Angular Scans Research Articles

A nonparametric method for detecting fixations and saccades using cluster analysis: Removing the need for arbitrary thresholds

Eye tracking is an important component of many human and non-human primate behavioral experiments. As behavioral paradigms have become more complex, including unconstrained viewing of natural images, eye movements measured in these paradigms have become more variable and complex as well. Accordingly, the common practice of using acceleration, dispersion, or velocity thresholds to segment viewing behavior into periods of fixations and saccades may be insufficient. Here we propose a novel algorithm, called Cluster Fix, which uses k-means cluster analysis to take advantage of the qualitative differences between fixations and saccades. The algorithm finds natural divisions in 4 state space parameters-distance, velocity, acceleration, and angular velocity-to separate scan paths into periods of fixations and saccades. The number and size of clusters adjusts to the variability of individual scan paths. Cluster Fix can detect small saccades that were often indistinguishable from noisy fixations. Local analysis of fixations helped determine the transition times between fixations and saccades. Because Cluster Fix detects natural divisions in the data, predefined thresholds are not needed. A major advantage of Cluster Fix is the ability to precisely identify the beginning and end of saccades, which is essential for studying neural activity that is modulated by or time-locked to saccades. Our data suggest that Cluster Fix is more sensitive than threshold-based algorithms but comes at the cost of an increase in computational time.

Two-Element Phased-Array Acousto-Optic Deflector at High Diffraction Efficiency: Scanning Range Broadening

An acousto-optic deflector with a two-element phased-array piezoelectric transducer is investigated at high diffraction efficiency (close to 100%). Significant broadening of the frequency band (and, thus, the angular scanning range) relative to the well-known low efficiency regime is theoretically predicted and experimentally demonstrated. Experiments with an off-axis deflector based on paratellurite (TeO2), a 1.06 µm light radiation and 6 mm interaction length gave frequency band from 17 to 48 MHz at an efficiency of no less than 94% of the maximum value.

A HMSIW Circularly Polarized Leaky-Wave Antenna With Backward, Broadside, and Forward Radiation

A miniaturized frequency-scanning leaky-wave antenna (LWA) with circular polarization (CP) and backward-broadside-forward radiation is presented. Half-mode substrate integrated waveguide (HMSIW) in combination with interdigital capacitors (IDCs) is utilized in order to achieve a composite right/left-handed leaky-wave structure. Ramp-shaped slots are introduced as interdigital capacitors. Using this structure, the balanced condition (in which series and shunt resonances are equal) can be obtained for the unit-cell. As a result, wide bandwidth of 7.4-13.5 GHz with continuous angular scanning of ~ -70 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> to 70 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> is achieved. The axial ratio in the direction of the main beam is lower than 3.1. The performance of the antenna is measured, and close agreement between the simulation and measurement is observed.

Bare Finger 3D Air-Touch System Using an Embedded Optical Sensor Array for Mobile Displays

Generally, 3-D interactive systems are used in systems with large displays and are not suitable for portable devices. To “touch” a floating 3-D image displayed from a mobile device, we proposed a camera-free, 3D, interactive, virtual-touch system for bare fingers. By embedding optical sensors into the display pixels and adding angular scanning illuminators to the edge of the display, a flat panel can sense the images reflected off a bare finger. The three-axis (x, y, z) information of the fingertip can be determined by analyzing these reflected images. The proposed 3-D virtual-touch system successfully functions with a 4-in mobile display.

Studying the fidelity of quantum memory based on control-field angular scanning

The fidelity of multimode cavity-assisted quantum storage based on control-field angular scanning is analysed as a function of an input pulse temporal shape, direction of propagation of the control field and spatial structure of the signal field. It is shown by numerical simulation that available range of the angular scanning is reduced with increasing the transverse mode index of the field to be stored. Outside of this range, the output field may contain contributions from undesirable transverse modes due to the cross-talk, which results in reducing efficiency and fidelity.

Maintaining a stationary laser footprint during angular scan in internal-reflection experiments

In internal-reflection metrology using prisms, the prism is usually mounted on a rotation/translation stage to enable adjusting angle and location of the laser footprint on the surface. If a visual inspection method is used to find the laser footprint, the task becomes impossible if invisible radiation in the near infrared is employed. In addition, it may be desirable to perform angular scan experiments with a stationary footprint on the surface during scans, or even to automatically probe specific points on an extended prism face for predetermined incidence angles. In this paper, a formulation is developed to determine the required translation along the prism face to allow maintaining the laser footprint stationary under a given rotation. A web-based app developed under the scope of this work demonstrates the applicability of the approach for silica, BK7 and SF2 glasses, in the wavelength range from 500 to 1500 nm and for an arbitrary geometry of the glass prism.

Epitaxial growth of highly compressively strained GeSn alloys up to 12.5% Sn

This paper reports on the growth and characterization of highly compressive strained GeSn layers on thin strain relaxed Ge virtual substrates on Si wafers. Sn concentration up to 12.5%, which is about more than 10 times the thermal equilibrium predicted for GeSn binaries, are successfully epitaxially grown by ultra-low temperature (160°C) molecular beam epitaxy. A minimum channeling yield of 9% evidence the high crystalline quality of the GeSn alloys while angular channeling scan demonstrate that all GeSn layers are fully pseudomorphic on the relaxed Ge virtual substrate. The strain analysis shows a deviation from the Vegard's law for Sn contents above 8%. The analysis is completed by the Raman mode dependence on the alloys composition.

Extension of the angular scanning range of the acousto-optic deflector with a two-element phased-array piezoelectric transducer

The acousto-optic deflector with a two-element phased-array piezoelectric transducer is studied at an almost limiting diffraction efficiency. Significant broadening of the working acoustic frequency band (and angular scanning range) relative to the well-studied low-efficiency regime is theoretically predicted and experimentally demonstrated. For the off-axial deflector based on paratellurite (TeO2), a radiation wavelength of 1.06 μm, and a two-element transducer with a total length of 6 mm, the working frequency band is 17–48 MHz (with the lower frequency determined by the electromechanical properties of the transducer) at an efficiency of no less than 94% of the maximum value.

Multielemental analysis of powder samples by direct measurement with TXRF

Total reflection X‐ray fluorescence analysis was used to measure various powder samples directly put on an adhesive carbon tab placed on a quartz carrier. In this paper, the ability of the method to perform quantitative multielemental analysis without sample digestion was demonstrated. To assess the optimal measurement conditions, angular scans to find the best glancing angle were carried out, different kinds of reference standard powders were measured, and matrix effects and detection limits were evaluated. The results show a good agreement of data obtained with certified values. This quick method can be applied to characterize powders without any chemical treatment, thus reducing time for analysis and minimizing the risk of sample contamination. As a consequence, a great advantage is that a large number of samples can be analyzed in a short time: This method can be very useful in environmental applications such as the analysis of many atmospheric particulate samples from a wide area and for repeated monitoring. Copyright © 2013 John Wiley &amp; Sons, Ltd.

A fluorescence LIDAR sensor for hyper-spectral time-resolved remote sensing and mapping

In this work we present a LIDAR sensor devised for the acquisition of time resolved laser induced fluorescence spectra. The gating time for the acquisition of the fluorescence spectra can be sequentially delayed in order to achieve fluorescence data that are resolved both in the spectral and temporal domains. The sensor can provide sub-nanometric spectral resolution and nanosecond time resolution. The sensor has also imaging capabilities by means of a computer-controlled motorized steering mirror featuring a biaxial angular scanning with 200 μradiant angular resolution. The measurement can be repeated for each point of a geometric grid in order to collect a hyper-spectral time-resolved map of an extended target.

Anisotropy of diffraction characteristics of thin pyrolytic graphite films

We have studied polar diagrams and local diffraction characteristics of thin highly oriented pyrolytic graphite (HOPG) films used for X-ray monochromatization and spectrometry. The measurements have been performed on a two-wave X-ray reflectometer. The angular azimuthal scanning of initial HOPG films by a probe with a cross section below 0.1 mm2; the diffraction reflection coefficient exhibited a sharp anisotropy. It is shown that the effect of anisotropy can be suppressed and an HOPG film can be used as a dispersive element for X-ray tomography and mapping, as well as for studying spectra with a single pulse of an X-ray laser.

Thermal deformation of cryogenically cooled silicon crystals under intense X-ray beams: measurement and finite-element predictions of the surface shape

X-ray crystal monochromators exposed to white-beam X-rays in third-generation synchrotron light sources are subject to thermal deformations that must be minimized using an adequate cooling system. A new approach was used to measure the crystal shape profile and slope of several cryogenically cooled (liquid nitrogen) silicon monochromators as a function of beam power in situ and under heat load. The method utilizes multiple angular scans across the Bragg peak (rocking curve) at various vertical positions of a narrow-gap slit downstream from the monochromator. When increasing the beam power, the surface of the liquid-nitrogen-cooled silicon crystal deforms from a concave shape at low heat load to a convex shape at high heat load, passing through an approximately flat shape at intermediate heat load. Finite-element analysis is used to calculate the crystal thermal deformations. The simulated crystal profiles and slopes are in excellent agreement with experiments. The parameters used in simulations, such as material properties, absorbed power distribution on the crystal and cooling boundary conditions, are described in detail as they are fundamental for obtaining accurate results.

White Matter and Visuospatial Processing in Autism: A Constrained Spherical Deconvolution Tractography Study

Autism spectrum disorders (ASDs) are associated with a marked disturbance of neural functional connectivity, which may arise from disrupted organization of white matter. The aim of this study was to use constrained spherical deconvolution (CSD)-based tractography to isolate and characterize major intrahemispheric white matter tracts that are important in visuospatial processing. CSD-based tractography avoids a number of critical confounds that are associated with diffusion tensor tractography, and to our knowledge, this is the first time that this advanced diffusion tractography method has been used in autism research. Twenty-five participants with ASD and aged 25, intelligence quotient-matched controls completed a high angular resolution diffusion imaging scan. The inferior fronto-occipital fasciculus (IFOF) and arcuate fasciculus were isolated using CSD-based tractography. Quantitative diffusion measures of white matter microstructural organization were compared between groups and associated with visuospatial processing performance. Significant alteration of white matter organization was present in the right IFOF in individuals with ASD. In addition, poorer visuospatial processing was associated in individuals with ASD with disrupted white matter in the right IFOF. Using a novel, advanced tractography method to isolate major intrahemispheric white matter tracts in autism, this research has demonstrated that there are significant alterations in the microstructural organization of white matter in the right IFOF in ASD. This alteration was associated with poorer visuospatial processing performance in the ASD group. This study provides an insight into structural brain abnormalities that may influence atypical visuospatial processing in autism.

Theoretical and experimental determination of steering mechanism for Risley prism systems

Two different analytical methods, the first-order paraxial approximation method and the nonparaxial ray tracing method, are applied to determine the steering mechanism of the Risley prism system, including the pointing prediction and the complete and exact inverse orientation solutions. The analytical results obtained with the two different methods are investigated in detail about the pointing prediction and the two groups of inverse orientation solutions, respectively. Risley prism equipment for wide angular range beam scanning is assembled and the experimental setup is built to test the steering mechanism of the Risley prism system. Experimental results validate the availability of the nonparaxial ray tracing method to discuss the beam steering mechanism for the Risley prism system.

Lattice site location and luminescence studies of AlxGa1−xN alloys doped with thulium ions

Rare earth doped AlGaN is being considered for the development of new optoelectronic devices. This wide band gap compound provides lower thermal quenching of rare earth intra-4fn transitions making room temperature operation possible. In this work a detailed study of AlxGa1−xN (x=0.15, 0.77) samples grown by halide vapor phase epitaxy on (0001) sapphire implanted with Tm is presented. The samples were implanted at room temperature with 300keVTm ions to fluences of 1×1014cm−2 and 1×1015cm−2. The damage accumulation and the rare earth lattice site location are investigated by Rutherford Backscattering/Channeling Spectrometry. The structural measurements show a higher resistance of the lattice to irradiation damage with the increase of the AlN content. The analysis of angular scans along different axes using the Monte Carlo code FLUX allows the determination of the rare earth lattice sites. Results for Al0.15Ga0.85N show that Tm ions occupy two preferential sites: the high symmetry substitutional Ga/Al site and a site displaced by ∼0.3Å along the c-axis from this regular site.Rapid thermal annealing treatments at 1200°C under N2 ambient were performed to remove implantation damage and promote the optical activation of rare earth intra-4fn transitions. Photoluminescence measurements were performed to characterize the thulium ions spectroscopic transitions. The effects of thermal annealing and fluence on the fraction of rare earth optically active ions are exploited and discussed.

Quantum storage based on control-field angular scanning

Continuous change of the propagation direction of a classical control field in the process of its off-resonant Raman interaction with a weak signal field in a three-level atomic medium is suggested for quantum storage of a single-photon wave packet. It is shown that due to phase matching condition such an angular control allows one to reversibly map the single-photon wave packet to the Raman spatial coherence grating. Thus, quantum storage and retrieval can be realized without using inhomogeneous broadening of the atomic transitions or manipulating the amplitude of the control field. Under some conditions the proposed scheme proves to be mathematically analogous to the quantum storage scheme based on controlled reversible inhomogeneous broadening of the atomic states.

Optimum design of shaped beam cylindrical array antenna with electronically scan radiation pattern

In this paper, the shaped beam cylindrical array is presented to obtain full angular scanning in the plane of the array. This array antenna is designed such that it produces sum and difference radiation patterns simultaneously. The array elements are wideband printed dipole antennas which operate in L- frequency band. To design of the array antenna at first step, certain numbers of the elements (16 elements) in a sector of the cylindrical array (active area) are used to synthesize by the Particle Swarm Optimization (PSO) method. In the second step to rotate the optimum radiation pattern extracted from the first step, appropriate feeding network is suggested to rotate the active area around the cylindrical array axis. Therefore the radiation patterns of the array antenna remain completely constant in all scan angles.

Kinetic-energy-driven enhancement of secondary-electron yields of highly charged ions impinging on thin films of C60on Au

The secondary electron yields as a result of slow highly charged ions (Ar4+, Ar13+) impinging on clean Au(111), highly oriented pyrolitic graphite, and thin films of C-60 on Au are presented. In order to investigate the dynamics of the neutralization of the highly charged ions in front of the surface, angular scans have been performed. The results give a clear indication that the observed increase in electron yield seen on C-60 compared to Au stems from kinetic-energy-driven processes and not from processes driven by the potential energy carried by the highly charged ion. DOI: 10.1103/PhysRevA.86.062904

Hydroacoustical emitter based on zero-order antisymmetric Lamb wave in a piezoelecrtric plate

A piezoelectric plate supporting the propagation of antisymmetric zero-order (A0) Lamb wave is proposed to be used as a hydroacoustical waveguide emitter that transmits a bulk acoustic wave into a liquid. The emitter's directional pattern has been theoretically and experimentally examined for a frequency band of 89–107 kHz. An angular acoustic beam scanning was revealed to be realized by varying the A0 wave frequency. It is shown that, unlike complicated emitting systems of phased array type, this nonmechanical scanning could be realized in a simple device. The obtained results are in a good agreement with the theoretical ones.

20 MHz forward-imaging single-element beam steering with an internal rotating variable-angle reflecting surface: Wire phantom and ex vivo pilot study

Feasibility is demonstrated for a forward-imaging beam steering system involving a single-element 20MHz angled-face acoustic transducer combined with an internal rotating variable-angle reflecting surface (VARS). Rotation of the VARS structure, for a fixed position of the transducer, generates a 2-D angular sector scan. If these VARS revolutions were to be accompanied by successive rotations of the single-element transducer, 3-D imaging would be achieved.In the design of this device, a single-element 20MHz PMN-PT press-focused angled-face transducer is focused on the circle of midpoints of a micro-machined VARS within the distal end of an endoscope. The 2-D imaging system was tested in water bath experiments with phantom wire structures at a depth of 10mm, and exhibited an axial resolution of 66μm and a lateral resolution of 520μm. Chirp coded excitation was used to enhance the signal-to-noise ratio, and to increase the depth of penetration. Images of an ex vivo cow eye were obtained. This VARS-based approach offers a novel forward-looking beam-steering method, which could be useful in intra-cavity imaging.