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At least 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A practical approach for identifying various polarization behaviors of redox-stable electrodes in symmetrical solid oxide fuel cells

In symmetrical solid oxide fuel cells, comprehensively understanding the elementary reaction processes and the polarization behaviors of redox-stable electrode materials is critical for further optimization of the electrode performance. In this work, a systematical and practical approach, based on electrochemical impedance spectroscopy technology, is applied to identify the rate-limiting elementary reactions of the redox-stable electrodes. The feasibility of this proposed method is demonstrated in symmetrical solid oxide fuel cells with Sr 2 Fe 1.5 Mo 0.5 O 6-σ -Ce 0.9 Gd 0.1 O 1.95 as electrodes. Based on the characteristic frequency ranges and the experimental results tested under various fuel gas components, operating temperatures, and discharge current densities, the rate-limiting steps of the cathode are associated with the formation of adsorbed oxygen ions and the combination of oxygen ions and oxygen vacancies, while the rate-limiting steps of the anode are ascribed to the hydrogen dissociated adsorption and the steam desorption processes. This experimental and analysis framework can be straightforwardly extended to other electrode materials to unravel their electrochemical performance in detail.

25 ENERGY STORAGE↗
DOE OSTI2015

Outdoor characterization of radio frequency electromagnetic fields in a Spanish birth cohort

There is considerable public concern in many countries about the possible adverse effects of exposure to non-ionizing radiation electromagnetic fields, especially in vulnerable populations such as children. The aim of this study was to characterize environmental exposure profiles within the frequency range 100 kHz–6 GHz in the immediate surrounds of the dwellings of 123 families from the INMA-Granada birth cohort in Southern Spain, using spot measurements. The arithmetic mean root mean-square electric field (E{sub RMS}) and power density (S{sub RMS}) values were, respectively, 195.79 mV/m (42.3% of data were above this mean) and 799.01 µW/m{sup 2} (30% of values were above this mean); median values were 148.80 mV/m and 285.94 µW/m{sup 2}, respectively. Exposure levels below the quantification limit were assigned a value of 0.01 V/m. Incident field strength levels varied widely among different areas or towns/villages, demonstrating spatial variability in the distribution of exposure values related to the surface area population size and also among seasons. Although recorded values were well below International Commission for Non-Ionizing Radiation Protection reference levels, there is a particular need to characterize incident field strength levels in vulnerable populations (e.g., children) because of their chronic and ever-increasing exposure. The effects of incident field strength have not been fully elucidated; however, it may be appropriate to apply the precautionary principle in order to reduce exposure in susceptible groups. - Highlights: • Spot measurements were performed in the immediate surrounds of children's dwellings. • Mean root mean-square electric field and power density values were calculated. • Most recorded values were far below international standard guideline limits. • Data demonstrate spatial variability in the distribution of exposure levels. • While adverse effects are proven, application of the precautionary principle may be appropriate.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Measurement of the environmental broadband electromagnetic waves in a mid-size European city

In this paper, the level of exposure to broadband radiofrequency electromagnetic field in a mid-size European city was evaluated in accordance with the International Commission on Non-ionizing Radiation Protection guidelines from 1998. With the aim to analyse all the potential electromagnetic waves present in the city up to 18 GHz, a total of 271 locations distributed along Terrassa (Spain) have been measured. To show the results in an easy-to-interpret way by the citizen, the results have been represented in a set of raster maps. The measurement results obtained showed that the electromagnetic wave measured in all broadband frequency range along the city is much lower than the safety level according to the international regulations for both public and occupational sectors.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Wide-Area Measurement-Based Modal Decoupling for Power System Oscillation Damping

Inter-area oscillation modes usually fall within the same frequency range of 0.1 to 1.0 Hz; thus, power oscillation damping (POD) control methods should avoid unnecessary excitation of weakly damped modes. This paper presents a decoupled control strategy to damp inter-area oscillations in the power grid. Pure oscillation mode signals are extracted from wide-area measurements and used as feedback input for POD actuators such as power system stabilizers or high-voltage direct current transmission. The decoupled control strategy is able to increase the damping of the concerned oscillation modes without deteriorating others. This proposed strategy could be implemented independently, or serve as a complement and work along with conventional POD controllers to damp concerned inter-area modes. The proposed method has been tested on a modied MinniWECC system. Extensive results indicate that inter-area oscillations can be successfully and precisely damped using the proposed decoupled strategy.

Fan, Rui↗
DOE OSTI2020

The Material Plasma Exposure eXperiment: Mission and conceptual design

Mastering Plasma Material Interactions (PMI) is key for obtaining a high performance, high duty-cycle and safe operating fusion reactor. Numerous gaps exist in PMI which have to be addressed before a reactor can be built. In particular the lack of data at high ion fluence, fusion reactor divertor relevant plasma conditions and neutron displacement damage requires new experimental devices to be able to develop plasma facing materials and components. This has been recognized in the community and the U.S. fusion program is addressing this need with a new linear plasma device—the Material Plasma Exposure eXperiment (MPEX). MPEX will be a superconducting linear plasma device with magnetic fields of up to 2.5 T. The plasma source is a high-power helicon source (200 kW, 13.56 MHz). The electrons will be heated via Electron Bernstein Waves with microwaves using multiple 70 GHz gyrotrons (up to 600 kW in total). Ions will be heated via ion cyclotron heating in the so-called “magnetic beach heating” scheme in the frequency range of 6–9 MHz (up to 400 kW in total). An overview of the conceptual design and the project/design requirements is given in this paper.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Development of real-time density feedback control on MAST-U in L-mode

In this paper we report on the development and demonstration of density feedback control for MAST-U. Sinusoidal perturbations are used to measure the frequency response from a deuterium gas valve (actuator) to line-integrated core electron density measured by the interferometer (sensor). In the frequency range relevant for control design, only two system-identification experiments were needed to regress a first-order dynamic model. This control-oriented model informs the offline design of a proportional integral controller with the established loop-shaping controller design method. After offline verification of the controller implementation, control is demonstrated by experimentally tracking a staircase reference for the line-integrated electron density. This paper demonstrates the efficiency of controller design using system-identification and loop-shaping, providing reliable density control for MAST-U.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Field-scale estimation of soil properties from spectral induced polarization tomography

Estimates of soil properties such as Cation Exchange Capacity (CEC), water content, grain size characteristics, and permeability are important in geotechnical engineering, water resources, and agriculture. We develop a non-intrusive approach to estimate these properties in the field using spectral induced polarization (SIP) tomography. This geophysical method provides information about the frequency dependence of the complex electrical conductivity of porous media. Using 18 soil samples collected from a Bordeaux vineyard, we first conducted a laboratory study using SIP over the frequency range 10 mHz-45 kHz. The laboratory data were used to confirm the accuracy of a recently developed dynamic Stern layer petrophysical model. The results are consistent with published values from previous works using soils. A comparison was made by comparing the field complex conductivity spectra and the experimental data at two locations where core samples were obtained. The model was then used in concert with field data to image the spatial distribution of CEC, water content, permeability, and mean grain size along a vineyard transect. For clay and sandy textures found in the field, measured and estimated CEC agree rather well (from 6 to 40% discrepancy). Furthermore, our approach provides an efficient way to estimate important soil properties in a non-invasive manner, in high resolution, and over field-relevant scales of the critical zone of the Earth.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Cell concentrations and metabolites enhance the SIP response to biofilm matrix components

Here we investigated the relative effect of different bacterial biofilm components to influence spectral induced polarization (SIP) signals and Cole-Cole model parameters (i.e. normalized chargeability (S m –1 ) and relaxation time ($τ$)) in order to reduce the ambiguity associated with interpretation of SIP signatures in biostimulated environments. SIP measurements were collected over a frequency range, (i.e. 0.1 Hz –1 kHz) from experimental columns containing Pseudomonas aeruginosa PAO1 (non-mucoid bacterial strain) cell suspensions alone and cell suspensions mixed with different molecules associated with P. aeruginosa biofilm matrix (alginate, DNA and phenazine). Results from SIP measurements of cell density investigations suggest an increase in phase (~ 200%), imaginary conductivity (σ" S m –1 ), and normalized chargeability (S m –1 ) values as cell densities increase (1.50–5.55 × 10 9 CFUml –1 ), yet no significant change in the real conductivity (σ' S m –1 ) or relaxation time was observed. The addition of alginate resulted in a suppression of phase (φ mrads), imaginary conductivity (σ" S m –1 ), and normalized chargeability (S m –1 ) response. However, a mixture of cells and alginate increased all parameters but with no significant changes in real conductivity (σ' S m –1 ) or relaxation time. Similar trend was observed in the DNA treatments; increasing concentrations of DNA reduced the imaginary conductivity (σ" S m –1 ), phase (φ mrads), and normalized chargeability (S m –1 ) response. In contrast, the addition of phenazine, a secondary metabolite of P. aeruginosa, resulted in a significant increase in both imaginary conductivity (σ" S m –1 ), phase (φ mrads), and normalized chargeability (S m –1 ) values especially at larger concentrations (>50 mM). Our work suggests that cell density and metabolites are significant factors increasing the polarization response in biofilms and advances the interpretation of electrical signals associated with biofilms in the subsurface.

58 GEOSCIENCES↗
DOE OSTI2020

A Study of the Conformational Isomerism of n-Propyl Nitrate by Microwave Spectroscopy

The rotational spectrum of n-propyl nitrate was measured in the frequency range between 6 to 18 GHz using a Balle-Flygare Fourier transform microwave jet/cavity spectrometer. Parent, 13C and 15N isotopologue transitions for the lower-energy anti-gauche (AG) conformer were found using this instrument. The search for spectra from other conformers was performed using a broadband chirped-pulse jet spectrometer. Transitions from the anti-anti (AA) conformer were observed in this manner. Parent, 13C and 15N isotopologue transitions for the AA conformer were rescanned using the cavity instrument to improve resolution and the signal-to-noise ratio. Rotational, centrifugal distortion, and nuclear electric quadrupole coupling constants for all conformers/isotopologues were fit using Pickett’s SPFIT program. The structure of n-propyl nitrate is discussed considering these results.

Orellana, Will D.↗
DOE OSTI2023

The microwave spectra of the conformers of $\mathcal{n}$-butyl nitrate

We report the microwave spectrum of n-butyl nitrate was recorded in the 5 to 20 GHz frequency range using broadband chirp and narrowband pulse excitation molecular jet Fourier transform microwave spectrometers. A quantum chemistry structural analysis yielded thirteen stable conformers. Among them, the five most energetically stable conformers were observed in the experimental spectra. The most stable conformer features a butyl chain with an anti-gauche-anti conformation (AGA) where the γ-carbon atom is about 64° out of the nitrate plane. For this conformer, spectra of all 13 C and 15 N minor isotopologues could be measured. The conformer with a straight butyl chain (AAA), and three other conformers (GAA, GGA, and AGG) were also observed. Accurate rotational constants, centrifugal distortion constants, and 14 N nuclear quadrupole coupling constants could be deduced and compared to the theoretical values.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Vanadium oxide nanotubes VOx-NTs: Hydrothermal synthesis, characterization, electrical study and dielectric properties

Vanadium oxide nanotubes (VOx-NTs) have been synthesized via one-step hydrothermal treatment. The compounds were analyzed through X-ray powder diffraction; scanning electron microscope, UV–Visible spectroscopy, X-ray photoelectron spectroscopy (XPS) and complex impedance spectroscopy. The electrical and dielectric properties dependence on temperature (302–523 K) and on frequency (5 Hz to 13 MHz) of VOx-NTs have been reported. The complex impedance plots exhibits the presence of grain and grain boundaries. Dielectric data were analyzed using complex permittivity and complex electrical modulus for the sample at various temperatures. The presence of non-Debye type of relaxation has been confirmed by the complex modulus analysis. AC conductivity exhibits two conduction mechanisms: at high temperature, a translational motion with a sudden hopping and at low temperature, a localized hopping with a small hopping or reorientational motion. DC conductivity indicated, negative temperature coefficient of resistance (NTCR) type behavior. - Graphical abstract: The imaginary part of dielectric constant decreases with the increase in frequency at all temperatures and the values of ε´´ exhibit considerable frequency dispersion in the lower frequency range . Highlights: •Vanadium oxide nanotubes (VOx-NTs) were synthesized. •Non-debye type of relaxation has been confirmed. •AC conductivity exhibits two conduction mechanisms. •DC conductivity indicated negative temperature coefficient of resistance type behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Hydrothermal crystal growth, piezoelectricity, and triboluminescence of KNaNbOF{sub 5}

Single crystals of the noncentrosymmetric KNaNbOF{sub 5} polymorph were grown for piezoelectric and triboluminescent measurements. Piezoelectric measurements yielded a d{sub 33} value of ±6.3 pCN{sup −1} and an effective electromechanical coupling coefficient of up to 0.1565 in the frequency range 1960–2080 kHz. Crystals of KNaNbOF{sub 5} were found to exhibit a strong triboluminscence effect visible to the naked eye as blue sparks when crystals are crushed. This triboluminescence effect is uncommon in that it is likely independent from both the piezoelectric effect and atmospheric electrical discharge. Instead, triboluminescence may originate from crystal defects or be related to an electroluminescence effect. - Graphical abstract: An optical emission visible to the naked eye as blue sparks is observed when KNaNbOF{sub 5} single crystals are fractured. - Highlights: • Single crystals of KNaNbOF{sub 5} were grown under hydrothermal conditions. • Piezoelectric and triboluminescent properties were characterized. • Piezoelectric measurements yielded a d{sub 33} value of ±pCN{sup −1}. • KNaNbOF{sub 5} exhibits strong triboluminscence visible to the naked eye as blue sparks.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structural and thermoelectric properties of zintl-phase CaLiPn (Pn=As, Sb, Bi)

First-principles calculations were carried out to study the structural, mechanical, dynamical and transport properties of zintl phase materials CaLiPn (Pn=As, Sb and Bi). We have used two different approaches to solve the system based on density functional theory. The plane wave pseudopotential approach has been used to study the structural and dynamical properties whereas, full potential linear augment plane wave method is used to examine the electronic structure, mechanical and thermoelectric properties. The calculated ground-state properties agree quite well with experimental values. The computed electronic structure shows the investigated compounds to be direct band gap semiconductors. Further, we have calculated the thermoelectric properties of all the investigated compounds for both the carriers at various temperatures. We found a high thermopower for both the carriers, especially n-type doping to be more favourable, which enabled us to predict that CaLiPn might have promising applications as a good thermoelectric material. Further, the phonon dispersion curves of the investigated compounds showed flat phonon modes and we also find lower optical and acoustic modes to cut each other at the lower frequency range, which further indicate the investigated compounds to possess reasonably low thermal conductivity. We have also analysed the low value of the thermal conductivity through the empirical relations and discussions are presented here. - Highlights: • Electronic band structure and chemical bonding. • Single crystalline elastic constants and poly crystalline elastic moduli. • Thermoelectric properties of zintl phase. • Lattice dynamics and phonon density of states.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Solvothermal synthesis, electromagnetic and electrochemical properties of jellylike cylinder graphene-Mn{sub 3}O{sub 4} composite with highly coupled effect

Jellylike cylinder graphene-Mn{sub 3}O{sub 4} composite with highly coupled effect was successfully synthesized by a simple solvothermal process. Without using toxic reducing agent and expensive equipment, this method is environmental compatible and suitable for low cost mass production. High capacitance Mn{sub 3}O{sub 4} nanoparticles are homogeneously anchored on excellent conductivity graphene framework and a growth mechanism is hypothesized. Excellent electron conductivity and unique structure of Mn{sub 3}O{sub 4}-graphene composite give rise to various applications such as microwave absorber and electrode material. As a microwave absorber, the composite exhibits lowest reflection loss of −14.2 dB in the frequency range of 2–18 GHz. Good microwave absorption performance is due to the structure of the composite where conductive channels form between nano sized Mn{sub 3}O{sub 4} and high conductivity graphene with defects and dangling bonds. As for electrochemical property, Mn{sub 3}O{sub 4}-graphene composite with coupled effect shows excellent performance with highest specific capacitance of 246.7 F g{sup −1} in saturated K{sub 2}SO{sub 4} at a scan rate of 5 mV s{sup −1}. Good electrochemical property is also attributed to the structure with high utilization of Mn{sub 3}O{sub 4}, fast charge carrier transmission, and excellent electronic conductivity. This composite shows a promising application in absorbing materials and electrodes. - Graphical abstract: Graphene-Mn{sub 3}O{sub 4} composite. Display Omitted - Highlights: • Strongly coupled graphene-Mn{sub 3}O{sub 4} composite is synthesized by a solvothermal method. • Excellent microwave absorption property is ascribed to the composite structure. • Good capacitance performance is attributed to the structure and physical property. • The composite shows promising application in absorbing material, and electrode.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Copper-nickel electroplating of 3D-printed acrylonitrile butadiene styrene for interference and radiation shielding applications

Here, in this study, electromagnetic and radiation shielding structures were fabricated by 3D printing acrylonitrile butadiene styrene (ABS) structures via fused filament fabrication and electroplating with copper (Cu) and nickel (Ni) metals. Prior to electroplating, the printed ABS materials were made conductive by surface electrodeposition of polypyrrole (PPy). ABS adsorbs the pyrrole monomer, which subsequently polymerizes via oxidation forming conductive PPy layer on the printed structures. The successful anchoring of PPy layer can be attributed to its hydrogen bonding and electrostatic interactions with ABS. Thermal analysis, optical, and electron microscopy equipped with energy dispersive X-ray were employed to characterize the printed shielding structures, while the interference and radiation shielding effectiveness were evaluated using a spectrum analyzer and dosimeter, respectively. The interference shielding was found to be effective at 60 ± 5 dB over relatively small frequency range. Shielding was also apparent against gamma and X-ray ionizing rays, but more significantly effective against beta rays. Furthermore, the Cu/Ni coating was able to reduce any heat-induced dimensional changes for the 3D printed ABS substrate without compromising the mechanical integrity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Structural, thermal and dielectric studies on the novel solution grown (4-dimethylaminopyridinium) chloroantimonate(III) and chlorobismuthate(III) crystals

Research Highlights: {yields} The one-dimensional (1D) and the zero-dimensional (0D) anionic structure. {yields} The 'crystal bending' discovered in RMX{sub 4}-type analogue. {yields} The low frequency relaxation processes attributed to the dynamics of the organic cations. -- Abstract: The single crystals of the following 4-dimethylaminopyridinium chloroantimonates(III) and chlorobismuthates(III) have been grown by the solvent evaporation method: (C{sub 7}H{sub 11}N{sub 2})SbCl{sub 4}, (C{sub 7}H{sub 11}N{sub 2})BiCl{sub 4} and (C{sub 7}H{sub 11}N{sub 2}){sub 4}Bi{sub 2}Cl{sub 10}. The one-dimensional (1D) structures for (C{sub 7}H{sub 11}N{sub 2})SbCl{sub 4} or (C{sub 7}H{sub 11}N{sub 2})BiCl{sub 4} and the zero-dimensional (0D) one for (C{sub 7}H{sub 11}N{sub 2}){sub 4}Bi{sub 2}Cl{sub 10} have been solved by the single-crystal X-ray diffraction method. (C{sub 7}H{sub 11}N{sub 2})SbCl{sub 4} and (C{sub 7}H{sub 11}N{sub 2})BiCl{sub 4} appeared to be isomorphous and crystallize in the monoclinic space group, C2/c, whereas (C{sub 7}H{sub 11}N{sub 2}){sub 4}Bi{sub 2}Cl{sub 10} in the orthorhombic one, Imma. The molecular arrangements in the subsequent crystal lattices have been studied. For all three compounds by using the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) no structural phase transition has been detected in temperature region between 100 and 400 K. Nevertheless, the dielectric relaxation processes in temperature region 100-450 K and frequency range between 100 Hz and 2 MHz have been found in all crystals studied. The experimental results of the real and imaginary parts of the dielectric permittivity allow us to estimate the parameters of the relaxation processes, i.e. macroscopic relaxation times, {tau}, and activation energies, E{sub A}. The dynamics of the dipolar organic cations is expected to contribute to the relaxations process in the crystals under investigation.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Investigation on growth, structural, optical, thermal, dielectric and mechanical properties of organic L-prolinium trichloroacetate single crystals

Graphical abstract: L-Prolinium trichloroacetate is an organic nonlinear optical crystal has been grown from the aqueous solution by slow evaporation solution growth technique. Single crystal X-ray diffraction analysis reveals that L-PTCA crystallizes in trigonal crystal system. The optical band gab is found to be 4.26 eV. Second harmonic conversion efficiency of L-PTCA has been found to be half that of KDP. Highlights: ► It deals with the synthesis, growth and characterization of L-PTCA an organic NLO crystal. ► Wide optical transparency window between 260 nm and 1100 nm. ► Thermal study reveals that the grown crystal is stable up to 127 °C. ► L-PTCA crystal exhibits the second order nonlinear optical properties. -- Abstract: A new organic nonlinear optical material L-prolinium trichloroacetate (L-PTCA) single crystal has been synthesized and grown by slow solvent evaporation technique at room temperature using water as solvent. Single-crystal X-ray diffractometer was utilized to measure unit cell parameters and to confirm lattice parameter. The powder X-ray diffraction pattern of the grown L-PTCA has been indexed. The modes of vibration of different molecular groups present in the sample were identified by the FTIR spectral analysis. The optical transmittance window and the lower cutoff wavelength of the L-PTCA have been identified by UV–vis–NIR studies. Thermal stability of the L-prolinium trichloroacetate was determined by TGA/DTA measurements. Dielectric measurements were carried out at various temperatures at frequency range 10–1 MHz. The mechanical properties of the grown crystals have been analyzed by Vickers microhardness method. The chemical etching studies were carried out on the grown crystals. Its SHG efficiency has been tested by Kurtz powder method.

36 MATERIALS SCIENCE↗