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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Nuclear physics without high-momentum potentials: Constructing the nuclear effective interaction directly from scattering observables

The traditional approach to nuclear physics encodes phase shift information in a nucleon-nucleon (NN) potential, producing a nucleon-level interaction that captures the sub-GeV consequences of QCD. A further reduction to the nuclear scale is needed to produce an effective interaction for soft Hilbert spaces, such as those employed in the shell model. Here we describe an alternative construction of the effective interaction that is simple and quite precise, proceeding from the QCD scale directly to the nuclear scale. This eliminates the need for constructing and renormalizing the high-momentum NN potential. Instead, continuum phase shifts and mixing angles are used directly at the nuclear scale. The method exploits the analytic continuity in energy of HOBET (Harmonic-Oscillator-Based Effective Theory) to connect bound states to continuum solutions at specific energies. The procedure is systematic, cutoff independent, and convergent, yielding keV accuracy at NNLO or N 3 LO, depending on the channel. Lepage plots are provided.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Zinc chloride affects chondrogenesis via VEGF signaling

Highlights: • ZnCl2 increases expression of various chondrogenic signaling intermediates. • VEGF/VEGFR play a key role in modulating levels of chondrogenesis. • Insulin mimetics are an appealing option for improvement of fracture healing. • Axitinib + ZnCl2 treatment results in decreased transcription of chondrogenic genes. Insulin mimetics, including zinc containing compounds, have previously been shown to influence chondrogenesis as it relates to healing of fractures in various preclinical models. However, the mechanism by which these compounds drive chondrogenic differentiation is yet undefined. Here, via next-generation sequencing (NGS) and in vitro functional validation, we show that Zinc Chloride (ZnCl{sub 2}) induces expression of both chondrogenic genes (Sox9, Runx1, collagen) as well as genes associated with VEGF-mediated signal transduction, including VEGF receptors 1 and 2 and their ligands; VEGF-A and VEGF-B. Noticeably, although insulin was able to also induce expression of these pro-angiogenic and pro-chondrogenic genes, the impact of insulin on expression of VEGF receptor and ligand genes was marginal when compared to that of ZnCl{sub 2.} Furthermore, while the VEGFR antagonist, Axitinib, was able to attenuate the pro-chondrogenic effects of both insulin and ZnCl{sub 2}; a reduction in gene and protein expression was most profoundly observed when the antagonist was applied to cells treated with ZnCl{sub 2.} Taken together, these data suggest an important role for the VEGF-mediated signal transduction pathways in the positive effects observed when applying zinc-based compounds as adjuvants for chondrogenesis-mediated fracture healing. In this regard, further mechanistic evaluation of ZnCl{sub 2} and other zinc-containing insulin mimetics may support rational design of therapies targeted for disease indications associated with impaired fracture healing.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Fundamental Forces, Lasting Impressions: Historical Documentation of the Sigma Press Building (TA-3-35) Volume 1

The US Department of Energy, National Nuclear Security Administration, Los Alamos Field Office (Field Office) has prepared final documentation for the resolution of adverse effects to Building 35 in Technical Area (TA) 3 at Los Alamos National Laboratory (LANL or the Laboratory). This documentation is being submitted to the New Mexico State Historic Preservation Officer (SHPO). TA-3-35, a Cold War-era press building, was determined eligible for listing in the National Register of Historic Places (Register) in the report Pressing Matters: An Evaluation of the Cold War Buildings at the Sigma Complex (LA-UR-15-28961). This report also identified Building TA-3-35 as excess property to be decontaminated, decommissioned, and demolished by the LANL Footprint Reduction Program in Fiscal Year 2016, an adverse effect requiring mitigation. The SHPO concurred with the both the eligibility determination of, and adverse impact to, Building TA-3-35 on February 29, 2016.

42 ENGINEERING↗
DOE OSTI2024

Understanding the Electronic and Structural Effects in ORR Intermediate Binding on Anion‐Substituted Zirconia Surfaces

Abstract For oxygen reduction reaction (ORR), the surface adsorption energies of O and OH* intermediates are key descriptors for catalytic activity. In this work, we investigate anion‐substituted zirconia catalyst surfaces and determine that adsorption energies of O and OH* intermediates is governed by both structural and electronic effects. When the adsorption energies are not influenced by the structural effects of the catalyst surface, they exhibit a linear correlation with integrated crystal orbital Hamiltonian population (ICOHP) of the adsorbate‐surface bond. The influence of structural effects, due to the re‐optimisation slab geometry after adsorption of intermediate species, leads to stronger adsorption of intermediates. Our calculations show that there is a change in the bond order to accommodate the incoming adsorbate species which leads to stronger adsorption when both structural and electronic effects influence the adsorption phenomena. The insights into the catalyst‐adsorbate interactions can guide the design of future ORR catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Exploring non-adiabaticity to CO reduction reaction through ab initio molecular dynamics simulation

Non-adiabatic chemical reaction refers to the electronic excitation during reactions. This effect cannot be modeled by the ground-state Born-Oppenheimer molecular dynamics (BO-MD), where the electronic structure is at the ground state for every step of ions' movement. Although the non-adiabatic effect has been explored extensively in gas phase reactions, its role in electrochemical reactions, such as water splitting and CO 2 reduction, in electrolyte has been rarely explored. On the other hand, electrochemical reactions usually involve electron transport; thus, a non-adiabatic process can naturally play a significant role. In this work, using one-step CO 2 reduction as an example, we investigated the role of the non-adiabatic effect in the reaction. The reaction barriers were computed by adiabatic BO-MD and non-adiabatic real-time time dependent density functional theory (rt-TDDFT). We found that by including the non-adiabatic effect, rt-TDDFT could increase the reaction barrier up to 6% compared to the BO-MD calculated barrier when the solvent model is used to represent water. Simulations were carried out using explicit water molecules around the reaction site under different overpotentials, and similar non-adiabatic effects were found.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Estimating the Effects of Module Area on Thin-Film Photovoltaic System Costs

We investigate the potential effects of module area on the cost and performance of photovoltaic systems. Applying a bottom-up methodology, we analyzed the costs associated with thin-film modules and systems as a function of module area. We calculate a potential for savings of up to 0.10/Wand0.13/W in module manufacturing costs for CdTe and CIGS respectively, with large area modules. We also find that an additional 0.04/W savings in balance-of-systems costs may be achieved. Sensitivity of the /W cost savings to module efficiency, manufacturing yield, and other parameters is presented. Lifetime energy yield must also be maintained to realize reductions in the levelized cost of energy; the effects of module size on energy yield for monolithic thin-film modules are not yet well understood. Finally, we discuss possible non-cost barriers to adoption of large area modules.

14 SOLAR ENERGY↗
NASA NTRSDate not supplied

Planetary Protection at Marshall Space Flight Center

Introduction: NASA Marshall Space Flight Center (MSFC) is historically known for its role in propulsion. While this is still the mainstay of MSFC’s expertise, many unique capabilities exist at MSFC which pertain to Planetary Protection (PP), including 1) identifying PP threats, and 2) developing novel methods to neutralize those threats. Furthermore, because these capabilities exist among diverse groups at MSFC, this work promotes collaboration both within and outside MSFC to expand and develop PP studies related to a full spectrum of NASA research, design, manufacture, and test interests. This abstract describes the PP research ongoing at MSFC and describes how it contributes to NASA’s overall PP objectives. Microbial Identification in Cleanrooms: One of the greatest threats to successful implementation of PP requirements is recontamination post bioburden reduction. One method to prevent recontamination is to keep the spacecraft in clean environments (i.e. cleanrooms) as much as possible during assembly and integration. However, cleanrooms are not without their own sources of contamination, which is why NASA is interested in monitoring the cleanliness of cleanrooms and characterizing the microbial species present. Such information allows a greater understanding of the resistance of these microbes to cleaning methods, as well as the risk of their contaminating the targeted planetary body of a given mission. MSFC has multiple cleanrooms of various ISO cleanliness levels onsite. We sampled the air and surfaces of three of these rooms, isolated microbes, and then sequenced the 16S rRNA gene or ITS region of the 18S rRNA gene for bacterial and fungal isolates, respectively. This has resulted in a microbial library which currently includes nearly 100 isolates. Microbial Enumeration of Spacecraft Materials: Currently, there are only a couple bioburden reduction methods approved by NASA, and often the harshness of these methods presents additional concerns or risks related to material properties. The goal of this research is to assess the microbial content of solid rocket motor (SRM) materials potentially used for lander missions. This work aims to more accurately define the risk of planetary contamination by providing empirical data associated with commonly used SRM raw materials. In this study, we pulverized nonmetallic SRM materials using a cryogenic grinder, then analyzed the resulting substrate for microbial colony forming units (CFU). We found that many SRM nonmetallic materials do not harbor detectable bioburden, though a range existed depending on the material. The results from this work provide quantitative data to potentially reduce concerns of contamination, while also providing a foundation for follow up studies into additional sterilization methods and molecular identification of contaminating microbes. Space Environmental Effects on Microbial Survival: One potential area of microbial reduction is the space environment. Understanding the survivability of hardy microbes in space-like conditions is a crucial first step in answering how space may reduce bioburden and if it can be relied upon for adherence to PP requirements. This work studied the effects of ultraviolet (UV) and ionizing radiation on survival of Bacillus atrophaeus spores. Microbes were dried on relevant polymeric materials then exposed to space environmental stressors. Coupons were submerged in water, diluted, and plated to determine survival compared with controls. We found that both UV and ionizing radiation were capable of reducing viability by nearly 99%, but there were still survivors, some with changed morphology indicating resistance mechanisms within certain cells. Manufacturing credit: Finally, given the above-mentioned limitations of the NASA-approved bioburden reduction methods, there is interest in understanding if manufacturing processes may provide enough bioburden reduction without additional PP-specific bakeouts. For instance, some material additives may be antimicrobial. Given this, we investigated the effects of several commonly used rubber additives on the growth of B. atrophaeus spores. We found that some of the materials inhibited growth of the spores, possibly supporting the use of these additives on missions with PP constraints. Future work into manufacturing credit for bioburden reduction includes inoculation of green insulation with B. atrophaeus spores, followed by a typical cure. Thermal profiles will be verified for appropriate temperature and durations to meet PP requirements, and cured samples will be analyzed using a cryogenic grinder to determine survivability of spores.

Chelsi D. Cassilly↗
DOE OSTI2025

Radiolytic Production of Radical Species in Gibbsite Doped with Iron and Chromium Ions

Gibbsite (aluminum hydroxide, Al(OH) 3 ) nanoparticles, synthesized from aluminum chloride or aluminum nitrate, were doped with metal ions, Cr(III) or Fe(III), and then irradiated with γ rays to determine the effect of the dopants on radiolytic hydrogen (H 2 ) production and radical generation. The addition of Cr(III) and Fe(III) ions at concentrations of 0.5% or 5% decreased the concentration of stable oxygen-centered radicals, with the strongest suppression in Cr(III) doped samples. A decrease in H 2 yields was observed with increasing Cr(III) or Fe(III) concentrations, with the greatest effect observed for the Fe(III)-doped samples. Reduction of the Cr(III) to Cr(II) and Fe(III) to Fe(II) was also observed, probably due to scavenging of radiolytically produced electrons. However, further processes differ for Fe(III)- and Cr(III)-doped systems. Both ions are reduced by the free electrons, leading to a decrease in H 2 production, but they react differently with the oxygen radicals. Cr(III) can be oxidized by oxygen radicals, whereas Fe(III) cannot. Fe(II) can interact with peroxides, possible products of intermediate oxygen oxidation, converting back to Fe(III) and leaving oxygen radicals behind. These oxidation reactions lead to a difference in the observed relative effects on H 2 yields and oxygen radical production between Cr(III)- and Fe(III)-doped gibbsite. In conclusion, the connection between electron scavenging and H 2 production indicates that radiolytically produced electrons are precursors to H 2 .

Anions↗
DOE OSTI2018

Estimating the Effects of Module Area on Thin-Film Photovoltaic System Costs: Preprint

We investigate the potential effects of module area on the cost and performance of photovoltaic systems. Applying a bottom-up methodology, we analyzed the costs associated with thin-film modules and systems as a function of module area. We calculate a potential for savings of up to 0.10 dollars/W and 0.13 dollars/W in module manufacturing costs for CdTe and CIGS respectively, with large area modules. We also find that an additional 0.04 dollars/W savings in balance-of-systems costs may be achieved. Sensitivity of the dollar/W cost savings to module efficiency, manufacturing yield, and other parameters is presented. Lifetime energy yield must also be maintained to realize reductions in the levelized cost of energy; the effects of module size on energy yield for monolithic thin-film modules are not yet well understood. Finally, we discuss possible non-cost barriers to adoption of large area modules.

14 SOLAR ENERGY↗
DOE OSTI2018

A Binary Offset Effect in CCD Readout and Its Impact on Astronomical Data

We have discovered an anomalous behavior of CCD readout electronics that affects their use in many astronomical applications. An offset in the digitization of the CCD output voltage that depends on the binary encoding of one pixel is added to pixels that are read out one, two, and/or three pixels later. One result of this effect is the introduction of a differential offset in the background when comparing regions with and without flux from science targets. Conventional data reduction methods do not correct for this offset. We find this effect in 16 of 22 instruments investigated, covering a variety of telescopes and many different front-end electronics systems. The affected instruments include LRIS and DEIMOS on the Keck telescopes, WFC3 UVIS and STIS on HST, MegaCam on CFHT, SNIFS on the UH88 telescope, GMOS on the Gemini telescopes, HSC on Subaru, and FORS on VLT. The amplitude of the introduced offset is up to 4.5 ADU per pixel, and it is not directly proportional to the measured ADU level. We have developed a model that can be used to detect this "binary offset effect" in data, and correct for it. Understanding how data are affected and applying a correction for the effect is essential for precise astronomical measurements.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1991

Technical activities of the configuration aeroelasticity branch

A number of recent technical activities of the Configuration Aeroelasticity Branch of the NASA Langley Research Center are discussed in detail. The information on the research branch is compiled in twelve separate papers. The first of these topics is a summary of the purpose of the branch, including a full description of the branch and its associated projects and program efforts. The next ten papers cover specific projects and are as follows: Experimental transonic flutter characteristics of supersonic cruise configurations; Aeroelastic effects of spoiler surfaces mounted on a low aspect ratio rectangular wing; Planform curvature effects on flutter of 56 degree swept wing determined in Transonic Dynamics Tunnel (TDT); An introduction to rotorcraft testing in TDT; Rotorcraft vibration reduction research at the TDT; A preliminary study to determine the effects of tip geometry on the flutter of aft swept wings; Aeroelastic models program; NACA 0012 pressure model and test plan; Investigation of the use of extension twist coupling in composite rotor blades; and Improved finite element methods for rotorcraft structures. The final paper describes the primary facility operation by the branch, the Langley TDT.

Cole, Stanley R.↗
DOE OSTI2018

A Modular and Flexible High-Frequency-Link Transformer with a Reduced Device Count and Zero High-Side Devices

In general, large power transformers (LPTs) are not interchangeable with each other and their high costs prohibit extensive spare inventories more so considering that on an average only 1.3 LPTs are manufactured for individual design. The latter pose a further challenge since given that the several existing LPTs are reaching their end of service lives, loss of plurality of such LPTs, that form the backbone of U.S. power grid, will clearly run into the problem of energy security related to the non-availability of sufficient spares (and extended lead time) exacerbated further by the fact that these spares are not interchangeable for installations at different locations. Conventional LPT cost millions of dollars and weighs significantly between approximately 100 and 400 tons. Two raw materials—copper and electrical steel—account for over 50 percent of the total cost of an LPT. In recent years, the price volatility of these two commodities in the global market has affected the manufacturing conditions and procurement strategy for LPTs. Transportation is also an important element of the total LPT cost, because an LPT can weigh significantly and often requires long-distance transport. Transporting an LPT is challenging—its large dimensions and heavy weight pose unique requirements to ensure safe and efficient transportation. Current road, rail, and port conditions are such that transportation is taking more time and becoming more expensive. Conventional low-frequency LPTs typically follow a monolithic approach to design due to historical reasons that need to transition to more modular and flexible (e.g., in voltage, impedance, and power flow) designs with ability to seamlessly/near-seamlessly scale. They should also have the ability to incorporate new technologies without in all cases redoing a LPT design from scratch. Given that the cost of raw materials has continued to increase, next-generation LPTs need to pursue avenues for reducing these costs. An added necessity is to reduce the transportability cost, which is significant in conventional LPTs. Further, given that LPTs are for the long term, they need to be durable, efficient, and fault tolerant with overloading capability. Given this backdrop, the objective and accomplishment of this one-year DOE (SPONSOR) R&D project, led by small business NextWatt LLC (PRIME, Lead PI: Dr. Sudip K. Mazumder) and University of Arkansas at Fayetteville (SUBAWARDEE, PI: Dr. Juan Balda) were to explore the design of a (8 – 20 kHz) high-frequency-link (HFL) based 100-MVA LPT with nominal voltage of 115/69 kV, with $15 - $22 dollars US per kVA when manufactured in “moderate” volume, with 99% energy-conversion efficiency, with 300% reduction in both volume and weight compared to a conventional LPT with the same electrical ratings, with impedance variation greater than 5%, with direct AC/AC power conversion capability, with very-high energy-conversion efficiency (using wide-bandgap SiC based field effect MOSFET devices) over a wide operating temperature, with reduction in both volume and weight with regard to conventional low frequency LPT, and with significant reduction in number of devices compared to state of the art solid state transformer topology.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2023

Effects of Ball Milling on the Electrochemical Capacity and Interfacial Stability of Li 2 MnO 3 Cathode Materials

The cycling mechanism of Li 2 MnO 3 cathode materials synthesized by conventional solid-state methods at high temperatures (800-900 °C) has been intensively investigated. Previous studies showed that CO 2 and O 2 gas evolution accounts for most of the charge capacity, followed by some Mn reduction during discharge. In this work, we analyze the effects of ball milling on the structure, surface contaminant, and electrochemical capacity of Li 2 MnO 3 cathode material, with or without a graphitic fluoride (C-F) additive. At the same time, C-F is added to form a protective coating layer that reduces unwanted reactions with the electrolyte during later electrochemical cycling. We find that the C-F ball-milled material shows Li 2 MnO 3 /LiMnO 2 composite phases, while the purely ball-milled material shows a single Li 2 MnO 3 phase. Furthermore, we characterize surface species and gas evolution during the first cycle, which reveals the decomposition of Li 2 CO 3 and the carbonate electrolyte during the first charge, especially during the high potential region (>4.4 V), and the electrochemical reduction of only a small fraction of the evolved gas on the first discharge (<2.75 V). The appearance further demonstrates the repetitive nature of this process during charge and disappearance during discharge of Mn 2p 3/2 X-ray photoelectron spectroscopy (XPS) spectra signals during the first two cycles. These processes result in first discharge specific capacities of only 155 and 170 mAh/g after first charge specific capacities of 210 and 320 mAh/g for the pure ball-milled and ball-milled with C-F materials, respectively. These studies demonstrate the interfacial instability introduced by ball milling. However, the electrochemical capacity is significantly increased, necessitating further investigation to determine whether ball milling can activate Mn-containing cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2020

P-model v1.0: an optimality-based light use efficiency model for simulating ecosystem gross primary production

Terrestrial photosynthesis is the basis for vegetation growth and drives the land carbon cycle. Accurately simulating gross primary production (GPP, ecosystem-level apparent photosynthesis) is key for satellite monitoring and Earth system model predictions under climate change. While robust models exist for describing leaf-level photosynthesis, predictions diverge due to uncertain photosynthetic traits and parameters which vary on multiple spatial and temporal scales. Here, we describe and evaluate a GPP (photosynthesis per unit ground area) model, the P-model, that combines the Farquhar–von Caemmerer–Berry model for C 3 photosynthesis with an optimality principle for the carbon assimilation–transpiration trade-off, and predicts a multi-day average light use efficiency (LUE) for any climate and C 3 vegetation type. The model builds on the theory developed in Prentice et al. (2014) and Wang et al. (2017a) and is extended to include low temperature effects on the intrinsic quantum yield and an empirical soil moisture stress factor. The model is forced with site-level data of the fraction of absorbed photosynthetically active radiation (fAPAR) and meteorological data and is evaluated against GPP estimates from a globally distributed network of ecosystem flux measurements. Although the P-model requires relatively few inputs, the R 2 for predicted versus observed GPP based on the full model setup is 0.75 (8 d mean, 126 sites) – similar to comparable satellite-data-driven GPP models but without predefined vegetation-type-specific parameters. The R 2 is reduced to 0.70 when not accounting for the reduction in quantum yield at low temperatures and effects of low soil moisture on LUE. The R 2 for the P-model-predicted LUE is 0.32 (means by site) and 0.48 (means by vegetation type). Applying this model for global-scale simulations yields a total global GPP of 106–122 Pg C yr –1 (mean of 2001–2011), depending on the fAPAR forcing data. The P-model provides a simple but powerful method for predicting – rather than prescribing – light use efficiency and simulating terrestrial photosynthesis across a wide range of conditions. The model is available as an R package (rpmodel).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1993

Degradation of optical components in space

This report concerns two types of optical components: multilayer filters and mirrors, and self-scanned imaging arrays using charge coupled device (CCD) readouts. For the filters and mirrors, contamination produces a strong reduction in transmittance in the ultraviolet spectral region, but has little or no effect in the visible and infrared spectral regions. Soft substrates containing halides are unsatisfactory as windows or substrates. Materials choice for dielectric layers should also reflect such considerations. Best performance is also found for the harder materials. Compaction of the layers and interlayer diffusion causes a blue shift in center wavelength and loss of throughput. For sensors using CCD's, shifts in gate voltage and reductions in transfer efficiency occur. Such effects in CCD's are in accord with expectations of the effects of the radiation dose on the device. Except for optical fiber, degradation of CCD's represents the only ionizing-radiation induced effect on the Long Duration Exposure Facility (LDEF) optical systems components that has been observed.

Blue, M. D.↗
NASA NTRS1994

Ultra-High Bypass Ratio Jet Noise

The jet noise from a 1/15 scale model of a Pratt and Whitney Advanced Ducted Propulsor (ADP) was measured in the United Technology Research Center anechoic research tunnel (ART) under a range of operating conditions. Conditions were chosen to match engine operating conditions. Data were obtained at static conditions and at wind tunnel Mach numbers of 0.2, 0.27, and 0.35 to simulate inflight effects on jet noise. Due to a temperature dependence of the secondary nozzle area, the model nozzle secondary to primary area ratio varied from 7.12 at 100 percent thrust to 7.39 at 30 percent thrust. The bypass ratio varied from 10.2 to 11.8 respectively. Comparison of the data with predictions using the current Society of Automotive Engineers (SAE) Jet Noise Prediction Method showed that the current prediction method overpredicted the ADP jet noise by 6 decibels. The data suggest that a simple method of subtracting 6 decibels from the SAE Coaxial Jet Noise Prediction for the merged and secondary flow source components would result in good agreement between predicted and measured levels. The simulated jet noise flight effects with wind tunnel Mach numbers up to 0.35 produced jet noise inflight noise reductions up to 12 decibels. The reductions in jet noise levels were across the entire jet noise spectra, suggesting that the inflight effects affected all source noise components.

Low, John K. C.↗
DOE OSTI2025

Unexpected origin of the quantum efficiency reduction in long-wavelength (In,Ga)⁢N light-emitting diodes

Differential carrier lifetime (DCL) measurements were performed on c-plane In 𝑥 ⁢Ga 1−𝑥⁢ N/Ga⁢N single-quantum-well (QW) light-emitting diodes (LEDs) with varying indium-content QWs (x = 13.5%, 16%, 22%), emitting with violet, blue, and green wavelengths. The recombination lifetimes of LEDs were found to increase with increasing indium composition, resulting in increased carrier densities n measured by DCL. Extraction of the A coefficients, which are assumed to not vary with n, and of the effective B(n) and C(n) coefficients of the ABC model of the internal quantum efficiency (IQE) of QWs showed no significant changes in the A coefficient with increasing indium content [In] in the In 𝑥 ⁢Ga 1−𝑥 ⁢N QW, and a reduction in the B(n) and C(n) coefficients with increasing [In]. When looking at the Shockley-Read-Hall (SRH) recombination rate An, the radiative recombination rate B(n)𝑛 2 , and the Auger-Meitner (AM) recombination rate C(n)𝑛 3 , we observed that at any given n, the SRH rate is the same for the three [In] measured, while the radiative rate decreases (by up to approximately 9 times) and the AM rate decreases (by up to approximately 7 times) with increasing indium content. This shows that the larger reduction in radiative recombination rates relative to nonradiative recombination rates with increasing [In] is the largest contributor to the decreased quantum efficiencies of LEDs (the “green gap”) at any given n. While some of the reduction in the effective recombination coefficients B(n) and C(n) can be explained by the reduced wave-function overlaps of the QW with increasing indium content, the larger reduction of B(n) relative to C(n) motivates further study of the intrinsic recombination coefficients 𝐵 0 and 𝐶 0 of bulk In 𝑥 ⁢Ga 1−𝑥 ⁢N alloys and how they are related to the effective recombination coefficients B(n) and C(n) in QWs. The relative contributions of nonradiative recombination are enhanced at any given current density due to the sublinear relationship between the carrier density n and the current density. Thus, the solution to the green gap, up to any intrinsic limitations set by the indium content of the QW, from an IQE perspective, requires the design of long-wavelength (In,Ga)⁢N LEDs with improved wave-function overlaps that can operate with a lower carrier density at any given current density.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

The impacts of effective stress and CO 2 sorption on the matrix permeability of shale reservoir rocks [The impacts of CO 2 sorption and effective stress on the matrix permeability of shale reservoir rocks]

We assess the impacts of effective stress and CO 2 sorption on the bedding-parallel matrix permeability of the Utica shale through pressure pulse-decay experiments. We first measure permeability using argon at relatively high (14.6 MPa) and low (2.8 MPa) effective stresses to assess both pressure dependence and recoverability. We subsequently measure permeability using supercritical CO 2 and again using argon to assess changes due to CO 2 sorption. We find that injection of both argon and supercritical CO 2 reduces matrix permeability in distinct fashion. Samples with permeability higher than 10 –20 m 2 experience a large permeability reduction after treatment with argon, but a minor change after treatment with supercritical CO 2 . However, samples with permeability lower than this threshold undergo a slight change after treatment with argon, but a dramatic reduction after treatment with supercritical CO 2 . These results indicate that effective stress plays an important role in the evolution of relatively permeable facies, while CO 2 sorption dominates the change of ultra-low permeability facies. The permeability reduction due to CO 2 sorption varies inversely with initial permeability, which suggests that increased surface area from hydraulic stimulation with CO 2 may be counteracted by sorption effects in ultra-low permeability facies. As a result, we develop a conceptual model to explain how CO 2 sorption induces porosity reduction and volumetric expansion to constrict fluid flow pathways in shale reservoir rocks.

58 GEOSCIENCES↗