Light Bands Research Articles

Spectroscopy of the 2015 Outburst of AG Pegasi

Abstract Between 2015 September and 2016 January, we obtained 18 spectra of the 2015 classical outburst of AG Pegasi—a symbiotic star consisting of a white dwarf (WD), red giant, and surrounding nebula. Modelling the flux contributions of these components reveals that nebular emission, from the reprocessing of high energy WD photons, dominates the 3200–6300 Å range. Nebular emission rises and falls in line with changes seen in the WD, whose properties have been derived using Hβ and He ii (4686 A) line flux, and emission measure calculations. WD parameters follow changes seen in visual band light curves. During the second peak of the outburst, WD temperatures reach 166,000 ± 6000 K, with a luminosity and radius of 14,000 ± 2000 L ⊙ and 0.149 ± 0.014 R ⊙ respectively. These features are consistent with an expansion of the WD pseudo-photosphere due to an accretion rate exceeding that required for stable hydrogen burning.

An ultra-fast optical analog-to-digital converter using nonlinear X-shaped photonic crystal ring resonators

This paper reports a new optical analog-to-digital converter (OADC) design based on nonlinear X-shaped photonic crystal ring resonators (X-PCRRs). The dielectric rods made of silicon and nonlinear rods composed of doped glass are used to form X-PCRRs. The proposed structure consists of a nonlinear three-channel demultiplexer and an optical encoder. The nonlinear demultiplexer converts the continuous input signal into three quantized discrete levels, and the optical encoder generates two-bit binary codes depending on the output channel number of the demultiplexer. Two well-known plane wave expansion and finite difference time domain methods are applied to study and analyze the photonic band structure and light propagation inside the PhC-based structure, respectively. The wide TM photonic band gap of the fundamental PhC covers the second window of telecommunication in the C-band. Our calculations reveal that the proposed OADC has a maximum response time of about 4 ps and a sampling rate of 125 GS/s that is much faster than the designed ADC in previous studies. The proposed ADC also has a total footprint of 1785 μm2 with a minimum leakage loss.

Genesis of the Zebra dolomites and relation to carbonate-hosted Au-Ag-Zn±Pb deposits in the Maden Village (Ulukışla-Niğde), Central Taurides, South Turkey

Zebra dolomites and carbonate - hosted Au - Ag - Zn ± Pb deposits of Maden village is located in the shelf type carbonate rocks of the Bolkar Mountains. The Zebra dolomite (ZD) locally form and there is no evidence for relation between dolomitization and mineralization. Maden village ZD is characterized by parallel light and dark bands that have similar mineralogy and chemistry by petrographic and SEM + EDX investigation. The δ13C (V - PDB) composition of the Zebra dolomite from 2.59‰ to 2.72‰ and the δ18O (V - PDB) values of the Zebra dolomite from -11.39 ‰ to -14.88 ‰. These isotopic values show that the source of oxygen and carbon was derived from marine carbonates and freshwater carbonates. Fluid inclusion studies on Zebra dolomite show homogenization temperatures of 80 °C - 180 °C. Based on petrographic, isotope values and fluid inclusion study, we can say that the dolomitization occurred during the late diagentic conditions prior mineralization.

Resonant Light Scattering by Optical Phonons in a Homoepitxial n-GaP Nanolayer Grown on a (001)n-GaP Substrate

The results of detection of resonant amplification of light scattering intensity by optical phonons in a homoepitaxial nanoscale 70 nm thick n-GaP layer grown by gas-phase epitaxy from organometallic compounds on a conducting strongly doped n-GaP crystal substrate oriented along the (001) axis have been presented. It has been shown that it is possible to detect rather narrow bands of second-order light scattering lines in the frequency range from 600 to 800 cm–1 at room temperature in the Raman light scattering spectrum of such a (001) n-GaP nanolayer in the n-GaP/n-GaP (001) sample in comparison with those in the spectrum of a high-resistance (001) si-GaP crystal sample. It has been established that such bands are caused by the total combinations and overtones of transverse TO(Γ) and longitudinal LO(Γ) optical phonons with wave vectors corresponding to the points Σ, K, X, L, and Γ of the Brillouin zone of a GaP crystal. It has been shown that the light scattering is resonant and caused by the presence of impurities because of the exciton-phonon interaction.

Enhancement of Transmission Efficiency on Pancharatnam−Berry Geometric Phase Encoding Metasurfaces

AbstractThe modulation of the required light wavefront polarization and phase based on the geometric phase encoding metasurface (GPEM) has recently become a hot topic. However, the transmission coefficient of a geometric phase metasurface is greatly decreased when the structure is rotated. To address this problem, a solution of adding a tapered antireflection layer to the substrate and design an all‐dielectric encoding metasurface composed of titanium dioxide and silicon dioxide in the visible light band with a transmission coefficient of 93.65%, is proposed. When circularly polarized light is incident on the designed encoding metasurfaces with rotating unit structures, the GPEM still maintain almost perfect transmission coefficient as with initial linearly polarized light is incident. By comparing the coded metasurface with and without conical structure, the coded metasurface with conical structure can greatly improve transmission efficiency. Importantly, the Fourier convolution theorem in digital signal processing is introduced on encoding metasurfaces. The scattering angle of transmission can be controlled arbitrarily by the all‐dielectric coded metasurface with Fourier convolution addition and subtraction operations.

Design and fabrication of off-axis meta-lens with large focal depth

<sec>A kind of off-axis meta-lens with large focal depth based on a single-layer metasurface is designed and fabricated. Our proposed off-axis focus is realized by combining the two functions of deflection and focus through phase superposition method, and the focal depth can be increased by optimizing the input aperture and off-axis deflection angle. Three-dimensional finite difference time domain (FDTD) method is used for numerical simulation to construct the off-axis meta-lens, then the off-axis meta-lens is fabricated and its focus performance is tested in a microwave anechoic chamber.</sec><sec>Experimental results indicate that at the designed electromagnetic wave frequency (9 GHz), the measured off-axis deflection angle is 27.5° and the focal length is 335.4 mm, which agree with the designed values of 30° and 350 mm. The measured full-wave half-maximum (FWHM) at the focal point is 48.2 mm, however, the simulated FWHM is 40.2 mm, which means that the imaging quality of the measured focus spot is slightly worse than the simulated one. This is mainly due to the fact that the actual parameters of the fabricated meta-lens are inconsistent with simulated parameters. In addition, during the measurement, the large sampling interval in the x- direction also leads to experimental errors.</sec><sec>The focusing efficiency of the off-axis meta-lens at the working frequency of 9 GHz is calculated to be 16.9%. The main reason for the low focusing efficiency is that the plasmonic metasurface works in the transmission mode, which can manipulate only the cross-polarized component of the incident wave, and the maximum efficiency will not exceed 25%. Moreover, the focal depths at 8 GHz, 9 GHz and 10 GHz are 263.2 mm, 278.5 mm and 298.2 mm, respectively, which are 7.02 times, 8.36 times and 9.98 times the corresponding wavelengths, indicating that a larger focal depth off-focus meta-lens is achieved. </sec><sec>This kind of off-axis meta-lens has a simple structure, good off-axis focus ability and large focal depth, which has potential applications in a compact and planar off-axis optical system and large focal depth imaging system. Although the working waveband in this article is the microwave band, according to the size scaling effect of the metasurface, it is also possible to design a large focal depth off-axis meta-lens in other bands such as visible light and terahertz bands by using the same method.</sec>

Carrier engineering of Zr-doped Ta3N5 film as an efficient photoanode for solar water splitting

Ta3N5 is regarded as a promising candidate material with adequate visible light absorption and band structure for photoelectrochemical water splitting.

Application of linked color imaging in the diagnosis of early gastrointestinal neoplasms and precancerous lesions: a review.

Introduction:Minimally invasive endoscopic resection is often effective in the management of early gastrointestinal tumors. However, advanced and more effective methods of endoscopic examination are required to improve the rate of diagnosing early gastrointestinal tumors.Discussion:The development of dye-based image-enhanced endoscopy (d-IEE) and equipment-based image-enhanced endoscopy (e-IEE) has helped improve the diagnostic rate of early gastrointestinal tumor using endoscopy. In some special cases, these methods are still not accurate in diagnosing lesions. On the basis of these e-IEEs, a new endoscopic technique, linked color imaging (LCI), that combines a specific short wavelength narrow band of light with white light, has been developed.Conclusion:In this article, we summarized the characteristics of LCI and the development of research regarding digestive tract examination.Plain language summary Application of linked color imaging in early gastrointestinal neoplasms At present, the complete diagnosis of early gastrointestinal tumors and precancerous lesions can be made by gastrointestinal endoscopy. With the improvement of therapeutic instruments and operators’ experience, endoscopic therapy can often achieve significant effect in the treatment of early gastrointestinal tumors. The development and spread of equipment-based image-enhanced endoscopy (e-IEE) mode has helped improve the diagnosis rate of early gastrointestinal tumors under endoscopy. However, in some special cases, these methods are still not accurate for the diagnosis of lesions. On the basis of these E-IEEs, a new endoscopic technique, linked color imaging (LCI), has been developed, which combines a specific short wavelength narrow band of light with white light. LCI can significantly improve the diagnostic rate of all types of gastrointestinal mucosal lesions. Tumor lesions and inflammatory lesions can be distinguished by observing the mucosal microvascular structure and color difference. LCI helps detect early gastrointestinal mucosal lesions by taking advantage of the differences in light absorption of different wavelengths and contrast of enhanced colors in the later stage.

超表面透镜的宽带消色差成像（特邀）

Metalens, the specific type of lens designed with the surfaces mading of two dimensional array at the subwavelength scale, has shown great flexibilities to control the light field, including the arbitrary modulation abilities of amplitude, phase and polarization at the subwavelength scale. Moreover, the metalens possesses the unique advantages of low loss, integratable and conformable design and ultrathin, therefore attracts immense attentions in recent years. However, in most cases, the metalens designed for a specific wavelength may penetrate through the large chromatic aberration, which limits their usefulness in multi-wavelength or broadband applications. On the other hand, the metalens has renewed new degrees of freedom due to its two-dimensional planar structure, which has the potential in the elimination of chromatic aberration. Some different typical achromatic metalens designs and their achromatic modulation mechanism were reviewed, the existing achromatic metalens were classified from the types of modulated light bands, such as the achromatic matelens for discrete and continuous wavelength respectively, and the latter can be classified as transmissive and reflective from the working mode. Finally, the application of metalenses array in imaging and their prospect of broadband achromatic devices of large depth of field were introduced.

Comparative Analysis of Edge Information and Polarization on SAR-to-Optical Translation Based on Conditional Generative Adversarial Networks

To accurately describe dynamic vegetation changes, high temporal and spectral resolution data are urgently required. Optical images contain rich spectral information but are limited by poor weather conditions and cloud contamination. Conversely, synthetic-aperture radar (SAR) is effective under all weather conditions but contains insufficient spectral information to recognize certain vegetation changes. Conditional adversarial networks (cGANs) can be adopted to transform SAR images (Sentinel-1) into optical images (Landsat8), which exploits the advantages of both optical and SAR images. As the features of SAR and optical remote sensing data play a decisive role in the translation process, this study explores the quantitative impact of edge information and polarization (VV, VH, VV&VH) on the peak signal-to-noise ratio, structural similarity index measure, correlation coefficient (r), and root mean squared error. The addition of edge information improves the structural similarity between generated and real images. Moreover, using the VH and VV&VH polarization modes as the input provides the cGANs with more effective information and results in better image quality. The optimal polarization mode with the addition of edge information is VV&VH, whereas that without edge information is VV. Near-infrared and short-wave infrared bands in the generated image exhibit higher accuracy (r > 0.8) than visible light bands. The conclusions of this study could serve as an important reference for selecting cGANs input features, and as a potential reference for the applications of cGANs to the SAR-to-optical translation of other multi-source remote sensing data.

Robust ferromagnetism and active visible-near infrared photocatalytic properties: Fe based Mn, Co and Ni codoped CuO nanostructures

Herein, we designed compositions with strong ferromagnetic and efficient Vis/NIR photocatalytic properties based on Fe/Mn, Co or Ni codoped CuO nanostructures. Pure CuO, Cu 0.97 Fe 0.03 O, Cu 0.94 Fe 0.03 Mn 0.03 O, Cu 0.94 Fe 0.03 Co 0.03 O and Cu 0.94 Fe 0.03 Ni 0.03 O nanopowders were synthesized by simple and low cost co-precipitation method. The XRD exhibits only the crystallographic planes of monoclinic CuO with reasoning variation tendency of lattice constant due to incorporation of Fe, Mn, Co or Ni ions. The TEM images demonstrate that the large agglomerated nanoparticles of pure CuO are altered to homogenous neighboring nanospherical particles after Fe/Mn, Co or Ni codoping. The binary doping extends the visible light band gap of CuO to more NIR absorption. Excellent intrinsic ferromagnetic hysteresis loop with high saturation magnetization of ~1 emu/g and retentivity of 0.252 emu/g was found in Cu 0.94 Fe 0.03 Mn 0.03 O structure which was attributed to coupling of bound magnetic polarons and Fe 3+ -Fe 3+ , Fe 3+ -Mn 2+ and Mn 2+ -Mn 2+ exchange interactions. Cu 0.94 Fe 0.03 Ni 0.03 O catalyst exhibits a strong Vis-NIR photodegradation activity for Congo red (99%) and Crystal violet (97%) dyes due to high separation of photogenerated charge carriers, small particles size (19 nm) and low band gap (1.43 eV). • New compositions based on Fe/Mn, Co or Ni codoped CuO. • Cu 0.94 Fe 0.03 Ni 0.03 O shows superior Vis-NIR dyeing photodegradation. • Degradation efficiency of 97-99% for Congo red and crystal violet. • Perfect stability and reusability for four cycles. • Cu 0.94 Fe 0.03 Mn 0.03 O exhibits robust ferromagnetic loop.

Hassas Tarım Uygulamaları Üzerinde Makine Öğrenmesi Teknikleri Kullanımı

Agricultural monitoring and analysis of data to be used in management decisions to increase the quality, profitability, sufficiency, continuity and efficiency of agricultural production is called Precision Agriculture.[1]Precision Agriculture technologies aim to help the farmers with the decision making process by providing them information and control over their land, crop status and environment using remote sensing systems. Remote sensing systems use multispectral cameras to gather information, which filter different wavelengths of light in separate bands. Vegetation indices derived from the spectral bands of the remote sensing systems carry useful information about crop characteristics such as nitrogen content, chlorophyll content and water stress which supports the farmers to plan irrigation and pesticide spraying processes without the need of manual examination, providing a cost and time-efficient solution. This study aims to explore three specific Precision Agriculture applications, such as crop segmentation, illness detection and yield prediction on olive trees in Manisa, Turkey by using machine learning algorithms. Using the spectral band information gathered from an Orange-Cyan-NIR (OCN) camera embedded UAV system, vegetation health index was calculated and the data was preprocessed by segmentating the tree pixels from background based on those values using MiniBatchKMeans algorithm. Optimal features were selected based on accuracy comparison for yield and disease predictions. A Decision Tree Regressor (DTR) model was trained for yield prediction while a Random Forest Classifier (RFC) model was trained for disease prediction. The results showed that crop segmentation had an accuracy rate of 0.85-0.95, while DTR and RFC models had an R2 score of 0.99 and accuracy rate of 0.98 respectively, which displayed the importance and usefulness of vegetation indices.

Distribution of Trace Elements Controlled by Sector and Growth Zonings in Zircon from Feldspathic Pegmatites (Ilmen Mountains, the Southern Urals)

The present study contains the detailed ion microprobe data on trace and rare earth elements distribution in the large zircon crystal about 10 × 6 mm in size with distinct growth and sector zonings from Ilmen Mountains feldspathic pegmatite. The zircon crystal morphology is a combination of a prism {110} and a dipyramid {111}. It is found out that the growth sector of the prism {110} generally contains higher concentrations of Th, U, REE, Y, and Nb and exhibits a more gently sloping HREE distribution pattern and a steeper LREE distribution pattern, in contrast to zircon from the growth sector of the dipyramid {111} development. Such a sector zoning pattern was formed at a late stage in crystal growth, when the prism {110} began to prevail over the dipyramid {111}. The zircon studied displays the growth zoning formed of alternating bands in back-scattered electron (BSE) image: wide dark and thin light bands. The last ones contain elevated Th, U, REE, Y, Nb, and Ti concentrations, Th/U ratio and Ce/Ce*. This growth zoning is most probably due to simultaneous crystallization of other minerals that concentrate trace elements, e.g., apatite and monazite, and the lack of equilibrium between zircon and fluid (melt).

Contour analysis of endoscopic images in the diagnosis of early gastric cancer

The purpose of the study: The main purpose of the study is creation of a system for digital processing of endoscopic images in white light and narrow band imaging for the early diagnosis of early forms of stomach cancer.Materials and methods: The object of the study is endoscopic images (6320 cases) with PENTAX EG-2790K and OLYMPUS H180 devices. The subjects of the research are mathematical models of gastric epithelial neoplasias, classifi cation of these tissues, methods of digital image processing and contour analysis, methods of mathematical modeling.Results: The work is divided into two stages to obtain quantitative estimates of the studied characteristics: 1. To make a diagnostic map — the image is segmented, then the boundaries between the pathologically altered tissues and the normal mucous membrane are drawn. 2. The calculation of the characteristics of the contour associated with diagnostic signs is made. As a measure of the symmetry of the figure, the symmetry coefficient k was used, defined as the ratio of the number of samples of the normalized autocorrelation function that exceeded the specified threshold in level to the total number of samples. The study revealed that the contours of malignant neoplasms have a symmetry coefficient k < 0,05, and the contours of benign neoplasms k > 0,2. This suggests the possibility of automated differentiation of neoplasms based on the analysis of their shape.The conclusion: An objective assessment of endoscopic signs of early gastric cancer is necessary to standardize and systematize the diagnostic approach. The unified digital processing of endoscopic images will allow the endoscopist to increase the frequency of detecting early forms of gastric cancer, which will affect to reduce mortality.

Effective mass of heavy, light, and spin split-off band electron and hole g-factor in cubic perovskite materials

Analytical expressions for the effective mass of heavy, light, and spin split-off electrons are obtained by diagonalizing the k⋅p Hamiltonian for cubic perovskite crystal structures and used to calculate these in nine perovskite materials. An expression for the effective hole g-factor is also derived and calculated in these perovskites. The calculated effective mass of heavy electrons ranges from 1.619 m0 to 0.201 m0, of light electrons from 0.357 m0 to 0.146 m0, and of spin split-off electrons from 0.584 m0 to 0.169 m0. It is found that Cl- and Pb-based perovskite materials have larger heavy, light, and spin split-off electron effective masses. It is also found that the effective g-factor increases with the atomic size, from Cl to I, for the series CsSnX3(X=Cl,Br,I).

Underwater ranging with intensity modulated 532 nm laser source

<sec>Laser underwater detection has important applications in underwater target search, resource exploration, and other fields. The absorption and scattering of light by water are a big challenge to underwater detection. Absorption causes the laser signal to attenuate, thus limiting the detection distance. Scattering causes not only attenuation but also noise, the strong scattering noise can even submerge the target information. To reduce the absorption, the blue-green light band in the transmission window of water is chosen for lidar. Optically carried microwave radar (OCMR) has the advantages of resistance to turbulence and scattering. The intensity of the detection beam is modulated at radio frequency. The photons reflected by the target retain the intensity modulation information, while interference phase-out is generated between photons scattered by particles suspending in turbid water at different distances, resulting in the average of high-frequency modulation signals. The signal-to-noise ratio is improved when the received signal by the detector is correlated with the modulation signal.</sec> <sec>High-power broadband intensity modulated light source is the key to achieving the long-distance, high-precision underwater ranging with the carrier modulation method. However, the carrier modulation technology for underwater detection is limited by the development of light source. The maximum power of intensity modulation green light used in underwater detection is on the order of hundreds of milliwatts, the receiver needs to adopt a photomultiplier tube (PMT).</sec><sec>In this paper, a laser underwater detection system is built with a 3-m-long water tank by using a home-made 532 nm light source. The maximum output power of the intensity-modulated 532 nm laser is 2.56 W. The modulation frequency is turned from 10 MHz to 2.1 GHz. Water with different attenuation coefficients is obtained by adding Mg(OH)<sub>2</sub> into the water tank. When the maximum modulation frequency is 500 MHz by phase ranging, 4.3 attenuation lengths(a.l.) are measured. The ranging error is about 12 cm. In the future study, a PMT will be used as the detector to increase the range resolution. We will also increase the bandwidth of the signal processing unit in order to take full advantage of the broadband intensity to modulate light source.</sec>

Spectroscopic investigation of rare earth activated potassium calcium pyrophosphate K2Ca1-xRExP2O7 (RE = Tb3+, Dy3+, Sm3+ and Eu3+) phosphors

This study investigates the spectroscopic properties of rare earth activated potassium calcium pyrophosphate K2Ca1-xRExP2O7 (RE = Tb3+, Dy3+, Sm3+ and Eu3+) phosphors synthesized by a solid-state reaction method. The synthesized phosphor samples were characterized by powder X-ray diffraction, Scanning electron microscope, Fourier transform infrared, and Photoluminescence spectroscopy. The phosphors exhibit a strong excitation band in near UV to blue region in the range 350–400 nm showing spectral overlap with the emission band of a UV light emitting diode (LED) chip. Spectroscopic analysis has also been carried out using the Judd-Ofelt theory. The obtained luminescence properties and calculated spectroscopic parameters indicate usefulness of these phosphors in solid-state lighting, white light emitting phosphor for near UV excited LEDs and other displays applications.

Photometry of the 2015 Outburst of AG Pegasi

Abstract In 2015 June, the symbiotic binary star AG Pegasi underwent a period of outburst. SkyCam T, mounted onboard the 2 m Liverpool Telescope, collected over 650 unfiltered images of this event, and several thousand images from before and after. This note presents Sloan r′ band light curves obtained from these images. In addition, a color–magnitude diagram (CMD) using AAVSO data is included to infer parameters of the system’s white dwarf (WD). Features in the light curve allow one to classify this outburst as that of classical (or Z And) type. The CMD suggests the temperature and luminosity of the WD increase concurrently to produce the light curve maxima. Light curves either side of the event show wave-like oscillations owing to the orbital period of AG Pegasi’s components, indicating quiescence.

Refractive index sensing and filtering characteristics of side-polished and gold-coated photonic crystal fiber with a offset core

The transmission characteristics of a side-polished eccentric photonic crystal fiber (PCF) is studied by using the full-vector finite element method (FV-FEM). The proposed structure is composed of air holes similar to a U-shaped arrangement, and there is a small air hole between the side polishing plane and the core region to enhance the leakage of the evanescent field in the y polarization direction. It integrates refractive index (RI) sensing and polarization filtering. The RI sensing mainly works in the visible light band, while polarization filtering is suitable for the near-infrared band. The maximum sensitivity of the sensor is 12,500 nm/RIU, and the resolution is 8.0 × 10−6 RIU in the detection RI range of 1.35–1.39. By changing the external RI or the thickness of the gold-coated film, the bandwidth-tunable PCF polarization filter with excellent performance can be obtained. Therefore, the design of side-polished PCF will be of great significance to the development of integration and miniaturization of optical devices.

VO2 based dynamic tunable absorber and its application in switchable control and real-time color display in the visible region.

Metasurface-based near perfect absorbers exhibit a wide range of potential applications in the fields of solar energy harvesting, thermal images and sensors due to their unique absorption regulation function. However, absorption characteristics of devices are locked by the device structure, leading to the limitation in real-time dynamic applications. In this work, we integrate the phase change material VO2 thin film into the metal-insulator-metal structured metasurface based absorber, and design a fully visible band switchable dynamically tunable absorber (DTA). By controlling the phase transition of VO2, the DTA can realize a novel switch function in the full band of visible light (400 ∼ 780 nm), with absorption contrast ranges from 42% to 60%. Furthermore, via accurate structural parameter control, the vivid cyan, magenta, and yellow pixels based on the VO2 DTA are designed and proposed in the real-time optical anti-counterfeiting, exhibiting outstanding characteristics of anti-glare interference and real-time encryption ability. The absorption spectrum and local electric field are simulated and analyzed to study the internal operation mechanism of DTA. The dynamic absorption adjustable function is attributed to the synergistic effect of insulator-metal transition of VO2 and Fabry-Pérot resonance of absorber.