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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

General aspects of Gauss-Bonnet models without potential in dimension four

In the present work, the isotropic and homogenous solutions with spatial curvature k =0 of four dimensional Gauss-Bonnet models are characterized. The main assumption is that the scalar field φ which is coupled to the Gauss-Bonnet term has no potential [1]–[2]. Some singular and some eternal solutions are described. The evolution of the universe is given in terms of a curve γ=( H (φ), φ) which is the solution of a polynomial equation P ( H {sup 2}, φ)=0 with φ dependent coefficients. In addition, it is shown that the initial conditions in these models put several restrictions on the evolution. For instance, an universe initially contracting will be contracting always for future times and an universe that is expanding was always expanding at past times. Thus, there are no cyclic cosmological solutions for this model. These results are universal, that is, independent on the form of the coupling f (φ) between the scalar field and the Gauss-Bonnet term. In addition, a proof that at a turning point φ-dot →0 a singularity necessarily emerges is presented, except for some specific choices of the coupling. This is valid unless the Hubble constant H → 0 at this point. This proof is based on the Raychaudhuri equation for the model. The description presented here is in part inspired in the works [3]–[4]. However, the mathematical methods that are implemented are complementary of those in these references, and they may be helpful for study more complicated situations in a future.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Continuous, edge localized ion heating during non-solenoidal plasma startup and sustainment in a low aspect ratio tokamak

Plasmas in the Pegasus spherical tokamak are initiated and grown by the non-solenoidal local helicity injection (LHI) current drive technique. The LHI system consists of three adjacent electron current sources that inject multiple helical current filaments that can reconnect with each other. Anomalously high impurity ion temperatures are observed during LHI with T i,OV ≤ 650 eV, which is in contrast to T i,OV ≤ 70 eV from Ohmic heating alone. Spatial profiles of T i,OV indicate an edge localized heating source, with T i,OV ~ 650 eV near the outboard major radius of the injectors and dropping to ~150 eV near the plasma magnetic axis. Experiments without a background tokamak plasma indicate the ion heating results from magnetic reconnection between adjacent injected current filaments. In these experiments, the HeII T i perpendicular to the magnetic field is found to scale with the reconnecting field strength, local density, and guide field, while ${{T}_{\text{i},\parallel}}$ experiences little change, in agreement with two-fluid reconnection theory. In conclusion, this ion heating is not expected to significantly impact the LHI plasma performance in Pegasus, as it does not contribute significantly to the electron heating. However, estimates of the power transfer to the bulk ion are quite large, and thus LHI current drive provides an auxiliary ion heating mechanism to the tokamak plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Software aspects of the Geant4 validation repository

The Geant4, GeantV and GENIE collaborations regularly perform validation and regression tests for simulation results. DoSSiER (Database of Scientic Simulation and Experimental Results) is being developed as a central repository to store the simulation results as well as the experimental data used for validation. DoSSiER is easily accessible via a web application. In addition, a web service allows for programmatic access to the repository to extract records in JSON or XML exchange formats. In this article, we describe the functionality and the current status of various components of DoSSiER as well as the technology choices we made.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Cryogenic aspects of a 20 MW class low-temperature superconducting generator for the renewables industry

In this paper we give a progress update on the cryogenic design for cooling a 20 MW class, partially superconducting generator with stationary field coils for offshore wind renewables industry [1-2]. This is a continuation of an earlier program on a 10 MW system dating back ten years. Whereas this new power rating increase leads to a radial diameter expansion of the superconducting field coils from 4 to > 9.5 m, it maintains the axial length. We show the design based on this scaled up with enlarged diameter. The field coil size increase asks for higher cooling power that leads to a bigger cold box size to accommodate the cryocoolers. In the design, as many as 8 cryocoolers can be accessed and serviced from the nacelle that houses the main cryogenic components. A typical thermal load balance sheet with all components is given and compared against the available cryocooler cooling power at different operating conditions. Due to the cryocoolers’ local point of contact cooling within the nacelle, the temperature gradient of the thermal shield that fully encloses the cold mass with its embedded field coils needs to be balanced out to minimize the heat burden on the field coils. This requires additional analytical efforts and implementation of further design features. The extended nacelle houses the cold box with its cryogenic infrastructure. The interface for the envisaged cryogenic pushbutton closed-loop circulating system remains invisible, requires no handling of cryogenic liquids and is hermetically closed. The field coil diameter increase also leads to a greater initial helium gas storage volume. In addition, it requires higher initial room temperature fill pressure within the toroidal helium vapor storage tanks and in cooling tubes connecting to the cryocoolers. The toroidal helium gas tanks are thermally coupled with the thermal shield so that helium convection inside the storage tank can improve heat transfer and reduce the temperature gradient of the thermal shield. Besides those heat transfer challenges, additional mechanical strain within this large structure is exerted on the torque tubes during initial cooldown and when energizing field coils. Some of those design challenges are quite unexpected, leading to novel workarounds in order to maintain the chosen cooling strategy. Finally, we assess those design limitations in view of further cryogenic scalability with emphasis on manufacturability and assembly.

cryogenics↗
DOE OSTI2014

NEW ASPECTS OF A LID-REMOVAL MECHANISM IN THE ONSET OF AN ERUPTION SEQUENCE THAT PRODUCED A LARGE SOLAR ENERGETIC PARTICLE (SEP) EVENT

We examine a sequence of two ejective eruptions from a single active region on 2012 January 23, using magnetograms and EUV images from the Solar Dynamics Observatory's (SDO) Helioseismic and Magnetic Imager (HMI) and Atmospheric and Imaging Assembly (AIA), and EUV images from STEREO/EUVI. This sequence produced two coronal mass ejections (CMEs) and a strong solar energetic particle event (SEP); here we focus on the magnetic onset of this important space weather episode. Cheng et al. showed that the first eruption's ({sup E}ruption 1{sup )} flux rope was apparent only in ''hotter'' AIA channels, and that it removed overlying field that allowed the second eruption ({sup E}ruption 2{sup )} to begin via ideal MHD instability; here we say that Eruption 2 began via a ''lid removal'' mechanism. We show that during Eruption 1's onset, its flux rope underwent a ''tether weakening'' (TW) reconnection with field that arched from the eruption-source active region to an adjacent active region. Standard flare loops from Eruption 1 developed over Eruption 2's flux rope and enclosed filament, but these overarching new loops were unable to confine that flux rope/filament. Eruption 1's flare loops, from both TW reconnection and standard-flare-model internal reconnection, were much cooler than Eruption 2's flare loops (GOES thermal temperatures of ∼7.5 MK and 9 MK, compared to ∼14 MK). The corresponding three sequential GOES flares were, respectively, due to TW reconnection plus earlier phase Eruption 1 tether-cutting reconnection, Eruption 1 later-phase tether-cutting reconnection, and Eruption 2 tether-cutting reconnection.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Identification of a ligand binding hot spot and structural motifs replicating aspects of tyrosyl-DNA phosphodiesterase I (TDP1) phosphoryl recognition by crystallographic fragment cocktail screening

Tyrosyl DNA-phosphodiesterase I (TDP1) repairs type IB topoisomerase (TOP1) cleavage complexes generated by TOP1 inhibitors commonly used as anticancer agents. TDP1 also removes DNA 3' end blocking lesions generated by chain-terminating nucleosides and alkylating agents, and base oxidation both in the nuclear and mitochondrial genomes. Combination therapy with TDP1 inhibitors is proposed to synergize with topoisomerase targeting drugs to enhance selectivity against cancer cells exhibiting deficiencies in parallel DNA repair pathways. A crystallographic fragment screening campaign against the catalytic domain of TDP1 was conducted to identify new lead compounds. Crystal structures revealed two fragments that bind to the TDP1 active site and exhibit inhibitory activity against TDP1. These fragments occupy a similar position in the TDP1 active site as seen in prior crystal structures of TDP1 with bound vanadate, a transition state mimic. Using structural insights into fragment binding, several fragment derivatives have been prepared and evaluated in biochemical assays. These results demonstrate that fragment-based methods can be a highly feasible approach toward the discovery of small-molecule chemical scaffolds to target TDP1, and for the first time, we provide co-crystal structures of small molecule inhibitors bound to TDP1, which could serve for the rational development of medicinal TDP1 inhibitors.

Lountos, George T.↗
DOE OSTI2023

Aspects of the Domain-Wall Standard Model

Abstract In the “Domain-Wall Standard Model,” all the Standard Model (SM) fields are localized in certain domains in a non-compact 5D space-time. While the SM is realized as a 4D effective theory at low energies, the model involves Kaluza–Klein (KK) modes of the SM particles. In this paper we introduce two simple solvable examples which lead to domain-wall configurations for the SM particles and their KK-modes. Based on the examples, we address a variety of phenomenologies of the Domain-Wall SM, such as the KK-mode gauge boson phenomenology at the Large Hadron Collider (LHC), the effect of the KK-mode SM fermions on Higgs boson phenomenology, and the KK-mode fermion search at the LHC with its decay into a corresponding SM fermion and a Nambu–Goldstone boson associated with a spontaneous breaking of the translational invariance in the 5th dimension. We also propose a simple unified picture of localizing all the SM fields.

Physics↗
DOE OSTI2025

New scaling and nuclear structure aspects in heavy-ion fusion reactions

Three new behaviors have been found in comparisons of fusion cross sections for different collision systems. root (1) Replacing the energy E with a scaling one, E scal = (E-V g )/($\sqrt{2}$W g ), is successful for washing out the Coulomb interaction in the spectra of fusion cross sections, where V g and W g are barrier height and width of the single-Gaussian barrier distribution model. (2) In a representation of σE vs the scaling energy, E scal , all data sets display in parallel. Here, the ratio for sigma E from any two fusion systems over the whole range is a constant value. That behavior is also studied in another representation, in which the data sets display as parallel horizontal lines for any heavy-ion fusion system. (3) The constant ratio value is the ratio of parameter products, $R^2_gW_g$, of the two systems; where R g is the barrier radius obtained in the single-Gaussian barrier distribution model. Moreover, when comparing neighboring collision systems at the same E scal , the ratio of sigma is near a constant value within a few percent over the whole range. Thus a quantitative comparison for the fusion enhancement for neighboring systems is developed. The present finding could be beneficial for predicting unmeasured fusion cross sections.

Jiang, C. L. [Argonne National Laboratory (ANL), A↗
DOE OSTI2020

Aspects of the normal state resistivity of cuprate superconductors

Planar normal state resistivity data taken from three families of cuprate superconductors are compared here with theoretical calculations from the recent extremely correlated Fermi liquid theory (ECFL). The two hole doped cuprate materials LSCO and BSLCO and the electron doped material LCCO have yielded rich data sets at several densities δ and temperatures T, thereby enabling a systematic comparison with theory. The recent ECFL resistivity calculations for the highly correlated t-t'-J model by us give the resistivity for a wide set of model parameters. After using X-ray diffraction and angle resolved photoemission data to fix parameters appearing in the theoretical resistivity, only one parameter, the magnitude of the hopping t, remains undetermined. For each data set, the slope of the experimental resistivity at a single temperature-density point is sufficient to determine t, and hence the resistivity on absolute scale at all remaining densities and temperatures. This procedure is demonstrated to give a fair account of the entire data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Prediction of superconductivity and topological aspects in single-layer β -Bi 2 Pd

Topological superconductors, characterized by topologically nontrivial states residing in a superconducting gap, are a recently discovered class of materials having Majorana fermions. The interplay of superconductivity and topological states gives rise to opportunities for achieving such topological superconductors in condensed matter systems. Up to now, several single-material topological superconductors in this form have been theoretically predicted and experimentally confirmed. Here, using the first-principles calculations, we study the superconducting single-layer β-Bi 2 Pd. In this work, the electronic density of states near Fermi level of this monolayer are dominated by the Bi-p and Pd-d orbitals, forming a two-band Fermi surface with multiclass sheets. The presence of soft phonon bands, in cooperation with the electron susceptibility, accounts for electron-phonon superconductivity of single-layer β-Bi 2 Pd. With the centrosymmetric structure, single-layer β-Bi 2 Pd possesses a continuous gap over the whole Brillouin zone and topological Dirac-like states at its one-dimensional boundary. The present findings would lead to the expectation of one-dimensional topological superconductivity and Majorana bound states in a monolayer candidate of β-Bi 2 Pd with intrinsic full-gap superconductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Nonperturbative aspects of the electromagnetic pion form factor at high energies

The structure of hadronic form factors at high energies and their deviations from perturbative quantum chromodynamics provide insight on nonperturbative dynamics. Using an approach that is consistent with dispersion relations, we construct a model that simultaneously accounts for the pion wave function, gluonic exchanges, and quark Reggeization. In particular, we find that quark Reggeization can be investigated at high energies by studying scaling violation of the form factor.

Form factors↗