Design optimization of orbital angular momentum fibers using the gray wolf optimizer.

Optical data communication based on the orbital angular momentum (OAM) of light is a recently proposed method to enhance the transmission capacity of optical fibers. This requires a new type of optical fiber, the main part of the optical communication system, to be designed. Typically, these fibers have a ring-shaped refractive index profile. We aim to find an optimized cross section refractive index profile for an OAM fiber in which the number of supported OAM modes (channels), mode purity, and the effective refractive index separation of OAM modes to other fibers modes are maximized. However, the complexity of the relationship between structural parameters and optical transmission properties of these fibers has resulted in the lack of a comprehensive analytical method to design them. In this paper, we investigate the process of designing OAM fibers and propose a framework to design such fibers by using artificial intelligence optimizers. It is worth mentioning here that this problem is intrinsically a multiobjective optimization problem, and the actual solution for such problems is not unique and leads to a set of optimum solutions. Therefore, at the end of the optimization process, a wide range of optimal designs will be obtained in which a trade-off is established in each of the solutions. We solve this problem with the multiobjective gray wolf optimizer (GWO) and compare the results with that of the single-objective GWO. The framework can easily find many optimal designs that support more than 20 OAM modes. The obtained results show that the proposed method is comprehensive and can optimize the structure of any OAM fibers. No human involvement, simplicity, and being straightforward are the main advantages of the proposed framework.

Effect of repeated x-ray exposure on the resolution of amorphous selenium based x-ray imagers.

PURPOSE: A numerical model and the experimental methods to study the x-ray exposure dependent change in the modulation transfer function (MTF) of amorphous selenium (a-Se) based active matrix flat panel imagers (AMFPIs) are described. The physical mechanisms responsible for the x-ray exposure dependent change in MTF are also investigated. METHODS: A numerical model for describing the x-ray exposure dependent MTF of a-Se based AMFPIs has been developed. The x-ray sensitivity and MTF of an a-Se AMFPI have been measured as a function of exposure. The instantaneous electric field and free and trapped carrier distributions in the photoconductor layer are obtained by numerically solving the Poisson's equation, continuity equations, and trapping rate equations using the backward Euler finite difference method. From the trapped carrier distributions, a method for calculating the MTF due to incomplete charge collection is proposed. RESULTS: The model developed in this work and the experimental data show a reasonably good agreement. The model is able to simultaneously predict the dependence of the sensitivity and MTF on accumulated exposure at different applied fields and bias polarities, with the same charge transport parameters that are typical of the particular a-Se photoconductive layer that is used in these AMFPIs. Under negative bias, the MTF actually improves with the accumulated x-ray exposure while the sensitivity decreases. The MTF enhancement with exposure decreases with increasing applied field. CONCLUSIONS: The most prevalent processes that control the MTF under negative bias are the recombination of drifting holes with previously trapped electrons (electrons remain in deep traps due to their long release times compared with the time scale of the experiments) and the deep trapping of drifting holes and electrons.

Comparative study of piroxicam and ibuprofen in rheumatoid arthritis.

Piroxicam was compared with ibuprofen in a 8 weeks randomised open clinical trial in 31 patients (16 patients with piroxicam and 15 patients with ibuprofen) with rheumatoid arthritis. Piroxicam was given in a dosage of 20mg once daily and ibuprofen 400mg three times a day. Both drugs appeared to be equally effective and there were only few minor side effects in patients on either drug. The once daily administration gives piroxicam a clear practical advantage over ibuprofen.

Dasherkandi project studies--health of the under fifteen.

Morbidity pattern of the under fifteen of a rural community was analysed and related to socio-economic factors. This was a part of Dasherkandi project studies carried out in a village near Dhaka city. 48.26% of the population was under the age of fifteen. Infants under the age of one year had low sickness rate which rose steeply between 1 and 4 years of life and then gradually declined after the age of 5 years. Commonest morbidity was worm infestation which was followed by flu and upper respiratory tract infection. The non-agriculturist and the low income group had the highest level of sickness. It is suggested that children in rural areas suffer mainly from diseases which are related to poor nutrition and hygiene resulting from unsatisfactory socio-economic condition. All the childhood mortality occurred under the age of one year and was found to be due to tetanus in this study.