Outer Ring Radius Research Articles

Completely revealing the amplitude properties of Laguerre-Gaussian vortex beams.

In this paper, the amplitude properties of the Laguerre-Gaussian (LG) vortex beams are analyzed theoretically and demonstrated experimentally. Firstly, the ring width of the LG vortex beam is almost a constant, which can be considered to be independent of the topological charge (l) and only determined by the waist radius ω(z), and its general expression is derived via investigating Lambert W function. On this basis, concise expressions for inner and outer ring radii, ratio of inner and outer ring radius, ring area and beam divergence are also given out. Moreover, modification functions are added to obtain more accurate expressions. In the experiment, a spatial light modulator is employed to generate the LG vortex beams with l = 1∼20 at ω0 = 0.3mm and ω0=0.4mm, and the LG vortex beams with l=10 at different propagation distances. The experimental results are in good agreement with the theoretical values. This work may help researchers to better understand the LG vortex beam and provide a useful guideline for its further applications.

Optical coherence tomography angiography findings in patients undergoing transcorneal electrical stimulation for treating retinitis pigmentosa

PurposeTranscorneal electrical stimulation (TES) is a novel treatment approach for patients with retinitis pigmentosa (RP). The aim of our study was to observe changes in optical coherence tomography angiography (OCTA) that would be attributed to TES treatment.MethodsA total of 73 eyes were included: 43 eyes of 22 subjects (11 ♀, 11 ♂) suffering from RP were examined at baseline (BL), after first stimulation (TS), 1 week (1W), and 6 months (6M) after treatment initiation and were compared with 30 control eyes of 15 subjects (8 ♀, 7 ♂). TES was performed simultaneously on both eyes for 30 min weekly. OCTA scans of 9 × 15 mm were recorded with a PLEX Elite 9000 swept-source OCTA device (Carl Zeiss Meditec AG, Jena). Vascular density metrics such as perfusion density (PD) and vessel density (VD) were calculated automatically for the macular area by using standardised extended early treatment diabetic retinopathy study (ETDRS) grids centred around the fovea. In addition, the capillary perfusion density (CPD) and the capillary flux index (CFI) of the peripapillary nerve fibre layer microvasculature in all four quadrants of an annulus centred at the optic disc were measured. All parameters were determined over all retinal layers and separately for the superficial (SCP) and deep capillary plexus (DCP). ANOVA-based linear mixed-effects models were calculated with SPSS®.ResultsThroughout the course of TES treatment, the macular VD and PD of all retinal layers in all subsections showed a slight decrement without reaching statistical significance, also when analysed separately in the SCP and DCP (p > 0.08). In analogy, the average CPD and CFI also presented with a slight decrement (p > 0.20). However, when compared with controls, most OCTA parameters showed a significant decrement (p < 0.05). When analysed systematically in all subsections of the extended ETDRS grid, the temporal macular subsections within the outer ring (radius 1.5–3 mm) and also of the peripheral C1, C2, and C3 rings (radius 3–7.5 mm) showed lower VD and PD values when compared with the other subsections (p < 0.05).ConclusionVascular density metrics in the macular region and the peripapillary microvasculature appear to remain unaffected by continuous TES treatment within a period of 6 months.

C-shaped split ring resonator terahertz toroidal dipole metasurfaces

We designed and fabricated terahertz toroidal dipole metasurfaces based on a C-shaped split ring resonator metallic pattern fabricated on a flexible dielectric material (mylar). The toroidal dipole moment (Ty) was demonstrated as the dominant contribution to two different resonances at low frequency (ω1) and at high frequency (ω2). Simulation and LC circuit model analysis offered a quantitative explanation to the blue shift of the resonant frequencies at ω1 and ω2 as the increase of the opening angle(θ). The resonant frequencies showed a red shift at ω1 and ω2 as the increase of the outer ring radius (QR). Furthermore, the enhancement of the Q factor was attributed to the increase of Ty and the decrease of radiative loss. It was further proven that the model provided a new scheme for designing the toroidal dipole metasurfaces under a terahertz band, which was expected to be used as terahertz functional devices.

Solving the general inter-ring distances optimization problem for concentric ring electrodes to improve Laplacian estimation

BackgroundSuperiority of noninvasive tripolar concentric ring electrodes over conventional disc electrodes in accuracy of surface Laplacian estimation has been demonstrated in a range of electrophysiological measurement applications. Recently, a general approach to Laplacian estimation for an (n + 1)-polar electrode with n rings using the (4n + 1)-point method has been proposed and used to introduce novel multipolar and variable inter-ring distances electrode configurations. While only linearly increasing and linearly decreasing inter-ring distances have been considered previously, this paper defines and solves the general inter-ring distances optimization problem for the (4n + 1)-point method.ResultsGeneral inter-ring distances optimization problem is solved for tripolar (n = 2) and quadripolar (n = 3) concentric ring electrode configurations through minimizing the truncation error of Laplacian estimation. For tripolar configuration with middle ring radius αr and outer ring radius r the optimal range of values for α was determined to be 0 < α ≤ 0.22 while for quadripolar configuration with an additional middle ring with radius βr the optimal range of values for α and β was determined by inequalities 0 < α < β < 1 and αβ ≤ 0.21. Finite element method modeling and full factorial analysis of variance were used to confirm statistical significance of Laplacian estimation accuracy improvement due to optimization of inter-ring distances (p < 0.0001).ConclusionsObtained results suggest the potential of using optimization of inter-ring distances to improve the accuracy of surface Laplacian estimation via concentric ring electrodes. Identical approach can be applied to solving corresponding inter-ring distances optimization problems for electrode configurations with higher numbers of concentric rings. Solutions of the proposed inter-ring distances optimization problem define the class of the optimized inter-ring distances electrode designs. These designs may result in improved noninvasive sensors for measurement systems that use concentric ring electrodes to acquire electrical signals such as from the brain, intestines, heart or uterus for diagnostic purposes.

Directly modulated quantum dot lasers on silicon with a milliampere threshold and high temperature stability

Microring lasers feature ultralow thresholds and inherent wavelength-division multiplexing functionalities, offering an attractive approach to miniaturizing photonics in a compact area. Here, we present static and dynamic properties of microring quantum dot lasers grown directly on exact (001) GaP/Si. Effectively, a single-mode operation was observed at 1.3 μm with modes at spectrally distant locations. High temperature stability with T0∼103 K has been achieved with a low threshold of 3 mA for microrings with an outer ring radius of 15 μm and a ring waveguide width of 4 μm. Small signal modulation responses were measured for the first time for the microrings directly grown on silicon, and a 3 dB bandwidth of 6.5 GHz was achieved for a larger ring with an outer ring radius of 50 μm and a ring waveguide width of 4 μm. The directly modulated microring laser, monolithically integrated on a silicon substrate, can incur minimal real estate cost while offering full photonic functionality.

Comparison of electrohysterogram signal measured by surface electrodes with different designs: A computational study with dipole band and abdomen models

Non-invasive measurement of uterine activity using electrohysterogram (EHG) surface electrodes has been attempted to monitor uterine contraction. This study aimed to computationally compare the performance of acquiring EHG signals using monopolar electrode and three types of Laplacian concentric ring electrodes (bipolar, quasi-bipolar and tri-polar). With the implementation of dipole band model and abdomen model, the performances of four electrodes in terms of the local sensitivity were quantified by potential attenuation. Furthermore, the effects of fat and muscle thickness on potential attenuation were evaluated using the bipolar and tri-polar electrodes with different radius. The results showed that all the four types of electrodes detected the simulated EHG signals with consistency. That the bipolar and tri-polar electrodes had greater attenuations than the others, and the shorter distance between the origin and location of dipole band at 20 dB attenuation, indicating that they had relatively better local sensitivity. In addition, ANOVA analysis showed that, for all the electrodes with different outer ring radius, the effects of fat and muscle on potential attenuation were significant (all p < 0.01). It is therefore concluded that the bipolar and tri-polar electrodes had higher local sensitivity than the others, indicating that they can be applied to detect EHG effectively.

Plasmonic metamaterial based unified broadband absorber/near infrared emitter for thermophotovoltaic system based on hexagonally packed tungsten doughnuts

In this paper, we report a simple and effective design of a polarization independent and wide incident angle plasmonic metamaterial based unified broadband absorber and thermal emitter consisting of hexagonally packed tungsten doughnuts (hexa-rings) for thermophotovoltaic system. The proposed design shows more than 85% of absorption over 0.3 to 2.18 μm, that is, over the broad spectral range from the ultraviolet to the near infrared (NIR), and 100% absorption and thermal emission at 2.18 μm. Further, the NIR plasmonic absorption and thermal emission peak is tuned from the spectral range 2.18 to 3 μm for different low bandgap photovoltaic materials by varying the design parameters such as inner and outer ring radius, instead of varying any other design parameters in the proposed design. The possibility of the realization of hexa-doughnut structures through a single-step phase engineered interference lithography technique is also demonstrated through the realization of micro/nanostructure samples over large area.

O-band electrically injected quantum dot micro-ring lasers on on-axis (001) GaP/Si and V-groove Si.

We report statistical comparisons of lasing characteristics in InAs quantum dot (QD) micro-rings directly grown on on-axis (001) GaP/Si and V-groove (001) Si substrates. CW thresholds as low as 3 mA and high temperature operation exceeding 80 °C were simultaneously achieved on the GaP/Si template template with an outer-ring radius of 50 µm and a ring width of 4 μm, while a sub-milliamp threshold of 0.6 mA was demonstrated on the V-groove Si template with a smaller cavity size of 5-μm outer-ring radius and 3-μm ring width. Evaluations were also made with devices fabricated simultaneously on native GaAs substrates over a significant sampling analysis. The overall assessment spotlights compelling insights in exploring the optimum epitaxial scheme for low-threshold lasing on industry standard Si substrates.

Magnetic field effects on linear optical properties of GaN/AlN multi-wells quantum rings and dots with constant total effective radiuses

In this work, we have studied the effect of external magnetic field on linear absorption coefficient of AlN/GaN constant total effective radius multi-wells quantum ring and dots. These properties have been investigated for systems with different number of wells, quantum ring thickness and dot radiuses. We showed that, the absorption peak amplitude increases sensibly when outer quantum ring radius Rout increases. Effect of the inner quantum ring radius Rin was different. For systems with small Rin, by increasing of the number of wells the absorption peak amplitude at first decreases and then increases. The threshold number of wells by increasing of the Rin decreases. For systems with large Rin the absorption peak amplitude increases monotonically. Increasing of Rin at fixed Rout also reduces the absorption peak amplitude and change of the Rout does not affect on this fact. Finally, effect of the magnetic field on the absorption peak amplitude depends on the Rout, Rin and the number of wells. In the meantime, There is not a unique trend when one of these parameters changes. However, effect of the magnetic field is more remarkable for systems with larger number of wells.

A quantitative planning method of variable feed rates for cold profiled ring rolling process

Cold profiled ring rolling (CPRR) is an advanced local incremental forming process with complexity and high nonlinearity. In this process, the feed rate of mandrel is a key factor affecting the expanding speed of ring outer radius and the filling behavior; thus, it is very significant to rationally design the feed rate for precise controlling the deformation process. Aimed at the CPRR process, the problem of feed rate planning under two variable feed patterns, which are constant expanding speed of ring outer radius (P CES) and constant feed amount per ring revolution (P CFA), has been solved successfully by using the hypothesis-testing approach in this paper. First, according to the relation between the ring outer radius R and the ring reduction ΔH, a novel mathematical solution for planning the feed rates under P CES and P CFA has been proposed, in which a series of points of (R, ΔH) under constant feed rate (P CFR) pattern have been taken into consideration. Second, two differential equations obtaining variable feed rate curves under P CES and P CFA have been built and their solving processes have also been given, and subsequently a new quantitative planning flow of variable feed rates has been presented. Third, an example of three feed rates planning under P CFR, P CES, and P CFA for a practical closed cold T-shaped ring rolling process in the design phase has been realized, and their validity has been proven by three-dimensional finite element numerical simulation. The achievements can provide a guideline for planning the feed rates of the relevant complex profiled ring rolling processes to improve efficiency and reduce cost.

Stresses and displacements in a circular ring loaded by symmetrically spaced radial forces

This paper presents the study of a plane elasticity problem for a concentric circular ring loaded by a system of equal radial forces equally spaced around its outer ring boundary. The problem is solved by the Kolosov–Muskhelishvili complex variables method. Explicit formulas are derived for calculating components of the stress tensor and of the displacement vector. Numerical values for circumferential stress and radial displacement are given for various ratios of inner and outer ring radii and various numbers of forces.

The effects of forming parameters on conical ring rolling process.

The plastic penetration condition and biting-in condition of a radial conical ring rolling process with a closed die structure on the top and bottom of driven roll, simplified as RCRRCDS, were established. The reasonable value range of mandrel feed rate in rolling process was deduced. A coupled thermomechanical 3D FE model of RCRRCDS process was established. The changing laws of equivalent plastic strain (PEEQ) and temperature distributions with rolling time were investigated. The effects of ring's outer radius growth rate and rolls sizes on the uniformities of PEEQ and temperature distributions, average rolling force, and average rolling moment were studied. The results indicate that the PEEQ at the inner layer and outer layer of rolled ring are larger than that at the middle layer of ring; the temperatures at the “obtuse angle zone” of ring's cross-section are higher than those at “acute angle zone”; the temperature at the central part of ring is higher than that at the middle part of ring's outer surfaces. As the ring's outer radius growth rate increases at its reasonable value ranges, the uniformities of PEEQ and temperature distributions increase. Finally, the optimal values of the ring's outer radius growth rate and rolls sizes were obtained.

Bar pattern speed evolution over the last 7 Gyr

The tumbling pattern of a bar is the main parameter characterising its dynamics. From numerical simulations, its evolution since bar formation is tightly linked to the dark halo in which the bar is formed through dynamical friction and angular momentum exchange. Observational measurements of the bar pattern speed with redshift can restrict models of galaxy formation and bar evolution. We aim to determine, for the first time, the bar pattern speed evolution with redshift based on morphological measurements. We have selected a sample of 44 low inclination ringed galaxies from the SDSS and COSMOS surveys covering the redshift range 0 <z< 0.8 to investigate the evolution of the bar pattern speed. We have derived morphological ratios between the deprojected outer ring radius (R_{ring}) and the bar size (R_{bar}). This quantity is related to the parameter {\cal R}=R_{CR}/R_{bar} used for classifiying bars in slow and fast rotators, and allow us to investigate possible differences with redshift. We obtain a similar distribution of $R$ at all redshifts. We do not find any systematic effect that could be forcing this result. The results obtained here are compatible with both, the bulk of the bar population (~70%) being fast-rotators and no evolution of the pattern speed with redshift. We argue that if bars are long-lasting structures, the results presented here imply that there has not been a substantial angular momentum exchange between the bar and halo, as predicted by numerical simulations. In consequence, this might imply that the discs of these high surface-brightness galaxies are maximal.

Opposing trends of geometrical parameters in maximisation of micro-ring resonator quality factor

Opposing trends of geometrical parameters in minimisation of bending loss and thus in maximising the quality factor are briefly discussed for micro-ring resonators. It is shown that, while the quality factor of low order modes is an oscillatory function of geometrical parameters, the quality factor of high order modes is a monotonic function. The former has discrete pairs of optimum inner and outer ring radii which maximises the quality factor. In contrast, the quality factor of the latter has no local maximum. Introduction of slight inhomogeneities does not change the overall behaviour of the quality factor but can increase its overall level when the refractive index of the ring region increases at its outer radius.

2-D Circle Measurement System for Small Rule Parts Based on Machine Vision

A Circle-shape is an important figure in most small rule mechanical parts, and usually be measured to get the radius or used as a stand calibration mark. In this paper, a 2-D circle measurement system for small rule mechanical parts based on machine vision is designed and built. The basic components and work principle of the machine vision measurement system are introduced, and the measurement produce is designed and discussed. An available algorithm for circle contour detected and fitted is described. Using this algorithm, the measurement software flow and architecture are built and the software system realized in the Microsoft visual studio program platform. Certainly, the calibration of machine vision system is introduced also. Using the system and method introduced above, an experiment is designed to measure the outer ring radius of one certain model bearing. The measured data is processed and analyzed. Through the experiment and result, it can be found that the measurement system can get relatively high precision and the measurement method is relatively steady, and the system precision and speed can be suit for the demand of on-line and real-time circle measurement.

Micro Stirling Engine Controlled by Light

Abstract This paper proposes a new technique for a micro Stirling engine operation using leaky light resonant or whispering gallery modes (WGMs) in a nano-waveguide, in which the nano-waveguide is designed and configured by a nanoring resonator. By using the Optiwave programming based on Finite Difference Time-Domain (FDTD) method, an InGaAsP/InP nanoring resonator was designed and simulated. The simulation results obtained have shown that the leaky light resonant modes can be controlled by the ring radius variations, whereas the maximum resonant peak of nanoring resonator is occurred at the inner and outer ring radii of 0.775 and 1.55 μm respectively. The maximum peak intensity of the nanoring resonator is 12000 W/m2. Finally, the use of leaky light mode resonant peak of the center nanoring resonator for micro-Stirling engine is discussed in details.

Magnetoexciton in semiconductor concentric double rings

We investigate theoretically the magnetoexciton states in semiconductor concentric quantum double rings using the multi-band effective mass theory. We find that a perpendicular magnetic field can lead to oscillations in the exciton energy which appear as kinks in the magneto-photoluminescence (PL) spectra as the magnetic field increases. The spatial distribution of the exciton over the rings depends sensitively on the thicknesses of the inner and outer rings. The tunneling coupling between the inner and outer rings and the heavy-hole and light-hole mixing results in different anticrossing behaviors. Exciton can be converted into a spatially separated type-II exciton by tuning the thickness, the inner and/or outer ring radius and the magnetic field. We show that this type I–type II transition is reflected in the oscillator strength of the PL spectrum which will be the experimental signature that will provide us with information about the spatial distribution of the exciton.

Polarization insensitive self-collimation waveguide in square lattice annular photonic crystals

The frequency bands for self-collimation at both TE and TM polarizations in square lattice annular photonic crystals are studied systematically by plane-wave expansion and finite difference time domain methods. By increasing the inner ring radius or reducing the outer ring radius, the self-collimation band will be moved to a lower frequency. Compared with the TM modes, TE ones have different frequency sensitivities to both the inner ring radius and outer ring radius tuning. Using these features, a polarization insensitive self-collimation waveguide in a high dielectric contrast system with bandwidth up to 102.9 nm is demonstrated as an example of the implementation of photonic integration circuits.

Energy spectrum in a concentric double quantum ring of GaAs–(Ga,Al)As under applied magnetic fields

The energy spectrum of an electron in a two-dimensional concentric double quantum ring is exactly calculated in the presence of an axial magnetic field using linear combinations of confluent hypergeometric functions. The influence of the geometric confinement on the energy spectrum is analyzed as a function of the inner and outer ring radii. The applied magnetic field modifies the electron energy spectrum and we discuss the appearance of the well-known Aharonov–Bohm oscillations. Interesting behavior of the probability amplitude of the electron state was found reflecting the competition between geometric and magnetic confinements. Electronic tunneling between the coupled rings may be reinforced or suppressed by conveniently modulating the barrier size separating the two rings, leading to drastic change in the electronic charge distribution through the nanostructure.

Theoretical evaluation of the collection efficiency at ring-disc microelectrodes

Abstract Ring-disc microelectrodes operating as collector-generators are capable of probing multiple aspects of mass transport and are becoming popular electrochemical detectors. In this paper, the key parameters affecting the efficiency of these detectors are modelled and compared to experimental measurements by us and others. The first parameters considered pertain to electrode geometry; the disc radius and inner and outer ring radii. Our model results and experimental measurements show that varying these parameters significantly changes the sensor’s efficiency. The influence of recess and protrusion of the active surfaces from the insulating face of the electrode is also studied over a reasonable range of distances. We find that in general, protrusions will increase the efficiency of the sensor whilst recesses decrease it. The other parameters considered pertain to the flux distribution at the surface of the ring and disc electrodes, focusing on the generator electrode. The flux distribution at the generator is influenced by the voltage applied and the relative rates of mass transport or electron transfer of the species used. We find that the sensor’s efficiency increases with increasing overpotential. When the level of overpotential is sufficiently high, D and k 0 have no effect on the value of the collection efficiency. However, to establish the required level of overpotential needed to ensure a maximum collection efficiency the reaction kinetics and diffusion coefficient of a species need to be specified. Our investigations highlight the best operating modes and points out problems and features of the ring-disc microelectrode and its use as a collector-generator.