Search NASA⌕ Search

SEARCH · Search NASA

Results for “asymmetric unit”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Buffer-layer effect on the ferromagnetism of manganite heterojunctions

Identifying and understanding interfacial magnetic structures of transition-metal oxides are of great importance not only for fundamental physics but also for potential device applications. Among them, manganite and ruthenate heterostructures have attracted considerable interest due to their intriguing interfacial properties induced by complex magnetic interactions. Here, we report the observation of dramatic buffer-layer dependence of ferromagnetism in ultrathin (L⁢a 2/3 ⁢C⁢a 1/3 )⁢Mn⁢O 3 (LCMO)-based heterostructures. Though all trilayers are nonmetallic, the SrRu⁢O 3 -buffered LCMO trilayer exhibits enhanced ferromagnetism with the Curie temperature (𝑇 C ∼ 198K) much higher than for CaRu⁢O 3 (𝑇 C ∼ 99K)- and SrTi⁢O 3 (𝑇 C ∼ 42K)-buffered counterparts, as well as the monolithic LCMO films with similar thickness. Combining atomically resolved scanning transmission electron microscopy imaging with electron energy loss spectroscopy mapping, we reveal that asymmetric interfaces exist in the SrRu⁢O 3 buffered trilayer, with one exhibiting 1 unit-cell Sr diffusion into LCMO, which is responsible for the 𝑇 C enhancement. In contrast, charge transfer, which has been proposed previously as a possible mechanism, is excluded in this study. In conclusion, our results may pave a promising road toward effective atomic control of interfacial magnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Under-capacitated and over-powered? Rural austerity and asymmetrical negotiating relationships in US wind energy development

Though rural local governments are central actors in renewable energy development, local governments in the United States (US) remain systematically under-funded. This paper considers what the manifestations of austerity in local governments broadly and rural localities specifically mean for renewable energy development and for energy transitions. Drawing on a survey of 262 elected county officials with experience with wind energy in eight US states, this paper asks how local officials understand the impacts of wind development, how local governments are involved in wind energy negotiations, how the resources and expertise needed to navigate negotiations are distributed among counties, and analyze the relationship between local capacity, access to resources, and involvement in negotiations. We find that local officials express simultaneously affective and material concerns with the impacts of wind development and see negotiations with the developer as central to realizing local benefits. However, the expertise and staffing needed to negotiate with developers is less accessible to poorer or sparsely populated counties, and counties with lower overall revenues have narrower scopes of negotiation, and counties incre. Our results suggest that uneven rural capacity heightens an already asymmetrical relationship between localities and developers. In analyzing how infrastructure developments are shaped by relationships between localities and developers that are conditioned by austerity and (under)capacity, this paper contributes to and bridges scholarly discussions on rural austerity, rescaling, and renewable energy transitions. These results challenge conventional wisdoms around centralizing energy siting processes, contextualize popular and academic debates about opposition to renewable energy development, and highlight the need for rural reinvestment to realize meaningfully participatory energy developments.

Elmallah, Salma↗
DOE OSTI2023

De novo design of knotted tandem repeat proteins

De novo protein design methods can create proteins with folds not yet seen in nature. These methods largely focus on optimizing the compatibility between the designed sequence and the intended conformation, without explicit consideration of protein folding pathways. Deeply knotted proteins, whose topologies may introduce substantial barriers to folding, thus represent an interesting test case for protein design. Here we report our attempts to design proteins with trefoil (3 1 ) and pentafoil (5 1 ) knotted topologies. We extended previously described algorithms for tandem repeat protein design in order to construct deeply knotted backbones and matching designed repeat sequences (N = 3 repeats for the trefoil and N = 5 for the pentafoil). We confirmed the intended conformation for the trefoil design by X ray crystallography, and we report here on this protein’s structure, stability, and folding behaviour. The pentafoil design misfolded into an asymmetric structure (despite a 5-fold symmetric sequence); two of the four repeat-repeat units matched the designed backbone while the other two diverged to form local contacts, leading to a trefoil rather than pentafoil knotted topology. Our results also provide insights into the folding of knotted proteins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Experimental and Numerical Analysis of Additively Manufactured Inconel 718 Coupons With Lattice Structure

Abstract In the present paper, two lattice geometries suitable for near surface and double wall cooling were developed and tested. The first type of unit cell consisted of six ligaments of 0.5 mm diameter joined at a common vertex near the middle. The second type of unit cell was derived from the first type by adding four mutually perpendicular ligaments in the middle plane. Two lattice configurations, referred to as L1 and L2, respectively, were obtained by repeating the corresponding unit cell in streamwise and spanwise directions in an inline fashion. Test coupons consisting of these lattice geometries embedded inside rectangular cooling channel with dimensions of 2.54 mm height, 38.07 mm width, and 38.1 mm in length were fabricated using Inconel 718 powder and selective laser sintering (SLS) process. The heat transfer and pressure drop performance was then evaluated using steady-state tests with constant wall temperature boundary condition and for channel Reynolds number ranging from 2800 to 15,000. The lattices depicted a higher heat transfer compared with a smooth channel and both the heat transfer and pressure drop increased with a decrease in the porosity from L1 to L2. Steady-state conjugate numerical results revealed formation of prominent vortical structures in the inter-unit cell spaces, which diverted the flow toward the top end wall and created an asymmetric heat transfer between the two end walls. In conclusion, these lattice structures provided an augmented heat transfer while favorably redistributing the coolant within channel.

Engineering↗
DOE OSTI2025

Reducing heat load density with asymmetric and inclined double-crystal monochromators: principles and requirements revisited

Asymmetric double-crystal monochromators (aDCMs) and inclined DCMs (iDCMs) can significantly expand the X-ray beam footprint and consequently reduce the heat load density and gradient. Based on rigorous dynamical theory calculations, the major principles and properties of aDCMs and iDCMs are presented to guide their design and development, particularly for fourth-generation synchrotrons. In addition to the large beam footprint, aDCMs have very large bandwidths (up to ∼10 eV) and angular acceptance, but the narrow angular acceptance of the second crystal requires precise control of the relative orientations and strains. Based on Fourier coupled-wave diffraction theory calculations, it is rigorously proved that the iDCM has almost the same properties as the conventional symmetric DCM, including the efficiency, angular acceptance, bandwidth, tuning energy range and sensitivity to misalignment. The exception is that, for the extremely inclined geometry that can achieve very large footprint expansion, the iDCM has (beneficially) a larger bandwidth and wider angular acceptance. Inclined diffraction has the `rho-kick effect' that can be cancelled by the second reflection of the iDCM (even with misalignment), except that inhomogeneous strains may cause non-uniform rho-kick angles. At present, fabrication/mounting-induced strains pose low risk since they can be controlled to <0.5 µrad over large areas. The only uncertain challenge is the thermally induced strains, yet it is estimated that these strains are naturally lowered by the large footprint and may be further mitigated by optimized cryogenic cooling to the 1–2 µrad level. Overall, aDCMs and iDCMs have more stringent requirements than normal DCMs, but they are feasible schemes in practice.

asymmetric monochromator↗
DOE OSTI2025

Imine Reductase-Catalyzed, Radical-Mediated Asymmetric Cyano Group Migration

Functional group migration (FGM) reactions represent a fundamental class of transformations in organic chemistry, enabling the repositioning of functional moieties in nonobvious ways. However, catalytic asymmetric radical-mediated FGMs remain rare due to the inherent challenges of achieving catalyst-controlled enantioselectivity over free radical intermediates. Herein, we repurpose imine reductases (IREDs), a class of biotechnologically important enzymes known for their substrate promiscuity, to enable the first examples of catalytic asymmetric cyano group migration via a radical mechanism. An orthogonal set of radical enzymes, including PbaIREDCym and SmiIREDCym, was engineered, allowing both 1,4- and 1,5-cyano group migration reactions to occur in an enantiodivergent fashion. The use of the nonionic surfactant TPGS-1000 was found to improve both the yield and enantioselectivity of these cyano migration reactions. Furthermore, this biocatalytic process exhibited a broad substrate scope and is readily scalable, affording a rare example of chiral nonamine product assembly with imine reductases. More broadly, stereoselective radical biocatalysis with engineered IREDs and other versatile enzymes provides a potentially general solution to challenging asymmetric FGM reactions.

Biocatalysis↗
DOE OSTI2025

Crack formation in strained β-(AlxGa 1−x ) 2 O 3 films grown on (010) β-Ga 2 O 3 substrates

The cracking and local strain relaxation in (010) (Al x Ga 1−x ) 2 O 3 films grown on Ga 2 O 3 substrates are assessed in terms of film composition and thickness. We utilize x-ray diffraction and electron microscopy techniques combined with simulation and modeling to investigate that film cracking on curvature (flatness) has a directly proportional relationship with film thickness and/or aluminum content. Cross section transmission electron microscopy reveals that cracks along both the (001) and (100) cleavage planes penetrate into the substrate. The diffuse scattered intensity observed in reciprocal space maps (RSMs) is directly correlated with the tilt that is introduced due to the change in the deformation conditions near the cracks. While asymmetric RSMs show that the layers are fully strained, the diffuse scattering distribution in reciprocal space can be interpreted to show that the cracking relaxes and locally tilts the lattice ∼350 nm from the crack edges, which is consistent with the larger radius of curvature associated with the films with higher crack densities. For example, a 200 nm (Al 0.13 Ga 0.87 ) 2 O 3 thick film has an average inter-crack spacing of 3.3 µm, so most of the epitaxial layer is fully strained except near the cracks where it deforms elastically and is consistent with the gallium oxide Poisson ratio. A reciprocal space model was developed, which imports the strain and tilt distributions (based on finite element modeling) to match the features observed in the experimental maps. We also note that previous studies involving (Al x Ga 1−x ) 2 O 3 films may show evidence of cracking as observed in their symmetric and asymmetric RSMs.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Dynamic Excitonic Beam Switching with Atomically‐Thin Binary Blazed Gratings

Abstract Beam steering metasurfaces are ultra‐compact optical coatings that offer on‐demand redirection of optical power to specific diffraction orders. To achieve this, spatial gradients are commonly introduced in the phase of light scattered by plasmon or Mie resonant nanoparticles within the metasurface grating's unit cell. However, these phase gradients are oftentimes difficult to tune post‐fabrication. Recently, excitons in monolayer 2D semiconductors have emerged as a new metasurface building block, due to their strong and electrically‐tunable resonant light‐matter interaction. These 2D excitonic metasurfaces offer the tantalizing prospect of beam switching within a single monolayer. Here, it is demonstrated how the 2D analog of binary blazed gratings enables such beam switching by mere nanopatterning of a large monolayer WS 2 , even though nanoscale ribbons of WS 2 do not support geometrical resonances. By introducing a gradient in the nanoribbon width within the metasurface unit cell, an amplitude gradient combined with a small phase gradient in the scattered fields results in asymmetric diffraction efficiencies. Using a scattered‐field analysis, it is shown that these gradients can be further engineered via interference effects with the substrate reflection. Finally, the electrical tunability of the exciton resonance is leveraged to achieve selective and dynamic beam switching with an atomically‐thin metasurface.

Guarneri, Ludovica [Van der Waals‐Zeeman Institute↗
DOE OSTI2021

Exploring the Interaction Between Head-Supported Mass, Posture, and Visual Stress on Neck Muscle Activation

Objective Assess neck muscle activity for varying interactions between helmet, posture, and visual stress in a simulated “helo-hunch” posture. Background Military aviators frequently report neck pain (NP). Risk factors for NP include head-supported mass, awkward postures, and mental workload. Interactions between these factors could induce constant low-level muscle activation during helicopter flight and better explain instances of NP. Method Interactions between physical loading (helmet doffed/donned), posture (symmetric/asymmetric), and visual stress (low/high contrast) were studied through neck muscle electromyography (EMG), head kinematics, subjective discomfort, perceived workload, and task performance. Subjects ( n = 16) performed eight 30-min test conditions (varied physical loading, posture, and visual stress) while performing a simple task in a simulated “helo-hunch” seating environment. Results Conditions with a helmet donned had fewer EMG median frequency cycles (which infer motor unit rotation for rest/recovery, where more cycles are better) in the left cervical extensor and left sternocleidomastoid. Asymmetric posture (to the right) resulted in higher normalized EMG activity in the right cervical extensor and left sternocleidomastoid and resulted in less lateral bending compared with neutral across all conditions. Conditions with high visual stress also resulted in fewer EMG cycles in the right cervical extensor. Conclusion A complex interaction exists between the physical load of the helmet, postural stress from awkward postures, and visual stress within a simulated “helo-hunch” seating environment. Application These results provide insight into how visual factors influence biomechanical loading. Such insights may assist future studies in designing short-term administrative controls and long-term engineering controls.

Behavioral Sciences↗
DOE OSTI2025

Highly enantioselective synthesis controlled by spin-exchange interaction

We present a strategy to achieve absolute asymmetric catalysis that is effectively controlled by an external magnetic field via a spin-exchange reaction leveraging the chirality-induced spin selectivity effect. Using an external magnetic field to achieve asymmetric synthesis has long been desired. Here, we demonstrate 90% enantiomeric excess (ee) in [3 + 2] cycloadditions and 89% ee in aldol reactions, where the handedness of the product is determined by the ~±150 mT external magnetic polarization of a ferromagnet (FM). Our approach uses an enantioselective crystallization of racemic catalysts on a FM surface, using a small-scale crystallization vial connected to a bulk racemic solution. Racemic catalysts controllably crystallize into their respective enantiopure forms and are directly used in asymmetric reactions. Thus, we demonstrate that an external magnetic field can serve as a versatile symmetry-breaking tool to achieve highly enantioselective organic synthesis eliminating the need of any enantioenriched reagents.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Chirality locking charge density waves in a chiral crystal

In Weyl semimetals, charge density wave (CDW) order can spontaneously break the chiral symmetry, gap out the Weyl nodes, and drive the material into the axion insulating phase. Investigations have however been limited since CDWs are rarely seen in Weyl semimetals. Here, using scanning tunneling microscopy/spectroscopy (STM/S), we report the discovery of a novel unidirectional CDW order on the (001) surface of chiral crystal CoSi – a unique Weyl semimetal with unconventional chiral fermions. The CDW is incommensurate with both lattice momentum and crystalline symmetry directions, and exhibits an intra unit cell π phase shift in the layer stacking direction. The tunneling spectrum shows a particle-hole asymmetric V-shaped energy gap around the Fermi level that modulates spatially with the CDW wave vector. Combined with first-principle calculations, we identify that the CDW is locked to the crystal chirality and is related by a mirror reflection between the two enantiomers of the chiral crystal. Our findings reveal a novel correlated topological quantum state in chiral CoSi crystals and raise the potential for exploring the unprecedented physical behaviors of unconventional chiral fermions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Quantifying and visualizing the microscopic degrees of freedom of grain boundaries in the Wigner–Seitz cell of the displacement-shift-complete lattice

Here we introduce a grain boundary (GB) translation vector, t ws , to describe and quantify the domain of the microscopic degrees of freedom of GBs. It has long been recognized that for fixed macroscopic degrees of freedom of a GB there exists a large multiplicity of states characterized by different relative grain translations. More recently another degree of freedom, [n], the number of GB atoms, has emerged and is now recognized as an equally important component of GB structural multiplicity. In this work, we show that all GB microstates can be uniquely characterized by their value of t ws , which is located within the Wigner–Seitz (WS) cell of the Displacement-Shift-Complete lattice (DSCL) of the GB. The GB translation vector captures information about both the translation state and the number of GB atoms. We show that the density of GB microstates inside the WS cell of the DSCL is not uniform and can form clusters that correspond to different GB phases. Further, the vectors connecting the centers of the clusters correspond to the Burgers vectors of GB phase junctions, which can be predicted without building the junctions. Using t ws , we quantify GB excess shear and argue that it is defined up to a DSCL vector, which has implications for thermodynamic equilibrium conditions. Additionally, this work generalizes the definition of the number of GB atoms [n] to asymmetric boundaries.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Multiscale investigation of thermomechanical and compositional developments in Ni alloy 718 under laser processing

Laser processing has been widely employed in various applications due to its exceptional spatial resolution. However, the rapid temperature gradients generated in localized areas present significant challenges for experimental characterization using conventional instruments. To characterize Ni alloy 718 during laser processing, we employed in-situ synchrotron X-ray diffraction with a high-speed detector, a method particularly well-suited for probing processes with high temporal and spatial resolution. Through a series of in-situ experiments, we investigated the local variations in the evolution of microstructures and thermomechanical behaviors within a keyhole mode melt pool. The in situ macroscopic thermomechanical behaviors were quantified using an empirical model derived from diffraction patterns, with experimental results showing reasonable agreement with finite element analysis. Various laser parameters were tested to assess their influences on the residual strains in the melt pools. The results revealed that the residual strain in the keyhole mode melt pool is relatively insensitive to variations in the parameters and is smaller than that in the melt pool created under conduction mode laser scanning. Additionally, we analyzed the shapes of individual diffraction spots, providing insights into the plastic behaviors and compositional developments in the resolidified alloy. The analysis confirmed that compositional variations in a dendritic microstructure manifest as asymmetric broadening of the diffraction spots.

Ni alloy 718↗
DOE OSTI2025

Analysis of the Blowout Plasma Wakefields Produced by Drive Beams with Elliptical Symmetry

In the underdense, or blowout regime, of plasma wakefield acceleration, the particle beam is denser than the plasma. In this scenario, the plasma electrons are nearly completely rarefied from the beam channel, leaving only a nominally uniform ion-filled “bubble.” Extensive investigations of this interaction assuming axisymmetry have been undertaken. However, the blowout produced by a transversely asymmetric (flat) driver, which would be present in linear collider “afterburner” schemes, possesses quite different characteristics. Such beams create an asymmetric plasma bubble which leads to unequal focusing in the two transverse dimensions, accompanied by a nonuniform accelerating gradient. The asymmetric blowout cross section is found through simulation to be elliptical, and treating it as such permits a simple extension of the symmetric theory. In particular, focusing fields linear in both transverse directions inside the bubble are found. The form of the wake potential and the associated beam-matching conditions in this elliptical cavity are discussed. Here, we also examine blowout boundary estimation in the long driver limit and applications of the salient asymmetric features of the wakefield.

Manwani, P. [University of California, Los Angeles↗
DOE OSTI2026

Laboratory Observation of Transition from Collisional Slow to Collisionless Fast Reconnection

Temporal transition of an externally driven antiparallel asymmetric magnetic reconnection from collisional slow to collisionless fast regime is observed in a laboratory plasma for the first time. Here, this transition is initiated when the two-fluid Hall effect begins to dominate over collisional effects at the X point, characterized by the ratio of electron-ion collision mean free path to current sheet thickness exceeding unity. Prior to the transition, an enhanced reconnection electric field develops on the low-density side where electrons are heated both ohmically and by large-amplitude lower-hybrid drift waves (LHDW) before collisionality at the X-point drop significantly. These LHDWs generate anomalous resistivity accounting for 30% of the reconnection electric field. The observed time evolution is consistent with the hybrid collisionless-collisional reconnection scenario relevant to onset of asymmetric reconnection in natural plasmas.

Shi, Peiyun [Princeton Plasma Physics Laboratory (↗
DOE OSTI2025

Lepton flavor asymmetries: from the early Universe to BBN

Large primordial lepton flavor asymmetries with almost vanishing total baryon-minus-lepton number can evade the usual BBN and CMB constraints if neutrino oscillations lead to perfect flavor equilibration. Solving the momentum averaged quantum kinetic equations (QKEs) describing neutrino oscillations and interactions, we perform the first systematic investigation of this scenario, uncovering a rich flavor structure in stark contradiction to the assumption of simple flavor equilibration. We find (i) a particular direction in flavor space, ∆ne ≃ – 2/3 (– 1)∆n μ for normal (inverted) neutrino mass hierarchy, in which the flavor equilibration is efficient and primordial asymmetries are essentially unconstrained, (ii) a minimal washout factor, ∆$n_{e}^{2}$| BBN ≤ 0.03 (0.016) ∑ α ∆$n_{α}^{2}$| ini yielding a conservative estimate for the allowed primordial asymmetries in a generic flavor direction, and (iii) particularly strong or weak washout if one of the initial flavor asymmetries vanishes due to non-adiabatic muon- or electron-driven MSW transitions. These results open up the possibility of a first-order QCD phase transition facilitated by large lepton asymmetries as well as baryogenesis from large and compensated ∆n e = ∆n μ asymmetries. Our systematic approach of deriving momentum averaged QKEs includes collision terms beyond the damping approximation, energy transfer between the neutrino and electron-photon plasma, and provides a fast and reliable way to investigate the impact of primordial lepton asymmetries at the time of BBN. We publicly release the Mathematica code COFLASY-M on https://github.com/mariofnavarro/COFLASY which solves the QKEs numerically.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗