Aperture Thickness Research Articles

Design of a novel gamma camera with large field of view for 16N diagnosis in the primary loop of nuclear reactor.

The assessment of the concentration and distribution of l6N, derived from 16O in the cooling water exposed to neutron irradiation, is essential for ensuring radiation safety during nuclear reactor operation. The imaging method allows for the visualization of the intensity distribution of these l6N by capturing gamma-rays emitted during their decay process. However, the existing gamma camera is exclusively compatible with gamma-rays below 2MeV. In this paper, a novel gamma camera featuring a thick double-conical penumbra aperture, a pixelated Lu1.8Y0.2SiO5:Ce scintillator array, and a position-sensitive photomultiplier tube is proposed to address this limitation. This innovative design offers a large field of view (FOV) and is suitable for high energy extended gamma source imaging. The optimization of key parameters of the camera was conducted, and a FOV of 60° and an angular resolution of up to 4.57° were achieved. Imaging simulations, including a simplified model of the primary loop of the pressurized-water reactor by GEANT4 code and image reconstruction using the expectation maximum algorithm, demonstrated that the proposed gamma camera could obtain a satisfactory spatial resolution for diagnosing the distribution of 16N in the primary loop of a nuclear reactor.

Investigation on the band narrowing and shifting effects of micro-perforated panel absorbers.

Micro-perforated panel (MPP) absorbers exhibit multiple resonance bands with increased bandwidth narrowing and shifting in higher frequencies, limiting their effectiveness. This study investigates the effects of narrowing and shifting in higher-order resonance bands of MPP absorbers. First, an acoustic impedance model for MPP absorbers is introduced, and the narrowing and shifting coefficients are defined and modeled to quantify these effects. It is observed that a larger ratio of acoustic resistance to acoustic mass is favorable for reducing the narrowing and shifting effects. Subsequently, the theoretical model is validated using a numerical model, and a parametric study is conducted to explore the influence of geometric parameters on the narrowing and shifting effects. The study reveals that decreasing aperture and panel thickness, while increasing perforation ratio and cavity depth, reduces the narrowing and shifting coefficients. Remarkably, ultra-micro-perforated panels (UMPPs) with an aperture below 0.1 mm and perforation constant below 0.0046, having relatively larger acoustic resistance and smaller acoustic mass, demonstrate near-zero band narrowing and shifting. Finally, UMPPs are fabricated using micro-electro-mechanical systems (MEMS) technology, and their normal absorption coefficients are measured. Results align with theoretical predictions, confirming UMPPs' ability to achieve zero narrowing and shifting compared to ordinary MPPs and verifying the study's findings.

Modelling small block aperture in an in-house developed GPU-accelerated Monte Carlo-based dose engine for pencil beam scanning proton therapy

Purpose. To enhance an in-house graphic-processing-unit accelerated virtual particle (VP)-based Monte Carlo (MC) proton dose engine (VPMC) to model aperture blocks in both dose calculation and optimization for pencil beam scanning proton therapy (PBSPT)-based stereotactic radiosurgery (SRS). Methods and materials. A module to simulate VPs passing through patient-specific aperture blocks was developed and integrated in VPMC based on simulation results of realistic particles (primary protons and their secondaries). To validate the aperture block module, VPMC was first validated by an opensource MC code, MCsquare, in eight water phantom simulations with 3 cm thick brass apertures: four were with aperture openings of 1, 2, 3, and 4 cm without a range shifter, while the other four were with same aperture opening configurations with a range shifter of 45 mm water equivalent thickness. Then, VPMC was benchmarked with MCsquare and RayStation MC for 10 patients with small targets (average volume 8.4 c.c. with range of 0.4–43.3 c.c.). Finally, 3 typical patients were selected for robust optimization with aperture blocks using VPMC. Results. In the water phantoms, 3D gamma passing rate (2%/2 mm/10%) between VPMC and MCsquare was 99.71 ± 0.23%. In the patient geometries, 3D gamma passing rates (3%/2 mm/10%) between VPMC/MCsquare and RayStation MC were 97.79 ± 2.21%/97.78 ± 1.97%, respectively. Meanwhile, the calculation time was drastically decreased from 112.45 ± 114.08 s (MCsquare) to 8.20 ± 6.42 s (VPMC) with the same statistical uncertainties of ~0.5%. The robustly optimized plans met all the dose–volume-constraints (DVCs) for the targets and OARs per our institutional protocols. The mean calculation time for 13 influence matrices in robust optimization by VPMC was 41.6 s and the subsequent on-the-fly ‘trial-and-error’ optimization procedure took only 71.4 s on average for the selected three patients. Conclusion. VPMC has been successfully enhanced to model aperture blocks in dose calculation and optimization for the PBSPT-based SRS.

Low-RCS Transmitarray Based on 2.5-D Cross-Polarization Converter

This paper presents a low radar cross section (RCS) transmitarray with absorption-transmission-absorption frequency response. In contrast to conventional transmitarrays based on multi-layer metallic patterns, a 2.5-dimensional cross polarization converter is employed to provide a large phase shifting range of high transmission efficiency. A benchmark transmitarray composed of the polarizer element with an aperture thickness of 2.3 mm (0.08λ) is designed to achieve a focused radiation beam. As a result, its peak gain is 22.1 dB and maximum aperture efficiency is 57.6%. Next, a low-RCS transmitarray is designed by introducing a lossy layer to absorb the out-of-band incident waves. Compared with the benchmark antenna, the radiation performance of the low-RCS transmitarray is maintained with a peak gain of 21.7 dB and maximum aperture efficiency of 53.7%. Meanwhile, dual-polarized significant RCS reduction can be obtained at both lower and higher frequencies.

Analytical model for steady-state solute diffusion in non-isothermal fractured porous media

Mass transfer in non-isothermal fractured porous media have a wide application in many natural phenomena and engineering processes. The current study focuses on developing alternative formulations of steady-state analytical modelling for thermally induced solute diffusion in fractured porous media. The proposed analytical frameworks are validated by two set of experimental data. The varied examples of coupled heat transfer and solute diffusion are evaluated by the proposed solution to discuss the effects of thermal diffusion, flow operational conditions, geometry and thermal properties of fracture and matrix on the overall transport of solute in a fractured porous media. It is found that thermal-diffusion process, or explicitly as a “Soret effect (ST)”, is a non-negligible part for investigating solute transport in non-isothermal fractured porous media. For example, increasing ST from 10-3 K−1 to 10-2 K−1 leads to a reduction of solute concentration by a factor of 1.2. We demonstrate that a larger Peclet number ensures the temperature of the solute along the fracture decreasing while its concentration along the fracture increasing. However, an increase of the temperature difference between the entry and the output shows an opposite trend. An increase in fracture aperture or matrix thickness leads to temperature decreasing and concentration increasing along the fracture and matrix as a larger amount of solute are injected from the inlet boundary. The presented analytical solutions may also serve as a benchmark test tool for alternative numerical studies of coupled heat transfer and solute diffusion in fractured porous media.

Relationships between fault characteristics and seismic responses in a large lab-scale tri-axial injection test conducted on a faulted Castlegate Sandstone

To investigate mechanisms causing microseismicity (Mw < 2) at a CO2 injection site, a large-scale triaxial block experiment was carried out on a faulted (saw-cut) cubic-meter of Castlegate Sandstone. The experiment consisted of injection tests at varying differential stresses, while monitoring and recording pore pressure and acoustic emissions (AEs). During the experiment, ∼33,000 AEs and ∼14 mm of horizontal displacement/slip, like a strike-slip fault movement, occurred. To understand the AE responses and ascertain fault characteristics near the located AEs, we modeled the topography of the fault surface, fault aperture, and fault-gouge thickness using pre- and post-experiment laser scans of the fault surface on each half of the block. Additionally, we characterized surface roughness parallel and perpendicular to slip. Models show crushing and flattening of the fault surfaces can be linked to the spatiotemporal distribution of AEs within 50 mm of the fault surface. Approximately 65% of AEs were in areas with small aperture (≤300 μm); thicker fault gouge was observed in adjacent areas with wider aperture and shows a two-fold reduction in grain size relative to unaltered Castlegate Sandstone. This work provides a conceptual understanding on fault surface evolution, which can be applied towards modeling of seismic slip.

AtGAP1 Promotes the Resistance to Pseudomonas syringae pv. tomato DC3000 by Regulating Cell-Wall Thickness and Stomatal Aperture in Arabidopsis.

GTP is an important signaling molecule involved in the growth, development, and stress adaptability of plants. The functions are mediated via binding to GTPases which are in turn regulated by GTPase-activating proteins (GAPs). Satellite reports have suggested the positive roles of GAPs in regulating ABA signaling and pathogen resistance in plants. However, the molecular mechanisms that bring forth the pathogen resistance have remained unclear. In this study, we demonstrated that the expression of AtGAP1 was inducible by Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). The overexpression of AtGAP1 in Arabidopsis promoted the expression of PR1 and the resistance to Pst DC3000. Proteomic analyses revealed the enhanced accumulation of cell-wall-modifying proteins as a result of AtGAP1 overexpression. By microscopic analyses, we showed that the overexpression of AtGAP1 resulted in increased thickness of the mesophyll cell wall and reduced stomatal aperture, which are effective strategies for restricting the entry of foliar pathogens. Altogether, we demonstrated that AtGAP1 increases the resistance to Pst DC3000 in Arabidopsis by promoting cellular strategies that restrict the entry of pathogens into the cells. These results point to a future direction for studying the modes of action of GAPs in regulating plant cell structures and disease resistance.

A New High Aperture Efficiency Transmitarray Antenna Based on Huygens Metasurfaces

In this article, a new transmitarray (TA) antenna is designed and fabricated based on Huygens metasurfaces (HMSs). An analytical method has been used to achieve the distribution of surface parameters equivalent to HMS. In this method, the required equations for computing the surface parameters are derived using ray tracing, generalized sheet transition conditions, and two conditions of local power consumption and local impedance equalization. In order to implement these surface parameters, wire and loop unit cells are utilized, which are exposed to the radiation transversely. The array of these unit cells offers high aperture efficiency broadband TA antennas in low aperture profile. The fabricated TA antenna with a low aperture thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.2\lambda $ </tex-math></inline-formula> exhibits the bandwidth, sidelobe level (SLL), and cross-polarization level of 14%, −19 dB, and −19 dB, respectively. In addition, the high aperture efficiency of 65% is reached with this TA, which shows great improvement in comparison to previous works.

Wave Dissipation and Energy-Absorption Characteristics of Wave-Absorbing Metal Plates with Different Aperture Sizes and Thicknesses under True-Triaxial Static-Dynamic-Coupling Loading

Deep rock masses exist in a complex environment with multi-field coupling; therefore, it is necessary to develop a true-triaxial static-dynamic-coupling loading test machine to explore their characteristics and mechanical response mechanism. To meet the test requirements of true-triaxial loading and strong disturbance, a wave-absorbing metal plate was selected as the boundary material between the granite and transmission end, and the modified SHPB was used to perform static-dynamic-coupling loading tests. In this study, two series of experiments on wave- absorbing metal plates were conducted, which were fixed aperture sizes with different thicknesses and fixed thicknesses with different aperture sizes. The static-dynamic-coupling loading tests on each aperture size and plate thickness were carried out under the condition of equal energy impact. The effects of the aperture size and plate thickness on the incident- and reflection-stress curves, reflectivity, energy consumption law, energy evolution, and other mechanical properties of the wave-absorbing metal plate materials were studied. The results show that the peak stress and reflectivity decrease with increasing aperture size and plate thickness, and the influence of the thickness is greater than that of the aperture size. The energy-absorption rate of the wave-absorbing metal plate increased with increasing thickness and aperture size and was maximized when the aperture size and thickness were 6–7 mm and 3–4 mm, respectively. The variation trend of the energy reflectance is opposite to that of the energy absorption and reaches a minimum when the aperture size is 6–7 mm and plate thickness is 3–4 mm. The energy transmittance of the wave-absorbing metal plate fluctuated in a stable range, but the variation range was less obvious compared to that of the energy-absorption rate.

Modeling of a photo-assisted refocusable adaptive modal liquid crystal lens with a photoconductive layer

We present a theoretical study and simulation of an adaptive modal liquid crystal lens (AMLCL) where the magnitude and distribution of the surface resistance in the modal layer can be manipulated via radiation. The modal layer of the presented AMLCL is composed of various semiconductor materials that, consequently, define its surface resistance. To modulate the magnitude and distribution of its surface resistance via radiation, a photoconductive layer can be added to the modal layer. We model an AMLCL with 5-mm aperture and 20-μm thickness theoretically. The results show that the lens reaches its maximum optical power at a surface resistance of 160 MΩ / □ and a driving voltage of 6 V for a frequency fixed at 1 kHz, which is in close agreement with a previously reported experiment. The effect of irradiation with a Gaussian beam on the optical power of the AMLCL is analyzed for different beam waists. Results indicate that the optical power of the lens increases by 15% and remains constant until the beam waist of the pump light reaches 70% of the aperture diameter. At the same time, AMLCL aberration is reduced by 10%. The optical power decreases rapidly when the beam waist exceeds 70% of the aperture diameter.

Geometrical Characterization of Glass Nanopipettes with Sub-10 nm Pore Diameter by Transmission Electron Microscopy.

Glass nanopipettes are widely used for various applications in nanosciences. In most of the applications, it is important to characterize their geometrical parameters, such as the aperture size and the inner cone angle at the tip region. For nanopipettes with sub-10 nm aperture and thin wall thickness, transmission electron microscopy (TEM) must be most instrumental in their precise geometrical measurement. However, this measurement has remained a challenge because heat generated by electron beam irradiation would largely deform sub-10 nm nanopipettes. Here, we provide methods for preparing TEM specimens that do not cause deformation of such tiny nanopipettes.

Implementation of a logarithmic division-of-focal-plane polarimeter to quantify changes in collagen alignment at varying levels of illumination.

We examine the impact of illumination, aperture, and sample thickness on two division-of-focal-plane (DoFP) polarimeters, one created using a standard 3 T pixel and the other with a forward-biased, logarithmic pixel. Across all measured metrics the logarithmic DoFP polarimeter was better able to track real-time changes in collagen alignment than the standard DoFP polarimeter.

FPCB Masked One-Step Etching Large Aperture Mirror for LiDAR

This paper presents a Flexible Printed Circuit Board (FPCB) masked one-step etching large aperture mirror for Light Detection and Ranging (LiDAR). A FPCB structure is bonded on a thin silicon wafer ( $50\sim 200~\mu \text{m}$ thick) coated with a 100 nm thick metal film and one-step of DRIE is used to etch the wafer with the FPCB structure as the mask and the metal film as the stop layer. The simple fabrication process and 0.1 mm (instead of $ needed for microfabrication) resolution photolithography lead to a very low cost of a few dollars. Copper coils embedded in the FPCB structure are attached to the backside of the large aperture mirror plate, instead of beside the mirror plate as the case in MEMS magnetic mirrors, to generate a high magnetic force and achieve a relatively high frequency considering the large aperture and high thickness. Modeling and prototyping of two designs, Mirror_A and Mirror_B, are presented to verify the novel mirror technology. LiDAR applications of the novel mirror technology are demonstrated and tested. Achieved performances are: Mirror_A, aperture $12 \times 12$ mm, oscillation frequency of 510 Hz, field of view (FOV) of 30° and radius of curvature (ROC) of 10 m; Mirror_B aperture $24 \times 24$ mm, oscillation frequency of 160 Hz, FOV of 20° and ROC of 10 m. [2020-0085]

Study on sound absorption properties of fiber materials and perforated components and their composite structures with different structural parameters

Fiber materials and perforated components are often used as basic structural units, which are widely used in the field of environmental noise reduction and automotive noise reduction.In this work, the effects of different structural parameters on the sound absorption properties of fiber materials, perforated components and their composite structures are studied. The sound absorption coefficients of fiber materials, perforated elements and their composite structures with different structural parameters were simulated by COMSOL finite element software. The transfer function method is used to measure the sound absorption in the impedance tube. The simulation results are in good agreement with the experimental results. The results show that the thickness of sound absorption material has a great influence on the sound absorption coefficient. The perforation rate is an important factor affecting the sound absorption performance of perforated components. When the perforation rate is high, it hardly absorbs sound. With the increase of aperture and wall thickness, the sound absorption performance increases in low frequency band and decreases in medium and high frequency bands. The non-periodic oscillation of sound absorption coefficient occurs with the change of cavity thickness.

A Wideband Low-Profile Efficiency-Improved Transmitarray Antenna With Over-1-bit Phase-Shifting Elements

This paper describes a wideband, low-profile and efficiency-improved transmitarray antenna achieved by employing over-1-bit phase-shifting elements and incorporating optimized phase compensation scheme. Firstly, a wideband ultrathin 1-bit phase-shifting unit cell is presented based on the polarization twisting feature of the twisted stacking aperture structure. A minor variation in unit-cell geometry is then introduced to add more degrees of freedom in phase adjustment while maintaining nearly same low insertion loss within a wide frequency range. Moreover, the resultant performances of transmitarrays using different phase compensation schemes are compared. An optimized scheme that has a minimized average phase error and effectively enhances the aperture efficiency is adopted. Results of a 21.5% 1-dB gain bandwidth, 0.127-λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> aperture thickness and 40% aperture efficiency are observed from the fabricated 14 × 14 transmitarray antenna.

Voice quality types and uses in North American English.

Voice quality has been defined variously in the literature ranging from states or postures of the glottis and vocal tract in general most broadly, to a narrower definition which refers to characteristics of vocal fold vibration during voiced phonation. Linguists have traditionally broken the voicing continuum into five basic categories based on roles they play in a language's phonology: (spread) voiceless, breathy, modal, creaky, (constricted) voiceless. Of these, the three central states, breathy, modal, creaky, are relevant to voice quality as discussed in this work. Voice qualities can be modelled as an interaction between subglottal pressure, degree of vocal fold approximation (aperture), longitudinal tension of the vocal folds (stiffness), and medial compression of the vocal folds (thickness). Breathy voicing is achieved with high glottal aperture, low stiffness, and low thickness, resulting in noise, low pitch, and increased spectral tilt. Creaky voicing has differing realizations depending on its linguistic role, prototypical creaky voice has low aperture, low stiffness, and high thickness, resulting in irregular and lower pitch, and decreased spectral tilt. Several other types of creaky voice quality exist including: 1) glottal fry, 2) multiply pulsed voice, and 3) nonconstricted creak. In this paper, we focus on creaky voice broadly-defined and concentrate on its distribution in North American English. While not contrastive, it plays an important role in phonology and a wide variety of other discourse, pragmatic, and social functions. In this context we present some of our current research into segmental and social factors relating to creaky voicing. We find a correlation between vowel height and creaky voicing. We also find evidence that voice quality is used by men to index gender in conversational speech. Our findings bear on the debate about the sociolinguistic uses of voice quality.

Embedded arrays of annular apertures with multiband near-zero-index behavior and demultiplexing capability at near-infrared

In this paper, we study transmission through the embedded arrays of subwavelength annular apertures at near-infrared. Single, i.e. non-embedded arrays of annular holes are known for their capability for high-efficiency transmission even through rather thick apertures in a wide frequency range, extending from microwaves to the visible. In the suggested structures, which contain up to four embedded arrays, multiband operation can be obtained, so that each array is mainly responsible for one of four transmission bands. In such a way, a demultiplexing-like functionality can be realized, i.e. the desired parts of the incident-wave spectrum are distributed between several transmission channels. In the studied structures, we obtain (nearly) zero phase advancement and that indicates near-zero-index behavior at the expected propagation thresholds of plasmonic modes in the frequency domain. Therefore, the earlier developed concept of supercoupling and squeezing into very narrow waveguide channels is applicable to the studied structures. The number of near-zero-index bands is determined by the number of the embedded arrays. The effects of thickness, width of the slits, and permittivity of the filling material are numerically studied and discussed in detail. It is shown that multiband transmission may exist in the near-zero-index regime in a very wide range of parameter variations.

Impact of aperture thickness on a Fraunhofer diffraction pattern

In this paper, we investigate in detail the effect of increasing aperture thickness on a Fraunhofer diffraction pattern. The scalar diffraction theory is employed to derive the solution of the far-field amplitude for a single-slit and a circular aperture in both normal and oblique incidents. Our results show that increasing the aperture thickness indisputably modifies the diffraction pattern, mainly for the wide apertures. It is proven that the maximum value of the diffracted field amplitude decreases for the non-zero values of the aperture thickness, resulting in the reduction of the fringe visibility. This study reveals that in the case of the single-guided-mode operation, the diffraction pattern is independent of the incident beam direction, and is the same for an aperture thickness larger than the attenuation length of the first evanescent mode. On the contrary, it is observed that the diffraction pattern of a wide aperture at the oblique incidence is entirely different from the popular laterally shifted normal incident diffraction profile. Therefore, we conclude that it is impossible to carefully examine the diffraction phenomena, without considering the effect of the aperture thickness.

An artificial X-ray wire test emitter and calculations on the resolution and field of view of X-ray pinhole optics by simulation

The PENELOPE Monte Carlo simulation code was used to evaluate pinhole mask parameters for X-ray backscatter imaging in a security application. This work makes four major contributions: it describes a convenient efficient test object for evaluating X-ray optics, it converts the PENELOPE output into a simulated CCD image, it compactly outlines how image characteristics can be simply and reproducibly quantified, and it gives guidance on suitable materials and geometries for pinhole masks for X-ray imaging that could be applied to more complicated X-ray optics, such as coded masks. A novel test object X-ray emitter with the shape of a thin wire was specifically designed to explore the effect of mask material thickness and pinhole aperture diameter on image quality. Setting the test object to be the X-ray emitter rather than being a passive scatterer increases computational speed. The photon energy distribution of the artificial test object was set flat between selected energy limits to avoid the model being specific to any particular X-ray source technology. The modelled detector is an array of 1040 x 1392 pixels’ area detector inside a lead-lined camera housing. The pixelated detector was modelled by digitising the surface area represented by the PENELOPE phase space file and integrating the energies of the photons impacting each pixel with MATLAB code. The pinhole must be wide enough for sufficient field of view, whilst narrow enough for sufficient spatial resolution and the mask material needs to be thick enough to absorb most X-rays. When the mask material was too thick and the aperture too narrow, a collimation effect occurred. The consequence of excess collimation in a coded aperture is partial coding giving poor image reconstruction. Pure tungsten appears the most versatile material tested, where a 2 mm thickness and 2 mm aperture gives the most appropriate image characteristics for X-ray security imaging.

Near-perfect transmission through thick apertures by inserting connected ring resonators

We report the largely enhanced transmission of electromagnetic waves through periodic subwavelength thick apertures in an opaque plate by inserting connected ring resonators through the apertures at selected microwave frequencies. In principle, nearly 100% of zero-order transmission could always be achieved theoretically without considering the loss and disorder for arbitrary thickness of the metallic plate. And this phenomenon is not highly sensitive to the geometrical parameters, which allows rather large fabrication errors. As a proof-of-concept study, two typical types of realistic samples composed of connected ring resonators are proposed and can achieve 0.8 or even higher transmittance both in simulations and experiments. In addition, one of them can also be made into a polarization converter with arbitrary rotation angles and high efficiency simultaneously. The frequency of low-order resonance-induced transmission is found to be determined mainly by the wire configuration and its geometric scale, but weakly dependent on the periodicity and diameters of holes and wires. The agreement between experimental results and numerical simulations also exhibits its great practicability in telecommunications.