Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Decay processes”

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 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Direct probes of flavor-changing neutral currents in e + e - -collisions

In this paper, we propose a novel method to study flavor-changing neutral currents in the e + e - → D * 0 and e + e - → B s * transitions, tuning the energy of e + e - - collisions to the mass of the narrow vector resonance D * 0 or B s * . We present a thorough study of both short-distance and long-distance contributions to e + e - → D * 0 in the Standard Model and investigate possible contributions of new physics in the charm sector. This process, albeit very rare, has clear advantages with respect to the D 0 → e + e - decay: the helicity suppression is absent, and a richer set of effective operators can be probed. Finally, implications of the same proposal for B s * are also discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

William A. Bardeen: A life in physics and the legacy of the chiral anomaly

William Allan Bardeen (September 15, 1941 − November 18, 2025) was an American theoretical physicist who worked at the Fermi National Accelerator Laboratory. He is renowned for his foundational work on the chiral anomaly, the Adler-Bardeen theorem, the non-Abelian anomaly and gravitational anomalies. He was instrumental in the development of quantum chromodynamics and its applications, such as semileptonic decays and the Λ $\overline{MS}$ scheme frequently used in perturbative analysis of high energy processes involving strong interactions. Bardeen also played a major role in developing a theory of dynamical breaking of electroweak symmetry via top quark condensates, leading to one of the first composite Brout-Englert-Higgs boson models. His work on the chiral symmetry dynamics of heavy-light quark bound states correctly predicted abnormally long-lived resonances which are chiral symmetry partners of the ground state.

Hill, Christopher T. [Fermi National Accelerator L↗
DOE OSTI2018

Optical control of polarization in ferroelectric heterostructures

In the ferroelectric devices, polarization control is usually accomplished by application of an electric field. In this paper, we demonstrate optically induced polarization switching in BaTiO 3 -based ferroelectric heterostructures utilizing a two-dimensional narrow-gap semiconductor MoS 2 as a top electrode. This effect is attributed to the redistribution of the photo-generated carriers and screening charges at the MoS 2 /BaTiO 3 interface. Specifically, a two-step process, which involves formation of intra-layer excitons during light absorption followed by their decay into inter-layer excitons, results in the positive charge accumulation at the interface forcing the polarization reversal from the upward to the downward direction. Theoretical modeling of the MoS 2 optical absorption spectra with and without the applied electric field provides quantitative support for the proposed mechanism. It is suggested that the discovered effect is of general nature and should be observable in any heterostructure comprising a ferroelectric and a narrow gap semiconductor.

36 MATERIALS SCIENCE↗
DOE OSTI2023

River thorium concentrations can record bedrock fracture processes including some triggered by distant seismic events

Fractures are integral to the hydrology and geochemistry of watersheds, but our understanding of fracture dynamics is very limited because of the challenge of monitoring the subsurface. Here we provide evidence that long-term, high-frequency measurements of the river concentration of the ultra-trace element thorium (Th) can provide a signature of bedrock fracture processes spanning neighboring watersheds in Colorado. River Th concentrations show abrupt (subdaily) excursions and biexponential decay with approximately 1-day and 1-week time constants, concentration patterns that are distinct from all other solutes except beryllium and arsenic. The patterns are uncorrelated with daily precipitation records or seasonal trends in atmospheric deposition. Groundwater Th analyses are consistent with bedrock release and dilution upon mixing with river water. Most Th excursions have no seismic signatures that are detectable 50 km from the site, suggesting the Th concentrations can reveal aseismic fracture or fault events. We find, however, a weak statistical correlation between Th and seismic motion caused by distant earthquakes, possibly the first chemical signature of dynamic earthquake triggering, a phenomenon previously identified only through geophysical methods.

58 GEOSCIENCES↗
DOE OSTI2011

Stability of shock waves in high temperature plasmas

The Dyakov-Kontorovich criteria for spontaneous emission of acoustic waves behind shock fronts are investigated for high temperature aluminum and beryllium plasmas. To this end, the Dyakov and critical stability parameters are calculated from Rankine-Hugoniot curves using a more realistic equation of state (EOS). The cold and ionic contributions to the EOS are obtained via scaled binding energy and mean field theory, respectively. A screened hydrogenic model, including l-splitting, is used to calculate the bound electron contribution to the electronic EOS. The free electron EOS is obtained from Fermi-Dirac statistics. Predictions of the model for ionization curves and shock Hugoniot are found to be in excellent agreement with available experimental and theoretical data. It is observed that the electronic EOS has significant effect on the stability of the planar shock front. While the shock is stable for low temperatures and pressures, instability sets in as temperature rises. The basic reason is ionization of electronic shells and consequent increase in electronic specific heat. The temperatures and densities of the unstable region correspond to those where electronic shells get ionized. With the correct modeling of bound electrons, we find that shock instability for Al occurs at a compression ratio {approx}5.4, contrary to the value {approx}3 reported in the literature. Free electrons generated in the ionization process carry energy from the shock front, thereby giving rise to spontaneously emitted waves, which decay the shock front.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Non-adiabatic dynamics investigation of the radiationless decay mechanism of trans-urocanic acid in the S{sub 2} state

The trans-urocanic acid, a UV chromophore in the epidermis of human skin, was found to exhibit a wavelength dependent isomerization property. The isomerization quantum yield to cis-urocanic is greatest when being excited to the S{sub 1} state, whereas exciting the molecule to the S{sub 2} state causes almost no isomerization. The comparative photochemical behavior of the trans-urocanic on the S{sub 1} and S{sub 2} states continues to be the subject of intense research effort. This study is concerned with the unique photo-behavior of this interesting molecule on the S{sub 2} state. Combining the on-the-fly surface hopping dynamics simulations and static electronic structure calculations, three decay channels were observed following excitation to the S{sub 2} state. An overwhelming majority of the molecules decay to the S{sub 1} state through a planar or pucker characterized minimum energy conical intersection (MECI), and then decay to the ground state along a relaxation coordinate driven by a pucker deformation of the ring. A very small fraction of molecules decay to the S{sub 1} state by a MECI characterized by a twisting motion around the CC double bond, which continues to drive the molecule to deactivate to the ground state. The latter channel is related with the photoisomerization process, whereas the former one will only generate the original trans-form products. The present work provides a novel S{sub 2} state decay mechanism of this molecule, which offers useful information to explain the wavelength dependent isomerization behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

INTERACTION OF CLOSE-IN PLANETS WITH THE MAGNETOSPHERE OF THEIR HOST STARS. II. SUPER-EARTHS AS UNIPOLAR INDUCTORS AND THEIR ORBITAL EVOLUTION

Planets with several Earth masses and orbital periods of a few days have been discovered through radial velocity and transit surveys. Regardless of their formation mechanism, an important evolution issue is the efficiency of their retention in the proximity of their host stars. If these 'super-Earths' attained their present-day orbits during or shortly after the T Tauri phase of their host stars, a large fraction of these planets would have encountered an intense stellar magnetic field. These rocky planets have a higher conductivity than the atmosphere of their host stars and, therefore, the magnetic flux tube connecting them would slip though the envelope of the host stars faster than across the planets. The induced electromotive force across the planet's diameter leads to a potential drop which propagates along a flux tube away from the planet with an Alfven speed. The foot of the flux tube would sweep across the stellar surface and the potential drop across the field lines drives a DC current analogous to that proposed for the electrodynamics of the Io-Jupiter system. The ohmic dissipation of this current produces potentially observable hot spots in the star envelope. It also heats the planet and leads to a torque which drives the planet's orbit to evolve toward both circularization and a state of synchronization with the spin of the star. The net effect is the damping of the planet's orbital eccentricity. Around slowly (or rapidly) spinning stars, this process also causes rocky planets with periods less than a few days to undergo orbital decay (or expansion/stagnation) within a few Myr. In principle, this effect can determine the retention efficiency of short-period hot Earths. We also estimate the ohmic dissipation interior to these planets and show that it can lead to severe structure evolution and potential loss of volatile material in them. However, these effects may be significantly weakened by the reconnection of the induced field.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Baryogenesis and gravitational waves from runaway bubble collisions

We propose a novel mechanism for production of baryonic asymmetry in the early Universe. The mechanism takes advantage of the strong first order phase transition that produces runaway bubbles in the hidden sector that propagate almost without friction with ultra-relativistic velocities. Collisions of such bubbles can non-thermally produce heavy particles that further decay out-of-equilibrium into the SM and produce the observed baryonic asymmetry. This process can proceed at the very low temperatures, providing a new mechanism of post-sphaleron baryogenesis. In this paper we present a fully calculable model which produces the baryonic asymmetry along these lines as well as evades all the existing cosmological constraints. We emphasize that the Gravitational Waves signal from the first order phase transition is completely generic and can potentially be detected by the future eLISA interferometer. We also discuss other potential signals, which are more model dependent, and point out the unresolved theoretical questions related to our proposal.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Constraining axion properties with radio telescopes

Axion dark matter or any ultralight bosonic dark matter can go through Bose-Einstein condensation due to the large phase density, leading to the formation of axion stars or solitons in dark matter halo centers. The formation rate is enhanced in the presence of the substructures expected in the postinflationary scenario for the QCD axion or axionlike particles. An axion star will continue to grow until a critical mass is reached, after which it collapses and then explodes, with the emission of relativistic axions, in a process called an “axinovae.” There can also be accompanying photon emission due to the stimulated decay of axions in the coherent compact axion star. In axion models with a modest enhancement (𝜅 ∼𝒪⁡(10)) of the axion-photon coupling 𝑔 𝑎⁢𝛾 = 𝜅⁢𝛼/(2⁢𝜋⁢𝑓 𝑎 ) axinovae will contain a significant flux of radio photons. We determine the range of parameters over which axinovae can be detectable with radio transient searches.

Fox, Patrick J. [Fermi National Accelerator Labora↗
DOE OSTI2017

Search for a hidden strange baryon-meson bound state from Φ production in a nuclear medium

We investigate the hidden strange light baryon-meson system. With the resonating-group method, two bound states, η'-N and Φ-N, are found in the quark delocalization color screening model. Focusing on the Φ-N bound state around 1950 MeV, we obtain the total decay width of about 4 MeV by calculating the phase shifts in the resonance scattering processes. To study the feasibility of an experimental search for the Φ-N bound state, we perform a Monte Carlo simulation of the bound state production with an electron beam and a gold target. In the simulation, we use the CLAS12 detector with the Forward Tagger and the BONUS12 detector in Hall B at Jefferson Lab. Both the signal and the background channels are estimated. We demonstrate that the signal events can be separated from the background with some momentum cuts. Therefore it is feasible to experimentally search for the Φ-N bound state through the near threshold Φ meson production from heavy nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Förster Energy Transfer in Arrays of Epitaxial CdSe/ZnSe Quantum Dots Involving Bright and Dark Excitons

Using time-resolved photoluminescence (PL) spectroscopy, we establish the presence of the Förster energy transfer mechanism between two arrays of epitaxial CdSe/ZnSe quantum dots (QDs) of different sizes. The mechanism operates through dipole–dipole interaction between ground excitonic states of the smaller QDs and excited states of the larger QDs. The dependence of energy transfer efficiency on the width of barrier separating the QD insets is shown to be in line with the Förster mechanism. The temperature dependence of the PL decay times and PL intensity suggests the involvement of dark excitons in the energy transfer process.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Search for direct top squark pair production in events with a Z boson, b-jets and missing transverse momentum in sqrt(s)=8 TeV pp collisions with the ATLAS detector

CERN-LHC. A search is presented for direct top squark pair production using events with at least two leptons including a same-flavour opposite-sign pair with invariant mass consistent with the Z boson mass, jets tagged as originating from b-quarks and missing transverse momentum. The analysis is performed with proton-proton collision data at sqrt(s) = 8 TeV collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20.3 fb^-1. No excess beyond the Standard Model expectation is observed. Interpretations of the results are provided in models based on the direct pair production of the heavier top squark state (t2) followed by the decay to the lighter top squark state (t1) via t2 --> Z t1, and for t1 pair production in natural gauge-mediated supersymmetry breaking scenarios where the neutralino (chi1^0) is the next-to-lightest supersymmetric particle and decays producing a Z boson and a gravitino (G) via the chi1^0 --> Z G process.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Radiative Bottomonium Spectroscopy at the Y(2, 3S) Resonances at BaBar

The compact bound state consisting of a bottom and anti-bottom quark pair interacting via the strong nuclear force is called “bottomonium.” A wealth of long-lived bottomonium states can be both experimentally produced and theoretically described, providing a unique tool to probe calculation techniques with experiment. Bottomonia with total angular momentum J = 1 and orbital angular momentum L = 0 at a variety of radial excitations n – called Υ(nS) – can be produced at electron-positron colliders. The BABAR experiment, located at the interaction point of such a collider (the PEP-II storage ring), has observed 122 million Υ(3S) and 100 million Υ(2S) decays. Some of these involve a transition to the bottomonium state χ bJ (nP) (L = 1 and J = (0, 1, 2)), emitting a photon, with subsequent transition to a lower Υ(nS), also emitting a photon. The final Υ(nS) can be identified through a decay to two muons. The dependence of the branching fractions and photon energies in this process on the spin state of the intermediate χ bJ (nP) is a key test of phenomenological models. To this end, this dissertation contains a nearly comprehensive study of these transitions with an emphasis on experimentally optimal discrimination between various models. This focus spurs innovative techniques that complement a large array of physics results, both presented in detail herein.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

ORNL Design Engineering Library: Validated Thermoelectric Digital Twins

Radioisotope thermoelectric generators (RTGs) serve a crucial role in supplying thermal and electrical energy for reliable and long-duration power in remote and extreme environments. The thermal energy is provided by the decay of radioisotopes and is converted into electrical energy using the steady-state thermoelectric process by exploiting the Seebeck effect. Maintaining a thermal gradient through the material is necessary to drive current production. Modern predictive multi-physics tools are able to effectively describe the complex and strongly coupled phenomena needed for accurate model-based system engineering efforts needed to develop higher performing RTGs. Experimental validation of model simulations is essential to confirm the accuracy, reliability, and applicability of predictive multiphysics tools. Validation fosters confidence among users, helps meet regulatory requirements, and contributes to the ongoing improvement of simulation techniques, ultimately leading to better, safer, and more efficient designs and processes. Validated models can then be used as digital twins and can be interrogated to understand and quantify the performance gaps between theoretical and physical systems. These insights can be used to build higher performing systems.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗