Orthogonal multi-distorted invariant Complex Exponent Moments (CEMs) are proposed. A fast and accurate 2-D Fast Fourier Transform (FFT) algorithm is used to calculate CEMs. Theoretical analysis is presented to demonstrate the multi-distorted invariant property of CEMs. The proposed method is applied in the pattern recognition of human faces, English letters and Chinese characters. Experimental results show that CEMs have higher quality and lower computational complexity than RHFMs in image reconstruction and pattern recognition.
Free-standing GaN substrates are urgently needed to fabricate high-power GaN-based devices. In this study, 2-inch free-standing GaN substrates with a thickness of ~250 μm were successfully fabricated on double-polished sapphire substrates, by taking advantage of a combined buffer layer using hydride vapor phase epitaxy (HVPE) and the laser lift-off technique. Such combined buffer layer intentionally introduced a thin AlN layer, using a mix of physical and chemical vapor deposition at a relatively low temperature, a 3-dimensional GaN interlayer grown under excess ambient H2, and a coalescent GaN layer. It was found that the cracks in the epitaxial GaN layer could be effectively suppressed due to the large size and orderly orientation of the AlN nucleus caused by pre-annealing treatment. With the addition of a 3D GaN interlayer, the crystal quality of the GaN epitaxial films was further improved. The 250-μm thick GaN film showed an improved crystalline quality. The full width at half-maximums for GaN (002) and GaN (102), respectively dropped from 245 and 412 to 123 and 151 arcsec, relative to those without the 3D GaN interlayer. The underlying mechanisms for the improvement of crystal quality were assessed. This method may provide a practical route for fabricating free-standing GaN substrates at low cost with HVPE.
We report here the FeMnP1−xGaxcompounds could be a possible candidate refrigerant for room-temperature magnetic refrigeration.
Recent fabrication of graphene nanoribbon (GNR) based field effect transistor (FET) has made all-carbon electronic device a reality. GNR can be metal or semiconductor with the variation of its edge orientation and width and is expected a promising material for quantum electronic devices in the future. In addition, magnetic properties which are difficult to be exploited in conventional semiconductor devices can be easily manipulated in GNRs via artificially introducing defects or doping. This great advantage together with the long coherence distance for both charge and spin in these structures has made GNR a very intriguing material for spintronics as well as electronics. In particular, zigzag GNR is one of the most attractive systems due to its peculiar edge states, which are showing ample potential in spintronic applications. Different methods have been proposed to developing useful properties of ZGNRs with the help of defects, gate voltage, chemical adsorption, doping, etc.We report ab initio simulations of spin transport in zigzag GNRs of different width when one carbon in various distances from the edge is substituted by an atom of other elements such as 0, AI, B, Be, and P etc., as illustrated in Fig.l, within the framework of density functional theory (DFT) combined with non-equilibrium Green's function (NEGF) method implemented in Atomistic TooKits. In some cases, this system shows unique properties different from those previously reported. For a perfect semiconductor 4-ZGNR, the transmission spectrum shows a gap near the Fermi energy with a narrow two-channel peak at the lower boundary of the gap. When a C atom at edge is substituted by a Be atom, it remains in similar profile with reduced amplitudes for spin-down electrons, but for spin-up electrons the transmission peak disappears and an extra narrow side gap appears at the upper boundary of the main gap as shown in Fig.2. The contrast effects of the doping on the spin-up and spin down energy bands and transmissions result in strong spin dependent charge transport.Negative differential conductance may appear only for spin-down electrons in the considered bias range as shown in Fig.3.
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