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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Sensitivity of Turbine-Height Wind Speeds to Parameters in Planetary Boundary-Layer and Surface-Layer Schemes in the Weather Research and Forecasting Model

We evaluate the sensitivity of simulated turbine-height winds to 26 parameters applied in a planetary boundary layer (PBL) scheme and a surface layer scheme of the Weather Research and Forecasting (WRF) model over an area of complex terrain during the Columbia Basin Wind Energy Study. An efficient sampling algorithm and a generalized linear model are used to explore the multiple-dimensional parameter space and quantify the parametric sensitivity of modeled turbine-height winds. The results indicate that most of the variability in the ensemble simulations is contributed by parameters related to the dissipation of the turbulence kinetic energy (TKE), Prandtl number, turbulence length scales, surface roughness, and the von Kármán constant. The relative contributions of individual parameters are found to be dependent on both the terrain slope and atmospheric stability. The parameter associated with the TKE dissipation rate is found to be the most important one, and a larger dissipation rate can produce larger hub-height winds. A larger Prandtl number results in weaker nighttime winds. Increasing surface roughness reduces the frequencies of both extremely weak and strong winds, implying a reduction in the variability of the wind speed. All of the above parameters can significantly affect the vertical profiles of wind speed, the altitude of the low-level jet and the magnitude of the wind shear strength. The wind direction is found to be modulated by the same subset of influential parameters. Remainder of abstract is in attachment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Solid state photon upconversion utilizing thermally activated delayed fluorescence molecules as triplet sensitizer

The ability to upconvert light is useful for a range of applications, from biological imaging to solar cells. But modern technologies have struggled to upconvert incoherent incident light at low intensities. Here, we report solid state photon upconversion employing triplet-triplet exciton annihilation in an organic semiconductor, sensitized by a thermally activated-delayed fluorescence (TADF) dye. Compared to conventional phosphorescent sensitizers, the TADF dye maximizes the wavelength shift in upconversion due to its small singlet-triplet splitting. The efficiency of energy transfer from the TADF dye is 9.1%, and the conversion yield of sensitizer exciton pairs to singlet excitons in the annihilator is 1.1%. Our results demonstrate upconversion in solid state geometries and with non-heavy metal-based sensitizer materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Structure sensitivity in oxide catalysis: First-principles kinetic Monte Carlo simulations for CO oxidation at RuO{sub 2}(111)

We present a density-functional theory based kinetic Monte Carlo study of CO oxidation at the (111) facet of RuO{sub 2}. We compare the detailed insight into elementary processes, steady-state surface coverages, and catalytic activity to equivalent published simulation data for the frequently studied RuO{sub 2}(110) facet. Qualitative differences are identified in virtually every aspect ranging from binding energetics over lateral interactions to the interplay of elementary processes at the different active sites. Nevertheless, particularly at technologically relevant elevated temperatures, near-ambient pressures and near-stoichiometric feeds both facets exhibit almost identical catalytic activity. These findings challenge the traditional definition of structure sensitivity based on macroscopically observable turnover frequencies and prompt scrutiny of the applicability of structure sensitivity classifications developed for metals to oxide catalysis.

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

Nano-textured high sensitivity ion sensitive field effect transistors

Nano-textured gate engineered ion sensitive field effect transistors (ISFETs), suitable for high sensitivity pH sensors, have been realized. Utilizing a mask-less deep reactive ion etching results in ultra-fine poly-Si features on the gate of ISFET devices where spacing of the order of 10 nm and less is achieved. Incorporation of these nano-sized features on the gate is responsible for high sensitivities up to 400 mV/pH in contrast to conventional planar structures. The fabrication process for this transistor is inexpensive, and it is fully compatible with standard complementary metal oxide semiconductor fabrication procedure. A theoretical modeling has also been presented to predict the extension of the diffuse layer into the electrolyte solution for highly featured structures and to correlate this extension with the high sensitivity of the device. The observed ultra-fine features by means of scanning electron microscopy and transmission electron microscopy tools corroborate the theoretical prediction.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Efficient estimators for likelihood ratio sensitivity indices of complex stochastic dynamics

We demonstrate that centered likelihood ratio estimators for the sensitivity indices of complex stochastic dynamics are highly efficient with low, constant in time variance and consequently they are suitable for sensitivity analysis in long-time and steady-state regimes. These estimators rely on a new covariance formulation of the likelihood ratio that includes as a submatrix a Fisher information matrix for stochastic dynamics and can also be used for fast screening of insensitive parameters and parameter combinations. The proposed methods are applicable to broad classes of stochastic dynamics such as chemical reaction networks, Langevin-type equations and stochastic models in finance, including systems with a high dimensional parameter space and/or disparate decorrelation times between different observables. Furthermore, they are simple to implement as a standard observable in any existing simulation algorithm without additional modifications.

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

The Atacama Cosmology Telescope: The Polarization-Sensitive ACTPol Instrument

The Atacama Cosmology Telescope (ACT) makes high angular resolution measurements of anisotropies in the Cosmic Microwave Background (CMB) at millimeter wavelengths. We describe ACTPol, an upgraded receiver for ACT, which uses feedhorn-coupled, polarization-sensitive detector arrays, a 3° field of view, 100 mK cryogenics with continuous cooling, and meta material antireflection coatings. ACTPol comprises three arrays with separate cryogenic optics: two arrays at a central frequency of 148 GHz and one array operating simultaneously at both 97 GHz and 148 GHz. The combined instrument sensitivity, angular resolution, and sky coverage are optimized for measuring angular power spectra, clusters via the thermal Sunyaev–Zel'dovich (SZ) and kinetic SZ signals, and CMB lensing due to large-scale structure. The receiver was commissioned with its first 148 GHz array in 2013, observed with both 148 GHz arrays in 2014, and has recently completed its first full season of operations with the full suite of three arrays. This paper provides an overview of the design and initial performance of the receiver and related systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Chemical kinetics of octane sensitivity in a spark-ignition engine (Chemical Kinetics of Octane Sensitivity in a Spark Ignition Engine)

This article uses a chemical kinetic modeling approach to study the influences of fuel molecular structure on Octane Sensitivity (OS) in Spark Ignition (SI) engines. Octane Sensitivity has the potential to identify fuels that can be used in next-generation high compression, turbocharged SI engines to avoid unwanted knocking conditions and extend the range of operating conditions that can be used in such engines. While the concept of octane numbers of different fuels has been familiar for many years, the variations of their values and their role in determining Octane Sensitivity have not been addressed previously in terms of the basic structures of the fuel molecules. In particular, the importance of electron delocalization on low temperature hydrocarbon reactivity and its role in determining OS in engine fuel is described here for the first time. Finally, the role of electron delocalization on fuel reactivity and Octane Sensitivity is illustrated for a very wide range of engine fuel types, including n-alkane, 1-olefin, n-alcohol, and n-alkyl benzenes, and the unifying features of these fuels and their common trends, using existing detailed chemical kinetic reaction mechanisms that have been collected and unified to produce an overall model with unprecedented capabilities.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2015

A Step Toward Efficient Panchromatic Multi-Chromophoric Sensitizers for Dye Sensitized Solar Cells

Panchromatic dyes with absorption profiles extending into the near infra-red are of interest to researchers in the field of dye sensitized solar cells (DSSCs), as they offer potential access to a wide energy range of photons necessary to enhance solar to electric power conversion efficiencies (PCEs). In this report, a porphyrin with a Soret band absorbing at high energy is combined with a squaraine absorbing at low energy $via$ an acetylene linker to form a bichromophoric sensitizer with molar extinctions on the order of 10 5 M -1 cm -1 and an incident photon-to-current efficiency (IPCE) onset of ~850 nm. Various bulky substituents were installed on both the porphyrin and squaraine moieties, and conjugation was increased with π-bridge spacers to achieve a PCE of 7.6%, which is up to 15% higher than a comparable squaraine-only dye. For the most part, charge injection dynamics indicate slower charge injection rates and lower injection quantum yields for these bichromophoric sensitizers compared to non-porphyrin squaraine-based DSSC sensitizers. Nevertheless, higher PCE was observed for most porphyrincontaining dyes due largely to increased panchromaticity.

14 SOLAR ENERGY↗
DOE OSTI2021

The temperature sensitivity of soil: microbial biodiversity, growth, and carbon mineralization

Abstract Microorganisms drive soil carbon mineralization and changes in their activity with increased temperature could feedback to climate change. Variation in microbial biodiversity and the temperature sensitivities (Q10) of individual taxa may explain differences in the Q10 of soil respiration, a possibility not previously examined due to methodological limitations. Here, we show phylogenetic and taxonomic variation in the Q10 of growth (5–35 °C) among soil bacteria from four sites, one from each of Arctic, boreal, temperate, and tropical biomes. Differences in the temperature sensitivities of taxa and the taxonomic composition of communities determined community-assembled bacterial growth Q10, which was strongly predictive of soil respiration Q10 within and across biomes. Our results suggest community-assembled traits of microbial taxa may enable enhanced prediction of carbon cycling feedbacks to climate change in ecosystems across the globe.

Wang, Chao (ORCID:0000000257567505)↗
DOE OSTI2016

Molecular engineering of cyanine dyes to design a panchromatic response in Co-sensitized dye-sensitized solar cells

Cyanines are optically tunable dyes with high molar extinction coefficients, suitable for applications in co-sensitized dye-sensitized solar cells (DSCs); yet, barely thus applied. This might be due to the lack of a rational molecular design strategy that efficiently exploits cyanine properties. This study computationally re-designs these dyes, to broaden their optical absorption spectrum and create dye···TiO 2 binding and co-sensitization functionality. This is achieved via a stepwise molecular engineering approach. Firstly, the structural and optical properties of four parent dyes are experimentally and computationally investigated: 3,3’-diethyloxacarbocyanine iodide, 3,3’-diethylthiacarbocyanine iodide, 3,3’-diethylthiadicarbocyanine iodide and 3,3’-diethylthiatricarbocyanine iodide. Secondly, the molecules are theoretically modified and their energetics are analyzed and compared to the parent dyes. A dye···TiO 2 anchoring group (carboxylic or cyanoacrylic acid), absent from the parent dyes, is chemically substituted at different molecular positions to investigate changes in optical absorption. We find that cyanoacrylic acid substitution at the para-quinoidal position affects the absorption wavelength of all parent dyes, with an optimal bathochromic shift of ca. 40 nm. The theoretical lengthening of the polymethine chain is also shown to effect dye absorption. Two molecularly engineered dyes are proposed as promising co-sensitizers. Finally, corresponding dye···TiO 2 adsorption energy calculations corroborate their applicability, demonstrating the potential of cyanine dyes in DSC research.

14 SOLAR ENERGY↗
DOE OSTI2020

Perovskite-sensitized β-Ga 2 O 3 nanorod arrays for highly selective and sensitive NO 2 detection at high temperature

Amongst various gaseous pollutants, NO 2 is one of the major exhausts originating from fossil fuel and gas combustions in vehicle engines and power plants at high temperature. Under such a scenario, in situ and real-time gas detection and monitoring solutions are largely limited, which hinders the energy-efficient and resource-saving operations of these advanced energy systems. Herein, a new type of perovskite-sensitized β-Ga 2 O 3 nanorod-array has been successfully fabricated to detect NO x at high temperature selectively and sensitively. The demonstrated gas sensors are highly sensitive to NO 2 at 800 °C, with excellent reversible and reproducible response characteristics. Through the surface decoration of perovskite-type La 0.8 Sr 0.2 CoO 3 (LSCO) nanoparticles, the sensitivity of β-Ga 2 O 3 nanorod array gas sensors is enhanced by nearly an order of magnitude, along with much faster response dynamics. A remarkable selectivity toward oxidative gases was also demonstrated with the robust differentiation of NO 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

β-Functionalized push–pull opp -dibenzoporphyrins as sensitizers for dye-sensitized solar cells: the push group effect

β-Functionalized push–pull zinc opp-dibenzoporphyrins were designed and synthesized as sensitizers for dye-sensitized solar cells. The utilization of arylamine to replace aliphatic amine as the donor group has been proved to be an effective strategy to solve the solar cell instability reported previously. Three different arylamino groups including carbazole (YH8), diphenylamine (YH9), and phenothiazine (YH10) were investigated as arylamine donor groups, and different electronic effects were observed for these donor groups. Diphenylamine carrying YH9 and phenothiazine carrying YH10 displayed strong push–pull characteristics including segregated HOMO/LUMO and red-shifted and broadened absorption bands. In sharp contrast, the incorporation of carbazole (YH8) cancels out the push–pull effect. YH9 and YH10 solar cells achieved high PCEs of 6.9% and 7.5% respectively, which are comparable to that of the best ruthenium dye, N719 (η = 7.7%), under similar conditions. Here this work demonstrates the great potential of π-extended porphyrins as sensitizers for dye-sensitized solar cells.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2015

Co-sensitization of ZnO by CdS quantum dots in natural dye-sensitized solar cells with polymeric electrolytes to improve the cell stability

The CdS quantum dots (QDs) were deposited on ZnO layer by chemical bath deposition method to absorb light in the shorter wavelength region and used as photoanode in the dye sensitized solar cell (DSSCs) with natural dye extracted from Noni leaves. Microstructures of CdS-ZnO from various dipping time were characterized by XRD, FE-SEM and EDX. The results showed that the CdS is hexagonal structure and the amount of CdS increases when the dipping time increases. The maximal conversion efficiency of 0.292% was achieved by the DSSCs based on CdS QDs-sensitized ZnO film obtained from 9 min-dipping time. Furthermore, the stability of DSSCs was improved by using polymeric electrolyte. Poly (acrylic acid) (PAA) and Polyacrylamide (PAM) were introduced to CdS QDs-sensitized ZnO film from 9 min-dipping time. Each polymeric electrolyte was prepared by swelling from 0.1-2.0 %w in H2O. The maximal conversion efficiency of 0.207% was achieved for DSSCs based on CdS QDs-sensitized ZnO film with PAM 1.0% and the conversion efficiency was decreased 25% when it was left for1 hr.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Spin-squeezing-induced enhancement of the sensitivity of an atomic clock using coherent population trapping

The coherent population trapping (CPT) effect is used for making compact atomic clocks. There are two types of CPT clocks: the one in which the Raman beams are applied continuously and the one in which two CPT pulses separated by a dark period are applied (Ramsey scheme). It is obvious that the technique of spin squeezing can only be applied to the Ramsey CPT clock to enhance the sensitivity. However, it is not apparent how to adapt to the CPT clock the protocols for the microwave clock using one-axis-twist squeezing (OATS), since the Ramsey CPT clock is not trivially equivalent to the Ramsey microwave clock. In this paper, we show explicitly how to adapt two protocols using OATS, namely, the Schrödinger cat state protocol (SCSP) and the generalization thereof, and the echo squeezing protocol (ESP), to the CPT clock. The ESP magnifies the phase shift by a factor of N / e , while the SCSP magnifies the phase shift by a factor of N / 2 , making it able to achieve a higher sensitivity in the presence of excess noise.

Li, Jinyang↗