Edge Of Disk Research Articles

Short- and Long-Range Microparticle Transport on Permalloy Disk Arrays in Time-Varying Magnetic Fields

We investigate maneuvering superparamagnetic microparticles, or beads, in a remotely-controlled, automated way across arrays of few-micron-diameter permalloy disks. This technique is potentially useful for applying tunable forces to or for sorting biological structures that can be attached to magnetic beads, for example nucleic acids, proteins, or cells. The particle manipulation method being investigated relies on a combination of stray fields emanating from permalloy disks as well as time-varying externally applied magnetic fields. Unlike previous work, we closely examine particle motion during a capture, rotate, and controlled repulsion mechanism for particle transport. We measure particle velocities during short-range motion—the controlled repulsion of a bead from one disk toward another—and compare this motion to a simulation based on stray fields from disk edges. We also observe the phase-slipping and phase-locked motion of particles engaging in long-range transport in this manipulation scheme.

Fourcade-Figueroa galaxy: A clearly disrupted superthin edge-on galaxy

Context. Studies of the stellar and the H I gas kinematics in dwarf and low surface brightness (LSB) galaxies are essential for deriving constraints on their dark matter distribution. Moreover, a key component to unveil in the evolution of LSBs is to determine why some of them can be classified as superthin. Aims. We aim to investigate the nature of the proto-typical superthin galaxy Fourcade-Figueroa (FF) to understand the role played by the dark matter halo in forming its superthin shape and to investigate the mechanism that explains the observed disruption in the approaching side of the galaxy. Methods. Combining new H I 21 cm observations obtained with the Giant Metrewave Radio Telescope with archival data from the Australia Telescope Compact Array we were able to obtain sensitive H I observations of the FF galaxy. These data were modelled with a 3D tilted ring model in order to derive the rotation curve and surface brightness density of the neutral hydrogen. We subsequently used this model, combined with a stellar profile from the literature, to derive the radial distribution of the dark matter in the FF galaxy. Additionally, we used a more direct measurement of the vertical H I gas distribution as a function of the galactocentric radius to determine the flaring of the gas disk. Results. For the FF galaxy, the Navarro-Frenk-White dark matter distribution provides the best fit to the observed rotation curve. However, the differences with a pseudo-isothermal halo are small. Both models indicate that the core of the dark matter halo is compact. Even though the FF galaxy classifies as superthin, the gas thickness about the galactic centre exhibits a steep flaring of the gas that agrees with the edge of the stellar disk. In addition, FF is clearly disrupted towards its north-west side, clearly observed at optical and H I wavelengths. As suggested previously in the literature, the compact dark matter halo might be the main cause for the superthin structure of the stellar disk in FF. This idea is strengthened through the detection of the disruption; the fact that the galaxy is disturbed also appears to support the idea that it is not isolation that causes its superthin structure.

ОПРЕДЕЛЕНИЕ АБСОЛЮТНОЙ СКОРОСТИ ПОЧВЫ, СМЕЩАЕМОЙ СФЕРИЧЕСКИМ ДИСКОМ КАТКА ГРЕБНЕВОЙ СЕЯЛКИ

Heuristic and technical analysis of various designs of tillage rollers of row-crop seeders has led to the conclusion that they are mainly intended for destruction of lumps and soil compaction before and after sowing on a flat field surface. When studying the available methods for assessing the impact on improvement criteria of the design parameters and surface features of individual working elements of the ridge-forming rollers, it was revealed that, currently, there are unresolved issues, in particular, the method for specification of the absolute speed of the soil displaced by the spherical discs of the ridge seeder roller. Thus, it is necessary to substantiate theoretically this parameter of the tillage roller, which directly affects the distance between the spherical discs of the roller of the ridge seeder. For the finishing operation of formation of the soil ridge of the required parameters and density simultaneously with sowing, a roller was developed, the novelty of which is confirmed by the patents of the Russian Federation № 194330, № 194348, № 196712. The design of the roller includes regulation of the angles of attack of the spherical discs and the degree of compression of the spring, because these parameters have a significant effect on the geometric dimensions of the formed ridge and the density of the soil inside it. The proposed roller is mounted on the rear beam holder of the sowing section of the ridge seeder. Moving on the surface of the field, the ridge seeder colters sow seeds on a wet compacted bed, the ridge formers form a loose soil hill above the sown seeds and the rollers compact the soil hill. The speeds and forces acting on the spherical disc of the roller have been determined. It was theoretically revealed that the absolute speed of soil particles thrown by the edge of the spherical disc towards the symmetry longitudinal axis of the soil ridge is maximum and depends on the angular velocity of the spherical disc, its radius and angle of attack, as well as the frictional properties of the soil. As moving to the center of the spherical disc, the absolute speed of soil particles thrown from a specific point of the studied roller working body decreases

The Fast Jitter in the O − C Curves of Cataclysmic Variables Is Caused by Ordinary Flickering in the Light Curve that Randomly Shifts Each Eclipse Time

Abstract For Cataclysmic Variables (CVs), the record of many eclipse times (as presented in the traditional O − C curves) often displays a small-amplitude fast jitter on timescales of under a few years, with these often being interpreted as physical effects such as from third bodies in the system (including planets), or from azimuthal movements of the Hot Spot around the edge of the accretion disk. Recently, with the new and excellent light curves from spacecraft missions TESS and Kepler, we can measure large numbers of eclipse times down to orbit-by-orbit timescales. For four representative CVs (DQ Her, U Sco, RW Tri, and UX UMa), I find that the O − C jitter is constant from one-orbit-to-the-next out to eclipses separated by many years. This demonstrates that the jitter is not caused by physical effects on the orbit, nor by moving Hot Spots. This result was predicted for the expected jitter in eclipse times arising from the ubiquitous flickering in all CV light curves, where random flickers before/after eclipse minima will shift the measured eclipse times later/earlier than the true time of conjunction.

Numerical investigation of conjugate heat transfer on a rotating disk under round liquid jet impingement

The two-phase flow and heat transfer characteristics of a free liquid jet impinging on a heated rotating disk are investigated by the CFD method. Numerical simulations are conducted over a range of rotational Reynolds numbers, jet Reynolds numbers, jet temperatures, nozzle diameter to disk spacing ratios, and disk to nozzle diameter ratios. The results show that the local Nusselt number increases first and then decreases along the radial direction, and it reaches the peak value in the core heat transfer zone close to the rotation center. The Nusselt number of the disk surface increases with the increase of rotational Reynolds number, jet Reynolds number, jet temperature, and nozzle diameter to disk spacing ratio, and the temperature distribution of the disk surface becomes more uniform. The increase of the disk to nozzle diameter ratio is not conducive to convective heat transfer. The temperature at the disk edge rises with the larger diameter ratio. Based on the numerical simulation results, a new correlation for the average Nusselt number is presented in terms of the dimensionless variables of jet Reynolds number, rotational Reynolds number, and Prandtl number in this study.

Formation number and pinch-off signals of disc vortex ring based on a Lagrangian analysis

As one fundamental flow structure, the vortex ring behind an impulsively starting disc can vividly characterize the vortex structure around the flapping flight and the drag-based paddling propulsions. In this paper, an elaborate experiment is performed to investigate the formation of the vortex rings (termed as DVR) by using digital particle image velocimetry (DPIV), as well as by investigating the ridges of finite-time Lyapunov exponent (FTLE) and the elliptic Lagrangian coherent structures (LCSs). Experimental results demonstrate that the circulation growth of DVRs satisfies the Logistic law and can be well predicted by a scaling model based on the shear-layer feeding velocity. Applying the criterion originated from the Kelvin-Benjamin variational principle, the formation number of DVRs when DVRs pinch off is found to stay within the range of F∗=3.35~4.1. Then, the pinch-off process of the DVRs is re-examined based on a Lagrangian analysis, and the dynamic signals are detected to coincide with the onset of DVRs pinch-off. Once DVRs pinch off, a trailing pressure maximum appears in the edge of disc and a closed boundary forms to define the region of DVRs based on the FTLE ridges, fluid detrainment by the dynamic lobes is observed, and a saturation phase of the circulation evolution is clearly observed in terms of the elliptic LCSs. Furthermore, the scaling laws, i.e., circulation growth and formation number, of DVR formation suggest a confined formation mode to understand the formation of wake vortices behind a moving body for reference.

About the modelling of the SED for the inner boundary of protoplanetary discs at the lower stellar mass regime

ABSTRACT In order to improve the physical interpretation about innermost dusty regions in protoplanetary discs around brown dwarf (BD), and even very low mass star (VLMS), we present a grid of models taking into account two different sets: (i) The set called standard model, that simulates an axisymmetric dusty disc with an inner curved wall. (ii) The perturbed one called non-standard where the axisymmetry of the inner edge has been broken. We have achieved a fitting for the disc structure able to explain the spectral energy distribution (SED). As the main condition, we assume that the changes of the inner wall geometry in the tongue-like shape depend on the Rayleigh–Taylor instability (R-TIns) generated in the inner disc edge. For each object, we parametrize the shape of the inner wall to find a time-dependent model that enables us to explain the photometric near-Infrared variability and connect the changes on the inner disc structure with the amplitude of such variability. We re-analysed photometric measurements from near to mid-infrared wavelengths of a sample of 6 BDs and one VLMS in different cloud associations which were previously studied by other authors. We also show that the flux change calculated between the non-standard and the standard configurations models the observed variability in LRLL 1679. The magnitude changes due to these fluctuations slightly depend on the wavelength and they can present differences of up to 0.9 mag. We suggest that if the R-TIns persist enough time, the features in the protoplanetary inner disc, e.g. inner holes or gaps evolve.

The water-ice line as a birthplace of planets: implications of a species-dependent dust fragmentation threshold

The thermodynamic structure of protoplanetary discs is determined by dust opacities, which depend on the size of the dust grains and their chemical composition. In the inner regions, the grain sizes are regulated by the level of turbulence (e.g. α viscosity) and by the dust fragmentation velocity that represents the maximal velocity that grains can have at a collision before they fragment. Here, we perform self-consistently calculated 2D hydrodynamical simulations that consider a full grain size distribution of dust grains with a transition in the dust fragmentation velocity at the water-ice line. This approach accounts for the results of previous particle collision laboratory experiments, in which silicate particles typically have a lower dust fragmentation velocity than water-ice particles. Furthermore, we probe the effects of variations in the water abundance, the dust-to-gas ratio, and the turbulence parameter on the disc structure. For the discs with a transition in the dust fragmentation velocity at the water-ice line, we find a narrow but striking zone of planetary outward migration, including for low viscosities. In addition, we find a bump in the radial pressure gradient profile that tends to be located slightly inside the ice line. Both of these features are present for all tested disc parameters. Thus, we conclude that the ice line can function both as a migration trap, which can extend the growth times of planets before they migrate to the inner edge of the protoplanetary disc, and as a pressure trap, where planetesimal formation can be initiated or enhanced.

Vortex-like kinematic signal, spirals, and beam smearing effect in the HD 142527 disk

Vortices are one of the most promising mechanisms to locally concentrate millimeter dust grains and allow the formation of planetesimals through gravitational collapse. The outer disk around the binary system HD 142527 is known for its large horseshoe structure with azimuthal contrasts of ~3–5 in the gas surface density and of ~50 in the dust. Using 13CO and C18O J = 3–2 transition lines, we detect kinematic deviations to the Keplerian rotation, which are consistent with the presence of a large vortex around the dust crescent, as well as a few spirals in the outer regions of the disk. Comparisons with a vortex model suggest velocity deviations up to 350 m s−1 after deprojection compared to the background Keplerian rotation, as well as an extension of ±40 au radially and ~200° azimuthally, yielding an azimuthal-to-radial aspect ratio of ~5. Another alternative for explaining the vortex-like signal implies artificial velocity deviations generated by beam smearing in association with variations of the gas velocity due to gas pressure gradients at the inner and outer edges of the circumbinary disk. The two scenarios are currently difficult to differentiate and, for this purpose, would probably require the use of multiple lines at a higher spatial resolution. The beam smearing effect, due to the finite spatial resolution of the observations and gradients in the line emission, should be common in observations of protoplanetary disks and may lead to misinterpretations of the gas velocity, in particular around ring-like structures.

Global Simulation of the Jovian Magnetosphere: Transitional Structure From the Io Plasma Disk to the Plasma Sheet

AbstractJupiter has a strong magnetic field, and a huge magnetosphere is formed through the solar wind‐Jupiter interaction. The generated magnetosphere–ionosphere system is reproduced based on the 9‐component Magnetohydrodynamics (MHD) and the current conservation in the ionosphere. Assuming Io plasma emission rate 1.4 t/sec, this paper reproduces self‐consistently global magnetic configuration, generations of the field‐aligned current (FAC) and aurora, formation of the Io plasma disk at 8–20 RJ, plasma corotation, instability in the plasma disk, transition from the Io plasma disk to the plasma sheet at 20–150 RJ, and the plasmoid ejection. The rotating Io plasma in the disk forms instabilities that promotes radial diffusion. H+ is supplied from the ionosphere along high‐latitude magnetic field lines and mixed with heavy ions around 15–20 RJ. Beyond 20 RJ, mixed plasma diffuses further outward by the centrifugal force that can exceed magnetic tension. In the ionosphere, the main oval occurs at 13.7°–15.5° colatitude. The Io disk is inner side of magnetic field lines traced from the low‐latitude edge of the main oval. Along magnetic field lines, the main oval is mapped from the outer edge of the Io disk to the entire plasma sheet accompanying rotation delay. Due to the corotation limit, convection is accompanied by plasmoid ejection. Back reaction of plasmoid ejection affects even transport process in the Io disk. The downward FAC occurs in the polar cap showing variability. The region of externally driven Dungey convection seems quite narrow.

Effect of ECG-gating Retinal Photographs on Retinal Vessel Caliber Measurements in Subjects with and without Type 2 Diabetes

ABSTRACT Purpose/Aim of this study: Retinal vessel caliber is an independent risk marker of cardiovascular disease risk. However, variable mechanical delays in capturing retinal photographs and cardiac cycle-induced retinal vascular changes have been shown to reduce the accuracy of retinal vessel caliber measurements, but this has only ever been investigated in healthy subjects. This cross-sectional study is the first study to investigate this issue in type 2 diabetes. The aim of this study was to determine whether ECG-gating retinal photographs reduce the variability in retinal arteriolar and venular caliber measurements in controls and type 2 diabetes. Materials and Methods: Fifteen controls and 15 patients with type 2 diabetes were arbitrarily recruited from Westmead Hospital, Sydney, Australia. A mydriatic fundoscope connected to our novel ECG synchronization unit captured 10 ECG-gated (at the QRS) and 10 ungated digital retinal photographs of the left eye in a randomized fashion, blinded to study participants. Two independent reviewers used an in-house semi-automated software to grade single cross-sectional vessel diameters across photographs, between 900 and 1800 microns from the optic disc edge. The coefficient of variation compared caliber variability between retinal arterioles and venules. Results: Our ECG synchronization unit reported the smallest time delay (33.1 ± 48.4 ms) in image capture known in the literature. All 30 participants demonstrated a higher reduction in retinal arteriolar (ungated: 1.02, 95%CI 0.88–1.17% vs ECG-gated: 0.39, 95%CI 0.29–0.49%, p < .0001) than venular (ungated 0.62, 95%CI 0.53–0.73% vs ECG-gated: 0.26, 95%CI 0.19–0.35%, p < .0001) coefficient of variation by ECG-gating photographs. Intra-observer repeatability and inter-observer reproducibility analysis reported high interclass correlation coefficients ranging from 0.80 to 0.86 and 0.80 to 0.93 respectively. Conclusion: ECG-gating photographs at the QRS are recommended for retinal vessel caliber analysis in controls and patients with type 2 diabetes as they refine measurements.

Possible single-armed spiral in the protoplanetary disk around HD 34282

Context. During the evolution of protoplanetary disks into planetary systems we expect to detect signatures that trace mechanisms such as planet–disk interaction. Protoplanetary disks display a large variety of structures in recently published high-spatial resolution images. However, the three-dimensional morphology of these disks is often difficult to infer from the two-dimensional projected images we observe. Aims. We aim to detect signatures of planet–disk interaction by studying the scattering surface of the protoplanetary disk around HD 34282. Methods. We spatially resolved the disk using the high-contrast imager VLT/SPHERE in polarimetric imaging mode. We retrieved a profile for the height of the scattering surface to create a height-corrected deprojection, which simulates a face-on orientation. Results. The detected disk displays a complex scattering surface. An inner clearing or cavity extending up to r &lt; 0.′′28 (88 au) is surrounded by a bright inclined (i = 56°) ring with a position angle of 119°. The center of this ring is offset from the star along the minor axis with 0.′′07, which can be explained with a disk height of 26 au above the midplane. Outside this ring, beyond its southeastern ansa we detect an azimuthal asymmetry or blob at r ~ 0.′′4. At larger separation, we detect an outer disk structure that can be fitted with an ellipse, which is compatible with a circular ring seen at r = 0.′′62 (=190 au) and a height of 77 au. After applying a height-corrected deprojection we see a circular ring centered on the star at 88 au; what had seemed to be a separate blob and outer ring could now both be part of a single-armed spiral. Conclusions. We present the first scattered-light image of the disk around HD 34282 and resolve a disk with an inner cavity up to r ≈ 90 au and a highly structured scattering surface of an inclined disk at a large height Hscat∕r = 0.′′29 above the midplane at the inner edge of the outer disk. Based on the current data it is not possible to conclude decisively whether Hscat∕r remains constant or whether the surface is flared with at most Hscat ∝ r1.35, although we favor the constant ratio based on our deprojections. The height-corrected deprojection allows for a more detailed interpretation of the observed structures, from which we discern the first detection of a single-armed spiral in a protoplanetary disk.

A Coplanar Circumbinary Protoplanetary Disk in the TWA 3 Triple M Dwarf System

Abstract We present sensitive ALMA observations of TWA 3, a nearby, young (∼10 Myr) hierarchical system composed of three pre-main-sequence M3–M4.5 stars. For the first time, we detected 12CO and 13CO J = 2–1 emissions from the circumbinary protoplanetary disk around TWA 3A. We jointly fit the protoplanetary disk velocity field, stellar astrometric positions, and stellar radial velocities to infer the architecture of the system. The Aa and Ab stars (0.29 ± 0.01 M ⊙ and 0.24 ± 0.01 M ⊙, respectively) comprising the tight (P = 35 days) eccentric (e = 0.63 ± 0.01) spectroscopic binary are coplanar with their circumbinary disk (misalignment &lt;6° with 68% confidence), similar to other short-period binary systems. From models of the spectral energy distribution, we found the inner radius of the circumbinary disk (r inner = 0.50–0.75 au) to be consistent with theoretical predictions of dynamical truncation r cav/a inner ≈ 3. The outer orbit of the tertiary star B (0.40 ± 0.28 M ⊙, a ∼ 65 ± 18 au, e = 0.3 ± 0.2) is not as well constrained as the inner orbit; however, orbits coplanar with the A system are still preferred (misalignment &lt; 20°). To better understand the influence of the B orbit on the TWA 3A circumbinary disk, we performed SPH simulations of the system and found that the outer edge of the gas disk (r outer = 8.5 ± 0.2 au) is most consistent with truncation from a coplanar, circular, or moderately eccentric orbit, supporting the preference from the joint orbital fit.

Simultaneous NICER and NuSTAR Observations of the Ultracompact X-Ray Binary 4U 1543–624

Abstract We present the first joint NuSTAR and NICER observations of the ultracompact X-ray binary (UCXB) 4U 1543−624 obtained in 2020 April. The source was at a luminosity of L 0.5−50 keV = 4.9(D/7 kpc)2 × 1036 erg s−1 and showed evidence of reflected emission in the form of an O viii line, Fe K line, and Compton hump within the spectrum. We used a full reflection model, known as xillverCO, that is tailored for the atypical abundances found in UCXBs, to account for the reflected emission. We tested the emission radii of the O and Fe line components and conclude that they originate from a common disk radius in the innermost region of the accretion disk (R in ≤ 1.07 R ISCO). Assuming that the compact accretor is a neutron star (NS) and the position of the inner disk is the Alfvén radius, we placed an upper limit on the magnetic field strength to be B ≤ 0.7(D/7 kpc) × 108 G at the poles. Given the lack of pulsations detected and position of R in, it was likely that a boundary layer region had formed between the NS surface and inner edge of the accretion disk with an extent of 1.2 km. This implies a maximum radius of the neutron star accretor of R NS ≤ 12.1 km when assuming a canonical NS mass of 1.4 M ⊙.

An Atacama Large Millimeter/submillimeter Array Survey of Chemistry in Disks around M4–M5 Stars

Abstract M-stars are the most common hosts of planetary systems in the Galaxy. Protoplanetary disks around M-stars thus offer a prime opportunity to study the chemistry of planet-forming environments. We present an Atacama Large Millimeter/submillimeter Array survey of molecular line emission toward a sample of five protoplanetary disks around M4–M5 stars (FP Tau, J0432+1827, J1100-7619, J1545-3417, and Sz 69). These observations can resolve chemical structures down to tens of astronomical units. Molecular lines of 12CO, 13CO, C18O, C2H, and HCN are detected toward all five disks. Lines of H2CO and DCN are detected toward 2/5 and 1/5 disks, respectively. For disks with resolved C18O, C2H, HCN, and H2CO emission, we observe substructures similar to those previously found in disks around solar-type stars (e.g., rings, holes, and plateaus). C2H and HCN excitation conditions estimated interior to the pebble disk edge for the bright disk J1100-7619 are consistent with previous measurements around solar-type stars. The correlation previously found between C2H and HCN fluxes for solar-type disks extends to our M4–M5 disk sample, but the typical C2H/HCN ratio is higher for the M4–M5 disk sample. This latter finding is reminiscent of the hydrocarbon enhancements found by previous observational infrared surveys in the innermost (&lt;10 au) regions of M-star disks, which is intriguing since our disk-averaged fluxes are heavily influenced by flux levels in the outermost disk, exterior to the pebble disk edge. Overall, most of the observable chemistry at 10–100 au appears similar for solar-type and M4–M5 disks, but hydrocarbons may be more abundant around the cooler stars.

Crossover from proximity to ordinary two-dimensional plasma excitation

We have investigated plasma excitations in a disk-shaped two-dimensional electron system (2DES), the edge of which was covered by an overlaying metallic gate. We have found that the microwave response of the structure is dominated by the proximity plasma mode propagating along the disk edge. Significantly, we find that as the overlap between the 2DES and the gate tends to zero, the frequency of the proximity plasmon makes a transition to that of an ordinary 2D plasmon in the ungated area of the 2DES. We also observe that tuning the electron density under the gate results in a crossover from the proximity to the laterally screened 2D plasmon. The experimental findings are analyzed using the plasmonic lumped-element approach.

Clinical observation of transforaminal endoscopy combined with interspinous fusion in the treatment of lumbar spinal stenosis with instability in the elderly

To observe the clinical effect of transforaminal endoscopy combined with interspinous fusion in the treatment of lumbar spinal stenosis with instability in the elderly. From February 2018 to February 2019, 82 elderly patients with lumbar spinal stenosis and instability were divided into control group and observation group. In the control group, there were 23 males and 18 females;the age was (68.9±4.1) years;the course of disease was (14.1±5.7) months;there were 5 cases of single segment lesions and 36 cases of multi segment lesions;simple bacfuse interspinous fusion was used. In the observation group, there were 22 males and 19 females;the age was (69.1±4.0) years;the course of diseasewas (14.4±5.5) months;there were 6 cases of single segment lesions and 35 cases of multi segment lesions;they were treated with transforaminal endoscopic surgery combined with Bacfuse interspinous fusion. The clinical efficacy, visual analogue scale (VAS), Japanese Orthopaedic Association scores (JOA), Oswestry disability index (ODI), Lehmann lumbar function score, posterior disc height and intervertebral foramen height, complication rate and recurrence rate of the two groups were compared. The clinical efficacy of the observation group was better than that of the control group;the VAS score of the observation group was lower than that of the control group, the JOA score was higher than that of the control group, and the ODI index at 3 months after operation and at the last follow-up was lower than that of the control group, the Lehmann lumbar function score was higher than that of the control group;the posterior edge height of intervertebral disc and intervertebral foramen height were higher than those of the controlgroup;the incidence of complications and recurrence rate (4.9% and 0.0%) of the observation group were lower than those of the control group (19.5%, 9.8%), the difference was statistically significant (P<0.05). The clinical effect of transforaminal endoscopy combined with interspinous process fusion in the treatment of lumbar spinal stenosis with instability in the elderly is ideal. It can reduce postoperative pain, improve lumbar function, improve the height of posterior edge of intervertebral disc and intervertebral foramen, and reduce the incidence and recurrence rate. It is worthy of clinical promotion.

Gradient microstructure evolution under thermo-mechanical coupling effects for a nickel-based powder metallurgy superalloy－Dynamic recrystallization coexist with static recrystallization

In order to withstand special working conditions, it is of great significance to manufacture turbine disks with a gradient microstructure (disk core with fine and uniform grains and disk edge with coarse grains) along the radial direction. A new and effective forming way-gradient hot deformation is proposed, and a gradient structure from the edge to the center can be obtained. In the present work, the gradient deformation behavior, dynamic recrystallization kinetics, and microstructural evolution of a nickel-based powder metallurgy superalloy are studied by thermal gradient compression. Dynamic recrystallization kinetics of this superalloy is established. Recrystallization fraction increases from 72.6 %–93.6 % because of the gradient deformation degree. Microstructure changes significantly from the center to the edge along the radial direction, and average grain size ranges from 6.65 μm to 15.62 μm. There is a big difference between experimental value and calculated data of recrystallization fraction, which indicates that dynamic and static recrystallization take place in different areas simultaneously. Static recrystallization can coexist with dynamic recrystallization in the trapezoid sample by gradient hot deformation. The difference between experimental and calculated results is the static recrystallization, and the maximum values of static recrystallization fraction is around 30 %. A great number of dynamic recrystallization grains distribute along pre-existing grain boundary, second phases and twin crystal. The main means of static recrystallization nucleation is the bulge of original grain boundaries.

The Wolf–Rayet + Black Hole Binary NGC 300 X-1: What is the Mass of the Black Hole?

Abstract We present new X-ray and UV observations of the Wolf–Rayet + black hole (BH) binary system NGC 300 X-1 with the Chandra X-ray Observatory and the Hubble Space Telescope Cosmic Origins Spectrograph. When combined with archival X-ray observations, our X-ray and UV observations sample the entire binary orbit, providing clues to the system geometry and interaction between the BH accretion disk and the donor star wind. We measure a binary orbital period of 32.7921 ± 0.0003 hr, in agreement with previous studies, and perform phase-resolved spectroscopy using the X-ray data. The X-ray light curve reveals a deep eclipse, consistent with inclination angles of i = 60°–75°, and a pre-eclipse excess consistent with an accretion stream impacting the disk edge. We further measure radial velocity variations for several prominent far-UV spectral lines, most notably H ii λ1640 and C iv λ1550. We find that the He ii emission lines systematically lag the expected Wolf–Rayet star orbital motion by a phase difference of Δϕ ∼ 0.3, while C iv λ1550 matches the phase of the anticipated radial velocity curve of the Wolf–Rayet donor. We assume the C iv λ1550 emission line follows a sinusoidal radial velocity curve (semi-amplitude = 250 km s−1) and infer a BH mass of 17 ± 4 M ⊙. Our observations are consistent with the presence of a wind-Roche lobe overflow accretion disk, where an accretion stream forms from gravitationally focused wind material and impacts the edge of the BH accretion disk.

Massively Multiplexed Electrohydrodynamic Tip Streaming from a Thin Disc.

We report an experimental study on the multiple tip streaming enabled by an externally wetted thin disc in electric fields. The electrohydrodynamic stress acting on the liquid-air interface triggers an interfacial instability that develops into multiple radial liquid ligaments at the rim of the disc. The scaling law suggests that the wave number is inversely proportional to the square of the peak electric field at the rim, which is determined by the combined thickness of the disc and the attached liquid layer. The thin disc edge effectively intensifies the electric field, which in turn leads to spacing between ligaments as short as 30 μm for ethanol, generating over 1000 cone jets for a 1cm diam thin disc.