| 1. |
- Koeck, Philip J. B.
(författare)
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Missing data in image and signal processing : The case of binary objects
- 2004
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Ingår i: Optik (Stuttgart). - : Elsevier BV. - 0030-4026 .- 1618-1336. ; 115:10, s. 459-472
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Tidskriftsartikel (refereegranskat)abstract
- I investigated which portions of the Fourier transform of binary signals, images and three-dimensional objects are necessary to correctly identify an object in the presence of noise. This is practically possible for very small binary data sets since the total number of possible objects is then very limited. There are for example 512 different binary images with 9 pixels. It is easy to see that this number soon becomes impractically large for bigger images or if one allows more than two possible pixel values. It turns out that even in the presence of large amounts of noise a relatively small portion of the Fourier transform is essential for deciding which of all possible binary objects the Fourier transform belongs to. These 'decision experiments' can be used as a standard for how well algorithms for retrieval of missing Fourier components perform. In another set of computer experiments I investigate the possibility of retrieving various missing Fourier components algorithmically. The main finding of this second set of computer experiments is that the simple retrieval algorithm (a limited form of 'projection onto convex sets') used falls very much short of what one might expect from the 'decision experiments'. I conclude with a discussion what this discrepancy might be due to and some suggestions how to improve the performance of retrieval algorithms for binary objects.
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| 2. |
- Abdullaev, F. Kh., et al.
(författare)
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Management of solitons in medium with competing cubic and quadratic nonlinearities
- 2023
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Ingår i: Optik (Stuttgart). - : Elsevier. - 0030-4026 .- 1618-1336. ; 274
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Tidskriftsartikel (refereegranskat)abstract
- Management of solitons in media with competing quadratic and cubic nonlinearities is investigated. Two schemes, using rapid modulations of a mismatch parameter, and of the Kerr nonlinearity parameter are studied. For both cases, the averaged in time wave equations are derived. In the case of mismatch management, the region of the parameters where stabilization is possible is found. In the case of Kerr nonlinearity management, it is shown that the effective chi(2) nonlinearity depends on the intensity imbalance between fundamental (FH) and second (SH) harmonics. Predictions obtained from the averaged equations are confirmed by numerical simulations of the full PDE’s.
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| 3. |
- Alibakhshikenari, Mohammad, et al.
(författare)
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Broadband 3-D shared aperture high isolation nine-element antenna array for on-demand millimeter-wave 5G applications
- 2022
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Ingår i: Optik (Stuttgart). - : Elsevier BV. - 0030-4026 .- 1618-1336. ; 267
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents the results of a novel 3-D shared aperture 3 x 3 matrix antenna-array for 26 GHz band 5 G wireless networks. Radiation elements constituting the array are hexagonal-shaped patches that are elevated above the common dielectric substrate by 3.35 mm and excited through a metallic rod of 0.4 mm diameter. The rod protrudes through the substrate of 0.8 mm thickness. It is shown that by isolating each radiating element in the array with a wall suppresses unwanted electromagnetic (EM) wave interactions, resulting in improvement in the antenna's impedance matching and radiation characteristics. Moreover, the results show that by embedding hexagonalshaped slots in the patches improve the antenna's gain and radiation efficiency performance. The subwavelength length slots in the patches essentially transform the radiating elements to exhibit metasurface characteristics when the array is illuminated by EM-waves. The proposed array structure has an average gain and radiation efficiency of 20 dBi and 93%, respectively, across 24.0-28.4 GHz. The isolation between its radiation elements is greater than 22 dB. Compared to the unslotted array the improvement in isolation between radiating elements is greater than 11 dB, and the gain and efficiency are better than 10.5 dBi, and 25%, respectively. The compact array has a fractional bandwidth of 16% and a form factor of 20 x 20 x 3.35 mm(3).
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| 4. |
- Andrekson, Peter, 1960
(författare)
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Applications of nonlinear four-wave mixing in optical communication
- 2023
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Ingår i: Optik. - : Elsevier BV. - 0030-4026. ; 279
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Tidskriftsartikel (refereegranskat)abstract
- In this paper I will briefly review some applications of nonlinear four-wave-mixing in optical fibers and silicon-nitride waveguides. This includes ultrafast all-optical waveform sampling and ‘noiseless’ phase-sensitive optical amplification which have been demonstrated to enable signal recovery at very low optical powers.
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| 5. |
- Aqeel-ur, Rehman, et al.
(författare)
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An efficient mixed inter-intra pixels substitution at 2bits-level for image encryption technique using DNA and chaos
- 2018
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Ingår i: Optik (Stuttgart). - : Elsevier BV. - 0030-4026 .- 1618-1336. ; 153, s. 117-134
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, an image encryption system is proposed that uses only addition operation to achieve higher efficiency at diffusion phase after DNA encoding at pixel level. The image is first permuted and then encoded into DNA bases using sub-set of DNA complementary rules chaotically. Afterwards, the adjacent columns of DNA encoded image are added in the substitution phase named as inter-intra pixels substitution which followed by row addition named as inter-pixels substitution. This substitution is performed by adding DNA bases where each DNA base is composed of 2-bits. The addition operation performs randomly between DNA bases named mixed inter-intra pixel substitution. To strengthen security, initial conditions for chaotic maps are computed from SHA-256 hash of plain image which leads to enhance the resistance against known/chosen-plaintext and differential attacks. Due to fewer computational operations, the efficiency of the proposed cipher is high. The simulated results show that the proposed technique is extremely robust against statistical and differential attacks. It successfully surpassed the statistical tests such as Histogram, Correlation, Chi-Square and Entropy. For differential attack, it passed quantitative as well as qualitative Number of Pixel Change Rate (NPCR) and Unified Average Cipher Intensity (UACI) tests in a single round of encryption.
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| 6. |
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| 7. |
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| 8. |
- El-Shabasy, Rehan, et al.
(författare)
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A green synthetic approach using chili plant supported Ag/Ag2O@P25 heterostructure with enhanced photocatalytic properties under solar irradiation
- 2019
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Ingår i: Optik (Stuttgart). - : ELSEVIER GMBH. - 0030-4026 .- 1618-1336. ; 192
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Tidskriftsartikel (refereegranskat)abstract
- As the environmental pollution is a global, catastrophic occurrence, green synthesis of different catalysts has long been pursued. Herein, Capsicum annuum L (chili) extract-based catalysts were used for the fabrication of Ag/Ag2O nanoparticles (NPs) without harsh conditions. The prepared Ag/Ag2O NPs were uniform with an average size of 11.4 nm. The Ag/Ag2O was smoothly coupled with P25 to produce Ag/Ag2O@P25 photocatalyst which had effective electron-hole pair separation and active sites for high photocatalytic activity. The catalyst degraded 98.7% of the model pollutant methylene blue (MB) and catalytic conversion of 100% 2,4-dinitroaniline (2,4-DNA) within 60 s were realized under energy saving solar-light illumination, matching the rules of "green chemistry". In addition, the prepared photocatalyst exhibited superior stability and reusability, and the hot filtration test proved the heterogeneity of the catalyst.
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| 9. |
- Esebamen, Omeime X.
(författare)
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Effect of UV radiation surface damage on silicon position sensitive photodetector
- 2016
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Ingår i: Optik (Stuttgart). - : Elsevier BV. - 0030-4026 .- 1618-1336. ; 127:2, s. 599-602
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Tidskriftsartikel (refereegranskat)abstract
- As a result of the ever increasing energetic UV radiation doses and the need for more radiation hard devices, damage and degradation testing of optical sensors have become very imperative. In this report, results describing the effect of prolonged UV beam irradiation on the performance of a p+n duo-lateral position sensitive detector (lPSD) are reported. The results include the use of a simple method to visualize in 3-dimensional graphs, the effect of radiation damage on the lPSD sensitivity and position detection deviation over the entire active area. The results also show that the ionization damage effects at the Silicon-Silicon oxide interface result in decrease in sensitivity, increase in position detection deviation, and increase in leakage and shot noise current.
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| 10. |
- Hatamvand, Mohammad, et al.
(författare)
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Fabrication parameters of low-temperature ZnO-based hole-transport-free perovskite solar cells
- 2017
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Ingår i: Optik (Stuttgart). - : Elsevier BV. - 0030-4026 .- 1618-1336. ; 40, s. 443-450
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite solar cells (PSCs) are a new generation solar cells. Low-Temperature techniques are used for fabrication PSCs on a flexible substrate that has a low thermal tolerance. In this paper, low-temperature PSCs with ZnO nanoparticles were prepared as electron transport material (ETM) without hole transport material (HTM). Effects of some of the fabrication parameters of low-temperature ZnO based PSCs without HTM, on their principal characteristics and performance, were investigated. Parameters such as the concentration of ZnO nanoparticles (NPs) dispersion, spin coating speed of ZnO NPs, and concentration of CH3NH3I on characteristics and performance of fabricated low-temperature PSCs were studied. The study shows that by changing these parameters, the performance of the fabricated PSCs changes considerably.
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