Results for “mode shift” — Page 49

NASA NTRS1987

Active control of flexural vibrations in beams

The feasibility of using piezoelectric actuators to control the flexural oscillations of large structures in space is investigated. Flexural oscillations are excited by impulsive loads. The vibratory response can degrade the pointing accuracy of cameras and antennae, and can cause high stresses at structural node points. Piezoelectric actuators have the advantage of exerting localized bending moments. In this way, vibration is controlled without exciting rigid body modes. The actuators are used in collocated sensor/driver pairs to form a feedback control system. The sensor produces a voltage that is proportional to the dynamic stress at the sensor location, and the driver produces a force that is proportional to the voltage applied to it. The analog control system amplifies and phase shifts the sensor signal to produce the voltage signal that is applied to the driver. The feedback control is demonstrated to increase the first mode damping in a cantilever beam by up to 100 percent, depending on the amplifier gain. The damping efficiency of the control system when the piezoelectrics are not optimally positioned at points of high stress in the beam is evaluated.

Gerhold, Carl H.↗

DOE OSTI2019

Observation of a beam-driven low-frequency mode in Heliotron J

A low-frequency electromagnetic mode (LF-mode) has been observed in a stellarator/heliotron device, Heliotron J. The LF-mode is observed only in neutral beam heated plasmas with a co-current, which increases the rotational transform. The observed LF-mode peaks at rho = 0.86–0.91, where rho = r/a is the normalized minor radius. The LF-mode propagates in the ion diamagnetic drift direction, and the poloidal mode number is m ~ 6–8, determined with a combination of Mirnov coil arrays and 2D fast camera measurement. A high m number induces significant Doppler shift from the background ion flow. The frequency is corrected with both E × B rotation and the ion diamagnetic flow. The corrected frequency is almost consistent with the beta-induced Alfvén eigenmode gap evaluated with the STELLGAP code, although very close to the accumulation point. The mode could also be a global Alfvén eigenmode.

BAE↗

DOE OSTI2023

Evolution of the Internal Climate Modes under Future Warming

Abstract Climate modes play an important role in weather and climate variability over multiple spatial and temporal scales. This research assesses Earth system model (ESM) projections of the spatiotemporal characteristics of key internal climate modes (NAM, SAM, PNA, ENSO, PDO, and AMO) under high (SSP585) and low (SSP126) radiative forcing scenarios and contextualizes those projections using historical fidelity. Time series analyses are used to assess trends and mode phase characteristics are summarized for the historical period and for the end of the twenty-first century. Spatial patterns are compared to infer morphological changes. Shifts in the power spectra are used to examine changes in variability at subannual, interannual, and interdecadal scales. Changes in time-lagged correlations are used to capture the evolution of first-order interactions. While differences in historical skill are predominantly ESM dependent, changing mode characteristics in a warmer climate also exhibit variability between individual ensemble realizations. NAM, SAM, and ENSO tend to evolve toward increased prevalence of the positive phase up to 2100 across the multimodel ensemble while the PNA and PDO exhibit little trend but increasing phase intensity. AMO characteristics are shown to depend on the method used to remove the external signal. ESMs that show higher historical fidelity tend to show more modest changes in those modes under global nonstationarity. Changes in mode interactions are found to be highly ESM dependent but exhibit broadly similar behavior to historical relationships. These findings have implications for our understanding of internal variability and make clear that the choice of ESM, and even the ESM realization, matters for applications of climate projections. Significance Statement Internal modes of variability are important to understand due to their impact on local, regional, and global weather and climate patterns. Future climate changes will not only be affected by the variability arising from these modes, but the modes will themselves change in response to the changing climate. Spatial and temporal aspects of the modes are assessed from projections of future climate and related to how well they are captured in the historical climate. This yields some measure of confidence in the changes exhibited by the models. In most cases, when historically skillful models exhibit changes that are different from those produced by less skillful models, they tend to produce more modest changes. These results, as well as the variability between model outcomes, mean decisions on which ESM to use for projections of the future climate matter significantly.

Meteorology & Atmospheric Sciences↗

DOE OSTI2018

Structural basis for the interaction between DJ-1 and Bcl-XL

Highlights: • Oxidized, but not reduced, DJ-1 interacts with Bcl-X{sub L}. • C-terminal α8-helix of DJ-1 acts as a binding motif for Bcl-X{sub L}. • C-terminal α8-helix of DJ-1 binds to the BH3 peptide-binding groove in Bcl-X{sub L}. • A conserved binding mode of the Bcl-X{sub L}/DJ-1 and other Bcl-X{sub L}/BH3 peptide complexes. • Understanding of structural basis for the binding between DJ-1 and Bcl-X{sub L}. DJ-1 is a multifunctional protein associated with Parkinson's disease (PD) and tumorigenesis. In response to ultraviolet B (UVB) irradiation, DJ-1 is translocated into the mitochondria, and its interaction with the mitochondrial protein Bcl-X{sub L} protects cells against death. In this study, we characterized the molecular interaction between DJ-1 and Bcl-X{sub L} by NMR spectroscopy. The NMR chemical shift perturbation data demonstrated that the oxidized but not the reduced form of DJ-1 binds to the predominantly hydrophobic groove surrounded by the BH1–BH3 domains in Bcl-X{sub L}. In addition, our results showed that the C-terminal α8-helix peptide (Cpep) of DJ-1 binds to the pro-apoptotic BH3 peptide-binding hydrophobic groove in Bcl-X{sub L} and, thus, acts as a Bcl-X{sub L}-binding motif. In combination with the NMR chemical shift perturbation data, a refined structural model of the Bcl-X{sub L}/DJ-1 Cpep complex revealed that the binding mode is remarkably similar to that of other Bcl-X{sub L}/pro-apoptotic BH3 peptide complexes. Taken together, our results provide a structural basis for the binding mechanism between DJ-1 and Bcl-X{sub L}, which will contribute to molecular understanding of the role of mitochondrial DJ-1 in Bcl-X{sub L} regulation in response to oxidative stress.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2021

Comments on the quantum field theory of the Coulomb gas formalism

The holomorphic Coulomb gas formalism, as developed by Feigin-Fuchs, Dotsenko-Fateev and Felder, is a set of rules for computing minimal model observables using free field techniques. We attempt to derive and clarify these rules using standard techniques of quantum field theory. We begin with a careful examination of the timelike linear dilaton. Although the background charge of the model breaks the scalar field’s continuous shift symmetry, the exponential of the action remains invariant under a discrete shift because the background charge is imaginary. Gauging this symmetry makes the dilaton compact and introduces winding modes into the spectrum. One of these winding operators corresponds to the anti-holomorphic completion of the BRST current first introduced by Felder, and the full left/right cohomology of this BRST charge isolates the irreducible representations of the Virasoro algebra within the degenerate Fock space of the linear dilaton. The “supertrace” in the BRST complex reproduces the minimal model partition function and exhibits delicate cancellations between states with both momentum and winding. The model at the radius $R=\sqrt{pp^{\prime }}$ has two marginal operators corresponding to the Dotsenko-Fateev “screening charges”. Deforming by them, we obtain a model that might be called a “BRST quotiented compact timelike Liouville theory”. The Hamiltonian of the zero-mode quantum mechanics of this model is not Hermitian, but it is PT -symmetric and exactly solvable. Its eigenfunctions have support on an infinite number of plane waves, suggesting an infinite reduction in the number of independent states in the full quantum field theory. Applying conformal perturbation theory to the exponential interactions reproduces the Coulomb gas calculations of minimal model correlation functions. In contrast to spacelike Liouville, these “resonance correlators” are finite because the zero mode is compact. We comment on subtleties regarding the reflection operator identification, as well as naive violations of truncation in correlators with multiple reflection operators inserted. This work is part of an attempt to understand the relationship between the JT model of two dimen- sional gravity and the worldsheet description of the (2 , p ) minimal string as suggested by Seiberg and Stanford.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Electrospray Generated from the Tip-Sealed Fine Glass Capillary Inserted with an Acupuncture Needle Electrode

In electrospray, excess charges are supplied to a sample solution by the occurrence of electrochemical reactions. Recently, different versions of electrospray, e.g., dielectric barrier electrospray ionization, inductive desorption electrospray ionization, and electrostatic-ionization driven by dielectric polarization, have been reported in which the sample solution was not in direct contact with the metal electrode but separated by dielectric materials. The objective of the current work is to elucidate the mechanism of dielectric barrier electrospray. A sealed borosilicate glass capillary inserted with a fine acupuncture needle was used as a probe. A sample solution (~ 400 nL) was captured on the glass capillary tip and a positive high voltage (HV) pulse (+ 4.5 kV) was applied to the internal metal electrode. Mass spectra were measured as a function of the HV pulse width from μs to 10 s. Ions started to be detected with the pulse width of ~ 5 ms. The ion intensities increased slowly with time and reached a plateau in a few seconds. The charge distribution of cytochrome c [M + nH]{sup n+} shifted to higher n values from a few ms to seconds. In addition to cone-jet mode normal electrospray that lasted until all the liquid sample was depleted from the glass tip, the polarization-induced electrospray ionization was observed at the early stage of the HV application. .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Nanoscale imaging of phonon dynamics by electron microscopy

Spatially resolved vibrational mapping of nanostructures is indispensable to the development and understanding of thermal nanodevices, modulation of thermal transport and novel nanostructured thermoelectric materials. Through the engineering of complex structures, such as alloys, nanostructures and superlattice interfaces, one can significantly alter the propagation of phonons and suppress material thermal conductivity while maintaining electrical conductivity. There have been no correlative experiments that spatially track the modulation of phonon properties in and around nanostructures due to spatial resolution limitations of conventional optical phonon detection techniques. Here we demonstrate two-dimensional spatial mapping of phonons in a single silicon–germanium (SiGe) quantum dot (QD) using monochromated electron energy loss spectroscopy in the transmission electron microscope. Tracking the variation of the Si optical mode in and around the QD, we observe the nanoscale modification of the composition-induced red shift. We observe non-equilibrium phonons that only exist near the interface and, furthermore, develop a novel technique to differentially map phonon momenta, providing direct evidence that the interplay between diffuse and specular reflection largely depends on the detailed atomistic structure: a major advancement in the field. Our work unveils the non-equilibrium phonon dynamics at nanoscale interfaces and can be used to study actual nanodevices and aid in the understanding of heat dissipation near nanoscale hotspots, which is crucial for future high-performance nanoelectronics.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Spatially quasi-periodic water waves of finite depth

We present a numerical study of spatially quasi-periodic gravity-capillary waves of finite depth in both the initial value problem and travelling wave settings. We adopt a quasi-periodic conformal mapping formulation of the Euler equations, where one-dimensional quasi-periodic functions are represented by periodic functions on a higher-dimensional torus. We compute the time evolution of free surface waves in the presence of a background flow and a quasi-periodic bottom boundary and observe the formation of quasi-periodic patterns on the free surface. Two types of quasi-periodic travelling waves are computed: small-amplitude waves bifurcating from the zero-amplitude solution and larger-amplitude waves bifurcating from finite-amplitude periodic travelling waves. We derive weakly nonlinear approximations of the first type and investigate the associated small-divisor problem. We find that waves of the second type exhibit striking nonlinear behaviour, e.g. the peaks and troughs are shifted non-periodically from the corresponding periodic waves due to the activation of quasi-periodic modes.

Science & Technology - Other Topics↗

DOE OSTI2018

Photoluminescence and gain/absorption spectra of a driven-dissipative electron-hole-photon condensate

Here, we investigate theoretically nonequilibrium effects on photoluminescence and gain/absorption spectra of a driven-dissipative exciton-polariton condensate, by employing the combined Hartree-Fock-Bogoliubov theory with the generalized random phase approximation extended to the Keldysh formalism. Our calculated photoluminescence spectra is in semiquantitative agreement with experiments, where features such as a blue shift of the emission from the condensate, the appearance of the dispersionless feature of a diffusive Goldstone mode, and the suppression of the dispersive profile of the mode are obtained. We show that the nonequilibrium nature of the exciton-polariton condensate strongly suppresses the visibility of the Bogoliubov dispersion in the negative energy branch (ghost branch) in photoluminescence spectra. We also show that the trace of this branch can be captured as a hole burning effect in gain/absorption spectra. Our results indicate that the nonequilibrium nature of the exciton-polariton condensate strongly reduces quantum depletion, while a scattering channel to the ghost branch is still present.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2020

Two-component dynamics and the liquid-like to gas-like crossover in supercritical water

Molecular-scale dynamics in sub- to super-critical water is studied with inelastic X-ray scattering and molecular dynamics simulations. The obtained longitudinal current correlation spectra can be decomposed into two main components: a low-frequency (LF), gas-like component and a high-frequency (HF) component arising from the O--O stretching mode between hydrogen-bonded molecules, reminiscent of the longitudinal acoustic mode in ambient water. With increasing temperature, the hydrogen-bond network diminishes and the spectral weight shifts from HF to LF, leading to a transition from liquid-like to gas-like dynamics with rapid changes around the Widom line.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Magnetic Control of Soft Chiral Phonons in PbTe

We report PbTe crystals have a soft transverse optical phonon mode in the terahertz frequency range, which is known to efficiently decay into heat-carrying acoustic phonons, resulting in anomalously low thermal conductivity. Here, we studied this phonon via polarization-dependent terahertz spectroscopy. We observed softening of this mode with decreasing temperature, indicative of incipient ferroelectricity, which we explain through a model including strong anharmonicity with a quartic displacement term. In magnetic fields up to 25 T, the phonon mode splits into two modes with opposite handedness, exhibiting circular dichroism. Their frequencies display Zeeman splitting together with an overall diamagnetic shift with increasing magnetic field. Using a group-theoretical approach, we demonstrate that these observations are the result of magnetic field-induced morphic changes in the crystal symmetries through the Lorentz force exerted on the lattice ions. Thus, our Letter reveals a novel process of controlling phonon properties in a soft ionic lattice by a strong magnetic field.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Coupling an Ensemble of Electrons on Superfluid Helium to a Superconducting Circuit

Not Available

Yang, Ge↗

DOE OSTI2016

Multifunctional cement for geothermal wells

This report compiles the work of BNL in support of Thermal Shock Resistant Cement evaluations (TSRC) by Schlumberger. BNL has worked on the formulation of thermal-shock resistant cement since 2011. All the materials on the blend including publications and presentations are in public domain and were sent to Schlumberger for review prior the beginning of the evaluations. Initial efforts focused on achieving long and controlled thickening time of TSRC at 85°C in thickening time tests in a pressurized consistometer. Since the results of BNL set control were not reproduced by Schlumberger technical feedback on Schlumberger testing was among the main efforts of the BNL team in the beginning of the collaboration. When it became clear that the main reason of results deviation was the difference in the mode of retarder addition (dry-blended at BNL and pre-dissolved at Schlumberger) the efforts shifted to the possible decrease in the cost of the formulation by changing concentrations and nature of the alkali activator as well as evaluating performance of more economical formulations with calcium-aluminate cement, Secar #51, Secar #71 and Ciment Fondu, suggested by Schlumberger based on communications with Kerneos (supplier of calcium aluminate cements). Another piece of information obtained by Schlumberger from Kerneos that prompted evaluations of different calcium-aluminate cements in the composition of TSRC was the fact that originally used Secar#80 contains some performance-improving additives that may interfere with the set control and rheological properties of the slurries. In summary, the report contains the following information: 1. Review of the setting behavior of TSRC slurries prepared by dry-blending TA powder or pre dissolving it in mix water in calorimetric tests at 85°C; 2. Results of evaluation of different alkali activators for improved compressive strength development and cost reduction; 3. Results of evaluation of Secar #51, 71 and cement Fondu as an alternative to Secar #80 in TSRC formulation – thermal shock tests and phases’ analyses of set cement; 4. A brief discussion of early-compressive-strength-development test conditions appropriate for geothermal wells.

15 GEOTHERMAL ENERGY↗

DOE OSTI2018

Multifunctional Cement for Geothermal Wells

This report compiles the work of BNL in support of Thermal Shock Resistant Cement evaluations (TSRC) by Schlumberger. BNL has worked on the formulation of thermal-shock resistant cement since 2011. All the materials on the blend including publications and presentations are in public domain and were sent to Schlumberger for review prior the beginning of the evaluations. Initial efforts focused on achieving long and controlled thickening time of TSRC at 85°C in thickening time tests in a pressurized consistometer. Since the results of BNL set control were not reproduced by Schlumberger technical feedback on Schlumberger testing was among the main efforts of the BNL team in the beginning of the collaboration. When it became clear that the main reason of results deviation was the difference in the mode of retarder addition (dry-blended at BNL and pre-dissolved at Schlumberger) the efforts shifted to the possible decrease in the cost of the formulation by changing concentrations and nature of the alkali activator as well as evaluating performance of more economical formulations with calcium-aluminate cement, Secar #51, Secar #71 and Ciment Fondu, suggested by Schlumberger based on communications with Kerneos (supplier of calcium aluminate cements). Another piece of information obtained by Schlumberger from Kerneos that prompted evaluations of different calcium-aluminate cements in the composition of TSRC was the fact that originally used Secar#80 contains some performance-improving additives that may interfere with the set control and rheological properties of the slurries. In summary, the report contains the following information: 1. Review of the setting behavior of TSRC slurries prepared by dry-blending TA powder or pre dissolving it in mix water in calorimetric tests at 85°C; 2. Results of evaluation of different alkali activators for improved compressive strength development and cost reduction; 3. Results of evaluation of Secar #51, 71 and cement Fondu as an alternative to Secar #80 in TSRC formulation – thermal shock tests and phases’ analyses of set cement; 4. A brief discussion of early-compressive-strength-development test conditions appropriate for geothermal wells.

36 MATERIALS SCIENCE↗

NASA NTRS1971

Vibration testing and analysis using holography

Time average holography is useful in recording steady state vibrational mode patterns. Phase relationships under steady state conditions are measured with real time holography and special phase shifting techniques. Data from Michelson interferometer verify vibration amplitudes from holographic data.

Source record↗

NASA NTRS1983

Simultaneous multiple-point velocity measurements using laser-induced iodine fluorescence

A technique is demonstrated for measuring velocity at multiple locations in a plane of a gaseous flowfield using Doppler-shifted absorption with fluorescence detection from iodine molecules, excited by a sheet of tunable single-axial-mode argon-ion laser radiation at 514.5 nm. Measurements were made simultaneously at 10,000 points in an iodine-seeded supersonic flow field with a 100 x 100 element photodiode array camera and were found to agree well with a numerical solution for the velocity field. The accuracy with which a component of velocity can be measured is limited, in the current approach, by the iodine linewidth to about 5 m/sec.

Mcdaniel, J. C.↗

NASA NTRS1989

The 5-kW arcjet power electronics

The initial design and evaluation of a 5 kW arcjet power electronics breadboard which as been integrated with a modified 1 kW design laboratory arcjet is presented. A single stage, 5 kW full bridge, pulse width modulated (PWM), power converter was developed which was phase shift regulated. The converter used metal oxide semiconductor field effect transistor (MOSFET) power switches and incorporated current mode control and an integral arcjet pulse ignition circuit. The unoptimized power efficiency was 93.5 and 93.9 percent at 5 kW and 50A output at input voltages of 130 and 150V, respectively. Line and load current regulation at 50A output was within one percent. The converter provided up to 6.6 kW to the arcjet with simulated ammonia used as a propellant.

Gruber, R. P.↗

NASA NTRS1989

5-kW arcjet power electronics

The initial design and evaluation of a 5 kW arcjet power electronics breadboard which as been integrated with a modified 1 kW design laboratory arcjet is presented. A single stage, 5 kW full bridge, pulse width modulated (PWM), power converter was developed which was phase shift regulated. The converter used metal oxide semiconductor field effect transistor (MOSFET) power switches and incorporated current mode control and an integral arcjet pulse ignition circuit. The unoptimized power efficiency was 93.5 and 93.9 percent at 5 kW and 50A output at input voltages of 130 and 150V, respectively. Line and load current regulation at 50A output was within one percent. The converter provided up to 6.6 kW to the arcjet with simulated ammonia used as a propellant.

Gruber, R. P.↗