Solubility parameter based screening methods for early stage formulation development of itraconazole amorphous solid dispersions

Objectives: This article uses conventional and newly extended solubility parameter (δ) methods to identify polymeric materials capable of forming amorphous dispersions with itraconazole (itz). Methods: Combinations of itz and Soluplus, Eudragit E PO (EPO), Kollidon 17PF (17PF) or Kollidon VA64 (VA64) were prepared as amorphous solid dispersions using quench cooling and hot melt extrusion. Storage stability was evaluated under a range of conditions using differential scanning calorimetry and powder X-ray diffraction. Key findings: The rank order of itz miscibility with polymers using both conventional and novel δ-based approaches was 17PF > VA64 > Soluplus > EPO, and the application of the Flory–Huggins lattice model to itz–excipient binary systems corroborated the findings. The solid-state characterisation analyses of the formulations manufactured by melt extrusion correlated well with pre-formulation screening. Long-term storage studies showed that the physical stability of 17PF/vitamin E TPGS–itz was poor compared with Soluplus and VA64 formulations, and for EPO/itz systems variation in stability may be observed depending on the preparation method. Conclusion: Results have demonstrated that although δ-based screening may be useful in predicting the initial state of amorphous solid dispersions, assessment of the physical behaviour of the formulations at relevant temperatures may be more appropriate for the successful development of commercially acceptable amorphous drug products.

Multilayer Dielectric Stack Parameter Modelling for FSS Design

This paper discusses modelling multilayer dielectric stacks for use as substrate support for frequency selective surface. A method of a fast simulation of multilayer dielectric stack as a complementary tool for FSS design is proposed. Using the method analysis of effect of different parts of the multilayer stack has been performed. The tool has also been used for extraction of material parameters from the measured results. Measured transmission and reflection of a sample manufactured material stack show good agreement with the simulated results obtained for extracted material parameters.

The white dwarf's carbon fraction as a secondary parameter of Type Ia supernovae

Context. Binary stellar evolution calculations predict thatChandrasekhar-mass carbon/oxygen white dwarfs (WDs) show a radiallyvarying profile for the composition with a carbon depleted core. Manyrecent multi-dimensional simulations of Type Ia supernovae (SNe Ia),however, assume the progenitor WD has a homogeneous chemicalcomposition.
Aims: In this work, we explore the impact ofdifferent initial carbon profiles of the progenitor WD on the explosionphase and on synthetic observables in the Chandrasekhar-mass delayeddetonation model. Spectra and light curves are compared to observationsto judge the validity of the model.
Methods: The explosion phaseis simulated using the finite volume supernova code Leafs, which isextended to treat different compositions of the progenitor WD. Thesynthetic observables are computed with the Monte Carlo radiativetransfer code Artis. Results: Differences in binding energies ofcarbon and oxygen lead to a lower nuclear energy release for carbondepleted material; thus, the burning fronts that develop are weaker andthe total nuclear energy release is smaller. For otherwise identicalconditions, carbon depleted models produce less 56Ni.Comparing different models with similar 56Ni yields showslower kinetic energies in the ejecta for carbon depleted models, butonly small differences in velocity distributions and line velocities inspectra. The light curve width-luminosity relation (WLR) obtained formodels with differing carbon depletion is roughly perpendicular to theobserved WLR, hence the carbon mass fraction is probably only asecondary parameter in the family of SNe Ia.
Tables 3 and 4 are available in electronic form at http://www.aanda.org

Towards generalized Doherty power amplifier design for multiband operation

This paper presents a new variant of broadband Doherty power amplifier that employs a novel output combiner. A new parameter ∝ is introduced to permit a generalized analysis of the recently reported Parallel Doherty power amplifier (PDPA),and hence offer design flexibility. The circuit prototype of the new DPA fabricated using GaN devices exhibits maximum drain efficiency of 85% at 43-dBm peak power and 63% at 6-dB backoff power (BOP). Measured drain efficiency of >60% at peak power across 500-MHz frequency range and >50% at 6-dB BOP across 480-MHz frequency range were achieved, confirming the  theoretical wideband characteristics of the new DPA.

Parameter Optimisation for Woodwind Single-Reed Models

Time-domain modelling of single-reed woodwind instruments usually involves a lumped model of the excitation mechanism. The parameters of this lumped model have to be estimated for use in numerical simulations. Several attempts have been made to estimate these parameters, including observations of the mechanics of isolated reeds, measurements under artificial or real playing conditions and estimations based on numerical simulations. In this study an optimisation routine is presented, that can estimate reed-model parameters, given the pressure and flow signals in the mouthpiece. The method is validated, tested on a series of numerically synthesised data. In order to incorporate the actions of the player in the parameter estimation process, the optimisation routine has to be applied to signals obtained under real playing conditions. The estimated parameters can then be used to resynthesise the pressure and flow signals in the mouthpiece. In the case of measured data, as opposed to numerically synthesised data, special care needs to be taken while modelling the bore of the instrument. In fact, a careful study of various experimental datasets revealed that for resynthesis to work, the bore termination impedance should be known very precisely from theory. An example is given, where the above requirement is satisfied, and the resynthesised signals closely match the original signals generated by the player.

Comprehensive numerical modelling of the performance of a second harmonic generation stage coupled with a low-gain optical parametric amplifier

We present a comprehensive model for predicting the full performance of a second harmonic generation-optical parametric amplification system that aims at enhancing the temporal contrast of laser pulses. The model simultaneously takes into account all the main parameters at play in the system such as the group velocity mismatch, the beam divergence, the spectral content, the pump depletion, and the length of the nonlinear crystals. We monitor the influence of the initial parameters of the input pulse and the interdependence of the two related non-linear processes on the performance of the system and show its optimum configuration. The influence of the initial beam divergence on the spectral and the temporal characteristics of the generated pulse is discussed. In addition, we show that using a crystal slightly longer than the optimum length and introducing small delay between the seed and the pump ensures maximum efficiency and compensates for the spectral shift in the optical parametric amplification stage in case of chirped input pulse. As an example, calculations for bandwidth transform limited and chirped pulses of sub-picosecond duration in beta barium borate crystal are presented.