Moire Interference Research Articles

Commensurate and incommensurate double moire interference in graphene encapsulated by hexagonal boron nitride

Interference of double moire patterns of graphene (G) encapsulated by hexagonal boron nitride (BN) can alter the electronic structure features near the primary/secondary Dirac points and the electron-hole symmetry introduced by a single G/BN moire pattern depending on the relative stacking arrangements of the top/bottom BN layers. We show that strong interference effects are found in nearly aligned BN/G/BN and BN/G/NB and obtain the evolution of the associated density of states as a function of moire superlattice twist angles. For equal moire periods and commensurate patterns with Δφ = 0° modulo 60° moire angle differences the patterns can add up constructively leading to large pseudogaps of about ∼ 50 meV on the hole side or cancel out destructively depending on their relative sliding, e.g. partially recovering electron-hole symmetry. The electronic structure of moire quasicrystals for Δφ = 30° differences reveal double moire features in the density of states with almost isolated van Hove singularities where we can expect strong correlations.

Cause and origin of moire interferences in recursive processes and with fixed-point and floating-point data types

In the calculation of the map of periods of the Mandelbrot Set and working with fixed-point and floating-point real number representation systems, moire interference patterns always appear. These result from the discretization that every computer sets in the finite encoding of its real values. It is not known from which original layers such interferences are obtained and how these initial layers are generated. This article aims at answering these two questions. In order to search these original layers thousands of images —created by means of two different encodings of the real values and with different accuracies— of the map of periods were analyzed. Some points with constant location, called Source Points, around which regular patterns with hyperbolic configuration are generated, were located as well. This answers the questions regarding the cause and origin of moire interferences. Some characteristics of Source Points are described hereinafter. It is also justified why moire interferences in the plane of periods have a hypersensitive behavior. Finally, it is shown how in dynamic systems accuracy does not only affect the precision of results, but also the configuration of the results themselves. The following interesting reflection is, therefore, open to discussion: if the real world should be seen with a fractal way of looking, accuracy configurates then the essence of everything.

Principle and observation of fluorescence moiré fringes for alignment in print and imprint methods

The authors report the principle and experimental observation of fluorescence moiré interference fringes for alignment in the print and imprint methods. Concave bar and cross alignment marks on a silica mold and substrate without the deposition of any light-shielding or high-refractive-index layers could be visualized by fluorescence microscopy with a fluorescent liquid sandwiched between the patterned surfaces. Fluorescence moiré interference fringes with a pitch of 44 μm were generated by the superimposition of two sets of mold bar arrays with respective pitches of p1 = 4.0 μm and p2 = 4.4 μm on substrate bar arrays with different periodicity of p2 and p1 through a thin fluorescent liquid layer. The fluorescence moiré fringes were attributed to an additive-type generation by the interference of two luminous gratings with different periodicities, which was different from a multiplicative-type generation by the superimposition of two light-shielding metal gratings with different periodicities under illumination. Coarse alignment with 2-μm-wide cross marks was performed by manually operating the substrate-side stages, and the misalignment was evaluated with the two sets of fluorescence moiré fringes. The alignment method by fluorescence microscopy with a fluorescent liquid provided the possibilities of not only fine alignment with fluorescence moiré fringes but also in situ monitoring of the residual layer thickness formed between the mold and substrate surfaces before curing for ultraviolet nanoimprinting.

Local interaction in retinal ganglion cell mosaics can generate a consistent spatial periodicity in cortical functional maps

Orientation map is one of the most studied functional maps in visual cortex, but the developmental mechanism of its consistent spatial periodicity is still elusive. Recently, a theoretical model suggested that a moire interference pattern between ON and OFF retinal ganglion cell (RGC) mosaics can develop a quasi-periodic orientation map, but it is remained unclear how this can explain the constant periodicity of the maps [1]. Here we suggest a developmental model that a simple local interaction in RGCs can generate a consistent spatial periodicity of orientation preference, by inducing (i) a hexagonal lattice structure in ON/OFF RGC mosaics and (ii) a constant alignment angle between them. First, we introduced a developmental model of a monotypic RGC mosaic to show that a local repulsive interaction can generate a hexagonal structure (Figure ​(Figure1A).1A). Previously, in the model study of the pairwise interaction point process, it was suggested that a local interaction alone cannot develop a long-range order in the mosaic structure [2]. We assumed a different type of local repulsive interaction that the cell positions can be gradually shifted by a repulsion from the neighbor cells and confirmed that this model can develop a long-range ordered structure that is well fitted to a hexagonal lattice. Figure 1 Simulation of RGC mosaics and orientation map. A. Development of monotypic mosaic and auto-correlation. B. Heterotypic interaction depends on inter-layer distance. C. Moire interference pattern of ON/OFF RGC mosaics. D. Simulated orentation map. ... Next, we assumed that there also exists a heterotypic repulsive interaction between ON and OFF RGC mosaics and examined how this can affect the alignment between the two mosaics (Figure ​(Figure1B).1B). When the inter-layer distance between ON/OFF mosaics was varied within a proper interval, the hexagonal structure was preserved in each mosaic, but the alignment angle (θ) between the two mosaics was restricted within a certain range of angles, and this induced a constant spatial periodicity in the ON/OFF interference pattern (Figure ​(Figure1C).1C). As observed in the moire interference, we confirmed a consistent hexagonal periodicity in the cortical orientation map that are simulated by statistical wiring model from the developed RGC mosaics (Figure 1D,E) [3].

Magic C60 islands forming due to moiré interference between islands and substrate

Recently proposed mechanism for self-organized formation of magic islands [Nat.Comm. 4(2013)1679] has received a new experimental confirmation. According to this mechanism, self-assembly is mediated by the moire interference between an island and underlying substrate lattice. It was first detected at C60 island growth on In-adsorbed Si(111)3×3-Au surface. Changing In adsorbate for Tl results in lowering the corrugations of the surface potential relief due to a greater surface metallization. This allows formation of the C60 arrays with novel moire pattern. As a result, a new set of magic C60 islands is formed on Tl-adsorbed Au/Si(111) surface differing from that observed on In-adsorbed surface. For example, the 19-C60 magic island which has a non-compact boomerang shape on In-adsorbed Au/Si(111) surfaces adopts a shape of a regular hexagon on Tl-adsorbed surface.

Life imitates op art

The beautiful, undulating orientation maps in visual cortex have motivated many developmental models. A new study finds that this functional organization could be seeded in the retina by moire interference between mosaics of ON-center and OFF-center retinal ganglion cells.

Experimental Studies on Thermal Strain of Aerial Laminated Glasses

Experimental studies on thermal strain of aerial laminated glasses by virtue of Moire Interferometry were done. The experimental results were as follows: in the U patterns of moire interference fringe, with temperature increasing, the fringes became denser and the thermal strain was augmented. In the V patterns of moire interference fringe, the sequence of the fringe patterns increased is intermediate film layer, external shielding layer and main bearing layer, respectively. The U and V fringe patterns results analyzed by digital image process system indicate that, with temperature increasing, the strain εx decreased. Because the difference of coefficients of thermal expansion of three materials is very large, the thermal strain is generated significantly, and the interlayer thermal shear strain exists in the end and intermediate position of the free boundary of the laminated glass.

Real-space mapping of magnetically quantized graphene states

Real-space mapping of the quantum Hall state at the Dirac point in epitaxial graphene reveals unexpected localized lifting of the degeneracy of this level. This could be the result of moire interference caused by the twisting of the top layer with respect to underlying layers, suggesting possible new ways to understand and control the unusual properties of graphene.

Periodic Stereo Image which Removes Viewing Zone Boundary by Using a Feature of Moire Interference

Periodic Stereo Image which Removes Viewing Zone Boundary by Using a Feature of Moire Interference

Orientation maps as Moire interference of retinal ganglion cell mosaics

Orientation maps as Moire interference of retinal ganglion cell mosaics

Study of dynamic crack propagation in 3PB steel specimens loaded by impact

Crack propagation in ductile steel was investigated using impact-loaded three-point bending (3PB) specimens. Results from experiments and numerical simulations were compared. The specimens were 320 × 75 mm by 10 mm thick. A new 3PB specimen design with reduced width at the ends was developed to avoid the influence of uncertain boundary conditions at the impact heads. One static and two dynamic tests with impact velocities of 30.2 and 45.2 m/s were performed. High-speed photography was used to obtain crack growth and crack tip opening displacement data. Moire interference patterns were used to directly measure the relative rotation of the two specimen halves. Shear lip fracture surfaces were obtained for all three loading conditions. The experiments indicated no, or only a slight, loading rate influence on the crack propagation.

A Method to Eliminate Measurement Error Caused by Residual Strain of Grating in Moire Interferometry

Moire interferometry is a very sensitive optical method to measure the in-plane displacement of a solid specimen, and is useful to measure small deformation of solids. But, there often appears measurement error caused by the residual strain of the grating that is pasted on a specimen in Moire interferometry. The present paper applies Moire interferometry to the measurement of opening displacement of a notch in a plate specimen, and proposes a method to eliminate the error brought by the residual strain of the grating. The proposed method measures the change of the order of Moire interference fringes with varying the tensile force applied to the specimen, and obtain the residual displacement of the grating and the true opening displacement of the notch. The experimental results show that the opening displacement given by the proposed method is proportional to the square root of the distance from the notch tip. This fact says that the proposed method is successful in eliminating the measurement error caused by the residual strain of grating, and can measure the true COD without any phase-shifting methods.

A ‘‘Fresnel-transducer’’ for prostate hyperthermia treatment

Simulations and construction methods will be described for a novel ‘‘Fresnel-transducer.’’ The transducer is designed for transrectal hyperthermia treatment of prostate cancer as an adjuvant to radiotherapy or chemotherapy. Forty nine 6.3 mm diameter 1.5 MHz PZT elements are arranged in a 3 by 7 cm honeycomb-like pattern. They are individually aimed so that their beams partially converge behind the prostate. The increased beam density away from the transducer compensates for the loss of acoustic intensity due to attenuation. The aiming of the beams is additionally biased toward the periphery of the heated region to compensate for cooling from lateral heat conduction. The elements are divided into three interspersed sets, each driven at a slightly different frequency, to minimize stationary Moire interference bands between the beams. The combined effect is to uniformly raise the prostate temperature to 43<th>°C without overheating the rectal wall. [Research supported by the Department of Defense Congressionally Directed Medical Prostate Cancer Research Program.]

Strain analysis for moiré interferometry using the two-dimensional continuous wavelet transform

In this paper, we introduce the two-dimensional continuous wavelet transform for the automated strain analysis of the moire interference fringe pattern. The Fourier transform method has been widely used for automated analysis of an optical interference fringe pattern. However, this method is hardly applicable to the analysis of the fringe pattern, which includes large displacement range or discontinuities. We show the advantages of the wavelet transform method by applying it to experimental results on composite laminates.

Measurement of yarn densities in fabrics using phase-shifted digital moire´

Yarn density, or yarn count, in a woven fabric is an important parameter that influences fabric structure and properties. The measurement of yarn density often involves tedious, inaccurate procedures. This paper presents a new method developed for rapid and accurate measurement of yarn density. The method takes advantage of the structural features of a woven fabric, and uses a computer-generated grating (a reference pattern) to produce digital moire interference on the fabric. The moire image is then demodulated and processed with a phase-shifting technique so that moire fringes can be extracted and counted. From the relation between the pitches of the grating and the moire fringes, the yarn density can be calculated. This technique does not need complicated optical setting or an interferometer to form moire fringes with fabrics, permitting fast and accurate measurement of yarn densities.

A moiré microscope for finite deformation micro-mechanical studies

A new version of a moire microscope is presented that embodies the theory of optical moire interferometry. To interrogate the deformed specimen grating, the device uses a transmission diffraction grating that allows for a simple and quick change of the virtual reference grating vector without disturbing the optical alignment of the other components in the optical train. To analyze deformation from the acquired moire interference fringe patterns, the displacement light-itensity moire optical law introduced by Sciammarella is revisited. The analysis of deformation is consistent with the continuum principles of finite deformation and can readily be used to obtain micro-mechanical quantities of interest such as the local strains, stretches and rotations.

Removing Halftone Patterns From Scanned Images

Abstract Using illustrations from published technical articles is part of many lectures and presentation citations, and given the availability of flat bed scanners, should be easy to accomplish. The problem that remains is removing halftone patterns and other periodic noise that result from printing and scanning technology. Practically all magazines and newspapers are printed using a regular halftone pattern that uses an array of dots varied in size to produce the visual illusion of continuous gray scale. Color images are usually printed with three, four or even more such patterns using different colored inks and different pattern orientations. Scanning such images into a computer can introduce a further pattern due to the moire interference between the printed pattern and the spacing of the sensors in the scanner. Such patterns are also characteristic of images obtained from single-chip video cameras because of the color filters present in front of the light sensors on the chip.

On the strain jump in shape memory alloys—A crystallographic-based mechanics analysis

The strain jump across the Austenite-Martensite (A-M) interface in single crystal Cu-14wt%Al-4.12wt%Ni Shape Memory Alloys (SMAs) under uniaxial tension was studied in this paper. A crystallographic-based mechanics analysis on the formation and microstructure of the interface was performed. By using the high sensitive Moire interference technique, the full-field deformation patterns during the transformation process were successfully recorded. The orientation of the habit plane (A-M interface) and the magnitude of the shape strain were determined precisely from the Moire fringe patterns. The theoretical predictions on the habit plane normal and the shape strain were compared with the measured results and good agreements were obtained.

Residual stress analysis of functionally gradient materials

Functionally gradient materials (FGM) are new engineering materials without fully understanding. One important aspect in mechanical analysis of FGM is to determine a gradient distribution that finally results in maximum thermal stress relaxation. In this paper, numerical analysis by finite element method and experimental analysis by Moire interference method were carried out to study the stress distribution in FGM. Much attention was paid on the edge effect stresses in the coating/substrate structures, and their dependence on the different gradient distribution of the new kind of composite materials.

On the Full-Field Deformation of Single Crystal CuAlNi Shape Memory Alloys—Stress-Induced β1 → γ'1 Martensitic Transformation

Using high sensitivity Moire interference technology, the full deformation fields about the stress-induced martensitic transformation β 1 → γ 1 of single crystal CuAlNi shape memory alloys (SMAs) are obtained. A straight and sharp interface between martensite and parent phases and its motion during transformation process are clearly observed. The elastic anisotropic properties of the crystal are also quantitatively characterized by this technique. The results show that there is no deformation incompatibility between the two phases, which is different from that of pseudoelasticity where another stress-induced martensitic transformation β 1 → β' 1 occurs. The present results provide an accurate experimental solution for the phase transformation problem in solids.