Reflection Geometry Research Articles

Validation of Pin Power Calculations Using DYN3D on MIDICORE Benchmark

Three-dimensional code DYN3D is widely used for the calculation of steady states and transients in light water reactors with hexagonal fuel assemblies like VVER. The capability of pin-by-pin power calculation is implemented in the code through an intranodal power reconstruction approach. The calculations of pin power distribution using DYN3D were performed for AER MIDICORE benchmark for the validation of given extension and developed cross-section library. MIDICORE VVER-1000 core periphery power distribution benchmark was proposed on the 20th Symposium of AER. It is a 2D calculation benchmark based on the VVER-1000 core cold state geometry taking into account the geometry of explicit radial reflector. The main issue of MIDICORE benchmark is to provide the reference solution for the validation of pin-by-pin power distribution at the VVER-1000 core periphery calculated by few-group diffusion codes.
 Various 3D neutron kinetics nodal solvers HEXNEM1, HEXNEM2 and HEXNEM3 are used in DYN3D for neutron flux distribution calculation. The AER MIDICORE benchmark was solved using all solvers implemented in DYN3D with regard to the three most representative fuel assemblies. Considered fuel assemblies are placed both in the inner part and in the peripheral part of the core, and contain the pin with integrated gadolinium burnable absorber. This paper provides results of comparing the effective multiplication factor, assembly-wise power distribution and pin-by-pin power distribution calculated by DYN3D with benchmark data.

Physicochemical Characterization and Antioxidant Activity Evaluation of Idebenone/Hydroxypropyl-β-Cyclodextrin Inclusion Complex †.

Idebenone (IDE) is an antioxidant drug active at the level of the central nervous system (CNS), whose poor water solubility limits its clinical application. An IDE/2-hydroxypropyl-β-cyclodextrin (IDE/HP-β-CD) inclusion complex was investigated by combining experimental methods and theoretical approaches. Furthermore, biological in vitro/ex vivo assays were performed. Phase solubility studies showed an AL type diagram, suggesting the presence of a 1:1 complex with high solubility. Scanning electron microscopy (SEM) allowed us to detect the morphological changes upon complexation. The intermolecular interactions stabilizing the inclusion complex were experimentally characterized by exploring the complementarity of Fourier-transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR) with mid-infrared light, Fourier-transform near-infrared (FT-NIR) spectroscopy, and Raman spectroscopy. From the temperature evolution of the O–H stretching band of the complex, the average enthalpy ΔHHB of the hydrogen bond scheme upon inclusion was obtained. Two-dimensional (2D) rotating frame Overhauser effect spectroscopy (ROESY) analysis and computational studies involving molecular modeling and molecular dynamics (MD) simulation demonstrated the inclusion of the quinone ring of IDE inside the CD ring. In vitro/ex vivo studies evidenced that complexation produces a protective effect of IDE against the H2O2-induced damage on human glioblastoma astrocytoma (U373) cells and increases IDE permeation through the excised bovine nasal mucosa.

Analysis of estimation of optical properties of sub superficial structures in multi layered tissue model using distribution function method

Background and objectiveThis paper is focused on the analysis of a method of estimation of the absorption and scattering coefficients of nonhomogeneous two layered structures in time resolved near infrared spectroscopy using method based on cumulative distributions of time of flight of photons. MethodsThe research is based on the analysis of the superposition of cumulative distributions of time of flight of photons. This approach allows for detailed analysis of small variations in characteristics of time of flight of photons caused by an electromagnetic propagation in highly scattering non-homogeneous media. The method presented, based on the variation of statistical minimum distance estimation, is compared to the method of standard curve fitting. It is analyzed by fitting the results obtained from Monte-Carlo simulations of light propagation in the turbid medium to the data from the simulated measurements. ResultsThe analysis is carried out for a vast range of optical properties of two layered medium in reflectance geometry. ConclusionsThe method allows the estimation of the optical parameters despite the noise in the measured signal, with higher accuracy and generally with smaller number of error function evaluations.

Sub-second infrared broadband-laser single-shot phase-amplitude polarimetry of thin films.

We report on the first, to the best of our knowledge, sub-second, sub-mm2 infrared (IR) spectroscopic measurements of thin organic films employing a laser-based phase-amplitude polarimeter in reflection geometry. The polarimeter uses a broadband mid-IR quantum cascade laser tunable between 1318 cm-1 and 1765 cm-1, as well as a single-shot beam division scheme for simultaneous single-pulse phase and amplitude measurements. The instrument achieves 120 μm spatial and <0.5 cm-1 spectral resolution, while providing unrivaled performance in terms of acquisition times. Spectral measurements within 100 ms and single-wavelength tracking at 16 μs are now possible. Investigating the vibrational properties accessible in the mid-IR, the polarimeter was applied for monitoring changes in molecular interactions of a 150 nm thin myristic acid film during its thermal phase transition around 55°C.

Misfit function for full waveform inversion based on the Wasserstein metric with dynamic formulation

Conventional full waveform inversion (FWI) using least square distance (L2 norm) between the observed and predicted seismograms suffers from local minima. Recently, the Wasserstein metric (W1 metric) has been introduced to FWI to compute the misfit between two seismograms. Instead of comparisons bin by bin, the W1 metric allows to compare signal intensities across different coordinates. This measure has great potential to account for time and space shifts of events within seismograms. However, there are two main challenges in application of the W1 metric to FWI. The first one is that the compared signals need to satisfy nonnegativity and mass conservation assumptions. The second one is that the computation of W1 metric between two seismograms is a computationally expensive problem. In this paper, a strategy is used to satisfy the two assumptions via decomposition and recombination of original seismic data. In addition, the computation of the W1 metric based on dynamic formulation is formulated as a convex optimization problem. A primal-dual hybrid gradient method with linesearch has been developed to solve this large-scale optimization problem on GPU device. The advantages of the new method are that it is easy to implement and has high computational efficiency. Compared to the L2 norm based FWI, the computation time of the proposed method will approximately increase by 11% in our case studies. A 1D time-shift signals case study has indicated that the W1 metric is more effective in capturing time shift and makes the misfit function more convex. Two applications to synthetic data using transmissive and reflective recording geometries have demonstrated the effectiveness of the W1 metric in mitigating cycle-skipping issues. We have also applied the proposed method to SEG 2014 benchmark data, which has further demonstrated that the W1 metric can mitigate local minima and provide reliable velocity estimations without using low frequency information in the recorded data.

Trapping waves with tunable prism-coupling terahertz metasurfaces absorber.

We experimentally demonstrated a corrugated metallic metasurface based tunable perfect absorber for terahertz (THz) frequencies in a total internal reflection geometry. The absorbance is strongly depend on the central layer of this three-layer absorber, which provides a feasible approach to tune the absorption. In particular, there exist an optimal gap that enables a perfect absorption at specific frequency. Due to the simple 1D geometric structure of metasurface, its absorption frequency can be easily tailored over a wide frequency range (0.625-1.499 THz). More importantly, the modulation of the effective refractive index and loss of medium environment can be accepted as an alternative approach for the absorption properties modulation. This prism coupling absorber provides a new route for modulation of the absorption characteristics with potential applications in biological sensing.

Study of Nitrogen Doping Effect on Lattice Strain Variation in 4H-SiC Substrates by Synchrotron X-Ray Contour Mapping Method

Variations in nitrogen doping concentration across the PVT-grown 4H-SiC wafers can induce significant lattice strain, leading to degradation on the performance of SiC-based power devices. A qualitative study on the lattice strain variation in facet and off-facet regions was carried out for 4H-SiC substrates. The lattice strain maps for 4H-SiC wafers were derived from the 11-20, 1-100 (transmission geometry) and 0008 (reflection geometry) using synchrotron double crystal contour mapping method. Results show that the lattice strain within the basal plane is isotropic, while along [0001] direction, lattice strain is one order of magnitude lower, indicating elastic anisotropy of strain due to doping in 4H-SiC crystals. The distribution of lattice strain inside the facet region is more uniform than in the off-facet region. Measurement of nitrogen doping concentration by Hall effect measurements shows over 45% of difference in doping level between heavily doped facet region and off-facet region. Existence of significant lattice distortion in facet region of 4H-SiC substrates was further confirmed by X-ray rocking curve measurements.

Multi Simulation Platform for Time Domain Diffuse Optical Tomography: An Application to a Compact Hand-Held Reflectance Probe

Time Domain Diffuse Optical Tomography (TD-DOT) enables a full 3D reconstruction of the optical properties of tissue, and could be used for non-invasive and cost-effective in-depth body exploration (e.g., thyroid and breast imaging). Performance quantification is crucial for comparing results coming from different implementations of this technique. A general-purpose simulation platform for TD-DOT clinical systems was developed with a focus on performance assessment through meaningful figures of merit. The platform was employed for assessing the feasibility and characterizing a compact hand-held probe for breast imaging and characterization in reflectance geometry. Important parameters such as hardware gating of the detector, photon count rate and inclusion position were investigated. Results indicate a reduced error (&lt;10%) on the absorption coefficient quantification of a simulated inclusion up to 2-cm depth if a photon count rate ≥ 106 counts per second is used along with a good localization (error &lt; 1 mm down to 25 mm-depth).

A High-Sensitivity AlGaN/GaN HEMT Terahertz Detector With Integrated Broadband Bow-Tie Antenna

Many emerging applications in the terahertz (THz) frequency range demand highly sensitive, broadband detectors for room-temperature operation. Field-effect transistors with integrated antennas for THz detection (TeraFETs) have proven to meet these requirements, at the same time offering great potential for scalability, high-speed operation, and functional integrability. In this contribution, we report on an optimized field-effect transistor with integrated broadband bow-tie antenna for THz detection (bow-tie TeraFET) and compare the detector's performance to other state-of-the-art broadband THz detector technologies. Implemented in a recently developed AlGaN/GaN MMIC process, the presented TeraFET shows a more than twice performance improvement compared to previously fabricated AlGaN/GaN-HEMT-based TeraFETs. The detector design is the result of detailed modeling of the plasma-wave-based detection principle embedded in a full-device detector model to account for power coupling of the THz radiation to the intrinsic gated FET channel. The model considers parasitic circuit elements as well as the high-frequency impedance of the integrated broadband antenna, and also includes optical losses from a silicon substrate lens. Calibrated characterization measurements have been performed at room temperature between 490 and 645 GHz, where we find values of the optical (total beam power referenced) noise-equivalent power of 25 and ${\text{31 pW}}/\surd{\text{Hz}}$ at 504 and 600 GHz, respectively, in good agreement with simulation results. We then show the broadband detection capability of our AlGaN/GaN detectors in the range from 0.2 to 1.2 THz and compare the TeraFETs’ signal-to-noise ratio to that of a Golay cell and a photomixer. Finally, we demonstrate an imaging application in reflection geometry at 504 GHz and determine a dynamic range of >40 dB.

Estimating the Dependence of Differential Pathlength Factor on Blood Volume and Oxygen Saturation using Monte Carlo method.

Differential Pathlength Factor (DPF) is a vital parameter for the Beer-Lambert law based calculations in estimating tissue perfusion using non-invasive optical techniques. A significant error in the measured concentration of oxyhemoglobin and deoxyhemoglobin has been reported due to the usage of wrong DPF values. The dependence of DPF on blood oxygen saturation and blood volume has never been studied earlier. In this work, a Monte Carlo model of perfused skin tissue was developed and executed at 660 nm and 940 nm optical wavelengths at a reflectance geometry. DPFs were simulated through 1-10 mm source detector separations at different blood volumes and oxygen saturations. Results showed higher DPFs at lower wavelengths and considerable variation with blood volume and oxygen saturation.

Evaluation of oxygenation in the surface layers of biological tissues based on diffuse optical spectroscopy with automated calibration of measurements

To assess the oxygen saturation (oxygenation) in the surface layers of biological tissues (at a depth of 4 mm), a compact system based on diffuse optical spectroscopy (DOS) with reflective measurement geometry in the wavelength range of 520 – 590 nm is proposed. The experimental DOS device is based on a broadband LED source of probe radiation and a spectrometer using a fibre-optic radiation delivery system. To calculate the oxygenation, an original method is proposed based on measuring the intensity of scattered light at four different locations of the source and receiver on the surface of the object under study (four-measurement method). The developed method allows for the device hardware parameters (optical contact with the tissue, transient characteristics of the radiation delivery system) and does not require any additional calibration measurements. The results of testing the DOS system using the four-measurement method for monitoring the oxygen saturation of tissues during the artificial occlusion of the blood vessels agree with the published data of other research teams.

Determination of the terahertz pulse emitting dipole orientation by terahertz emission measurements

Terahertz pulse emission from the photoexcited semiconductor surface heavily depends on the orientation of the photo-induced electric dipole. Two methods to determine the orientation of the terahertz pulse emitting dipole have been demonstrated. Method I relies on the measurement of THz emission dependencies on the angle of incidence in the transmission geometry, while method II is based on the measurements of THz emission in the reflection geometry. Theoretical reasoning for both of these methods has been presented. Both of these methods have been tested with a semi-insulating GaAs substrate using an external magnetic field in order to change the tilt angle of the electric dipole. The investigation presented in this work leads to an assumption that the magnetic field induced change in the dipole tilt angle is proportional to the mobility of electrons. Thus, the suggested method may become a promising tool for testing the quality of substrates and epitaxial layers.

Exploiting Total Internal Reflection Geometry for Terahertz Devices and Enhanced Sample Characterization

AbstractTo promote potential applications of terahertz (THz) technology, more advanced functional THz devices with high performance are needed, including modulators, polarizers, lenses, wave retarders, and antireflection coatings. This work summarizes recent progress in THz components built on functional materials including graphene, vanadium dioxide, and metamaterials. The key message is that, while the choice of materials used in such devices is important, the geometry in which they are employed also has a significant effect on the performance achieved. In particular, devices operating in total internal reflection geometry are reviewed, and it is explained how this geometry is able to be exploited to achieve a variety of THz devices with broadband operation.

A corner reflector of graphene Dirac fermions as a phonon-scattering sensor

Dirac fermion optics exploits the refraction of chiral fermions across optics-inspired Klein-tunneling barriers defined by high-transparency p-n junctions. We consider the corner reflector (CR) geometry introduced in optics or radars. We fabricate Dirac fermion CRs using bottom-gate-defined barriers in hBN-encapsulated graphene. By suppressing transmission upon multiple internal reflections, CRs are sensitive to minute phonon scattering rates. Here we report on doping-independent CR transmission in quantitative agreement with a simple scattering model including thermal phonon scattering. As a signature of CRs, we observe Fabry-Pérot oscillations at low temperature, consistent with single-path reflections. Finally, we demonstrate high-frequency operation which promotes CRs as fast phonon detectors. Our work establishes the relevance of Dirac fermion optics in graphene and opens a route for its implementation in topological Dirac matter.

Reflection geometries in absorbed and unabsorbed AGN

Context. The hard X-ray emission of active galactic nuclei (AGN), and in particular, the reflection component, is shaped by the innermost and outer regions of the galactic nucleus. Aims. Our main goal is to investigate the variation of the Compton hump amongst a population of sources and correlate it with other spectral properties to constrain the source geometry. Methods. We studied the NuSTAR hard X-ray spectra of a sample of 83 AGN and performed a detailed spectral analysis of each of them. Based on their spectral shape, we divided the sample into five categories and also studied their stacked spectra. Results. We found a stronger reflection in mildly obscured sources, which verifies the results reported in previous works. In addition, the reflection behaviour, and probably origin, varies with absorption. The accretion disc seems to be the main reflector in unabsorbed sources. A clumpy torus seems to produce most of the reflection in obscured sources. The filling factor of the clouds surrounding the active nucleus is a key parameter that drives the appearance of AGN. Finally, we found that the Fe line and the Compton hump are roughly correlated, as expected.

A benchtop shock physics laboratory: Ultrafast laser driven shock spectroscopy and interferometry methods.

Common Ti:sapphire chirped pulse amplified laser systems can be readily adapted to be both a generator of adjustable pressure shock waves and a source for multiple probes of the ensuing ultrafast shock dynamics. In this paper, we detail experimental considerations for optimizing the shock generation, interferometric characterization, and spectroscopic probing of shock dynamics with visible and mid-infrared transient absorption. While we have reported results using these techniques elsewhere, here we detail how the spectroscopies are integrated with the shock and interferometry experiment. The interferometric characterization uses information from beams at multiple polarizations and angles of incidence combined with thin film equations and shock dynamics to determine the shock velocity, particle velocity, and shocked refractive index. Visible transient absorption spectroscopy uses a white light supercontinuum in a reflection geometry, synchronized to the shock wave, to time resolve shock-induced changes in visible absorption such as changes to electronic structure or strongly absorbing products and intermediates due to reaction. Mid-infrared transient absorption spectroscopy uses two color filamentation supercontinuum generation combined with a simple thermal imaging microbolometer spectrometer to enable broadband single shot detection of changes in the vibrational spectra. These methods are demonstrated here in the study of shock dynamics at stresses from 5 to 30 GPa in organic materials and from a few GPa to >70 GPa in metals with spatial resolution of a few micrometers and temporal resolution of a few picoseconds. This experiment would be possible to replicate in any ultrafast laser laboratory containing a single bench top commercial chirped pulse amplification laser system.

Deployable cylindrical phased-array applicator mimicking a concentric-ring configuration for minimally-invasive delivery of therapeutic ultrasound

A novel design for a deployable catheter-based ultrasound applicator for endoluminal and laparoscopic intervention is introduced. By combining a 1D cylindrical ring phased array with an expandable paraboloid or conical-shaped balloon-based reflector, the applicator can be controllably collapsed for compact delivery and deployed to mimic a forward-firing larger diameter concentric ring array with tight focusing and electronic steering capabilities in depth. Comprehensive acoustic and biothermal parametric studies were employed to characterize the capabilities of the applicator design as a function of transducer dimensions, phased array configuration, and balloon reflector geometry. Modeling results indicate that practical balloon sizes (43–57 mm expanded diameter), transducer array configurations (e.g. 1.5 MHz, 10 mm OD × 20 mm length, 8 or 16 array elements), and sonication durations (30 s) are capable of producing spatially-localized acoustic intensity focal patterns and ablative thermal lesions (width: 2.8–4.8 mm; length: 5.3–40.1 mm) in generalized soft tissue across a 5–100 mm depth range. Larger focal intensity gain magnitudes and narrower focal dimensions are attainable using paraboloid-shaped balloon reflectors with natural geometric focal depths of 25–55 mm, whereas conical-shaped reflectors (angled 45–55°) produce broader foci and extend electronic steering range in depth. A proof-of-concept phased array applicator assembly was fabricated and characterized using hydrophone and radiation force balance measurements and demonstrated good agreement with simulation. The results of this study suggest that combining small diameter cylindrical phased arrays with expandable balloon reflectors can enhance minimally invasive ultrasound-based intervention by augmenting achievable focal gains and penetration depths with dynamic adjustment of treatment depth.

Evaluating Impact of Rain Attenuation on Space-borne GNSS Reflectometry Wind Speeds

The novel space-borne Global Navigation Satellite System Reflectometry (GNSS-R) technique has recently shown promise in monitoring the ocean state and surface wind speed with high spatial coverage and unprecedented sampling rate. The L-band signals of GNSS are structurally able to provide a higher quality of observations from areas covered by dense clouds and under intense precipitation, compared to those signals at higher frequencies from conventional ocean scatterometers. As a result, studying the inner core of cyclones and improvement of severe weather forecasting and cyclone tracking have turned into the main objectives of GNSS-R satellite missions such as Cyclone Global Navigation Satellite System (CYGNSS). Nevertheless, the rain attenuation impact on GNSS-R wind speed products is not yet well documented. Evaluating the rain attenuation effects on this technique is significant since a small change in the GNSS-R can potentially cause a considerable bias in the resultant wind products at intense wind speeds. Based on both empirical evidence and theory, wind speed is inversely proportional to derived bistatic radar cross section with a natural logarithmic relation, which introduces high condition numbers (similar to ill-posed conditions) at the inversions to high wind speeds. This paper presents an evaluation of the rain signal attenuation impact on the bistatic radar cross section and the derived wind speed. This study is conducted simulating GNSS-R delay-Doppler maps at different rain rates and reflection geometries, considering that an empirical data analysis at extreme wind intensities and rain rates is impossible due to the insufficient number of observations from these severe conditions. Finally, the study demonstrates that at a wind speed of 30 m/s and incidence angle of 30°, rain at rates of 10, 15, and 20 mm/h might cause overestimation as large as ≈0.65 m/s (2%), 1.00 m/s (3%), and 1.3 m/s (4%), respectively, which are still smaller than the CYGNSS required uncertainty threshold. The simulations are conducted in a pessimistic condition (severe continuous rainfall below the freezing height and over the entire glistening zone) and the bias is expected to be smaller in size in real environments.

Reflector dip estimates based on seismic waveform curvature/flexure analysis

Reliable estimation of the reflector dip serves as a fundamental and essential tool for subsurface structure interpretation from 3D seismic surveys. We have developed a new method for accurate dip estimation, which consists of two major components. First, the curvature/flexure concept is adapted from the traditional reflector geometry analysis to work for the seismic waveforms, denoted as the waveform curvature and waveform flexure, respectively. Physically, both of them are capable of measuring the most and least apparent variation of the local waveforms in a seismic profile, and thus the corresponding measuring orientations represent the normal and dipping directions of the seismic reflectors, respectively. Second, the complex seismic trace is incorporated into our workflow of waveform curvature/flexure analysis to enhance the accuracy of dip estimation in the presence of seismic noises, especially in the zones of weak reflection intensity, such as zero crossings. The added values of our method are verified through various applications, such as horizon tracking and fault detection, to two 3D seismic data sets, one from the Netherlands North Sea and the other from the Great South Basin in New Zealand that is rich of faults. The results not only demonstrate the good accuracy of the generated dip vectors in guiding the seeded horizon tracking, but they also hold great potential for assisting seismic interpretation in more ways, such as structural-oriented filtering and attribute analysis.

Properties of Reflection Geometries and the Corresponding Group Spaces

To any reflection group, i.e. a pair \((G, \mathfrak {D})\) consisting of a group G and a set \( \mathfrak {D}\) of involutory generators satisfying the “Three Reflection Axiom” there can be associated a planar (called reflection geometry) and a spatial (called group space) incidence structure. In the spatial case the elements \(\alpha \) of \(\mathfrak {D}^2 \) are called “points” and via the notion pencil and proper pencil we define certain subsets of \(\mathfrak {D}^2 \) as lines and projective lines. Let \(\mathfrak {G}\) denote the set of all lines and \(\mathfrak {G}_0\) the subset of all projective lines. Then \((G,\mathfrak {G})\) is an incidence space which can be provided with two parallelism \(\parallel _l\) and \(\parallel _r\) such that \((G,\mathfrak {G},\parallel _l,\parallel _r)\) becomes a double space. Between a point \(\alpha \) and the elements \(\varepsilon \) of \(\mathfrak {D}^3 \) we define an incidence relation by \(\varepsilon \cdot \alpha \in \mathfrak {D}\). Then \(\langle \varepsilon \rangle := \{\xi \in \mathfrak {D}^2 \ | \ \varepsilon \cdot \xi \in \mathfrak {D} \}\) is a 2-dimensional subspace of \((G,\mathfrak {G})\), i.e. a plane. In this paper we show: If \(L \in \mathfrak {G}_0\) is a projective line and \(\varepsilon \in \mathfrak {D}^3\) then \(L \cap \langle \varepsilon \rangle \ne \emptyset \). If \(|L \cap \langle \varepsilon \rangle | \ge 2\) then \(L \subseteq \langle \varepsilon \rangle \). If \( \alpha \in \mathfrak {D}^2 {\setminus } L\) then there is exactly one \(\delta \in \mathfrak {D}^3\) with \(\alpha \cup L \subseteq \langle \delta \rangle \). There is exactly one line \(M \subseteq \langle \varepsilon \rangle \) with \( M \parallel _l L\) denoted by \((\varepsilon \parallel _l, L) := M \) (resp. \(M \parallel _r L\) denoted by \((\varepsilon \parallel _r, L) \)) (cf. Theorem 3.10).