Search NASA⌕ Search

SEARCH · Search NASA

Results for “triangularity”

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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Crystal and electronic structure of the ternary Zintl bismuthide BaLiBi

Reported is the accurate refinement of the structure of the ternary bismuthide BaLiBi, based on single-crystal X-ray diffraction data. This compound crystallizes with the ZrBeSi structure type with the space group P6 3 /mmc (no. 194), a=4.9917(6) Å, c=9.079(2) Å, V=195.92(7) Å 3 with two formula units per unit cell. In addition to being a colored ternary variant of the AlB 2 type, the crystal structure of BaLiBi can be also viewed as a “stuffed” variant of the NiAs structure, where the Bi atoms form a hexagonal close packing, the Ba atoms occupy the octahedral voids in this packing, and the Li atoms are located between adjacent tetrahedral voids on their common triangular faces. Furthermore, in the absence of direct Bi–Bi interactions, the BaLiBi crystal structure rationalized according to the notation (Ba 2+ )(Li + )(Bi 3− ), suggesting an electron-balanced composition, i. e., a Zintl phase. In line with this notation, scalar-relativistic first-principle calculations with the LMTO code reveal a semiconducting ground state, with a bandgap of about 0.6 eV. Fully relativistic electronic structure calculations predict a semimetallic ground state.

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

OpenMP Target Task: Tasking and Target Offloading on Heterogeneous Systems

This work evaluated the use of OpenMP tasking with target GPU offloading as a potential solution for programming productivity and performance on heterogeneous systems. Also, it is proposed a new OpenMP specification to make the implementation of heterogeneous codes simpler by using OpenMP target task, which integrates both OpenMP tasking and target GPU offloading in a single OpenMP pragma. As a test case, the authors used one of the most popular and widely used Basic Linear Algebra Subprogram Level-3 routines: triangular solver (TRSM). To benefit from the heterogeneity of the current high-performance computing systems, the authors propose a different parallelization of the algorithm by using a nonuniform decomposition of the problem. This work used target GPU offloading inside OpenMP tasks to address the heterogeneity found in the hardware. This new approach can outperform the state-of-the-art algorithms, which use a uniform decomposition of the data, on both the CPU-only and hybrid CPU-GPU systems, reaching speedups of up to one order of magnitude. The performance that this approach achieves is faster than the IBM ESSL math library on CPU and competitive relative to a highly optimized heterogeneous CUDA version. One node of Oak Ridge National Laboratory’s supercomputer, Summit, was used for performance analysis.

Valero Lara, Pedro↗
DOE OSTI2022

Prompt D 0 , D + , and D* + production in Pb–Pb collisions at $ \sqrt{s_{\mathrm{NN}}} $ = 5.02 TeV

The production of prompt D 0 , D + , and D* + mesons was measured at midrapidity (|y| < 0.5) in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair $\sqrt{s_{NN}}$ = 5.02 TeV with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decay channels and their production yields were measured in central (0–10%) and semicentral (30–50%) collisions. The measurement was performed up to a transverse momentum (p T ) of 36 or 50 GeV/c depending on the D meson species and the centrality interval. For the first time in Pb–Pb collisions at the LHC, the yield of D 0 mesons was measured down to p T = 0, which allowed a model-independent determination of the p T -integrated yield per unit of rapidity (dN/dy). A maximum suppression by a factor 5 and 2.5 was observed with the nuclear modification factor (R AA ) of prompt D mesons at p T = 6–8 GeV/c for the 0–10% and 30–50% centrality classes, respectively. The D-meson RAA is compared with that of charged pions, charged hadrons, and J/ψ mesons as well as with theoretical predictions. The analysis of the agreement between the measured R AA , elliptic (v 2 ) and triangular (v 3 ) flow, and the model predictions allowed us to constrain the charm spatial diffusion coefficient D s . Furthermore the comparison of R AA and v 2 with different implementations of the same models provides an important insight into the role of radiative energy loss as well as charm quark recombination in the hadronisation mechanisms.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Linearizing the BPS equations with vector and tensor multiplets

We analyse the BPS equations of N = (1, 0) supergravity theory in six dimensions coupled to a vector and tensor multiplet. We show how these BPS equations can be reduced to a set of linear differential equations. This system is triangular in that each layer of equations, while linear, is quadratically sourced by the solutions of the previous layers. We examine several explicit examples and discuss the construction of new families of microstate geometries. We expect that the result presented here will open up new branches of superstrata in which the momentum is encoded in a new class of charge carriers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Exact moments of the Sachdev-Ye-Kitaev model up to order 1/ N 2

We analytically evaluate the moments of the spectral density of the q-body Sachdev-Ye-Kitaev (SYK) model, and obtain order 1/ N 2 corrections for all moments, where N is the total number of Majorana fermions. To order 1/ N , moments are given by those of the weight function of the Q-Hermite polynomials. Representing Wick contractions by rooted chord diagrams, we show that the 1/ N 2 correction for each chord diagram is proportional to the number of triangular loops of the corresponding intersection graph, with an extra grading factor when q is odd. Therefore the problem of finding 1/ N 2 corrections is mapped to a triangle counting problem. Since the total number of triangles is a purely graph-theoretic property, we can compute them for the q = 1 and q = 2 SYK models, where the exact moments can be obtained analytically using other methods, and therefore we have solved the moment problem for any q to 1/ N 2 accuracy. The moments are then used to obtain the spectral density of the SYK model to order 1/ N 2 . We also obtain an exact analytical result for all contraction diagrams contributing to the moments, which can be evaluated up to eighth order. This shows that the Q-Hermite approximation is accurate even for small values of N .

1/N Expansion↗
DOE OSTI2016

Higher harmonic flow coefficients of identified hadrons in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76 $ TeV

The elliptic, triangular, quadrangular and pentagonal anisotropic flow coefficients for π ± , K ± and p + $\bar{p}$ in Pb-Pb collisions at √s NN =2.76 TeV were measured with the ALICE detector at the Large Hadron Collider. The results were obtained with the Scalar Product method, correlating the identified hadrons with reference particles from a different pseudorapidity region. Effects not related to the common event symmetry planes (non-flow) were estimated using correlations in pp collisions and were subtracted from the measurement. The obtained flow coefficients exhibit a clear mass ordering for transverse momentum (p T ) values below ≈ 3 GeV/c. In the intermediate p T region (3 < p T < 6 GeV/c), particles group at an approximate level according to the number of constituent quarks, suggesting that coalescence might be the relevant particle production mechanism in this region. The results for p T < 3 GeV/c are described fairly well by a hydrodynamical model (iEBE-VISHNU) that uses initial conditions generated by A Multi-Phase Transport model (AMPT) and describes the expansion of the fireball using a value of 0.08 for the ratio of shear viscosity to entropy density (η/s), coupled to a hadronic cascade model (UrQMD). Finally, expectations from AMPT alone fail to quantitatively describe the measurements for all harmonics throughout the measured transverse momentum region. However, the comparison to the AMPT model highlights the importance of the late hadronic rescattering stage to the development of the observed mass ordering at low values of p T and of coalescence as a particle production mechanism for the particle type grouping at intermediate values of p T for all harmonics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Anisotropic flow of identified particles in Pb-Pb collisions at $ {\sqrt{s}}_{\mathrm{NN}}=5.02 $ TeV

The elliptic (v 2 ), triangular (v 3 ), and quadrangular (v 4 ) flow coefficients of π ± , K ± , p+$ \overline{p}\ $,Λ+$ \overline{Λ}\ $,K S 0 , and the Φ-meson are measured in Pb-Pb collisions at $ {\sqrt{s}}_{\mathrm{NN}}=5.02 $ TeV. Results obtained with the scalar product method are reported for the rapidity range |y| < 0.5 as a function of transverse momentum, p T , at different collision centrality intervals between 0–70%, including ultra-central (0–1%) collisions for π ± , K ± , and p + $ \overline{p}\ $. For p T < 3 GeV/c, the flow coefficients exhibit a particle mass dependence. At intermediate transverse momenta (3 < p T < 8–10 GeV/c), particles show an approximate grouping according to their type (i.e., mesons and baryons). The Φ-meson v 2 , which tests both particle mass dependence and type scaling, follows p + $ \overline{p}\ $ v 2 at low p T and π ± v 2 at intermediate p T . The evolution of the shape of v n (p T ) as a function of centrality and harmonic number n is studied for the various particle species. Flow coefficients of π ± , K ± , and p + $ \overline{p}\ $ for p T < 3 GeV/c are compared to iEBE-VISHNU and MUSIC hydrodynamical calculations coupled to a hadronic cascade model (UrQMD). The iEBE-VISHNU calculations describe the results fairly well for p T < 2.5 GeV/c, while MUSIC calculations reproduce the measurements for p T < 1 GeV/c. A comparison to v n coefficients measured in Pb-Pb collisions at $ {\sqrt{s}}_{\mathrm{NN}}=2.76 $ TeV is also provided. [Figure not available: see fulltext.].

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Gravitational wave and CMB probes of axion kination

Rotations of an axion field in field space provide a natural origin for an era of kination domination, where the energy density is dominated by the kinetic term of the axion field, preceded by an early era of matter domination. Remarkably, no entropy is produced at the end of matter domination and hence these eras of matter and kination domination may occur even after Big Bang Nucleosynthesis. We derive constraints on these eras from both the cosmic microwave background and Big Bang Nucleosynthesis. We investigate how this cosmological scenario affects the spectrum of possible primordial gravitational waves and find that the spectrum features a triangular peak. We discuss how future observations of gravitational waves can probe the viable parameter space, including regions that produce axion dark matter by the kinetic misalignment mechanism or the baryon asymmetry by axiogenesis. For QCD axion dark matter produced by the kinetic misalignment mechanism, a modification to the inflationary gravitational wave spectrum occurs above 0.01 Hz and, for high values of the energy scale of inflation, the prospects for discovery are good. We briefly comment on implications for structure formation of the universe.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Anisotropic flow of identified hadrons in $\mathrm{X}$e-$\mathrm{X}$e collisions at $\sqrt{s_{NN}}$ = 5.44 $\mathrm{T}$e$\mathrm{V}$

Measurements of elliptic (v 2 ) and triangular (v 3 ) flow coefficients of π ± , K ± , $p+\bar{p}$, $K$$^{0}_{S}$, and $Λ+\bar{Λ}$ obtained with the scalar product method in Xe-Xe collisions at $\sqrt{s_{NN}}$ = 5.44 TeV are presented. The results are obtained in the rapidity range |y| < 0.5 and reported as a function of transverse momentum, p T , for several collision centrality classes. The flow coefficients exhibit a particle mass dependence for p T < 3 GeV/c, while a grouping according to particle type (i.e., meson and baryon) is found at intermediate transverse momenta (3 < p T < 8 GeV/c). The magnitude of the baryon v 2 is larger than that of mesons up to p T = 6 GeV/c. The centrality dependence of the shape evolution of the p T -differential v 2 is studied for the various hadron species. The v 2 coefficients of π ± , K ± , and $p+\bar{p}$ are reproduced by MUSIC hydrodynamic calculations coupled to a hadronic cascade model (UrQMD) for p T < 1 GeV/c. A comparison with v n measurements in the corresponding centrality intervals in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV yields an enhanced v 2 in central collisions and diminished value in semicentral collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Probing the chiral magnetic wave with charge-dependent flow measurements in Pb-Pb collisions at the LHC

The Chiral Magnetic Wave (CMW) phenomenon is essential to provide insights into the strong interaction in QCD, the properties of the quark-gluon plasma, and the topological characteristics of the early universe, offering a deeper understanding of fundamental physics in high-energy collisions. Measurements of the charge-dependent anisotropic flow coefficients are studied in Pb-Pb collisions at center-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV to probe the CMW. In particular, the slope of the normalized difference in elliptic (v 2 ) and triangular (v 3 ) flow coefficients of positively and negatively charged particles as a function of their event-wise normalized number difference, is reported for inclusive and identified particles. The slope ${r}_3^{\textrm{Norm}}$ is found to be larger than zero and to have a magnitude similar to ${r}_2^{\textrm{Norm}}$, thus pointing to a large background contribution for these measurements. Furthermore, ${r}_2^{\textrm{Norm}}$ can be described by a blast wave model calculation that incorporates local charge conservation. In addition, using the event shape engineering technique yields a fraction of CMW (f CMW ) contribution to this measurement which is compatible with zero. This measurement provides the very first upper limit for f CMW , and in the 10–60% centrality interval it is found to be 26% (38%) at 95% (99.7%) confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

The hepatic capsular arteries: imaging features and clinical significance

Background: Although the anatomical features of the hepatic capsular arteries have been previously reported, the radiological and clinical importance of these arteries has not been well documented. Imaging findings: We injected barium sulfate into the intra- and extra-hepatic arteries in cadavers to investigate the hepatic capsular arteries. The web-like hepatic capsular arteries derived from the capsular branch of the peripheral hepatic arteries are called isolated arteries. There were anastomoses between the intra- and extra-hepatic arteries (inferior phrenic artery, superior falciform ligament artery, and cystic artery) through the hepatic capsular arteries. Clinical significance: We reviewed the radiology database and assessed clinical cases. When the hepatic artery is occluded, the collateral vessels, such as the inferior phrenic artery and the superior falciform ligament artery, develop via the hepatic capsular arteries at the right triangular ligament and falciform ligament, respectively. Bleeding from capsular arteries causes extensions of the subcapsular hematoma. Conclusion: The hepatic capsular arteries spread along the hepatic surface and constitute the vascular network throughout the liver. These arteries play an important role in collateral circulation in various clinical situations, as well as subcapsular hematoma.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Multiscale two-stage solver for Biot’s poroelasticity equations in subsurface media

In this paper, we propose a two-stage preconditioner for accelerating the iterative solution by a Krylov subspace method of Biot’s poroelasticity equations based on a displacement-pressure formulation. The spatial discretization combines a finite element method for mechanics and a finite volume approach for flow. The fully implicit backward Euler scheme is used for time integration. The result is a 2 × 2 block linear system for each timestep. The preconditioning operator is obtained by applying a two-stage scheme. The first stage is a global preconditioner that employs multiscale basis functions to construct coarse-scale coupled systems using a Galerkin projection. This global stage is effective at damping low-frequency error modes associated with long-range coupling of the unknowns. The second stage is a local block-triangular smoothing preconditioner, which is aimed at high-frequency error modes associated with short-range coupling of the variables. Lastly, various numerical experiments are used to demonstrate the robustness of the proposed solver.

58 GEOSCIENCES↗
DOE OSTI2016

Direct discontinuous Galerkin method and its variations for second order elliptic equations

In this study, we study direct discontinuous Galerkin method (Liu and Yan in SIAM J Numer Anal 47(1):475–698, 2009) and its variations (Liu and Yan in Commun Comput Phys 8(3):541–564, 2010; Vidden and Yan in J Comput Math 31(6):638–662, 2013; Yan in J Sci Comput 54(2–3):663–683, 2013) for 2nd order elliptic problems. A priori error estimate under energy norm is established for all four methods. Optimal error estimate under L 2 norm is obtained for DDG method with interface correction (Liu and Yan in Commun Comput Phys 8(3):541–564, 2010) and symmetric DDG method (Vidden and Yan in J Comput Math 31(6):638–662, 2013). A series of numerical examples are carried out to illustrate the accuracy and capability of the schemes. Numerically we obtain optimal (k+1)th order convergence for DDG method with interface correction and symmetric DDG method on nonuniform and unstructured triangular meshes. An interface problem with discontinuous diffusion coefficients is investigated and optimal (k+1)th order accuracy is obtained. Peak solutions with sharp transitions are captured well. Highly oscillatory wave solutions of Helmholz equation are well resolved.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Rapid Discoloration of Methyl Orange in Water by Conductive Cu/Cu{sub 2}O/rGO Modified Polyester Fabric

A new rapid dye removal method is introduced by using a conductive polyester fabric prepared through in-situ synthesis of Cu/Cu{sub 2}O/rGO nanocomposites. Cu{sub 2}O and Cu nanoparticles were deposited on the polyester fabric with triangular, spherical and rod-like shapes due to introducing GO nanosheets and EDTA into the synthesis media. The cauliflower-like Cu/Cu{sub 2}O/rGO nanocomposites coated polyester fabric exhibited remarkable removal of methyl orange (MO) in a short time (more than 92% within 30 min). This can be attributed to the shape, presence of GO or EDTA that was subsequently created nanoparticles with smaller size, higher electrical conductivity and more specific surface area for removal of MO.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Quantum Phase Transition Induced by Magnetic Impurity

The Yu–Shiba–Rusinov bound states can arise around magnetic impurities in conventional superconductors. Competition between screened and unscreened states can lead to the quantum phase transition. We discuss basic properties of this quantum phase transition in the case of the triangular lattice with on-site pairing. We show that the quantum phase transistion results from the change of the ground state of the system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Structure of Rank-One Matrices Over the Domain of Principal Ideals Relative to Similarity Transformations

We study the structure of rank-one matrices over the domain of principal ideals relative to equivalence and similarity transformations. The canonical form of rank-one matrices relative to similarity transformations is established. We propose conditions under which a pair of rank-one matrices is reduced to the triangular form by a similarity transformation.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Refractive index from negative to positive with frequencies at the Dirac-like cone in a photonic crystal

In this paper, we numerically study the threefold accidental degeneracy conical dispersion (Driac-like cone) at the Brillouin zone center of the two-dimensional photonic crystals, which are composed of silicon pillars arranging in a triangular lattice. The effective permittivity and permeability near the Dirac-like point evolve from negative to positive by using the method of eigen-field averaging. Also, the isotropic behaviour of the Dirac-like cone is revealed by analysing the isofrequency contours. Moreover, we carry out numerical simulations including the reverse Snell’s law effect, negative Goos–Hänchen shifts and superfocusing lens to verify the negative refractive index characteristics of the designed structure. The proposed structure might find significant applications in the on-chip photonic interconnect and the photonic integrated circuit techniques.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Implications of theoretical analysis to explore the functional core dimension in one-rod core microstructured optical fibers

A new development in optical fiber technology that has attracted interest for multitude of novel and potential applications is an all-in-silica microstructured optical fibre (MOF) with one-rod core. We aim to estimate the functional core dimension for one-rod core triangular MOF (T-MOF) from its geometrical characteristics by using an alternative analytical field model. Moreover, to scrutinize the validity of the choice of effective core dimension (by adapting V-parameter, i.e., the normalized frequency) for T-MOF, we have explored the rudimentary propagation characteristics of the T-MOF in single mode guidance realm. We made comparisons with those which are based on the experimental and numerical studies. Relative errors are also reported.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗