Nonlinear Dynamics of a Passively Mode-Locked Fiber Laser Containing a Long-Period Fiber Grating

We report on a numerical investigation of the nonlinear dynamics of a passively mode-locked fiber laser containing a long period fiber grating. The model is based on the normalized complex Ginzburg-Landau equation and the nonlinear coupled mode equations of the grating. The numerical results indicate the existence of passive mode-locking and autosoliton generation in the cavity of the laser. Both single and bound soliton pulse trains exhibit period doubling bifurcations and a route to chaos as the normalized saturated gain is increased. Furthermore, we show the presence of long period pulsation, soliton sidebands and possible coexisting attractors excited by multisoliton formation and soliton energy quantization.     

Adsorptive treatment of phenol from aqueous solution using chitosan/calcined eggshell adsorbent: Optimization of preparation process using Taguchi statistical analysis

Phenol and its derivatives are known to be toxic causing adverse impact on human health and environment. Adsorption utilising waste materials is a cost effective method for abatement of such pollutants. The present study thus aims to remove the phenol from aqueous solutions using chitosan/calcined eggshell adsorbent. Taguchi L₂₇ Orthogonal array design methodology was used for the optimization of preparation variables. The statistical results obtained using ANOVA and S/N ratios showed that adsorption of phenol was significantly influenced by activation temperature (54.90%) and activation time (43.70%) whereas the mix ratio had fairly low impact on the output response (1.14%). The confirmation run in optimum preparation conditions of temperature (800 ?°C), time (60mins) and mix ratio (1:1) resulted in maximum adsorption capacity (10.82 ?mg/g) which confirmed that the optimization done by Taguchi model was valid and reliable. The characterization of adsorbent prepared under optimum conditions were done using scanning electron microscopy, X-ray diffraction (XRD), and the Fourier transform Infrared spectroscopy (FTIR). Adsorption and kinetic studies manifested that the adsorption phenomenon onto prepared adsorbent is illustrated well by linear Langmuir isotherm and pseudo second order kinetics.     

Structural,morphological and photoluminescence characteristics of sol-gel derived nano phase CeO<Subscript>2</Subscript> films deposited using citric acid

Homogenous nano structured CeO₂ films have been prepared by a sol-gel process using different mole ratios of citric acid as additive. XPS studies clearly illustrate an increase in Ce³⁺ proportion upon the use of higher citric acid content for the deposition of films. The crystallite sizes in the films lie in the nanorange. Photoluminescence emission in the films is attributed to various defects resulting from crystallization. Lowest transparency, high Ce³⁺ content and optimum sized crystallites in CeO₂ (1:1.5) films have led to its highest PL characteristics. Ce³⁺ chemical state is the major contributor to the PL activity of these films. The SEM micrographs show a reduced level of CeO₂ agglomeration in the films deposited using higher citric acid contents. A comparison of different properties of CeO₂ films deposited using citric acid and CeO₂–TiO₂ films has also been made.      

Structure, microstructure and photoluminescence properties of Fe doped SnO2 thin films

In this paper, effects of Fe doping on crystallinity, microstructure and photoluminescence (PL) properties of sol-gel derived SnO₂ thin films are reported. It is shown that doping of Fe³⁺ ions leads to crystallite size reduction and higher strain in SnO₂ thin films. The room temperature PL spectra show marked changes in intensity and blue-shift of the emission lines upon Fe doping. These observations have been correlated with structural changes and defect chemistry of Fe doped SnO₂ thin films.     

Analysis of nano-grating-assisted light absorption enhancement in metal-semiconductor-metal photodetectors patterned using focused ion-beam lithography

We present finite-difference time-domain (FDTD) analysis results of light absorption enhancement factor dependence on the profile shape of nano-gratings etched into the surfaces of metal-semiconductor-metal photodetector (MSM-PD) structures. The MSM-PDs patterned by nano-gratings are optimized geometrically, improving the light absorption near the design wavelength through plasmon-assisted electric field concentration effects. FDTD simulation results show about 50 times light absorption enhancement prediction for 850 nm light due to improved optical signal propagation through the nano-gratings in comparison with the conventional MSM-PD designs employing only a subwavelength aperture. We also report on the nano-grating profile shapes obtained typically in our experiments using focused ion-beam lithography and discuss the dependency of light absorption enhancement on the geometric parameters of nano-gratings inscribed into MSM-PDs.     

3-Hydroxy-7,8,9,10-tetrahydro-6H-benzo[c]chromen-6-one and 3-hydroxy-6H-benzo[c]chromen-6-one act as on-off selective fluorescent sensors for Iron (III) under in vitro and ex vivo conditions

Regarding the abundant use of metals for different purposes, it becomes more critical from various scientific and technological perspectives to discover novel agents as selective probes for the detection of specific metals. In our previous studies, we have shown that aqueous solutions of natural urolithins (i.e., hydroxyl-substituted benzo[c]chromen-6-one derivatives) are selective Iron (III) sensors in fluorescence assays. In this study, we have extrapolated these findings to another coumarine compound (i.e., 3-Hydroxy-7,8,9,10-tetrahydro-6H-benzo[c]chromen-6-one) and compared the selective metal binding properties with Urolithin B (i.e., 3-Hydroxy-6H-benzo[c]chromen-6-one). Following the synthesis and structure identification studies, the fluorometric studies pointed out that the lactam group in the structure still persists to be the important scaffold for maintaining selective on-off sensor capacity that renders the compound a selective Iron (III) binding probe. Moreover, for the first time, fluorescence cellular imaging studies concomitant to cytotoxicity assays with the title compounds were also performed and the results displayed the cell-penetrative, safe, and fluorescent detectable characteristics of the compounds in neuroblastoma and glioblastoma cells through servings as intracellular Iron (III) on-off sensors.     

A Relativistic Model for Strange Quark Star

We propose a relativistic model for strange quark stars within the framework of MIT Bag model. In our model, we assume that the highly compact strange stars are anisotropic in nature which is an expected feature in the ultra high density regime. We discuss various physical features of the model and show that the model satisfies all the regularity conditions. By estimating the value of the Bag constant for strange star candidates like 4U 1820-30, Her X-1 and SAX J 1808.4-3658, we show that a wire range of values of the Bag constant are possible for such stars though, in the case of 4U 1820-30, the estimated value of the Bag constant has been found to be very close to its currently acceptable range. Nevertheless, our results are in agreement with the recent CERN-SPS and RHIC data.