GaS multi-walled nanotubes from the lamellar precursor

Inorganic fullerene-like (IF) nanotubes constructed from layered metal chalcogenides are of particular significance because of their excellent physical properties and potential application in wide fields. But very few previous studies were focused on the IF nanotubes of layered III-VI semiconductor. Therefore we investigate the preparation, structure and photoluminescence (PL) properties of GaS nanotube (an important III-VI semiconductor IF nanotube). A simple method is introduced to prepare GaS multi-walled nanotubes for the first time by annealing the natural lamellar precursor in Ar. The reaction temperature is crucial for the formation of nanotube. A suitable temperature range is 500–850 °C. Bulk quantities of GaS nanotubes with diameters of 30–150 nm and lengths up to ten micrometers were produced. Some of these nanotubes show corrugated and interlinked structure and form many segments, demonstrating a bamboo-like structure. As compared to bulk materials, the obvious distinction of the products in PL spectra at liquid nitrogen temperature of 77 K was due to the structure variety. PACS 61.46.+w; 81.07.De; 81.16.Be     

EPR-NMR Signal Enhancement with a Small Computer

A Digital Equipment Corporation PDP 8/S Computer is interfaced with an EPR Spectrameter to achieve signal enhancement.

A computer-based system for spectrum accumulation and noise averaging of EPR or NMR signals has been designed and implemented. The computer-based system was chosen over other perhaps more conventional systems because of its greater flexibility in the processing of spectra, especially after the accumulation is complete.(1)     

Three-dimensional profile measurement of the blade based on surface structured light

As the blade must have precise size and accurate shape, three-dimensional profile measurement of the blade is very important. In this paper, three-dimensional profile measurement method of the blade based on surface structured light is proposed. A new phase unwrapping method is also proposed. This encoding method combined coding fringe pattern with the four-step phase-shifting method, the coding information is embedded into the phase, which can be used to determine fringe order for absolute phase retrieval. The encoding method is simple and easy to implement, so the phase unwrapping of the blade can be quickly perform. The experimental and simulation results show that the method can achieve a high precision, high speed and low cost three-dimensional profile measurement of the blade.     

Focusing of helico-conical cosh-Gaussian beam

Helico-conical beam is attractive for its phase front is nonseparable helical and conical phase function, which produces a spiral intensity distribution occurs at the focal plane. In this letter, the focal properties of cosh-Gaussian beam with helico-conical wavefront were investigated to show that helico-conical phase front does not always produce spiral intensity distribution. On increasing decentered parameters in cosh parts of the beams, the spiral focal pattern evolves into multiple intensity peaks with center main strongest peak. Under condition of higher decentered parameters, the focal spiral curve disappears. In addition, the topological charge also affects the focal pattern considerably.     

Potential PDP phosphors with strong absorption around 172 nm: Rare earth doped NaLaP2O7 and NaGdP2O7

NaLaP₂O₇ and NaGdP₂O₇ powder samples are prepared by solid-state reactions at 750 and 600 °C, respectively, and the VUV-excited luminescence properties of Ln³⁺ (Ln=Ce, Pr, Tb, Tm, Eu) in both diphosphates are studied. Ln³⁺ ions in both hosts show analogous luminescence. For Ce³⁺-doped samples, the five Ce³⁺ 5d levels can be clearly identified. As for Pr³⁺ and Tb³⁺-doped samples, strong 4f-5d absorption band around 172 nm is observed, which matches well with Xe-He excimer in plasma display panel (PDP) devices. As a result, Pr³⁺ can be utilized as sensitizer to absorb 172 nm VUV photon and transfer energy to appropriate activators, and Tb³⁺-doped NaREP₂O₇(RE=La, Gd) are potential 172 nm excited green PDP phosphors. For Tm³⁺ and Eu³⁺-doped samples, the Tm³⁺-O²⁻ charge transfer band (CTB) is observed to be at 177 nm, but the CTB of Eu³⁺ is observed at abnormally low energy position, which might originate from multi-position of Eu³⁺ ions. The similarity in luminescence properties of Ln³⁺ in both hosts indicates certain structural resemblance of coordination environment of Ln³⁺ in the two sodium rare earth diphosphates.     

Realization of an efficient coherent combination via Michelson cavity

An intracavity coherent coupling Michelson erbium-doped fibre (EDF) laser (MCEDFL) is proposed and demonstrated. By using this laser system, we find a means to obtain a maximum power output at the same pumping power level. From the experiment based on fibre Bragg gratings (FBGs) with different reflectivities from 6{\%} to 100{\%}, we find that the reflectivity of the FBG plays a vital role in improving the performance of the MCEDFL. At the same time, the MCEDFL with a polarizer can be coherently combined effectively. This type of system, in principle, is compatible with other more powerful pumping methods, such as cladding pumping, and brings some novel perspectives to the realization of high power lasers.     

High-resolution in vivo imaging of blood vessels without labeling

We demonstrate that both oxyhemoglobin and deoxyhemoglobin have sequential two-color, two-photon absorption properties that can serve as endogenous contrasts in microvasculature imaging. Using a sensitive modulation transfer technique, we are able to image hemoglobin in red blood cells with micrometer resolution, both in vitro and in vivo. We show that excellent contrast from hemoglobin without any labeling can be obtained in tissue.     

A Fe<Superscript>3+</Superscript>/Hg<Superscript>2+</Superscript>-Selective Anthracene-Based Fluorescent PET Sensor with Tridentate Ionophore of Amide/β-Amino Alcohol

A new anthracene-based fluorescent PET sensor 1 with a tridentate ionophore of amide/β-amino alcohol displays very good selectivity and sensitivity for Fe³⁺ (K _a = 1.6 × 10³ M⁻¹) and Hg²⁺ (K _a = 2.1 × 10³ M⁻¹) in CH₃CN–H₂O (3:7, v/v) with detection limit of 1 μM. More fluorescence enhancement was observed when 1 selectively detected Fe³⁺ or Hg²⁺ in CH₃CN and its detection limit was up to 0.03 μM.     

Initiation of petroleum formation and antioxidant function – a DFT study of sulfur?sulfur bond dissociation enthalpies

Experimental studies showed that sulfur radicals play the vital role in petroleum formation. 1 Sulfur‐ centered radicals also exhibit activities in antioxidant functions. Here we conduct a theoretical investigation of their precursor‐disulfides. By investigation into substituent effect on sulfur? sulfur bond dissociation enthalpies (S? S BDEs), we would like to find the most effective provider for sulfur radicals. In the present work, 50 alpha‐substituted disulfides and 16 para‐substituted aryl disulfides are studied systematically, with the general formula XS‐SX or HS‐SX. The substituent effect on S? S BDEs is found to be very eminent, ranging from 33.2 to 75.0 kcal/mol for alpha‐substituted disulfide, and from 43.7 to 59.7 kcal/mol for para‐substituted phenyl disulfides. We also evaluate the performance of 44 density functional methods to get an accurate prediction. A further study indicates that substituents play a major role in radical energies, instead of molecule energies, which is substantiated by the good linearity between XS‐SX bond dissociation enthalpy (BDE) and HS‐SX BDE. Copyright © 2007 John Wiley & Sons, Ltd.     

基于系统非线性的红外焦平面非均匀性校正

采用系统非线性描述和分析方法,从基于红外参考辐射源的校正算法原理入手,提出了一种新的红外焦平面非均匀性校正方法.该算法将每个探测器单元视为一个非线性系统,因此,该算法原理既对基于红外参考辐射源的非均匀性校正算法成立,对基于场景的校正算法在一定条件下也有效,能够适应非均匀性随时间和环境改变而发生缓慢变化的情形,是一种自适应算法.