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All sources NASA NTRS DOE OSTI

DOE OSTI2016

A comparative study of Rosenbrock-type and implicit Runge-Kutta time integration for discontinuous Galerkin method for unsteady 3D compressible Navier-Stokes equations

A comparative study of two classes of third-order implicit time integration schemes is presented for a third-order hierarchical WENO reconstructed discontinuous Galerkin (rDG) method to solve the 3D unsteady compressible Navier-Stokes equations: — 1) the explicit first stage, single diagonally implicit Runge-Kutta (ESDIRK3) scheme, and 2) the Rosenbrock-Wanner (ROW) schemes based on the differential algebraic equations (DAEs) of Index-2. Compared with the ESDIRK3 scheme, a remarkable feature of the ROW schemes is that, they only require one approximate Jacobian matrix calculation every time step, thus considerably reducing the overall computational cost. A variety of test cases, ranging from inviscid flows to DNS of turbulent flows, are presented to assess the performance of these schemes. Here, numerical experiments demonstrate that the third-order ROW scheme for the DAEs of index-2 can not only achieve the designed formal order of temporal convergence accuracy in a benchmark test, but also require significantly less computing time than its ESDIRK3 counterpart to converge to the same level of discretization errors in all of the flow simulations in this study, indicating that the ROW methods provide an attractive alternative for the higher-order time-accurate integration of the unsteady compressible Navier-Stokes equations.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2015

Comparative study of donor-induced quantum dots in Si nano-channels by single-electron transport characterization and Kelvin probe force microscopy

We comparatively study donor-induced quantum dots in Si nanoscale-channel transistors for a wide range of doping concentration by analysis of single-electron tunneling transport and surface potential measured by Kelvin probe force microscopy (KPFM). By correlating KPFM observations of donor-induced potential landscapes with simulations based on Thomas-Fermi approximation, it is demonstrated that single-electron tunneling transport at lowest gate voltages (for smallest coverage of screening electrons) is governed most frequently by only one dominant quantum dot, regardless of doping concentration. Doping concentration, however, primarily affects the internal structure of the quantum dot. At low concentrations, individual donors form most of the quantum dots, i.e., “donor-atom” quantum dots. In contrast, at high concentrations above metal-insulator transition, closely placed donors instead of individual donors form more complex quantum dots, i.e., “donor-cluster” quantum dots. The potential depth of these “donor-cluster” quantum dots is significantly reduced by increasing gate voltage (increasing coverage of screening electrons), leading to the occurrence of multiple competing quantum dots.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2017

A Comparative Study of the Application of FACTS Devices in Wind Power Plants of the Southeast Area of the Mexican Electric System

This paper presents a comparative study of the application of Flexible AC Transmission System (FACTS) devices, as Thyristor Controlled Series Capacitor (TCSC), Static Synchronous Compensator (STATCOM) and Unified Power Controller (UPFC) on congestion management and voltage support in the area of the Istmo of Tehuantepec, Oaxaca, Mexico. The present work provides an analysis about the performance of the control of active and reactive power of the FACTS controllers applied to mentioned problems in the power system.

17 WIND ENERGY↗

DOE OSTI2018

Selective Lead(II) Adsorption and Flocculation Characteristics of the Grafted Sodium Alginate: A Comparative Study

Synthesis of sodium alginate-g-poly(acrylamide-co-N-methylacrylamide) [S-III], sodium alginate-g-poly(N-methylacrylamide-co-N,N-dimethylacrylamide) [S-II], sodium alginate-g-poly(acrylamide-co-N,N-dimethylacrylamide) [S-I]. Sodium alginate-g-poly(N,N-dimethylacrylamide) [SAG-g-PDMA] and sodium alginate-g-poly(acrylamide) [SAG-g-PAM] were prepared by solution polymerization technique using potassium peroxydisulfate as the initiator at 70 °C in water medium. The graft copolymers were characterized by FTIR and NMR ({sup 1}H and {sup 13}C) spectroscopy, SEM and XRD studies. All the five graft copolymers were used to remove Pb(II) ions from the aqueous solution and also in flocculation studies of kaolin clay (1.0 wt%), silica (1.0 wt%) and iron ore slime (0.25 wt%) suspensions. A comparative studies of all the five graft copolymers were also made in both the two cases. The Pb(II) ion removal capacity of all the graft copolymers follows the order S-III > SAG-g-PAM > S-II > SAG-g-PDMA > S-I. But the flocculation performance of the graft copolymers follows the order S-II > S-I > S-III > SAG-g-PDMA > SAG-g-PAM. S-III was also used for the competitive metal ion removal with Hg(II), Cd(II), Cu(II) and Zn(II). Pb(II) adsorption of S-III (the best Pb(II) ion adsorber) follows pseudo second order rate equation and Langmuir adsorption isotherm.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2019

A Comparative Study of Constitutive Characteristics and Microstructure Evolution between Uniaxial and Plane Strain Compression of an AA6061 Alloy

The hot deformation behavior of an AA6061 alloy was comparatively studied by uniaxial compression (UC) and plane strain compression (PSC) in the temperature range of 300-450 °C and strain rate range of 0.01-5 s{sup −1}. The processing maps were constructed based on a dynamic materials model, and the associated microstructures were observed. Under the same deformation conditions, the flow stress of the AA6061 alloy during PSC is higher than that during UC, which can be characterized by the Zener–Hollomon (Z) parameter in a hyperbolic sine-type equation with an activation energy Q of 175.2 kJ mol{sup −1} and 201.9 kJ mol{sup −1}, respectively. In addition, the instability domain is narrower under PSC compared to that under UC. The observed microstructures also indicate that as the Z value decreases, the tendency of dynamic recrystallization increases during PSC. The softening mechanisms in the AA6061 alloy after PSC and UC mainly consist of the dynamic recovery that is accompanied by a slight dynamic recrystallization. The optimum parameters are in the temperature range of 360-450 °C and strain rate range of 0.03-0.3 s{sup −1} for UC, and for PSC, the optimum parameters are in the temperature range of 320-400 °C and strain rate range of 0.01-0.05 s{sup −1}.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Comparative Study of the Magnetoelectric Effect in HoAl{sub 3}(BO{sub 3}){sub 4} and HoGa{sub 3}(BO{sub 3}){sub 4} Single Crystals

The comparative study of the magnetoelectric properties and magnetostriction of HoGa{sub 3}(BO{sub 3}){sub 4} and HoAl{sub 3}(BO{sub 3}){sub 4} single crystals has been carried out. The investigated compounds exhibit qualitatively similar magnetodielectric and inverse magnetoelectric ME{sub E} effects with the close absolute values, which is indicative of the weak effect of a nonmagnetic metal ion. On the contrary, the magnetostriction of the galloborate has been found to be threefold higher than that of the alumoborate. In addition, the difference between the qualitative behaviors of magnetostriction has been established: the magnetic-field dependence of magnetostriction for the alumoborate has the maximum near 70 kOe at T = 4.2 K, while the galloborate magnetostriction has no maximum and does not saturate in a field of 140 kOe.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

A comparative study on charge carrier recombination across the junction region of Cu{sub 2}ZnSn(S,Se){sub 4} and Cu(In,Ga)Se{sub 2} thin film solar cells

A comparative study with focusing on carrier recombination properties in Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) and the CuInGaSe{sub 2} (CIGS) solar cells has been carried out. For this purpose, electroluminescence (EL) and also bias-dependent time resolved photoluminescence (TRPL) using femtosecond (fs) laser source were performed. For the similar forward current density, the EL-intensity of the CZTSSe sample was obtained significantly lower than that of the CIGS sample. Primarily, it can be attributed to the existence of excess amount of non-radiative recombination center in the CZTSSe, and/or CZTSSe/CdS interface comparing to that of CIGS sample. In case of CIGS sample, TRPL decay time was found to increase with the application of forward-bias. This can be attributed to the reduced charge separation rate resulting from the reduced electric-field at the junction. However, in CZTSSe sample, TRPL decay time has been found almost independent under the forward and reverse-bias conditions. This phenomenon indicates that the charge recombination rate strongly dominates over the charge separation rate across the junction of the CZTSSe sample. Finally, temperature dependent V{sub OC} suggests that interface related recombination in the CZTSSe solar cell structure might be one of the major factors that affect EL-intensity and also, TRPL decay curves.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Numerical modeling of carrier gas flow in atomic layer deposition vacuum reactor: A comparative study of lattice Boltzmann models

This paper characterizes the carrier gas flow in the atomic layer deposition (ALD) vacuum reactor by introducing Lattice Boltzmann Method (LBM) to the ALD simulation through a comparative study of two LBM models. Numerical models of gas flow are constructed and implemented in two-dimensional geometry based on lattice Bhatnagar–Gross–Krook (LBGK)-D2Q9 model and two-relaxation-time (TRT) model. Both incompressible and compressible scenarios are simulated and the two models are compared in the aspects of flow features, stability, and efficiency. Our simulation outcome reveals that, for our specific ALD vacuum reactor, TRT model generates better steady laminar flow features all over the domain with better stability and reliability than LBGK-D2Q9 model especially when considering the compressible effects of the gas flow. The LBM-TRT is verified indirectly by comparing the numerical result with conventional continuum-based computational fluid dynamics solvers, and it shows very good agreement with these conventional methods. The velocity field of carrier gas flow through ALD vacuum reactor was characterized by LBM-TRT model finally. The flow in ALD is in a laminar steady state with velocity concentrated at the corners and around the wafer. The effects of flow fields on precursor distributions, surface absorptions, and surface reactions are discussed in detail. Steady and evenly distributed velocity field contribute to higher precursor concentration near the wafer and relatively lower particle velocities help to achieve better surface adsorption and deposition. The ALD reactor geometry needs to be considered carefully if a steady and laminar flow field around the wafer and better surface deposition are desired.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2013

Application of convergence acceleration to the reactor kinetic equations: A comparative study

This presentation provides a comparison of two methodologies for the solution of reactor kinetic equations, namely for a standard finite difference and a semi-analytical approach. The above-mentioned methods are implemented in a convergence acceleration framework to enhance their efficiency and a comparative study is reported to verify whether it is more convenient to use a rudimentary but fast algorithm (finite difference) with respect to the more refined but computationally intense approach of the semi-analytical method. Performance on several test cases from the literature are compared. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2017

A comparative study of surface energies and water adsorption on Ce-bastnäsite, La-bastnäsite, and calcite via density functional theory and water adsorption calorimetry

Bastnäsite, a fluoro-carbonate mineral, is the single largest mineral source of light rare earth elements (REE), La, Ce and Nd. Enhancing the efficiency of separation of the mineral from gangue through froth flotation is the first step towards meeting an ever increasing demand for REE. To design and evaluate collector molecules that selectively bind to bastnäsite, a fundamental understanding of the structure and surface properties of bastnäsite is essential. In our earlier work (J Phys Chem C, 2016, 120, 16767), we carried out an extensive study of the structure, surface stability and water adsorption energies of La-bastnäsite. Here in this work, we make a comparative study of the surface properties of Ce-bastnäsite, La-bastnäsite, and calcite using a combination of density functional theory (DFT) and water adsorption calorimetry. Spin polarized DFT+U calculations show that the exchange interaction between the electrons in Ce 4f orbitals is negligible and that these orbitals do not participate in bonding with the oxygen atom of the adsorbed water molecule. In agreement with calorimetry, DFT calculations predict larger surface energies and stronger water adsorption energies on Ce-bastnäsite than on La-bastnäsite. The order of stabilities for stoichiometric surfaces is as follows: [100] > [101] > [102] > [0001] > [112] > [104] and the most favorable adsorption sites for water molecules are the same as for La-bastnäsite. In agreement with water adsorption calorimetry, at low coverage water molecules are strongly stabilized via coordination to the surface Ce3+ ions, whereas at higher coverage they are adsorbed less strongly via hydrogen bonding interaction with the surface anions. Lastly, due to similar water adsorption energies on bastnäsite [101] and calcite [104] surfaces, the design of collector molecules that selectively bind to bastnäsite over calcite must exploit the structural differences in the predominantly exposed facets of these minerals.

36 MATERIALS SCIENCE↗

DOE OSTI2016

A comparative study on the frequency effects of the electrical characteristics of the pulsed dielectric barrier discharge in He/O{sub 2} and in Ar/O{sub 2} at atmospheric pressure

In this work, a comparative study on the frequency effects of the electrical characteristics of the pulsed dielectric barrier discharges in He/O{sub 2} and in Ar/O{sub 2} at atmospheric pressure has been performed by means of the numerical simulation based on a 1-D fluid model at frequencies below 100 kHz. The frequency dependences of the characteristic quantities of the discharges in the two gases have been systematically calculated and analyzed under the oxygen concentrations below 2%. The characteristic quantities include the discharge current density, the averaged electron density, the electric field, and the averaged electron temperature. Especially, the frequency effects on the averaged particle densities of the reactive species have also been calculated. This work gives the following significant results. For the two gases, there are two bipolar discharges in one period of applied voltage pulse under the considered frequency range and oxygen concentrations, as occurred in the pure noble gases. The frequency affects the two discharges in He/O{sub 2}, but in Ar/O{sub 2}, it induces a strong effect only on the first discharge. For the first discharge in each gas, there is a characteristic frequency at which the characteristic quantities reach their respective minimum, and this frequency appears earlier for Ar/O{sub 2}. For the second discharge in Ar/O{sub 2}, the averaged electron density presents a slight variation with the frequency. In addition, the discharge in Ar/O{sub 2} is strong and the averaged electron temperature is low, compared to those in He/O{sub 2.} The total averaged particle density of the reactive species in Ar/O{sub 2} is larger than those in He/O{sub 2} by about one order of magnitude.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Matter power spectra in modified gravity: a comparative study of approximations and N -body simulations

ABSTRACT Testing gravity and the concordance model of cosmology, $\Lambda$CDM, at large scales is a key goal of this decade’s largest galaxy surveys. Here we present a comparative study of dark matter power spectrum predictions from different numerical codes in the context of three popular theories of gravity that induce scale-independent modifications to the linear growth of structure: nDGP, Cubic Galileon, and K-mouflage. In particular, we compare the predictions from N-body simulations solving the full scalar field equation, two N-body codes with approximate time integration schemes, a parametrized modified N-body implementation, and the analytic halo model reaction approach. We find the modification to the $\Lambda$CDM spectrum is in 2 per cent agreement at $z\le 1$ and $k\le 1~h\,{\rm Mpc}^{-1}$ over all gravitational models and codes, in accordance with many previous studies, indicating these modelling approaches are robust enough to be used in forthcoming survey analyses under appropriate scale cuts. We further make public the new code implementations presented, specifically the halo model reaction K-mouflage implementation and the relativistic Cubic Galileon implementation.

Bose, B. (ORCID:0000000319658614)↗

DOE OSTI2016

Patient Satisfaction After Femoral Arterial Access Site Closure Using the ExoSeal{sup ®} Vascular Closure Device Compared to Manual Compression: A Prospective Intra-individual Comparative Study

PurposeTo intra-individually compare discomfort levels and patient satisfaction after arterial access closure using the ExoSeal{sup ®} vascular closure device (VCD) and manual compression (MC) in a prospective study design.MethodsPatients undergoing two planned interventions from 07/2013 to 09/2014 could participate in the study. Access closure was performed with an ExoSeal{sup ®}-VCD in one and MC in the other intervention. Patients were clinically and sonographically examined and were given questionnaires 1 day after intervention [groin- and back-pain during bedrest (100-point visual analog scale; 0: no pain); comfortability of bedrest (10-point Likert scale, 1: comfortable), satisfaction with closure (10-point Likert scale, 1: very satisfied)]. Results were analyzed in a cross-over design.Results48 patients (29 male, median age 62.5 (32–88) years) were included. An ExoSeal{sup ®}-VCD was used first in 25 cases. As four of these subsequently refused MC as second intervention, data from 44 patients could be analyzed. All closures were technically successful (successful device deployment) without major complications. Groin- and back-pain after VCD-use/MC was 0 (0–15) vs. 10 (0–80) and 0 (0–75) vs. 25 (0–90), respectively (p < 0.0001). Bedrest after VCD-use was more comfortable than after MC [1 (range 1–7) vs. 6 (2–10); p < 0.0001]. Satisfaction with the closure procedure and with the intervention in general was higher after VCD-use compared to MC [1 (1–3) vs. 5 (2–10) and 1 (1–2) vs. 2 (1–4), respectively; p < 0.0001].ConclusionIntra-individual comparison showed pain levels and discomfort to be significantly lower after ExoSeal{sup ®} use compared to MC. VCD closure was associated with higher satisfaction both with the closure itself and with the intervention in general.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

NASA NTRS1990

A comparative study of advanced shock-capturing schemes applied to Burgers' equation

Several variations of the TVD scheme, ENO scheme, FCT scheme, and geometrical schemes, such as MUSCL and PPM, are considered. A comparative study of these schemes as applied to the Burgers' equation is presented. The objective is to assess their performance for problems involving formation and propagation of shocks, shock collisions, and expansion of discontinuities.

Yang, H. Q.↗

DOE OSTI2018

Comparative Study of the Lateral Photovoltaic Effect in Fe{sub 3}O{sub 4}/SiO{sub 2}/n-Si and Fe{sub 3}O{sub 4}/SiO{sub 2}/p-Si Structures

The results of a comparative study of the lateral photovoltaic effect in Fe{sub 3}O{sub 4}/SiO{sub 2}/n-Si and Fe{sub 3}O{sub 4}/SiO{sub 2}/p-Si structures are presented. The lateral photovoltage reaches its maximum near the measurement contacts in both structures, but the signs of this voltage differ. As the light spot moves away from the contacts, the photovoltage varies linearly in Fe{sub 3}O{sub 4}/SiO{sub 2}/n-Si and decreases exponentially in Fe{sub 3}O{sub 4}/SiO{sub 2}/p-Si. It is found that interface states at the SiO{sub 2}/Si interface induce the photovoltage polarity inversion associated with a change in the conductivity type of silicon. An extreme thickness dependence of the photovoltage with an optimum Fe{sub 3}O{sub 4} film thickness of ~50 nm is observed in both structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

A comparative study of physico-chemical properties of CBD and SILAR grown ZnO thin films

Graphical abstract: Schematic model indicating ZnO nanorods by CBD (Z{sub 1}) and nanograins by SILAR (Z{sub 2}). - Highlights: • Simple methods for the synthesis of ZnO thin films. • Comparative study of physico-chemical properties of ZnO thin films prepared by CBD and SILAR methods. • CBD outperforms SILAR method. - Abstract: In the present work, nanocrystalline zinc oxide (ZnO) thin films have been successfully deposited onto glass substrates by simple and economical chemical bath deposition (CBD) and successive ionic layer adsorption reaction (SILAR) methods. These films were further characterized for their structural, optical, surface morphological and wettability properties. The X-ray diffraction (XRD) patterns for both CBD and SILAR deposited ZnO thin films reveal the highly crystalline hexagonal wurtzite structure. From optical studies, band gaps obtained are 2.9 and 3.0 eV for CBD and SILAR deposited thin films, respectively. The scanning electron microscope (SEM) patterns show growth of well defined randomly oriented nanorods and nanograins on the CBD and SILAR deposited samples, respectively. The resistivity of CBD deposited films (10{sup 2} Ω cm) is lower than that of SILAR deposited films (10{sup 5} Ω cm). Surface wettability studies show hydrophobic nature for both films. From the above results it can be concluded that CBD grown ZnO thin films show better properties as compared to SILAR method.

36 MATERIALS SCIENCE↗

NASA NTRS1985

Comparative study of the phase of diurnal anisotropy on quiet and disturbed days on a long term basis up to recent period

The data from the world wide grid of neutron monitoring stations was analyzed for a comparative study of the phase of diurnal anisotropy on quiet and disturbed days on a long term basis up to recent period. It has been observed that the phase of the diurnal anisotropy on disturbed days where the value of the Ap-index is higher, is found to shift towards earlier hours in comparison to the phase of the diurnal anisotropy on quiet days where the value of Ap-index is lower on all the stations from 1965 to 71. Such a trend is not observable for the later period. This affect is found to be more pronounced on equatorial stations, in particular, in comparison to high latitude stations. It was derived from these observational facts that the relationship between Ap-index and the phase of the diurnal anisotropy is not invariant throughout the period of consideration. Furthermore, the exact cause of such a drastic change is not known, but it demonstrates very clearly that the interplanetary conditions which are responsible for both, diurnal anisotropy of cosmic ray intensity and the geomagnetic Ap-index variation, have drastically changed during the period 1971 and onwards.

Kumar, S.↗

DOE OSTI2018

Eye-Safe KGd(WO{sub 4}){sub 2} Raman Lasers: Comparative Study of Pumping of Nd:KGd(WO{sub 4}){sub 2} Lasers With {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 13/2} Working Transitions{sup **}

This is a comparative study of eye-safe extracavity KGd(WO{sub 4}){sub 2} (KGW) Raman lasers that convert multimode emission from pulsed Nd:KGW lasers operating on the {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 13/2} transitions into the third Stokes component at λ = 1500 nm and the first Stokes component at λ = 1507 or 1538 nm. For equal sizes of the Raman and laser sections of a Raman laser emitting the third Stokes component, the pulse energy is higher (~14.2 mJ) and the divergence of the Stokes beam is lower (~9.4 mrad) for a lower energy of the Nd:KGW laser (~6.7 J). For pump pulse energies of 29–34 mJ, all the Raman lasers have essentially the same optical lasing efficiency of up to 36%. In terms of the electrical energy delivered to the flashlamp, however, the overall efficiency of the Raman laser for the third Stokes component is a factor of ~1.7 higher. The duration of the Raman pulses is comparable to that of the pump pulses and is ~20 ns for the first Stokes components. The pulse in the third Stokes component is shorter by a factor of 2.5–3. Given the different pump levels and the differences in the thermallyinduced optical distortions of the Nd:KGW laser components, the energy density distribution for beams of the first Stokes components is elliptical, while that of the third Stokes components is almost circular. The possibility of simultaneous lasing at wavelengths of 1507 and 1538 nm with parallel and mutually orthogonal polarizations of the Stokes waves is demonstrated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗