Visible Window Research Articles

Performance Improvement by Upgrading of the Multi-Field Test Facility of Superconducting Wires/Tapes

A versatile test facility capable of providing cryogenic-electro-magnetic multifield was constructed for field-dependent and mechanical property measurements of superconducting wires/tapes at Lanzhou University of China. It firstly realized a continuous variation of cryogenic temperature from 4.2 K to 77 K (∼5 K/min) and a transport current from 0–1000 A (∼1 A/min) in a background magnetic field of 3.5 T. Aiming at improvements of samples in a larger scope, the facility was upgraded on several sub-systems, for example, the background superconducting magnet, variable-temperature cryogenic and mechanical loading and control system. This paper presents the latest upgrading of the multifield test facility. A semi-open split NbTi magnet with a combined cooling system was newly fabricated to generate a transverse background filed up to 5 T in a relatively larger test space of ∅100 mm × H800 mm. To improve the cryogenic system for refrigeration, a compact cryostat of cylinder-like vacuum Dewar vessel with a visible window, cooled by a Gifford–McMahon (GM) cryocoolers, was constructed. The continuous temperature variations from 4 to 353 K (∼10 K/min) and a high transport current application 0–1000 A (∼3 A/min) for testing superconducting wires/tapes were achieved. Additionally, a data acquisition system with accurate and synchronous measurements of multifield including current, temperature, strain, and AC losses was enhanced. Some tests illustrated that the upgrading of sub-systems and extend of operation range for the test facility were well improved. It will contribute to the progress in understanding design issues for superconducting wires/tapes under intense multiple fields.

Molecular Engineering Approaches Towards All-Organic White Light Emitting Materials.

White light emitting (WLE) materials are of increasing interest owing to their promising applications in artificial lighting, display devices, molecular sensors, and switches. In this context, organic WLE materials cater to the interest of the scientific community owing to their promising features like color purity, long-term stability, solution processability, cost-effectiveness, and low toxicity. The typical method for the generation of white light is to combine three primary (red, green, and blue) or the two complementary (e.g., yellow and blue or red and cyan) emissive units covering the whole visible spectral window (400-800 nm). The judicious choice of molecular building blocks and connecting them through either strong covalent bonds or assembling through weak noncovalent interactions are the key to achieve enhanced emission spanning the entire visible region. In the present review article, molecular engineering approaches for the development of all-organic WLE materials are analyzed in view of different photophysical processes like fluorescence resonance energy transfer (FRET), excited-state intramolecular proton transfer (ESIPT), charge transfer (CT), monomer-excimer emission, triplet-state harvesting, etc. The key aspect of tuning the molecular fluorescence under the influence of pH, heat, and host-guest interactions is also discussed. The white light emission obtained from small organic molecules to supramolecular assemblies is presented, including polymers, micelles, and also employing covalent organic frameworks. The state-of-the-art knowledge in the field of organic WLE materials, challenges, and future scope are delineated.

Density Functional Theory Investigation of Nonlinear Optical Properties of T-Graphene Quantum Dots.

Using density functional theory calculations, we have analyzed nonlinear optical properties of a series of T-graphene quantum dots differing in their shape and size. Electronic polarizability and first-order and second-order hyperpolarizability of these systems are investigated and shed light on their stability and electronic properties. Negative cohesive energy shows that they are energetically stable. The effect of size and incident frequency on their nonlinear responses are comprehensively discussed. Most of the systems exhibit a strong NLO response, and it is enhanced in the presence of an external field. All these systems show absorption maximum ranging from UV to visible window. Overall, this theoretical framework highlighted the nonlinear optical properties of T-graphene quantum dots that may provide valuable information in designing potential NLO materials.

Thermomechanical modelling for the linear friction welding process of Ni-based superalloy and verification

This paper presents a fully coupled thermomechanical model for the linear friction welding process of Inconel-718 nickel-based superalloy by using the finite element method. Friction heat, plastic work, and contact formulation were taken into account for two deformable plastic bodies oscillating relative to each other under large compressive force. The modelling results of the thermal history at the weldline interface and thermal field at a distance away from the rubbing surfaces were compared to instrumented data sourced from related publications for model verification. Optimal linear friction welding process parameters were identified via comparison of weld temperature to the liquidus temperature of Inconel-718 alloy. Comparison of interface temperature showed a consistent range of values above the solidus melting temperature (1250 ℃) and below the liquidus melting temperature (1360 ℃) of Inconel-718 alloy. For the first time, a visible linear friction welding process window is identified using a thermomechanical computational modelling method. Through computational modelling, the influence of welding process parameters on the heat transfer and deformation of weld was systematically investigated.

Efficient synthesis of NIR emitting bis[2-(2'-hydroxylphenyl)benzoxazole] derivative and its potential for imaging applications.

Unassymetric bis[2-(2'-hydroxyphenylbenzoxole)] bis(HBO) derivatives with a DPA functionality for zinc binding have been developed with an efficient synthetic route, using the retrosynthetic analysis. Comparison of bis(HBO) derivatives with different substitution patterns allows us to verify and optimize their unique fluorescence properties. Upon binding zinc cation, bis(HBO) derivatives give a large fluorescence turn-on in both visible (λem≈536nm) and near-infrared (NIR) window (λem≈746nm). The probes are readily excitable by a 488nm laser, making this series of compounds a suitable imaging tool for in vitro and in vivo study on a confocal microscope. The application of zinc binding-induced fluorescence turn-on is successfully demonstrated in cellular environments and thrombus imaging.

Synergistic effect of flow pattern evolution of dispersed and continuous phases in direct-contact heat transfer process

The marker-controlled multiple watershed segmentation are achieved to distinguish darker continuous phase in gas-liquid two-phase flow patterns efficiently. Each plot of the Betti numbers βi is curve-fitted using a four-parameter logistics model, for characterizing mixing effects. Similarity between adjacent pixels can be quantified by the distance. The β1 of continuous phase decreases linearly at distance ≥ 2, which can be used to determine the threshold for segmentation. Repeated tests with different pixels and methods are conducted to ensure the repeatability and effectiveness of this model. More interestingly, we find that the rapid increase of β1 of bubbles swarm coincides with the evolution of β1 of continuous phase, and the median of difference of β1 between the two phases in the visible window, as a novel metric of flow regime control is obtained and correlated with average volumetric heat transfer coefficient. This dynamic image analysis method, equipped with computational homology, provides the ability of evaluation of the spatial flow structure from a two-dimensional image and can be used to control the process.

Multi-satellite scheduling framework and algorithm for very large area observation

This paper presents a multi-satellite scheduling problem for very large area observation with given specific constraints, derived from satellite capacity and customer requests. It is assumed that the profit was proportional to the coverage of acquired area, and the objective is therefore to maximize the total profits of generated observation schedule. To address the satellite scheduling problem, we first demonstrate a detailed problem description and then transform the problem into set covering problem within several criteria and constraints. Based on that, a mathematical model is established. In order to solve the multi-satellite scheduling problem for large area observation, a new solving framework is proposed. The framework is composed of three phases. In the discretizing phase, an area discretization method is adopted to establish the evaluation system. In the target decomposing phase, area target is decomposed into strips and corresponding visible time windows are calculated. In the scheduling phase, with crossover, mutation and feasibility operators, a genetic algorithm is introduced to generate an optimal observation schedule. Through extensive computational experiments on realistically generated problem with Chinese satellite platform, the effectiveness and reliability of the proposed solving framework are verified.

A statistical method for the identification of stars enriched in neutron-capture elements from medium-resolution spectra

We present an automated statistical method that uses medium-resolution spectroscopic observations of a set of stars to select those that show evidence of possessing significant amounts of neutron-capture elements. Our tool was tested against a sample of ∼70 000 F- and G-type stars distributed among 215 plates from the Galactic Understanding and Exploration (SEGUE) survey, including 13 that were directed at stellar Galaxy clusters. Focusing on five spectral lines of europium in the visible window, our procedure ranked the stars by their likelihood of having enhanced content of this atomic species and identifies the objects that exhibit signs of being rich in neutron-capture elements as those scoring in the upper 2.5%. We find that several of the cluster plates contain relatively large numbers of stars with significant absorption around at least three of the five selected lines. The most prominent is the globular cluster M 3, where we measured a fraction of stars that are potentially rich in heavy nuclides, representing at least 15%.

Boosting the Performance of Environmentally Friendly Quantum Dot-Sensitized Solar Cells over 13% Efficiency by Dual Sensitizers with Cascade Energy Structure.

Generally, high light-harvesting efficiency, electron-injection efficiency, and charge-collection efficiency are the prerequisites for high-efficiency quantum-dot-sensitized solar cells (QDSCs). However, it is fairly difficult for a single QD sensitizer to meet these three requirements simultaneously. It is demonstrated that these parameters can be felicitously balanced by a cosensitization strategy through the adoption of environmental-friendly Zn-Cu-In-Se and Zn-Cu-In-S dual QD sensitizers with cascade energy structure. Experimental results indicate that: i) the combination of the dual QDs can improve the light-harvesting capability of the cells, especially in the visible light window; ii) the cosensitization approach can facilitate electron injection, benefitting from the cascade energy structure of the two QD sensitizers employed; iii) the charge-collection efficiency can be remarkably enhanced by the suppressed charge-recombination process due to the improved QD coverage on TiO2 . Consequently, this cosensitization strategy delivers a new certified efficiency record of 12.98% for liquid-junction QDSCs under AM 1.5G 1 sun irradiation. Moreover, the constructed cells exhibit good stability in a high-humidity environment.

Synthesis and optical properties of tunable dual emission copper doped CdTe1-xSex alloy nanocrystals

Tunable and dual emission Cu2+-doped CdTe1-xSex alloy nanocrystals (NCs) were successfully synthesized by the wet chemical method. The morphology and chemical compositions of the synthesized NCs were assessed by transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The structural and optical properties were characterized by X-ray diffraction (XRD), absorption spectroscopy (Abs), photoluminescence (PL) spectroscopy, PL-decay lifetime. With the Cu2+ dopant concentration in the range of 0.5–5% and x of 0.5 in the precursors, the fabricated Cu2+-doped CdTe1-xSex NCs exhibited the dual emissions in the visible window at about 665 nm and near infrared window ranging from 830 to 840 nm which correspond to the excitonic emission of CdTe1-xSex NCs and Cu2+ dopant ions, respectively. With the increase in dopant concentration, the fluorescence lifetime of Cu-doped CdTe0.5Se0.5 NCs significantly improved (up to μs) and the lattice constant of NCs decreased. By varying x from 0 to 1.0, both excitonic and dopant emissions of Cu-doped CdTe1-xSex NCs could be tuned in a wild range from 758 to 563 nm and from 918 to 748 nm, respectively. Interestingly, the crystal structure of these NCs changed gradually from the zinc blende (ZB) to wurtzite (WZ) structure when x increased. The results revealed that the dual emission, fluorescence lifetime and crystal structure of the Cu-doped NCs could be controlled by varying dopant concentration and chemical composition of the host.

Mononuclear Ru(II) Complexes of an Arene and Asymmetrically Substituted 2,2'-Bipyridine Ligands: Photophysics, Computation, and NLO Properties.

By using monosubstituted 2,2'-bipyridine asymmetric ancillary ligands with different electron donor moieties and an arene ligand (p-cymene), we successfully designed and synthesized six Ru(II) compounds (RuBPY1-6) that belong to a piano-stool-type system. The NLO properties of the synthesized complexes have been studied in both solution and the solid state. The electronic spectra of these compounds show a broad feature with two absorption bands in the visible window (350-650 nm). RuBPY1-6 complexes exhibit NIR emission spectra in the solution state (at >720 nm), the maxima of which are bathochromically shifted in comparison to those of the concerned ligands. Interestingly, compounds RuBPY1-6 show NIR emission in their solid state too. Title compounds RuBPY1-6 have lifetimes in the range of 0.2 to 0.9 ns. An important feature of this work is the π-association of the p-cymene ligand to Ru(II) in the synthesized complexes; the π complex is formed by breaking the symmetry of p-cymene, found in the starting precursor (Ru2 dimer). This has been established by NMR spectral studies along with DFT calculations on the 1H NMR spectra. We could derive the molecular structure of the cationic part of this system by density functional theory (DFT), associated with 1H NMR spectral studies. The minimum energy structures for RuBPY1 and RuBPY2 have been optimized at DFT/B3LYP along with the LANL2DZ basis set for ruthenium atoms. These optimized structures are further considered to calculate the excited state properties using the TDDFT method. The electrochemical studies of the complexes, investigated in acetonitrile solution, show that this system is associated with a well-defined Ru(III)/Ru(II) reversible couple, rarely observed for a Ru(II) piano-stool-type compound, along with a feature of irreversible ligand oxidation. The absorption cross-section values, obtained from the two-photon absorption studies of title compounds RuBPY1-6, are worth reporting and lie in the range of 3-28 GM (in the femtosecond case).

Multiplexing Optical Fiber Macro-Bend Load Sensors

This paper shows the multiplexing prospects of a load sensing array composed of six in-series optical fiber macro-bends. These fiber loops were individually embedded in silicone elastomer to constitute six sensor elements. Load configurations combining 0.0, 0.5, 1.0, and 1.5 kg were applied on the sensors to study the device performance. The sensor array, composed of standard fibers for optical communications, is spectrally interrogated in the visible window of the electromagnetic spectrum in a multimodal regime of operation. A simple linear regression model was used to estimate an unknown load configuration applied to the array from its associated transmittance spectrum. A sample space of 411 load configurations was used for training and testing the system. The ability of reconstruction was assessed by comparing the actual and predicted configurations of loads. A mean absolute error of 0.12 kg for the estimate was found under the testing conditions. In order to decrease the dimensionality of the dataset, principal component analysis and a discarding variable method were employed. Under 39% of data reduction, no significant impairment on the sensor array performance was observed.

"Three-Bullets" Loaded Mesoporous Silica Nanoparticles for Combined Photo/Chemotherapy.

This contribution reports the design, preparation, photophysical and photochemical characterization, as well as a preliminary biological evaluation of mesoporous silica nanoparticles (MSNs) covalently integrating a nitric oxide (NO) photodonor (NOPD) and a singlet oxygen (1O2) photosensitizer (PS) and encapsulating the anticancer doxorubicin (DOX) in a noncovalent fashion. These MSNs bind the NOPD mainly in their inner part and the PS in their outer part in order to judiciously exploit the different diffusion radius of the cytotoxic NO and 1O2. Furthermore this silica nanoconstruct has been devised in such a way to permit the selective excitation of the NOPD and the PS with light sources of different energy in the visible window. We demonstrate that the individual photochemical performances of the photoactive components of the MSNs are not mutually affected, and remain unaltered even in the presence of DOX. As a result, the complete nanoconstruct is able to deliver NO and 1O2 under blue and green light, respectively, and to release DOX under physiological conditions. Preliminary biological results performed using A375 cancer cells show a good tolerability of the functionalized MSNs in the dark and a potentiated activity of DOX upon irradiation, due to the effect of the NO photoreleased.

Defect engineered ZnO whispering gallery modes via doping with alkali metal ions for label-free optical sensors

A systematic investigation on the proper utilization of defect levels present in ZnO is very much in demand to avail many applications of photonics in visible and near infrared (NIR) regions. In this paper, we have engineered intrinsic defects of zinc oxide (ZnO) to achieve high-quality intense whispering gallery modes (WGMs) in a single ZnO microsphere optical resonator by doping with alkali metal ions. Here, a single microsphere of undoped and doped ZnO was considered to investigate WGMs by recording luminescence spectra using a microphotoluminescence system under green laser excitation having a central wavelength of 532 nm and a fixed power of 55 mW/cm2. We have found that there is a significant enhancement in the intensity of WGMs in the case of doped ZnO in comparison to undoped ones. Among all the doped ZnO microspheres, 2 mol. % Li-doped ZnO yields the strongest and intense WGMs, which are accompanied by high-quality (Q)-factors. Furthermore, the pump power dependence measurement performed in 2 mol. % Li-doped ZnO reveals the lasing action in the visible optical window by explicitly exploiting the defect levels present in the material. Thus, our proposed defect engineered ZnO microsphere may represent a promising optical microresonator for developing highly sensitive WGMs based optical sensors.

Photoacoustic imaging in the second near-infrared window: a review.

.Photoacoustic (PA) imaging is an emerging medical imaging modality that combines optical excitation and ultrasound detection. Because ultrasound scatters much less than light in biological tissues, PA generates high-resolution images at centimeters depth. In recent years, wavelengths in the second near-infrared (NIR-II) window (1000 to 1700 nm) have been increasingly explored due to its potential for preclinical and clinical applications. In contrast to the conventional PA imaging in the visible (400 to 700 nm) and the first NIR-I (700 to 1000 nm) window, PA imaging in the NIR-II window offers numerous advantages, including high spatial resolution, deeper penetration depth, reduced optical absorption, and tissue scattering. Moreover, the second window allows a fivefold higher light excitation energy density compared to the visible window for enhancing the imaging depth significantly. We highlight the importance of the second window for PA imaging and discuss the various NIR-II PA imaging systems and contrast agents with strong absorption in the NIR-II spectral region. Numerous applications of NIR-II PA imaging, including whole-body animal imaging and human imaging, are also discussed.

Postsynthesis Spontaneous Coalescence of Mixed-Halide Perovskite Nanocubes into Phase-Stable Single-Crystalline Uniform Luminescent Nanowires.

All inorganic mixed-halide perovskite, CsPb(Br xI1- x)3 (0 ≤ x ≤ 1), nanocrystals possess tunable photoluminescence with high quantum yield in the visible window. However, the photoluminescence degrades rapidly with postsynthetic aging due to the spontaneous ion separation and phase instability. Here we show that the postsynthetic aging of CsPb(Br xI1- x)3 nanocubes spontaneously forms highly uniform single-crystalline nanowires with a diameter of 9 ± 0.5 nm and length of up to several micrometers. The nanowires show bright photoluminescence with an absolute photoluminescence quantum yield of 41%. Rietveld refinement identifies the stable orthorhombic phase of the nanowires, implying a phase transition from the cubic crystallographic phase of the nanocubes during the morphology evolution. Transient absorption spectroscopy reveals a faster excited-state decay dynamic with a large exciton delocalization length in 1D nanowires. Our findings elucidate the insights into the postsynthesis morphology evolution of mixed-halide perovskite nanocrystals leading to luminescent nanowires with excellent crystal phase stability for potential optoelectronic applications.

Scheduling multiple agile earth observation satellites with an edge computing framework and a constructive heuristic algorithm

Abstract The effective scheduling of multiple agile earth observation satellites plays a key role in improving the efficiency of the agile satellite observation system. Due to the complex constraints and large solution space (increases exponentially with the problem size), it has been a big challenge to effectively solve the multiple agile satellites scheduling problem. In this study, an edge computing framework is proposed in order to solve this problem in a flexible manner. In this framework, a central node and several edge nodes are included. The central node corresponds to the operation center of the satellite observation system while each edge node corresponds to an agile satellite. The central node filters tasks for edge nodes according to the time of scheduling period and visible time windows. Tasks in each edge node are scheduled according to the order of scheduling periods by a constructive heuristic algorithm based on the density of residual tasks (HADRT). The efficiency of this algorithm is proved. The time and space complexity are analyzed in detail. The proposed method is compared with other three advanced methods, and the experimental results show that HADRT could achieve higher task completion rate and reward rate than other algorithms with acceptable computing time.

NaCa5BO3(SiO4)2 with Interesting Isolated [BO3] and [SiO4] Units in Alkali- and Alkaline-Earth-Metal Borosilicates.

A new borosilicate, NaCa5BO3(SiO4)2, has been synthesized by a high-temperature solution method, which crystallizes in the centrosymmetric monoclinic space group P21/ c (No. 14), having a tangled three-dimensional (3D) network including isolated [BO3] triangles, isolated [SiO4] tetrahedra, and [CaO n] ( n = 7-9) and [NaO7] polyhedra. According to our surveys, it is the first compound containing both isolated [BO3] triangles and isolated [SiO4] tetrahedra in alkali- and alkaline-earth-metal borosilicates, which enriches the structure chemistry of borosilicates. The UV-vis-NIR diffuse reflectance spectrum shows that NaCa5BO3(SiO4)2 exhibits a wide transparent region which covers the near-IR, visible, and UV windows and displays a short UV cutoff edge at about 240 nm. Additionally, the thermal behavior (TG and DSC) and IR spectrum were also analyzed. For a deeper understanding of the relationships between the structure and properties, an analysis of theoretical calculations by density functional theory was also performed.

Measurement of the neutrino-oxygen neutral-current quasielastic cross section using atmospheric neutrinos at Super-Kamiokande

Neutral current (NC) interactions of atmospheric neutrinos on oxygen form one of the major backgrounds in the search for supernova relic neutrinos with water-based Cherenkov detectors. The NC channel is dominated by neutrino quasi-elastic (NCQE) scattering off nucleons inside $^{16}$O nuclei. In this paper we report the first measurement of NCQE cross section using atmospheric neutrinos at Super-Kamiokande (SK). The measurement used 2,778 live days of SK-IV data with a fiducial volume of 22.5 kiloton water. Within the visible energy window of 7.5-29.5 MeV, we observed $117$ events compared to the expected $71.9$ NCQE signal and $53.1$ background events. Weighted by the atmospheric neutrino spectrum from 160 MeV to 10 GeV, the flux averaged NCQE cross section is measured to be $(1.01\pm0.17(\text{stat.})^{+0.78}_{-0.30}(\text{sys.}))\times10^{-38}$ cm$^2$.

A Heuristic Algorithm Based on Temporal Conflict Network for Agile Earth Observing Satellite Scheduling Problem

Agile Earth Observing Satellite (AEOS) scheduling problem consists of selecting a subset of tasks and developing observation plans for a set of agile satellite resources with the purpose of maximizing the total reward of arranged mission observations. This problem has attracted much attention in recent years since AEOS is a new generation satellite being developed all over the world. Due to its NP-hardness, heuristic methods are widely adopted when solving the AEOS scheduling problem (AEOSSP). In this paper, we propose a temporal conflict network-based heuristic algorithm (TBHA), for AEOSSP. The novelty of TBHA lies in the fact that the heuristics are extracted from a temporal conflict network, which characterizes the overlaps (conflicts) of the visible time windows of the problem. These heuristics are highly effective since they well address the time window conflicts which otherwise pose a significant challenge on the choice of the imaging start time for satellite observations. The extensive simulation experiments with the comparison to a number of heuristic algorithm variants and sophisticated meta-heuristic algorithms are conducted to show that the TBHA algorithm performs very well in terms of both solution quality and computational efficiency.