Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Interference”

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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Magneto-optical measurement of magnetic field and electrical current on a short pulse high energy pulsed power accelerator

We describe a direct magneto-optical approach to measuring the magnetic field driven by a narrow pulse width (<10 ns), 20 kA electrical current flow in the transmission line of a high energy pulsed power accelerator. The magnetic field and electrical current are among the most important operating parameters in a pulsed power accelerator and are critical to understanding the properties of the radiation output. However, accurately measuring these fields and electrical currents using conventional pulsed power diagnostics is difficult due to the strength of ionizing radiation and electromagnetic interference. Our approach uses a fiber coupled laser beam with a rare earth element sensing crystal sensor that is highly resistant to electromagnetic interference and does not require external calibration. Here, we focus on device theory, operating parameters, results from an experiment on a high energy pulsed power accelerator, and comparison to a conventional electrical current shunt sensor.

42 ENGINEERING↗
DOE OSTI2012

Femtosecond laser pulse filamentation under anomalous dispersion in fused silica. Part 2. Experiment and physical interpretation

We have studied experimentally and analytically the formation of the supercontinuum (SC) spectrum during femtosecond laser pulse filamentation in fused silica under conditions of zero and anomalous group velocity dispersions. It is found that with increasing centre wavelength from 1300 to 2300 nm, the SC spectrum of the anti-Stokes wing narrows, shifting to the blue. It is shown that the anti-Stokes (blue) shift of the SC spectrum increases with the multiphoton order of the medium ionisation by the light field in the filament. It is found that a broad minimum in the SC spectrum, separating the anti-Stokes wing from the centre wavelength, is a result of the interference of radiation from a moving broadband source, stemming from self-phase modulation of the high-intensity light field. The interference factors of the SC spectra obtained for this source, which moves along the emitting region of the filament in a dispersive medium, are in agreement with experimental and numerical results. (nonlinear optical phenomena)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

On the possibility of an experiment on 'nonlocality' of electrodynamics

It has been known since the 19th century that a circularly polarised electromagnetic wave carries an angular momentum. A simple experiment (Righi, 1882) apparently indicates that the angular momentum is distributed over the entire cross section of the beam. According to some modern ideas, the angular momentum of the beam with the given polarisation is localised near the beam 'surface' and represents a spin of photons, while the energy in the beam is distributed throughout its cross section, which is inconsistent with the principle of locality. For the experimental determination of the localisation of the angular momentum, we propose a new scheme, in which we study the interference pattern of two coherent circularly polarised beams. Each beam first passes through a half-wave plate, one of the plates being divided into two coaxial parts. With (manual) rotation of one parts of the plate we change the frequency of the light passing through it: the plate absorbs the momentum and, therefore, work is done. This change in frequency should cause a movement of the interference fringes and show the distribution of the angular momentum over the beam cross section. (light polarisation)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Reflection of a TE-polarised Gaussian beam from a layered structure under conditions of resonance excitation of waveguide modes

The problem of reflection of a TE-polarised Gaussian light beam from a layered structure under conditions of resonance excitation of waveguide modes using a total internal reflection prism is considered. Using the spectral approach we have derived the analytic expressions for the mode propagation lengths, widths and depths of m-lines (sharp and narrow dips in the angular dependence of the specular reflection coefficient), depending on the structure parameters. It is shown that in the case of weak coupling, when the propagation lengths l{sub m} of the waveguide modes are mainly determined by the extinction coefficient in the film, the depth of m-lines grows with the mode number m. In the case of strong coupling, when l{sub m} is determined mainly by the radiation of modes into the prism, the depth of m-lines decreases with increasing m. The change in the TE-polarised Gaussian beam shape after its reflection from the layered structure is studied, which is determined by the energy transfer from the incident beam into waveguide modes that propagate along the structure by the distance l{sub m}, are radiated in the direction of specular reflection and interfere with a part of the beam reflected from the working face of the prism. It is shown that this interference can lead to the field intensity oscillations near m-lines. The analysis of different methods for determining the parameters of thin-film structures is presented, including the measurement of mode angles θ{sub m} and the reflected beam shape. The methods are based on simultaneous excitation of a few waveguide modes in the film with a strongly focused monochromatic Gaussian beam, the waist width of which is much smaller than the propagation length of the modes. As an example of using these methods, the refractive index and the thickness of silicon monoxide film on silica substrate at the wavelength 633 nm are determined. (fibre and integrated-optical structures)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Kinetics of atoms in a bichromatic field formed by elliptically polarised waves

The kinetics of atoms in a bichromatic field formed by waves with an arbitrary elliptical polarisation is considered. Analytical expressions are derived for the force and the friction and diffusion coefficients within the model of an atom with the j {sub g} = 1/2 → j {sub e} = 3/2 optical transition. These expressions are presented in the general form as an expansion in gradients of light field parameters. Some specific features of the kinetics of atoms are found, which are due to the interference contributions to the friction and diffusion coefficients. The kinetics of atoms in the field of an optical lattice formed as a result of the interference of a wave with a uniform elliptical polarisation and a nonuniformly polarised dissipative field is analysed. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Peculiarities of electromagnetic field distribution in a finite one-dimensional photonic crystal at oblique incidence of radiation

The effect of increasing an electric field E is investigated for oblique incidence of radiation on a finite one-dimensional photonic crystal. The peculiarities in the field distribution in the structure E(x) are found to be due to the interference of counterpropagating Bloch waves; therefore, the conditions for increasing the field to a maximum value |E|{sub max} coincide with those for achieving the maximum band gap E{sub g} of an infinite crystal. It is shown that a significant (several times for structures with 30 periods) growth of |E|{sub max} is observed with increasing angle of incidence θ for wavelengths λ, which correspond to transmission maxima T nearest to the band gap boundaries. The increased interference of the counterpropagating Bloch modes is caused by an enhancement of the x-component contrast (perpendicular to the planes of the layers) of the wave numbers k{sub 1x}/k{sub 2x} in the structure layers. Along with this, there also arise characteristic features in the distribution of E(x) associated with the vanishing of the forbidden band width. In this case, the field distribution in all periods is the same. Two types of such features are observed in the case of oblique incidence. The former takes place for p-polarisation at an angle of incidence θ, which is an analogue of the Brewster angle. The latter corresponds to the situation when the length of each structure layer is equal to an integer of half-waves. This occurs simultaneously for s- and p-polarisations and is observed in a limited range of layer widths only for the second and highest forbidden bands. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Flat-field VLS spectrometer for a wavelength range of 50 – 275 Å

A flat-field VLS spectrograph for a wavelength range ∼50 – 275 Å with an average linear dispersion of 0.18 mm Å{sup −1}, which makes use of a grazing-incidence varied line-space (VLS) grating, was calculated and implemented (a spectrograph of Harada class). To fabricate the VLS grating by interference lithography technique, an algorithm was developed for calculating the writing configuration with an auxiliary aberrating mirror (the solution of the inverse problem of interference lithography). The spectrograph was put to a test and line spectra were recorded from the laser-produced plasma of lithium fluoride and teflon targets, which were excited by a focused laser beam (0.5 J, 8 ns, 1.06 μm). A resolving power λ/d l = 800 was demonstrated in a wavelength region of 135 Å. (x-ray spectrometry)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Homogeneous broadening in the spectrum of a broadband erbium-doped fibre light source

Interference of wave trains separated out in an inhomogeneous emission spectrum of a superluminescent erbium-doped fibre source has been studied by scanning the wavelength of a spectrum analyser. The results demonstrate that, as the spectral resolution of the spectrum analyser decreases to a level corresponding to a sharp drop in interference fringe visibility relative to its original level, near 100 %, fringe visibility becomes dependent on the wavelength in the inhomogeneous spectrum of the source. The reason for this is that, at some characteristic resolution δλ (δλ > 0.5 nm in our case), the coherence time of wave trains is not limited by the spectral resolution of the spectrum analyser and is related to the inhomogeneous spectrum of the source, whose limiting width can be thought of as the homogeneous linewidth in the spectrum of the source. This feature can be used for evaluating homogeneous line broadening. (paper)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

A Novel Technique Applying Spectral Estimation to Johnson Noise Thermometry

Johnson noise thermometry is one of many important measurement techniques used to monitor the safety levels and stability in a nuclear reactor. However, this measurement is very dependent on the minimal electromagnetic environment. Properly removing unwanted electromagnetic interference (EMI) is critical for accurate drift-free temperature measurements. The two techniques developed by Oak Ridge National Laboratory (ORNL) to remove transient and periodic EMI are briefly discussed here. Spectral estimation is a key component in the signal processing algorithm used for EMI removal and temperature calculation. The cross-power spectral density is a key component in the Johnson noise temperature computation. Applying either technique requires the simple addition of electronics and signal processing to existing resistive thermometers. With minimal installation changes, the system discussed here can be installed on existing nuclear power plants. The Johnson noise system developed is tested at three locations: ORNL, Sandia National Laboratory, and the Tennessee Valley Authority’s Kingston Fossil Plant. Each of these locations enabled improvement on the EMI removal algorithm. Finally, the conclusions made from the results at each of these locations is discussed, as well as possible future work.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2012

ALL TRANSIENTS, ALL THE TIME: REAL-TIME RADIO TRANSIENT DETECTION WITH INTERFEROMETRIC CLOSURE QUANTITIES

We demonstrate a new technique for detecting radio transients based on interferometric closure quantities. The technique uses the bispectrum, the product of visibilities around a closed loop of baselines of an interferometer. The bispectrum is calibration independent, resistant to interference, and computationally efficient, so it can be built into correlators for real-time transient detection. Our technique could find celestial transients anywhere in the field of view and localize them to arcsecond precision. At the Karl G. Jansky Very Large Array (VLA), such a system would have a high survey speed and a 5{sigma} sensitivity of 38 mJy on 10 ms timescales with 1 GHz of bandwidth. The ability to localize dispersed millisecond pulses to arcsecond precision in large volumes of interferometer data has several unique science applications. Localizing individual pulses from Galactic pulsars will help find X-ray counterparts that define their physical properties, while finding host galaxies of extragalactic transients will measure the electron density of the intergalactic medium with a single dispersed pulse. Exoplanets and active stars have distinct millisecond variability that can be used to identify them and probe their magnetospheres. We use millisecond timescale visibilities from the Allen Telescope Array and VLA to show that the bispectrum can detect dispersed pulses and reject local interference. The computational and data efficiency of the bispectrum will help find transients on a range of timescales with next-generation radio interferometers.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Searching for pulsars using image pattern recognition

In the modern era of big data, many fields of astronomy are generating huge volumes of data, the analysis of which can sometimes be the limiting factor in research. Fortunately, computer scientists have developed powerful data-mining techniques that can be applied to various fields. In this paper, we present a novel artificial intelligence (AI) program that identifies pulsars from recent surveys by using image pattern recognition with deep neural nets—the PICS (Pulsar Image-based Classification System) AI. The AI mimics human experts and distinguishes pulsars from noise and interference by looking for patterns from candidate plots. Different from other pulsar selection programs that search for expected patterns, the PICS AI is taught the salient features of different pulsars from a set of human-labeled candidates through machine learning. The training candidates are collected from the Pulsar Arecibo L-band Feed Array (PALFA) survey. The information from each pulsar candidate is synthesized in four diagnostic plots, which consist of image data with up to thousands of pixels. The AI takes these data from each candidate as its input and uses thousands of such candidates to train its ∼9000 neurons. The deep neural networks in this AI system grant it superior ability to recognize various types of pulsars as well as their harmonic signals. The trained AI's performance has been validated with a large set of candidates from a different pulsar survey, the Green Bank North Celestial Cap survey. In this completely independent test, the PICS ranked 264 out of 277 pulsar-related candidates, including all 56 previously known pulsars and 208 of their harmonics, in the top 961 (1%) of 90,008 test candidates, missing only 13 harmonics. The first non-pulsar candidate appears at rank 187, following 45 pulsars and 141 harmonics. In other words, 100% of the pulsars were ranked in the top 1% of all candidates, while 80% were ranked higher than any noise or interference. The performance of this system can be improved over time as more training data are accumulated. This AI system has been integrated into the PALFA survey pipeline and has discovered six new pulsars to date.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Polarized scattering with Paschen-Back effect, hyperfine structure, and partial frequency redistribution in magnetized stellar atmospheres

F-state interference significantly modifies the polarization produced by scattering processes in the solar atmosphere. Its signature in the emergent Stokes spectrum in the absence of magnetic fields is depolarization in the line core. In the present paper, we derive the partial frequency redistribution (PRD) matrix that includes interference between the upper hyperfine structure states of a two-level atom in the presence of magnetic fields of arbitrary strengths. The theory is applied to the Na I D{sub 2} line that is produced by the transition between the lower J = 1/2 and upper J = 3/2 states which split into F states because of the coupling with the nuclear spin I{sub s} = 3/2. The properties of the PRD matrix for the single-scattering case is explored, in particular, the effects of the magnetic field in the Paschen-Back regime and their usefulness as a tool for the diagnostics of solar magnetic fields.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

ISOTROPIC INELASTIC COLLISIONS IN A MULTITERM ATOM WITH HYPERFINE STRUCTURE

A correct modeling of the scattering polarization profiles observed in some spectral lines of diagnostic interest, the sodium doublet being one of the most important examples, requires taking hyperfine structure (HFS) and quantum interference between different J-levels into account. An atomic model suitable for taking these physical ingredients into account is the so-called multiterm atom with HFS. In this work, we introduce and study the transfer and relaxation rates due to isotropic inelastic collisions with electrons, which enter the statistical equilibrium equations (SEE) for the atomic density matrix of this atomic model. Under the hypothesis that the electron–atom interaction is described by a dipolar operator, we provide useful relations between the rates describing the transfer and relaxation of quantum interference between different levels (whose numerical values are in most cases unknown) and the usual rates for the atomic level populations, for which experimental data and/or approximate theoretical expressions are generally available. For the particular case of a two-term atom with HFS, we present an analytical solution of the SEE for the spherical statistical tensors of the upper term, including both radiative and collisional processes, and we derive the expression of the emission coefficient in the four Stokes parameters. Finally, an illustrative application to the Na i D{sub 1} and D{sub 2} lines is presented.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Arecibo pulsar survey using ALFA. IV. Mock spectrometer data analysis, survey sensitivity, and the discovery of 40 pulsars

The on-going Arecibo Pulsar-ALFA (PALFA) survey began in 2004 and is searching for radio pulsars in the Galactic plane at 1.4 GHz. Here we present a comprehensive description of one of its main data reduction pipelines that is based on the PRESTO software and includes new interference-excision algorithms and candidate selection heuristics. This pipeline has been used to discover 40 pulsars, bringing the survey’s discovery total to 144 pulsars. Of the new discoveries, eight are millisecond pulsars (MSPs; P<10 ms) and one is a Fast Radio Burst (FRB). This pipeline has also re-detected 188 previously known pulsars, 60 of them previously discovered by the other PALFA pipelines. We present a novel method for determining the survey sensitivity that accurately takes into account the effects of interference and red noise: we inject synthetic pulsar signals with various parameters into real survey observations and then attempt to recover them with our pipeline. We find that the PALFA survey achieves the sensitivity to MSPs predicted by theoretical models but suffers a degradation for P≳100 ms that gradually becomes up to ∼10 times worse for P>4 s at DM<150 pc cm{sup −3}. We estimate 33 ± 3% of the slower pulsars are missed, largely due to red noise. A population synthesis analysis using the sensitivity limits we measured suggests the PALFA survey should have found 224 ± 16 un-recycled pulsars in the data set analyzed, in agreement with the 241 actually detected. The reduced sensitivity could have implications on estimates of the number of long-period pulsars in the Galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

POLARIZED SCATTERING OF LIGHT FOR ARBITRARY MAGNETIC FIELDS WITH LEVEL-CROSSINGS FROM THE COMBINATION OF HYPERFINE AND FINE STRUCTURE SPLITTINGS

Interference between magnetic substates of the hyperfine structure states belonging to different fine structure states of the same term influences the polarization for some of the diagnostically important lines of the Sun's spectrum, like the sodium and lithium doublets. The polarization signatures of this combined interference contain information on the properties of the solar magnetic fields. Motivated by this, in the present paper, we study the problem of polarized scattering on a two-term atom with hyperfine structure by accounting for the partial redistribution in the photon frequencies arising due to the Doppler motions of the atoms. We consider the scattering atoms to be under the influence of a magnetic field of arbitrary strength and develop a formalism based on the Kramers–Heisenberg approach to calculate the scattering cross section for this process. We explore the rich polarization effects that arise from various level-crossings in the Paschen–Back regime in a single scattering case using the lithium atomic system as a concrete example that is relevant to the Sun.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Statistical sensitivity on right-handed currents in presence of eV scale sterile neutrinos with KATRIN

The KATRIN experiment aims to determine the absolute neutrino mass by measuring the endpoint region of the tritium β-spectrum. As a large-scale experiment with a sharp energy resolution, high source luminosity and low background it may also be capable of testing certain theories of neutrino interactions beyond the standard model (SM). An example of a non-SM interaction are right-handed currents mediated by right-handed W bosons in the left-right symmetric model (LRSM). In this extension of the SM, an additional SU(2){sub R} symmetry in the high-energy limit is introduced, which naturally includes sterile neutrinos and predicts the seesaw mechanism. In tritium β decay, this leads to an additional term from interference between left- and right-handed interactions, which enhances or suppresses certain regions near the endpoint of the beta spectrum. In this work, the sensitivity of KATRIN to right-handed currents is estimated for the scenario of a light sterile neutrino with a mass of some eV. This analysis has been performed with a Bayesian analysis using Markov Chain Monte Carlo (MCMC). The simulations show that, in principle, KATRIN will be able to set sterile neutrino mass-dependent limits on the interference strength. The sensitivity is significantly increased if the Q value of the β decay can be sufficiently constrained. However, the sensitivity is not high enough to improve current upper limits from right-handed W boson searches at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

THE POLARIZATION OF THE SOLAR Mg II h AND k LINES

Although the h and k lines of Mg II are expected to be of great interest for probing the upper solar chromosphere, relatively little is known about their polarization properties which encode the information on the magnetic field. Here we report the first results of an investigation whose main goal is to understand the physical mechanisms that control the scattering polarization across these resonance lines and to achieve a realistic radiative transfer modeling in the presence of arbitrary magnetic fields. We show that the joint action of partial frequency redistribution (PRD) and quantum interference between the upper J-levels of the two lines produces a complex fractional linear polarization (Q/I) pattern with large polarization amplitudes in the blue and red wings, and a negative feature in the spectral region between the two lines. Another remarkable peculiarity of the Q/I profile is a conspicuous antisymmetric signal around the center of the h line, which cannot be obtained unless both PRD and J-state interference effects are taken into account. In the core of the k line, PRD effects alone produce a triplet peak structure in the Q/I profile, the modeling of which can also be achieved via the two-level atom approximation. In addition to the Hanle effect in the core of the k line, we also emphasize the diagnostic potential of the circular polarization produced by the Zeeman effect in the h and k lines, as well as in other Mg II lines located in their wings.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Union: An Automatic Workload Manager for Accelerating Network Simulation

With the rapid growth of the machine learning applications, the workloads of future HPC systems are anticipated to be a mix of scientific simulation, big data analytics, and machine learning applications. Simulation is a great research vehicle to understand the performance implications of co-running scientific applications with big data and machine learning workloads on large-scale systems. In this paper, we present Union, a workload manager that provides an automatic framework to facilitate hybrid workload simulation in CODES. Furthermore, we use Union, along with CODES, to investigate various hybrid workloads composed of traditional simulation applications and emerging learning applications on two dragonfly systems. The experiment results show that both message latency and communication time are important performance metrics to evaluate network interference. Network interference on HPC applications is more reflected by the message latency variation, whereas ML application performance depends more on the communication time.

heterogeneous workloads↗