Image enhancement technology plays a very important role to improve image quality in image processing. By enhancing some information and restraining other information selectively, it can improve image visual effect. The objective of this work is to implement the image enhancement to gray scale images using different techniques. After the fundamental methods of image enhancement processing are demonstrated, image enhancement algorithms based on space and frequency domains are systematically investigated and compared. The advantage and defect of the above-mentioned algorithms are analyzed. The algorithms of wavelet based image enhancement are also deduced and generalized. Wavelet transform modulus maxima(WTMM) is a method for detecting the fractal dimension of a signal, it is well used for image enhancement. The image techniques are compared by using the mean(μ),standard deviation(?), mean square error(MSE) and PSNR(peak signal to noise ratio). A group of experimental results demonstrate that the image enhancement algorithm based on wavelet transform is effective for image de-noising and enhancement. Wavelet transform modulus maxima method is one of the best methods for image enhancement.
考虑到超宽带通信系统对现有其它无线通信系统运行的影响,设计一种具有WiMAX陷波特性的超宽带天线。该天线尺寸大小为0.8 mm ×30 mm ×34 mm,采用圆弧状T形贴片作为辐射单元,并通过在该辐射贴片上开L形槽来实现陷波特性。仿真实验结果表明:天线的带宽为2.9~10.8 GHz,同时具有3.2~3.8 GHz的陷波,平均增益约为4.0 dBi,并具有稳定的准全向性辐射特性。该天线能够满足多种超宽带通信系统的应用要求。
Biocompatible NaREF_4（RE=0.4Y＋0.4La＋0.2（Yb,Er,Tm）（molar ratio）） upconversion nanoparticles（UCNPs） with strong visible fluorescence were synthesized by a solvothermal method and subsequent surface modification. Modulated upconversion luminescence emission spectra were obtained via changing the doping. In vitro and in vivo bioimagings were carried out with shrimps. The upconversion nanoprobes with an acidic/PEG hybrid ligand could quickly capture the basic Rhodamine-B（RB） in shrimp cells and formed a close UCNPs@RB system. The residual organic dye RB in shrimps could be detected on the basis of luminescent resonance energy transfer（LRET）. It could be rapidly addressed based on LRET detection that RB residue existed in the shrimps after incubating in the aqueous solution of RB higher than 3 μg/m L for 12 h.
By using the numerical simulation for the temperature field in the metal organic vapor deposition （MOCVD） reactor by induction heating, it is found that the temperature distribution in the conventional cylinder-shaped susceptor is nonuniform due to the skin effect of the induced current, which makes the temperature distribution of the wafer nonuniform. Therefore, a novel susceptor with a A-shaped slot is proposed. This slot changes the mode and the rate of the heat transfer in the susceptor, which improves the uniformity of the temperature distribution in the wafer. By using the finite element method （FEM）, the susceptor with this structure for heating a wafer of four inches in diameter is optimized. It is observed that the optimized susceptor with the A-shaped slot makes the uniformity of the temperature distribution in the wafer improve by more than 85%, and a good uniformity of temperature distributions is kept under different wafer temperatures, which may be beneficial to the film growth.
Metal organic chemical vapor deposition(MOCVD) is a key equipment in the manufacturing of semiconductor optoelectronic devices and microwave devices in industry. Heating system is a vital part of MOCVD. Specific heating device and thermal control technology are needed for each new reactor design. By using resistance-wire heating MOCVD reaction chamber model, thermal analysis and structure optimization of the reactor were developed from the vertical position and the distance between coils of the resistance-wire heater. It is indicated that, within a certain range, the average temperature of the graphite susceptor varies linearly with the vertical distance of heater to susceptor, and with the changed distances between the coils; furthermore, single resistance-wire heater should be placed loosely in the internal and tightly in the external. The modulate accuracy of the temperature field approximately equals the change of the average temperature corresponding to the change of the coil position.
Lanthanide doped bifunctional materials are potentially important for developing multifunctional devices. Here, NaLuF4:Yb3+/Tm3+/Gd3+/Sm3+ optical-magnetic bifunctional microcrystals were successfully synthesized by hydrothermal method, which could emit ~480 nm blue light from the1G4→3H6 electronic transition and ~800 nm infrared light from the3H4→3H6electronic transition of Tm3+ ion, under the excitation of 980 nm infrared light. By doping Sm3+ ion into NaLuF4:Yb3+/Tm3+/Gd3+, the infrared emission peak centered at 800 nm would shift obviously to longer wavelength. This indicated that Sm3+ ion could efficiently tune the energy level gaps of Tm3+ ions in NaLuF4 host which was demonstrated based on the crystal field theory. In addition, these NaLuF4:Yb3+/Tm3+/Gd3+/Sm3+ microcrystals presented unique ferromagnetic property instead of usually reported paramagnetic prop-erty. Importantly, the ferromagnetic property decreased with increasing the concentration of Gd3+ ion. This was in good agreement with Swift’s theoretical investigation that the coexistence of light rare earth (Gd3+) and heavy rare earth (Yb3+/Tm3+) would lead to the anti-ferromagnetic coupling in the sub-lattices.
Upconversion NaLuF4 nanoparticles were synthesized by the solvothermal method which could emit multicolor visible light under the excitation of 980 nm near-infrared (NIR) photons. These upconversion nanoparticles (UCNPs) with an acidic ligand could rapidly capture the basic rhodamine-B (RB) in plant cells to generate a close UCNPs@RB system. RB could efficiently absorb the green fluorescence from NaLuF4:18 mol.%Yb3+,2 mol.%Er3+ UCNPs and then emitted red light in the UCNPs@RB system by a robust luminescence resonance energy transfer (LRET) from UCNPs to RB. The detection limit of RB with these upconversion fluo-rescent nanoprobes could reach 0.25μg/cm3 in plant cell even under an ultra low excitation power source of 0.2 W/mm2. This LRET phenomenon was also extended to NaLuF4:18 mol.%Yb3+,0.5 mol.%Tm3+@Sodium fluorescein (SF) system. In addition, the differ-ential imaging could be achieved by successively incubating plant cells with fluorescent dyes and UCNPs. The fluorescent dyes ag-gregated in cell wall while UCNPs with surface modification distributed both in cell wall and cytoplasm, so that UCNPs@Dyes formed in cell walls which could emit multicolor light by LRET which was different from the emission in cytoplasm with only UCNPs.
