A Novel Technique for Spatial Phase-shifting Interferometry

Abstract

A novel technique for phase detection using three-step spatial phase-shifting interferometry is presented. The presented technique overcomes and studies the two main problems presented in the commonly used three-step phase-stepping technique. These problems deal with the leak of carrier frequency in the detected phase and the optimal carrier frequency to obtain the highest phase noise robustness.     

Scattering of light from metamaterial gratings with finite length

Using an integral equation approach based on the Rayleigh hypothesis, we investigate the scattering of a plane wave at the rough surface of a metamaterial with a finite number of sinusoidal grooves. To show the adequacy of the model, we present results that are in agreement with the predictions of physical optics and that quantitatively reproduce the polarization and angular dependences predicted by the C-formalism for metamaterial gratings with an infinite number of grooves.     

Isolation,identification, and antioxidant activity of anthocyanin compounds in Camarosa strawberry

This paper explores the bioactive composition of strawberry (Camarosa variety) [Fragaria × ananassa (Rosaceae Family)] describing its anthocyanin composition and measuring the antioxidant activity (AA) of isolated pigments.     

Applications and challenges of the 802.11e EDCA mechanism: an experimental study

In this article we conduct an experimental study of the enhanced distributed channel access mechanism of the upcoming 802.11e standard. The main focus of the study is on two applications of EDCA: traffic engineering and service guarantees. With traffic engineering we aim at distributing the bandwidth in the WLAN according to a given throughput allocation criterion. With service guarantees the objective is to ensure that the performance metrics (throughput and delay) experienced by a station meet a given quality criterion. We build a testbed with wireless cards that support a substantial subset of the EDCA functionality and analyze performance against different sets of requirements. Experimental results show that EDCA can effectively be used for traffic engineering purposes. The goal of providing service guarantees with EDCA is shown to be more challenging; we identify future research directions that need to be addressed in order to achieve this goal.     

Robustness margin for attitude control of a four rotor mini-rotorcraft: Case of study

In this paper we present new results to compute the robustness margin of an attitude control algorithm for a quad-rotor mini-rotorcraft known as X4-flyer. The maximum parametric uncertainty is calculated when multivariable PD controller is used to stabilize the attitude of the aerial vehicle. This work is based on the value set characterization approach of the mathematical model for the closed-loop control system, which is represented by an interval plant with time delay. The zero exclusion principle is used to compute the robustness margin of the closed-loop system. This approach transforms the original robust stability problem into simple problem of graphic inspection, where we only needed to verify if a graph on the complex plane does not contain the origin of the plane. Additionally, different experiments were made in order to validate theoretical results; these experimental results will be presented at the end of this work.     

Natural antioxidants from herbs and spices improve the oxidative stability and frying performance of vegetable oils

Lipid oxidation has been identified as the major deterioration process of vegetable oils. Undesirable effects are even more profound when food processing involves high temperatures in the presence of oxygen. Natural ground herbs (black pepper, ginger, turmeric, rosemary and oregano) were assessed for their antioxidant capacity, phenolic content and ability to improve the oxidative stability of vegetable oils. The most potent herb was incorporated in vegetable oils formulations which were subjected to consecutive frying cycles. The oxidative stability of the vegetable oils, the formation of conjugated dienes/trienes and the decimation of tocopherol levels after the frying process were assessed. Rosemary powder was the most effective antioxidant among the ones tested. The oxidative stability of tocopherol‐stripped corn oil with rosemary powder (1.53 ± 0.06 h) was significantly higher than the control (0.84 ± 0.02 h) and the oil with synthetic antioxidants (1.20 ± 0.03 h). Rosemary powder effectively improved the oxidative stability of sunflower (128.91%), olive (55.61%) and rapeseed (73.20%) oil during deep‐frying and prevented CD and CT formation in rapeseed oil.     

Adaptive control of a class of nonlinear systems with convex/concave parameterization

This paper deals with adaptive control of a class of second-order nonlinear systems with a triangular structure and convex/concave parameterization. In Annaswamy et al. (Automatica 33(11) (1998) 1975–1995) it was shown that nonlinearly parameterized systems that satisfy certain matching conditions can be adaptively controlled in a stable manner. In this paper, we relax these matching conditions and include additional dynamics between the nonlinearities and the control input. Global boundedness and convergence to within a desired precision is established. No overparameterization of the adaptive controller is required.     

Direct ray aberration estimation in Hartmanngrams by use of a regularized phase-tracking system

The Hartmann test is a well-known technique for testing large telescope mirrors. The Hartmann technique samples the wave front under analysis by use of a screen of uniformly spaced array of holes located at the pupil plane. The traditional technique used to gather quantitative data requires the measurement of the centroid of these holes as imaged near the paraxial focus. The deviation from its unaberrated uniform position is proportional to the slope of the wave-front asphericity. The centroid estimation is normally done manually with the aid of a microscope or a densitometer; however, newer automatic fringe-processing techniques that use the synchronous detection technique or the Fourier phase-estimation method may also be used. Here we propose a new technique based on a regularized phase-tracking (RPT) system to detect the transverse aberration in Hartmanngrams in a direct way. That is, it takes the dotted pattern of the Hartmanngram as input, and as output the RPT system gives the unwrapped transverse ray aberration in just one step. Our RPT is compared with the synchronous and the Fourier methods, which may be regarded as its closest competitors.