Light Objects Research Articles

Characterization of human lightness discrimination thresholds for independent spectral variations.

The lightness of an object is an intrinsic property that depends on its surface reflectance spectrum. The visual system estimates an object's lightness from the light reflected off its surface. However, the reflected light also depends on object extrinsic properties of the scene, such as the light source. For stable perception, the visual system needs to discount the variations due to the object extrinsic properties. We characterize this perceptual stability for variation in two spectral properties of the scene: the reflectance spectra of background objects and the intensity of light sources. We measure human observers' thresholds of discriminating computer-generated images of 3D scenes based on the lightness of a spherical target object in the scene. We measured change in discrimination thresholds as we varied the reflectance spectra of the objects and the intensity of the light sources in the scene, both individually and simultaneously. For small amounts of extrinsic variations, the discrimination thresholds remained nearly constant indicating that the thresholds were dominated by observers' intrinsic representation of lightness. As extrinsic variation increased, it started affecting observers' lightness judgment and the thresholds increased. We estimated that the effects of extrinsic variations were comparable to observers' intrinsic variation in the representation of object lightness. Moreover, for simultaneous variation of these spectral properties, the increase in threshold squared compared to the no-variation condition was a linear sum of the corresponding increase in threshold squared for the individual properties, indicating that the variations from these independent sources combine linearly.

Repeated Partial Disruptions in a White Dwarf–Neutron Star or White Dwarf–Black Hole Merger Modulate the Prompt Emission of Long-duration Merger-type GRBs

The progenitors of gamma-ray bursts (GRBs) have long been an unresolved issue. GRB 230307A stands out as an exceptionally bright event, belonging to the long-duration GRBs but also exhibiting a late-emission component reminiscent of a kilonova. Together with the similar events GRBs 060614 and 211211A, they make up a new subgroup of GRBs with intriguing progenitors. If such long-duration merger-type GRBs originated from the coalescence of a white dwarf (WD) with a neutron star (NS) or a black hole (BH), as proposed in the recent literature, then the larger tidal disruption radius of the WD, together with a nonnegligible residual orbital eccentricity, would make repeated partial tidal disruptions inevitable. This may modulate the mass accretion and jet launching process at the NS or BH, resulting in a quasiperiodic modulation (QPM) in the light curve of the GRB, with a period equal to the orbital period. The detection of potential QPMs during the early episode of prompt emission of these three GRBs supports this scenario, and the relatively slow QPM (> 1 s) suggests that the lighter object cannot be an NS. We propose that the progenitor system of GRBs 230307A, 060614, and 211211A consist of a WD of mass 1.3 M ⊙, 0.9 M ⊙, and 1.4 M ⊙, respectively, and an NS (or BH). After several cycles of modulations, the WD is completely destroyed, and the accretion of the remaining debris dominates the extended emission episode.

Self-Similar Growth of Bose Stars.

We analytically solve the problem of Bose star growth in the bath of gravitationally interacting particles. We find that after nucleation of this object, the bath is described by a self-similar solution of the kinetic equation. Together with the conservation laws, this fixes mass evolution of the Bose star. Our theory explains, in particular, the slowdown of the star growth at a certain "core-halo" mass, but also predicts formation of heavier and lighter objects in magistral dark matter models. The developed "adiabatic" approach to self-similarity may be of interest for kinetic theory in general.

Segregation and Collisions in Galactic Nuclei: Rates of Destructive Events Near a Supermassive Black Hole

The centers of galaxies host a supermassive black hole (SMBH) surrounded by a dense stellar cluster. The cluster is expected to develop mass segregation, in which gravitational scatterings among the stars cause heavier objects to sink closer to the central black hole, while lighter objects will tend to be overconcentrated in the outer regions. This work focuses on the implications of mass segregation on the different channels for violent destruction of stars in the cluster: tidal disruptions, gravitational-wave-driven inspirals and high-velocity destructive collisions between stars. All such events occur close to the central black hole, where the heavier objects congregate. The analysis is based on a simplified Monte Carlo simulation, which evolves a two-mass population in a cluster surrounding a Milky Way–like SMBH. The simulation is based on the single-mass scheme used by Sari & Fragione and Balberg & Yassur, which has been extended to allow for the dynamical friction effects typical of unequal-mass populations. The effects of mass segregation on the rates of the different destruction channels are analyzed self-consistently in the overall evolution of the cluster. Also considered are stars which are injected into the cluster after being disrupted from a binary system by the SMBH. Such stars are captured in the inner regions of the cluster, and so their orbital evolution, as well as their destruction rate, are therefore influenced by heavy objects that might be abundant in the vicinity of the SMBH.

Existence of Dark Energy Stars within Lower Mass Gap in the Realm of f(Q)$f(Q)$ Gravity

AbstractThe object of this article is to study a new class of dark energy stars in the background of gravity by using the metric potentials proposed by Krori‐Barua [J. Phys. A, Math. Gen. 8:508 (1975)]. To achieve the goal, a quadratic form of as is taken into account for the static spherically symmetric spacetime,`a' being a coupling parameter of gravity. The maximum allowable masses with corresponding radii have been obtained via plots for and 8. The obtained maximum masses from our analysis are found in the range . For a smaller value of the coupling parameter ‘a’ associated with gravity, more massive stars are found. The radii corresponding to the maximum masses also increase with decreasing ‘a’. In particular, when , the theory can achieve a dark energy star of mass for certain specific combinations of model parameters. This obtained mass is located within a mass in the range of and that can be a lighter object in the GW190814 event detected by LIGO/VIRGO experiments.

Comparative evaluation of operational land imager sensor on board landsat 8 and landsat 9 for land use land cover mapping over a heterogeneous landscape

Since its advent in 1972, the Landsat satellites have witnessed consistent improvements in sensor characteristics, which have significantly improved accuracy. In this study, a comparison of the accuracy of Landsat Operational Land Imager (OLI) and OLI-2 satellites in land use land cover (LULC) mapping has been made. For this, image fusion techniques have been applied to enhance the spatial resolution of both OLI and OLI-2 multispectral images, and then a support vector machine (SVM) classifier has been used for LULC mapping. The results show that LULC classification from OLI-2 has better accuracy than OLI. The validation of classified LULC maps shows that the OLI-2 data is more accurate in distinguishing dense and sparse vegetation as well as darker and lighter objects. The relationship between LULC maps and surface biophysical parameters using Local Moran’s I also shows better performance of the OLI-2 sensor in LULC mapping than the OLI sensor.

Automatic and continuous separation of mixed waste plastics via magneto-Archimedes levitation

High efficiency separation is a significant process of the mechanical recycling to manage the mixed waste plastics. However, most of the extant methods can only deal with binary mixtures. In this paper, a novel automatic and continuous separation method based on magneto-Archimedes levitation is proposed to handle multi-plastics. A theoretical model on how the object is levitated above a single square magnet with the aid of paramagnetic media is established. The model revealed that object with different densities would be levitated at different heights. Lighter object would be levitated rapidly to a certain height and then be pushed away slowly. Thereby, the separated plastics could be collected automatically and the continuous separation of the mixtures can be addressed. The separation of polyurethane (PU), polyamide (PA6), and polytetrafluoroethylene (PTFE) demonstrated that the method can deal with multiple plastics with purities over 96.2%. Combined with additional advantages of low cost and no energy consumed in separation process, the method has the potential to be industrialized into an economically-viable and environmentally-friendly mass production procedure.

Bayesian analysis of multimessenger M-R data with interpolated hybrid EoS

We introduce a family of equations of state (EoS) for hybrid neutron star (NS) matter that is obtained by a two-zone parabolic interpolation between a soft hadronic EoS at low densities and a set of stiff quark matter EoS at high densities within a finite region of chemical potentials mu _H< mu < mu _Q. Fixing the hadronic EoS as the APR one and choosing the color-superconducting, nonlocal NJL model with two free parameters for the quark phase, we perform Bayesian analyses with this two-parameter family of hybrid EoS. Using three different sets of observational constraints that include the mass of PSR J0740+6620, the tidal deformability for GW170817, and the mass-radius relation for PSR J0030+0451 from NICER as obligatory (set 1), while set 2 uses the possible upper limit on the maximum mass from GW170817 as an additional constraint and set 3 instead of the possibility that the lighter object in the asymmetric binary merger GW190814 is a neutron star. We confirm that in any case, the quark matter phase has to be color superconducting with the dimensionless diquark coupling approximately fulfilling the Fierz relation eta _D=0.75 and the most probable solutions exhibiting a proportionality between eta _D and eta _V, the coupling of the repulsive vector interaction that is required for a sufficiently large maximum mass. We used the Bayesian analysis to investigate with the method of fictitious measurements the consequences of anticipating different radii for the massive 2~M_odot PSR J0740+6220 for the most likely equation of state. With the actual outcome of the NICER radius measurement on PSR J0740+6220 we could conclude that for the most likely hybrid star EoS would not support a maximum mass as large as 2.5~M_odot so that the event GW190814 was a binary black hole merger.

Studying the onset of deconfinement with multi‐messenger astronomy of neutron stars

AbstractWith the first multi‐messenger observation of a binary neutron star merger (GW170817), new constraints became available for masses and radii of neutron stars. We introduce a class of hybrid EoS that fulfills all these constraints and predicts a region in the mass‐radius diagram that could be populated only by hybrid neutron stars with quark matter cores. A confirmation of this conjecture would be provided when the NICER radius measurement for the high‐mass pulsar PSR J0740 + 6620 yields a radius significantly less than 11 km. Would this radius measurement yield a result in excess of 12 km, this would allow for both, a purely hadronic and a hybrid nature of this star. In the latter case, the maximum mass could reach 2.6 M⊙ so that the lighter object in the asymmetric binary merger GW190814 could have been a hybrid star. We demonstrate that this high mass can be compatible with an early onset of deconfinement for stars with masses below 1 M⊙ and the occurrence of low‐mass twin stars. In such a case, the remnant of GW170817 could be a long‐lived hypermassive pulsar.

A Deep CFHT Optical Search for a Counterpart to the Possible Neutron Star–Black Hole Merger GW190814

Abstract We present a wide-field optical imaging search for electromagnetic counterparts to the likely neutron star–black hole (NS–BH) merger GW190814/S190814bv. This compact binary merger was detected through gravitational waves by the LIGO/Virgo interferometers, with masses suggestive of an NS–BH merger. We imaged the LIGO/Virgo localization region using the MegaCam instrument on the Canada–France–Hawaii Telescope (CFHT). We describe our hybrid observing strategy of both tiling and galaxy-targeted observations, as well as our image differencing and transient detection pipeline. Our observing campaign produced some of the deepest multiband images of the region between 1.7 and 8.7 days post-merger, reaching a 5σ depth of g &gt; 22.8 (AB mag) at 1.7 days and i &gt; 23.1 and i &gt; 23.9 at 3.7 and 8.7 days, respectively. These observations cover a mean total integrated probability of 67.0% of the localization region. We find no compelling candidate transient counterparts to this merger in our images, which suggests that the lighter object was tidally disrupted inside of the BH’s innermost stable circular orbit, the transient lies outside of the observed sky footprint, or the lighter object is a low-mass BH. We use 5σ source detection upper limits from our images in the NS–BH interpretation of this merger to constrain the mass of the kilonova ejecta to be M ej ≲ 0. 015M ⊙ for a “blue” ( ) kilonova and M ej ≲ 0. 04M ⊙ for a “red” ( ) kilonova. Our observations emphasize the key role of large-aperture telescopes and wide-field imagers such as CFHT MegaCam in enabling deep searches for electromagnetic counterparts to gravitational-wave events.

Misconception Profile of Newton’s Law Concept Using Certainty of Response Index (CRI)

Misconception is an understanding that is believed to be correct but not according to the understanding of the experts. Misconceptions can occur because students build their knowledge gained from daily activities. This study aims to identify misconceptions about Newton's law concept and the causes of the misconceptions. The research type is descriptive quantitative. A total of 30 students of SMA Multazam IBS Semarang were given a true-false objective test and drew a style diagram accompanied by a certainty of response index (CRI). The cause of the misconception was obtained by interviewing 4 students. The results obtained were as many as 20.99% of students experienced misconceptions, 9.99% of students understood the concept, and 69.02% did not understand the concept of Newton's law concept. The most common misconception is that students think that heavier objects will fall faster than lighter objects. The cause of students experiencing misconceptions is the understanding they build themselves; students' carelessness in choosing answers; low reasoning ability; and forget the material that has been delivered.

The Night as We Know It

Sejak penemuan pertama lampu pijar, manusia semakin terbiasa hidup di bawah gemerlap cahaya artifisial yang berlebihan setiap malam. Penggunaan cahaya artifisial yang tidak tepat menyebabkan polusi cahaya yang kini dialami oleh lebih dari 80% populas dunia di kota-kota padat penduduk, termasuk Kota Bandung. Data dari penelitian terbaru menunjukkan bahwa luas polusi cahaya kategori tinggi di Bandung mengalami peningkatan di tahun 2013-2017 sebesar 13,79 km2/tahun. Sebagai imbasnya, estetika alami langit malam di Kota Bandung tak lagi bisa dinikmati lantaran cahaya objek astronomi, termasuk galaksi Bima Sakti, terhalangi oleh kubah skyglow akibat cahaya polutan yang naik ke angkasa. . Sebagai pribadi yang memiliki ketertarikan khusus terhadap dunia astronomi, penulis yang juga merupakan warga asli kota Bandung memiliki keprihatinan tersendiri terhadap ‘hilangnya’ pesona langit malam Bandung akibat polusi cahaya. Keinginan untuk meningkatkan kesadaran terhadap isu ini dituangkan penulis melalui karya instalasi yang mengeksplorasi medium lampu, cat reflektif, dan video.

Simulation of Translational Data Acquisition Scheme of X-Ray Computed Tomography for Application in NDT

The invention of computed tomography some few decades ago, coupled with its applications in the field of non-destructive testing for industrial objects inspection has revolutionized the way inspections were formerly done. Despite the conventional data acquisition scheme which is integrated with a rotational stage in between the source and the detector works perfectly for small and lighter objects, hence, it seems impossible to investigate complicated, bulky objects with interconnected unbalanced composites. Moreover, it will be very expensive to harnessed technologies into the rotational stage which can be incorporated into this conventional technique with an optimum degree of accuracy. Therefore, this paper will consider the translational data acquisition scheme which is proven mathematically as an alternative method to the conventional technique [1]. This translational scheme takes into account the variations and the magnification of both the source x-ray and the detector around the object and then proceeded by scans from different focal distances. Python packages with necessary plugins were used in implementing the reconstructive algorithm generated in simulating and modelling a suitable image of inspected object.

Do objects of different weight fall at the same time? Updating naive beliefs about free-falling objects from fictional and informational books in young children

ABSTRACTThis study examined whether children 4- and 5-years-old (N = 156) can revise a physical science misconception from different types of picture books. A realistic fiction book and informational book with identical images matched in word count and reading difficulty level were compared to a control book about plants. In the pretest and posttest, children were asked to make predictions about pairs of objects that either had the same or different weight. The pretest scores showed that many children began with the misconception that heavier objects fall faster than lighter objects. Posttest scores revealed that children revised this misconception after reading the realistic fiction and informational picture books but not after reading the control book. These findings provide evidence that children as young as age 4 can acquire physical science knowledge from picture books and that both realistic fiction and informational books can be used effectively to expose children to science concepts.

Infants' perception of lightness changes related to cast shadows.

When humans perceive the lightness of an object’s surface in shadows there is an implicit assumption that cast shadows dim the surface. In two experiments, we investigated whether 5- to 8-month-old infants make this assumption about shadows. According to this shadow assumption, the apparent change in lightness produced by shadows on an object’s surface are attributed to blocked light sources. If infants can use the shadow assumption to perceive the object’s lightness in shadows, they will also be able to detect unnatural lightness changes in shadows. We compared the infants’ looking times to the unnatural and the natural lightness changes in the shadow when an object (duck) goes through the cast shadow. In Experiment 1, we examined whether infants could detect the unnatural lightness changes of the object’s surface in shadows. We created computer-graphic movies of unnatural and natural lightness changes to the duck’s surface. Our results showed that 7- to 8-month-olds but not 5- to 6-month-olds significantly preferred the movie with the unnatural changes in lightness, indicating that only the older infants could detect these changes. In Experiment 2, we confirmed that the infants’ preference was based on the detection of unnatural lightness changes according to the shadow assumption. The natural and the unnatural lightness changes of Experiment 1 were presented without cast shadows. Under these conditions, neither younger nor older infants showed a significant preference. Taken together, the experiments showed that 7- to 8-month-old infants could detect the unnaturalness of a surface’s lightness changes produced by shadows. In conclusion, our findings suggest that 7- to 8-month-old infants can perceive an object’s lightness in shadows by using an assumption that cast shadows dim the surface of an object.

Infant Brain Responses to Object Weight: Exploring Goal‐Directed Actions and Self‐Experience

Recent work has suggested the value of electroencephalographic (EEG) measures in the study of infants' processing of human action. Studies in this area have investigated desynchronization of the sensorimotor mu rhythm during action execution and action observation in infancy. Untested but critical to theory is whether the mu rhythm shows a differential response to actions which share similar goals but have different motor requirements or sensory outcomes. By varying the invisible property of object weight, we controlled for the abstract goal (reach, grasp, and lift the object), while allowing other aspects of the action to vary. The mu response during 14-month-old infants' own executed actions showed a differential hemispheric response between acting on heavier and lighter objects. EEG responses also showed sensitivity to "expected object weight" when infants simply observed an experimenter reach for objects that the infants' prior experience indicated were heavier versus lighter. Crucially, this neural reactivity was predictive - during the observation of the other reaching toward the object, before lifting occurred. This suggests that infants' own self-experience with a particular object's weight influences their processing of others' actions on the object, with implications for developmental social-cognitive neuroscience.

Effects of Upper Extremity Movements on Sternal Skin Stress

Purpose: Sternal precautions given to patients following median sternotomy are based on expert opinion. Although specific limits are often stated within different versions of sternal precautions, no evidence exists to support any specific cut-off values. The purpose is to determine whether evidence exists for lifting restrictions and transfer methods given as sternal precautions. Methods: 22 healthy subjects (18 female, 4 male), ages 40-69 (mean 53) were instrumented with a Doppler blood flow probe to measure acceleration of skin overlying the sternum. Participants performed 3 trials each of 4 lifting tasks (arm only, 12-ounce can, 1-liter bottle and gallon jug from countertop to shelf). Sit-to-stand and supine-to-sit were each performed two different ways. Sternal skin stress was recorded while subjects performed transfer techniques taught by therapists to minimize upper extremity use and when using transfers that allow pushing up on the hands. Doppler shift caused by skin acceleration was recorded during each procedure. Results: Sternal skin stress during each lifting task was significantly different from all others (p < 0.001, repeated measures ANOVA, Tukey post-hoc tests). Sternal skin stress during transfers as taught by therapists was significantly less than that recorded during typical patient-selected transfer technique (paired t-tests, p = .007 for sit-to-stand and p = 0.015 for supine-to-sit). Conclusions: Lifting heavier objects causes more sternal skin stress than lighter objects. Transfer techniques taught as sternal precautions cause less sternal skin stress than commonly used transfer techniques. Although sternal precautions may be based on real differences in sternal skin stress within subjects during movements involving the upper extremities, the large variation among subjects in sternal skin stress suggests that no clear cut off for activities can be supported.

Effects of Upper Extremity Movements on Sternal Skin Stress

Purpose: Sternal precautions given to patients following median sternotomy are based on expert opinion. Although specific limits are often stated within different versions of sternal precautions, no evidence exists to support any specific cut-off values. The purpose is to determine whether evidence exists for lifting restrictions and transfer methods given as sternal precautions. Methods: 22 healthy subjects (18 female, 4 male), ages 40-69 (mean 53) were instrumented with a Doppler blood flow probe to measure acceleration of skin overlying the sternum. Participants performed 3 trials each of 4 lifting tasks (arm only, 12-ounce can, 1-liter bottle and gallon jug from countertop to shelf). Sit-to-stand and supine-to-sit were each performed two different ways. Sternal skin stress was recorded while subjects performed transfer techniques taught by therapists to minimize upper extremity use and when using transfers that allow pushing up on the hands. Doppler shift caused by skin acceleration was recorded during each procedure. Results: Sternal skin stress during each lifting task was significantly different from all others (p < 0.001, repeated measures ANOVA, Tukey post-hoc tests). Sternal skin stress during transfers as taught by therapists was significantly less than that recorded during typical patient-selected transfer technique (paired t-tests, p = .007 for sit-to-stand and p = 0.015 for supine-to-sit). Conclusions: Lifting heavier objects causes more sternal skin stress than lighter objects. Transfer techniques taught as sternal precautions cause less sternal skin stress than commonly used transfer techniques. Although sternal precautions may be based on real differences in sternal skin stress within subjects during movements involving the upper extremities, the large variation among subjects in sternal skin stress suggests that no clear cut off for activities can be supported.

Binocular Vision, Training and Lightness Constancy

Lightness constancy refers to the ability to estimate an object's lightness (ie, surface reflectance), regardless of variations in the light being reflected from the object—for example, when the illumination changes or the object moves. Buckley et al (1994) observed that binocular cues improve lightness constancy. Here we explored how training improved lightness constancy under binocular, bi-ocular (identical images to each eye), and monocular viewing. Stimuli consisted of a diffusely illuminated Lambertian grey box, containing a single target: a faceted rectangular block that could be presented at a range of depths within the box. Stimuli were presented stereoscopically (to provide full binocular cues), monocularly, and bi-ocularly. In the experiment, participants were asked to select one of a number of blocks, presented below the box, that was of the same material as the target block. Four groups of participants received differing training regimes. Active training involved moving a block of fixed reflectance within the box along a user-defined path (by pressing keyboard buttons). Passive training was the same as active, except block movements were pre-recorded. One group received both active and passive training. No-training used a static presentation of blocks to indicate depth. We found that stereoscopic presentation produced the best lightness constancy. Training regimes delivered a performance difference for stereoscopic, monocular, and bi-ocular presentations, with passive and active training being equally effective. With some training regimes participants took longer to achieve their best performance.

Monte Carlo study of a 3D Compton imaging device with GEANT4

In this paper we investigate, with a detailed Monte-Carlo simulation based on Geant4, the novel approach [Nucl. Instrum. Methods A588 (2008) 457] to 3D imaging with photon scattering. A monochromatic and well collimated gamma beam is used to illuminate the object to be imaged and the photons Compton scattered are detected by means of a surrounding germanium strip detector. The impact position and the energy of the photons are measured with high precision and the scattering position along the beam axis is calculated. We study as an application of this technique the case of brain imaging but the results can be applied as well to situations where a lighter object, with localized variations of density, is embedded in a denser container. We report here the attainable sensitivity in the detection of density variations as a function of the beam energy, the depth inside the object and size and density of the inclusions. Using a 600 keV gamma beam, for an inclusion with a density increase of 30% with respect to the sorrounding tissue and thickness along the beam of 5 mm, we obtain at midbrain position a resolution of about 2 mm and a contrast of 12%. In addition the simulation indicates that for the same gamma beam energy a complete brain scan would result in an effective dose of about 1 mSv.