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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Invariant amplitudes, unpolarized cross sections, and polarization asymmetries in neutrino-nucleon and antineutrino-nucleon elastic scattering

At leading order in weak and electromagnetic couplings, cross sections for (anti)neutrino-nucleon elastic scattering are determined by four nucleon form factors that depend on the momentum transfer Q 2 . Including radiative corrections in the Standard Model and potential new physics contributions beyond the Standard Model, eight invariant amplitudes are possible, depending on both Q 2 and the (anti)neutrino energy E ν . We review the definition of these amplitudes and use them to compute both unpolarized and polarized observables including radiative corrections. We show that unpolarized accelerator neutrino cross-section measurements can probe new physics parameter space within the constraints inferred from precision beta decay measurements. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

p -adic reconstruction of rational functions in multiloop amplitudes

Numerical reconstruction techniques are widely employed in the calculation of multiloop scattering amplitudes. In recent years, it has been observed that the rational functions in multiloop calculations greatly simplify under partial fractioning. In this article, we present a technique to reconstruct rational functions directly in partial-fractioned form, by evaluating the functions at special integer points chosen for their properties under a p -adic metric. As an application, we apply this technique to reconstruct the largest rational function in the integration-by-parts reduction of one of the rank-5 integrals appearing in two-loop five-point full-color massless amplitude calculations in quantum chromodynamics. The number of required numerical probes (per prime field) is found to be around 25 times smaller than in conventional techniques, and the obtained result is 130 times smaller. The reconstructed result displays signs of additional structure that could be used to further reduce its size and the number of required probes. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

Embedding space approach to Lorentzian CFT amplitudes and causal spherical functions

Conformal field theory in a Minkowski setting is discussed in an embedding space approach, paying special attention to causality constraints for four-point amplitudes. The physics of dilatation and Lorentz boost is emphasized in specifying the noncompact maximal Abelian subgroup of S O ( d , 2 ) . Reduction of a conformal field theory four-point amplitudes as functions of cross ratios is shown to be equivalent to enforcing H bi-invariance, i.e., F ( h g h ′ ) = F ( g ) , with g ∈ S O ( d , 2 ) and H an appropriate subgroup. Causality is imposed by introducing appropriate semigroups. Causal zonal spherical functions are constructed, making contact with Minkowski conformal blocks introduced previously. Published by the American Physical Society 2024

Agarwal, Pulkit (ORCID:0000000346581691)↗
DOE OSTI2019

Maximally supersymmetric amplitudes at infinite loop momentum

We investigate the asymptotically large loop-momentum behavior of multiloop amplitudes in maximally supersymmetric ($N$ = 4, 8) quantum field theories in four dimensions. We check residue-theorem identities among color-dressed leading singularities in $N$ = 4 supersymmetric Yang-Mills theory to demonstrate the absence of poles at infinity of all n-point MHV amplitudes through three loops. Considering the same test for $N$ = 8 supergravity leads us to discover that this theory does support nonvanishing residues at infinity starting at two loops, and the degree of these poles grow arbitrarily with multiplicity. This causes a tension between simultaneously manifesting ultraviolet finiteness—which would be automatic at two loops for representation obtained by color-kinematic duality—and gauge invariance—which would follow from unitarity-based methods.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Two-Loop Four-Gluon Amplitudes from Numerical Unitarity

We present the first numerical computation of two-loop amplitudes based on the unitarity method. As a proof of principle, we compute the four-gluon process in the leading-color approximation. We discuss the new method, analyze its numerical properties, and apply it to reconstruct the analytic form of the amplitudes. The numerical method is universal, and can be automated to provide multiscale two-loop computations for phenomenologically relevant signatures at hadron colliders.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Kinetic Simulations of the Interruption of Large-Amplitude Shear-Alfvén Waves in a High- β Plasma

Using two-dimensional hybrid-kinetic simulations, we explore the nonlinear “interruption” of standing and traveling shear-Alfvén waves in collisionless plasmas. Interruption involves a self-generated pressure anisotropy removing the restoring force of a linearly polarized Alfvénic perturbation, and occurs for wave amplitudes δB ⊥ /B 0 ≳β –1/2 (where β is the ratio of thermal to magnetic pressure). We use highly elongated domains to obtain maximal scale separation between the wave and the ion gyroscale. For standing waves above the amplitude limit, we find that the large-scale magnetic field of the wave decays rapidly. The dynamics are strongly affected by the excitation of oblique firehose modes, which transition into long-lived parallel fluctuations at the ion gyroscale and cause significant particle scattering. Traveling waves are damped more slowly, but are also influenced by small-scale parallel fluctuations created by the decay of firehose modes. Our results demonstrate that collisionless plasmas cannot support linearly polarized Alfvén waves above δB ⊥ /B 0 ~β –1/2 . Here, they also provide a vivid illustration of two key aspects of low-collisionality plasma dynamics: (i) the importance of velocity-space instabilities in regulating plasma dynamics at high β, and (ii) how nonlinear collisionless processes can transfer mechanical energy directly from the largest scales into thermal energy and microscale fluctuations, without the need for a scale-by-scale turbulent cascade.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Amplitude Analysis of the B 0 → K * 0 μ + μ − Decay

An amplitude analysis of the B 0 → K * 0 μ + μ − decay is presented using a dataset corresponding to an integrated luminosity of 4.7 fb − 1 of p p collision data collected with the LHCb experiment. For the first time, the coefficients associated to short-distance physics effects, sensitive to processes beyond the standard model, are extracted directly from the data through a q 2 -unbinned amplitude analysis, where q 2 is the μ + μ − invariant mass squared. Long-distance contributions, which originate from nonfactorizable QCD processes, are systematically investigated, and the most accurate assessment to date of their impact on the physical observables is obtained. The pattern of measured corrections to the short-distance couplings is found to be consistent with previous analyses of b - to s -quark transitions, with the largest discrepancy from the standard model predictions found to be at the level of 1.8 standard deviations. The global significance of the observed differences in the decay is 1.4 standard deviations. © 2024 CERN, for the LHCb Collaboration 2024 CERN

Aaij, R. (ORCID:0000000305331952)↗
DOE OSTI2024

Observation of D + → K S 0 a 0 ( 980 ) + in the Amplitude Analysis of D + → K S 0 π + η

We perform for the first time an amplitude analysis of the decay D + → K S 0 π + η and report the observation of the decay D + → K S 0 a 0 ( 980 ) + using 2.93 fb − 1 of e + e − collision data taken at a center-of-mass energy of 3.773 GeV with the BESIII detector. As the only W -annihilation-free decay among D to a 0 ( 980 ) pseudoscalar, D + → K S 0 a 0 ( 980 ) + is the ideal decay in extracting the contributions of the W -emission amplitudes involving a 0 ( 980 ) and to study the final-state interactions. The absolute branching fraction of D + → K S 0 π + η is measured to be ( 1.27 ± 0.0 4 stat ± 0.0 3 syst ) % . The branching fractions of intermediate processes D + → K S 0 a 0 ( 980 ) + with a 0 ( 980 ) + → π + η and D + → π + K ¯ 0 * ( 1430 ) 0 with K ¯ 0 * ( 1430 ) 0 → K S 0 η are measured to be ( 1.33 ± 0.0 5 stat ± 0.0 4 syst ) % and ( 0.14 ± 0.0 3 stat ± 0.0 1 syst ) % , respectively. Published by the American Physical Society 2024

Physics↗
DOE OSTI2018

Microscopic signatures of yielding in concentrated nanoemulsions under large-amplitude oscillatory shear

Here, we report x-ray photon correlation spectroscopy (XPCS) experiments on a series of concentrated oil-in-water nanoemulsions with varying droplet volume fraction subjected to in situ steady-state large-amplitude oscillatory shear (LAOS). The shear strain causes periodic echoes in the x-ray speckle patterns that lead to peaks in the intensity autocorrelation function. Above an onset strain amplitude that depends on nanoemulsion concentration, the peaks become attenuated, signaling spatially heterogeneous, shear-induced droplet dynamics. These dynamics include irreversible re- arrangements among the droplets that occur in some regions of the nanoemulsions during a given shear cycle and residual strain-like displacements in those regions that do not re-arrange. The wave-vector dependence of the peak attenuation indicates a power-law distribution in the size of regions undergoing shear-induced rearrangement that is similar to that observed previously in LAOS-XPCS measurements on concentrated nanocolloidal gels. The values of the onset strains for re-arrangement correlate with the concentration-dependent macroscopic yielding behavior of the nanoemulsions. Specically, they occur below the strains at which the nanoemulsions become effectively uidized and, except for the lowest concentration nanoemulsion in the study, signicantly above the threshold strain for nonlinear rheological response.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structure-factor amplitude reconstruction from serial femtosecond crystallography of two-dimensional membrane-protein crystals

Serial femtosecond crystallography of two-dimensional membrane-protein crystals at X-ray free-electron lasers has the potential to address the dynamics of functionally relevant large-scale motions, which can be sterically hindered in three-dimensional crystals and suppressed in cryocooled samples. In previous work, diffraction data limited to a two-dimensional reciprocal-space slice were evaluated and it was demonstrated that the low intensity of the diffraction signal can be overcome by collecting highly redundant data, thus enhancing the achievable resolution. Here, the application of a newly developed method to analyze diffraction data covering three reciprocal-space dimensions, extracting the reciprocal-space map of the structure-factor amplitudes, is presented. Despite the low resolution and completeness of the data set, it is shown by molecular replacement that the reconstructed amplitudes carry meaningful structural information. Therefore, it appears that these intrinsic limitations in resolution and completeness from two-dimensional crystal diffraction may be overcome by collecting highly redundant data along the three reciprocal-space axes, thus allowing the measurement of large-scale dynamics in pump–probe experiments.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Analytic Estimation Method of Forced Oscillation Amplitude Under Stochastic Continuous Disturbances

This paper proposes an analytic method for the amplitude estimation of the forced oscillation under stochastic continuous disturbances (SCDs). There is considerable interest in the integration of intermittent renewable energy resources into a power system, which leads to the power system in an environment with SCDs. Thus, the forced oscillation issues under SCDs are of concern. In this paper, the SCDs are described as continuous-time stochastic processes, and then the systems under SCDs are modeled by stochastic differential algebraic equations. Furthermore, by employing stochastic theory, an efficient analytic method for calculating the statistics of system states during the forced oscillation is proposed. Moreover, a novel forced oscillation phenomenon, which presents system states oscillate with stationary distributions under SCDs, is clearly characterized and theoretically explained. Based on the proposed analytic method, a scheme is put forth to estimate amplitudes of system states during forced oscillation under SCDs. Finally, compared to Monte Carlo simulation, the proposed scheme has two significant advantages. First, the proposed scheme offers a fast and effective solution for engineering applications. Second, the impact mechanism of SCDs on forced oscillation in power system is clearer, by the proposed scheme.

42 ENGINEERING↗
DOE OSTI2019

Separation of Frequency and Amplitude Modulation Contributions Due to External Vibration on a SAW Resonator

Surface SAW resonators (SAWR) are widely used in radio-frequency (RF) communications, frequency-control, and sensing applications. External vibration-induced modulations of a SAWR’s RF response can be detrimental in communications and frequency-control as it generates undesired spurious signals and unwanted phase noise. In sensing applications, vibration-induced response can either be a primary measurand or an undesired spurious signal that reduces sensor accuracy and precision. Therefore, characterization of vibration-induced modulations is important to improve device performance in all the applications listed above. This paper presents an in-phase and quadrature signal analysis technique to demodulate a SAWR RF signal exposed to external vibrations and separate the contributions of amplitude modulation (AM) and frequency modulation (FM). A SAWR was mounted in a cantilever configuration and exposed to external mechanical vibrating signals using a vibration generator. The SAWR was excited close to its resonant frequency using a RF synthesizer and its echo response was measured using a vector signal analyzer. The experimental results and findings reported in this paper confirm that the I-Q analysis developed in this work is effective not only to determine the frequency and spectral amplitude of a mechanical vibrating signal on a SAWR, but also to separate the AM and FM contributions. Here, this analysis contributes to the quantification and understanding of induced external vibrations on SAWRs used in contemporary communications, frequency control, and sensing applications.

42 ENGINEERING↗
DOE OSTI2023

Understanding the transient large amplitude oscillatory shear behavior of yield stress fluids

A full understanding of the sequence of processes exhibited by yield stress fluids under large amplitude oscillatory shearing is developed using multiple experimental and analytical approaches. A novel component rate Lissajous curve, where the rates at which strain is acquired unrecoverably and recoverably are plotted against each other, is introduced and its utility is demonstrated by application to the analytical responses of four simple viscoelastic models. Using the component rate space, yielding and unyielding are identified by changes in the way strain is acquired, from recoverably to unrecoverably and back again. The behaviors are investigated by comparing the experimental results with predictions from the elastic Bingham model that is constructed using the Oldroyd–Prager formalism and the recently proposed continuous model by Kamani, Donley, and Rogers in which yielding is enhanced by rapid acquisition of elastic strain. The physical interpretation gained from the transient large amplitude oscillatory shear (LAOS) data is compared to the results from the analytical sequence of physical processes framework and a novel time-resolved Pipkin space. The component rate figures, therefore, provide an independent test of the interpretations of the sequence of physical processes analysis that can also be applied to other LAOS analysis frameworks. Each of these methods, the component rates, the sequence of physical processes analysis, and the time-resolved Pipkin diagrams, unambigiously identifies the same material physics, showing that yield stress fluids go through a sequence of physical processes that includes elastic deformation, gradual yielding, plastic flow, and gradual unyielding.

Kamani, Krutarth M. (ORCID:0000000338975420)↗
DOE OSTI2019

Amplitude Instability of Charged Particles in a Body-Centered Cubic Cell

The conditions for the formation of amplitude instabilities in 3D Yukawa systems consisting of nine charged particles in a body-centered cubic (bcc) cell have been investigated. The criterion for the formation of amplitude instability has been sought using an analytic approach based on determining the point of inflection of the potential energy of the system during deviation of particles from their equilibrium position. The results have been compared with melting criteria for extended bcc lattices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Off-shell amplitudes and Grassmannians

The Grassmannian representation for gauge-invariant amplitudes for arbitrary number of legs with one of them being off-shell is derived for the case of N = 4 SYM. The obtained formula are successfully checked against known BCFW results for MHV{sub n}, NMHV{sub 4} and NMHV{sub 5} amplitudes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

N* resonances from K $\Lambda$ Λ amplitudes in sliced bins in energy

The two reactions $\gamma p\to K^+\Lambda$ and $\pi^-p\to K^0\Lambda$ are analyzed to determine the leading photoproduction multipoles and the pion-induced partial wave amplitudes in slices of the invariant mass. The multipoles and the partial-wave amplitudes are simultaneously fitted in a multichannel Laurent+Pietarinen model (L+P model), which determines the poles in the complex energy plane on the second Riemann sheet close to the physical axes. The results from the L+P fit are compared with the results of an energy-dependent fit based on the Bonn-Gatchina (BnGa) approach. The study confirms the existence of several poles due to nucleon resonances in the region at about 1.9\,GeV with quantum numbers $J^P = 1/2^+$, $3/2^+, 1/2^-, 3/2^-, 5/2^-$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measuring the effects of pore-pressure changes on seismic amplitude using crosswell continuous active-source seismic monitoring (CASSM)

Monitoring of time-varying reservoir properties, such as the state of stress, is a primary goal of geophysical investigations, including for geological sequestration of CO 2 , enhanced hydrocarbon recovery (EOR), and other subsurface engineering activities. In this work, we used Continuous Active-Source Seismic Monitoring (CASSM), with cross-well geometry, to measure variation in seismic coda amplitude, as a consequence of effective stress change (in the form of changes in pore fluid pressure). To our knowledge, the presented results are the first in-situ example of such crosswell measurement at reservoir scale and in field conditions. Data compliment the findings of our previous work which investigated the relationship between pore fluid pressure and seismic velocity (velocity-stress sensitivity) using the CASSM system at the same field site (Marchesini et al., 2017, in review). We find that P-wave coda amplitude decreases with decreasing pore pressure (increasing effective stress).

58 GEOSCIENCES↗
DOE OSTI2018

Magnetron R&D toward the Amplitude Modulation Control for SRF Accelerator

The scheme of using a high efficiency magnetron to drive a superconducting radio frequency (SRF) accelerator cavity needs not only the injection phase locking but also the amplitude modulation to compensate the cavity's microphomics caused cavity voltage change and the beam loading variation. To be able to do a fast and efficient modulation, the magnetron's magnetic field has to be trimmed by an external coil to compensate the frequency pushing effect due to the anode current change [1]. A low eddy current magnetron body has been designed and built [2]. This paper will present the analytical prediction, simulation and experimental results on the 2.45 GHz magnetron test stand with the modulation frequency up to 1 kHz. In addition, the progresses on the injection lock to a copper cavity, new 1497 MHz magnetron prototype, 13 kW high power magnetron test stand development and newly built low level RF (LLRF) controller for the amplitude modulation will be reported.

Rimmer, Robert A.↗