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Results for “ELECTROMAGNETIC RADIATION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Effect of electromagnetic radiation on an array of weakly interacting carbon nanotubes in the presence of nanosecond pulses

For metallic 'zigzag'-type carbon nanotubes, the dependence of a nonlinear current on an ac electric field with an inclined-leading-edge width of {Delta}T = 3 Multiplication-Sign 10{sup -11} s and wavelength of {lambda} Almost-Equal-To 1 mm is studied. It is theoretically and numerically shown that the surface current is almost independent of the nanotube radius. In the case of semiconductor zigzag-type nanotubes, the radiation of a two-frequency CO{sub 2} laser with a constant amplitude is considered as an ac electric field. The dependence on the relaxation time in the Boltzmann kinetic equation is studied. The optimal conditions for terahertz-radiation generation are achieved when the relaxation time is 40 fs. It is numerically found that the amplified radiation amplitude behaves as beats.

36 MATERIALS SCIENCE↗
DOE OSTI2016

PRIMORDIAL GRAVITATIONAL WAVES AND RESCATTERED ELECTROMAGNETIC RADIATION IN THE COSMIC MICROWAVE BACKGROUND

Understanding the interaction of primordial gravitational waves (GWs) with the Cosmic Microwave Background (CMB) plasma is important for observational cosmology. In this article, we provide an analysis of an apparently as-yet-overlooked effect. We consider a single free electric charge and suppose that it can be agitated by primordial GWs propagating through the CMB plasma, resulting in periodic, regular motion along particular directions. Light reflected by the charge will be partially polarized, and this will imprint a characteristic pattern on the CMB. We study this effect by considering a simple model in which anisotropic incident electromagnetic (EM) radiation is rescattered by a charge sitting in spacetime perturbed by GWs, and becomes polarized. As the charge is driven to move along particular directions, we calculate its dipole moment to determine the leading-order rescattered EM radiation. The Stokes parameters of the rescattered radiation exhibit a net linear polarization. We investigate how this polarization effect can be schematically represented out of the Stokes parameters. We work out the representations of gradient modes (E-modes) and curl modes (B-modes) to produce polarization maps. Although the polarization effect results from GWs, we find that its representations, the E- and B-modes, do not practically reflect the GW properties such as strain amplitude, frequency, and polarization states.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Effect of electromagnetic radiation on an array of noninteracting carbon nanoribbons in the presence of nanosecond electrical pulses

For zigzag carbon nanoribbons (m-ZGNR), the dependence of the nonlinear current on the intensity of terahertz radiation with an inclined leading-edge width ΔT = 10{sup −10} s under a dc electric field is studied for odd m. It is theoretically and numerically shown that the nonlinear surface current can be two orders higher in comparison with ordinary carbon nanotubes. A strong dependence of the current on the ribbon width is established.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Reflection of electromagnetic radiation from plasma with an anisotropic electron velocity distribution

The reflection of a test electromagnetic pulse from the plasma formed as a result of tunnel ionization of atoms in the field of a circularly polarized high-power radiation pulse is analyzed using the kinetic approach to describe electron motion. It is shown that the reflected pulse is significantly amplified due to the development of Weibel instability. The amplification efficiency is determined by the maximum value of the instability growth rate, which depends on the degree of anisotropy of the photoelectron distribution function.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Adaptive materials and systems for manipulation of electromagnetic radiation

Fully artificial, adaptive composite materials and systems, having variable transmittance, reflectance, and/or absorptance to radiation in visible, infrared, or other desired region of the electromagnetic spectrum, and methods of the manufacture and use thereof are provided. The adaptive composite materials and systems possess an unprecedented combination of properties and are, therefore, poised to enable a broad range of practical applications. The adaptive composite material incorporates at least one size-variable active area having a variable transmittance, reflectance, and/or absorptance in at least a portion of the electromagnetic spectrum and comprises at least: an elastomer substrate, a texturizing layer disposed on top of the substrate, and an optional reflective coating disposed on top of the texturizing layer. In operation, the stretching and relaxation of the elastomer substrate causes changes in the surface morphology of the texturized layers (e.g., the change in the size and depth of surface features in the texturizing layer), this in turn results in the increased or decreased transmittivity, reflectivity, and/or absorptivity of the active area.

Gorodetsky, Alon A.↗
DOE OSTI2014

Spontaneous emission of electromagnetic radiation in turbulent plasmas

Known radiation emission mechanisms in plasmas include bremmstrahlung (or free-free emission), gyro- and synchrotron radiation, cyclotron maser, and plasma emission. For unmagnetized plasmas, only bremmstrahlung and plasma emissions are viable. Of these, bremmstrahlung becomes inoperative in the absence of collisions, and the plasma emission requires the presence of electron beam, followed by various scattering and conversion processes. The present Letter proposes a new type of radiation emission process for plasmas in a state of thermodynamic quasi-equilibrium between particles and enhanced Langmuir turbulence. The radiation emission mechanism proposed in the present Letter is not predicted by the linear theory of thermal plasmas, but it relies on nonlinear wave-particle resonance processes. The electromagnetic particle-in-cell numerical simulation supports the new mechanism.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

The effect of initial conditions on the electromagnetic radiation generation in type III solar radio bursts

Extensive particle-in-cell simulations of fast electron beams injected in a background magnetised plasma with a decreasing density profile were carried out. These simulations were intended to further shed light on a newly proposed mechanism for the generation of electromagnetic waves in type III solar radio bursts [D. Tsiklauri, Phys. Plasmas, 18, 052903 (2011)]. The numerical simulations were carried out using different density profiles and fast electron distribution functions. It is shown that electromagnetic L and R modes are excited by the transverse current, initially imposed on the system. In the course of the simulations, no further interaction of the electron beam with the background plasma could be observed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Information Carried by Electromagnetic Radiation Launched from Accelerated Polarization Currents

We show experimentally that a continuous, linear, dielectric antenna in which a superluminal polarization-current distribution accelerates can be used to transmit a broadband signal that is reproduced in a comprehensible form at a chosen target distance and angle. The requirement for this exact correspondence between broadcast and received signals is that each moving point in the polarization-current distribution approaches the target at the speed of light at all times during its transit along the antenna. This results in a one-to-one correspondence between the time at which each point on the moving polarization current enters the antenna and the time at which all of the radiation emitted by this particular point during its transit through the antenna arrives simultaneously at the target. This has the effect of reproducing the desired time dependence of the original broadcast signal. For other observer-detector positions, the time dependence of the signal is scrambled, due to the nontrivial relationship between emission (retarded) time and reception time. This technique represents a contrast to conventional radio transmission methods; in most examples of the latter, signals are broadcast with little or no directivity, selectivity of reception being achieved through the use of narrow frequency bands. In place of this, the current paper uses a spread of frequencies to transmit information to a particular location; the signal is weaker and has a scrambled time dependence elsewhere. Here, we point out the possible relevance of this mechanism to 5G neighborhood networks and pulsar astronomy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

The impact of r -process heating on the dynamics of neutron star merger accretion disc winds and their electromagnetic radiation

Neutron star merger accretion discs can launch neutron-rich winds of >10 -2 M⊙. This ejecta is a prime site for r-process nucleosynthesis, which will produce a range of radioactive heavy nuclei. The decay of these nuclei releases enough energy to accelerate portions of the wind by ~0.1c. Here, we investigate the effect of r-process heating on the dynamical evolution of disc winds. We extract the wind from a 3D general relativistic magnetohydrodynamic simulation of a disc from a post-merger system. This is used to create inner boundary conditions for 2D hydrodynamic simulations that continue the original 3D simulation. We perform two such simulations: one that includes the r-process heating, and another one that does not. We follow the hydrodynamic simulations until the winds reach homology (60 s). Using time-dependent multifrequency multidimensional Monte Carlo radiation transport simulations, we then calculate the kilonova light curves from the winds with and without dynamical r-process heating. We find that the r-process heating can substantially alter the velocity distribution of the wind, shifting the mass-weighted median velocity from 0.06c to 0.12c. The inclusion of the dynamical r-process heating makes the light curve brighter and bluer at $\sim 1\, \mathrm{d}$ post-merger. However, the high-velocity tail of the ejecta distribution and the early ($\lesssim 1\, \mathrm{d}$) light curves are largely unaffected.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Exposure to non‐ionizing electromagnetic radiation of public risk prevention instruments threatens the quality of spermatozoids

Contents The use of artificial insemination in cattle breeding has evolved to global extent, and insemination doses are often shipped via air transport which requires strict radiation‐based examinations. For the determination of effect of non‐ionizing radiation (NIR), to which are beings frequently exposed due to protection of airport or cultural event security, freshly ejaculated and cryopreserved bovine spermatozoa were used as experimental model. Following radiation with hand‐held metal detector in various exposition times (0, 10 s, 15, 30 and 60 min—groups FR, FR10, FR15, FR30 and FR60) the spermatozoa underwent motility and DNA fragmentation analyses. Study on cryoconserved semen treated with NIR was performed in time intervals 0, 10 s, 1 and 5 min (insemination doses radiated before cryoconservation—CB, CB10, CB1, CB5; samples radiated after freezing—CA, CA10, CA1 and CA5). Fresh semen and insemination doses radiated after cryoconservation showed significantly lower total and progressive motility. No effect on motility parameters was detected in semen extended with cryopreservative medium and radiated prior to freezing. Surprisingly, NIR showed a potential to stimulate spermatozoa velocity; however, the effect was modulated throughout the post‐thawing incubation. Based on the DNA fragmentation assay, sperm DNA stayed intact. Present study underlines the potential harm of NIR, which is frequently used in everyday life, with overall adverse impact on human and animal reproduction. Current study also points out on interesting short‐term spermatozoa stimulation induced by NIR.

Tirpak, Filip↗
DOE OSTI2016

Electromagnetic radiation of electrons in corrugated graphene

Bremsstrahlung in corrugated single-layer graphene in the presence of a ballistic transport current is analyzed. Radiation of a similar nature is observed in undulators and wigglers. Regular and chaotic corrugations (ripples) are considered. It is shown that the quadratic relation between the Monge membrane function and the synthetic calibration field leads to the appearance of a central peak in the radiation spectral density. Possible formation mechanisms of single-layer graphene corrugation are proposed. In one case, the corrugation is considered as an incommensurate superstructure in a two-dimensional crystal, resulting from instability developing in the optical phonon subsystem with the formation of a periodic soliton train. Corrugation results from the interaction of subsystems. Another possible mechanism consists in instability of the membrane flat state due to strong fluctuations characteristic of two-dimensional systems.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Combining Particle Tracking with Electromagnetic Radiation Showers: Merging GPT and Geant4 with Visualization

Field emitted electrons can seriously affect the operation of high-field, high-duty factor electron accelerators. Accelerated field emission can result in high average power beams which can radiation damage beamline components. In addition, localized losses generate thermal hot spots whose outgassing degrades the ultra-high vacuum required in photoinjectors and cryomodules. However, despite their importance, the effects of field emission are rarely included in the design and engineering of electron injectors. This work attempts to remedy this situation by combining two well-known and well-documented programs, GPT and Geant4, to track electrons and their losses in an injector beamline. This paper describes a system of programs which simulates electron paths and losses along the beamline. In addition, the tracking results can be zoomed and panned along and about the beampipe envelope using an open-source 3D CAD program. The scattering albedo calculations of the combined program, GPT-Geant4, are shown to be in good agreement with the literature albedos. The paper concludes with a dark current simulation for the LCLS-II injector from the cathode to the collimator at 1.5 m from the cathode.

Dowell, David H.↗