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Corrosion is one of the key technical challenges affecting the large-scale application of magnesium and its alloys.Superhydrophobic surfaces are an effective way to improve the corrosion resistance of magnesium alloys，as they can effectively isolate direct contact between the metal substrate from the corrosive medium，thereby reducing the corrosion rate.A superhydrophobic film composed of Copper-Metal Organic Framework-Stearic Acid (Cu-MOF-SA) was successfully fabricated on an AZ31 magnesium alloy substrate using a one-step electrodeposition method.Comprehensive studies were conducted on the corrosion resistance，chemical stability and thermal stability of the superhydrophobic film.Results showed that the water contact angle of the superhydrophobic film surface reached up to 158°；the sample coated by superhydrophobic film exhibited good corrosion resistance in a 3.5%NaCl solution.Compared with the AZ31 magnesium substrate，the corrosion potential of the superhydrophobic film increased by 0.24 V，and the corrosion current density was reduced by one order of magnitude.The water contact angle of the superhydrophobic film remained larger than 135° after being immersed in solutions with a pH of 1～14 for 24 h.The corrosion potential of superhydrophobic film after being immersed in solution with a pH of 1 for 24 h was 0.21 V higher than that of the AZ31 magnesium substrate.After being insulated in air at 20 ～90 ℃for 24 h，the water contact angle of the Cu-MOF-SA superhydrophobic film’s surface remained above 154°.Additionally，after being insulated in air at 80 ℃for 24 h，the corrosion potential of the superhydrophobic film was 0.22 V higher than that of the AZ31 magnesium substrate.The corrosion current density of the superhydrophobic film was one order of magnitude smaller than that of AZ31 magnesium alloy substrate.In brief，the Cu-MOF-SA superhydrophobic film fabricated in this study demonstrated excellent superhydrophobicity and corrosion resistance.

In a spectroholographic storage system the defocusing method is often used to obtain spectrum uniformity and improve the quality of the recorded information. However, defocusing introduces vignette and stronger interpixel cross talk in the marginal field of view. We report a method that defocuses the aperture and medium together. Based on the pixel spread function, two inequalities are introduced to estimate the upper and lower bounds of the energy received at the CCD. We balance the spectrum uniformity with interpixel cross talk and vignette and then allow the designer to select optimal structure values of the defocusing spectroholographic storage system, i.e., the defocusing value, aperture size, and fill factors for the spatial light modulator and CCD. OCIS codes: 210.2860, 110.0110.

In spectroholographic storage systems the defocusing method is often used for spectrum uniformity and quality improvement of recorded information. The same purpose is served by the fractional Fourier transform (FRFT) storage system. To simplify the numerical analysis, we derive the expressions of the Fraunhofer spectrum and the reconstructed image at the detected plane (CCD) for both cases instead of using the Fresnel spectrum and the FRFT spectrum. The recording aperture, spectrum uniformity, and reconstructed information of both systems are investigated. A numerical comparison is also presented. OCIS codes: 210.2860, 070.0070, 210.0210.

A nonuniform photovoltaic field is created in Fe:LiNb[O.sub.3] during hologram recording exposures. Experimental results and analysis show the degradation of the volume holograms in the presence of the quality. Experimental results to demonstrate the effectiveness of the proposed method are presented. OCIS codes: 090.4220, 090.7330.

A spatial-encoding scheme for the one-step implementation of the optical hit-miss transform (HMT) is presented. The rank-order HMT, which yields better performance in the presence of noise and clutter, can also be carried out by the use of this scheme. Numerical simulations and experimental results have proved the scheme to be feasible. Key words: Hit-miss transform, optical pattern recognition, optical correlation.

A photorefractive optical processor that uses complementary encoding is presented for the real-time implementation of truth-table lookup. Recording a multiexposure hologram in a photorefractive crystal permits different truth-table patterns to be stored. The processor is capable of performing the functions of fall addition, half-addition, subtraction, multiplication, and the calculation of complex multinominal with any number system. Key words: Optical computing, truth-table lookup, photorefractive crystal.

We describe a joint wavelet-transform correlator in which the wavelet function is combined with the input image as the input joint image to realize the wavelet transform of the objective image. The Haar wavelet and the Roberts filter are chosen as the wavelet functions to extract the features of the objective image. The relationship of the Haar wavelet and the Roberts filter is analyzed mathematically based on admissible condition of the wavelet. Computer simulations are provided to verify the theory and to illustrate the performance of this correlator. Key words: Wavelet transform, joint transform correlator, feature extraction.

A chemical cleaving method to improve the resolution of relief modulation in dichromated gelatin is presented. The process (which uses hydroxylamine) yields higher relief resolution and better profile fidelity than a process that uses the enzyme trypsin because it has many fewer cleaving sites. Experiments prove that relief modulation can produce a resolution of as much as 500 lines/mm. With a projection exposure system, a microprism array with a 30-[micro]m-wide, 0.8-[micro]m-high cell is fabricated by this method. A method for forming a continuous relief on dichromated gelatin is also discussed. [C] 2000 Optical Society of America OCIS codes: 000.1570, 050.1970, 160.4670, 220.3740, 230.4000.