and elucidated the dynamical rearrangements of the electronic structure that was obtained from our previous study in which ab initio quantum mechanics/molecular mechanics molecular dynamics simulations were performed. Notable results that we obtained include the generation of a reactive HOMO that is responsible for bond formation in the initial stages of the reaction, and the appearance of a reactive LUMO that is involved in the bond rupture that leads to products. We denote these changes as dynamical induction of the reactive HOMO (DIRH) and LUMO (DIRL), respectively. Interestingly, we also find that the induction of the reactive HOMO is enhanced by the formation of a low-barrier hydrogen bond (LBHB), which, to the best of our knowledge, represents a novel role for LBHBs in enzymatic systems.

  5. Electron Acceleration in Shock-Shock Interaction: Simulations and Observations

    NASA Astrophysics Data System (ADS)

    Nakanotani, M.; Matsukiyo, S.; Mazelle, C. X.; Hada, T.

    2015-12-01

    Collisionless shock waves play a crucial role in producing high energy particles (cosmic rays) in space. While most of the past studies about particle acceleration assume the presence of a single shock, in space two shocks frequently come close to or even collide with each other. Hietala et al. [2011] observed the collision of an interplanetary shock and the earth's bow shock and the associated acceleration of energetic ions. The kinetic natures of a shock-shock collision has not been well understood. Only the work done by using hybrid simulation was reported by Cargill et al. [1986], in which they focus on a collision of two supercritical shocks and the resultant ion acceleration. We expect similarly that electron acceleration can also occur in shock-shock collision. To investigate the electron acceleration process in a shock-shock collision, we perform one-dimensional full particle-in-cell (PIC) simulations. In the simulation energetic electrons are observed between the two approaching shocks before colliding. These energetic electrons are efficiently accelerated through multiple reflections at the two shocks (Fermi acceleration). The reflected electrons create a temperature anisotropy and excite large amplitude waves upstream via the electron fire hose instability. The large amplitude waves can scatter the energetic electrons in pitch angle so that some of them gain large pitch angles and are easily reflected when they encounter the shocks subsequently. The reflected electrons can sustain, or probably even strengthen, them. We further discuss observational results of an interaction of interplanetary shocks and the earth's bow shock by examining mainly Cluster data. We focus on whether or not electrons are accelerated in the shock-shock interaction.

  6. Electronic bandstructure of semiconductor dilute bismide structures

    NASA Astrophysics Data System (ADS)

    Erucar, T.; Nutku, F.; Donmez, O.; Erol, A.

    2017-02-01

    In this work electronic band structure of dilute bismide GaAs/GaAs1-xBix quantum well structures with 1.8% and 3.75% bismuth compositions have been investigated both experimentally and theoretically. Photoluminescence (PL) measurements reveal that effective bandgap of the samples decreases approximately 65 meV per bismuth concentration. Temperature dependence of the effective bandgap is obtained to be higher for the sample with higher bismuth concentration. Moreover, both asymmetric characteristic at the low energy tail of the PL and full width at half maximum (FWHM) of PL peak increase with increasing bismuth composition as a result of increased Bi related defects located above valence band (VB). In order to explain composition dependence of the effective bandgap quantitatively, valence band anti-crossing (VBAC) model is used. Bismuth composition and temperature dependence of effective bandgap in a quantum well structure is modeled by solving Schrödinger equation and compared with experimental PL data.

  7. Electronic structure interpolation via atomic orbitals.

    PubMed

    Chen, Mohan; Guo, G-C; He, Lixin

    2011-08-17

    We present an efficient scheme for accurate electronic structure interpolation based on systematically improvable optimized atomic orbitals. The atomic orbitals are generated by minimizing the spillage value between the atomic basis calculations and the converged plane wave basis calculations on some coarse k-point grid. They are then used to calculate the band structure of the full Brillouin zone using the linear combination of atomic orbitals algorithms. We find that usually 16-25 orbitals per atom can give an accuracy of about 10 meV compared to the full ab initio calculations, and the accuracy can be systematically improved by using more atomic orbitals. The scheme is easy to implement and robust, and works equally well for metallic systems and systems with complicated band structures. Furthermore, the atomic orbitals have much better transferability than Shirley's basis and Wannier functions, which is very useful for perturbation calculations.

  8. Comparison of plasma plume expansion simulations using fully kinetic electron treatment and electron fluid models

    NASA Astrophysics Data System (ADS)

    Pfeiffer, M.; Copplestone, S.; Binder, T.; Fasoulas, S.; Munz, C.-D.

    2016-11-01

    The expansion of a plasma plume resulting from laser ablation plays an important role in a large number of applications, e.g., material processing, medical laser applications or novel space propulsion concepts. Here, a high-order three-dimensional Particle-In-Cell code is used to simulate such a plasma plume expansion. A major challenge in this kind of simulation is the handling of the electrons due to their low inertia and resultant high acceleration. Therefore, two separate treatments of electron modeling are compared. Firstly, the electrons are simulated as a normal particle species in a kinetic manner, which strongly decreases the time step size and thereby increases the computational effort. Secondly, the electrons are simulated using an electron fluid model that reduces the computational cost but is less accurate [1]. Additionally, the results from the fully kinetic model are compared regarding chemical reactions, in this case ionization and ion recombination. The electron potential is solved using a high-order highly parallel Hybrid Discontinuous Galerkin (HDG) method [2]. This method also allows simulating computationally expensive three-dimensional setups.

  9. Photonic band gap structure simulator

    DOEpatents

    Chen, Chiping; Shapiro, Michael A.; Smirnova, Evgenya I.; Temkin, Richard J.; Sirigiri, Jagadishwar R.

    2006-10-03

    A system and method for designing photonic band gap structures. The system and method provide a user with the capability to produce a model of a two-dimensional array of conductors corresponding to a unit cell. The model involves a linear equation. Boundary conditions representative of conditions at the boundary of the unit cell are applied to a solution of the Helmholtz equation defined for the unit cell. The linear equation can be approximated by a Hermitian matrix. An eigenvalue of the Helmholtz equation is calculated. One computation approach involves calculating finite differences. The model can include a symmetry element, such as a center of inversion, a rotation axis, and a mirror plane. A graphical user interface is provided for the user's convenience. A display is provided to display to a user the calculated eigenvalue, corresponding to a photonic energy level in the Brilloin zone of the unit cell.

  10. Thermal transfer structures coupling electronics card(s) to coolant-cooled structure(s)

    DOEpatents

    David, Milnes P; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Parida, Pritish R; Schmidt, Roger R

    2014-12-16

    Cooling apparatuses and coolant-cooled electronic systems are provided which include thermal transfer structures configured to engage with a spring force one or more electronics cards with docking of the electronics card(s) within a respective socket(s) of the electronic system. A thermal transfer structure of the cooling apparatus includes a thermal spreader having a first thermal conduction surface, and a thermally conductive spring assembly coupled to the conduction surface of the thermal spreader and positioned and configured to reside between and physically couple a first surface of an electronics card to the first surface of the thermal spreader with docking of the electronics card within a socket of the electronic system. The thermal transfer structure is, in one embodiment, metallurgically bonded to a coolant-cooled structure and facilitates transfer of heat from the electronics card to coolant flowing through the coolant-cooled structure.

  11. Detailed Monte Carlo Simulation of electron transport and electron energy loss spectra.

    PubMed

    Attarian Shandiz, M; Salvat, F; Gauvin, R

    2016-11-01

    A computer program for detailed Monte Carlo simulation of the transport of electrons with kinetic energies in the range between about 0.1 and about 500 keV in bulk materials and in thin solid films is presented. Elastic scattering is described from differential cross sections calculated by the relativistic (Dirac) partial-wave expansion method with different models of the scattering potential. Inelastic interactions are simulated from an optical-data model based on an empirical optical oscillator strength that combines optical functions of the solid with atomic photoelectric data. The generalized oscillator strength is built from the adopted optical oscillator strength by using an extension algorithm derived from Lindhard's dielectric function for a free-electron gas. It is shown that simulated backscattering fractions of electron beams from bulk (semi-infinite) specimens are in good agreement with experimental data for beam energies from 0.1 keV up to about 100 keV. Simulations also yield transmitted and backscattered fractions of electron beams on thin solid films that agree closely with measurements for different film thicknesses and incidence angles. Simulated most probable deflection angles and depth-dose distributions also agree satisfactorily with measurements. Finally, electron energy loss spectra of several elemental solids are simulated and the effects of the beam energy and the foil thickness on the signal to background and signal to noise ratios are investigated. SCANNING 38:475-491, 2016. © 2015 Wiley Periodicals, Inc.

  12. Monte Carlo simulations of electron transport in strongly attaching gases

    NASA Astrophysics Data System (ADS)

    Petrovic, Zoran; Miric, Jasmina; Simonovic, Ilija; Bosnjakovic, Danko; Dujko, Sasa

    2016-09-01

    Extensive loss of electrons in strongly attaching gases imposes significant difficulties in Monte Carlo simulations at low electric field strengths. In order to compensate for such losses, some kind of rescaling procedures must be used. In this work, we discuss two rescaling procedures for Monte Carlo simulations of electron transport in strongly attaching gases: (1) discrete rescaling, and (2) continuous rescaling. The discrete rescaling procedure is based on duplication of electrons randomly chosen from the remaining swarm at certain discrete time steps. The continuous rescaling procedure employs a dynamically defined fictitious ionization process with the constant collision frequency chosen to be equal to the attachment collision frequency. These procedures should not in any way modify the distribution function. Monte Carlo calculations of transport coefficients for electrons in SF6 and CF3I are performed in a wide range of electric field strengths. However, special emphasis is placed upon the analysis of transport phenomena in the limit of lower electric fields where the transport properties are strongly affected by electron attachment. Two important phenomena arise: (1) the reduction of the mean energy with increasing E/N for electrons in SF6, and (2) the occurrence of negative differential conductivity in the bulk drift velocity of electrons in both SF6 and CF3I.

  13. Extraordinary electronic properties in uncommon structure types

    NASA Astrophysics Data System (ADS)

    Ali, Mazhar Nawaz

    In this thesis I present the results of explorations into several uncommon structure types. In Chapter 1 I go through the underlying idea of how we search for new compounds with exotic properties in solid state chemistry. The ideas of exploring uncommon structure types, building up from the simple to the complex, using chemical intuition and thinking by analogy are discussed. Also, the history and basic concepts of superconductivity, Dirac semimetals, and magnetoresistance are briefly reviewed. In chapter 2, the 1s-InTaS2 structural family is introduced along with the discovery of a new member of the family, Ag0:79VS2; the synthesis, structure, and physical properties of two different polymorphs of the material are detailed. Also in this chapter, we report the observation of superconductivity in another 1s structure, PbTaSe2. This material is especially interesting due to it being very heavy (resulting in very strong spin orbit coulping (SOC)), layered, and noncentrosymmetric. Electronic structure calculations reveal the presence of a bulk 3D Dirac cone (very similar to graphene) that is gapped by SOC originating from the hexagonal Pb layer. In Chapter 3 we show the re-investigation of the crystal structure of the 3D Dirac semimetal, Cd3As2. It is found to be centrosymmetric, rather than noncentrosymmetric, and as such all bands are spin degenerate and there is a 4-fold degenerate bulk Dirac point at the Fermi level, making Cd3As2 a 3D electronic analog to graphene. Also, for the first time, scanning tunneling microscopy experiments identify a 2x2 surface reconstruction in what we identify as the (112) cleavage plane of single crystals; needle crystals grow with a [110] long axis direction. Lastly, in chapter 4 we report the discovery of "titanic" (sadly dubbed ⪉rge, nonsaturating" by Nature editors and given the acronym XMR) magnetoresistance (MR) in the non-magnetic, noncentrosymmetric, layered transition metal dichalcogenide WTe2; over 13 million% at 0.53 K in

  14. Pu electronic structure and photoelectron spectroscopy

    SciTech Connect

    Joyce, John J; Durakiewicz, Tomasz; Graham, Kevin S; Bauer, Eric D; Moore, David P; Mitchell, Jeremy N; Kennison, John A; Martin, Richard L; Roy, Lindsay E; Scuseria, G. E.

    2010-01-01

    The electronic structure of PuCoGa{sub 5}, Pu metal, and PuO{sub 2} is explored using photoelectron spectroscopy. Ground state electronic properties are inferred from temperature dependent photoemission near the Fermi energy for Pu metal. Angle-resolved photoemission details the energy vs. crystaJ momentum landscape near the Fermi energy for PuCoGa{sub 5} which shows significant dispersion in the quasiparticle peak near the Fermi energy. For the Mott insulators AnO{sub 2}(An = U, Pu) the photoemission results are compared against hybrid functional calculations and the model prediction of a cross over from ionic to covalent bonding is found to be reasonable.

  15. Structural and electronic properties of fluorographene.

    PubMed

    Samarakoon, Duminda K; Chen, Zhifan; Nicolas, Chantel; Wang, Xiao-Qian

    2011-04-04

    The structural and electronic characteristics of fluorinated graphene are investigated based on first-principles density-functional calculations. A detailed analysis of the energy order for stoichiometric fluorographene membranes indicates that there exists prominent chair and stirrup conformations, which correlate with the experimentally observed in-plane lattice expansion contrary to a contraction in graphane. The optical response of fluorographene is investigated using the GW-Bethe-Salpeter equation approach. The results are in good conformity with the experimentally observed optical gap and reveal predominant charge-transfer excitations arising from strong electron-hole interactions. The appearance of bounded excitons in the ultraviolet region can result in an excitonic Bose-Einstein condensate in fluorographene.

  16. Geometric and electronic structures of potassium-adsorbed rubrene complexes

    SciTech Connect

    Li, Tsung-Lung; Lu, Wen-Cai

    2015-06-28

    The geometric and electronic structures of potassium-adsorbed rubrene complexes are studied in this article. It is found that the potassium-rubrene (K{sub 1}RUB) complexes inherit the main symmetry characteristics from their pristine counterparts and are thus classified into D{sub 2}- and C{sub 2h}-like complexes according to the relative orientations of the four phenyl side groups. The geometric structures of K{sub 1}RUB are governed by two general effects on the total energy: Deformation of the carbon frame of the pristine rubrene increases the total energy, while proximity of the potassium ion to the phenyl ligands decreases the energy. Under these general rules, the structures of D{sub 2}- and C{sub 2h}-like K{sub 1}RUB, however, exhibit their respective peculiarities. These peculiarities can be illustrated by their energy profiles of equilibrium structures. For the potassium adsorption-sites, the D{sub 2}-like complexes show minimum-energy basins, whereas the C{sub 2h}-like ones have single-point minimum-energies. If the potassium atom ever has the energy to diffuse from the minimum-energy site, the potassium diffusion path on the D{sub 2}-like complexes is most likely along the backbone in contrast to the C{sub 2h}-like ones. Although the electronic structures of the minimum-energy structures of D{sub 2}- and C{sub 2h}-like K{sub 1}RUB are very alike, decompositions of their total spectra reveal insights into the electronic structures. First, the spectral shapes are mainly determined by the facts that, in comparison with the backbone carbons, the phenyl carbons have more uniform chemical environments and far less contributions to the electronic structures around the valence-band edge. Second, the electron dissociated from the potassium atom mainly remains on the backbone and has little effects on the electronic structures of the phenyl groups. Third, the two phenyls on the same side of the backbone as the potassium atom have more similar chemical environments

  17. Simulating Electron Cloud Effects in Heavy-Ion Beams

    SciTech Connect

    Cohen, R.H.; Friedman, A.; Lund, S.W.; Molvik, A.W.; Azevedo, T.; Vay, J.-L.; Stoltz, P.; Veitzer, S.

    2004-08-04

    Stray electrons can be introduced in heavy ion fusion accelerators as a result of ionization of ambient gas or gas released from walls due to halo-ion impact, or as a result of secondary-electron emission. We summarize here results from several studies of electron-cloud accumulation and effects: (1) Calculation of the electron cloud produced by electron desorption from computed beam ion loss; the importance of ion scattering is shown; (2) Simulation of the effect of specified electron cloud distributions on ion beam dynamics. We find electron cloud variations that are resonant with the breathing mode of the beam have the biggest impact on the beam (larger than other resonant and random variations), and that the ion beam is surprisingly robust, with an electron density several percent of the beam density required to produce significant beam degradation in a 200-quadrupole system. We identify a possible instability associated with desorption and resonance with the breathing mode. (3) Preliminary investigations of a long-timestep algorithm for electron dynamics in arbitrary magnetic fields.

  18. Dark Current Simulation for Linear Collider Accelerator Structures

    SciTech Connect

    Ng, C.K.; Li, Z.; Zhan, X.; Srinivas, V.; Wang, J.; Ko, K.; /SLAC

    2011-08-25

    The dynamics of field-emitted electrons in the traveling wave fields of a constant gradient (tapered) disk-loaded waveguide is followed numerically. Previous simulations have been limited to constant impedance (uniform) structures for sake of simplicity since only the fields in a unit cell is needed. Using a finite element field solver on a parallel computer, the fields in the tapered structure can now be readily generated. We will obtain the characteristics of the dark current emitted from both structure types and compare the two results with and without the effect of secondary electrons. The NLC and JLC detuned structures are considered to study if dark current may pose a problem for high gradient acceleration in the next generation of Linear Colliders.

  19. Low energy electrons and swift ion track structure in PADC

    SciTech Connect

    Fromm, Michel; Quinto, Michele A.; Weck, Philippe F.; Champion, Christophe

    2015-05-27

    The current work aims at providing an accurate description of the ion track-structure in poly-allyl dyglycol carbonate (PADC) by using an up-to-date Monte-Carlo code-called TILDA-V (a French acronym for Transport d’Ions Lourds Dans l’Aqua & Vivo). In this simulation the ion track-structure in PADC is mainly described in terms of ejected electrons with a particular attention done to the Low Energy Electrons (LEEs). After a brief reminder of the most important channels through which LEEs are prone to break a chemical bond, we will report on the simulated energetic distributions of LEEs along an ion track in PADC for particular incident energies located on both sides of the Bragg-peak position. Lastly, based on the rare data dealing with LEEs interaction with polymers or organic molecules, we will emphasise the role played by the LEEs in the formation of a latent track in PADC, and more particularly the one played by the sub-ionization electrons.

  20. Low energy electrons and swift ion track structure in PADC

    NASA Astrophysics Data System (ADS)

    Fromm, Michel; Quinto, Michele A.; Weck, Philippe F.; Champion, Christophe

    2015-10-01

    The current work aims at providing an accurate description of the ion track-structure in poly-allyl dyglycol carbonate (PADC) by using an up-to-date Monte-Carlo code-called TILDA-V (a French acronym for Transport d'Ions Lourds Dans l'Aqua & Vivo). In this simulation the ion track-structure in PADC is mainly described in terms of ejected electrons with a particular attention done to the Low Energy Electrons (LEEs). After a brief reminder of the most important channels through which LEEs are prone to break a chemical bond, we will report on the simulated energetic distributions of LEEs along an ion track in PADC for particular incident energies located on both sides of the Bragg-peak position. Finally, based on the rare data dealing with LEEs interaction with polymers or organic molecules, we will emphasise the role played by the LEEs in the formation of a latent track in PADC, and more particularly the one played by the sub-ionization electrons.

  1. Low energy electrons and swift ion track structure in PADC

    DOE PAGES

    Fromm, Michel; Quinto, Michele A.; Weck, Philippe F.; ...

    2015-05-27

    The current work aims at providing an accurate description of the ion track-structure in poly-allyl dyglycol carbonate (PADC) by using an up-to-date Monte-Carlo code-called TILDA-V (a French acronym for Transport d’Ions Lourds Dans l’Aqua & Vivo). In this simulation the ion track-structure in PADC is mainly described in terms of ejected electrons with a particular attention done to the Low Energy Electrons (LEEs). After a brief reminder of the most important channels through which LEEs are prone to break a chemical bond, we will report on the simulated energetic distributions of LEEs along an ion track in PADC for particularmore » incident energies located on both sides of the Bragg-peak position. Lastly, based on the rare data dealing with LEEs interaction with polymers or organic molecules, we will emphasise the role played by the LEEs in the formation of a latent track in PADC, and more particularly the one played by the sub-ionization electrons.« less

  2. Electronic Structure of Buried Interfaces - Oral Presentation

    SciTech Connect

    Porter, Zachary

    2015-08-25

    In the electronics behind computer memory storage, the speed and size are dictated by the performance of permanent magnets inside devices called read heads. Complicated magnets made of stacked layers of thin films can be engineered to have properties that yield more energy storage and faster switching times compared to conventional iron or cobalt magnets. The reason is that magnetism is a result of subtle interactions amongst electrons; just how neurons come together on large scales to make cat brains and dog brains, ensembles of electrons interact and become ferromagnets and paramagnets. These interactions make magnets too difficult to study in their entirety, so I focus on the interfaces between layers, which are responsible for the coupling materials physicists hope to exploit to produce next-generation magnets. This project, I study a transition metal oxide material called LSCO, Lanthanum Cobaltite, which can be a paramagnet or a ferromagnet depending on how you tweak the electronic structure. It exhibits an exciting behavior: its sum is greater than the sum of its parts. When another similar material called a LSMO, Lanthanum Manganite, is grown on top of it, their interface has a different type of magnetism from the LSCO or the LSMO! I hope to explain this by demonstrating differently charged ions in the interface. The typical method for quantifying this is x-ray absorption, but all conventional techniques look at every layer simultaneously, averaging the interfaces and the LSCO layers that we want to characterize separately. Instead, I must use a new reflectivity technique, which tracks the intensity of reflected x-rays at different angles, at energies near the absorption peaks of certain elements, to track changes in the electronic structure of the material. The samples were grown by collaborators at the Takamura group at U.C. Davis and probed with this “resonant reflectivity” technique on Beamline 2-1 at the Stanford Synchrotron Radiation Lightsource

  3. Simulating Vibrations in a Complex Loaded Structure

    NASA Technical Reports Server (NTRS)

    Cao, Tim T.

    2005-01-01

    The Dynamic Response Computation (DIRECT) computer program simulates vibrations induced in a complex structure by applied dynamic loads. Developed to enable rapid analysis of launch- and landing- induced vibrations and stresses in a space shuttle, DIRECT also can be used to analyze dynamic responses of other structures - for example, the response of a building to an earthquake, or the response of an oil-drilling platform and attached tanks to large ocean waves. For a space-shuttle simulation, the required input to DIRECT includes mathematical models of the space shuttle and its payloads, and a set of forcing functions that simulates launch and landing loads. DIRECT can accommodate multiple levels of payload attachment and substructure as well as nonlinear dynamic responses of structural interfaces. DIRECT combines the shuttle and payload models into a single structural model, to which the forcing functions are then applied. The resulting equations of motion are reduced to an optimum set and decoupled into a unique format for simulating dynamics. During the simulation, maximum vibrations, loads, and stresses are monitored and recorded for subsequent analysis to identify structural deficiencies in the shuttle and/or payloads.

  4. Compressed Sensing Electron Tomography for Determining Biological Structure

    NASA Astrophysics Data System (ADS)

    Guay, Matthew D.; Czaja, Wojciech; Aronova, Maria A.; Leapman, Richard D.

    2016-06-01

    There has been growing interest in applying compressed sensing (CS) theory and practice to reconstruct 3D volumes at the nanoscale from electron tomography datasets of inorganic materials, based on known sparsity in the structure of interest. Here we explore the application of CS for visualizing the 3D structure of biological specimens from tomographic tilt series acquired in the scanning transmission electron microscope (STEM). CS-ET reconstructions match or outperform commonly used alternative methods in full and undersampled tomogram recovery, but with less significant performance gains than observed for the imaging of inorganic materials. We propose that this disparity stems from the increased structural complexity of biological systems, as supported by theoretical CS sampling considerations and numerical results in simulated phantom datasets. A detailed analysis of the efficacy of CS-ET for undersampled recovery is therefore complicated by the structure of the object being imaged. The numerical nonlinear decoding process of CS shares strong connections with popular regularized least-squares methods, and the use of such numerical recovery techniques for mitigating artifacts and denoising in reconstructions of fully sampled datasets remains advantageous. This article provides a link to the software that has been developed for CS-ET reconstruction of electron tomographic data sets.

  5. Compressed Sensing Electron Tomography for Determining Biological Structure

    PubMed Central

    Guay, Matthew D.; Czaja, Wojciech; Aronova, Maria A.; Leapman, Richard D.

    2016-01-01

    There has been growing interest in applying compressed sensing (CS) theory and practice to reconstruct 3D volumes at the nanoscale from electron tomography datasets of inorganic materials, based on known sparsity in the structure of interest. Here we explore the application of CS for visualizing the 3D structure of biological specimens from tomographic tilt series acquired in the scanning transmission electron microscope (STEM). CS-ET reconstructions match or outperform commonly used alternative methods in full and undersampled tomogram recovery, but with less significant performance gains than observed for the imaging of inorganic materials. We propose that this disparity stems from the increased structural complexity of biological systems, as supported by theoretical CS sampling considerations and numerical results in simulated phantom datasets. A detailed analysis of the efficacy of CS-ET for undersampled recovery is therefore complicated by the structure of the object being imaged. The numerical nonlinear decoding process of CS shares strong connections with popular regularized least-squares methods, and the use of such numerical recovery techniques for mitigating artifacts and denoising in reconstructions of fully sampled datasets remains advantageous. This article provides a link to the software that has been developed for CS-ET reconstruction of electron tomographic data sets. PMID:27291259

  6. Electron heating during magnetic reconnection: A simulation scaling study

    SciTech Connect

    Shay, M. A. Haggerty, C. C.; Phan, T. D.; Oieroset, M.; Drake, J. F.; Swisdak, M.; Cassak, P. A.; Wu, P.; Malakit, K.

    2014-12-15

    Electron bulk heating during magnetic reconnection with symmetric inflow conditions is examined using kinetic particle-in-cell simulations. Inflowing plasma parameters are varied over a wide range of conditions, and the increase in electron temperature is measured in the exhaust well downstream of the x-line. The degree of electron heating is well correlated with the inflowing Alfvén speed c{sub Ar} based on the reconnecting magnetic field through the relation ΔT{sub e}=0.033 m{sub i} c{sub Ar}{sup 2}, where ΔT{sub e} is the increase in electron temperature. For the range of simulations performed, the heating shows almost no correlation with inflow total temperature T{sub tot}=T{sub i}+T{sub e} or plasma β. An out-of-plane (guide) magnetic field of similar magnitude to the reconnecting field does not affect the total heating, but it does quench perpendicular heating, with almost all heating being in the parallel direction. These results are qualitatively consistent with a recent statistical survey of electron heating in the dayside magnetopause (Phan et al., Geophys. Res. Lett. 40, 4475, 2013), which also found that ΔT{sub e} was proportional to the inflowing Alfvén speed. The net electron heating varies very little with distance downstream of the x-line. The simulations show at most a very weak dependence of electron heating on the ion to electron mass ratio. In the antiparallel reconnection case, the largely parallel heating is eventually isotropized downstream due a scattering mechanism, such as stochastic particle motion or instabilities. The simulation size is large enough to be directly relevant to reconnection in the Earth's magnetosphere, and the present findings may prove to be universal in nature with applications to the solar wind, the solar corona, and other astrophysical plasmas. The study highlights key properties that must be satisfied by an electron heating mechanism: (1) preferential heating in the parallel direction; (2) heating

  7. Simulation Tools for Power Electronics Courses Based on Java Technologies

    ERIC Educational Resources Information Center

    Canesin, Carlos A.; Goncalves, Flavio A. S.; Sampaio, Leonardo P.

    2010-01-01

    This paper presents interactive power electronics educational tools. These interactive tools make use of the benefits of Java language to provide a dynamic and interactive approach to simulating steady-state ideal rectifiers (uncontrolled and controlled; single-phase and three-phase). Additionally, this paper discusses the development and use of…

  8. Simulation of tail distributions in electron-positron circular colliders

    SciTech Connect

    Irwin, J.

    1992-02-01

    In addition to the Gaussian shaped core region, particle bunches in electron-positron circular colliders have a rarefied halo region of importance in determining beam lifetimes and backgrounds in particle detectors. A method is described which allows simulation of halo particle distributions.

  9. Quantum simulations of small electron-hole complexes

    SciTech Connect

    Lee, M.A.; Kalia, R.K.; Vashishta, P.D.

    1984-09-01

    The Green's Function Monte Carlo method is applied to the calculation of the binding energies of electron-hole complexes in semiconductors. The quantum simulation method allows the unambiguous determination of the ground state energy and the effects of band anisotropy on the binding energy. 22 refs., 1 fig.

  10. Simulation results for the electron-cloud at the PSR

    SciTech Connect

    Furman, M.A.; Pivi, M.

    2001-06-26

    We present a first set of computer simulations for the main features of the electron cloud at the Proton Storage Ring (PSR), particularly its energy spectrum. We compare our results with recent measurements, which have been obtained by means of dedicated probes.

  11. Surface structure and electronic properties of materials

    NASA Technical Reports Server (NTRS)

    Siekhaus, W. J.; Somorjai, G. A.

    1975-01-01

    A surface potential model is developed to explain dopant effects on chemical vapor deposition. Auger analysis of the interaction between allotropic forms of carbon and silicon films has shown Si-C formation for all forms by glassy carbon. LEED intensity measurements have been used to determine the mean square displacement of surface atoms of silicon single crystals, and electron loss spectroscopy has shown the effect of structure and impurities on surface states located within the band gap. A thin film of Al has been used to enhance film crystallinity at low temperature.

  12. Structural, electronic and optical properties of carbonnitride

    SciTech Connect

    Cohen, Marvin L.

    1996-01-31

    Carbon nitride was proposed as a superhard material and a structural prototype, Beta-C3N4, was examined using several theoretical models. Some reports claiming experimental verifications have been made recently. The current status of the theory and experiment is reviewed, and a detailed discussion is presented of calculations of the electronic and optical properties of this material. These calculations predict that Beta-C3N4 will have a minimum gap which is indirect at 6.4 plus or minus 0.5 eV. A discussion of the possibility of carbon nitride nanotubes is also presented.

  13. Numerically simulating the sandwich plate system structures

    NASA Astrophysics Data System (ADS)

    Feng, Guo-Qing; Li, Gang; Liu, Zhi-Hui; Niu, Huai-Lei; Li, Chen-Feng

    2010-09-01

    Sandwich plate systems (SPS) are advanced materials that have begun to receive extensive attention in naval architecture and ocean engineering. At present, according to the rules of classification societies, a mixture of shell and solid elements are required to simulate an SPS. Based on the principle of stiffness decomposition, a new numerical simulation method for shell elements was proposed. In accordance with the principle of stiffness decomposition, the total stiffness can be decomposed into the bending stiffness and shear stiffness. Displacement and stress response related to bending stiffness was calculated with the laminated shell element. Displacement and stress response due to shear was calculated by use of a computational code write by FORTRAN language. Then the total displacement and stress response for the SPS was obtained by adding together these two parts of total displacement and stress. Finally, a rectangular SPS plate and a double-bottom structure were used for a simulation. The results show that the deflection simulated by the elements proposed in the paper is larger than the same simulated by solid elements and the analytical solution according to Hoff theory and approximate to the same simulated by the mixture of shell-solid elements, and the stress simulated by the elements proposed in the paper is approximate to the other simulating methods. So compared with calculations based on a mixture of shell and solid elements, the numerical simulation method given in the paper is more efficient and easier to do.

  14. A simple approach for electron-electron scattering in nonequilibrium Green's function simulations (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Winge, David O.; Franckie, Martin; Verozzi, Claudio; Wacker, Andreas; Pereira, Mauro F.

    2016-10-01

    Regardless of all the success of Mid Infrared Quantum Cascade Lasers (QCLs), they still do not operate at room temperature in the THz range. The main temperature degrading mechanism for THz QCLs is not known in time of writing this abstract and it is still a topic of debate by the community [S. Khanal et al, J. Opt. 16 094001, 2014]. This is a challenge to theory and it is crucial to treat all possible scattering channels with the same mathematical footing. A summary of different methods for simulating these structures is found in [C. Jirauschek et al, Appl. Phys. Rev. 1 011307, 2014]. In this work we include and study the effects of electron-electron scattering via the Single Plasmon Pole Approximation (SPPA). In this approximation we capture both the static limit as well as dynamic effects. This gives an energy dependent (non-local in time) interaction beyond the Hartree-Fock approximation. This has been studied in a similar model with promising results [T. Schmielau and M.F. Pereira, Appl. Phys. Lett. 95 231111, 2009], and with this work we want to adapt the idea into the model described in Ref. [A. Wacker et a, IEEE Journal of Sel. Top. in Quantum Electron.,19 1200611, 2013]. We start by summarizing the theory underlying the SPPA and we show how it is implemented in the context of our formalism, by showing good agreement with the results for a four well quantum cascade laser [M. Amanti et al, New J. Phys. 11 125022, 2009].

  15. Simulating Dark Current in NLC Structures

    SciTech Connect

    Ng, C.K.; Folwell, N.; Guetz, A.; Ivanov, V.; Lee, L.Q.; Li, Z.H.; Schussman, G.; Ko, K.; /SLAC

    2007-10-11

    Dark current generation and capture are of great importance in high gradient accelerating structure R&D especially for the NLC which aims to operate at 65 MV/m with specific limits on dark current and RF breakdown rates. Although considerable effort has been devoted to building and testing various types of structures to meet these requirements, few theoretical studies have been done to understand these effects in actual structures. This paper focuses on the simulation of dark current in a NLC test structure for which experimental data are available. The parallel time-domain field solver Tau3P and the parallel particle tracking code Track3P are used together to simulate, for the first time, a dark current pulse to compare with the data measured downstream. Results from SLAC X-band 30-cell constant impedance structure for RF drive pulses with different rise times are presented and discussed.

  16. The structure of the hydrated electron in bulk and at interfaces: Does the hydrated electron occupy a cavity?

    NASA Astrophysics Data System (ADS)

    Casey, Jennifer Ryan

    Since its discovery over fifty years ago, the hydrated electron has been the subject of much interest. Hydrated electrons, which are free electrons in water, are found in fields ranging from biochemistry to radiation chemistry, so it is important that we understand the structure and dynamics of this species. Because of its high reactivity, the hydrated electron's structure has proven difficult to pin down, especially its molecular details. One-electron mixed quantum/classical molecular dynamics simulations have proven useful in helping elucidate the structure of the hydrated electron. The picture most commonly presented from these studies is one of the electron residing in a cavity, disrupting the local water structure much like an anion the size of bromide. Our group has recently proposed a completely different structure for the hydrated electron, which arose from rigorous calculations of a new electron-water potential. The picture that emerged was of an electron that does not occupy a cavity but instead draws water within itself; this non-cavity electron resides in a region of enhanced water density. The one-electron cavity and non-cavity models all predict similar experimental observables that probe the electronic structure of the hydrated electron, such as the optical absorption spectrum, which makes it difficult to determine which model most accurately describes the true structure of the hydrated electron. In this thesis, we work to calculate experimental observables for various simulated cavity and non-cavity models that are particularly sensitive to the local water structure near the electron, in an effort to distinguish the various models from each other. Two particular observables we are interested in are the resonance Raman spectrum and the temperature dependent optical absorption spectrum of the hydrated electron. We find that for both of these experiments, only the non-cavity model has qualitative agreement with experiment; the cavity models miss the

  17. Simulation of free-electron lasers seeded with broadband radiation

    SciTech Connect

    Bajlekov, Svetoslav; Fawley, William; Schroeder, Carl; Bartolini, Riccardo; Hooker, Simon

    2011-03-10

    The longitudinal coherence of free-electron laser (FEL) radiation can be enhanced by seeding the FEL with high harmonics of an optical laser pulse. The radiation produced by high-harmonic generation (HHG), however, has a fast-varying temporal profile that can violate the slowly varying envelope approximation and limited frequency window that is employed in conventional free-electron laser simulation codes. Here we investigate the implications of violating this approximation on the accuracy of simulations. On the basis of both analytical considerations and 1D numerical studies, it is concluded that, for most realistic scenarios, conventional FEL codes are capable of accurately simulating the FEL process even when the seed radiation violates the slowly varying envelope approximation. We additionally discuss the significance of filtering the harmonic content of broadband HHG seeds.

  18. Electronic-structural dynamics in graphene.

    PubMed

    Gierz, Isabella; Cavalleri, Andrea

    2016-09-01

    We review our recent time- and angle-resolved photoemission spectroscopy experiments, which measure the transient electronic structure of optically driven graphene. For pump photon energies in the near infrared ([Formula: see text]), we have discovered the formation of a population-inverted state near the Dirac point, which may be of interest for the design of THz lasing devices and optical amplifiers. At lower pump photon energies ([Formula: see text]), for which interband absorption is not possible in doped samples, we find evidence for free carrier absorption. In addition, when mid-infrared pulses are made resonant with an infrared-active in-plane phonon of bilayer graphene ([Formula: see text]), a transient enhancement of the electron-phonon coupling constant is observed, providing interesting perspective for experiments that report light-enhanced superconductivity in doped fullerites in which a similar lattice mode was excited. All the studies reviewed here have important implications for applications of graphene in optoelectronic devices and for the dynamical engineering of electronic properties with light.

  19. Electronic-structural dynamics in graphene

    PubMed Central

    Gierz, Isabella; Cavalleri, Andrea

    2016-01-01

    We review our recent time- and angle-resolved photoemission spectroscopy experiments, which measure the transient electronic structure of optically driven graphene. For pump photon energies in the near infrared (ℏωpump=950 meV), we have discovered the formation of a population-inverted state near the Dirac point, which may be of interest for the design of THz lasing devices and optical amplifiers. At lower pump photon energies (ℏωpump<400 meV), for which interband absorption is not possible in doped samples, we find evidence for free carrier absorption. In addition, when mid-infrared pulses are made resonant with an infrared-active in-plane phonon of bilayer graphene (ℏωpump=200 meV), a transient enhancement of the electron-phonon coupling constant is observed, providing interesting perspective for experiments that report light-enhanced superconductivity in doped fullerites in which a similar lattice mode was excited. All the studies reviewed here have important implications for applications of graphene in optoelectronic devices and for the dynamical engineering of electronic properties with light. PMID:27822486

  20. Electron beam coupling to a metamaterial structure

    SciTech Connect

    French, David M.; Shiffler, Don; Cartwright, Keith

    2013-08-15

    Microwave metamaterials have shown promise in numerous applications, ranging from strip lines and antennas to metamaterial-based electron beam driven devices. In general, metamaterials allow microwave designers to obtain electromagnetic characteristics not typically available in nature. High Power Microwave (HPM) sources have in the past drawn inspiration from work done in the conventional microwave source community. In this article, the use of metamaterials in an HPM application is considered by using an effective medium model to determine the coupling of an electron beam to a metamaterial structure in a geometry similar to that of a dielectric Cerenkov maser. Use of the effective medium model allows for the analysis of a wide range of parameter space, including the “mu-negative,”“epsilon-negative,” and “double negative” regimes of the metamaterial. The physics of such a system are modeled analytically and by utilizing the particle-in-cell code ICEPIC. For this geometry and effective medium representation, optimum coupling of the electron beam to the metamaterial, and thus the optimum microwave or RF production, occurs in the epsilon negative regime of the metamaterial. Given that HPM tubes have been proposed that utilize a metamaterial, this model provides a rapid method of characterizing a source geometry that can be used to quickly understand the basic physics of such an HPM device.

  1. Analysis of boron carbides' electronic structure

    NASA Technical Reports Server (NTRS)

    Howard, Iris A.; Beckel, Charles L.

    1986-01-01

    The electronic properties of boron-rich icosahedral clusters were studied as a means of understanding the electronic structure of the icosahedral borides such as boron carbide. A lower bound was estimated on bipolaron formation energies in B12 and B11C icosahedra, and the associated distortions. While the magnitude of the distortion associated with bipolaron formation is similar in both cases, the calculated formation energies differ greatly, formation being much more favorable on B11C icosahedra. The stable positions of a divalent atom relative to an icosahedral borane was also investigated, with the result that a stable energy minimum was found when the atom is at the center of the borane, internal to the B12 cage. If incorporation of dopant atoms into B12 cages in icosahedral boride solids is feasible, novel materials might result. In addition, the normal modes of a B12H12 cluster, of the C2B10 cage in para-carborane, and of a B12 icosahedron of reduced (D sub 3d) symmetry, such as is found in the icosahedral borides, were calculated. The nature of these vibrational modes will be important in determining, for instance, the character of the electron-lattice coupling in the borides, and in analyzing the lattice contribution to the thermal conductivity.

  2. Experimental Benchmarking of Pu Electronic Structure

    SciTech Connect

    Tobin, J.G.; Moore, K.T.; Chung, B.W.; Wall, M.A.; Schwartz, A.J.; Ebbinghaus, B.B.; Butterfield, M.T.; Teslich, Jr., N.E.; Bliss, R.A.; Morton, S.A.; Yu, S.W.; Komesu, T.; Waddill, G.D.; van der Laan, G.; Kutepov, A.L.

    2008-10-30

    The standard method to determine the band structure of a condensed phase material is to (1) obtain a single crystal with a well defined surface and (2) map the bands with angle resolved photoelectron spectroscopy (occupied or valence bands) and inverse photoelectron spectroscopy (unoccupied or conduction bands). Unfortunately, in the case of Pu, the single crystals of Pu are either nonexistent, very small and/or having poorly defined surfaces. Furthermore, effects such as electron correlation and a large spin-orbit splitting in the 5f states have further complicated the situation. Thus, we have embarked upon the utilization of unorthodox electron spectroscopies, to circumvent the problems caused by the absence of large single crystals of Pu with well-defined surfaces. Our approach includes the techniques of resonant photoelectron spectroscopy, x-ray absorption spectroscopy, electron energy loss spectroscopy, Fano Effect measurements, and Bremstrahlung Isochromat Spectroscopy, including the utilization of micro-focused beams to probe single-crystallite regions of polycrystalline Pu samples.

  3. Experimental Benchmarking of Pu Electronic Structure

    SciTech Connect

    Tobin, J G; Moore, K T; Chung, B W; Wall, M A; Schwartz, A J; Ebbinghaus, B B; Butterfield, M T; Teslich, Jr., N E; Bliss, R A; Morton, S A; Yu, S W; Komesu, T; Waddill, G D; der Laan, G v; Kutepov, A L

    2005-10-13

    The standard method to determine the band structure of a condensed phase material is to (1) obtain a single crystal with a well defined surface and (2) map the bands with angle resolved photoelectron spectroscopy (occupied or valence bands) and inverse photoelectron spectroscopy (unoccupied or conduction bands). Unfortunately, in the case of Pu, the single crystals of Pu are either nonexistent, very small and/or having poorly defined surfaces. Furthermore, effects such as electron correlation and a large spin-orbit splitting in the 5f states have further complicated the situation. Thus, we have embarked upon the utilization of unorthodox electron spectroscopies, to circumvent the problems caused by the absence of large single crystals of Pu with well-defined surfaces. Our approach includes the techniques of resonant photoelectron spectroscopy [1], x-ray absorption spectroscopy [1,2,3,4], electron energy loss spectroscopy [2,3,4], Fano Effect measurements [5], and Bremstrahlung Isochromat Spectroscopy [6], including the utilization of micro-focused beams to probe single-crystallite regions of polycrystalline Pu samples. [2,3,6

  4. Simulation of electron thermal transport in H-mode discharges

    NASA Astrophysics Data System (ADS)

    Rafiq, T.; Pankin, A. Y.; Bateman, G.; Kritz, A. H.; Halpern, F. D.

    2009-03-01

    Electron thermal transport in DIII-D H-mode tokamak plasmas [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] is investigated by comparing predictive simulation results for the evolution of electron temperature profiles with experimental data. The comparison includes the entire profile from the magnetic axis to the bottom of the pedestal. In the simulations, carried out using the automated system for transport analysis (ASTRA) integrated modeling code, different combinations of electron thermal transport models are considered. The combinations include models for electron temperature gradient (ETG) anomalous transport and trapped electron mode (TEM) anomalous transport, as well as a model for paleoclassical transport [J. D. Callen, Nucl. Fusion 45, 1120 (2005)]. It is found that the electromagnetic limit of the Horton ETG model [W. Horton et al., Phys. Fluids 31, 2971 (1988)] provides an important contribution near the magnetic axis, which is a region where the ETG mode in the GLF23 model [R. E. Waltz et al., Phys. Plasmas 4, 2482 (1997)] is below threshold. In simulations of DIII-D discharges, the observed shape of the H-mode edge pedestal is produced when transport associated with the TEM component of the GLF23 model is suppressed and transport given by the paleoclassical model is included. In a study involving 15 DIII-D H-mode discharges, it is found that with a particular combination of electron thermal transport models, the average rms deviation of the predicted electron temperature profile from the experimental profile is reduced to 9% and the offset to -4%.

  5. Structure and navigation for electronic publishing

    NASA Astrophysics Data System (ADS)

    Tillinghast, John; Beretta, Giordano B.

    1998-01-01

    The sudden explosion of the World Wide Web as a new publication medium has given a dramatic boost to the electronic publishing industry, which previously was a limited market centered around CD-ROMs and on-line databases. While the phenomenon has parallels to the advent of the tabloid press in the middle of last century, the electronic nature of the medium brings with it the typical characteristic of 4th wave media, namely the acceleration in its propagation speed and the volume of information. Consequently, e-publications are even flatter than print media; Shakespeare's Romeo and Juliet share the same computer screen with a home-made plagiarized copy of Deep Throat. The most touted tool for locating useful information on the World Wide Web is the search engine. However, due to the medium's flatness, sought information is drowned in a sea of useless information. A better solution is to build tools that allow authors to structure information so that it can easily be navigated. We experimented with the use of ontologies as a tool to formulate structures for information about a specific topic, so that related concepts are placed in adjacent locations and can easily be navigated using simple and ergonomic user models. We describe our effort in building a World Wide Web based photo album that is shared among a small network of people.

  6. A complete comparison of simulated electron diffraction patterns using different parameterizations of the electron scattering factors.

    PubMed

    Lobato, I; Van Dyck, D

    2015-08-01

    The steadily improving experimental possibilities in instrumental resolution as in sensitivity and quantization of the data recording put increasingly higher demands on the precision of the scattering factors, which are the key ingredients for electron diffraction or high-resolution imaging simulation. In the present study, we will systematically investigate the accuracy of fitting of the main parameterizations of the electron scattering factor for the calculation of electron diffraction intensities. It is shown that the main parameterizations of the electron scattering factor are consistent to calculate electron diffraction intensities for thin specimens and low angle scattering. Parameterizations of the electron scattering factor with the correct asymptotic behavior (Lobato and Dyck [5], Kirkland [4], and Weickenmeier and Kohl [2]) produce similar results for both the undisplaced lattice model and the frozen phonon model, except for certain thicknesses and reflections.

  7. Multigrid Methods in Electronic Structure Calculations

    NASA Astrophysics Data System (ADS)

    Briggs, Emil

    1996-03-01

    Multigrid techniques have become the method of choice for a broad range of computational problems. Their use in electronic structure calculations introduces a new set of issues when compared to traditional plane wave approaches. We have developed a set of techniques that address these issues and permit multigrid algorithms to be applied to the electronic structure problem in an efficient manner. In our approach the Kohn-Sham equations are discretized on a real-space mesh using a compact representation of the Hamiltonian. The resulting equations are solved directly on the mesh using multigrid iterations. This produces rapid convergence rates even for ill-conditioned systems with large length and/or energy scales. The method has been applied to both periodic and non-periodic systems containing over 400 atoms and the results are in very good agreement with both theory and experiment. Example applications include a vacancy in diamond, an isolated C60 molecule, and a 64-atom cell of GaN with the Ga d-electrons in valence which required a 250 Ry cutoff. A particular strength of a real-space multigrid approach is its ready adaptability to massively parallel computer architectures. The compact representation of the Hamiltonian is especially well suited to such machines. Tests on the Cray-T3D have shown nearly linear scaling of the execution time up to the maximum number of processors (512). The MPP implementation has been used for studies of a large Amyloid Beta Peptide (C_146O_45N_42H_210) found in the brains of Alzheimers disease patients. Further applications of the multigrid method will also be described. (in collaboration D. J. Sullivan and J. Bernholc)

  8. Electronic Structure and Bonding in Complex Biomolecule

    NASA Astrophysics Data System (ADS)

    Ouyang, Lizhi

    2005-03-01

    For over a century vitamin B12 and its enzyme cofactor derivates have persistently attracted research efforts for their vital biological role, unique Co-C bonding, rich red-ox chemistry, and recently their candidacies as drug delivery vehicles etc. However, our understanding of this complex metalorganic molecule's efficient enzyme activated catalytic power is still controversial. We have for the first time calculated the electronic structure, Mulliken effective charge and bonding of a whole Vitamin B12 molecule without any structural simplification by first- principles approaches based on density functional theory using structures determined by high resolution X-ray diffraction. A partial density of states analysis shows excellent agreement with X-ray absorption data and has been used successfully to interpret measured optical absorption spectra. Mulliken bonding analysis of B12 and its derivatives reveal noticeable correlations between the two axial ligands which could be exploited by the enzyme to control the catalytic process. Our calculated X-ray near edge structure of B12 and its derivates using Slater's transition state theory are also in good agreement with experiments. The same approach has been applied to other B12 derivatives, ferrocene peptides, and recently DNA molecules.

  9. Multidimensional simulations of the ELFA superradiant free electron laser

    NASA Astrophysics Data System (ADS)

    Pierini, P.; Fawley, W. M.; Sharp, W. M.

    1991-07-01

    ELFA (electron laser facility for acceleration) is a high-gain, microwave ( ν = 100 GHz) free electron laser (FEL) facility driven by an rf linac. ELFA will test the existence of the theoretically predicted regimes of strong and weak superradiance. Both regimes can be studied with the same FEL by changing the height of the interaction waveguide, which controls the radiation group velocity, and thus the relative slippage between electrons and photons. The operation of ELFA has been modeled using a modified version of the two-dimensional, time-dependent sideband code GINGER. The simulations take into account the time and space variations of the radiation field, as well as the space charge and transverse emittance of the electron beam. The sensitivity of the superradiant signal to variations of the beam emittance, energy and energy spread is examined.

  10. Observation of fine structures in laser-driven electron beams using coherent transition radiation.

    PubMed

    Glinec, Y; Faure, J; Norlin, A; Pukhov, A; Malka, V

    2007-05-11

    We have measured the coherent optical transition radiation emitted by an electron beam from laser-plasma interaction. The measurement of the spectrum of the radiation reveals fine structures of the electron beam in the range 400-1000 nm. These structures are reproduced using an electron distribution from a 3D particle-in-cell simulation and are attributed to microbunching of the electron bunch due to its interaction with the laser field. When the radiator is placed closer to the interaction point, spectral oscillations have also been recorded, signature of the interference of the radiation produced by two electron bunches delayed by 74 fs. The second electron bunch duration is shown to be ultrashort to match the intensity level of the radiation. Whereas transition radiation was used at longer wavelengths in order to estimate the electron bunch length, this study focuses on the ultrashort structures of the electron beam.

  11. Electronic structure of Ca, Sr, and Ba under pressure.

    NASA Technical Reports Server (NTRS)

    Animalu, A. O. E.; Heine, V.; Vasvari, B.

    1967-01-01

    Electronic band structure calculations phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure

  12. Quantum-classical simulation of electron localization in negatively charged methanol clusters.

    PubMed

    Mones, Letif; Rossky, Peter J; Turi, László

    2011-08-28

    A series of quantum molecular dynamics simulations have been performed to investigate the energetic, structural, dynamic, and spectroscopic properties of methanol cluster anions, [(CH(3)OH)(n)](-), (n = 50-500). Consistent with the inference from photo-electron imaging experiments, we find two main localization modes of the excess electron in equilibrated methanol clusters at ∼200 K. The two different localization patterns have strikingly different physical properties, consistent with experimental observations, and are manifest in comparable cluster sizes to those observed. Smaller clusters (n ≤ 128) tend to localize the electron in very weakly bound, diffuse electronic states on the surface of the cluster, while in larger ones the electron is stabilized in solvent cavities, in compact interior-bound states. The interior states exhibit properties that largely resemble and smoothly extrapolate to those simulated for a solvated electron in bulk methanol. The surface electronic states of methanol cluster anions are significantly more weakly bound than the surface states of the anionic water clusters. The key source of the difference is the lack of stabilizing free hydroxyl groups on a relaxed methanol cluster surface. We also provide a mechanistic picture that illustrates the essential role of the interactions of the excess electron with the hydroxyl groups in the dynamic process of the transition of the electron from surface-bound states to interior-bound states.

  13. Progress in Simulating Turbulent Electron Thermal Transport in NSTX

    SciTech Connect

    Guttenfelder, Walter; Kaye, S. M.; Ren, Y.; Bell, R. E.; Hammett, G. W.; LeBlanc, B. P.; Mikkelsen, D. R.; Peterson, J. L.; Nevins, W. M.; Candy, J.; Yuh, H.

    2013-07-17

    Nonlinear simulations based on multiple NSTX discharge scenarios have progressed to help differentiate unique instability mechanisms and to validate with experimental turbulence and transport data. First nonlinear gyrokinetic simulations of microtearing (MT) turbulence in a high-beta NSTX H-mode discharge predict experimental levels of electron thermal transport that are dominated by magnetic flutter and increase with collisionality, roughly consistent with energy confinement times in dimensionless collisionality scaling experiments. Electron temperature gradient (ETG) simulations predict significant electron thermal transport in some low and high beta discharges when ion scales are suppressed by E x B shear. Although the predicted transport in H-modes is insensitive to variation in collisionality (inconsistent with confinement scaling), it is sensitive to variations in other parameters, particularly density gradient stabilization. In reversed shear (RS) Lmode discharges that exhibit electron internal transport barriers, ETG transport has also been shown to be suppressed nonlinearly by strong negative magnetic shear, s<<0. In many high beta plasmas, instabilities which exhibit a stiff beta dependence characteristic of kinetic ballooning modes (KBM) are sometimes found in the core region. However, they do not have a distinct finite beta threshold, instead transitioning gradually to a trapped electron mode (TEM) as beta is reduced to zero. Nonlinear simulations of this "hybrid" TEM/KBM predict significant transport in all channels, with substantial contributions from compressional magnetic perturbations. As multiple instabilities are often unstable simultaneously in the same plasma discharge, even on the same flux surface, unique parametric dependencies are discussed which may be useful for distinguishing the different mechanisms experimentally.

  14. Simulations of one- and two-electron systems by Bead-Fourier path integral molecular dynamics

    NASA Astrophysics Data System (ADS)

    Ivanov, Sergei D.; Lyubartsev, Alexander P.

    2005-07-01

    The Bead-Fourier path integral molecular dynamics technique introduced earlier [S. D. Ivanov, A. P. Lyubartsev, and A. Laaksonen, Phys. Rev. E 67 066710 (2003)] is applied for simulation of electrons in the simplest molecules: molecular hydrogen, helium atom, and their ions. Special attention is paid to the correct description of electrons in the core region of a nucleus. In an attempt to smooth the Coulomb potential at small distances, a recipe is suggested. The simulation results are in excellent agreement with the analytical solution for the "harmonic helium atom", as well as with the vibrational potential of the H2 molecule and He ionization energies. It is demonstrated, that the Bead-Fourier path integral molecular dynamics technique is able to provide the accuracy required for the description of electron structure and chemical bonds in cases when electron exchange effects need not be taken into account.

  15. X-ray and photoelectron spectroscopy of the structure, reactivity, and electronic structure of semiconductor nanocrystals

    SciTech Connect

    Hamad, Kimberly Sue

    2000-01-01

    Semiconductor nanocrystals are a system which has been the focus of interest due to their size dependent properties and their possible use in technological applications. Many chemical and physical properties vary systematically with the size of the nanocrystal and thus their study enables the investigation of scaling laws. Due to the increasing surface to volume ratio as size is decreased, the surfaces of nanocrystals are expected to have a large influence on their electronic, thermodynamic, and chemical behavior. In spite of their importance, nanocrystal surfaces are still relatively uncharacterized in terms of their structure, electronic properties, bonding, and reactivity. Investigation of nanocrystal surfaces is currently limited by what techniques to use, and which methods are suitable for nanocrystals is still being determined. This work presents experiments using x-ray and electronic spectroscopies to explore the structure, reactivity, and electronic properties of semiconductor (CdSe, InAs) nanocrystals and how they vary with size. Specifically, x-ray absorption near edge spectroscopy (XANES) in conjunction with multiple scattering simulations affords information about the structural disorder present at the surface of the nanocrystal. X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) probe the electronic structure in terms of hole screening, and also give information about band lineups when the nanocrystal is placed in electric contact with a substrate. XPS of the core levels of the nanocrystal as a function of photo-oxidation time yields kinetic data on the oxidation reaction occurring at the surface of the nanocrystal.

  16. Mechanisms of electron acceptor utilization: Implications for simulating anaerobic biodegradation

    USGS Publications Warehouse

    Schreiber, M.E.; Carey, G.R.; Feinstein, D.T.; Bahr, J.M.

    2004-01-01

    Simulation of biodegradation reactions within a reactive transport framework requires information on mechanisms of terminal electron acceptor processes (TEAPs). In initial modeling efforts, TEAPs were approximated as occurring sequentially, with the highest energy-yielding electron acceptors (e.g. oxygen) consumed before those that yield less energy (e.g., sulfate). Within this framework in a steady state plume, sequential electron acceptor utilization would theoretically produce methane at an organic-rich source and Fe(II) further downgradient, resulting in a limited zone of Fe(II) and methane overlap. However, contaminant plumes often display much more extensive zones of overlapping Fe(II) and methane. The extensive overlap could be caused by several abiotic and biotic processes including vertical mixing of byproducts in long-screened monitoring wells, adsorption of Fe(II) onto aquifer solids, or microscale heterogeneity in Fe(III) concentrations. Alternatively, the overlap could be due to simultaneous utilization of terminal electron acceptors. Because biodegradation rates are controlled by TEAPs, evaluating the mechanisms of electron acceptor utilization is critical for improving prediction of contaminant mass losses due to biodegradation. Using BioRedox-MT3DMS, a three-dimensional, multi-species reactive transport code, we simulated the current configurations of a BTEX plume and TEAP zones at a petroleum- contaminated field site in Wisconsin. Simulation results suggest that BTEX mass loss due to biodegradation is greatest under oxygen-reducing conditions, with smaller but similar contributions to mass loss from biodegradation under Fe(III)-reducing, sulfate-reducing, and methanogenic conditions. Results of sensitivity calculations document that BTEX losses due to biodegradation are most sensitive to the age of the plume, while the shape of the BTEX plume is most sensitive to effective porosity and rate constants for biodegradation under Fe(III)-reducing and

  17. Reversible Hydrogen Storage Materials – Structure, Chemistry, and Electronic Structure

    SciTech Connect

    Robertson, Ian M.; Johnson, Duane D.

    2014-06-21

    To understand the processes involved in the uptake and release of hydrogen from candidate light-weight metal hydride storage systems, a combination of materials characterization techniques and first principle calculation methods have been employed. In addition to conventional microstructural characterization in the transmission electron microscope, which provides projected information about the through thickness microstructure, electron tomography methods were employed to determine the three-dimensional spatial distribution of catalyst species for select systems both before and after dehydrogenation. Catalyst species identification as well as compositional analysis of the storage material before and after hydrogen charging and discharging was performed using a combination of energy dispersive spectroscopy, EDS, and electron energy loss spectroscopy, EELS. The characterization effort was coupled with first-principles, electronic-structure and thermodynamic techniques to predict and assess meta-stable and stable phases, reaction pathways, and thermodynamic and kinetic barriers. Systems studied included:NaAlH4, CaH2/CaB6 and Ca(BH4)2, MgH2/MgB2, Ni-Catalyzed Magnesium Hydride, TiH2-Catalyzed Magnesium Hydride, LiBH4, Aluminum-based systems and Aluminum

  18. Proline puckering parameters for collagen structure simulations

    SciTech Connect

    Wu, Di

    2015-03-15

    Collagen is made of triple helices rich in proline residues, and hence is influenced by the conformational motions of prolines. Because the backbone motions of prolines are restricted by the helical structures, the only side chain motion—proline puckering—becomes an influential factor that may affect the stability of collagen structures. In molecular simulations, a proper proline puckering population is desired so to yield valid results of the collagen properties. Here we design the proline puckering parameters in order to yield suitable proline puckering populations as demonstrated in the experimental results. We test these parameters in collagen and the proline dipeptide simulations. Compared with the results of the PDB and the quantum calculations, we propose the proline puckering parameters for the selected collagen model simulations.

  19. Hierarchical Simulation of Hot Composite Structures

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Murthy, P. L. N.; Singhal, S. N.

    1993-01-01

    Computational procedures are described to simulate the thermal and mechanical behavior of high temperature metal matrix composites (HT-MMC) in the following three broad areas: (1) Behavior of HT-MMC's from micromechanics to laminate via Metal Matrix Composite Analyzer (METCAN), (2) tailoring of HT-MMC behavior for optimum specific performance via Metal Matrix Laminate Tailoring (MMLT), and (3) HT-MMC structural response for hot structural components via High Temperature Composite Analyzer (HITCAN). Representative results from each area are presented to illustrate the effectiveness of computational simulation procedures. The sample case results show that METCAN can be used to simulate material behavior such as strength, stress-strain response, and cyclic life in HTMMC's; MMLT can be used to tailor the fabrication process for optimum performance such as that for in-service load carrying capacity of HT-MMC's; and HITCAN can be used to evaluate static fracture and fatigue life of hot pressurized metal matrix composite rings.

  20. Computational Simulation of Composite Structural Fatigue

    NASA Technical Reports Server (NTRS)

    Minnetyan, Levon; Chamis, Christos C. (Technical Monitor)

    2005-01-01

    Progressive damage and fracture of composite structures subjected to monotonically increasing static, tension-tension cyclic, pressurization, and flexural cyclic loading are evaluated via computational simulation. Constituent material properties, stress and strain limits are scaled up to the structure level to evaluate the overall damage and fracture propagation for composites. Damage initiation, growth, accumulation, and propagation to fracture due to monotonically increasing static and cyclic loads are included in the simulations. Results show the number of cycles to failure at different temperatures and the damage progression sequence during different degradation stages. A procedure is outlined for use of computational simulation data in the assessment of damage tolerance, determination of sensitive parameters affecting fracture, and interpretation of results with insight for design decisions.

  1. Proline puckering parameters for collagen structure simulations

    NASA Astrophysics Data System (ADS)

    Wu, Di

    2015-03-01

    Collagen is made of triple helices rich in proline residues, and hence is influenced by the conformational motions of prolines. Because the backbone motions of prolines are restricted by the helical structures, the only side chain motion—proline puckering—becomes an influential factor that may affect the stability of collagen structures. In molecular simulations, a proper proline puckering population is desired so to yield valid results of the collagen properties. Here we design the proline puckering parameters in order to yield suitable proline puckering populations as demonstrated in the experimental results. We test these parameters in collagen and the proline dipeptide simulations. Compared with the results of the PDB and the quantum calculations, we propose the proline puckering parameters for the selected collagen model simulations.

  2. Computational Simulation of Composite Structural Fatigue

    NASA Technical Reports Server (NTRS)

    Minnetyan, Levon

    2004-01-01

    Progressive damage and fracture of composite structures subjected to monotonically increasing static, tension-tension cyclic, pressurization, and flexural cyclic loading are evaluated via computational simulation. Constituent material properties, stress and strain limits are scaled up to the structure level to evaluate the overall damage and fracture propagation for composites. Damage initiation, growth, accumulation, and propagation to fracture due to monotonically increasing static and cyclic loads are included in the simulations. Results show the number of cycles to failure at different temperatures and the damage progression sequence during different degradation stages. A procedure is outlined for use of computational simulation data in the assessment of damage tolerance, determination of sensitive parameters affecting fracture, and interpretation of results with insight for design decisions.

  3. Simulating the formation of cosmic structure.

    PubMed

    Frenk, C S

    2002-06-15

    A timely combination of new theoretical ideas and observational discoveries has brought about significant advances in our understanding of cosmic evolution. Computer simulations have played a key role in these developments by providing the means to interpret astronomical data in the context of physical and cosmological theory. In the current paradigm, our Universe has a flat geometry, is undergoing accelerated expansion and is gravitationally dominated by elementary particles that make up cold dark matter. Within this framework, it is possible to simulate in a computer the emergence of galaxies and other structures from small quantum fluctuations imprinted during an epoch of inflationary expansion shortly after the Big Bang. The simulations must take into account the evolution of the dark matter as well as the gaseous processes involved in the formation of stars and other visible components. Although many unresolved questions remain, a coherent picture for the formation of cosmic structure is now beginning to emerge.

  4. Annular dark field transmission electron microscopy for protein structure determination.

    PubMed

    Koeck, Philip J B

    2016-02-01

    Recently annular dark field (ADF) transmission electron microscopy (TEM) has been advocated as a means of recording images of biological specimens with better signal to noise ratio (SNR) than regular bright field images. I investigate whether and how such images could be used to determine the three-dimensional structure of proteins given that an ADF aperture with a suitable pass-band can be manufactured and used in practice. I develop an approximate theory of ADF-TEM image formation for weak amplitude and phase objects and test this theory using computer simulations. I also test whether these simulated images can be used to calculate a three-dimensional model of the protein using standard software and discuss problems and possible ways to overcome these.

  5. Simulated Performance of the Wisconsin Superconducting Electron Gun

    SciTech Connect

    R.A. Bosch, K.J. Kleman, R.A. Legg

    2012-07-01

    The Wisconsin superconducting electron gun is modeled with multiparticle tracking simulations using the ASTRA and GPT codes. To specify the construction of the emittance-compensation solenoid, we studied the dependence of the output bunch's emittance upon the solenoid's strength and field errors. We also evaluated the dependence of the output bunch's emittance upon the bunch's initial emittance and the size of the laser spot on the photocathode. The results suggest that a 200-pC bunch with an emittance of about one mm-mrad can be produced for a free-electron laser.

  6. Electron fishbone simulations in tokamak equilibria using XHMGC

    NASA Astrophysics Data System (ADS)

    Vlad, G.; Briguglio, S.; Fogaccia, G.; Zonca, F.; Fusco, V.; Wang, X.

    2013-08-01

    This paper discusses the first nonlinear numerical simulation results of fishbone excitation by a magnetically trapped supra-thermal electron population with pressure profile peaked on axis due to, e.g. electron cyclotron resonance heating. The precession resonance underlying the linear instability is clearly identified. Meanwhile, mode saturation is shown to occur because of the secular resonant particle motion, pumping particles out of the radial region where the wave-particle power exchange is initially localized. The mode nonlinear saturation is accompanied by downward frequency chirping, due to phase-locking of the mode with resonant particles, consistent with the ‘mode particle pumping’ mechanism.

  7. Global Kinetic Modeling of Banded Electron Structures in the Plasmasphere

    NASA Technical Reports Server (NTRS)

    Liemohn, M. W.; Khazanov, G. V.

    1997-01-01

    Significant fluxes of 10 eV to 30 keV electrons have been detected in the plasmasphere, appearing as banded structures in energy with broad spatial extents and slowly evolving over several days. It is thought that these populations are decaying plasma sheet electrons injected into the corotating region of near-Earth space. This capture can occur when the convective electric field drops rapidly and the Alfven boundary suddenly outward, trapping the inner edge of the plasma sheet along closed drift paths. Our bounce-averaged kinetic model of superthermal electron transport is able to simulate this capture and the subsequent drift, diffusion, and decay of the plasma cloud. Results of this simulation will be shown and discussed, from the initial injection during the elevated convection to the final loss of the particles. It is thought that not only Coulomb collisions but also wave-particle interactions play a significant role in altering the plasma cloud. Quasilinear diffusion is currently being incorporated into the model and the importance of this mechanism will be examined. Also, the high anisotropy of the trapped population could be unstable and generate plasma waves. These and other processes will be investigated to determine the final fate of the cloud and to quantify where, how, and when the energy of the plasma cloud is deposited. Comparisons with CRRES observations of these events are shown to verify the model and explain the data.

  8. Electronic band structure of defect chalcopyrites

    NASA Astrophysics Data System (ADS)

    Jiang, Xiaoshu; Lambrecht, Walter R. L.

    2001-03-01

    The defect chalcopyrites of chemical composition II-III-VI4 in which II, III and VI mean group-II elements such as Cd or Hg, group-III elements such as Al and Ga and group-VI elements such as S, Se, Te, form an interesting family of semiconductor compounds with potential nonlinear optical applications. They can be thought of as derived from the regular I-III-VI2 chalcopyrites by doubling the formula unit and replacing the group I element, for example, Ag by the group-II element and a vacancy in an ordered manner. The chalcopyrites themselves are derived from II-VI compounds by replacing the group-II by a group I and a group-III element. In this contribution we present electronic band structure calculations of some of these compounds, calculated using the linear muffin-tin orbital method combined with the local density functional approximation. We discuss the relation of the band structures of the corresponding zincblende, chalcopyrite and defect chalcopyrite compounds. In particular, the role of the group I or group II d-band energy will be shown to be important. The trends with chemical substutions and the effects of structural distortions c/a and internal parameters accompanying the chemical distortion will be discussed.

  9. Xyce™ Parallel Electronic Simulator Reference Guide, Version 6.5

    SciTech Connect

    Keiter, Eric R.; Aadithya, Karthik V.; Mei, Ting; Russo, Thomas V.; Schiek, Richard L.; Sholander, Peter E.; Thornquist, Heidi K.; Verley, Jason C.

    2016-06-01

    This document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users’ Guide. The focus of this document is (to the extent possible) exhaustively list device parameters, solver options, parser options, and other usage details of Xyce. This document is not intended to be a tutorial. Users who are new to circuit simulation are better served by the Xyce Users’ Guide. The information herein is subject to change without notice. Copyright © 2002-2016 Sandia Corporation. All rights reserved.

  10. Electron Beam Lifetime in SPEAR3: Measurement and Simulation

    SciTech Connect

    Corbett, J.; Huang, X.; Lee, M.; Lui, P.; Sayyar-Rodsari, B.; /Pavilon Tech., Austin

    2007-12-19

    In this paper we report on electron beam lifetime measurements as a function of scraper position, RF voltage and bunch fill pattern in SPEAR3. We then outline development of an empirical, macroscopic model using the beam-loss rate equation. By identifying the dependence of loss coefficients on accelerator and beam parameters, a numerically-integrating simulator can be constructed to compute beam decay with time. In a companion paper, the simulator is used to train a parametric, non-linear dynamics model for the system [1].

  11. Electronic structures of ytterbocene-imine complexes

    SciTech Connect

    Da Re, R. E.; Kuehl, C. J.; John, K. D.; Morris, D. E.

    2004-01-01

    The electronic structures of complexes of the form [(C{sub 5}Me{sub 5}){sub 2}Yb(L)]{sup +/0} (L = bipyridine, phenanthroline, terpyridine) have been probed using cyclic voltammetry and electronic spectroscopy. Remarkably, the voltammetric data reveal that the imine-based LUMO is stabilized and the redox-active metal f orbital is destabilized by ca. 1 V each upon formation of the ytterbocene-imine adduct, which is presumably responsible for the [(f){sup 13}({pi}*(L)){sup 1}] charge-transfer ground state characteristic of these complexes. The ca. 0.8 V separation between ligand-based oxidation and metal-based reduction waves for each ytterbocene adduct correlates with the energy of its optically promoted {pi}*(L)-f(Yb) charge transfer (LMCT) transition (ca. 5000 cm{sup -1}). The coupling between this LMCT excited state and the {sup 2}F{sub 7/2} ground and {sup 2}F{sub 5/2} excited states of Yb(III) leads to unusually large intensities ({var_epsilon} {approx} 1000) for the metal-localized f-f bands, which will be discussed in the context of an intensity borrowing mechanism that invokes exchange between the ligand-based {sup 2}S and metal-based {sup 2}F spin states.

  12. Electron Liquids in Semiconductor Quantum Structures

    SciTech Connect

    Aron Pinczuk

    2009-05-25

    The groups led by Stormer and Pinczuk have focused this project on goals that seek the elucidation of novel many-particle effects that emerge in two-dimensional electron systems (2DES) as the result from fundamental quantum interactions. This experimental research is conducted under extreme conditions of temperature and magnetic field. From the materials point of view, the ultra-high mobility systems in GaAs/AlGaAs quantum structures continue to be at the forefront of this research. The newcomer materials are based on graphene, a single atomic layer of graphite. The graphene research is attracting enormous attention from many communities involved in condensed matter research. The investigated many-particle phenomena include the integer and fractional quantum Hall effect, composite fermions, and Dirac fermions, and a diverse group of electron solid and liquid crystal phases. The Stormer group performed magneto-transport experiments and far-infrared spectroscopy, while the Pinczuk group explores manifestations of such phases in optical spectra.

  13. Electronic structures of reconstructed zigzag silicene nanoribbons

    SciTech Connect

    Ding, Yi E-mail: wangyanli-04@tsinghua.org.cn; Wang, Yanli E-mail: wangyanli-04@tsinghua.org.cn

    2014-02-24

    Edge states and magnetism are crucial for spintronic applications of nanoribbons. Here, using first-principles calculations, we explore structural stabilities and electronic properties of zigzag silicene nanoribbons (ZSiNRs) with Klein and pentagon-heptagon reconstructions. Comparing to unreconstructed zigzag edges, deformed bare pentagon-heptagon ones are favored under H-poor conditions, while H-rich surroundings stabilize di-hydrogenated Klein edges. These Klein edges have analogous magnetism to zigzag ones, which also possess the electric-field-induced half-metallicity of nanoribbons. Moreover, diverse magnetic states can be achieved by asymmetric Klein and zigzag edges into ZSiNRs, which could be transformed from antiferromagnetic-semiconductors to bipolar spin-gapless-semiconductors and ferromagnetic-metals depending on edge hydrogenations.

  14. Multilevel domain decomposition for electronic structure calculations

    SciTech Connect

    Barrault, M. . E-mail: maxime.barrault@edf.fr; Cances, E. . E-mail: cances@cermics.enpc.fr; Hager, W.W. . E-mail: hager@math.ufl.edu; Le Bris, C. . E-mail: lebris@cermics.enpc.fr

    2007-03-01

    We introduce a new multilevel domain decomposition method (MDD) for electronic structure calculations within semi-empirical and density functional theory (DFT) frameworks. This method iterates between local fine solvers and global coarse solvers, in the spirit of domain decomposition methods. Using this approach, calculations have been successfully performed on several linear polymer chains containing up to 40,000 atoms and 200,000 atomic orbitals. Both the computational cost and the memory requirement scale linearly with the number of atoms. Additional speed-up can easily be obtained by parallelization. We show that this domain decomposition method outperforms the density matrix minimization (DMM) method for poor initial guesses. Our method provides an efficient preconditioner for DMM and other linear scaling methods, variational in nature, such as the orbital minimization (OM) procedure.

  15. Structure, Stability and Electronic Properties of Nanodiamonds

    NASA Astrophysics Data System (ADS)

    Galli, Giulia

    Diamond nanoparticles, or nanodiamonds, have the most disparate origins. They are found in crude oil at concentrations up to thousands of parts per million, in meteorites, interstellar dust, and protoplanetary nebulae, as well as in certain sediment layers on Earth. They can also be produced in the laboratory by chemical vapor deposition or by detonating high explosive materials. Here we summarize what is known about nanodiamond sources; we then describe the atomic and electronic structure, and stability of diamond nanoparticles, highlighting the role of theory and computations in understanding and predicting their properties. Possible technological applications of thin films composed of nanodiamonds, ranging from micro-resonators to substrates for drug delivery, are briefly discussed.

  16. Site-specific ionisation edge fine-structure of Rutile in the electron microscope.

    PubMed

    Hetaba, Walid; Löffler, Stefan; Willinger, Marc-Georg; Schuster, Manfred Erwin; Schlögl, Robert; Schattschneider, Peter

    2014-08-01

    Combined Bloch-wave and density functional theory simulations are performed to investigate the effects of different channelling conditions on the fine-structure of electron energy-loss spectra. The simulated spectra compare well with experiments. Furthermore, we demonstrate that using this technique, the site-specific investigation of atomic orbitals is possible. This opens new possibilities for chemical analyses.

  17. Note: Simulation and test of a strip source electron gun

    SciTech Connect

    Iqbal, Munawar; Islam, G. U.; Misbah, I.; Iqbal, O.; Zhou, Z.

    2014-06-15

    We present simulation and test of an indirectly heated strip source electron beam gun assembly using Stanford Linear Accelerator Center (SLAC) electron beam trajectory program. The beam is now sharply focused with 3.04 mm diameter in the post anode region at 15.9 mm. The measured emission current and emission density were 1.12 A and 1.15 A/cm{sup 2}, respectively, that corresponds to power density of 11.5 kW/cm{sup 2}, at 10 kV acceleration potential. The simulated results were compared with then and now experiments and found in agreement. The gun is without any biasing, electrostatic and magnetic fields; hence simple and inexpensive. Moreover, it is now more powerful and is useful for accelerators technology due to high emission and low emittance parameters.

  18. Simulating electron energy loss spectroscopy with the MNPBEM toolbox

    NASA Astrophysics Data System (ADS)

    Hohenester, Ulrich

    2014-03-01

    Within the MNPBEM toolbox, we show how to simulate electron energy loss spectroscopy (EELS) of plasmonic nanoparticles using a boundary element method approach. The methodology underlying our approach closely follows the concepts developed by García de Abajo and coworkers (Garcia de Abajo, 2010). We introduce two classes eelsret and eelsstat that allow in combination with our recently developed MNPBEM toolbox for a simple, robust, and efficient computation of EEL spectra and maps. The classes are accompanied by a number of demo programs for EELS simulation of metallic nanospheres, nanodisks, and nanotriangles, and for electron trajectories passing by or penetrating through the metallic nanoparticles. We also discuss how to compute electric fields induced by the electron beam and cathodoluminescence. Catalogue identifier: AEKJ_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEKJ_v2_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 38886 No. of bytes in distributed program, including test data, etc.: 1222650 Distribution format: tar.gz Programming language: Matlab 7.11.0 (R2010b). Computer: Any which supports Matlab 7.11.0 (R2010b). Operating system: Any which supports Matlab 7.11.0 (R2010b). RAM:≥1 GB Classification: 18. Catalogue identifier of previous version: AEKJ_v1_0 Journal reference of previous version: Comput. Phys. Comm. 183 (2012) 370 External routines: MESH2D available at www.mathworks.com Does the new version supersede the previous version?: Yes Nature of problem: Simulation of electron energy loss spectroscopy (EELS) for plasmonic nanoparticles. Solution method: Boundary element method using electromagnetic potentials. Reasons for new version: The new version of the toolbox includes two additional classes for the simulation of electron energy

  19. Simulated E-Bomb Effects on Electronically Equipped Targets

    DTIC Science & Technology

    2009-09-01

    SUBTITLE Simulated E-Bomb Effects on Electronically Equipped Targets 6. AUTHOR( S ) Enes Yurtoğlu 5. FUNDING NUMBERS 7. PERFORMING ORGANIZATION NAME( S ...NAME( S ) AND ADDRESS(ES) N/A 10. SPONSORING/MONITORING AGENCY REPORT NUMBER 11. SUPPLEMENTARY NOTES The views expressed in this thesis are...of weapons are technically feasible and economical to build in comparison to 2 established weapons of mass destruction . Such weapons can employ a

  20. Electron transport in magnetrons by a posteriori Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Costin, C.; Minea, T. M.; Popa, G.

    2014-02-01

    Electron transport across magnetic barriers is crucial in all magnetized plasmas. It governs not only the plasma parameters in the volume, but also the fluxes of charged particles towards the electrodes and walls. It is particularly important in high-power impulse magnetron sputtering (HiPIMS) reactors, influencing the quality of the deposited thin films, since this type of discharge is characterized by an increased ionization fraction of the sputtered material. Transport coefficients of electron clouds released both from the cathode and from several locations in the discharge volume are calculated for a HiPIMS discharge with pre-ionization operated in argon at 0.67 Pa and for very short pulses (few µs) using the a posteriori Monte Carlo simulation technique. For this type of discharge electron transport is characterized by strong temporal and spatial dependence. Both drift velocity and diffusion coefficient depend on the releasing position of the electron cloud. They exhibit minimum values at the centre of the race-track for the secondary electrons released from the cathode. The diffusion coefficient of the same electrons increases from 2 to 4 times when the cathode voltage is doubled, in the first 1.5 µs of the pulse. These parameters are discussed with respect to empirical Bohm diffusion.

  1. Stochastic Simulation Tool for Aerospace Structural Analysis

    NASA Technical Reports Server (NTRS)

    Knight, Norman F.; Moore, David F.

    2006-01-01

    Stochastic simulation refers to incorporating the effects of design tolerances and uncertainties into the design analysis model and then determining their influence on the design. A high-level evaluation of one such stochastic simulation tool, the MSC.Robust Design tool by MSC.Software Corporation, has been conducted. This stochastic simulation tool provides structural analysts with a tool to interrogate their structural design based on their mathematical description of the design problem using finite element analysis methods. This tool leverages the analyst's prior investment in finite element model development of a particular design. The original finite element model is treated as the baseline structural analysis model for the stochastic simulations that are to be performed. A Monte Carlo approach is used by MSC.Robust Design to determine the effects of scatter in design input variables on response output parameters. The tool was not designed to provide a probabilistic assessment, but to assist engineers in understanding cause and effect. It is driven by a graphical-user interface and retains the engineer-in-the-loop strategy for design evaluation and improvement. The application problem for the evaluation is chosen to be a two-dimensional shell finite element model of a Space Shuttle wing leading-edge panel under re-entry aerodynamic loading. MSC.Robust Design adds value to the analysis effort by rapidly being able to identify design input variables whose variability causes the most influence in response output parameters.

  2. Simulations of space charge neutralization in a magnetized electron cooler

    NASA Astrophysics Data System (ADS)

    Bruhwiler, David; Gerity, James; Hall, Christopher; McIntyre, Peter; Park, Chong Shik; Moens, Vince; Stancari, Giulio

    2016-10-01

    Magnetized electron cooling at relativistic energies and Ampere scale current is essential to achieve the proposed ion luminosities in a future electron-ion collider (EIC). Neutralization of the space charge in such a cooler can significantly increase the magnetized dynamic friction and, hence, the cooling rate. The Warp framework is being used to simulate magnetized electron beam dynamics during and after the build up of neutralizing ions, via ionization of residual gas in the cooler. The design follows previous experiments at Fermilab as a verification case. We also discuss the relevance to EIC designs. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Award Number DE-SC0015212.

  3. Modelling and simulation of beam formation in electron guns

    NASA Astrophysics Data System (ADS)

    Sabchevski, S.; Mladenov, G.; Titov, A.; Barbarich, I.

    1996-02-01

    This paper describes a new PC version of the software package GUN-EBT for computer simulation of beam formation in rotationally symmetric electron guns with thermionic cathodes. It is based on a self-consistent physical model which takes into account the beam space charge and the initial velocities effects. The theoretical framework used for both the formulation of the model and for the interpretation of the results of numerical experiments is the formalism of the charged particle dynamics in phase space. This enables not only a trajectory analysis (ray tracing) but also a phase-space analysis of beams to be performed. The package can be used as an effective tool for computer aided design and optimization of electron guns in various electron-optical systems. The operation of the package is illustrated with a typical example.

  4. Structure and design of the electron lens for RHIC

    SciTech Connect

    Pikin, A.; Fischer, W.; Alessi, J.; Anerella, M.; Beebe, E. Gassner, D.; Gu, X.; Gupta, R.; Hock, J.; Jain, A.; Lambiase, R.; Luo, Y.; Montag, C.; Okamura, M.; Tan, Y.; Tuozzolo, J.; Thieberger, P.; Zhang, W.

    2011-03-28

    Two electron lenses for a head-on beam-beam compensation are being planned for RHIC; one for each circulating proton beam. The transverse profile of the electron beam will be Gaussian up to a maximum radius of r{sub e} = 3{sigma}. Simulations and design of the electron gun with Gaussian radial emission current density profile and of the electron collector are presented. Ions of the residual gas generated in the interaction region by electron and proton beams will be removed by an axial gradient of the electric field towards the electron collector. A method for the optical observation of the transverse profile of the electron beam is described.

  5. Multiscale approach to the electronic structure of doped semiconductor surfaces

    NASA Astrophysics Data System (ADS)

    Sinai, Ofer; Hofmann, Oliver T.; Rinke, Patrick; Scheffler, Matthias; Heimel, Georg; Kronik, Leeor

    2015-02-01

    The inclusion of the global effects of semiconductor doping poses a unique challenge for first-principles simulations, because the typically low concentration of dopants renders an explicit treatment intractable. Furthermore, the width of the space-charge region (SCR) at charged surfaces often exceeds realistic supercell dimensions. Here, we present a multiscale technique that fully addresses these difficulties. It is based on the introduction of a charged sheet, mimicking the SCR-related field, along with free charge which mimics the bulk charge reservoir, such that the system is neutral overall. These augment a slab comprising "pseudoatoms" possessing a fractional nuclear charge matching the bulk doping concentration. Self-consistency is reached by imposing charge conservation and Fermi level equilibration between the bulk, treated semiclassically, and the electronic states of the slab, which are treated quantum-mechanically. The method, called CREST—the charge-reservoir electrostatic sheet technique—can be used with standard electronic structure codes. We validate CREST using a simple tight-binding model, which allows for comparison of its results with calculations encompassing the full SCR explicitly. Specifically, we show that CREST successfully predicts scenarios spanning the range from no to full Fermi level pinning. We then employ it with density functional theory, obtaining insight into the doping dependence of the electronic structures of the metallic "clean-cleaved" Si(111) surface and its semiconducting (2 ×1 ) reconstructions.

  6. Interfacial Ga-As suboxide: Structural and electronic properties

    SciTech Connect

    Colleoni, Davide Pasquarello, Alfredo

    2015-07-20

    The structural and electronic properties of Ga-As suboxide representative of the transition region at the GaAs/oxide interface are studied through density functional calculations. Two amorphous models generated by quenches from the melt are taken under consideration. The absence of As–O bonds indicates that the structure is a mixture of GaAs and Ga-oxide, in accordance with photoemission experiments. The band edges of the models are found to be closely aligned to those of GaAs. The simulation of charging and discharging processes leads to the identification of an As-related defect with an energy level at ∼0.7 eV above the GaAs valence band maximum, in good agreement with the experimental density of interface states.

  7. Classical molecular dynamics simulation of electronically non-adiabatic processes.

    PubMed

    Miller, William H; Cotton, Stephen J

    2016-12-22

    Both classical and quantum mechanics (as well as hybrids thereof, i.e., semiclassical approaches) find widespread use in simulating dynamical processes in molecular systems. For large chemical systems, however, which involve potential energy surfaces (PES) of general/arbitrary form, it is usually the case that only classical molecular dynamics (MD) approaches are feasible, and their use is thus ubiquitous nowadays, at least for chemical processes involving dynamics on a single PES (i.e., within a single Born-Oppenheimer electronic state). This paper reviews recent developments in an approach which extends standard classical MD methods to the treatment of electronically non-adiabatic processes, i.e., those that involve transitions between different electronic states. The approach treats nuclear and electronic degrees of freedom (DOF) equivalently (i.e., by classical mechanics, thereby retaining the simplicity of standard MD), and provides "quantization" of the electronic states through a symmetrical quasi-classical (SQC) windowing model. The approach is seen to be capable of treating extreme regimes of strong and weak coupling between the electronic states, as well as accurately describing coherence effects in the electronic DOF (including the de-coherence of such effects caused by coupling to the nuclear DOF). A survey of recent applications is presented to illustrate the performance of the approach. Also described is a newly developed variation on the original SQC model (found universally superior to the original) and a general extension of the SQC model to obtain the full electronic density matrix (at no additional cost/complexity).

  8. Xyce Parallel Electronic Simulator : users' guide, version 4.1.

    SciTech Connect

    Mei, Ting; Rankin, Eric Lamont; Thornquist, Heidi K.; Santarelli, Keith R.; Fixel, Deborah A.; Coffey, Todd Stirling; Russo, Thomas V.; Schiek, Richard Louis; Keiter, Eric Richard; Pawlowski, Roger Patrick

    2009-02-01

    This manual describes the use of the Xyce Parallel Electronic Simulator. Xyce has been designed as a SPICE-compatible, high-performance analog circuit simulator, and has been written to support the simulation needs of the Sandia National Laboratories electrical designers. This development has focused on improving capability over the current state-of-the-art in the following areas: (1) Capability to solve extremely large circuit problems by supporting large-scale parallel computing platforms (up to thousands of processors). Note that this includes support for most popular parallel and serial computers. (2) Improved performance for all numerical kernels (e.g., time integrator, nonlinear and linear solvers) through state-of-the-art algorithms and novel techniques. (3) Device models which are specifically tailored to meet Sandia's needs, including some radiation-aware devices (for Sandia users only). (4) Object-oriented code design and implementation using modern coding practices that ensure that the Xyce Parallel Electronic Simulator will be maintainable and extensible far into the future. Xyce is a parallel code in the most general sense of the phrase - a message passing parallel implementation - which allows it to run efficiently on the widest possible number of computing platforms. These include serial, shared-memory and distributed-memory parallel as well as heterogeneous platforms. Careful attention has been paid to the specific nature of circuit-simulation problems to ensure that optimal parallel efficiency is achieved as the number of processors grows. The development of Xyce provides a platform for computational research and development aimed specifically at the needs of the Laboratory. With Xyce, Sandia has an 'in-house' capability with which both new electrical (e.g., device model development) and algorithmic (e.g., faster time-integration methods, parallel solver algorithms) research and development can be performed. As a result, Xyce is a unique electrical

  9. Xyce parallel electronic simulator : users' guide. Version 5.1.

    SciTech Connect

    Mei, Ting; Rankin, Eric Lamont; Thornquist, Heidi K.; Santarelli, Keith R.; Fixel, Deborah A.; Coffey, Todd Stirling; Russo, Thomas V.; Schiek, Richard Louis; Keiter, Eric Richard; Pawlowski, Roger Patrick

    2009-11-01

    This manual describes the use of the Xyce Parallel Electronic Simulator. Xyce has been designed as a SPICE-compatible, high-performance analog circuit simulator, and has been written to support the simulation needs of the Sandia National Laboratories electrical designers. This development has focused on improving capability over the current state-of-the-art in the following areas: (1) Capability to solve extremely large circuit problems by supporting large-scale parallel computing platforms (up to thousands of processors). Note that this includes support for most popular parallel and serial computers. (2) Improved performance for all numerical kernels (e.g., time integrator, nonlinear and linear solvers) through state-of-the-art algorithms and novel techniques. (3) Device models which are specifically tailored to meet Sandia's needs, including some radiation-aware devices (for Sandia users only). (4) Object-oriented code design and implementation using modern coding practices that ensure that the Xyce Parallel Electronic Simulator will be maintainable and extensible far into the future. Xyce is a parallel code in the most general sense of the phrase - a message passing parallel implementation - which allows it to run efficiently on the widest possible number of computing platforms. These include serial, shared-memory and distributed-memory parallel as well as heterogeneous platforms. Careful attention has been paid to the specific nature of circuit-simulation problems to ensure that optimal parallel efficiency is achieved as the number of processors grows. The development of Xyce provides a platform for computational research and development aimed specifically at the needs of the Laboratory. With Xyce, Sandia has an 'in-house' capability with which both new electrical (e.g., device model development) and algorithmic (e.g., faster time-integration methods, parallel solver algorithms) research and development can be performed. As a result, Xyce is a unique electrical

  10. Probabilistic simulation of uncertainties in thermal structures

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.; Shiao, Michael

    1990-01-01

    Development of probabilistic structural analysis methods for hot structures is a major activity at Lewis Research Center. It consists of five program elements: (1) probabilistic loads; (2) probabilistic finite element analysis; (3) probabilistic material behavior; (4) assessment of reliability and risk; and (5) probabilistic structural performance evaluation. Recent progress includes: (1) quantification of the effects of uncertainties for several variables on high pressure fuel turbopump (HPFT) blade temperature, pressure, and torque of the Space Shuttle Main Engine (SSME); (2) the evaluation of the cumulative distribution function for various structural response variables based on assumed uncertainties in primitive structural variables; (3) evaluation of the failure probability; (4) reliability and risk-cost assessment, and (5) an outline of an emerging approach for eventual hot structures certification. Collectively, the results demonstrate that the structural durability/reliability of hot structural components can be effectively evaluated in a formal probabilistic framework. In addition, the approach can be readily extended to computationally simulate certification of hot structures for aerospace environments.

  11. Hybrid simulations of magnetic reconnection with kinetic ions and fluid electron pressure anisotropy

    DOE PAGES

    Le, A.; Daughton, W.; Karimabadi, H.; ...

    2016-03-16

    We present the first hybrid simulations with kinetic ions and recently developed equations of state for the electron fluid appropriate for reconnection with a guide field. The equations of state account for the main anisotropy of the electron pressure tensor.Magnetic reconnection is studied in two systems, an initially force-free current sheet and a Harris sheet. The hybrid model with the equations of state is compared to two other models, hybrid simulations with isothermal electrons and fully kinetic simulations. Including the anisotropicequations of state in the hybrid model provides a better match to the fully kinetic model. In agreement with fullymore » kinetic results, the main feature captured is the formation of an electron current sheet that extends several ion inertial lengths. This electron current sheet modifies the Hall magnetic field structure near the X-line, and it is not observed in the standard hybrid model with isotropic electrons. The saturated reconnection rate in this regime nevertheless remains similar in all three models. Here, implications for global modeling are discussed.« less

  12. Hybrid simulations of magnetic reconnection with kinetic ions and fluid electron pressure anisotropy

    SciTech Connect

    Le, A.; Daughton, W.; Karimabadi, H.; Egedal, J.

    2016-03-16

    We present the first hybrid simulations with kinetic ions and recently developed equations of state for the electron fluid appropriate for reconnection with a guide field. The equations of state account for the main anisotropy of the electron pressure tensor.Magnetic reconnection is studied in two systems, an initially force-free current sheet and a Harris sheet. The hybrid model with the equations of state is compared to two other models, hybrid simulations with isothermal electrons and fully kinetic simulations. Including the anisotropicequations of state in the hybrid model provides a better match to the fully kinetic model. In agreement with fully kinetic results, the main feature captured is the formation of an electron current sheet that extends several ion inertial lengths. This electron current sheet modifies the Hall magnetic field structure near the X-line, and it is not observed in the standard hybrid model with isotropic electrons. The saturated reconnection rate in this regime nevertheless remains similar in all three models. Here, implications for global modeling are discussed.

  13. Hybrid simulations of magnetic reconnection with kinetic ions and fluid electron pressure anisotropy

    NASA Astrophysics Data System (ADS)

    Le, A.; Daughton, W.; Karimabadi, H.; Egedal, J.

    2016-03-01

    We present the first hybrid simulations with kinetic ions and recently developed equations of state for the electron fluid appropriate for reconnection with a guide field. The equations of state account for the main anisotropy of the electron pressure tensor. Magnetic reconnection is studied in two systems, an initially force-free current sheet and a Harris sheet. The hybrid model with the equations of state is compared to two other models, hybrid simulations with isothermal electrons and fully kinetic simulations. Including the anisotropic equations of state in the hybrid model provides a better match to the fully kinetic model. In agreement with fully kinetic results, the main feature captured is the formation of an electron current sheet that extends several ion inertial lengths. This electron current sheet modifies the Hall magnetic field structure near the X-line, and it is not observed in the standard hybrid model with isotropic electrons. The saturated reconnection rate in this regime nevertheless remains similar in all three models. Implications for global modeling are discussed.

  14. Test report: Vibration testing of the electron/proton spectrometer structural test unit

    NASA Technical Reports Server (NTRS)

    Vincent, D. L.

    1972-01-01

    The structural test unit of the electron-proton spectrometer was tested to a random vibration spectra and to a sinusoidal resonant search to comply with the requirements of a verification plan for the spectrometer. The test item consisted of mass simulated electronic and printed circuit boards mounted in a flight type electronic housing. The arrangement, center of gravity, and weight were as proposed for flight units.

  15. Experimental and theoretical electronic structure of quinacridone

    NASA Astrophysics Data System (ADS)

    Lüftner, Daniel; Refaely-Abramson, Sivan; Pachler, Michael; Resel, Roland; Ramsey, Michael G.; Kronik, Leeor; Puschnig, Peter

    2014-08-01

    The energy positions of frontier orbitals in organic electronic materials are often studied experimentally by (inverse) photoemission spectroscopy and theoretically within density functional theory. However, standard exchange-correlation functionals often result in too small fundamental gaps, may lead to wrong orbital energy ordering, and do not capture polarization-induced gap renormalization. Here we examine these issues and a strategy for overcoming them by studying the gas phase and bulk electronic structure of the organic molecule quinacridone (5Q), a promising material with many interesting properties for organic devices. Experimentally we perform angle-resolved photoemission spectroscopy (ARUPS) on thin films of the crystalline β phase of 5Q. Theoretically we employ an optimally tuned range-separated hybrid functional (OT-RSH) within density functional theory. For the gas phase molecule, our OT-RSH result for the ionization potential (IP) represents a substantial improvement over the semilocal PBE and the PBE0 hybrid functional results, producing an IP in quantitative agreement with experiment. For the bulk crystal we take into account the correct screening in the bulk, using the recently developed optimally tuned screened range-separated hybrid (OT-SRSH) approach, while retaining the optimally tuned parameters for the range separation and the short-range Fock exchange. This leads to a band gap narrowing due to polarization effects and results in a valence band spectrum in excellent agreement with experimental ARUPS data, with respect to both peak positions and heights. Finally, full-frequency G0W0 results based on a hybrid functional starting point are shown to agree with the OT-SRSH approach, improving substantially on the PBE-starting point.

  16. RESCU: A real space electronic structure method

    NASA Astrophysics Data System (ADS)

    Michaud-Rioux, Vincent; Zhang, Lei; Guo, Hong

    2016-02-01

    In this work we present RESCU, a powerful MATLAB-based Kohn-Sham density functional theory (KS-DFT) solver. We demonstrate that RESCU can compute the electronic structure properties of systems comprising many thousands of atoms using modest computer resources, e.g. 16 to 256 cores. Its computational efficiency is achieved from exploiting four routes. First, we use numerical atomic orbital (NAO) techniques to efficiently generate a good quality initial subspace which is crucially required by Chebyshev filtering methods. Second, we exploit the fact that only a subspace spanning the occupied Kohn-Sham states is required, and solving accurately the KS equation using eigensolvers can generally be avoided. Third, by judiciously analyzing and optimizing various parts of the procedure in RESCU, we delay the O (N3) scaling to large N, and our tests show that RESCU scales consistently as O (N2.3) from a few hundred atoms to more than 5000 atoms when using a real space grid discretization. The scaling is better or comparable in a NAO basis up to the 14,000 atoms level. Fourth, we exploit various numerical algorithms and, in particular, we introduce a partial Rayleigh-Ritz algorithm to achieve efficiency gains for systems comprising more than 10,000 electrons. We demonstrate the power of RESCU in solving KS-DFT problems using many examples running on 16, 64 and/or 256 cores: a 5832 Si atoms supercell; a 8788 Al atoms supercell; a 5324 Cu atoms supercell and a small DNA molecule submerged in 1713 water molecules for a total 5399 atoms. The KS-DFT is entirely converged in a few hours in all cases. Our results suggest that the RESCU method has reached a milestone of solving thousands of atoms by KS-DFT on a modest computer cluster.

  17. Geometry, mechanics, and electronics of singular structures and wrinkles in graphene.

    PubMed

    Pereira, Vitor M; Castro Neto, A H; Liang, H Y; Mahadevan, L

    2010-10-08

    As the thinnest atomic membrane, graphene presents an opportunity to combine geometry, elasticity, and electronics at the limits of their validity. We describe the transport and electronic structure in the neighborhood of conical singularities, the elementary excitations of the ubiquitous wrinkled and crumpled graphene. We use a combination of atomistic mechanical simulations, analytical geometry, and transport calculations in curved graphene, and exact diagonalization of the electronic spectrum to calculate the effects of geometry on electronic structure, transport, and mobility in suspended samples, and how the geometry-generated pseudomagnetic and pseudoelectric fields might disrupt Landau quantization.

  18. Xyce Parallel Electronic Simulator : users' guide, version 2.0.

    SciTech Connect

    Hoekstra, Robert John; Waters, Lon J.; Rankin, Eric Lamont; Fixel, Deborah A.; Russo, Thomas V.; Keiter, Eric Richard; Hutchinson, Scott Alan; Pawlowski, Roger Patrick; Wix, Steven D.

    2004-06-01

    This manual describes the use of the Xyce Parallel Electronic Simulator. Xyce has been designed as a SPICE-compatible, high-performance analog circuit simulator capable of simulating electrical circuits at a variety of abstraction levels. Primarily, Xyce has been written to support the simulation needs of the Sandia National Laboratories electrical designers. This development has focused on improving capability the current state-of-the-art in the following areas: {sm_bullet} Capability to solve extremely large circuit problems by supporting large-scale parallel computing platforms (up to thousands of processors). Note that this includes support for most popular parallel and serial computers. {sm_bullet} Improved performance for all numerical kernels (e.g., time integrator, nonlinear and linear solvers) through state-of-the-art algorithms and novel techniques. {sm_bullet} Device models which are specifically tailored to meet Sandia's needs, including many radiation-aware devices. {sm_bullet} A client-server or multi-tiered operating model wherein the numerical kernel can operate independently of the graphical user interface (GUI). {sm_bullet} Object-oriented code design and implementation using modern coding practices that ensure that the Xyce Parallel Electronic Simulator will be maintainable and extensible far into the future. Xyce is a parallel code in the most general sense of the phrase - a message passing of computing platforms. These include serial, shared-memory and distributed-memory parallel implementation - which allows it to run efficiently on the widest possible number parallel as well as heterogeneous platforms. Careful attention has been paid to the specific nature of circuit-simulation problems to ensure that optimal parallel efficiency is achieved as the number of processors grows. One feature required by designers is the ability to add device models, many specific to the needs of Sandia, to the code. To this end, the device package in the Xyce

  19. Dynamic Deployment Simulations of Inflatable Space Structures

    NASA Technical Reports Server (NTRS)

    Wang, John T.

    2005-01-01

    The feasibility of using Control Volume (CV) method and the Arbitrary Lagrangian Eulerian (ALE) method in LSDYNA to simulate the dynamic deployment of inflatable space structures is investigated. The CV and ALE methods were used to predict the inflation deployments of three folded tube configurations. The CV method was found to be a simple and computationally efficient method that may be adequate for modeling slow inflation deployment sine the inertia of the inflation gas can be neglected. The ALE method was found to be very computationally intensive since it involves the solving of three conservative equations of fluid as well as dealing with complex fluid structure interactions.

  20. Toward the Accurate Simulation of Two-Dimensional Electronic Spectra

    NASA Astrophysics Data System (ADS)

    Giussani, Angelo; Nenov, Artur; Segarra-Martí, Javier; Jaiswal, Vishal K.; Rivalta, Ivan; Dumont, Elise; Mukamel, Shaul; Garavelli, Marco

    2015-06-01

    Two-dimensional pump-probe electronic spectroscopy is a powerful technique able to provide both high spectral and temporal resolution, allowing the analysis of ultrafast complex reactions occurring via complementary pathways by the identification of decay-specific fingerprints. [1-2] The understanding of the origin of the experimentally recorded signals in a two-dimensional electronic spectrum requires the characterization of the electronic states involved in the electronic transitions photoinduced by the pump/probe pulses in the experiment. Such a goal constitutes a considerable computational challenge, since up to 100 states need to be described, for which state-of-the-art methods as RASSCF and RASPT2 have to be wisely employed. [3] With the present contribution, the main features and potentialities of two-dimensional electronic spectroscopy are presented, together with the machinery in continuous development in our groups in order to compute two-dimensional electronic spectra. The results obtained using different level of theory and simulations are shown, bringing as examples the computed two-dimensional electronic spectra for some specific cases studied. [2-4] [1] Rivalta I, Nenov A, Cerullo G, Mukamel S, Garavelli M, Int. J. Quantum Chem., 2014, 114, 85 [2] Nenov A, Segarra-Martí J, Giussani A, Conti I, Rivalta I, Dumont E, Jaiswal V K, Altavilla S, Mukamel S, Garavelli M, Faraday Discuss. 2015, DOI: 10.1039/C4FD00175C [3] Nenov A, Giussani A, Segarra-Martí J, Jaiswal V K, Rivalta I, Cerullo G, Mukamel S, Garavelli M, J. Chem. Phys. submitted [4] Nenov A, Giussani A, Fingerhut B P, Rivalta I, Dumont E, Mukamel S, Garavelli M, Phys. Chem. Chem. Phys. Submitted [5] Krebs N, Pugliesi I, Hauer J, Riedle E, New J. Phys., 2013,15, 08501

  1. Vlasov Simulation of Electrostatic Solitary Structures in Multi-Component Plasmas

    NASA Technical Reports Server (NTRS)

    Umeda, Takayuki; Ashour-Abdalla, Maha; Pickett, Jolene S.; Goldstein, Melvyn L.

    2012-01-01

    Electrostatic solitary structures have been observed in the Earth's magnetosheath by the Cluster spacecraft. Recent theoretical work has suggested that these solitary structures are modeled by electron acoustic solitary waves existing in a four-component plasma system consisting of core electrons, two counter-streaming electron beams, and one species of background ions. In this paper, the excitation of electron acoustic waves and the formation of solitary structures are studied by means of a one-dimensional electrostatic Vlasov simulation. The present result first shows that either electron acoustic solitary waves with negative potential or electron phase-space holes with positive potential are excited in four-component plasma systems. However, these electrostatic solitary structures have longer duration times and higher wave amplitudes than the solitary structures observed in the magnetosheath. The result indicates that a high-speed and small free energy source may be needed as a fifth component. An additional simulation of a five-component plasma consisting of a stable four-component plasma and a weak electron beam shows the generation of small and fast electron phase-space holes by the bump-on-tail instability. The physical properties of the small and fast electron phase-space holes are very similar to those obtained by the previous theoretical analysis. The amplitude and duration time of solitary structures in the simulation are also in agreement with the Cluster observation.

  2. Auroral Electrons Trapped and Lost: A Vlasov Simulation Study

    NASA Astrophysics Data System (ADS)

    Gunell, H.; Andersson, L.; De Keyser, J. M.; Mann, I.

    2014-12-01

    In the upward current region of the aurora, about two thirds of the total voltage between the auroral ionosphere and the equatorial magnetosphere can be concentrated in a stationary double layer at an altitude of about one earth radius, as Vlasov simulations of the plasma on a magnetic field line have shown (Gunell, et al., Ann. Geophys., 31, 1227-1240, 2013). We perform numerical experiments, changing the total voltage between the ionosphere and the equatorial magnetosphere during the course of the simulation. In the initial state, the total acceleration voltage is 3 kV and there is a double layer approximately 5000 km above the ionospheric end of the system. When the voltage is increased, electrons are trapped between the double layer and the magnetic mirror in a region of velocity space that initially was empty. When the voltage is decreased to its initial value these trapped electrons are released upwards. If the voltage is lowered first and then raised back to where it started, the newly trapped electrons remain trapped. As a consequence of the difference between the two cases, the electron pitch angle distribution, below the double layer, carries information about the recent history of the acceleration voltage. In both cases, most of the change in voltage, ΔV, is assumed by the double layer, in agreement with a study of Cluster data that could confine most of ΔV to altitudes below the spacecraft (Forsyth et al., JGR, 117, A12203, 2012). Hysteresis effects in the double layer position are seen in connection with the electron trapping. This work was supported by the Belgian Science Policy Office through the Solar-Terrestrial Centre of Excellence and by PRODEX/Cluster contract 13127/98/NL/VJ(IC)-PEA 90316.

  3. Kinetic Simulations of Electron Plasma Waves: trapped electron filamentation and sideband instabilities

    NASA Astrophysics Data System (ADS)

    Brunner, Stephan; Berger, R. L.; Banks, J. W.; Cohen, B. I.; Chapman, T.; Hittinger, J. A. F.; Rozmus, W.; Strozzi, D. J.; Winjum, B. J.; Valeo, E. J.

    2012-10-01

    Kinetic simulations of nonlinear electron plasma waves (EPW) are presented in 2D with the Vlasov code LOKI (2 space and 2 velocity dimensions; Banks et al., Phys. Plasmas 18, 052102 (2011)). Propagating EPWs are created with an external wave potential with uniform transverse amplitude. The evolution of the plasma wave field and its self-consistent quasi-steady distribution of trapped electrons is studied after the external drive is turned off. For finite-amplitude EPWs, the onset of the trapped-electron-induced filamentation instability (H. Rose, Phys. Plasmas 15, 042311 (2008)) and trapped electron sideband instability (S. Brunner and E. Valeo, PRL 93, 145003 (2004)) are studied as a function of wave amplitude and k0λDe, where k0 is the wavenumber of the external potential. We extend the theory of Kruer et al PRL 23, 1969 to 2D to find growth rates of both instabilities and compare these to the ones obtained from the simulations. In the nonlinear state, the distribution of resonant electrons is dramatically modified

  4. Electronic structure of cyclohexane on Ni(111)

    NASA Astrophysics Data System (ADS)

    Huber, W.; Zebisch, P.; Bornemann, T.; Steinrück, H.-P.

    1990-12-01

    Mono- and multilayers of cyclohexane adsorbed on a Ni(111) surface have been studied by angle resolved UV photoelectron spectroscopy (ARUPS) using linearly polarized synchrotron radiation, temperature programmed desorption (TPD) and low energy electron diffraction (LEED). Cyclohexane is molecularly adsorbed on Ni(111) at temperatures below 200 K and desorbs without dehydrogenation. Desorption from the first layer exhibits zeroth-order desorption behavior indicative of desorption from two-dimensional islands. The first layer exhibits a well ordered ( 7 × 7)R19.1° LEED structure starting at coverages of 0.04 ML up to the saturation coverage of 0.143 ML, also indicative of island formation. For cyclohexane in the first layer the binding energies of the various molecular levels are, apart from an overall shift to smaller values by 0.7 eV, within ± 0.1 eV identical to those of condensed cyclohexane. This absence of chemical shifts indicates that there is only very weak (if any) chemical interaction between cyclohexane and the Ni(111) surface. From the normal emission ARUPS spectra and symmetry selection rules we conclude that the symmetry of cyclohexane adsorbed on Ni(111) is lower than C 3v. This is attributed to a slightly inclined adsorption geometry with intramolecular C 3v symmetry of the adsorbed molecules.

  5. Structural, Electronic, and Mechanical Properties of Chains of Silicon Clusters with Trigonal Bipiramidal Structures

    NASA Astrophysics Data System (ADS)

    Tchernatinsky, Alex; Jayanthi, C. S.; Wu, S. Y.

    2002-03-01

    We report here our investigation of structural, electronic, and mechanical properties of non-trivial silicon chains. These chains are built from elementary blocks of clusters of 5 and 8 silicon atoms, arranged into trigonal bipiramidal structures and periodically continued along the axial direction. The initial configurations are constructed such that there are no dangling bonds associated with any atom along the chains. The stable configurations of the chains are determined by molecular dynamics simulations based on the first-principles method of Sankey and Niklewski [1] using the self-consistency scheme given in Ref. [2]. Mechanical and electronic properties of the resulting stable chains will be presented. 1. O.F.Sankey, and D.J.Niklewski, Phys. Rev. B 40 3979(1989). 2. P.Ordejon, E.Artacho, and J.M.Soler, Phys.Rev. B 53,10441 (1996).

  6. Simulations of nanocrystals under pressure: Combining electronic enthalpy and linear-scaling density-functional theory

    SciTech Connect

    Corsini, Niccolò R. C. Greco, Andrea; Haynes, Peter D.; Hine, Nicholas D. M.; Molteni, Carla

    2013-08-28

    We present an implementation in a linear-scaling density-functional theory code of an electronic enthalpy method, which has been found to be natural and efficient for the ab initio calculation of finite systems under hydrostatic pressure. Based on a definition of the system volume as that enclosed within an electronic density isosurface [M. Cococcioni, F. Mauri, G. Ceder, and N. Marzari, Phys. Rev. Lett.94, 145501 (2005)], it supports both geometry optimizations and molecular dynamics simulations. We introduce an approach for calibrating the parameters defining the volume in the context of geometry optimizations and discuss their significance. Results in good agreement with simulations using explicit solvents are obtained, validating our approach. Size-dependent pressure-induced structural transformations and variations in the energy gap of hydrogenated silicon nanocrystals are investigated, including one comparable in size to recent experiments. A detailed analysis of the polyamorphic transformations reveals three types of amorphous structures and their persistence on depressurization is assessed.

  7. Simulations of nanocrystals under pressure: combining electronic enthalpy and linear-scaling density-functional theory.

    PubMed

    Corsini, Niccolò R C; Greco, Andrea; Hine, Nicholas D M; Molteni, Carla; Haynes, Peter D

    2013-08-28

    We present an implementation in a linear-scaling density-functional theory code of an electronic enthalpy method, which has been found to be natural and efficient for the ab initio calculation of finite systems under hydrostatic pressure. Based on a definition of the system volume as that enclosed within an electronic density isosurface [M. Cococcioni, F. Mauri, G. Ceder, and N. Marzari, Phys. Rev. Lett. 94, 145501 (2005)], it supports both geometry optimizations and molecular dynamics simulations. We introduce an approach for calibrating the parameters defining the volume in the context of geometry optimizations and discuss their significance. Results in good agreement with simulations using explicit solvents are obtained, validating our approach. Size-dependent pressure-induced structural transformations and variations in the energy gap of hydrogenated silicon nanocrystals are investigated, including one comparable in size to recent experiments. A detailed analysis of the polyamorphic transformations reveals three types of amorphous structures and their persistence on depressurization is assessed.

  8. Electronic Structure and Dynamics of Nitrosyl Porphyrins

    PubMed Central

    Scheidt, W. Robert; Barabanschikov, Alexander; Pavlik, Jeffrey W.; Silvernail, Nathan J.; Sage, J. Timothy

    2010-01-01

    fully successful at capturing the interaction between the axial NO and imidazole ligands. This supports previous conclusions that hemeNO complexes exhibit an unusual degree of variability with respect to computational method, and we speculate that this variability hints at a genuine electronic instability that a protein can exploit to tune reactivity. We anticipate that ongoing characterization of heme-NO complexes will deepen our understanding of their structure, dynamics, and reactivity. PMID:20666384

  9. PIC simulations on the termination shock: Microstructure and electron acceleration

    NASA Astrophysics Data System (ADS)

    Matsukiyo, S.; Scholer, M.

    2013-05-01

    The ability of the termination shock as a particle accelerator is totally unknown. Voyager data and recent kinetic numerical simulations revealed that the compression ratio of the termination shock is rather low due to the presence of pickup ions, i.e., the termination shock appears to be a weak shock. Nevertheless, two Voyager spacecraft observed not only high energy ions called termination shock particles, which are non-thermal but less energetic compared to the so-called anomalous cosmic rays, but also high energy electrons. In this study we focus especially on microstructure of the termination shock and the associated electron acceleration process by performing one-dimensional full particle-in-cell (PIC) simulations for a variety of parameters. For typical solar wind parameters at the termination shock, a shock potential has no sharp ramp with the spatial scale of the order of electron inertial length which is suitable for the injection of anomalous cosmic ray acceleration. Solar wind ions are not so much heated, which is consistent with Voyager spacecraft data. If a shock angle is close to 90 deg., a shock is almost time stationary or weakly breathing when a relative pickup ion density is 30%, while it becomes non-stationary if the relative pickup ion density is 20%. When the shock angle becomes oblique, a self-reformation occurs due to the interaction of solar wind ions and whistler precursors. Here, the shock angle is defined as the angle between upstream magnetic field and shock normal. For the case with relatively low beta solar wind plasma (electron beta is 0.1 and solar wind ion temperature equals to electron temperature), modified two-stream instability (MTSI) gets excited in the extended foot sustained by reflected pickup ions, and both solar wind electrons and ions are heated. If the solar wind plasma temperature gets five times higher, on the other hand, the MTSI is weakened and the pre-heating of the solar wind plasma in the extended foot is

  10. Numerical simulation of electron beam welding with beam oscillations

    NASA Astrophysics Data System (ADS)

    Trushnikov, D. N.; Permyakov, G. L.

    2017-02-01

    This research examines the process of electron-beam welding in a keyhole mode with the use of beam oscillations. We study the impact of various beam oscillations and their parameters on the shape of the keyhole, the flow of heat and mass transfer processes and weld parameters to develop methodological recommendations. A numerical three-dimensional mathematical model of electron beam welding is presented. The model was developed on the basis of a heat conduction equation and a Navier-Stokes equation taking into account phase transitions at the interface of a solid and liquid phase and thermocapillary convection (Marangoni effect). The shape of the keyhole is determined based on experimental data on the parameters of the secondary signal by using the method of a synchronous accumulation. Calculations of thermal and hydrodynamic processes were carried out based on a computer cluster, using a simulation package COMSOL Multiphysics.

  11. Xyce Parallel Electronic Simulator Reference Guide Version 6.4

    SciTech Connect

    Keiter, Eric R.; Mei, Ting; Russo, Thomas V.; Schiek, Richard; Sholander, Peter E.; Thornquist, Heidi K.; Verley, Jason; Baur, David Gregory

    2015-12-01

    This document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users' Guide [1] . The focus of this document is (to the extent possible) exhaustively list device parameters, solver options, parser options, and other usage details of Xyce . This document is not intended to be a tutorial. Users who are new to circuit simulation are better served by the Xyce Users' Guide [1] . Trademarks The information herein is subject to change without notice. Copyright c 2002-2015 Sandia Corporation. All rights reserved. Xyce TM Electronic Simulator and Xyce TM are trademarks of Sandia Corporation. Portions of the Xyce TM code are: Copyright c 2002, The Regents of the University of California. Produced at the Lawrence Livermore National Laboratory. Written by Alan Hindmarsh, Allan Taylor, Radu Serban. UCRL-CODE-2002-59 All rights reserved. Orcad, Orcad Capture, PSpice and Probe are registered trademarks of Cadence Design Systems, Inc. Microsoft, Windows and Windows 7 are registered trademarks of Microsoft Corporation. Medici, DaVinci and Taurus are registered trademarks of Synopsys Corporation. Amtec and TecPlot are trademarks of Amtec Engineering, Inc. Xyce 's expression library is based on that inside Spice 3F5 developed by the EECS Department at the University of California. The EKV3 MOSFET model was developed by the EKV Team of the Electronics Laboratory-TUC of the Technical University of Crete. All other trademarks are property of their respective owners. Contacts Bug Reports (Sandia only) http://joseki.sandia.gov/bugzilla http://charleston.sandia.gov/bugzilla World Wide Web http://xyce.sandia.gov http://charleston.sandia.gov/xyce (Sandia only) Email xyce@sandia.gov (outside Sandia) xyce-sandia@sandia.gov (Sandia only)

  12. Simulation study of a 'fission electron-collection' neutron detector

    SciTech Connect

    Wang Dong; Zhang Chuanfei

    2015-07-01

    In this work, a 'fission electron-collection' neutron detector was studied using the Monte Carlo method. The detector consists of two metal electrodes mounted in a vacuum, named coated and collection electrodes, respectively. The first electrode is coated with triuranium octoxide. The detector uses the 'fission electron-collection' technique, which does not need an intermediate material but directly collects electrons from the coating. Such a detector can realize a flat energy response and a fast time response, both of which are important in the fluence measurement of pulsed neutron sources. In this paper, the physical processes of detection are presented, as well as Monte Carlo simulation studies using the Geant4 toolkit. From the results, the sensitivity of the detector is approximately 1.5 x 10{sup -21} [C/(n/cm{sup 2})], and the FWHM of response function is 2.5 nanoseconds. Additionally, the characterization of escaping electrons is also presented, and the sensitivity of the detector is determined for various coating thicknesses. (authors)

  13. Simulation and Characterization of a Miniaturized Scanning Electron Microscope

    NASA Technical Reports Server (NTRS)

    Gaskin, Jessica A.; Jerman, Gregory A.; Medley, Stephanie; Gregory, Don; Abbott, Terry O.; Sampson, Allen R.

    2011-01-01

    A miniaturized Scanning Electron Microscope (mSEM) for in-situ lunar investigations is being developed at NASA Marshall Space Flight Center with colleagues from the University of Alabama in Huntsville (UAH), Advanced Research Systems (ARS), the University of Tennessee in Knoxville (UTK) and Case Western Reserve University (CWRU). This effort focuses on the characterization of individual components of the mSEM and simulation of the complete system. SEMs can provide information on the size, shape, morphology and chemical composition of lunar regolith. Understanding these basic properties will allow us to better estimate the challenges associated with In-Situ Resource Utilization and to improve our basic science knowledge of the lunar surface (either precluding the need for sample return or allowing differentiation of unique samples to be returned to Earth.) The main components of the mSEM prototype includes: a cold field emission electron gun (CFEG), focusing lens, deflection/scanning system and backscatter electron detector. Of these, the electron gun development is of particular importance as it dictates much of the design of the remaining components. A CFEG was chosen for use with the lunar mSEM as its emission does not depend on heating of the tungsten emitter (lower power), it offers a long operation lifetime, is orders of magnitude brighter than tungsten hairpin guns, has a small source size and exhibits low beam energy spread.

  14. Hopping electron model with geometrical frustration: kinetic Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Terao, Takamichi

    2016-09-01

    The hopping electron model on the Kagome lattice was investigated by kinetic Monte Carlo simulations, and the non-equilibrium nature of the system was studied. We have numerically confirmed that aging phenomena are present in the autocorrelation function C ({t,tW )} of the electron system on the Kagome lattice, which is a geometrically frustrated lattice without any disorder. The waiting-time distributions p(τ ) of hopping electrons of the system on Kagome lattice has been also studied. It is confirmed that the profile of p (τ ) obtained at lower temperatures obeys the power-law behavior, which is a characteristic feature of continuous time random walk of electrons. These features were also compared with the characteristics of the Coulomb glass model, used as a model of disordered thin films and doped semiconductors. This work represents an advance in the understanding of the dynamics of geometrically frustrated systems and will serve as a basis for further studies of these physical systems.

  15. Online Simulation of Radiation Track Structure Project

    NASA Technical Reports Server (NTRS)

    Plante, Ianik

    2015-01-01

    Space radiation comprises protons, helium and high charged and energy (HZE) particles. High-energy particles are a concern for human space flight, because they are no known options for shielding astronauts from them. When these ions interact with matter, they damage molecules and create radiolytic species. The pattern of energy deposition and positions of the radiolytic species, called radiation track structure, is highly dependent on the charge and energy of the ion. The radiolytic species damage biological molecules, which may lead to several long-term health effects such as cancer. Because of the importance of heavy ions, the radiation community is very interested in the interaction of HZE particles with DNA, notably with regards to the track structure. A desktop program named RITRACKS was developed to simulate radiation track structure. The goal of this project is to create a web interface to allow registered internal users to use RITRACKS remotely.

  16. Probing Actinide Electronic Structure through Pu Cluster Calculations

    DOE PAGES

    Ryzhkov, Mickhail V.; Mirmelstein, Alexei; Yu, Sung-Woo; ...

    2013-02-26

    The calculations for the electronic structure of clusters of plutonium have been performed, within the framework of the relativistic discrete-variational method. Moreover, these theoretical results and those calculated earlier for related systems have been compared to spectroscopic data produced in the experimental investigations of bulk systems, including photoelectron spectroscopy. Observation of the changes in the Pu electronic structure as a function of size provides powerful insight for aspects of bulk Pu electronic structure.

  17. Short Rayleigh length free electron laser: Experiments and simulations

    SciTech Connect

    Crooker, P.P.; Colson, William; Blau, Joe; Burggraff, D.; Sans Aguilar, J.; Benson, Stephen; Neil, George; Michelle D. Shinn; Evtushenko, Pavel

    2008-09-01

    DOI: http://dx.doi.org/10.1103/PhysRevSTAB.11.090701
    We report experiments at Jefferson National Accelerator Facility (Jlab) and computer simulations performed at the Naval Postgraduate School (NPS) designed to probe the small Rayleigh length regime. We compare the gain, power, and sensitivity to mirror and electron beam misalignments as a function of decreasing Rayleigh length. The agreement is quite good, with experiments and simulations showing comparable trends as the Rayleigh length is decreased. In particular, we find that the gain and power do not decrease substantially at short Rayleigh length, contrary to a common Gaussian-mode filling factor argument. Within currently achievable alignment tolerances, the gain and power are still acceptable for FEL operation.

  18. Electron acceleration at nearly perpendicular collisionless shocks. I - One-dimensional simulations without electron scale fluctuations

    NASA Technical Reports Server (NTRS)

    Krauss-Varban, D.; Burgess, D.; Wu, C. S.

    1989-01-01

    Under certain conditions electrons can be reflected and effectively energized at quasi-perpendicular shocks. This process is most prominent close to the point where the upstream magnetic field is tangent to the curved shock. A theoretical explanation of the underlying physical mechanism has been proposed which assumes conservation of magnetic moment and a static, simplified shock profile are performed. Test particle calculations of the electron reflection process in order to examine the results of the theoretical analysis without imposing these restrictive conditions. A one-dimensional hybrid simulation code generates the characteristic field variations across the shock. Special emphasis is placed on the spatial and temporal length scales involved in the mirroring process. The simulation results agree generally well with the predictions from adiabatic theory. The effects of the cross-shock potential and unsteadiness are quantified, and the influence of field fluctuations on the reflection process is discussed.

  19. Design, simulation and construction of a Wire Chamber electronics

    NASA Astrophysics Data System (ADS)

    Istemihan, Zehra

    2017-02-01

    Tracking charged particles has a wide spectrum of applications in scientific and industrial projects. The Delay Wire Chamber (DWC) is a kind of gaseous detector which is a simpler form of the Multi Wire Proportional Chamber, and was developed by the Beam Instrumentation Group at CERN. It is preferred in accelerator and particle physics experiments because of its ease of use, affordability and durability, and it also provides decent position precision. In this work, we describe the working principles of the readout electronics of a new DWC that is being designed and constructed at our laboratory. Results from the simulation of the circuit and the constructed prototype will be presented.

  20. Simulation analysis for ion assisted fast ignition using structured targets

    NASA Astrophysics Data System (ADS)

    Sakagami, H.; Johzaki, T.; Sunahara, A.; Nagatomo, H.

    2016-05-01

    As the heating efficiency by fast electrons in the fast ignition scheme is estimated to be very low due to their large divergence angle and high energy. To mitigate this problem, low-density plastic foam, which can generate not only proton (H+) but also carbon (C6+) beams, can be introduced to currently used cone-guided targets and additional core heating by ions is expected. According to 2D PIC simulations, it is found that the ion beams also diverge by the static electric field and concave surface deformation. Thus structured targets are suggested to optimize ion beam characteristics, and their improvement and core heating enhancement by ion beams are confirmed.

  1. Digital system for structural dynamics simulation

    NASA Technical Reports Server (NTRS)

    Krauter, A. I.; Lagace, L. J.; Wojnar, M. K.; Glor, C.

    1982-01-01

    State-of-the-art digital hardware and software for the simulation of complex structural dynamic interactions, such as those which occur in rotating structures (engine systems). System were incorporated in a designed to use an array of processors in which the computation for each physical subelement or functional subsystem would be assigned to a single specific processor in the simulator. These node processors are microprogrammed bit-slice microcomputers which function autonomously and can communicate with each other and a central control minicomputer over parallel digital lines. Inter-processor nearest neighbor communications busses pass the constants which represent physical constraints and boundary conditions. The node processors are connected to the six nearest neighbor node processors to simulate the actual physical interface of real substructures. Computer generated finite element mesh and force models can be developed with the aid of the central control minicomputer. The control computer also oversees the animation of a graphics display system, disk-based mass storage along with the individual processing elements.

  2. Three-Dimensional Simulations of Electron Beams Focused by Periodic Permanent Magnets

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.

    1999-01-01

    A fully three-dimensional (3D) model of an electron beam focused by a periodic permanent magnet (PPM) stack has been developed. First, the simulation code MAFIA was used to model a PPM stack using the magnetostatic solver. The exact geometry of the magnetic focusing structure was modeled; thus, no approximations were made regarding the off-axis fields. The fields from the static solver were loaded into the 3D particle-in-cell (PIC) solver of MAFIA where fully 3D behavior of the beam was simulated in the magnetic focusing field. The PIC solver computes the time-integration of electromagnetic fields simultaneously with the time integration of the equations of motion of charged particles that move under the influence of those fields. Fields caused by those moving charges are also taken into account; thus, effects like space charge and magnetic forces between particles are fully simulated. The electron beam is simulated by a number of macro-particles. These macro-particles represent a given charge Q amounting to that of several million electrons in order to conserve computational time and memory. Particle motion is unrestricted, so particle trajectories can cross paths and move in three dimensions under the influence of 3D electric and magnetic fields. Correspondingly, there is no limit on the initial current density distribution of the electron beam, nor its density distribution at any time during the simulation. Simulation results including beam current density, percent ripple and percent transmission will be presented, and the effects current, magnetic focusing strength and thermal velocities have on beam behavior will be demonstrated using 3D movies showing the evolution of beam characteristics in time and space. Unlike typical beam optics models, this 3D model allows simulation of asymmetric designs such as non- circularly symmetric electrostatic or magnetic focusing as well as the inclusion of input/output couplers.

  3. Xyce™ Parallel Electronic Simulator Users' Guide, Version 6.5.

    SciTech Connect

    Keiter, Eric R.; Aadithya, Karthik V.; Mei, Ting; Russo, Thomas V.; Schiek, Richard L.; Sholander, Peter E.; Thornquist, Heidi K.; Verley, Jason C.

    2016-06-01

    This manual describes the use of the Xyce Parallel Electronic Simulator. Xyce has been designed as a SPICE-compatible, high-performance analog circuit simulator, and has been written to support the simulation needs of the Sandia National Laboratories electrical designers. This development has focused on improving capability over the current state-of-the-art in the following areas: Capability to solve extremely large circuit problems by supporting large-scale parallel computing platforms (up to thousands of processors). This includes support for most popular parallel and serial computers. A differential-algebraic-equation (DAE) formulation, which better isolates the device model package from solver algorithms. This allows one to develop new types of analysis without requiring the implementation of analysis-specific device models. Device models that are specifically tailored to meet Sandia's needs, including some radiation- aware devices (for Sandia users only). Object-oriented code design and implementation using modern coding practices. Xyce is a parallel code in the most general sense of the phrase -- a message passing parallel implementation -- which allows it to run efficiently a wide range of computing platforms. These include serial, shared-memory and distributed-memory parallel platforms. Attention has been paid to the specific nature of circuit-simulation problems to ensure that optimal parallel efficiency is achieved as the number of processors grows. The information herein is subject to change without notice. Copyright © 2002-2016 Sandia Corporation. All rights reserved.

  4. Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA)

    National Institute of Standards and Technology Data Gateway

    SRD 100 Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA) (PC database for purchase)   This database has been designed to facilitate quantitative interpretation of Auger-electron and X-ray photoelectron spectra and to improve the accuracy of quantitation in routine analysis. The database contains all physical data needed to perform quantitative interpretation of an electron spectrum for a thin-film specimen of given composition. A simulation module provides an estimate of peak intensities as well as the energy and angular distributions of the emitted electron flux.

  5. Xyce Parallel Electronic Simulator Users Guide Version 6.2.

    SciTech Connect

    Keiter, Eric R.; Mei, Ting; Russo, Thomas V.; Schiek, Richard Louis; Sholander, Peter E.; Thornquist, Heidi K.; Verley, Jason C.; Baur, David Gregory

    2014-09-01

    This manual describes the use of the Xyce Parallel Electronic Simulator. Xyce has been de- signed as a SPICE-compatible, high-performance analog circuit simulator, and has been written to support the simulation needs of the Sandia National Laboratories electrical designers. This development has focused on improving capability over the current state-of-the-art in the following areas: Capability to solve extremely large circuit problems by supporting large-scale parallel com- puting platforms (up to thousands of processors). This includes support for most popular parallel and serial computers. A differential-algebraic-equation (DAE) formulation, which better isolates the device model package from solver algorithms. This allows one to develop new types of analysis without requiring the implementation of analysis-specific device models. Device models that are specifically tailored to meet Sandia's needs, including some radiation- aware devices (for Sandia users only). Object-oriented code design and implementation using modern coding practices. Xyce is a parallel code in the most general sense of the phrase -- a message passing parallel implementation -- which allows it to run efficiently a wide range of computing platforms. These include serial, shared-memory and distributed-memory parallel platforms. Attention has been paid to the specific nature of circuit-simulation problems to ensure that optimal parallel efficiency is achieved as the number of processors grows. Trademarks The information herein is subject to change without notice. Copyright c 2002-2014 Sandia Corporation. All rights reserved. Xyce TM Electronic Simulator and Xyce TM are trademarks of Sandia Corporation. Portions of the Xyce TM code are: Copyright c 2002, The Regents of the University of California. Produced at the Lawrence Livermore National Laboratory. Written by Alan Hindmarsh, Allan Taylor, Radu Serban. UCRL-CODE-2002-59 All rights reserved. Orcad, Orcad Capture, PSpice and Probe are

  6. Simulation of electron transport in quantum well devices

    NASA Technical Reports Server (NTRS)

    Miller, D. R.; Gullapalli, K. K.; Reddy, V. R.; Neikirk, D. P.

    1992-01-01

    Double barrier resonant tunneling diodes (DBRTD) have received much attention as possible terahertz devices. Despite impressive experimental results, the specifics of the device physics (i.e., how the electrons propagate through the structure) are only qualitatively understood. Therefore, better transport models are warranted if this technology is to mature. In this paper, the Lattice Wigner function is used to explain the important transport issues associated with DBRTD device behavior.

  7. Gyrokinetic Particle Simulation of Fast Electron Driven Beta-induced Alfven Eigenmodes

    NASA Astrophysics Data System (ADS)

    Zhang, Wenlu; Cheng, Junyi; Lin, Zhihong

    2016-10-01

    The fast electron driven beta induced Alfven eigenmode (e-BAE) has been routinely observed in HL-2A tokamak. We study e-BAE for the first time using global gyrokinetic GTC simulation, where the fast electrons are described by the drift kinetic model. Frequency chirping is observed in nonlinear simulations in the absence of sources and sinks, which provide a new nonlinear paradigm beyond the standard ``bump-on-tail'' model. For weakly driven case, nonlinear frequency is observed to be in phase with particle flux, and nonlinear mode structure is almost the same as linear stage. In the strongly driven case, BAAE is also unstable and co-exists with BAE after the BAE saturation. Analysis of nonlinear wave-particle interactions shows that the frequency chirping is induced by the nonlinear evolution of the coherent structures in the fast electron phase space, where the dynamics of the coherent structure is controlled by the formation and destruction of phrase space islands in the canonical variables. Zonal fields are found to affect wave-particle resonance in the nonlinear e-BAE simulations.

  8. Using Laboratory Experiments and Circuit Simulation IT Tools in an Undergraduate Course in Analog Electronics

    NASA Astrophysics Data System (ADS)

    Baltzis, Konstantinos B.; Koukias, Konstantinos D.

    2009-12-01

    Laboratory-based courses play a significant role in engineering education. Given the role of electronics in engineering and technology, laboratory experiments and circuit simulation IT tools are used in their teaching in several academic institutions. This paper discusses the characteristics and benefits of both methods. The content and structure of an introductory laboratory course in analog electronics is described. The aim of the course is the better understanding of the basic principles of analog electronic circuits without the need of specific technical and computer skills. The impact of the proposed method on the learning process is investigated. The evaluation of our proposal was based on both quantitative and qualitative data. Interesting conclusions about the teaching of electronics in undergraduate education are finally drawn.

  9. Computational methods for the electronic structure of defects in insulators

    NASA Astrophysics Data System (ADS)

    Harker, A. H.

    It is clear that one of the weakest points of current theories of point defects is in the treatment of the electronic structure of the host lattice. One of the advantages of cluster calculations is that the defect and lattice can be treated together. Great care is needed to incorporate the electrostatic field of the lattice outside the cluster correctly. Polarisation and distortion can be handled by cluster models where they are of short range, that is, for neutral defects. For charged defects hybrid models similar to those used by Wood and Opik(7,8) will have to be developed. The final method may well involve three regions: an innermost region in which the electronic structure is calculated in detail and self-consistently; a second region with model ions, interacting with each other through potentials of Born-Mayer type and with the inner region through pseudopotentials; and an outer continuum. The distortion of the whole would be controlled by some efficient algorithm similar to that used in the lattice simulation methods discussed in Chapter (1).

  10. Atomistic modeling of electronic structure and transport in disordered nanostructures

    NASA Astrophysics Data System (ADS)

    Kharche, Neerav

    and illuminate the interesting physics of these disordered nanostructures that otherwise can not be explained using the traditional averaging methods such as the virtual crystal approximation. Finally, a multiscale modeling approach is employed, which combines the atomistic tight-binding method to compute the electronic structure and the real-space effective mass based quantum transport model including gate leakage to simulate the three terminal characteristics of III-V quantum well field effect transistors (QWFETs). The simulation methodology has been benchmarked against experimental data and it is then applied to investigate the logic performance of ultra-scaled III-V QWFETs with high mobility InAs channels.

  11. Dramatic changes in electronic structure revealed by fractionally charged nuclei

    NASA Astrophysics Data System (ADS)

    Cohen, Aron J.; Mori-Sánchez, Paula

    2014-01-01

    Discontinuous changes in the electronic structure upon infinitesimal changes to the Hamiltonian are demonstrated. These are revealed in one and two electron molecular systems by full configuration interaction (FCI) calculations when the realm of the nuclear charge is extended to be fractional. FCI electron densities in these systems show dramatic changes in real space and illustrate the transfer, hopping, and removal of electrons. This is due to the particle nature of electrons seen in stretched systems and is a manifestation of an energy derivative discontinuity at constant number of electrons. Dramatic errors of density functional theory densities are seen in real space as this physics is missing from currently used approximations. The movements of electrons in these simple systems encapsulate those in real physical processes, from chemical reactions to electron transport and pose a great challenge for the development of new electronic structure methods.

  12. Monte Carlo computer simulations and electron microscopy of colloidal cluster formation via emulsion droplet evaporation

    NASA Astrophysics Data System (ADS)

    Schwarz, Ingmar; Fortini, Andrea; Wagner, Claudia Simone; Wittemann, Alexander; Schmidt, Matthias

    2011-12-01

    We consider a theoretical model for a binary mixture of colloidal particles and spherical emulsion droplets. The hard sphere colloids interact via additional short-ranged attraction and long-ranged repulsion. The droplet-colloid interaction is an attractive well at the droplet surface, which induces the Pickering effect. The droplet-droplet interaction is a hard-core interaction. The droplets shrink in time, which models the evaporation of the dispersed (oil) phase, and we use Monte Carlo simulations for the dynamics. In the experiments, polystyrene particles were assembled using toluene droplets as templates. The arrangement of the particles on the surface of the droplets was analyzed with cryogenic field emission scanning electron microscopy. Before evaporation of the oil, the particle distribution on the droplet surface was found to be disordered in experiments, and the simulations reproduce this effect. After complete evaporation, ordered colloidal clusters are formed that are stable against thermal fluctuations. Both in the simulations and with field emission scanning electron microscopy, we find stable packings that range from doublets, triplets, and tetrahedra to complex polyhedra of colloids. The simulated cluster structures and size distribution agree well with the experimental results. We also simulate hierarchical assembly in a mixture of tetrahedral clusters and droplets, and find supercluster structures with morphologies that are more complex than those of clusters of single particles.

  13. The inner structure of collisionless magnetic reconnection: The electron-frame dissipation measure and Hall fields

    SciTech Connect

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Black, Carrie; Kuznetsova, Masha

    2011-12-15

    It was recently proposed that the electron-frame dissipation measure, the energy transfer from the electromagnetic field to plasmas in the electron's rest frame, identifies the dissipation region of collisionless magnetic reconnection [Zenitani et al., Phys. Rev. Lett. 106, 195003 (2011)]. The measure is further applied to the electron-scale structures of antiparallel reconnection, by using two-dimensional particle-in-cell simulations. The size of the central dissipation region is controlled by the electron-ion mass ratio, suggesting that electron physics is essential. A narrow electron jet extends along the outflow direction until it reaches an electron shock. The jet region appears to be anti-dissipative. At the shock, electron heating is relevant to a magnetic cavity signature. The results are summarized to a unified picture of the single dissipation region in a Hall magnetic geometry.

  14. Simulations of Electron Transport in Laser Hot Spots

    SciTech Connect

    S. Brunner; E. Valeo

    2001-08-30

    Simulations of electron transport are carried out by solving the Fokker-Planck equation in the diffusive approximation. The system of a single laser hot spot, with open boundary conditions, is systematically studied by performing a scan over a wide range of the two relevant parameters: (1) Ratio of the stopping length over the width of the hot spot. (2) Relative importance of the heating through inverse Bremsstrahlung compared to the thermalization through self-collisions. As for uniform illumination [J.P. Matte et al., Plasma Phys. Controlled Fusion 30 (1988) 1665], the bulk of the velocity distribution functions (VDFs) present a super-Gaussian dependence. However, as a result of spatial transport, the tails are observed to be well represented by a Maxwellian. A similar dependence of the distributions is also found for multiple hot spot systems. For its relevance with respect to stimulated Raman scattering, the linear Landau damping of the electron plasma wave is estimated for such VD Fs. Finally, the nonlinear Fokker-Planck simulations of the single laser hot spot system are also compared to the results obtained with the linear non-local hydrodynamic approach [A.V. Brantov et al., Phys. Plasmas 5 (1998) 2742], thus providing a quantitative limit to the latter method: The hydrodynamic approach presents more than 10% inaccuracy in the presence of temperature variations of the order delta T/T greater than or equal to 1%, and similar levels of deformation of the Gaussian shape of the Maxwellian background.

  15. Quantum Monte Carlo for electronic structure: Recent developments and applications

    SciTech Connect

    Rodriquez, Maria Milagos Soto

    1995-04-01

    Quantum Monte Carlo (QMC) methods have been found to give excellent results when applied to chemical systems. The main goal of the present work is to use QMC to perform electronic structure calculations. In QMC, a Monte Carlo simulation is used to solve the Schroedinger equation, taking advantage of its analogy to a classical diffusion process with branching. In the present work the author focuses on how to extend the usefulness of QMC to more meaningful molecular systems. This study is aimed at questions concerning polyatomic and large atomic number systems. The accuracy of the solution obtained is determined by the accuracy of the trial wave function`s nodal structure. Efforts in the group have given great emphasis to finding optimized wave functions for the QMC calculations. Little work had been done by systematically looking at a family of systems to see how the best wave functions evolve with system size. In this work the author presents a study of trial wave functions for C, CH, C2H and C2H2. The goal is to study how to build wave functions for larger systems by accumulating knowledge from the wave functions of its fragments as well as gaining some knowledge on the usefulness of multi-reference wave functions. In a MC calculation of a heavy atom, for reasonable time steps most moves for core electrons are rejected. For this reason true equilibration is rarely achieved. A method proposed by Batrouni and Reynolds modifies the way the simulation is performed without altering the final steady-state solution. It introduces an acceleration matrix chosen so that all coordinates (i.e., of core and valence electrons) propagate at comparable speeds. A study of the results obtained using their proposed matrix suggests that it may not be the optimum choice. In this work the author has found that the desired mixing of coordinates between core and valence electrons is not achieved when using this matrix. A bibliography of 175 references is

  16. First principles study of structural, electronic and mechanical properties of alkali nitride-KN

    SciTech Connect

    Murugan, A.; Rajeswarapalanichamy, R. Santhosh, M.; Iyakutti, K.

    2015-06-24

    The structural, electronic and elastic properties of alkali- metal nitride (KN) is investigated by the first principles calculations based on density functional theory as implemented in Vienna ab-initio simulation package. At ambient pressure KN is stable in the ferromagnetic state with NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that the KN is half metallic ferromagnet at normal pressure. A pressure-induced structural phase transition from NaCl to ZB phase is observed in KN. Half metallicity and ferromagnetism is maintained at all pressures.

  17. Affordable, Lightweight, Highly Conductive Polymer Composite Electronic Packaging Structures

    DTIC Science & Technology

    1996-06-01

    matrix composite materials and how various material designs can be utilized in various structural/thermal configurations to produce electronic housings and...conductive polymer composite electronic packaging (i.e., electronic housings and heat sinks). The research will center on predominately polymer

  18. Monte Carlo simulations of Kα source generated by hot electrons-nanobrush target interactions

    NASA Astrophysics Data System (ADS)

    Zhao, Jincui; Zheng, Jianhua; Cao, Lihua; Zhao, Zongqing; Li, Shu; Gu, Yuqiu; Liu, Jie

    2016-09-01

    We focus on the transport processes from hot electrons to Kα x-ray emission in a copper nanobrush target. The physics on the enhancement of Kα photon yield and conversion efficiency from laser to Kα x-ray ηL→Kα is studied by combining Monte Carlo simulations and previous particle-in-cell simulation results. Simulation results show that Kα photon yield and electron- Kα photon conversion efficiency ηe-→Kα from nanobrush targets rise gradually and then stay nearly constant. Kα photon yield from the structured nanobrush target increases with peak number density n0, but the yield is a little less than that from the same-size planar target when the electron temperature T =400 keV and n0=1021 cm-3 . It is because the number density of atoms and ions in the nanobrush target is almost one half of the foil target. Compared to the planar target, Kα photons after the nanobrush target are more than those before the target. Because it is easier for the electrons to enter the structured target surface, and Kα x-ray source is produced in the deeper position of the structured nanobrush target. Considering the realistic number of hot electrons produced by laser-nanobrush and -planar targets interaction, Kα photon yield in nanobrush targets has a significant enhancement of over 2-6 folds relative to laser-foil irradiation. The yield and ηL→K α from the nanobrush target are, respectively, 5.42 ×109 sr-1 and 7.32 ×10-5 when laser strength I λ2≈2 ×1018 W cm-2 μm2 . The yield and ηL→Kα decrease gradually with the laser strength, but the values are always higher than that from the planar target. Therefore, the laser-nanobrush target interaction can produce brighter and smaller-size Kα photon source, compared to a planar target.

  19. ELECTRON COOLING SIMULATIONS FOR LOW-ENERGY RHIC OPERATION.

    SciTech Connect

    FEDOTOV,A.V.; BEN-ZVI, I.; CHANG, X.; KAYRAN, D.; SATOGATA, T.

    2007-09-10

    Recently, a strong interest emerged in running the Relativistic Heavy Ion Collider (RHIC) at low beam total energies of 2.5-25 GeV/nucleon, substantially lower than the nominal beam total energy of 100 GeV/nucleon. Collisions in this low energy range are motivated by one of the key questions of quantum chromodynamics (QCD) about the existence and location of critical point on the QCD phase diagram. Applying electron cooling directly at these low energies in RHIC would result in significant luminosity increase and long beam stores for physics. Without direct cooling in RHIC at these low energies, beam lifetime and store times are very short, limited by strong transverse and longitudinal intrabeam scattering (IBS). In addition, for the lowest energies of the proposed energy scan, the longitudinal emittance of ions injected from the AGS into RHIC may be too big to fit into the RHIC RF bucket. An improvement in the longitudinal emittance of the ion beam can be provided by an electron cooling system at the AGS injection energy. Simulations of electron cooling both for direct cooling at low energies in RHIC and for injection energy cooling in the AGS were performed and are summarized in this report.

  20. Bragg's Law diffraction simulations for electron backscatter diffraction analysis.

    PubMed

    Kacher, Josh; Landon, Colin; Adams, Brent L; Fullwood, David

    2009-08-01

    In 2006, Angus Wilkinson introduced a cross-correlation-based electron backscatter diffraction (EBSD) texture analysis system capable of measuring lattice rotations and elastic strains to high resolution. A variation of the cross-correlation method is introduced using Bragg's Law-based simulated EBSD patterns as strain free reference patterns that facilitates the use of the cross-correlation method with polycrystalline materials. The lattice state is found by comparing simulated patterns to collected patterns at a number of regions on the pattern using the cross-correlation function and calculating the deformation from the measured shifts of each region. A new pattern can be simulated at the deformed state, and the process can be iterated a number of times to converge on the absolute lattice state. By analyzing an iteratively rotated single crystal silicon sample and recovering the rotation, this method is shown to have an angular resolution of approximately 0.04 degrees and an elastic strain resolution of approximately 7e-4. As an example of applications, elastic strain and curvature measurements are used to estimate the dislocation density in a single grain of a compressed polycrystalline Mg-based AZ91 alloy.

  1. Scaling and universality of inherent structure simulations.

    PubMed

    Witkoskie, James B; Cao, Jianshu

    2004-06-01

    In this paper we explore the inherent structures (IS) approach to the dynamics of the East constrained kinetic Ising model. The inherent structures do not capture the nature of the dynamics of many quantities, including the spin autocorrelation function. Simply monitoring the quenched energy fluctuations, i.e., IS energy, results in an oversimplified single order-parameter description of the system's dynamics, but examining other features, such as domain dynamics or normal modes, may give a more complete and useful picture of the dynamics. The universality in the behavior of the IS energy of this model does not reveal nonuniversal features of the kinetics that determine long-time relaxation of the system. As a result, popular functional forms, such as the stretched exponential relaxation or Gaussian distribution of energies, may be a numerical fit to data with little physical justification. Filtering data can be shown to erase features of the system and the resulting quantities resemble more universal functional forms that lack physical insight. These results for the East model have implications for IS simulations of realistic systems and suggest careful analysis including the examination of other potential order parameters is necessary to evaluate the validity of applications of universal and scaling arguments to IS simulations.

  2. Simulations of kinetically irreversible protein aggregate structure.

    PubMed Central

    Patro, S Y; Przybycien, T M

    1994-01-01

    We have simulated the structure of kinetically irreversible protein aggregates in two-dimensional space using a lattice-based Monte-Carlo routine. Our model specifically accounts for the intermolecular interactions between hydrophobic and hydrophilic protein surfaces and a polar solvent. The simulations provide information about the aggregate density, the types of inter-monomer contacts and solvent content within the aggregates, the type and extent of solvent exposed perimeter, and the short- and long-range order all as a function of (i) the extent of monomer hydrophobic surface area and its distribution on the model protein surface and (ii) the magnitude of the hydrophobic-hydrophobic contact energy. An increase in the extent of monomer hydrophobic surface area resulted in increased aggregate densities with concomitant decreased system free energies. These effects are accompanied by increases in the number of hydrophobic-hydrophobic contacts and decreases in the solvent-exposed hydrophobic surface area of the aggregates. Grouping monomer hydrophobic surfaces in a single contiguous stretch resulted in lower aggregate densities and lower short range order. More favorable hydrophobic-hydrophobic contact energies produced structures with higher densities but the number of unfavorable protein-protein contacts was also observed to increase; greater configurational entropy produced the opposite effect. Properties predicted by our model are in good qualitative agreement with available experimental observations. Images FIGURE 6 FIGURE 13 PMID:8061184

  3. Multiscale Simulation of Microbe Structure and Dynamics

    PubMed Central

    Joshi, Harshad; Singharoy, Abhishek; Sereda, Yuriy V.; Cheluvaraja, Srinath C.; Ortoleva, Peter J.

    2012-01-01

    A multiscale mathematical and computational approach is developed that captures the hierarchical organization of a microbe. It is found that a natural perspective for understanding a microbe is in terms of a hierarchy of variables at various levels of resolution. This hierarchy starts with the N -atom description and terminates with order parameters characterizing a whole microbe. This conceptual framework is used to guide the analysis of the Liouville equation for the probability density of the positions and momenta of the N atoms constituting the microbe and its environment. Using multiscale mathematical techniques, we derive equations for the co-evolution of the order parameters and the probability density of the N-atom state. This approach yields a rigorous way to transfer information between variables on different space-time scales. It elucidates the interplay between equilibrium and far-from-equilibrium processes underlying microbial behavior. It also provides framework for using coarse-grained nanocharacterization data to guide microbial simulation. It enables a methodical search for free-energy minimizing structures, many of which are typically supported by the set of macromolecules and membranes constituting a given microbe. This suite of capabilities provides a natural framework for arriving at a fundamental understanding of microbial behavior, the analysis of nanocharacterization data, and the computer-aided design of nanostructures for biotechnical and medical purposes. Selected features of the methodology are demonstrated using our multiscale bionanosystem simulator DeductiveMultiscaleSimulator. Systems used to demonstrate the approach are structural transitions in the cowpea chlorotic mosaic virus, RNA of satellite tobacco mosaic virus, virus-like particles related to human papillomavirus, and iron-binding protein lactoferrin. PMID:21802438

  4. Multiscale simulation of microbe structure and dynamics.

    PubMed

    Joshi, Harshad; Singharoy, Abhishek; Sereda, Yuriy V; Cheluvaraja, Srinath C; Ortoleva, Peter J

    2011-10-01

    A multiscale mathematical and computational approach is developed that captures the hierarchical organization of a microbe. It is found that a natural perspective for understanding a microbe is in terms of a hierarchy of variables at various levels of resolution. This hierarchy starts with the N -atom description and terminates with order parameters characterizing a whole microbe. This conceptual framework is used to guide the analysis of the Liouville equation for the probability density of the positions and momenta of the N atoms constituting the microbe and its environment. Using multiscale mathematical techniques, we derive equations for the co-evolution of the order parameters and the probability density of the N-atom state. This approach yields a rigorous way to transfer information between variables on different space-time scales. It elucidates the interplay between equilibrium and far-from-equilibrium processes underlying microbial behavior. It also provides framework for using coarse-grained nanocharacterization data to guide microbial simulation. It enables a methodical search for free-energy minimizing structures, many of which are typically supported by the set of macromolecules and membranes constituting a given microbe. This suite of capabilities provides a natural framework for arriving at a fundamental understanding of microbial behavior, the analysis of nanocharacterization data, and the computer-aided design of nanostructures for biotechnical and medical purposes. Selected features of the methodology are demonstrated using our multiscale bionanosystem simulator DeductiveMultiscaleSimulator. Systems used to demonstrate the approach are structural transitions in the cowpea chlorotic mosaic virus, RNA of satellite tobacco mosaic virus, virus-like particles related to human papillomavirus, and iron-binding protein lactoferrin.

  5. Effect of Small Changes in Secondary Structure on the Electron Transfer Rate in Proteins

    NASA Astrophysics Data System (ADS)

    Wolfgang, J.; Risser, S. M.

    1996-03-01

    In the non-adiabatic limit, the rate of electron transfer reactions is proportional to the square of the electronic coupling between donor and acceptor. The distance decay of the coupling in a protein is sensitive to the protein geometry and the tunneling energy of the electron. In this paper, we use Green's function methods combined with molecular dynamics simulations to examine how the electronic coupling is modulated by the primary, secondary and tertiary structure of polypeptides. We also will explore the sensitivity of the coupling to small changes in atomic coordinates. This work was supported by the Research Corporation and East Texas State University.

  6. Direct numerical simulations of structure and transport in dense plasmas

    NASA Astrophysics Data System (ADS)

    Whitley, Heather; Castor, John; Murillo, Michael; Graziani, Frank; Cimarron Collaboration

    2011-10-01

    In recent years, high power laser facilities, such as NIF, and advanced diagnostics have enabled the determination of detailed properties of dense plasmas over unprecedented regimes. Understanding such plasmas, which may be partially degenerate and/or moderately coupled, represents a major challenge to the plasma physics community. We examine the accuracy and applicability of approximate effective potentials in the study of structural and dynamic properties of one and two component systems in the partially and fully ionized regimes. The diffractive Coulomb potential is derived from an exact quantum solution for a pair of particles while the fermionic character of the electrons is handled via an effective Pauli potential. We utilize classical hypernetted chain and molecular dynamics (MD) simulations to calculate static structure factors that can be compared to recent x-ray Thompson scattering experiments. We also examine whether these approximate potentials can be used to simulate electronic transport properties, such as thermal conductivity, and compare to recent quantum molecular dynamics calculations for hydrogen plasmas. Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-490775.

  7. Magnetic field structure influence on primary electron cusp losses for micro-scale discharges

    SciTech Connect

    Dankongkakul, Ben; Araki, Samuel J.; Wirz, Richard E.

    2014-04-15

    An experimental effort was used to examine the primary electron loss behavior for micro-scale (≲3 cm diameter) discharges. The experiment uses an electron flood gun source and an axially aligned arrangement of ring-cusps to guide the electrons to a downstream point cusp. Measurements of the electron current collected at the point cusp show an unexpectedly complex loss pattern with azimuthally periodic structures. Additionally, in contrast to conventional theory for cusp losses, the overall radii of the measured collection areas are over an order of magnitude larger than the electron gyroradius. Comparing these results to Monte Carlo particle tracking simulations and a simplified analytical analysis shows that azimuthal asymmetries of the magnetic field far upstream of the collection surface can substantially affect the electron loss structure and overall loss area.

  8. Development of a model electronic Hamiltonian for understanding electronic relaxation dynamics of [Fe(bpy){sub 3}]{sup 2+} through molecular dynamics simulations

    SciTech Connect

    Iuchi, Satoru; Koga, Nobuaki

    2015-12-31

    A model electronic Hamiltonian of [Fe(bpy){sub 3}]{sup 2+}, which was recently refined for use in molecular dynamics simulations, is reviewed with some additional results. In particular, the quality of the refined model Hamiltonian is examined in terms of the vibrational frequencies and solvation structures of the lowest singlet and quintet states.

  9. PIC simulations of the trapped electron filamentation instability in finite-width electron plasma waves

    NASA Astrophysics Data System (ADS)

    Winjum, B. J.; Banks, J. W.; Berger, R. L.; Cohen, B. I.; Chapman, T.; Hittinger, J. A. F.; Rozmus, W.; Strozzi, D. J.; Brunner, S.

    2012-10-01

    We present results on the kinetic filamentation of finite-width nonlinear electron plasma waves (EPW). Using 2D simulations with the PIC code BEPS, we excite a traveling EPW with a Gaussian transverse profile and a wavenumber k0λDe= 1/3. The transverse wavenumber spectrum broadens during transverse EPW localization for small width (but sufficiently large amplitude) waves, while the spectrum narrows to a dominant k as the initial EPW width increases to the plane-wave limit. For large EPW widths, filaments can grow and destroy the wave coherence before transverse localization destroys the wave; the filaments in turn evolve individually as self-focusing EPWs. Additionally, a transverse electric field develops that affects trapped electrons, and a beam-like distribution of untrapped electrons develops between filaments and on the sides of a localizing EPW. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the Laboratory Research and Development Program at LLNL under project tracking code 12-ERD-061. Supported also under Grants DE-FG52-09NA29552 and NSF-Phy-0904039. Simulations were performed on UCLA's Hoffman2 and NERSC's Hopper.

  10. Trapped Electron Instability of Electron Plasma Waves: Vlasov simulations and theory

    NASA Astrophysics Data System (ADS)

    Berger, Richard; Chapman, Thomas; Brunner, Stephan

    2013-10-01

    The growth of sidebands of a large-amplitude electron plasma wave is studied with Vlasov simulations for a range of amplitudes (. 001 < eϕ0 /Te < 1) and wavenumbers (0 . 25 simulations allows the growth rate of the unstable modes to be determined accurately and compared to theory. Despite the simplicity of the dispersion relation, growth rates found with the Kruer-Dawson-Sudan model [Kruer et al. PRL 23, 838 (1969)] agree quite well with the numerical results. The most unstable modes with frequency and wavenumber ω , k satisfy the relation, ω - k .vph = +/-ωbe , where vph =ω0 /k0 and ωbe is the bounce frequency of a deeply trapped electron. In 2D simulations, we find that the instability persists and co-exists with the filamentation instability. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the Laboratory Research and Development Program at LLNL under project tracking code 12-ERD.

  11. Singular structures in magneto- and electron-magneto-hydrodynamic flows

    NASA Astrophysics Data System (ADS)

    Grauer, Rainer

    2002-11-01

    We present results of numerical simulations of magneto- and electron-magnetohydrodynamic systems using adaptive mesh refinement. The simulations suggest that there is no finite time singularity in the two and three dimensional MHD equations whereas the situation for the electron MHD equation is much more subtle. In the EMHD case it turns out that the growth of vorticity is scale dependent. Although an effective resolution of 65536x131072 mesh point was achieved, a definite scaling could not be reached. We propose a new massive parallel AMR code developed by J. Dreher and R. Grauer for the next step of singularity simulations.

  12. Xyce Parallel Electronic Simulator Reference Guide Version 6.6.

    SciTech Connect

    Keiter, Eric R.; Aadithya, Karthik Venkatraman; Mei, Ting; Russo, Thomas V.; Schiek, Richard; Sholander, Peter E.; Thornquist, Heidi K.; Verley, Jason

    2016-11-01

    This document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users' Guide [1] . The focus of this document is (to the extent possible) exhaustively list device parameters, solver options, parser options, and other usage details of Xyce . This document is not intended to be a tutorial. Users who are new to circuit simulation are better served by the Xyce Users' Guide [1] . The information herein is subject to change without notice. Copyright c 2002-2016 Sandia Corporation. All rights reserved. Acknowledgements The BSIM Group at the University of California, Berkeley developed the BSIM3, BSIM4, BSIM6, BSIM-CMG and BSIM-SOI models. The BSIM3 is Copyright c 1999, Regents of the University of California. The BSIM4 is Copyright c 2006, Regents of the University of California. The BSIM6 is Copyright c 2015, Regents of the University of California. The BSIM-CMG is Copyright c 2012 and 2016, Regents of the University of California. The BSIM-SOI is Copyright c 1990, Regents of the University of California. All rights reserved. The Mextram model has been developed by NXP Semiconductors until 2007, Delft University of Technology from 2007 to 2014, and Auburn University since April 2015. Copyrights c of Mextram are with Delft University of Technology, NXP Semiconductors and Auburn University. The MIT VS Model Research Group developed the MIT Virtual Source (MVS) model. Copyright c 2013 Massachusetts Institute of Technology (MIT). The EKV3 MOSFET model was developed by the EKV Team of the Electronics Laboratory-TUC of the Technical University of Crete. Trademarks Xyce TM Electronic Simulator and Xyce TM are trademarks of Sandia Corporation. Orcad, Orcad Capture, PSpice and Probe are registered trademarks of Cadence Design Systems, Inc. Microsoft, Windows and Windows 7 are registered trademarks of Microsoft Corporation. Medici, DaVinci and Taurus are registered trademarks of Synopsys Corporation. Amtec and TecPlot are

  13. Hybrid simulation of reforming shocks with electron mass and pressure tensor effects

    NASA Astrophysics Data System (ADS)

    Yuan, Xingqiu; Cairns, Iver H.; Robinson, Peter A.

    2007-01-01

    We examine the dynamics of low plasma beta (β = 0.05), high Alfvén Mach number (M A = 4 ˜ 5), quasi-perpendicular (theta bn = 87°) collisionless shocks using two one-dimensional hybrid simulation codes, a standard hybrid code with massless fluid electrons and a new extended hybrid code with finite electron mass, and the full electron pressure tensor. Both hybrid codes predict similar macroscopic shock structures with well defined foot, ramp, overshoot and downstream regions and a shock that reforms with a quasi-cyclic change of the shock front structure. The shock reformation period predicted by the standard hybrid code is 1.8Ω ci -1 (Ω ci is the upstream ion gyrofrequency). In contrast to the standard hybrid simulations, the additional electron dissipation in the new extended hybrid code leads to a strong ion thermalization and phase space mixing between upstream incoming and reflected ions via plasma wave interactions in the foot, and formation of ion phase space holes. Whistler waves with typical wavelength ≃0.3v A Ω ci -1 and frequency ≃5.5Ω ci -1 are observed in the foot, and ramp region which help to stop the shock steepening, and reduce the predicted shock reformation period to 1.6Ω ci -1.

  14. Non-equilibrium Green function method: theory and application in simulation of nanometer electronic devices

    NASA Astrophysics Data System (ADS)

    Do, Van-Nam

    2014-09-01

    We review fundamental aspects of the non-equilibrium Green function method in the simulation of nanometer electronic devices. The method is implemented into our recently developed computer package OPEDEVS to investigate transport properties of electrons in nano-scale devices and low-dimensional materials. Concretely, we present the definition of the four real-time Green functions, the retarded, advanced, lesser and greater functions. Basic relations among these functions and their equations of motion are also presented in detail as the basis for the performance of analytical and numerical calculations. In particular, we review in detail two recursive algorithms, which are implemented in OPEDEVS to solve the Green functions defined in finite-size opened systems and in the surface layer of semi-infinite homogeneous ones. Operation of the package is then illustrated through the simulation of the transport characteristics of a typical semiconductor device structure, the resonant tunneling diodes.

  15. Simulation study of interactions of Space Shuttle-generated electron beams with ambient plasmas

    NASA Technical Reports Server (NTRS)

    Lin, Chin S.

    1992-01-01

    This report summarizes results obtained through the support of NASA Grant NAGW-1936. The objective of this report is to conduct large scale simulations of electron beams injected into space. The topics covered include the following: (1) simulation of radial expansion of an injected electron beam; (2) simulations of the active injections of electron beams; (3) parameter study of electron beam injection into an ionospheric plasma; and (4) magnetosheath-ionospheric plasma interactions in the cusp.

  16. DNA strand breaks induced by electrons simulated with Nanodosimetry Monte Carlo Simulation Code: NASIC.

    PubMed

    Li, Junli; Li, Chunyan; Qiu, Rui; Yan, Congchong; Xie, Wenzhang; Wu, Zhen; Zeng, Zhi; Tung, Chuanjong

    2015-09-01

    The method of Monte Carlo simulation is a powerful tool to investigate the details of radiation biological damage at the molecular level. In this paper, a Monte Carlo code called NASIC (Nanodosimetry Monte Carlo Simulation Code) was developed. It includes physical module, pre-chemical module, chemical module, geometric module and DNA damage module. The physical module can simulate physical tracks of low-energy electrons in the liquid water event-by-event. More than one set of inelastic cross sections were calculated by applying the dielectric function method of Emfietzoglou's optical-data treatments, with different optical data sets and dispersion models. In the pre-chemical module, the ionised and excited water molecules undergo dissociation processes. In the chemical module, the produced radiolytic chemical species diffuse and react. In the geometric module, an atomic model of 46 chromatin fibres in a spherical nucleus of human lymphocyte was established. In the DNA damage module, the direct damages induced by the energy depositions of the electrons and the indirect damages induced by the radiolytic chemical species were calculated. The parameters should be adjusted to make the simulation results be agreed with the experimental results. In this paper, the influence study of the inelastic cross sections and vibrational excitation reaction on the parameters and the DNA strand break yields were studied. Further work of NASIC is underway.

  17. Mechanism Study of Gate Leakage Current for AlGaN/GaN High Electron Mobility Transistor Structure Under High Reverse Bias by Thin Surface Barrier Model and Technology Computer Aided Design Simulation

    NASA Astrophysics Data System (ADS)

    Hayashi, Kazuo; Yamaguchi, Yutaro; Oishi, Toshiyuki; Otsuka, Hiroshi; Yamanaka, Koji; Nakayama, Masatoshi; Miyamoto, Yasuyuki

    2013-04-01

    Gate leakage current mechanism in GaN high electron mobility transistors (HEMTs) has been studied using a two-dimensional thin surface barrier (TSB) model to represent two unintentional donor thin layers that exit under and outside the gate electrode due to the existence of surface defects. The donor thin layer outside the gate affects the reverse gate current at the high gate voltage above the pinch-off voltage. Higher donor concentration of thin layer outside the gate results in larger ratio of lateral to vertical components of the electric field at the gate edge. On the other hand, the electric field at the center of the gate has only the vertical electric field component. As a result, the two-dimensional effects are only important for the reverse gate current above the pinch-off voltage. We have confirmed in this paper that the simulation results provided by our model correlate very well with the experimental reverse gate current characteristics of the device for a very wide range of reverse gate voltage from 0.1 to 90 V.

  18. Simulation of electron beam formation and transport in a gas-filled electron-optical system with a plasma emitter

    NASA Astrophysics Data System (ADS)

    Grishkov, A. A.; Kornilov, S. Yu.; Rempe, N. G.; Shidlovskiy, S. V.; Shklyaev, V. A.

    2016-07-01

    The results of computer simulations of the electron-optical system of an electron gun with a plasma emitter are presented. The simulations are performed using the KOBRA3-INP, XOOPIC, and ANSYS codes. The results describe the electron beam formation and transport. The electron trajectories are analyzed. The mechanisms of gas influence on the energy inhomogeneity of the beam and its current in the regions of beam primary formation, acceleration, and transport are described. Recommendations for optimizing the electron-optical system with a plasma emitter are presented.

  19. Velocity-space structure of runaway electrons

    SciTech Connect

    Fuchs, V.; Cairns, R.A.; Lashmore-Davies, C.N.; Shoucri, M.M.

    1986-09-01

    The region of velocity space is determined in which electron runaway occurs because of a dc electric field. Phase-space analysis of the relaxation equations describing test electrons, corroborated by two-dimensional (2-D) numerical integration of the Fokker--Planck equation, reveals that the Dreicer condition for runaway v-italic/sup 2//sub parallel/> or =(2+Z-italic/sub i-italic/)E-italic/sub c-italic//E-italic is only sufficient. A weaker condition v-italic/sup 2//sub parallel/> or =(2+Z-italic/sub i-italic/)/sup 1//sup ///sup 2/E-italic/sub c-italic//E-italic is established, and it is shown, in general, that runaway in velocity space only occurs for those electrons that are outside one of the separatrices of the relaxation equations. The scaling with v-italic/sub parallel/ of the parallel distribution function and of the perpendicular temperature is also derived.

  20. Xyce Parallel Electronic Simulator - Users' Guide Version 2.1.

    SciTech Connect

    Hutchinson, Scott A; Hoekstra, Robert J.; Russo, Thomas V.; Rankin, Eric; Pawlowski, Roger P.; Fixel, Deborah A; Schiek, Richard; Bogdan, Carolyn W.; Shirley, David N.; Campbell, Phillip M.; Keiter, Eric R.

    2005-06-01

    This manual describes the use of theXyceParallel Electronic Simulator.Xycehasbeen designed as a SPICE-compatible, high-performance analog circuit simulator, andhas been written to support the simulation needs of the Sandia National Laboratorieselectrical designers. This development has focused on improving capability over thecurrent state-of-the-art in the following areas:%04Capability to solve extremely large circuit problems by supporting large-scale par-allel computing platforms (up to thousands of processors). Note that this includessupport for most popular parallel and serial computers.%04Improved performance for all numerical kernels (e.g., time integrator, nonlinearand linear solvers) through state-of-the-art algorithms and novel techniques.%04Device models which are specifically tailored to meet Sandia's needs, includingmany radiation-aware devices.3 XyceTMUsers' Guide%04Object-oriented code design and implementation using modern coding practicesthat ensure that theXyceParallel Electronic Simulator will be maintainable andextensible far into the future.Xyceis a parallel code in the most general sense of the phrase - a message passingparallel implementation - which allows it to run efficiently on the widest possible numberof computing platforms. These include serial, shared-memory and distributed-memoryparallel as well as heterogeneous platforms. Careful attention has been paid to thespecific nature of circuit-simulation problems to ensure that optimal parallel efficiencyis achieved as the number of processors grows.The development ofXyceprovides a platform for computational research and de-velopment aimed specifically at the needs of the Laboratory. WithXyce, Sandia hasan %22in-house%22 capability with which both new electrical (e.g., device model develop-ment) and algorithmic (e.g., faster time-integration methods, parallel solver algorithms)research and development can be performed. As a result,Xyceis a unique electricalsimulation capability, designed to

  1. Linear delta-f simulations of nonlocal electron heat transport

    NASA Astrophysics Data System (ADS)

    Brunner, S.; Valeo, E.; Krommes, J. A.

    2000-07-01

    Nonlocal electron heat transport calculations are carried out by making use of some of the techniques developed previously for extending the δf method to transport time scale simulations [S. Brunner, E. Valeo, and J. Krommes, Phys. Plasmas 6, 4504 (1999)]. By considering the relaxation of small amplitude temperature perturbations of an homogeneous Maxwellian background, only the linearized Fokker-Planck equation has to be solved, and direct comparisons can be made with the equivalent, nonlocal hydrodynamic approach [V. Yu. Bychenkov et al., Phys. Rev. Lett. 75, 4405 (1995)]. A quasineutrality-conserving algorithm is derived for computing the self-consistent electric fields driving the return currents. In the low-collisionality regime, results illustrate the importance of taking account of nonlocality in both space and time.

  2. Numerical simulation of condensation on structured surfaces.

    PubMed

    Fu, Xiaowu; Yao, Zhaohui; Hao, Pengfei

    2014-11-25

    Condensation of liquid droplets on solid surfaces happens widely in nature and industrial processes. This phase-change phenomenon has great effect on the performance of some microfluidic devices. On the basis of micro- and nanotechnology, superhydrophobic structured surfaces can be well-fabricated. In this work, the nucleating and growth of droplets on different structured surfaces are investigated numerically. The dynamic behavior of droplets during the condensation is simulated by the multiphase lattice Boltzmann method (LBM), which has the ability to incorporate the microscopic interactions, including fluid-fluid interaction and fluid-surface interaction. The results by the LBM show that, besides the chemical properties of surfaces, the topography of structures on solid surfaces influences the condensation process. For superhydrophobic surfaces, the spacing and height of microridges have significant influence on the nucleation sites. This mechanism provides an effective way for prevention of wetting on surfaces in engineering applications. Moreover, it suggests a way to prevent ice formation on surfaces caused by the condensation of subcooled water. For hydrophilic surfaces, however, microstructures may be submerged by the liquid films adhering to the surfaces. In this case, microstructures will fail to control the condensation process. Our research provides an optimized way for designing surfaces for condensation in engineering systems.

  3. ElePhant--an anatomical electronic phantom as simulation-system for otologic surgery.

    PubMed

    Grunert, R; Strauss, G; Moeckel, H; Hofer, M; Poessneck, A; Fickweiler, U; Thalheim, M; Schmiedel, R; Jannin, P; Schulz, T; Oeken, J; Dietz, A; Korb, W

    2006-01-01

    This paper describes the ElePhant (Electronic Phantom)-an anatomical correct simulation system based on 3D rapid prototyping models for the otologic intervention "Mastoidectomy". The anatomical structures of the head are created with plaster as base material using 3D-printing as rapid prototyping technology (RPT). Structures at risk, represented by electrically conductible material and fiber optics, are realized as an electric circuit and can be detected during the simulation of the surgical procedure. An accuracy study of 15 identical RPT-models compared to the 3D reconstructed CT-dataset of the patient showed that the mean accuracy is lower than the reconstructed CT layer thickness of 0.5 mm. An evaluation study of the ElePhant-system for "Mastoidectomy" was performed by 7 ENT-surgeons. The mean value of the study questionnaire (evaluation range from -2 (not at all) to +2 (very good)) was +1.2. The results showed that the ElePhant can simulate "Mastoidectomy" realistically. It is especially suitable for the simulation of the correct representation and position of the anatomical structures, realistic operation setting, and realistic milling properties of the bone structure. Furthermore it is applicable for training of surgeons.

  4. Xyce Parallel Electronic Simulator Users' Guide Version 6.6.

    SciTech Connect

    Keiter, Eric R.; Aadithya, Karthik Venkatraman; Mei, Ting; Russo, Thomas V.; Schiek, Richard; Sholander, Peter E.; Thornquist, Heidi K.; Verley, Jason

    2016-11-01

    This manual describes the use of the Xyce Parallel Electronic Simulator. Xyce has been de- signed as a SPICE-compatible, high-performance analog circuit simulator, and has been written to support the simulation needs of the Sandia National Laboratories electrical designers. This development has focused on improving capability over the current state-of-the-art in the following areas: Capability to solve extremely large circuit problems by supporting large-scale parallel com- puting platforms (up to thousands of processors). This includes support for most popular parallel and serial computers. A differential-algebraic-equation (DAE) formulation, which better isolates the device model package from solver algorithms. This allows one to develop new types of analysis without requiring the implementation of analysis-specific device models. Device models that are specifically tailored to meet Sandia's needs, including some radiation- aware devices (for Sandia users only). Object-oriented code design and implementation using modern coding practices. Xyce is a parallel code in the most general sense of the phrase -- a message passing parallel implementation -- which allows it to run efficiently a wide range of computing platforms. These include serial, shared-memory and distributed-memory parallel platforms. Attention has been paid to the specific nature of circuit-simulation problems to ensure that optimal parallel efficiency is achieved as the number of processors grows. The information herein is subject to change without notice. Copyright c 2002-2016 Sandia Corporation. All rights reserved. Acknowledgements The BSIM Group at the University of California, Berkeley developed the BSIM3, BSIM4, BSIM6, BSIM-CMG and BSIM-SOI models. The BSIM3 is Copyright c 1999, Regents of the University of California. The BSIM4 is Copyright c 2006, Regents of the University of California. The BSIM6 is Copyright c 2015, Regents of the University of California. The BSIM-CMG is Copyright c 2012

  5. Xyce Parallel Electronic Simulator Users Guide Version 6.4

    SciTech Connect

    Keiter, Eric R.; Mei, Ting; Russo, Thomas V.; Schiek, Richard; Sholander, Peter E.; Thornquist, Heidi K.; Verley, Jason; Baur, David Gregory

    2015-12-01

    This manual describes the use of the Xyce Parallel Electronic Simulator. Xyce has been de- signed as a SPICE-compatible, high-performance analog circuit simulator, and has been written to support the simulation needs of the Sandia National Laboratories electrical designers. This development has focused on improving capability over the current state-of-the-art in the following areas: Capability to solve extremely large circuit problems by supporting large-scale parallel com- puting platforms (up to thousands of processors). This includes support for most popular parallel and serial computers. A differential-algebraic-equation (DAE) formulation, which better isolates the device model package from solver algorithms. This allows one to develop new types of analysis without requiring the implementation of analysis-specific device models. Device models that are specifically tailored to meet Sandia's needs, including some radiation- aware devices (for Sandia users only). Object-oriented code design and implementation using modern coding practices. Xyce is a parallel code in the most general sense of the phrase -- a message passing parallel implementation -- which allows it to run efficiently a wide range of computing platforms. These include serial, shared-memory and distributed-memory parallel platforms. Attention has been paid to the specific nature of circuit-simulation problems to ensure that optimal parallel efficiency is achieved as the number of processors grows. Trademarks The information herein is subject to change without notice. Copyright c 2002-2015 Sandia Corporation. All rights reserved. Xyce TM Electronic Simulator and Xyce TM are trademarks of Sandia Corporation. Portions of the Xyce TM code are: Copyright c 2002, The Regents of the University of California. Produced at the Lawrence Livermore National Laboratory. Written by Alan Hindmarsh, Allan Taylor, Radu Serban. UCRL-CODE-2002-59 All rights reserved. Orcad, Orcad Capture, PSpice and Probe are

  6. First-Principles Simulations of Inelastic Electron Tunneling Spectroscopy of Molecular Electronic Devices

    NASA Astrophysics Data System (ADS)

    Jiang, Jun; Kula, Mathias; Lu, Wei; Luo, Yi

    2005-08-01

    A generalized Green's function theory is developed to simulate the inelastic electron tunneling spectroscopy (IETS) of molecular junctions. It has been applied to a realistic molecular junction with an octanedithiolate embedded between two gold contacts in combination with the hybrid density functional theory calculations. The calculated spectra are in excellent agreement with recent experimental results. Strong temperature dependence of the experimental IETS spectra is also reproduced. It is shown that the IETS is extremely sensitive to the intra-molecular conformation and to the molecule-metal contact geometry.

  7. Simulation tools for pinched-electron-beam radiographic diodes

    NASA Astrophysics Data System (ADS)

    Humphries, Stanley; Orzechowski, Thaddeus

    2006-02-01

    We describe capabilities of an integrated software suite to simulate pinched-electron-beam diodes for pulsed radiography. In contrast to other reported work using particle-in-cell methods, we employ a ray-tracing code (Trak) with advanced capabilities for modeling beam-generated magnetic fields. Ray tracing is a direct approach to a steady-state solution and involves less work than a particle-in-cell calculation. The second software component, GamBet, is a new Monte Carlo code for radiation transport that incorporates effects of the complex electric and magnetic fields at the radiation target. The ray-tracing approach exhibits good convergence in calculations for the diode geometry of the compact radiography (CRAD) program at Lawrence Livermore National Laboratory. With a 1.5 MV, 30 ns driver, we predict that the diode can produce a beam with axial length ˜1 mm that generates isotropic bremsstrahlung radiation exceeding 1 rad at 1 m. The ray-tracing procedure encounters convergence problems when applied to the rod-pinch geometry, a configuration used in several pulsed radiographic machines. We observe a fundamental difference in the nature of electron orbits in the two diodes. There is an increased chance for particle-orbit feedback in the rod pinch, so that equilibrium solutions are sensitive to small changes in emission characteristics.

  8. Selected CERES electronic component survivability under simulated overvoltage conditions

    NASA Astrophysics Data System (ADS)

    Chapman, John J.; Grant, Michael S.; Bockman, James; Clark, Vernon M.; Hess, Phillip C.

    1999-09-01

    In August, 1998, a Clouds and the Earth's Radiant Energy System (CERES) instrument telemetry housekeeping parameter generated a yellow warning message that indicated an on- board +15V Data Acquisition Assembly (DAA) power converter deregulation anomaly. An exhaustive investigation was undertaken to understand this anomaly and the long-term consequnces which have severely reduced CERES operations on the Tropical Rainfall Measuring Mission (TRMM) spacecraft. Among investigations performed were groudn tests that approximated the on-board electronic circuitry using a small quantity of flight identical components exposed to maximum spacecraft bus over-voltage conditions. These components include monolithic integrated microcircuits that perform analog signal conditions on instrument sensor signals and an analog-to-digital converter (ADC) for the entire DAA. All microcircuit packages have either a bipolar silicon design with internal current limiting protections or have a complementary metal oxide semiconductor (CMOS) design with bias protections. Ground test that have been running for approximately 8 months have indicated that these components are capable of withstanding as much as twice their input supply voltage ratings without noticeable performance degradation. This data provided CERES operators with assured confidence to be able to continue instrument science operations over the remaining life of the TRMM. This paper will discuss this anomaly and some possible cause, a simulator of affected electronics, test results, prognosis for future CERES operations, and conclusions.

  9. Crashworthiness simulation of composite automotive structures

    SciTech Connect

    Botkin, M E; Johnson, N L; Simunovic, S; Zywicz, E

    1998-06-01

    In 1990 the Automotive Composites Consortium (ACC) began the investigation of crash worthiness simulation methods for composite materials. A contract was given to Livermore Software Technology Corporation (LSTC) to implement a new damage model in LS-DYNA3DTM specifically for composite structures. This model is in LS-DYNA3DTM and is in use by the ACC partners. In 1994 USCAR, a partnership of American auto companies, entered into a partnership called SCAAP (Super Computing Automotive Applications Partnership) for the express purpose of working with the National Labs on computational oriented research. A CRADA (Cooperative Research and Development Agreement) was signed with Lawrence Livermore National Laboratory, Oak Ridge National Laboratory, Sandia National Laboratory, Argonne National Laboratory, and Los Alamos National Laboratory to work in three distinctly different technical areas, one of which was composites material modeling for crash worthiness. Each Laboratory was assigned a specific modeling task. The ACC was responsible for the technical direction of the composites project and provided all test data for code verification. All new models were to be implemented in DYNA3D and periodically distributed to all partners for testing. Several new models have been developed and implemented. Excellent agreement has been shown between tube crush simulation and experiments.

  10. Beam Dynamics Simulations of Optically-Enhanced Field Emission from Structured Cathodes

    SciTech Connect

    Seymour, A.; Grote, D.; Mihalcea, D.; Piot, P.; Vay, J.-L.

    2014-01-01

    Structured cathodes - cathodes with a segmented emission surface - are finding an increasing number of applications and can be combined with a variety of emission mechanisms, including photoemission and field emission. These cathodes have been used to enhance the quantum efficiency of metallic cathodes when operated as plasmonic cathodes, have produced high-current electron bunches though field emission from multiple tips, and can be used to form beams with transverse segmentations necessary for improving the performance of accelerator-based light sources. In this report we present recent progress towards the development of finite-difference time-domain particle-in-cell simulations using the emission process in structured cathodes based on the WARP framework. The simulations give further insight on the localized source of the emitted electrons which could be used for additional high-fidelity start-to-end simulations of electron accelerators that employ this type of electron source.

  11. Driving Plasmaspheric Electron Density Simulations During Geomagnetic Storms

    NASA Astrophysics Data System (ADS)

    De Pascuale, S.; Kletzing, C.; Jordanova, V.; Goldstein, J.; Wygant, J. R.; Thaller, S. A.

    2015-12-01

    We test global convection electric field models driving plasmaspheric electron density simulations (RAM-CPL) during geomagnetic storms with in situ measurements provided by the Van Allen Probes (RBSP). RAM-CPL is the cold plasma component of the ring-current atmosphere interactions suite (RAM-SCB) and describes the evolution of plasma density in the magnetic equatorial plane near Earth. Geomagnetic events observed by the RBSP satellites in different magnetic local time (MLT) sectors enable a comparison of local asymmetries in the input electric field and output densities of these simulations. Using a fluid MHD approach, RAM-CPL reproduces core plasmaspheric densities (L<4) to less than 1 order of magnitude difference. Approximately 80% of plasmapause crossings, defined by a low-density threshold, are reproduced to within a mean radial difference of 0.6 L. RAM-CPL, in conjunction with a best-fit driver, can be used in other studies as an asset to predict density conditions in locations distant from RBSP orbits of interest.

  12. Syntheses and electronic structures of decamethylmetallocenes

    SciTech Connect

    Robbins, J.L.

    1981-04-01

    The synthesis of decamethylmanganocene ((eta-C/sub 5/(CH/sub 3/)/sub 5/)/sub 2/Mn or (Me/sub 5/Cp)/sub 2/Mn)) is described. Magnetic susceptibility and electron paramagnetic resonance (EPR) studies show that (Me/sub 5/Cp)/sub 2/Mn is a low-spin, 17-electron compound with an orbitally degenerate, /sup 2/E/sub 2g/ (e/sub 2g//sup 3/ a/sub 1g//sup 2/) ground state. An x-ray crystallographic study of (Me/sub 5/Cp)/sub 2/Mn shows that it is a monomeric, D/sub 5d/ decamethylmetallocene with metal to ring carbon distances that are about 0.3 A shorter than those determined for high-spin manganocenes. The syntheses of new (Me/sub 5/Cp)/sub 2/M (M = Mg,V,Cr,Co, and Ni) and ((Me/sub 5/Cp)/sub 2/M)PF/sub 6/ (M = Cr,Co, and Ni) compounds are described. In addition, a preparative route to a novel, dicationic decamethylmetallocene, ((Me/sub 5/Cp)/sub 2/Ni)(PF/sub 6/)/sub 2/ is reported. Infrared, nuclear magnetic resonance, magnetic susceptibility, and/or x-ray crystallographic studies indicate that all the above compounds are D/sub 5d/ or D/sub 5h/ decamethylmetallocenes with low-spin electronic configurations. Cyclic voltammetry studies verify the reversibility and the one-electron nature of the (Me/sub 5/Cp)/sub 2/M ..-->.. ((Me/sub 5/Cp)/sub 2/M)/sup +/ (M = Cr,Mn,Fe,Co,Ni), ((Me/sub 5/Cp)/sub 2/Mn)/sup -/ ..-->.. (Me/sub 5/Cp)/sub 2/Mn and ((Me/sub 5/Cp)/sub 2/Ni)/sup +/ ..-->.. (Me/sub 5/Cp)/sub 2/Ni)/sup 2 +/ redox reactions. These studies reveal that the neutral decamethylmetallocenes are much more easily oxidized than their metallocene counterparts. This result attests to the electron-donating properties of the ten substituent methyl groups. Proton and carbon-13 NMR data are reported for the diamagnetic Mg(II), Mn(I), Fe(II), Co(III), and Ni(IV) decamethylmetallocenes and for ((Me/sub 5/Cp)/sub 2/V(CO)/sub 2/)/sup +/. The uv-visible absorption spectra of the 15-, 18- and 20- electron decamethylmetallocenes are also reported.

  13. Electronic structure and optical properties of solid C 60

    NASA Astrophysics Data System (ADS)

    Mattesini, M.; Ahuja, R.; Sa, L.; Hugosson, H. W.; Johansson, B.; Eriksson, O.

    2009-06-01

    The electronic structure and the optical properties of face-centered-cubic C 60 have been investigated by using an all-electron full-potential method. Our ab initio results show that the imaginary dielectric function for high-energy values looks very similar to that of graphite, revealing close electronic structure similarities between the two systems. We have also identified the origin of different peaks in the dielectric function of fullerene by means of the calculated electronic density of states. The computed optical spectrum compares fairly well with the available experimental data for the Vis-UV absorption spectrum of solid C 60.

  14. Physics and simulation study of nanoscale electronic devices

    NASA Astrophysics Data System (ADS)

    Mehrotra, Saumitra R.

    Silicon based CMOS technology has seen continuous scaling of device dimensions for past three decades. There is a lot of focus on incorporating different high mobility channel materials and new device architectures for post-Si CMOS logic technology, making it a multifaceted problem. In this thesis some of the multiple challenges concerning new CMOS technologies are addressed. High carrier mobility alloyed channel materials like SiGe and InGaAs suffer from scattering due to disorder called, alloy scattering. The current theory of alloy scattering present in literature/text books can be called rudimentary at the best due to lack of a strong theoretical foundation and/or use of fitting parameters to explain experimental measurements. We present a new atomistic approach based on tight-binding parameters to understanding the alloy disorder. Using this approach we are able to provide new insights into the theory of alloy scattering and explain the experimental measurements in bulk SiGe and InGaAs that were till now based on just fitting parameters. With an updated understanding of alloy scattering, hole mobility in SiGe nanowires is calculated using a linearized Boltzmann formalism. Bulk Ge exhibits high hole mobility makeing it ideal for PMOS devices. Nano patterning of Ge/SiGe leads to Ge nanofins with both uniaxial and biaxial strain components, making it a device architecture design problem. Fully atomistic simulations involving molecular dynamics (ReaxFF force field) based relaxation for strain relaxation; tight-binding based bandstructure calculations and a linearized Boltzmann transport model for mobility calculations are performed. Final phonon mobility calculations reveal nearly 3.5 X improvements compared to biaxial strained Ge in Ge nanofins with width reduction. High electron mobility III--V's are projected to be a material of choice for post-Si NMOS. These low electron mass materials suffer from the 'DOS bottleneck' issue. Transistor designs based on using

  15. Energy-filtered Electron Transport Structures for Low-power Low-noise 2-D Electronics

    PubMed Central

    Pan, Xuan; Qiu, Wanzhi; Skafidas, Efstratios

    2016-01-01

    In addition to cryogenic techniques, energy filtering has the potential to achieve high-performance low-noise 2-D electronic systems. Assemblies based on graphene quantum dots (GQDs) have been demonstrated to exhibit interesting transport properties, including resonant tunnelling. In this paper, we investigate GQDs based structures with the goal of producing energy filters for next generation lower-power lower-noise 2-D electronic systems. We evaluate the electron transport properties of the proposed GQD device structures to demonstrate electron energy filtering and the ability to control the position and magnitude of the energy passband by appropriate device dimensioning. We also show that the signal-to-thermal noise ratio performance of the proposed nanoscale device can be modified according to device geometry. The tunability of two-dimensional GQD structures indicates a promising route for the design of electron energy filters to produce low-power and low-noise electronics. PMID:27796343

  16. Energy-filtered Electron Transport Structures for Low-power Low-noise 2-D Electronics.

    PubMed

    Pan, Xuan; Qiu, Wanzhi; Skafidas, Efstratios

    2016-10-31

    In addition to cryogenic techniques, energy filtering has the potential to achieve high-performance low-noise 2-D electronic systems. Assemblies based on graphene quantum dots (GQDs) have been demonstrated to exhibit interesting transport properties, including resonant tunnelling. In this paper, we investigate GQDs based structures with the goal of producing energy filters for next generation lower-power lower-noise 2-D electronic systems. We evaluate the electron transport properties of the proposed GQD device structures to demonstrate electron energy filtering and the ability to control the position and magnitude of the energy passband by appropriate device dimensioning. We also show that the signal-to-thermal noise ratio performance of the proposed nanoscale device can be modified according to device geometry. The tunability of two-dimensional GQD structures indicates a promising route for the design of electron energy filters to produce low-power and low-noise electronics.

  17. Energy-filtered Electron Transport Structures for Low-power Low-noise 2-D Electronics

    NASA Astrophysics Data System (ADS)

    Pan, Xuan; Qiu, Wanzhi; Skafidas, Efstratios

    2016-10-01

    In addition to cryogenic techniques, energy filtering has the potential to achieve high-performance low-noise 2-D electronic systems. Assemblies based on graphene quantum dots (GQDs) have been demonstrated to exhibit interesting transport properties, including resonant tunnelling. In this paper, we investigate GQDs based structures with the goal of producing energy filters for next generation lower-power lower-noise 2-D electronic systems. We evaluate the electron transport properties of the proposed GQD device structures to demonstrate electron energy filtering and the ability to control the position and magnitude of the energy passband by appropriate device dimensioning. We also show that the signal-to-thermal noise ratio performance of the proposed nanoscale device can be modified according to device geometry. The tunability of two-dimensional GQD structures indicates a promising route for the design of electron energy filters to produce low-power and low-noise electronics.

  18. Electron Precipitation Associated with Small-Scale Auroral Structures

    NASA Astrophysics Data System (ADS)

    Michell, R.; Samara, M.; Grubbs, G. A., II; Hampton, D. L.; Bonnell, J. W.; Ogasawara, K.

    2014-12-01

    We present results from the Ground-to-Rocket Electrons Electrodynamics Correlative Experiment (GREECE) sounding rocket mission, where we combined high-resolution ground-based auroral imaging with high time-resolution precipitating electron measurements. The GREECE payload successfully launched from Poker Flat, Alaska on 03 March 2014 and reached an apogee of approximately 335 km. The narrow field-of-view auroral imaging was taken from Venetie, AK, which is directly under apogee. This enabled the small-scale auroral features at the magnetic footpoint of the rocket payload to be imaged in detail. The electron precipitation was measured with the Acute Precipitating Electron Spectrometer (APES) onboard the payload. Features in the electron data are matched up with their corresponding auroral structures and boundaries, enabling measurement of the exact electron distributions responsible for the specific small-scale auroral features. These electron distributions will then be used to infer what the potential electron acceleration processes were.

  19. Simulation of electron energy loss spectra of nanomaterials with linear-scaling density functional theory

    NASA Astrophysics Data System (ADS)

    Tait, E. W.; Ratcliff, L. E.; Payne, M. C.; Haynes, P. D.; Hine, N. D. M.

    2016-05-01

    Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree with those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. Finally, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable.

  20. Sensitivity Simulation of Compressed Sensing Based Electronic Warfare Receiver Using Orthogonal Matching Pursuit Algorithm

    DTIC Science & Technology

    2016-02-01

    AFRL-RY-WP-TR-2016-0006 SENSITIVITY SIMULATION OF COMPRESSED SENSING BASED ELECTRONIC WARFARE RECEIVER USING ORTHOGONAL MATCHING PURSUIT...TITLE AND SUBTITLE SENSITIVITY SIMULATION OF COMPRESSED SENSING BASED ELECTRONIC WARFARE RECEIVER USING ORTHOGONAL MATCHING PURSUIT ALGORITHM 5a...August 2014. Report contains color. 14. ABSTRACT The wideband coverage of the traditional fast Fourier transform (FFT)-based electronic warfare

  1. Structural phase transition and electronic properties of NdBi

    SciTech Connect

    Sahu, Ashvini K.; Patiya, Jagdish; Sanyal, Sankar P.

    2015-06-24

    The structural and electronic properties of NdBi from an electronic structure calculation have been presented. The calculation is performed using self-consistent tight binding linear muffin tin orbital (TB-LMTO) method within the local density approximation (LDA). The calculated equilibrium structural parameters are in good agreement with the available experimental results. It is found that this compound shows metallic behavior under ambient condition and undergoes a structural phase transition from the NaCl structure to the CsCl structure at the pressure 20.1 GPa. The electronic structures of NdBi under pressure are investigated. It is found that NdBi have metallization and the hybridizations of atoms in NdBi under pressure become stronger.

  2. Electronic and structural properties of ultrathin tungsten nanowires and nanotubes by density functional theory calculation

    SciTech Connect

    Sun, Shih-Jye; Lin, Ken-Huang; Li, Jia-Yun; Ju, Shin-Pon

    2014-10-07

    The simulated annealing basin-hopping method incorporating the penalty function was used to predict the lowest-energy structures for ultrathin tungsten nanowires and nanotubes of different sizes. These predicted structures indicate that tungsten one-dimensional structures at this small scale do not possess B.C.C. configuration as in bulk tungsten material. In order to analyze the relationship between multi-shell geometries and electronic transfer, the electronic and structural properties of tungsten wires and tubes including partial density of state and band structures which were determined and analyzed by quantum chemistry calculations. In addition, in order to understand the application feasibility of these nanowires and tubes on nano-devices such as field emitters or chemical catalysts, the electronic stability of these ultrathin tungsten nanowires was also investigated by density functional theory calculations.

  3. Electron transport in the solar wind -results from numerical simulations

    NASA Astrophysics Data System (ADS)

    Smith, Håkan; Marsch, Eckart; Helander, Per

    A conventional fluid approach is in general insufficient for a correct description of electron trans-port in weakly collisional plasmas such as the solar wind. The classical Spitzer-Hürm theory is a not valid when the Knudsen number (the mean free path divided by the length scale of tem-perature variation) is greater than ˜ 10-2 . Despite this, the heat transport from Spitzer-Hürm a theory is widely used in situations with relatively long mean free paths. For realistic Knud-sen numbers in the solar wind, the electron distribution function develops suprathermal tails, and the departure from a local Maxwellian can be significant at the energies which contribute the most to the heat flux moment. To accurately model heat transport a kinetic approach is therefore more adequate. Different techniques have been used previously, e.g. particle sim-ulations [Landi, 2003], spectral methods [Pierrard, 2001], the so-called 16 moment method [Lie-Svendsen, 2001], and approximation by kappa functions [Dorelli, 2003]. In the present study we solve the Fokker-Planck equation for electrons in one spatial dimension and two velocity dimensions. The distribution function is expanded in Laguerre polynomials in energy, and a finite difference scheme is used to solve the equation in the spatial dimension and the velocity pitch angle. The ion temperature and density profiles are assumed to be known, but the electric field is calculated self-consistently to guarantee quasi-neutrality. The kinetic equation is of a two-way diffusion type, for which the distribution of particles entering the computational domain in both ends of the spatial dimension must be specified, leaving the outgoing distributions to be calculated. The long mean free path of the suprathermal electrons has the effect that the details of the boundary conditions play an important role in determining the particle and heat fluxes as well as the electric potential drop across the domain. Dorelli, J. C., and J. D. Scudder, J. D

  4. Observation Technique of Surface Magnetic Structure Using Type-I Magnetic Contrast in the Scanning Electron Microscope

    NASA Astrophysics Data System (ADS)

    Kotera, Masatoshi; Katoh, Misao; Suga, Hiroshi

    1995-12-01

    The type-I magnetic contrast in the scanning electron microscope is simulated. The magnetic flux that leaked from the surface magnetic domain is calculated based on the Maxwell equation. Trajectories of secondary electrons emitted from the surface are traced considering this magnetic field and the electric field generated by the secondary electron detector. On the basis of the characteristic variation of the spatial deviation of electrons arriving at the detector, the original domain structure at the specimen surface is estimated.

  5. Electron Debye scale Kelvin-Helmholtz instability: Electrostatic particle-in-cell simulations

    SciTech Connect

    Lee, Sang-Yun; Lee, Ensang Kim, Khan-Hyuk; Lee, Dong-Hun; Seon, Jongho; Jin, Ho

    2015-12-15

    In this paper, we investigated the electron Debye scale Kelvin-Helmholtz (KH) instability using two-dimensional electrostatic particle-in-cell simulations. We introduced a velocity shear layer with a thickness comparable to the electron Debye length and examined the generation of the KH instability. The KH instability occurs in a similar manner as observed in the KH instabilities in fluid or ion scales producing surface waves and rolled-up vortices. The strength and growth rate of the electron Debye scale KH instability is affected by the structure of the velocity shear layer. The strength depends on the magnitude of the velocity and the growth rate on the velocity gradient of the shear layer. However, the development of the electron Debye scale KH instability is mainly determined by the electric field generated by charge separation. Significant mixing of electrons occurs across the shear layer, and a fraction of electrons can penetrate deeply into the opposite side fairly far from the vortices across the shear layer.

  6. Electron Debye scale Kelvin-Helmholtz instability: Electrostatic particle-in-cell simulations

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Yun; Lee, Ensang; Kim, Khan-Hyuk; Lee, Dong-Hun; Seon, Jongho; Jin, Ho

    2015-12-01

    In this paper, we investigated the electron Debye scale Kelvin-Helmholtz (KH) instability using two-dimensional electrostatic particle-in-cell simulations. We introduced a velocity shear layer with a thickness comparable to the electron Debye length and examined the generation of the KH instability. The KH instability occurs in a similar manner as observed in the KH instabilities in fluid or ion scales producing surface waves and rolled-up vortices. The strength and growth rate of the electron Debye scale KH instability is affected by the structure of the velocity shear layer. The strength depends on the magnitude of the velocity and the growth rate on the velocity gradient of the shear layer. However, the development of the electron Debye scale KH instability is mainly determined by the electric field generated by charge separation. Significant mixing of electrons occurs across the shear layer, and a fraction of electrons can penetrate deeply into the opposite side fairly far from the vortices across the shear layer.

  7. Electron Energization and Structure of the Diffusion Region During Asymmetric Reconnection

    NASA Technical Reports Server (NTRS)

    Chen, Li-Jen; Hesse, Michael; Wang, Shan; Bessho, Naoki; Daughton, William

    2016-01-01

    Results from particle-in-cell simulations of reconnection with asymmetric upstream conditions are reported to elucidate electron energization and structure of the electron diffusion region (EDR). Acceleration of unmagnetized electrons results in discrete structures in the distribution functions and supports the intense current and perpendicular heating in the EDR. The accelerated electrons are cyclotron turned by the reconnected magnetic field to produce the outflow jets, and as such, the acceleration by the reconnection electric field is limited, leading to resistivity without particle-particle or particle-wave collisions. A map of electron distributions is constructed, and its spatial evolution is compared with quantities previously proposed to be EDR identifiers to enable effective identifications of the EDR in terrestrial magnetopause reconnection.

  8. Two-dimensional simulation and modeling in scanning electron microscope imaging and metrology research.

    PubMed

    Postek, Michael T; Vladár, András E; Lowney, Jeremiah R; Keery, William J

    2002-01-01

    Traditional Monte Carlo modeling of the electron beam-specimen interactions in a scanning electron microscope (SEM) produces information about electron beam penetration and output signal generation at either a single beam-landing location, or multiple landing positions. If the multiple landings lie on a line, the results can be graphed in a line scan-like format. Monte Carlo results formatted as line scans have proven useful in providing one-dimensional information about the sample (e.g., linewidth). When used this way, this process is called forward line scan modeling. In the present work, the concept of image simulation (or the first step in the inverse modeling of images) is introduced where the forward-modeled line scan data are carried one step further to construct theoretical two-dimensional (2-D) micrographs (i.e., theoretical SEM images) for comparison with similar experimentally obtained micrographs. This provides an ability to mimic and closely match theory and experiment using SEM images. Calculated and/or measured libraries of simulated images can be developed with this technique. The library concept will prove to be very useful in the determination of dimensional and other properties of simple structures, such as integrated circuit parts, where the shape of the features is preferably measured from a single top-down image or a line scan. This paper presents one approach to the generation of 2-D simulated images and presents some suggestions as to their application to critical dimension metrology.

  9. Classical molecular dynamics simulation of the photoinduced electron transfer dynamics of plastocyanin.

    PubMed Central

    Ungar, L W; Scherer, N F; Voth, G A

    1997-01-01

    Classical molecular dynamics simulations are used to investigate the nuclear motions associated with photoinduced electron transfer in plastocyanin. The blue copper protein is modeled using a molecular mechanics potential; potential parameters for the copper-protein interactions are determined using an x-ray crystallographic structure and absorption and resonance Raman spectra. Molecular dynamics simulations yield a variety of information about the ground (oxidized) and optically excited (charge-transfer) states: 1) The probability distribution of the potential difference between the states, which is used to determine the coordinate and energy displacements, places the states well within the Marcus inverted region. 2) The two-time autocorrelation function of the difference potential in the ground state and the average of the difference potential after instantaneous excitation to the excited state are very similar (confirming linear response in this system); their decay indicates that vibrational relaxation occurs in about 1 ps in both states. 3) The spectral densities of various internal coordinates begin to identify the vibrations that affect the optical transition; the spectral density of the difference potential correlation function should also prove useful in quantum simulations of the back electron transfer. 4) Correlation functions of the protein atomic motions with the difference potential show that the nuclear motions are correlated over a distance of more than 20 A, especially along proposed electron transport paths. Images FIGURE 1 FIGURE 7 PMID:8994588

  10. Computer Simulation of Reflection High Energy Electron Diffraction and Low Energy Electron Diffraction

    NASA Astrophysics Data System (ADS)

    Flexner, Soren; Davidson, Bruce; Odonnell, James; Eckstein, J. N.

    2000-03-01

    Simulation software for Reflection High Energy Electron Diffraction (RHEED) and Low Energy Electron Diffraction (LEED) imaging has been developed using the C programming language. This software models experimental electron diffraction patterns obtained in-situ during deposition of oxide films by molecular beam epitaxy in our lab. Using the kinematical approximation the software considers the phase contributions from scatterers via a modifiable, finite, two or three-dimensional real lattice to construct the RHEED and LEED images. We have found quantitative agreement in the positions of diffraction maxima, and proceed to use the software to explore the qualitative aspects of La and Mn termination in LaMnO2, surface Jahn-Teller distortion in perovskites, terracing in various materials, and domain formation in a-axis DBCO resulting from in-plane rotation of the c-axis. In addition the software is used to examine proposed surface reconstructions capable of producing, e.g. the elevated half-order streaks seen along the [100] azimuth during growth of LaMnO2.

  11. Writing silica structures in liquid with scanning transmission electron microscopy.

    PubMed

    van de Put, Marcel W P; Carcouët, Camille C M C; Bomans, Paul H H; Friedrich, Heiner; de Jonge, Niels; Sommerdijk, Nico A J M

    2015-02-04

    Silica nanoparticles are imaged in solution with scanning transmission electron microscopy (STEM) using a liquid cell with silicon nitride (SiN) membrane windows. The STEM images reveal that silica structures are deposited in well-defined patches on the upper SiN membranes upon electron beam irradiation. The thickness of the deposits is linear with the applied electron dose. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrate that the deposited patches are a result of the merging of the original 20 nm-diameter nanoparticles, and that the related surface roughness depends on the electron dose rate used. Using this approach, sub-micrometer scale structures are written on the SiN in liquid by controlling the electron exposure as function of the lateral position.

  12. Electronic Structure of PbSe Nanowires

    NASA Astrophysics Data System (ADS)

    Avdeev, I. D.; Nestoklon, M. O.

    2016-11-01

    We present the tight binding calculations of the lead selenide nanowires: energy spectra of quantum confined states as a function of nanowire radius, dispersion in the full Brillouin zone, and the radial part of local electronic state density, which helps us to recognise valley splitting in the spectra. Also, we compare our results to KP perturbation theory predictions. We show that the value of the valley splitting is comparable with the distance between two levels of size quantization and that it strongly depends on the arrangement of the atoms in the wire.

  13. Advancing Efficient All-Electron Electronic Structure Methods Based on Numeric Atom-Centered Orbitals for Energy Related Materials

    NASA Astrophysics Data System (ADS)

    Blum, Volker

    This talk describes recent advances of a general, efficient, accurate all-electron electronic theory approach based on numeric atom-centered orbitals; emphasis is placed on developments related to materials for energy conversion and their discovery. For total energies and electron band structures, we show that the overall accuracy is on par with the best benchmark quality codes for materials, but scalable to large system sizes (1,000s of atoms) and amenable to both periodic and non-periodic simulations. A recent localized resolution-of-identity approach for the Coulomb operator enables O (N) hybrid functional based descriptions of the electronic structure of non-periodic and periodic systems, shown for supercell sizes up to 1,000 atoms; the same approach yields accurate results for many-body perturbation theory as well. For molecular systems, we also show how many-body perturbation theory for charged and neutral quasiparticle excitation energies can be efficiently yet accurately applied using basis sets of computationally manageable size. Finally, the talk highlights applications to the electronic structure of hybrid organic-inorganic perovskite materials, as well as to graphene-based substrates for possible future transition metal compound based electrocatalyst materials. All methods described here are part of the FHI-aims code. VB gratefully acknowledges contributions by numerous collaborators at Duke University, Fritz Haber Institute Berlin, TU Munich, USTC Hefei, Aalto University, and many others around the globe.

  14. Do electron-capture supernovae make neutron stars?. First multidimensional hydrodynamic simulations of the oxygen deflagration

    NASA Astrophysics Data System (ADS)

    Jones, S.; Röpke, F. K.; Pakmor, R.; Seitenzahl, I. R.; Ohlmann, S. T.; Edelmann, P. V. F.

    2016-09-01

    Context. In the classical picture, electron-capture supernovae and the accretion-induced collapse of oxygen-neon white dwarfs undergo an oxygen deflagration phase before gravitational collapse produces a neutron star. These types of core collapse events are postulated to explain several astronomical phenomena. In this work, the oxygen deflagration phase is simulated for the first time using multidimensional hydrodynamics. Aims: By simulating the oxygen deflagration with multidimensional hydrodynamics and a level-set-based flame approach, new insights can be gained into the explosive deaths of 8-10 M⊙ stars and oxygen-neon white dwarfs that accrete material from a binary companion star. The main aim is to determine whether these events are thermonuclear or core-collapse supernova explosions, and hence whether neutron stars are formed by such phenomena. Methods: The oxygen deflagration is simulated in oxygen-neon cores with three different central ignition densities. The intermediate density case is perhaps the most realistic, being based on recent nuclear physics calculations and 1D stellar models. The 3D hydrodynamic simulations presented in this work begin from a centrally confined flame structure using a level-set-based flame approach and are performed in 2563 and 5123 numerical resolutions. Results: In the simulations with intermediate and low ignition density, the cores do not appear to collapse into neutron stars. Instead, almost a solar mass of material becomes unbound from the cores, leaving bound remnants. These simulations represent the case in which semiconvective mixing during the electron-capture phase preceding the deflagration is inefficient. The masses of the bound remnants double when Coulomb corrections are included in the equation of state, however they still do not exceed the effective Chandrasekhar mass and, hence, would not collapse into neutron stars. The simulations with the highest ignition density (log 10ρc = 10.3), representing the case

  15. Basis functions for electronic structure calculations on spheres

    SciTech Connect

    Gill, Peter M. W. Loos, Pierre-François Agboola, Davids

    2014-12-28

    We introduce a new basis function (the spherical Gaussian) for electronic structure calculations on spheres of any dimension D. We find general expressions for the one- and two-electron integrals and propose an efficient computational algorithm incorporating the Cauchy-Schwarz bound. Using numerical calculations for the D = 2 case, we show that spherical Gaussians are more efficient than spherical harmonics when the electrons are strongly localized.

  16. Electronic structure of warm dense copper studied by ultrafast x-ray absorption spectroscopy.

    PubMed

    Cho, B I; Engelhorn, K; Correa, A A; Ogitsu, T; Weber, C P; Lee, H J; Feng, J; Ni, P A; Ping, Y; Nelson, A J; Prendergast, D; Lee, R W; Falcone, R W; Heimann, P A

    2011-04-22

    We use time-resolved x-ray absorption spectroscopy to investigate the unoccupied electronic density of states of warm dense copper that is produced isochorically through the absorption of an ultrafast optical pulse. The temperature of the superheated electron-hole plasma, which ranges from 4000 to 10 000 K, was determined by comparing the measured x-ray absorption spectrum with a simulation. The electronic structure of warm dense copper is adequately described with the high temperature electronic density of state calculated by the density functional theory. The dynamics of the electron temperature is consistent with a two-temperature model, while a temperature-dependent electron-phonon coupling parameter is necessary.

  17. Secondary electron emission from surfaces with small structure

    NASA Astrophysics Data System (ADS)

    Dzhanoev, A. R.; Spahn, F.; Yaroshenko, V.; Lühr, H.; Schmidt, J.

    2015-09-01

    It is found that for objects possessing small surface structures with differing radii of curvature the secondary electron emission (SEE) yield may be significantly higher than for objects with smooth surfaces of the same material. The effect is highly pronounced for surface structures of nanometer scale, often providing a more than 100 % increase of the SEE yield. The results also show that the SEE yield from surfaces with structure does not show a universal dependence on the energy of the primary, incident electrons as it is found for flat surfaces in experiments. We derive conditions for the applicability of the conventional formulation of SEE using the simplifying assumption of universal dependence. Our analysis provides a basis for studying low-energy electron emission from nanometer structured surfaces under a penetrating electron beam important in many technological applications.

  18. Linear Scaling Electronic Structure Methods with Periodic Boundary Conditions

    SciTech Connect

    Gustavo E. Scuseria

    2008-02-08

    The methodological development and computational implementation of linear scaling quantum chemistry methods for the accurate calculation of electronic structure and properties of periodic systems (solids, surfaces, and polymers) and their application to chemical problems of DOE relevance.

  19. Stacking dependent electronic structures of transition metal dichalcogenides heterobilayer

    NASA Astrophysics Data System (ADS)

    Lee, Yea-Lee; Park, Cheol-Hwan; Ihm, Jisoon

    The systematic study of the electronic structures and optical properties of the transition metal dichalcogenides (TMD) heterobilayers can significantly improve the designing of new electronic and optoelectronic devices. Here, we theoretically study the electronic structures and optical properties of TMD heterobilayers using the first-principles methods. The band structures of TMD heterobilayer are shown to be determined by the band alignments of the each layer, the weak interlayer interactions, and angle dependent stacking patterns. The photoluminescence spectra are investigated using the calculated band structures, and the optical absorption spectra are examined by the GW approximations including the electron-hole interaction through the solution of the Bethe-Salpeter equation. It is expected that the weak interlayer interaction gives rise to the substantial interlayer optical transition which will be corresponding to the interlayer exciton.

  20. Electron Transport Simulations of 4-Terminal Crossed Graphene Nanoribbons Devices

    NASA Astrophysics Data System (ADS)

    Brandimarte, Pedro; Papior, Nick R.; Engelund, Mads; Garcia-Lekue, Aran; Frederiksen, Thomas; Sánchez-Portal, Daniel

    Recently, it has been reported theoretically a current switching mechanism by voltage control in a system made by two perpendicular 14-armchair graphene nanoribbons (GNRs). In order to investigate the possibilities of using crossed GNRs as ON/OFF devices, we have studied their electronic and transport properties as function structural parameters determining the crossing. Our calculations were performed with TranSIESTA code, which has been recently generalized to consider N >= 1 arbitrarily distributed electrodes at finite bias. We find that the transmission along each individual GNR and among them strongly depends on the stacking. For a 60° rotation angle, the lattice matching in the crossing region provokes a strong scattering effect that translates into an increased interlayer transmission. FP7 FET-ICT PAMS-project (European Commission, contract 610446), MINECO (Grant MAT2013-46593-C6-2-P) and Basque Dep. de Educación, UPV/EHU (Grant IT-756-13).

  1. Electron Diffraction Determination of Nanoscale Structures

    SciTech Connect

    Parks, Joel H

    2013-03-01

    Dominant research results on adsorption on gold clusters are reviewed, including adsorption of H{sub 2}O and O{sub 2} on gold cluster cations and anions, kinetics of CO adsorption to middle sized gold cluster cations, adsorption of CO on Au{sub n}{sup +} with induced changes in structure, and H{sub 2}O enhancement of CO adsorption.

  2. A Structured Debriefing Process for International Business Culture Simulations.

    ERIC Educational Resources Information Center

    McGraw, Peter; Palmer, Ian

    1999-01-01

    Outlines a nine-step structure for debriefing an international business culture simulation. Stresses the need to address three stages in the experiential learning cycle: reflection, processing, and transfer. Appendices include the specific simulation used and a debriefing note. (DB)

  3. Electron-cloud simulation results for the SPS and recent results for the LHC

    SciTech Connect

    Furman, M.A.; Pivi, M.T.F.

    2002-06-19

    We present an update of computer simulation results for some features of the electron cloud at the Large Hadron Collider (LHC) and recent simulation results for the Super Proton Synchrotron (SPS). We focus on the sensitivity of the power deposition on the LHC beam screen to the emitted electron spectrum, which we study by means of a refined secondary electron (SE) emission model recently included in our simulation code.

  4. Coarse-graining away electronic structure: a rigorous route to accurate condensed phase interaction potentials

    NASA Astrophysics Data System (ADS)

    Knight, Chris; Voth, Gregory A.

    2012-05-01

    The molecular simulation of condensed phase systems with electronic structure methods can be prohibitively expensive if the length and time scales necessary to observe the desired chemical phenomena are too large. One solution is to map the results of a representative electronic structure simulation onto a computationally more efficient model that reproduces the original calculation, while allowing for statistical sampling relevant to the required length and time scales. The statistical mechanical multiscale coarse-graining procedure is one methodology in which a model can be developed by integrating over the subset of fast degrees of freedom to construct a reduced representation of the original system that reproduces thermodynamic, and in some instances dynamic, properties. The coarse-graining away of electronic structure is one application of this general method, wherein the electronic degrees of freedom are integrated out and the full dimensionality of the system is mapped to that of only the nuclei. The forces on the nuclei in this reduced representation are obtained from a variational force-matching procedure applied to the Hellman-Feynman forces of the original full electron + nuclear system. This work discusses the coarse-graining procedure and its application to ab initio molecular dynamics simulations of the aqueous hydroxide ion.

  5. The electronic and optical properties of warm dense nitrous oxide using quantum molecular dynamics simulations

    SciTech Connect

    Zhang Yujuan; Wang Cong; Zhang Ping

    2012-11-15

    First-principles molecular-dynamics simulations based on density-functional theory have been used to study the electronic and optical properties of fluid nitrous oxide under extreme conditions. Systematic descriptions of pair-correlation function, atomic structure, and the charge density distribution are used to investigate the dissociation of fluid nitrous oxide. The electrical and optical properties are derived from the Kubo-Greenwood formula. It is found that the nonmetal-metal transition for fluid nitrous oxide can be directly associated to the dissociation and has significant influence on the optical properties of the fluid.

  6. Direct investigation of subsurface interface electronic structure by ballistic-electron-emission microscopy

    NASA Technical Reports Server (NTRS)

    Kaiser, W. J.; Bell, L. D.

    1988-01-01

    A new technique for spectroscopic investigation of subsurface interface electronic structure has been developed. The method, ballistic-electron-emission microscopy (BEEM), is based on scanning tunneling microscopy. BEEM makes possible, for the first time, direct imaging of subsurface interface properties with nanometer spatial resolution. The first application of BEEM to subsurface Schottky-barrier interfaces is reported.

  7. Geometric simulation of structures containing rigid units

    NASA Astrophysics Data System (ADS)

    Wells, Stephen

    2005-03-01

    Much insight into the behaviour of the framework silicates can be obtained from the Rigid Unit model. I review results from geometric analyses [1] of framework structures, quantifying the significance of rigid unit motion in thermal disorder and in defect accomodation, and from a method of simulation [2,3] based on a whole-body `geometric potential' rather than on interatomic potentials. I show the application of the geometric potential to the symmetry-constrained generation of hypothetical zeolite frameworks [4], and to the rapid generation of protein conformations using insights from rigid cluster decomposition [5]. 1. Wells, Dove and Tucker, Journal of Applied Crystallography, 37:536--544 (2004). 2. G.D. Gatta and S.A. Wells, Phys. Chem. Min. 31:1--10 (2004). 3. A. Sartbaeva, S. A. Wells, S. A. T. Redfern, J. Phys.: Condens. Matter 16, 8173 (2004) 4. M. M. J. Treacy, I. Rivin, E. Balkovsky, K. H. Randall and M. D. Foster, Micropor. Mesopor. Mater. 74, 121-132 (2004). 5. M.F. Thorpe, Ming Lei, A.J. Rader, Donald J. Jacobs, and Leslie A. Kuhn, Journal of Molecular Graphics and Modelling 19, 1:60 - 69, (2001).

  8. Time-Dependent, Three-Dimensional Simulation of Free-Electron-Laser Oscillators

    SciTech Connect

    Slot, P. J. M. van der; Boller, K.-J.; Freund, H. P.; Miner, W. H. Jr.; Benson, S. V.; Shinn, M.

    2009-06-19

    We describe a procedure for the simulation of free-electron-laser (FEL) oscillators. The simulation uses a combination of the MEDUSA simulation code for the FEL interaction and the OPC code to model the resonator. The simulations are compared with recent observations of the oscillator at the Thomas Jefferson National Accelerator Facility and are in substantial agreement with the experiment.

  9. Electronic structure calculations of ESR parameters of melanin units.

    PubMed

    Batagin-Neto, Augusto; Bronze-Uhle, Erika Soares; Graeff, Carlos Frederico de Oliveira

    2015-03-21

    Melanins represent an important class of natural pigments present in plants and animals that are currently considered to be promising materials for applications in optic and electronic devices. Despite their interesting properties, some of the basic features of melanins are not satisfactorily understood, including the origin of their intrinsic paramagnetism. A number of experiments have been performed to investigate the electron spin resonance (ESR) response of melanin derivatives, but until now, there has been no consensus regarding the real structure of the paramagnetic centers involved. In this work, we have employed electronic structure calculations to evaluate the ESR parameters of distinct melanin monomers and dimers in order to identify the possible structures associated with unpaired spins in this biopolymer. The g-factors and hyperfine constants of the cationic, anionic and radicalar structures were investigated. The results confirm the existence of at least two distinct paramagnetic centers in melanin structure, identifying the chemical species associated with them and their roles in electrical conductivity.

  10. Structural properties of amorphous silicon produced by electron irradiation

    SciTech Connect

    Yamasaki, J.; Takeda, S.

    1999-07-01

    The structural properties of the amorphous Si (a-Si), which was created from crystalline silicon by 2 MeV electron irradiation at low temperatures about 25 K, are examined in detail by means of transmission electron microscopy and transmission electron diffraction. The peak positions in the radial distribution function (RDF) of the a-Si correspond well to those of a-Si fabricated by other techniques. The electron-irradiation-induced a-Si returns to crystalline Si after annealing at 550 C.

  11. Distinct electronic structure for the extreme magnetoresistance in YSb

    SciTech Connect

    He, Junfeng; Zhang, Chaofan; Ghimire, Nirmal J.; Liang, Tian; Jia, Chunjing; Jiang, Juan; Tang, Shujie; Chen, Sudi; He, Yu; Mo, S. -K.; Hwang, C. C.; Hashimoto, M.; Lu, D. H.; Moritz, B.; Devereaux, T. P.; Chen, Y. L.; Mitchell, J. F.; Shen, Z. -X.

    2016-12-23

    An extreme magnetoresistance (XMR) has recently been observed in several nonmagnetic semimetals. Increasing experimental and theoretical evidence indicates that the XMR can be driven by either topological protection or electron-hole compensation. Moreover, by investigating the electronic structure of a XMR material, YSb, we present spectroscopic evidence for a special case which lacks topological protection and perfect electron-hole compensation. Further investigations reveal that a cooperative action of a substantial difference between electron and hole mobility and a moderate carrier compensation might contribute to the XMR in YSb.

  12. Electronic structure modulation of graphene edges by chemical functionalization

    NASA Astrophysics Data System (ADS)

    Taira, Remi; Yamanaka, Ayaka; Okada, Susumu

    2016-11-01

    Using the density functional theory with the effective screening medium method, we study the electronic properties of graphene nanoribbons with zigzag edges that are terminated by hydrogen and ketone, hydroxyl, carbonyl, and carboxyl functional groups. Our calculations showed that the work function and electronic structures of the edges of the nanoribbons are sensitive to the functional groups attached to the edges. The nearly free electron state emerges in the vacuum region outside the hydroxylated edges and crosses the Fermi level, indicating the possibility of negative electron affinity at the edges.

  13. Electron beam enhanced surface modification for making highly resolved structures

    DOEpatents

    Pitts, John R.

    1986-01-01

    A method for forming high resolution submicron structures on a substrate is provided by direct writing with a submicron electron beam in a partial pressure of a selected gas phase characterized by the ability to dissociate under the beam into a stable gaseous leaving group and a reactant fragment that combines with the substrate material under beam energy to form at least a surface compound. Variations of the method provide semiconductor device regions on doped silicon substrates, interconnect lines between active sites, three dimensional electronic chip structures, electron beam and optical read mass storage devices that may include color differentiated data areas, and resist areas for use with selective etching techniques.

  14. Electron beam enhanced surface modification for making highly resolved structures

    DOEpatents

    Pitts, J.R.

    1984-10-10

    A method for forming high resolution submicron structures on a substrate is provided by direct writing with a submicron electron beam in a partial pressure of a selected gas phase characterized by the ability to dissociate under the beam into a stable gaseous leaving group and a reactant fragment that combines with the substrate material under beam energy to form at least a surface compound. Variations of the method provide semiconductor device regions on doped silicon substrates, interconnect lines between active sites, three dimensional electronic chip structures, electron beam and optical read mass storage devices that may include color differentiated data areas, and resist areas for use with selective etching techniques.

  15. Solitary structures with ion and electron thermal anisotropy

    NASA Astrophysics Data System (ADS)

    Khusroo, Murchana; Bora, Madhurjya P.

    2015-11-01

    The formation of electrostatic solitary structures is analysed for a magnetised plasma with ion and electron thermal anisotropies. The ion thermal anisotropy is modelled with the help of the Chew-Goldberger-Low (CGL) double adiabatic equations of state while the electrons are treated as inertia-less species with an anisotropic bi-Maxwellian velocity distribution function. A negative electron thermal anisotropy ≤ft({{T}e\\bot}/{{T}e\\parallel}>1\\right) is found to help form large amplitude solitary structures which are in agreement with observational data.

  16. Modeling a Miniaturized Scanning Electron Microscope Focusing Column - Lessons Learned in Electron Optics Simulation

    NASA Technical Reports Server (NTRS)

    Loyd, Jody; Gregory, Don; Gaskin, Jessica

    2016-01-01

    /Fourier series hybrid approach. The presentation will give background remarks about the MSFC mini Lunar SEM concept and electron optics modeling, followed by a description of the alternate field modeling techniques that were tried, along with their incorporation into a ray-trace simulation. Next, the validation of this simulation against commercially available software will be discussed using an example lens as a test case. Then, the efficacy of aberration assessment using direct ray-tracing will be demonstrated, using this same validation case. The discussion will include practical error checks of the field solution. Finally, the ray-trace assessment of the MSFC mini Lunar SEM concept will be shown and discussed. The authors believe this presentation will be of general interest to practitioners of modeling and simulation, as well as those with a general optics background. Because electron optics and photon optics share many basic concepts (e.g., lenses, images, aberrations, etc.), the appeal of this presentation need not be restricted to just those interested in charged particle optics.

  17. Path Integral Monte Carlo finite-temperature electronic structure of quantum dots

    NASA Astrophysics Data System (ADS)

    Leino, Markku; Rantala, Tapio T.

    2003-03-01

    Quantum Monte Carlo methods allow a straightforward procedure for evaluation of electronic structures with a proper treatment of electronic correlations. This can be done even at finite temperatures [1]. We apply the Path Integral Monte Carlo (PIMC) simulation method [2] for one and two electrons in a single and double quantum dots. With this approach we evaluate the electronic distributions and correlations, and finite temperature effects on those. Temperature increase broadens the one-electron distribution as expected. This effect is smaller for correlated electrons than for single ones. The simulated one and two electron distributions of a single and two coupled quantum dots are also compared to those from experiments and other theoretical (0 K) methods [3]. Computational capacity is found to become the limiting factor in simulations with increasing accuracy. This and other essential aspects of PIMC and its capability in this type of calculations are also discussed. [1] R.P. Feynman: Statistical Mechanics, Addison Wesley, 1972. [2] D.M. Ceperley, Rev.Mod.Phys. 67, 279 (1995). [3] M. Pi, A. Emperador and M. Barranco, Phys.Rev.B 63, 115316 (2001).

  18. Unveiling the complex electronic structure of amorphous metal oxides

    PubMed Central

    Århammar, C.; Pietzsch, Annette; Bock, Nicolas; Holmström, Erik; Araujo, C. Moyses; Gråsjö, Johan; Zhao, Shuxi; Green, Sara; Peery, T.; Hennies, Franz; Amerioun, Shahrad; Föhlisch, Alexander; Schlappa, Justine; Schmitt, Thorsten; Strocov, Vladimir N.; Niklasson, Gunnar A.; Wallace, Duane C.; Rubensson, Jan-Erik; Johansson, Börje; Ahuja, Rajeev

    2011-01-01

    Amorphous materials represent a large and important emerging area of material’s science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today’s integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5–10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.

  19. Electron-interface phonon interaction in multiple quantum well structures

    NASA Astrophysics Data System (ADS)

    Sun, J. P.; Teng, H. B.; Haddad, G. I.; Stroscio, M. A.

    1998-08-01

    Intersubband relaxation rates due to electron interactions with the interface phonons are evaluated for multiple quantum well structures designed for step quantum well lasers operating at mid-infrared to submillimetre wavelengths. The interface phonon modes and electron-phonon interaction Hamiltonians for the structures are derived using the transfer matrix method, based on the macroscopic dielectric continuum model, whereas the electron wavefunctions are obtained by solving the Schrödinger equation. Fermi's golden rule is employed to calculate the electron relaxation rates between the subbands in these structures. The relaxation rates for two different structures are examined and compared with those calculated using the bulk phonon modes and the Fröhlich interaction Hamiltonian. The sum rule for the relationship between the form factors of the various localized phonon modes and the bulk phonon modes is verified. The results obtained in this work illustrate that the transfer matrix method provides a convenient way for deriving the properties of the interface phonon modes in different structures of current interest and that, for preferential electron relaxation in intersubband laser structures, the effects of the interface phonon modes are significant and should be considered for optimal design of these laser structures.

  20. Nano-structured electron transporting materials for perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Liu, Hefei; Huang, Ziru; Wei, Shiyuan; Zheng, Lingling; Xiao, Lixin; Gong, Qihuang

    2016-03-01

    Organic-inorganic hybrid perovskite solar cells have been developing rapidly in the past several years, and their power conversion efficiency has reached over 20%, nearing that of polycrystalline silicon solar cells. Because the diffusion length of the hole in perovskites is longer than that of the electron, the performance of the device can be improved by using an electron transporting layer, e.g., TiO2, ZnO and TiO2/Al2O3. Nano-structured electron transporting materials facilitate not only electron collection but also morphology control of the perovskites. The properties, morphology and preparation methods of perovskites are reviewed in the present article. A comprehensive understanding of the relationship between the structure and property will benefit the precise control of the electron transporting process and thus further improve the performance of perovskite solar cells.

  1. Nano-structured electron transporting materials for perovskite solar cells.

    PubMed

    Liu, Hefei; Huang, Ziru; Wei, Shiyuan; Zheng, Lingling; Xiao, Lixin; Gong, Qihuang

    2016-03-28

    Organic-inorganic hybrid perovskite solar cells have been developing rapidly in the past several years, and their power conversion efficiency has reached over 20%, nearing that of polycrystalline silicon solar cells. Because the diffusion length of the hole in perovskites is longer than that of the electron, the performance of the device can be improved by using an electron transporting layer, e.g., TiO2, ZnO and TiO2/Al2O3. Nano-structured electron transporting materials facilitate not only electron collection but also morphology control of the perovskites. The properties, morphology and preparation methods of perovskites are reviewed in the present article. A comprehensive understanding of the relationship between the structure and property will benefit the precise control of the electron transporting process and thus further improve the performance of perovskite solar cells.

  2. Structural complexities in the active layers of organic electronics.

    PubMed

    Lee, Stephanie S; Loo, Yueh-Lin

    2010-01-01

    The field of organic electronics has progressed rapidly in recent years. However, understanding the direct structure-function relationships between the morphology in electrically active layers and the performance of devices composed of these materials has proven difficult. The morphology of active layers in organic electronics is inherently complex, with heterogeneities existing across multiple length scales, from subnanometer to micron and millimeter range. A major challenge still facing the organic electronics community is understanding how the morphology across all of the length scales in active layers collectively determines the device performance of organic electronics. In this review we highlight experiments that have contributed to the elucidation of structure-function relationships in organic electronics and also point to areas in which knowledge of such relationships is still lacking. Such knowledge will lead to the ability to select active materials on the basis of their inherent properties for the fabrication of devices with prespecified characteristics.

  3. Resonance Raman spectrum of the solvated electron in methanol: simulation within a cluster model.

    PubMed

    Neumann, Stefanie; Eisfeld, Wolfgang; Sobolewski, Andrzej L; Domcke, Wolfgang

    2006-05-04

    The microsolvation of the CH(3)OH(2) hypervalent radical in methanol clusters has been investigated by density functional theory. It is shown that the CH(3)OH(2) radical spontaneously decomposes within methanol clusters into protonated methanol and a localized solvated electron cloud. The geometric and electronic structures of these clusters as well as their vibrational frequencies have been characterized. Resonance Raman intensities, associated with the s --> p transition of the unpaired electron, have been estimated for CH(3)OH(2)M(n) (M = CH(3)OH, n = 1-3) clusters. It is shown that with increasing cluster size the simulated spectra converge toward the resonance Raman spectrum of the solvated electron in methanol measured recently by Tauber and Mathies (J. Am. Chem. Soc. 2004, 126, 3414). The results suggest that CH(3)OH(2)M(n) clusters are useful finite-size model systems for the computational investigation of the spectroscopic properties of the solvated electron in liquid methanol.

  4. The role of the electron convection term for the parallel electric field and electron acceleration in MHD simulations

    SciTech Connect

    Matsuda, K.; Terada, N.; Katoh, Y.; Misawa, H.

    2011-08-15

    There has been a great concern about the origin of the parallel electric field in the frame of fluid equations in the auroral acceleration region. This paper proposes a new method to simulate magnetohydrodynamic (MHD) equations that include the electron convection term and shows its efficiency with simulation results in one dimension. We apply a third-order semi-discrete central scheme to investigate the characteristics of the electron convection term including its nonlinearity. At a steady state discontinuity, the sum of the ion and electron convection terms balances with the ion pressure gradient. We find that the electron convection term works like the gradient of the negative pressure and reduces the ion sound speed or amplifies the sound mode when parallel current flows. The electron convection term enables us to describe a situation in which a parallel electric field and parallel electron acceleration coexist, which is impossible for ideal or resistive MHD.

  5. Electronic band structure of surface-doped black phosphorus

    NASA Astrophysics Data System (ADS)

    Kim, Jimin; Ryu, Sae Hee; Sohn, Yeongsup; Kim, Keun Su

    2015-03-01

    There are rapidly growing interests in the study of few-layer black phosphorus owing to its promising device characteristics that may impact our future electronics technology. The low-energy band structure of black phosphorus has been widely predicted to be controllable by external perturbations, such as strain and doping. In this work, we attempt to control the electronic band structure of black phosphorous by in-situ surface deposition of alkali-metal atoms. We found that surface doping induces steep band bending towards the bulk, leading to the emergence of new 2D electronic states that are confined within only few phosphorene layers of black phosphorus. Using angle-resolved photoemission spectroscopy, we directly measured the electronic band structure and its evolution as a function of dopant density. Supported by IBS.

  6. Electronic structure of a graphene superlattice with massive Dirac fermions

    SciTech Connect

    Lima, Jonas R. F.

    2015-02-28

    We study the electronic and transport properties of a graphene-based superlattice theoretically by using an effective Dirac equation. The superlattice consists of a periodic potential applied on a single-layer graphene deposited on a substrate that opens an energy gap of 2Δ in its electronic structure. We find that extra Dirac points appear in the electronic band structure under certain conditions, so it is possible to close the gap between the conduction and valence minibands. We show that the energy gap E{sub g} can be tuned in the range 0 ≤ E{sub g} ≤ 2Δ by changing the periodic potential. We analyze the low energy electronic structure around the contact points and find that the effective Fermi velocity in very anisotropic and depends on the energy gap. We show that the extra Dirac points obtained here behave differently compared to previously studied systems.

  7. Topological Insulators: Electronic Band Structure and Spectroscopy

    NASA Astrophysics Data System (ADS)

    Palaz, S.; Koc, H.; Mamedov, A. M.; Ozbay, E.

    2017-02-01

    In this study, we present the results of our ab initio calculation of the elastic constants, density of states, charge density, and Born effective charge tensors for ferroelectric (rhombohedral) and paraelectric phases (cubic) of the narrow band ferroelectrics (GeTe, SnTe) pseudopotentials. The related quantities such as bulk modulus and shear modulus using obtained elastic constants have also been estimated in the present work. The total and partial densities of states corresponding to the band structure of Sn(Ge)Te(S,Se) were calculated. We also calculated the Born effective charge tensor of an atom (for instance, Ge, Sn, Te, etc.), which is defined as the induced polarization of the solid along the main direction by a unit displacement in the perpendicular direction of the sublattice of an atom at the vanishing electric field.

  8. Electronic Structure and Transport in Magnetic Multilayers

    SciTech Connect

    2008-02-18

    ORNL assisted Seagate Recording Heads Operations in the development of CIPS pin Valves for application as read sensors in hard disk drives. Personnel at ORNL were W. H. Butler and Xiaoguang Zhang. Dr. Olle Heinonen from Seagate RHO also participated. ORNL provided codes and materials parameters that were used by Seagate to model CIP GMR in their heads. The objectives were to: (1) develop a linearized Boltzmann transport code for describing CIP GMR based on realistic models of the band structure and interfaces in materials in CIP spin valves in disk drive heads; (2) calculate the materials parameters needed as inputs to the Boltzmann code; and (3) transfer the technology to Seagate Recording Heads.

  9. The roles of electronic exchange and correlation in charge-transfer- to-solvent dynamics: Many-electron nonadiabatic mixed quantum/classical simulations of photoexcited sodium anions in the condensed phase.

    PubMed

    Glover, William J; Larsen, Ross E; Schwartz, Benjamin J

    2008-10-28

    The charge-transfer-to-solvent (CTTS) reactions of solvated atomic anions serve as ideal models for studying the dynamics of electron transfer: The fact that atomic anions have no internal degrees of freedom provides one of the most direct routes to understanding how the motions of solvent molecules influence charge transfer, and the relative simplicity of atomic electronic structure allows for direct contact between theory and experiment. To date, molecular dynamics simulations of the CTTS process have relied on a single-electron description of the atomic anion-only the electron involved in the charge transfer has been treated quantum mechanically, and the electronic structure of the atomic solute has been treated via pseudopotentials. In this paper, we examine the severity of approximating the electronic structure of CTTS anions with a one-electron model and address the role of electronic exchange and correlation in both CTTS electronic structure and dynamics. To do this, we perform many-electron mixed quantum/classical molecular dynamics simulations of the ground- and excited-state properties of the aqueous sodium anion (sodide). We treat both of the sodide valence electrons quantum mechanically and solve the Schrodinger equation using configuration interaction with singles and doubles (CISD), which provides an exact solution for two electrons. We find that our multielectron simulations give excellent general agreement with experimental results on the CTTS spectroscopy and dynamics of sodide in related solvents. We also compare the results of our multielectron simulations to those from one-electron simulations on the same system [C. J. Smallwood et al., J. Chem. Phys. 119, 11263 (2003)] and find substantial differences in the equilibrium CTTS properties and the nonadiabatic relaxation dynamics of one- and two-electron aqueous sodide. For example, the one-electron model substantially underpredicts the size of sodide, which in turn results in a dramatically

  10. Simulation of electrons irradiation damages to optimize the performance of IGBT

    SciTech Connect

    Elmazria, O.; Hoffmann, A.; Lepley, B.; Charles, J.P.; Adams, L.

    1997-02-01

    Electron irradiation (IE) is a technique used to control the IGBT switching performances and then produce series of IGBT`s with various switching velocities. However, this irradiation introduces undesirable effects on other parameters, such as forward voltage drop and leakage current. In this paper, the authors propose a method to optimize the performances of the IGBT`s considering the degradation effects. The IE effects are simulated using the two-dimensional device simulator ATLAS. Defects densities defined by their energy levels and capture cross section, and densities are introduced into all the structure layers. The energy levels and capture cross sections are extracted from literature and densities are obtained by an iterative process, where the simulated characteristics are fitted to the experimental ones. This method validity is confirmed by comparison of simulation results with experimental ones performed onto a series of IGBT`s irradiated to various doses. Steady states and switching characteristics obtained by both simulation and measurements are in good agreement and variations of forward voltage drop versus turn-off time for various doses are obtained and used for performance optimization purposes.

  11. Electronic correlation in magnetic contributions to structural energies

    NASA Astrophysics Data System (ADS)

    Haydock, Roger

    For interacting electrons the density of transitions [see http://arxiv.org/abs/1405.2288] replaces the density of states in calculations of structural energies. Extending previous work on paramagnetic metals, this approach is applied to correlation effects on the structural stability of magnetic transition metals. Supported by the H. V. Snyder Gift to the University of Oregon.

  12. Simulation-Guided 3D Nanomanufacturing via Focused Electron Beam Induced Deposition

    SciTech Connect

    Fowlkes, Jason D.; Winkler, Robert; Lewis, Brett B.; Stanford, Michael G.; Plank, Harald; Rack, Philip D.

    2016-06-10

    Focused electron beam induced deposition (FEBID) is one of the few techniques that enables direct-write synthesis of free-standing 3D nanostructures. While the fabrication of simple architectures such as vertical or curving nanowires has been achieved by simple trial and error, processing complex 3D structures is not tractable with this approach. This is due, inpart, to the dynamic interplay between electron–solid interactions and the transient spatial distribution of absorbed precursor molecules on the solid surface. Here, we demonstrate the ability to controllably deposit 3D lattice structures at the micro/nanoscale, which have received recent interest owing to superior mechanical and optical properties. Moreover, a hybrid Monte Carlo–continuum simulation is briefly overviewed, and subsequently FEBID experiments and simulations are directly compared. Finally, a 3D computer-aided design (CAD) program is introduced, which generates the beam parameters necessary for FEBID by both simulation and experiment. In using this approach, we demonstrate the fabrication of various 3D lattice structures using Pt-, Au-, and W-based precursors.

  13. Simulation-Guided 3D Nanomanufacturing via Focused Electron Beam Induced Deposition

    DOE PAGES

    Fowlkes, Jason D.; Winkler, Robert; Lewis, Brett B.; ...

    2016-06-10

    Focused electron beam induced deposition (FEBID) is one of the few techniques that enables direct-write synthesis of free-standing 3D nanostructures. While the fabrication of simple architectures such as vertical or curving nanowires has been achieved by simple trial and error, processing complex 3D structures is not tractable with this approach. This is due, inpart, to the dynamic interplay between electron–solid interactions and the transient spatial distribution of absorbed precursor molecules on the solid surface. Here, we demonstrate the ability to controllably deposit 3D lattice structures at the micro/nanoscale, which have received recent interest owing to superior mechanical and optical properties.more » Moreover, a hybrid Monte Carlo–continuum simulation is briefly overviewed, and subsequently FEBID experiments and simulations are directly compared. Finally, a 3D computer-aided design (CAD) program is introduced, which generates the beam parameters necessary for FEBID by both simulation and experiment. In using this approach, we demonstrate the fabrication of various 3D lattice structures using Pt-, Au-, and W-based precursors.« less

  14. Particle-in-cell simulations of electron acceleration by a simple capacitative antenna in collisionless plasma

    NASA Astrophysics Data System (ADS)

    Dieckmann, M. E.; Rowlands, G.; Eliasson, B.; Shukla, P. K.

    2004-12-01

    We examine the electron acceleration by a localized electrostatic potential oscillating at high frequencies by means of particle-in-cell (PIC) simulations, in which we apply oscillating electric fields to two neighboring simulation cells. We derive an analytic model for the direct electron heating by the externally driven antenna electric field, and we confirm that it approximates well the electron heating obtained in the simulations. In the simulations, transient waves accelerate electrons in a sheath surrounding the antenna. This increases the Larmor radii of the electrons close to the antenna, and more electrons can reach the antenna location to interact with the externally driven fields. The resulting hot electron sheath is dense enough to support strong waves that produce high-energy sounder-accelerated electrons (SAEs) by their nonlinear interaction with the ambient electrons. By increasing the emission amplitudes in our simulations to values that are representative for the ones of the sounder on board the OEDIPUS C (OC) satellites, we obtain electron acceleration into the energy range which is comparable to the 20 keV energies of the SAE observed by the OC mission. The emission also triggers stable electrostatic waves oscillating at frequencies close to the first harmonic of the electron cyclotron frequency. We find this to be an encouraging first step of examining SAE generation with kinetic numerical simulation codes.

  15. Decoupling of structural and electronic phase transitions in VO2.

    PubMed

    Tao, Zhensheng; Han, Tzong-Ru T; Mahanti, Subhendra D; Duxbury, Phillip M; Yuan, Fei; Ruan, Chong-Yu; Wang, Kevin; Wu, Junqiao

    2012-10-19

    Using optical, TEM, and ultrafast electron diffraction experiments we find that single crystal VO(2) microbeams gently placed on insulating substrates or metal grids exhibit different behaviors, with structural and metal-insulator transitions occurring at the same temperature for insulating substrates, while for metal substrates a new monoclinic metal phase lies between the insulating monoclinic phase and the metallic rutile phase. The structural and electronic phase transitions in these experiments are strongly first order and we discuss their origins in the context of current understanding of multiorbital splitting, strong correlation effects, and structural distortions that act cooperatively in this system.

  16. Electronic states in hybrid boron nitride and graphene structures

    NASA Astrophysics Data System (ADS)

    Zhao, M.; Huang, Y. H.; Ma, F.; Hu, T. W.; Xu, K. W.; Chu, Paul K.

    2013-08-01

    The energy bands and electronic states of hybrid boron nitride (BN) and graphene structures are studied by first principle calculations. The electronic states change from semi-metallic to insulating depending on the number of B and N atoms as well as domain symmetry. When there are unequal numbers of B and N atoms, mid-gap states usually appear around the Fermi level and the corresponding hybrid structure possesses magnetic and semi-metallic properties. However, when the numbers of B and N atoms are equal, a band gap exists indicative of a semiconducting or insulating nature which depends on the structural symmetry.

  17. Engineering the Electronic Band Structure for Multiband Solar Cells

    SciTech Connect

    Lopez, N.; Reichertz, L.A.; Yu, K.M.; Campman, K.; Walukiewicz, W.

    2010-07-12

    Using the unique features of the electronic band structure of GaNxAs1-x alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the Band Anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.

  18. Engineering the electronic band structure for multiband solar cells.

    PubMed

    López, N; Reichertz, L A; Yu, K M; Campman, K; Walukiewicz, W

    2011-01-14

    Using the unique features of the electronic band structure of GaN(x)As(1-x) alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the band anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.

  19. Electronic structure and bonding in skutterudite-type phosphides

    NASA Astrophysics Data System (ADS)

    Llunell, Miquel; Alemany, Pere; Alvarez, Santiago; Zhukov, Vladlen P.; Vernes, Andreas

    1996-04-01

    The electronic structures of the skutterudite-type phosphides CoP3 and NiP3 have been investigated by means of first-principles linear muffin-tin orbital-atomic sphere approximation band-structure calculations. The presence of P4 rings in the skutterudite structure is of great importance in determining the nature of the electronic bands around the Fermi level, composed mainly of π-type molecular orbitals of these units. The metallic character found for NiP3 should be ascribed to the phosphorus framework rather than to the metal atoms.

  20. Properties and features of structure formation CuCr-contact alloys in electron beam cladding

    SciTech Connect

    Durakov, Vasiliy G.; Dampilon, Bair V. E-mail: gnusov@rambler.ru; Gnyusov, Sergey F. E-mail: gnusov@rambler.ru

    2014-11-14

    The microstructure and properties of the contact CuCr alloy produced by electron-beam cladding have been investigated. The effect of the electron beam cladding parameters and preheating temperature of the base metal on the structure and the properties of the coatings has been determined. The bimodal structure of the cladding coating has been established. The short circuit currents tests have been carried out according to the Weil-Dobke synthetic circuit simulating procedure developed for vacuum circuit breakers (VCB) test in real electric circuits. Test results have shown that the electron beam cladding (EBC) contact material has better breaking capacity than that of commercially fabricated sintered contact material. The application of the technology of electron beam cladding for production of contact material would significantly improve specific characteristics and reliability of vacuum switching equipment.

  1. Goeppert-Mayer Award Recipient: Electron Scattering and Nucleon Structure

    NASA Astrophysics Data System (ADS)

    Beise, Elizabeth

    1998-04-01

    Electron scattering from hydrogen and light nuclear targets has long been recognized as one of the best tools for understanding the electromagnetic structure of protons, neutrons and few-nucleon systems. In the last decade, considerable progress has been made in the field through advances in polarized beams and polarized targets. Improvements in polarized electron sources has made it feasible to also study the structure of the nucleon through parity-violating electron scattering, where the nucleon's neutral weak structure is probed. In this talk, a summary of the present experimental status of the nucleon's electroweak structure will be presented, with an emphasis on recent results from the MIT-Bates and Jefferson Laboratories.

  2. Advanced accelerating structures and their interaction with electron beams.

    SciTech Connect

    Gai, W.; High Energy Physics

    2008-01-01

    In this paper, we give a brief description of several advanced accelerating structures, such as dielectric loaded waveguides, photonic band gap, metamaterials and improved iris-loaded cavities. We describe wakefields generated by passing high current electron beams through these structures, and applications of wakefields to advanced accelerator schemes. One of the keys to success for high gradient wakefield acceleration is to develop high current drive beam sources. As an example, the high current RF photo injector at the Argonne Wakefield Accelerator, passed a {approx}80 nC electron beam through a high gradient dielectric loaded structure to achieve a 100 MV/m gradient. We will summarize recent related experiments on beam-structure interactions and also discuss high current electron beam generation and propagation and their applications to wakefield acceleration.

  3. Advanced Accelerating Structures and Their Interaction with Electron Beams

    SciTech Connect

    Gai Wei

    2009-01-22

    In this paper, we give a brief description of several advanced accelerating structures, such as dielectric loaded waveguides, photonic band gap, metamaterials and improved iris-loaded cavities. We describe wakefields generated by passing high current electron beams through these structures, and applications of wakefields to advanced accelerator schemes. One of the keys to success for high gradient wakefield acceleration is to develop high current drive beam sources. As an example, the high current RF photo injector at the Argonne Wakefield Accelerator, passed a {approx}80 nC electron beam through a high gradient dielectric loaded structure to achieve a 100 MV/m gradient. We will summarize recent related experiments on beam-structure interactions and also discuss high current electron beam generation and propagation and their applications to wakefield acceleration.

  4. Formation of electrostatic structures by wakefield acceleration in ultrarelativistic plasma flows: Electron acceleration to cosmic ray energies

    SciTech Connect

    Dieckmann, M.E.; Shukla, P.K.; Eliasson, B.

    2006-06-15

    The ever increasing performance of supercomputers is now enabling kinetic simulations of extreme astrophysical and laser produced plasmas. Three-dimensional particle-in-cell (PIC) simulations of relativistic shocks have revealed highly filamented spatial structures and their ability to accelerate particles to ultrarelativistic speeds. However, these PIC simulations have not yet revealed mechanisms that could produce particles with tera-electron volt energies and beyond. In this work, PIC simulations in one dimension (1D) of the foreshock region of an internal shock in a gamma ray burst are performed to address this issue. The large spatiotemporal range accessible to a 1D simulation enables the self-consistent evolution of proton phase space structures that can accelerate particles to giga-electron volt energies in the jet frame of reference, and to tens of tera-electron volt in the Earth's frame of reference. One potential source of ultrahigh energy cosmic rays may thus be the thermalization of relativistically moving plasma.

  5. Structure of a Bacterial Cell Surface Decaheme Electron Conduit

    SciTech Connect

    Clarke, Thomas A.; Edwards, Marcus; Gates, Andrew J.; Hall, Andrea; White, Gaye; Bradley, Justin; Reardon, Catherine L.; Shi, Liang; Beliaev, Alex S.; Marshall, Matthew J.; Wang, Zheming; Watmough, Nicholas; Fredrickson, Jim K.; Zachara, John M.; Butt, Julea N.; Richardson, David J.

    2011-05-23

    Some bacterial species are able to utilize extracellular mineral forms of iron and manganese as respiratory electron acceptors. In Shewanella oneidensis this involves deca-heme cytochromes that are located on the bacterial cell surface at the termini of trans-outermembrane (OM) electron transfer conduits. The cell surface cytochromes can potentially play multiple roles in mediating electron transfer directly to insoluble electron sinks, catalyzing electron exchange with flavin electron shuttles or participating in extracellular inter-cytochrome electron exchange along ‘nanowire’ appendages. We present a 3.2 Å crystal structure of one of these deca-heme cytochromes, MtrF, that allows the spatial organization of the ten hemes to be visualized for the first time. The hemes are organized across four domains in a unique crossed conformation, in which a staggered 65 Å octa-heme chain transects the length of the protein and is bisected by a planar 45 Å tetra-heme chain that connects two extended Greek key split β-barrel domains. The structure provides molecular insight into how reduction of insoluble substrate (e.g. minerals), soluble substrates (e.g. flavins) and cytochrome redox partners might be possible in tandem at different termini of a trifurcated electron transport chain on the cell surface.

  6. Structure of a bacterial cell surface decaheme electron conduit.

    PubMed

    Clarke, Thomas A; Edwards, Marcus J; Gates, Andrew J; Hall, Andrea; White, Gaye F; Bradley, Justin; Reardon, Catherine L; Shi, Liang; Beliaev, Alexander S; Marshall, Matthew J; Wang, Zheming; Watmough, Nicholas J; Fredrickson, James K; Zachara, John M; Butt, Julea N; Richardson, David J

    2011-06-07

    Some bacterial species are able to utilize extracellular mineral forms of iron and manganese as respiratory electron acceptors. In Shewanella oneidensis this involves decaheme cytochromes that are located on the bacterial cell surface at the termini of trans-outer-membrane electron transfer conduits. The cell surface cytochromes can potentially play multiple roles in mediating electron transfer directly to insoluble electron sinks, catalyzing electron exchange with flavin electron shuttles or participating in extracellular intercytochrome electron exchange along "nanowire" appendages. We present a 3.2-Å crystal structure of one of these decaheme cytochromes, MtrF, that allows the spatial organization of the 10 hemes to be visualized for the first time. The hemes are organized across four domains in a unique crossed conformation, in which a staggered 65-Å octaheme chain transects the length of the protein and is bisected by a planar 45-Å tetraheme chain that connects two extended Greek key split β-barrel domains. The structure provides molecular insight into how reduction of insoluble substrate (e.g., minerals), soluble substrates (e.g., flavins), and cytochrome redox partners might be possible in tandem at different termini of a trifurcated electron transport chain on the cell surface.

  7. Electronic Structure and Phase Stability of PdPt Nanoparticles.

    PubMed

    Ishimoto, Takayoshi; Koyama, Michihisa

    2016-03-03

    To understand the origin of the physicochemical nature of bimetallic PdPt nanoparticles, we theoretically investigated the phase stability and electronic structure employing the PdPt nanoparticles models consisting of 711 atoms (ca. 3 nm). For the Pd-Pt core-shell nanoparticle, the PdPt solid-solution phase was found to be a thermodynamically stable phase in the nanoparticle as the result of difference in surface energy of Pd and Pt nanoparticles and configurational entropy effect, while it is well known that the Pd and Pt are the immiscible combination in the bulk phase. The electronic structure of nanoparticles is conducted to find that the electron transfer occurs locally within surface and subsurface layers. In addition, the electron transfer from Pd to Pt at the interfacial layers in core-shell nanoparticles is observed, which leads to unique geometrical and electronic structure changes. Our results show a clue for the tunability of the electronic structure of nanoparticles by controlling the arrangement in the nanoparticles.

  8. Structure and electronic properties of lead-selenide nanocrystal solids

    NASA Astrophysics Data System (ADS)

    Whitham, Kevin

    Recent advances in the controlled formation of nanocrystal superlattices have potential for creating materials with properties by design. The ability to tune nanocrystal size, shape and composition as well as symmetry of the superlattice opens routes to new materials. Calculations of such materials predict interesting electronic phenomena including topological states and Dirac cones, however experimental support is lacking. We have investigated electron localization in nanocrystal superlattices using a combination of advanced structural characterization techniques and charge transport measurements. Recent experimental efforts to improve the electronic properties of nanocrystal solids have focused on increasing inter-dot coupling. However, this approach only leads to electronic bands if the coupling energy can overcome energetic and translational disorder. We have investigated oriented-attachment as a method to create nanocrystal superlattices with increased coupling and translational order. We show that epitaxially connected superlattices form by a coherent phase transformation that is sensitive to structural defects and ligand length. In order to measure intrinsic electronic properties we demonstrate control over electronic defects by tailoring surface chemistry and device architecture. To probe charge transport in these structures we performed variable temperature field-effect measurements. By integrating structure analysis, surface chemistry, and transport measurements we find that carriers are localized to a few superlattice constants due to disorder. Importantly, our analysis shows that greater delocalization is possible by optimizing dot-to-dot bonding, thus providing a path forward to create quantum dot solids in which theoretically predicted properties can be realized.

  9. Electron Energy-Loss Spectroscopy Theory and Simulation Applied to Nanoparticle Plasmonics

    NASA Astrophysics Data System (ADS)

    Bigelow, Nicholas Walker

    In this dissertation, the capacity of electron energy-loss spectroscopy (EELS) to probe plasmons is examined in detail. EELS is shown to be able to detect both electric hot spots and Fano resonances in contrast to the prevailing knowledge prior to this work. The most detailed examination of magnetoplasmonic resonances in multi-ring structures to date and the utility of electron tomography to computational plasmonics is explored, and a new tomographic method for the reconstruction of a target is introduced. Since the observation of single-molecule surface-enhanced Raman scattering (SMSERS) in 1997, questions regarding the nature of the electromagnetic hot spots responsible for such observations still persist. A computational analysis of the electron- and photon-driven surface-plasmon resonances of monomer and dimer metal nanorods is presented to elucidate the differences and similarities between the two excitation mechanisms in a system with well understood optical properties. By correlating the nanostructure's simulated electron energy loss spectrum and loss-probability maps with its induced polarization and scattered electric field we discern how certain plasmon modes are selectively excited and how they funnel energy from the excitation source into the near- and far-field. Using a fully retarded electron-scattering theory capable of describing arbitrary three-dimensional nanoparticle geometries, aggregation schemes, and material compositions, we find that electron energy-loss spectroscopy (EELS) is able to indirectly probe the same electromagnetic hot spots that are generated by an optical excitation source. EELS is then employed in a scanning transmission electron microscope (STEM) to obtain maps of the localized surface plasmon modes of SMSERS-active nanostructures, which are resolved in both space and energy. Single-molecule character is confirmed by the bianalyte approach using two isotopologues of Rhodamine 6G. The origins of this observation are explored

  10. Parallel adaptive mesh refinement for electronic structure calculations

    SciTech Connect

    Kohn, S.; Weare, J.; Ong, E.; Baden, S.

    1996-12-01

    We have applied structured adaptive mesh refinement techniques to the solution of the LDA equations for electronic structure calculations. Local spatial refinement concentrates memory resources and numerical effort where it is most needed, near the atomic centers and in regions of rapidly varying charge density. The structured grid representation enables us to employ efficient iterative solver techniques such as conjugate gradients with multigrid preconditioning. We have parallelized our solver using an object-oriented adaptive mesh refinement framework.

  11. Electronic simulation of a barometric pressure sensor for the meteorological monitor assembly

    NASA Technical Reports Server (NTRS)

    Guiar, C. N.; Duff, L. W.

    1982-01-01

    An analysis of the electronic simulation of barometric pressure used to self-test the counter electronics of the digital barometer is presented. The barometer is part of the Meteorological Monitor Assembly that supports navigation in deep space communication. The theory of operation of the digital barometer, the design details, and the verification procedure used with the barometric pressure simulator are presented.

  12. Nanoscale heat transport via electrons and phonons by molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Lin, Keng-Hua

    Nanoscale heat transport has become a crucial research topic due to the growing importance of nanotechnology for manufacturing, energy conversion, medicine and electronics. Thermal transport properties at the nanoscale are distinct from the macroscopic ones since the sizes of nanoscale features, such as free surfaces and interfaces, are comparable to the wavelengths and mean free paths of the heat carriers (electrons and phonons), and lead to changes in thermal transport properties. Therefore, understanding how the nanoscale features and energy exchange between the heat carriers affect thermal transport characteristics are the goals of this research. Molecular dynamics (MD) is applied in this research to understand the details of nanoscale heat transport. The advantage of MD is that the size effect, anharmonicity, atomistic structure, and non-equilibrium behavior of the system can all be captured since the dynamics of atoms are described explicitly in MD. However, MD neglects the thermal role of electrons and therefore it is unable to describe heat transport in metal or metal-semiconductor systems accurately. To address this limitation of MD, we develop a method to simulate electronic heat transport by implementing electronic degrees of freedom to MD. In this research, nanoscale heat transport in semiconductor, metal, and metal-semiconductor systems is studied. Size effects on phonon thermal transport in SiGe superlattice thin films and nanowires are studied by MD. We find that, opposite to the macroscopic trend, superlattice thin films can achieve lower thermal conductivity than nanowires at small scales due to the change of phonon nature caused by adjusting the superlattice periodic length and specimen length. Effects of size and electron-phonon coupling rate on thermal conductivity and thermal interface resistivity in Al and model metal-semiconductor systems are studied by MD with electronic degrees of freedom. The results show that increasing the specimen

  13. A split-step method to include electron-electron collisions via Monte Carlo in multiple rate equation simulations

    NASA Astrophysics Data System (ADS)

    Huthmacher, Klaus; Molberg, Andreas K.; Rethfeld, Bärbel; Gulley, Jeremy R.

    2016-10-01

    A split-step numerical method for calculating ultrafast free-electron dynamics in dielectrics is introduced. The two split steps, independently programmed in C++11 and FORTRAN 2003, are interfaced via the presented open source wrapper. The first step solves a deterministic extended multi-rate equation for the ionization, electron-phonon collisions, and single photon absorption by free-carriers. The second step is stochastic and models electron-electron collisions using Monte-Carlo techniques. This combination of deterministic and stochastic approaches is a unique and efficient method of calculating the nonlinear dynamics of 3D materials exposed to high intensity ultrashort pulses. Results from simulations solving the proposed model demonstrate how electron-electron scattering relaxes the non-equilibrium electron distribution on the femtosecond time scale.

  14. Variability of Protein Structure Models from Electron Microscopy.

    PubMed

    Monroe, Lyman; Terashi, Genki; Kihara, Daisuke

    2017-03-02

    An increasing number of biomolecular structures are solved by electron microscopy (EM). However, the quality of structure models determined from EM maps vary substantially. To understand to what extent structure models are supported by information embedded in EM maps, we used two computational structure refinement methods to examine how much structures can be refined using a dataset of 49 maps with accompanying structure models. The extent of structure modification as well as the disagreement between refinement models produced by the two computational methods scaled inversely with the global and the local map resolutions. A general quantitative estimation of deviations of structures for particular map resolutions are provided. Our results indicate that the observed discrepancy between the deposited map and the refined models is due to the lack of structural information present in EM maps and thus these annotations must be used with caution for further applications.

  15. Semiconducting properties of amorphous GaZnSnO thin film based on combinatorial electronic structures

    SciTech Connect

    Kim, B. K.; Park, J. S.; Kim, D. H.; Chung, K. B.

    2014-05-05

    Semiconducting properties and electronic structures of amorphous GaZnSnO (GZTO) thin films are investigated with respect to metal cationic composition. An increase of the cationic Sn ratio resulted in an increase of the carrier concentration and a decrease of the mobility of the films. Combinatorial analysis revealed that the electrical characteristics of GZTO films are strongly correlated to changes in electronic structure. The increase in carrier concentration is related to the generation of vacancies by the changes of oxygen coordination around the cationic metal and the shallow band edge state below the conduction band. On the other hand, the decrease of mobility can be explained by the deep band edge state, and the difference between the experimental conduction band and simulated conduction band by the combinatorial electronic structure based on the chemical composition.

  16. Simulation of high-speed (orbital) releases of electron attachment materials in the ionosphere

    NASA Technical Reports Server (NTRS)

    Scales, W. A.; Bernhardt, P. A.

    1991-01-01

    The dynamics of ionospheric plasma irregularities produced by the release of electron attachment materials at orbital velocities across the geomagnetic field is studied. A two-dimensional electrostatic fluid model which includes electron attachment and mutual neutralization chemistry, self-consistent electric fields, and three-species transport is developed. Numerical simulations are performed to study the behavior at early and at late times after the release. At early times, of the order of or less than the attachment material neutral collision time, the negative ion cloud produced by the release may structure owing to the shear in the E x B velocity within the cloud. At high altitudes the cloud may bifurcate and form vortices on the back. At lower altitudes where ion-neutral collisional effects dominate, this structuring is suppressed. At late times, after a plasma depletion has formed due to neutralization chemistry, the cloud structures by the E x B interchange instability. Depending on the release altitude, the depletion structures by the collisional or inertial limit of this instability.

  17. Computer Simulations of Molecular Electronic Devices in Vacuum and in Organic Solvents

    NASA Astrophysics Data System (ADS)

    Wang, Huachuan

    The main aim of this dissertation is to study the structure and dynamics of molecular electronic devices in vacuum and in solvent environment, with special focus on the mechanical properties and cross-section geometries of the break-junction down to the atomic level. The problem statement relies on how to overcome the limitations of observations from experiments, to interpret and reduce the gap between experiential measurements and theoretical studies. In order to reach this goal, a molecular system involving gold nano-electrodes, organic dithiol molecules and a driving-spring model has been built based on the experimental set-up of the break junction (BJ) technique. This technique can be classified as the mechanical controllable break junction (MCBJ) and scanning tunneling / atomic force microscope break junction (STM/AFM-BJ). We then generated self-assembled monolayers and molecular junctions by combining grand-canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation. These approaches allow us to calibrate the structure and dynamics of molecular junctions under multiple environmental factors simultaneously. In the final stage, conductance calculations are performed using the density functional theory (DFT) in combination with the Green's function techniques. The intermediate molecular junction structures could be used to perform electronic transport calculations to eventually close the force-structure-conductance loop.

  18. Thermochemical, structural and electronic properties of amorphous oxides, nitrides and sulfides

    NASA Astrophysics Data System (ADS)

    Zawadzki, Pawel; Lany, Stephan

    2015-03-01

    Amorphous thin films materials become increasingly important components of many functional devices such as thin film displays, photovoltaic cells or thin film transistors. Due to lack of grain boundaries, they have superior uniformity and smoothest, flexibility and corrosion resistance. Amorphous thin films are typically prepared using physical vapor deposition (PVD) techniques at temperatures well below the melting point of deposited material (<0.2Tm). Computational models of amorphous structures, however, are almost elusively constructed from a high temperature equilibrated crystal melt using simulated annealing (SA) protocol. To account for low temperature growth conditions of amorphous thin films we recently developed a new simulation technique. The method, kinetically limited minimization (KLM), starts from a randomly initialized structure and minimizes the total energy in a number of local structural perturbation-relaxation events. We apply KLM to model amorphous structures of 20 binary oxides, nitrides and sulfides and compare their thermochemical, structural and electronic properties.

  19. Electronic structure of tetraphenylporphyrin layers on Ag(100)

    NASA Astrophysics Data System (ADS)

    Classen, Andrej; Pöschel, Rebecca; Di Filippo, Gianluca; Fauster, Thomas; Malcıoǧlu, Osman Barış; Bockstedte, Michel

    2017-03-01

    The electronic structure of Mg and free-base tetraphenylporphyrin films on Ag(100) is investigated by one- and two-photon photoemission in combination with electronic structure calculations using density functional theory and the self-consistent G W0 method. We determine the two highest occupied and the nearly degenerate lowest unoccupied molecular orbitals. Higher unoccupied states are seen in an enhanced emission as a final-state effect. For photon energies close to the prominent absorption of the Soret band we observe a strong electron emission attributed to the break up of the bound electron-hole pairs in the S2 excited state. The experimental results on the occupied and unoccupied energy levels for the molecular films on Ag(100) nicely agree with calculated quasiparticle energies and experiments of the molecules in the gas phase.

  20. Enhancement of electron mobility in asymmetric coupled quantum well structures

    SciTech Connect

    Das, S.; Nayak, R. K.; Sahu, T. Panda, A. K.

    2014-02-21

    We study the low temperature multisubband electron mobility in a structurally asymmetric GaAs/Al{sub x}Ga{sub 1-x}As delta doped double quantum well. We calculate the subband energy levels and wave functions through selfconsistent solution of the coupled Schrodinger equation and Poisson's equation. We consider ionized impurity scattering, interface roughness scattering, and alloy disorder scattering to calculate the electron mobility. The screening of the scattering potentials is obtained by using static dielectric response function formalism within the random phase approximation. We analyze, for the first time, the effect of asymmetric structure parameters on the enhancement of multisubband electron mobility through intersubband interactions. We show that the asymmetric variation of well width, doping concentration, and spacer width considerably influences the interplay of scattering mechanisms on mobility. Our results of asymmetry induced enhancement of electron mobility can be utilized for low temperature device applications.

  1. Progress and new advances in simulating electron microscopy datasets using MULTEM.

    PubMed

    Lobato, I; Van Aert, S; Verbeeck, J

    2016-09-01

    A new version of the open source program MULTEM is presented here. It includes a graphical user interface, tapering truncation of the atomic potential, CPU multithreading functionality, single/double precision calculations, scanning transmission electron microscopy (STEM) simulations using experimental detector sensitivities, imaging STEM (ISTEM) simulations, energy filtered transmission electron microscopy (EFTEM) simulations, STEM electron energy loss spectroscopy (EELS) simulations along with other improvements in the algorithms. We also present a mixed channeling approach for the calculation of inelastic excitations, which allows one to considerably speed up time consuming EFTEM/STEM-EELS calculations.

  2. Molecular and electronic structure of the peptide subunit of Geobacter sulfurreducens conductive pili from first principles.

    PubMed

    Feliciano, Gustavo T; da Silva, Antonio J R; Reguera, Gemma; Artacho, Emilio

    2012-08-02

    The respiration of metal oxides by the bacterium Geobacter sulfurreducens requires the assembly of a small peptide (the GS pilin) into conductive filaments termed pili. We gained insights into the contribution of the GS pilin to the pilus conductivity by developing a homology model and performing molecular dynamics simulations of the pilin peptide in vacuo and in solution. The results were consistent with a predominantly helical peptide containing the conserved α-helix region required for pilin assembly but carrying a short carboxy-terminal random-coiled segment rather than the large globular head of other bacterial pilins. The electronic structure of the pilin was also explored from first principles and revealed a biphasic charge distribution along the pilin and a low electronic HOMO-LUMO gap, even in a wet environment. The low electronic band gap was the result of strong electrostatic fields generated by the alignment of the peptide bond dipoles in the pilin's α-helix and by charges from ions in solution and amino acids in the protein. The electronic structure also revealed some level of orbital delocalization in regions of the pilin containing aromatic amino acids and in spatial regions of high resonance where the HOMO and LUMO states are, which could provide an optimal environment for the hopping of electrons under thermal fluctuations. Hence, the structural and electronic features of the pilin revealed in these studies support the notion of a pilin peptide environment optimized for electron conduction.

  3. Structural Composites Corrosive Management by Computational Simulation

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.; Minnetyan, Levon

    2006-01-01

    A simulation of corrosive management on polymer composites durability is presented. The corrosive environment is assumed to manage the polymer composite degradation on a ply-by-ply basis. The degradation is correlated with a measured Ph factor and is represented by voids, temperature, and moisture which vary parabolically for voids and linearly for temperature and moisture through the laminate thickness. The simulation is performed by a computational composite mechanics computer code which includes micro, macro, combined stress failure, and laminate theories. This accounts for starting the simulation from constitutive material properties and up to the laminate scale which exposes the laminate to the corrosive environment. Results obtained for one laminate indicate that the ply-by-ply managed degradation degrades the laminate to the last one or the last several plies. Results also demonstrate that the simulation is applicable to other polymer composite systems as well.

  4. Moving solvated electrons with light: Nonadiabatic mixed quantum/classical molecular dynamics simulations of the relocalization of photoexcited solvated electrons in tetrahydrofuran (THF)

    SciTech Connect

    Bedard-Hearn, Michael J.; Larsen, Ross E.; Schwartz, Benjamin J.

    2006-11-21

    Motivated by recent ultrafast spectroscopic experiments [Martini et al., Science 293, 462 (2001)], which suggest that photoexcited solvated electrons in tetrahydrofuran (THF) can relocalize (that is, return to equilibrium in solvent cavities far from where they started), we performed a series of nonequilibrium, nonadiabatic, mixed quantum/classical molecular dynamics simulations that mimic one-photon excitation of the THF-solvated electron. We find that as photoexcited THF-solvated electrons relax to their ground states either by continuous mixing from the excited state or via nonadiabatic transitions, {approx}30% of them relocalize into cavities that can be over 1 nm away from where they originated, in close agreement with the experiments. A detailed investigation shows that the ability of excited THF-solvated electrons to undergo photoinduced relocalization stems from the existence of preexisting cavity traps that are an intrinsic part of the structure of liquid THF. This explains why solvated electrons can undergo photoinduced relocalization in solvents like THF but not in solvents like water, which lack the preexisting traps necessary to stabilize the excited electron in other places in the fluid. We also find that even when they do not ultimately relocalize, photoexcited solvated electrons in THF temporarily visit other sites in the fluid, explaining why the photoexcitation of THF-solvated electrons is so efficient at promoting recombination with nearby scavengers. Overall, our study shows that the defining characteristic of a liquid that permits the photoassisted relocalization of solvated electrons is the existence of nascent cavities that are attractive to an excess electron; we propose that other such liquids can be found from classical computer simulations or neutron diffraction experiments.

  5. Vibrational stability and electronic structure of a B80 fullerene

    NASA Astrophysics Data System (ADS)

    Baruah, Tunna; Pederson, Mark R.; Zope, Rajendra R.

    2008-07-01

    We investigate the vibrational stability and the electronic structure of the proposed icosahedral fullerenelike cage structure of B80 [N. G. Szwacki, A. Sadrzadeh, and B. I. Yakobson, Phys. Rev. Lett. 98, 166804 (2007)], by an all electron density-functional theory using polarized Gaussian basis functions containing 41 basis functions per atom. The vibrational analysis of B80 indicates that the icosahedral structure is vibrationally unstable with seven imaginary frequencies. The equilibrium structure has Th symmetry and a smaller gap of 0.96 eV between the highest occupied and the lowest unoccupied molecular orbital energy levels compared to the icosahedral structure. The static dipole polarizability of a B80 cage is 149Å3 , and the first ionization energy is 6.4 eV. The B80 cage has rather large electron affinity of 3 eV making it a useful candidate as electron acceptor if it is synthesized. The infrared and Raman spectra of the highly symmetric structure are characterized by a few absorption peaks.

  6. Human enamel structure studied by high resolution electron microscopy

    SciTech Connect

    Wen, S.L. )

    1989-01-01

    Human enamel structural features are characterized by high resolution electron microscopy. The human enamel consists of polycrystals with a structure similar to Ca10(PO4)6(OH)2. This article describes the structural features of human enamel crystal at atomic and nanometer level. Besides the structural description, a great number of high resolution images are included. Research into the carious process in human enamel is very important for human beings. This article firstly describes the initiation of caries in enamel crystal at atomic and unit-cell level and secondly describes the further steps of caries with structural and chemical demineralization. The demineralization in fact, is the origin of caries in human enamel. The remineralization of carious areas in human enamel has drawn more and more attention as its potential application is realized. This process has been revealed by high resolution electron microscopy in detail in this article. On the other hand, the radiation effects on the structure of human enamel are also characterized by high resolution electron microscopy. In order to reveal this phenomenon clearly, a great number of electron micrographs have been shown, and a physical mechanism is proposed. 26 references.

  7. Computer Simulation Methods for Defect Configurations and Nanoscale Structures

    SciTech Connect

    Gao, Fei

    2010-01-01

    This chapter will describe general computer simulation methods, including ab initio calculations, molecular dynamics and kinetic Monte-Carlo method, and their applications to the calculations of defect configurations in various materials (metals, ceramics and oxides) and the simulations of nanoscale structures due to ion-solid interactions. The multiscale theory, modeling, and simulation techniques (both time scale and space scale) will be emphasized, and the comparisons between computer simulation results and exprimental observations will be made.

  8. Electronic and optical properties of novel carbon structures

    NASA Astrophysics Data System (ADS)

    Matthews, Manyalibo Joseph

    Novel carbon structures in the form of fullerenes and disordered carbon clusters offer a wide variety of physical systems, possessing both long or short range order, which can generally be tuned through non- combustive heat-treatment at various elevated temperatures, THT. Due to the sheer complexity and diversity of the possible nanoscale arrangements, the optical and electronic properties of carbon structures with finite dimensions and crystallinity are still not fully understood. In this study, we focus mainly on the structures produced from carbonization of the hydrocarbon polymer polyparaphenylene (PPP), but we also present experimental results from carbons based on other precursors (e.g. mesophase pitch) which yield quite different structures with both comparable and contrasting physical properties. In terms of electronic properties, we show that in the low-THT PPP-based structures, which exemplify extreme disorder, the electronic states are strongly localized, giving rise to a Mott T1/4 hopping conductivity and self-trapped spin defects AS evidenced by low-temperature transport and electron spin resonance experiments. Electronic transitions which give rise to ~2-3 eV photoluminescent emissions in PPP-based structures are found to be influenced most strongly by residual semi-localized polymeric states which weakly couple to low-frequency PPP phonon modes. However, at intermediate heat-treatment temperatures (THT~ 1500[-]2500oC), all sp2-bonded carbon compounds in this study exhibit a characteristic phonon spectrum (as evidenced by Raman spectroscopy) in which disorder may be characterized by non-zone-center phonon scattering arising from finite crystallite sizes. Because of its intimate connection to carrier confinement and structural disorder, the anomalous 'disorder-induced' graphite D-band is thoroughly investigated by use of Raman spectroscopy, showing that strong dispersion effects are due to a photon-phonon coupling mediated by electronic transitions

  9. Momentum space analysis of the electronic structure of biphenyl

    NASA Astrophysics Data System (ADS)

    Morini, F.; Shojaei, S. H. Reza; Deleuze, M. S.

    2014-11-01

    The results of a yet to come experimental study of the electronic structure of biphenyl employing electron momentum spectroscopy (EMS) have been theoretically predicted, taking into account complications such as structural mobility in the electronic ground state, electronic correlation and relaxation, and a dispersion of the inner-valence ionization intensity to electronically excited (shake-up) configurations in the cation. The main purpose of this work is to explore the current limits of EMS in unraveling details of the molecular structure, namely the torsional characteristics of large and floppy aromatic molecules. At the benchmark ADC(3)/cc-pVDZ level of theory, the influence of the twist angle between the two phenyl rings is found to be extremely limited, except for individual orbital momentum profiles corresponding to ionization lines at electron binding energies ranging from 15 to 18 eV. When taking band overlap effects into account, this influence is deceptively far too limited to allow for any experimental determination of the torsional characteristics of biphenyl by means of EMS.

  10. Theoretical studies of the electronic structure of small metal clusters

    NASA Technical Reports Server (NTRS)

    Jordan, K. D.

    1982-01-01

    Theoretical studies of the electronic structure of metal clusters, in particular clusters of Group IIA and IIB atoms were conducted. Early in the project it became clear that electron correlation involving d orbitals plays a more important role in the binding of these clusters than had been previously anticipated. This necessitated that computer codes for calculating two electron integrals and for constructing the resulting CI Hamiltonions be replaced with newer, more efficient procedures. Program modification, interfacing and testing were performed. Results of both plans are reported.

  11. Electronic Structure Methods Based on Density Functional Theory

    DTIC Science & Technology

    2010-01-01

    L. Nordström, L. Tongming, and B. Johansson, “Relativistic Effects on the Thermal Expansion of the Actinide Elements ”, Phys. Rev. B 42, 1990, p 4544...In-house 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 62102F 6. AUTHOR(S) Christopher F. Woodward (AFRL/RXLMD) 5d. PROJECT NUMBER 4347 5e...in valence electrons change the structure of the core electrons. For example in the actinides , where the f-electrons are coupled to the core states

  12. Structural and electronic properties of dense liquid and amorphous nitrogen

    SciTech Connect

    Boates, B; Bonev, S A

    2011-02-11

    We present first-principles calculations of the structural and electronic properties of liquid nitrogen in the pressure-temperature range of 0-200 GPa and 2000-6000 K. The molecular-polymerization and molecular-atomic liquid phase boundaries have been mapped over this region. We find the polymeric liquid to be metallic, similar to what has been reported for the higher-temperature atomic fluid. An explanation of the electronic properties is given based on the structure and bonding character of the transformed liquids. We discuss the structural and bonding differences between the polymeric liquid and insulating solid cubic-gauche nitrogen to explain the differences in their electronic properties. Furthermore, we discuss the mechanism responsible for charge transport in polymeric nitrogen systems to explain the conductivity of the polymeric fluid and the semi-conducting nature of low-temperature amorphous nitrogen.

  13. Electronic structure and enthalpy of hydrogen and helium mixtures

    NASA Astrophysics Data System (ADS)

    Ross, M.; Klepeis, J. E.; Schafer, K. J.; Barbee, T. W., III

    1992-11-01

    The first local density approximation (LDA) calculations of the electronic structure, equation of state, and enthalpy of mixing were carried out for a number of different compositions of hydrogen and helium in bcc and fcc lattices. These are fully quantum mechanical, self-consistent calculations utilizing state-of-the-art methods of electron band theory, which make no assumptions regarding pressure ionization. The major approximation in the LDA method is that the exchange and correlation energy is given by a free electron functional in terms of the local electron density. The majority of previous mixture calculations start with the assumption that both hydrogen and helium are pressure-ionized so that the electronic structure is approximately that of free or weakly screened electrons in the presence of positive ions. Stevenson used a hard-sphere mixture model for the ions with an ion-ion pseudopotential to account for electron screening and predicted that a mixture containing 7% helium by number, the composition believed to be present in Jupiter and Saturn, would phase separate at a temperature of about 7000 K at 8 Mbar. Subsequent calculations carried out for the fully ionized mixture and for a mixture of screened ions (linear response theory) have all arrived at predictions similar to those of Stevenson. MacFarlane and Hubbard performed Thomas-Fermi-Dirac calculations for mixing enthalpies of hydrogen and helium in bcc and fcc lattices and predicted that phase separation would not occur at any temperature.

  14. Electronic Structure Analysis for Proteins on the FMO Method

    NASA Astrophysics Data System (ADS)

    Kobori, Tomoki; Tsuneyuki, Shinji; Sodeyama, Keitaro; Akagi, Kazuto; Terakura, Kiyoyuki; Fukuyama, Hidetoshi

    2009-03-01

    The enormity and complexity of proteins have rendered their electronic structure calculation very costly. Although recently established Fragment Molecular Orbital (FMO) method enables us to calculate total energy of a huge protein precisely based on quantum mechanics, the method does not refer to one-electron orbitals and one-electron energy spectrum. In this paper we propose a method of analyzing electronic structure of a protein based on first principles calculation with reasonable accuracy and CPU cost. We construct one- electron Hamiltonian of proteins by assembling the output of the FMO method: fragment orbitals are determined by fragment monomer calculation, while interaction and overlap between fragment orbitals in different fragments are obtained from dimer calculation. After one-electron Hamiltonian matrix of the whole system is fabricated with the fragment orbital basis, one- electron energy spectrum is obtained by its diagonalization. If the matrix dimension is too large, unimportant orbitals are eliminated from the matrix so that the diagonalization of the Hamiltonian becomes feasible. The method is applicable to both the Hartree-Fock method and the density functional theory. In this paper, validity of the method is verified by some test calculations of small peptides.

  15. Electronic Structure and Effectively Unpaired Electron Density Topology in closo-Boranes: Nonclassical Three-Center Two-Electron Bonding.

    PubMed

    Lobayan, Rosana M; Bochicchio, Roberto C; Torre, Alicia; Lain, Luis

    2011-04-12

    This article provides a detailed study of the structure and bonding in closo-borane cluster compounds X2B3H3 (X = BH(-), P, SiH, CH, N), with particular emphasis on the description of the electron distribution using the topology of the quantum many-body effectively unpaired density. The close relationship observed between the critical points of this quantity and the localization of the electron cloud allows us to characterize the nonclassical bonding patterns of these systems. The obtained results confirm the suitability of the local rule to detect three-center two-electron bonds, which was conjectured in our previous study on boron hydrides.

  16. Ab initio study of electron-ion structure factors in binary liquids with different types of chemical bonding

    SciTech Connect

    Klevets, Ivan; Bryk, Taras

    2014-12-07

    Electron-ion structure factors, calculated in ab initio molecular dynamics simulations, are reported for several binary liquids with different kinds of chemical bonding: metallic liquid alloy Bi–Pb, molten salt RbF, and liquid water. We derive analytical expressions for the long-wavelength asymptotes of the partial electron-ion structure factors of binary systems and show that the analytical results are in good agreement with the ab initio simulation data. The long-wavelength behaviour of the total charge structure factors for the three binary liquids is discussed.

  17. Banded Electron Structure Formation in the Inner Magnetosphere

    NASA Technical Reports Server (NTRS)

    Liemohn, M. W.; Khazanov, G. V.

    1997-01-01

    Banded electron structures in energy-time spectrograms have been observed in the inner magnetosphere concurrent with a sudden relaxation of geomagnetic activity. In this study, the formation of these banded structures is considered with a global, bounce-averaged model of electron transport, and it is concluded that this structure is a natural occurrence when plasma sheet electrons are captured on closed drift paths near the Earth. These bands do not appear unless there is capture of plasma sheet electrons; convection along open drift paths making open pass around the Earth do not have time to develop this feature. The separation of high-energy bands from the injection population due to the preferential advection of the gradient-curvature drift creates spikes in the energy distribution, which overlap to form a series of bands in the energy spectrograms. The lowest band is the bulk of the injected population in the sub-key energy range. Using the Kp history for an observed banded structure event, a cloud of plasma sheet electrons is captured and the development of their distribution function is examined and discussed.

  18. Optimal Design for Nonperiodic Fine Grating Structure Controlled by Proximity Correction with Electron-Beam Lithography

    NASA Astrophysics Data System (ADS)

    Okano, Masato; Hirai, Yoshihiko; Kikuta, Hisao

    2007-02-01

    We describe a method for designing nonperiodic fine grating structures such as a small F-number diffractive cylindrical lens, to be fabricated by direct-writing electron-beam lithography. The design is based on a resist development simulator for estimating a proximity effect of electron dose and the finite difference time domain (FDTD) method for simulating an electromagnetic field. The surface profile and electron dose distribution are simultaneously optimized to obtain the high diffraction efficiency. For the design of a diffractive lens of 50 μm width and 25 μm focal length, the calculated diffraction efficiency is 49% for 650-nm-wavelength light, which is slightly lower than that of a diffractive lens profile optimized by electromagnetic analysis without restrictions on fabrication limits.

  19. Energetics and electronic structure of armchair nanotubes with topological line defects.

    PubMed

    Okada, Susumu; Nakada, Kyoko; Kawai, Takazumi

    2007-09-12

    We study the electronic structure and energetics of carbon nanotubes with topological line defects consisting of fused pentagons and octagon rings by means of first-principles calculation in density functional theory and tight-binding molecular dynamics simulations. The tubes with the topological line defects are found to exhibit magnetic ordering where polarized electron spins are localized around the topological defect and ferromagnetically aligned along the defect. Our analyses of the electronic energy band and spin density distributions reveal that this ferromagnetic spin ordering is associated with the edge states that are inherent in the graphite ribbon with zigzag edges. The tight-binding molecular dynamics simulations show that the nanotubes with the topological line defects are thermally stable up to temperature of 3000 K and disrupted over 4000 K.

  20. Probing the band structure and local electronic properties of low-dimensional semiconductor structures

    NASA Astrophysics Data System (ADS)

    Walrath, Jenna Cherie

    Low-dimensional semiconductor structures are important for a wide variety of applications, and recent advances in nanoscale fabrication are paving the way for increasingly precise nano-engineering of a wide range of materials. It is therefore essential that the physics of materials at the nanoscale are thoroughly understood to unleash the full potential of nanotechnology, requiring the development of increasingly sophisticated instrumentation and modeling. Of particular interest is the relationship between the local density of states (LDOS) of low-dimensional structures and the band structure and local electronic properties. This dissertation presents the investigation of the band structure, LDOS, and local electronic properties of nanostructures ranging from zero-dimensional (0D) quantum dots (QDs) to two-dimensional (2D) thin films, synthesizing computational and experimental approaches including Poisson-Schrodinger band structure calculations, scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and scanning thermoelectric microscopy (SThEM). A method is presented for quantifying the local Seebeck coefficient (S) with SThEM, using a quasi-3D conversion matrix approach to directly convert temperature gradient-induced voltages S. For a GaAs p-n junction, the resulting S-profile is consistent with that computed using the free carrier concentration profile. This combined computational-experimental approach is expected to enable nanoscale measurements of S across a wide variety of heterostructure interfaces. The local carrier concentration, n, is profiled across epitaxial InAs/GaAs QDs, where SThEM is used to profile the temperature gradient-induced voltage, which is converted to a profile of the local S and finally to an n profile. The S profile is converted to a conduction band-edge profile and compared with Poisson-Schrodinger band-edge simulations. The combined computational-experimental approach suggests a reduced n in the QD center in

  1. A simulation framework for the CMS Track Trigger electronics

    NASA Astrophysics Data System (ADS)

    Amstutz, C.; Magazzù, G.; Weber, M.; Palla, F.

    2015-03-01

    A simulation framework has been developed to test and characterize algorithms, architectures and hardware implementations of the vastly complex CMS Track Trigger for the high luminosity upgrade of the CMS experiment at the Large Hadron Collider in Geneva. High-level SystemC models of all system components have been developed to simulate a portion of the track trigger. The simulation of the system components together with input data from physics simulations allows evaluating figures of merit, like delays or bandwidths, under realistic conditions. The use of SystemC for high-level modelling allows co-simulation with models developed in Hardware Description Languages, e.g. VHDL or Verilog. Therefore, the simulation framework can also be used as a test bench for digital modules developed for the final system.

  2. The electronic structure and chemical bonding of vitamin B12

    NASA Astrophysics Data System (ADS)

    Kurmaev, E. Z.; Moewes, A.; Ouyang, L.; Randaccio, L.; Rulis, P.; Ching, W. Y.; Bach, M.; Neumann, M.

    2003-05-01

    The electronic structure and chemical bonding of vitamin B12 (cyanocobalamin) and B12-derivative (methylcobalamin) are studied by means of X-ray emission (XES) and photoelectron (XPS) spectroscopy. The obtained results are compared with ab initio electronic structure calculations using the orthogonalized linear combination of the atomic orbital method (OLCAO). We show that the chemical bonding in vitamin B12 is characterized by the strong Co-C bond and relatively weak axial Co-N bond. It is further confirmed that the Co-C bond in cyanocobalamin is stronger than that of methylcobalamin resulting in their different biological activity.

  3. Structural and luminescent properties of electron-irradiated silicon

    SciTech Connect

    Sobolev, N. A.; Loshachenko, A. S.; Aruev, P. N.; Kalyadin, A. E.; Shek, E. I.; Zabrodskiy, V. V.; Shtel'makh, K. F.; Vdovin, V. I.; Xiang, Luelue; Yang, Deren

    2014-02-21

    Structural defects induced by electron irradiation of p-Cz-Si wafers were identified. The influence of the annealing conditions in a chlorine-containing atmosphere on the structural and luminescent properties of the samples was examined. Light-emitting diodes based on electron-irradiated and high-temperature-annealed wafers were fabricated by a vapour-phase epitaxy technique and their luminescence properties were studied. A high-intensity dislocation-related D1 line was observed at 1.6 μm in the room-temperature electroluminescence spectrum.

  4. Electronic structure of Sn/Cu(100)-[Formula: see text].

    PubMed

    Martínez-Blanco, J; Joco, V; Fujii, J; Segovia, P; Michel, E G

    2009-02-04

    We present measurements of the Fermi surface and underlying band structure of Sn/Cu(100)-[Formula: see text]. This phase is observed for a coverage of 0.60-0.65 monolayers. Its electronic structure is characterized by a free-electron-like surface band folded with the reconstruction periodicity. At variance with other surface phases of Sn on Cu(100), no temperature-induced phase transition is observed for this phase from 100 K up to the desorption of Sn.

  5. Electronic Structure of Lanthanum Hydrides with Switchable Optical Properties

    SciTech Connect

    Ng, K.; Zhang, F.; Ng, K.; Zhang, F.; Anisimov, V.; Rice, T.; Anisimov, V.

    1997-02-01

    Recent dramatic changes in the optical properties of LaH{sub 2+x} and YH{sub 2+x} films discovered by Huiberts {ital et al.}[Nature (London) {bold 380}, 231 (1996)] suggest their electronic structure is described best by a local model. Electron correlation is important in H{sup -} centers and in explaining the transparent insulating behavior of LaH{sub 3}. The metal-insulator transition at x{approximately}0.8 takes place in a band of highly localized states centered on the H vacancies in the LaH{sub 3} structure. {copyright} {ital 1997} {ital The American Physical Society}

  6. Comparison of electronic structure between monolayer silicenes on Ag (111)

    NASA Astrophysics Data System (ADS)

    Chun-Liang, Lin; Ryuichi, Arafune; Maki, Kawai; Noriaki, Takagi

    2015-08-01

    The electronic structures of monolayer silicenes (4 × 4 and ) grown on Ag (111) surface are studied by scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations. While both phases have similar electronic structures around the Fermi level, significant differences are observed in the higher energy unoccupied states. The DFT calculations show that the contributions of Si 3pz orbitals to the unoccupied states are different because of their different buckled configurations. Project supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) through Grants-in-Aid for Scientific Research (Grant Nos. 24241040 and 25110008) and the World Premier International Research Center Initiative (WPI), MEXT, Japan.

  7. Electronic transitions induced by short-range structural order in amorphous TiO2

    NASA Astrophysics Data System (ADS)

    Triana, C. A.; Araujo, C. Moyses; Ahuja, R.; Niklasson, G. A.; Edvinsson, T.

    2016-10-01

    Several promising applications of amorphous titanium dioxide, a TiO2 , have appeared recently, but the correlation between electronic properties and atomic short-range structural order is poorly understood. Herein we show that structural disorder yields local undercoordinated TiOx units which influence electronic hybridization of Ti-[4 p ] and Ti-[3 d ] orbitals with a low crystal-field splitting [E (eg) -E (t2 g) =2.4 ±0.3 eV ] . The short-range order and electronic properties of a TiO2 thin-film oxides are described through an integrated approach based on x-ray-absorption experiments and ab initio computational simulations where the energy splitting of the electronic levels in the Ti-[4 p -3 d ] manifold are analyzed. Structural disorder provides enough p -d orbital mixing for the hybridized electronic transitions from the Ti-[1 s ] core level into the [Ti -t2 g] and [Ti -eg] bands [1 s →4 p -3 d excitations], to be allowed. This yields an intense pre-edge structure in the Ti K -edge x-ray-absorption near-edge structure spectrum of a TiO2 , which is consistent with the projected density of states on the photoabsorbing Ti atoms.

  8. Interactive Electronic Circuit Simulation on Small Computer Systems

    DTIC Science & Technology

    1979-11-01

    this is the most effective way of completing a computer-aided engineering design cycle. Compar- isons of the interactive versus batch simulation...run on almost any computer system with few if any modifications. Also included are the four benchmark test circuits which were used in many of the...the ensuing FORTRAN version. 2.2 Circuit Simulation Using BIAS-D (BASIC Version) Any circuit-simulation program can be di- vided into three

  9. Electron Accelerations at High Mach Number Shocks: Two-dimensional Particle-in-cell Simulations in Various Parameter Regimes

    NASA Astrophysics Data System (ADS)

    Matsumoto, Yosuke; Amano, Takanobu; Hoshino, Masahiro

    2012-08-01

    Electron accelerations at high Mach number collisionless shocks are investigated by means of two-dimensional electromagnetic particle-in-cell simulations with various Alfvén Mach numbers, ion-to-electron mass ratios, and the upstream electron β e (the ratio of the thermal pressure to the magnetic pressure). We find electrons are effectively accelerated at a super-high Mach number shock (MA ~ 30) with a mass ratio of M/m = 100 and β e = 0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with a large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low.

  10. Electron Accelerations at High Mach Number Shocks: Two-Dimensional Particle-in-Cell Simulations in Various Parameter Regimes

    NASA Astrophysics Data System (ADS)

    Matsumoto, Y.; Amano, T.; Hoshino, M.

    2012-12-01

    Electron accelerations at high Mach number collision-less shocks are investigated by means of two-dimensional electromagnetic Particle-in-Cell simulations with various Alfven Mach numbers, ion-to-electron mass ratios, and the upstream electron βe (the ratio of the thermal pressure to the magnetic pressure). We found electrons are effectively accelerated at a super-high Mach number shock (MA ~ 30) with a mass ratio of M/m=100 and βe=0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with the large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely-high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low. Matsumoto et al., Astrophys. J., 755, 109, 2012.

  11. ELECTRON ACCELERATIONS AT HIGH MACH NUMBER SHOCKS: TWO-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS IN VARIOUS PARAMETER REGIMES

    SciTech Connect

    Matsumoto, Yosuke; Amano, Takanobu; Hoshino, Masahiro

    2012-08-20

    Electron accelerations at high Mach number collisionless shocks are investigated by means of two-dimensional electromagnetic particle-in-cell simulations with various Alfven Mach numbers, ion-to-electron mass ratios, and the upstream electron {beta}{sub e} (the ratio of the thermal pressure to the magnetic pressure). We find electrons are effectively accelerated at a super-high Mach number shock (M{sub A} {approx} 30) with a mass ratio of M/m = 100 and {beta}{sub e} = 0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with a large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low.

  12. Free electron laser-driven ultrafast rearrangement of the electronic structure in Ti

    PubMed Central

    Principi, E.; Giangrisostomi, E.; Cucini, R.; Bencivenga, F.; Battistoni, A.; Gessini, A.; Mincigrucci, R.; Saito, M.; Di Fonzo, S.; D'Amico, F.; Di Cicco, A.; Gunnella, R.; Filipponi, A.; Giglia, A.; Nannarone, S.; Masciovecchio, C.

    2015-01-01

    High-energy density extreme ultraviolet radiation delivered by the FERMI seeded free-electron laser has been used to create an exotic nonequilibrium state of matter in a titanium sample characterized by a highly excited electron subsystem at temperatures in excess of 10 eV and a cold solid-density ion lattice. The obtained transient state has been investigated through ultrafast absorption spectroscopy across the Ti M2,3-edge revealing a drastic rearrangement of the sample electronic structure around the Fermi level occurring on a time scale of about 100 fs. PMID:26798835

  13. Structural and electronic properties of monolayer group III monochalcogenides

    NASA Astrophysics Data System (ADS)

    Demirci, S.; Avazlı, N.; Durgun, E.; Cahangirov, S.

    2017-03-01

    We investigate the structural, mechanical, and electronic properties of the two-dimensional hexagonal structure of group III-VI binary monolayers, M X (M =B , Al, Ga, In and X =O , S, Se, Te) using first-principles calculations based on the density functional theory. The structural optimization calculations and phonon spectrum analysis indicate that all of the 16 possible binary compounds are thermally stable. In-plane stiffness values cover a range depending on the element types and can be as high as that of graphene, while the calculated bending rigidity is found to be an order of magnitude higher than that of graphene. The obtained electronic band structures show that M X monolayers are indirect band-gap semiconductors. The calculated band gaps span a wide optical spectrum from deep ultraviolet to near infrared. The electronic structure of oxides (M O ) is different from the rest because of the high electronegativity of oxygen atoms. The dispersions of the electronic band edges and the nature of bonding between atoms can also be correlated with electronegativities of constituent elements. The unique characteristics of group III-VI binary monolayers can be suitable for high-performance device applications in nanoelectronics and optics.

  14. Electron-Phonon Renormalization of Electronic Band Structures of C Allotropes and BN Polymorphs

    NASA Astrophysics Data System (ADS)

    Tutchton, Roxanne M.; Marchbanks, Christopher; Wu, Zhigang

    The effect of lattice vibration on electronic band structures has been mostly neglected in first-principles calculations because the electron-phonon (e-ph) renormalization of quasi-particle energies is often small (< 100 meV). However, in certain materials, such as diamond, the electron-phonon coupling reduces the band gap by nearly 0.5 eV, which is comparable to the many-body corrections of the electronic band structures calculated using the density functional theory (DFT). In this work, we compared two implementations of the Allen-Heine-Cardona theory in the EPW code and the ABINIT package respectively. Our computations of Si and diamond demonstrate that the ABINIT implementation converges much faster. Using this method, the e-ph renormalizations of electronic structures of three C allotropes (diamond, graphite, graphene) and four BN polymorphs (zincblend, wurtzite, mono-layer, and layered-hexagonal) were calculated. Our results suggest that (1) all of the zero-point renormalizations of band gaps in these materials, except for graphene, are larger than 100 meV, and (2) there are large variations in e-ph renormalization of band gaps due to differences in crystal structure. This work was supported by a U.S. DOE Early Career Award (Grant No. DE-SC0006433). Computations were carried out at the Golden Energy Computing Organization at CSM and the National Energy Research Scientific Computing Center (NERSC).

  15. Enhanced Electron Heating and Mixing in a 3D Kinetic Simulation for MMS Magnetopause Crossings with Weak Guide Fields

    NASA Astrophysics Data System (ADS)

    Le, Ari; Daughton, William; Chen, Li-Jen; Egedal, Jan

    2016-10-01

    We present a 3D kinetic simulation of asymmetric reconnection with plasma parameters matching the MMS magetopause diffusion region crossing reported by Burch et al. (Science 2016). The simulation was performed with the code VPIC on LANL's Trinity machine, which enabled relatively high grid resolution and numerical particle numbers to resolve the electron diffusion region dynamics. The simulation not only reproduces the reported crescent distributions but also appears to account for new features observed by MMS in other diffusion region events with weak guide fields. Compared to a 2D simulation with the same plasma parameters, drift turbulence in the 3D simulation substantially enhances the mixing and parallel heating of electrons on the magnetosphere side. This modifies the reconnection rate inferred from a recently introduced electron mixing diagnostic. To the magnetosphere side of the in-plane magnetic null, the parallel electric field exhibits a bipolar structure with polarities opposite to the large-scale parallel electric field. The 3D structure of the X line and the particle signature of the inverted bipolar parallel electric field have been observed by MMS.

  16. Electronic structure, chemical bonding, and geometry of pure and Sr-doped CaCO3.

    PubMed

    Stashans, Arvids; Chamba, Gaston; Pinto, Henry

    2008-02-01

    The electronic structure, chemical bonding, geometry, and effects produced by Sr-doping in CaCO(3) have been studied on the basis of density-functional theory using the VASP simulation package and molecular-orbital theory utilizing the CLUSTERD computer code. Two calcium carbonate structures which occur naturally in anhydrous crystalline forms, calcite and aragonite, were considered in the present investigation. The obtained diagrams of density of states show similar patterns for both materials. The spatial structures are computed and analyzed in comparison to the available experimental data. The electronic properties and atomic displacements because of the trace element Sr-incorporation are discussed in a comparative manner for the two crystalline structures.

  17. Structural, electronic and mechanical properties of rare earth nitride-ErN: A first principles study

    SciTech Connect

    Murugan, A.; Rajeswarapalanichamy, R. Santhosh, M.; Priyanga, G. Sudha; Kanagaprabha, S.; Iyakutti, K.

    2015-06-24

    The structural, electronic and mechanical properties of rare earth nitride ErN is investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation package. At ambient pressure ErN is stable in the ferromagnetic state with NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that ErN is half metallic at normal pressure. A pressure-induced structural phase transition from NaCl (B1) to CsCl (B2) phase is observed in ErN. Ferromagnetic to non magnetic phase transition is predicted in ErN at high pressure.

  18. Simulations of Surface Effects and Electron Emission from Diamond-Amplifier Cathodes

    SciTech Connect

    Dimitrov D. A.; Rao T.; Busby, R.; Smithe, D.; Cary, J.R.; Ben-Zvi, I.; Chang, X.; Smedley, J.; Wu, Q.; Wang, E.

    2011-09-30

    Emission of electrons in diamond experiments based on the promising diamond-amplifier concept was recently demonstrated. Transmission mode experiments have shown the potential to realize over two orders of magnitude charge amplification. However, the recent emission experiments indicate that surface effects should be understood in detail to build cathodes with optimal properties. We have made progress in understanding secondary electron generation and charge transport in diamond with models we implemented in the VORPAL particle-in-cell computational framework. We introduce models that we have been implementing for surface effects (band bending and electron affinity), charge trapping, and electron emission from diamond. Then, we present results from 3D VORPAL diamond-vacuum simulations with the integrated capabilities on generating electrons and holes, initiated by energetic primary electrons, charge transport, and then emission of electrons from diamond into vacuum. Finally, we discuss simulation results on the dependence of the electron emission on diamond surface properties.

  19. Electronic structure of nitrides PuN and UN

    NASA Astrophysics Data System (ADS)

    Lukoyanov, A. V.; Anisimov, V. I.

    2016-11-01

    The electronic structure of uranium and plutonium nitrides in ambient conditions and under pressure is investigated using the LDA + U + SO band method taking into account the spin-orbit coupling and the strong correlations of 5 f electrons of actinoid ions. The parameters of these interactions for the equilibrium cubic structure are calculated additionally. The application of pressure reduces the magnetic moment in PuN due to predominance of the f 6 configuration and the jj-type coupling. An increase in the occupancy of the 5 f state in UN leads to a decrease in the magnetic moment, which is also detected in the trigonal structure of the UN x β phase (La2O3-type structure). The theoretical results are in good agreement with the available experimental data.

  20. Chiral phosphorus nanotubes: structure, bonding, and electronic properties.

    PubMed

    Fernández-Escamilla, H N; Quijano-Briones, J J; Tlahuice-Flores, A

    2016-05-14

    The study of black phosphorus nanotubes (PNTs) had been devoted to zigzag and armchair structures, with no consideration of chiral structures to date. In this communication, we studied the structural and electronic (band structure) properties of chiral nanotubes using a periodic plane wave-pseudopotential approach. We found that some chiral nanotubes display similar bandgaps and binding energies per atom (BEA) as armchair PNTs and Born-Oppenheimer molecular dynamics (BOMD) calculations attest their thermal stability. Interestingly, we determined that the bandgap is tuned by varying the PNTs chirality and it is not related to their diameters. This feature can be exploited in optical and electronic applications wherein a direct and sizable bandgap is required.

  1. Structural and electronic properties of small silicon clusters

    NASA Astrophysics Data System (ADS)

    Baturin, V. S.; Lepeshkin, S. V.; Magnitskaya, M. V.; Matsko, N. L.; Uspenskii, Yu A.

    2014-05-01

    The atomic structure and electronic spectrum of silicon nanoclusters (Si-ncs) Si7, Si10,Si10H16 and Si10H20 are calculated using the evolutionary algorithm with total energy computed within density functional theory and generalized gradient approximation (DFT-GGA). When analysing the low-energy structures, we pay significant attention to their symmetry and interatomic bond geometry. The candidate structures arising in the process of evolutionary algorithm convergence are also considered and classified by their topology and grouping near local energy minima. Possible ways to improve the convergence of evolutionary computation are discussed. Addressing qualitative criteria for the ground-state atomic structure of Si-ncs, we consider correlations between the density of electronic states and the total energetics of clusters in the ground state and low-energy-isomer configurations.

  2. Visualizing Structure and Dynamics of Disaccharide Simulations

    SciTech Connect

    Matthews, J. F.; Beckham, G. T.; Himmel, M. E.; Crowley, M. F.

    2012-01-01

    We examine the effect of several solvent models on the conformational properties and dynamics of disaccharides such as cellobiose and lactose. Significant variation in timescale for large scale conformational transformations are observed. Molecular dynamics simulation provides enough detail to enable insight through visualization of multidimensional data sets. We present a new way to visualize conformational space for disaccharides with Ramachandran plots.

  3. Layer-stacking effect on electronic structures of bilayer arsenene

    NASA Astrophysics Data System (ADS)

    Mi, Kui; Xie, Jiafeng; Si, M. S.; Gao, C. X.

    2017-01-01

    A monolayer of orthorhombic arsenic (arsenene) is a promising candidate for nano-electronic devices due to the uniquely electronic properties. To further extend its practical applications, an additional layer is introduced to tune the electronic structures. Four layer-stacking manners, namely AA-, AB-, AB‧-, and AC-stacking, are constructed and studied through using first-principles calculations. Compared with monolayer, an indirect-direct gap transition is realized in AB-stacking. More importantly, a semimetal feature appears in the AC- and AB‧-stacked bilayers, leaving the electronic structure of AA-stacking trivial. In addition, the energy dispersion around Γ is largely tuned from the layer-stacking effect. To understand the underlying physics, the \\textbf{k}\\cdot\\textbf{p} approximation is taken to address this issue. Our results show that the level repulsion from the additional layer domaintes the anisotropy of energy dispersion around Γ. The works like ours would shed new light on the tunability of the electronic structure in layered arsenene.

  4. Molecular and electronic structure of electroactive self-assembled monolayers

    NASA Astrophysics Data System (ADS)

    Méndez De Leo, Lucila P.; de la Llave, Ezequiel; Scherlis, Damián; Williams, Federico J.

    2013-03-01

    Self-assembled monolayers (SAMs) containing electroactive functional groups are excellent model systems for the formation of electronic devices by self-assembly. In particular ferrocene-terminated alkanethiol SAMs have been extensively studied in the past. However, there are still open questions related with their electronic structure including the influence of the ferrocene group in the SAM-induced work function changes of the underlying metal. We have thus carried out a thorough experimental and theoretical investigation in order to determine the molecular and electronic structure of ferrocene-terminated alkanethiol SAMs on Au surfaces. In agreement with previous studies we found that the Fc-containing alkanethiol molecules adsorb forming a thiolate bond with the Au surface with a molecular geometry 30° tilted with respect to the surface normal. Measured surface coverages indicate the formation of a compact monolayer. We found for the first time that the ferrocene group has little influence on the observed work function decrease which is largely determined by the alkanethiol. Furthermore, the ferrocene moiety lies 14 Å above the metal surface covalently bonded to the alkanethiol SAM and its HOMO is located at -1.6 eV below the Fermi level. Our results provide new valuable insight into the molecular and electronic structure of electroactive SAMs which are of fundamental importance in the field of molecular electronics.

  5. Molecular and electronic structure of electroactive self-assembled monolayers.

    PubMed

    Méndez De Leo, Lucila P; de la Llave, Ezequiel; Scherlis, Damián; Williams, Federico J

    2013-03-21

    Self-assembled monolayers (SAMs) containing electroactive functional groups are excellent model systems for the formation of electronic devices by self-assembly. In particular ferrocene-terminated alkanethiol SAMs have been extensively studied in the past. However, there are still open questions related with their electronic structure including the influence of the ferrocene group in the SAM-induced work function changes of the underlying metal. We have thus carried out a thorough experimental and theoretical investigation in order to determine the molecular and electronic structure of ferrocene-terminated alkanethiol SAMs on Au surfaces. In agreement with previous studies we found that the Fc-containing alkanethiol molecules adsorb forming a thiolate bond with the Au surface with a molecular geometry 30° tilted with respect to the surface normal. Measured surface coverages indicate the formation of a compact monolayer. We found for the first time that the ferrocene group has little influence on the observed work function decrease which is largely determined by the alkanethiol. Furthermore, the ferrocene moiety lies 14 Å above the metal surface covalently bonded to the alkanethiol SAM and its HOMO is located at -1.6 eV below the Fermi level. Our results provide new valuable insight into the molecular and electronic structure of electroactive SAMs which are of fundamental importance in the field of molecular electronics.

  6. The correlation of ring distributions with electron conics - Simulations of the production of upper hybrid waves

    NASA Astrophysics Data System (ADS)

    Menietti, J. D.; Lin, C. S.; Wong, H. K.

    Using the High Altitude Plasma Instrument on board the Dynamics Explorer 1 satellite, an example of electron conics associated with ring (trapped) distributions of warm electrons is shown. Using an electrostatic P-I-C code, numerical simulations of the generation of upper hybrid waves with ring distributions as the free energy source are performed. These waves heat the electrons perpendicular to the magnetic field, and thus provide a very efficient mechanism for the production of electron conics.

  7. Electron Diffraction and High-Resolution Electron Microscopy of Mineral Structures

    NASA Astrophysics Data System (ADS)

    Nord, Gordon L., Jr.

    This book is a well-written English translation of the original 1981 Russian edition, Strukturnoye issledovaniye mineralov metodami mikrodifraktsii i elechtronnoi mikroskopii vysokogo razresheniya. The 1987 English version has been extensively updated and includes references up to 1986. The book is essentially a text on the theoretical and experimental aspects of transmission electron microscopy and has chapters on the reciprocal lattice, electron diffraction (both kinematic and dynamic), and high-resolution electron microscopy.Electron diffraction is emphasized, especially its use for structure analysis of poorly crystalline and fine-grained phases not readily determined by the more exact X ray diffraction method. Two methods of electron diffraction are discussed: selected area electron diffraction (SAED) and oblique-texture electron diffraction (OTED); the latter technique is rarely used in the west and is never discussed in western electron microscopy texts. A SAED pattern is formed by isolating a small micrometer-size area with an aperture and obtaining single-crystal patterns from the diffracted beams. By tilting the sample and obtaining many patterns, a complete picture of the reciprocal lattice can be taken. An OTED pattern is formed when the incident electron beam passes through an inclined preparation consisting of a great number of thin platy crystals lying normal to the texture axis (axis normal to the support grid). To form an OTED pattern, the plates must all lie on a common face, such as a basal plane in phyllosilicates. Upon tilting the plates, an elliptical powder diffraction pattern is formed. Intensities measured from these patterns are used for a structural analysis of the platy minerals.

  8. Electronic Structure of Crystalline 4He at High Pressures

    SciTech Connect

    Mao, Ho Kwang; Shirley, Eric L.; Ding, Yang; Eng, Peter; Cai, Yong Q.; Chow, Paul; Xiao, Yuming; Jinfu Shu, A=Kao, Chi-Chang; Hemley, Russell J.; Kao, Chichang; Mao, Wendy L.; /Stanford U., Geo. Environ. Sci. /SLAC

    2011-01-10

    Using inelastic X-ray scattering techniques, we have succeeded in probing the high-pressure electronic structure of helium crystal at 300 K which has the widest known electronic energy bandgap of all materials, that was previously inaccessible to measurements due to the extreme energy and pressure range. We observed rich electron excitation spectrum, including a cut-off edge above 23 eV, a sharp exciton peak showing linear volume dependence, and a series of excitations and continuum at 26 to 45 eV. We determined electronic dispersion along the {Gamma}-M direction over two Brillouin zones, and provided a quantitative picture of the helium exciton beyond the simplified Wannier-Frenkel description.

  9. Modulated structures in calcian dolomite: A study by electron microscopy

    NASA Astrophysics Data System (ADS)

    van Tendeloo, G.; Wenk, H. R.; Gronsky, R.

    1985-11-01

    Calcian dolomite from the Devonian Lost Burro formation has been investigated with electron microscopy techniques. Electron diffraction shows evidence for “c” and “d” type reflections which may occur independently and are indicative of ordered superstructures. High resolution electron microscopy combined with selected area optical diffraction is the basis for models to explain the superstructures in calcian dolomite. It is proposed that “c” reflections are due to ordered substitution of Mg by Ca in basal cation layers. “d” reflections result when the rhombohedral stacking of basal layers is interrupted by intercalation of additional Ca layers. During electron irradiation at 1 MeV the Mg-Ca distribution becomes disordered and the crystal structure attains calcite symmetry. The arrangement of CO3 groups remains ordered.

  10. Electronic structure and isomer shifts of neptunium compounds

    NASA Astrophysics Data System (ADS)

    Svane, A.; Petit, L.; Temmerman, W. M.; Szotek, Z.

    2002-08-01

    The electronic structures of αNp metal and 28 Np compounds are calculated with the generalized gradient approximation to density-functional theory, implemented with the full-potential linear-muffin-tin-orbital method. The calculations are compared to experimental isomer shifts providing a calibration of the 237Np isomeric transition with a value of Δ=(-40.1+/-1.3)×10- 3 fm2 for the difference in nuclear radius between the excited isomeric level and the ground state. The isomer shift is primarily determined by the chemical environment. Decreasing the volume, either by external or chemical pressure, causes an f-->s+d charge transfer on Np, which leads to a higher electron contact density. The possible f-electron localization in Np compounds is discussed using self-interaction corrections, and it is concluded that f-electron localization has only a minor influence on the isomer shift.

  11. Superconducting properties and electronic structure of NaBi.

    PubMed

    Kushwaha, S K; Krizan, J W; Xiong, J; Klimczuk, T; Gibson, Q D; Liang, T; Ong, N P; Cava, R J

    2014-05-28

    Resistivity, dc magnetization, and heat capacity measurements are reported for superconducting NaBi. T(c), the electronic contribution to the specific heat γ, the ΔC(p)/γT(c) ratio, and the Debye temperature are found to be 2.15 K, 3.4 mJ mol(-1) K(-2), 0.78, and 140 K respectively. The calculated electron-phonon coupling constant (λ(ep) = 0.62) implies that NaBi is a moderately coupled superconductor. The upper critical field and coherence length are found to be 250 Oe and 115 nm, respectively. Electronic structure calculations show NaBi to be a good metal, in agreement with the experiments; the p(x) and p(y) orbitals of Bi dominate the electronic states at the Fermi Energy.

  12. Correlative Light Electron Microscopy: Connecting Synaptic Structure and Function

    PubMed Central

    Begemann, Isabell; Galic, Milos

    2016-01-01

    Many core paradigms of contemporary neuroscience are based on information obtained by electron or light microscopy. Intriguingly, these two imaging techniques are often viewed as complementary, yet separate entities. Recent technological advancements in microscopy techniques, labeling tools, and fixation or preparation procedures have fueled the development of a series of hybrid approaches that allow correlating functional fluorescence microscopy data and ultrastructural information from electron micrographs from a singular biological event. As correlative light electron microscopy (CLEM) approaches become increasingly accessible, long-standing neurobiological questions regarding structure-function relation are being revisited. In this review, we will survey what developments in electron and light microscopy have spurred the advent of correlative approaches, highlight the most relevant CLEM techniques that are currently available, and discuss its potential and limitations with respect to neuronal and synapse-specific applications. PMID:27601992

  13. Surface crystallography and electronic structure of potassium yttrium tungstate

    SciTech Connect

    Atuchin, V. V.; Pokrovsky, L. D.; Khyzhun, O. Yu.; Sinelnichenko, A. K.; Ramana, C. V.

    2008-08-01

    Structural and electronic characteristics of KY(WO{sub 4}){sub 2} (KYW) (010) crystal surfaces have been studied using reflection high-energy electron diffraction (RHEED) and x-ray photoelectron spectroscopy (XPS). The results indicate that the crystal structure and chemical composition of the mechanically polished pristine surface is stoichiometrically well maintained as expected for KYW crystals. Combined measurements of RHEED and XPS as a function of 1.5 keV Ar{sup +} ion irradiation of the KYW (010) surfaces indicate amorphization, partial loss of potassium atoms, and partial transformation of chemical valence state of tungsten from W{sup 6+} to a lower valence state, W{sup 0} state predominantly, which induces electronic states at the top of valence band.

  14. Electronic, magnetic, and geometric structure of metallo-carbohedrenes

    SciTech Connect

    Reddy, B.V.; Khanna, S.N.; Jena, P. )

    1992-12-04

    The energetics and the electronic, magnetic, and geometric structure of the metallocarbohedrene Ti[sub 8]C[sub 12] have been calculated self-consistently in the density functional formulation. The structure of Ti[sub 8]C[sub 12] is a distorted dodecahedron with a binding energy of 6.1 electron volts per atom. The unusual stability is derived from covalent-like bonding between carbon atoms and between titanium and carbon atoms with no appreciable interaction between titanium atoms. The density of states at the Fermi energy is high and is derived from a strong hybridization between titanium 3d and carbon sp electrons. Titanium sites carry a small magnetic moment of 0.35 Bohr magneton per atom and the cluster is only weakly magnetic. 13 refs., 3 figs., 1 tab.

  15. Two-dimensional simulation research of secondary electron emission avalanche discharge on vacuum insulator surface

    SciTech Connect

    Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui

    2015-01-15

    Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data.

  16. Two-dimensional simulation research of secondary electron emission avalanche discharge on vacuum insulator surface

    NASA Astrophysics Data System (ADS)

    Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui

    2015-01-01

    Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data.

  17. Simulation of radial expansion of an electron beam injected into a background plasma

    NASA Technical Reports Server (NTRS)

    Koga, J.; Lin, C. S.

    1989-01-01

    A 2-D electrostatic particle code was used to study the beam radial expansion of a nonrelativistic electron beam injected from an isolated equipotential conductor into a background plasma. The simulations indicate that the beam radius is generally proportional to the beam electron gyroradius when the conductor is charged to a large potential. The simulations also suggest that the charge buildup at the beam stagnation point causes the beam radial expansion. From a survey of the simulation results, it is found that the ratio of the beam radius to the beam electron gyroradius increases with the square root of beam density and decreases inversely with beam injection velocity. This dependence is explained in terms of the ratio of the beam electron Debye length to the ambient electron Debye length. These results are most applicable to the SEPAC electron beam injection experiments from Spacelab 1, where high charging potential was observed.

  18. Highlighting material structure with transmission electron diffraction correlation coefficient maps.

    PubMed

    Kiss, Ákos K; Rauch, Edgar F; Lábár, János L

    2016-04-01

    Correlation coefficient maps are constructed by computing the differences between neighboring diffraction patterns collected in a transmission electron microscope in scanning mode. The maps are shown to highlight material structural features like grain boundaries, second phase particles or dislocations. The inclination of the inner crystal interfaces are directly deduced from the resulting contrast.

  19. Electron Heat Flux in Pressure Balance Structures at Ulysses

    NASA Technical Reports Server (NTRS)

    Yamauchi, Yohei; Suess, Steven T.; Sakurai, Takashi; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Pressure balance structures (PBSs) are a common feature in the high-latitude solar wind near solar minimum. Rom previous studies, PBSs are believed to be remnants of coronal plumes and be related to network activity such as magnetic reconnection in the photosphere. We investigated the magnetic structures of the PBSs, applying a minimum variance analysis to Ulysses/Magnetometer data. At 2001 AGU Spring meeting, we reported that PBSs have structures like current sheets or plasmoids, and suggested that they are associated with network activity at the base of polar plumes. In this paper, we have analyzed high-energy electron data at Ulysses/SWOOPS to see whether bi-directional electron flow exists and confirm the conclusions more precisely. As a result, although most events show a typical flux directed away from the Sun, we have obtained evidence that some PBSs show bi-directional electron flux and others show an isotropic distribution of electron pitch angles. The evidence shows that plasmoids are flowing away from the Sun, changing their flow direction dynamically in a way not caused by Alfven waves. From this, we have concluded that PBSs are generated due to network activity at the base of polar plumes and their magnetic structures axe current sheets or plasmoids.

  20. Structural and electronic properties of perylene from first principles calculations.

    PubMed

    Fedorov, I A; Zhuravlev, Y N; Berveno, V P

    2013-03-07

    The electronic structure of crystalline perylene has been investigated within the framework of density functional theory including van der Waals interactions. The computations of the lattice parameters and cohesive energy have good agreement with experimental values. We have also calculated the binding distance and energy of perylene dimers, using different schemes, which include van der Waals interactions.