Development and validation of a capillary electrophoresis method for determination of enantiomeric purity and related substances of esomeprazole in raw material and pellets

A capillary electrophoresis method using CDs for quality control of esomeprazole (ESO) in terms of enantiomeric purity and related substances in raw material and pellets was developed. ESO is the S‐enantiomer of omeprazole (OMZ). Several parameters were evaluated, including type and concentration of buffer and CD, concentration of additives and electrolyte pH. Resolution between the enantiomers of OMZ obtained for each parameter tested was calculated and the presence of the main related substance such as OMZ sulfone was carefully monitored. The optimized system consisted of 100 mM Tris‐phosphate buffer pH 2.5 with 20 mM 2‐hydroxypropyl‐β‐CD, 1 mM sodium dithionite, temperature at 15°C, voltage at 28 kV, and UV detection at 301 nm. Once optimized, the electrophoretic system was validated according to ICH guidelines. The limits of detection and quantification for R‐OMZ were 0.6 μg/mL (0.06% w/w of ESO) and 2.0 μg/mL (0.2% w/w of ESO), respectively. A mean concentration of R‐OMZ <0.2% limit established by the United States Pharmacopeia (USP) was found in the raw material and six‐pellet samples of ESO. No other impurities were found in the samples under these conditions. Therefore, the developed method was found to be appropriate not only for enantiomeric quality control of ESO but also for the analysis of ESO and the main related substance in raw material and pharmaceutical formulations as well as for stability indicating studies.     

Y junctions in photonic crystal channel waveguides: high transmission and impedance matching

We investigate the efficiency of transmission through photonic crystal Y junctions and show the importance of matching mode symmetries. Furthermore, we show that by adding tuning holes to the input waveguide it is possible to achieve almost perfect impedance matching, leading ideally to unitary transmission through the junction. The model system is based on a triangular photonic lattice of holes in dielectrics to reflect experimental reality.     

Autosoliton transmission in dispersion-managed systems guided by in-line nonlinear optical loop mirrors

We examine the feasibility of optical pulse transmission in dispersion-managed fiber systems with in-line nonlinear optical loop mirrors. Applying numerical analysis, we find regimes of stable propagation over long distances in such lines, with a significant increase in the signal-to-noise ratio.     

Superprism Behaviour of an Array of Photonic Crystal Waveguides

The behaviour of an array of photonic crystal waveguides is numerically investigated. It is shown that high dispersion may be achieved in the telecommunication window around 1550 nm, with a device whose dimensions are in the order of half a mm².     

A 1-MW, 1-mm continuous-wave FELtron for toroidal plasma heating

A powerful, continuous-wave millimeter radiation source is presented. An electrostatic Cockcroft-Walton accelerator (2.5 MV) drives an FEL (free-electron laser) of 1 MW power. The accelerator has a new design in order to obtain a very powerful (50 MW) electron beam and very small ripple. A recovery system is used to increase RF power and efficiency. The FEL oscillator is 1.5-m long, with a permanent magnet helical wiggler. The cavity is equipped with Bragg mirrors. The FEL is set at the high voltage terminal     

An analysis of the Transverse Optical Klystron (TOK) and the Free Electron Laser (FEL) through the exact solution of their evolution equation

We give the exact analytical solution of the evolution equation of an electron beam interacting in a wiggler with an electromagnetic wave. The initial energy distribution is assumed both monochromatic and gaussian. Furthermore, the evolution in a drift space is considered. Some basic characteristics of the FEL and TOK are derived from the mathematical properties of the solution.     

Efficient optimisation of per-channel pre-compensation in WDM 20-Gbit/s RZ-DPSK transmission in non-slope matched submarine links

We propose a computationally efficient method to the per-channel dispersion optimisation applied to 50 GHz-spaced N × 20-Gbit/s wavelength division multiplexing return-to-zero differential phase shift keying transmission in non-zero dispersion-shifted fibre based submarine systems.     

Exact dynamic stiffness elements based on one-dimensional higher-order theories for free vibration analysis of solid and thin-walled structures

In this paper, an exact dynamic stiffness formulation using one-dimensional (1D) higher-order theories is presented and subsequently used to investigate the free vibration characteristics of solid and thin-walled structures. Higher-order kinematic fields are developed using the Carrera Unified Formulation, which allows for straightforward implementation of any-order theory without the need for ad hoc formulations. Classical beam theories (Euler–Bernoulli and Timoshenko) are also captured from the formulation as degenerate cases. The Principle of Virtual Displacements is used to derive the governing differential equations and the associated natural boundary conditions. An exact dynamic stiffness matrix is then developed by relating the amplitudes of harmonically varying loads to those of the responses. The explicit terms of the dynamic stiffness matrices are also presented. The resulting dynamic stiffness matrix is used with particular reference to the Wittrick–Williams algorithm to carry out the free vibration analysis of solid and thin-walled structures. The accuracy of the theory is confirmed both by published literature and by extensive finite element solutions using the commercial code MSC/NASTRAN^®$\mathrm{MSC}/{\mathrm{NASTRAN}}^{\circledR }$.     

“Magic” Dispersion Maps with Distributed Raman Amplification

We analyze pulse propagation in an optical fiber with a periodic dispersion map and distributed amplification. Using an asymptotic theory and a momentum method, we identify a family of dispersion management schemes that are advantageous for massive multichannel soliton transmission. For the case of two-step dispersion maps with distributed Raman amplification to compensate for the fiber loss, we find special schemes that have optimal (chirp-free) launch point locations that are independent of the fiber dispersion. Despite the variation of dispersion with wavelength due to the fiber dispersion slope, the transmission in several different channels can be optimized simultaneously using the same optimal launch point. The theoretical predictions are verified by direct numerical simulations. The obtained results are applied to a practical multichannel transmission system.     

RF cavity for gas laser excitation

Summary A new technique for RF transverse excitation of gas laser has been tested: the plasma tube has been put inside a quarter wave strip line RF cavity. Excellent field uniformity and arcing problem avoidance have been observed. The efficiency is greater than 15%. The guidelines for cavity design are discussed. Work partially supported by ENEA-Contract No. C/451 (Dip. Fusione Associazione EURATOM-ENEA, CRE Frascati).