Low temperature fired Ni-Cu-Zn ferrite with Bi4Ti3O12

The Ni-Cu-Zn ferrites with different contents of Bi₄Ti₃O₁₂ ceramics (1-8 wt%) as sintering additives were prepared by the usual ceramic technology and sintered at 900 °C to adapt to the low temperature co-fired ceramic (LTCC) technology. The magnetic and dielectric properties of the ferrite can be effectively improved with the effect of an appropriate amount of Bi₄Ti₃O₁₂. For all samples, the ferrite sintered with 2 wt% Bi₄Ti₃O₁₂ has relatively high density (98.8%) and permeability, while the ferrite with 8 wt% Bi₄Ti₃O₁₂ has relatively good dielectric properties in a wide frequency range. The influences of Bi₄Ti₃O₁₂ addition on microstructure, magnetic and dielectric properties of the ferrite have been discussed.     

Optical wavelet de-noising applied in multi-span nonlinear fiber links

In this work, optical wavelet de-noising with several different types of wavelets such as db4, coif4 and dmey wavelet was applied at the end of the 40 Gbit/s multi-span intensity-modulated fiber communication systems. The results of numerical simulations carried out in different fiber links demonstrated that the optical wavelet de-noising method could remove the random amplitude fluctuation induced by the interaction of EDFA’s ASE noise and optical fiber’s dispersion and nonlinearity. The SNR and BER curves of the optical bit sequence without and with optical wavelet de-noising in dispersion compensation fiber link were plotted to show the effectiveness of the wavelet de-noising in the fiber-optic communication systems and wavelet de-noising with demy wavelet can achieve better result than with other type wavelet.     

Gray photorefractive polymeric optical spatial solitons

We show that gray spatial optical solitons are possible in biased photorefractive polymers under steady-state conditions. We find that for a given material parameter the absolute value of a gray photorefractive polymeric soliton's phase decreases with an increase in the beam's grayness, whereas it increases with the material parameter for a given beam's grayness and that the full width half maximum (FWHM) of the gray soliton beam's intensity increases with the beam's grayness when the normalized background intensity and the material parameter are fixed and decreases with an increase in the normalized background intensity when the material parameter is fixed. On the other hand, we also show that N coupled beam evolution equations in biased photorefractive polymers can exhibit multicomponent gray solitons. These multicomponent gray solitons can be obtained provided that the N coupled beams share the same polarization, wavelength, and are incoherent with one another. The characteristics and stability properties of these multicomponent gray solitons are also discussed in detail.     

Densification behavior of gas and water atomized 316L stainless steel powder during selective laser melting

The densification during selective laser melting (SLM) process is an important factor determining the final application of SLM-part. In the present work, the densifications under different processing conditions were investigated and the densification mechanisms were elucidated. It was found that the higher laser power, lower scan speed, narrower hatch spacing and thinner layer thickness could enable a much smoother melting surface and consequently a higher densification.The gas atomized powder possessed better densification than water atomized powder, due to the lower oxygen content and higher packing density of gas atomized powder. A large number of regular-shaped pores can be generated at a wider hatch spacing, even if the scanning track is continuous and wetted very well. The densification mechanisms were addressed and the methods for building dense metal parts were also proposed as follows: inhibiting the balling phenomenon, increasing the overlap ratio of scanning tracks and reducing the micro-cracks.     

Aligned synthesis of multi-walled carbon nanotubes with high purity by aerosol assisted chemical vapor deposition: Effect of water vapor

Aligned multi-walled carbon nanotubes (MWCNTs) with high purity and bulk yield were achieved on a silicon substrate by an aerosol-assisted chemical vapor deposition. The introduction of specific amounts of water vapor played a key role in in situ controlling the purity and surface defects of the nanotubes. The morphology, surface quality and structure of MWCNTs were characterized by secondary and backscattered electron imaging in a field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). Crystallinity and defects of the MWCNTs’ were investigated by high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. In this work, water vapor was found to provide a weak oxidative environment, which enhanced and purified the MWCNTs’ growth. However, excessive water vapor would inhibit the MWCNTs growth with a poor surface quality. In addition, it has been found that the surface morphology of the CNTs can be modified intentionally through producing some surface defects by tuning the amount of the water vapor, which may offer more nucleation sites on the chemically inert CNT surface for various applications such as catalyst support.     

Long SiC nanowires synthesized from off-gases of the polycarbosilane-derived SiC preparation

In this communication, we report on the attempt to make full use of the off-gases from polycarbosilane-derived SiC preparation, and we successfully synthesized long SiC nanowires in large areas with Fe(NO₃)₃ as catalyst. The nanowires have diameters of about 80–300 nm and lengths of millimeters, and they are identified as single crystals β-SiC along the 〈111〉 direction. The VLS mechanism was employed to interpret the nanowire growth.     

Mechanochemical-synthesized Al-doped manganese dioxides for electrochemical supercapacitors

Al-doped MnO₂ as electrode materials for supercapacitor were synthesized by high-energy ball milling. The morphologies and structures of prepared MnO₂ were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Electrochemical investigation indicated that doped MnO₂ presented preferable electrochemical performances than un-doped MnO₂, but there were obvious capacitance decline in the first several dozen of cycles for all doped MnO₂ samples. The Al_0.05/Mn_0.95O₂ electrode, especially, showed the largest capacitance among all prepared MnO₂ samples. Excellent conductivity of Al in doped MnO₂ was considered to be responsible for enhanced electrochemical performances of doped MnO₂.     

Density-functional study of Si<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>C<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 10–15) clusters

Density-functional theory with generalized gradient approximation for the exchange-correlation potential has been used to calculate the structural and electronic properties of Si _n C _n (n = 10–15) clusters. We find that the Si _n C _n clusters prefer cagelike structures. An extensive isomer search shows that the lowest-energy arrangements are those in which the silicon atoms and the carbon atoms form two distinct subunits. It is found that the carbon atoms favor to form fullerene-like structure due to the sp ²-like bond. The silicon atoms are trying to cope with an unfavorable sp ² environment, but distorted tetrahedra still show up somewhere of the cagelike structures. On the basis of the lowest-energy geometries obtained, the binding energy, HOMO–LUMO gap, Mulliken charge, ionization potential and electron affinity of the clusters have been computed and analyzed. An electronic charge transfer from the Si-populated to the C-populated regions is observed.     

Jet ejection from droplets near the Leidenfrost temperature

Abstract  

Droplets impinging on a hot surface that is near the Leidenfrost temperature were experimentally investigated. Ejection of jets from the top of the droplet was observed during the transient interaction between the droplet and a hot wall. We term this phenomenon jet ejection from droplets. When the bottom of the droplet initially impacts the hot surface, a jet is to be ejected from the top of the droplet. The jet ejection occurred only at low impact velocities and around the wetting limit temperature. It was not observed when droplets were dropped from large heights or when the surface was at a high temperature.     

The properties and mechanism of long-term memory in nonparametric volatility

Recent empirical literature documents the presence of long-term memory in return volatility. But the mechanism of the existence of long-term memory is still unclear. In this paper, we investigate the origin and properties of long-term memory with nonparametric volatility, using high-frequency time series data of the Chinese Shanghai Composite Stock Price Index. We perform Detrended Fluctuation Analysis (DFA) on three different nonparametric volatility estimators with different sampling frequencies. For the same volatility series, the Hurst exponents reduce as the sampling time interval increases, but they are still larger than 1/2, which means that no matter how the interval changes, it still cannot change the existence of long memory. RRV presents a relatively stable property on long-term memory and is less influenced by sampling frequency. RV and RBV have some evolutionary trends depending on time intervals, which indicating that the jump component has no significant impact on the long-term memory property. This suggests that the presence of long-term memory in nonparametric volatility can be contributed to the integrated variance component. Considering the impact of microstructure noise, RBV and RRV still present long-term memory under various time intervals. We can infer that the presence of long-term memory in realized volatility is not affected by market microstructure noise. Our findings imply that the long-term memory phenomenon is an inherent characteristic of the data generating process, not a result of microstructure noise or volatility clustering.