Observation Angle Research Articles

Confirmation of Sgr A* Using the Event Horizon Telescope Data as Extreme Binary of the Supermassive Black Holes Concluded by Decameter Radio Wave Pulse Observations

We analyzed the time variation of the visibilities in the publicly released event horizon telescope (EHT) data provided by the EHT Collaboration, who carried out observations of Sgr A* on April 6 and 7, 2017. The EHT consists of the 1.3 mm wavelength very long baseline interferometry (VLBI) system associated with globally distributed six stations with eight antennas. The analyses were not intended to make image of Sgr A*; instead, we searched for periodic time variations in the observed individual baseline data of the EHT by applying a method to compare with the model visibility, for 1.3 mm VLBI detection that was constructed to reflect the effects of the supermassive black hole binary (SMBHB) concluded from the study on the observation of the decameter radio wave pulses from Sgr A*. The SMBHB, orbiting with a period of 2200 ± 50 sec and an orbit size of 4.1×107 km, is observable with an observation angle width of 32.6 μas in a plane nearly parallel to the Galactic equatorial plane. After confirming the possible correspondence between the visibilities of EHT data and constructed model via direct comparison in real-time space, we applied the modified Fourier transformation to confirm the coincidence between observation data and model visibilities. The modified Fourier transformation was uniquely restructured in this paper to eliminate the artificially modulated data sampling time interval by utilizing Fourier transformation of the random noises distributed over time synchronized with data sample timing of the EHT data. We identified significant periodic time variations in the radiation within a range below 70 μas with an orbiting period of 2193.3±27.5 sec that is associated with an eclipse cycle period of 1096.5 sec caused by the SMBHB orbiting motion.

Inclusion of Dye in Cyclodextrin for Isotropically Radiative Robust Droplet Laser toward Lens-free Remote Optical Detection

Abstract Micrometer-scale organic liquid droplets are of particular interest due to their excellent lasing performance together with extreme flexibility and responsivity. Here, we report the synthesis of novel lasing microdroplets with suppressed spontaneous emission. A supramolecular complex of a dye and a cyclodextrin works as robust and excellent laser dye in the droplet. Moreover, the laser emission from the single droplet is strong enough for all directions irrespective of the observation angle and detectable without an objective lens.

On-site road properties evaluation for dry and wet asphalt roads using an imaging luminance measurement device

A method was developed to investigate the reflected properties of LED and HPS-lighted wet roads using on-site measurement of luminance images. An ILMD was used to obtain high observation angles by placing it at a close distance to the ROI. The luminance images were analyzed to derive a distribution of reflected luminance as a function of deviation, incidence, and observation angles. Furthermore, an investigation of the reflected characteristics of a dry asphalt road illuminated by LED lighting was conducted, employing on-site measurements of the images of luminance and the distribution of illuminance. The results provide valuable insights for designing lighting systems and mitigating the adverse effects of glare and specular reflection on road safety.

The Talbot effect in oblique observation of a diffraction pattern

Speaking about the oblique Talbot effect, one usually assumes the case when the diffraction grating is illuminated by a plane wave at an angle, while the screen for observing the diffraction pattern is located parallel to the plane of the diffraction grating. At the same time, as the presented consideration shows, if the grating is illuminated at an angle, then in order to observe the Talbot effect, the observation screen must be tilted as well. In the present work, we considered the inclined Talbot effect for a grating with a finite number of slits, when the observation of the diffraction pattern and the illumination of the grating are performed at an angle. The dependence of the Talbot length on the angles of observation and illumination is determined. It is shown that the effect of self-reproduction can be observed only at certain values of these angles. It is proved that the value of the Talbot length does not depend on the parity of the number of lattice slits. At the same time, the number of slits determines the character of the distribution of maximums on the screen. Thus, in the case of a diffraction grating with an even number of slits, a maximum is observed in the center of the screen. In the case of a grating with an odd number of slits, the pattern of maximums is shifted by half the period of the grating compared to the pattern of maximums in the case of gratings with an even number of slits.

Afterglow Polarizations in a Stratified Medium with Effect of the Equal Arrival Time Surface

The environment of a γ-ray burst has an important influence on the evolution of jet dynamics and its afterglow. Here we investigate the afterglow polarizations in a stratified medium with the equal arrival time surface (EATS) effect. Polarizations of multiband afterglows are predicted. The effects of the parameters of the stratified medium on the afterglow polarizations are also investigated. We found the influences of the EATS effect on the afterglow polarizations become important for off-axis detections and polarization degree (PD) bumps move to later times with the EATS effect. Even if the magnetic field configurations, jet structure, and observational angles are fixed, polarization properties of the jet emission could still evolve. Here, we assume a large-scale ordered magnetic field in the reverse-shock region and a two-dimensional random field in the forward-shock region. Then, PD evolution is mainly determined by the evolution of the f 32 parameter (the flux ratio between the reverse-shock region and forward-shock region) at the early stage and by the evolution of the bulk Lorentz factor γ at the late stage. Through the influences on the f 32 or γ, the observational energy band, observational angles, and the parameters of the stratified medium will finally affect the afterglow polarizations.

Investigating the gamma-ray burst from decaying MeV-scale axion-like particles produced in supernova explosions

We investigate the characteristics of the gamma-ray signal following the decay of MeV-scale Axion-Like Particles (ALPs) coupled to photons which are produced in a Supernova (SN) explosion. This analysis is the first to include the production of heavier ALPs through the photon coalescence process, enlarging the mass range of ALPs that could be observed in this way and giving a stronger bound from the observation of SN 1987A. Furthermore, we present a new analytical method for calculating the predicted gamma-ray signal from ALP decays. With this method we can rigorously prove the validity of an approximation that has been used in some of the previous literature, which we show here to be valid only if all gamma rays arrive under extremely small observation angles (i.e. very close to the line of sight to the SN). However, it also shows where the approximation is not valid, and offers an efficient alternative to calculate the ALP-induced gamma-ray flux in a general setting when the observation angles are not guaranteed to be small. We also estimate the sensitivity of the Fermi Large Area Telescope (Fermi-LAT) to this gamma-ray signal from a future nearby SN and show that in the case of a non-observation the current bounds on the ALP-photon coupling gaγ are strengthened by about an order of magnitude. In the case of an observation, we show that it may be possible to reconstruct the product gaγ 2 ma , with ma the mass of the ALP.

Determination of the coherence interval of radar targets using a multipoint signal reflection model

The problem of determining the coherence interval of the target (CIT) is considered – the time interval during which the signal reflected from the target can be considered coherent. In this case, the criterion of signal coherence is the condition of limiting the random phase fluctuation of the reflected signal to a value. The basis of the method of determining the CIT is the use of a multipoint model of a target that performs a rectilinear motion at a constant speed. When describing the resulting signal, the complex envelope method is used. It is shown that for an arbitrary number of reflection points, the resulting signal can be represented as a product of two functions. The first function is deterministic and determines the dependence of the signal phase on the speed of movement of the target center. The second function determines the amplitude and phase fluctuations of the reflected signal and, due to the unknown number and location of the reflection points, as well as the angle of observation of the target, can be considered random. In the case of a two-point target model, an approximate ratio for the CIT is obtained, depending on the relative size of the target, its range and speed of movement. It is shown that for typical target sizes and ranges of the order of several tens of kilometers, the errors in calculating the CIT when using the obtained approximate ratio do not exceed 10% of the true value of the CIT. It is also shown that the frequently used approach of calculating the CIT based on the calculation of the backscattering diagram of the target does not take into account the target range and therefore can lead to large errors in calculating the CIT. At the same time, the calculated values of the CIT, depending on the size of the target and its range, may differ from the true values by an order of magnitude or more. When switching to the multipoint model of the target, differences in comparison with the two-point model in the calculation of the CIT are determined and estimates of the most rational number of reflection points are obtained, the choice of which can be limited to five or six points.

Modification method of the infrared attitude measurement model for projectiles based on odd-power functions

The attitude measurement method based on infrared is a new type of projectile autonomous attitude measurement method, which has attracted more and more researchers. However, the attitude measurement mathematical model currently used for projectiles is the simplified model after fitting. To improve the accuracy of the infrared attitude measurement theoretical model and the subsequent attitude calculation accuracy, a modified model of the infrared attitude measurement for projectiles is put forward based on the odd-power functions. After analyzing the infrared attitude measurement model for projectiles, the infrared radiance between the sky and the earth at different observation angles is obtained by using the MODTRAN simulation software. And the odd-power functions are introduced to modify the infrared attitude measurement model to approach the infrared radiance curve. Finally, the accuracy of the current and the modified infrared attitude measurement models are compared through the semi-physical experiments, which indicates that the modified infrared attitude measurement model has the smaller Sum of Squares due to Error (SSE) and the Root Mean Square Error (RMSE) of 1.0686 and 0.0612 and the bigger R-square of 0.9985. The results of this study provide the theoretical basis for the reduction of the projectile infrared attitude measurement error from the root.

Influence of accretion disk on the optical appearance of the Kazakov-Solodukhin black hole

The optical characteristics of the Kazakov-Solodukhin black hole (BH) surrounded by a thin disk is investigated. By utilizing the ray-tracing method, we derive the direct and secondary images to illustrate the influence of observational inclination angle (${\ensuremath{\theta}}_{0}$) and quantum correction parameter ($a$) on the observable properties. Our calculation involves determining the effective potential, light deflection, and azimuthal angle of the BH as well as the radiation flux of the accretion disk. By assuming three function models, we determine that the exponential function is the most suitable for describing the relationship between the observed flux and the quantum deformation parameter. Our research reveals that the observable characteristics of a BH are affected not only by the shape of the accretion disk but also by its spatiotemporal properties and the observer's inclination angle. We observe that a BH encircled by an optically thick accretion disk yields different results from those of an optically thin disk.

Core-shell structured polystyrene microspheres for improving plugging performance of oil-based drilling fluids

To avoid damage to wellbore stability in shale formations from drilling fluid intrusion and pressure transmission, it is important to develop a plugging material that can effectively plug micropores and fractures in shale formations. In this paper, polystyrene microspheres (CPM) with core-shell structure were synthesized by seed emulsion polymerization, and characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), particle size analysis, TEM observation and contact angle test. The effects of CPM on emulsion stability and emulsion rheological performance were evaluated by electrical stability tests and rheological performance tests, respectively. The plugging performance was evaluated using filter materials with different pore sizes as filter media. The experimental results showed that CPM had good thermal stability with a thermal decomposition temperature up to 374.3 °C. CPM had a core-shell structure with a median value (D50) of 229 nm and a three-phase contact angle of 116.2°. The synergistic effect of CPM and organoclay can significantly improve the stability of emulsions and viscosity at low shear rates. For different pore sizes of filter media, CPM achieved effective plugging of micropores, reducing fluid loss volume to less than 6 mL for different pore sizes of micropore filter membranes and 29.6% for ceramic sand discs. In this paper, a preparation method of plugging material with good plugging performance was given, which provided technical support for the development of plugging agents for Oil-based drilling fluids (OBDFs).

An Exploratory Study on Management Competence for Better Work Practices of The Traditional Metal Fabrication Industry in Kumasi, Ghana

One of the identifiable resources that an industry can utilize as a driver for survival is managerial competence. Although literature is replete with evidence on this subject matter, no research work has been conducted on the relationship between managerial competence and performance of the traditional metal fabrication industries in Ghana. To address this information gap, this study explored the work place practices of three traditional metal craft industries in Kumasi, Ghana with managerial competence as a moderating factor. An inductive research approach based on qualitative research methodology was adopted. The target population was 300 people of which a sample size of 171 respondents was selected. Data were collected through the use of questionnaire designed with open and close-ended responses as well as personal observations conducted using a well-designed observation guide with clear attributes and angles of observation. The results showed that all the study participants interviewed exhibited various levels of operational competence of knowledge, technical skills, experience and character attitude needed to enhance the performance and day-to-day administration of their work. They also had good conflict resolution abilities and good decision-making skills, as well as an excellent apprenticeship system embodied in a succession plan. On the other hand, the study identified several factors that impacted negatively on the operations of their work including the inability to create a conducive work environment for high performance, poor equipment and tool maintenance culture, lack of proper PPEs, poor record keeping, poor innovation and creativity skills, and nonexistence of a system for the acquisition and utilization of modern equipment and technology. These limitations suggest lack of management competence. The study considers this as quite worrisome and recommends for the needed support from both governmental and NGOs, to safeguard the survival of the metal craft industry in Ghana.

Combined Biological and Numerical Modeling Approach for Better Understanding of the Cancer Viability and Apoptosis.

Nowadays, biomedicine is a multidisciplinary science that requires a very broad approach to the study and analysis of various phenomena essential for a better understanding of human health. This study deals with the use of numerical simulations to better understand the processes of cancer viability and apoptosis in treatment with commercial chemotherapeutics. Starting from many experiments examining cell viability in real-time, determining the type of cell death and genetic factors that control these processes, a lot of numerical results were obtained. These in vitro test results were used to create a numerical model that gives us a new angle of observation of the proposed problem. Model systems of colon and breast cancer cell lines (HCT-116 and MDA-MB-231), as well as a healthy lung fibroblast cell line (MRC-5), were treated with commercial chemotherapeutics in this study. The results indicate a decrease in viability and the appearance of predominantly late apoptosis in the treatment, a strong correlation between parameters. A mathematical model was created and employed for a better understanding of investigated processes. Such an approach is capable of accurately simulating the behavior of cancer cells and reliably predicting the growth of these cells.

Evaluation and uncertainty analysis of Himawari-8 hourly aerosol product version 3.1 and its influence on surface solar radiation before and during the COVID-19 outbreak

The hourly Himawari-8 version 3.1 (V31) aerosol product has been released and incorporates an updated Level 2 algorithm that uses forecast data as an a priori estimate. However, there has not been a thorough evaluation of V31 data across a full-disk scan, and V31 has yet to be applied in the analysis of its influence on surface solar radiation (SSR). This study firstly investigates the accuracy of V31 aerosol products, which includes three categories of aerosol optical depth (AOD) (AODMean, AODPure, and AODMerged) as well as the corresponding Ångström exponent (AE), using ground-based measurements from the AERONET and SKYNET. Results indicate that V31 AOD products are more consistent with ground-based measurements compared to previous products (V30). The highest correlation and lowest error were seen in the AODMerged, with a correlation coefficient of 0.8335 and minimal root mean square error of 0.1919. In contrast, the AEMerged shows a larger discrepancy with measurements unlike the AEMean and AEPure. Error analysis reveals that V31 AODMerged has generally stable accuracy across various ground types and geometrical observation angles, however, there are higher uncertainties in areas with high aerosol loading, particularly for fine aerosols. The temporal analysis shows that V31 AODMerged performs better compared to V30, particularly in the afternoon. Finally, the impacts of aerosols on SSR based on the V31 AODMerged are investigated through the development of a sophisticated SSR estimation algorithm in the clear sky. Results demonstrate that the estimated SSR is significant consistency with those of well-known CERES products, with preservation of 20 times higher spatial resolution. The spatial analysis reveals a significant reduction of AOD in the North China Plain before and during the COVID-19 outbreak, resulting in an average 24.57 W m−2 variation of the surface shortwave radiative forcing in clear sky daytime.

Electrooptical switching and photopatterning of luminescence in nematic liquid crystals doped with mesogenic europium complex

Stimuli-responsive self-organized soft matter such as liquid crystals, polymers, gels attracts great attention due to a variety of possible applications in modern technologies. Electroinduced hydrodynamic (EHD) instability in liquid crystals is one of long-discovered effects that shows a great potential for future applications. However, this effect is insufficiently studied and its practical implementation has yet to be found. In the present paper, we applied an EHD instability to tuning luminescent properties of nematic mixtures doped with a highly emissive europium complex, which has good solubility in a liquid crystalline (LC) matrix and high quantum yield of luminescence. Nematic mixtures studied in this work possess negative anisotropy of dielectric constant and positive anisotropy of conductivity that allow for observing convective EHD patterns induced by ionic conductivity. The influence of field frequency on the threshold voltage was studied and optimal conditions for induction of EHD patterns were determined. The luminescence intensity was found to substantially decrease or increase under an applied electric field depending on the alignment behavior of LC molecules inside the cells and the angle of observation. In a tilted cell (60°), the emission intensity gradually increases under applied electric field and reaches values ca. 2.5 times higher than in zero field conditions. This phenomenon is associated with alignment of the europium complex molecules along electric field direction (cooperatively with LC molecules) and EHD-induced light scattering. Kinetics of electrooptic switching was studied and different approaches to luminescence photopatterning of the studied nematic mixture with polymerizable monoacrylate and diacrylate were demonstrated.

Experimental study of the effect of fallen leaf shading on the polarization characteristics of photovoltaic modules

Coverings have an important impact on the output and safety of photovoltaic (PV) modules. However, due to the complex on-site environment and difficult identification, it is difficult to obtain timely and effective cleaning. In this paper, the optical polarization characteristics of fallen leaf are studied to find the difference for the PV modules with or without fallen leaves covered, which is one of the typical coverings, based on the basic theory of polarization imaging. Firstly, a polarimetric imaging platform with a SALSA camera for PV modules is built. Then, several experiments are conducted and the corresponding images of PV modules shaded by heather or camphor leaves are obtained. Finally, shaded by the impacts on the polarization characteristics of the PV module from fallen leaves, the waveband of the incident light, and the observation angle are analyzed. The results show that the optical polarization characteristics of PV modules at bands of 420 nm and 546 nm are significantly different from others, wherever there existed shading leaves or not; The degree of polarization decreases and then increases with the observation angle from 0° to 70° at 9:00–12:00 a.m. on sunny days; At 0° observation angle, the stokes parameter S_{0} of PV modules with or without fallen leaves has the greatest difference. HighlightsThe influence of fallen leaves on the polarization characteristics of PV modules is studied.The polarization characteristic parameter with the largest difference between the PV modules with and without fallen leaves is obtained.This parameter is more conducive to detecting fallen leaves on the surface of PV modules.

Enhanced water permeability of hollow fiber composite reverse osmosis membrane using porous α-cellulose/polysulfone hollow fiber membrane as the substrate

The hollow fiber composite (HFC) reverse osmosis (RO) membrane with a special self-supporting structure has attracted a great deal of attention in the fields of separation and purification. However, low permeability is an urgent problem restricting its wide application. A porous polysulfone (PSF) hollow fiber support membrane was fabricated through the dry–wet spinning technique and hydrophilic α-cellulose © powder was incorporated in the PSF membrane matrix to improve the membrane’s water permeability. The HFC RO membrane was prepared via the interfacial polymerization process on the inner surface of the C/PSF support membrane. The membrane morphology and surface hydrophilicity were evaluated through scanning electron microscopy observation and dynamic water contact angle (WCA) measurement. The effects of α-cellulose incorporation on the separation performance of PSF hollow fiber membranes and HFC RO membranes were investigated. The results showed that the surface hydrophilicity and water permeability of the PSF membrane were significantly improved after the introduction of α-cellulose. The WCA of the modified PSF support membrane decreased from 84.6° for the neat PSF membrane to 70.25°, and the pure water flux can reach a maximum value of 102.1 L/(m2 · h) (0.1 Mpa), which was 1.3 times that of the pristine membrane. The HFC RO membrane using the hydrophilic modified PSF membrane as the substrate exhibited an enhanced water flux of 15.6 L/(m2 · h) and, meanwhile, the membrane salt rejection remained above 97.6% (1.0 wt% NaCl aqueous solution, 0.7 Mpa). The HFC RO membrane showed extremely high rejection rates (99%) for different dyes (congo red and methylene blue). No obvious performance deterioration was observed for the HFC RO membrane during continuous vacuum membrane distillation (VMD) experiments for 60 h.

Doped sol-gel based microstructured layers to improve the light emission of luminescent coatings

Sol-gel based layers doped with Rhodamine B phosphors (RB) were directly microstructured to produce sub-lambda 2D gratings, using nanoimprint lithography. Such an approach enables the simplification of technological processes, since no further etching process is required, which reduces considerably the number of technological steps and thus production costs. Surface microstructuring improved fluorophore emission in the visible range. Demonstrations were performed experimentally and samples were characterized using angle-resolved fluorescence. The emissions measured on microstructured luminescent coatings were 3–4 times higher, depending on the angle of observation, than those recorded on flat surfaces. This technological approach is very promising for the next generation of low-cost, high-performance anti-counterfeiting marking processes and for the traceability of objects based on unique optical effects.

Dot Off Dot Screen Printing with RGBW Reflective Inks

Recent advances in pigment production resulted in the possibility to print with RGBW primaries instead of CMYK and performing additive color mixing in printing. The RGBW pigments studied in this work have the properties of structural colors, as the primary colors are a result of interference in a thin film coating of mica pigments. In this work, we investigate the angle-dependent gamut of RGBW primaries. We have elucidated optimal angles of illumination and observation for each primary ink and found the optimal angle of observation under diffuse illumination. We investigated dot off dot halftoned screen printing with RGBW inks on black paper and in terms of angle-dependent dot gain. Based on our observations, optimal viewing condition for the given RGBW inks is in a direction of around 30∘ to the surface normal. Here, the appearance of the resulting halftoned prints can be estimated well by Neugebauer formula (weighted averaging of the individual reflected spectra). Despite the negative physical dot gain during the dot off dot printing, we observe angularly dependent positive optical dot gain for halftoned prints. Application of interference RGBW pigments in 2.5D and 3D printing is not fully explored due to the technological limitations. In this work, we provide colorimetric data for efficient application of the angle-dependent properties of such pigments in practical applications.

Research on requirement fusion of imaging reconnaissance satellites

Aiming at the problem of how to improve the requirement satisfaction of multi-point target imaging reconnaissance tasks and the utilization efficiency of satellite resources, a multi-point target imaging reconnaissance requirement fusion method based on genetic optimization is proposed in this paper. Firstly, the basic constraints that can be fused between multi-point targets are analysed, and on this basis, a point-target synthetic observation model is constructed. Secondly, considering the constraints of observation time window, observation angle and transition time between synthetic tasks, a genetic algorithm-based multi-point target requirements fusion method is designed. Finally, through the simulation analysis, it is concluded that with the continuous increase of user requirements, the fusion method based on genetic optimization can still achieve better task satisfaction to the user’s imaging requirements, which greatly improves the use efficiency of imaging satellites.

Reflection Spectra Coupling Analysis and Polarized Modeling of Optically Active Particles in Lakes

The coupling between optically active substances of algae particles and inorganic suspended solids of water makes the characteristics of reflection spectra of water complex and changeable. This makes modeling and inversion of polarization remote sensing in class II water difficult. In our study, considering the influence of the mixing ratio of algae particles and inorganic suspended solids, the sensor incidence angle, and the solar zenith angle on the polarization reflection spectrum, we analyzed the coupling characteristics of the polarized bidirectional reflectance of particulate matter through control experiments of mixed components of water particles in the laboratory. With Chaohu Lake in China as an example, the polarized reflectance coupling characteristics of water particles was investigated by the water-leaving radiation. The results showed that in the characteristic bands of 570, 675, and 705 nm, the degree of linear polarization (DOLP) was sensitive to the water-leaving radiation of the particles rather than to the reflectance. With the variation of observation angle, the reflection spectra were strongly interfered with by solar flare when the sensor zenith angle was close to 50° on the meridian plane with an azimuth angle of 180°, but DOLP was less affected, while also having a low correlation in the high concentration region. Combined with the coupling characteristics of particles at 675 and 705 nm, the model of DOLP ratio was established by partial least squares regression (PLSR) with a determination coefficient (R2) of 0.91, root mean square error (RMSE) 0.035, and a verification accuracy of 0.959. This shows that the model has better prediction ability for the coupling characteristics of water particles by the polarization reflection spectra and provides good support for mixed spectral unmixing of class II water.