Ring-shaped Regions Research Articles

Optimization criteria and design of few-mode Erbium-doped fibers for cladding-pumped amplifiers.

We propose a novel optimization method that combines two design criteria to reduce the differential modal gain (DMG) in few-mode cladding-pumped erbium-doped fiber amplifiers (FM-EDFAs). In addition to the standard criterion that considers the mode intensity and dopant profile overlap, we introduce a second criterion that ensures that all doped regions have the same saturation behavior. With these two criteria, we define a figure-of-merit (FOM) that allows the design of FM-EDFAs with low DMG without high computational cost. We illustrate this method with the design of six-mode erbium-doped fibers (EDFs) for amplification over the C-Band targeting designs that are compatible with standard fabrication processes. The fibers have either a step-index or a staircase refractive index profile (RIP), with two ring-shaped erbium-doped regions in the core. With a staircase RIP, a fiber length of 29 m and 20 W of pump power injected in the cladding, our best design leads to a minimum gain of 22.6 dB while maintaining a DMGmax under 0.18 dB. We further show that the FOM optimization achieves a robust design with low DMG over a wide range of variations in signal power, pump power and fiber length.

Hydrodynamic Analysis of Two Coaxial Moonpool Floaters Using Theoretical Methodologies

The present contribution aims at presenting a semi-analytical solution methodology of the linear hydrodynamic diffraction and radiation problems induced by two coaxial moonpool-type floaters subjected to incident waves. The flow field around the floaters is subdivided into ring-shaped fluid regions, in each of which axisymmetric eigenfunction-expansions of the velocity potential are made. The applied theoretical formulation is complemented by numerical-panel methodologies, using pulsating singularities distributed over the floaters’ wetted surface. Extensive numerical results in terms of exciting forces and hydrodynamic coefficients are given by applying frequency-domain techniques. The effect of the water trapped between the solids’ vertical walls on the floaters’ hydrodynamics is investigated and discussed. The presented analysis led to some remarkable trapping phenomena in the enclosed water areas, broadening the resonance-frequency bandwidth of the floaters when compared to a single moonpool body.

A probabilistic neighbourhood pooling-based attention network for hyperspectral image classification

ABSTRACT Attention mechanisms are recently deployed in deep learning models for hyperspectral image (HSI) classification. Conventional spectral attentions typically use global pooling to aggregate spatial information, without sufficiently considering the spatial dependencies of the central pixel to be classified and its neighbours. Moreover, the limited training samples with high-dimensional spectral information make deep learning models prone to over-fitting. In view of these, we propose an end-to-end probabilistic neighbourhood pooling-based attention network (PNPAN) for HSI classification. In PNPAN, we divided the feature maps of input HSI cubes into ring-shaped neighbouring regions and probabilistically selected them as pooling regions to compute channel-wise attention. Based on this, we built a spectral attention-based module and a 3-D convolution module to extract spectral-spatial features. Experiments on three benchmark data sets demonstrate that PNPAN achieves promising results for HSI classification with limited training samples.

Zero-Sum Space on the Copper Surface Under Ultrasound

In the overlapped shell space between two adjacent cavitation bubbles, there theoretically exists a Zero-sum space without vibration due to the cavitation effect but still with pressure, high temperature and a high concentration of substances. Within the Zero-sum space, a stable environment for a chemical reaction is achievable under the ultrasound. In this work, some ring-shaped regions (outer diameter 48.90±3.5 μm, inner diameter 40.94±3.5 μm) on copper foil with distinctive morphology were investigated in the area covered by visible bubbles under ultrasound treatment in 1M NaOH for 3 h. The morphology and composition of these regions were found to be similar to that of sample fabricated in the same environment without ultrasound. It has confirmed the long-term existence of Zero-sum space and raised a hypothesis of Zero-sum space maintenance. This work may lead to release the ultrasonic synthesis from the limitation of ultrasonic frequency.

Perinidal Angiogenesis Is a Predictor for Neurovascular Uncoupling in the Periphery of Brain Arteriovenous Malformations: A Task‐Based and Resting‐State fMRI Study

Potential neurovascular uncoupling (NVU) related to perinidal angiogenesis (PA) of brain arteriovenous malformations (AVMs) may cause inappropriate presurgical mapping using functional magnetic resonance imaging (fMRI), resulting in overconfident resection and postoperative morbidity. To evaluate the potential impact of PA upon fMRI blood oxygen level-dependent signal in the periphery of AVMs. Prospective. Twenty-one patients with AVMs located in the primary sensorimotor cortex (SM1) undergoing task-based fMRI (hand motor), and 19 patients with supratentorial AVMs undergoing resting-state fMRI. 3.0T, echo-planar, time-of-flight, and magnetization-prepared rapid gradient-echo. The presence of PA was determined by three observers (Y.C., J.W., and X.C.) according to digital subtraction angiography and MR angiography. Interhemispheric asymmetry of fMRI activations contralateral to hand movements was evaluated with the interhemispheric ratio of the average t-value within ipsilesional SM1 to contralesional SM1. Regional homogeneity (ReHo) and fractional amplitude of low-frequency fluctuations (fALFF) were extracted from ring-shaped perinidal regions and contralateral homologous regions, and the corresponding interhemispheric ratios were calculated. The effect of PA on the interhemispheric asymmetry of motor activations, ReHo, and fALFF was estimated. Pearson analysis, paired and independent t-test, multiple linear regression, Friedman test, and factorial analysis of variance were used. Motor activations were significantly reduced in ipsilesional SM1 compared to contralesional SM1 (P < 0.05). The presence of PA was the independent predictor of activation loss in ipsilateral SM1(P < 0.05). Furthermore, perinidal regions exhibited reduced ReHo compared to the homologous regions (P < 0.05). PA was significantly associated with the decline of ReHo and fALFF in perinidal regions (P < 0.05, for both). The presence of PA can predict perinidal NVU that may confound the interpretation of both task-based and resting-state fMRI, highlighting the importance of alternative approaches of brain functional localization in improving treatment of AVMs. 2 TECHNICAL EFFICACY STAGE: 2.

Surface Stabilized Topological Solitons in Nematic Liquid Crystals

Photo-alignment is a versatile tool to pattern the alignment at the confining substrates in a liquid crystal (LC) cell. Arbitrary alignment patterns can be created by using projection with a spatial light modulator (SLM) for the illumination. We demonstrate that a careful design of the alignment patterns allows the stabilization of topological solitons in nematic liquid crystal (NLC) cells, without the need for chirality or strong confinement. The created LC configurations are stabilized by the anchoring conditions imposed at the substrates. The photo-aligned background at both substrates is uniformly planar aligned, and ring-shaped regions with a 180° azimuthal rotation are patterned with an opposite sense of rotation at the top and bottom substrate. A disclination-free structure containing a closed ring of vertically oriented directors is formed when the patterned rings at the top and bottom substrate overlap. Thanks to the topological stability, a vertical director orientation in the bulk is observed even when the centra of both patterned rings are shifted over relatively large distances. The combination of numerical simulations with experimental measurements allows identification of the 3D director configuration in the bulk. A finite element (FE) Q-tensor simulation model is applied to find the equilibrium director configuration and optical simulations are used to confirm the correspondence with experimental microscopy measurements. The created LC configurations offer opportunities in the field of optical devices, light guiding and switching, particle trapping and studies of topological LC structures.

Theoretical Analysis of a Vertical Cylindrical Floater in Front of an Orthogonal Breakwater

This study investigates the effect of an orthogonal-shaped reflecting breakwater on the hydrodynamic characteristics of a vertical cylindrical body. The reflecting walls are placed behind the body, which can be conceived as a floater for wave energy absorption. Linear potential theory is assumed, and the associated diffraction and motion radiation problems are solved in the frequency domain. Axisymmetric eigenfunction expansions of the velocity potential are introduced into properly defined ring-shaped fluid regions surrounding the floater. The hydrodynamic interaction phenomena between the body and the adjacent breakwaters are exactly taken into account by using the method of images. Results are presented and discussed concerning the exciting wave forces on the floater and its hydrodynamic coefficients, concluding that the hydrodynamics of a vertical cylindrical body in front of an orthogonally shaped breakwater differ from those in unbounded waters.

Wave Power Absorption by Arrays of Wave Energy Converters in Front of a Vertical Breakwater: A Theoretical Study

The present paper deals with the theoretical evaluation of the efficiency of an array of cylindrical Wave Energy Converters (WECs) having a vertical symmetry axis and placed in front of a reflecting vertical breakwater. Linear potential theory is assumed, and the associated diffraction and motion radiation problems are solved in the frequency domain. Axisymmetric eigenfunction expansions of the velocity potential are introduced into properly defined ring-shaped fluid regions surrounding each body of the array. The potential solutions are matched at the boundaries of adjacent fluid regions by enforcing continuity of the hydrodynamic pressures and redial velocities. A theoretical model for the evaluation of the WECs’ performance is developed. The model properly accounts for the effect of the breakwater on each body’s hydrodynamic characteristics and the coupling between the bodies’ motions and the power take-off mechanism. Numerical results are presented and discussed in terms of the expected power absorption. The results show how the efficiency of the array is affected by (a) the distance between the devices and the wall, (b) the shape of the WEC array configuration, as well as (c) the angle of the incoming incident wave.

Theoretical Evaluation of the Hydrodynamic Characteristics of Arrays of Vertical Axisymmetric Floaters of Arbitrary Shape in front of a Vertical Breakwater

The present paper deals with the analytical evaluation of the hydrodynamic characteristics of an array of vertical axisymmetric bodies of arbitrary shape, placed in front of a reflecting vertical breakwater, which can be conceived as floaters for wave power absorption. At the first part of the paper, the hydrodynamic interactions between the floaters and the adjacent breakwater are exactly taken into account using the method of images, whereas, the interaction phenomena between the floaters of the array are estimated using the multiple scattering approach. For the solution of the problem, the flow field around each floater of the array is subdivided into ring-shaped fluid regions, in each of which axisymmetric eigenfunction expansions for the velocity potential are made. In the second part of the paper, extensive theoretical results are presented concerning the exciting wave forces and the hydrodynamic coefficients for various arrays’ arrangements of axisymmetric floaters. The aim of the study is to show parametrically the effect that the vertical breakwater has on the hydrodynamic characteristics of each particular floater.

Engineered hyperuniformity for directional light extraction

By leveraging the concept of isotropic stealthy hyperuniform arrays (ISHAs), in this paper, we design and experimentally demonstrate novel scattering arrays of dielectric nanoparticles, here referred to as optimized isotropic scattering arrays (OISAs), which give rise to ring-shaped regions in Fourier space (k-space), with intensity optimized by the collective coordinate optimization method. These arrays feature the ideal circular k-space structure required to achieve enhanced directional light extraction from light emitting devices (LEDs), with significantly reduced diffuse scattering compared with both Poisson random point patterns and Vogel spiral arrays. Enhanced directional emission from OISAs is demonstrated experimentally on large-scale arrays (1 × 1 mm2) of TiO2 nanoparticles fabricated atop LED ceramic converter materials. The enhanced directional light emission of OISAs of dielectric nanoparticles demonstrated in this work make them very attractive candidates for integration with commercially available LED active materials.

Localized air-mediated heating method for isothermal and rapid thermal processing on lab-on-a-disk platforms

In this study, an air-mediated local heating method is developed for Lab-on-a-Disk platforms. The hot air is blown on a rotating disk through a dual-sided nozzle for heating up the specific ring-shaped regions on the rotating disk surface. The local heating can be used for combining different thermal based fluidic functions and reactions in a single disk. A numerical simulation has been performed for analyzing the air flow and temperature distribution on different regions of the disk and surrounding air. The effects of the operational parameters including hot air temperature and flow rates as well as the angular velocity of the disk are evaluated using an exclusive experimental setup. The results show that without considerable thermal effect on other regions of the disk, a uniform temperature can be achieved for the liquid sample (25 μl in this study) with a considerable temperature changing rates. The proposed method has been implemented for a PCR amplification of the β actin gene. The heating and cooling rates of the thermocycling process were 1.8 °C/s and 2.2 °C/s respectively.

Исследование сезонных особенностей формирования областей повышения электронной температуры в субавроральной ионосфере

The electron temperature enhancement is known to occur in the main ionospheric trough during geomagnetic disturbances. In this paper, we study fea-tures of the formation of the electron temperature (Te) enhancement in the subauroral ionosphere by comparing results of the numerical simulation with measurements of Te onboard the CHAMP satellite under moderate geomagnetic activity conditions. It is shown that depending on the terminator position and universal time (UT), the location of the enhanced Te regions in the subauroral ionosphere varies in different seasons. So, in winter ring-shaped and sickle-shaped regions can be formed, whereas during the equinox and summer periods sickle-shaped regions of different lengths and clarity are generally observed.

Investigating seasonal features of electron temperature enhancement regions in the subauroral ionosphere

The electron temperature enhancement is known to occur in the main ionospheric trough during geomagnetic disturbances. In this paper, we study fea-tures of the formation of the electron temperature (Te) enhancement in the subauroral ionosphere by comparing results of the numerical simulation with measurements of Te onboard the CHAMP satellite under moderate geomagnetic activity conditions. It is shown that depending on the terminator position and universal time (UT), the location of the enhanced Te regions in the subauroral ionosphere varies in different seasons. So, in winter ring-shaped and sickle-shaped regions can be formed, whereas during the equinox and summer periods sickle-shaped regions of different lengths and clarity are generally observed.

Characterization of fast deuterons involved in the production of fusion neutrons in a dense plasma focus

This paper considers regions of a fast deuteron production in a correlation with an evolution of ordered structures inside a pinch column of a mega-ampere plasma focus discharge. Ion pinhole cameras equipped with plastic PM-355 track-detectors recorded fast deuterons escaping in the downstream and other directions (up to 60° to the z-axis). Time-integrated ion images made it possible to estimate sources of the deuteron acceleration at the known magnetic field and deuteron energy values. The images of the fast deuterons emitted in the solid angle ranging from 0° to 4° showed two forms: central spots and circular images. The spots of 1–2 cm in diameter were produced by deuterons from the central pinch regions. The circular-shaped images of a radius above 3 cm (or their parts) were formed by deuterons from the region surrounding the dense pinch column. The ion pinhole cameras placed at angles above 20° to the z-axis recorded the ion spots only, and the ring-images were missing. The central region of the deuteron acceleration could be associated mainly with plasmoids, and the circular images could be connected with ring-shaped regions of the radius corresponding to tops of the plasma lobules outside the dense pinch column. The deuteron tracks forming ring-shaped images of a smaller (0.5–1) cm radius could be produced by deflections of the fast deuterons, which were caused by a magnetic field inside the dense pinch column.

Effects of the stroke length and nozzle-to-plate distance on synthetic jet impingement heat transfer

This study focuses on the combined effect of the nozzle-to-plate distance and of the stroke length on the cooling performances of impinging synthetic jets. Infrared thermography is used as temperature transducer in conjunction with the heated thin foil heat transfer sensor to measure time- and phase-averaged convective heat transfer. All the experiments have been performed at a fixed Reynolds number equal to 5250, while different values of the dimensionless stroke length (L0/D equal to 5, 10 and 20) and nozzle-to-plate distance (H/D between 2 and 10) have been considered. At high L0/D, the heat transfer behaviour resembles that of a continuous impinging jet. It is characterized by a time-averaged stagnation Nusselt number maximum between H/D equal to 4 and 6 and inner and outer ring-shaped regions of Nusselt number maximum at short H/D. These two regions are replaced by a bell-shaped distribution at higher nozzle-to-plate distances. The existence of these regions is clearly observed through the phase-averaged heat transfer measurements. At short H/D, the heat transfer evolution reveals the simultaneous presence of two outer ring-shaped regions. The external outer region is ascribed to the strong coherence of the primary vortex ring, while the internal one is mainly due to the vortex rings generated by the Kelvin–Helmholtz instability along the trailing jet shear layer. At high H/D, the internal outer-ring shaped region disappears because of the weakening of the trailing jet Kelvin–Helmholtz vortex rings. In opposition, at short L0/D, the time-averaged stagnation point Nusselt number is found to have a maximum at lower values of H/D, and no inner ring-shaped region of heat transfer maximum is observed. This region is not present, at low dimensionless stroke lengths, because of the weakness and reduced extent of the trailing jet in the flow field. Indeed, the phase-averaged measurements mainly show the heat transfer caused by the impinging primary vortex ring. Despite the weakness of the trailing jet, the outer ring-shaped region of heat transfer maximum is observed at short H/D because of the presence of a strong primary vortex ring. In addition to that, the dimensionless stroke length and nozzle-to-plate distance also affect the heat transfer fluctuations, which decrease as L0/D decreases and/or H/D increases.

Topological Structures in a Model Cuprate

We address a minimal model to describe the charge degree of freedom in the CuO2 planes with the on-site Hilbert space reduced to only a charge triplet of the three effective valence centers, nominally Cu1+;2+;3+, and made use of the S = 1 pseudospin formalism. The 2D S = 1 pseudospin system is prone to a creation of different topological structures which form topologically protected inhomogeneous distributions of the eight local S = 1 pseudospin order parameters including charge density and superfluid order parameters. We focus on the so-called quadrupole skyrmion which is believed to be a candidate for a topological charge excitation in parent or underdoped cuprates. Puzzlingly, such an unconventional structure is characterized by a uniform distribution of the mean on-site charge that makes the quadrupole skyrmion texture to be invisible for X-rays. We suppose that the parent insulating antiferromagnetic cuprates may be unstable with regard to nucleation of topological defects in the unconventional form of the one- or multi-center skyrmion-like object with ring-shaped superfluid regions.

Synthesis of self-organized TiO2 nanotube arrays: Microstructural, stereoscopic, and topographic studies

In this work, titanium dioxide nanotubes were prepared by using titanium foils via electrochemical anodization in ethylene glycol solutions containing different amounts of water and fluoride in the ranges of 1%–3% and 0.15%–0.5%, respectively, to determine their effects on morphology, optical, and crystalline structure properties. Annealing processes were performed on all samples in the range between 273 and 723 K. Morphology and structure properties of the samples were studied by scanning electron microscopy, X-ray diffraction (XRD), and transmission electron microscopy. Titanium dioxide (TiO2) nanotubes, through anodization method, are strongly influenced by conditions, like fluoride concentration and applied voltages. Tube lengths between 2 and 7 μm were obtained, exhibiting different diameters and wall thicknesses. When alternating voltage was applied, the outer surface of the nanotubes exhibited evenly spaced ring-shaped regions, while smooth tubes were observed when constant voltage was applied. Reflection peaks, corresponding to Brookite, Anatase, and Rutile, of TiO2 phases, were observed from the XRD pattern. These phases were corroborated via μXRD measurements, and the Ti3O5 phase was also observed in detail. Absorption coefficient (α), optical band gap (Eg), and extinction coefficient (ε) of TiO2 nanotubes were calculated by transmittance spectra in the UV–Vis range. Strong absorption was noted in the UV region from reflectance and absorbance measurements. A correlation between synthesis parameters and physical properties is presented.

Spatially localised luminescence emission properties induced by formation of ring-shaped quasi-potential trap around V-pits in InGaN epi-layers

The correlation between surface structural and luminescence properties of InGaN epi-layers grown by metal organic chemical vapour deposition has been investigated. Ring-shaped regions with high In-content are observed around V-pits by spatial resolved cathodoluminescence and energy dispersive X-ray spectroscopy. These ring-shaped regions are found to form a potential energy well with depth about 300 meV with respect to the ordinary regions, which can attract carriers and suppress non-radiative recombination. The causes of the formation of high-In-content region are discussed. This localised characteristic of carriers is supported further by power and temperature dependent photoluminescence results. The understanding of the spatially emission characteristics might be helpful to improving the internal quantum efficiency of InGaN/GaN light emitting diodes (LEDs).

Effects of floaters’ hydrodynamics on the performance of tightly moored wave energy converters

This study investigates the effect that several different floaters’ geometries have on the performance characteristics of tightly moored vertical axisymmetric wave energy converters (WECs). A cylindrical buoy with and without vertical and horizontal skirts mounted at its bottom, a cone, as well as two piston-like arrangements, consisting of an internal floater (cone or cylinder) and an exterior torus, have been examined and comparatively assessed. The WEC&apos;s first-order hydrodynamic characteristics are evaluated using a linearised diffraction–radiation semi-analytical method. Axisymmetric eigenfunction expansions of the velocity potential are introduced into properly defined ring-shaped fluid regions surrounding the bodies and the potential solutions are matched at the boundaries of adjacent fluid regions by enforcing continuity of the hydrodynamic pressures and radial velocities. A dynamical model for the floaters’ performance in time domain is developed that properly accounts for the floater&apos;s hydrodynamic behaviour, the coupling terms between the different modes of motion and of the power take-off mechanism. Numerical results are presented and discussed, in terms of the expected power production. The results show parametrically the effect that the varying hydrodynamic characteristics of each particular floater&apos;s geometry have on the investigated WEC&apos;s performance characteristics.

Formation of elliptically polarized ring-shaped electric field structures on the self-focusing of light in an isotropic medium featuring a spatially disperse nonlinearity

The possibility is demonstrated that the self-focusing of an elliptically polarized beam in a medium featuring a spatially disperse cubic nonlinearity can give rise to several radially symmetric ring-shaped regions of the same sense of rotation (right or left) of the electric-field vector in the cross-section of the beam. The formation dynamics and propagation features of such electric field structures are studied for various parameters of the incident radiation and nonlinear medium.