Effects of shepherd conjunctions on Saturn's F ring

A comparison of light curves during occultation of stars by ε ring of Uranus indicate that this ring assembly possesses stable fine structures. The light curves observed during several events show almost similar fine structure across its width. Nicholson et al. (1982) quantitatively compared the separation of the five optical depth maxima, and concluded that no systematic variation of the normalised spacing, either with ring segment width or with data of observation was apparent. We have investigated the possibility of this having structure of a twisted bundle of narrow lanes of condensed material similar to that of Saturn’s F ring (Ref 4) and report the findings.

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Saturn's E, G and F rings: modulated by the plasma sheet

International Astronomical Union Colloquium ◽

10.1017/s0252921100101666 ◽

1984 ◽

Vol 75 ◽

pp. 597

Author(s):

E. Grün ◽

G.E. Morfill ◽

T.V. Johnson ◽

G.H. Schwehm

Keyword(s):

Solar Wind ◽

Direct Contact ◽

Transport Processes ◽

Time Variable ◽

Dust Particles ◽

Spatial Diffusion ◽

Drag Forces ◽

Orbit Perturbation ◽

Time Variations ◽

F Ring

ABSTRACTSaturn's broad E ring, the narrow G ring and the structured and apparently time variable F ring(s), contain many micron and sub-micron sized particles, which make up the “visible” component. These rings (or ring systems) are in direct contact with magnetospheric plasma. Fluctuations in the plasma density and/or mean energy, due to magnetospheric and solar wind processes, may induce stochastic charge variations on the dust particles, which in turn lead to an orbit perturbation and spatial diffusion. It is suggested that the extent of the E ring and the braided, kinky structure of certain portions of the F rings as well as possible time variations are a result of plasma induced electromagnetic perturbations and drag forces. The G ring, in this scenario, requires some form of shepherding and should be akin to the F ring in structure. Sputtering of micron-sized dust particles in the E ring by magnetospheric ions yields lifetimes of 102to 104years. This effect as well as the plasma induced transport processes require an active source for the E ring, probably Enceladus.

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Synthesis of 20-substituted chlorophyll derivatives with F-ring and optical properties of their less distorted chlorin π-systems

Tetrahedron ◽

10.1016/j.tet.2021.132260 ◽

2021 ◽

pp. 132260

Author(s):

Yuki Takarada ◽

Marie Doi ◽

Shin Ogasawara ◽

Hitoshi Tamiaki

Keyword(s):

Optical Properties ◽

F Ring ◽

Chlorophyll Derivatives

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The number of intracorneal ring segments in asymmetric and central cones

Eye and Vision ◽

10.1186/s40662-021-00234-6 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Canan Asli Utine ◽

Denizcan Özizmirliler ◽

Mustafa Kayabaşı ◽

Üzeyir Günenç

Keyword(s):

Corneal Astigmatism ◽

Laser Device ◽

Double Ring ◽

Ring Segment ◽

Corneal Asphericity ◽

Intracorneal Ring Segment ◽

Group 2 ◽

Postoperative Improvement ◽

Single Versus ◽

Group 1

Abstract Background To compare the results of single versus double intracorneal ring segment (ICRS) (KeraRing) implantation in keratoconus with respect to different cone locations. Methods Twenty-two eyes of 18 patients with totally asymmetric cones (20–80% or 0–100% distribution along steep axis) were implanted with single ICRS (Group 1), 38 eyes of 32 patients with central or partially asymmetric cones (50–50% or 40–60% distribution along steep axis) were implanted with double ICRS (Group 2), at a depth of 80% of the site of implantation, in channels created with femtosecond laser device. All patients had uncorrected and corrected distance visual acuities (UDVA and CDVA, respectively) of ≤ 0.3 Snellen lines. Results In both groups, patients had median UDVA and CDVA gain of 3 Snellen lines (P > 0.05). Postoperative improvement in indices of vertical asymmetry and height decentration in Group 1; simulated keratometry, corneal astigmatism and anterior corneal asphericity values in Group 2 were greater (P < 0.05). A total of 10 eyes (45.5%) in Group 1 were recommended double ring implantation by the manufacturer’s nomogram, but underwent single ICRS implantation and achieved visual, refractive, tomographic outcomes comparable to that in Group 2, although corneal cylindrical correction was less and final topographic astigmatism was greater. Conclusion Double ICRS implantation seems to be superior in terms of keratometry, corneal astigmatism and anterior corneal asphericity improvement. Single ICRS implantation in totally asymmetric cones seems to provide satisfactory visual, refractive and tomographic results, similar to double ICRS implantation in central and partially asymmetric cones, by inducing central shift of the cone.

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Analytical Model of Induction Machines with Multiple Cage Faults Using the Winding Tensor Approach

Sensors ◽

10.3390/s21155076 ◽

2021 ◽

Vol 21 (15) ◽

pp. 5076

Author(s):

Javier Martinez-Roman ◽

Ruben Puche-Panadero ◽

Angel Sapena-Bano ◽

Carla Terron-Santiago ◽

Jordi Burriel-Valencia ◽

...

Keyword(s):

Computational Cost ◽

Induction Machines ◽

Diagnostic Techniques ◽

Analytical Models ◽

Tensor Algebra ◽

Diagnostic Systems ◽

Technical Literature ◽

Twin Model ◽

Ring Segment ◽

The One

Induction machines (IMs) are one of the main sources of mechanical power in many industrial processes, especially squirrel cage IMs (SCIMs), due to their robustness and reliability. Their sudden stoppage due to undetected faults may cause costly production breakdowns. One of the most frequent types of faults are cage faults (bar and end ring segment breakages), especially in motors that directly drive high-inertia loads (such as fans), in motors with frequent starts and stops, and in case of poorly manufactured cage windings. A continuous monitoring of IMs is needed to reduce this risk, integrated in plant-wide condition based maintenance (CBM) systems. Diverse diagnostic techniques have been proposed in the technical literature, either data-based, detecting fault-characteristic perturbations in the data collected from the IM, and model-based, observing the differences between the data collected from the actual IM and from its digital twin model. In both cases, fast and accurate IM models are needed to develop and optimize the fault diagnosis techniques. On the one hand, the finite elements approach can provide highly accurate models, but its computational cost and processing requirements are very high to be used in on-line fault diagnostic systems. On the other hand, analytical models can be much faster, but they can be very complex in case of highly asymmetrical machines, such as IMs with multiple cage faults. In this work, a new method is proposed for the analytical modelling of IMs with asymmetrical cage windings using a tensor based approach, which greatly reduces this complexity by applying routine tensor algebra to obtain the parameters of the faulty IM model from the healthy one. This winding tensor approach is explained theoretically and validated with the diagnosis of a commercial IM with multiple cage faults.

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Intracorneal circular ring implant with femtosecond laser: Pocket versus tunnel

European Journal of Ophthalmology ◽

10.1177/1120672121994729 ◽

2021 ◽

pp. 112067212199472

Author(s):

Luis Izquierdo ◽

Ana M Rodríguez ◽

Ramón A Sarquis ◽

Diego Altamirano ◽

Maria A Henriquez

Keyword(s):

Visual Acuity ◽

Femtosecond Laser ◽

Randomized Study ◽

Circular Ring ◽

Continuous Ring ◽

Refractive Outcomes ◽

Scheimpflug Imaging ◽

Ring Segment ◽

Intracorneal Ring Segment ◽

Student’S T

Purpose: To evaluate and compare visual and refractive outcomes after implantation of the intracorneal continuous ring 360° arc (ICCR) versus the intracorneal ring segment 340° arc (ICRS) using femtosecond laser for central keratoconus. Setting: Research Department, Oftalmosalud, Instituto de Ojos, Lima, Peru. Methods: Randomized study that included 40 eyes of 32 patients diagnosed with central keratoconus between November 2014 and March 2015. Twenty eyes had an implantation of ICCR (MyoRing, Dioptex GmbH, Austria) through an intrastromal pocket and 20 eyes had an implantation of ICRS (Keraring, Mediphacos, Brazil) through an intrastromal tunnel. Both procedures were performed with a femtosecond laser (LDV Z6 model, Ziemer Ophthalmic Systems AG). Visual acuity (VA), refraction, and Scheimpflug imaging analysis were performed pre- and postoperatively at 1 month and 1 year. Comparisons of means were performed using the Student’s t-test. Results: At 1 year, uncorrected VA improved 0.77 LogMAR ( p < 0.001) in the ICCR group and 0.79 LogMAR ( p = 0.01) in the ICRS group; mean sphere improvement was 5.13 Diopters (D) in the ICCR group and 6.27 D in the ICRS group ( p < 0.001 both); mean Steeper Keratometry improvement was 4.24 D in the ICCR group and 5.53 D in the ICRS group ( p < 0.001 both). In the ICCR group, mean decrease in the pachymetry at the thinnest point of the cornea was 32.16 µm ( p = 0.01), and in the ICRS group, mean increase was 4.2 µm at 1 year ( p = 0.61). Conclusion: Intracorneal continuous ring 360° arc (ICCR) and intracorneal ring segment 340° (ICRS) are effective treatments for central keratoconus. No significant differences between rings were found on visual acuity, refraction, and keratometry improvement.

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Corneal densitometry in patients with keratoconus undergoing intrastromal Ferrara ring implantation

European Journal of Ophthalmology ◽

10.1177/11206721211020631 ◽

2021 ◽

pp. 112067212110206

Author(s):

Pablo Felipe Rodrigues ◽

Bernardo Kaplan Moscovici ◽

Guilherme Ferrara ◽

Luciano Lamazales ◽

Marcela Mara Silva Freitas ◽

...

Keyword(s):

Visual Acuity ◽

Medical Records ◽

Spherical Equivalent ◽

Interventional Study ◽

Data Comparison ◽

Corneal Densitometry ◽

Corrected Visual Acuity ◽

Ring Segment ◽

The Mean

Objective: Evaluation of central corneal densitometry changes following Ferrara corneal ring segment implantation in patients with keratoconus, especially the correlation between corneal densitometry and keratometry. Methods: Retrospective, non-comparative, interventional study based on the review of medical records of patients diagnosed with keratoconus who underwent Ferrara corneal ring segment implantation. Pre and post-operative corneal densitometry measurements obtained with Pentacam HR (Oculus, Wetzlar, Germany) were analyzed. The follow-up time was 3 months, and data comparison was made, using specific statistical analysis, with the data of 3 months postoperatively. Results: The study sample consisted of 43 eyes of 36 patients. The mean corrected visual acuity improved from 0.82 LogMAR preoperatively (SD ± 0.33) to 0.19 LogMAR (SD ± 0.13) postoperatively. The mean spherical equivalent varied from −4.63 (SD ± 3.94) preoperatively to −2.16 (SD ± 2.63) postoperatively. Asphericity varied from −0.69 (SD ± 0.32) preoperatively to −0.27 (SD ± 0.31) postoperatively. The mean maximum K was 54.01D (SD ± 3.38) preoperatively and 51.50D (SD ± 2.90) postoperatively. The mean anterior densitometric value was 18.26 (SD ± 2.03) preoperatively and 17.66 (SD ± 1.84) postoperatively. Conclusion: Corneal densitometry is an interesting technology that should be studied in keratoconus patients. Our results suggest that the corneal densitometry in the cornea’s anterior layer reduces after ICRS implantation and correlates with corneal keratometry. Further studies should be performed to increase the knowledge in this field.

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