Luminosity Variations Research Articles

Impact of Cosmic-Ray Feedback on Accretion and Chemistry in Circumstellar Disks

Abstract We use the gas-grain chemistry code uclchem to explore the impact of cosmic-ray feedback on the chemistry of circumstellar disks. We model the attenuation and energy losses of the cosmic rays as they propagate outward from the star and also consider ionization due to stellar radiation and radionuclides. For accretion rates typical of young stars of M ⊙ yr−1, we show that cosmic rays accelerated by the stellar accretion shock produce an ionization rate at the disk surface ζ ≳ 10−15 s−1, at least an order of magnitude higher than the ionization rate associated with the Galactic cosmic-ray background. The incident cosmic-ray flux enhances the disk ionization at intermediate to high surface densities (Σ > 10 g cm−2), particularly within 10 au of the star. We find that the dominant ions are C+, S+, and Mg+ in the disk surface layers, while the ion dominates at surface densities above 1.0 g cm−2. We predict the radii and column densities at which the magnetorotational instability (MRI) is active in T Tauri disks and show that ionization by cosmic-ray feedback extends the MRI-active region toward the disk midplane. However, the MRI is only active at the midplane of a minimum-mass solar nebula disk if cosmic rays propagate diffusively (ζ ∝ r −1) away from the star. The relationship between accretion, which accelerates cosmic rays, the dense accretion columns, which attenuate cosmic rays, and the MRI, which facilitates accretion, creates a cosmic-ray feedback loop that mediates accretion and may produce variable luminosity.

New insight on accretion shocks onto young stellar objects

Context.Material accreted onto classical T Tauri stars is expected to form a hot quasi-periodic plasma structure that radiates in X-rays. Simulations of this phenomenon only partly match observations. They all rely on a static model for the chromosphere and on the assumption that radiation and matter are decoupled.Aims.We explore the effects of a shock-heated chromosphere and of the coupling between radiation and hydrodynamics on the structure and dynamics of the accretion flow.Methods.We simulated accretion columns that fall onto a stellar chromosphere using the 1D ALE code AstroLabE. This code solves the hydrodynamics equations along with the first two moment equations for radiation transfer, with the help of a dedicated opacity table for the coupling between matter and radiation. We derive the total electron and ion densities from collisional-radiative model.Results.The chromospheric acoustic heating affects the duration of the cycle and the structure of the heated slab. In addition, the coupling between radiation and hydrodynamics leads to a heating of the accretion flow and of the chromosphere: the whole column is pushed up by the inflating chromosphere over several times the steady chromosphere thickness. These last two conclusions are in agreement with the computed monochromatic intensity. Acoustic heating and radiation coupling affect the amplitude and temporal variations of the net X-ray luminosity, which varies between 30 and 94% of the incoming mechanical energy flux, depending on which model is considered.

NuSTAR Discovery of Dead Quasar Engine in Arp 187

Abstract Recent active galactic nucleus (AGN) and quasar surveys have revealed a population showing rapid AGN luminosity variability by a factor of ∼10. Here we present the most drastic AGN luminosity decline by a factor of ≳103 constrained by a NuSTAR X-ray observation of the nearby galaxy Arp 187, which is a promising “dead” quasar whose current activity seems quiet but whose past activity of erg s−1 is still observable at a large scale by its light echo. The obtained upper bound of the X-ray luminosity is , corresponding to , indicating an inactive central engine. Even if a putative torus model with cm−2 is assumed, the strong upper bound still holds with or . Given the expected size of the narrow-line region, this luminosity decrease by a factor of ≳103 must have occurred within ≲104 yr. This extremely rapid luminosity/accretion shutdown is puzzling, and it requires one burst-like accretion mechanism producing a clear outer boundary for an accretion disk. We raise two possible scenarios realizing such an accretion mechanism: a mass accretion (1) by the tidal disruption of a molecular cloud and/or (2) by the gas depletion as a result of vigorous nuclear star formation after rapid mass inflow to the central engine.

Temporal and angular variations of 3D core-collapse supernova emissions and their physical correlations

Abstract We provide the time series and angular distributions of the neutrino and gravitational wave emissions of 11 state-of-the-art 3D non-rotating core-collapse supernova models and explore correlations between these signatures and the real-time dynamics of the shock and the proto-neutron star (PNS) core. The neutrino emissions are roughly isotropic on average, with instantaneous excursions about the mean inferred luminosity of as much as ±20 per cent. The deviation from isotropy is least for the ‘νμ’-type neutrinos and the lowest mass progenitors. Instantaneous temporal luminosity variations along a given direction for exploding models average ∼2–4 per cent, but can be as high as ∼10 per cent. For non-exploding models, they can achieve ∼25 per cent. The temporal variations in the neutrino emissions correlate with the temporal and angular variations in the mass accretion rate. We witness the lepton-number emission self-sustained asymmetry (LESA) phenomenon in all our models and find that the vector direction of the LESA dipole and that of the inner Ye distribution are highly correlated. For our entire set of 3D models, we find strong connections between the cumulative neutrino energy losses, the radius of the proto-neutron star, and the f-mode frequency of the gravitational wave emissions. When physically normalized, the progenitor-to-progenitor variation in any of these quantities is no more than ∼10 per cent. Moreover, the reduced f-mode frequency is independent of time after bounce to better than ∼10 per cent. Therefore, simultaneous measurement of gravitational waves and neutrinos from a given supernova event can be used synergistically to extract real physical quantities of the supernova core.

Identification and Tracking of Physiological Parameters from Skin using Video Photoplethysmography.

In recent years, there has been a growing interest in video Photoplethysmography (vPPG), a technique able to estimate cardiovascular parameters from video recordings of the skin. Despite the growing interest in vPPG technology, there are still problems in extracting the correct waveform of blood volume pulse, mainly due to real world artifacts, such as changes in light condition and movement artifacts. Another important issue is the correct definition of skin against background. Therefore, we propose an algorithm of skin detection that is able to recognize skin pixels solid to variations of luminosity. We recorded the signals of interest during an experimental protocol designed to provide thermal stimulation and observe the resulting Autonomic Nervous System changes. Experimental data were gathered from 10 young healthy subjects (age: 21±2 years). Video recordings are processed using a band-pass filter and then an automatic algorithm of peak detection is applied to detect the pulse wave peaks, then used to estimate heart rate variability (HRV). The efficiency and stability of the algorithm are compared against finger-PPG waveforms. Preliminary results show an overall statistical agreement between time and frequency domain indexes. However, further efforts are required to improve the estimation of frequency components, particularly during rest.

Preliminary results of simultaneous recording of auroral and geomagnetic pulsations at the ISTP SB RAS station Istok

The paper presents the results on first synchronous observations of variations in auroral luminosity and geomagnetic field, made with high temporal resolution at the ISTP SB RAS high-latitude station Istok (70° N, 88° E) in September–December 2018. Auroras were recorded with all-sky camera, pulsations in the auroras were recorded by a photometer in four spectral ranges with silicon photomultipliers. Continuous monitoring of geomagnetic pulsations was performed using a LEMI-30 three-component induction magnetometer.
 Both synchronous bursts of auroras and magnetic field pulsations, as well as disturbances of auroras, not accompanied by disturbances in the geomagnetic field, were observed. We note that the photometer clearly recorded short-period (~20 min) variations in in auroral luminosity. At the same time, some instability of the photometer signal level occurred at sufficiently long time intervals.
 In the photometer data, there are powerful signal bursts, probably of a hardware nature. Nevertheless, the temporary distribution analysis of the registration moments (registration frequency) of signal bursts indicates the possible dependence of the burst registration frequency on the geomagnetic activity level.

Предварительные результаты синхронной регистрации авроральных и геомагнитных пульсаций на станции «Исток» ИСЗФ СО РАН

The paper presents the results on first synchronous observations of variations in auroral luminosity and geomagnetic field, made with high temporal resolution at the ISTP SB RAS high-latitude station Istok (70° N, 88° E) in September–December 2018. Auroras were recorded with all-sky camera, pulsations in the auroras were recorded by a photometer in four spectral ranges with silicon photomultipliers. Continuous monitoring of geomagnetic pulsations was performed using a LEMI-30 three-component induction magnetometer.
 Both synchronous bursts of auroras and magnetic field pulsations, as well as disturbances of auroras, not accompanied by disturbances in the geomagnetic field, were observed. We note that the photometer clearly recorded short-period (~20 min) variations in in auroral luminosity. At the same time, some instability of the photometer signal level occurred at sufficiently long time intervals.
 In the photometer data, there are powerful signal bursts, probably of a hardware nature. Nevertheless, the temporary distribution analysis of the registration moments (registration frequency) of signal bursts indicates the possible dependence of the burst registration frequency on the geomagnetic activity level.

Variations in Luminosity, Temperature and Osmotic Potential Affect the Eragrostis plana Germination

One of the exotic invasive species of greatest impact on the Pampa biome is lovegrass (Eragrostis plana Nees). This species, native of southwest Africa, was accidentally introduced in Brazil in the 1950s and has since become a troublesome weed of natural pasture, due to its high spreading power. In order to assess lovegrass seeds behavior against different potentially stressful factors, we evaluated wide ranges of luminosity, temperature and osmotic potential on E. plana germination. After exposure to treatments, vigor and seed germination were analyzed through the following: germination speed index (GSI), first count and accumulated germination. All evaluated variables influenced E. plana germination, suggesting a relative susceptibility to environmental factors such as light, temperature, and water availability, with respect to in vitro germination. This information can be used as an aid to planning future strategies to control the spread of this invasive grass.

On the origin of the dramatic spectral variability of WPVS 007

We report the discovery of large-amplitude mid-infrared variabilities (MIR; $\sim 0.3$ mag) in the Wide-field Infrared Survey Explorer W1 and W2 bands of the low-luminosity narrow-line Seyfert 1 galaxy WPVS 007, which exhibits prominent and varying broad-absorption lines (BALs) with blueshifted velocity up to $\rm \sim 14000\ km\ s^{-1}$. The observed significant MIR variability, the UV to optical color variabilities in the Swift bands that deviate from the predictions of pure dust attenuation models, and the fact that Swift light curves can be well fitted by the stochastic AGN variability model suggest that its observed flux variabilities in UV-optical-MIR bands should be intrinsic, rather than owing to variable dust extinction. Furthermore, the variations of BAL features (i.e., trough strength and maximum velocity) and continuum luminosity are concordant. Therefore, we propose that the BAL variability observed in WPVS 007 is likely induced by the intrinsic ionizing continuum variation, alternative to the rotating-torus model proposed in a previous work. The BAL gas in WPVS 007 might be in the low-ionization state as traced by its weak N V BAL feature; as the ionizing continuum strengthens, the Ci IV and Si IV column densities also increase, resulting in stronger BALs and the emergence of high-velocity components of the outflow. The outflow launch radius might be as small as $\sim 8 \times 10^{-4}$ pc under the assumption of being radiatively driven, but a large-scale origin (e.g., torus) cannot be fully excluded because of the unknown effects from additional factors, e.g., the magnetic field.

Piercing through Highly Obscured and Compton-thick AGNs in the Chandra Deep Fields. I. X-Ray Spectral and Long-term Variability Analyses

Abstract We present a detailed X-ray spectral analysis of 1152 active galactic nuclei (AGNs) selected in the Chandra Deep Fields (CDFs), in order to identify highly obscured AGNs ( > ). By fitting spectra with physical models, 436 (38%) sources with are confirmed to be highly obscured, including 102 Compton-thick (CT) candidates. We propose a new hardness ratio measure of the obscuration level that can be used to select highly obscured AGN candidates. The completeness and accuracy of applying this method to our AGNs are 88% and 80%, respectively. The observed log N−log S relation favors cosmic X-ray background models that predict moderate (i.e., between optimistic and pessimistic) CT number counts. Nineteen percent (6/31) of our highly obscured AGNs that have optical classifications are labeled as broad-line AGNs, suggesting that, at least for part of the AGN population, the heavy X-ray obscuration is largely a line-of-sight effect, i.e., some high column density clouds on various scales (but not necessarily a dust-enshrouded torus) along our sight line may obscure the compact X-ray emitter. After correcting for several observational biases, we obtain the intrinsic distribution and its evolution. The CT/highly obscured fraction is roughly 52% and is consistent with no evident redshift evolution. We also perform long-term (≈17 yr in the observed frame) variability analyses for 31 sources with the largest number of counts available. Among them, 17 sources show flux variabilities: 31% (5/17) are caused by the change of , 53% (9/17) are caused by the intrinsic luminosity variability, 6% (1/17) are driven by both effects, and 2 are not classified owing to large spectral fitting errors.

Phenotypical Variability of Functional Groups of Plants in an Urban Rainforest

The functional characteristics of plants can be used to understand the changes of vegetation under different environmental pressures, since during the process of succession, the species deal with variations of luminosity, an important resource for the regeneration and growth of plants in humid tropical forests. From the perspective that along the succession there is variation of light availability and that leaf characteristics such as specific leaf area, chlorophyll content and leaf dry matter content are more plastic in groups linked to the rapid acquisition of the resource at the beginning of the succession, it was tested the hypothesis that at the beginning of the succession, where there is greater availability of light, leaf characteristics would be more plastic for the acquisitive group. It was initially found that the geographic distances did not influence the values ​​of the variability indices of the groups, which allows to infer that the distance between the areas does not interfere in the variability of the leaf characteristics. To answer the hypothesis that at the beginning of the succession, in which there is greater light availability, the leaf characteristics would be more plastic for the purchasing group than for the conservative ones, a simple linear regression analysis (ARLS) was performed in the indices of variability for the groups (acquisitive and conservative) and abiotic factor (light) in each area of ​​occurrence. However, the hypothesis that at the beginning of the succession, where there is greater light availability, the characteristics of the leaf would be more plastic for the species was rejected for the species acquisitive, since all indices were reduced for the purchasing group. It is important to take into account that the variation of leaf characteristics as a function of the light availability in an urban tropical fragment is different from what occurs in the classic succession commonly reported, pointing out that possible disturbances caused by the surroundings are the main agents of the functional structure of the community.

Mass loss via solar wind and coronal mass ejections during solar cycles 23 and 24

ABSTRACT Similar to the Sun, other stars shed mass and magnetic flux via ubiquitous quasi-steady wind and episodic stellar coronal mass ejections (CMEs). We investigate the mass loss rate via solar wind and CMEs as a function of solar magnetic variability represented in terms of sunspot number and solar X-ray background luminosity. We estimate the contribution of CMEs to the total solar wind mass flux in the ecliptic and beyond, and its variation over different phases of the solar activity cycles. The study exploits the number of sunspots observed, coronagraphic observations of CMEs near the Sun by SOHO/LASCO, in situ observations of the solar wind at 1 AU by WIND, and GOES X-ray flux during solar cycles 23 and 24. We note that the X-ray background luminosity, occurrence rate of CMEs and ICMEs, solar wind mass flux, and associated mass loss rates from the Sun do not decrease as strongly as the sunspot number from the maximum of solar cycle 23 to the next maximum. Our study confirms a true physical increase in CME activity relative to the sunspot number in cycle 24. We show that the CME occurrence rate and associated mass loss rate can be better predicted by X-ray background luminosity than the sunspot number. The solar wind mass loss rate which is an order of magnitude more than the CME mass loss rate shows no obvious dependency on cyclic variation in sunspot number and solar X-ray background luminosity. These results have implications for the study of solar-type stars.

Neutron star cooling via axion emission by nucleon–nucleon axion bremsstrahlung

Neutron stars generally cool off by the emission of $$\gamma $$ -rays and neutrinos. But axions can also be produced inside a neutron star by the process of nucleon–nucleon axion bremsstrahlung. The escape of these axions adds to the cooling process of the neutron star. We explore the nature of cooling of neutron stars including the axion emission and compare our result with the scenario when the neutron star is cooled by only the emission of $$\gamma $$ -rays and neutrinos. In our calculations we consider both the degenerate and non-degenerate limits for such axion energy loss rate and the resulting variation of luminosity with time and variation of surface temperature with time of the neutron star. In short, the thermal evolution of a neutron star is studied with three neutron star masses (1.0, 1.4 and 1.8 solar masses) and by including the effect of axion emission for different axion masses ( $$m_{a}=10^{-5}, 10^{-3}$$ and $$10^{-2}\,\mathrm{eV}$$ ) and compared with the same when the axion emission is not considered. We compared theoretical cooling curve with the observational data of three pulsars PSR B0656 $$+$$ 14, Geminga and PSR B1055-52 and finally gave an upper bound on axion mass limits $$m_{a}\le 10^{-3}\,\mathrm{eV}$$ which implies that the axion decay constant $$f_{a}\ge 0.6\times 10^{10}\,\mathrm{GeV}$$ .

Variability-selected Low-luminosity Active Galactic Nuclei Candidates in the 7 Ms Chandra Deep Field-South

Abstract In deep X-ray surveys, active galactic nuclei (AGNs) with a broad range of luminosities have been identified. However, cosmologically distant low-luminosity AGN (LLAGN, erg s−1) identification still poses a challenge because of significant contamination from host galaxies. Based on the 7 Ms Chandra Deep Field-South (CDF-S) survey, the longest-timescale (∼17 years) deep X-ray survey to date, we utilize an X-ray variability selection technique to search for LLAGNs that remain unidentified among the CDF-S X-ray sources. We find 13 variable sources from 110 unclassified CDF-S X-ray sources. Except for one source that could be an ultraluminous X-ray source, the variability of the remaining 12 sources is most likely due to accreting supermassive black holes. These 12 AGN candidates have low intrinsic X-ray luminosities, with a median value of 7 × 1040 erg s−1. They are generally not heavily obscured, with an average effective power-law photon index of 1.8. The fraction of variable AGNs in the CDF-S is independent of X-ray luminosity and is only restricted by the total number of observed net counts, confirming previous findings that X-ray variability is a near-ubiquitous property of AGNs over a wide range of luminosities. There is an anticorrelation between X-ray luminosity and variability amplitude for high-luminosity AGNs, but as the luminosity drops to ≲1042 erg s−1, the variability amplitude no longer appears dependent on the luminosity. The entire observed luminosity–variability trend can be roughly reproduced by an empirical AGN variability model based on a broken power-law power spectral density function.

Unstained cell imaging: Morphological insights from coupled fixation and darkfield microscopy

Cell staining techniques are well established in cell biology and associated with a broad range of dedicated dyes; however, they are accompanied by non-negligible costs, preparation time and unavoidable alterations of the sample with foreign molecules. In this context, we point out and propose the use of darkfield microscopy (DM) combined with different fixation protocols (to be used anyway) to enhance the different cell structures and districts as a timesaving and inexpensive support to the techniques that need staining or immuno-staining protocols and products. In a first step, we have analysed the effect of different fixation protocols on DM images for various human cellular lines. The presented imaging study shows that cell morphology actually changes with the fixation protocols that enhance, through contrast and luminosity variations, different shapes and patterns and thus structures of the cells. The different chemical action of various fixations, in fact, modifies the local scattering coefficient, thus affecting in a different way the morphology shown by DM images. As a second step we have compared the observed DM morphologies to those of selective fluorescent staining being therefore able to associate them to specific cell districts (e.g. nucleus, membrane or cytoskeleton).The obtained results indicate that this common microscopy technique can give images with particular cellular structures or districts enhanced more than others depending on the choice of fixation protocol. Therefore Darkfield Microscopy can be considered as a simpler, cheaper and faster method to provide morphological indications, respect to staining techniques, even at low and medium magnifications

The obscured active nucleus of NGC 7172 as seen BY NuSTAR

We analyse the properties of the X-ray emission from Seyfert 2 NGC 7172 which are based on the 32 ks observational data from NuSTAR in 2014. This source showed a constant Compton-thin obscuration $N_{H}\approx 8\cdot 10^{22} cm^{-2}$, which is similar to that observed by XMM-Newton, Suzaku, ASCA and BeppoSAX over past 30 years. We revealed the presence of a moderate reflection component with ~0.44 and a narrow FeK{\alpha} line with $67^{+13}_{-14}$ eV. The applied numerical models of torus confirmed the Compton-thin type of the Seyfert nucleus and allowed us to obtain an estimate of the torus opening angle ${\Theta}_{t}\sim59\deg$ and inclination ${\Theta}_{i}\sim61\deg$. Using the observation data of previous observation, we demonstrate also the long-term variability of intrinsic luminosity $L_{intr}$(2-10 keV) almost by order and EW $FeK_{\alpha}$ by factor $\sim4$ on a timescale of $\sim12$ years, that coincides to the distance of $d\sim$3.7 pc between central source and reprocessing medium. Such changes of intrinsic luminosity without changes in $N_{H}$ value indicate the variability of a central source. In the same time the spectral analysis results with the presence of the lag between variability of intrinsic luminosity $L_{intr}$(2-10 keV) and EW $FeK_{\alpha}$, as well as a behaviour of intensity $I_{FeK_{\alpha}}$ of the line are in agreement with the scenario, where observed $FeK_{\alpha}$ line is generated in a distant gas-dust torus.

Obscured Active Nucleus of NGC 7172 as Seen by NuSTAR

We analyse the properties of the X-ray emission from Seyfert 2 NGC 7172 which are based on the 32 ks observational data from NuSTAR in 2014. This source showed a constant Compton-thin obscuration $N_{H}\approx 8\cdot 10^{22} cm^{-2}$, which is similar to that observed by XMM-Newton, Suzaku, ASCA and BeppoSAX over past 30 years. We revealed the presence of a moderate reflection component with <R>~0.44 and a narrow FeK{\alpha} line with $67^{+13}_{-14}$ eV. The applied numerical models of torus confirmed the Compton-thin type of the Seyfert nucleus and allowed us to obtain an estimate of the torus opening angle ${\Theta}_{t}\sim59\deg$ and inclination ${\Theta}_{i}\sim61\deg$. Using the observation data of previous observation, we demonstrate also the long-term variability of intrinsic luminosity $L_{intr}$(2-10 keV) almost by order and EW $FeK_{\alpha}$ by factor $\sim4$ on a timescale of $\sim12$ years, that coincides to the distance of $d\sim$3.7 pc between central source and reprocessing medium. Such changes of intrinsic luminosity without changes in $N_{H}$ value indicate the variability of a central source. In the same time the spectral analysis results with the presence of the lag between variability of intrinsic luminosity $L_{intr}$(2-10 keV) and EW $FeK_{\alpha}$, as well as a behaviour of intensity $I_{FeK_{\alpha}}$ of the line are in agreement with the scenario, where observed $FeK_{\alpha}$ line is generated in a distant gas-dust torus.

Specifics of the focused electron beam transport in the forevacuum range of pressure

We have investigated electron beam transport at an elevated forevacuum pressure of tens of Pascals of helium. The continuous electron beam (6–14 keV, 300 mA) is generated by a forevacuum-pressure plasma-cathode electron source utilizing a hollow-cathode discharge. A beam-plasma discharge is generated in the beam transport zone, which is characterized by increased plasma density in the region of the most intense beam-plasma interaction. We find that the location and distribution of the beam-plasma discharge depend on the electron beam energy and current density. Under certain conditions, we observe that the beam plasma is stratified, with a periodic variation of plasma density and luminosity along the direction of electron beam propagation.

Atmospheres and wind properties of non-spherical AGB stars

Context. The wind-driving mechanism of asymptotic giant branch (AGB) stars is commonly attributed to a two-step process: first, gas in the stellar atmosphere is levitated by shockwaves caused by stellar pulsation, then accelerated outwards by radiative pressure on newly formed dust, inducing a wind. Dynamical modelling of such winds usually assumes a spherically symmetric star. Aims. We explore the potential consequences of complex stellar surface structures, as predicted by three-dimensional (3D) star-in-a-box modelling of M-type AGB stars, on the resulting wind properties with the aim to improve the current wind models. Methods. Two different modelling approaches are used; the CO5BOLD 3D star-in-a-box code to simulate the convective, pulsating interior and lower atmosphere of the star, and the DARWIN one-dimensional (1D) code to describe the dynamical atmosphere where the wind is accelerated. The gas dynamics of the inner atmosphere region at distances of R ∼ 1−2 R⋆, which both modelling approaches simulate, are compared. Dynamical properties and luminosity variations derived from CO5BOLD interior models are used as input for the inner boundary in DARWIN wind models in order to emulate the effects of giant convection cells and pulsation, and explore their influence on the dynamical properties. Results. The CO5BOLD models are inherently anisotropic, with non-uniform shock fronts and varying luminosity amplitudes, in contrast to the spherically symmetrical DARWIN wind models. DARWIN wind models with CO5BOLD-derived inner boundary conditions produced wind velocities and mass-loss rates comparable to the standard DARWIN models, however the winds show large density variations on time-scales of 10–20 yr. Conclusions. The method outlined in this paper derives pulsation properties from the 3D star-in-a-box CO5BOLD models, to be used in the DARWIN models. If the current grid of CO5BOLD models is extended, it will be possible to construct extensive DARWIN grids with inner boundary conditions derived from 3D interior modelling of convection and pulsation, and avoid the free parameters of the current approach.

How Munsell system could help visualize color variation on cement tiles

AbstractCement tiles are particularly susceptible to intense shade variation. We have observed that there are many factors which influence the tiles coloring, from the way the mixture and the paint are prepared and manipulated to the weather conditions on the day of manufacturing and during the 40 days of the drying process, and even the way the tiles are displayed on the shelves. Partial results have shown that even pieces from the same batch, which are painted the same color using the same pigment, will display some color variation. The wonder of such work is that each piece might be unique, once there is no way to ensure the whole lot will have the same value and chroma. By applying the Munsell System to the colors in the company's catalog, this study has aimed to detect the range of possible luminosity and saturation variation, considering such tonality variation as a legit product of handcrafted production.