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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Spin-Orbit Interactions in Transdimensional Heterostructures (Final Technical Report)

A summary of the theory development for the fundamental understanding of intrinsic electronic processes and interactions in transdimensional heterostructures. The transdimensional regime lays in between three (3D) and two (2D) dimensions. Current research has been largely focused on purely 2D or conventional 3D materials, being guided by a traditional view that only the dimensionality and the chemical composition are important to control the physical properties of quantum materials. The transitional, transdimensional regime has been largely overlooked. The theoretical and experimental results reported herewith fill in this gap by providing the missing aspects of the spin-orbit interaction theory and the associated magneto-optical response for ultrathin films of metals and semiconductors in the transdimensional regime.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Entropic order parameters in weakly coupled gauge theories

The entropic order parameters measure in a universal geometric way the statistics of non-local operators responsible for generalized symmetries. In this article, we compute entropic order parameters in weakly coupled gauge theories. To perform this computation, the natural route of evaluating expectation values of physical (smeared) non-local operators is prevented by known difficulties in constructing suitable smeared Wilson loops. We circumvent this problem by studying the smeared non-local class operators in the enlarged non-gauge invariant Hilbert space. This provides a generic approach for smeared operators in gauge theories and explicit formulas at weak coupling. In this approach, the Wilson and ’t Hooft loops are labeled by the full weight and co-weight lattices respectively. We study generic Lie groups and discuss couplings with matter fields. Smeared magnetic operators, as opposed to the usual infinitely thin ones, have expectation values that approach one at weak coupling. The corresponding entropic order parameter saturates to its maximum topological value, except for an exponentially small correction, which we compute. On the other hand, smeared ’t Hooft loops and their entropic disorder parameter are exponentially small. We verify that both behaviors match the certainty relation for the relative entropies. In particular, we find upper and lower bounds (that differ by a factor of 2) for the exact coefficient of the linear perimeter law for thin loops at weak coupling. This coefficient is unphysical/non-universal for line operators. We end with some comments regarding the RG flows of entropic parameters through perturbative beta functions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Strain localization criteria for viscoplastic geomaterials

This report presents a viscoplastic localization criterion to detect quasi-instantaneous (i.e., load-induced) and delayed (creep-induced) strain localization in rate-dependent solids. The study is based on the theory of controllability and a viscoplastic description of the mechanical response. Analytical precursors of unstable states are defined through systems of ordinary differential equations (OEDs). The use of the proposed criteria is illustrated at the material point level through a set of strain localization analyses simulating active strain localization of a porous rock. In addition, full-field finite element simulations of compression tests conducted under various pressures are reported to demonstrate the role of local unstable viscoplasticity in the spontaneous propagation of deformation bands under stationary boundary conditions. The study shows that the viscoplastic localization criterion maintains a negative sign as long as the behavior is unstable, that is, the rate of deformation is accelerating. The sign switch coincides with the transition to decelerating deformation. The analyses revealed that pulses of overstress always emerge in correspondence with the growth of unstable behavior, and the peak matches the transition to stable behavior. The local responses recovered from full-field analyses were consistent with those observed in analyses at material point level and the predictions of the presented theory.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Strong-Field Control of Plasmonic Properties in Core–Shell Nanoparticles

Utilization of the plasmonic response in nanosystems is a key component of nanophotonics that is typically altered by varying the incident optical frequency or the material configuration. However, in this work we demonstrate that employing intense, femtosecond laser fields unlock nonlinear light–matter interactions such that precise control of the optical response is achieved solely by adjusting the incident intensity. The plasmonic properties of Au/SiO 2 nanoshells are manipulated by exploiting the nonlinear index of refraction of gold and experimentally observed by employing photoelectrons emitted during the interaction as a sensitive, sub-wavelength probe. A striking transition seen in the photoelectron energy spectrum between the weak and strong-field regime is verified by a modified Mie theory simulation that incorporates the nonlinear dielectric nanoshell response. The exhibited intensity-dependent optical control of the plasmonic response in prototypical core–shell nanoparticles paves the way toward ultrafast switching and opto-electronic signal modulation with more complex nanostructures.

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

When Will MISR Detect Rising High Clouds?

It is predicted by both theory and models that high-altitude clouds will occur higher in the atmosphere as a result of climate warming. This produces a positive longwave feedback and has a substantial impact on the Earth's response to warming. This effect is well established by theory, but is poorly constrained by observations, and there is large spread in the feedback strength between climate models. For this study, we use the NASA Multi-angle Imaging SpectroRadiometer (MISR) to examine changes in Cloud-Top-Height (CTH). MISR uses a stereo-imaging technique to determine CTH. This approach is geometric in nature and insensitive to instrument calibration and therefore is well suited for trend analysis and studies of variability on long time scales. In this article we show that the current MISR record does have an increase in CTH for high-altitude cloud over Southern Hemisphere (SH) oceans but not over Tropical or the Northern Hemisphere (NH) oceans. We use climate model simulations to estimate when MISR might be expected to detect trends in CTH, that include the NH. The analysis suggests that according to the models used in this study MISR should detect changes over the SH ocean earlier than the NH, and if the model predictions are correct should be capable of detecting a trend over the Tropics and NH very soon (3–10 years). This result highlights the potential value of a follow-on mission to MISR, which no longer maintains a fixed equator crossing time and is unlikely to be making observations for another 10 years.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Modulation of Tropical Convection-Circulation Interaction by Aerosol Indirect Effects in Convective Self-Aggregation Simulations of a Gray Zone Global Model

Disentangling the response of tropical convective updrafts to enhanced aerosol concentrations has been challenging. Leading theories for explaining the influence of aerosol concentrations on tropical convection are based on the dynamical response of convection to changes in cloud microphysics, neglecting possible changes in the environment. In recent years, global convection-permitting models (GCPM) have been developed to circumvent problems arising from imposing artificial scale separation on physical processes associated with deep convection. Here, we use a global model in the convective gray zone that partially simulates deep convection to investigate how enhanced concentrations of aerosols that act as cloud condensate nuclei (CCN) impact tropical convection features by modulating the convection-circulation interaction. Results from a pair of idealized non-rotating radiative-convective equilibrium simulations show that the enhanced CCN concentration leads to weaker large-scale circulation, the closeness of deep convective systems to the moist cluster edges, and more mid-level cloud water at an equilibrium state in which convective self-aggregation occurred. Correspondingly, the enhanced CCN concentration modulates how the physical processes that support or oppose convective aggregation maintain the aggregated state at equilibrium. Overall, the enhanced CCN concentration facilitates the development of deep convection in a drier environment but reduces mean precipitation. Our results emphasize the importance of allowing atmospheric phenomena to evolve continuously across spatial and temporal scales in simulations when investigating the response of tropical convection to changes in cloud microphysics.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Non-resonant Raman optical activity from phase-space electronic structure theory

In order to model experimental non-resonant Raman optical activity, chemists must compute a host of second-order response tensors (e.g., the electric-dipole–magnetic-dipole polarizability) and their nuclear derivatives along a set of vibrational modes. While these response functions are almost always computed within a Born–Oppenheimer (BO) framework, here we provide a natural interpretation of the electric-dipole–magnetic-dipole polarizability within phase space electronic structure theory, a beyond-BO model whereby the electronic structure depends on nuclear momentum (P) in addition to nuclear position (R). By coupling to nuclear momentum, phase space electronic structure theory is able to capture the asymmetric response of the electronic properties to an external field, in so far as for a vibrating (non-stationary) molecule, $\frac{∂μ}{∂B}$≠$\frac{∂m}{∂F}$, where μ and m are the electrical linear and magnetic dipoles, and F and B are electric and magnetic fields. As an example, for a prototypical methyloxirane molecule, we show that phase space electronic structure theory is able to deliver a reasonably good match with experimental results in a manner that is formally invariant to gauge origin G 0 —provided that one uses a complete basis or, alternatively, gauge invariant atomic orbitals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Static response and Love numbers of Schwarzschild black holes

We derive the quadratic action for the physical degrees of freedom of massless spin-0, spin-1, and spin-2 perturbations on a Schwarzschild-(A)dS background in arbitrary dimensions. Here, we then use these results to compute the static response of asymptotically flat Schwarzschild black holes to external fields. Our analysis reproduces known facts about black hole Love numbers — in particular that they vanish for all types of perturbation in four spacetime dimensions — but also leads to new results. For instance, we find that neutral Schwarzschild black holes polarize in the presence of an electromagnetic background in any number of spacetime dimensions except four. Moreover, we calculate for the first time black hole Love numbers for vector-type gravitational perturbations in higher dimensions and find that they generically do not vanish. Along the way, we shed some light on an apparent discrepancy between previous results in the literature, and clarify some aspects of the matching between perturbative calculations of static response on a Schwarzschild background and the point-particle effective theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Snowmass white paper: Light dark matter direct detection at the interface with condensed matter physics

Direct detection experiments for light (sub-GeV) dark matter are making enormous leaps in reaching previously unexplored theory space. The need for accurate characterizations of target responses has led to a growing interplay between particle and condensed matter physics. This white paper summarizes recent progress on direct detection calculations that utilize state-of-the-art numerical tools in condensed matter physics and effective field theory techniques. These new results provide the theoretical framework for interpreting ongoing and planned experiments using electronic and collective excitations, and for optimizing future searches.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

A tipping point in cancer epidemiology: embracing a life course exposomic framework

In this work, we show how the pathogenesis of multifactorial malignant diseases, with variable onset, severity, and natural history, reflects development-specific exposures and individual responses to these exposures influenced by underlying genetic predisposition. Embedded in life course theory, exposomics provides a framework to more fully elucidate how environmental factors alter cancer risk, disease course, and response to treatment across the lifespan.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Specific resonance mode enhancement and suppression using non-uniform polarization of piezoelectric wafers: Theory and experiments

In this work, we present experimental demonstration of specific resonance mode enhancement and suppression in circular and rectangular piezoelectric wafers with engineered non-uniform polarization profiles. The polarization profiles are designed based on the electromechanical impedance response of non-uniformly polarized wafers as obtained from the theory. The circular wafers are fabricated with non-uniform polarization profiles that involve a central polarized region surrounded by an unpolarized region. The radius of the polarization zone is designed based on the condition for specific mode enhancement obtained from the electromechanical impedance response of non-uniformly polarized wafers. We actually show how the condition can not only be used to enhance but also to suppress electromechanical resonances. Two kinds of wafers are designed and fabricated to specifically suppress second and third radial modes respectively. Similarly, rectangular wafers are designed with two different kinds of non-uniform polarization profiles — the first of which enhances the second in-plane extensional mode in the impedance spectrum and the second polarization profile suppresses all the electromechanical resonances pertaining to the in-plane extensional modes and selectively excites only the in-plane bending modes. The proposed approach of using non-uniformly polarized wafers finds application in designing multi-frequency sensors/transducers, frequency-tuned receivers, acoustic beamforming, and other non-traditional applications such as information storage.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Wavelength-Dependent Excitonic Properties of Covalent Organic Frameworks Explored by Theory and Experiments

Many aspects of the correlation between physical structure, light harvesting, and excitonic properties of covalent organic frameworks (COFs) remain unclear despite being key properties determining their photocatalytic function. One area of COF research that could bring clarity is through using both electronic structure theory and time-resolved spectroscopic analysis over a series of isomeric COFs. Here, we show structure-property relationships between four imine COFs built from a combination of ditopic and tritopic monomers using transient absorption spectroscopy together with time-dependent density functional theory. We find that monomer selection only moderately affects the charge transfer (CT) behavior of the COFs. Instead, we infer that imine chemistry profoundly impacts CT by acting as a CT mediator. Moreover, we discover two distinct valence bands arising from varying degrees of locally excited/CT mixing, which is responsible for energy dependent exciton dynamics. Finally, we use theory to hypothesize that interlayer interactions can modify excitonic properties that we correlate with tail states commonly observed, but rarely investigated in COFs. Furthermore, these results reveal that imine chemistry should be recognized as a very important factor to consider in the development of COF photocatalysts and the correlation of their structural environment with light harvesting and CT properties that should ultimately determine their photocatalytic function.

14 SOLAR ENERGY↗
DOE OSTI2025

Optical conductivity study of mixed-valent quasi-one-dimensional CeIr 3 ⁢B 2

Here, we present a combined theoretical and experimental study on the optical conductivity of CeIr 3 ⁢B 2 , where quasi-one-dimensional Ce chains form along the 𝑐 axis of the monoclinic crystal. Significant hybridization-induced features are observed along the Ce chains by broadband infrared spectroscopy, demonstrating mixed-valent behavior over a wide range of temperatures (6–300 K) and energies (up to 0.8 eV). The ferromagnetic transition at 41 K had no noticeable influence on the temperature evolution of the optical conductivity. A comparison with density functional theory plus dynamic mean-field theory calculations demonstrates the quasi-one-dimensional nature of CeIr 3 ⁢B 2 and the local character of the interactions responsible for the electronic renormalization. Furthermore, we demonstrate how the spectroscopic signatures of this mixed-valent compound are captured by theory, providing a clear distinction from the response expected in the integer-valent Kondo regime.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Unconventional nonlinear Hall effects in twisted multilayer 2D materials

We present the first investigation of unusual nonlinear Hall effects in twisted multilayer 2D materials. Contrary to expectations, our study shows that these nonlinear effects are not merely extensions of their monolayer counterparts. Instead, we find that stacking order and pairwise interactions between neighboring layers, mediated by Berry curvatures, play a pivotal role in shaping their collective nonlinear optical response. By combining large-scale Real-Time Time-Dependent Density Functional Theory (RT-TDDFT) simulations with model Hamiltonian analyses, we demonstrate a remarkable second-harmonic transverse response in hexagonal boron nitride four-layers, even in cases where the total Berry curvature cancels out. Furthermore, our symmetry analysis of the layered structures provides a simplified framework for predicting nonlinear responses in multilayer materials in general. Our investigation challenges the prevailing understanding of nonlinear optical responses in layered materials and opens new avenues for the design and development of advanced materials with tailored optical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Response tailoring of elasto-plastic trusses

Abstract In this work we tailor the response of trusses loaded beyond their yield limit. The truss structures are modeled using finite strain theory and rate-independent elasto-plasticity. We design trusses with a tailored mechanical response that is between “elastic” and “elastic-ideal-plastic” subject to the volume constraint. The design updates are generated by the gradient-based Method of Moving Asymptotes (MMA) solver and the sensitivities of the response functions are computed using a path-dependent adjoint sensitivity analysis. The computations are performed in Matlab.

42 ENGINEERING↗
DOE OSTI2022

In-situ synthesized N-doped ZnO for enhanced CO 2 sensing: Experiments and DFT calculations

Chemiresistive CO 2 sensing is attractive due to low cost and ease of chip-level integration. Our previous studies (Yong Xia, 2021) showed the well-developed ZnO material fabricated by in-situ annealing exhibited good CO 2 sensing performance. Here, we have expanded on those studies, including CO 2 cyclic tests under both dry air and N 2 background whereby a much higher response to CO 2 in N 2 background was observed. In this study, detailed density functional theory calculations were conducted to understand the behavior. The results indicated nitrogen doping is mainly responsible for the observed response. In the presence of pre-adsorbed O 2 , N-doped ZnO can no longer interact with CO 2 , which agrees well with the observation of higher response in N 2 background. Furthermore, density of states analysis showed N sp 2 hybridized orbital and N 2p orbital of the N dopant mixed with sp 2 hybridized orbital of C atom and 2p orbitals of C/O atoms in CO 2 to form σ and π bonds, respectively. However, they mixed with O 2s/2p orbitals of O atom in O 2 when pre-adsorbed O 2 was present, hindering CO 2 interaction with N-doped ZnO, and resulting in limited response in air. The illustrated mechanism does not only further the understanding of metal oxide-based CO 2 sensing, but also guide the design of new functional materials for CO 2 sensing or capture.

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

Ba 6 (Cu x Z y )Sn 4 S 16 (Z = Mg, Mn, Zn, Cd, In, Bi, Sn): High Chemical Flexibility Resulting in Good Nonlinear-Optical Properties

Seven acentric sulfides Ba 6 (Cu x Z y )Sn 4 S 16 (Z = Mg, Mn, Zn, Cd, In, Bi, Sn) were grown by a high-temperature salt flux method. The crystal structures of the Ba 6 (Cu x Z y )Sn 4 S 16 (Z = Mg, Mn, Zn, Cd, In, Bi, Sn) compounds were determined by single-crystal X-ray diffraction with the aid of solid-state NMR spectroscopy. The Ba 6 (Cu x Z y )Sn 4 S 16 (Z = Mg, Mn, Zn, Cd, In, Bi) compounds are isostructural and crystallize in the Ba 6 Ag 4 Sn 4 S 16 structure type. The Sn-containing compound exhibits high structural similarity to Ba 6 (Cu x Z y )Sn 4 S 16 (Z = Mg, Mn, Zn, Cd, In, Bi) with the presence of an interstitial atomic position partially occupied by Sn atoms. The chemical bonding characteristics of Ba 6 (Cu 2.9 Sn 0.4 )Sn 4 S 16 were understood with electron localization function calculations coupled with crystal orbital Hamilton population calculations. The Ba–S and Cu–S interactions are dominantly ionic, but the Sn–S interactions consist of strong covalent bonding characteristics in Ba 6 (Cu 2.9 Sn 0.4 )Sn 4 S 16 . The monovalent Cu atoms, mixed with certain metals with various oxidation states, significantly shift the optical properties of the Ba 6 (Cu x Z y )Sn 4 S 16 (Z = Mg, Mn, Zn, Cd, In, Bi) compounds. This results in a good balance between the second-harmonic-generation (SHG) response and laser damage threshold (LDT). Ba 6 (Cu 1.9 Zn 1.1 )Sn 4 S 16 possesses a high SHG response and a high LDT of 2.8 × AGS and 3 × AGS, respectively. Here, a density functional theory calculation revealed that CuS 4 and SnS 4 tetrahedra significantly contribute to the SHG response in Ba 6 (Cu 2 Mg)Sn 4 S 16 , which also confirmed that CuS 4 tetrahedra are crucial for the stability and optical properties of the Ba 6 (Cu x Z y )Sn 4 S 16 (Z = Mg, Mn, Zn, Cd, In, Bi, Sn) compounds revealed by electronic structure analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Demand Response Under Stochastic, Price-Dependent User Behavior

This letter focuses on price-based demand response (DR) implemented through dynamic adjustments of electricity prices. It extends existing DR models to a stochastic framework in which customer response is represented by price-dependent random variables, leveraging models and tools from the theory of stochastic optimization with decision-dependent distributions. The inherent epistemic uncertainty in the customers' responses renders open-loop, model-based DR strategies impractical. We propose a stochastic, feedback-based pricing strategy to compensate for estimation errors and uncertainty in customer response, establish theoretical results demonstrating the stability and near-optimality of the proposed approach, and validate its effectiveness through numerical simulations.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗