Outflow Features Research Articles

Clinical and electrophysiological characteristics in patients with sustained monomorphic reentrant ventricular tachycardia associated with dilated-phase hypertrophic cardiomyopathy

Little is known about sustained monomorphic ventricular tachycardia (SMVT) associated with dilated-phase hypertrophic cardiomyopathy (DHCM). The purpose of this study was to clarify the clinical characteristics and effectiveness of catheter ablation for SMVTs in DHCM patients. Five patients with DHCM (mean age; 67.0 years old, five males) who underwent catheter ablation for drug-refractory SMVTs were included the study. Four of five patients suffered from electrical storm. When the endocardial ablation failed, epicardial and/or intracoronary ethanol ablation, or surgical cryoablation was performed. We reviewed all ablation procedures and electrocardiogram (ECG) of targeted SMVTs. A total of 13 SMVTs were targeted for ablation. Mechanism of all ventricular tachycardias (VTs) was diagnosed as reentry. Endocardial ablation successfully eliminated all VTs in two patients. The remaining three patients needed epicardial ablation, intracoronary ethanol ablation, and surgical cryoablation. All but one VT arose from the basal septum, basal anterior to anterolateral left ventricle (LV). Although the ECGs demonstrated similar features of idiopathic outflow or mitral annulus VTs reflecting the origins, there were characteristic multiple QRS deflections. Following the ablation, four (80%) of the five patients are free from VT recurrence during 18 months of the follow-up period. In DHCM patients, VT circuits predominantly distributed in the basal septum and the basal anterior to anterolateral LV. In addition to the endocardial ablation, alternative approaches were required in some patients.

JETS AND WIDE-ANGLE OUTFLOWS IN CEPHEUS E: NEW EVIDENCE FROMSPITZER

In some protostellar objects both wide angle outflows and collimated jets are seen, while in others only one is observed. Spitzer provides unprecedented sensitivity in the infrared to study both the jet and outflow features. Here, we use HiRes deconvolution to improve the visualization of spatial morphology by enhancing resolution (to sub-arcsecond levels in the IRAC bands) and removing the contaminating sidelobes from bright sources. We apply this approach to study the jet and outflow features in Cep E a young, energetic Class 0 protostar. In the reprocessed images we detect: (i) wide angle outflow seen in scattered light; (ii) morphological details on at least 29 jet driven bow shocks and jet heads or knots; (iii) three compact features in 24 micron continuum image as atomic/ionic line emission coincident with the jet heads; and, (iv) a flattened 35 arcsec size protostellar envelope seen against the interstellar background PAH emission as an absorption band across the protostar at 8 micron. By separating the protostellar photospheric scattered emission in the wide angle cavity from the jet emission we show that we can study directly the scattered light spectrum. We present the H2 emission line spectra, as observed in all IRAC bands, for 29 knots in the jets and bowshocks and use them in the IRAC color -- color space as a diagnostic of the thermal gas in the shocks driven by the jets. The data presented here will enable detailed modeling of the individual shocks retracing the history of the episodic jet activity and the associated accretion on to the protostar. The Spitzer data analysis presented here shows the richness of its archive as a resource to study the jet/outflow features in H2 and scattered light in a large homogeneous sample.

Improved modelling of downburst outflows for wind engineering applications using a cooling source approach

Large eddy simulations (LES), with a range of different practical ground roughness lengths ( z 0=0.001–0.1 m), are used to compare near surface outflow features of a physically realistic cooling source downburst model, previously validated by meteorological observations, with those of the more commonly used transient impinging impulsive jet. A scaling procedure is proposed, based on length, velocity, and vorticity scales from within the outflow, allowing for direct comparison between outflows from the two models. Five scaling parameters are presented, capturing the horizontal and vertical position of maximum velocity, the ring vortex aspect ratio, the height of the ring vortex above the surface, and a non-dimensional vorticity term representative of the relative contribution of the ring vortex to the near surface wind field. It is shown that the impinging jet model is not capable of capturing the outflow features predicted by the cooling source model, due to its unrealistic forcing parameters, and is, therefore, unable to capture the physics of an actual downburst event. This difference dominates the non-dimensional vorticity term, showing that impinging jet results deviate by at least 56% from the cooling source results, at times when all other scaling parameter differences are minimized.

A parametric study of downburst line near-surface outflows

Large Eddy Simulations (LES) of two identical downburst events, representing part of a downburst line, with a range of spatial (1, 2, and 3 km) and temporal (30, 60, 90, and 120 s) separations, are used to compare near-surface outflow features with those of an isolated event. Peak maximum wind speed and total damaging surface footprints are used to determine the expected critical wind loading conditions and likelihood of a surface structure being exposed to such an event. The results show that significant wind speed amplification factors of up to 1.55 and increases in damaging surface footprint of at least 70% can be expected from a two event downburst line. In addition, the peak maximum horizontal velocity in a downburst line is associated with smaller scale structures in the flow caused by downdraft interactions aloft, as opposed to the primary ring vortex expected for an isolated event. Subsequently, conventional downburst velocity profiles, used for an isolated event, cannot be applied in the collision region of a downburst line.

New Results on Quasar Outflows

AbstractAccretion disk outflows are an important part of the quasar phenomenon. They might play a major role in distributing metals to the galactic surroundings, halting growth of the central black hole and providing kinetic energy “feedback” to regulate star formation in the host galaxies. Some models of galaxy evolution indicate that feedback requires kinetic energy luminosities, LK, that are ~5% of the quasar bolometric; LK/L = Ṁwν2/2η:Ṁaccc2 ~ 5% is possible if Ṁw ~ Ṁacc (with ν~ 0.1c, and η ~ 0.1). Here we describe results from two studies designed to test the theoretical energetics of radiatively driven outflows and derive observational constraints on the outflow geometry and physical properties emphasizing weaker outflow features like NALs and mini-BALs.

A regional modeling study of the entraining Mediterranean outflow

We have evaluated a regional‐scale simulation of the Mediterranean outflow by comparison with field data obtained in the 1988 Gulf of Cádiz Expedition. Our ocean model is based upon the Hybrid Coordinate Ocean Model (HYCOM) and includes the Richardson number–dependent entrainment parameterization of Xu et al. (2006). Given realistic topography and sufficient resolution, the model reproduces naturally the major, observed features of the Mediterranean outflow in the Gulf of Cádiz: the downstream evolution of temperature, salinity, and velocity profiles, the mean path and the spreading of the outflow plume, and most importantly, the localized, strong entrainment that has been observed to occur just west of the Strait of Gibraltar. As in all numerical solutions, there is some sensitivity to horizontal and vertical resolution. When the resolution is made coarser, the simulated currents are less vigorous and there is consequently less entrainment. Our Richardson number–dependent entrainment parameterization is therefore not recommended for direct application in coarse‐resolution climate models. We have used the high‐resolution regional model to investigate the response of the Mediterranean outflow to a change in the freshwater balance over the Mediterranean basin. The results are found in close agreement with the marginal sea boundary condition (MSBC): A more saline and dense Mediterranean deep water generates a significantly greater volume transport of the Mediterranean product water having only very slightly greater salinity.

Modeling the water line emission from the high-mass star-forming region AFGL 2591

Context. Observations of water lines are a sensitive probe of the geometry, dynamics and chemical structure of dense molecular gas. The launch of Herschel with on board HIFI and PACS allows to probe the behaviour of multiple water lines with unprecedented sensitivity and resolution. Aims. We investigate the diagnostic value of specific water transitions in high-mass star-forming regions. As a test case, we apply our models to the AFGL 2591 region. Methods. A multi-zone escape probability method is used in two dimensions to calculate the radiative transfer. Similarities and differences of constant and jump abundance models are displayed, as well as when an outflow is incorporated. Results. In general, for models with a constant water abundance, the ground state lines, i.e., 110–101 ,1 11–000 ,a nd 2 12–101 ,a re predicted in absorption, all the others in emission. This behaviour changes for models with a water abundance jump profile in that the line profiles for jumps by a factor of ∼10–100 are similar to the line shapes in the constant abundance models, whereas larger jumps lead to emission profiles. Asymmetric line profiles are found for models with a cavity outflow and depend on the inclination angle. Models with an outflow cavity are favoured to reproduce the SWAS observations of the 110–101 ground-state transition. PACS spectra will tell us about the geometry of these regions, both through the continuum and through the lines. Conclusions. It is found that the low-lying transitions of water are sensitive to outflow features, and represent the excitation conditions in the outer regions. High-lying transitions are more sensitive to the adopted density and temperature distribution which probe the inner excitation conditions. The Herschel mission will thus be very helpful to constrain the physical and chemical structure of high-mass star-forming regions such as AFGL 2591.

Numerical analysis of funnel formation during unsteady fluid outflow from a rotating cylindrical vessel

The main features of the unsteady outflow of a fluid from a cylindrical vessel rotating together with it at a constant angular velocity through a central drain hole in the bottom are studied. The software package STAR-CD tested on the results of experiments with water in the absence of rotation is used. Certain important features of the phenomenon under consideration related with the formation of vortex funnels in the fluid are established. The effect of the main control parameters of the problem, namely, angular velocity, viscosity, initial depth, etc., is analyzed.

Proposed large-scale modelling of the transient features of a downburst outflow

A preceding companion article introduced the slot jet approach for large-scale quasi-steady modelling of a downburst outflow. This article extends the approach to model the time-dependent features of the outflow. A two-dimensional slot jet with an actuated gate produces a gust with a dominant roll vortex. Two designs for the gate mechanism are investigated. Hot-wire anemometry velocity histories and profiles are presented. As well, a three-dimensional, subcloud numerical model is used to approximate the downdraft microphysics, and to compute stationary and translating outflows at high resolution. The evolution of the horizontal and vertical velocity components is examined. Comparison of the present experimental and numerical results with field observations is encouraging.

Two Bipolar Outflows and Magnetic Fields in the Multiple Protostar System L1448 IRS 3

We present spectral line observations of CO J = 2 → 1, 13CO J = 1 → 0, and C18O J = 1 → 0 and polarimetric observations in the λ = 1.3 mm continuum and in CO J = 2 → 1 toward the multiple protostar system L1448 IRS 3, using the BIMA array. In the λ = 1.3 mm continuum, two sources (IRS 3A and 3B) were clearly detected with estimated envelope masses of 0.21 and 1.15 M☉, and one source (IRS 3C) was marginally detected with an upper mass limit of 0.03 M☉. In CO J = 2 → 1, we revealed two outflows originating from IRS 3A and 3B. The masses, mean number densities, momentums, and kinetic energies of outflow lobes were estimated. Based on those estimates and outflow features, we conclude that the two outflows are interacting and that the IRS 3A outflow is nearly perpendicular to the line of sight. In addition, we estimate the velocity, inclination, and opening of the IRS 3B outflow using Bayesian statistics. Linear polarization was detected in both the λ = 1.3 mm continuum and CO J = 2 → 1. The linear polarization in the continuum shows a magnetic field at the central source (IRS 3B) perpendicular to the outflow direction, and the linear polarization in the CO J = 2 → 1 was detected in the outflow regions either parallel or perpendicular to the outflow direction. Moreover, we comprehensively discuss whether the binary system of IRS 3A and 3B is gravitationally bound, based on the velocity differences detected in 13CO J = 1 → 0 and C18O J = 1 → 0 observations and on the outflow features. The specific angular momentum of the system is estimated as ~3 × 1020 cm2 s-1, comparable to the values obtained from previous studies of binary stars and molecular cloud cores.

The Remarkable Far‐Ultraviolet Spectrum of FK Comae Berenices: King of Spin

A Far Ultraviolet Spectroscopic Explorer (FUSE) pointing on the ultrafast rotating yellow giant FK Comae Berenices (HD 117555; v sin i ~ 163 km s-1) recorded emission profiles of C III λ977 (T ~ 8 × 104 K) and O VI λ1031 (T ~ 3 × 105 K) that are exceptionally broad and asymmetric, but nearly identical in shape, aside from a blueward absorption component in the latter (identified as interstellar O I, rather than, say, a C III outflow feature). The FWHMs exceed 500 km s-1, twice the broadest far-UV line shape of any normal late-type star observed to date, but similar to the Hα profiles of FK Com, and following the trend of other fast spinning early G giants that often display superrotational broadening of their UV hot lines. Although the red-asymmetric O VI λ1031 profile is suggestive of an outflow at ~3 × 105 K, the weaker member of the doublet, λ1037, does not display the differential absorption pattern expected from a warm wind. Furthermore, at times the chromospheric Mg II λ2796 + λ2803 composite profile, from a collection of International Ultraviolet Explorer (IUE) echellegrams obtained two decades earlier, is nearly identical in shape to red-asymmetric O VI λ1031. A contemporaneous optical Doppler map places the photospheric dark spots mainly in the polar regions of the approaching hemisphere. The dominantly redward biased profiles of C III and O VI could be explained if the associated emission zones were leading the starspots in phase and partially rooted in lower latitudes.

Signatures in flowing fluid electric conductivity logs

Flowing fluid electric conductivity logging provides a means to determine hydrologic properties of fractures, fracture zones, or other permeable layers intersecting a borehole in saturated rock. The method involves analyzing the time-evolution of fluid electric conductivity (FEC) logs obtained while the well is being pumped and yields information on the location, hydraulic transmissivity, and salinity of permeable layers. The original analysis method was restricted to the case in which flows from the permeable layers or fractures were directed into the borehole (inflow). Recently, the method was adapted to permit treatment of both inflow and outflow, including analysis of natural regional flow in the permeable layer. A numerical model simulates flow and transport in the wellbore during flowing FEC logging, and fracture properties are determined by optimizing the match between simulation results and observed FEC logs. This can be a laborious trial-and-error procedure, especially when both inflow and outflow points are present. Improved analyses methods are needed. One possible tactic would be to develop an automated inverse method, but this paper takes a more elementary approach and focuses on identifying the signatures that various inflow and outflow features create in flowing FEC logs. The physical insight obtained provides a basis for more efficient analysis of these logs, both for the present trial and error approach and for a potential future automated inverse approach. Inflow points produce distinctive signatures in the FEC logs themselves, enabling the determination of location, inflow rate, and ion concentration. Identifying outflow locations and flow rates typically requires a more complicated integral method, which is also presented in this paper.

IR Mergers/Qsos with Galactic Winds

We report, as a part of a long-term study of IR mergers and IR QSOs, detailed spectroscopic evidences for outflow (OF) features in nearby IR mergers/QSOs (with low and extreme velocity OF, LVOF and EVOF, respectively). We found EVOF in IRAS 01003-2238, 11119+3257, 13218+0552, 14394+5332, 15130-1958 and 15462-0450. The low velocity OF components were detected mainly in objects with starburst processes. Meanwhile the EVOF were found mainly in objects with obscured IR QSOs plus strong starbursts.HST images of IR+BAL+Fe II QSOs show in practically all of these objects “arc or shell” features probably associated to galactic winds (GW) and/or merger processes. We present also new results of a study of the morphology, kinematics and ionized structure of IR mergers/QSOs with GW. This new study is based mainly in INTEGRAL two-dimensional (2D) fibre spectroscopy (obtained at La Palma 4.2 m telescope).

CO Outflows from Young Stellar Objects

We have mapped the CO J = 1-0 emission from molecular outflows associated with six young stellar systems using the BIMA array. The systems are all relatively nearby, have low-luminosity, and range from Class 0 to Class II sources. The CO outflows in these systems are complicated, showing multipolar structures, multiple cavities, and asymmetric lobes. The complicated appearance of the CO outflows may result from the interactions between one or more outflows and the nonuniform ambient cloud. The CO emission typically arises from shell structures around the outflow axis. For some outflows, there are also clumpy and bowlike structures in CO along the outflow axis within the shell. Comparing the observed outflow features to that of jet- and wind-driven models, we find that the outflow systems show some features that are characteristic of the jet-driven model and others characteristic of the wind-driven model. Simple models of jets or winds cannot reproduce the full range of kinematic features found in observed outflows. The jet-driven model requires jet wandering to produce the observed outflow width and momentum content for most of these outflows, while the wind-driven model needs to have a collimated core with a strong velocity gradient away from the core to produce the highly collimated outflows and the observed curved internal H2 bow shock structures.

A test particle simulation of the motion of oxygen ions and solar wind protons near Mars

Outflowing oxygen ions (O+) have been observed to be a persistent feature in the Martian tail. However, not much is known of the spatial distribution of oxygen ions, of the correlation between oxygen ions and solar wind protons (H+), and, especially, of the acceleration of oxygen ions in the tail. We present a test particle simulation study of the motion of O+ and H+ ions and compare the results to Automatic Space Plasma Experiment with a Rotating Analyzer (ASPERA) Phobos 2 particle measurements. We have studied the spatial distribution, velocity, density, and flux of oxygen ions in the nightside. In the simulation the oxygen ions were ionized from the Martian hot oxygen corona and the H+ ions were solar wind protons. We used an empirical flow model to derive the magnetic and electric field everywhere around the planet. The work is the first test particle simulation for Mars where a fully three‐dimensional magnetotail configuration has been used. The model reproduces many observed plasma features. The solar wind protons flow fluid‐like near the terminator despite their finite Larmor radii. The oxygen ions produce a plasmasheet‐like layer near the cross‐tail current sheet and empty magnetic lobes, and have north‐to‐south asymmetry in the magnetosheath and in the tail much as observed. The energy of oxygen ions in the tail is close to, but slightly less than, observed. The particle density and the particle flux of oxygen ions also agree quite well with the observations, suggesting that the total O+ outflow rate is ∼ 2 × 1025 s−1. Overall, the study suggest that most of the observed O+ outflow features can be understood by assuming that the ions are accelerated by the convective electric field associated with the flow of the solar wind protons.

Thermal ion measurements on board Interball Auroral Probe by the Hyperboloid experiment

Abstract. Hyperboloid is a multi-directional mass spectrometer measuring ion distribution functions in the auroral and polar magnetosphere of the Earth in the thermal and suprathermal energy range. The instrument encompasses two analyzers containing a total of 26 entrance windows, and viewing in two almost mutually perpendicular half-planes. The nominal angular resolution is defined by the field of view of individual windows ≈13° × 12.5°. Energy analysis is performed using spherical electrostatic analyzers providing differential measurements between 1 and 80 eV. An ion beam emitter (RON experiment) and/or a potential bias applied to Hyperboloid entrance surface are used to counteract adverse effects of spacecraft potential and thus enable ion measurements down to very low energies. A magnetic analyzer focuses ions on one of four micro-channel plate (MCP) detectors, depending on their mass/charge ratio. Normal modes of operation enable to measure H+, He+, O++, and O+ simultaneously. An automatic MCP gain control software is used to adapt the instrument to the great flux dynamics encountered between spacecraft perigee (700 km) and apogee (20 000 km). Distribution functions in the main analyzer half-plane are obtained after a complete scan of windows and energies with temporal resolution between one and a few seconds. Three-dimensional (3D) distributions are measured in one spacecraft spin period (120 s). The secondary analyzer has a much smaller geometrical factor, but offers partial access to the 3D dependence of the distributions with a few seconds temporal resolution. Preliminary results are presented. Simultaneous, local heating of both H+ and O+ ions resulting in conical distributions below 80 eV is observed up to 3 Earth's radii altitudes. The thermal ion signatures associated with large-scale nightside magnetospheric boundaries are investigated and a new ion outflow feature is identified associated to the polar edge of the auroral oval. Detailed distribution functions of injected magnetosheath ions and ouflowing cleft fountain ions are measured down to a few eVs in the dayside.Key words. Ionosphere (auroral ionosphere; particle acceleration; ionosphere-magnetosphere interactions)

Thermal ion measurements on board Interball Auroral Probe by the Hyperboloid experiment

Hyperboloid is a multi-directional mass spectrometer measuring ion distribution functions in the auroral and polar magnetosphere of the Earth in the thermal and suprathermal energy range. The instrument encompasses two analyzers containing a total of 26 entrance windows, and viewing in two almost mutually perpendicular half-planes. The nominal angular resolution is defined by the field of view of individual windows ≈13° × 12.5°. Energy analysis is performed using spherical electrostatic analyzers providing differential measurements between 1 and 80 eV. An ion beam emitter (RON experiment) and/or a potential bias applied to Hyperboloid entrance surface are used to counteract adverse effects of spacecraft potential and thus enable ion measurements down to very low energies. A magnetic analyzer focuses ions on one of four micro-channel plate (MCP) detectors, depending on their mass/charge ratio. Normal modes of operation enable to measure H+, He+, O++, and O+ simultaneously. An automatic MCP gain control software is used to adapt the instrument to the great flux dynamics encountered between spacecraft perigee (700 km) and apogee (20 000 km). Distribution functions in the main analyzer half-plane are obtained after a complete scan of windows and energies with temporal resolution between one and a few seconds. Three-dimensional (3D) distributions are measured in one spacecraft spin period (120 s). The secondary analyzer has a much smaller geometrical factor, but offers partial access to the 3D dependence of the distributions with a few seconds temporal resolution. Preliminary results are presented. Simultaneous, local heating of both H+ and O+ ions resulting in conical distributions below 80 eV is observed up to 3 Earth's radii altitudes. The thermal ion signatures associated with large-scale nightside magnetospheric boundaries are investigated and a new ion outflow feature is identified associated to the polar edge of the auroral oval. Detailed distribution functions of injected magnetosheath ions and ouflowing cleft fountain ions are measured down to a few eVs in the dayside.Key words. Ionosphere (auroral ionosphere; particle acceleration; ionosphere-magnetosphere interactions)

Oxygen outflow in the Martian magnetotail

Characteristic features of the oxygen ion (O+) outflow in the nightside of Mars have been studied. The data set used includes all high telemetry O+ energy spectra observations made by the ASPERA particle instrument onboard the Phobos 2 spacecraft. Oxygen outflow within the optical shadow of Mars was detected on all orbits, but no clear structure was found when the ions were organised according to the cross‐flow component of the interplanetary magnetic field (IMF). Oxygen ions in the tail outside the shadow were, in contrast, detected only on a few orbits and were related to fluctuating magnetosheath magnetic and electric fields with non‐Parker spiral IMF orientation. The analysis indicates that O+ ions within the optical shadow from a “steady”, ever persisting outflow feature. The high energy O+ ions in the tail outside the optical shadow are in contrast possibly a manifestation of the dynamic nature of the Martian tail, although effects associated to an asymmetric tail can not be fully excluded.

A molecular line study of NGC 1333/IRAS 4.

Molecular line surveys and fully sampled spectral line maps at 1.3 and 0.87 mm are used to examine the physical and chemical characteristics of the extreme Class I sources IRAS 4A and 4B in the L1450/NGC 1333 molecular cloud complex. A very well collimated, jetlike molecular outflow emanates from IRAS 4A, with a dynamical age of a few thousand years. Symmetric, clumpy structure along the outflow lobes suggests that there is considerable variability in the mass-loss rate or wind velocity even at this young age. Molecular emission lines toward IRAS 4A and 4B are observed to be weak in the velocity range corresponding to quiescent material surrounding the young stellar objects (YSOs). Depletion factors of 10-20 are observed for all molecules, including CO, even for even for very conservative mass estimates from the measured millimeter and submillimeter dust continuum. However, abundances scaled with respect to CO are similar to other dark molecular cloud cores. Such depletions could be mimicked by high dust optical depths or increased grain emissivities at the observing frequencies of 230 and 345 GHz, but the millimeter and submillimeter spectral energy distributions suggest that this is unlikely over the single-dish size scales of 5000-10,000 AU. Dense, outflowing gas is found to be kinematically, but not spatially, distinct from the quiescent material on these size scales. If CO is used as a chemical standard for the high-velocity gas, we find substantial enhancements in the abundances of several molecules in outflowing material, most notably CS, SiO, and CH3OH. The SiO emission is kinematically well displaced from the bulk cloud velocity and likely arises from directly shocked material. As is the case for CO, however, the outflow features from more volatile species are centered near the cloud velocity and are often characterized by quite low rotational temperatures. We suggest that grain-grain collisions induced by velocity shear zones surrounding the outflow axes transiently desorb the grain mantles, resulting in large abundance enhancements of selected species. Similar results have recently been obtained in several other low-mass YSOs, where the outflowing gas is often both kinematically and spatially distinct, and are illustrative of the ability of accretion and outflow processes to simultaneously modify the composition of the gas and dust surrounding young stars.

Fluid outflows from Venus impact craters: Analysis from Magellan data

Many impact craters on Venus have unusual outflow features originating in or under the continuous ejecta blankets and continuing downhill into the surrounding terrain. These features clearly resulted from flow of low‐viscosity fluids, but the identity of those fluids is not clear. In particular, it should not be assumed a priori that the fluid is an impact melt. A number of candidate processes by which impact events might generate the observed features are considered, and predictions are made concerning the rheological character of flows produced by each mechanism. A sample of outflows was analyzed using Magellan images and a model of unconstrained Bingham plastic flow on inclined planes, leading to estimates of viscosity and yield strength for the flow materials. It is argued that at least two different mechanisms have produced outflows on Venus: an erosive, channel‐forming process and a depositional process. The erosive fluid is probably an impact melt, but the depositional fluid may consist of fluidized solid debris, vaporized material, and/or melt.