Talbot Images of an Array Source with Correlated Phase Fluctuation Using the Propagation Law of a Gaussian Beam

Talbot images of a two-dimensional array source such as a surface-emitting array laser are investigated with the help of the propagation law of a Gaussian beam. The effect of the phase fluctuation existing between the elements of the source on the formation of Talbot images is revealed by computer simulation. In the study, the correlation extent of the phase fluctuation is taken into consideration together with its magnitude (standard deviation), and Talbot images of good quality are found to be formed when the correlation extent is larger than the extent of the diffraction of a Gaussian beam in the observation plane. It is further shown that the contrast of Talbot images is governed, in a statistical sense, not by the magnitude of the phase itself but by the phase-fluctuation slope in the array source.     

CW CO2-laser annealing of arsenic implanted silicon

CW CO₂-laser annealing of arsenic implanted silicon was investigated in comparison with thermal annealing. Ion channeling, ellipsometry, and Hall effect measurements were performed to characterize the annealed layers and a correlation among the different methods was made. The laser annealing was done with power densities of 100 to 640 W cm⁻² for 1 to 20 s. It was found that the lattice disorder produced during implantation can be completely annealed out by laser annealing with a power density of 500 W cm⁻² and the arsenic atoms are brought on lattice sites up to 96±2%. The maximum sheet carrier concentration of 6×10¹⁵ cm⁻² was obtained for 1×10¹⁶ cm⁻² implantation after laser annealing, which was up to 33% higher than that after thermal annealing at 600 to 900°C for 30 min.     

Speckle reduction by a rotating aperture at the fourier transform plane

Statistical properties of the time-averaged speckle-reduced pattern at the image plane of a coherently illuminated uniform diffuse object are theoretically and experimentally studied. The diffuse object is assumed to be approximated by a deep random phase screen and zero-mean circular complex Gaussian statistics is also assumed to hold for the formation of speckles. The time-averaging process is performed by using a rotating aperture at the Fourier transform plane of the object. A theoretical study of the speckle reduction is conducted for a rotating Gaussian soft aperture at the Fourier transform plane. Expressions are analytically derived for the mean, autocorrelation function, power spectrum, and contrast of the time-averaged speckle pattern at the image plane. In particular, the contrast of the time-averaged speckle pattern is theoretically evaluated and its characteristics are discussed in detail. The theoretical results for the contrast are experimentally confirmed using a TV/film recording system. Excellent agreement between theoretical and experimental results is obtained.     

Nitrogen implantation in GaAs1−xPx (x=0.4; 0.65)

Nitrogen ions were implanted in GaAs_1−xP_x (x=0.4; 0.65) at room temperature at various doses from 5×10¹² cm⁻² to 5×10¹⁵ cm⁻² and annealed at temperatures from 600°C up to 950°C using a sputtered SiO₂ encapsulation to investigate the possibility of creating isoelectronic traps by ion implantation. Photoluminescence and channeling measurements were performed to characterize implanted layers. The effects of damage induced by optically inactive neon ion implantation on photoluminescence spectrum were also investigated. By channeling measurements it was found that damage induced by nitrogen implantation is removed by annealing at 800°C. A nitrogen induced emission intensity comparable to the intensity of band gap emission for unimplanted material was observed for implanted GaAs_0.6P_0.4 after annealing at 850°C, while an enhancement of the emission intensity by a factor of 180 as compared with an unimplanted material was observed for implanted GaAs_0.35P_0.65 after annealing at 950°C. An anomalous diffusion of nitrogen atoms was found for implanted GaAs_0.6P_0.4 after annealing at and above 900°C.     

Atomic Level Characterization Based on Focus Modulation Electron Microscopy

Defocus image modulation processing and three-dimensional Fourier filtering methods are compared from the viewpoint of application to high-resolution phase transmission electron microscopy. Both methods can successfully correct the spherical aberration in TEM by image processing using through-focus images resulting in resolution improvement from the Scherzer resolution limit to the information limit. Comparing the processed images demonstrates that the potential to determine localized atomic structures between the two methods is at the same level when the sample thickness is thin. However, the achieved signal-to-noise ratio is better in images processed by the three-dimensional Fourier filtering method because the filtering process in Fourier space effectively reduces quantum noises involved in the original images. Spherical aberration-free phase observation by the latter method clearly shows the existence of individual gadolinium atoms in C₈₂ molecules encapsulated in single wall carbon nanotubes. It is demonstrated that the three-dimensional Fourier filtering method works effectively for atomic level characterization even when a sample consisting of light atoms is observed under the condition of a low electron dose.     

Discriminating animal fats and their origins: assessing the potentials of Fourier transform infrared spectroscopy,gas chromatography,immunoassay and polymerase chain reaction techniques

The objective of the reported study was to assess the abilities of various methods to differentiate the sources of fats used in feedstuff formulations. The main target was the identification of tallow (ruminant fat) and its differentiation from non-ruminant fats. Four different techniques were compared in terms of their suitability for enforcing existing and upcoming legislation on animal by-products: (1) Fourier transform infrared spectroscopy (FT-IR) applied to fat samples, (2) gas chromatography coupled with mass spectrometry (GC–MS) to determine fatty acid profiles, (3) immunoassays focusing on the protein fraction included in the fat, and (4) polymerase chain reaction (PCR) for the detection of bovine-specific DNA. Samples of the different fats and oils as well as mixtures of these fats were probed using these analytical methods. FT-IR and GC–MS differentiated pure fat samples quite well but showed limited ability to identify the animal species or even the animal class the fat(s) belonged to; no single compound or spectral signal that could permit species identification could be found. However, immunoassays and PCR were both able to identify the species or groups of species that the fats originated from, and they were the only techniques able to identify low concentrations of tallow in a mixture of fats prepared by the rendering industry, even when the samples had been sterilised at temperatures >133 °C. Fats used in animal nutrition come mainly from the rendering industry, thereby confirming the suitability of PCR and immunoassays for their identification. However, neither of these latter techniques was able to detect premier jus tallow, representing the highest quality standard of fat with extremely low protein concentration.     

Resorufin as an electron acceptor in glucose oxidase-catalyzed oxidation of glucose

Resorufin (1) has been found to act as an electron acceptor in glucose oxidase (GOD)-catalyzed oxidation of glucose. When a 1: 1: 1 mixture of solutions of 1 (5.0 microM), glucose, and GOD (4.0 mg/ml) in phosphate buffer (pH 7.4, 0.1 M) was incubated at 36 degrees C under aerobic conditions and the reaction was followed by a measurement of changes in fluorescence intensity due to 1, only two types of fluorometric traces were observed: (1) when a glucose solution of less than 0.7 mM was subjected to the enzymatic reaction, no consumption of 1 was observed; (2) the reaction with glucose at more than 1.0 mM always consumed 1, affording a regression fluorometric curve, and yet the obtained fluorometric traces could be almost superimposed on one another with no dependence on the glucose concentration. The reasons for the observed phenomena are discussed.     

Selective formation of stable triplexes including a TA or a CG interrupting site with new bicyclic nucleoside analogues (WNA)

Triplex-forming oligonucleotides (TFOs) are potential DNA-targeting molecules and would become powerful tools for genomic research. As the stabilization of the TFO is partially provided by hydrogen bonds to purine bases, the most stable triplexes form with homopurine/homopyrimidine sequences, and a pyrimidine base in the purine strand of the duplex interrupts triplex formation. If a TFO can recognize sequences including such an interrupting site, the target regions in the genome would be expanded to a greater extent. However, this problem has not been generally solved despite extensive studies. We have previously reported a new base analogue (WNA) constructed of three parts, a benzene ring, a heterocyclic ring, and a bicyclic skeleton to hold these two parts. In this study, we have further investigated modification of WNA systematically and determined two useful WNA analogues, WNA-beta T and WNA-beta C, for selective stabilization of triplexes at a TA and a CG interrupting site, respectively. The triplexes with WNA analogues have exhibited an interesting property in that they are more stable than natural-type triplexes even at low Mg(2+) concentration. From comparison of the results with H-WNA-beta T lacking benzene and those with WNA-H without thymine, it has been suggested that benzene is a major contributor for triplex stability and thymine provides selectivity. Thus, it has been successfully demonstrated that WNA-beta T/TA and WNA-beta C/CG combinations may expand triplex recognition codes in addition to the natural A/AT and G/GC base triplet codes. The results of this study will provide useful information for the design of new WNA analogues to overcome inherent problems for further expansion of triplex recognition codes.