Comparison of the properties of various optically stimulated luminescence signals from potassium feldspar

Various optically stimulated luminescence signals from K-feldspar have been used to determine the equivalent doses of sediment samples. Understanding the properties of these optical signals is critical to evaluate their applicability and limitations to optical dating. In this paper, some properties of IRSL, post-IR OSL and post-IR IRSL signals (detected in the UV region using U-340 filters) from a museum sample of K-feldspar were investigated by analyzing the relationships between optical and TL signals, and the effect of optical bleaching and heating on optical signals. The trap parameters of the different optical signals were calculated using the pulse annealing method. The results show that this sample exhibits two regenerated TL peaks at ～140 and ～330 °C. Corresponding to the low temperature TL peak, the OSL and post-IR OSL signals appear to be more associated with lower temperature TL than the IRSL signal measured at 50 °C. Corresponding to the high temperature TL peak, the post-IR IRSL signals mainly originate from the more thermally stable traps associated with the high temperature TL, compared with the IRSL and post-IR OSL signals. However, the post-IR IRSL_225 °C signal is shown to be hard to be bleached by blue light and simulated sunlight, compared with the IRSL_50 °C and low temperature post-IR IRSL signals. The implication for optical dating is that the elevated temperature post-IR IRSL signals can be preferentially applied over other signals from K-feldspar, but it is desirable that the effectiveness of the pre-depositional zeroing of these signals is assessed.     

Oxygen vacancy‐induced microstructural changes of annealed CeO2−x nanocrystals

Nanocrystalline ceria (CeO₂) is known for its ionic conductivity and oxygen storage properties, which depend on the presence of oxygen ion vacancies. The vacancies cause several important changes in CeO₂ involving microstrain, electronic structure, magnetic properties, etc. In this article, we focus our attention to the microstructural changes of nanocrystalline CeO_2−x annealed at different temperatures in the range 200–500 °C. Structural and vibrational properties were investigated by X‐ray diffraction and Raman spectroscopy. It was observed that the content of oxygen vacancies changed significantly with increasing annealing temperature, which plays an important role in the observed microstructural changes of the annealed samples. We demonstrate that the observed microstrain changes, because of variable defect content, dominate over the crystallite size effect. This finding is opposite to the conclusions made by several other authors. A new mode, classified as a probable surface mode, was observed in the Raman spectra at ∼480 cm⁻¹, the appearance of which can be explained by the large defective structure and disorder in the ceria lattice. Copyright © 2011 John Wiley & Sons, Ltd.     

An authentication case study: Antonio Palomino versus Vicente Guillo paintings in the vaulted ceiling of the Sant Joan del Mercat church (Valencia,Spain)

In 1695, the Valencian artist Vicente Guillo was engaged in painting the vault of the Sant Joan del Mercat church in Valencia, Spain. After preliminary work was carried out, his contract was cancelled. In 1697, Antonio Palomino, renowned for the publication of his technical treatise entitled El Museo Pictorio y Escala Optica, was finally selected as the painter in charge of decorating the vaulted ceiling of Sant Joan del Mercat. This paper reports an analytical study focused on the characterisation and discrimination of the palette and painting procedures used by Palomino and Guillo in the frescoes of Sant Joan del Mercat. For this purpose, Raman spectroscopy combined with light microscopy, scanning electron microscopy–X‐ray microanalysis, voltammetry of microparticles, X‐ray diffraction, Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry has been employed. The use of gypsum as stucco material for the ground layers contrasts with the recommendations made by Palomino in his treatise about the convenience of using slaked lime‐sand mortars according to traditional fresco recipes. Although lead‐based pigments were not traditionally recommended for frescoes because of their empirically known alterations when subjected to strong alkaline fresco medium, both Guillo and Palomino used them. Palomino, probably supported by his personal experience as a painter, recommended and used Naples yellow, which has been found in a good state of preservation. In contrast, white lead areas found on Guillo's paintings have transformed into lead oxides. Other pigments found in the vaulted ceiling such as smalt, goethite, haematite, azurite and malachite have also undergone substantial changes because of the extreme temperature conditions to which they were subjected in the church. Copyright © 2012 John Wiley & Sons, Ltd.     

红外搜索跟踪系统的半实物仿真系统设计

信息处理组件的设计与验证是红外搜索与跟踪系统研制过程中的关键环节;设计了一个基于嵌入式多媒体系统的红外信息处理组件半实物仿真测试系统,能够通过嵌入式系统完成红外目标场景视频流的实时生成、伺服控制模型的在线解算,软件仿真环境通过以太网与实物系统交互,实现针对红外信息处理组件的半实物闭环仿真测试,为信息处理组件的设计、仿真验证和性能评估提供了集成验证环境,将能够有效缩短整个系统的研制周期,提高研制质量。     

Two-dimensional electron transport in AlGaN/GaN heterostructures

We present a theoretical study of electron transport properties of two-dimensional electron gas in AlGaN/GaN heterostructures. By assuming a drifted Fermi–Dirac distribution and taking into account all major scattering mechanisms, including polar optical and acoustic phonons, background impurities, dislocation and interface roughness, the momentum- and energy-balance equations derived from Boltzmann equation are solved self-consistently. The dependence of the electron drift velocity and electron temperature as a function of the applied electric field are obtained and discussed.     

Evolution of excess electron binding motifs under both internal‐push (from exo C–F bonds) and external‐push (from endo C–F bonds) electron effects in endohedral metallofullerenes with endo C–F bonds

How does the endo C–F bond influence the excess electron binding motif? For lithium‐doped endohedral perfluorofullerenes with endo C–F bonds, under both internal‐push (from exo C–F bonds) and external‐push (from endo C–F bonds) electron effects, the singly occupied molecular orbital electron cloud of the sphere‐like Li···F₈@C₆₀F₅₂ (D₂) is partially dispersed within the σ_p–s antibonding orbital of endo C–F bonds and the space between C^δ+–F_endo^δ– double electric layers, which makes Li···F₈@C₆₀F₅₂ have partial excess electron (electride characteristics) and partial lithium salt characteristics, while in the tube‐like Li···F₂@C₆₀F₅₈ (C_s), as the Li is changing from approaching F to keeping away from F and to approaching another one, the singly occupied molecular orbital electron cloud is mainly dispersed from within the p orbital of the short endo C–F bond to within the middle of the two F atoms and again to within the p orbital of the short endo C–F bond, which indicates an evolution from lithium salt characteristic to excess electron characteristic, and again to lithium salt characteristic. Copyright © 2012 John Wiley & Sons, Ltd.     

Electronic structure and enhanced visible‐light absorption of N,B‐codoped TiO2

We present GGA+U calculations to investigate the electronic structure and visible‐light absorption of N,B‐codoped anatase TiO₂. The N_sB_i (substitutional N, interstitial B) codoped TiO₂ produces significant Ti 3d and N 2p mid‐gap states when the distance of N and B atoms is far, whereas the N_iB_i (interstitial N and B) and N_sB_s (substitutional N and B) codoped TiO₂ prefer to form localized p states at 0.3–1.2 eV above the valence band maximum. Further, the optical band edges of the three codoped systems shift slightly to the visible region, but only the far‐distance N_sB_i codoped TiO₂ clearly shows an optical transition. These results indicate that N_sB_i codoped TiO₂ has a dominant contribution to the optical absorption of N,B‐codoped TiO₂. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)