Optical performance of a new design of trifocal intraocular lens based on the Devil's diffractive lens

In this work, we propose a new diffractive trifocal intraocular lens design with focus extension, conceived to provide a high visual performance at intermediate distances. This design is based on a fractal structure known as the "Devil's staircase". To assess its optical performance, numerical simulations have been performed with a ray tracing program using the Liou-Brennan model eye under polychromatic illumination. The simulated through the focus visual acuity was the merit function employed to test its pupil-dependence and its behavior against decentering. A qualitative assessment of the multifocal intraocular lens (MIOL) was also performed experimentally with an adaptive optics visual simulator. The experimental results confirm our numerical predictions. We found that our MIOL design has a trifocal profile, which is very robust to decentration and has low degree of pupil dependence. It performs better at intermediate distances than at near distances and, for a pupil diameter of 3 mm, it works like an EDoF lens over almost the entire defocus range

The Gettysburg Battlefield, One Century Ago

In the fall of 1899, Colonel John Nicholson reported on the recent changes being made to the Gettysburg National Military park. The park held a dedication ceremony that July for a new equestrian statue to General John Reynolds erected northwest of town. It was a shiny goldenbrown, polished-bronze statue sculpted by Henry Kirke Bush-Brown (his second equestrian statue at Gettysburg in three years). The horse and rider, balancing on two legs stood on a large pedestal near the new avenue in his name. Reynolds Avenue and adjoining Wadsworth, Doubleday, and Robinson Avenues were new to the battlefield as well. These were exciting times. The first-day\u27s battlegrounds were being made accessible to visitors and veterans. In fact, the entire battlefield was being paved, marked, and restored by the Gettysburg National Park Commission (GNPC). Colonel John Nicholson (USA), Major William Robbins (CSA), and Major Charles Richardson (USA) comprised the GNPC. Each a veteran of the battle, they had been appointed by the War Department to restore the field at Gettysburg. Former Confederate veteran Robbins was specifically appointed to oversee the placement of new markers detailing the Army of Northern Virginia\u27s role in the battle. Ever since the War Department took over care of the grounds six years prior because the local Gettysburg Battlefield Memorial Association (GBMA) could no longer afford the upkeep, signs for both Union and Confederate troop placements were ordered. Confederate markings were just one of several radical changes to the park\u27s landscape design in 1899. [excerpt

Locking of Commensurate Phases in the Planar Model in an External Magnetic Field

Commensurate configuration locking is known in models like the anisotropic next-nearest-neighbor Ising model and the Frenkel-Kontorova model. We find an analogous scenario in the planar model with competing interactions when an external magnetic field is applied in the plane in which the spins lie. This model falls in the same symmetry class of the Heisenberg model with planar anisotropy. We performed a low-field, low-temperature expansion for the free energy of the model and we find phase locking energy for states with wave vectors of the form G/p where p is an integer and G is a reciprocal-lattice vector. The helix characterized by p=3 is peculiar because the commensuration energy vanishes at zero temperature. The helix corresponding to p=4 is not stable against the switching of a magnetic field that forces the spins into an up-up-down-down configuration analogous to the spin-flop phase of an antiferromagnet. For a generic commensurate value of p\u3e4, we expect locking both at zero and finite temperature as we have verified for p=5 and 6. The consequences of our results are examined for the 3N model (a tetragonal spin lattice with in-plane competitive interactions up to third-nearest neighbors)

Devil's staircase route to chaos in a forced relaxation oscillator

Este es el documento que se ha publicado a texto completo en https://doi.org/10.5802/aif.1391.https://aif.centre-mersenne.org/Este trabajo ha sido parcialmente financiado por la beca DGICYT número PB90-0695.Financiación Naciona

Comportement d'une goutte de liquide magnetique dans un champ magnetique variable: thèorie et simulation

Bakgrund: Aktieindex används världen över som placeringsalternativ, jämförelsemått inom portföljförvaltning och som underlag för portföljoptimering. Forskare har under senare tid ifrågasatt index viktade efter börsvärdet och alternativa viktningsmetoder för index har framtagits som substitut till det kapitalviktade indexet och prestationsjämförelser har gjorts. Studier har främst gjorts i USA och denna studie ämnar göra en liknande undersökning på den svenska marknaden.  Syfte: Syftet med vår studie är att undersöka alternativa viktningsmetoder på det svenska aktieindexet OMXS30 och dess historiska prestation under åren 1995-2011 i förhållande till det traditionellt kapitalviktade OMXS30. Syftet är vidare att analysera de alternativt viktade indexen som grund för portföljoptimering enligt Single-Index Model.  Genomförande: Fem alternativt viktade index konstrueras i studien där viktningen grundas på fundamentala värden, Sharpekvoter, standardavvikelse, likaviktning och handelsvolym och jämförs prestationsmässigt mot OMXS30. Indexen används sedan vid portföljoptimering enligt SIM där aktiers och portföljers karakteristika analyseras. Indexens prognostisering av betavärden utvärderas i studien för att urskilja om något index är mer träffsäkert gällande aktiens beta för nästkommande period.  Slutsats: Ett flertal av de konstruerade alternativa indexen genererar signifikant högre avkastning till lägre risk i den nedgångsperiod som analyserats varför dessa kan ses som en mer lönsam investering. Tendenser till högre avkastning för den totala perioden finns även om signifikanta skillnader inte föreligger. De alternativa indexen har föranlett skilda allokeringsbeslut vid portföljoptimeringen vilket har gett stora utslag i portföljernas förväntade prestation såväl som faktisk prestation efter optimeringen genomförts. Background: Stock market indexes are widely used as investment strategies and as a benchmark when portfolios are being constructed and evaluated. Researchers have recently questioned the capital weighted index in favor of other available weighting schemes. By comparing alternative weighted indexes to the traditionally capital weighted index one has been made aware of the significantly lower risk adjusted performance for the capital weighted index.  Aim: Our aim is to investigate in alternative weighting schemes used on the Swedish index OMXS30 and evaluate the historical performance of these alternative indexes in comparison to the traditionally capital weighted index during the period 1995-2011. Furthermore, our objective is to analyze the effects alternative weighting schemes have on portfolio optimization through Single-Index Model.  Completion: To fulfill the purpose of this thesis, five alternative weighting schemes have been applied on the Swedish index OMXS30. The weights have been calculated on fundamental measures, Sharpe ratios, standard deviation, equally weighted and trade volume and they have been compared to the traditionally cap-weighted index. Furthermore, the constructed indexes will be used to optimize portfolios with Single Index Model to compare the portfolios characteristics when different indexes have been used.  Results/Findings: The majority of the alternative weighted indexes generate significantly higher returns in one of our analyzed periods and this was during a market recession. For the total analyzed period no statistical differences among the indexes could be determined even though differences in total return are made clear. The indexes had a big effect on the portfolio optimization in terms of different share allocation.

Anomalous temperature behavior of the chiral spin helix in CrNb3S6 thin lamellae

Using Lorentz transmission electron microscopy and small-angle electron scattering techniques, we investigate the temperature-dependent evolution of a magnetic stripe pattern period in thin-film lamellae} of the prototype monoaxial chiral helimagnet CrNb 3 S 6 . The sinusoidal stripe pattern appears due to formation of a chiral helimagnetic order (CHM) in this material. We found that as the temperature increases, the CHM period is initially independent of temperature and then starts to shrink above the temperature of about 90 K}, which is far below the magnetic phase transition temperature for the bulk material, T c (123~K)}. The stripe order disappears at around 140~K, far above T c . We argue that this cascade of transitions reflects a three-stage hierarchical behavior of melting in two dimensions