Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “LEADING ABSTRACT”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Kinetic Destabilization of Metal–Metal Single Bonds: Isolation of a Pentacoordinate Manganese(0) Monoradical

Abstract The 17e − monoradical [Mn(CO) 5 ] is widely recognized as an unstable organometallic transient and is known to dimerize rapidly with the formation of a MnMn single bond. As a result of this instability, isolable analogues of [Mn(CO) 5 ] have remained elusive. Herein, we show that two sterically encumbering isocyanide ligands can destabilize the MnMn bond leading to the formation of the isolable, manganese(0) monoradical [Mn(CO) 3 (CNAr Dipp2 ) 2 ] (Ar Dipp2 =2,6‐(2,6‐( i Pr) 2 C 6 H 3 ) 2 C 6 H 3 ). The persistence of [Mn(CO) 3 (CNAr Dipp2 ) 2 ] has allowed for new insights into nitrosoarene spin‐trapping studies of [Mn(CO) 5 ].

Agnew, Douglas W.↗
DOE OSTI2020

Highly Efficient and Stable Perovskite Solar Cells Enabled by Low‐Cost Industrial Organic Pigment Coating

Abstract Surface passivation of perovskite solar cells (PSCs) using a low‐cost industrial organic pigment quinacridone (QA) is presented. The procedure involves solution processing a soluble derivative of QA, N , N ‐bis(tert‐butyloxycarbonyl)‐quinacridone (TBOC‐QA), followed by thermal annealing to convert TBOC‐QA into insoluble QA. With halide perovskite thin films coated by QA, PSCs based on methylammonium lead iodide (MAPbI 3 ) showed significantly improved performance with remarkable stability. A PCE of 21.1 % was achieved, which is much higher than 18.9 % recorded for the unmodified devices. The QA coating with exceptional insolubility and hydrophobicity also led to greatly enhanced contact angle from 35.6° for the pristine MAPbI 3 thin films to 77.2° for QA coated MAPbI 3 thin films. The stability of QA passivated MAPbI 3 perovskite thin films and PSCs were significantly enhanced, retaining about 90 % of the initial efficiencies after more than 1000 hours storage under ambient conditions.

He, Qingquan↗
DOE OSTI2020

Highly Efficient and Stable Perovskite Solar Cells Enabled by Low‐Cost Industrial Organic Pigment Coating

Abstract Surface passivation of perovskite solar cells (PSCs) using a low‐cost industrial organic pigment quinacridone (QA) is presented. The procedure involves solution processing a soluble derivative of QA, N , N ‐bis(tert‐butyloxycarbonyl)‐quinacridone (TBOC‐QA), followed by thermal annealing to convert TBOC‐QA into insoluble QA. With halide perovskite thin films coated by QA, PSCs based on methylammonium lead iodide (MAPbI 3 ) showed significantly improved performance with remarkable stability. A PCE of 21.1 % was achieved, which is much higher than 18.9 % recorded for the unmodified devices. The QA coating with exceptional insolubility and hydrophobicity also led to greatly enhanced contact angle from 35.6° for the pristine MAPbI 3 thin films to 77.2° for QA coated MAPbI 3 thin films. The stability of QA passivated MAPbI 3 perovskite thin films and PSCs were significantly enhanced, retaining about 90 % of the initial efficiencies after more than 1000 hours storage under ambient conditions.

He, Qingquan↗
DOE OSTI2024

Crystallography Reveals Metal‐Triggered Restructuring of β‐Hairpins

Abstract Metal binding to β‐sheets occurs in many metalloproteins and is also implicated in the pathology of Alzheimer's disease. De novo designed metallo‐β‐sheets have been pursued as models and mimics of these proteins. However, no crystal structures of canonical β‐sheet metallopeptides have yet been obtained, in stark contrast to many examples for ɑ‐helical metallopeptides, leading to a poor understanding for their chemistry. To address this, we have engineered tryptophan zippers, stable 12‐residue β‐sheet peptides, to bind Cu(II) ions and obtained crystal structures through single crystal X‐ray diffraction (SC‐XRD). We find that metal binding triggers several unexpected supramolecular assemblies that demonstrate the range of higher‐order structures available to metallo‐β‐sheets. Overall, these findings underscore the importance of crystallography in elucidating the rich structural landscape of metallo‐β‐sheet peptides.

Thuc Dang, Viet↗
DOE OSTI2023

Delayed leaf greening involves a major shift in the expression of cytosolic and mitochondrial ribosomes to plastid ribosomes in the highly phosphorus-use-efficient Hakea prostrata (Proteaceae)

Abstract Background and aims Hakea prostrata (Proteaceae) is a highly phosphorus-use-efficient plant native to southwest Australia. It maintains a high photosynthetic rate at low leaf phosphorus (P) and exhibits delayed leaf greening, a convergent adaptation that increases nutrient-use efficiency. This study aimed to provide broad physiological and gene expression profiles across leaf development, uncovering pathways leading from young leaves as nutrient sinks to mature leaves as low-nutrient, energy-transducing sources. Methods To explore gene expression underlying delayed greening, we analysed a de novo transcriptome for H. prostrata across five stages of leaf development. Photosynthesis and respiration rates, and foliar pigment, P and nitrogen (N) concentrations were determined, including the division of P into five biochemical fractions. Key results Transcripts encoding functions associated with leaf structure generally decreased in abundance across leaf development, concomitant with decreases in foliar concentrations of 85% for anthocyanins, 90% for P and 70% for N. The expression of genes associated with photosynthetic function increased during or after leaf expansion, in parallel with increases in photosynthetic pigments and activity, much later in leaf development than in species that do not have delayed greening. As leaves developed, transcript abundance for cytosolic and mitochondrial ribosomal proteins generally declined, whilst transcripts for chloroplast ribosomal proteins increased. Conclusions There was a much longer temporal separation of leaf cell growth from chloroplast development in H. prostrata than is found in species that lack delayed greening. Transcriptome-guided analysis of leaf development in H. prostrata provided insight into delayed greening as a nutrient-saving strategy in severely phosphorus-impoverished landscapes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Surface acetone reactions on ZnxZryOz: A DRIFTS-MS study

We report a systematic DRIFTS-MS study of surface acetone aldolization and self-deoxygenation reactions on ZrO2 and Zn1Zr10Oz, using temperature programmed surface reactions of both acetone reactant and possible intermediate compounds including diacetone alcohol, mesityl oxide, phorone, and isophorone. DRIFTS was used to monitor the evolution of surface species while MS was used to track corresponding gas phase products, in an attempt to identify the distinct reaction pathways observed on the two catalysts as well as the role zinc plays in the corresponding reaction pathways. It is found that aldol condensation (or aldolization) of acetone occurs readily at low temperature (298?K), forming mainly acetone dimers (i.e., diacetone alcohol, DAA/mesityl oxide, MSO) on both ZrO2 and Zn1Zr10Oz with the latter being more active. At elevated temperatures, secondary MSO reactions are diverted, mainly caused by the different Lewis basicity on the two catalysts. Over ZrO2, MSO reacts with activated acetone (acetone enolate) to form a surface 4,4-dimethyl-2,6-heptadione (phorone-C), which is further converted into a stable isophorone intermediate. At temperatures above 473?K, polymerization/oligomerization of isophorone along with basic hydroxyl promoted decomposition reactions occur, leading to the formation of heavier carbonaceous surface species and gas-phase side products (methane and CO2). The addition of zinc balances the surface acid-base properties on ZnxZryOz (i.e., Zn1Zr10Oz) via not only enhancing the surface Lewis basicity but passivating the strong acidity. This balance, especially the enhanced surface Lewis basicity largely promotes the a-H abstraction of MSO to form MSO enolate on the Zn1Zr10Oz, which thus favors the aldolization of MSO enolate and acetone, a reaction tends to form 2,6-dimethyl-2,5-heptadien-4-one (phorone-A). Phorone-A then readily decomposes to produce isobutene as a major product at temperature as low as 373?K. Note that, despite the facile formation of isobutene at low temperatures, a high temperature (673?K) is still necessary to release the strongly adsorbed formate/carbonate/acetate species via CO2 formation.

Li, Houqian↗
DOE OSTI2018

Microstructure evolution and a new mechanism of B2 phase on room temperature mechanical properties of Ti-47Al-2Cr-2Nb alloy prepared by hot isostatic pressing

Highlights: • The microstructure evolution of Ti-47Al-2Cr-2Nb alolly was investigated in detail. • The foramtion of B{sub 2} phase can be adjusted in Ti-47Al-2Cr-2Nb alloy. • A new mechanism of B{sub 2} phase on room temperature mechanical properties of Ti-47Al-2Cr-2Nb alloy was proposed. - Abstract: The formation of B{sub 2} phase was adjusted via various hot isostatic pressing processes in Ti-47Al-2Cr-2Nb alloy. The microstructure evolution and a new mechanism of B{sub 2} phase on room temperature mechanical properties was investigated by BSE, EBSD and TEM in detail. The result shows that the formation of B{sub 2} phase leads to Cr element content decrease in γ matrix phase, which results in lattice parameter increase, namely the c/a ratio of γ matrix phase. Finally, at room temperature the mechanical properties of Ti-47Al-2Cr-2Nb alloy deteriorates.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Porous NaTi2(PO4)3@C nanocubes as improved anode for sodium-ion batteries

Highlights: • Porous NaTi{sub 2}(PO{sub 4}){sub 3}@C nanocubes are synthesized. • Oleic acid is utilized as the carbon source. • NaTi{sub 2}(PO{sub 4}){sub 3}@C is to be measured at 0.01–3 V for SIBs. • NaTi{sub 2}(PO{sub 4}){sub 3}@C achieves 201 mAh g{sup −1} at 100 mA g{sup −1} after 100 cycles. • NaTi{sub 2}(PO{sub 4}){sub 3}@C delivers 140 mAh g{sup −1} at 1 A g{sup −1} for 1000 times. - Abstract: The NASICON-type NaTi{sub 2}(PO{sub 4}){sub 3} has drawn much attention as anode material for sodium-ion batteries owing to its stable structural characteristics and low cost. Nevertheless, the insulating property of NaTi{sub 2}(PO{sub 4}){sub 3} and the high working potential of about 2.1 V vs. Na{sup +}/Na lead to its poor cycling stability, low rate performance as well as inferior capacity. In this work, we synthesize the porous NaTi{sub 2}(PO{sub 4}){sub 3}@C nanocubes by hydrothermal method and a subsequent coating process with using oleic acid as the carbon source. When utilized as the anode for sodium-ion battery in the voltage range between 0.01 V and 3.0 V, The as-synthesized porous NaTi{sub 2}(PO{sub 4}){sub 3}@C nanocubes deliver a discharge capacity of 201 mAh·g{sup −1} at the current density of 100 mA g{sup −1} after 100 cycles. Additionally, the reserved capacity of 140 mAh·g{sup −1} could be achieved at the current density of 1 A g{sup −1} after 1000 cycles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Enhanced DSSCs performance of TiO2 nanostructure by surface passivation layers

Highlights: • Passivation layers of MgO, CaCO{sub 3}, ZrO{sub 2} and SnO{sub 2} on TiO{sub 2} electrode deposited in copper container by spin coating method. • XRD and EDX analysis give detail information about surface passivation layers deposition on TiO{sub 2} electrode. • Achieved highest efficiency for electrode with MgO passivation layer it is about 6.05%. • Highest electron lifetime of 0.65 ms. - Abstract: Rutile titanium oxide (TiO{sub 2}) synthesized in copper containers, was spin-coated with different surface passivation layers such as magnesium oxide (MgO), calcium carbonate (CaCO{sub 3}), zirconium oxide (ZrO{sub 2}), and tin oxide (SnO{sub 2}). The deposition of these passivation layers on TiO{sub 2} confirmed with the help of XRD and EDX analysis, leads to changes in surface morphology induced by the passivation layers demonstrated by FE-SEM imaging. The highest photoconversion efficiency obtained for TiO{sub 2} electrode with MgO passivation layer (6.05%), respective incident photon conversion efficiency was 52%. After introduction of passivation layers on the TiO{sub 2} nanostructure, electron lifetime increased from 0.48 ms to 0.65 ms and charge transfer resistance decreased from 36.9 Ω cm (pristine TiO{sub 2} electrode) to 20.16 Ω cm (MgO passivation layer).

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Witnessing light-driven entanglement using time-resolved resonant inelastic X-ray scattering

Abstract Characterizing and controlling entanglement in quantum materials is crucial for the development of next-generation quantum technologies. However, defining a quantifiable figure of merit for entanglement in macroscopic solids is theoretically and experimentally challenging. At equilibrium the presence of entanglement can be diagnosed by extracting entanglement witnesses from spectroscopic observables and a nonequilibrium extension of this method could lead to the discovery of novel dynamical phenomena. Here, we propose a systematic approach to quantify the time-dependent quantum Fisher information and entanglement depth of transient states of quantum materials with time-resolved resonant inelastic x-ray scattering. Using a quarter-filled extended Hubbard model as an example, we benchmark the efficiency of this approach and predict a light-enhanced many-body entanglement due to the proximity to a phase boundary. Our work sets the stage for experimentally witnessing and controlling entanglement in light-driven quantum materials via ultrafast spectroscopic measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Rejuvenation as the origin of planar defects in the CrCoNi medium entropy alloy

Abstract High or medium- entropy alloys (HEAs/MEAs) are multi-principal element alloys with equal atomic elemental composition, some of which have shown record-breaking mechanical performance. However, the link between short-range order (SRO) and the exceptional mechanical properties of these alloys has remained elusive. The local destruction of SRO by dislocation glide has been predicted to lead to a rejuvenated state with increased entropy and free energy, creating softer zones within the matrix and planar fault boundaries that enhance the ductility, but this has not been verified. Here, we integrate in situ nanomechanical testing with energy-filtered four-dimensional scanning transmission electron microscopy (4D-STEM) and directly observe the rejuvenation during cyclic mechanical loading in single crystal CrCoNi at room temperature. Surprisingly, stacking faults (SFs) and twin boundaries (TBs) are reversible in initial cycles but become irreversible after a thousand cycles, indicating SF energy reduction and rejuvenation. Molecular dynamics (MD) simulation further reveals that the local breakdown of SRO in the MEA triggers these SF reversibility changes. As a result, the deformation features in HEAs/MEAs remain planar and highly localized to the rejuvenated planes, leading to the superior damage tolerance characteristic in this class of alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Rising atmospheric moisture escalates the future impact of atmospheric rivers in the Antarctic climate system

Abstract Despite their relative rarity, atmospheric rivers are key contributors to the surface mass balance of Antarctica. However, the future role of atmospheric rivers in modulating Antarctic sea-level contributions is a major area of uncertainty. Here, we leverage high-resolution climate simulations to show that Antarctic atmospheric rivers are highly sensitive to future increases in atmospheric moisture, leading to a doubling of atmospheric river frequencies and 2.5 × increase in precipitation from 2066–2100 under present-day thresholds for atmospheric river detection. However, future precipitation impacts are critically dependent on the detection threshold: accounting for moisture increases in the threshold produces smaller, regional changes in atmospheric river frequency, primarily resulting from an eastward shift in the polar jet maximum wind speeds. Our results underscore the importance of using large ensembles to quantify Antarctic atmospheric river responses to variability in projected moisture, which may not be captured when using only a few ensemble members.

Environmental Sciences & Ecology↗
DOE OSTI2024

Dipolar focusing in laser-assisted positronium formation

Abstract We consider positronium formation in collisions of positrons with excited hydrogen atoms H(n) in an infrared laser field theoretically. This process is assisted by the dipolar focusing effect: a positron moving in a superposition of a laser field and the dipolar field can approach the atomic target even if its trajectory starts with a very large impact parameter, leading to a significant enhancement of the Ps formation cross section. The classical trajectory Monte Carlo method, which is justified for n ⩾ 3 , allows efficient calculation of this enhancement. A similar effect can occur in collisions of positrons with other atoms in excited states, which can lead to improvements in the efficiency of positronium formation.

Optics↗
DOE OSTI2021

The cosmological evolution of self-interacting dark matter

We study the evolution of cosmological perturbations in dark-matter models with elastic and velocity-independent self interactions. Such interactions are imprinted in the matter-power spectrum as dark acoustic oscillations, which can be experimentally explored to determine the strength of the self scatterings. Models with self interactions have similarities to warm dark matter, as they lead to suppression of power on small scales when the dark-matter velocity dispersion is sizable. Nonetheless, both the physical origin and the extent of the suppression differ for self-interacting dark matter from conventional warm dark matter, with a dark sound horizon controlling the reduction of power in the former case, and a free-streaming length in the latter. We thoroughly analyze these differences by performing computations of the linear power spectrum using a newly developed Boltzmann code. We find that while current Lyman-α data disfavor conventional warm dark matter with a mass less than 5.3 keV, when self interactions are included at their maximal value consistent with bounds from the Bullet Cluster, the limits are relaxed to 4.4 keV. Lastly, we make use of our analysis to set novel bounds on light scalar singlet dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

SDSS J0159 as an outlier in the M BH–σ space: further clues to support a central tidal disruption event?

ABSTRACT In this Letter, properties of black hole (BH) mass are well checked for the interesting object SDSS J0159, a changing-look active galactic nuclei and also a host galaxy of a tidal disruption event (TDE). Through spectral absorption features, the stellar velocity dispersion of SDSS J0159 can be well measured as $\sigma \sim 81~{\rm km\, s}^{-1}$, leading to SDSS J0159 being an apparent outlier in the MBH–σ space, because of the BH mass estimated through the MBH–σ relation about two magnitudes lower than the reported virial BH mass of about 108 M⊙. After considerations of contributions of stellar debris from the central TDE to broad line emission clouds, the overestimated virial BH mass could be well explained in SDSS J0159. Therefore, overestimated virial BH masses through broad-line properties in the MBH–σ space could be treated as interesting clues to support central TDEs.

Zhang, Xue-Guang↗