No abstract

The effect of the optical feedback on the polarization flipping point and hysteresis loop was studied. The polarization flipping occurred at all angles between the polarizer axis and the laser polarization. The polarization flipping point changed by an optical feedback occurred at angles from 0° to 90°. Ability of choosing or controlling the laser polarization was determined by changing the direction of vertical and horizontal polarization by polarizer rotation in the external cavity from 0° to 90°.

In this work, hologram-chaos technique was used to encrypt information as one of the hologram applications using MATLAB program. The results showed that the information to be transmitted in complete secrecy can be easily identified using computer generated holograms through the process of computer hologram reconstruction, so this technique is not able to guarantee the confidentiality of information transmission. When coupling the hologram technology with the chaotic Lorenz system by performing several arithmetic operations of addition, multiplication and division for the matrices of Fourier transforms of the information to be sent (the Mona Lisa image) and the hologram of the Lorenz system, the results showed a complete encryption of the images to be sent and the disappearance of their features using the division process.

Due to the progress of modern technologies in covert communication, in this work a new communication system is proposed using the chaotic system resulting from optoelectronic feedback of semiconductor laser. Where the sinusoidal signal (amplitude A and frequency f were 0.01 a.u and 0.1 a.u respectively) was used to examine the transmission efficiency of the signal and it was found that the purity of the received signal at the receiving unit depends on the amount of synchronization between the two systems, i.e. on the coupling factor between the transmitting and receiving systems. It was found that the ideal value of the coupling factor was 270 a.u at initial condition xi1, yi1, zi1, xi2, yi2, and zi2 are 1, 1, 0.005, 1, 1, and 0.05 respectively, as the two systems showed full synchronization between them. Through the results obtained, it was found that the chaotic system resulting from the optoelectronic feedback (OEFB) presents a modern technique for encoding the signal to send it with high confidentiality, and the reason is due to the wide bandwidth of the spectrum of the chaotic system, which allows easy selection of the appropriate frequency for encoding information, and in this way it was possible to open a new field in secret communications.

The most common materials used for fabrication of denture base are poly methyl methacrylate (PMMA) and methyl methacrylate (MMA). Preparation of heat cured, ultered or modified, denture base acrylic resin was carried out by preparing of poly (methyl methacrylate) Polymer, -PMMA-(75%) and poly vinyl chloride -PVC -(25%), and the liquid part composed of methyl methacrylate -MMA-monomer. All the specimens were cured by using short curing cycle (90 min. at 74ºC followed by 30 min. at 100º C). Some mechanical properties of the prepared material were evaluated in comparison with the control denture base acrylic resin. The polymer was prepared by graft copolymerization method. The total 40 specimens, 20 specimens for each experimental or control material were tested.The results showed that the experimental polymer has hardness and impact strength higher than that of control polymer.