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High‐pressure neutron powder diffraction data from PbNCN were collected on the high‐pressure diffraction beamline SNAP located at the Spallation Neutron Source (SNS) of Oak Ridge National Laboratory (Tennessee, USA). The diffraction data were analyzed using the novel method of multidimensional (two dimensions for now, potentially more in the future) Rietveld refinement and, for comparison, employing the conventional Rietveld method. To achieve two‐dimensional analysis, a detailed description of the SNAP instrument characteristics was created, serving as an instrument parameter file, and then yielding both cell and spatial parameters as refined under pressure for the first time for solid‐state cyanamides/carbodiimides. The bulk modulus B0 = 25.1 (15) GPa and its derivative B′0 = 11.1 (8) were extracted for PbNCN following the Vinet equation of state. Surprisingly, an internal transition was observed beyond 2.0 (2) GPa, resulting from switching the bond multiplicities (and bending direction) of the NCN2− complex anion. The results were corroborated using electronic structure calculation from first principles, highlighting both local structural and chemical bonding details. [ABSTRACT FROM AUTHOR]

Nonlinear metasurfaces and photonic crystals provide a significant way to generate and manipulate nonlinear signals owing to the resonance- and symmetry-based light-matter interactions supported by the artificial structures. However, the nonlinear conversion efficiency is generally limited by the angular dispersion of optical resonances especially in nonparaxial photonics. Here, we propose a metagrating realizing a quasi-bound-state in the continuum in a flat band to dramatically improve the third harmonic generation (THG) efficiency. A superior operating angular range is achieved based on the interlayer and intralayer couplings, which are introduced by breaking the mirror symmetry of the metagrating. We demonstrate the relation of angular dispersion between the nonlinear and linear responses at different incident angles. We also elucidate the mechanism of these off-axis flat-band-based nonlinear conversions through different mode decomposition. Our scheme provides a robust and analytical way for nonparaxial nonlinear generation and paves the way for further applications such as wide-angle nonlinear information transmission and enhanced nonlinear generation under tight focusing. [ABSTRACT FROM AUTHOR]

Angular dispersion can counterbalance normal group‐velocity dispersion (GVD) that increases the wave‐vector length in a dispersive medium. By tilting the wave vector, angular dispersion reduces the axial wave number in this case to match the pre‐GVD value. By the same token, however, angular dispersion fails to counterbalance anomalous GVD, which in contrast reduces the wave‐vector length. Consequently, GVD‐cancellation via angular dispersion has not been demonstrated to date in the anomalous dispersion regime. Here, structed femtosecond pulsed beams, known as 'space‐time' wave packets, are designed to realize dispersion‐cancellation symmetrically in either the normal‐ or anomalous‐GVD regimes by virtue of non‐differentiable angular dispersion inculcated into the pulsed field. Furthermore, GVD‐inversion is also verified by reversing the GVD sign experienced by the field with respect to that dictated by the chromatic dispersion of the medium itself. [ABSTRACT FROM AUTHOR]

This study has developed paleomagnetic secular variation (PSV) records from Sites 1060, 1061, 1062, and 1063 (ODP Leg 172) from the western North Atlantic Ocean during MIS 11–12 (374–478 ka). We have identified 46 inclination features and 49 declination features that can be correlated among the records. We have also developed relative paleointensity records and identified 13 paleointensity features that can be correlated among them. These features can also be dated using the oxygen-isotope dated Global relative-paleointensity record PISO-1500 of Channell et al. (2009). There is one excursion located in these four records. We use the name Levantine/Bermuda Excursion developed elsewhere by Ryan (1972) and Channell et al. (2017). The Excursion occurred at 408 ± 4 ka. The excursion is recorded at Sites 1061, 1062, and 1063. The most detailed excursion records occur at Site 1062 where we have both shipboard PSV records and one u-channel PSV record of the excursion. The excursion has two intervals of excursional directions, one short interval (∼I ky) followed by a long interval (∼5 ky). Both intervals have counter-clockwise looping of the excursional directions and the excursion is considered to be a Class I Excursion (Lund et al., 2005). Statistical study of the PSV records after removal of the excursion directions has identified two characteristics of the 'normal' PSV. The first feature is a long-term (>104 yrs) deviation in inclination and declination averages from the overall site averages. These deviations suggest some type on long-term memory in the regional dynamo process. The second feature is the variation in PSV angular dispersion (a measure of directional variability). The angular dispersion is quite low (∼12°) for most of the 374–478 ka interval. But, there is a short (∼8 ky) interval with angular dispersion more than double the amplitude (∼25°-30°). This interval has a sharp (<3 ky) onset and termination, This interval contains the Levantine/Bermuda Excursion. Such high-angular dispersion intervals with associated excursions and low paleointensity appear to be regular distinctive features of the Brunhes Chron PSV. • Paleomagnetic secular variation for MIS 11/12. • Levantine/Bermuda Excursion. • Statistical study of PSV. [ABSTRACT FROM AUTHOR]

Orbital angular momentum (OAM) multiplexing of electromagnetic (EM) waves is of great significance for high-speed wireless communication and remote sensing. To achieve high-efficiency OAM multiplexing for multi-channel incident EM waves, this paper presents a novel angle-dispersive meta-atom structure, which can introduce the required anti-symmetric phase dispersion as well as high transmission efficiency for OAM multiplexing. These meta-atoms are then arranged delicately to form an angle-dispersive metasurface working at the X band, which enables three-channel OAM multiplexing by converting highly directional transverse-magnetic (TM) waves incident from 0 and ±45° to coaxial OAM beams with l = 0 and ±2 modes, respectively. The simulation and experimental results reveal that the proposed metasurface can convert a higher proportion of energy to the required OAM modes compared to the conventional OAM multiplexing metasurfaces, which can significantly improve the coaxial transmission efficiency of multi-channel OAM multiplexing.

Solar energy is an inexhaustible renewable energy resource, which is a potential solution to global warming and aids sustainable development. The use of solar-thermal collectors to harness solar energy facilitates low-cost heat storage and can improve the stability of power grids based on renewable energy. In solar-thermal collectors, traditional concentrators, such as parabolic troughs and dishes, are typically used but inevitably require high-precise supports and complex tracking sun systems, which increase the cost of solar-thermal power stations and hinder their further applications. In contrast, planar meta-lenses (so-called metasurface-based concentrators) consisting of two-dimensional nanostructured arrays are allowed to engineer the frequency dispersion and angular dispersion of the incident light through delicately arranging the aperture phase distribution, thereby correcting their inherent aberrations. Accordingly, the novel meta-lenses offer tremendous potentials to effectively capture broadband, wide-angle sunlight without the extra tracking system. This review summarizes the research motivation, design principles, building materials, and large-area fabrication methods of meta-lens for solar energy harvesting in terms of focusing efficiency, operation bandwidth, and angular dependence. In addition, the main challenges and future goals are examined. [ABSTRACT FROM AUTHOR]

Multi-wavelength digital holographic microscopy (MDHM) is widely used in biological and industrial applications because of increased unambiguous height measurement range and the ability to measure concentration from the spectral dependence of phase delay. Acousto-optic tunable filters (AOTFs) provide the simultaneous selection of several bands with tunable central wavelengths to create a multiplexed hologram, but may limit the field of view (FOV) in off-axis holography because of the short coherence length of the filtered light. We analyzed the performance of the AOTF-based off-axis MDHM setup with a diffraction grating or a prism in the reference arm necessary to increase the efficiency of angular multiplexing. This allows varying the number of spectral channels selected simultaneously without setup realignment. Mathematical description relates the spectral bandwidth of the AOTF, tilt of the coherence plane induced by the angular dispersion of a prism or a grating, width of the FOV determined by interference pattern visibility, spatial resolution, and optimal intermediate wavelengths. We theoretically and experimentally demonstrated that the FOV may be expanded by changing the angle of light incidence on the AOTF and that the prism changes the wavelength dependence of the FOV. We validated this technique by single-shot acquisition of the height maps of the transparent test chart at four wavelengths with an error similar to that of four sequentially captured single-wavelength holograms. The results may be helpful for multiple applications of MDHM using spectrally tunable light sources. [ABSTRACT FROM AUTHOR]

We report the characterization of an achromatic focusing metasurface at oblique incident angles. We show that in addition to the inherent off-axis aberrations that occur due to the hyperbolic phase profile of the metasurface, the focusing performance is significantly degraded due to the meta-atoms’ angular dispersion. To obtain insights into how the angular and spectral bandwidth of meta-atoms relate to the metasurface focusing performance, point dipole models are used which incorporate different aspects of the meta-atoms’ angular response. It is emphasized that despite the meta-atoms being designed under the assumption that they support a single dipolar resonance, other resonances exist within the meta-atom geometry and become stronger at oblique incidence. These resonances disturb the designed phase and amplitude responses, resulting in lower focusing efficiency at higher incident angles. The modeling of higher order modes leads to good agreement with the experimental measurements, confirming that angular dispersion of the meta-atoms is the dominant mechanism in determining off-axis aberrations. [ABSTRACT FROM AUTHOR]

Propagation models constitute a fundamental building block of wireless communications research. Before we build and operate real systems, we must understand the science of radio propagation, and develop channel models that both reflect the important propagation processes and allow a fair comparison of different systems. In the past five decades, wireless systems have gone through five generations, from supporting voice applications to enhanced mobile broadband. To meet the ever increasing data rate demands of wireless systems, frequency bands covering a wide range from 800 MHz to 100 GHz have been allocated for use. The standardization of these systems started in the early/mid 1980s in Europe by the European Telecommunications Standards Institute with the advent of Global System for Mobile Communications. This motivated the development of the first standardized propagation model by the European Cooperation in Science and Technology (COST) 207 working group. These standardization activities were continued and expanded for the third, fourth, and fifth generations of COST, as well as by the Third Generation Partnership Project, and the International Telecommnunication Union. This paper presents a historical overview of the standardized propagation models covering first to fifth-generation systems. In particular, we discuss the evolution and standardization of pathloss models, as well as large and small-scale fading parameters for single antenna and multiple antenna systems. Furthermore, we present insights into the progress of deterministic modelling across the five generations of systems, as well as discuss more advanced modelling components needed for the detailed simulations of millimeter-wave channels. A comprehensive bibliography at the end of the paper will aid the interested reader to dig deeper. [ABSTRACT FROM AUTHOR]

The group velocity of an optical beam in free space is usually considered to be equal to the speed of light in vacuum. However, it has been recently realized that, by structuring the beam’s angular and temporal spectra, one can achieve well pronounced and controlled subluminal and superluminal propagation. In this work, we consider multifrequency Bessel beams that are known to propagate without divergence and show a variety of possibilities to adjust the group velocity of the beam by means of designed angular dispersion. We present several examples of multifrequency Bessel beams with negative and arbitrary positive group velocities, as well as longitudinally accelerating beams and beams with periodically oscillating local group velocities. The results of these studies can be of interest to scientists working in the fields of optical beam engineering, light amplitude and intensity interferometry, ultrafast optics, and optical tweezers.

Reflection phase gratings based on write-once optical discs are proposed. Their morphology and backward diffraction characteristics are investigated. Home-made phase gratings with well-defined spacing about 1 524, 751, 335 nm are readily produced by pulling off ordinary optical discs. The backward diffraction characteristics of three phase gratings are compared. The research results show that diffraction phenomena of CD-R, DVD-R and BD-R gratings are observed in visible, visible-NIR and ultraviolet regions, respectively; successive spectra overlap are observed in diffraction spectra of the CD-R grating and angular dispersion of diffraction spectra increases as the diffraction order increases; diffraction angle of the three gratings is linearly proportional to the diffraction peak, angular dispersion increases as the grating constants decreases and the maximum angular dispersion is 0.333(°)/nm. In addition, when wavelength of incident light is more than the grating period, there is only zero-order diffraction wave in diffraction spectra of the DVD-R and BD-R subwavelength gratings. [ABSTRACT FROM AUTHOR]

Gratings are key components in many optical systems such as spectrometers. Improving their dispersion is very important for their applications, but improving the single-order diffraction efficiency of an ultrahigh dispersion grating is still very challenging. Here, we propose an analytical approach for the design of a new type of grating named hybrid grating, which consists of a subwavelength grating and a non-subwavelength grating. The proposed analytical approach is based on a physical model in which the non-subwavelength grating acts as an ultrathin reflection grating and the subwavelength grating acts as an antireflection coating. Using the rigorous coupled-wave analysis and the finite-difference time-domain method, we numerically demonstrate that multiple hybrid gratings designed at different wavelengths using the proposed analytical approach show a diffraction efficiency of greater than 95 % in the -1st diffraction order for TE-polarized light, an angular dispersion of greater than 0.8 mrad/nm and a deflection angle of greater than 80°. Furthermore, we numerically demonstrate that by using a combined approach to optimize the parameters of a hybrid grating, the diffraction efficiency in the -1st diffraction order for TE-polarized light can be increased to more than 97 % under the condition that the angular dispersion and the deflection angle of the hybrid grating remain unchanged. Our work provides an avenue for rapid design of gratings with high angular dispersion, large deflection angle and high diffraction efficiency. • An analytical approach was proposed as a rapid design tool for high-performance hybrid gratings. • A combined approach was proposed as a time-saving tool to optimize the parameters of a hybrid grating. • A diffraction efficiency of 97.5 %, an angular dispersion of 3.91 mrad/nm and a deflection angle of 80.63° can be achieved. • The diffraction efficiency of multiple designed hybrid gratings can be greater than 80 % over a bandwidth exceeding 240 nm. [ABSTRACT FROM AUTHOR]

High quality factor optical nanostructures provide a great opportunity to enhance nonlinear optical processes such as third harmonic generation. However, the field enhancement in these high quality factor structures is typically accompanied by optical mode nonlocality. As a result, the enhancement of nonlinear processes comes at the cost of their local control as needed for nonlinear wavefront shaping, imaging, and holography. Here we show simultaneous strong enhancement and spatial control over third harmonic generation with a local high- Q metasurface relying on higher-order Mie resonant modes. Our results demonstrate third harmonic generation at an efficiency of up to 3.25 × 10 -5 , high quality wavefront shaping as illustrated by a third harmonic metalens, and a flatband, angle independent, third harmonic response up to ±11° incident angle. The demonstrated high level of local control and efficient frequency conversion offer promising prospects for realizing novel nonlinear optical devices.

Angle-dependent next-generation displays have potential applications in 3D stereoscopic and head-mounted displays, image combiners, and encryption for augmented reality (AR) and security. Metasurfaces enable such exceptional functionalities with groundbreaking achievements in efficient displays over the past decades. However, limitations in angular dispersion control make them unfit for numerous nanophotonic applications. Here, we propose a spin-selective angle-dependent all-dielectric metasurface with a unique design strategy to manifest distinct phase information at different incident angles of light. As a proof of concept, the phase masks of two images are encoded into the metasurface and projected at the desired focal plane under different angles of left circularly polarized (LCP) light. Specifically, the proposed multifunctional metasurface generates two distinct holographic images under LCP illumination at angles of +35 and -35°. The presented holographic displays may provide a feasible route toward multifunctional meta-devices for potential AR displays, encrypted imaging, and information storage applications.

Prebunching is an effective technique to reduce the radiation saturation length and to improve the longitudinal coherence and output stability in storage‐ring‐based free‐electron lasers (FELs). A novel technique is proposed which uses angular dispersion to enhance the high‐harmonic bunching with very small laser‐induced energy spread. This technique can effectively reduce the radiation saturation length without significantly reducing the peak power of the FEL. Numerical simulations demonstrate that this technique can be used for the generation of 100 MW scale level, fully temporal coherent femtosecond extreme‐ultraviolet and soft X‐ray radiation pulses through a 10 m‐long undulator based on a diffraction‐limited storage ring. [ABSTRACT FROM AUTHOR]

This paper presents a fast iterative method for the synthesis of linear and planar antenna arrays of arbitrary geometry that provides pattern reconfigurability for 5G applications. The method enables to generate wide null regions shaped according to a Gaussian distribution, which complies with recent measurements on millimeter-wave (mmWave) angular dispersion. A phase-only control approach is adopted by moving from the pattern provided by a uniformly excited array and iteratively modifying the sole phases of the excitations. This allows the simplification of the array feeding network, hence reducing the cost of realization of 5G base stations and mobile terminals. The proposed algorithm, which is based on the method of successive projections, relies on closed-form expressions for both the projectors and the null positions, thus allowing a fast computation of the excitation phases at each iteration. The effectiveness of the proposed solution is checked through numerical examples compliant with 5G mmWave scenarios and involving linear and concentric ring arrays. [ABSTRACT FROM AUTHOR]

Abstract Development of spatial multiplexing techniques and co-channel operation of different wireless systems require a way to assess the mutual influence of emitted signals. This paper focuses on the signal level evaluation as a function of the path loss that depends on the parameters of a transmitting and receiving antenna in the multipath propagation conditions. The developed procedure uses a multi-elliptical propagation model to estimate a power angular spectrum, which is the basis for evaluation of the received signal power. This procedure provides adaptation of the close-in free space reference distance path loss propagation model by considering parameters of directional parameters. Simulation studies are the basis for assessing the impact of the antenna parameters on the path loss and consequently on the received signal power. The results of these studies show the influence of the width of the main lobe and, most importantly, the direction of the antennas on the level and angular dispersion of the received signals. A comparison of the results for multi-path and free-space propagation conditions demonstrates the viability of the developed procedure for the purposes of predicting power distribution and reception direction. [ABSTRACT FROM AUTHOR]

In this study, we reported the amplitude and phase modulation based on the VO 2 tunable metasurface and verified the impact of incident angle on the reflection spectrum. The maximum reflectance modulation is 80.5 % when VO 2 changes from insulating to metallic state, at resonance wavelength 1550 nm the phase shifts of TE polarization and TM polarization are 219° and 141°, respectively. We also investigated the angular dispersion characteristics of this metasurface, and the results showed that the resonance wavelength under TE polarization is not affected by the incident angle, while the resonance wavelength under TM polarization shifts when increasing incident angle. In addition, the resonate peak spacing of TE and TM modes is over 200 nm. Angular dispersion and polarization dependence give our device the ability of angle multiplexing and polarization multiplexing. • The metasurface has polarization multiplexing capability, and the resonance summit undergoes a 200 nm shift when the polarization state of the incident light changes from TE polarization to TM polarization. • 80.5 % of the maximum reflectivity modulation occurs at the wavelength of 1550 nm, which corresponds to the resonance wavelength of the metasurface under TE polarization. • At 1550 nm, the phase shift of 141° at TM polarization and 219° at TE polarization was verified, verifying that phase shift can be enhanced by optical resonance. • We verified the effect of incidence angle on the reflected spectrum, showing that the metasurface exhibits different angular dispersion in oblique incident waves with transverse electrical (TE) or transverse magnetic (TM) polarization. [ABSTRACT FROM AUTHOR]

The increase of angular dispersion and slit resolution limit of grating spectrometers by means of variation of grating parameters is limited by its period and allowable order of diffraction. The special solutions (echelle, holographic, immersion gratings) are acceptable in a limited parameter range and are technologically complex in fabrication, thus hardly applicable to instruments of mass production. We propose to decrease slit resolution limit by one-dimensional beam widening in dispersion plane by means of passing it through oblique prism before incidence onto diffraction grating. The increase of angular dispersion can be achieved by narrowing of dispersed beams after grating while passing through other oblique prism. We prove that slit resolution limit in such a system changes approximately as multiplied by angular magnification of the first prism (that is less than 1 times). Also angular dispersion changed approximately as multiplied by angular magnification of the second prism. The Fresnel reflection from the faces of prisms is analyzed. Accounting for that factor gives the increase of resolution about 1,4–1,6 times without loss of light (and can be 2 and more times while using anti-reflective coating). The proposed method is different from the similar ones first of all by its simplicity because it uses simple optical elements – plane reflective grating and thin prisms. It can be applied to amend the analytical characteristics of dispersive spectrometers, first of all the small-sized ones.

Orbital angular momentum (OAM) multiplexing of electromagnetic (EM) waves is of great significance for high-speed wireless communication and remote sensing. To achieve high-efficiency OAM multiplexing for multi-channel incident EM waves, this paper presents a novel angle-dispersive meta-atom structure, which can introduce the required anti-symmetric phase dispersion as well as high transmission efficiency for OAM multiplexing. These meta-atoms are then arranged delicately to form an angle-dispersive metasurface working at the X band, which enables three-channel OAM multiplexing by converting highly directional transverse-magnetic (TM) waves incident from 0 and ±45° to coaxial OAM beams with l = 0 and ±2 modes, respectively. The simulation and experimental results reveal that the proposed metasurface can convert a higher proportion of energy to the required OAM modes compared to the conventional OAM multiplexing metasurfaces, which can significantly improve the coaxial transmission efficiency of multi-channel OAM multiplexing.

Abstract A series of experiments were carried out using the 200 TW laser facility at LLP, SJTU aiming to explore parametric scalings of laser driven protons employing a low cost and stable high repetition rate tape drive target system. For numerous laser shots at a repetition rate of ∼ 0.2 Hz with maximum laser intensity up to ∼ 5 × 1019 W/cm2 maximum energy of protons were measured by varying laser energy, focal spot size and laser pulse duration. The data suggests that the maximum energy of protons scales as I ∼ 0. 6 while changing the incident laser energy. Scaling trends are in good agreement with the previously reported experimental results and theoretical models. This study may provide a platform to investigate the characteristics of proton beams, such as source size and angular dispersion at a repetition rate required for many potential applications. [ABSTRACT FROM AUTHOR]

The intrinsic reaction mechanism of proton-induced composite particle pre-equilibrium emission is well known to be a statistical multistep process. However, until recently it was still not clear how important the competition between pickup and knockout is to produce a composite ejectile in the multistep sequence. An evaluation of recent (p , α) results at incident energies from 65 to 160 MeV and on representative target nuclei is presented. The virtue of analyzing power angular distributions to unravel the details of the reaction mechanism is discussed and future possible avenues of investigation are explored. [ABSTRACT FROM AUTHOR]

In this paper, a novel method to quantify the incubation of damage on piezoelectric crystal is presented. An intrinsic length scale parameter obtained from nonlocal field theory is used as a novel measure for quantification of damage precursor. Features such as amplitude decay, attenuation, frequency shifts and higher harmonics of guided waves are commonly-used damage features. Quantification of the precursors to damage by considering the mentioned features in a single framework is a difficult proposition. Therefore, a nonlocal field theory is formulated and a nonlocal damage index is proposed. The underlying idea of the paper is that inception of the damage at the micro scale manifests the evolution of damage at the macro scale. In this paper, we proposed a nonlocal field theory, which can efficiently quantify the inception of damage on piezoelectric crystals. The strength of the method is demonstrated by employing the surface acoustic waves (SAWs) and longitudinal bulk waves in Lithium Niobate (LiNbO3) single crystal. A control damage was introduced and its manifestation was expressed using the intrinsic dominant length scale. The SAWs were excited and detected using interdigital transducers (IDT) for healthy and damage state. The acoustic imaging of microscale damage in piezoelectric crystal was conducted using scanning acoustic microscopy (SAM). The intrinsic damage state was then quantified by overlaying changes in time of flight (TOF) and frequency shift on the angular dispersion relationship. [ABSTRACT FROM AUTHOR]

The biaxial magnetic-field setup for angular-dependent measurements of magnetic thin films and spintronic nanodevices is designed and presented. The setup allows for the application of the in-plane magnetic field using a quadrupole electromagnet, controlled by power supply units and integrated with an electromagnet biaxial magnetic field sensor. The setup may be used in a wide range of experiments, where the application of precise in-plane magnetic field is needed. In our experiment, the probe station is equipped with a microwave circuitry, which enables angle-resolved spin-torque measurements. The angular dependences of magnetoresistance and spin diode effect in a multilayer patterned into $\mu \text{m}$ -scale strips are shown as an operational verification of the experimental setup. We adapted an analytical macrospin model to reproduce both the resistance and spin-diode angular dependence measurements. [ABSTRACT FROM AUTHOR]

Summary: The wettability of granular solids such as soil is known to depend primarily on two factors: their inherent chemistry and their physical properties, such as their particle size, particle shape and surface roughness. Nevertheless, the distinctive physical properties of such materials have not been fully explored to gauge their wettability. In this study, the difference in wettability between a flat solid (microscope slide) and three granular solids, namely glass beads (GB), Leighton Buzzard Sand (LBS) and crushed Glass (CG), which have different physical properties, were examined. The effect of chemistry was isolated by strongly hydrophobizing the above materials by treatment with dimethyldichlorosilane. Wettability measurements were made by measuring the water–solid contact angle (CA) by the sessile drop method after adhering one layer of uniformly oriented granular solids on to double‐sided adhesive tape initially attached to a microscope slide. Techniques for particle characterization included sieving for particle size, dynamic image analysis for particle shape and confocal laser microscopy to determine surface roughness. Results show that all CAs of the granular solids exceeded that of the hydrophobized microscope slide (103°). The crushed glass had the largest CA (125°). With all three granular solids, there was an increase in CAs as particle size decreased. In addition, as particles became more angular, CAs increased. The influence of shape on wettability became more predominant as particle size decreased. The surface roughness parameter, Ra, was investigated and shown to be sensitive to both the size and shape of the particles. A decrease in Ra from 95.4 to 34.1 μm increased CAs from 107 to 125°. A similar change in CA was shown to correspond to an increase in void fraction from 40.7 to 77.4%. Our results have practical implications for the optimum use of soil by enhancing or suppressing water repellency. Highlights: How do the physical properties of granular solids such as soil influence their wettability? Effects of physical properties of particles on CAs were investigated when isolated from effect of chemistry. Particle shape becomes more important in gauging wettability as particle size decreases. Wettability of granular solids may be physically controlled by specific particle characteristics. [ABSTRACT FROM AUTHOR]

Nowadays face recognition systems are facing a new problem after having won the challenge of reliability. The problem is that these systems have become vulnerable to attacks by identity theft. In order to deceive the recognition systems hackers use several methods, such as the use of face images or videos of people belonging to the system database. Luckily, this type of attack is thwarted by the use of adapted systems. But unfortunately another type of attack that uses 3D face masks appeared. This type of attack is very efficient, since as will be shown, a high percentage of hackers who use 3D masks can mislead a good facial recognition system, like the one used in our investigation. In this paper, a new method is proposed for the detection of hackers that use 3D masks to deceive face recognition systems. This method uses the Angular Radial Transformation (ART) to extract pertinent features that are fed into a classifier to decide whether the captured image represents a face image. The performance of the proposed method was evaluated using a public 3D Mask Attack Database (3DMAD). The obtained results show the efficiency of the proposed method, since it can reduce the error rate in discriminating between a real face and a face mask down to 0.90%. [ABSTRACT FROM AUTHOR]

In this contribution, experimental analysis is introduced to determine the unloading characteristics of granular solid from flights. In a flighted rotary drum operated at optimum-loading. The studied unloading characteristics are: kinetic angle of repose of solid reside inside a flight, individual flight holdup, final discharge angle, cascading rate, and height and time of falling curtains. These characteristics are determined as a continuous function of the flight angular position. The tested drum is 0.5 m diameter and 0.15 m length, the rpm changes from 1 to 5, two number of flights 12 and 18, and two flight length ratios 0.375 and 0.75 are researched. Results revealed that: flights holdup is mainly influenced by flight length ratio among other studied parameters. Maximum height of falling curtains can be achieved when operating rotary drums at optimum-loading, since the bottom solid bed is no longer exists compared to over-loaded drums. [ABSTRACT FROM AUTHOR]

In this paper, the direction of arrival (DOA) localization of spatially distributed sources impinging on a sensor array is considered. The performance of the Distributed Source Parameter Estimator (DSPE) is studied in the presence of model errors due to the angular distribution shapes of the sources. Taking into account the coherently distributed source model proposed in Valaee et al.[1], we propose a definition of angular dispersion which makes DSPE robust to the angular distribution shapes of sources, and establish closed-form expressions of the DOA estimation bias and mean square error (MSE) due to both the model errors and the effects of a finite number of snapshots. The analytical results are validated by numerical simulations and allow to analyze the performance of DSPE for coherently distributed sources. The results also show the advantage of DSPE for the localization of spatially distributed sources even if the source angular distribution shape is not exactly known. [ABSTRACT FROM AUTHOR]

A new scheme for generating high-energy terahertz (THz) pulses based on using a multistep phase mask (MSPM) is suggested and analyzed. The mask is placed on the entrance surface of the nonlinear optical (NLO) crystal eliminating the necessity of the imaging optics. In contrast to the contact grating method, introduction of large amounts of angular dispersion is avoided. The operation principle of the suggested scheme is based on the fact that the MSPM splits a single input beam into many smaller time-delayed 'beamlets,' which together form a discretely tilted-front laser pulse in NLO crystal. The analysis of THz-pulse generation in ZnTe and lithium niobate (LN) crystals shows that application of ZnTe crystal is more preferable, especially when long-wavelength pump sources are used. The dimensions of the mask's steps required for high-energy THz-pulse generation in ZnTe and LN crystals are calculated. The optimal number of steps is estimated, taking into account individual beamlet's spatial broadening and problems related to the mask fabrication. The proposed method is a promising way to develop high-energy, monolithic, and alignment-free THz-pulse sources. [ABSTRACT FROM AUTHOR]

Atomically thin transition metal dichalcogenides like MoS2 monolayers exhibit unique luminescent properties. However, weak quantum yield and low light absorption hinder their practical applications in two-dimensional light emitting devices. Here, we report 1300 times enhancement in photoluminescence emission from a MoS2 monolayer via simultaneous Fano resonances in a dielectric photonic crystal. The spatially extended double Fano resonance scheme allows resonant enhancement of both the MoS2 absorption and emission. We also achieve unidirectional emission within a narrow divergence angle of 5° by engineering the Fano resonance angular dispersion. Our approach provides a new platform for efficient light sources with high directionality based on emerging two-dimensional materials. [ABSTRACT FROM AUTHOR]

Coherent Cherenkov radiation (ChR) generated by an electron bunch passing through a vacuum channel in the dielectric target has been considered. Simulation of ChR characteristics has been carried out basing on polarization current method. Spectral-angular distributions of coherent ChR generated by the short electron bunches are presented for a flat target with a slit and a conical target with a vacuum channel. We demonstrate feasibility of using cesium iodide conical target for bunch length diagnostics. Bunch length of about 100 fs (rms) could be determined measuring the angular distribution of coherent ChR due to material frequency dispersion. [ABSTRACT FROM AUTHOR]

A new capacitive sensor that is suitable for measuring both linear and angular displacements of a shaft over a wide range is reported in this paper. The sensor consists of a cylindrical shaft with a semi-hollow cylinder attached in the center; the shaft is capable of moving along the axis as well as rotating about the axis. Two pairs of semi-hollow-cylindrical electrodes surround the shaft, which is grounded. The amount of linear displacement and rotation is calculated by measuring the change in the capacitance of each of the four electrodes with respect to the shaft. A prototype sensor was constructed and tested; the rms error obtained is 0.6% for the linear displacement and less than 0.6% for the angular displacement. The proposed sensor has potential applications in several robotic, industrial, and automotive fields. [ABSTRACT FROM PUBLISHER]

Temperature sensitive magnetic fluid has a great potential with high performance heat transport ability as well as long distance energy (heat) transporting. In the present study experimental set-up was newly designed and constructed in order to measure basic heat transport characteristics under various magnetic field conditions. Angular dependence for the device (heat transfer section) was also taken into consideration for a sake of practical applications. The energy transfer characteristic (heat transport capability) in the magnetically-driven heat transport (cooling) device using the binary TSMF was fully investigated with the set-up. The obtained results indicate that boiling of the organic mixture (before the magnetic fluid itself reaching boiling point) effectively enhances the heat transfer as well as boosting the flow to circulate in the closed loop by itself. A long-distance heat transport of 5 m is experimentally confirmed, transferring the thermal energy of 35.8 W, even when the device (circulation loop) is horizontally placed. The highlighted results reveal that the proposed cooling device is innovative in a sense of transporting substantial amount of thermal energy (heat) as well as a long distance heat transport. The development of the magnetically-driven heat transport device has a great potential to be replaced for the conventional heat pipe in application of thermal engineering. [ABSTRACT FROM AUTHOR]

An accurate and simple technique for determining the focal length of a lens is presented. It consists of measuring the period of the fringes produced by a diffraction grating at the near field when it is illuminated with a beam focused by the unknown lens. In paraxial approximation, the period of the fringes varies linearly with the distance. After some calculations, a simple extrapolation of data is performed to obtain the locations of the principal plane and the focal plane of the lens. Thus, the focal length is obtained as the distance between the two mentioned planes. The accuracy of the method is limited by the collimation degree of the incident beam and by the algorithm used to obtain the period of the fringes. We have checked the technique with two commercial lenses, one convergent and one divergent, with nominal focal lengths (+100±1) mm and (−100±1) mm respectively. We have experimentally obtained the focal lengths resulting into the interval given by the manufacturer but with an uncertainty of 0.1%, one order of magnitude lesser than the uncertainty given by the manufacturer. [ABSTRACT FROM AUTHOR]

The article presents experimental and theoretical studies of angular dependent diffraction properties of 2D monolayer arrays of silica microspheres. High-quality large area defect-free monolayers of 1 μm diameter silica microspheres were deposited by the Langmuir-Blodgett technique under an accurate optical control. Measured angular dependencies of zeroth and one of the first order diffraction efficiencies produced by deposited samples were simulated by the rigorous Generalized Source Method taking into account particle size dispersion and lattice nonideality. [ABSTRACT FROM AUTHOR]

We investigate the possibility of the generation of arrays of single-crystal islands with small angular dispersion in order to use them as active media for solving the problems of controlling the parameters of X-ray beams. Using the example of a three-layer structure of substrate-adhesive-single-crystal wafer, we experimentally demonstrate the possibility of controlling the profile of diffractive elements by changing its temperature. It is revealed that the main reason for island misorientation is shrinkage of the adhesive material upon its solidification. Another reason for misorientation is softening the adhesive, which occurs upon plasma-chemical etching of the wafer. These effects can be eliminated by changing the temperature of attaching the wafer to the substrate surface and by using a nonsoftening adhesive. The temperature of attaching a single-crystal wafer to the substrate is calculated from the shrinkage coefficients of the adhesive and the thermal- expansion coefficients of the components of the structure. [ABSTRACT FROM AUTHOR]