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Structural, energetic and spectroscopic studies of new luminescent complexes based on 2-(2′-hydroxyphenyl)imidazo[1,2- <i>a</i> ]pyridines and 1,2-phenylenediboronic acid
摘要： Three new blue-luminescent complexes of selected imidazo[1,2-a]pyridine derivatives and 1,2-phenylenediboronic acid have been synthesized and structurally characterized using single-crystal X-ray diffraction. Additionally, the crystal structures of two of the (N,O)-donor compounds have been evaluated for the first time. The crystal packing and molecular motifs observed in the studied crystals have been thoroughly analysed, including computational studies, and are also discussed within the context of analogous systems reported in the literature. It appears that the new compounds form different crystal networks with regard to the asymmetric unit content and packing, although some similarities can be found. In all cases a typical centrosymmetric dimer bound via boronic acid groups is formed, characterized by an interaction energy of about -80 kJ mol-1, while the 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridine complex and its methoxy derivative form solvate structures, somewhat resembling the previously studied 8-oxyquinolinate analogues. As far as the spectroscopic properties are concerned, the lowest energy excitation observed in the studied complexes is based on the highest occupied molecular orbital–lowest unoccupied molecular orbital transition, and both these molecular orbitals are centred predominantly on the (N,O)-donor species according to the results of time-dependent density functional theory. Thus, the charge transfer observed for the 8-oxyquinolinate equivalents does not occur in these cases. Consequently, the spectroscopic behaviour of the series is very much comparable with that of the parent imidazo[1,2-a]pyridine derivatives, if the excited-state intramolecular proton-transfer process does not take place, as shown by the absorption and emission spectra collected in toluene and acetone solutions. Complexation causes a reduction in the Stokes shift compared with the respective (N,O)-donor molecules.
关键词： periodic calculations,TDDFT,UV–Vis spectroscopy,X-ray diffraction,time-dependent density functional theory,spectroscopic properties,luminescent boron complexes,transferred aspherical atom model (TAAM) refinement
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE International Conference on Mechatronics and Automation (ICMA) - Changchun (2018.8.5-2018.8.8)] 2018 IEEE International Conference on Mechatronics and Automation (ICMA) - Signal Recognition Method of X-ray Pulsar Based on Instantaneous Amplitude Feature
摘要： The X-ray pulsar signal recognition method based on instantaneous amplitude feature is proposed in this paper. The instantaneous amplitude of the X-ray pulsar signal after Hilbert transform is the main feature of the signal, and the signal recognition algorithm based on the minimum distance of the eigenvector is designed. In the simulation experiment, the feature samples of the pulsar navigation database are constructed. The results show that the proposed X-ray pulsar signal recognition algorithm is effective, which has the advantages of high reliability and fast recognition speed.
关键词： X-ray pulsar,signal recognition,instantaneous amplitude feature,Hilbert transform
更新于2025-09-23 15:22:29
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[ACM Press SIGGRAPH Asia 2017 Posters - Bangkok, Thailand (2017.11.27-2017.11.30)] SIGGRAPH Asia 2017 Posters on - SA '17 - 4D computed tomography measurement for growing plant animation
摘要： Detailed observation of plant growth is essential for botanical analysis and realistic animation design. This study introduces spatial-temporal measurement techniques for a growing plant using X-ray Computed Tomography (CT). We scanned a target plant using CT over the course of couple of days with fixed time intervals to obtain four-dimensional (4D) volumetric images. We present a technique to segment the obtained 4D-CT images semi-automatically. We provide a 4D-CT measurement of budding bean sprouts to illustrate the feasibility of it.
关键词： Plant Animation,4D Measurement,Segmentation,X-ray CT
更新于2025-09-23 15:22:29
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Peripheral Defocus of the Monkey Crystalline Lens With Accommodation in a Lens Stretcher
摘要： PURPOSE. To characterize the peripheral defocus of the monkey crystalline lens and its changes with accommodation. METHODS. Experiments were performed on 15 lenses from 11 cynomolgus monkey eyes (age: 3.8–12.4 years, postmortem time: 33.5 6 15.3 hours). The tissue was mounted in a motorized lens stretcher to allow for measurements of the lens in the accommodated (unstretched) and unaccommodated (stretched) states. A custom-built combined laser ray tracing and optical coherence tomography system was used to measure the paraxial on-axis and off-axis lens power for delivery angles ranging from (cid:2)208 to t208 (in air). For each delivery angle, peripheral defocus was quanti?ed as the difference between paraxial off-axis and on-axis power. The peripheral defocus of the lens was compared in the unstretched and stretched states. RESULTS. On average, the paraxial on-axis lens power was 52.0 6 3.4 D in the unstretched state and 32.5 6 5.1 D in the stretched state. In both states, the lens power increased with increasing delivery angle. From 08 to t208, the relative peripheral lens power increased by 10.7 6 1.4 D in the unstretched state and 7.5 6 1.6 D in the stretched state. The change in ?eld curvature with accommodation was statistically signi?cant (P < 0.001), indicating that the unstretched (accommodated) lens has greater curvature or relative peripheral power. CONCLUSIONS. The cynomolgus monkey lens has signi?cant accommodation-dependent curvature of ?eld, which suggests that the lens asserts a signi?cant contribution to the peripheral optical performance of the eye that also varies with the state of accommodation.
关键词： crystalline lens,accommodation,laser ray tracing,peripheral defocus
更新于2025-09-23 15:22:29
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Electrical Properties of Midwave and Longwave InAs/GaSb Superlattices Grown on GaAs Substrates by Molecular Beam Epitaxy
摘要： In the present work, we report on the in-plane electrical transport properties of midwave (MWIR) and longwave infrared (LWIR) InAs/GaSb type-II superlattices (T2SLs) grown by molecular beam epitaxy (MBE) system on GaAs (001) substrate. The huge lattice mismatch between the T2SL and GaAs substrate is reduced by the growth of GaSb buffer layer based on interfacial misfit array (IMF) technique. In order to compensate the strain in the InAs/GaSb T2SL, we utilized a special shutters sequence to get InSb-like and GaAs-like interfaces. It is found that the MWIR InAs/GaSb T2SL exhibits a p- and n-type conduction at low and high temperatures, respectively. Interestingly, the conduction change temperature is observed to be dependent on the growth temperature. On the other hand, LWIR T2SL conduction is dominated only by electrons. It is important to note that the dominant scattering mechanism in LWIR T2SL at low temperatures is the interface roughness scattering mechanism.
关键词： Hall effect,High-resolution X-ray diffraction,Type-II superlattices,Molecular beam epitaxy
更新于2025-09-23 15:22:29
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Fabrication and Photoluminescence Properties of Monodispersed SiO2@SrAl2Si2O8:Eu2+ Core-Shell Submicron Spheres
摘要： Nanocrystalline SrAl2Si2O8:Eu2+ phosphor layers were coated on the surface of preformed submicron silica spheres by sol-gel method. The resulted monodispersed SiO2@SrAl2Si2O8:Eu2+ core-shell submicron spherical phosphors were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence spectra. The XRD results demonstrated that the SrAl2Si2O8:Eu2+ layers began to crystallize on the SiO2 spheres at 900 °C and the crystallinity increased with raising the annealing temperature. The obtained monodispersed core-shell spherical phosphors have perfect spherical shape with narrow size distribution (average size 500 nm). The Eu2+ shows a strong photoluminescence (dominated by 4f65d1 → 4f7 red emission at 390 nm) due to an efficient energy transfer from vanadate groups to Eu2+. The photoluminescence intensity of Eu2+ increases with raising the annealing temperature.
关键词： Nanostructures,Sol-gel processes,Optical properties,X-ray diffraction,Phosphers
更新于2025-09-23 15:22:29
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Temperature effect on structural, optical and NH<SUB align="right">3 gas sensing properties of TeO<SUB align="right">2 thin films
摘要： TeO2 thin films with different temperatures (400, 450 and 500°C) were deposited on glass substrates by thermal evaporation technique from a Te powder. XRD patterns indicate that as the temperature increases, the crystallisation improves. Observing the images obtained by SEM, it is seen that the grain size decreases as the temperature increases. The optical energy gap of the films was determined from transmittance and reflectance spectra. The optical energy gap decreased continuously from 3.95 eV to 3.80 eV with increasing temperature. Studying the effect of deposition temperature on NH3 gas measurement, it became obvious that as the deposition temperature increases, the sensitivity increases and the response and recovery times decrease.
关键词： scanning electron microscope,XRD,thin films,sensitivity,X-ray diffraction,energy gap,SEM,optical
更新于2025-09-23 15:22:29
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Accuracy validation of incident photon fluence on detective quantum efficiency in mammography
摘要： X-ray image evaluation is commonly performed by determining the detective quantum efficiency (DQE). DQE is calculated with a presampled modulation transfer function (MTF), incident photon fluence, and digital noise power spectrum (NPS). Accurate evaluation of MTF, incident photon fluence, and NPS is important for precise DQE determination. In this study, we focused on the accuracy of the incident photon fluence in mammography. The incident photon fluence is calculated using the squared signal-to-noise ratio (SNRin^2) value as specified in the International Electrotechnical Commission (IEC) 62220-1-2 report. However, the reported SNRin^2 values were determined using a computer program, and the reported values may differ from those calculated from an X-ray spectrum that is measured with actual mammography equipment. Therefore, we evaluated the error range of reported SNRin^2 values in mammography to assess the accuracy of the incident photon fluence. First, X-ray spectra from various mammography systems were measured with a CdTe spectrometer. Six mammographic X-ray units were used in this study. Second, the SNRin^2 values were calculated from the measured X-ray spectra. The calculated values were compared to the reported values. The results show that the percentage differences between the calculated and reported SNRin^2 values were within -4.1% of each other. The results obtained in this study indicate that the SNRin^2 values provided in the IEC report are a robust and convenient tool for calculating the incident photon fluence for DQE evaluation in mammography.
关键词： Incident photon fluence,CdTe spectrometer,Mammographic X-ray spectroscopy,Detective quantum efficiency
更新于2025-09-23 15:22:29
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Diagnostic performance of free-breathing coronary computed tomography angiography without heart rate control using 16-cm z-coverage CT with motion-correction algorithm
摘要： Objectives: To evaluate the feasibility of coronary computed tomography angiography (CCTA) in patients with free-breathing using 16-cm z-coverage CT with motion correction algorithm. Methods: 616 patients underwent CCTA without heart rate control. 325 examinations were performed during breath-holding (group A), and the remaining 291 were performed during free-breathing (group B). The image quality scores were defined as 1 (excellent), 2 (good), 3 (adequate), and 4 (poor). 22 patients in group A and 24 in group B underwent invasive coronary angiography (ICA) after CCTA within two weeks. The image quality score, diagnostic accuracy using ICA as reference, signal-to-noise ratio (SNR), and effective dose (ED) were compared between the two groups. Results: Mean heart rate during scanning was 70.8±13.8bpm in group A and 70.7±13.2bpm in group B (P=0.950). No significant differences were observed in SNR and image quality score (1.49±0.62 vs. 1.53±0.67; P=0.647) between the breath-holding and free-breathing groups. ED (1.99±0.83mSv vs. 2.01±0.88mSv) was not significantly different between the two groups (P=.975). In a segment-based analysis, the sensitivity, specificity and diagnostic accuracy in the detection of coronary stenosis of more than 50% were 82.1%, 96.8% and 92.2%, respectively in the breath-holding group and 82.2%, 96.6% and 92.2%, respectively in the free-breathing group with no significant differences for these parameters between the two groups. Conclusions: CCTA for patients without heart rate control and during free-breathing using 16-cm z-coverage CT with motion correction algorithm showed no significant difference in image quality and diagnostic performance compared with CCTA during breath-holding.
关键词： X-ray computed,Free breathing,Breath holding,Coronary vessel,Tomography
更新于2025-09-23 15:22:29
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Fingerprints of sp1 Hybridized C in the Near-Edge X-ray Absorption Spectra of Surface-Grown Materials
摘要： Carbon structures comprising sp1 chains (e.g., polyynes or cumulenes) can be synthesized by exploiting on-surface chemistry and molecular self-assembly of organic precursors, opening to the use of the full experimental and theoretical surface-science toolbox for their characterization. In particular, polarized near-edge X-ray absorption fine structure (NEXAFS) can be used to determine molecular adsorption angles and is here also suggested as a probe to discriminate sp1/sp2 character in the structures. We present an ab initio study of the polarized NEXAFS spectrum of model and real sp1/sp2 materials. Calculations are performed within density functional theory with plane waves and pseudopotentials, and spectra are computed by core-excited C potentials. We evaluate the dichroism in the spectrum for ideal carbynes and highlight the main differences relative to typical sp2 systems. We then consider a mixed polymer alternating sp1 C4 units with sp2 biphenyl groups, recently synthesized on Au(111), as well as other linear structures and two-dimensional networks, pointing out a spectral line shape specifically due to the presence of linear C chains. Our study suggests that the measurements of polarized NEXAFS spectra could be used to distinctly fingerprint the presence of sp1 hybridization in surface-grown C structures.
关键词： density functional theory,self-assembly,carbynes,on-surface chemistry,near edge X-ray absorption spectroscopy,C 1s absorption
更新于2025-09-23 15:22:29