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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Analytic Properties of Force-free Jets in the Kerr Spacetime. III. Uniform Field Solution

The structure of the steady axisymmetric force-free magnetosphere of a Kerr black hole (BH) is governed by a second-order partial differential equation of A {sub ϕ} depending on two “free” functions Ω(A{sub ϕ}) and I(A{sub ϕ}), where A {sub ϕ} is the ϕ component of the vector potential of the electromagnetic field, Ω is the angular velocity of the magnetic field lines, and I is the poloidal electric current. In this paper, we investigate the solution uniqueness. Taking the asymptotically uniform field as an example, analytic studies imply that there are infinitely many solutions approaching the uniform field at infinity, while only a unique one is found in general relativistic magnetohydrodynamic simulations. To settle the disagreement, we reinvestigate the structure of the governing equation and numerically solve it with given constraint and boundary conditions. We find that the constraint condition (field lines smoothly crossing the light surface) and boundary conditions at the horizon and at infinity are connected via radiation conditions at horizon and at infinity, rather than being independent. With appropriate constraint and boundary conditions, we numerically solve the governing equation and find a unique solution. Contrary to naive expectations, our numerical solution yields a discontinuity in the angular velocity of the field lines and a current sheet along the last field line crossing the event horizon. We also briefly discuss the applicability of the perturbation approach to solving the governing equation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Behavioural phenotypes in mice after prenatal and early postnatal exposure to intermediate frequency magnetic fields

Highlights: • Human exposure to intermediate frequency magnetic fields (MF) is increasing. • We exposed prenatal and early postnatal male mice to 7.5 kHz MFs at 12 and 120 μT. • A behavioural teratology study focused on the developing nervous system. • No consistent adverse effects were observed. Electromagnetic fields are ubiquitous in the environment. Human exposure to intermediate frequency (IF) fields is increasing due to applications like electronic article surveillance systems, wireless power transfer, and induction heating cooking hobs. However, there are limited data on possible health effects of exposure to IF magnetic fields (MF). In the present study, we set out to assess cognitive and behavioural effects of IF MF in mice exposed during prenatal and early postnatal periods. Pregnant female mice were exposed continuously to 7.5 kHz MFs at 12 and 120 μT, from mating until weaning of pups. Sham exposed pregnant mice were used as a control group. A behavioural teratology study was conducted on the male offspring at two months of age to detect possible effects on the developing nervous system. Body weight development did not differ between the exposure groups. The exposure did not alter spontaneous motor activity when exploring a novel cage or anxiety in novelty-suppressed feeding or marble burying tests. Improved performance in the Rotarod task was observed in the 12 µT group, while the 120 μT exposure group swam more slowly than the sham exposed group in the Morris swim navigation task. However, indices of learning and memory (path length and escape latency during task acquisition and search bias during the probe test) did not differ between the exposure groups. Furthermore, the passive avoidance task did not indicate any impairment of long-term memory over a 48 h interval in the exposed groups. In a post-mortem histopathological analysis, there was no evidence for an effect of IF MF exposure on astroglial reactivity or hippocampal neurogenesis. The results suggest that the IF MF used did not have detrimental effects on spatial learning and memory or histological markers of tissue reaction. The two statistically significant findings that were observed (improved performance in the Rotarod task in the 12 µT group and decreased swimming speed in the 120 µT group) are likely to be chance findings, as they do not form an internally consistent, dose-dependent pattern indicative of specific developmental effects.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1997

3-D Deformable Grid Electomagnetic PIC for Parallel Computers

We have developed a three-dimensional non-orthogonal grid electromagnetic PIC code for parallel supercomputers. The numerical formulation is based on hexahedral cells which are logically connected cubic cells but distorted to body-fit complex geometries in physical space. An outstanding area of research is to improve the accuracy of the electromagnetic field solve on distorted meshes.

3D deformable non-orthogonal grid code PIC codes p↗
DOE OSTI2018

Raman Scattering of Light by Molecules of Methyl Orange Dye on the Surface of Silicon Containing Ion-Synthesized Silver Nanoparticles

The possibility of using a new composite material based on porous silicon containing silver nanoparticles and synthesized by means of a unique implantation nanotechnology as an optically sensitive material in biological and chemical sensors is tested experimentally. It is demonstrated that detection of small amounts of the studied organic substance (methyl orange dye) is possible due to the effect of surface-enhanced Raman scattering (SERS) from the molecules affected by the local electromagnetic field of the silver nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Study of a Single-Power Two-Circuit ESR Process with Current-Carrying Mold: Mathematical Simulation of the Process and Experimental Verification

A novel single-power two-circuit ESR process (ESR-STCCM) with current-carrying mold has been investigated via numerical simulation and experimental research in this paper. A 2D quasi-steady-state mathematical model is developed to describe ESR-STCCM. The electromagnetic field, flow field, slag pool temperature distribution, and the shape of a molten steel pool in ESR-STCCM have been investigated by FLUENT software as well as user-defined functions (UDF). The results indicate that ESR-STCCM is different from the conventional ESR process. The maximum electromagnetic force, current density, Joule heat, and slag pool flow velocity are located in the lower part of the conductor in the ESR-STCCM process. The direction of the maximum electromagnetic force inclines upward. There are two distinct vortices in the slag pool. The larger swirl rotates counterclockwise near the conductor, with a value of 0.0263 m s{sup −1} due to the interaction of the electromagnetic force and gravity. The maximum temperature of the slag pool is 2070 K (1797 °C) and is located in the center of the swirl with a filling ratio of 0.6 and a 20 mm electrode immersion depth. The depth of a molten steel pool is shallower, which is conducive to improving solidification quality. In addition, the filling ratio of 0.6 is conducive to controlling steel solidification quality. Some experiments have been done, and the numerical model is confirmed by experimental results.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Waveguide modes of 1D photonic crystals in a transverse magnetic field

We analyze waveguide modes in 1D photonic crystals containing layers magnetized in the plane. It is shown that the magnetooptical nonreciprocity effect emerges in such structures during the propagation of waveguide modes along the layers and perpendicularly to the magnetization. This effect involves a change in the phase velocity of the mode upon reversal of the direction of magnetization. Comparison of the effects in a nonmagnetic photonic crystal with an additional magnetic layer and in a photonic crystal with magnetic layers shows that the magnitude of this effect is several times larger in the former case in spite of the fact that the electromagnetic field of the modes in the latter case is localized in magnetic regions more strongly. This is associated with asymmetry of the dielectric layers contacting with the magnetic layer in the former case. This effect is important for controlling waveguide structure modes with the help of an external magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Generation and subsequent amplification of few-cycle femtosecond pulses from a picosecond pump laser

Using a new approach, in which generation of femtosecond pulses as short as a few field cycles is implemented directly from the radiation of a picosecond pump laser, pulses with the microjoule energy, the repetition rate 10 kHz, and the duration less than 26 fs are generated in the spectral range 1.3 − 1.4 μm. In the process of generating this radiation, use was made of a method providing passive phase stabilisation of the carrier oscillation of the electromagnetic field and its slow envelope. The radiation spectrum was converted into the range of parametric amplification in the BBO crystal by the broadband second harmonic generation; the pulse was parametrically amplified up to the microjoule level and compressed by chirped mirrors to a duration of 28 fs. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Effect of the corrected ionization potential and spatial distribution on the angular and energy distribution in tunnel ionization

Within the framework of the Ammosov–Delone–Krainov theory, we consider the angular and energy distribution of outgoing electrons due to ionization by a circularly polarized electromagnetic field. A correction of the ground ionization potential by the ponderomotive and Stark shift is incorporated in both distributions. Spatial dependence is analyzed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The axial anomaly in chiral tilted Weyl semimetals

The axial anomaly is investigated based on Fujikawa’s method for chiral tilted Weyl semimetals, in which the Weyl cones with different chiralities tilt to opposite directions. When the electric field (EF) is parallel to the magnetic field (MF), the axial anomaly contributed by electromagnetic fields along tilt direction is reduced less than that along other directions. This results in that the associated effects, such as anomalous Hall effect, chiral magnetic effect and negative magnetoresistivity, are suppressed anisotropically. More interestingly, when the EF is perpendicular to MF, the axial anomaly has a new contribution from the mixed product of tilt vector, EF and MF, which is asymmetry under reversing tilt direction (electron–hole asymmetry) and leads to a current between Dirac cones with different tilt directions and novel magnetoresistivity (MR). Specifically, this contribution can change the properties of MR in some experimental establishments and makes trivial components of MR in un-tilted Weyl semimetal develop non-trivial properties. These changes are consistent with the MR phenomena observed in experiments, such as gate-tunable negative longitudinal MR, Hall MR, extremely large and non-saturating MR.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Tunable axial gauge fields in engineered Weyl semimetals: semiclassical analysis and optical lattice implementations

In this work, we describe a toolbox to realize and probe synthetic axial gauge fields in engineered Weyl semimetals. These synthetic electromagnetic fields, which are sensitive to the chirality associated with Weyl nodes, emerge due to spatially and temporally dependent shifts of the corresponding Weyl momenta. First, we introduce two realistic models, inspired by recent cold-atom developments, which are particularly suitable for the exploration of these synthetic axial gauge fields. Second, we describe how to realize and measure the effects of such axial fields through center-ofmass observables, based on semiclassical equations of motion and exact numerical simulations. Finally, in particular, we suggest realistic protocols to reveal an axial Hall response due to the axial electric field E 5 , as well as axial cyclotron orbits and chiral pseudo-magnetic effect due to the axial magnetic field B 5 .

36 MATERIALS SCIENCE↗
DOE OSTI2020

Space charge fields in azimuthally symmetric beams: Integrated Green's function approach

Electromagnetic fields induced by the space charge in relativistic beams play an important role in Accelerator Physics. They lead to emittance growth, slice energy change, and the microbunching instability. Typically, these effects are modeled numerically since simple description exists only inthe limits of large- or small-scale current variations. In this paper we consider an axially symmetric charged beam inside a round pipe and find the solution of the space charge problem that is valid in the full range of current variations. We express the solution for the field components in terms of Green’s functions, which are fully determined by just a single function. We then find that this function is an on-axis potential from a charged disk in a round pipe, with transverse charge density ρ⊥(r), and it has a compact analythical expression. We finally provide an integrated Green’s function based approach for efficient numerical evaluation in the case when the transverse charge density stays the same along the beam

43 PARTICLE ACCELERATORS↗
NASA NTRS1976

Evaluation of a method to shield a welding electron beam from magnetic interference

It is known that electron beams are easily deflected by magnetic and electrostatic fields. Therefore, to prevent weld defects, stray electromagnetic fields are avoided in electron beam welding chambers if at all possible. The successful results of tests conducted at MSFC to evaluate a simple magnetic shield made from steel tubing are reported. Tests indicate that this shield was up to 85 percent effective in reducing magnetic effects on the electron beam of a welding machine. In addition, residual magnetic fields within the shield were so nearly uniform that the net effect on the beam alignment was negligible. It is concluded that the shield, with the addition of a tungsten liner, could be used in production welding.

Wall, W. A.↗
NASA NTRS1987

Containerless Atomic-Fluorescence Property Measurements

Report describes studies conducted to establish and verify use of laser-induced fluorescence in monitoring and controlling high-temperature containerless processes. Specimens levitated by gas jets or electromagnetic fields and heated by laser beams or electromagnetic induction while being irradiated and detected by fluorescence technique. Makes quantitative and qualitative comparisons among three new methods of temperature measurement; all rely on laser-induced fluorescence. One method gas-density thermometry with seed gas. Other two methods involve measurements of velocities of evaporating atoms or of population ratios of different electronic states.

Nordine, P.↗
NASA NTRS1987

A VLSI Processor Engine to Support Calculation of the Vector Wave Equation

The development of a VLSI processor engine tailored to support computation of the near-field vector wave equation (VWE) is presented. Calculation of the near field is essential for evaluation of the electromagnetic fields generated by a complex radiating structure. The processor engine presented is optimized such that it takes advantage of the extensive parallelism inherent in the computational algorithm. The utilization of very large scale integration (VLSI) circuit technology and a customized reduced instruction set computer (RISC) architecture support development of a system of these processor engines, each of which is capable of performing the VWE algorithm calculation. By taking maximum advantage of the parallelism present in the calculation and dividing the problem among an array of these processor engines, the calculation can be computed in a realistic time frame.

J W Degroat↗
NASA NTRS1995

Computing Radiation From Multiple-Circular-Aperture Antennas

Mutual Coupling Program for Circular Waveguide-fed Aperture Array (CWG) computer program developed to calculate electromagnetic interactions among elements of antenna arrays with circular apertures with specified distributions of electromagnetic fields in apertures. Distributions assumed superpositions of electromagnetic modes existing in circular waveguide. Various external media included to provide flexibility of use; for example, flexibility to determine effects of dielectric covers upon impedances of aperture-type antennas. Written in VAX FORTRAN for DEC VAX-series computers running VMS (LAR-15236) and IBM PC-series and compatible computers running MS-DOS (LAR-15226).

Bailey, M. C.↗
DOE OSTI2020

In situ SRF cavity processing using optical ionization of gases

A system and method for the in situ processing of internal SRF cavity surfaces to reduce field emission and improve maximum gradient. An electromagnetic radiation source is introduced in the bore of a superconducting cavity to enhance ionization or dissociation of gases which then remove contaminants from the surface of the cavity, either through direct surface bombardment, chemical reaction or through the production of radiation which interacts with the contaminants. An RF or low frequency electromagnetic field may be established in the cavity which further enhances the ionization or dissociation process and may cause the ions to bombard sites with enhanced electric fields. The invention removes the requirement that the RF field be sufficient by itself to ionize gas in the cavity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗