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Abstract-Recently, Wang introduced a novel (2, n) region incrementing visual cryptographic scheme (RIVCS), which can gradually reconstruct secrets in a single image with multiple security levels. In RIVCS, the secret image is subdivided into multiple regions in such a way that any t shadow images, where 2 ≤ t ≤ n, can be used to reveal the (t − 1)th region. However, Wang's scheme suffers from the incorrect-color problem, which the colors of reconstructed images may be reversed (i.e., the black and white are reversed). If the color of text is also the secret information, the incorrect-color problem will compromise the secret. Additionally, Wang's scheme is only suitable for the 2-out-of-n case, i.e., (k, n)-RIVCS where k = 2. In this paper, we propose a general (k, n)-RIVCS, where k and n are any integers, that is able to reveal correct colors of all regions. This paper has made three main contributions: 1) our scheme is a general (k, n)-RIVCS, where k and n can be any integers; 2) the incorrectcolor problem is solved; and 3) our (k, n)-RIVCS is theoretically proven to satisfy the security and contrast conditions. Index Terms-Image secret sharing, secret sharing, visual cryptography, visual secret sharing.

Maleic anhydride grafted poly(lactic acid) (PLA g MAH) was prepared by blending with wood flour (WF). The effect of MAH and WF inclusion on the mechanical and thermal properties of the compos ites was examined. PLA g MAH/WF had optimum tensile properties compared with PLA/WF. Scanning electron microscopic images indicated poor interfacial adhesion of the PLA/WF. It was enhanced after MAH was grafted onto PLA; the PLA g MAH/WF showed excellent compatible morphology. Results also revealed that the biodegradation of PLA and PLA g MAH was improved with increasing of WF content.

*In this study, biodegradable fluorine-containing polyurethanes (PU/OFHD) were synthesized using 4,4'-diphenylmethane diisocyanate, polycaprolactone diol (PCL), and 2, 2,3,3,4,4,5,5,. PCL is a biodegradable soft segment, and OFHD is a fluoro chain extender. In addition, other polyurethanes (PU/HD) were synthesized using 4,4'-diphenylmethane diisocyanate, PCL, and another chain extender [i.e., 1,6-hexanediol (HD)] for comparison.Gel permeation chromatography analysis indicated that the molecular weight of PU/OFHD is greater than that of PU/HD.19 F nuclear magnetic resonance analysis revealed that the OFHD chain extender was successfully incorporated into the backbone of PU. According to Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses, strong interactions between the C=O and CF 2 groups in PU/OFHD exist. Based on thermal analysis, PU/OFHD exhibited an initial decomposition temperature that was 6.5-7.9°C higher than that of PU/HD. Differential scanning calorimetry and dynamic mechanical analysis analyses indicated that both the glass transition (Tg) and dynamic Tg of PU/OFHD are higher than those of PU/HD. Mechanical property analysis demonstrated that the tensile strength of PU/OFHD is higher than that of PU/HD. Moreover, PU/OFHD exhibited better chemical resistance than PU/HD. The scanning electron microscope images indicated that both PU/HD and PU/OFHD exhibited higher hydrolytic degradation at a higher PCL content. However, PU/OFHD is less degradable than PU/HD. Copyright