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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 721 records · Page 40

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DOE OSTI2014

Brownian dynamics without Green's functions

We develop a Fluctuating Immersed Boundary (FIB) method for performing Brownian dynamics simulations of confined particle suspensions. Unlike traditional methods which employ analytical Green's functions for Stokes flow in the confined geometry, the FIB method uses a fluctuating finite-volume Stokes solver to generate the action of the response functions “on the fly.” Importantly, we demonstrate that both the deterministic terms necessary to capture the hydrodynamic interactions among the suspended particles, as well as the stochastic terms necessary to generate the hydrodynamically correlated Brownian motion, can be generated by solving the steady Stokes equations numerically only once per time step. This is accomplished by including a stochastic contribution to the stress tensor in the fluid equations consistent with fluctuating hydrodynamics. We develop novel temporal integrators that account for the multiplicative nature of the noise in the equations of Brownian dynamics and the strong dependence of the mobility on the configuration for confined systems. Notably, we propose a random finite difference approach to approximating the stochastic drift proportional to the divergence of the configuration-dependent mobility matrix. Through comparisons with analytical and existing computational results, we numerically demonstrate the ability of the FIB method to accurately capture both the static (equilibrium) and dynamic properties of interacting particles in flow.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Ultrahigh stability of atomically thin metallic glasses

We report the fabrication and study of thermal stability of atomically thin ZrCu-based metallic glass films. The ultrathin films exhibit striking dynamic properties, ultrahigh thermal stability, and unique crystallization behavior with discrete crystalline nanoparticles sizes. The mechanisms for the remarkable high stability and crystallization behaviors are attributed to the dewetting process of the ultrathin film. We demonstrated a promising avenue for understanding some fundamental issues such as glassy structure, crystallization, deformation, and glass formation through atomic resolution imaging of the two dimensional like metallic glasses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Experimental dynamical characterization of five autonomous chaotic oscillators with tunable series resistance

In this paper, an experimental characterization of the dynamical properties of five autonomous chaotic oscillators, based on bipolar-junction transistors and obtained de-novo through a genetic algorithm in a previous study, is presented. In these circuits, a variable resistor connected in series to the DC voltage source acts as control parameter, for a range of which the largest Lyapunov exponent, correlation dimension, approximate entropy, and amplitude variance asymmetry are calculated, alongside bifurcation diagrams and spectrograms. Numerical simulations are compared to experimental measurements. The oscillators can generate a considerable variety of regular and chaotic sine-like and spike-like signals.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Three-dimensional dust-ion-acoustic rogue waves in a magnetized dusty pair-ion plasma with nonthermal nonextensive electrons and opposite polarity dust grains

Dust-ion-acoustic (DIA) rogue waves are investigated in a three-dimensional magnetized plasma containing nonthermal electrons featuring Tsallis distribution, both positive and negative ions, and immobile dust grains having both positive and negative charges. Via the reductive perturbation method, a (3 + 1)-dimensional nonlinear Schrödinger (NLS) equation is derived to govern the dynamics of the DIA wave packets. The modulation instability of DIA waves described by the (3 + 1)-dimensional NLS equation is investigated. By means of the similarity transformation and symbolic computation, both the first- and second-order rogue wave solutions of the (3 + 1)-dimensional NLS equation are constructed in terms of rational functions. Moreover, the dynamics properties and the effects of plasma parameters on the nonlinear structures of rogue waves are discussed in detail. The results could be useful for understanding the physical mechanism of rogue waves in laboratory experiments where pair-ion plasmas with electrons and dust grains can be found.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2014

Study of asymmetric fission yield behavior from neutron-deficient Hg isotope

A study of asymmetric fission yield behavior from a neutron-deficient Hg isotope has been conducted. The fission yield calculation of the neutron-deficient Hg isotope using Brownian Metropolis shape had showed unusual result at decreasing energy. In this paper, this interesting feature will be validated by using nine degree of scission shapes parameterization from Brosa model that had been implemented in TALYS nuclear reaction code. This validation is intended to show agreement between both model and the experiment result. The expected result from these models considered to be different due to dynamical properties that implemented in both models.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2014

Microwave generation by spin Hall nanooscillators with nanopatterned spin injector

We experimentally study spin Hall nano-oscillators based on Pt/ferromagnet bilayers with nanopatterned Pt spin injection layer. We demonstrate that both the spectral characteristics and the electrical current requirements can be simultaneously improved by reducing the spin injection area. Moreover, devices with nanopatterned Pt spin injector exhibit microwave generation over a wide temperature range that extends to room temperature. Studies of devices with additional Pt spacers under the device electrodes show that the oscillation characteristics are affected not only by the spin injection geometry but also by the effects of Pt/ferromagnet interface on the dynamical properties of the ferromagnet.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Positive feedback can lead to dynamic nanometer-scale clustering on cell membranes

Clustering of molecules on biological membranes is a widely observed phenomenon. A key example is the clustering of the oncoprotein Ras, which is known to be important for signal transduction in mammalian cells. Yet, the mechanism by which Ras clusters form and are maintained remains unclear. Recently, it has been discovered that activated Ras promotes further Ras activation. Here we show using particle-based simulation that this positive feedback is sufficient to produce persistent clusters of active Ras molecules at the nanometer scale via a dynamic nucleation mechanism. Furthermore, we find that our cluster statistics are consistent with experimental observations of the Ras system. Interestingly, we show that our model does not support a Turing regime of macroscopic reaction-diffusion patterning, and therefore that the clustering we observe is a purely stochastic effect, arising from the coupling of positive feedback with the discrete nature of individual molecules. These results underscore the importance of stochastic and dynamic properties of reaction diffusion systems for biological behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Multi-scale simulation of the stability and diffusion of lithium in the presence of a 90° partial dislocation in silicon

The stable positions, binding energies, and dynamic properties of Li impurity in the presence of a 90° partial dislocation in Si have been studied by using the multi-scale simulation method. The corresponding results are compared with the defect-free Si crystal in order to reflect how the dislocation defect affects the performances of Li-ion batteries (LIBs) at the atomic level. It is found that the inserted Li atom in the dislocation core and nearest regions is more stable, since the binding energies are 0.13 eV to 0.52 eV larger than the bulk Si. Moreover, it is easier for Li atom to diffuse into those defect areas and harder to diffuse out. Thus, Li dopant may tend to congregate in the dislocation core and nearest regions. On the other side, the 90° partial dislocation can glide in the (111) plane accompanied by the diffusion of Li impurity along the pentagon ring of core. In addition, the spacious heptagon ring of dislocation core can lower the migration barrier of Li atom from 0.63 eV to 0.34 eV, which will enhance the motion of the dopant. Therefore, the presence of 90° partial dislocations may provide a fast and favorable diffusion path for the congregated Li impurity, which finally facilitates the lithiation of LIBs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Adjustable ferromagnetic resonance frequency in CoO/CoFeB system

Static and dynamic properties of (CoO/CoFeB){sub n} multilayers have been investigated. An anisotropy field enhancement was evidenced when the CoO layer was deposited under the CoFeB layer. Tuning the relative CoFeB and CoO layers thicknesses, high ferromagnetic resonance frequencies up to 4 GHz were achieved. The coupling effect between the CoO and CoFeB layers was induced by a dipolar coupling due to the anisotropic roughness topology of the CoO layer. This anisotropic roughness was induced by the deposition geometry and evidenced by atomic force microscopy. The strength of the dipolar interfacial coupling was calculated thanks to Schlömann's model. Multilayer stacks were fabricated and the magnetic properties observed for the trilayers could be maintained.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Synthesis of the unmanned aerial vehicle remote control augmentation system

Medium size Unmanned Aerial Vehicle (UAV) usually flies as an autonomous aircraft including automatic take-off and landing phases. However in the case of the on-board control system failure, the remote steering is using as an emergency procedure. In this reason, remote manual control of unmanned aerial vehicle is used more often during take-of and landing phases. Depends on UAV take-off mass and speed (total energy) the potential crash can be very danger for airplane and environment. So, handling qualities of UAV is important from pilot-operator point of view. In many cases the dynamic properties of remote controlling UAV are not suitable for obtaining the desired properties of the handling qualities. In this case the control augmentation system (CAS) should be applied. Because the potential failure of the on-board control system, the better solution is that the CAS algorithms are placed on the ground station computers. The method of UAV handling qualities shaping in the case of basic control system failure is presented in this paper. The main idea of this method is that UAV reaction on the operator steering signals should be similar - almost the same - as reaction of the 'ideal' remote control aircraft. The model following method was used for controller parameters calculations. The numerical example concerns the medium size MP-02A UAV applied as an aerial observer system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Wetting behavior of nonpolar nanotubes in simple dipolar liquids for varying nanotube diameter and solute-solvent interactions

Atomistic simulations of model nonpolar nanotubes in a Stockmayer liquid are carried out for varying nanotube diameter and nanotube-solvent interactions to investigate solvophobic interactions in generic dipolar solvents. We have considered model armchair type single-walled nonpolar nanotubes with increasing radii from (5,5) to (12,12). The interactions between solute and solvent molecules are modeled by the well-known Lennard-Jones and repulsive Weeks-Chandler-Andersen potentials. We have investigated the density profiles and microscopic arrangement of Stockmayer molecules, orientational profiles of their dipole vectors, time dependence of their occupation, and also the translational and rotational motion of solvent molecules in confined environments of the cylindrical nanopores and also in their external peripheral regions. The present results of structural and dynamical properties of Stockmayer molecules inside and near atomistically rough nonpolar surfaces including their wetting and dewetting behavior for varying interactions provide a more generic picture of solvophobic effects experienced by simple dipolar liquids without any specific interactions such as hydrogen bonds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Generation of a magnetic island by edge turbulence in tokamak plasmas

We investigate, through extensive 3D magneto-hydro-dynamics numerical simulations, the nonlinear excitation of a large scale magnetic island and its dynamical properties due to the presence of small-scale turbulence. Turbulence is induced by a steep pressure gradient in the edge region [B. D. Scott, Plasma Phys. Controlled Fusion 49, S25 (2007)], close to the separatrix in tokamaks where there is an X-point magnetic configuration. We find that quasi-resonant localized interchange modes at the plasma edge can beat together and produce extended modes that transfer energy to the lowest order resonant surface in an inner stable zone and induce a seed magnetic island. The island width displays high frequency fluctuations that are associated with the fluctuating nature of the energy transfer process from the turbulence, while its mean size is controlled by the magnetic energy content of the turbulence.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2015

Nanocluster building blocks of artificial square spin ice: Stray-field studies of thermal dynamics

We present measurements of the thermal dynamics of a Co-based single building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition. We employ micro-Hall magnetometry, an ultra-sensitive tool to study the stray field emanating from magnetic nanostructures, as a new technique to access the dynamical properties during the magnetization reversal of the spin-ice nanocluster. The obtained hysteresis loop exhibits distinct steps, displaying a reduction of their “coercive field” with increasing temperature. Therefore, thermally unstable states could be repetitively prepared by relatively simple temperature and field protocols allowing one to investigate the statistics of their switching behavior within experimentally accessible timescales. For a selected switching event, we find a strong reduction of the so-prepared states' “survival time” with increasing temperature and magnetic field. Besides the possibility to control the lifetime of selected switching events at will, we find evidence for a more complex behavior caused by the special spin ice arrangement of the macrospins, i.e., that the magnetic reversal statistically follows distinct “paths” most likely driven by thermal perturbation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Adaptive resolution simulation of polarizable supramolecular coarse-grained water models

Multiscale simulations methods, such as adaptive resolution scheme, are becoming increasingly popular due to their significant computational advantages with respect to conventional atomistic simulations. For these kind of simulations, it is essential to develop accurate multiscale water models that can be used to solvate biophysical systems of interest. Recently, a 4-to-1 mapping was used to couple the bundled-simple point charge water with the MARTINI model. Here, we extend the supramolecular mapping to coarse-grained models with explicit charges. In particular, the two tested models are the polarizable water and big multiple water models associated with the MARTINI force field. As corresponding coarse-grained representations consist of several interaction sites, we couple orientational degrees of freedom of the atomistic and coarse-grained representations via a harmonic energy penalty term. This additional energy term aligns the dipole moments of both representations. We test this coupling by studying the system under applied static external electric field. We show that our approach leads to the correct reproduction of the relevant structural and dynamical properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Protein search for multiple targets on DNA

Protein-DNA interactions are crucial for all biological processes. One of the most important fundamental aspects of these interactions is the process of protein searching and recognizing specific binding sites on DNA. A large number of experimental and theoretical investigations have been devoted to uncovering the molecular description of these phenomena, but many aspects of the mechanisms of protein search for the targets on DNA remain not well understood. One of the most intriguing problems is the role of multiple targets in protein search dynamics. Using a recently developed theoretical framework we analyze this question in detail. Our method is based on a discrete-state stochastic approach that takes into account most relevant physical-chemical processes and leads to fully analytical description of all dynamic properties. Specifically, systems with two and three targets have been explicitly investigated. It is found that multiple targets in most cases accelerate the search in comparison with a single target situation. However, the acceleration is not always proportional to the number of targets. Surprisingly, there are even situations when it takes longer to find one of the multiple targets in comparison with the single target. It depends on the spatial position of the targets, distances between them, average scanning lengths of protein molecules on DNA, and the total DNA lengths. Physical-chemical explanations of observed results are presented. Our predictions are compared with experimental observations as well as with results from a continuum theory for the protein search. Extensive Monte Carlo computer simulations fully support our theoretical calculations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Enhanced magnetic damping in La{sub 0.7}Sr{sub 0.3}MnO{sub 3} capped by normal metal layer

La{sub 0.7}Sr{sub 0.3}MnO{sub 3}(LSMO) and Pt capped La{sub 0.7}Sr{sub 0.3}MnO{sub 3} 20 nm thick films have been grown on SrTiO{sub 3} substrates by pulsed laser deposition. Microstrip line ferromagnetic resonance (MS-FMR) technique is then used to investigate their magnetic dynamic properties and to particularly measure the damping constant based on the frequency dependence of microwave absorption linewidth. The results show that the effective damping constant of LSMO(20nm)/Pt(5.5nm) is three times larger than that of LSMO(20nm) and the films present weak in-plane uniaxial anistropy. The enhancement of the magnetic damping constant due to the capping of Pt is the manifestaction of the generation of spin current in Pt layer. Furthermore, the spin current induces an inverse spin Hall effect (ISHE) in LSMO(20nm)/Pt(5.5nm) system, measured using the FMR in cavity with 9.8 GHz excitation frequency. The linear dependence of ISHE on microwave power validates the mechenism of spin pumping in this bilayer system.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Periodicity, chaos, and multiple attractors in a memristor-based Shinriki's circuit

In this contribution, a novel memristor-based oscillator, obtained from Shinriki's circuit by substituting the nonlinear positive conductance with a first order memristive diode bridge, is introduced. The model is described by a continuous time four-dimensional autonomous system with smooth nonlinearities. The basic dynamical properties of the system are investigated including equilibria and stability, phase portraits, frequency spectra, bifurcation diagrams, and Lyapunov exponents' spectrum. It is found that in addition to the classical period-doubling and symmetry restoring crisis scenarios reported in the original circuit, the memristor-based oscillator experiences the unusual and striking feature of multiple attractors (i.e., coexistence of a pair of asymmetric periodic attractors with a pair of asymmetric chaotic ones) over a broad range of circuit parameters. Results of theoretical analyses are verified by laboratory experimental measurements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Imaginary time density-density correlations for two-dimensional electron gases at high density

We evaluate imaginary time density-density correlation functions for two-dimensional homogeneous electron gases of up to 42 particles in the continuum using the phaseless auxiliary field quantum Monte Carlo method. We use periodic boundary conditions and up to 300 plane waves as basis set elements. We show that such methodology, once equipped with suitable numerical stabilization techniques necessary to deal with exponentials, products, and inversions of large matrices, gives access to the calculation of imaginary time correlation functions for medium-sized systems. We discuss the numerical stabilization techniques and the computational complexity of the methodology and we present the limitations related to the size of the systems on a quantitative basis. We perform the inverse Laplace transform of the obtained density-density correlation functions, assessing the ability of the phaseless auxiliary field quantum Monte Carlo method to evaluate dynamical properties of medium-sized homogeneous fermion systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗