Counter Jet Research Articles

Single cavitation bubble generation and observation of the bubble collapse flow induced by a pressure wave

This study utilizes a U-shape platform device to generate a single cavitation bubble for a detailed analysis of the flow field characteristics and the cause of the counter jet during the process of bubble collapse caused by sending a pressure wave. A high speed camera is used to record the flow field of the bubble collapse at different distances from a solid boundary. It is found that a Kelvin–Helmholtz vortex is formed when a liquid jet penetrates the bubble surface after the bubble is compressed and deformed. If the bubble center to the solid boundary is within one to three times the bubble’s radius, a stagnation ring will form on the boundary when impinged by the liquid jet. The fluid inside the stagnation ring will be squeezed toward the center of the ring to form a counter jet after the bubble collapses. At the critical position, where the bubble center from the solid boundary is about three times the bubble’s radius, the bubble collapse flow will vary. Depending on the strengths of the pressure waves applied, the collapse can produce a Kelvin–Helmholtz vortex, the Richtmyer–Meshkov instability, or the generation of a counter jet flow. If the bubble surface is in contact with the solid boundary, the liquid jet can only move inside-out without producing the stagnation ring and the counter jet; thus, the bubble collapses along the radial direction. The complex phenomenon of cavitation bubble collapse flows is clearly manifested in this study.

DeepChandraObservation of the Pulsar Wind Nebula Powered by Pulsar PSR J1846−0258 in the Supernova Remnant KES 75

We present the results of detailed spatial and spectral analysis of the pulsar wind nebula (PWN) in supernova remnant Kes 75 (G29.7–0.3) using a deep exposure with Chandra X-Ray Observatory. The PWN shows a complex morphology with clear axisymmetric structure. We identified a one-sided jet and two bright clumps aligned with the overall nebular elongation, and an arclike feature perpendicular to the jet direction. We interpret the arc as an equatorial torus or wisp and the clumps could be shock interaction between the jets and the surrounding medium. Spatial modeling of the features with a torus and jet model indicates a position angle 207°± 8° for the PWN symmetry axis. The lack of any observable counter jet implies a flow velocity larger than 0.4 c. Comparing to an archival observation 6 yr earlier, some small-scale features in the PWN demonstrate strong variability: the flux of the inner jet doubles, and the peak of the northern clump broadens and shifts 2'' outward. As recently reported from RXTE observations, magnetar-like bursts of the central pulsar occurred coincidentally 7 days before the Chandra exposure. Accompanied with the bursts is a temporary increase in the pulsar flux: during the Chandra observation, the pulsar luminosity is 6 times larger than in quiescent state, and shows substantial spectral softening from Γ = 1.1 to 1.9 with an emerging thermal component.

Detailed study of the GRB 030329 radio afterglow deep into the non-relativistic phase

Context. We explore the physics behind one of the brightest radio afterglows ever, GRB 030329, at late times when the jet is nonrelativistic. Aims. We determine the physical parameters of the blast wave and its surroundings, in particular the index of the electron energy distribution, the energy of the blast wave, and the density (structure) of the circumburst medium. We then compare our results with those from image size measurements. Methods. We observed the GRB 030329 radio afterglow with the Westerbork Synthesis Radio Telescope and the Giant Metrewave Radio Telescope at frequencies from 325 MHz to 8.4 GHz, spanning a time range of 268−1128 days after the burst. We modeled all the available radio data and derived the physical parameters. Results. The index of the electron energy distribution is p = 2.1, the circumburst medium is homogeneous, and the transition to the non-relativistic phase happens at tNR ∼ 80 days. The energy of the blast wave and density of the surrounding medium are comparable to previous findings. Conclusions. Our findings indicate that the blast wave is roughly spherical at tNR, and they agree with the implications from the VLBI studies of image size evolution. It is not clear from the presented dataset whether we have seen emission from the counter jet or not. We predict that the Low Frequency Array will be able to observe the afterglow of GRB 030329 and many other radio afterglows, constraining the physics of the blast wave during its non-relativistic phase even further.

301 対向噴流によるタンク圧力制御の試み(流対工学I)

301 対向噴流によるタンク圧力制御の試み(流対工学I)

Discovery of a bipolar X-ray jet from the T Tauri star DG Tauri

Aims. We have obtained and analyzed Chandra ACIS-S observations of the strongly accreting classical T Tauri star DG Tau. Our principal goals are to map the immediate environment of the star to characterize possible extended X-rays formed in the jet, and to re-visit the anomalous, doubly absorbed X-ray spectrum of DG Tau itself. Methods. We combine our new ACIS-S data with a data set obtained previously. The data are superimposed to obtain flux and hardness images. Separate X-ray spectra are extracted for DG Tau and areas outside its point spread function. Results. We detect a prominent X-ray jet at a position angle of PA ≈ 225 deg (tentatively suggested by Gudel et al. 2005, ApJ, 626, L53), coincident with the optical jet axis. We also identify a counter jet at PA = 45 deg. The X-ray jets are detected out to a distance of ≈5 �� from the star, their sources being extended at the ACIS-S resolution. The jet spectra are soft, with a best-fit electron temperature of 3.4 MK. We find evidence for excess absorption of the counter jet. The spectrum of the DG Tau point source shows two components with largely different temperatures and absorption column densities. Conclusions. The similar temperatures and small absorbing gas columns of the jet sources and the soft component of the “stellar” source suggest that these sources are related, produced either by shocks or by magnetic heating in the jets. Cooling estimates suggest that the pressure in the hot gas contributes to jet expansion. The hard “stellar” component, on the other hand, is associated with a stellar corona or magnetosphere. The excessive photoelectric absorption of this component suggests the presence of dust-depleted accretion streams above coronal magnetic fields.

The jet-powered optical nebula of Cygnus X-1

We present Hα and [O iii] (5007 Å) images of the nebula powered by the jet of the black hole candidate and microquasar Cygnus X–1, observed with the 2.5-m Isaac Newton Telescope (INT). The ring-like structure is luminous in [O iii] and there exists a thin outer shell with a high [O iii]/Hα flux ratio. This outer shell probably originates in the collisionally excited atoms close to the front of the bow shock. Its presence indicates that the gas is shock excited as opposed to photoionized, supporting the jet-powered scenario. The shock velocity was previously constrained at 20 < vs < 360 km s−1; here we show that vs≥ 100 km s−1 (1σ confidence) based on a comparison of the observed [O iii]/Hα ratio in the bow shock with a number of radiative shock models. From this we further constrain the time-averaged power of the jet: PJet= (4–14) × 1036 erg s−1. The Hα flux behind the shock front is typically 4 × 10−15 erg s−1 cm−2 arcsec−2, and we estimate an upper limit of ∼ 8 × 10−15 erg s−1 cm−2 arcsec−2 (3σ) to the optical (R-band) continuum flux of the nebula. The inferred age of the structure is similar to the time Cyg X–1 has been close to a bright H ii region (due to the proper motion of the binary), indicating a dense local medium is required to form the shock wave. In addition, we search a >1 deg2 field of view to the south of Cyg X–1 in Hα (provided by the INT Photometric Hα Survey of the Northern Galactic Plane; IPHAS) for evidence of the counter jet interacting with the surrounding medium. Two candidate regions are identified, whose possible association with the jet could be confirmed with follow-up observations in [S ii] and deeper observations in [O iii] and radio.

Statistical Characteristics of the Cross-Sectional Concentration Field in a Round Counter Jet

The concentration field of a diffusing matter in the cross plane of a turbulent round jet injected into a counter-flowing uniform stream has been investigated using the PLIF technique. In order to capture images in good focus from a camera oriented obliquely to the object plane, the camera configuration has been designed according to the Scheimpflug condition and a water prism has been introduced to reduce the amount of radial distortions that are caused by capturing images through a channel wall. In addition to the mean and rms concentration fields in the cross-section, turbulent dispersion properties, such as the centroid and the absolute and relative spreads, have been examined by integrating the instantaneous concentration field over a cross-sectional area. It has been confirmed that a random fluctuation in the centroid of instantaneous concentration field exists in the cross plane and its amplitude increases downstream more rapidly as compared with the conventional jet in a quiescent ambient. These results could have a close relation with a radial oscillation of the jet core, which is expected to be responsible for its enhanced mixing efficiency.

WS1-4 PLIFによる対向噴流中の物質拡散場の実験(1)(WS1 乱流拡散・混合・反応流研究の最前線(その2),ワークショップ)

WS1-4 PLIFによる対向噴流中の物質拡散場の実験(1)(WS1 乱流拡散・混合・反応流研究の最前線(その2),ワークショップ)

Polarization and structure of relativistic parsec-scale AGN jets

We consider the polarization properties of optically thin synchrotron radiation emitted by relativistically moving electron-positron jets carrying large-scale helical magnetic fields. In our model, the jet is cylindrical, and the emitting plasma moves parallel to the jet axis with a characteristic Lorentz factor {Lambda}. We draw attention to the strong influence that the bulk relativistic motion of the emitting relativistic particles has on the observed polarization. Our computations predict and explain the following behavior. (1) For jets unresolved in the direction perpendicular to their direction of propagation, the position angle of the electric vector of the linear polarization has a bimodal distribution, being oriented either parallel or perpendicular to the jet. (2) If an ultra-relativistic jet with {Lambda} >> 1 whose axis makes a small angle to the line of sight, {theta} {approx} 1/{Lambda}, experiences a relatively small change in the direction of propagation, velocity or pitch angle of the magnetic fields, the polarization is likely to remain parallel or perpendicular; on the other hand, in some cases, the degree of polarization can exhibit large variations and the polarization position angle can experience abrupt 90{sup o} changes. This change is more likely to occur in jets with flatter spectra. (3)more » In order for the jet polarization to be oriented along the jet axis, the intrinsic toroidal magnetic field (in the frame of the jet) should be of the order of or stronger than the intrinsic poloidal field; in this case, the highly relativistic motion of the jet implies that, in the observer's frame, the jet is strongly dominated by the toroidal magnetic field B{sub {phi}}/B{sub z} {ge} {Lambda}. (4) The emission-weighted average pitch angle of the intrinsic helical field in the jet must not be too small to produce polarization along the jet axis. In force-free jets with a smooth distribution of emissivities, the emission should be generated in a limited range of radii not too close to the jet core. (5) For mildly relativistic jets, when a counter jet can be seen, the polarization of the counter jet is preferentially orthogonal to the axis, unless the jet is strongly dominated by the toroidal magnetic field in its rest frame. (6) For resolved jets, the polarization pattern is not symmetric with respect to jet axis. Under certain conditions, this can be used to deduce the direction of the spin of the central object (black hole or disk), whether it is aligned or anti-aligned with the jet axis. (7) In resolved ''cylindrical shell'' type jets, the central parts of the jet are polarized along the axis, while the outer parts are polarized orthogonal to it, in accordance with observations. We conclude that large-scale magnetic fields can explain the salient polarization properties of parsec-scale AGN jets. Since the typical degrees of polarization are {le} 15%, the emitting parts of the jets must have comparable rest-frame toroidal and poloidal fields. In this case, most relativistic jets are strongly dominated by the toroidal magnetic field component in the observer's frame, B{sub {phi}}/B{sub z} {approx} {Lambda}. We also discuss the possibility that relativistic AGN jets may be electromagnetically (Poynting flux) dominated. In this case, dissipation of the toroidal magnetic field (and not fluid shocks) may be responsible for particle acceleration.« less

Delayed Flashes from Counterjets of Gamma‐Ray Bursts

If X-ray flashes are due to the forward jet emissions from gamma ray bursts (GRBs) observed with large viewing angles, we show that a prompt emission from a counter jet should be observed as a delayed flash in the UV or optical band several hours to a day after the X-ray flash. Ultraviolet and Optical Telescope on Swift can observe the delayed flashes within ~13 Mpc, so that (double-sided) jets of GRBs may be directly confirmed. Since the event rate of delayed flashes detected by Swift may be as small as 6*10^{-5}events/yr, we require more sensitive detectors in future experiments.

305 対向吐出ジェットファンを有する自動車用トンネル内の局所風速低減

305 対向吐出ジェットファンを有する自動車用トンネル内の局所風速低減

On the Asymmetries in Powerful Extragalactic Radio Sources

We have investigated the correlations between the asymmetries in depolarization and spectral index in a bright source sample. We find a significant correlation between these asymmetries which can be understood in terms of the relativistic beaming hypothesis in which the counter jet side is steeper and more polarized than the jet side due to the presence of a halo of hot gas surrounding the source and contribution from the beamed jet and hot spot emission to the observed lobe emission. This simple interpretation is however complicated by the presence of a stronger correlation between these parameters and extended luminosity which is expected to be aspect-invariant; suggesting that the observed spectral index – depolarization correlation is an artefact of their being separately correlated with radio luminosity.

低温気流粉砕したそば粉の性質

低温気流粉砕そば粉と従来のロール挽そば粉の性質を比較した.低温気流粉砕そば粉は13.7%のタンパク質を含有し,平均粒度が15μmであった.低温気流粉砕そば粉は水分を吸収する力が強く,自重の2.8倍に膨潤した.低温気流粉砕そば粉100%から製造した茹で麺は,切断の少ない長い麺線となった.ロール挽そば粉から作った麺は,茹でと水洗いにより短い麺線に切断された.ロール挽そば粉と低温気流粉砕そば粉を等量使用した場合も切断のない麺線の比率が高くなった.匂いセンサ出力の主成分分析により,低温気流粉砕そば粉とロール挽そば粉は区別された.

Bubble dynamics, shock waves and sonoluminescence

Sound and light emission by bubbles is studied experimentally. Single bubbles kept in a bubble trap and single lasergenerated bubbles are investigated using ultrafast and highspeed photography in c...

The Radio Jet of Quasar 0153+744

AbstractWe highlight a few aspects of the radio jet of quasar 0153+744. Some challenge the relativistic beaming model to explain a stationary jet of short length and ending in a bright secondary component, extreme bending of the jet, and the lack of any emission on the counter jet side. We discuss a model of a precessing mildly relativistic jet for 0153+744.

Combined-array images of quasar 3C 286 at 18 cm wavelength

MERLIN, VLBI and MERLIN+VLBI images of QSO 3C286 at wave-length 18cm are presented. Low-brightness features in the MERLIN image are just resolved in the MERLIN+VLBI image. But some vestiges still remain. The extension of the central part of the MERLIN+VLBI image is longer than that of the VLBI image. Even though the dynamic range of the MERLIN+VLBI image is better than 1000:1, the counter jet is not found. Several models are used to interpret the observed structures.

Near-infrared imaging of HH 1/2 in shocked molecular hydrogen and (Fe II)

view Abstract Citations (49) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-infrared imaging of HH 1/2 in shocked molecular hydrogen and [Fe II] Davis, Chris J. ; Eisloeffel, Jochen ; Ray, Thomas P. Abstract We report here on near-infrared imaging of the HH 1/2 region in the H2 nu = 1 goes to 0 S(1) (2.121 micrometer) and (Fe II) (1.645 micrometer) lines. These observations reveal in detail the morphology of low and intermediate-velocity shocks in this area. In H2 only the eastern boundary of the HH 1 bow shock is observed, presumably because of an asymmetrical distribution of ambient gas. Diffuse emission is also seen northwest (downstream) of HH 1. The VLA 1 jet is found to be more continuous, but of a similar length compared to that in the optical. A bright H2 knot is found along the jet. Close to, and within, HH 2 we see evidence for the first time of a possible counter jet: in H2 the faint optical tail to the northwest of HH 2 is seen as a series of clumps, while a string of fainter knots runs through HH 2 (and along the outflow axis) toward its southeastern corner. Many of the H2 knots in HH 2 can be identified with corresponding optical knots, though there are clear differences in morphology and relative brightness. In particular their arc-shaped geometry in H2 is indicative of 'minibow shocks' which may result from a collection of 'bullets' within HH 2. Features in the (Fe II) images are in general similar to the brightest optical emission observed in the (S II) lambda lambda 6717, 6731 low-excitation lines. Publication: The Astrophysical Journal Pub Date: May 1994 DOI: 10.1086/187348 Bibcode: 1994ApJ...426L..93D Keywords: Herbig-Haro Objects; Hydrogen Clouds; Infrared Imagery; Iron; Molecular Clouds; Shock Waves; Stellar Mass Ejection; Astronomical Photometry; Astronomical Spectroscopy; Infrared Astronomy; Astronomy full text sources ADS | data products SIMBAD (31)

Counter jet stagnation flows

The present paper concerns the stagnation flow produced by counter flowing air jets. Little experimental information exists on such flows in spite of their extensive employment in the theoretical treatment of diffusion flames. To remedy this situation, laser-Doppler measurements were performed to quantify the entire flow field. The experiments are described and the results of the velocity measurements presented. Differences between the investigated flow field and the ideal flow field, employed in theoretical studies, are pointed out.

The nature of the optical filaments in Centaurus A. Evidence for a beamed ionizing continuum⋆

New observations, including both narrow-band imaging and long-slit spectroscopy, of the optical filaments in Centaurus A are presented. The line-emitting filaments which compose part of the well-known optical-jet are complex and highly structured at the limit of ground-based resolution. Variations in the surface brightness, line intensity ratios and the velocity field occur on spatial scales ∼ 100 pc. No evidence of [O III] λ5007 emission associated with either the inner jet or a possible counter jet are found. The emission line spectra of the filaments are very similar in character to those of the spatially extended nebulosities in more distant radio galaxies and radio quasars.

B211 トゥインクルレーザシート法を用いた車室内空調流れの流速測定

In this study, the velocity distributions of the flow in 1/4 model of air conditioned car room were measured by Twinkle-Laser-Sheet Technique which is based on the flow visualization technique of the so-called tracer method. As a result, the jet flow from the nozzle in front of the front sheet and the existence of local recirculating flows were clearly shown. Moreover, it was known that the counter jet flow from the nozzle beside the foot-rest made better flow pattern in the model car room. It has been confirmed from the present experimental study that this velocity measurement technique could be one of the simplest and most convinient methods for 3-D and complex flow fields.