Negative Velocity Component Research Articles

Robot-LDA Plane Measurements And Smoke Investigations On A 30° Inclined Flat Plate In An Open Wind Channel With And Without Plasma Actuation Effect

Active flow control is a relatively new approach to influence the velocity vector field for plane airfoils or process engineering applications with a plasma source. The goal is to positively effect the point of separation to increase the lift/drag ratio or increase separation efficiency and to reduce pressure drop. In the presented study two approaches, the Robot-LDA measurements and smoke investigations, are chosen to find out whether the plasma source has an effect on the velocity vector field on a 30°inclined flat plate and the separation point. A flow rate of 250 m³/h resulting in a Reynolds number of 100 000 is chosen, since this is typical for already presented results within the field of plasma source investigations. With Robot-LDA in total 825 measurements points of the axial wind channel velocity components are captured twice, with and without activated plasma source. The measurement plane was set 80 mm x 50 mm orthogonal to the flat plate in the middle of the wind channel axis. The plasma source was powered with 14 kVp−p and 5 kHz. Due to stability of the plasma actuator, the LDA measurements were subdivided into eight regions. For the same configurations smoke investigations are performed. A chromium-nickel wire with a diameter of 0.213 mm is heated by an electronic circuit including capacitor and power source to vaporize liquid paraffin. The flow field is captured by a highspeed camera. Robot-LDA measurement results show a free-stream axial wind channel velocity component of about 15 m/s. In the shadow region of the 30°inclined flat plate a recirculation zone is found due to negative velocity components. At a distance up to 12 mm close to the plat plate, wall reflections dominated and to find valid LDA measurement results were not possible. With and without activated plasma source velocity differences between -0.5 m/s and 0.5 m/s are found. The biggest velocity differences are in the region of 15 mm to 45 mm relative to the tip of the inclined flat plate. For post-processing purposes, the 3D wind channel geometry and the Robot-LDA measurement results are loaded in ParaView 5.10.1. Smoke investigations show that the plasma source minimally attach the flow to the flat plate. This effect is higher with smaller flow rates (50 m³/h) than with 250 m³/h. Robot-LDA and smoke measurement results are promising that flow influence due to plasma has potential in various applications in future.

Study of diffuse H II regions potentially forming part of the gas streams around Sgr A*

We present a study of diffuse extended ionised gas toward three clouds located in the Galactic Centre (GC). One line of sight (LOS) is toward the 20 km s$^{-1}$ cloud (LOS$-$0.11) in the Sgr A region, another LOS is toward the 50 km s$^{-1}$ cloud (LOS$-$0.02), also in Sgr A, while the third is toward the Sgr B2 cloud (LOS+0.693). The emission from the ionised gas is detected from H$n\alpha$ and H$m\beta$ radio recombination lines (RRLs). He$n\alpha$ and He$m\beta$ RRL emission is detected with the same $n$ and $m$ as those from the hydrogen RRLs only toward LOS+0.693. RRLs probe gas with positive and negative velocities toward the two Sgr A sources. The H$m\beta$ to H$n\alpha$ ratios reveal that the ionised gas is emitted under local thermodynamic equilibrium conditions in these regions. We find a He to H mass fraction of 0.29$\pm$0.01 consistent with the typical GC value, supporting the idea that massive stars have increased the He abundance compared to its primordial value. Physical properties are derived for the studied sources. We propose that the negative velocity component of both Sgr A sources is part of gas streams considered previously to model the GC cloud kinematics. Associated massive stars with what are presumably the closest HII regions to LOS$-$0.11 (positive velocity gas), LOS$-$0.02 and LOS+0.693 could be the main sources of UV photons ionising the gas. The negative velocity components of both Sgr A sources might be ionised by the same massive stars, but only if they are in the same gas stream.

Comparative analysis of two kinds of pneumatic compact spinning using finite element method

PurposeThe purpose of this paper is to know airflow field and its distribution of pneumatic compact spinning systems. Complete compact spinning (CCS) and four-line rollers compact spinning (FRCS) are both two kinds of pneumatic compact spinning systems, which utilizes airflow in condensing equipment to condense fiber bundle and improve yarn properties.Design/methodology/approachThe paper opted for an exploratory study using finite element method, the airflow field in the condensing area of CCS and FRCS were simulated. First, a periodic movement of the fibers in bundle in condensing area was detected, and the yarn tracks were described veritably under the high-speed-video-camera and AutoCAD Software. Then the physical models of the condensing zone were constructed according to the physical parameters of the practical system. The simulation of airflow velocities were extracted along the yarn tracks using ANSYS Software. Finally, the numerical results were verified by spinning experiments.FindingsThe results show that the negative velocity component along the Y-axis helps keeping beneficial hairiness. CCS has higher negative velocity value and more abundant beneficial hairiness than FRCS. The velocity component in the X-axis direction has a direct effect on yarn evenness. For the same liner density of CCS and FRCS, the larger the value of the velocity component on X-axis is, the better the yarn evenness is. For 9.7tex, CCS has larger velocity component in the X-axis direction and better yarn evenness than FRCS, showing that CCS is more suitable for spinning fine count yarn. The velocity component in the Z-axis direction has a direct effect on breaking strength. CCS has little velocity component in the Z-axis direction and little breaking strength than FRCS.Originality/valueTo know airflow field and its distribution by finite element method is helpful to investigate the condensing principles of the fiber bundle and improve yarn properties.

Multi-wavelength observations of a nearby multi-phase interstellar cloud

High-resolution spectroscopic observations (UV HST/STIS and optical) are used to characterize the physical state and velocity structure of the multiphase interstellar medium seen towards the nearby (170 pc) star HD102065, located behind the tail of a cometary-shaped, infrared cirrus-cloud, in the area of interaction between the Sco-Cen OB association and the Local Bubble. We analyze interstellar components present along the line of sight by fitting multiple transitions from CO, CH, CH+, C I, S I, Fe I, Mg I, Mg II, Mn II, P II, Ni II, C II, N I, O I, Si III, C IV, and Si IV. The absorption spectra are complemented by H I, CO and C II emission-line spectra, H$_2$ column-densities derived from FUSE spectra, and IRAS images. Gas components of a wide range of temperatures and ionization states are detected along the line of sight. Most of the hydrogen column-density is in cold, diffuse, molecular gas at low LSR velocity. This gas is mixed with traces of warmer molecular gas traced by H2 in the J>2 levels, in which the observed CH+ must be formed. We also identify three distinct components of warm gas at negative velocities down to -20 km/s. The temperature and gas excitation are shown to increase with increasing velocity shift from the bulk of the gas. Hot gas at temperatures of several 10^5 K is detected in the most negative velocity component in the highly-ionized species. This hot gas is also detected in very strong lines of less-ionized species (Mg II, Si II* and C II*) for which the bulk of the gas is cooler. We relate the observational results to evidence for dynamical impact of the Sco-Cen stellar association on the nearby ISM. We propose a scenario where the cirrus cloud has been hit a few 10^5 yr ago by a supernova blast wave originating from the Lower Centaurus Crux group of the Sco-Cen association.

Constraints on the Proper Motion of the Andromeda Galaxy Based on the Survival of Its Satellite M33

A major uncertainty in the dynamical history of the local group of galaxies originates from the unknown transverse speed of the Andromeda galaxy (M31) relative to the Milky Way. We show that the recent VLBA measurement of the proper motion of Andromeda's satellite, M33, severely constrains the possible values of M31's proper motion. The condition that M33's stellar disk will not be tidally disrupted by either M31 or the Milky Way over the past 10 billion years, favors a proper motion amplitude of 100+-20km/s for M31 with the quadrant of a negative velocity component along Right Ascension and a positive component along Declination strongly ruled-out. This inference can be tested by future astrometric measurements with SIM, GAIA, or the SKA. Our results imply that the dark halos of Andromeda and the Milky Way will pass through each other within the next 5-10 billion years.

Kinetic study of quasi‐ballistic electron transport in nanoscale semiconductor devices

AbstractWe studied the effect of the scattering accompanying dispersion in quasi‐ballistic transport at room temperature in nanoscale semiconductor devices primarily by using numerical calculations. The electron velocity distribution function based on a simple n+‐n‐n+ structure was directly determined by solving the semiclassical Boltzmann transport equation. We discovered that the velocity distribution function of electrons near the potential barrier obtained from the Boltzmann transport equation differs from the function assuming ballistic transport and always has a negative velocity component due to scattering in the channel region that cannot be ignored. This analysis result means that the scattering effect in the channel region cannot be ignored even for nanoscale elements. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(11): 1–9, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20196

NaI and CaII absorption components observed towards the Orion-Eridanus Superbubble

We present medium-resolution spectra (R ∼ 7.5 km s −1 ) of the interstellar NaI and CaII interstellar absorption lines observed towards 16 early-type stars with distances of 160-1 kpc in the line-of-sight towards the Orion-Eridanus Superbubble (OE-S). These data have been supplemented with measurements of NaI absorption towards a further 13 stars with similar sight-lines taken from the literature. We detect two major absorption components with velocities of Vlsr ∼ +7.0 and −8.0 km s −1 . The former component, seen in 70% of the sight-lines is associated with the boundary to the Local Bubble cavity located at a distance of 140-150 pc. The other absorption component is only detected towards a limited region of the sky bounded by (190 ◦ 220 pc within an area coincident with that of the 0.75 keV X-ray enhancement of the OE-S. Column density ratios, N(NaI)/N(CaII), for the most negative velocity components have values 500 pc. Finally, we place a similar distance limit for any coherently structured rear shell of neutral gas associated with expansion of the OE-S towards the galactic halo.

Observations of interstellar Na I and Ca II towards five southern stars and some comments on the location of the denser diffuse clouds in the southern Milky Way

High-resolution observations (3.6 km s–1 FWHM) of interstellar Na I and Ca II lines towards five southern early-type stars are presented. All five stars have strong absorption lines with low LSR radial velocities (|υlsr|≲5kms−1) which are interpreted as arising in material associated with the ridge of local molecular clouds identified by Dame et al. It is argued that the strong, low-velocity, atomic and molecular lines observed towards other southern stars close to the galactic plane also arise in this material, and special reference is made to the foreground interstellar spectrum of the Sco OB1 association. Four of the observed stars also have absorption components consistent with an origin in the Sagittarius–Carina spiral arm, and two (HD 111904 and 164402) have highly negative velocity components (υlsr≲−40kms−1) which are interpreted as arising in expanding shells centered on the Cen OB1 and Sgr OB1 associations, respectively.

Interferometric Observation of the F-Corona Radial Velocities Field Between 3 and 7 R⊚

AbstractDuring the July 31, 1981 solar eclipse, F-corona interferograms near MgI λ 5184 Å were obtained using a Fabry-Perot etalon (FPE) with an FWHM of 0.5 Å (corresponding to 30 km/sec) and an image tube. Radial velocities Vr of the interplanetary dust (i.d.) were measured in different directions.Both prograde and retrograde motions of i.d. in the ecliptic region is discovered. Most of velocity values do not exceed 50 km/sec. A negative velocity component appears after averaging all Vr for all directions. Its average increases to − 20 km/sec toward the Sun. Some ejections are observed. The strongest (+ 130 km/sec) is located at the north ecliptic pole at a distance of 6 to 7 R⊙.From the lack of unshifted Fraunhofer lines in the scattered sky light, we conclude that the sky brightness continuous component is predominant and its source is K-corona scattered light in the Earth’ s atmosphere.

IUE OBSERVATIONS OF THE ULTRAVIOLET SPECTRUM OF THE CLOSE BINARY DEL PIC.

ABSTRACT The eclipsing binary δ Pic has been observed with the International Ultraviolet Explorer (IUE) satellite. Two high-resolution spectrograms in the far-ultraviolet (NA1 150-1900) and one high-resolution spectrogram in the mid-ultraviolet of (λλ1900-3200) were obtained. The far-ultraviolet resonance lines of C III (λ1175) and Si IV (λλ1393 and 1402) show the presence of excess absorption due to gas leaving the primary star with velocities as high as 600-700 km s-1, Many of the interstellar lines are doubled with the two components having mean velocities of -40.6 and +9.0 km s-1. It is suggested that the negative velocity component may be due to an expanding circumstellar shell surrounding the binary system.