Development and application of a validated stability-indicating HPLC method for simultaneous determination of granisetron hydrochloride, benzyl alcohol and their main degradation products in parenteral dosage forms

A simple, rapid and sensitive reversed phase high performance liquid chromatographic method using photodiode array detection was developed and validated for the simultaneous determination of granisetron hydrochloride, benzyl alcohol, 1-methyl-1H-indazole-3-carboxylic acid (the main degradation product of granisetron) and benzaldehyde (the main degradation product of benzyl alcohol) in granisetron injections. The separation was achieved on Hypersil BDS C8 (250 mm × 4.6 mm i.d., 5 μm particle diameter) column using a mobile phase consisted of acetonitrile:0.05 M KH₂PO₄:triethylamine (22:100:0.15) adjusted to pH 4.8. The column was maintained at 25 °C and 20 μL of solutions was injected. Photodiode array detector was used to test the peak purity and the chromatograms were extracted at 210 nm. Naphazoline hydrochloride was used as internal standard. The method was validated with respect to specificity, linearity, accuracy, precision, limit of quantitation and limit of detection. The validation acceptance criteria were met in all cases. Identification of the pure peaks was carried out using library match programmer and wavelengths of derivative optima of the spectrograms of the peaks. The method was successfully applied to the determination of the investigated drugs and their degradation products in different batches of granisetron injections. The method was proved to be sensitive for the determination down to 0.03 and 0.01% of granisetron degradation product and benzaldehyde, respectively, which are far below the compendia limits for testing these degradation products in their corresponding intact drugs.     

Effect of electron phonon interaction on the optical conductivity of zigzag carbon nanotubes

Optical conductivity of a zigzag carbon nanotube is investigated in the context of the Holstein model. Green??s function approach is applied to calculate the optical conductivity as a function of photon frequency, temperature, and electron?Cphonon coupling strength. Based on our results, optical conductivity decreases with electron?Cphonon coupling constant for both metallic and semiconducting carbon nanotubes. Our results show that temperature yields shortening the height of peaks of zigzag CNT optical absorption.     

Nonlinear optical properties of a three-electron quantum dot with account of the Rashba spin–orbit interaction

In this study, a detailed investigation of the nonlinear optical properties such as optical absorption and refractive index change associated with intersubband transitions in a three-electron quantum dot in two dimensions in the presence of the Rashba spin–orbit interaction has been carried out. We present the exact wave functions and energy levels of the system. Numerical results on typical GaAs/AlGaAs materials show that the decrease of the quantum dot radius blueshifts and amplifies the absorption coefficients as well as the refractive index changes, as expected. Additionally, an increase of the optical intensity and relaxation time considerably changes the absorption coefficients and the refractive index changes.     

Stability improvement and regenerative chatter suppression in nonlinear milling process via tunable vibration absorber

In this paper, a tunable vibration absorber set (TVAs) is designed to suppress regenerative chatter in milling process (as a semi-active controller). An extended dynamic model of the peripheral milling with closed form expressions for the nonlinear cutting forces is presented. The extension part of the cutting tool is modeled as an Euler–Bernoulli beam with in plane lateral vibrations (x–y directions). Tunable vibration absorbers in x–y directions are composed of mass, spring and dashpot elements. In the presence of regenerative chatter, coupled dynamics of the system (including the beam and x–y absorbers) is described through nonlinear delay differential equations. Using an optimal algorithm, optimum values of the absorbers' position and their springs' stiffness in both x–y directions are determined such that the cutting tool vibration is minimized. Results are compared for both linear and nonlinear models. According to the results obtained, absorber set acts effectively in chatter suppression over a wide range of chatter frequencies. Stability limits are obtained and compared with two different approaches: a trial and error based algorithm and semi-discretization method. It is shown that in the case of self-excited vibrations, the optimum absorber improves the process stability. Therefore, larger values of depth of cut and consequently more material removal rate (MRR) can be achieved without moving to unstable conditions.     

Dynamics of regenerative chatter and internal resonance in milling process with structural and cutting force nonlinearities

In this paper, internal resonance and nonlinear dynamics of regenerative chatter in milling process is investigated. An extended dynamic model of the peripheral milling process including both structural and cutting force nonlinearities is presented. Closed form expressions for the nonlinear cutting forces are derived through their Fourier series components. In the presence of the large vibration amplitudes, the loss of contact effect is included in this model. Using the multiple-scales approach, analytical approximate response of the delayed nonlinear system is obtained. Considering the internal resonance dynamics (i.e. mode coupling), the energy transfer between the coupled x–y modes is studied. The results show that during regenerative chatter under specific cutting conditions, one mode can decay. Furthermore, it is possible to adjust the rate at which the x-mode (or y-mode) decays by implementation of the internal resonance. Therefore, under both internal resonance and regenerative chatter conditions, it is possible to suppress the undesirable vibration of one mode (direction) in which accurate surface finish is required. Under the steady-state motion, jump phenomenon is investigated for the process with regenerative chatter under various cutting conditions. Moreover, the effects of structural and cutting force nonlinearities on the stability lobes diagram of the process are investigated.     

Proposal for a 4-channel all optical demultiplexer using 12-fold photonic quasicrystal

In this work, 12-fold photonic quasicrystal (PQC) with cross section equals to 138 μm² has been used to design a 4-channel optical demultiplexer. The size of structure promises its applications in optical integrated circuits (OICs) and also, wavelength division multiplexing (WDM) communication devices. Finite difference time domain (FDTD) method has been employed in order to investigate the structure's band gap and output waveforms of each channel. Four channels, with spacing less than 1 nm and cross-talk level better than ? 2.8 dB have been separated by introducing defects in L-shaped and line defect waveguides (LDWs) in the crystal's structure. It has been shown that, L-shaped waveguides (LWs) are quite more frequency selective than line defect waveguides. Also, it has been found that the exact tuning of the central wavelength of each channel is possible by making use of defects with different radiuses and sites in the waveguides.