Growth and characterization of thiourea mixed cadmium – lead chloride – a nonlinear optical crystal

Nonlinear optical (NLO) crystal of thiourea mixed cadmium–lead chloride dihydrate Cd[(PbCl₃)(NH₂CSNH₂)].2H₂O (TCCPC) have been grown in solution by slow evaporation technique at room temperature. The powder X‐ray diffraction pattern has been recorded and indexed. The UV‐Vis‐NIR transmittance and FT‐IR spectrum have been recorded in the range 200‐1090 nm and 400‐4000 cm^‐1, respectively. The lower cut‐off wavelength is 280 nm in the UV region, which is higher than that of pure Cd(PbCl₃) (CCPC) crystal. The presence of functional groups has been confirmed by FT‐IR analysis. The TCCPC crystal was characterized by SEM and EDX spectrum. The second harmonic generation (SHG) of the thiourea mixed cadmium–lead chloride (TCCPC) crystal is demonstrated by the Kurtz Perry method using Nd:YAG laser and the results confirm that the grown crystal is roughly three times more efficient than ADP. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Probabilistic modeling of forced ignition of alternative jet fuels

Fast and reliable high altitude re-ignition is a critical requirement for the development of alternative jet fuels (AJFs). To achieve stable combustion, a spark kernel needs to transit in a partially or fully extinguished flow to develop a flame front. Understanding the relight characteristics of the AJFs is complicated by the chaoticity of the turbulent flow and variations in the spark properties. The focus of this study is the prediction of such characteristics by high-fidelity simulations, with a specific focus on fuel composition effect on the ignition process. For this purpose, a previously developed computational framework is applied, which utilizes high-fidelity LES simulations, a hybrid tabulation approach for modeling forced ignition and detailed quantification of uncertainty resulting from initial and boundary conditions to predict ignition probability. The method is applied to two alternative fuels (named C1 and C5) and Jet-A fuel (named A2) under gaseous conditions. Results show that the mixing of kernel and fuel–air mixture is not affected by the ignition process, but chemistry effects strongly dominate ignition probability. In particular, C1 exhibits much lower ignition probability than the other two fuels, especially at lean operating conditions. More importantly, this behavior is contradictory to ignition delay experiments which predict longer delay times for C5 compared to C1. Comparisons with experiments show that the comprehensive modeling approach captures the ignition trends. Analysis of kernel trajectories in composition space shows that the variations are caused by the relative effects of kernel mixing, response to strain, and ignition properties of the fuel.     

Deriving crisp and consistent priorities for fuzzy AHP-based multicriteria systems using non-linear constrained optimization

Fuzzy optimization models are used to derive crisp weights (priority vectors) for the fuzzy analytic hierarchy process (AHP) based multicriteria decision making systems. These optimization models deal with the imprecise judgements of decision makers by formulating the optimization problem as the system of constrained non linear equations. Firstly, a Genetic Algorithm based heuristic solution for this optimization problem is implemented in this paper. It has been found that the crisp weights derived from this solution for fuzzy-AHP system, sometimes lead to less consistent or inconsistent solutions. To deal with this problem, we have proposed a consistency based constraint for the optimization models. A decision maker can set the consistency threshold value and if the solution exists for that threshold value then crisp weights can be derived, otherwise it can be concluded that the fuzzy comparison matrix for AHP is not consistent for the given threshold. Three examples are considered to demonstrate the effectiveness of the proposed method. Results with the proposed constraint based fuzzy optimization model are more consistent than the existing optimization models.     

Visualization of supersonic screeching jets using a phase conditioned focusing schlieren system

This study describes a technique that combines the benefits of focusing schlieren and phase conditioning. Focusing schlieren blurs and drops contrast of non-critical features whereas phase conditioning emphasizes periodic flow features, and their combination produces unique results. The supersonic jets that we studied produced an intense tone referred to as screech. The measured screech tone signal was used as input to the phase conditioning circuit that adjusted the strobing light source to the vertical synchronization pulse of a CCD camera. The sharp video images obtained by this technique could either be frozen or continuously swept through one period of screech to acquire a slow motion video record of the jet unsteadiness. Two cases were visualized in this study: first, an underexpanded jet from a convergent rectangular nozzle at various fully expanded Mach numbers. Second, a supersonic jet emerging from a convergent-divergent rectangular nozzle at a design Mach number of 1.4, artificially excited by impingement tones. The results of this study illustrate the usefulness of this system in visualizing oscillatory flows.The authors would like to thank Dr. Edward J. Rice for his contributions including the design of the impingement obstacles. The efforts of Brentley C. Nowlin (NASA Lewis), and James E. Little (NYMA Inc.) in the design and construction of the strobe trigger mechanism are highly appreciated. We also thank Janet Ivancic (NASA Lewis Photo Lab) for the image enhancement.     

Parametrizing the lepton mixing matrix in terms of charged lepton corrections

We consider a parametrization of the lepton mixing matrix in which the deviations from maximal atmospheric mixing and vanishing reactor mixing are obtained in terms of small corrections from the charged lepton sector. Relatively large deviations for the reactor mixing angle from zero as indicated by T2K experiment can be obtained in this parametrization. We are able to further reduce the number of complex phases, thus, simplifying the analysis. In addition, we have obtained the sides of unitarity triangles and the vacuum oscillation probabilities in this parametrization. The Jarlskog rephasing invariant measure of CP violation at the leading order has a single phase difference which can be identified as Dirac-type CP violating phase in this parametrization.     

Mode spectra of natural disturbances in a circular jet and the effect of acoustic forcing

A modal spectrum technique was used to study coherent instability modes (both axisymmetric and azimuthal) triggered by naturally occurring disturbances in a circular jet. This technique was applied to a high Reynolds number (400,000) jet for both untripped (transitional) and tripped (turbulent) nozzle exit boundary layers, with both cases having a core turbulence level of 0.15%. The region up to the end of the potential core was dominated by the axisymmetric mode, with the azimuthal modes dominating further downstream. The growth of the azimuthal modes was observed closer to the nozzle exit for the jet with a transitional boundary layer. Whether for locally parallel flow or slowly diverging flow, even at low levels of acoustic forcing, the inviscid linear theory is seen to be inadequate for predicting the amplitude of the forced mode. In contrast, the energy integral approach reasonably predicts the evolution of the forced mode.     

In situ, on-resin synthesis of 8-Br/NH2 adeninyl peptide nucleic acid (PNA) oligomers and complementation studies with DNA

A new, novel and efficient in situ synthesis of 8-aminoadeninyl PNA oligomers from corresponding 8-bromoadeninyl PNA oligomers is reported. The study of hybridisation properties of (8-Br/8-NH₂) PNA oligomers with cDNA reveals substitution-site dependent stabilization of derived triplexes and duplexes.