Symmetric Spot Research Articles

2D CFD modeling for pyrolysis of a large biomass particle: Effect of L/D ratio, internal convection and shrinkage

A transient 2D kinetic-heat transfer model for the pyrolysis of a large biomass particle, incorporating, primary and secondary reaction kinetics, internal convection and shrinkage in particles was developed and validated with experimental results. The RMS errors between the predicted and experimental temperature and residual mass fraction were estimated to be small - 0.020, 0.017, 0.011, 0.018 and 0.024, 0.022, 0.016, 0.025 at reactor temperatures of 573, 623, 673, 723 K, respectively. The pyrolysis behaviour was explained by the computed spatial distributions of velocity, pressure, temperature and residual mass fraction within the biomass particle. At a high L/D (∼5), two symmetric hot spots were formed near the two axial flat edges after 400 s, which formed a single dumbbell-shaped in the axial central core after 600 s and existed for a long time of 1500 s. It merged into a single spherical hot spot at the centre after a long reaction time. For a low L/D (∼1), however, an elliptical-shaped hot spot formed after 400 s changes to a spherical hot spot at the particle centre after 500 s. Uniformity in temperature inside the particle was attained much earlier at a smaller L/D ratio.

2D Modeling and Simulation of Pyrolysis of a Thermally Thick Biomass Particle

ABSTRACT A transient 2D kinetic-heat transfer model incorporating primary and secondary reactions is proposed to investigate the effect of reactor temperature and particle length/diameter (L/D) ratio on the pyrolysis behavior and validate it with the experimental results. The RMS error between the experimental and the model predictions are found to be 0.36–1.89% for 2D model and 13.00–13.11% for 1D model at reactor temperatures 723–798 K and L/D of 1.0. This uncderscores the necessity for the use of the 2D model in place of the 1D model, particularly at the lower L/D ratio. Temporal propagation of temperature and mass fractional residue profiles at different locations of the pyrolyzing casuarina (Casuarina equisetifolia) biomass particle is analyzed. At a high L/D (~6), two symmetric hot spots are found to appear at two axial end faces, which gradually merge to form a dumbbell-shaped hot spot near the central core. For a low L/D (~1), a symmetrical, concentric, elliptical, shell-shaped hot spot appears at a short distance from the outer surface, which quickly propagates toward the center, eventually merging into a sphere at the particle center. It is estimated that for a 0.0254 m diameter particle at the reactor temperature of 673 K, the optimal residence time is 10 min for L/D = 1, while it is 17 min for L/D = 2.

Laser beam shaping using a photoinduced azopolymer droplet-based mask.

The dewetting of an azopolymer droplet, followed by the photostructuration of the evaporated droplet, is employed to create an amplitude mask. This straightforward process yields a large area featuring periodic micro- and nanostructures. The resulting pattern is utilized to generate a nondiffracting beam. Starting with a Gaussian beam illuminating the amplitude mask, the critical aspect is the production of a bright, ring-shaped beam with a high radius-to-width ratio and symmetric central laser spots, each with the same intensity. This alternative approach to shaping a laser beam is demonstrated as a rapid and cost-effective fabrication technique.

A comprehensive case study on vitiligo: Navigating challenges and treatment strategies

This in-depth case study examines the complex terrain of vitiligo and the difficulties that thirty-year-old Mrs. A. must overcome. The storey is told via a thorough analysis of her clinical appearance, which includes the emergence of distinct, symmetrical white spots on several body regions. Given Mrs. A's medical history of general health and her elevated stress levels prior to the depigmentation, the diagnostic procedure is carefully broken down, including physical examinations, medical history evaluations, and pertinent laboratory testing. Examining the epidemiology of vitiligo, the study clarifies its worldwide frequency, age at start, genetic predispositions, autoimmune correlations, and subtle effects on people from various ethnic origins. This case study stands out for its examination of the discrepancy between traditional textbook representations and the dynamic, Mrs. A's emotional and psychological reactions to vitiligo require individualised care. A multidisciplinary approach guides the development of treatment strategies that include photo therapy, topical corticosteroids, and specialised psychological support. The storey ends with a discussion of the follow-up procedure, an assessment of the effectiveness of the treatment, emotional healing, and the continued difficulties of long-term care. This case study provides insightful information about the comprehensive care of vitiligo sufferers, highlighting the significance of customised, team-based approaches in addressing the complex aspects of this skin disease.

Absence of the impurity-resonance spot at a Bi defect located near the Zn impurity in Bi2Sr2Ca(Cu1-xZnx)2O8+δ

Zn dopants to Cu sites in high-Tc cuprates strongly suppress superconductivity and act as impurities with a strong quasiparticle scattering resonance. Using the scanning tunneling microscope, we investigate the electronic structure in the atomic scale around Zn impurities in Bi2Sr2Ca(Cu1-xZnx)2O8+δ. The intense scattering resonance of the Zn impurity in the CuO2 layer strongly affects the measured local density of states of the BiO layer on the surface. The pattern of the bound state induced by a Zn impurity consists of a central spot at the Bi atom just above the Zn impurity and eight symmetric spots at the next nearest neighboring (NNN) and the third nearest neighboring (3NN) sites of Bi atoms. When the Bi atom above the NNN Cu atom is missing, the corresponding scattering spot is absent simultaneously. Our results indicate that the measured impurity-induced bound state pattern is strongly influenced by Bi atoms on the surface and therefore supports the “filter” theoretical model of the nonlocal interlayer tunneling effect from the CuO2 layer to the BiO layer on the surface. Our research provides extra information about the impurity-induced bound state by Zn impurities.

Large Amplitude Radially Symmetric Spots and Gaps in a Dryland Ecosystem Model

We construct far-from-onset radially symmetric spot and gap solutions in a two-component dryland ecosystem model of vegetation pattern formation on flat terrain, using spatial dynamics and geometric singular perturbation theory. We draw connections between the geometry of the spot and gap solutions with that of traveling and stationary front solutions in the same model. In particular, we demonstrate the instability of spots of large radius by deriving an asymptotic relationship between a critical eigenvalue associated with the spot and a coefficient which encodes the sideband instability of a nearby stationary front. Furthermore, we demonstrate that spots are unstable to a range of perturbations of intermediate wavelength in the angular direction, provided the spot radius is not too small. Our results are accompanied by numerical simulations and spectral computations.

Imaging through a square multimode fiber by scanning focused spots with the memory effect.

The existence of a shift-shift memory effect in square waveguides, whereby any translation of the input field induces translations in the output field in four symmetrical directions, has been previously observed by correlation measurements. Here we demonstrate that this memory effect is also observed in real space and can be put to use for imaging purposes. First, a focus is created at the output of a square-core multimode fiber, by wavefront shaping based on feedback from a guide-star. Then, because of the memory effect, four symmetrical spots can be scanned at the fiber output by shifting the wavefront at the fiber input. We demonstrate that this property can be exploited to perform fluorescence imaging through the multimode fiber, without requiring the measurement of a transmission matrix.

2D reciprocal space map of etched metalorganic chemical vapor deposited CdTe(001) film surface on miscut GaAs(001)

CdTe thin films have drawn continued interest in research and applications in various fields such as optoelectronics. We report on the study of a two-dimensional (2D) reciprocal space map of Br-methanol etched CdTe(001) epitaxial film grown by metalorganic chemical vapor deposition on miscut GaAs(001) using azimuthal reflection high-energy electron diffraction (ARHEED), which reveals a two-fold symmetric surface with a rectangular unit mesh. This is in contrast to the observed four-fold symmetry with a square unit mesh on an etched miscut single crystal CdTe(001). Two sets of two-fold symmetric diffraction spots with unequal intensities indicate unequal populations of two 90° orientation domains in the etched film. Based on the 2D maps and tilted azimuthal dependent RHEED patterns of the etched film, it unveils that the short length of rectangular unit mesh in the dominant domain aligns with the step edge direction. A simple method to characterize the miscut angle of a heteroepitaxial film grown on a miscut substrate is demonstrated using ARHEED. Both etched single crystal and film surfaces are Te rich with a higher Te to Cd ratio on the elongated hillocks in the etched film disclosed by scanning Auger electron spectroscopy mapping. This methodology can be applied to examine etched epitaxial film's surfaces that might deviate from bulk structure or bulk stoichiometry before interfacing with other materials to form heterojunctions or making ohmic contacts with metals.

Stellar Obliquity from Spot Transit Mapping of Kepler-210

Stellar obliquity, the angle between the stellar spin and the perpendicular to the planetary orbit, also known as the spin–orbit angle, holds clues to the formation and evolution of planetary systems. When a planet transits a star periodically, it may cross in front of a stellar spot, producing a noticeable signal on the transit light curve. Spot transit mapping can be used to measure stellar obliquity. Here we present the analysis of Kepler-210, a K-dwarf star with two mini-Neptune-size planets in orbit. Interestingly, the spot mapping from the outer planet, Kepler-210 c, resulted in a spot distribution with no spots detected at longitudes >38°, whereas the spots occulted by Kepler-210 b displayed all range of longitudes. The best explanation for this was that Kepler-210 c exhibited an inclined orbit, while the orbit of Kepler-210 b was parallel to the stellar equator. Thus, transits of Kepler-210 c occulted different latitude bands of the star. The observed maximum spot topocentric longitude of 38° implied an orbital obliquity of 18°–45° for Kepler-210 c. Further considering a symmetric spot distribution in latitude with respect to the stellar equator, the obliquity was restricted to 34.°8, implying a maximum spot latitude of 40°. The differential rotation profile calculated from the oblique orbit for Kepler-210 c agreed with that obtained from the spots occulted by Kepler-210 b. Combining results from both planets yields a rotational shear of ΔΩ = 0.0353 ± 0.0002 rad day−1 and a relative rotational shear of 6.9%. The causes of the Kepler-210 c misalignment remain to be explained.

Is cysteamine use effective in the treatment of melasma? A systematic review and meta-analysis.

Melasma is a recurrent hypermelanosis disorder characterized by the appearance of brownish and symmetrical spots on the skin. It affects the quality of life and is resistant to available treatment approaches. Cysteamine has been reported as a promising depigmenting agent for melasma treatment and following formulation enhancement, its use is being reported. This review aimed to evaluate the efficacy of the use of depigmenting formulations containing 5% cysteamine in the treatment of patients with melasma. A systematic search was performed in PubMed, Science Direct, and Scielo databases until December 27, 2021, based on criteria selected by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Statistical analysis was performed with Review Manager 5.4 software. The risk of bias was assessed using the Cochrane Risk of Bias Tool for Randomized Trials. A total of six studies containing 120 melasma patients treated with 5% cysteamine were included in this meta-analysis. The meta-analysis demonstrated that 5% cysteamine is effective for the treatment of patients with melasma (MD 6.26 [95% CI 3.68-8.83], p < 0.0001, I2 =86%). In this review, through meta-analysis allows concluding that 5% cysteamine is effective in the treatment of melasma and presents a low probability of side or adverse effects.

Acoustic Holograms for Bilateral Blood-Brain Barrier Opening in a Mouse Model.

Transcranial focused ultrasound (FUS) in conjunction with circulating microbubbles injection is the sole non-invasive technique that temporally and locally opens the blood-brain barrier (BBB), allowing targeted drug delivery into the central nervous system (CNS). However, single-element FUS technologies do not allow the simultaneous targeting of several brain structures with high-resolution, and multi-element devices are required to compensate the aberrations introduced by the skull. In this work, we present the first preclinical application of acoustic holograms to perform a bilateral BBB opening in two mirrored regions in mice. The system consisted of a single-element focused transducer working at 1.68 MHz, coupled to a 3D-printed acoustic hologram designed to produce two symmetric foci in anesthetized mice in vivo and, simultaneously, compensate the aberrations of the wavefront caused by the skull bones. T1-weighed MR images showed gadolinium extravasation at two symmetric quasi-spherical focal spots. By encoding time-reversed fields, holograms are capable of focusing acoustic energy with a resolution near the diffraction limit at multiple spots inside the skull of small preclinical animals. This work demonstrates the feasibility of hologram-assisted BBB opening for low-cost and highly-localized targeted drug delivery in the CNS in symmetric regions of separate hemispheres.

Study of magnetic fringe fields and interference effects on beam dynamics for proton facility gantry

ABSTRACT Proton therapy facilities require a beamline that effectively delivers particles to a nozzle that forms symmetric and achromatic beam spots. In the gantry lattice of the SC200 facility, the magnetic components are designed with a compact layout due to space constraints. This makes it important to properly deal with fringe fields and their interference when more accurate simulations of beam dynamics are required. In this paper, we establish field distributions based on real extracted magnetic maps and analyse the influences of linear fields on beam qualities by combining a perturbation model with Monte Carlo code in BDSIM. To verify the results, COSY INFINITY with the Enge function was used to quantify the beam variations at the isocenter; the results were in good agreement with those of BDSIM. Compared with the conventional hard edge model, beam mismatch at the isocenter is evidence of the impacts of fringe fields, which pose challenges to clinical dose planning. Hence, linear optical optimization on the gantry is also necessary to meet safety and precision requirements. These efforts will guide the commissioning of the beamline.

Optical analysis of facial nerve degeneration in Bell’s palsy

This paper is an initial proof of concept for an optical speckled-based method for the evaluation of facial nerve paralysis. Differences between the affected and the healthy sides of the face were measured in patients with Bell's palsy—a peripheral facial nerve paralysis. The patients’ faces were illuminated with two symmetrical spots on their nasolabial folds and the reflected speckle patterns were analyzed. Muscle activity was evaluated by muscle tone contraction-release motion inducing associated skin tilting movements. The skin movements were imaged with a defocused lens, which enables extraction of the speckle pattern's time changing trajectory. We found an asymmetry ratio expression that may be the key for the estimation of the degeneration level in Bell's palsy.

Endless Single-Mode Photonics Crystal Fiber Metalens for Broadband and Efficient Focusing in Near-Infrared Range.

The advent of the ‘lab-on-fiber’ concept has boosted the prosperity of optical fiber-based platforms integrated with nanostructured metasurface technology which are capable of controlling the light at the nanoscale for multifunctional applications. Here, we propose an endless single-mode large-mode-area photonic crystal fiber (LMA-PCF) integrated metalens for broadband and efficient focusing from 800 to 1550 nm. In the present work, the optical properties of the substrate LMA-PCF were investigated, and the metalens, consisting of dielectric TiO2 nanorods with varying radii, was elaborately designed in the fiber core region with a diameter of 48 μm to cover the required phase profile for efficient focusing with a high transmission. The focusing characteristics of the designed metalens were also investigated in detail over a wide wavelength range. It is shown that the in-fiber metalens is capable of converging the incident beams into the bright, symmetric, and legible focal spots with a large focal length of 315–380 μm depending on the operating wavelength. A high and average focusing efficiency of 70% was also obtained with varying wavelengths. It is believed the proposed fiber metalens may show great potential in applications including fiber laser configuration, machining, and fiber communication.

Single-layer multitasking vortex-metalens for ultra-compact two-photon excitation STED endomicroscopy imaging.

With the novel capabilities of engineering the optical wavefront at the nanoscale, the dielectric metalens has been utilized for fluorescence microscopy imaging system. However, the main technical difficulty is how to realize the achromatic focusing and light modulation simultaneously by a single-layer metalens in the two-photon excitation STED (TPE-STED) endomicroscopy imaging system. Herein, by combining the spatial multiplexing technology and vortex phase modulation, a single-layer multitasking vortex-metalens as a miniature microscopy objective on the end of fiber was proposed. The multitasking vortex-metalens with 36-sectors interleaving (diameter of 100 μm) could focus the excitation beam (1050 nm) and depletion beam (599 nm) to the same focal distance, modulate a doughnut-shaped depletion spot with vortex phase and reshape the focal spots to further make improvement in the quality and symmetry. According to the TPE-STED theory, a symmetrical effective fluorescent spot with the lateral resolution of 30 nm was obtained by the proposed metalens. Thus, with the advantage of ultra-compact and lightweight, we prospect that the subminiature multitasking metalens will help guide future developments in high-performance metalenses toward high-resolution and real-time images for deep biological tissue in vivo and enable scientific high-end miniature endomicroscopy imaging system.

More Symmetrical "Hot Spots" Ensure Stronger Plasmon-Enhanced Fluorescence: From Au Nanorods to Nanostars.

Plasmon-enhanced fluorescence (PEF) is considered to be a powerful signal amplification technology to overcome intrinsic shortcomings of photobleaching and brightness of the traditional fluorescent dyes. Nevertheless, exploitation of PEF-based probes for bioimaging application is still at a very early stage. In this work, a simple but powerful gold nanostar (Au NST)@SiO2-based PEF probe with 20 symmetric "hot spots" was developed for highly sensitive "lighting up" in situ imaging of intracellular microRNAs (miRNAs). By regulating the thickness of the silica shell, the distance between Au NSTs and fluorescent dyes was controlled, and the optimum fluorescence enhancement (21-fold) was obtained with the silica shell thickness of approximately 22 nm. Thanks to the 20 more powerful "hot spots" that can produce stronger localized electric fields, the Au NST-based PEF probe exhibits stronger PEF effects than the traditional plasmonic nanostructures such as gold nanorods (Au NRs), gold nanobipyramids (Au NBPs), and triangular gold nanoprisms (Au NPRs), resulting in high sensitivity and improved detection limit (LOD) of 0.21 pM for miRNA-21 analysis. Moreover, not only cancer cells (MCF-7 and Hela) and normal cells (L02) with distinct miRNA-21 expression levels can be discriminated but also tumor cells in co-cultured mixtures can be recognized, indicating its promising potential in clinical diagnosis.

An Asymptotic Analysis of Localized Three-Dimensional Spot Patterns for the Gierer--Meinhardt Model: Existence, Linear Stability, and Slow Dynamics

Localized spot patterns, where one or more solution components concentrates at certain points in the domain, are a common class of localized pattern for reaction-diffusion systems, and they arise in a wide range of modeling scenarios. In an arbitrary bounded 3-D domain, the existence, linear stability, and slow dynamics of localized multi-spot patterns is analyzed for the well-known singularly perturbed Gierer-Meinhardt (GM) activator-inhibitor system in the limit of a small activator diffusivity $\varepsilon^2\ll 1$. Our main focus is to classify the different types of multi-spot patterns, and predict their linear stability properties, for different asymptotic ranges of the inhibitor diffusivity $D$. For the range $D={\mathcal O}(\varepsilon^{-1})\gg 1$, although both symmetric and asymmetric quasi-equilibrium spot patterns can be constructed, the asymmetric patterns are shown to be always unstable. On this range of $D$, it is shown that symmetric spot patterns can undergo either competition instabilities or a Hopf bifurcation, leading to spot annihilation or temporal spot amplitude oscillations, respectively. For $D={\mathcal O}(1)$, only symmetric spot quasi-equilibria exist and they are linearly stable on ${\mathcal O}(1)$ time intervals. On this range, it is shown that the spot locations evolve slowly on an ${\mathcal O}(\varepsilon^{-3})$ time scale towards their equilibrium locations according to an ODE gradient flow, which is determined by a discrete energy involving the reduced-wave Green's function. The central role of the far-field behavior of a certain core problem, which characterizes the profile of a localized spot, for the construction of quasi-equilibria in the $D={\mathcal O}(1)$ and $D={\mathcal O}(\varepsilon^{-1})$ regimes, and in establishing some of their linear stability properties, is emphasized.

Edge-Plane Exposed N-Doped Carbon Nanofibers Toward Fast K-Ion Adsorption/Diffusion Kinetics for K-Ion Capacitors

Sluggish kinetics severely limit the development of potassium-ion hybrid capacitors (PIHCs). Exposing active sites is recognized as an ideal strategy to resolve this issue, but the corresponding ma...

Combustion synthesis of hexagonal boron nitride nanoplates with high aspect ratio

High crystalline hexagonal boron nitride nanoplates with high aspect ratio of ~400 have been synthesized by combustion synthesis method through magnesiothermic reduction reaction between B2O3 and Mg in N2 pressure. The synthesized hexagonal boron nitride nanoplates were about 50 nm in thickness and larger than 20 μm in lateral size. The six-fold symmetric spots electron diffraction pattern of transmission electron microscopy shows that the nanoplate is well crystallized. Hexagonal boron nitride nanoplates grow via an Oswald ripening process and have larger lateral size when it was prepared with larger magnesium particles. High temperature liquid magnesium provides an important environment for the growth and crystallization of boron nitride. This work provides an effective way to achieve low-cost and large-scale preparation of high-quality boron nitride nanoplates.

Generation of a three-dimensional array of optical bottle beams by use of an orthogonal binary phase plate

The passage of a beam through an orthogonal two-dimensional binary phase plate (BPP) is analyzed. It is found that, when the phase modulation difference of the two type lattices of the BPP is not equal to π, an extra central spot corresponding to the direct current component (DC component) will be obtained, besides the common central four symmetrical bright spots and many outer symmetrical weak spots in the spatial spectrum. By use of a low-pass filter, a three-dimensional array of optical bottle beams can be generated via the interference of the five plane waves from the central five spots in the spatial spectrum due to the modulated phase distribution of the BPP. This method has a high energy efficiency more than 90% and its feasibility is demonstrated experimentally.