Trailing Tail Research Articles

Numerical study on the hydrodynamic lubrication performance improvement of bio-inspired peregrine falcon wing-shaped microtexture

Bio-inspired surface microtexture has been adopted in mechanical systems for its advanced lubrication performance. In this study, we discerned the aerodynamic characteristics of different parts of the peregrine falcon’s wing, summarized the influence of its distinctive shape on the fluid flow, and, based on simplified geometries and the bionic concept, designed a novel wing-shaped microtexture to enhance lubrication performance in friction pairs. Its shape was simplified by the following parameters: area ratio Sp, dimensionless depth h*, and orientation angle α. Using a multiphase flow model, we investigated the effect of the above geometrical parameters on the lubrication performance of the wing-shaped microtexture by numerical simulation. The corresponding geometrical parameters of the wing-shaped microtexture to achieve optimum lubrication performance were: Sp = 30%/h*=1.75/α = 0°. The wing-shaped microtexture’s friction coefficient(COF) corresponded to a reduction of 18.8% and 20.7%, respectively, compared to the triangle and rectangular microtexture, which had the best lubrication performance for existing applications. The results showed that the wing-shaped microtexture enhanced the lubrication performance for three reasons: 1. The biomimetic leading edge created more negative pressure and cavitation zones; 2. The interference between positive and negative pressure zones was effectively mitigated; 3. The sharp design of the biomimetic trailing edge and tail wing concentrated the positive pressure zone while increasing its area. Two double-layer composite wing-shaped microtextures were further introduced to maximize friction reduction. The impact of inner-outer layer area ratio Sp* and inner-outer depth ratio h* on the lubrication performance was investigated. Their simulation results revealed that the optimal geometric parameters for the composite microtextures were Sp*=6.3%/hp*=3.0 and Sp*=12.7%/hp*=2.0, respectively. The configurations led to additional COF reductions of 7.6% and 10.56% compared to the single-layer wing-shaped microtexture. These insights offer valuable guidance for reducing friction and wear in mechanical systems.

Existence of tidal tails for the globular cluster NGC 5824

Context. Several dynamically cold streams have been associated with certain globular clusters (GCs) based on orbital energies and angular momenta. Some of these streams are surprisingly far apart from their progenitors and one such pair is Triangulum and NGC 5824. Triangulum can be considered as a piece of the leading tail of NGC 5824 since the cluster’s future orbit matches well with the stream’s track. The existence of the leading tail of NGC 5824 is the motivation behind the search for its trailing tail. Aims. Our goal is to confirm the connection between Triangulum and NGC 5824. We also search for the trailing tail of the cluster. Methods. The selection of member stars of Triangulum is made through various cuts in metallicity, proper motions (PMs), radial velocity and a color–magnitude diagram (CMD). The selected members are compared in phase space to a mock stream that models the disruption of NGC 5824. We then try to detect the trailing tail of the cluster based on a modified matched-filter technique. Stars are assigned weights using their color differences from the cluster’s locus in the CMD. These weights are further scaled, based on the stars’ departures from expected PMs of the model stream. Results. A total of 26 member stars for Triangulum are obtained, 16 of which are newly identified. These members are consistent with the mock stream in the phase space, and their metalicity and position on the CMD are in good agreement with NGC 5824. By applying the matched filter, a tenuous trailing tail of the cluster is detected, spanning ∼50° long on sky. The signature matches well with the mock stream’s trajectory. Conclusions. Our results support that the Triangulum stream acts as a part of the leading tail for NGC 5824. On the trailing side, we detected a 50° tail extending from the cluster. The existence of both leading and trailing tails for the GC NGC 5824 is verified.

Forward and back: kinematics of the Palomar 5 tidal tails

ABSTRACTThe tidal tails of Palomar 5 (Pal 5) have been the focus of many spectroscopic studies in an attempt to identify individual stars lying along the stream and characterize their kinematics. The well-studied trailing tail has been explored out to a distance of 15○ from the cluster centre, while less than 4° have been examined along the leading tail. In this paper, we present results of a spectroscopic study of two fields along the leading tail that we have observed with the AAOmega spectrograph on the Anglo-Australian telescope. One of these fields lies roughly 7○ along the leading tail, beyond what has been previously been explored spectroscopically. Combining our measurements of kinematics and line strengths with Pan-STARRS1 photometric data and Gaia EDR3 astrometry, we adopt a probabilistic approach to identify 16 stars with a high probability of belonging to the Pal 5 stream. Eight of these stars lie in the outermost field and their sky positions confirm the presence of ‘fanning’ in the leading arm. We also revisit previously published radial velocity studies and incorporate Gaia EDR3 astrometry to remove interloping field stars. With a final sample of 109 bona fide Pal 5 cluster and tidal stream stars, we characterize the 3D kinematics along the the full extent of the system. We provide this catalogue for future modeling work.

Jet-like structures from PSR J1135–6055

Pulsar wind nebulae (PWNe) produced from supersonic runaway pulsars can render extended X-ray structures in the form of tails and prominent jets. In this Letter, we report on the analysis of ∼130 ks observations of the PWN around PSR J1135–6055 that were obtained with the Chandra satellite. The system displays bipolar jet-like structures of uncertain origin, a compact nebula around the pulsar likely formed by the bow shock ahead of it, and a trailing tail produced by the pulsar fast proper motion. The spectral and morphological properties of these structures reveal strong similarities with the PWNe in other runaway pulsars, such as PSR J1509–5850 and Geminga. We discuss their physical origin considering both canonical PWN and jet formation models as well as alternative scenarios that can also yield extended jet-like features following the escape of high-energy particles into the ambient magnetic field.

Stellar streams in chameleon gravity

Theories of gravity that incorporate new scalar degrees of freedom typically require screening mechanisms to ensure consistency with Solar System tests. One widely-studied mechanism -- the chameleon -- can lead to violations of the equivalence principle (EP), as screened and unscreened objects fall differently. If the stars are screened but the surrounding dark matter is not, this leads to asymmetry between leading and trailing streams. We provide analytic estimates of the magnitude of this effect for realistic Galactic mass distributions. Using a restricted N-body code, we simulate 4 satellites with a range of masses and orbits, together with a variety of strengths of the fifth force and screening levels of the Milky Way and satellite. The ratio of the cumulative number function of stars in the leading and trailing stream as a function of longitude from the satellite is computable from simulations, measurable from the stellar data and can provide a direct test. We forecast constraints for streams at large Galactocentric distances, using the specific example case of Hu-Sawicki gravity. Streams with apocentres between 100 and 200 kpc provide attainable constraints at the level of $|f_{R0}| = 10^{-7}$. Still more stringent constraints at the level of $10^{-7.5}$ or even $10^{-8}$ are plausible provided the environmental screening of the satellite is accounted for. These would be among the tightest astrophysical constraints to date. We note further signatures of chameleon gravity: (i) the trailing stellar stream may become detached from the dark matter progenitor if all the stars are lost, (ii) in the extreme fifth force regime, striations in the stellar trailing tail may develop, (iii) if the satellite is fully screened, its orbital frequency is lower than that of the associated dark matter, which is preferentially liberated into the leading tidal tail.

Diagnosing the Stellar Population and Tidal Structure of the Blanco 1 Star Cluster

Abstract We present the stellar population, using Gaia DR2 parallax, kinematics, and photometry, of the young (∼100 Myr), nearby (∼230 pc) open cluster, Blanco 1. A total of 644 member candidates are identified via the unsupervised machine learning method StarGO to find the clustering in the five-dimensional position and proper motion parameter (X, Y, Z, , μ δ ) space. Within the tidal radius of 10.0 ± 0.3 pc, there are 488 member candidates, 3 times more than those outside. A leading tail and a trailing tail, each of 50–60 pc in the Galactic plane, are found for the first time for this cluster, with stars further from the cluster center streaming away faster, manifest stellar stripping. Blanco 1 has a total detected mass of 285 ± 32 M ⊙ with a mass function consistent with a slope of α = 1.35 ± 0.2 in the sense of , in the mass range of 0.25–2.51 M ⊙, where N is the number of members and m is stellar mass. A minimum spanning tree (ΛMSR) analysis shows the cluster to be moderately mass segregated among the most massive members (≳1.4 M ⊙), suggesting an early stage of dynamical disintegration.

Non-Gaussian Features of Local Wind Pressure for Typical Gable Roof of Low-rise Building

The non-Gaussian characteristics of local wind pressure of typical gable roof of low-rise building with a slop angle of 18.4° were monitored by means of the wind tunnel test under terrain roughness regimes of A,B and C. The probability density distribution features of wind pressure coefficient series are investigated, the characteristics of non-Gaussian zones distribution of wind pressure relative to different wind angles and different terrain conditions are analyzed and the relationships between non-Gaussian pressure and distinctions of flow field on roof are discussed. The studying results indicate that GEV distribution and Gamma distribution fit the probability density distribution of wind pressure coefficient better than Gaussian distribution and Lognormal distribution, but the fitting effect for long trailing tail part is undesirable, when skewness and kurtosis are large in magnitude (absolute value). The variation of terrain roughness and wind directions have significant influence on the distribution of non-Gaussian pressure regions on low-rise building roof. Under the oblique wind direction, the Gaussian pressure zone is divided into three sections along the approaching wind direction, along which the areas move with the change of terrain roughness regimes. The non-Gaussian features of wind pressure is positively related to mutual correlation coefficient of it’s time-history.

Hyades tidal tails revealed by Gaia DR2

Aims. Within a 200 pc sphere around the Sun, we search for the Hyades tidal tails in the Gaia DR2 dataset. Methods. We used a modified convergent-point method to search for stars with space velocities close to the space velocity of the Hyades cluster. Results. We find a clear indication for the existence of the Hyades tidal tails, a leading tail extending up to 170 pc from the centre of the Hyades with 292 stars (36 contaminants), and a trailing tail up to 70 pc with 237 stars (32 contaminants). A comparison with an N-body model of the cluster and its tails shows remarkably good coincidence. Five white dwarfs are found in the tails.

High-speed imaging of wave modes in an RDC

Various operating modes have been observed in the rotating detonation combustor (RDC) studied here, as well as by others. These modes can be generally categorized into two groups: one or more co-rotating waves and counter-rotating waves. The combustor is able to stabilize both types of operation, however the stabilization mechanism remains unclear. In order to better understand these cases, these operational modes are investigated with high-speed pressure transducers installed in the combustor annulus combined with simultaneous high-speed video imaging of the natural luminosity of the detonation wave from the aft end of the RDC. These results confirm the operation in both the steady single wave mode as well as the counter-rotating waves mode. The presence of this mode further demonstrates the complex dynamics inherent in the stabilization of the detonation wave. As each wave propagates, they initially begin to weaken followed by re-strengthening after collision which serves to stabilize the mode. Differences in the velocities of the waves was also observed to result in a beating phenomenon expressed as an amplitude modulation of the pressure traces. High-speed video imaging of the high-temperature emission from H2O in the RDC annulus was used in conjunction with the pressure traces for a range of flow rates and equivalence ratios. Processing of the images into the wave frame of reference allowed for the identification of the average luminosity profile, characterized by a steep increase in natural luminosity near the wave front, followed by a trailing tail extending approximately half the annulus perimeter.

The Post-pericenter Evolution of the Galactic Center Source G2

Abstract In early 2014, the fast-moving near-infrared source G2 reached its closest approach to the supermassive black hole Sgr A* in the Galactic center. We report on the evolution of the ionized gaseous component and the dusty component of G2 immediately after this event, revealed by new observations obtained in 2015 and 2016 with the SINFONI integral field spectrograph and the NACO imager at the ESO VLT. The spatially resolved dynamics of the Brγ line emission can be accounted for by the ballistic motion and tidal shearing of a test-particle cloud that has followed a highly eccentric Keplerian orbit around the black hole for the last 12 years. The non-detection of a drag force or any strong hydrodynamic interaction with the hot gas in the inner accretion zone limits the ambient density to less than a few at the distance of closest approach ( ), assuming G2 is a spherical cloud moving through a stationary and homogeneous atmosphere. The dust continuum emission is unresolved in L′-band, but stays consistent with the location of the Brγ emission. The total luminosity of the Brγ and L′ emission has remained constant to within the measurement uncertainty. The nature and origin of G2 are likely related to that of the precursor source G1, since their orbital evolution is similar, though not identical. Both objects are also likely related to a trailing tail structure, which is continuously connected to G2 over a large range in position and radial velocity.

The fully nonlinear stratified geostrophic adjustment problem

Abstract. The study of the adjustment to equilibrium by a stratified fluid in a rotating reference frame is a classical problem in geophysical fluid dynamics. We consider the fully nonlinear, stratified adjustment problem from a numerical point of view. We present results of smoothed dam break simulations based on experiments in the published literature, with a focus on both the wave trains that propagate away from the nascent geostrophic state and the geostrophic state itself. We demonstrate that for Rossby numbers in excess of roughly 2 the wave train cannot be interpreted in terms of linear theory. This wave train consists of a leading solitary-like packet and a trailing tail of dispersive waves. However, it is found that the leading wave packet never completely separates from the trailing tail. Somewhat surprisingly, the inertial oscillations associated with the geostrophic state exhibit evidence of nonlinearity even when the Rossby number falls below 1. We vary the width of the initial disturbance and the rotation rate so as to keep the Rossby number fixed, and find that while the qualitative response remains consistent, the Froude number varies, and these variations are manifested in the form of the emanating wave train. For wider initial disturbances we find clear evidence of a wave train that initially propagates toward the near wall, reflects, and propagates away from the geostrophic state behind the leading wave train. We compare kinetic energy inside and outside of the geostrophic state, finding that for long times a Rossby number of around one-quarter yields an equal split between the two, with lower (higher) Rossby numbers yielding more energy in the geostrophic state (wave train). Finally we compare the energetics of the geostrophic state as the Rossby number varies, finding long-lived inertial oscillations in the majority of the cases and a general agreement with the past literature that employed either hydrostatic, shallow-water equation-based theory or stratified Navier–Stokes equations with a linear stratification.

Characterization of thermal desorption with the Deans-switch technique in gas chromatographic analysis of volatile organic compounds

This study presents a novel application based on the Deans-switch cutting technique to characterize the thermal-desorption (TD) properties for gas chromatographic (GC) analysis of ambient volatile organic compounds (VOCs). Flash-heating of the sorbent bed at high temperatures to desorb trapped VOCs to GC may easily produce severe asymmetric or tailing GC peaks affecting resolution and sensitivity if care is not taken to optimize the TD conditions. The TD peak without GC separation was first examined for the quality of the TD peak by analyzing a standard gas mixture from C2 to C12 at ppb level. The Deans switch was later applied in two different stages. First, it was used to cut the trailing tail of the TD peak, which, although significantly improved the GC peak symmetry, led to more loss of the higher boiling compounds than the low boiling ones, thus suggesting compound discrimination. Subsequently, the Deans switch was used to dissect the TD peak into six 30s slices in series, and an uneven distribution in composition between the slices were found. A progressive decrease in low boiling compounds and increase in higher boiling ones across the slices indicated severe inhomogeneity in the TD profile. This finding provided a clear evidence to answer the discrimination problem found with the tail cutting approach to improve peak symmetry.Through the use of the innovated slicing method based on the Deans-switch cutting technique, optimization of TD injection for highly resolved, symmetric and non-discriminated GC peaks can now be more quantitatively assessed and guided.

SELECTING M GIANTS WITH INFRARED PHOTOMETRY: DISTANCES, METALLICITIES, AND THE SAGITTARIUS STREAM

ABSTRACT Using a spectroscopically confirmed sample of M giants, M dwarfs, and quasars from the LAMOST survey, we assess how well Wide-field Infrared Survey Explorer (WISE) and Two Micron All Sky Survey color cuts can be used to select M giant stars. The WISE bands are very efficient at separating M giants from M dwarfs, and we present a simple classification that can produce a clean and relatively complete sample of M giants. We derive a new photometric relation to estimate the metallicity for M giants, calibrated using data from the APOGEE survey. We find a strong correlation between the color and , where almost all of the scatter is due to photometric uncertainties. We show that previous photometric distance relations, which are mostly based on stellar models, may be biased and devise a new empirical distance relation, investigating trends with metallicity and star formation history. Given these relations, we investigate the properties of M giants in the Sagittarius stream. The offset in the orbital plane between the leading and trailing tails is reproduced, and by identifying distant M giants in the direction of the Galactic anticenter, we confirm that the previously detected debris in the outer halo is the apocenter of the trailing tail. We also find tentative evidence supporting an existing overdensity near the leading tail in the northern Galactic hemisphere, possibly an extension to the trailing tail (so-called Branch C). We have measured the metallicity distribution along the stream, finding a clear metallicity offset between the leading and trailing tails, in agreement with models for the stream formation. We include an online table of M giants to facilitate further studies.

Numerical Simulation of Temperature Field and Stress Field to Multiple Laser Cladding Co Coatings

In order to analyze temperature field and stress field of Co-based alloys laser cladding, the model of Co-based alloys laser cladding with preset-powder method has been made on low carbon steel substrate. The temperature field and stress field of laser cladding process was analyzed by SYSWELD software, and Experimental verification is done. The results showed that temperature field is appear to a trailing tail of comet, favorable metallurgy bonding with 12.3% dilution was obtained by scanning velocity was 4 mm/s. and instantaneous cooling rate of molten pool with 4 mm/s and 5 mm/s are increased to 1.47 times and 2.02 times of 3 mm/s. The transverse residual stress different nodes on the surface of coatings are always tensile stress, and it is almost steady, the maximum deformation is 0.34 mm at the edge of work-piece, these are consistent with experimental results. These results provide reference and guide to obtain high quality coatings.

Tiam1 interaction with the PAR complex promotes talin-mediated Rac1 activation during polarized cell migration

Migrating cells acquire front-rear polarity with a leading edge and a trailing tail for directional movement. The Rac exchange factor Tiam1 participates in polarized cell migration with the PAR complex of PAR3, PAR6, and atypical protein kinase C. However, it remains largely unknown how Tiam1 is regulated and contributes to the establishment of polarity in migrating cells. We show here that Tiam1 interacts directly with talin, which binds and activates integrins to mediate their signaling. Tiam1 accumulated at adhesions in a manner dependent on talin and the PAR complex. The interactions of talin with Tiam1 and the PAR complex were required for adhesion-induced Rac1 activation, cell spreading, and migration toward integrin substrates. Furthermore, Tiam1 acted with talin to regulate adhesion turnover. Thus, we propose that Tiam1, with the PAR complex, binds to integrins through talin and, together with the PAR complex, thereby regulates Rac1 activity and adhesion turnover for polarized migration.

CHANDRAOBSERVATIONS OF NGC 4342, AN OPTICALLY FAINT, X-RAY GAS-RICH EARLY-TYPE GALAXY

Chandra X-ray observations of NGC4342, a low stellar mass (M_K=-22.79 mag) early-type galaxy, show luminous, diffuse X-ray emission originating from hot gas with temperature of kT~0.6 keV. The observed 0.5-2 keV band luminosity of the diffuse X-ray emission within the D_25 ellipse is L_0.5-2keV = 2.7 x 10^39 erg/s. The hot gas has a significantly broader distribution than the stellar light, and shows strong hydrodynamic disturbances with a sharp surface brightness edge to the northeast and a trailing tail. We identify the edge as a cold front and conclude that the distorted morphology of the hot gas is produced by ram pressure as NGC4342 moves through external gas. From the thermal pressure ratios inside and outside the cold front, we estimate the velocity of NGC4342 and find that it moves supersonically (M~2.6) towards the northeast. Outside the optical extent of the galaxy we detect ~17 bright (L_0.5-8keV > 3 x 10^37 erg/s) excess X-ray point sources. The excess sources are presumably low-mass X-ray binaries (LMXBs) located in metal-poor globular clusters (GCs) in the extended dark matter halo of NGC4342. Based on the number of excess sources and the average frequency of bright LMXBs in GCs, we estimate that NGC4342 may host roughly 850-1700 GCs. In good agreement with this, optical observations hint that NGC4342 may harbor 1200 +/- 500 GCs. This number corresponds to a GC specific frequency of S_N = 19.9 +/- 8.3, which is among the largest values observed in full-size galaxies.

The anatomy of Leo I: how tidal tails affect the kinematics

We model the recently published kinematic data set for Leo I dwarf spheroidal (dSph) galaxy by fitting the solutions of the Jeans equations to the velocity dispersion and kurtosis profiles measured from the data. We demonstrate that when the sample is cleaned of interlopers the data are consistent with the assumption that mass follows light and isotropic stellar orbits with no need for an extended dark matter halo. Our interloper removal scheme does not clean the data of contamination completely, as demonstrated by the rotation curve of Leo I. When moving away from the centre of the dwarf, the rotation appears to be reversed. We interpret this behaviour using the results of an N-body simulation of a dwarf galaxy possessing some intrinsic rotation, orbiting in the Milky Way potential and show that it can be reproduced if the galaxy is viewed almost along the tidal tails so that the leading (background) tail contaminates the western part of Leo I while the trailing (foreground) tail the eastern one. We show that this configuration leads to a symmetric and Gaussian distribution of line-of-sight velocities. The simulation is also applied to test our modelling method on mock data sets. We demonstrate that when the data are cleaned of interlopers and the fourth velocity moment is used the true parameters of the dwarf are typically within 1σ errors of the best-fitting parameters. Restricting the fitting to the inner part of Leo I our best estimate for the anisotropy is β= -0.2 +0.3 -0.4 and the total mass M = (4.5 ± 0.7) x 10 7 M ⊙ . The mass-to-light ratio (M/L) including the errors in mass, brightness and distance is M/L V = 8.2 ± 4.5 solar units.

CAMP Inhibits Cell Migration by Interfering with Rac-induced Lamellipodium Formation

Cell migration is critical for animal development and physiological as well as pathological responses. One important step during cell migration is the formation of lamellipodia at the leading edge of migrating cells. Here we report that the second messenger cAMP inhibits the migration of mouse embryonic fibroblast cells and mouse breast tumor cells. cAMP acts downstream of the small GTPase Rac and interferes with the formation of lamellipodia. Moreover, cAMP decreases the phosphorylation of the myosin light chain at the leading edge of cells and increases the phosphorylation of the vasodilator-stimulated phosphoprotein. Together with our previous report of a positive role of another second messenger, cGMP, in lamellipodium formation, our data indicate that cAMP and cGMP play opposite roles in modulating lamellipodium formation.

KINEMATICS OF STARS IN KAPTEYN SELECTED AREA 71: SAMPLING THE MONOCEROS AND SAGITTARIUS TIDAL STREAMS

We present a 3D kinematical analysis of stars located in Kapteyn Selected Area 71 (l = 167.1, b = -34.7), where previously a stellar excess was found (Dinescu et al. 2002, Newberg et al. 2002). Previous findings indicated that the stellar excess has a cold kinematical signature as inferred from proper motions, and was initially associated with debris from the Sagittarius dwarf galaxy (Sgr) -- namely the southern trailing tail. We have obtained radial velocities using the Hydra multiobject spectrograph on the WIYN 3.5 m telescope. Results for 183 proper-motion selected stars indicate that the dominant population in this stellar excess is not debris from Sgr, but rather a population that kinematically belongs to the ring-like stream that is now known as the Monoceros stream. The orbit determined for this population agrees very well with the predictions for the Monoceros stream from Penarrubia et al. (2005). The radial-velocity dispersion of this population is between 20 and 30 km/s, lower than that of the Galactic field. Also, the shape of the radial-velocity distribution shows a sharp cut-off on one side, which is more in line with model predictions of the disruption of a satellite rather than with the distribution of the Galactic field. Despite the fact that we now believe most of the stars in the stellar excess to be part of Monoceros, about ten stars in this stellar excess have highly negative radial velocities, which is a clear indication of their membership to the Sgr trailing tidal tail.

GAS-DYNAMICAL FRICTION OF A PERTURBER MOVING ON A CIRCULAR ORBIT

Dynamical friction plays an important role in reducing angular momenta of objects in orbital motions. While astronomical objects usually follow curvilinear orbits, most previous studies focused on the linear-trajectory cases. Here, we present the gravitational wake due to, and dynamical friction on, a perturber moving on a circular orbit in a uniform gaseous medium using a semi-analytic method. The circular orbit causes the density wakes to bend along the orbit into asymmetric configurations, resulting in the drag forces in both opposite (azimuthal) and lateral (radial) directions to the perturber motion, although the latter does not contribute to the orbital decay much. For a subsonic perturber, the bending of a wake is only modest and the resulting drag force in the opposite direction is remarkably similar to the linear-trajectory counterpart. On the other hand, a supersonic perturber is able to overtake its own wake, possibly multiple times, creating a high-density trailing tail. Despite the dramatic changes in the wake morphologies, the azimuthal drag force is in surprisingly good agreement with the formulae of Ostriker for the linear-trajectory cases, provided $V_pt