Shape Of Radial Profiles Research Articles

FEASTS Combined with Interferometry. II. Significantly Changed H i Surface Densities and Even More Inefficient Star Formation in Galaxy Outer Disks

We update the H i surface density measurements for a subset of 17 THINGS galaxies by dealing with the short-spacing problem of the original Very Large Array (VLA) H i images. It is the same sample that Bigiel et al. used to study the relation between H i surface densities and star formation (SF) rate surface densities in galaxy outer disks, which are beyond the optical radius r 25. For 10 galaxies, the update is based on combining original THINGS VLA H i images with H i images taken by the single-dish FAST in the FEASTS program. The median increment of H i surface densities in outer disks is 0.15–0.4 dex at a given new H i surface density. Several galaxies change significantly in the shape of radial profiles H i surface densities, and seven galaxies are now more than 1σ below the H i size–mass relation. We update the H i star formation laws in outer disks. The median relation between the H i surface densities and SF rate surface densities based on pixel-wise measurements shifts downward by around 0.15 dex because the H i surface density values shift rightward, and the scatter increases significantly. The scatter of the relation, indicating the star-forming efficiency, exhibits a much stronger positive correlation with the stellar mass surface density than before. Thus, detecting the previously missed, diffuse H i due to the short-spacing problem of the Very Large Array observations is important in revealing the true condition and variation in SF possibly regulated by stellar feedbacks in the localized environment of outer disks.

An updated global survey of alluvial fans on Mars: Distinguishing alluvial fans from other fan-shaped features through morphologic characterization

Alluvial fans formed on Mars during the late Hesperian to early Amazonian in a climatic transition from a time of regular surface water activity to the current dry and cold climate. The depositional environments recorded by alluvial fans represent the final era of potential habitability on the Martian surface. Alluvial fan deposits can often look similar to deltaic or fluvial systems in visible remote sensing images but are formed in depositional and climatic environments that are distinct from those that lead to other radial depositional features. In order to better constrain regional and global depositional environments and further inform the analysis of the sedimentary history of Mars, we expanded the global catalog of alluvial fans on Mars by adding newly identified features and characterizing all new and previously identified features based on morphologic parameters. Using planform shape, radius, average radial slope, and radial profile shape, we classified features as alluvial fans, possible alluvial fans, and non-alluvial radial features (NARFs), based on how closely they fit the morphologic definition of alluvial fans. Other radial-shaped depositional features form in more water-rich depositional environments whereas alluvial fans form by subaerial deposition in arid to hyper arid environments from sporadic high-energy flow events interspersed with long dry periods of inactivity. By identifying new features and distinguishing alluvial fans from other fan-shaped features in the global catalog, we have isolated distinct depositional environments on a local scale and updated the global perspective of the distribution and variety of aqueous depositional environments during the early history of Mars. Newly identified alluvial fans are found as far as 78°S latitude as well as in numerous locations within the Hesperian to Noachian transition unit along the dichotomy and occur both in craters and along non-crater topographic features, expanding the global range of alluvial fan environments into regions that previously have been overlooked.

The width of Herschel filaments varies with distance

Context. Filamentary structures in nearby molecular clouds have been found to exhibit a characteristic width of 0.1 pc, as observed in dust emission. Understanding the origin of this universal width has become a topic of central importance in the study of molecular cloud structure and the early stages of star formation. Aims. We investigate how the recovered widths of filaments depend on the distance from the observer by using previously published results from the Herschel Gould Belt Survey. Methods. We obtained updated estimates on the distances to nearby molecular clouds observed with Herschel by using recent results based on 3D dust extinction mapping and Gaia. We examined the widths of filaments from individual clouds separately, as opposed to treating them as a single population. We used these per-cloud filament widths to search for signs of variation amongst the clouds of the previously published study. Results. We find a significant dependence of the mean per-cloud filament width with distance. The distribution of mean filament widths for nearby clouds is incompatible with that of farther away clouds. The mean per-cloud widths scale with distance approximately as 4−5 times the beam size. We examine the effects of resolution by performing a convergence study of a filament profile in the Herschel image of the Taurus Molecular Cloud. We find that resolution can severely affect the shapes of radial profiles over the observed range of distances. Conclusions. We conclude that the data are inconsistent with 0.1 pc being the universal characteristic width of filaments.

Estimating local noise power spectrum from a few FBP-reconstructed CT scans.

Traditional ways to estimate 2D CT noise power spectrum (NPS) involve an ensemble average of the power spectrums of many noisy scans. When only a few scans are available, regions of interest are often extracted from different locations to obtain sufficient samples to estimate the NPS. Using image samples from different locations ignores the nonstationarity of CT noise and thus cannot accurately characterize its local properties. The purpose of this work is to develop a method to estimate local NPS using only a few fan-beam CT scans. As a result of FBP reconstruction, the CT NPS has the same radial profile shape for all projection angles, with the magnitude varying with the noise level in the raw data measurement. This allows a 2D CT NPS to be factored into products of a 1D angular and a 1D radial function in polar coordinates. The polar separability of CT NPS greatly reduces the data requirement for estimating the NPS. The authors use this property and derive a radial NPS estimation method: in brief, the radial profile shape is estimated from a traditional NPS based on image samples extracted at multiple locations. The amplitudes are estimated by fitting the traditional local NPS to the estimated radial profile shape. The estimated radial profile shape and amplitudes are then combined to form a final estimate of the local NPS. We evaluate the accuracy of the radial NPS method and compared it to traditional NPS methods in terms of normalized mean squared error (NMSE) and signal detectability index. For both simulated and real CT data sets, the local NPS estimated with no more than six scans using the radial NPS method was very close to the reference NPS, according to the metrics of NMSE and detectability index. Even with only two scans, the radial NPS method was able to achieve a fairly good accuracy. Compared to those estimated using traditional NPS methods, the accuracy improvement was substantial when a few scans were available. The radial NPS method was shown to be accurate and efficient in estimating the local NPS of FBP-reconstructed 2D CT images. It presents strong advantages over traditional NPS methods when the number of scans is limited and can be extended to estimate the in-plane NPS of cone-beam CT and multislice helical CT scans.

Comparison of geosynchronous energetic particle flux responses to solar wind dynamic pressure enhancements and substorms

Geosynchronous energetic particle fluxes are used to examine the differences and similarities between the particle disturbances due to an enhancement in solar wind dynamic pressure Pdyn and those caused by substorms. Disturbances are also distinguished by IMF conditions. First, for not strongly southward IMF conditions (weakly southward or northward IMF), we find that the magnetospheric compression by a Pdyn enhancement usually causes particle fluxes to increase simultaneously at all energy channels. The increase is global around the Earth, but it usually occurs first on the dayside and then propagates to the nightside within a few minutes. We also find that a magnetospheric compression sometimes leads to a flux decrease or no flux change for at least one energy channel at some MLTs, which we attribute to the shape of radial profiles at constant adiabatic invariants. However, we find no evidence for substorm‐like injections in our Pdyn enhancement events when the IMF is not strongly southward. Following prolonged strongly southward IMF, substorms caused by IMF changes that lead to convection electric field reduction and are not associated with a Pdyn change generate flux disturbances that are quite similar to typical substorm flux disturbances for less strongly southward IMF conditions. However, the dispersionless injection front is found over a much wider azimuthal region, sometimes extending to the late afternoonside for protons. We find that under prolonged steady, strongly southward IMF conditions, a Pdyn enhancement leads to a two‐mode type disturbance. The disturbance due to magnetospheric compression can be clearly identified and is seen primarily on the dayside, and a substorm‐like injection associated with current wedge formation is seen on the nightside. The dayside compression effect is seen in both species, but is often more easily identified in the proton fluxes than in the electron fluxes. The substorm‐like injection feature is also seen in both species but is usually more evident in the electron fluxes. In the events studied here, the dayside compression disturbance precedes the substorm‐like injection on the nightside by a few minutes.

Study of properties of CO2 laser mixture

The positive column of DC glow discharge sustained in CO2 mixture (containing CO2, N2 and He) has been studied in pressure range (300÷1400) Pa and for discharge currents up to 40 mA. Parameters of discharge — electrical field strength and emission spectra — have been studied by means of double-probe method and optical emission spectroscopy. Optical scanner of original construction that enables us to study radial variations of intensities of emission lines and bands has been used for the collection of emission spectra. We have focused on the investigation of intensities of spectral bands of the second positive system of molecular nitrogen corresponding to the transition N2(C)→N2(B) in the presented paper. It has been found that shapes of radial profiles of studied bands are independent on pressure and discharge current, despite the fact that intensity of N2(C) bands decreases with increasing pressure and with decreasing current. It has also been possible to estimate vibrational temperatureTvib from measured intensities of N2(C) bands. It was observed thatTvib stays almost constant in the radial direction under our experimental conditions, but it increases with increasing discharge current and slightly decreases with increasing pressure.

Radial Profiles of Particle Velocity in a Large Scale CFB Downer

Radial profiles of particle velocity in a large scale (418 mm I.D.) downward Circulating Fluidized Bed (CFB downer) were obtained via a Laser Doppler Velocimetry (LDV) system. Results show that particle velocity is gradually increasing along the radial direction and there exists a peak value in the near wall region. Such unique radial profile shape can be explained by the solids accumulating trend in the near wall region of the downer. Experiment results in this large scale downer are also compared with those obtained by other researchers in small scale units so as to investigate the scale-up effect on the radial particle velocity distribution in the downer.

The Broadband Optical Properties of Galaxies with Redshifts 0.02 < z < 0.22

Using photometry and spectroscopy of 144,609 galaxies from the Sloan Digital Sky Survey, we present bivariate distributions of pairs of seven galaxy properties: four optical colors, surface brightness, radial profile shape as measured by the Sersic index, and absolute magnitude. In addition, we present the dependence of local galaxy density (smoothed on 8 h^{-1} Mpc scales) on all of these properties. Several classic, well-known relations among galaxy properties are evident at extremely high signal-to-noise ratio: the color-color relations of galaxies, the color-magnitude relations, the magnitude-surface brightness relation, and the dependence of density on color and absolute magnitude. We show that most of the i-band luminosity density in the universe is in the absolute magnitude and surface brightness ranges used. Some of the relationships between parameters, in particular the color--magnitude relations, show stronger correlations for exponential galaxies and concentrated galaxies taken separately than for all galaxies taken together. We provide a simple set of fits of the dependence of galaxy properties on luminosity for these two sets of galaxies.

Alpha-Particle-Induced Toroidal Flows in Tokamak Reactor Plasma

In this paper the toroidal rotation of a plasma with alpha particles is studied. The various mechanisms and factors of alpha-particle influence on rotation are considered: the difference between the actual radial profile shape of the alpha particles and the profile shape of alpha-particle production; the finite relaxation times of the toroidal angular momentum for the various components of a fusion plasma; and the nonzero average longitudinal velocity of alpha particles escaping from a plasma. The alpha-particle longitudinal current in the peripheral region of an International Thermonuclear Experimental Reactor-like tokamak is found, using the assumption that the alpha-particle radial distribution is determined by the diffusion of the toroidally trapped particles.