Opaque Disk Research Articles

Point Spread Function And Spatial Resolution Analysis Of Multi-Focus Plenoptic Cameras

With the recent development of plenoptic cameras, light field imaging has become a reliable solution for 3D metrology. Plenoptic cameras allow recovering the 3D information of a scene with a single acquisition and only one camera. These advantages make light field imaging particularly interesting for the metrology of two-phase flows. The measurement depth of a back-light imaging setup can be determined by the calibration of the Point Spread function (PSF) of the optical system. This study provides a method adapted to multi-focus plenoptic cameras to measure the PSF width from reconstructed images. We used a calibration target composed of multiple calibrated opaque disks and a diffuse backlight illumination set-up. The PSF width is estimated by measuring the grayscale gradient at the interface of the images of the disks. Coupled with the depth information provided by the plenoptic camera, we obtained the evolution of the PSF at different depth planes. The information on the PSF enables us to obtain the focus criterion, which sets the limits of the measurement volume. The spatial resolution of the reconstructed images is obtained from the PSF. The results obtained for the resolution as a function of virtual depth are consistent with results from previous studies.

Effects of Hollow–Gaussian beams on Fresnel diffraction by an opaque disk

Effects of Hollow–Gaussian beams on Fresnel diffraction by an opaque disk

The 2020 Eclipse of R Aquarii in the Near-infrared: Mid-eclipse Observations of Disk Distress

The Mira in the bright, dusty, symbiotic binary R Aquarii undergoes eclipses of multiyear duration every ∼44 yr by a large, opaque accretion disk. The 2020 eclipse was confirmed by I-band photometry. High-resolution M- and K-band spectra were observed near the midpoint of the eclipse, in 2020 August and September. The 4.5–5.5 μm spectrum during eclipse is a complex blend of disk and Mira features. Continuum emission from the disk region contributes to both the 2.3 μm and 4.6 μm region. The lowest energy vibration-rotation CO lines contain multiple absorption features from ∼780 K gas flowing across the disk away from the Mira. CO fundamental and overtone emission lines are also present. The eccentricity of the orbit results in significant orbital variation in the size of the Roche lobes. At periastron the Roche radius of the secondary is ∼4.0 au, smaller than both the 5 au geometric radius for the disk and estimates for the disk size from models. Fundamental band CO 2–1 emission originates from a thin, eccentric ring with inner radius ∼4.75 au and outer radius ∼6.9 au. The CO emission is identified with regions where the disk has been disrupted near the time of periastron. CO 3–2 fundamental band lines and low-excitation lines in the CO 2–0 and 3–1 overtone bands originate in a Mira-facing spot, 6.3 au from the accretion disk center, near the inner Lagrange point.

The on-axis intensity behavior of the diffracted Laguerre-Gaussian beam, LGp , by an opaque disk

In this work, we present a detailed study of the on-axis intensitydistribution of the Laguerre-Gaussian beam with no azimuthal index,diffracted by an opaque disk, by means of numerical simulation ofFresnel-Kirchhoff diffraction integral. We investigate the effect of theopaque disk size, the beam order, the beam waist, and the focal length.The results show that different focal phenomena may occur includingthe focal shift, focal split, and focal switch.
 

K2 discovery of a circumsecondary disk transiting EPIC 220208795

Context. Observations of the star EPIC 220208795 (2MASS J01105556+0018507) reveal a single, deep and asymmetric eclipse, which we hypothesise is due to an eclipsing companion surrounded by a tilted and inclined opaque disk, similar to those seen around V928 Tau and EPIC 204376071. Aims. We aim to derive physical parameters of the disk and orbital parameters for the companion around the primary star. Methods. The modelling is carried out using a modified version of the python package pyPplusS, and optimisation is done using emcee. The period analysis makes use of photometry from ground-based surveys, where we performed a period folding search for other possible eclipses by the disk. Parameters obtained by the best model fits are used to obtain the parameter space of the orbital parameters, while the most likely period obtained is used to constrain these parameters. Results. The best model has an opaque disk with a radius of 1.14 ± 0.03 R⊙, an impact parameter of 0.61 ± 0.02 R⊙, an inclination of 77.01° ± 0.03°, a tilt of 36.81° ± 0.05°, and a transverse velocity of 77.45 ± 0.05 km s−1. The two most likely periods are ~290 days and ~236 days, corresponding to an eccentricity of ~0.7, allowing us to make predictions for the epochs of the next eclipses. All models with tilted and inclined disks result in a minimum derived eccentricity of 0.3, which in combination with the two other known small transiting disk candidates V928 Tau and EPIC 204376071, suggest that there may be a common origin for their eccentric orbits.

Poisson-Arago spot for gravitational waves

For the observer at infinity, a Schwarzschild black hole serves as an attractive opaque disk with a radius of $$3\,\sqrt 3 M$$ that will produce the diffraction pattern of gravitational waves (GWs). In this study, we demonstrate that a bright spot, which is a diffraction effect analogous to the Poisson-Arago spot in optics, will appear when an ingoing (quasi-)plane GW is diffracted by a Schwarzschild black hole. Here, we propose the diffraction effect of the GWs described by the exact diffraction solution of the GWs using the Heun function. For the first time, the Fresnel half-wave zone method is proposed to calculate the angular part of the GW scattering stripes for the observer at infinity. The prospect of observing the diffraction bright spot is discussed with an eikonal approximation. For normal incidence (quasi)-plane waves with 100 Hz (0.1 Hz) frequency diffracted by the central black hole of the Milky Way, the time delay between the Earth bathed in a bright spot and the minimum of the first dark stripe is 3.86 (3860) d. We will witness the second bright fringe (40% amplitude of the central bright spot) after 6.2 (6200) d. This new diffraction pattern involving the early phase of inspirals and pulsars as continuous gravitational wave sources is a potential scientific target for future space-and ground-based gravitational wave detectors, respectively.

Retrospective Study of the Round Radiopaque Foreign Bodies in the Oesophagus

Introduction Ingested foreign bodies (FBs) of the digestive tract can be divided into radiolucent and radiopaque, based on their appearance in Roentgenogram. Coins and button-batteries (BBs) constitute majority of the radiopaque FBs that are round in shape. Materials and Methods Medical records of children admitted with foreign bodies in the GI tract during the last 5 years have been reviewed. We have taken into our study, round radio-opaque FBs and analyzed the results. Results Out of 120 radiopaque FBs, in 112 cases they are lodged in cricopharyngeal sphincter (CPS), which were removed. Of these, 103 were coins and 9 were BBs. Five coins, which had crossed the CPS, ultimately passed out naturally with faeces. Three BBs, impacted in the oesophagus, distal to the CPS, were removed via esophagoscopy, on emergency basis. One child with impacted BB developed mediastinitis and died. Conclusion A round opaque disc shaped FB which is impacted or seen below CPS should not be treated as coin every time. High index of suspicion is needed to rule out BB ingestion as it is associated with high morbidity and mortality. Aim of this study is to stress on the need for educating primary care physicians and rural medical practitioners to avoid wait and watch policy, thus reducing misdiagnosis of coins for BBs.

Modeling the Variable Polarization of ϵ Aurigae In and Out of Eclipse

Abstract The eclipsing binary ϵ Aur is unique in being a very-long-period binary involving an evolved, variable F star and a suspected B main-sequence star enshrouded in an opaque circumstellar disk. The geometrical arrangement is that the disk is viewed almost perfectly edge on, with the alignment leading to a partial eclipse of the F star. Despite a global observing campaign for the 2009–11 eclipse, there remain outstanding questions about the nature of the binary, its components, the disk, and the evolutionary state of the system. We analyze optical-band polarimetry in conjunction with broadband color variations to interpret brightness variations across the surface of the F star. We model this both during and after the 1982–84 eclipse for which an extensive and dense data set exists. We develop a model in terms of surface temperature variations characterized by a small global variation overlaid with a temperature variation described with low-order spherical harmonics. While not providing a detailed fit to the data set, our modeling captures the overall characterization of the color and polarimetric variability. In particular, we are able to recover the gross behavior of the polarimetric excursion in the Q–U plane as observed during eclipse of the F star when compared to posteclipse behavior.

Assessment about Luneberg integrals and application to digital in-line holography

In this publication, the Luneberg integrals are revisited and the conditions of the using of such integrals have been recalled. Additivity law of Luneberg’s integrals and the link with the Frenel kernel for the propagation are discussed. By means of the definition of the Luneberg’s integrals, the propagation of a vectorial electromagnetic field (Hertz potentials) is developed and a new approach of the computation have been proposed based on Zernike polynomials. With this new approach simulations of holograms is illustrated in the case of the digital in-line holography with an opaque disk.

Masking ability of bleach-shade resin composites using the multilayering technique.

Evaluate the masking ability of bleach-shade resin composites applied by multilayering techniques over colored substrates. Disc-shaped specimens were fabricated from bleach-shade resin composites using different multilayering techniques. Substrates were produced in opaque ceramic discs simulating colored substrates (A2, A3, A3.5, C2, C3, C4) and a bleached tooth (0M1). Color coordinates were obtained using a reflectance spectrophotometer. Color difference was calculated by CIEDE2000 using coordinates of 0M1 ceramic as standard reference. Data were analyzed by one-way ANOVA and Tukey's post-hoc test (p ≤ 0.05). Masking ability interpretation was based on perceptibility and acceptability thresholds. All combinations presented ΔE00 above the acceptable threshold (ΔE00 >1.8), ranging from 2.49 to 7.42, regardless of the restorative system, multilayering strategy or substrate color. Multilayering combinations placed over A2, A3 and A3.5 were moderately (1.8<ΔE00 ≤3.6) and clearly unacceptable (3.6<ΔE00 ≤5.4), combinations associated with C2, C3 and C4 were clearly unacceptable and, extremely unacceptable (ΔE00 >5.4). Lower ΔE00 was observed for combinations with 0.5 mm extra white enamel layer (2.49), or 1.0 mm white dentin layer (2.69), over A2 and A3.5 substrates. Lightness difference showed the greatest contribution to ΔE00 . Bleach-shade resin composite systems applied by the multilayering technique were not able to ensure effective masking ability. Bleach-shade resin composites applied with different combinations of the multilayering technique were not effective in masking colored substrates. Alternative strategies, techniques and dental materials should be explored to obtain acceptable masking.

Do Laguerre–Gaussian beams recover their spatial properties after all obstacles?

It has been known for some time that Bessel–Gaussian beams and their associated families self-heal after encountering obstacles. Recently, it has been shown theoretically and experimentally that radial mode Laguerre–Gaussian (LG) beams would likewise self-heal. In this work, we show that the self-healing occurs after opaque disks but not after circular apertures. We put forward arguments to explain this and perform key experiments, assessing the impact of obstructions on the usual intensity reconstruction, as well as the focal shift effect and the beam propagation factor, $$M^2$$ . In addition, these results are supported by a physical interpretation based on the Abbe experiment of spatial frequency filtering, highlighting that the self-healing process requires a high-spatial frequency component to the field, i.e., LG beams self-heal when modulated by a low spatial frequency filter (opaque disk) but not when modulated by a high-spatial frequency filter (circular aperture). We believe that this work will contribute significantly to the field of laser beam propagation through obstacles.

Reproducing the Fresnel-Arago experiment to illustrate physical optics

Is there a bright spot in the shadow of an opaque disk? Nearly 200 years ago, Augustin Fresnel and François Arago’s remarkable answer to this question validated the wave theory of light and inaugurated the modern theories of diffraction. Today, their renowned experiment can be easily reproduced using lasers and cameras. Far beyond its historical interest, the experiment is a versatile platform to illustrate the main concepts of optical physics, including diffraction, interference, speckle, and Fourier optics.

Formation of magnetized spatial structures in the Beta Lyrae system. I. Observation as a research background of this phenomenon

The discovery of the donor magnetic field has repeatedly posed the task of a thorough study of the phenomenon, which is based on the concept of the influence of the magnetic field on the processes of the formation of gaseous structures and mass transfer in the Beta Lyrae system. This article provides an overview, analysis, and synthesis of the results of a variety of long-term observations as a necessary basis for further clarification of issues aimed primarily at the study of magnetized gaseous structures. As a part of such a study, it was found that the structure of the gaseous flows between the donor and the gainer varies in some way depending on the phases of the orbital period; and, accordingly, that the donor magnetic field influences the formation of these moving magnetized structures. The analysis of the masses of both components for use in further scientific works suggests that the following values are optimal: 2.9 M_sun for the donor and 13 M_sun for the gainer. The study of satellite lines as a certain phenomenon leads to the fact that the accretion disk surrounding the gainer consists of two parts: the external satellite disk and the internal massive opaque disk. From the analysis of all observations and studies of the magnetic field, observations on the 6-m telescope can be considered the most reliable. They have formed the spatial configuration of the donor magnetic field, which is important for studying and understanding the features of the mass transfer in this interacting system. Further evidence regarding the picture of the magnetized accretion structures as the special phenomenon will be presented in the following articles.

Experimental analysis of submicrometer optical intensity distributions after an opaque disk.

Generation of subwavelength beam sizes is a fascinating challenge with several implications. The observation of a 120 nm laser spot in the visible part of the spectrum is reported here. It has a size variation of less than 10% in a distance of $ 50\;\unicode{x00B5}{\rm m} $50µm along the axis of propagation. This so-called Arago spot results from the diffraction of the light from a laser diode by the edges of an absorbing disk. Applications are discussed and hollow beams carrying orbital angular momentum with a 400 nm diameter dark spot in the center are evidenced. This paves the way toward atom lithography via atom guiding or new spectroscopy on forbidden transitions.

Inorganic Porous Bulk Discs as a Matrix for Thin-Layer Chromatography and Translucent Hard Composite Materials.

Magnesium-stabilized amorphous calcium carbonate (Mg-ACC), amorphous magnesium calcium silicate hydrate (MCSH), and hydroxyapatite (HAp) are prepared by a precipitation method. By cold-pressing these particles, it is possible to produce porous bulk discs with a narrow pore size distribution. These porous inorganic discs (Mg-ACC, MCSH, and HAp) are investigated as stationary phases to study the chromatographic behavior and adsorption ability of rhodamine B, methylene blue, and ribonuclease. The adsorption affinities of different biomolecules can be easily observed and evaluated through this method. Furthermore, by infiltrating fabricated opaque porous discs with benzyl ether, which has a similar refractive index as the used inorganic particles (Mg-ACC, MCSH, and HAp), their optical properties significantly change and the discs become translucent. Moreover, by infiltrating the MCSH discs with a light-curing polymer, translucent composites with good surface hardness are fabricated. By doping particles with ions such as Ni2+, Co2+, Fe3+, and Eu3+, the color and UV-visible spectrum of the bulk discs can be adjusted. Typically, by using iron-doped MCSH particles as the inorganic matrix, nanocomposites, which show a steep UV-absorption edge at 400 nm, are fabricated. Our work provides a simple and economical method to evaluate the affinity of biomolecules to inorganic materials and a novel way to fabricate translucent hard composite materials. The fabricated nanocomposite discs show a great UV shielding effect and superior surface hardness compared to polymethyl methacrylate and commercial sunglasses, suggesting their potential as new sunglass materials.

Strong Light Intensifications Yielded by Arbitrary Defects: Fresnel Diffraction Theory Applied to a Set of Opaque Disks

Two centuries ago, Fresnel, Poisson, and Arago showed how the wave nature of light induces a bright spot behind an opaque disk. We develop an analytical model based on the Fresnel diffraction theory to show how small perturbations such as digs or scratches can yield intense light enhancements on the downstream axis. The impact of defects with complex morphology on light diffraction is shown to be accurately modeled by the Fresnel theory applied to a set of opaque disks characterized by phase shift and trans-mittance. This model can be used either to define the geometry of the defects that optimizes the light enhancement or to improve the defect specification on the surface of the optical components. We explain why partial information of the defect morphology can suffice to specify a safety distance beyond which light intensifications are not dangerous. The validity of this analytical approach is studied by measuring the intensifications created by three different microdefects.

Development and characterization of biological bovine dentin posts

This study aimed at evaluating the use of biological dentin post (BDP), achieved by milling bovine root, through the analyses of mechanical and optical properties. BDPs were compared to a glass fiber post (GFP) in the following tests (n = 10): a) elastic modulus (E) and flexural resistance (σ) by three point bending test; b) fracture resistance (FR) by compressive load at 45° and failure pattern; c) light transmitting (LT) ability and their influence on the resin cement's degree of conversion (DC%); d) bond strength (BS) by push-out test and failure pattern. Bovine teeth were decoronated and root length was standardized at 14 mm. The canals were prepared and irrigated with 2.5% NaOCl. GFP's surface was conditioned by 1 min immersion in 24% H2O2 solution before silanization. After root embedment, the root canal walls and the BDP's surface were hybridized (H3PO4 37% + self-cured adhesive) for FR and DC% analyses. Posts were fixed into the root canals using a conventional dual resin cement. For BS test, both posts were luted using the conventional and the self-adhesive cementation. A universal testing machine (EMIC DL2000; 1 mm/min) was employed for the mechanical tests (E, σ, FR and BS). For the LT analysis, opaque polyethylene discs were transfixed by the posts, leaving 10 mm of the posts’ apical section for measurements. Posts’ cervical portion was irradiated (800 mW/cm2) and a spectrometer recorded the number of photons transmitted to previously chosen lateral post regions and at the apical tip. The resin cement DC% was evaluated in several sites of the cement film. After normal distribution were checked (Shapiro-Wilk test), data were submitted to ANOVA (5%) and Scheffe post-hoc test (5%). Results showed that: a) E: BDP > GFP; b) σ: BDP < GFP; c) RF: BDP < GFP; d) LT could not be observed for BDP. For GFPs, the greatest number of photons was observed at the post apical tip. An exponential decay was observed from the cervical to the apical post region; e) resin cement DC% was statistically similar at all points of measurements for both posts; and, f) BS: BDP = GFP, regardless the adhesive protocol used. It was concluded that: a) teeth restored with BDP exhibited lower fracture resistance than those restored with GFP; b) resin cement DC% was not influenced by the light transmitting ability of the post; c) the retention provided by the BDP was similar to the one provided by GFP, independently of the luting protocol.

Momentum exchange theory of photon diffraction

Momentum exchange theory (MET) provides an alternative picture for optical diffraction based on a distribution of photon paths through momentum transfer probabilities determined at the scattering aperture. This is contrasted with classical optical wave theory that uses the Huygens–Fresnel principle and sums the phased contributions of wavelets at the point of detection. Single-slit, multiple-slit (Talbot effect), and straight-edge diffraction provide significant clues to the geometric parameters controlling momentum transfer probabilities and the relation to Fresnel zone numbers. Momentum transfer is primarily dependent on preferred momentum states at the aperture and the specific location and distance for momentum exchange. Diffraction by an opaque disc provides insight to negative (attractive) dispersions. MET should simplify the analysis of a broadened set of aperture configurations and experimental conditions.

Toward a Common Ground for Gravity and Optics

A long enough period of observation of the Sun’s gravitational dragging effects by using a modified Cavendish’s balance output of experimental evidence shows new patterns. Those patterns can be explained assuming that the Sun has a torus with rotation, precession, and nutation. This purpose of this paper is to introduce the frequencies of all those movements. The torus’s rotational period can be used to explain the Sun’s magnetic pole reversal. Utilizing a modified Cavendish’s balance showed an output of dragging forces stronger than the attraction between the gravitational masses. This tool afforded this research a new experimental possibility to a more precise determination of the Universal Gravitational Constant Big G. Moreover, the dragging forces directly affect any volume of mass, which includes the atmosphere. This paper shows a correlation between the Sun’s dragging peaks and density of the air squared. The aforementioned correlation and the inverse cubic relation with the distance to the Sun are common for the dragging and tide forces providing the possibility that tidal forces are also a gravitational dragging consequence. The last 2017 total Solar eclipse created a new temporal reaction on the modified Cavendish’s balance. That temporal pattern looks as the spatial pattern created by an opaque disk. This similarity allows the researcher to calculate that the dragging forces are transmitted by photons with spatial periodicity of value λ = 6.1 km.

A circumbinary debris disk in a polluted white dwarf system

Planetary systems commonly survive the evolution of single stars, as evidenced by terrestrial-like planetesimal debris observed orbiting and polluting the surfaces of white dwarfs. This letter reports the identification of a circumbinary dust disk surrounding a white dwarf with a substellar companion in a 2.27 hr orbit. The system bears the dual hallmarks of atmospheric metal pollution and infrared excess, however the standard (flat and opaque) disk configuration is dynamically precluded by the binary. Instead, the detected reservoir of debris must lie well beyond the Roche limit in an optically thin configuration, where erosion by stellar irradiation is relatively rapid. This finding demonstrates that rocky planetesimal formation is robust around close binaries, even those with low mass ratios.