Disk Density Research Articles

Minimum density of triangulated packing’s three different size circles

The results of a study to determine the minimum and maximum packing density of disks are presented. The minimum and maximum packing densities of disks of three different sizes on a torus are determined. The minimum density is obtained from the ratio of the sectors of the circle to all parts of the triangle on the torus. Heron’s formula is used to find the minimum and maximum density of triangular packing. A diagram of a triangle formed by combining the centers of three circles of three mutually tangent circles and the minimum triangular packing density is given.

JWST/MIRI Spectroscopy of the Disk of the Young Eruptive Star EX Lup in Quiescence

EX Lup is a low-mass pre-main-sequence star that occasionally shows accretion-related outbursts. Here, we present JWST/MIRI medium-resolution spectroscopy obtained for EX Lup 14 yr after its powerful outburst. EX Lup is now in quiescence and displays a Class II spectrum. We detect a forest of emission lines from molecules previously identified in infrared spectra of classical T Tauri disks: H2O, OH, H2, HCN, C2H2, and CO2. The detection of organic molecules demonstrates that they are back after disappearing during the large outburst. Spectral lines from water and OH are for the first time deblended and will provide a much-improved characterization of their distribution and density in the inner disk. The spectrum also shows broad emission bands from warm, submicron-size amorphous silicate grains at 10 and 18 μm. During the outburst, in 2008, crystalline forsterite grains were annealed in the inner disk within 1 au, but their spectral signatures in the 10 μm silicate band later disappeared. With JWST we rediscovered these crystals via their 19.0, 20.0, and 23.5 μm emission, the strength of which implies that the particles are at ∼3 au from the star. This suggests that crystalline grains formed in 2008 were transported outwards and now approach the water snowline, where they may be incorporated into planetesimals. Containing several key tracers of planetesimal and planet formation, EX Lup is an ideal laboratory to study the effects of variable luminosity on the planet-forming material and may provide an explanation for the observed high crystalline fraction in solar system comets.

Double-layer magnetic recording with multilayer perceptron decoder for single-reader/two-track reading in BPMR systems

To expand an areal density of hard disk drives, bit-patterned magnetic recording (BPMR) using a patterned medium instead of a granular medium as employed in perpendicular magnetic recording is attracting much attention as the next-generation recording technology. To further increase the storage capacity of BPMR, multi-layer magnetic recording can be combined with BPMR. Therefore, this paper considers double-layer magnetic recording with a single-reader/two-track reading technique for the staggered BPMR system, which is performed together with a rate-3/5 modulation code. This paper proposes to utilize a multilayer perceptron decoder to decode and estimate the log-likelihood ratio value of the recorded bit sequence that is obtained from the equalized channel. Simulation results show that at a bit-error rate of 10−4, the proposed system with a double-layer recording medium can achieve an improvement gain of about 1.2 decibel if compared to that with a regular single-layer recording medium, even in the presence of media noise.

Optic disc and retinal vessel densities assessment by optical coherence tomography angiography in patients with keratoconus.

This study aimed to evaluate retinal and optic disc vascular changes in patients with keratoconus (KC) using optical coherence tomography angiography (OCTA). Thirty-two eyes of 22 patients with KC and 24 eyes of 24 age- and sex-matched healthy controls were included in this study. Corneal topography and OCTA were performed. Quantitative vessel density of the macular superficial capillary plexus (SCP), macular deep capillary plexus (DCP), and radial peripapillary capillaries (RPC); choriocapillaris flow area; and choroidal thickness were compared between the KC and control groups. SCP and DCP vessel densities showed a significant reduction in the KC group compared to that in the control group (p < 0.001 and p < 0.001 in the whole image and parafovea, respectively). Choriocapillaris flow area was significantly higher in patients with KC than in the control group (p=0.003). The foveal avascular zone area did not significantly differ between the two groups (p=0.949). RPC inside disc vessel density was significantly decreased in the KC group compared to that in the control group (p < 0.001). This study revealed important macular, choroidal, and optic disc vessel densities changes in patients with KC. Macular whole vessel density and parafoveal vessel density of the SCP and DCP decreased, while choriocapillaris flow area increased in patients with KC.

Hydrodynamical Simulations of Black Hole Binary Formation in AGN Disks

We study close encounters between two single black holes (BHs) embedded in an AGN disk using a series of global 2D hydrodynamics simulations. We find that when the disk density is sufficiently high, bound BH binaries can be formed by the collision of their circum-single disks. Our analysis demonstrates that, after a BH pair passes the pericenter of their relative trajectory, post-collision gas drag may slow down the BHs, possibly forcing the two BHs to stay tightly bound. A binary formed by a close encounter can have a compact semimajor axis, large eccentricity, and retrograde orbital angular momentum. We provide a fitting formula that can accurately predict whether a close encounter can form a binary based on the gas mass and the incoming energy of the encounter. This fitting formula can be easily implemented in other long-term simulations that study the dynamical evolution of BHs in active galactic nucleus disks.

Changes in strain energy density in the temporomandibular joint disk after sagittal split ramus osteotomy using acomputed tomography-based finite element model.

We evaluated the changes in the strain energy density (SED) in the temporomandibular joint (TMJ) disk after sagittal split ramus osteotomy (SSRO) at three time points. Afinite element model (FEM) based on real patient-based computed tomography (CT) data was used to examine the effect of SSRO on the TMJ. Measurements of the condylar position and angulation in CT images and FEM analyses were performed for 17patients scheduled to undergo SSROs at the following time points: before surgery, immediately after surgery, and 1year after surgery. SED on the entire disk was calculated at each of the three time points using FEM. Furthermore, the relationship between individual SED values and the corresponding condylar position was also evaluated. No significant change was observed in the condylar position at the three time points. The FEM analysis showed that SED was the highest and lowest immediately after and 1year after surgery, respectively. Apossible SED distribution imbalance between the left and right joints was improved 1year after SSRO. Concerning the effect of fossa morphometry and condylar position, wide and deep glenoid fossae and amore posterior condylar position tended to show lower SED. SED in the articular disk temporarily increased after surgery and significantly decreased 1year after surgery compared with that before surgery. SSRO generally improved the imbalance between the left and right joints. Thus, SSRO, which improves maxillofacial morphology, may also improve components of temporomandibular disorders.

On the crown formation and cavity dynamics of free-falling thick disks

The water entry, crown formation, and cavity dynamics of gravity-driven thick solid and annular disks were studied by conducting a series of detailed laboratory experiments. Three different release conditions were examined to study the fully guarded and partially guarded release conditions on the cavity dynamics. The effects of aspect ratio, geometry, and density of disks on crown formation, interface impact, seal development, and air entrainment were investigated. Four crown shapes were identified, and the crown structure was classified based on the dimensionless moment of inertia, I*, and the impact Froude number, Fro. The effects of controlling parameters on variations of crown dimensions were investigated. It was found that the normalized crown diameter decreased with I* and crown geometries were found to be smaller in annular disks. Experimental observations have shown that high-density disks have larger pinch-off depth and form a deep seal in the ambient water. The normalized pinch-off depth increased with Fro and the normalized pinch-off depth in cylindrical thick disks were smaller than thin disks and spherical objects. The temporal variations of cavity indicated a non-linear correlation between the growth rate of normalized pinch-off depth and time. The disk's velocities in three different stages were measured, it was found that the settling velocities followed a linear relationship with I*, and it was affected by the release conditions. The velocity and vortex fields were extracted from the particle image velocimetry data. The velocity fields showed that the solid disks affected a greater surrounding ambient in comparison to the annular disks due to their higher initial momentum. Periodic vortex shedding was formed in the wake of annular disks, and the frequency of the vortex field was found to be proportional to the disk density.

Evolution of Accreting Neutron Star Common Envelopes and Their Nucleosynthesis Possible P-nuclide Production

In a binary system, a short lived phase called a common envelope can occur in which both stars share the envelope of the primary. During this phase, there is the opportunity for nucleosynthesis to occur at high temperatures and densities in the accretion disk which forms around the secondary star. The system of interest is one in which the secondary star is a neutron star. After introducing the system, our model is described and preliminary results are presented. Preliminary simulations show that light p-nuclides 92Mo and 96,98Ru are overproduced, and that the closer the material is to the neutron star prior to ejection, the fewer p-nuclides are produced.

Changes of Optic Disc and Macular Vessel Perfusion Density in Primary Angle Closure Glaucoma: A Quantitative Study Using Optical Coherence Tomography Angiograph

Introduction: This study aims to investigate the changes of retinal vascular system in primary angle closure glaucoma (PACG) and acute primary angle closure (APAC) by optical coherence tomography (OCT) angiograph (OCTA) and to evaluate the diagnostic ability of changes of vessel density (VD) in different sectors and layers of optic disc and macular area in APAC and PACG. Methods: In this cross-sectional, observational study, 21 APAC patients (22 eyes) and 21 PACG patients (27 eyes) along with 17 healthy people were enrolled from August 2018 to March 2019. Optic disc region and macular region were imaged using swept-source OCTA system. VD of the macular region was quantified by Image J (1.52a, USA) and Matlab 2018a. The circumpapillary retinal nerve fiber layer (cpRNFL) thickness and ganglion cell complex thickness were obtained by spectral-domain OCT. Results: Compared with the healthy group, the cpRNFL thickness in superior sector was thicker in the APAC group, and this area had the most diffuse microvascular dropout as well. The difference in the macular superficial capillary plexus (SCP) VD between APAC and the control group was not statistically significant. The area under the ROC curves (AUC) of the total optic disc VD in the radial peripapillary capillary (RPC) layer was higher than the AUC of the papillary VD in the optic nerve head (ONH) layer. Compared to the control group, the total optic disc VD, peripapillary VD, and each quadrant of peripapillary VD were decreased in PACG (p < 0.01). In PACG macular region, SCP VD, and deep capillary plexus (DCP) VD, parafovea VD (except temporal sectors) decreased (p < 0.01). The PACG eyes had a greater decrease percentage of VD in total ONH than total macula. The diagnostic value of the VD in the ONH layer and the RPC layer was similar. The diagnostic value of the SCP VD in the macula was greater than the DCP VD in the macula. The AUC was no significant difference between cpRNFL thickness and the total optic disc VD AUC. Conclusion: Elevated intraocular pressure preferentially affects vascular perfusion in the optic disc region more than the macular region in APAC and PACG. In the APAC eyes, there was a perfusion defect in the optic disc region and an increase in RNFL thickness. In this study, the OCTA vascular parameters have similar performance to the OCT structural parameters for glaucoma diagnosis in PACG.

Chemical Analysis of Single Graphene Overcoat and Lubricant For Next Generation High Density Magnetic Disk

Chemical Analysis of Single Graphene Overcoat and Lubricant For Next Generation High Density Magnetic Disk

Effects of Oxygen on Smear Formation in Heat Assisted Magnetic Recording System

Heat-assisted magnetic recording (HAMR) is expected to be a realistic next-generation technology for increasing the recording density of hard disks. However, the magnetic layer is heated above the Curie temperature, and, as a result, the heated lubricant is desorbed from the disk by decomposition and evaporation, which causes a problem as it adheres to the air-bearing surface (ABS) as a smear. In this study, pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) analysis was performed in helium and air environments to investigate the decomposition mechanism of perfluoropolyether (PFPE) lubricant D-4OH by heating and in the presence of oxygen. In the helium environment, thermal decomposition of the end groups was confirmed at 350°C and above with a possibility of main chain decomposition at 450°C. In the air environment, decomposition of the end group was confirmed at 250°C and above, and decomposition of the main chain was confirmed at 450°C. Experiments using a pin-on-disk tester were conducted to confirm what happens to the area of smear when a thin film of D-4OH lubricant coated on an actual disk is laser heated. As a result, it was confirmed that the area of smear decreased even at an oxygen concentration of 5%.

Impact of a binary black hole on its outer circumbinary disc

ABSTRACTAccreting supermassive binary black holes (SMBBHs) are potential targets for multimessenger astronomy as they emit gravitational waves (GW) while their environment emits electromagnetic (EM) waves. In order to get the most out of a joint GW–EM detection we first need to obtain theoretically predicted EM signals unambiguously linked to BBHs. In that respect, this is the first of a series of papers dedicated to accreting pre-merger BBHs and their associated EM observables. Here, we extend our Numerical Observatory of Violent Accreting systems, e-NOVAs, to any space–time. Unlike previous studies, almost exclusively focused on the inner regions, we investigated the impact of the BBH on its outer circumbinary disc, located in the radiation (or wave) zone, after implementing an approximate analytical space–time of spinning, inspiralling BBHs in e-NOVAs. We follow the formation of a weak spiral structure in disc density arising from the retardation effects in the radiation zone metric. Simulation data are then post-processed with a general-relativistic ray-tracing code incorporating the same BBH space–time, assuming SMBBH sources. The density spiral creates a small $({\lt }1{{\ \rm per\ cent}})$ but unambiguous modulation of the light curve at the semi-orbital period. This signal, although weak, is fundamentally different from that of an axisymmetric disc around a single BH providing a lower limit on the impact of a BBH on its outer disc. This potential difference being found, we study how binary parameters impact this modulation in order to find the optimal case which is a high source inclination of any binary mass ratio (from 0.1 to 1).

Black Hole Encircled by a Thin Disk: Fully Relativistic Solution* * Dedicated to our teacher, colleague, and friend, Professor Oldřich Semerák, on the occasion of his 60th orbit around the Sun. Oldřich’s well-known lectures—famous not only among us (former) students of “math-phys” in Prague—were the first impulse that led us to devote our studies to general relativity.

We give a full metric describing the gravitational field of a static and axisymmetric thin disk without radial pressure encircling a Schwarzschild black hole. The disk density profiles are astrophysically realistic, stretching from the horizon to radial infinity, yet falling off quickly at both these locations. The metric functions are expressed as finite series of Legendre polynomials. The main advantages of the solution are that (i) the disks have no edges, so their fields are regular everywhere (outside the horizon), and (ii) all nontrivial metric functions are provided analytically and in closed forms. We examine and illustrate basic properties of the black hole−disk spacetimes.

Estimating the depth of gaps opened by planets in eccentric orbit

ABSTRACT Planets can carve gaps in the surface density of protoplanetary discs. The formation of these gaps can reduce the corotation torques acting on the planets. In addition, gaps can halt the accretion of solids on to the planets as dust and pebbles can be trapped at the edge of the gap. This accumulation of dust could explain the origin of the ring-like dust structures observed using high-resolution interferometry. In this work, we provide an empirical scaling relation for the depth of the gap cleared by a planet on an eccentric orbit as a function of the planet-to-star mass ratio q, the disc aspect ratio h, Shakura–Sunyaev viscosity parameter α, and planetary eccentricity e. We construct the scaling relation using a heuristic approach: we calibrate a toy model based on the impulse approximation with 2D hydrodynamical simulations. The scaling reproduces the gap depth for moderate eccentricities (e ≤ 4h) and when the surface density contrast outside and inside the gap is ≤102. Our framework can be used as the basis of more sophisticated models aiming to predict the radial gap profile for eccentric planets.

THE ROLE OF OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IN PATIENTS WITH PREECLAMPSIA.

To investigate the changes in the microvascular structure of the retina and optic disk by comparing the optical coherence tomography angiography findings in preeclamptic patients with those in healthy pregnant women and healthy nonpregnant women and also to evaluate the preeclamptic patients after delivery by showing whether the changes are permanent or not. Fifty preeclamptic, 50 healthy pregnant, and 50 healthy nonpregnant women enrolled in three groups (preeclamptic pregnant women group, healthy pregnant women group, and nonpregnant women group; respectively). Patients in the preeclamptic pregnant women group were evaluated at three different time points including up to 3 hours before delivery (Group 1), 2, or 3 days after delivery (Group 2), and 6 weeks after delivery (Group 3), and compared with each other. All patients underwent a comprehensive ophthalmologic examination including optical coherence tomography angiography. Choriocapillaris blood flow area, deep foveal density, deep temporal density, deep nasal density, and radial peripapillary capillary inside disk density values were significantly lower in the preeclamptic pregnant women group than in the healthy pregnant women group. Deep foveal density and deep nasal density values were significantly higher in Group 3 than in Group 1 and 2, and deep temporal density was significantly higher in Group 3 than in Group 1. Optical coherence tomography angiography diagnosed decreased deep retinal capillary density values in the macula of patients with preeclampsia, but these results improved after delivery.

Dynamical Unification of Tidal Disruption Events

The ∼100 tidal disruption events (TDEs) observed so far exhibit a wide range of emission properties both at peak and over their lifetimes. Some TDEs radiate predominantly at X-ray energies, while others radiate chiefly at UV and optical wavelengths. While the peak luminosities across TDEs show distinct properties, the evolutionary behavior can also vary between TDEs with similar peak emission properties. In particular, for optical TDEs, while their UV and optical emissions decline somewhat following the fallback pattern, some events can greatly rebrighten in X-rays at late time. In this Letter, we conduct three-dimensional general relativistic radiation magnetohydrodynamics simulations of TDE accretion disks at varying accretion rates in the regime of super-Eddington accretion. We make use of Monte Carlo radiative transfer simulations to calculate the reprocessed spectra at various inclinations and at different evolutionary stages. We confirm the unified model proposed by Dai et al., which predicts that the observed emission largely depends on the viewing angle of the observer with respect to the disk orientation. Furthermore, we find that disks with higher accretion rates have elevated wind and disk densities, which increases the reprocessing of the high-energy radiation and thus generally augments the optical-to-X-ray flux ratio along a particular viewing angle. This implies that at later times, as the accretion level declines, we expect that more X-rays will leak out along intermediate viewing angles. Such dynamical model for TDEs can provide a natural explanation for the diversity in the emission properties observed in TDEs at peak and along their temporal evolution.

Micromagnetic Simulation of L10-FePt-Based Transition Jitter of Heat-Assisted Magnetic Recording at Ultrahigh Areal Density.

The areal density of hard disk drives increases every year. Increasing the areal density has limitations. Therefore, heat-assisted magnetic recording (HAMR) technology has been the candidate for increasing the areal density. At ultrahigh areal density, the main problem of the magnetic recording process is noise. Transition jitter is noise that affects the read-back signal. Hence, the performance of the magnetic recording process depends on the transition jitter. In this paper, the transition jitter of L10-FePt-based HAMR technology was simulated at the ultrahigh areal density. The micromagnetic simulation was used in the magnetic recording process. The average grain size was 5.1 nm, and the standard deviation was 0.08 nm. The recording simulation format was five tracks in a medium. It was found that a bit length of 9 nm with a track width of 16.5 nm at the areal density of 4.1 Tb/in2 had the lowest transition jitter average of 1.547 nm. In addition, the transition jitter average decreased when increasing the areal density from 4.1 to 8.9 Tb/in2. It was found that the lowest transition jitter average was 1.270 nm at an 8 nm track width and a 9 nm bit length, which achieved an ultrahigh areal density of 8.9 Tb/in2.

Packing Disks into Disks with Optimal Worst-Case Density

We provide a tight result for a fundamental problem arising from packing disks into a circular container: The critical density of packing disks in a disk is 0.5. This implies that any set of (not necessarily equal) disks of total area delta le 1/2 can always be packed into a disk of area 1; on the other hand, for any varepsilon >0 there are sets of disks of area 1/2+varepsilon that cannot be packed. The proof uses a careful manual analysis, complemented by a minor automatic part that is based on interval arithmetic. Beyond the basic mathematical importance, our result is also useful as a blackbox lemma for the analysis of recursive packing algorithms.

Theoretical and Experimental Understanding of Metal Single-Atom Electrocatalysts for Accelerating the Electrochemical Reaction of Lithium-Sulfur Batteries.

Metal single-atom materials have attracted tremendous attention in the research field of lithium-sulfur (Li-S) batteries because they can effectively improve the reaction kinetics of sulfur cathodes. However, it is still difficult to determine the best metal single-atom catalyst for Li-S batteries, due to the lack of a unified measurement and evaluation method. Herein, a series of metal single-atom- and nitrogen-doped graphene materials (M-NG, M = Fe, Co, Ni, Ir, Ru) have been prepared as the catalysts for promoting the reaction kinetics of the sulfur reduction reaction process. Using rotating disk electrode measurements and density functional theory-based theoretical calculations, Ni-NG was screened out to be the best catalyst. It is found that Ni-NG materials can provide a kinetically favorable pathway for the reversible conversion of polysulfide conversion, thus increasing the utilization of sulfur. By coating the Ni-NG materials on the separator as a multifunctional interlayer, a commercially available sulfur cathode presents a stable specific capacity of 701.8 mAh g-1 at a current rate of 0.5C over 400 cycles. Even with a high sulfur loading of 3.8 mg cm-2, a high areal capacity of 4.58 mAh cm-2 can be achieved. This work will provide a fundamental understanding of efficient single-atom catalyst materials for Li-S batteries.

The X-ray Emission of γ Cassiopeiae During the 2020–2021 disc eruption

Context. γ Cas is known for its unusually hard and intense X-ray emission. This emission could trace accretion by a compact companion, wind interaction with a hot sub-dwarf companion, or magnetic interaction between the star and its Be decretion disc. Aims. These various scenarios should lead to diverse dependences of the hard X-ray emission on disc density. To test these scenarios, we collected X-ray observations of γ Cas during an episode of enhanced disc activity that took place around January 2021. Methods. We investigate the variations in the disc properties using time series of dedicated optical spectroscopy and existing broadband photometry. Equivalent widths and peak velocity separations are measured for a number of prominent emission lines. Epoch-dependent Doppler maps of the Hα, Hβ, and He I λ 5876 emission lines are built to characterise the emission regions in velocity space. We analyse four XMM-Newton observations obtained between January 2021 and January 2022 at key phases of the episode of enhanced disc activity. Archival XMM-Newton, Chandra, MAXI, and RXTE-ASM data are also used to study the long-term correlation between optical and X-ray emission. Results. Optical spectroscopy unveils a clear increase in the radial extent of the emission regions during the episode of enhanced disc activity, whilst no increase in the V-band flux is recorded. Our Doppler maps do not reveal any stable feature in the disc resulting from the putative action of the companion on the outer parts of the Be disc. Whilst the hard X-ray emission is found to display the usual level and type of variability, no specific increase in the hard emission is observed in relation to the enhanced disc activity. However, at two occasions, including at the maximum disc activity, the soft X-ray emission of γ Cas is strongly attenuated, suggesting more efficient obscuration by material from a large flaring Be disc. In addition, there is a strong correlation between the long-term variations in the X-ray flux and the optical variations in the V-band photometry. Conclusions. The observed behaviour of γ Cas suggests no direct link between the properties of the outer regions of the Be disc and the hard X-ray emission, but it favours a link between the level of X-ray emission and the properties of the inner part of the Be disc. These results thus disfavour an accretion or colliding wind scenario.