Bright Spot Pattern Research Articles

Analysis of optical properties and internal structures of γ-ray-irradiated holographic devices formed using liquid crystal composites

A holographic memory with optical writing information for an optically reconfigurable gate array was fabricated and investigated under increasing γ-ray irradiation doses. The bright spot pattern in a 20 × 17 array, reconstructed from the holographic memory, was correctly reproduced with an increasing radiation dose till 300 Mrad. The diffraction efficiency corresponding to each bright spot was maintained at a high value of 50% and, in some cases, over 60%, indicating radiation resistance up to a total dose of 300 Mrad. In addition, four holographic devices, formed via the same process and under similar conditions using liquid crystal composites, were simultaneously used to evaluate the differences among the multiple samples through polarizing optical microscopy and scanning electron microscopy.

Bright spot analysis for photodynamic diagnosis of brain tumors using confocal microscopy.

In a previous study of photodynamic tumor diagnosis using 5-aminolevulinic acid (5-ALA), the authors proposed using fluorescence intensity and bright spot analyses under confocal microscopy for the precise discrimination of tumorous brain tissue (such as glioblastoma, GBM) from normal tissue. However, it remains unclear if bright spot analysis can discriminate infiltrating tumor in the boundary zone and whether this method is suitable for GBM with no 5-ALA fluorescence or for other tumor types. Brain tumor tissue resected from 5-ALA-treated patients was sectioned to evaluate bright spots under confocal microscopy with a 544.5 - 619.5 nm band-pass filter, which eliminated the fluorescence induced by 5-ALA. Border regions and adjacent normal tissues were observed for differences in bright spot distribution. Histopathology was also conducted by hematoxylin and eosin (H&E) staining of serial slices from the same samples to confirm the locations of tumorous, infiltrating, and normal regions. Bright spot areas were then calculated for the same regions evaluated by histopathology. This method was applied for GBM with and without 5-ALA-induced fluorescence as well as for lower-grade gliomas and other brain tumor types. The bright spot area was substantially smaller in the GBM body than in normal brain tissues. Bright spot area was also smaller in infiltrating tumors than in normal tissue at the margin. The same bright spot pattern was observed in tumorous tissues with no 5-ALA-induced fluorescence and in non-GBM tumors. The bright spot fluorescence is suggested to arise from lipofuscin based on emission spectra (mainly within 544.5 - 619.5 nm) and optimum excitation wavelength (about 405 nm). Bright spot analysis is useful for discriminating infiltrating tumor from bordering normal tissue as an alternative or complement to photodynamic diagnosis with 5-ALA. This method is also potentially useful for tumors with no 5-ALA-derived red fluorescence and other nervous system tumors.

Enhanced Photodetection by Glancing Angle Deposited Vertically Aligned TiO2Nanowires

The TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film (TF) and nanowires (NWs) have been synthesized on Si substrate from pellets of pressed and sintered TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> powder using e-beam evaporation. The glancing angle deposition technique is adopted for the growth of TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> NWs. Field emission gun-scanning electron microscope analysis manifests the growth of vertically aligned NWs of length ~362 nm and diameters ranging from ~50 to ~290 nm. Energy dispersive X-ray analysis of NW sample shows the presence of Titanium (Ti), Oxygen (O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) and Silicon (Si). The transmission electron microscope analysis also confirms successful growth of NWs and the selected area diffraction pattern shows the bright spot patterns from the crystals. X-ray diffraction of TF and NWs deposited at ambient temperature demonstrate multiple peaks from the anatase phase of TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> which supports the selective area diffraction pattern result. Under light exposure, the current densities for TF and NW device are ~5.11 and ~10.03 μA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, at +6.5 V. A maximum photosensitivity of ~10 times is recorded for the NW device at -6.5 V. An excellent response with rise and fall times of ~0.16 and ~0.17 s respectively is observed during switching on and off of white light at +8 V for the NW device, which confirms promising photodetection applications.

Transition between scanning tunneling microscopy images of alkane derivatives on graphite

Self-assembled monolayers of alkylated sulfides containing two alkyl chains and a sulfur atom positioned at the center of the molecules were studied on a graphite surface using scanning tunneling microscopy (STM). STM images of the closed-packed alkyl chains that extend linearly from the sulfur atoms change reversibly between a zigzag pattern and an aligned bright spot pattern on a time scale of minutes. The observation times of the zigzag and aligned bright spot patterns indicate that the difference between the free energies of these two stable molecular configurations with respect to the graphite surface is smaller than their thermal energies in the presence of a solvent, and 10 times smaller than the theoretical free energy between parallel and perpendicular configurations of the alkyl chains on graphite under vacuum. The change in the contrast of the STM images occurred owing to the electronic effects that depend on the registry of the alkyl chains on the graphite surface, and not by the classical observation of transfer between parallel and perpendicular orientations of alkyl chains on the surface.

Detection of Micro-Probe Displacement Using a Shack-Hartmann Wavefront Sensor

To decrease the effort to detect micromechanical features by touch probe measuring systems, multiple touch probes composed in an array are used to measure some of these structures at the same time, owing to the alignment of many similar structures on a wafer. While usually the touch probe signal is read out electronically, in this investigation a Shack-Hartmann sensor is used to observe the reflective back plane of the micro probe array. Shack-Hartmann wave-front sensors use microlens arrays in conjunction with a CCD array. A planar wave-front that is transmitted through a microlens array and imaged on a CCD sensor will form a regular pattern of bright spots. If, however, the wave-front is distorted, the light imaged on the CCD sensor will consist of some regularly spaced spots mixed with displaced spots and missing spots. This information is used to calculate the shape of the wave-front that occurred on the microlens array.

STM images apparently corresponding to a stable structure: considerable fluctuation of a phase boundary of the Si(111)-(square root of (3) x square root of (3))-Ag surface.

We study scanning tunneling microscopy (STM) images near a phase boundary of the Si(111)- (square root of (3) x square root of (3))-Ag surface by using Monte Carlo simulations based on results of first-principles calculations. The boundary is found to fluctuate from snapshot to snapshot, and the feature of the simulated STM images differs distinctly from the observed one with a straightly extending honeycomb pattern of bright spots. Remarkably, statistical averages of the simulated images reproduce the observed feature. This study gives a warning of our tendency to relate STM images revealing clear arrangement of bright spots with some stable structure.

Tunneling Mechanism Implications from an STM Study of H3C(CH2)15HCCCH(CH2)15CH3 on Graphite and C14H29OH on MoS2

The observations reported herein confirm that the bright spots in high-resolution STM images of adsorbed alkanes and alkanols are predominantly due to the electronic and topographic structure of the molecule, and not predominantly due to the substrate. STM images of a monolayer of 17,18-pentatriacontadiene, H3C(CH2)15HCCCH(CH2)15CH3, adsorbed on graphite were obtained to evaluate whether changes in the orientation of the exposed methylene hydrogen atoms relative to the STM tip produced changes in the observed pattern of bright spots in a STM image. STM images of this system showed a pattern of bright spots within individual molecules that appears to change on either side of the allene −CCC− functionality. STM images were also obtained for tetradecanol overlayers on graphite and MoS2 surfaces. The angles and distances observed in the images of tetradecanol on MoS2 were nearly identical to those measured previously in our laboratories for alkanol and alkane monolayers on graphite despite that fact that the separation between bright spots in an STM image of graphite is 2.46 Å, while the separation between bright spots in STM images of MoS2 is 3.16 Å.

Neural networks for seismic principal components analysis

The neural network, using an unsupervised generalized Hebbian algorithm (GHA), is adopted to find the principal eigenvectors of a covariance matrix in different kinds of seismograms. The authors have shown that the extensive computer results of the principal components analysis (PCA) using the neural net of GHA can extract the information of seismic reflection layers and uniform neighboring traces. The analyzed seismic data are the seismic traces with 20-, 25-, and 30-Hz Ricker wavelets, the fault, the reflection and diffraction patterns after normal moveout (NMO) correction, the bright spot pattern, and the real seismogram at Mississippi Canyon. The properties of high amplitude, low frequency, and polarity reversal can be shown from the projections on the principal eigenvectors. For PCA, a theorem is proposed, which states that adding an extra point along the direction of the existing eigenvector can enhance that eigenvector. The theorem is applied to the interpretation of a fault seismogram and the uniform property of other seismograms. The PCA also provides a significant seismic data compression.

Hexagonal spatial patterns for a Kerr slice with a feedback mirror.

We study analytically and numerically a very simple nonlinear optical system, a thin slice of Kerr material with a single feedback mirror. Theoretical analysis shows that for both a focusing and defocusing medium the plane-wave solution is unstable above a certain input intensity and a hexagonal pattern of bright spots should form. The amplitude equations for this system are three coupled Ginzburg-Landau type equations. Numerical analysis confirms these results; moreover by further increasing the input intensity, the hexagonal solution becomes itself unstable and turbulent motion sets in.

Syntactic pattern recognition for the recognition of bright spots

Syntactic pattern recognition techniques are applied to the analysis of one-dimensional seismic traces and two-dimensional seismograms for the detection of bright spots. The calculation between error probability and Levenshtein distance is proposed. The system for two-dimensional seismic analysis includes three kinds of string distance computation to test the continuity of a bright spot pattern.