Spectral and defect analysis of Cu-doped combustion synthesized new SrAl4O7 phosphor

A simple solution combustion synthesis route for preparation of Cu-doped SrAl₄O₇ has been described. Average particle size of 33 nm and platelet-like morphology has been observed. ESR studies confirm the presence of Cu in polycrystalline SrAl₄O₇. Bright-green luminescence under near-UV irradiation arising due to transition between Cu⁺ levels with microsecond level decay time makes it suitable for application in phosphor converted light emitting diode (LED). TL measurements show broad glow peaks which when deconvoluted indicate activation energies in the range of 0.6-1.1 eV and elucidate the trapping dynamics.     

The dynamic behavior of magnetic fluid adsorbed to small permanent magnet in alternating magnetic field

The dynamic behavior of a magnetic fluid adsorbed to a small NdFeB permanent magnet subjected to an alternating magnetic field was studied with a high speed video camera system. The directions of alternating magnetic field are parallel and opposite to that of the permanent magnet. It was found that the surface of magnetic fluid responds to the external alternating magnetic field in elongation and contraction with a lot of spikes. Generation of a capillary magnetic fluid jet was observed in the neighbourhood of a specific frequency of alternating field. The effect of gravitational force on surface phenomena of magnetic fluid adsorbed to the permanent magnet was revealed.     

Fullerenes as mass sensors: A numerical investigation

This paper investigates the novel development of a mass sensitive nanosensor based on the use of individual spherical fullerenes. The main advantage of the mass sensing ability of spherical fullerenes in comparison with other nanomaterials such as carbon nanotubes (CNTs) or graphene nanoribbons (GNRs) is the fact that they present almost perfect geometric symmetry and thus a unique vibrational behavior which is independent from the location of the externally added nanoparticle. The study is conducted by the use of a computationally effective numerical scheme based on the adoption of appropriate three dimensional line spring elements as well as point mass elements to simulate the atomistic structure of fullerenes and interatomic interactions appearing between carbon atoms. The free vibration of C₂₀, C₆₀, C₈₀ and C₁₈₀ molecules is analyzed without and with an external nanoparticle of specific mass attached on their structure to calculate the arisen change in their natural frequencies and corresponding shape modes. A parametric study concerning the magnitude and location of the added mass is performed in order to evaluate the mass sensing ability of the fullerenes under consideration.     

Frequency analysis of a two-stage planetary gearbox using two different methodologies

This paper is focused on the characterization of the frequency content of vibration signals issued from a two-stage planetary gearbox. To achieve this goal, two different methodologies are adopted: the lumped-parameter modeling approach and the phenomenological modeling approach. The two methodologies aim to describe the complex vibrations generated by a two-stage planetary gearbox. The phenomenological model describes directly the vibrations as measured by a sensor fixed outside the fixed ring gear with respect to an inertial reference frame, while results from a lumped-parameter model are referenced with respect to a rotating frame and then transferred into an inertial reference frame. Two different case studies of the two-stage planetary gear are adopted to describe the vibration and the corresponding spectra using both models. Each case presents a specific geometry and a specific spectral structure.     

Effects of multi-frequency ultrasound pretreatment under low power density on the enzymolysis and the structure characterization of defatted wheat germ protein

The effects of ultrasonic frequency mode, power density, pretreatment time and other parameters under low power density on the degree of hydrolysis (DH) of defatted wheat germ protein (DWGP) and angiotensin-I-converting enzyme (ACE) inhibitory activity of DWGP hydrolysate were studied in this research. Ultraviolet–visible (UV–Vis) spectra, free sulfhydryl (SH), disulfide bond (SS), surface hydrophobicity and hydrophobic protein content of ultrasound-pretreated protein and hydrophobic amino acid (HAA) content of alcalase-hydrolysate of DWGP were measured under optimized ultrasonic condition. The ultrasonic frequency mode with dual-fixed frequency combination of 28/40 kHz showed higher ACE inhibitory activity of DWGP hydrolysate compared with that of other ultrasound frequency modes and all the ultrasonic frequency combinations involving in 28 kHz showed higher ACE inhibitory activity. Under the dual-fixed frequency ultrasound mode of 28/40 kHz, ultrasonic power density of 60 W/L, pretreatment time of 70 min, temperature of 60°C and substrate concentration of 60 g/L, the ACE inhibitory activity of DWGP hydrolysate was the highest with its value of 74.75% (increased by 62.30% compared to control). However, all the ultrasonic pretreatment did not increase the DH of DWGP significantly (p > 0.05). The changes in UV–Vis spectra, SH and SS groups, surface hydrophobicity and hydrophobic protein content indicated that the structure of DWGP unfolded after ultrasound pretreatment. The HAA content of hydrolysate from the pretreated DWGP increased significantly (p < 0.05). The results proved that ultrasound pretreatment loosed the protein structure and exposed more HAA residues of protein to be attacked easily by alcalase. This resulted in the increase in the HAA content which related to the ACE inhibitory activity.     

Effect of glycine–starch mixing ratio on the structural characteristics of MgAl2O4 nano-particles synthesized by sol–gel combustion

Sol–gel auto-ignition was used to prepare nano-scale magnesium aluminate spinel, using nitrate salts as an oxidizer and glycine–starch mixtures as the fuel. The glycine–starch mixture was varied to understand the effect of fuel mixing ratio on the structural characteristics of the resulting magnesium aluminate. The products were characterized by thermogravimetric-differential thermal analyses, Fourier-transform infrared spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller surface area measurements, and transmission electron microscopy. The phase purity and crystallite size of the powder products depended on the fuel mixing ratio. The presence of starch in the fuel facilitated the preparation of pure nano-particles. To prepare nano-particles of uniform spherical morphology and diameter of <13 nm, the starch content should be optimized to avoid agglomeration.     

原位晶化FCC催化剂传质性能的频率响应法辨析

以苯为探针分子,采用频率响应(FR)技术和智能重量分析仪(IGA)研究了原位晶化流化催化裂化(FCC)催化剂上的传质行为。结合N₂吸附和扫描电镜(SEM)剖析所得织构性质数据,并与传统半合成FCC催化剂以及稀土改性Y分子筛传质性能进行对比,结果表明原位晶化FCC催化剂所具有的独特纳米化和高度分散的分子筛组分分布状态,显著改善了基质大孔/介孔结构与分子筛微孔孔道的贯通性,削弱了分子筛孔道与基质界面间的传质阻力,从而优化了成型催化剂颗粒的传质性能。本研究再次证实了频率响应技术可以检测和辨析多孔催化材料体系中发生的复杂吸附-扩散过程,是一种有效的多级孔催化材料传质性能的研究手段。     

光泵THz激光器输出频率稳定特性研究

在太赫兹(THz)成像、雷达探测、相干通信等许多应用领域中,THz辐射源的频率稳定性是直接影响其应用效果的核心问题之一。基于双光子迁移效应建立了光泵THz激光器输出激光频率漂移的物理模型,推导出THz激光频率漂移的解析计算公式。以光泵甲醇(CH₃OH)为例, 给出了不同压强下的甲醇吸收谱线,定量分析了泵浦光频率漂移和泵浦功率对THz激光频率稳定性的影响,并讨论了THz激光腔内工作气体压强对THz激光频率漂移的影响。研究结果表明：随着泵浦光功率的增加,THz激光频率的漂移量逐渐增加;随着THz腔内工作气体压强升高,THz激光的频率漂移逐渐下降;当泵浦光频率漂移量在一定范围时,将出现THz激光的频率漂移量极值,且泵浦光的频率漂移量等于工作气体吸收谱线宽度的1/4时,THz激光输出的频率漂移达到极值。由此可见,在实际工作中,不仅需要合理选择腔内的工作条件(压强、温度),而且还需要采取措施将泵浦光的频率漂移控制在一定范围以内,以提高THz激光的输出频率稳定性。     

基于经验模态分解提高太赫兹频率分辨率的方法

太赫兹频率分辨率是影响物质鉴别的重要因素,但是由于太赫兹时域光谱系统中存在器件反射,使得参考信号和测量信号出现多个反射峰,时域信号长度截断导致频率分辨率很低。为了去除反射峰的影响,提出基于经验模态分解去除时域反射峰,从而提高太赫兹频率分辨率的方法。通过与太赫兹主峰的互相关定位时域反射峰,计算反射峰的上下包络和求平均值,获取本征模函数并代替反射峰,增加时域信号有效长度,提高太赫兹频域分辨率。空气中水蒸汽的太赫兹透射谱实验结果表明,该方法具有自适应去除多个反射峰的能力,对太赫兹时域信号修复效果良好,频率分辨率提高了12倍,而且未丢失有用的吸收谱信息,吸收峰的位置和个数与真实谱一致,很好地保留了太赫兹谱的鉴别能力。     

非对称空间外差光谱仪自适应频率跟踪处理方法

非对称空间外差光谱技术是一种新型的超高分辨率遥感探测技术,要求后期的数据处理技术也具有相应的超高准确度.从数字信号处理的角度,提出了一种自适应的频率跟踪处理方法,根据信号的空间频率来插值补偿信号的相位偏移,并且递归迭代出最接近真实值的相位信息.经仿真实验对比验证表明,在噪声干扰强度不大的条件下,相较于传统傅里叶变换方法,本文算法对信号频率和相位提取的准确度提高了约100倍以上,能够有效降低非对称空间外差光谱技术的系统误差.