Table of Contents

Abstract: In this review, recent advances in two-photon absorbing photochromic molecules, as potential materials for 3D optical memory, are presented. The investigations introduced in this review indicate that 3D data storage processing at the molecular level is possible. As 3D memory using two-photon absorption allows advantages over existing systems, the use of two-photon absorbing photochromic molecules is preferable. Although there are some photochromic molecules with good properties for memory, in most cases, the two-photon absorption efficiency is not high. Photochromic molecules with high two-photon absorption efficiency are desired. Recently, molecules having much larger two-photon absorption cross sections over 10,000 GM (GM= 10⁻⁵⁰ cm⁴ s molecule⁻¹ photon⁻¹) have been discovered and are expected to open the way to realize two-photon absorption 3D data storage.

Abstract: Volume phase gratings, recorded in a photosensitive polymer by two-beam interference exposure, are studied by means of optical microscopy. Transmission gratings and reflection gratings, with periods in the order of 10 μm down to 130 nm, were investigated. Mapping of holograms by means of imaging in sectional view is introduced to study reflection-type gratings, evading the resolution limit of classical optical microscopy. In addition, this technique is applied to examine so-called parasitic gratings, arising from interference from the incident reference beam and the reflected signal beam. The appearance and possible avoidance of such unintentionally recorded secondary structures is discussed.

Abstract: The terahertz plasmon dispersion of a multilayer system consisting of graphene on dielectric and/or plasma thin layers is systematically investigated. We show that graphene plasmons can couple with other quasiparticles such as phonons and plasmons of the substrate; the characteristics of the plasmon dispersion of graphene are dramatically modified by the presence of the coupling effect. The resultant plasmon dispersion of the multilayer system is a strong function of the physical parameters of the spacer and the substrate, signifying the importance of the substrate selection in constructing graphene-based plasmonic devices.

Abstract: The underwater contact angle behavior on oxide layers of varying thicknesses was studied. These oxide layers were grown by thermally oxidizing C84400 copper alloys in N₂-0.75 wt.% O₂ and N₂-5 wt.% O₂ gas mixtures at 650 °C. Characterization of the oxidized specimens was effected using X-ray diffraction, scanning electron microscope (SEM) and contact angle goniometer. The results from the X-ray diffraction analyses confirmed the formation of CuO, ZnO and PbO. The average sizes of the oxide granules were in the range of 70 nm to 750 nm, with the average thickness of the oxide layer increasing with the increase in the weight percent of oxygen in the N₂-O₂ gas mixtures. The results showed that the oxide layer growth followed the parabolic law. The underwater oil contact angles increased, due to the change in the surface morphology and porosity of the oxide layer. The small sizes and irregular packing of the oxide granules cause hierarchical rough surface layers with pores. The estimated pore sizes, in the range of 88 ± 40 to 280 ± 76, were predominant on the oxide layers of the samples processed in the N₂-5 wt.% O₂ gas mixture. The presence of these pores caused an increase in the porosities as the thickness of the oxide layers increased. At oxide layer thickness above 25 microns, the measured contact angle exceeded 150° as underwater superoleophobicity was recorded.

Abstract: The editors of Applied Sciences would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2013.

Abstract: In this study, we proposed a method to determine the optimal focal position for micro-holographic storage systems, using vector diffraction theory; the theory provides exact solutions when the numerical aperture (NA) exceeds 0.6. The best diffraction focus was determined by the position and wavelength corresponding to minimal spherical aberration. The calculated refractive index modulation, polarization illumination, and boundary conditions at the interface of different media were analyzed. From the results of our analysis, we could confirm the size of micrograting as a function of NA and wavelength, based on vector diffraction theory, compared with scalar diffraction theory which defines the micrograting by . To demonstrate our analysis, we adapted an optical alignment method using a Twyman-Green interferometer, and could obtain good agreement between analysis and experimental results.

Abstract: Two α-synuclein ligands, 3-methoxy-7-nitro-10H-phenothiazine (2a, K_i = 32.1 ± 1.3 nM) and 3-(2-fluoroethoxy)-7-nitro-10H-phenothiazine (2b, K_i = 49.0 ± 4.9 nM), were radiolabeled as potential PET imaging agents by respectively introducing ¹¹C and ¹⁸F. The syntheses of [¹¹C]2a and [¹⁸F]2b were accomplished in a good yield with high specific activity. Ex vivo biodistribution studies in rats revealed that both [¹¹C]2a and [¹⁸F]2b crossed the blood-brain barrier (BBB) and demonstrated good brain uptake 5 min post-injection. MicroPET imaging of [¹¹C]2a in a non-human primate (NHP) confirmed that the tracer was able to cross the BBB with rapid washout kinetics from brain regions of a healthy macaque. The initial studies suggested that further structural optimization of [¹¹C]2a and [¹⁸F]2b is necessary in order to identify a highly specific positron emission tomography (PET) radioligand for in vivo imaging of α-synuclein aggregation in the central nervous system (CNS).

Abstract: Several techniques have been proposed that attempt to reconstruct a sparse signal from fewer samples than the ones required by the Nyquist theorem. In this paper, an undersampling technique is presented that allows the reconstruction of the sparse information that is transmitted through Orthogonal Frequency Division Multiplexing (OFDM) modulation. The properties of the Discrete Fourier Transform (DFT) that is employed by the OFDM modulation, allow the estimation of several samples from others that have already been obtained on the side of the receiver, provided that special relations are valid between the original data values. The inherent sparseness of the original data, as well as the Forward Error Correction (FEC) techniques employed, can assist the information recovery from fewer samples. It will be shown that up to 1/4 of the samples can be omitted from the sampling process and substituted by others on the side of the receiver for the successful reconstruction of the original data. In this way, the size of the buffer memory used for sample storage, as well as the storage requirements of the Fast Fourier Transform (FFT) implementation at the receiver, may be reduced by up to 25%. The power consumption of the Analog Digital Converter on the side of the receiver is also reduced when a lower sampling rate is used.