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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Capturing intrinsic site-dependent spectral signatures and lifetimes of isolated OH oscillators in extended water networks

The extremely broad infrared spectrum of water in the OH stretching region is a manifestation of how profoundly a water molecule is distorted when embedded in its extended hydrogen-bonding network. Many effects contribute to this breadth in solution at room temperature, which raises the question as to what the spectrum of a single OH oscillator would be in the absence of thermal fluctuations and coupling to nearby OH groups. We report the intrinsic spectral responses of isolated OH oscillators embedded in two cold (~20 K), hydrogen-bonded water cages adopted by the Cs + ·(HDO)(D 2 O) 19 and D 3 O + ·(HDO)(D 2 O) 19 clusters. Most OH oscillators yield single, isolated features that occur with linewidths that increase approximately linearly with their redshifts. Oscillators near 3,400 cm -1 , however, occur with a second feature, which indicates that OH stretch excitation of these molecules drives low-frequency, phonon-type motions of the cage. Finally, the excited state lifetimes inferred from the broadening are considered in the context of fluctuations in the local electric fields that are available even at low temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Oscillations of the thermal conductivity in the spin-liquid state of α-RuCl 3

In the class of materials called spin liquids a magnetically ordered state cannot be attained even at millikelvin temperatures because of conflicting constraints on each spin; for example, from geometric or exchange frustration. The resulting quantum spin-liquid state is currently of intense interest because it exhibits unusual excitations as well as wave-function entanglement. The layered insulator α-RuCl 3 orders as a zigzag antiferromagnet at low temperature in zero magnetic field. The zigzag order is destroyed when a magnetic field is applied parallel to the zigzag axis. At moderate magnetic field strength, there is growing evidence that a quantum spin-liquid state exists. Here we report the observation of oscillations in its thermal conductivity in that field range. The oscillations, whose amplitude is very large within this field range and strongly suppressed on either side, are periodic. This is analogous to quantum oscillations in metals, even though α-RuCl 3 is an excellent insulator with a large gap. As the temperature is raised above 0.5 K, the oscillation amplitude decreases exponentially, anticorrelating with the emergence of an anomalous planar thermal Hall conductivity above approximately 2 K.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Joint neutrino oscillation analysis from the T2K and NOvA experiments

The landmark discovery that neutrinos have mass and can change type (or flavour) as they propagate—a process called neutrino oscillation—has opened up a rich array of theoretical and experimental questions being actively pursued today. Neutrino oscillation remains the most powerful experimental tool for addressing many of these questions, including whether neutrinos violate charge-parity (CP) symmetry, which has possible connections to the unexplained preponderance of matter over antimatter in the Universe. Oscillation measurements also probe the mass-squared differences between the different neutrino mass states (Δ$m^2$), whether there are two light states and a heavier one (normal ordering) or vice versa (inverted ordering), and the structure of neutrino mass and flavour mixing. Here we carry out the first joint analysis of datasets from NOvA and T2K, the two currently operating long-baseline neutrino oscillation experiments (hundreds of kilometres of neutrino travel distance), taking advantage of our complementary experimental designs and setting new constraints on several neutrino sector parameters. This analysis provides new precision on the $Δm_{32}^2$ mass difference, finding $-2.43_{−0.03}^{+0.04}$ x $10^{-13}$ $\textrm{eV}^2$ in the normal ordering and $-2.43^{+0.03}_{-0.04}$ x $10^{-13}$ $\textrm{eV}^2$ in the inverted ordering, as well as a 3σ interval on δ CP of [−1.38π, 0.30π] in the normal ordering and [−0.92π, −0.04π] in the inverted ordering. The data show no strong preference for either mass ordering, but notably, if inverted ordering were assumed true within the three-flavour mixing model, then our results would provide evidence of CP symmetry violation in the lepton sector.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Fractional magnetoresistance oscillations in spin-triplet superconducting rings

Abstract Half-quantum vortices in spin-triplet superconductors are predicted to host Majorana zero modes and may provide a viable platform for topological quantum computation. Recent works also suggested that, in thin mesoscopic rings, the superconducting pairing symmetry can be probed via Little-Parks-like magnetoresistance oscillations of periodicity Φ 0 = h /2 e that persist below the critical temperature. Here we use the London limit of Ginzburg-Landau theory to study these magnetoresistance oscillations resulting from thermal vortex tunneling in spin-triplet superconducting rings. For a range of temperatures in the presence of disorder, we find magnetoresistance oscillations with an emergent fractional periodicity Φ 0 / n , where the integer n ≥ 3 is entirely determined by the ratio of the spin and charge superfluid densities. These fractional oscillations can unambiguously confirm the spin-triplet nature of superconductivity and directly reveal the tunneling of half-quantum vortices in real-world candidate materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

UV patternable thin film chemistry for shape and functionally versatile self-oscillating gels

We describe a new planar processing chemistry that allows the synthesis and patterning of dynamically self-actuating gels of diverse form. The chemical reaction covalently incorporates a methacrylate-modified ruthenium trisbipyridine monomer within a poly acrylamide (PAAm) gel, modified to provide a flexible chemistry for UV-curable, self-oscillating Belousov–Zhabotinsky (BZ) gels. The photoinitiated polymerization offers significant advantages over previously reported BZ gel chemistries – fast polymerization rates, broad flexibility in the structural and functional attributes that impact the BZ reaction driven mechanics, and a facility for net shape fabrication via projection mode photo lithographic exposure. The facility of the synthetic method enabled an opportunity to broadly explore the structure/property and structure/rate correlations characterizing the dynamics of these gels and develop means to both control and predict the detailed features of the self-oscillating chemical waves they embed. The PAAm systems initiate under the control of transport-dominated influences weighted heavily by the diffusion/depletion of reagents present in the ambient contacting fluid medium. These initiating modes of oscillation are generally unstable temporally, showing shape- and property-sensitive conversions to oscillating modes controlled by the attributes of the gel-phase environment. The present work establishes the nature of these sensitivities, developing insights related to such features in patterned gel objects or films as composition, size, thickness, shape, degree of crosslinking, and gradient forms of structure within the gel. We observed in this work that, across a broad design-rule and compositional space, the PAAm based BZ gel systems exhibit contractions in dimension for regions in which the Ru catalyst is present in the +3 oxidation state (PNIPAAm BZ gels expand in this state). The chemomechanics of the PAAm system are further differentiated from those of PNIPAAm in the generally (and relatively) fast oscillatory rates it can sustain. Furthermore, this work suggests the dynamics in the PAAm gels do not reflect a simple osmotic force driven by differences in the solvation of Ru(II/III) centers. Computational modeling supports a mechanism in which the charge state of Ru centers mediate a differential degree of intra/inter-chain segmental interactions – dynamics that mediate a temporally varying degree of reversibly formed association crosslinks within the gel.

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

Oscillating plasma bubbles. III. Internal electron sources and sinks

An internal electron source has been used to neutralize ions injected from an ambient plasma into a spherical grid. The resultant plasma is termed a plasma 'bubble.' When the electron supply from the filament is reduced, the sheath inside the bubble becomes unstable. The plasma potential of the bubble oscillates near but below the ion plasma frequency. Different modes of oscillations have been observed as well as a subharmonic and multiple harmonics. The frequency increases with ion density and decreases with electron density. The peak amplitude occurs for an optimum current and the instability is quenched at large electron densities. The frequency also increases if Langmuir probes inside the bubble draw electrons. Allowing electrons from the ambient plasma to enter, the bubble changes the frequency dependence on grid voltage. It is concluded that the net space charge density in the sheath determines the oscillation frequency. It is suggested that the sheath instability is caused by ion inertia in an oscillating sheath electric field which is created by ion bunching.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Oscillating plasma bubbles. IV. Grids, geometry, and gradients

Plasma bubbles are created in an ambient plasma. The bubble is formed inside a cavity bounded by a negatively biased grid. Ions are injected through the grid and neutralized by electrons from either the background plasma or an internal electron emitter. The external electron supply is controlled by the grid bias relative to the external plasma potential. When the electron flux is restricted to the ion flux, the sheath of the bubble becomes unstable and causes the plasma potential to oscillate near the ion plasma frequency. The exact frequency depends on the net space charge density in the bubble sheath. The frequency increases with density and grid voltage, provided the grid forms a parallel equipotential surface. The present investigation shows that when the Debye length becomes smaller than the grid openings the electron flux cannot be controlled by the grid voltage. The frequency dependence on grid voltage and density is modified creating frequency and amplitude jumps. Low frequency sheath oscillations modulate the high frequency normal oscillations. Harmonics and subharmonics are excited by electrons in an ion-rich sheath. When the plasma parameters vary over the bubble surface, the sheath may oscillate at different frequencies. A cavity with two isolated grids has been used to investigate anisotropies of the energetic electron flux in a discharge plasma. The frequency dependence on grid voltage is entirely different when the grid controls the energetic electrons or the bulk electrons. These observations are important to several fields of basic plasma physics, such as sheaths, sheath instabilities, diagnostic probes, current, and space charge neutralization of ion beams.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Theoretical analysis of conditions for observation of plasma oscillations in semiconductors from pulsed terahertz emission

Oscillations of electron-hole plasma generated by femtosecond optical pulse in freestanding semiconductor are studied using hydrodynamic model and Monte Carlo simulations. The conditions required for the observation of coherent plasma oscillations in THz emission from semiconductor are determined. It is shown that several conditions have to be fulfilled in order to observe coherent plasma oscillations. First, the intensity of the optical pulse must exceed some threshold value. Second, the optical absorption depth must exceed the thickness of the built-in electric field region. Third, the generation of electron-hole pairs with uniform illumination is required, i.e., the laser beam with the flattop intensity profile has to be used. It is found that the duration of the optical pulse does not play a vital role in the development of plasma oscillations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Thickness dependent quantum oscillations of transport properties in topological insulator Bi{sub 2}Te{sub 3} thin films

The dependences of the electrical conductivity, the Hall coefficient, and the Seebeck coefficient on the layer thickness d (d = 18−600 nm) of p-type topological insulator Bi{sub 2}Te{sub 3} thin films grown by thermal evaporation in vacuum on glass substrates were obtained at room temperature. In the thickness range of d = 18–100 nm, sustained oscillations with a substantial amplitude were revealed. The observed oscillations are well approximated by a harmonic function with a period Δd = (9.5 ± 0.5) nm. At d > 100 nm, the transport coefficients practically do not change as d is increased. The oscillations of the kinetic properties are attributed to the quantum size effects due to the hole confinement in the Bi{sub 2}Te{sub 3} quantum wells. The results of the theoretical calculations of Δd within the framework of a model of an infinitely deep potential well are in good agreement with the experimental results. It is suggested that the substantial amplitude of the oscillations and their sustained character as a function of d are connected with the topologically protected gapless surface states of Bi{sub 2}Te{sub 3} and are inherent to topological insulators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Stability of entrainment of a continuum of coupled oscillators

Complex natural and engineered systems are ubiquitous, and their behavior is challenging to characterize and control. Here, we examine the design of the entrainment process for an uncountably infinite collection of coupled phase oscillators that are all subject to the same periodic driving signal. In the absence of coupling, an appropriately designed input can result in each oscillator attaining the frequency of the driving signal, with a phase offset determined by its natural frequency. We also consider a special case of interacting oscillators in which the coupling tends to destabilize the phase configuration to which the driving signal would send the collection in the absence of coupling. In this setting, we derive stability results that characterize the trade-off between the effects of driving and coupling, and compare these results to the well-known Kuramoto model of a collection of free-running coupled oscillators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Sawtooth oscillation behavior with varying amounts of applied stellarator rotational transform.

In this study, tokamak-like sawtooth oscillations are observed in the Compact Toroidal Hybrid (CTH), a current-carrying stellarator. CTH has the unique ability to change the amount of the applied vacuum rotational transform from external stellarator coils relative to the rotational transform generated by the internal plasma current to investigate the effects of strong three-dimensional magnetic shaping on sawtooth behavior. The observed sawteeth in CTH, for plasmas with monotonically decreasing rotational transform profiles dominated by the plasma current, have characteristics of those observed on tokamaks including (1) a central emissivity rise and then a sudden crash with a well-defined inversion radius, (2) the presence of an m = 1 emissivity fluctuation, and (3) the normalized inversion surface radius scales with the total edge rotational transform. We explore the properties of an ensemble of discharges in CTH in which the fractional rotational transform, defined as the vacuum rotational transform divided by the total rotational transform, is systematically varied from 0.04 to 0.42 to observe changes in sawtooth oscillation dynamics. Over this range of the fractional rotational transform, the measured sawtooth period decreased by a factor of two. At a high fractional rotational transform, the sawtooth amplitude is observed to consist of only low-amplitude oscillations while the measured crash time of the sawtooth oscillation does not appear to have a strong dependence on the amount of the fractional transform applied. Lastly, experimental results indicate that the low-amplitude sawteeth are accompanied by a decrease in the sawtooth period and predominantly correlated with the mean elongation (due to the increasing fractional rotational transform) of the non-axisymmetric plasmas within CTH rather than other global equilibrium parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Illumination-induced modulation of conductivity and Gunn oscillation properties in epitaxial GaAs

In this work, we illuminate a gallium arsenide (GaAs) Gunn device and study the light-induced changes of Gunn oscillation properties. We observe that illumination leads to the modulation of the Gunn threshold voltage, the Gunn oscillation magnitude, and the coherency of Gunn oscillation, with the nature of the modulation being closely related to the position of illumination on the device. These effects are attributed to the generation of optically excited carriers, which results in the modulation of conductivity and the electric field profile along the device. The finite element method is used to simulate the change of the field profile of the Gunn device caused by illumination. We also report an unexpected phenomenon of Gunn oscillation property manipulation with an optical chopper. In addition, wavelength-dependent, power-dependent, and pulsed illumination measurements are performed to help with further understanding the observations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

A driven Kerr oscillator with two-fold degeneracies for qubit protection

We present the experimental finding of multiple simultaneous two-fold degeneracies in the spectrum of a Kerr oscillator subjected to a squeezing drive. This squeezing drive resulting from a three-wave mixing process, in combination with the Kerr interaction, creates an effective static two-well potential in the phase space rotating at half the frequency of the sinusoidal drive generating the squeezing. Remarkably, these degeneracies can be turned on-and-off on demand, as well as their number by simply adjusting the frequency of the squeezing drive. We find that when the detuning Δ between the frequency of the oscillator and the second subharmonic of the drive equals an even multiple of the Kerr coefficient K , Δ / K = 2 m , the oscillator displays m + 1 exact, parity-protected, spectral degeneracies, insensitive to the drive amplitude. These degeneracies can be explained by the unusual destructive interference of tunnel paths in the classically forbidden region of the double well static effective potential that models our experiment. Exploiting this interference, we measure a peaked enhancement of the incoherent well-switching lifetime, thus creating a protected cat qubit in the ground state manifold of our oscillator. Our results illustrate the relationship between degeneracies and noise protection in a driven quantum system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

THE EFFECTS OF LINE-OF-SIGHT INTEGRATION ON MULTISTRAND CORONAL LOOP OSCILLATIONS

Observations have shown that transverse oscillations are present in a multitude of coronal structures. It is generally assumed that these oscillations are driven by (sub)surface footpoint motions. Using fully three-dimensional MHD simulations, we show that these footpoint perturbations generate propagating kink (Alfvenic) modes which couple very efficiently into (azimuthal) Alfven waves. Using an ensemble of randomly distributed loops, driven by footpoint motions with random periods and directions, we compare the absolute energy in the numerical domain with the energy that is 'visible' when integrating along the line of sight (LOS). We show that the kinetic energy derived from the LOS Doppler velocities is only a small fraction of the actual energy provided by the footpoint motions. Additionally, the superposition of loop structures along the LOS makes it nearly impossible to identify which structure the observed oscillations are actually associated with and could impact the identification of the mode of oscillation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Monte Carlo uncertainty estimation for an oscillating-vessel viscosity measurement

This paper discusses the initial design and evaluation of a high temperature viscosity measurement system with the focus on the uncertainty assessment. Numerical simulation of the viscometer is used to estimate viscosity uncertainties through the Monte Carlo method. The simulation computes the system response for a particular set of inputs (viscosity, moment of inertia, spring constant and hysteretic damping), and the viscosity is calculated using two methods: the Roscoe approximate solution and a numerical-fit method. For numerical fitting, a residual function of the logarithmic decay of oscillation amplitude and oscillation period is developed to replace the residual function of angular oscillation, which is mathematically stiff. The results of this study indicate that the method using computational solution of the equations and fitting for the parameters should be used, since it almost always out-performs the Roscoe approximation in uncertainty. The hysteretic damping and spring stiffness uncertainties translate into viscosity uncertainties almost directly, whereas the moment of inertial and vessel-height uncertainties are magnified approximately two-fold. As the hysteretic damping increases, so does the magnification of its uncertainty, therefore it should be minimized in the system design. The result of this study provides a general guide for the design and application of all oscillation-vessel viscosity measurement systems.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2025

Global optimization of harmonic oscillator basis in covariant density functional theory

The present investigation focuses on the improvement of the accuracy of the description of binding energies within moderately sized fermionic basis. Using the solutions corresponding to infinite fermionic basis it was shown that in the case of meson exchange (ME) covariant energy density functionals (CEDFs) the global accuracy of the description of binding energies in the finite $N_F$ = 16 - 20 bases can be drastically (by a factor ranging from ~3 up to ~9 dependent on the functional and $N_F$) improved by a global optimization of oscillator frequency of the basis. This is a consequence of the unique feature of the ME functionals in which with increasing fermionic basis size fermionic and mesonic energies approach the exact (infinite basis) solution from above and below, respectively. As a consequence, an optimal oscillator frequency $\hbar\omega_0$ of the basis can be defined which provides an accurate reproduction of exact total binding energies by the ones calculated in truncated basis. This leads to a very high accuracy of the calculations in moderately sized $N_F=20$ basis when mass dependent oscillator frequency is used: global rms differences $\delta B_{rms}$ between the binding energies calculated in infinite and truncated bases are only 0.025 MeV and 0.031 MeV for the NL5(Z) and DD-MEZ functionals, respectively. Optimized values of the oscillator frequency $\hbar\omega_0$ are provided for three major classes of CEDFs, i.e. for density dependent meson exchange functionals, nonlinear meson exchange ones and point coupling functionals.

Binding energy & masses↗
DOE OSTI2026

Constraints on the polarization angle oscillations of the Crab Nebula with the Simons Array and its applications to the search for axionlike particles

Here, we present a search for polarization oscillation of the Crab Nebula, also known as Tau A, at millimeter wavelengths using observations with the Simons Array, the successor experiment to POLARBEAR. We follow up on previous work by POLARBEAR using 90 GHz band data of the 2023 observing season of the Simons Array to evaluate the variability of Tau A’s polarization angle. Tau A is widely used as a polarization angle calibration source in millimeter-wave astronomy, and thus it is necessary to validate the stability. Additionally, an interesting application of the time-resolved polarimetry of Tau A is to search for axionlike particles (ALPs). We do not detect a global signal across the frequencies considered in this analysis and place a median 95% upper bound of polarization oscillation amplitude A < 0.12° over oscillation frequencies from 3.39 yr -1 to 1.50 day -1 . This constrains the ALP-photon coupling at a median 95% upper bound of g aγγ < 3.84 × 10 -12 × (m a /10 -21 eV) in the mass range from 4.4 × 10 -22 to 7.2 × 10 -20 eV, assuming the ALP constitutes all of dark matter, its field is a stochastic Gaussian field, and it is the sole source of Tau A’s polarization angle oscillation. Additionally, we do not detect signal at the frequencies where 2.5σ hints were previously reported by POLARBEAR, but we do not exclude these signals at the 95% confidence level.

Adkins, Tylor [University of California, Berkeley]↗
DOE OSTI2020

Symmetric Bloch oscillations of matter waves

Cold atoms in an optical lattice provide an ideal platform for studying Bloch oscillations. Here we extend Bloch oscillations to two superposed optical lattices that are accelerated away from one another, and show that these symmetric Bloch oscillations can split, reflect, and recombine matter waves coherently. Using the momentum parity symmetry of the Hamiltonian, we map out the energy band structure of the process and show that superpositions of momentum states are created by adiabatically following the ground state of the Hamiltonian. The relative phase and velocity of the two lattices completely determines the trajectories of different branches of the matter wave. Experimentally we demonstrate symmetric Bloch oscillations using cold cesium atoms where we form interferometers with up to 240ℏk momentum splitting, one of the largest coherent momentum splittings achieved to date. This work has applications in macroscopic tests of quantum mechanics, measurements of fundamental constants, and searches for new physics.

36 MATERIALS SCIENCE↗