Synthesis and characterization of organosoluble polyetherimides with bulky triaryl imidazole moiety: Study of photophysical properties and kinetic of thermal degradation

Novel fluorescent polyetherimides containing bulky triaryl imidazole pendant and ether linkage in the main chains were prepared from a diamine, 2,2-phenoxy-bis[4-amino-2(4,5-diphenyl-2H-imidazole-2-yl)]propane, and commercially available dianhydrides. All the resulting polymers were amorphous with inherent viscosities ranged from 0.45 to 0.75 dl/g and were readily soluble in many organic solvents which could be solution-cast into transparent and tough films. They had useful levels of thermal stability associated with relatively high T _g (245?C254°C), 10% weight loss temperatures in excess of 500°C, and char yields at 600°C in air up to 62%. These polymers exhibited strong UV-vis absorption maxima in solution and in solid state. Photoluminescence efficiency of the polyetherimides was affected by their chemical structure with quantum yields in the range 10?C28%.     

Small signal gain and loss measurement of a CW Nd:YAG laser using an antiresonant ring interferometer

An antiresonant ring (ARR) interferometer configuration is introduced for the characterization of a continuous wave (CW) Nd:YAG laser output. The output of the ARR device is precisely characterized todetermine the gain and loss of a laboratory CW Nd:YAG laser by using the Findlay-Clay approach. TheARR arm is then experimentally arranged inside the cavity of an arranged high power side-pumped CWNd:YAG laser. A coated beam splitter with 50–50% reflectivity at normal incidence is placed inside thecavity to provide a wide range of reflectivity from 0 to 100%. This is performed by a rotatable stage and tilting the beam splitter by 10°with the steps of 0.05. By changing the input electrical power of the laser pump the variation of the output laser power is monitored for 20 individual reflectivity of ARR arm.Average pump threshold power of about 180 W is obtained. With the help of the derived equations and obtained threshold power, small signal gain and loss associated with the emerging beam is estimated. It is verified that the former is very dependent to the input parameters. Laser efficiency is also measures 5.6% which is quite comparable with the reported values.     

Net analyte signal-based simultaneous determination of antazoline and naphazoline using wavelength region selection by experimental design-neural networks

Net analyte signal (NAS)-based multivariate calibration methods were employed for simultaneous determination of anthazoline and naphazoline. The NAS vectors calculated from the absorbance data of the drugs mixture were used as input for classical least squares (CLS), principal component and partial least squares regression PCR and PLS methods. A wavelength selection strategy was used to find the best wavelength region for each drug separately. As a new procedure, we proposed an experimental design-neural network strategy for wavelength region optimization. By use of a full factorial design method, some different wavelength regions were selected by taking into account different spectral parameters including the starting wavelength, the ending wavelength and the wavelength interval. The performance of all the multivariate calibration methods, in all selected wavelength regions for both drugs, was evaluated by calculating a fitness function based on the root mean square error of calibration and validation. A three-layered feed-forward artificial neural network (ANN) model with back-propagation learning algorithm was employed to model the nonlinear relationship between the spectral parameters and fitness of each regression method. From the resulted ANN models, the spectral regions in which lowest fitness could be obtained were chosen. Comparison of the results revealed that the net NAS-PLS resulted in lower prediction error than the other models. The proposed NAS-based calibration method was successfully applied to the simultaneous analyses of anthazoline and naphazoline in a commercial eye drop sample.     

Walk-off reduction,using an external optical plate and Bessel–Gaussian interaction

To reduce the walk-off angle of the extraordinary third-harmonic ultraviolet wave at 355 nm generated by type ⅡKTiOPO_4 and type I β-BaB_2O_4 optical crystals,and the Gaussian output beam of a Q-switched Nd:YAG laser,a simple theoretical model was developed based on a rotatable BK7 plate of variable thickness.By rotating the plate up to 35°along the beam direction,we reduced the walk-off angle up to ~ 13%.The same phenomenon is predicted by the model,confirming the performance of the model.It is found that,due to the walk-off effect,the intensity profile of the thirdharmonic generation beam is slightly degraded.To compensate for the observed phenomena and further reduce the walkoff,we used a combination of a convex lens and an axicon to transform the beam profile of the interacting fundamental and second-harmonic generation waves to the zero-order Bessel-Gaussian form.As a result,the walk-off is decreased to~ 48.81 mrad,providing ~ 30%relative reduction.By using the same BK7 plate rotated up to 35° along the third-harmonic beam direction,the walk-off angle is further reduced to 38.9 mrad.Moreover,it is observed that the beam profile of the emerged Bessel-Gaussian third-harmonic generation beam remains unchanged with no degradation.     

Nonparallelism of the Ricci Tensor of Pseudo-cylindric Metrics

We describe examples of metrics in the conformal class [g] on some conformally flat Riemannian manifolds (M,g]. These metrics have a constant scalar curvature and an harmonic curvature with nonparallel Ricci tensor.     

Nonlinear Marangoni instability in dielectric superposed fluids

Summary The nonlinear Marangoni instability of two dielectric superposed fluids is investigated. The system is stressed by a normal electric field such that it allows for the presence of surface charges at the interface. The method of multiple scale perturbations is used in order to obtain uniformly valid expansions. Two nonlinear Schrödinger equations describing the perturbed system are obtained. One of these equations is used to describe analytically and numerically the necessary conditions for stability and instability near the marginal state, while the other equation is used to obtain the nonlinear electrohydrodynamic cutoff wavenumber separating stable and unstable disturbances for the system.