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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Observation of a Goldstone mode in the broken helix by time-resolved optical polarimetry

Magnets with isotropic easy-plane symmetry host Goldstone modes that can be leveraged for efficient spin transport. Here, we present a time-resolved optical polarimetry technique that allows us to detect and characterize such low-frequency modes, and use it to observe the Goldstone mode in the multi-Q broken helix phase of EuIn2As2. The strength of our technique comes from the ability to distinguish between nematic and magnetization dynamics in order to yield information about the mode structure, in addition to its frequency. We find that the nearly uniform spin precession characteristic of a Goldstone mode is realized only when a small magnetic field is used to unpin the broken helix from local strain generated during crystal growth. In this regime, the mode frequency scales linearly with the applied field due to the ground state C2z symmetry of the broken helix. Our work shows how optical polarimetry can be used to study the Goldstone modes of complex magnets.

Liebman-Peláez, A↗
DOE OSTI2023

EuCd 2 ⁢As 2 : A Magnetic Semiconductor

EuCd 2 ⁢As 2 is now widely accepted as a topological semimetal in which a Weyl phase is induced by an external magnetic field. Here, we challenge this view through firm experimental evidence using a combination of electronic transport, optical spectroscopy, and excited-state photoemission spectroscopy. We show that the EuCd 2 ⁢As 2 is in fact a semiconductor with a gap of 0.77 eV. We show that the externally applied magnetic field has a profound impact on the electronic band structure of this system. This is manifested by a huge decrease of the observed band gap, as large as 125 meV at 2 T, and, consequently, by a giant redshift of the interband absorption edge. However, the semiconductor nature of the material remains preserved. EuCd 2 ⁢As 2 is therefore a magnetic semiconductor rather than a Dirac or Weyl semimetal, as suggested by ab initio computations carried out within the local spin-density approximation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Fundamental limits to the generation of highly displaced bright squeezed light using linear optics and parametric amplifiers

High-quality squeezed light is an important resource for a variety of applications. Multiple methods for generating squeezed light are known, having been demonstrated theoretically and experimentally. However, the effectiveness of these methods—in particular, the inherent limitations to the signals that can be produced—has received little consideration. Here we present a comparative theoretical analysis for generating a highly displaced squeezed light from a linear optical method—a beamsplitter mixing a squeezed vacuum and a strong coherent state—and well-studied parametric amplification methods including an optical parametric oscillator, an optical parametric amplifier, and a dissipative optomechanical squeezer seeded with coherent states. We show that the quality of highly displaced squeezed states that can be generated using these methods is limited on a fundamental level by the physical mechanism utilized; across all methods there are significant trade-offs between displacement, squeezing, and overall uncertainty. We explore the nature and extent of these trade-offs specific to each mechanism and identify the optimal operation modes for each. Finally, we identify the conditions for minimum-uncertainty squeezing in arbitrary parametric amplifying systems and show that displacing the output signal will in general violate these conditions, adding noise and degrading squeezing. Published by the American Physical Society 2025

Young, Steve M. (ORCID:0000000173839366)↗
DOE OSTI2024

Multimodal Approach Reveals the Symmetry-Breaking Pathway to the Broken Helix in EuIn 2 ⁢As 2

Understanding and manipulating emergent phases, which are themes at the forefront of quantum-materials research, rely on identifying their underlying symmetries. This general principle has been particularly prominent in materials with coupled electronic and magnetic degrees of freedom, in which magnetic order influences the electronic band structure and can lead to exotic topological effects. However, identifying symmetry of a magnetically ordered phase can pose a challenge, particularly in the presence of small domains. Here we introduce a multimodal approach for determining magnetic structures, which combines symmetry-sensitive optical probes, scattering, and group-theoretical analysis. We apply it to EuIn 2 ⁢As 2 , a material that has received attention as a candidate axion insulator. While first-principles calculations predict this state on the assumption of a simple collinear antiferromagnetic structure, subsequent neutron-scattering measurements reveal a much more intricate magnetic ground state characterized by two coexisting magnetic wave vectors reached by successive thermal phase transitions. The proposed high- and low-temperature phases are a spin helix and a state with interpenetrating helical and Néel antiferromagnetic order termed a “broken helix,” respectively. Employing a multimodal approach, we identify the magnetic structure associated with these two phases of EuIn 2 ⁢As 2 . We find that the higher-temperature phase is characterized by a variation of the magnetic moment amplitude from layer to layer, with the moment vanishing entirely in every third Eu layer. The lower-temperature structure is similar to the broken helix, with one important difference: Because of local strain, the relative orientation of the magnetic structure and the lattice is not fixed. Consequently, the symmetry required to protect the axion phase is not generically protected in EuIn 2 ⁢As 2 , but we show that it can be restored if the magnetic structure is tuned with uniaxial strain. Finally, we present a spin Hamiltonian that identifies the spin interactions that account for the complex magnetic order in EuIn 2 ⁢As 2 . Our work highlights the importance of a multimodal approach in determining the symmetry of complex order parameters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Fast Active-Set Thresholding Method for Nonnegative Least Squares

Nonnegative Least Squares (NNLS) is a fundamental constrained optimization problem encountered in many applications such as image deblurring, signal processing, nonnegative matrix factorization, magnetic microscopy, and hyperspectral imaging. Active-set based methods are a common class of algorithms for solving NNLS which identify the optimal variable set of the NNLS solution. They do so by iteratively solving a series of unconstrained least squares problems, identifying which variables violate the nonnegativity constraints, and then swapping variables in/out of consideration until the optimal set of variables is found. Several variations improving upon this method exist in the literature. In this work, we propose an active-set swap heuristic which further improves upon existing active-set based methods for NNLS. Our optimizations are based upon adding multiple variables to the passive set within a threshold of the smallest gradient value and removing variables within a similar threshold of the closest boundary constraint. We leverage these optimizations to yield a Fast Active-Set Thresholding NNLS (FAST-NNLS) algorithm which significantly outperforms the existing state-of-the-art NNLS algorithms for a wide range of problems. Rigorous convergence guarantees are proven for the proposed method. We demonstrate the effectiveness of our proposed method on multiple synthetic datasets and two realworld text analysis applications. In doing so, we present the most comprehensive NNLS solver comparison in the literature to date.

Cobb, Benjamin [Georgia Institute of Technology]↗
DOE OSTI2024

Accelerated Constrained Sparse Tensor Factorization on Massively Parallel Architectures

This study presents the first constrained sparse tensor factorization (cSTF) framework that optimizes and fully offloads computation to massively parallel GPU architectures, and the first performance characterization of cSTF on GPU architectures. In contrast to prior work on tensor factorization, where the matricized tensor times Khatri-Rao product (MTTKRP) is the primary performance bottleneck, our systematic analysis of the cSTF algorithm on GPUs reveals that adding constraints creates an additional bottleneck in the update operation for many real-world sparse tensors. While executing the update operation on the GPU brings significant speedup over its CPU counterpart, it remains a significant bottleneck. To further accelerate the update operation, we propose cuADMM, a new update algorithm that leverages algorithmic and code optimization strategies to minimize both computation and data movement on GPUs. As a result, our framework delivers significantly improved performance compared to prior state-of-the-art. On 10 real-world sparse tensors, our framework achieves geometric mean speedup of 5.1 × (max 41.59 ×) and 7.01 × (max 58.05 ×) on the NIVIDA A100 and H100 GPUs, respectively, over the state-of-the-art SPLATT library running on a 26-core Intel Ice Lake Xeon CPU.

Soh, Yongseok↗
DOE OSTI2019

Oncologic Outcomes of Self-Expandable Metallic Stent as a Bridge to Surgery and Safety and Feasibility of Minimally Invasive Surgery for Acute Malignant Colonic Obstruction

Background: Although self-expandable metal stents (SEMS) are widely used as a bridge to surgery (BTS) in patients with malignant colorectal cancer obstruction, there has been some debate about their effect on long-term oncological outcomes. Furthermore, data on the safety and feasibility of minimally invasive surgery (MIS) combined with stent placement are scarce. We aimed to determine the long-term oncological outcomes of SEMS as a BTS, and the short-term outcomes of SEMS used with minimally invasive colorectal surgery. Methods: Data from patients who were admitted with malignant obstructing colon cancer between January 2006 and December 2015 were retrospectively reviewed; 71 patients underwent direct surgery and 182 patients underwent SEMS placement as a BTS. Long-term and short-term outcomes of the groups were compared. In a subgroup analysis of the BTS group, the short-term outcomes of conventional open surgery and MIS were compared. Results: There were no differences in long-term oncologic outcomes between groups. The primary anastomosis rate was higher in the stent group than in the direct surgery group. In the stent group, postoperative complication rates were lower in the minimally invasive group than in the open surgery group. Time to flatus and time to soft diet resumption were shorter in the minimally invasive group, as was length of hospital stay. Conclusions: Elective surgery after stent insertion does not adversely affect long-term oncologic outcomes. Furthermore, MIS combined with stent insertion for malignant colonic obstruction is safe and feasible.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Recipes for a Successful Exit for Clean- and Hard-tech Startups

This study demonstrates the combinations of multiple causal factors that formulate a startup’s strategy to successfully “exit”, namely “recipes for a successful exit,” in the clean- and hard-tech sector. We identify seven key causal factors (i.e., causal conditions) that impact startup success, including commercial readiness, investor interactions, favorable industry, non-financial support, straightforward development path, experienced team, and visibility to investors. We also investigate the combinations of selective causal conditions that can provide further synergetic impact. We conduct the fuzzy-set qualitative comparative analysis (fsQCA) on seven US clean and hard-tech startups that exited between 2005 and 2016. The successful companies all demonstrate distinctive characteristics based on three general categories (1) robust ecosystem; (2) heavy-lifting team; or (3) external opportunity. Across these three categories, commercial readiness and strong investor interactions are necessary conditions for all exit cases. But there are important differences that drive success in each category, such as the interaction with non-financial support (in the robust ecosystem case), experienced team (in the heavy-lifting team case), and favorable industry (in the external opportunity case). Furthermore, our findings are meant to support entrepreneurs in reaching an exit by optimizing the given internal and external circumstances, and policymakers to build a robust ecosystem that can increase the success rate of the clean- and hardtech development.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2020

Quantum Super-resolution Bioimaging using Massively Entangled Multimode Squeezed Light

This report presents a new method for realizing a super-resolution quantum imaging using massively entangled multimode squeezed light (MEMSL). Each branch of the entangled multimode light interacts with the sample and bears the spatially varying optical phase delay. When imaging optics with finite pupil sizes are used, information is lost. Thanks to the analyticity in the Fourier plane, a noiseless measurement would recover the lost information and accomplish super resolution imaging beating the Rayleigh diffraction limit. I proved rigorously in a fully quantum formalism and presented that (1) such information recovery is possible and (2) the information recovery can be accomplished with much less resources when MEMSL is used than those needed in any non-entangled or non-squeezed classical imaging method. Furthermore, the action of the optical loss in the imaging system that degrades the imaging performance is also rigorously analyzed and presented. Several bioimaging applications that can benefit tremendously from the proposed quantum imaging scheme are also suggested.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Modeling of Atom Interferometer Accelerometer

This report presents the theoretical effort to model and simulate the atom-interferometer accelerometer operating in a highly mobile environment. Multitudes of non-idealities may occur in such a rapidly-changing environment with a large acceleration whose amplitude and direction both change quickly. We studied the undesired effect of high mobility in the atom-interferometer accelerator in a detailed model and a simulator. The undesired effects include the atom cloud's movement during Raman pulses, the Doppler effect due to the relative movement between the atom-cloud and the supporting platform, the finite atom cloud temperature, and the lateral movement of the atom cloud. We present the relevant feed-forward mitigation strategies for each identified non-ideality to neutralize the impact and obtain accurate acceleration measurements.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Tuning the Optical and Photophysical Properties of Boron Aza-Dipyridylmethene dyes for Optoelectronics Application

A series of substituted boron aza-dipyridylmethene (aD) compounds are explored for their attractive photophysical and electrochemical properties as fluorescent emitters for blue OLEDs. Previous work in our lab have demonstrated the synthetic ease of dipyridylmethene monomers and their interesting photophysical properties as homoleptic meso-linked dimers. Using Density Functional Theory (DFT) modeling, we combine our theoretical and experimental efforts to synthesize a library of aD compounds by replacing the meso carbon with nitrogen to destabilize the HOMO energy. The synthesized aD derivatives emit blue light with λ max between 400-460 nm and internal quantum efficiencies above 85 % . From TD-DFT calculations, estimation of the singlet and triplet energies that are deduced from fluorescence and phosphorescence emission, respectively, closely matches the experimental data of ΔE ST ≤ 0.4 eV. Aza-dipyridylmethene show promising potential as blue emitting fluorophores in OLEDs with EQE max = 4.5 %, approaching the maximum theoretical limit of fluorescent (fl) OLED of 5.5 %. Boron aza-dipyridylmethene are synthetically tunable compounds which show interesting photophysical properties for applications in organic electronics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Tuning Singlet and Triplet Excited State Energies and Frontier Orbitals of Imidazole Host/Emitter for Hybrid White OLEDs

In this work, we report hybrid fluorescent/phosphorescent WOLEDs employing blue fluorescent and green and red phosphorescent emitters doped into a host matrix. The fluorescent emitting dopant harnesses all electrically generated high energy singlet excitons for blue emission, and the phosphorescent dopants harvest the remainder of lower-energy triplet excitons for green and red emission. This design requires the singlet state (S1) of the host to be higher than the S1 of the fluorescent dopant so that the singlet excitons generated on the host are transferred to the fluorescent dopant. Furthermore, the triplet state (T1) of the host matrix should be lower than the T1 of the fluorescent dopant so the triplet excitons generated on the fluorescent dopant can be transferred to the host matrix which will then be transferred to the green and red phosphors. To develop a host material that can serve this purpose, we tune the electronic properties of phenanthro[9,10-d]imidazole by incorporating phenyl and/or pyridyl moieties at the N1 and C2 positions of phenanthro[9,10-d]imidazole. This substitution resulted in variety of host materials with different singlet/triplet energies, quantum efficiency and redox values. The resulting phenanthro[9,10-d]imidazoles are employed as host materials for fluorescent and phosphorescent dopants and as neat fluorescent emitters. Monochromatic devices with a fluorescent emitter and the phenanthro[9,10-d]imidazoles as host materials or as neat fluorescent emitter achieved near theoretical maximum efficiency. Finally, efficient three-color hybrid WOLEDs were fabricated using the phenanthro[9,10-d]imidazoles as hosts for a fluorescent dopant or as neat fluorescent emitters and host for green and red phosphors.

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

Lossless Quantum Hard-Drive Memory Using Parity-Time Symmetry

We theoretically studied the feasibility of building a long-term read-write quantum memory using the principle of parity-time (PT) symmetry, which has already been demonstrated for classical systems. The design consisted of a two-resonator system. Although both resonators would feature intrinsic loss, the goal was to apply a driving signal to one of the resonators such that it would become an amplifying subsystem, with a gain rate equal and opposite to the loss rate of the lossy resonator. Consequently, the loss and gain probabilities in the overall system would cancel out, yielding a closed quantum system. Upon performing detailed calculations on the impact of a driving signal on a lossy resonator, our results demonstrated that an amplifying resonator is physically unfeasible, thus forestalling the possibility of PT-symmetric quantum storage. Our finding serves to significantly narrow down future research into designing a viable quantum hard drive.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Single Photon Detection with On-Chip Number Resolving Capability

Single photon detection (SPD) plays an important role in many forefront areas of fundamental science and advanced engineering applications. In recent years, rapid developments in superconducting quantum computation, quantum key distribution, and quantum sensing call for SPD in the microwave frequency range. We have explored in this LDRD project a new approach to SPD in an effort to provide deterministic photon-number-resolving capability by using topological Josephson junction structures. In this SAND report, we will present results from our experimental studies of microwave response and theoretical simulations of microwave photon number resolving detector in topological Dirac semimetal Cd 3 As 2 . These results are promising for SPD at the microwave frequencies using topological quantum materials.

47 OTHER INSTRUMENTATION↗