Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “JET MODEL”

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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Measurements of acoustic sources in motion

Results of the far-field pressures measured from three different types of moving sources are presented. These acoustic sources consist of a point monopole, a small model jet, and an aircraft. Results for the pressure time history produced by the point source show good agreement with those predicted analytically. Both actual and simulated forward motion of the model jet show reductions in noise levels with forward speed at all angles between the source and observer. Measurement with the aircraft over both an anechoic floor and over the ground yields a method for evaluating the transfer function for ground reflections at various angles between the moving aircraft and measurement position.

Maestrello, L.↗
NASA NTRS1979

Experimental measurements of moving noise sources

The far-field pressure was measured from three different types of moving sources: a point monopole, a small model jet, and an aircraft. Results for the pressure time history produced by the point source show good agreement with those predicted analytically. Both actual and simulated forward motion of the model jet show reductions in noise levels with forward speed at all angles between the source and observer. Measurement with the aircraft over both an anechoic floor and over the ground yields a method for evaluating the transfer function for ground reflections at various angles between the moving aircraft and measurement position.

Maestrello, L.↗
NASA NTRS2010

Galactic Black Holes in the Hard State: A Multi-Wavelength View of Accretion and Ejection

The canonical hard state is associated with emission from all three fundamental accretion components: the accretion disk, the hot accretion disk corona and the jet. On top of these, the hard state also hosts very rich temporal variability properties (low frequency QPOs in the PDS, time lags, long time scale evolution). Our group has been working on the major questions of the hard state both observationally (with mult i-wavelength campaigns using RXTE, Swift, Suzaku, Spitzer, VLA, ATCA, SMARTS) and theoretically (through jet models that can fit entire SEDs). Through spectral and temporal analysis we seek to determine the geometry of accretion components, and relate the geometry to the formation and emission from a jet. In this presentation I will review the recent contributions of our group to the field, including the Swift results on the disk geometry at low accretion rates, the jet model fits to the hard state SEDs (including Spitzer data) of GRO J1655-40, and the final results on the evolution of spectral (including X-ray, radio and infrared) and temporal properties of elected black holes in the hard states. I will also talk about impact of ASTROSAT to the science objective of our group.

Kalemci↗
DOE OSTI2015

Extremely soft X-ray flash as the indicator of off-axis orphan GRB afterglow

We verified the off-axis jet model of X-ray flashes (XRFs) and examined a discovery of off-axis orphan gamma-ray burst (GRB) afterglows. The XRF sample was selected on the basis of the following three factors: (1) a constraint on the lower peak energy of the prompt spectrum E{sub obs}{sup src}, (2) redshift measurements, and (3) multicolor observations of an earlier (or brightening) phase. XRF 020903 was the only sample selected on the basis of these criteria. A complete optical multicolor afterglow light curve of XRF 020903 obtained from archived data and photometric results in the literature showed an achromatic brightening around 0.7 days. An off-axis jet model with a large observing angle (0.21 rad, which is twice the jet opening half-angle, θ{sub jet}) can naturally describe the achromatic brightening and the prompt X-ray spectral properties. This result indicates the existence of off-axis orphan GRB afterglow light curves. Events with a larger viewing angle (>∼2θ{sub jet}) could be discovered using an 8 m class telescope with wide-field imagers such as the Subaru Hyper-Suprime-Cam and the Large Synoptic Survey Telescope.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

A multifrequency study of sub-parsec jets with the Event Horizon Telescope

Context. The 2017 observing campaign of the Event Horizon Telescope (EHT) delivered the first very long baseline interferometry (VLBI) images at the observing frequency of 230 GHz, leading to a number of unique studies on black holes and relativistic jets from active galactic nuclei (AGN). In total, eighteen sources were observed, including the main science targets, Sgr A* and M 87, and various calibrators. Sixteen sources were AGN.Aims. We investigated the morphology of the sixteen AGN in the EHT 2017 data set, focusing on the properties of the VLBI cores: size, flux density, and brightness temperature. We studied their dependence on the observing frequency in order to compare it with the Blandford-Königl (BK) jet model. In particular, we aimed to study the signatures of jet acceleration and magnetic energy conversion.Methods. We modeled the source structure of seven AGN in the EHT 2017 data set using linearly polarized circular Gaussian components (1749+096, 1055+018, BL Lac, J0132–1654, J0006–0623, CTA 102, and 3C 454.3) and collected results for the other nine AGN from dedicated EHT publications, complemented by lower frequency data in the 2–86 GHz range. Combining these data into a multifrequency EHT+ data set, we studied the dependences of the VLBI core component flux density, size, and brightness temperature on the frequency measured in the AGN host frame (and hence on the distance from the central black hole), characterizing them with power law fits. We compared the observations with the BK jet model and estimated the magnetic field strength dependence on the distance from the central black hole.Results. Our observations spanning event horizon to parsec scales indicate a deviation from the standard BK model, particularly in the decrease of the brightness temperature with the observing frequency. Only some of the discrepancies may be alleviated by tweaking the model parameters or the jet collimation profile. Either bulk acceleration of the jet material, energy transfer from the magnetic field to the particles, or both are required to explain the observations. For our sample, we estimate a general radial dependence of the Doppler factor δ ∝ r≤0.5. This interpretation is consistent with a magnetically accelerated sub-parsec jet. We also estimate a steep decrease of the magnetic field strength with radius B ∝ r−3, hinting at jet acceleration or efficient magnetic energy dissipation.Key words: techniques: interferometric / galaxies: active / galaxies: jets / galaxies: nuclei / quasars: general / quasars: supermassive black holes⋆⋆ Deceased.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

13 TeV pp collisions, Exotics type, PYTHIA8 generator: tev13pp_pythia8_darkqcd

The Dark pions (emerging jets) model with the settings as for the CMS publication JHEP 02 (2019) 179 (https://arxiv.org/abs/1810.10069). The files use the A14 ATLAS tune with NNPDF23_lo_as_0130_qed. The luminosity was estimated from the first file and is not accurate for the entire dataset. All parameter settings and cross sections are included in the logfiles inside separate ProMC files. The emerging jet model is described in: Y. Bai and P. Schwaller, “Scale of dark QCD”,Phys. Rev. D89(2014) 063522,doi:10.1103/PhysRevD.89.063522,arXiv:1306.4676; P. Schwaller, D.Stolarski, and A. Weiler, “Emerging jets”,JHEP05(2015) 59,doi:10.1007/JHEP05(2015)059,arXiv:1502.05409. Evens are created using a fixed dark pion mass of 5 GeV and different decay length (ctau). Each file has the substring "_mXX_ctYY" where XX and YY indicate the mediator mass and the decay length (in mm) of dark pion with the mass 5 GeV (fixed).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1976

Interaction studies on a jet engine model by characteristic methodologies

It is shown how the generalized characteristic locus method developed by MacFarlane (1972) can be used for the step-by-step design of multivariable closed-loop compensators. The design procedure attempts to strike a balance between four conflicting objectives: stability, integrity, interaction, and accuracy. The generalized locus method is illustrated by a jet engine example.

Seshadri, V.↗
NASA NTRS1994

Morphological changes in the NGC 6251 jet

The giant radio galaxy NGC 6251 is a particularly good object for observational tests of relativistic jet models. Due to its high declination and approximately 0.5 Jy radio nucleus, high-quality Very Long Baseline Interferometry (VLBI) images of the central regions of the source can be made with northern hemisphere arrays. In addition, the large-scale radio morphology strongly suggests that the radio axis lies close to the plane of the sky, so Doppler boosting should be less extreme than in the core-dominated superluminal sources. Earlier 18 cm VLBI observations of NGC 6251 revealed an unexpectedly large jet/counterjet brightness ratio and small transverse motion of a feature in the parsec-scale jet. These early results are difficult to reconcile with the simplest symmetric relativistic jet models. In this paper we present a third-epoch 18 cm VLBI image of the parsec-scale radio jet in NGC 6251, and compare jet morphology over a 5 year time span. The jet shows a minor brightness peak at nearly the same distance from the core as the '25 mas knot' seen in the first- and second-epoch VLBI images. This feature is much less pronounced in the third epoch, and a relatively bright, new knot has appeared approximately 12 mas from the core. If this new component had a constant brightness during the 5 years separating the first and third observing epochs, then it must have moved away from the core with an apparent speed of at least 1.2c (compared with an upper limit of 0.23c for motion of the 25 mas knot). However, we cannot yet rule out a local brightening of the inner jet in favor of a new moving component. We determine a lower limit for the jet/couterjet brightness ratio of 100:1 within 6 mas of the core. We also present a new Very Large Array (VLA) image of the kpc-scale jet with 3 sec resolution, made from data obtained during the VLBI observations. The rate of decrease in jet surface brightness from parsec to kiloparsec scales is similar to jets in known superluminal radio sources.

Jones, Dayton L.↗
DOE OSTI2020

27 TeV pp collisions, Exotics type, PYTHIA8 generator: tev27pp_pythia8_darkpion_scan

The dark pions (emerging jets) model with the settings as those similar to the CMS paper in JHEP 02 (2019) 179 (https://arxiv.org/abs/1810.10069). The files use the A14 ATLAS tune with NNPDF23_lo_as_0130_qed. The luminosity was estimated from the first file and is not accurate for the entire dataset. All parameter settings and cross sections are included in the logfiles inside separate ProMC files. The files are designed for a detector scans. The emerging jet model is described in: Y. Bai and P. Schwaller, “Scale of dark QCD”,Phys. Rev. D89(2014) 063522,doi:10.1103/PhysRevD.89.063522,arXiv:1306.4676; P. Schwaller, D.Stolarski, and A. Weiler, “Emerging jets”,JHEP05(2015) 59,doi:10.1007/JHEP05(2015)059,arXiv:1502.05409. Evens are created using a fixed mediator mass of 10 TeV. The dark pion mass, m(DP), changes in the range 5 GeV - 2500 GeV. Together with the pion mass, Rho mass is m(DP)*4. pTminFSR changes as m(DP)*2+20 GeV. The decay length (ctau) changes in the range 1 -1500 mm. One file per a combination m(DP) - ctau is produced. How to use: Each file has the substring "_mXX_ctYY" where XX and YY indicate the dark pion mass and the decay length (in mm).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2001

Frequency Stratification of the Nonthermal Emission in Blazars

Research supported by this grant involved theoretical investigations of the multifrequency nonthermal emission from the relativistic jets in blazars, which are quasars and related objects with highly variable brightness. In the initial stage of the project, one-dimensional, conical (i.e., spherical symmetry between the jet axis and surface is assumed) jet models were used to explain the multi-waveband spectra and variability of blazars. The results were applied to two flares observed in the object PKS 2155-304, leading to the conclusion that the distinct differences in the observed characteristics of the two flares can be explained with the same jet model if two different physical parameters (the magnetic field in the first flare and the efficiency of acceleration of electrons to high energies in the second) varied.

Marscher, Alan P.↗
DOE OSTI2015

230 GHz VLBI observations of M87: Event‐horizon‐scale structure during an enhanced very‐high‐energy γ‐ray state in 2012

We report on 230 GHz (1.3 mm) very long baseline interferometry (VLBI) observations of M87 with the Event Horizon Telescope using antennas on Mauna Kea in Hawaii, Mt. Graham in Arizona, and Cedar Flat in California. For the first time, we have acquired 230 GHz VLBI interferometric phase information on M87 through measurement of the closure phase on the triangle of long baselines. Most of the measured closure phases are consistent with 0° as expected by physically motivated models for 230 GHz structure such as jet models and accretion disk models. The brightness temperature of the event-horizon-scale structure is ∼1×10{sup 10} K derived from the compact flux density of ∼1 Jy and the angular size of ∼40 μas ∼ 5.5 R{sub s}, which is broadly consistent with the peak brightness of the radio cores at 1–86 GHz located within ∼10{sup 2} R{sub s}. Our observations occurred in the middle of an enhancement in very-high-energy (VHE) γ-ray flux, presumably originating in the vicinity of the central black hole. Our measurements, combined with results of multi-wavelength observations, favor a scenario in which the VHE region has an extended size of ∼20–60 R{sub s}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Simulations on Head-Tail Radio Galaxies Using Magnetic Tower Model

The presentation is a series of slides showing diagrams, equations, and various photographs. In summary, a detailed comparison was carried out between hydrodynamic jet and MHD jet models (the magnetic tower jet, more precisely), in an effort to understand the underlying physics of observed radio galaxies, and also its possible indications for jet feedback. It was found that the results of magnetic tower model usually lie in a reasonable regime, and in several aspects, the magnetic tower jet seems more preferred than pure hydrodynamic jet models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Radio observations of a sample of broad-line type Ic supernovae discovered by PTF/IPTF: a search for relativistic explosions

Long duration γ-ray bursts are a rare subclass of stripped-envelope core-collapse supernovae (SNe) that launch collimated relativistic outflows (jets). All γ-ray-burst-associated SNe are spectroscopically Type Ic, with broad-lines, but the fraction of broad-lined SNe Ic harboring low-luminosity γ-ray bursts remains largely unconstrained. Some SNe should be accompanied by off-axis γ-ray burst jets that initially remain invisible, but then emerge as strong radio sources (as the jets decelerate). However, this critical prediction of the jet model for γ-ray bursts has yet to be verified observationally. Here, we present K. G. Jansky Very Large Array observations of 15 broad-lined SNe of Type Ic discovered by the Palomar Transient Factory in an untargeted manner. Most of the SNe in our sample exclude radio emission observationally similar to that of the radio-loud, relativistic SN 1998bw. We constrain the fraction of 1998bw-like broad-lined SNe Ic to be ≲41% (99.865% confidence). Most of the events in our sample also exclude off-axis jets similar to GRB 031203 and GRB 030329, but we cannot rule out off-axis γ-ray bursts expanding in a low-density wind environment. Three SNe in our sample are detected in the radio. PTF11qcj and PTF14dby show late-time radio emission with average ejecta speeds of ≈0.3–0.4 c, on the dividing line between relativistic and “ordinary” SNe. The speed of PTF11cmh radio ejecta is poorly constrained. We estimate that ≲85% (99.865% confidence) of the broad-lined SNe Ic in our sample may harbor off-axis γ-ray bursts expanding in media with densities in the range probed by this study.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

CONSTRAINING THE PHYSICAL CONDITIONS IN THE JETS OF γ-RAY FLARING BLAZARS USING CENTIMETER-BAND POLARIMETRY AND RADIATIVE TRANSFER SIMULATIONS. II. EXPLORING PARAMETER SPACE AND IMPLICATIONS

We analyze the shock-in-jet models for the γ-ray flaring blazars 0420-014, OJ 287, and 1156+295 presented in Paper I, quantifying how well the modeling constrains internal properties of the flow (low-energy spectral cutoff, partition between random and ordered magnetic field), the flow dynamics (quiescent flow speed and orientation), and the number and strength of the shocks responsible for radio-band flaring. We conclude that well-sampled, multifrequency polarized flux light curves are crucial for defining source properties. We argue for few, if any, low-energy particles in these flows, suggesting no entrainment and efficient energization of jet material, and for approximate energy equipartition between the random and ordered magnetic field components, suggesting that the ordered field is built by nontrivial dynamo action from the random component, or that the latter arises from a jet instability that preserves the larger-scale, ordered flow. We present evidence that the difference between orphan radio-band (no γ-ray counterpart) and non-orphan flares is due to more complex shock interactions in the latter case.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1999

Origin of Gamma-Ray Emissions from the MeV Blazars

More than sixty gamma-ray emitting blazars have been detected by the Compton Gamma Ray Observatory (CGRO). A sub-class of these blazars is known as MeV blazars that are most luminous at the MeV energies. Spectra of these sources show a break somewhere between 1 MeV and 30 MeV with break amplitude as large as DELTA-GAMMA = 1.5. Different models like Compton cooling jet models, synchrotron self-Compton models, etc., have been suggested to explain the observed properties of the MeV luminous blazars. However these models are unable to account for spectral break amplitudes in excess of 0.5. Here we suggest an inverse-Compton model based on recent published experimental data where MeV gamma rays were produced via Compton backscattering of UV photons with 500 MeV electrons. We show that the high energy electrons of the relativistic jet can collide with the copious ultraviolet photons of the big blue bump of the blazar, and produce photons peaked in the MeV region. Also we show that the X rays and the soft gamma rays in these sources are produced through the synchrotron self-Compton process. Flux computed from our model have been used to compare with the observed X-ray/gamma-ray spectra of the MeV luminous blazars. Details of the model are discussed in the present paper.

Ghosh, K. K.↗
NASA NTRS1998

Origin of Gamma-Ray Emissions from the MeV Blazars

More than sixty gamma-ray emitting blazars have been detected by the Compton Gamma Ray Observatory (CGRO). A sub-class of these blazars is known as MeV blazars that are most luminous at the MeV energies. Spectra of these sources show a break somewhere between 1 MeV and 30 MeV with break amplitude as large as Delta(Gamma) = 1.5. Different models like Compton cooling jet models, synchrotron self-Compton models, etc., have been suggested to explain the observed properties of the MeV luminous blazars. However these models are unable to account for spectral break amplitudes in excess of 0.5. Here we suggest an inverse-Compton model based on recent published experimental data where MeV gamma rays were produced via Compton backscattering of UV photons with 500 MeV electrons. We show that the high energy electrons of the relativistic jet can collide with the copious ultraviolet photons of the big blue bump of the blazar, and produce photons peaked in the MeV region. Also we show that the X rays and the soft gamma rays in these sources are produced through the synchrotron self-Compton process. Flux computed from our model have been used to compare with the observed X-ray/ gamma-ray spectra of the MeV luminous blazars. Details of the model are discussed in the present paper.

Ghosh, K. K.↗
NASA NTRS1993

Morphological Changes in the NGC 6251 Jet

The giant radio galaxy NGC 6251 is a particularly good object for observational tests of relativistic jet models. Due to its high declination and similar 0.5 Jy radio nucleus, high quality VLBI images of the central regions of the source can be made with northern hemisphere arrays. In addition, the large-scale radio morphology strongly suggests that the radio axis lies close to the plane of the sky, so Doppler boosting should be less extreme than in the core-dominated superluminal sources. Earlier 18-cm VLBI observations of NGC 6251 revealed an unexpectedly large jet/counterjet brightness ratio and small transverse motion of a feature in the parsec-scale jet. These early results are difficult to reconcile with the simplest symmetric relativistic jet models.

Wehrle, A. E.↗
DOE OSTI2017

Analysis of ELM stability with extended MHD models in JET, JT-60U and future JT-60SA tokamak plasmas

The stability with respect to a peeling–ballooning mode (PBM) was investigated numerically with extended MHD simulation codes in JET, JT-60U and future JT-60SA plasmas. The MINERVA-DI code was used to analyze the linear stability, including the effects of rotation and ion diamagnetic drift (${\omega }_{* {\rm{i}}}$), in JET-ILW and JT-60SA plasmas, and the JOREK code was used to simulate nonlinear dynamics with rotation, viscosity and resistivity in JT-60U plasmas. It was validated quantitatively that the ELM trigger condition in JET-ILW plasmas can be reasonably explained by taking into account both the rotation and ${\omega }_{* {\rm{i}}}$ effects in the numerical analysis. When deuterium poloidal rotation is evaluated based on neoclassical theory, an increase in the effective charge of plasma destabilizes the PBM because of an acceleration of rotation and a decrease in ${\omega }_{* {\rm{i}}}$. The difference in the amount of ELM energy loss in JT-60U plasmas rotating in opposite directions was reproduced qualitatively with JOREK. By comparing the ELM affected areas with linear eigenfunctions, it was confirmed that the difference in the linear stability property, due not to the rotation direction but to the plasma density profile, is thought to be responsible for changing the ELM energy loss just after the ELM crash. A predictive study to determine the pedestal profiles in JT-60SA was performed by updating the EPED1 model to include the rotation and ${\omega }_{* {\rm{i}}}$ effects in the PBM stability analysis. It was shown that the plasma rotation predicted with the neoclassical toroidal viscosity degrades the pedestal performance by about 10% by destabilizing the PBM, but the pressure pedestal height will be high enough to achieve the target parameters required for the ITER-like shape inductive scenario in JT-60SA.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗