Edge Of Disk Research Articles

The light curve simulations of the 2021 anomalous event in SS Cygni

Abstract The prototype dwarf nova SS Cyg unexpectedly exhibited an anomalous event in its light curve in the early few months of 2021 in which regular dwarf nova-type outbursts stopped, and only small-amplitude fluctuations occurred. Inspired by this event, we have performed numerical simulations of light curves of SS Cyg by varying mass transfer rates and varying viscosity parameters in the cool disk. We have also studied the effect of gas-stream overflows beyond the outer disk edge in the light curve simulations. We have confirmed that the enhanced mass transfer is not likely to be responsible for the 2021 anomalous event or its forerunner. We have found that the enhancement of the viscosity in the disk may reproduce the forerunner of that event but may not be sufficient to explain the 2021 anomalous event, although the latter result might be particular to the thermal equilibrium curve we used. Within our simulations, a model of the gas-stream overflow with a slightly higher mass transfer rate than that of our standard model reproduces light curves similar to the 2021 anomalous event. We suggest that the gas-stream overflow is necessary to reproduce that event. The gas-stream overflow may also be responsible for the abnormally high X-ray flux during the normal quiescent state in SS Cyg.

Deep learning-based 3D OCT imaging for detection of lamina cribrosa defects in eyes with high myopia

The lamina cribrosa (LC) is a collagenous tissue located in the optic nerve head, and its dissection is observed in eyes with pathologic myopia as a LC defect (LCD). The diagnosis of LCD has been difficult because the LC is located deep beneath the retinal nerve fibers. The purpose of this study was to determine the prevalence and three-dimensional shape of LCDs in highly myopic eyes. Swept-source OCT scan images of a 3 × 3-mm cube centered on the optic disc were obtained from 119 eyes of 62 highly myopic patients. Each LC was manually labelled in cross-sectional OCT images along the axial, coronal, and sagittal planes. A deep convolutional neural network (DCNN) was trained with the manually labeled images, and the trained DCNN was applied to the detection of the LC in every image in each plane. Three-dimensional images of the LC were generated from the labeled image of each eye. The results showed that LCDs were detected in 12 of the 42 (29%) eyes in which an LC was visible. The LCDs ran vertically at the temporal edge of the optic disc. In conclusion, 3D OCT imaging with the application of DCNN is helpful in diagnosing LCDs.

Seagull wings appearance on optical coherence tomography: A case of peripapillary detachment in pathologic myopia.

To report the case of a patient who presented with a peripapillary retinal detachment caused by pathological myopia. A 73-year-old female with a clinical history of high myopia was admitted to our ophthalmic department complaining of vision loss in her right eye. Her best-corrected visual acuity was 20/25 in the right eye and 20/400 in the left eye. The refractive error was -9.00 D in both eyes. The anterior segment and pupillary reflex were normal. Dilated fundus examination revealed myopic retinopathy in both eyes and a yellow peripapillary lesion, distinct from the myopic conus and encircling almost the whole optic disc, in her right eye. The left eye displayed macular atrophy with macular pigmentation due to a previous myopic choroidal neovascularization. Optical coherence tomography showed a localized retinal detachment in the peripapillary area, adjacent to the inferior edge of the optic disc, giving a strange "seagull wings" appearance. In case of peripapillary neuroepithelial detachment the presence of PDPM in high myopic patients should always be excluded. Further research is due in order to better understand this clinical entity's pathogenesis and prognosis.

A Low-mass Pre-main-sequence Eclipsing Binary in Lower Centaurus Crux Discovered with TESS

We report the discovery of 2M1222−57 as a low-mass, pre-main-sequence (PMS) eclipsing binary (EB) in the Lower Centaurus Crux (LCC) association for which, using Gaia parallaxes and proper motions with a neural net age estimator, we determine an age of 16.2 ± 2.2 Myr. The broadband spectral energy distribution (SED) shows clear excess at ≳10 μm indicative of a circumbinary disk, and new speckle imaging observations reveal a faint, tertiary companion separated by ∼100 au. Hα emission is modulated on the orbital period, consistent with theoretical models of orbitally pulsed accretion streams reaching from the inner disk edge to the central stars. From a joint analysis of spectroscopically determined radial velocities and TESS light curves, together with additional tight constraints provided by the SED and the Gaia parallax, we measure masses for the eclipsing stars of 0.74 M ⊙ and 0.67 M ⊙; radii of 0.98 R ⊙ and 0.94 R ⊙; and effective temperatures of 3750 K and 3645 K. The masses and radii of both stars are measured to an accuracy of ∼1%. The measured radii are inflated, and the temperatures suppressed, relative to predictions of standard PMS evolutionary models at the age of LCC; also, the Li abundances are ∼2 dex less depleted than predicted by those models. However, models that account for the global and internal effects of surface magnetic fields are able to simultaneously reproduce the measured radii, temperatures, and Li abundances at an age of 17.0 ± 0.5 Myr. Altogether, the 2M1222−57 system presents very strong evidence that magnetic activity in young stars alters both their global properties and the physics of their interiors.

Spectral Evolution of Ultraluminous X-Ray Pulsar NGC 300 ULX-1

We report on results from a 1 yr soft X-ray observing campaign of the ultraluminous X-ray pulsar NGC 300 ULX-1 by the Neutron star Interior Composition Explorer (NICER) during 2018–2019. Our analysis also made use of data from Swift/XRT and XMM-Newton in order to model and remove contamination from the nearby eclipsing X-ray binary NGC 300 X-1. We constructed and fitted a series of 5 day averaged NICER spectra of NGC 300 ULX-1 in the 0.4–4.0 keV range to evaluate the long-term spectral evolution of the source, and we found that an absorbed power-law model provided the best fit overall. Over the course of our observations, the source flux (0.4–4.0 keV; absorbed) dimmed from 2 × 10−12 to below 10−13 erg s−1 cm−2 and the spectrum softened, with the photon index going from Γ ≈ 1.6 to Γ ≈ 2.6. We interpret the spectral softening as reprocessed emission from the accretion disk edge coming into view while the pulsar was obscured by the possibly precessing disk. Some spectral fits were significantly improved by the inclusion of a disk blackbody component, and we surmise that this could be due to the pulsar emerging in between obscuration episodes by partial covering absorbers. We posit that we observed a low-flux state of the system (due to line-of-sight absorption) punctuated by the occasional appearance of the pulsar, indicating short-term source variability nested in longer-term accretion disk precession timescales.

Outer disc edge: properties of low-frequency aperiodic variability in ultracompact interacting binaries

ABSTRACT Flickering, and more specifically aperiodic broad-band variability, is an important phenomenon used in understanding the geometry and dynamics of accretion flows. Although the inner regions of accretion flows are known to generate variability on relatively fast time-scales, the broad-band variability generated in the outer regions has mostly remained elusive due to its long intrinsic variability time-scales. Ultracompact AM CVn systems are relatively small when compared to other accreting binaries and are well suited to search and characterize low-frequency variability. Here, we present the first low-frequency power spectral analysis of the ultracompact accreting white dwarf system SDSS J1908+3940. The analysis reveals a low-frequency break at ∼6.8 × 10−7 Hz in the time-averaged power spectrum as well as a second higher frequency component with characteristic frequency of ∼1.3 × 10−4 Hz. We associate both components with the viscous time-scales within the disc through empirical fits to the power spectrum as well as analytical fits using the fluctuating accretion disc model. Our results show that the low-frequency break can be associated with the outer disc regions of a geometrically thin accretion flow. The detection of the low-frequency break in SDSS J1908+3940 provides a precedent for further detection of similar features in other ultracompact accreting systems. More importantly, it provides a new observable that can help constrain simulations of accretion flows.

First detection of the outer edge of an AGN accretion disc: very fast multiband optical variability of NGC 4395 with GTC/HiPERCAM and LT/IO:O

ABSTRACT We present fast (∼200 s sampling) $\it ugriz$ photometry of the low -mass AGN NGC 4395 with the Liverpool Telescope, followed by very fast (3 s sampling) us, gs, rs, is, and zs simultaneous monitoring with HiPERCAM on the 10.4m GTC. These observations provide the fastest ever AGN multiband photometry and very precise lag measurements. Unlike in all other AGN, gs lags us by a large amount, consistent with disc reprocessing but not with reprocessing in the broad-line region (BLR). There is very little increase in lag with wavelength at long wavelengths, indicating an outer edge (Rout) to the reprocessor. We have compared truncated disc reprocessing models to the combined HiPERCAM and previous X-ray/UV lags. For the normally accepted mass of 3.6 × 105M⊙, we obtain reasonable agreement with zero spin, Rout ∼ 1700Rg and the done physically motivated temperature-dependent disc colour-correction factor (f$\rm _{col}$). A smaller mass of 4 × 104M⊙ can only be accommodated if f$\rm _{col}=2.4$, which is probably unrealistically high. Disc self gravity is probably unimportant in this low-mass AGN but an obscuring wind may provide an edge. For the small mass, the dust sublimation radius is similar to Rout so the wind could be dusty. However, for the more likely large mass, the sublimation radius is further out so the optically thick base of a line-driven gaseous wind is more likely. The inner edge of the BLR is close to Rout in both cases. These observations provide the first good evidence for a truncated AGN disc and caution that truncation should be included in reverberation lag modelling.

Incidence and risk factors of lumbar plexus injury in patients undergoing oblique lumbar interbody fusion surgery.

To investigate the incidence and risk factors of lumbar plexus injury (LPI) after oblique lumbar interbody fusion (OLIF) surgery. A total of 110 patients who underwent OLIF surgery between January 2017 and January 2021 were retrospectively reviewed. Patients were divided into two groups: the group with LPI (LPI group) and the group without LPI (non-LPI group). The baseline demographic data, surgical variables and radiographic parameters were compared and analyzed between these two groups. Among all participants, 13 (8.5%) had LPI-related symptoms postoperatively (short-term), and 6 (5.5%) did not fully recover after one year (long-term). Statistically, there were no significant differences in the baseline demographic data, surgery duration, intraoperative blood loss, preoperative diagnosis, surgical procedures used and incision length. Compared with the non-LPI group, patients in the LPI group had a narrower OLIF channel space. In LPI group, the anterior edge of left psoas major muscle overpasses the anterior edge of surgical intervertebral disk (IVD) on axial MRI. Logistic regression analysis revealed that narrow OLIF channel space and the anterior edge of left psoas major muscle overpassing the anterior edge of surgical IVD on axial MRI were independently associated with both short-term and long-term LPI. Narrow OLIF channel space and the anterior edge of left psoas major muscle overpassing the anterior edge of surgical IVD are significant risk factors of OLIF surgery-related LPI. Surgeons should use preoperative imaging to adequately assess these risk factors to reduce the occurrence of LPI.

Circumplanetary disk ices

Context. The large icy moons of Jupiter formed in a circumplanetary disk (CPD). CPDs are fed by vertically infalling circumstellar gas and dust which may be shock-heated upon accretion. Accreted material is then either incorporated into moons, falls into the planet, or is lost beyond the disk edge on relatively short timescales. If ices are sublimated during accretion onto the CPD we know there must be sufficient time for them to recondense or moons such as Ganymede or Callisto could not form. The chemical timescale to form sufficiently icy solids places a novel constraint on the dynamical behaviour and properties of CPDs.Aims. We aim to explore the process of ice formation in CPDs to constrain which disk properties (such as the mass, viscosity, and dust-to-gas ratio) are consistent with the formation of an icy moon system.Methods. We use the radiation thermochemical code ProDiMo(Protoplanetary Disk Model) to analyze how the radial ice abundance evolves in CPDs. We consider different initial chemical conditions of the disk to explore the consequences of infalling material being inherited from the circumstellar disk or being reset to atomic conditions by shock-heating. We contrast the timescales of ice formation with disk viscous timescales and radial dust drift.Results. We have derived the radial ice abundance and rate of ice formation in a small grid of model CPDs. Water ice can form very efficiently in the CPD from initially atomic conditions, as a significant fraction is efficiently re-deposited on dust grains within <1 yr. Radial grain drift timescales are in general longer than those of ice formation on grains. Icy grains of sizea <3 mm retain their icy mantles while crossing an optically thin circumstellar disk gap at 5 au forL*< 10L⊙.Conclusions. Three-body reactions play an important role in water formation in the dense midplane condition of CPDs. The CPD midplane must be depleted in dust relative to the circumstellar disk by a factor 10-50 to produce solids with the ice to rock ratio of the icy Galilean satellites. The CPD snowline is not erased by radial grain drift, which is consistent with the compositional gradient of the Galilean satellites being primordial.

Influence of Degree of Severe Plastic Deformation on Thermal Stability of an HfNbTiZr Multi-Principal Element Alloy Processed by High-Pressure Torsion.

Severe plastic deformation (SPD) is an effective route for the nanocrystallization of multi-principal element alloys (MPEAs). The stability of the refined microstructure is important, considering the high temperature applications of these materials. In the present study, the effect of SPD on the stability of a body-centered cubic (bcc) HfNbTiZr MPEA was investigated. SPD was performed using a high-pressure torsion (HPT) technique by varying the number of turns between ½ and 10. The evolution of phase composition and microstructure was studied near the disk centers and edges where the imposed strain values were the lowest and highest, respectively. Thus, the shear strain caused by HPT varies between 3 (½ turn, near the center) and 340 (10 turns, near the edge). It was found that during annealing up to 1000 K, the bcc HfNbTiZr alloy decomposed into two bcc phases with different lattice constants at 740 K. In addition, at high strains a hexagonal close packed (hcp) phase was formed above 890 K. An inhomogeneous elemental distribution was developed at temperatures higher than 890 K due to the phase decomposition. The scale of the chemical heterogeneities decreased from about 10 µm to 30 nm where the shear strain increased from 3 to 340, which is similar to the magnitude of grain refinement. Anneal-induced hardening was observed in the MPEA after HPT for both low and high strains at 740 K, i.e., the hardness of the HPT-processed samples increased due to heat treatment. At low strain, the hardness remained practically unchanged between 740 and 1000 K, while for the alloy receiving high strains there was a softening in this temperature range.

Magnetic Drag and 3D Effects in Theoretical High-resolution Emission Spectra of Ultrahot Jupiters: the Case of WASP-76b

Ultrahot Jupiters are ideal candidates to explore with high-resolution emission spectra. Detailed theoretical studies are necessary to investigate the range of spectra that we can expect to see from these objects throughout their orbit, because of the extreme temperature and chemical longitudinal gradients that exist across their dayside and nightside regions. Using previously published 3D general circulation models of WASP-76b with different treatments of magnetic drag, we postprocess the 3D atmospheres to generate high-resolution emission spectra for two wavelength ranges, throughout the planet’s orbit. We find that the high-resolution emission spectra vary strongly as a function of phase, at times showing emission features, absorption features, or both, which are a direct result of the 3D structure of the planet. At phases exhibiting both emission and absorption features, the Doppler shift differs in direction between the two spectral features, making them differentiable, instead of canceling each other out. Through the use of cross correlation, we find different patterns in net Doppler shift for models with different treatments of drag: the nightside spectra show opposite signs in their Doppler shift, while the dayside phases display a reversal in the trend of net shift with phase. Finally, we caution researchers against using a single spectral template throughout the planet’s orbit; this can bias the corresponding net Doppler shift returned, as it can pick up on a bright region on the edge of the planet disk that is highly redshifted or blueshifted.

The characteristic length scales in direct mode of drop formation from the edges of spinning discs with different surface wetting characteristics

The characteristic length-scales responsible for primary and secondary drop size in direct droplet mode are probed using discs of different surface wettability through exposure controlled high resolution static imaging. The primary drop formation from the edge of a hydrophobic disc is found to be mechanistically different from its hydrophilic counterparts. The disc wetting factor (w) influences primary drop size only at low Weber number (We). A single mean primary/secondary drop size-We relationship represents discs of different surface characteristics. It points to insignificance of surface wettability. For hydrophilic discs the mean primary drop size and the mean incipient bulge size vary as We-0.47 and We-0.5 respectively, which hints at incipient bulge size dependence of primary drop size. The two capillary wave-based length scales tested as characteristic length scales for secondary drops show high size variability, which is a distinctive feature of secondary drops..

The dynamics of magnetized viscous-resistive ADAFs under a self-similar evolution

In this paper, we explore the self-similarity time evolution of a hot accretion flow around a compact object in the presence of a toroidal magnetic field. We focus on a simplified model which is axisymmetric, rotating, unsteady viscous-resistive under an advection-dominated stage. In this work, we suppose that both the kinematic viscosity and the magnetic diffusivity to be a result of turbulence in the accretion flow. To describe such a flow, we apply magneto-hydrodynamics equations in spherical coordinates, [Formula: see text] and adopt unsteady self-similar solutions. By neglecting the latitudinal dependence of the flow, we obtain a set of one-dimensional differential equations governing the accretion system. In this research, we encounter two parameters related to the magnetic field; one of them is, [Formula: see text], defined as the ratio of the magnetic pressure to the gas pressure and the other one, [Formula: see text] applied in the magnetic diffusivity definition. Our results show that [Formula: see text] is a function of position, and increases towards outer layers. On the other hand, we examine different strength of magnetic field by choosing different value of [Formula: see text] which is the value of [Formula: see text] at the inner edge of disc. We see that both [Formula: see text] and [Formula: see text] have positive effect on growing the radial infall velocity but density and gas pressure decrease by larger values of these parameters. Moreover, the rotational velocity and temperature of accreting material reduce considerably under the influence of a stronger magnetic field. We also focus on the behavior of the mass accretion rate appearing as a descending function of position. Finally, our solutions confirm that the radial trend of the physical quantities in a dynamical accretion flow is different from the ones in a steady flow. However, the effect of various parameters on the physical quantities in our model is qualitatively consistent with similar steady models.

Study on the process of intervertebral disc disease by the theory of continuum damage mechanics

BackgroundRecently, more and more people suffer from low back pain triggered by lumbar degenerative disc disease. The mechanical factor is one of the most significant causes of disc degeneration. This study aims to explore the biomechanical responses of the intervertebral disc, and investigate the process of disc injury by the theory of continuum damage mechanics. MethodsA finite element model of the L4–L5 lumbar spine was developed and validated. The model not only considered changes in permeability coefficient with strain, but also included physiological factors such as osmotic pressure. Three loading conditions were simulated: (A) static loads, (B) vibration loads, (C) injury process. FindingsThe simulation results revealed that the facet joints shared massive stresses of the intervertebral discs, and prevented excessive lumbar spine movement. However, their asymmetrical position may have led to degeneration. The von Mises stress and pore pressure of annulus fibrosus showed significantly different trends under static loads and vibration loads. The von Mises stress of nucleus pulposus was not sensitive to vibration loads, but its pore pressure was conspicuously influenced by vibration loads. The injury first appeared at the posterior centre, and then, it gradually expanded along the edge of the intervertebral disc. With an increase in the loading steps, the damage rate of the intervertebral disc increased logarithmically. InterpretationThe variation in the biomechanical performance of the intervertebral disc could be attributed to the periodic movement of internal fluids. This study might be helpful for understanding the mechanism of intervertebral disc degeneration.

Optic disc coloboma associated with macular retinoschisis: A case report

BACKGROUNDTo report an unusual case of bilateral optic disc coloboma associated with macular retinoschisis in the left eye.CASE SUMMARYA 37-year-old woman presented with complaints of blurred and distorted vision in her left eye for more than 1 year. Fundus examination demonstrated choroidal atrophy around the optic disc in both eyes, with a cup-to-disc ratio of 0.9. Serous retinal detachment in the macular area of the left eye. Left eye macular blood flow imaging optical coherence tomography (Angio-OCT) showed macular retinal serous cleavage. En-face OCT showed that the canal gully-like structure formed by the defect of the optic disc nerve fiber layer between the optic disc and macula, serous detachment area was connected with the enlarged optic disc coloboma through the canal gully-like structure, and the fluid leaked from the enlarged and thinned optic disc coloboma into the retinal layer of the macular area. Patients with optic disc abnormalities and macular degeneration must be monitored appropriately. During the follow-up period, the use of optic disc stereography and 3D-OCT, en-face, and Angio-OCT imaging can clarify the correlation between macular retinoschisis and optic disc coloboma.CONCLUSIONMacular retinoschisis may be owing to the combined force of disc edge loss, enlarged optic disc coloboma, the canal gully-like structure formed by the defect of the nerve fiber layer around the optic disc, and the traction of the posterior vitreous cortex.

Amperometric Detection of Ethanol Vapors by Screen Printed Electrodes Modified by Paper Crowns Soaked with Room Temperature Ionic Liquids

AbstractA convenient assembly recently proposed for screen printed gold electrodes (SPEs) suitable for measurements in gaseous samples is here tested for the analysis of the ethanol content in alcoholic drinks. This assembly involves the use of a circular crown of filter paper, soaked in the room temperature ionic liquid (RTIL) 1‐butyl‐3‐methylimidazolium hydrogen sulfate, which is simply placed upon a disposable screen printed cell, so as to contact the outer edge of the gold disc working electrode, as well as peripheral counter and reference electrodes. The electrical contact between the paper crown soaked in RTIL and the SPE electrode is assured by a gasket and all components are installed in a polylactic acid holder. This assembly provides a portable and disposable electrochemical platform, assembled by the easy immobilization onto a porous and inexpensive supporting material such as paper of a RTIL characterized by profitable electrical conductivity and negligible vapor pressure. The electroanalytical performance of this device was assayed for the flow injection analysis of the ethanol concentration in some real samples of wine and beer and the results obtained are compared with the alcoholic degree reported in the relevant bottle‐labels, thus highlighting a substantially satisfactory agreement. Repeatable sharp peaks (RSD=6–8 %) were detected for ethanol over a wide linear range (1–20 % v/v in water) and a detection and quantitation limit of 0.55 % v/v and 1.60 % v/v were inferred for a signal‐to‐noise ratio of 3 and 10, respectively.

High thermal stability of nanocrystalline FeNi2CoMo0.2V0.5 high-entropy alloy by twin boundary and sluggish diffusion

A nanocrystalline (NC) face-centered cubic FeNi2CoMo0.2V0.5 high-entropy alloy was produced by high pressure torsion (HPT). The evolutions of microhardness and microstructure of the NC alloy during subsequent isochronal annealing were investigated systematically by electron back-scattering diffraction (EBSD) and high-resolution transmission electron microscopy (HRTEM). It was found that nano-grains and deformation nano-twin lamella were obtained at outer disk edge after HPT process with a hardness plateau of 450 HV. Isochronal annealing below 600 °C induced an evident hardening without precipitation effect, due to the annihilation of mobile dislocations and sustained deformation twin barriers. Evident recrystallization and grain growth of the NC FeNi2CoMo0.2V0.5 high-entropy alloy occurred during isochronal annealing at temperatures higher than 600 °C. The activation energies of recrystallization and grain growth of the NC FeNi2CoMo0.2V0.5 high-entropy alloy were calculated to be 350 kJ/mol and 272 kJ/mol, respectively, corresponding to a slow defects recovery process and a swift GB migration process. The high thermal stability of the NC FeNi2CoMo0.2V0.5 high-entropy was mainly caused by kinetic sluggish diffusion effect and deformation twin boundaries with thermodynamic low boundary energy, which retarded the movements of dislocations and grain boundary.

Analogue of electromagnetically induced transparency in all-dielectric metasurface induced by quasi-bound state in the continuum for switching

We design and numerically investigate an all-dielectric metasurface composed of ring/disk cavity supporting quasi-bound state in the continuum (BIC) by breaking the in-plane symmetry of the cavity through removing a part from the edge of the central disk that invokes a leakage channel in the form of weakly radiating electromagnetically induced transparency. Far-field radiations and near-field distributions explain the evolution from BIC to quasi-BIC and further point out the dominant magnetic quadrupole component in quasi-BIC. Such quasi-BIC can be switched on and off at orthogonal polarizations and modulated by the intrinsic material loss. Further, we compare the effects of quasi-BICs excited by the offset and removing a part from the edge of the central disk on Q-factors and near-field enhancement, which can be tailored and optimized by selecting the appropriate degree and way of asymmetry.

Model parameters of a horizontal seismometer with an optical diffraction vibration sensor

Subject of study. This study investigates the model of a horizontal seismometer composed of a physical pendulum and an optical diffraction sensor for angular vibrations that comprises a laser, an assembly of two relief phase diffraction gratings (DGs), a diaphragm isolating the radiation of the first diffraction order after the diffraction grating assembly, and a photodetector. The physical pendulum comprises a disk mounted on the rotation axis, pullback springs, and an additional weight on the disk edge. The assembly of DGs was positioned on the disk. The signal from the photodetector output was proportional to the small linear displacements of the additional weight owing to the inertial forces under horizontal vibrations of the seismometer base. Model parameters. The diameter and mass of the disk are 250 mm and 2 kg, respectively. The free swing period of the pendulum is 3 s. The mass of the additional weight is 0.1 kg. The laser power is 5 mW. Two relief phase DGs with a groove depth of 0.32 µm and a period of 0.1 mm are positioned on the opposite facets of a glass block of DGs with a thickness of 13 mm. The grooves of the first DG are parallel to the grooves of the second DG. An FD-24k photodiode, a load resistor, an amplifier, and a filter with a bandwidth of 1800 Hz are connected to the output. Test results. The model of the optical diffraction seismometer and SM-3 reference seismometer were mounted on a single platform. Periodic oscillations of the platform with a period of 0.475 s were applied in the first series of experiments. The dependence of the signals from the outputs of seismometers of both types were similar; however, a 90° phase shift of the output signal from the investigated model with respect to the SM-3 output signal was present. This is because the output signal of the sensor in the optical diffraction seismometer is proportional to the angular displacement of the physical pendulum, whereas the signal from the coil of the SM-3 sensor is proportional to the speed of pendulum movement. A slow weak linear force was applied to the platform with seismometers in the second experiment series. In this case, the SM-3 output signal did not exceed the noise level, whereas the output signal of the optical seismometer model was triple the noise level. The sensitivity of the seismometer model significantly exceeds the sensitivity of the SM-3 seismometer under slow perturbations. Practical significance. The output signal from the optical diffraction vibration sensor is proportional to the angular displacement of the pendulum instead of the speed of its movement. Thus, the sensitivity of the seismometer model does not decrease in the range of low frequency vibrations. A seismometer with negative feedback for investigation of weak low-frequency vibrations of the Earth’s surface can be designed based on this scheme.

Probing the shot behaviour in Cygnus X-1 using simultaneous AstroSat-NICER observation

ABSTRACT We analyse the aperiodic flaring features, also known as shots, observed in Cyg X-1 in the 0.1–80 keV energy band using a 6.39 ks simultaneous observation with AstroSat and Neutron star Interior Composition ExploreR (NICER). We detect 49 simultaneous shots in the soft and hard X-ray bands with NICER and AstroSat-LAXPC, respectively. We observe the shot profile for the first time in soft X-rays (0.1–3 keV), which shows a spectral peak at ∼2 keV. Using time-averaged spectroscopy, we measured the truncation of the inner accretion disc at 6.7 ± 0.2 gravitational radii. The shot-phase-resolved spectroscopy allowed us to identify the origin of some of the brightest aperiodic peaks in the soft X-rays. We find that the accretion rate is consistent with a constant during the shots while the inner edge of the accretion disc moves inwards/outwards as these shots rise/decay. We discuss the possible mechanisms causing the swing in the inner radius.