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In recent years, Digital holography has emerged as an exceptional imaging technology for tracking high-contrast object particles and, interestingly, analyzing 3D object data in real time. The best quality images can be obtained effectively using the auto-focusing algorithm. In this paper, the focus location of the object is traced with a deep learning-based auto-focusing algorithm. The proposed model constructs a large feature pool by considering different focus measures to reconstruct objects from two out-of-focus images. The preferred features are selected through the proposed Support vector Machine-based Recursive Feature Elimination (SVM-RFE) method. Therefore, the inappropriate features are eliminated, and the reconstruction distance is obtained by the suggested stacked autoencoder with sparse Bayesian regression (SAE-SBR) model training. It is common to find a twin image in the reconstructed image, and such noise interference is minimized with the presented high-speed iterative shrinkage/thresholding (HS-IST) based compressive sensing (CS) algorithm. Reconstruction distances are predicted by the proposed method with a standard variation of about 0.036μm. The proposed SAE-SBR predicts the right reconstruction distance of a single hologram, and it is 600 times faster than traditional autofocusing techniques like Dubois and Tamura of Gradient (ToG). Also, the computation time of the proposed model is 33.3% less than the well-known FocusNET model. [ABSTRACT FROM AUTHOR]

Electromagnetic (EM) lens antenna designs using cascaded metasurfaces for gain enhancement and beam steering applications are proposed. Two different lens aperture designs are proposed and populated with aperiodic unit cells of size 0.2λo × 0.2λo. In lens Design 1, the unit cells of different phases are distributed in concentric circular zones, whereas in lens Design 2, the unit cells of different phases are distributed in vertical linear zones on the aperture of the EM lens. Both lenses are composed of two cascaded metasurfaces with an air gap of 0.047λo (where λo = 51.7 mm at 5.8 GHz). For gain enhancement, the metasurfaces are positioned at an optimum focal distance, f = 0.61λo above source patch antenna (f/D = 0.3). Beam steering is accomplished by phase transformation of the source antenna, which can be realized by mechanically sliding the passive metasurfaces in one direction (i.e., ±x‐direction) above the source antenna. The prototype of the two proposed lenses are fabricated and tested. The measured peak boresight gain obtained from Design 1 and 2 are 14.98 and 15.12 dBi, respectively. The experimental results show −25° to +25° and −27° to +27° beam steering range for Design 1 and 2, respectively, with a little gain degradation at other angles. [ABSTRACT FROM AUTHOR]

In most augmented reality (AR) or virtual reality (VR) devices, a virtual image is formed in front of the eye at a specific focal distance. Focal distance is the distance to the virtual image produced by the virtual image optics and is a display parameter of interest. In this study, a method to measure the focal distance is proposed. A positive lens was added adjacent to the AR device, and the image of the virtual image formed by this lens was photographed at the different distances with the translation of complementary metal–oxide–semiconductor (CMOS), which was used as two‐dimensional spatial sensor arrays. Grating pattern with the various line thickness was used as input signal. Once the distance of the image of the virtual image formed by the addition of the positive lens was determined, the focal distance of the virtual image was found from the lens equation. The measurement accuracy of the proposed method with regard to the CMOS translation step was compared with the other conventional methods. [ABSTRACT FROM AUTHOR]

A single, versatile fabrication method for producing microfluidic chips on poly(methyl methacrylate) (PMMA) substrates is described. First, we processed the microchannel using CO2 laser beam machining on the PMMA substrate. In this course the influence of laser power, scanning speed and focal distance on the processing quality of microchannel were investigated by orthogonal experiment. The experimental result shows that the greatest influence factor is focal distance. Based on the experiment, we found a set of optimal parameters to process the microchannel within the set parameters. Next, the substrate with the microchannels and the cover are combined using thermal bonding. Since the previous bonding technology has a low success rate, we have proposed a new bonding termed a pre-bonding technique for bonding chips. The principle of this technology is to first remove the material stress with low pressure, and then use high pressure bonding. Finally, the processing quality of the microchannel and the feasibility of the pre-bonding method were verified successfully by the mixed experiment. This study can help people pay attention to the effect of focal distance on the shape of microchannels when using CO2 laser beam machining to process microchannels. [ABSTRACT FROM AUTHOR]

Near‐field‐focused (NFF) antennas have been studied to focus the electromagnetic power in the near‐field (NF) region of the antenna aperture over a long time. Some focal parameters have been adopted to evaluate the focused performance of NFF antennas. Research work on smaller NFF aperture antennas with electrically large size is limited for the similarities between array antennas and aperture ones increasing with their size increasing. It is meaningful to study smaller aperture (several wavelengths) antennas because the physical size of antennas is limited for low‐frequency applications. This paper investigates the impacts of four factors on six focal parameters for NFF aperture antennas when the electrical size is not large enough. The results of six focal parameters are given as functions of the focal distance for different aperture shapes, aperture sizes, and aperture amplitude distributions, respectively. Finally, the differences of two focal parameters between the focal plane and the focal sphere are discussed as well. Unlike the previous work on the scalar diffraction field of NFF aperture antennas using the Fresnel region field approximation, the integral expression of scalar diffraction field is calculated directly and exactly in this paper to produce the focused field at an arbitrarily selected point. [ABSTRACT FROM AUTHOR]

An $8\times8$ microstrip planar array antenna with near-field focused beams is presented in this paper, whose elements are series fed in both E- and H-planes. The focus is designed at a distance of 200 mm above the array plane at 10 GHz, and by carefully designing the feed network, the focal distance can be frequency tunable. Eventually, a steerable focal distance from 78 to 249 mm is achieved as frequency varies from 9.25 to 10.5 GHz, with near-field sidelobes below −8 dB. Theoretical analysis is performed first, which is further proven by simulations and experiments. Finally, the method of tuning the sensitivity and range of frequency scan is discussed, which is proven by numerical study. To the best of our knowledge, the proposed design is the first array approach to realize tunable focal distance without any beam-forming components. [ABSTRACT FROM AUTHOR]

We explore the relation among volume, curvature and properness of an m-dimensional isometric immersion in a Riemannian manifold. We show that, when the Lp-norm of the mean curvature vector is bounded for some m ≤ p≤∞, and the ambient manifold is a Riemannian manifold with bounded geometry, properness is equivalent to the finiteness of the volume of extrinsic balls. We also relate the total absolute curvature of a surface isometrically immersed in a Riemannian manifold with its properness. Finally, we relate the curvature and the topology of a complete and non-compact 2-Riemannian manifold M with non-positive Gaussian curvature and finite topology, using the study of the focal points of the transverse Jacobi fields to a geodesic ray in M. In particular, we have explored the relation between the minimal focal distance of a geodesic ray and the total curvature of an end containing that geodesic ray. [ABSTRACT FROM AUTHOR]

Objective: To investigate the clinical effect of intra-articular fractures of the knee joint by sustentaculum Tali screw fixation. Methods: 80 cases of knee joint fractures according to the fracture fixation were divided into two groups. Experiment group were treated by load spur screw fixation technology. Control group were treated by the fracture degree was observed after the opening, the smoothness of the joints was repaired, the needle and traction technique was performed. Results: Compared with the control group, the total efficiency of experimental group was higher, the incidence of complications is low (P<0.05); HSS score of experimental group was significantly higher than that of the control group (P<0.05). Conclusion: Sustentaculum Tali screw fixation technique can improve the clinical efficacy of intra-articular fractures of the knee joint of patients, reduce the incidence of complications, improve the function of knee joint. [ABSTRACT FROM AUTHOR]

This study aimed at assessing the applicability of a robust method to determine and correct lens distortion before using the direct linear transformation (DLT) algorithm in three-dimensional motion analysis. The known length of a rigid bar was reconstructed under different conditions of working volume (interpolation or extrapolation), number of cameras (2 or 4), position of the cameras (wide or narrow angle between optical axes), camera focal distance (4 or 8 mm) and number of control points (CPs; 8, 12, 18 or 162), through four different camera set-ups. The accuracy (percent root mean square error) of Set-up 2 (non-extrapolated working volume; two cameras; 4 mm focal distance; narrow optical axes angle) decreased with less CPs (162: 0.73%; 8: 2.78%). Set-up 1 (non-extrapolated working volume; two cameras; 8 mm focal distance; wide optical axes angle), Set-up 3 (Set-ups 1 and 2 used simultaneously) and Set-up 4 (extrapolated working volume; two cameras; 4 mm focal distance; wide optical axes angle) showed minor differences in accuracy across groups of CPs, with maximum values of 0.84%, 1.20% and 1.71%, respectively. Random errors were the main source of decreased accuracy of Set-ups 2 and 4.The proposed procedure enables accurate results with no modification in the DLT-based analysis system, even with smaller calibration frames, less CPs and wide field-of-view cameras. [ABSTRACT FROM AUTHOR]

Mathematical models that provide an adequate description of the effect of laser cutting parameters on the roughness of the cut surface with no burr, the extent of the heat-affected area, and the nonperpendicularity of the cut surface are devised. Nomograms that allow one to select the laser cutting regimes designed to minimize the surface roughness, the heat-affected area, and the nonperpendicularity for sheets of St. 3 steel of different thickness are proposed. [ABSTRACT FROM AUTHOR]

Abstract: Within applications conducted in immersive virtual environments such as CAVE, eye gaze convergent distance (also called focal distance) is an important parameter used in several fields such as telepresence, virtual scenes depth perception, HRI, and others. By knowing the object that is focused by the operator, various interaction interfaces may be developed. This paper focuses on measuring with precision the convergent distance from an operator working inside an immersive virtual environment, to the gazed virtual object. Measurement errors are handled by an error filtration algorithm. The study concludes with proposing a method of selecting gazed virtual objects using proximity selection. [Copyright &y& Elsevier]

Abstract: Behavior of spin-wave propagation in ferromagnetic medium with non-uniform distribution of magnetic parameters is studied. In particular, the influence of external magnetic field, spin-wave frequency and exchange parameter on behavior of surface spin-wave propagating through inhomogeneity made in form of lens (lens is biaxial ferromagnet placed into uniaxial ferromagnetic medium) is studied. [Copyright &y& Elsevier]

The article provides information on optometers. A description of how the finding from a series of experiments at the University of Illinois in 1950s has led to the objective measurement of the focal distance of the eyes under various viewing conditions while observers are performing tasks is presented. Information on several optometers is provided, including infrared tracking optometer and laser optometer, citing the use, advantages and disadvantages of each.

When using quantitative light-induced fluorescence a number of factors can influence illumination level. The purpose of this study was to investigate, using a high-resolution camera and fibre-optic light source, the impact of illumination level and focal distance on common quantitative light-induced fluorescence outcomes. Twenty-four extracted teeth were examined using 6 illumination levels and 4 focal distances. Analysis was conducted using multiple linear regression models fitted to log ΔQ, log ΔF and log area with clustering of teeth and robust standard errors. Separate models were used for the different light and focal levels. The regression coefficients were significant for both ΔQ and ΔF but not area. Despite the significant regressions the actual effect was very small, and unlikely to confound clinical trial or practice results. Copyright © 2006 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]