Preparation of gold nanoparticles on silica substrate by radio frequency sputtering

Radio frequency sputtering of gold on amorphous silica substrates was used for the preparation of Au nanoparticles on SiO2. Deposition experiments were carried out in Ar plasmas under mild conditions (RF power = 5/10 W, total pressure = 0.38 mbar, substrate temperature < or = 210 degrees C), focusing in particular on the effect of sputtering time (5/30 min) and substrate temperature on gold nucleation and coalescence, with the aim of obtaining SiO2-supported Au nanoparticles characterized by precise structural and morphological features. To this aim, several analytical techniques were employed for a thorough characterization of the systems properties, including glancing incidence X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and UV-Vis absorption spectroscopy. In particular, the evolution of optical spectra, i.e., of the surface plasmon resonance peak, was used as a probe for the structural features and was related to the results obtained by other characterization techniques. Gold nanoclusters (phi approximately 4/10 nm) dispersed uniformly on silica matrices were obtained under soft conditions, with morphology ranging from island to cluster like. The obtained results make possible a careful modulation of substrate coverage and gold nanoparticle size.     

A novel technique for synthesis of silver nanoparticles by laser-liquid interaction

Ultrafine particles of many materials have received much attention over the last few years by researchers because of their unique physical and mechanical properties due to increased surface area to volume ratio. A novel laser–liquid interaction technique has been developed to synthesize silver nanoparticles from inexpensive silver nitrate solution in distilled water. The shape, size distribution, microchemistry and crystal structure of the silver nanoparticles were studied using X-ray diffraction, scanning electron microscopy and electron probe X-ray microanalysis.     

Sorting ZnO particles of different shapes with low frequency AC electric fields

Separation of nanoparticles from a mixture of particles with different geometries by applying non-uniform AC electric field is investigated. For this propose, two morphologies of ZnO, rod and cubic shape, were synthesized in two separate processes. Then, they were mixed and dispersed in acetone and exposed to the electric field for being separated. It was found that combination of AC-electroosmosis which is present at low frequencies, and dielectrophoretic (DEP) force exerted on particles in non-uniform AC electric fields may yield to separation of particles based on their shape difference. This paper introduces an effective method for sorting and purification of nanoparticles after chemical synthesis based on their geometrical shape.     

Effect of monodispersed silica nanoparticles on DNA separation by micro-capillary electrophoresis

In this work, we investigate micro-capillary electrophoresis (μ-CE) using monodispersed SiO₂ nanoparticles added to an electrophoresis buffer solution to obtain high mobility and high separation of double-strand DNA. Various particle sizes of monodispersed SiO₂ nanoparticle solutions were mixed with conventional 0.7% hydroxyl propyl methyl cellulose (HPMC) buffer solution to achieve μ-CE. We achieved perfect separation of the DNA specimen (100 bp to 1.5 kbp) at a certain SiO₂ nanoparticle size. In addition, we discuss the effect of SiO₂ nanoparticles during electrophoresis.     

A novel fast balance technique for the digital AC bridge

A wide range, fast balance technique for digital AC bridges is proposed in this paper. We introduce a novel method that can give the balance parameters of a digital AC bridge in a closed form. Unlike the traditional heuristic methods used to balance AC bridges, the proposed method only needs to arbitrarily change one adjustable parameter two times including the setting of original values. The balance parameters can then be computed using two closed-form formulas. Finally, the applicability of the proposed theory is discussed, and simulation examples are given and analyzed. Our algorithm is noniterative and precise and offers clear benefits for real-world applications     

A new high-precision optical technique to measure magnetostrictionof a thin magnetic film deposited on a substrate

The drive in data storage technology towards utilizing magnetic films with lower magnetostriction (to reduce the magnetoelastic energy term) and reduced thickness has resulted in the requirement for more sensitive, reliable, and easy-to-use tools to monitor magnetostriction. A measurement tool based on an in-plane rotating and saturating magnetic field and laser-beam-deflection technique, which is able to meet these requirements, is described. The tool developed offers high accuracy, large dynamic range, long-term stability, simple sample insertion, and a fast, easy measurement procedure. With this tool, the measurement of small magnetostriction coefficients of thin soft-magnetic films can become a simple, fast, and reliable procedure, thus helping the development of magnetic thin-film production processes and routine composition control     

A simple technique for analog tuning of frequency synthesizers

An analog implementation of the fractional N-phase-locked-loop variable-frequency synthesis technique is presented. In addition to its simplicity, this implementation allows tuning over broad frequency ranges. The synthesizer was developed in response to a need for a compact, low-power, local oscillator for a swept heterodyne, low-frequency, battery-operated, portable spectrum analyzer. The resulting prototype synthesizer was constructed on a 4-in×4-in circuit board using standard CMOS integrated circuits. The total power requirements were +7 V at 8 mA and -7 V at 1 mA when the synthesizer is operated in the 380-580-kHz frequency range. Further reductions in size may be expected from the use of surface mount devices. Spectral data are presented for the prototype circuit serving as the local oscillator in a prototype swept-frequency spectrum analyzer. That is, instead of a spectral analysis of a fixed synthesizer frequency, the synthesizer was swept through a range of frequencies about a stable reference applied to the input of the prototype analyzer. Thus the results are conservative , since they include the effects of noise coupled to the sweep voltage from other circuitry within the prototype analyzer. This method of evaluation demonstrates one of the distinct advantages of this circuit     

低频成分的频谱校正

目前已经提出了多种频谱校正方法,但是将它们应用于低频成分时,其精度显著下降,这是由于模型忽略了实信号所包含的负频率的贡献.给出了一种考虑负频率贡献的显式校正新方法,它利用局部谱峰附近的3条谱线.采用351×180个仿真样本对提出的方法进行了考核.不同仿真样本所含低频成分的周期数(CiR)从1变化到8,步长为0.02;相位从0°变化到179°.步长为1°.考察了每个CiR的180个不同相位算例的最大误差.结果表明:1)就所考查的参数范围,校正频率的误差小于0.000 6△ω(△ω为快速傅立叶频率分辨率);2)幅值和相位误差上限不超过0.3%和0.3°;3)误差的大体趋势随CiR增加而下降,精度最高的条件仍然是整周期采样.     

Fabrication of resistive CO gas sensor based on SnO2 nanopowders via low frequency AC electrophoretic deposition

A resistive CO gas sensor has been fabricated using AC electrophoretic deposition (ACEPD) technique. SnO₂ thick films are deposited by applying low frequency (0.01–1,000 Hz) AC electric field to a stable suspension of SnO₂ nanoparticles in acetyl acetone. A carbon film base electrode is used as deposit substrate. Effect of CO gas exposure on conductivity of the SnO₂ film at 300 °C is investigated. Results show that the sensor is sensitive and its response is repeatable. This work shows that ACEPD can be used as an easy and cheap technique for fabrication of electronic devices such as ceramic gas sensors.     

A swept frequency multiplication technique for air-coupled ultrasonic NDE

A new technique has been investigated for improving the signals that can be obtained in air-coupled nondestruction evaluation (NDE). This relies on the wide bandwidth available from polymer-filmed capacitive transducers. The technique relies on a swept-frequency "chirp" signal, which is transmitted from a transducer in air. The new technique differs from existing time-domain correlation techniques, such as pulse compression, in that a single multiplication process is performed in the time domain to give a difference frequency signal. This then can be isolated easily in the frequency domain. It will be demonstrated that this new swept frequency multiplication (SFM) approach gives the potential for rapid air-coupled imaging.     

A high resolution digital frequency meter for low frequencies

A digital frequency meter using frequency multiplication is described. It can be used in utility power system control centers and other low-frequency applications where resolutions of the order of 1/100 Hz and almost instantaneous readouts are essential. Possible improvements of the circuit are suggested     

A new kind of energy transfer from high frequency mode to low frequency mode in a composite laminated plate

This paper brings to light a new type of nonlinear resonant motion in a fiber-reinforced composite laminated rectangular thin plate, which is not reported in other literature. The investigated system is a simply supported symmetric cross-ply composite laminated rectangular thin plate subjected to parametric excitation whose frequency is near to the first-order natural frequency of the plate. This new phenomenon demonstrates that the responses of a low-order frequency mode can be excited by those of a high-order frequency mode. The high-order frequency is the first-order natural frequency of the test plate, and the low-order frequency here is lower than the first-order nature frequency. Experimental research works on the nonlinear vibrations of the composite laminated rectangular thin plate have been carried out for the first time. It is found from the experimental results that the nonlinear dynamic responses consist of four modes, whose frequencies include a lower frequency than the first-order natural frequency, 1/3 sub-harmonic, 2/3 sub-harmonic and the first-order natural frequencies. In this case, the amplitude of the mode for lower frequency is larger than those of modes for the aforementioned frequencies. Moreover, the theoretical job goes to analyze this new phenomenon. An analytical mode is given to explain the interactions between the first-order mode and the lower-frequency mode observed in the experiment. Based on Reddy’s third-order shear deformation plate theory, the nonlinear governing equations of motion are formulated for the test plate under parametric excitation. Galerkin’s method is utilized to discretize the partial differential governing equations of motion for the composite laminated rectangular thin plate to a two-degree-of-freedom nonlinear system. The results of numerical simulations qualitatively agree very well with the experimental results. In addition, the multi-pulse chaotic motions are also found in numerical simulations.     

An investigation on the behavior of electrospun ZnO nanofibers under the application of low frequency AC electric fields

In present study, the behavior of electrospun ZnO nanofibers under the application of low frequency alternating (AC) electric fields within the range of 1 Hz–20 kHz was investigated using planar parallel electrodes. In the first stage, ZnO nanofibers with diameters up to 100 nm were prepared by electrospinning. At 1 Hz, the strong electric field-induced fluid flow due to charge redistribution around the electrode swept the fibers on the electrode surface farther from the edges. As the frequency was increased to 1 kHz, most depositing fibers accumulated on the electrode edges and in the meantime, a small fraction of them was pushed into the surface as a result of AC electroosmosis effect. Above 1 kHz, the fibers were assembled within the electrode gap bridging the interelectrode space. The dielectrophoresis force was considered responsible for the assembly and relative alignment of ZnO nanofibers above 1 kHz.     

Diffractive electron imaging of nanoparticles on a substrate

The observation of the detailed atomic arrangement within nanostructures has previously required the use of an electron microscope for imaging. The development of diffractive (lensless) imaging in X-ray science and electron microscopy using ab initio phase retrieval provides a promising tool for nanostructural characterization. We show that it is possible experimentally to reconstruct the atomic-resolution complex image (exit-face wavefunction) of a small particle lying on a thin carbon substrate from its electron microdiffraction pattern alone. We use a modified iterative charge-flipping algorithm and an estimate of the complex substrate image is subtracted at each iteration. The diffraction pattern is recorded using a parallel beam with a diameter of approximately 50 nm, illuminating a gold nanoparticle of approximately 13.6 nm diameter. Prior knowledge of the boundary of the object is not required. The method has the advantage that the reconstructed exit-face wavefunction is free of the aberrations of the objective lens normally used in the microscope, whereas resolution is limited only by thermal vibration and noise.     

A note on the low frequency diffraction of elastic waves by a Griffith crack

The two dimensional problem of the diffraction of normally incident compressional and antiplane shear waves by a Griffith crack in an infinite isotropic elastic medium is considered. For wavelengths long compared to the crack length, the stress intensity factors as well as the maximum crack openings are expressed in series of ascending powers of the normalized wave number. The approximate solutions are compared with exact solutions obtained in a previous paper[1], for a Poisson's solid. The results indicate that a five term expansion of each of the series solutions is sufficiently accurate for most problems of practical interest.     

A new recoil distance technique using low energy coulomb excitation in inverse kinematics

We report on the first experiment combining the Recoil Distance Doppler Shift technique and multistep Coulomb excitation in inverse kinematics at beam energies of 3-10 A MeV. The setup involves a standard plunger device equipped with a degrader foil instead of the normally used stopper foil. An array of particle detectors is positioned at forward angles to detect target-like recoil nuclei which are used as a trigger to discriminate against excitations in the degrader foil. The method has been successfully applied to measure lifetimes in ¹²⁸Xe and is suited to be a useful tool for experiments with radioactive ion beams.