Spark plasma sintering synthesis of Ni1−xZnxFe2O4 ferrites: Mössbauer and catalytic study

Nickel-zinc ferrite nanoparticles, Ni_1−xZn_xFe₂O₄ (x = 0, 0.2, 0.5, 0.8, 1.0) were prepared by combination of chemical precipitation and spark plasma sintering (SPS) techniques and conventional thermal treatment of the obtained precursors. The phase composition and structural properties of the obtained materials were investigated by X-ray diffraction and Mössbauer spectroscopy and their catalytic activity in methanol decomposition was tested. A strong effect of reaction medium leading to the transformation of ferrites to a complex mixture of different iron containing phases was detected. A tendency of formation of Fe-carbide was found for the samples synthesized by SPS, while predominantly iron-nickel alloys ware registered in TS obtained samples. The catalytic activity and selectivity in methanol decomposition to CO and methane depended on the current phase composition of the obtained ferrites, which was formed by the influence of the reaction medium.     

Low temperature studies on magnetic properties of Tm2O3

Magnetic properties of Tm₂O₃ were studied by means of magnetometry as well as by heat capacity measurements. The specific heat data were collected down to 0.35 K, and yielded some new information about crystal field splitting of the ³H₆ thulium multiplet. Some anomalous behaviour of the specific heat below 5 K was observed. It turned out, that this anomaly can be nicely described by Schottky contribution originating from crystal field levels distribution of the Tm³⁺ multiplet. No magnetic ordering was evidenced down to the lowest temperatures studied.     

Point target detection utilizing super-resolution strategy for infrared scanning oversampling system

To improve the resolution of remote sensing infrared images, infrared scanning oversampling system is employed with information amount quadrupled, which contributes to the target detection. Generally the image data from double-line detector of infrared scanning oversampling system is shuffled to a whole oversampled image to be post-processed, whereas the aliasing between neighboring pixels leads to image degradation with a great impact on target detection. This paper formulates a point target detection method utilizing super-resolution (SR) strategy concerning infrared scanning oversampling system, with an accelerated SR strategy proposed to realize fast de-aliasing of the oversampled image and an adaptive MRF-based regularization designed to achieve the preserving and aggregation of target energy. Extensive experiments demonstrate the superior detection performance, robustness and efficiency of the proposed method compared with other state-of-the-art approaches.     

尖晶石结构MFe2O4(M=Ca,Mg,Cu,Zn)纳米晶粉末的制备和磁性能

采用新型氨基凝胶自燃法成功制备出尖晶石结构MFe₂O₄（M=Ca,Mg,Cu,Zn）纳米晶粉末。对合成粉体样品的物相、形貌和磁性能进行了详细的研究。经能量色散X射线谱分析确定了合成MFe₂O₄粉末的高纯度。系统地研究了所合成的MFe₂O₄纳米晶粉末的磁性能。所有样品的磁滞回线均较窄,表明了它们具有软磁的特征。经测试得出4种铁氧体的饱和磁化强度（M_s）分别为2.1,29.3,24.1和4.2 emu·g^-1;剩余磁化强度（M_r）分别为0.2,2.3,11.4和0.2 emu·g^-1。这4种铁氧体样品的M_r/M_s值均小于0.5。对CaFe₂O₄和MgFe₂O₄两种典型铁氧体的零场冷却和场冷磁性能作了详细的研究。其中CaFe₂O₄样品的磁化强度在75 K以下有不一致的变化趋势,这是由于其发生了磁相变。     

基于咪唑离子液体的锰（Ⅱ）配合物的合成、晶体结构及发光性能

室温下,通过改变卤化咪唑类离子液体的种类,合成了2个结构和光学性能不同的低维锰(Ⅱ)配合物(C_4H_7N_2)[MnCl_3(H_2O)](1)和(C_4H_7N_2)_2[MnBr_4](2)。采用单晶X射线衍射、光致发光光谱、X射线激发发射光谱、衰减曲线、热重分析等手段对配合物进行了详细的表征。X射线单晶衍射结果表明:配合物1属单斜晶系,P2_1/n空间群,中心离子Mn(Ⅱ)为八面体构型;配合物2属三斜晶系,空间群为■,中心离子Mn(Ⅱ)为四面体构型。在370 nm紫外光的激发下,固体配合物1和2分别发射深红色光和绿色光,其荧光寿命分别为200.11和37.23μs,量子产率分别为23.52%和5.54%,并且在X射线激发下,表现出优良的X射线荧光性能。     

Antireflection coating on germanium for dual channel (3–5 and 7.5–10.6 μm) thermal imagers

The dual channel thermal imager, operating in the 3–5 and 7.5–10.6 μm wavelength bands, is one of the latest achievements in instrumentation for target recognition and acquisition. While the 3–5 μm band is utilised for detecting hot objects such as engine exhausts of vehicles and fighter planes, the 7.5–10.6 μm band is employed for human bodies and objects at ambient temperatures. Many substrates are available which transmit in both these wavelength bands and their transmission can be enhanced by providing a suitable antireflection coating. In this paper, a broad band antireflection coating on germanium substrate is reported. The design approach involves achieving a continuously varying refractive index from that of the incident medium to the substrate. The continuously varying refractive index profile may be generated by using a sequence of thin layers of high and low refractive index materials. In this design a continuous refractive index profile is approximated by using a 13-layer stack of thorium fluoride and germanium as low and high index coating materials respectively. This coating conforms to environmental stability standards and shows an average transmission of 91% in 3–5 μm band and 94.5% in 7.5–10.6 μm band with a peak of 97% at 9 μm on 10 mm thick germanium substrate. Polycrystalline germanium has 2.5% absorption for a 10 mm thick substrate.     

Glass formation and physical properties of Sb2S3–CuI chalcogenide system

Novel chalcogenide glasses of pseudo-binary(100-x)Sb₂S_3-xCuI systems were synthesized by traditional meltquenching method.The glass-forming region of Sb₂S₃-CuI system was determined ranging from x=30 mol% to 40 mol%.CuI acts as a non-bridging modifier to form appropriate amount of [SbSI] structural units for improving the glass-forming ability of Sb₂S₃.Particularly,as-prepared glassy sample is able to transmit light beyond 14 μm,which is the wider transparency region than most sulfide glasses.Their physical properties,including Vickers hardness(Hv),density(ρ),and ionic conductivity(σ) were characterized and analyzed with the compositional-dependent Raman spectra.These experimental results would provide useful knowledge for the development of novel multi-spectral optical materials and glassy electrolytes.     

Measurement and thermodynamic modeling of the phase equilibrium of aqueous N-methyldiethanolamine solutions

Isobaric vapor–liquid equilibrium (VLE) measurements at 40.0, 53.3 and 66.7 kPa (300, 400 and 500 mmHg) of aqueous N-methyldiethanolamine (MDEA) solutions were performed using a modified ebulliometer. The concentration of MDEA in the liquid phase ranged from about 0.06 to 0.93 in mole fraction and the temperatures from about 76 to 186 °C. The data measured in this work, along with other experimental data taken from the literature, are used for the improvement of the thermodynamic modeling of the water/MDEA binary system.     

Static dielectric constant assessment from capacitance over a wide range of electrode separations

Static dielectric constant extraction from two-electrode capacitance measurement over a wide range of electrode separations and dielectric constants involves careful assessment of fringe fields. Finite-element method has been employed to compute capacitance and quantify fringe fields for parallel electrode capacitor of (finite thickness, radii r, electrode separation d), with a homogeneous dielectric medium extending up to the geometric limits of the electrodes. Two distinct regimes, in the fringe field contributions are seen. A procedure to extract the static dielectric constant has been proposed for the first regime and a validation has been provided for the same.     

锥形构象含氟杯芳烃衍生物对铜离子的高选择性识别

合成了具有锥形构象的含氟功能基团的杯芳烃衍生物1~3,并用单晶X射线衍射和核磁共振证实了其锥形构象。在混合溶剂中,研究了杯芳烃衍生物1~3对多种金属离子的识别行为。测试了化合物1~3的紫外-可见吸收光谱和荧光发射光谱,结果显示铜离子对化合物1~3具有明显的荧光猝灭特性,而其它金属离子（如Na^',K^',Cs^',Mg^2',Ca^2',Ba^2',Fe^3',Cd^2',Mn^2',Co^2',Ni^2',Zn^2'）对化合物1~3的紫外-可见吸收光谱和荧光发射强度无显著的影响,表明化合物1~3对铜离子的识别具有高选择性。