Disk Radius Research Articles

Self-consistent Conditions for 26Al Injection into a Protosolar Disk from a Nearby Supernova

The early solar system contained a short-lived radionuclide, 26Al (its half-life time t 1/2 = 0.7 Myr). The decay energy of 26Al is thought to have controlled the thermal evolution of planetesimals and, possibly, the water contents of planets. Many hypotheses have been proposed for the origin of 26Al in the solar system. One of the possible hypotheses is the “disk injection scenario”: when the protoplanetary disk of the solar system had already formed, a nearby (<1 pc) supernova injected radioactive material directly into the disk. Such a 26Al injection hypothesis has been tested so far with limited setups for disk structure and supernova distance, which have treated disk disruption and 26Al injection separately. Here, we revisit this problem, to investigate whether there are self-consistent conditions under which the surviving disk radius can receive enough 26Al to account for the abundance in the early solar system. We also consider a range of disk masses and structures, 26Al yields from supernova, and a large dust mass fraction η d. We find that 26Al yields of supernova are required as ≳2.1×10−3M⊙(ηd/0.2)−1 , which are challenging to achieve with the known possible 26Al ejection and dust mass fraction ranges. Furthermore, we find that even if the above conditions are met, the supernova flow changes the disk temperature, which may not be consistent with the solar system record. Our results place a strong constraint on the disk injection scenario. Rather, we suggest that the fresh 26Al of the early solar system must have been synthesized/injected in other ways.

Evolution of accretion disk structure of the black hole X-ray binary MAXI J1820+070 during the rebrightening phase

Abstract To understand the evolution of global accretion disk structure in the “rebrightening” phase of MAXI J1820+070, we perform a comprehensive analysis of its near infrared/optical/UV to X-ray spectral energy distribution (SED) utilizing data obtained by OISTER, Las Cumbres Observatory (LCO), Swift, NICER, and NuSTAR in 2019. Optical spectra observed with Seimei telescope in 2019 and 2020 are also analyzed. On the basis of the optical and X-ray light curves and their flux ratios, we divide the whole phase into three periods, Periods I (flux rise), II (decay), and III (dim). In the first two periods, the source stayed in the low/hard state (LHS), where the X-ray (0.3–30 keV) and optical/UV SED can both be fitted with power-law models. We interpret that the X-ray emission arises from hot corona via Comptonization, whereas the optical/UV flux is dominated by synchrotron radiation from the jets, with a partial contribution from the irradiated disk. The optical/UV power-law component smoothly connects to a simultaneous radio flux, supporting its jet origin. Balmer line profiles in the optical spectra indicate that the inner radius of an irradiated disk slightly decreased from ∼2 × 105rg (Period I) to ∼1 × 105rg (Period II), where rg is the gravitational radius, implying a change of the hot corona geometry. In Period III, the SED can be reproduced by an advection-dominated accretion flow and jet emission. However, the double-peaked Hα emission line indicates that a cool disk remained at large radii.

The range set of zero for harmonic mappings of the unit disk with sectorial boundary normalization

Given a family \(\mathcal F\) of all complex-valued functions in a domain \(\Omega\subset\hat{\mathbb{C}}\), the authors introduce the range set \(RS_{\mathcal F}(A)\) of a set \(A\subset\Omega\) under the class in question, i.e. the set of all \(w\in\Bbb C\) such that \(w\in F(A)\) for a certain \(F\in\mathcal F\). Let \(T_1,T_2,T_3\) be closed arcs contained in the unit circle \(\Bbb T\) of the same length \(2\pi/3\) and covering \(\Bbb T\). The paper deals with the range set \(RS_{\mathcal F}(\{0\})\), where \(\mathcal F\) is the class of all complex-valued harmonic functions \(F\) of the unit disk \(\Bbb D\) into itself satisfying the following sectorial condition: For each \(k\in\{1,2,3\}\) and for almost every \(z\in T_k\) the radial limit \(F^*(z)\) of the function \(F\) at the point \(z\) belongs to the angular sector determined by the convex hull spanned by the origin and arc \(T_k\). In 2014 the authors proved that for any \(F\in\mathcal F\), \(|F(z)|\le\frac{4}{3}-\frac{2}{\pi}\arctan\left(\frac{\sqrt{3}}{1+2|z|}\right), \quad z\in\Bbb D\), by which \(|F(0)|\le 2/3\). This implies that \(RS_{\mathcal F}(\{0\})\) is a subset of the closed disk of radius 2/3 and centred at the origin. In the paper the range set \(RS_{\mathcal F}(\{0\})\) is precisely determined.

Critical point asymptotics for Gaussian random waves with densities of any Sobolev regularity

We consider Gaussian random monochromatic waves u on the plane depending on a real parameter s that is directly related to the regularity of its Fourier transform. Specifically, the Fourier transform of u is fdσ, where dσ is the Hausdorff measure on the unit circle and the density f is a function on the circle that, roughly speaking, has exactly s−12 derivatives in L2 almost surely. When s=0, one recovers the classical setting for random waves with a translation-invariant covariance kernel. The main thrust of this paper is to explore the connection between the regularity parameter s and the asymptotic behavior of the number N(∇u,R) of critical points that are contained in the disk of radius R≫1. More precisely, we show that the expectation EN(∇u,R) grows like the area of the disk when the regularity is low enough (s<32) and like the diameter when the regularity is high enough (s>52), and that the corresponding exponent changes according to a linear interpolation law in the intermediate regime. The transitions occurring at the endpoint cases involve the square root of the logarithm of the radius. Interestingly, the highest asymptotic growth rate occurs only in the classical translation-invariant setting, s=0. A key step of the proof of this result is the obtention of precise asymptotic expansions for certain Neumann series of Bessel functions. When the regularity parameter is s>5, we show that in fact N(∇u,R) grows like the diameter with probability 1, albeit the ratio is not a universal constant but a random variable.

Nine New Cataclysmic Variable Stars with Negative Superhumps

Negative superhumps (NSHs) are signals a few percent shorter than the orbital period of a binary star and are considered to originate from the reverse precession of the tilted disk. Based on TESS photometry, we find nine new cataclysmic variable stars with NSHs. Three (ASAS J1420, TZ Per, and V392 Hya) of these stars similar to AH Her still have NSHs during dwarf nova outbursts, and the NSH amplitude varies with the outburst. The variation in the radius of the accretion disk partially explains this phenomenon. However, it does not explain the rebound of the NSH amplitude after the peak of the outburst and the fact that the NSH amplitude of the quiescence is sometimes not the largest, and it is necessary to include the disk instability model (DIM) and add other ingredients. Therefore, we suggest that the variation of NSH amplitude with outburst can be an important basis for studying the origin of NSHs and improving the DIM. The six (ASASSN-V J1137, ASASSN-V J0611, 2MASS J0715, LAMOST J0925, ASASSN-17qj, and ZTF 18acakuxo) remaining stars have been poorly studied, and for the first time we determine their orbital periods, NSHs, and superorbital signal (SOR) periods. The NSH periods and amplitudes of ASASSN-V J1137 and ASASSN-17qj vary with the SOR, and based on the comparison of the observations with the theory, we suggest that a single change in tilted disk angle does not explain the observations of the SOR and that other ingredients need to be considered as well.

Typical X-Ray Outburst Light Curves of Aql X-1

We show that the typical X-ray outburst light curve of Aql X-1 can be reproduced by accretion onto a neutron star in the frame of the disk instability model without invoking partial accretion or the propeller effect. The knee and the subsequent sharp decay in the X-ray light curve can be generated naturally by taking into account the weak dependence of the disk aspect ratio, h/r, on the disk mass-flow rate, Ṁin , in the X-ray irradiation flux calculation. This Ṁin dependence of h/r only slightly modifies the irradiation temperature profile along the hot disk in comparison to that obtained with a constant h/r. Nevertheless, this small difference has a significant cumulative effect on the hot disk radius, leading to a much faster decrease in the size of the hot disk and thereby to a sharper decay in the X-ray outburst light curve. The same model also produces the long-term evolution of Aql X-1, consistent with its observed outburst recurrence time and typical light curve. Our results imply that the source accretes matter from the disk in the quiescent state as well. We also estimate that the dipole moment of the source μ ≲ 4 × 1026 G cm3 (B ≲ 4 × 108 G at the surface).

Diffusion Enhancement and Taylor Dispersion for Rotationally Symmetric Flows in Discs and Pipes

In this note, we study the long-time dynamics of passive scalars driven by rotationally symmetric flows. We focus on identifying precise conditions on the velocity field in order to prove enhanced dissipation and Taylor dispersion in three-dimensional infinite pipes. As a byproduct of our analysis, we obtain an enhanced decay for circular flows on a disc of arbitrary radius.

Studies on the soft intermediate state X-ray flare of MAXI J1535−571 during its 2017 outburst

ABSTRACT We analysed an observation with the Nuclear Spectroscopic Telescope Array of the black hole X-ray binary MAXI J1535−571 in the soft intermediate state, in which we detected a 2.5-ks long flare. Our spectral fitting results suggest that MAXI J1535−571 possesses a high spin of $0.97_{-0.10}^{+0.02}$ and a low inclination of approximately 24°. We observed a gradual increase in the inner disc radius, as determined from fits to the continuum spectrum. This trend is inconsistent with an increased flux ratio of the thermal component, as well as the source evolving towards the soft state. This inconsistency may be attributed to a gradual decrease of the colour correction factor. Additionally, with a flare velocity of approximately 0.5 c and a higher hardness ratio during the flare period, the quasi-simultaneous detection of a type-B QPO in the Neutron Star Interior Composition Explorer data, and quasi-simultaneous ejecta launch through radio observations collectively provide strong evidence supporting the possibility that the flare originated from a discrete jet ejection.

Electrostatic interaction energy between the electrodes of a concentric coplanar sensor

The capacitive testing method using coplanar capacitive sensors represents a relatively new technique for non-destructive evaluation of the properties of a given material. The most conventional design of a coplanar capacitive sensor is that of two oppositely charged coplanar electrodes located at some separation distance from each other. The electrodes can have any shape including designs with circular symmetry. The concentric coplanar sensor is a special case of a device with circular symmetry. It comprises a disk as the inner electrode and an annulus as the outer one. In this work we analyze the features of the electrostatic interaction energy between the two electrodes of a concentric coplanar sensor by considering a model consisting of a uniformly charged disk and a uniformly charged annulus that is concentric and coplanar to the disk. For the sake of generality, we assume that the two objects carry an arbitrary amount of net charge and their dimensions are arbitrary. We obtain an exact expression for the electrostatic interaction energy of the system as a function of three important length scales, radius of disk and inner/outer radii of the annulus. The interplay between these parameters determines the features of the electrostatic interaction energy between the electrodes as well as the overall performance of the sensor.

Cosmological gas accretion history on to the stellar discs of Milky Way-like galaxies in the Auriga simulations – II. The inside–out growth of discs

ABSTRACT We investigate the growth of stellar discs in Milky Way-mass galaxies using the magnetohydrodynamical simulations of the Auriga Project in a full cosmological context. We focus on the gas accretion process along the discs, calculating the net, infall and outflow rates as a function of galactocentric distance, and investigate the relation between them and the star formation activity. The stellar distributions of around 70 per cent of the simulated galaxies exhibit an ‘inside–out’ pattern, with older (younger) stellar populations preferentially located in the inner (outer) disc regions. In all cases, we find a very tight correlation between the infall, outflow, and net accretion rates, as well as between these three quantities and the star formation rate. This is because the amount of gas which is ultimately available for star formation in each radial ring depends not only on the infall rates, but also on the amount of gas leaving the disc in outflows, which directly relates to the local star formation level. Therefore, any of these rates can be used to identify galaxies with inside–out growth. For these galaxies, the correlation between the dominant times of accretion/star formation and disc radius is well fitted by a linear function. We also find that, when averaged over galaxies with formation histories similar to the Milky Way, the simulated accretion rates show a similar evolution (both temporally and radially integrated) to the usual accretion prescriptions used in chemical evolution models, although some major differences arise at early times and in the inner disc regions.

Star-forming environments in smoothed particle magnetohydrodynamics simulations II: re-simulating isolated clumps to determine equivalence of extracted clumps and parent simulations

ABSTRACT What is the numerical reproducibility of a stellar system (including its discs) when evolving only a subset of (partially-evolved) smoothed particle hydrodynamics (SPH) particles? To investigate this, we modelled the evolution of 29 star-forming clumps that were extracted from our previous simulations that investigated the formation and early evolution of low-mass star clusters. These clumps were evolved using a three-dimensional smoothed particle radiation magnetohydrodynamics code, where we included or excluded non-ideal magnetohydrodynamics to match the cluster simulation. While star formation proceeded as expected, we were unable to identically reproduce any of the systems present at the end of the cluster simulations. However, the final distributions of stellar mass, stellar system mass, disc mass, and disc radii were reproduced statistically; unfortunately, the distribution of average magnetic field strengths in the discs was not reproduced statistically, but this may be a result of our updated algorithms governing the evolution of the magnetic field. Therefore, given that our clumps yield stellar masses that are statistically similar to those in the original low-mass star clusters, we have demonstrated that we can statistically reproduce systems (aside from their magnetic field strength) by evolving a subset of SPH particles. Therefore, clumps such as these can be used as initial conditions to investigate the formation of isolated stars from less-contrived initial environments.

Light Curve of HT Cassiopeiae

Photometric observations of the eclipsing dwarf nova HT Cas are presented in its quiescent state on 2022 October 20th for one complete orbital period. These data were taken with the RISE imager mounted on the Liverpool Telescope. The lcurve code was used to fit the light curve. System parameters were derived of mass ratio q = M 2/M 1 = 0.15 ± 0.01, angle of inclination i = 80.°98 ± 0.°18 and white dwarf radius of R 1 = 0.0128 ± 0.0003R ⊙. This gives solutions for the masses of the white dwarf and donor star of M 1 = 0.571 ± 0.017M ⊙ and M 2 = 0.088 ± 0.005M ⊙. The disk radius and bright spot radius with the best fit from the model were R disk = 0.51 ± 0.04a and R spot = 0.32 ± 0.02a. These are consistent with previous published observations.

Disc corona radii and QPO frequencies in black hole binaries: testing Lense– Thirring precession origin

ABSTRACT Stellar-mass black hole binary systems in the luminous X-ray states show a strong quasi-periodic oscillation (QPO) in their Comptonized emission. The frequency of this feature correlates with the ratio of a disc to Comptonized emission rather than with total luminosity. Hence, it changes dramatically during spectral transitions between the hard and soft states. Its amplitude is also strongest in these intermediate states, making them an important test of QPO models. However, these have complex spectra which generally require a disc and two separate Comptonization components, making it difficult to uniquely derive the spectral parameters. We build a new energy-conserving model of the accretion flow, SSsed model, which assumes a fixed radial emissivity but with a changing emission mechanism. This is similar to the agnsed model in xspec but tuned to be more suitable for stellar mass black holes. It uses a combination of the disc luminosity and temperature to constrain the inner radius of the (colour temperature corrected) blackbody disc, separating this from the more complex Comptonization spectra emitted inwards of this radius. We show a pilot study of this model fit to hundreds of RXTE spectra of the black hole binary XTE J1550 − 564. We show that the derived disc radius tightly anticorrelates with the central frequencies of the low-frequency QPO detected in the same observations. The relation is consistent with the quantitative predictions of Lense–Thirring precession of the entire inner Comptonization regions for the assumed system parameters. This supports the scenario that low-frequency QPOs are caused by Lense–Thirring precession.

Scanning Laser Ophthalmoscopy Demonstrates Pediatric Optic Disc and Peripapillary Strain During Horizontal Eye Rotation

Purpose: We employed automated analysis of scanning laser ophthalmoscopy (SLO) to determine if mechanical strains imposed on disc, and retinal and choroidal vessels during horizontal duction in children differ from those of adults. Methods: Thirty-one children aged 11.3 ± 2.7 (standard deviation) years underwent SLO in central gaze, and 35° ab- and adduction. Automated registration with deep learning-based optical flow analysis quantified vessel deformations as horizontal, vertical, shear, and equivalent strains. Choroidal vessel displacements in lightly pigmented fundi, and central disc vessel displacements, were also observed. Results: As in adults, strain in vessels during horizontal duction was greatest at the disc and decreased with distance from it. Strain in the pediatric disc was similar to published values in young adults, 1 but in the peripapillary region was greater and propagated significantly more peripherally to at least three disc radii from it. During adduction in children, the nasal disc was compressed and disc vessels distorted, but the temporal half experienced tensile strain, while peripapillary tissues were compressed. The pattern was similar but strains were less in abduction (p < .001). Choroidal vessels were visualized in 24 of the 62 eyes and shifted directionally opposite overlying retinal vessels. Conclusions: Horizontal duction deforms the normal pediatric optic disc, central retinal vessels, peripapillary retina, and choroid, shearing the inner retina over the choroid. These mechanical effects occur at the sites of remodeling of the disc, sclera, and choroid associated with typical adult features that later emerge later, including optic cup enlargement, temporal disc tilting, and peripapillary atrophy.

Numerical computation of temperature on steel and an insulator with simulation compared toexperimental data.

In this report, we are computing the temperature from the heat equation for a disk of a given thickness. A laser beam of Gaussian profile is assumed at the surface of a circular sample. Prediction of temperature for a laser pulse with a Gaussian profile is shown for a circular symmetry. Temperature distributions are performed analytically and numerically for a power with a Gaussian profile at different depths from the surface. In the previous computation the laser beam was assumed to be small compared to the disk's radius. The calculations performed are useful to predict the proper spacing between marks during a laser procedure. Computations of the temperature for a beam spot size much larger than the sample dimensions are also shown for a modulated laser beam. The computation of temperature for the modulated laser beam is also compared to experimental data points obtained on bone.

Self-assembled active actomyosin gels spontaneously curve and wrinkle similar to biological cells and tissues.

Living systems adopt a diversity of curved and highly dynamic shapes. These diverse morphologies appear on many length scales, from cells to tissues and organismal scales. The common driving force for these dynamic shape changes are contractile stresses generated by myosin motors in the cell cytoskeleton, that converts chemical energy into mechanical work. A good understanding of how contractile stresses in the cytoskeleton arise into different three-dimensional (3D) shapes and what are the shape selection rules that determine their final configurations is still lacking. To obtain insight into the relevant physical mechanisms, we recreate the actomyosin cytoskeleton in vitro, with precisely controlled composition and initial geometry. A set of actomyosin gel discs, intrinsically identical but of variable initial geometry, dynamically self-organize into a family of 3D shapes, such as domes and wrinkled shapes, without the need for specific preprogramming or additional regulation. Shape deformation is driven by the spontaneous emergence of stress gradients driven by myosin and is encoded in the initial disc radius to thickness aspect ratio, which may indicate shaping scalability. Our results suggest that while the dynamical pathways may depend on the detailed interactions between the different microscopic components within the gel, the final selected shapes obey the general theory of elastic deformations of thin sheets. Altogether, our results emphasize the importance for the emergence of active stress gradients for buckling-driven shape deformations and provide insights on the mechanically induced spontaneous shape transitions in contractile active matter, revealing potential shared mechanisms with living systems across scales.

COVERING A MAXIMUM NUMBER OF POINTS BY A FIXED NUMBER OF EQUAL DISKS VIA SIMULATED ANNEALING

The presented paper considers the problem of covering a maximum number of n given points in the plane by m equal disks of radius r. A point is covered if it is inside one or more than one disk. The disks need to be placed in the plane in such a way that a maximum number of points are covered. To solve the problem, an objective function, called energy, is introduced in such a way that the greater the covering is, the lower the energy is. Thus, a configuration of disks with minimum energy is a configuration with maximum covering. To find a configuration of disks that minimizes the energy, a stochastic algorithm based on the Monte Carlo simulated annealing technique is proposed. The algorithm overcomes potential local minima, which, as shown in the paper, are quite likely to occur. The computational complexity of the algorithm is O(mn). The algorithm is tested on several cases demonstrating its efficiency in finding global minima of the energy, i.e. configurations with maximum covering.

Understanding the universal dust attenuation scaling relation of star-forming galaxies

ABSTRACT Star-forming galaxies (SFGs) adhere to a surprisingly tight scaling relation of dust attenuation parametrized by the infrared excess (IRX≡ LIR/LUV), being jointly determined by the star formation rate (SFR), galaxy size (Re), metallicity (Z/Z⊙), and axial ratio (b/a). We examine how these galaxy parameters determine the effective dust attenuation and give rise to the universal IRX relation, utilizing a simple two-component star-dust geometry model in which dust in the dense and diffuse interstellar medium (ISM) follows exponential mass density profiles, connected with but not necessarily identical to the stellar mass profiles. Meanwhile, empirical relations are adopted to link galaxy properties, including the gas–star formation relation, the dust-to-stellar size relation, as well as the dust-to-gas ratio versus metallicity relation. By fitting a large sample of local SFGs with the model, we obtain the best-fitting model parameters as a function of metallicity, showing that the two-component geometry model is able to successfully reproduce the dependence of IRX on SFR, Re, b/a at given Z/Z⊙, as well as the dependence of power-law indices on metallicity. Moreover, we also retrieve constraints on the model geometry parameters, including the optical depth of birth clouds (BCs), BC-to-total dust mass fraction, BC covering factor of UV-emitting stars, and star-to-total dust disc radius ratio, which all evolve with galaxy metallicity. Finally, a consistent picture of how the star-dust geometry in SFGs evolves with galaxy metallicity is discussed.

POLYNOMIALS LEAST DEVIATING FROM ZERO IN \(L^p(-1;1)\), \(0 \le p \le \infty \), WITH A CONSTRAINT ON THE LOCATION OF THEIR ROOTS

We study Chebyshev's problem on polynomials that deviate least from zero with respect to \(L^p\)-means on the interval \([-1;1]\) with a constraint on the location of roots of polynomials. More precisely, we consider the problem on the set \(\mathcal{P}_n(D_R)\) of polynomials of degree \(n\) that have unit leading coefficient and do not vanish in an open disk of radius \(R \ge 1\). An exact solution is obtained for the geometric mean (for \(p=0\)) for all \(R \ge 1\); and for \(0&lt;p&lt;\infty\) for all \(R \ge 1\) in the case of polynomials of even degree. For \(0&lt;p&lt;\infty\) and \(R\ge 1\), we obtain two-sided estimates of the value of the least deviation.

Synchronous Vibration Parameter Recognition of Constant-Speed Blades Based on Blade Tip Clearance Measurement

A new method for the synchronous vibration parameter identification of constant-speed rotating blades based on blade tip clearance (BTC) measurement and blade tip timing (BTT) is introduced. A BTC sensor is used to measure the BTC when the blade tip passes through each sensor. The BTT method is used to determine whether the blade tip arrives in advance or lags. The geometric model between the BTC and the blade tip vibration displacement (BTVD) is established, and the BTVD of the blade tip passing through each sensor is obtained. Then, the nonlinear least squares method is used to determine the synchronous vibration parameters of the constant-speed rotating blade. The results show that with an increase in amplitude, the higher the accuracy of the vibration parameter identification proposed in this paper; with a decrease in the random error of the BTC measurement, the higher the accuracy of the vibration parameter identification proposed in this paper; with a decrease in the random error in the measurement of the blade disk dimensions, the higher the accuracy of the vibration parameter identification proposed in this paper. In addition, the smaller the ratio of the blade length to the blade disk radius, the higher the accuracy of the vibration parameter identification method introduced in this paper. Because the structure of the gas turbine compressor and turbine blade disk has a small blade disk ratio, the method proposed in this paper is suitable for the simultaneous vibration parameter identification of gas turbine compressor blades and turbine blades.