Ultraviolet Wavebands Research Articles

Localizing Quasiperiodic Pulsations in Hard X-Ray, Microwave, and Lyα Emissions of an X6.4 Flare

We report the simultaneous observations of quasiperiodic pulsations (QPPs) in wavelengths of hard X-ray (HXR), microwave, Lyα, and ultraviolet (UV) emissions during the impulsive phase of an X6.4 flare on 2024 February 22 (SOL2024-02-22T22:08). The X6.4 flare shows three repetitive and successive pulsations in HXR and microwave wavebands, and they have an extremely large modulation depth. The onset of flare QPPs is almost simultaneous with the start of magnetic cancellation between positive and negative fields. The wavelet power spectra suggest the presence of double periods, which are centered at ∼200 and ∼95 s, respectively. The long-period QPP can also be detected in Lyα and UV wavebands at the flare area, and it could be observed in the adjacent sunspot. Our observations indicate that the flare QPPs are most likely triggered by accelerated electrons that are associated with periodic magnetic reconnections. The long period at ∼200 s is probably modulated by the slow magnetoacoustic wave originating from the neighboring sunspot, while the short period at ∼95 s could be regarded as its second harmonic mode.

Light-sensitive and strain-controlled flexible DNA/graphene/GaN bio-hybrid sensor based on the piezophototronic effect

A significant need exists for high-sensitivity, high-flexibility, and low-power piezophototronic sensors (PS) capable of monitoring small deformations or vibrations and polarization-sensitive photodetection in critical situations. Recently, interest in flexible optoelectronics has been initiated with the incorporation of biomolecules into photoelectric and piezoelectric principles, particularly because of the rapid development of organic-inorganic-based bio-hybrid PSs (Bio-HPSs). In this study, we provide a novel method for fabricating flexible, light-sensitive Bio-HPS based on the piezophototronic effect by employing DNA biomolecules on a graphene/GaN substrate. Flexible Bio-HPSs are responsive to infrared, halogen, and ultraviolet (UV) wavebands. Furthermore, in the dark, the flexible Bio-HPS displayed a gauge factor of 459 at an applied compressive strain of −0.32%. Furthermore, the gauge factors for the infrared, halogen, and UV wavelengths increased to 645, 788, and 898, respectively, under the same strain conditions. The integration of high-mobility graphene with DNA biomolecules on a GaN substrate through the piezophototronic effect may be the cause of the fluctuation in gauge factor values under various lighting conditions. These findings facilitate adaptable applications in real-world industries such as soft robotics, healthcare, and artificial intelligence.

Excellent ultraviolet optical limiting properties of Se nanosheets

Selenium (Se) is located in the fourth period of the periodic table in group VIA (element 34). In this experiment, three different solvents (isopropyl alcohol, N-methyl-2-pyrrolidone, and ethanol) were used to prepare the two-dimensional Se nanosheets, which were manufactured by the liquid phase exfoliation method with a thickness of 3.35–4.64 nm and a transverse scale of several hundred nanometers. The nonlinear absorption properties at 355, 532, and 1064 nm were studied using the open aperture Z-scan technique. Final results showed that Se nanosheets exhibited optical limiting (OL) effect in all three wavebands and three solvents, and had large two-photon absorption coefficients, especially in ultraviolet (UV) waveband. Which proved that Se nanosheets had great potential application as excellent OL materials in UV waveband. Our research broadens the path for the semiconductor field of Se, inspires the application of Se in nonlinear optics field.

Attention-Based Deep Learning Model for Image Desaturation of SDO/AIA

The Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) captures full-disk solar images in seven extreme ultraviolet wave bands. As a violent solar flare occurs, incoming photoflux may exceed the threshold of an optical imaging system, resulting in regional saturation/overexposure of images. Fortunately, the lost signal can be partially retrieved from non-local unsaturated regions of an image according to scattering and diffraction principle, which is well consistent with the attention mechanism in deep learning. Thus, an attention augmented convolutional neural network (AANet) is proposed to perform image desaturation of SDO/AIA in this paper. It is built on a U-Net backbone network with partial convolution and adversarial learning. In addition, a lightweight attention model, namely criss-cross attention, is embedded between each two convolution layers to enhance the backbone network. Experimental results validate the superiority of the proposed AANet beyond state-of-the-arts from both quantitative and qualitative comparisons.

Ultraviolet spectroscopy of AlO from first principle

The spectrum of AlO is widely used in various applications including the explorations of interstellar space, studies of laser ablation, combustions of Al-containing fuels and so on. In this work, we reported the spectroscopy of the AlO radical at temperatures of 300 ∼ 15,000 K for the wavenumber range of 1 ∼ 55,000 cm−1. Firstly, we extended our previous calculations of the potential energy curves (PECs) and transition dipole moments (TDMs) for AlO (Bai, Qin & Liu, MNRAS, 2022, 510:1649–1656) to higher B2Σ+, D2Σ+, 1′2Π and 1′'2Π electronic states, with the consideration of Davidson correction, scalar relativistic correction and core-valence correlation. Partition functions, Einstein coefficients and radiative lifetimes of AlO were then obtained by solving the nuclear-motion Schrödinger equation. The partition functions reveal that the AlO molecules mainly exist in the X2Σ+ state at temperatures of 10 ∼ 6270 K and in the A2Π state at temperatures of 6270 ∼ 15,000 K in the thermodynamic equilibrium. Finally, line intensities and spectra for different electronic transitions of AlO were calculated. The results show that the X2Σ+ → C2Π and X2Σ+ → D2Σ+ transitions dominate in the ultraviolet waveband. Comparisons of the TDMs, radiative lifetimes, line intensities and spectra with previous theoretical and experimental values indicate that our calculated data in the ultraviolet waveband are reliable and may be used for the radiation field calculation.

Aluminum Quantum Dots with Surface Controlled Blue-UV Photoluminescence

Aluminum quantum dots (AlQDs) are an emerging class of optical material due to their unique photoluminescence in the ultraviolet waveband. Herein, a strategy is presented to control their photoluminescence emission. The synthesized AlQDs displayed photoluminescence from the UV-B region (<320 nm) to the near-ultraviolet region (∼425 nm) and high quantum yields. Our investigation revealed that surfactants and phosphonic acids (PAs) were competitively bound to the surface of AlQDs, and this was affected by the space volume of surfactants and charge of head groups. The steady-state and time-resolved spectroscopic data suggested the emission properties of AlQDs mainly originated from the surface-mediated states. The red-shifting of emission peak was a result of increased amount of PAs on the surface of AlQDs, which could be related to the surface oxygen presented in both ligands and surfactants. Overall, this study indicates a method to control the photoluminescence of AlQDs by changing the surfactants and surface ligands, which is fundamental to their applications in photonics and applications to energy and environment, in addition to biomedicine.

Image Desaturation for SDO/AIA Using Mixed Convolution Network

The Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) provides full-disk solar images with high temporal cadence and spatial resolution over seven extreme ultraviolet (EUV) wave bands. However, as violent solar flares happen, images captured in EUV wave bands may have saturation in active regions, resulting in signal loss. In this paper, we propose a deep learning model to restore the lost signal in saturated regions by referring to both unsaturated/normal regions within a solar image and statistical probability model of massive normal solar images. The proposed model, namely mixed convolution network (MCNet), is established over conditional generative adversarial network (GAN) and the combination of partial convolution (PC) and validness migratable convolution (VMC). These two convolutions were originally proposed for image inpainting. In addition, they are implemented only on unsaturated/valid pixels, followed by certain compensation to compensate the deviation of PC/VMC relative to normal convolution. Experimental results demonstrate that the proposed MCNet achieves favorable desaturated results for solar images and outperforms the state-of-the-art methods both quantitatively and qualitatively.

Y2O3:Eu3+@SiO2 nanocomposites as a convertor for a broadband solar‐blind UV photodetector

AbstractCore–shell nanocomposites have attracted extensive attention in the photoelectric field because of their improved material properties and the combination of multiple functions. Particularly, these nanocomposites exhibit tunable structure and excellent optical properties. Inspired by these unique features, a novel optically active nanocomposites, Y2O3:Eu3+@SiO2 with a core–shell structure, is designed and fabricated by a hydrothermal method and electrophoretic deposition. In addition, the Y2O3:Eu3+@SiO2 composite film is also successfully developed and applied as a spectral down‐converter in the solar‐blind ultraviolet (UV) waveband region of 200–280 nm. Moreover, a broadband solar‐blind UV photodetector device is elaborated and a notable enhancement in the UV sensitivity is achieved. The findings not only provide a new idea for the development of broadband solar‐blind UV photodetector but also extended the application range of core–shell nanocomposites in photonics.

Nonlinear Generation of Perfect Vector Beams in Ultraviolet Wavebands

Perfect vector beams are a class of special vector beams with invariant radius and intensity profiles under changing topological charges. However, with the limitation of current devices, the generation of these vector beams is limited in the visible and infrared wavebands. Herein, we generate perfect vector beams in the ultraviolet region assisted by nonlinear frequency conversion. Experimental and simulation results show that the radius of the generated ultraviolet perfect vector beams remains invariant and is thus independent of the topological charge. Furthermore, we measure the power of the generated ultraviolet perfect vector beams with the change of their topological charges. This study provides an alternative approach to generating perfect vector beams for ultraviolet wavebands and may promote their application to optical trapping and optical communication.

Study of synergistic disinfection by UVC and positive/negative air ions for aerosolized Escherichia coli, Salmonella typhimurium, and Staphylococcus epidermidis in ventilation duct flow.

The efficacy of the in-duct application of ultraviolet waveband C (UVC) emitting at 254nm wavelength and air ions against aerosolized bacteria was studied in a full-scale 9-m long ventilation duct. Combined positive and negative ion polarities (bipolar ions) and combined UVC and ions were tested. The UVC was generated by a mercury-type UVC lamp and air ions were generated by positive and negative polarity ionizers. Escherichia coli (E. coli), Salmonella typhimurium (S. typhimurium), and Staphylococcus epidermidis (S. epidermidis)were tested at a concentration of 108 to109 cells in 50 ml of sterilized distilled water. The case in which the positive ionizer was placed first, followed by the negative ionizer, demonstrated significantly higher disinfection efficiencies for E. coli (p=0.007) and S. typhimurium (p<0.001), but lower efficiency for S. epidermidis (p=0.01) than the reversed sequence. The combination of UVC (3.71J/m2 ) and air ions (1.13×1012 ions/m3 for positive ions and 8.00×1011 ions/m3 for negative ions) led to higher inactivation than individual disinfection agents operating under the same dose. A synergetic inactivation effect was observed for S. epidermidis under the combined UVC and positive ion case, while the combined UVC and negative ion case showed significant synergy effects for E. coli and S. typhimurium.

Transverse and longitudinal coupling of LSPPs in isolated triangular Al–SiO2–Al hybrid nanoplates for generation of local electromagnetic fields with enhanced intensity and increased decay time

Achieving a large enhancement of local electromagnetic fields in the ultraviolet waveband is desirable for some applications such as surface-enhanced Raman scattering and surface-enhanced fluorescence. In addition, it is more significant for some applications such as plasmon-enhanced harmonic generation to enhance the intensity of local electromagnetic fields and increase their decay time at the same time. In this paper, using the finite-difference time-domain method, we numerically demonstrate that using the linearly polarized light with a wavelength of 325 nm as the illumination light, an isolated triangular Al–SiO2–Al hybrid nanoplate with optimized geometric parameters can produce a local electric field enhanced by a factor of about 108 at one of its top apexes, and produce two local electric fields enhanced by a factor of about 150 at two transverse dielectric/metal interfaces of one of its longitudinal side edges. Moreover, we also numerically demonstrate that the decay time of enhanced local electric fields produced by the isolated triangular Al–SiO2–Al hybrid nanoplate is about 1.6 times as large as that of enhanced local electric fields produced by an isolated triangular Al nanoplate. These unique properties of the isolated triangular Al–SiO2–Al hybrid nanoplate arise because of both the transverse coupling and the longitudinal coupling of localized surface plasmon polaritons in this structure. Our findings make triangular Al–SiO2–Al hybrid nanoplates very promising for application in many fields such as surface-enhanced Raman scattering and plasmon-enhanced harmonic generation.

A Search for the Counterparts of Quiet-Sun Radio Transients in Extreme Ultraviolet Data

Recently nonthermal radio transients from the quiet sun have been discovered and it has been hypothesised using rough calculations that they might be important for coronal heating. It is well realized that energy calculations using coherent emissions are often subject to poorly constrained parameters and hence have large uncertainties associated with them. However energy estimates using observations in the extreme ultraviolet (EUV) and soft X-ray bands are routinely done and the techniques are pretty well established. This work presents our first attempt to identify the EUV counterparts of these radio transients and then use the counterpart to estimate the energy deposited into the corona during the event. I show that the group of radio transients studied here was associated with an brightening observed in the extreme ultraviolet waveband and was produced due to a flare of energy $\sim 10^{25}$ ergs. The fact that the flux density of the radio transient is only $\sim 2\,$mSFU suggests that it might be possible to do large statistical studies in future for understanding the relationship between these radio transients and other EUV and X-ray counterparts and also for understanding their importance in coronal heating.

Ultraviolet waveband vector beams generation assisted by the nonlinear frequency conversion

Vector beams with a nonseparable polarization distribution are almost thoroughly studied from their generation to application in infrared and visible regimes. Until now, the nonlinear generation of ultraviolet vector beams is only focused on the nonlinear optical processes of gas molecules, which seriously impacts its further applications due to the unstable property. Here, we present a study on the generation of ultraviolet vector beams assisted by the nonlinear frequency conversion processes in potassium dihydrogen phosphate crystals. The vectorial properties of the generated ultraviolet waveband vector beams are characterized in both theoretical and experimental environments. The proposed method paves the way for the generation of extreme ultraviolet vector beams with solid-state nonlinear crystal, which is a more compact and stable way compared with the gas nonlinear method. This work also opens a route for photolithographic techniques and laser processing based on ultraviolet waveband vector beams.

On the multiwavelength variability of Mrk 110: two components acting at different time-scales

ABSTRACT We present the first intensive continuum reverberation mapping study of the high accretion-rate Seyfert galaxy Mrk 110. The source was monitored almost daily for more than 200 d with the Swift X-ray and ultraviolet (UV)/optical telescopes, supported by ground-based observations from Las Cumbres Observatory, the Liverpool Telescope, and the Zowada Observatory, thus extending the wavelength coverage to 9100 Å. Mrk 110 was found to be significantly variable at all wavebands. Analysis of the intraband lags reveals two different behaviours, depending on the time-scale. On time-scales shorter than 10 d the lags, relative to the shortest UV waveband (∼1928 Å), increase with increasing wavelength up to a maximum of ∼2 d lag for the longest waveband (∼9100 Å), consistent with the expectation from disc reverberation. On longer time-scales, however, the g-band lags the Swift BAT hard X-rays by ∼10 d, with the z-band lagging the g-band by a similar amount, which cannot be explained in terms of simple reprocessing from the accretion disc. We interpret this result as an interplay between the emission from the accretion disc and diffuse continuum radiation from the broad-line region.

Stress Birefringence Analysis in Fused Silica at Deep Ultraviolet Waveband Based on Finite Element Simulation Method

Stress Birefringence Analysis in Fused Silica at Deep Ultraviolet Waveband Based on Finite Element Simulation Method

Design of Pt/C X-ray supermirror by needle optimization

Needle optimization is widely used in visible and infrared region, but it is rarely utilized in X-ray and extreme ultraviolet waveband. We use Needle optimization to design Pt/C X-ray supermirrors, and the grazing incidence angles are 1.0, 1.4, and 1.7 degree, respectively. A modified target is introduced into optilayer software. A good result is obtained by Optilayer software combined with IMD software. The difference of design results between block method and needle optimization is discussed.

Proximal Methods for Plant Stress Detection Using Optical Sensors and Machine Learning.

Plant stresses have been monitored using the imaging or spectrometry of plant leaves in the visible (red-green-blue or RGB), near-infrared (NIR), infrared (IR), and ultraviolet (UV) wavebands, often augmented by fluorescence imaging or fluorescence spectrometry. Imaging at multiple specific wavelengths (multi-spectral imaging) or across a wide range of wavelengths (hyperspectral imaging) can provide exceptional information on plant stress and subsequent diseases. Digital cameras, thermal cameras, and optical filters have become available at a low cost in recent years, while hyperspectral cameras have become increasingly more compact and portable. Furthermore, smartphone cameras have dramatically improved in quality, making them a viable option for rapid, on-site stress detection. Due to these developments in imaging technology, plant stresses can be monitored more easily using handheld and field-deployable methods. Recent advances in machine learning algorithms have allowed for images and spectra to be analyzed and classified in a fully automated and reproducible manner, without the need for complicated image or spectrum analysis methods. This review will highlight recent advances in portable (including smartphone-based) detection methods for biotic and abiotic stresses, discuss data processing and machine learning techniques that can produce results for stress identification and classification, and suggest future directions towards the successful translation of these methods into practical use.

Origin of Ultraviolet Intermediate-width Emission Lines in Partially Obscured Quasar SDSS J151653.22+190048.2

The quasar SDSS J151653.22+190048.2 (J1516+1900) exhibits very peculiar spectral characters in the observed ultraviolet, optical, and infrared bands: the full widths at half maximum (FWHM) of its optical Hα, Hβ, and infrared Paα and Paβ emission lines are all larger than 5000km/s, and the equivalent widths of these emission lines also approach to those of normal quasars; while the ultraviolet emission lines (Lyβ, OVI, Lyα, NV, SiIV, and CIV) are dominated by intermediate-width emission lines (IELs) with a FWHM of ∼ 1700km/s. This phenomenon can be explained as the effect of partial obscuration: the broad emission lines (BELs) in the ultraviolet waveband are heavily suppressed by the dust extinction, and thus the IELs become prominent; while the dust extinction is not significant in optical and infrared bands, and the IELs can hardly be detected due to the brightness of BELs. Using the IEL width and central supermassive black hole mass MBH∼5.75×108 M⊙ of J1516+1900, and assuming that the intermediate-width emission line region (IELR) is virialized, we estimate the distance of the IEL region to the central black hole is about 1.6pc. On the other side, by combining the photoionization model calculations and observed IELs, we find that the IELR has a density of ∼1012 cm−3, and the ionization parameter of ∼10−0.65, and that its distance to the central region is ∼0.016pc, which is only one percent of the virialized distance. This contradiction can provide an important clue for studying the geometry, physical condition, and origin of the IELRs in active galactic nuclei.

The Bipolar Magnetic Emergence in the Solar Polar Region

Abstract Due to projection effect and polarization sensitivity, it is still unknown whether the bipolar magnetic emergence (BME) exists in the solar polar region. In this study, combining the magnetic observations from the Helioseismic and Magnetic Imager and imaging observations of the 211 Å waveband from the Atmospheric Imaging Assembly, we try to identify and diagnose the BME. Considering the magnetic evolution and the corresponding intensity variation in the extreme ultraviolet waveband, we find definite events of the BMEs in the solar polar region. In total, we identify more than 300 BMEs in the solar polar region in the whole year from 2010 June to 2011 May. We find that whether on the southern or northern polar region, the leading polarity of the BMEs is almost half-positive and half-negative, and the BMEs’ magnetic axes show random distribution in that direction. These results imply the possible existence of local dynamo in the solar polar region.

Caught in the web: A tale of filament galaxies

AbstractThe Coma supercluster is one of the largest, nearby (∼100h−1Mpc) gravitationally bound structures known in the universe. It comprises two large clusters of galaxies and several galaxy groups intersected by a complex network of filaments, providing the perfect laboratory for studying the evolution of galaxies in a range of ‘continuous’ environments. We characterised the different components of the environment to study the properties of galaxies in the optical and ultraviolet (UV) wavebands. Our analysis shows that galaxies experience accelerated evolution as they approach the spine of the filament, suggesting that the intermediate-density environment prevalent in the filaments can accelerate the evolution of galaxies.