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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1958

The Interaction of a Reflected Shock Wave with the Boundary Layer in a Shock Tube

Ideally, the reflection of a shock from the closed end of a shock tube provides, for laboratory study, a quantity of stationary gas at extremely high temperature. Because of the action of viscosity, however, the flow in the real case is not one-dimensional, and a boundary layer grows in the fluid following the initial shock wave. In this paper simplifying assumptions are made to allow an analysis of the interaction of the shock reflected from the closed end with the boundary layer of the initial shock afterflow. The analysis predicts that interactions of several different types will exist in different ranges of initial shock Mach number. It is shown that the cooling effect of the wall on the afterflow boundary layer accounts for the change in interaction type. An experiment is carried out which verifies the existence of the several interaction regions and shows that they are satisfactorily predicted by the theory. Along with these results, sufficient information is obtained from the experiments to make possible a model for the interaction in the most complicated case. This model is further verified by measurements made during the experiment. The case of interaction with a turbulent boundary layer is also considered. Identifying the type of interaction with the state of turbulence of the interacting boundary layer allows for an estimate of the state of turbulence of the boundary layer based on an experimental investigation of the type of interaction. A method is proposed whereby the effect of the boundary-layer interaction on the strength of the reflected shock may be calculated. The calculation indicates that the reflected shock is rapidly attenuated for a short distance after reflection, and this result compares favorably with available experimental results.

Mark, Herman↗
DOE OSTI2017

High-energy Emissions from the Pulsar/Be Binary System PSR J2032+4127/MT91 213

PSR J2032+4127 is a radio-loud gamma-ray-emitting pulsar; it is orbiting around a high-mass Be type star with a very long orbital period of 25–50 years, and is approaching periastron, which will occur in late 2017/early 2018. This system comprises a young pulsar and a Be type star, which is similar to the so-called gamma-ray binary PSR B1259–63/LS2883. It is expected therefore that PSR J2032+4127 shows an enhancement of high-energy emission caused by the interaction between the pulsar wind and Be wind/disk around periastron. Ho et al. recently reported a rapid increase in the X-ray flux from this system. In this paper, we also confirm a rapid increase in the X-ray flux along the orbit, while the GeV flux shows no significant change. We discuss the high-energy emissions from the shock caused by the pulsar wind and stellar wind interaction and examine the properties of the pulsar wind in this binary system. We argue that the rate of increase of the X-ray flux observed by Swift indicates (1) a variation of the momentum ratio of the two-wind interaction region along the orbit, or (2) an evolution of the magnetization parameter of the pulsar wind with the radial distance from the pulsar. We also discuss the pulsar wind/Be disk interaction at the periastron passage, and propose the possibility of formation of an accretion disk around the pulsar. We model high-energy emissions through the inverse-Compton scattering process of the cold-relativistic pulsar wind off soft photons from the accretion disk.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1981

Jikiken /EXOS-B/ observation of Siple transmissions

Preliminary results of observations by the Japanese magnetospheric satellite Jikiken (EXOS-B) of Siple transmissions and VLF emissions triggered by the Siple signals are reviewed. The experiments discussed were carried out in July, August, and September of 1979 and in December 1979 and January 1980. Only four events concentrated within the period from August 14 to 18 were found in which triggered emissions were associated with Siple transmissions. The electron distributions observed on the equatorial crossing passes, when Siple triggered emissions were detected, suggest that the cyclotron resonance condition is satisfied for Siple signals and electrons of energy around 1 keV or less, provided the interaction region is inside the plasmapause. It is noted that if these emissions were generated outside the plasmapause, electron energies much higher than 10 keV would be necessary for the cyclotron interaction, which were above the range of the measurements. For the high latitude passes of August 14 and 17, the electron fluxes were found to be very small.

Kimura, I.↗
DOE OSTI2015

Structural basis for Notch1 engagement of Delta-like 4

Notch receptors guide mammalian cell fate decisions by engaging the proteins Jagged and Delta-like (DLL). The 2.3 angstrom resolution crystal structure of the interacting regions of the Notch1-DLL4 complex reveals a two-site, antiparallel binding orientation assisted by Notch1 O-linked glycosylation. Notch1 epidermal growth factor–like repeats 11 and 12 interact with the DLL4 Delta/Serrate/Lag-2 (DSL) domain and module at the N-terminus of Notch ligands (MNNL) domains, respectively. Threonine and serine residues on Notch1 are functionalized with O-fucose and O-glucose, which act as surrogate amino acids by making specific, and essential, contacts to residues on DLL4. In conclusion, the elucidation of a direct chemical role for O-glycans in Notch1 ligand engagement demonstrates how, by relying on posttranslational modifications of their ligand binding sites, Notch proteins have linked their functional capacity to developmentally regulated biosynthetic pathways.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Kent Island Boundary Layer Field Campaign Report

Understanding the mechanisms governing the urban atmospheric environment is critical for informing urban populations about the impacts of climate change and associated mitigation and adaptation measures. The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) User Facility’s Coast-Urban-Rural Atmospheric Gradient Experiment (CoURAGE) was conducted to study the interactions among the earth’s surface, the atmospheric boundary layer (ABL), aerosols, atmospheric composition, clouds, radiation, and precipitation at each experimental site, and to examine how the spatial gradients across the region interact to create the climate conditions in Baltimore. In this activity we performed weekly soundings, alternating between day and night from Kent Island, to get low-frequency, long-term observations of ABL/lower tropospheric thermodynamic structure. However, during the CoURAGE intensive operational period (IOP), we performed high-frequency sampling (2x/day), at times coinciding with CoURAGE IOP soundings at the main site. The short-term, high-frequency sounding information that was launched at 12Z and 18Z was to complement the longer-term data set.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1981

On the acceleration of thermal coronal ions by flare induced shock waves

The energy spectra of solar flare ions are calculated by assuming that the process which accelerates solar wind ions to MeV/ nucleon energies in the interplanetary corotating interaction region (CIR) also occurs in flare induced magnetosonic fast-mode (MFM) shocks in the corona. Solar wind ions are considered to be accelerated to MeV/nucleon energies by wave-particle interactions in the shock front and the downstream flow, being compressed between upstream and downstream magnetic field irregularities, and then accelerated by the shock drift acceleration mechanism. The energy spectra of the accelerated ions is calculated from the number of shock encounters as a function of the post- and preacceleration energies. A best fit by an exponential in momentum is determined for ions in the 50 MeV to a few GeV range, and from 20-80 MeV by a suitable power law in kinetic energy with a mean spectral index. Comparisons with observed solar protons show good agreement.

Decker, R. B.↗
DOE OSTI2018

Spatial evolution of quantum mechanical states

The time-dependent Schrödinger equation is solved traditionally as an initial-time value problem, where its solution is obtained by the action of the unitary time-evolution propagator on the quantum state that is known at all spatial locations but only at t=0. We generalize this approach by examining the spatial evolution from a state that is, by contrast, known at all times t, but only at one specific location. The corresponding spatial-evolution propagator turns out to be pseudo-unitary. In contrast to the real energies that govern the usual (unitary) time evolution, the spatial evolution can therefore require complex phases associated with dynamically relevant solutions that grow exponentially. By introducing a generalized scalar product, for which the spatial generator is Hermitian, one can show that the temporal integral over the probability current density is spatially conserved, in full analogy to the usual norm of the state, which is temporally conserved. As an application of the spatial propagation formalism, we introduce a spatial backtracking technique that permits us to reconstruct any quantum information about an atom from the ionization data measured at a detector outside the interaction region.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2015

CFD Validation Experiment of a Mach 2.5 Axisymmetric Shock-Wave/Boundary-Layer Interaction

Preliminary results of an experimental investigation of a Mach 2.5 two-dimensional axisymmetric shock-wave/ boundary-layer interaction (SWBLI) are presented. The purpose of the investigation is to create a SWBLI dataset specifically for CFD validation purposes. Presented herein are the details of the facility and preliminary measurements characterizing the facility and interaction region. These results will serve to define the region of interest where more detailed mean and turbulence measurements will be made.

Shock-Wave/Boundary Layer Interaction↗
DOE OSTI2014

Versatile attosecond beamline in a two-foci configuration for simultaneous time-resolved measurements

We present our attoline which is a versatile attosecond beamline at the Ultrafast Laser Physics Group at ETH Zurich for attosecond spectroscopy in a variety of targets. High-harmonic generation (HHG) in noble gases with an infrared (IR) driving field is employed to generate pulses in the extreme ultraviolet (XUV) spectral regime for XUV-IR cross-correlation measurements. The IR pulse driving the HHG and the pulse involved in the measurements are used in a non-collinear set-up that gives independent access to the different beams. Single attosecond pulses are generated with the polarization gating technique and temporally characterized with attosecond streaking. This attoline contains two target chambers that can be operated simultaneously. A toroidal mirror relay-images the focus from the first chamber into the second one. In the first interaction region a dedicated double-target allows for a simple change between photoelectron/photoion measurements with a time-of-flight spectrometer and transient absorption experiments. Any end station can occupy the second interaction chamber. A surface analysis chamber containing a hemispherical electron analyzer was employed to demonstrate successful operation. Simultaneous RABBITT measurements in two argon jets were recorded for this purpose.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Effects of Coronal Magnetic Field Configuration on Particle Acceleration and Release during the Ground Level Enhancement Events in Solar Cycle 24

Ground level enhancements (GLEs) are extreme solar energetic particle (SEP) events that are of particular importance in space weather. In solar cycle 24, two GLEs were recorded on 2012 May 17 (GLE 71) and 2017 September 10 (GLE 72), respectively, using a range of advanced modern instruments. Here we conduct a comparative analysis of the two events by focusing on the effects of large-scale magnetic field configuration near active regions on particle acceleration and release. Although the active regions are both located near the western limb, temporal variations of SEP intensities and energy spectra measured in situ display different behaviors at early stages. By combining a potential field model, we find the coronal mass ejection (CME) in GLE 71 originated below the streamer belt, while in GLE 72 it originated near the edge of the streamer belt. We reconstruct the CME shock fronts with an ellipsoid model based on nearly simultaneous coronagraph images from multiple viewpoints and further derive the 3D shock geometry at the GLE onset. The highest-energy particles are primarily accelerated in the shock–streamer interaction regions, i.e., likely at the nose of the shock in GLE 71 and the eastern flank in GLE 72, due to quasi-perpendicular shock geometry and confinement of closed fields. Subsequently, they are released to the field lines connecting to near-Earth spacecraft when the shocks move through the streamer cusp region. This suggests that magnetic structures in the corona, especially shock–streamer interactions, may have played an important role in the acceleration and release of the highest-energy particles in the two events.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1983

Solar wind disturbances in th outer heliosphere caused by successive solar flares from the same active region

Solar wind disturbances caused by successive flares from the same active region are traced to about 20 AU, using the modeling method developed by Hakamada and Akasofu (1982). It is shown that the flare-generated shock waves coalesce with the co-rotating interaction region of the interplanetary magnetic field, resulting in a large-scale magnetic field structure in the outer heliosphere. Such a structure may have considerable effects on the propagation of galactic cosmic rays.

Akasofu, S. I.↗
DOE OSTI2023

Energetic Electron Precipitation Driven by Electromagnetic Ion Cyclotron Waves from ELFIN’s Low Altitude Perspective

We review comprehensive observations of electromagnetic ion cyclotron (EMIC) wave-driven energetic electron precipitation using data collected by the energetic electron detector on the Electron Losses and Fields InvestigatioN (ELFIN) mission, two polar-orbiting low-altitude spinning CubeSats, measuring 50-5000 keV electrons with good pitch-angle and energy resolution. EMIC wave-driven precipitation exhibits a distinct signature in energy-spectrograms of the precipitating-to-trapped flux ratio: peaks at >0.5 MeV which are abrupt (bursty) (lasting ~17 s, or ΔL ~ 0.56) with significant substructure (occasionally down to sub-second timescale). We attribute the bursty nature of the precipitation to the spatial extent and structuredness of the wave field at the equator. Multiple ELFIN passes over the same MLT sector allow us to study the spatial and temporal evolution of the EMIC wave - electron interaction region. Case studies employing conjugate ground-based or equatorial observations of the EMIC waves reveal that the energy of moderate and strong precipitation at ELFIN approximately agrees with theoretical expectations for cyclotron resonant interactions in a cold plasma. Using multiple years of ELFIN data uniformly distributed in local time, we assemble a statistical database of ~50 events of strong EMIC wave-driven precipitation. Most reside at L ~ 5 – 7 at dusk, while a smaller subset exists at L ~ 8 – 12 at post-midnight. The energies of the peak-precipitation ratio and of the half-peak precipitation ratio (our proxy for the minimum resonance energy) exhibit an L-shell dependence in good agreement with theoretical estimates based on prior statistical observations of EMIC wave power spectra. The precipitation ratio’s spectral shape for the most intense events has an exponential falloff away from the peak (i.e., on either side of ~ 1.45 MeV). It too agrees well with quasi-linear diffusion theory based on prior statistics of wave spectra. It should be noted though that this diffusive treatment likely includes effects from nonlinear resonant interactions (especially at high energies) and nonresonant effects from sharp wave packet edges (at low energies). Sub-MeV electron precipitation observed concurrently with strong EMIC wave-driven >1 MeV precipitation has a spectral shape that is consistent with efficient pitch-angle scattering down to ~ 200-300 keV by much less intense higher frequency EMIC waves at dusk (where such waves are most frequent). At ~100 keV, whistler-mode chorus may be implicated in concurrent precipitation. These results confirm the critical role of EMIC waves in driving relativistic electron losses. Nonlinear effects may abound and require further investigation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1989

Modeling of the cometary nucleus-coma interface region

A well-developed dusty cometary atmosphere extends to distances over 4 orders of magnitude larger than the size of the nucleus. Pre-encounter models of the inner coma were based on the assumption that a spherically symmetric description was adequate to describe the dust-gas interaction region. Recent observational evidence together with a new generation of multidimensional theoretical models demonstrate that the inner cometary environment is far from spherical symmetry and a number of unexpected phenomena (dust jet broadening, subsolar dust spike formation, etc.) might play a significant role in this region.

Gombosi, T. I.↗
DOE OSTI2015

Scanning Synchronization of Colliding Bunches for MEIC Project

Synchronization of colliding beams is one of the major issues of an electron-ion collider (EIC) design because of sensitivity of ion revolution frequency to beam energy. A conventional solution for this trouble is insertion of bent chicanes in the arcs space. In our report we consider a method to provide space coincidence of encountering bunches in the crab-crossing orbits Interaction Region (IR) while repetition rates of two beams do not coincide. The method utilizes pair of fast kickers realizing a bypass for the electron bunches as the way to equalize positions of the colliding bunches at the Interaction Point (IP). A dipole-mode warm or SRF cavities fed by the magnetron transmitters are used as fast kickers, allowing a broad-band phase and amplitude control. The proposed scanning synchronization method implies stabilization of luminosity at a maximum via a feedback loop. This synchronization method is evaluated as perspective for the Medium Energy Electron-Ion collider (MEIC) project of JLab with its very high bunch repetition rate.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Effect of mass and density of ambient gas on the interaction of laser-blow-off plasma plumes propagating in close proximity

The effects of mass and pressure of ambient gas on the propagation dynamics of two laser-blow-off plasma plumes created in close proximity are investigated. A time gated fast imaging technique is used for recording the images of the laterally colliding plumes under different experimental conditions. Pressure is varied from 0.1 to 3 mbar in three ambient, i.e., helium, neon, and argon. Emphasis is given on the nature of shock-shock interaction under different ambient conditions. It has been observed that the shock-velocity, shape, strength, and their interactions are strongly dependent on the mass and density of the ambient gases. The role of the interacting shocks and their subsequent reflections on the formation and geometrical shape of the interaction region in different ambient conditions is briefly described.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2015

CFD Validation Experiment of a Mach 2.5 Axisymmetric Shock-Wave Boundary-Layer Interaction

Preliminary results of an experimental investigation of a Mach 2.5 two-dimensional axisymmetric shock-wave/boundary-layer interaction (SWBLI) are presented. The purpose of the investigation is to create a SWBLI dataset specifically for CFD validation purposes. Presented herein are the details of the facility and preliminary measurements characterizing the facility and interaction region. The results will serve to define the region of interest where more detailed mean and turbulence measurements will be made.

Superonic Flow↗
DOE OSTI2024

Performance of the ATLAS forward proton Time-of-Flight detector in Run 2

We present performance studies of the Time-of-Flight (ToF) subdetector of the ATLAS Forward Proton (AFP) detector at the LHC. Efficiencies and resolutions are measured using high-statistics data samples collected at low and moderate pile-up in 2017, the first year when the detectors were installed on both sides of the interaction region. While low efficiencies are observed, of the order of a few percent, the resolutions of the two ToF detectors measured individually are 21 ps and 28 ps, yielding an expected resolution of the longitudinal position of the interaction, z vtx , in the central ATLAS detector of 5.3 ± 0.6 mm. This is in agreement with the observed width of the distribution of the difference between z vtx , measured independently by the central ATLAS tracker and by the ToF detector, of 6.0 ± 2.0 mm.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Integration of the full-acceptance detector into the JLEIC

For physics requirements, the JLEIC (Jefferson Lab Electron Ion Collider) has a full-acceptance detector, which brings many new challenges to the beam dynamics integration. For example, asymmetric lattice and beam envelopes at interaction region (IR), forward detection, and large crossing angle with crab dynamics. Also some common problems complicate the picture, like coupling and coherent orbit from detector solenoid, high chromaticity and high multipole sensitivity from low beta-star at interaction point (IP), collision mode with different energy and ion species. Meanwhile, to get a luminosity level of a few 1033 cm-2sec-1, small ?* are necessary at the IP, which also means large ? in the final focus area, chromaticity correction sections, etc. This sets a constraint on the field quality of magnets in large beta areas, in order to ensure a large enough dynamic aperture (DA). In this context, limiting multipole components of magnets are surveyed to get a standard line. And continuously, multipole magnets as dedicated correctors are studied to provide semi-local corrections of specific multipole components beyond the standard line. This report will mention those contents.

Wei, G.H.↗