Size Of Central Hole Research Articles

Optical metrology on primary mirror of visible emission line coronagraph on board Aditya-L1 mission

The visible emission line coronagraph (VELC) on board the Aditya-L1 mission is an internally occulted reflective coronagraph. It is capable of simultaneous observations of the solar corona in imaging, spectroscopic, and spectropolarimetric modes very close to the solar limb, to 1.05 R ⊙ (R ⊙ – solar radius). Primary mirror (M1) of the VELC receives the light from both the solar disk and the corona up to 3 R ⊙ . In the VELC, occultation happens at the focus of the M1. Secondary mirror (M2) with a central hole size equal to 1.05 R ⊙ is mounted at the focal plane of M1 and serves the purpose of an internal occulter. To meet the proposed science goals of the payload, M1 surface should be super polished with good imaging characteristics. This results in stringent requirements of the surface figure and microroughness on the mirror surface. M1 is an off-axis parabola, so achieving the demanding requirements is quite challenging. At the same time, testing of M1 after development is crucial for evaluating its performance. This paper provides the details of the optical metrology tests carried out on M1 along with the results obtained and their implications on the performance of the VELC.

Refractive Index Sensing Simulations of CsPbBr3 Quantum Dots/Gold Bilayer Coated Triangular-Lattice Photonic Crystal Fibers

With the incorporation of noble metal materials, photonic crystal fibers (PCFs) could be performed as an effective platform for refractive index sensing of the filling analytes. Furthermore, by coating functional dielectric layers upon the metal surfaces, the resonance energy transfer is modulated from the core mode of the PCFs towards the surface plasmon resonance mode of the metals, and the sensing performance could be boosted. Here, considering that the exciton-plasmon coupling is efficient between perovskite quantum dots (QDs) and gold, a kind of CsPbBr3 QDs/Au bilayer coated triangular-lattice PCFs has been simulated numerically as the refractive index sensors. With the optimization of the QDs and gold layer thicknesses, together with the variation of the central hole size of the PCFs, in the refractive index (RI) region of 1.26 to 1.34, a rather narrow full width at half maximum (FWHM) of the loss spectra was achieved as 13.74nm when the central hole size was 1.28 µm and the highest figure of merit was 63.79RIU (the central hole size was 1.53 µm). This work demonstrates that the analyte identification accuracy was enhanced by FWHM narrowing of the loss spectra; in addition, taking the abundance of the material choice of perovskite QDs into consideration, more analytes could be detected effectively. Moreover, by adopting asymmetric structures, the sensitivity of the PCFs based refractive index sensors could be further improved.

A sensor based on D-shaped photonic crystal fiber with elliptical holes

A sensor based on D-shaped photonic crystal fiber (PCF) with elliptical holes is designed and numerical studied by finite element method (FEM). The refractive index (RI) of analyte can be detected by using surface plasma resonance effect and optical fiber with elliptical holes can solve the phase matching problem. The size of central hole, the major axis of the two elliptical holes near polishing plane in first layer and polishing depth are adjusted to explore the influence of these parameters on wavelength sensitivity and amplitude sensitivity of the sensor. Polishing depth has a great influence on wavelength sensitivity of the sensor. As a result, higher sensitivity is obtained with larger polishing depth in the range of 1.33–1.39 and smaller polishing depth is more suitable with RI changing from 1.39–1.42. The wavelength sensitivity of the designed sensor is 10,200 nm/RIU, which means the designed sensor has a promising application prospect.

Erratum to: Effect of hole size on fluid dynamics of a posterior-chamber phakic intraocular lens with a central perforation by using computational fluid dynamics

A modified implantable collamer lens (ICL) with a central hole with a diameter of 0.36 mm, referred to as a hole-ICL, was created to improve aqueous humour circulation. The aim of this study is to investigate the ideal hole size in a hole-ICL from the standpoint of the fluid dynamic characteristics of the aqueous humour using computational fluid dynamics. Fluid dynamics simulation using an ICL was performed with thermal-hydraulic analysis software FloEFD V 12.2 (Mentor Graphics Corp.). In the simulation, three-dimensional eye models based on a modified Liou-Brennan model eye with a conventional ICL (Model ICM, Staar Surgical) and a hole-ICL were used. The hole-ICL was −9.0 dioptres (D) and 12.0 mm in length, with an optic zone of 5.5 mm. The vaulting was 0.50 mm. The quantity of aqueous humour produced by the ciliary body was set at 2.80 μL/min. Flow distribution between the anterior surface of the crystalline lens and the posterior surface of the ICL was calculated, and trajectory analysis was performed. With an increase in the central hole size, the velocity of the aqueous humour increased, with the peak velocity occurring at a diameter of approximately 0.4 mm. Once the diameter had increased above 0.4 mm, the velocity then decreased. The velocity difference between the cases of a central hole size of 0.1 mm and 0.2 mm was significant. The desirable central hole size was 0.2 mm or larger in terms of flow dynamics. The current model, based on a central hole size of 0.36 mm, was close to ideal. The optimisation of the hole size should be performed based on results from a long-term clinical study so as to analyse the incidence rate of secondary cataract and optical performance.

Effect of hole size on fluid dynamics of a posterior-chamber phakic intraocular lens with a central perforation by using computational fluid dynamics.

A modified implantable collamer lens (ICL) with a central hole with a diameter of 0.36mm, referred to as a hole-ICL, was created to improve aqueous humour circulation. The aim of this study is to investigate the ideal hole size in a hole-ICL from the standpoint of the fluid dynamic characteristics of the aqueous humour using computational fluid dynamics. Fluid dynamics simulation using an ICL was performed with thermal-hydraulic analysis software FloEFD V 12.2 (Mentor Graphics Corp.). In the simulation, three-dimensional eye models based on a modified Liou-Brennan model eye with a conventional ICL (Model ICM, Staar Surgical) and a hole-ICL were used. The hole-ICL was -9.0 dioptres (D) and 12.0mm in length, with an optic zone of 5.5mm. The vaulting was 0.50mm. The quantity of aqueous humour produced by the ciliary body was set at 2.80μL/min. Flow distribution between the anterior surface of the crystalline lens and the posterior surface of the ICL was calculated, and trajectory analysis was performed. With an increase in the central hole size, the velocity of the aqueous humour increased, with the peak velocity occurring at a diameter of approximately 0.4mm. Once the diameter had increased above 0.4mm, the velocity then decreased. The velocity difference between the cases of a central hole size of 0.1mm and 0.2mm was significant. The desirable central hole size was 0.2mm or larger in terms of flow dynamics. The current model, based on a central hole size of 0.36mm, was close to ideal. The optimisation of the hole size should be performed based on results from a long-term clinical study so as to analyse the incidence rate of secondary cataract and optical performance.

NEAR-INFRARED VARIABILITY IN YOUNG STARS IN CYGNUS OB7

We present the first results from a 124 night J, H, K near-infrared monitoring campaign of the dark cloud L 1003 in Cygnus OB7, an active star-forming region. Using 3 seasons of UKIRT observations spanning 1.5 years, we obtained high-quality photometry on 9,200 stars down to J=17 mag, with photometric uncertainty better than 0.04 mag. On the basis of near-infrared excesses from disks, we identify 30 pre-main sequence stars, including 24 which are newly discovered. We analyze those stars and find the NIR excesses are significantly variable. All 9,200 stars were monitored for photometric variability; among the field star population, about 160 exhibited near-infrared variability (1.7% of the sample). Of the 30 YSOs (young stellar objects), 28 of them (93%) are variable at a significant level. 25 of the 30 YSOs have near-infrared excess consistent with simple disk-plus-star classical T Tauri models. Nine of these (36%) drift in color space over the course of these observations and/or since 2MASS observations such that they cross the boundary defining the NIR excess criteria; effectively, they have a transient near-infrared excess. About half of the YSOs have color-space variations parallel to either the classical T Tauri star locus or a hybrid track which includes the dust reddening trajectory. This indicates that the NIR variability in YSOs that possess accretion disks arises from a combination of variable extinction and changes in the inner accretion disk: either in accretion rate, central hole size and/or the inclination of the inner disk. While some variability may be due to stellar rotation, the level of variability on the individual stars can exceed a magnitude. This is a strong empirical suggestion that protoplanetary disks are quite dynamic and exhibit more complex activity on short timescales than is attributable to rotation alone or captured in static disk models.

Confinement Model for Axially Loaded Concrete Confined by Circular Fiber-Reinforced Polymer Tubes

This paper introduces an analytical model to predict the behavior of axially loaded circular concrete columns confined by fiber-reinforced polymer (FRP) tubes. The model, an extension of an earlier confinement model for concrete confined by steel reinforcement, is based on equilibrium, compatibility conditions, and the biaxial strength failure criteria of FRP tubes. It can be used to predict the behavior of prefabricated FRP tubes totally or partially filled with concrete, as well as concrete wrapped with FRP sheets. The model can account for the case of axially loaded concrete core only as well as the composite section of the concrete core and FRP tube, and is verified by experimental results reported by the authors and other researchers. A parametric study is presented to examine the effect of stiffness of the FRP tube, the effect of loading the FRP tube axially, and the effect of presence of inner hole inside the concrete core. The study shows that increasing the central hole size reduces the confinement effect, increasing the stiffness of the tube improves the confinement, and axial loading of the FRP tube significantly reduces the confinement.

An engineering model to predict perforation damage to plates impacted by high velocity debris clouds

This paper describes experiments and the development of a model to predict damage to metallic plates impacted by high velocity, multi-particle debris clouds. The experiments involved single steel spheres fired at a steel shatter plate at speeds near 1.5 and 2.0 km/sec to generate the debris clouds. In each series of tests, the impact velocity was controlled, and a witness plate was placed at increasing distances behind the shatter plate to observe the effects of debris particle dispersion on plate damage. This paper focuses on the variations, with plate spacing, in the size of the central region removed from the witness plates. The central hole size model compares the post impact kinetic energy distribution in a witness plate impacted by a debris cloud to the free impact residual kinetic energy in an equivalent plate impacted by an L/D=1 steel cylinder, at the ballistic limit velocity. This approach permits extension of the model to other plate materials through utilization of existing ballistic limit velocity data.