Greener synthetic approach for the preparation of substituted flexible dimeric pyridinium salts and its importance

We have prepared substituted flexible dimeric pyridinium bromide using conventional and greener approach. Solvent-free solid phase (greener) approach is superior than the conventional owing to nontoxic, easy workup procedure, and 20 times lesser reaction time. Toxic organic solvents and column chromatography are avoided. Aldol condensation reaction is studied with various substituted aromatic aldehyde and compared with available recent literatures. Synthesized substituted flexible dimeric pyridinium salts acted as potential catalysts because of their better performance even in low concentration, recyclability, and activation of two molecules of aldehydes at the same time for aldol condensation reaction.     

Influence of pH and microwave calcination on the morphology of KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> particles derived by Pechini Sol–Gel method

KGd(WO₄)₂ (KGW) particles were synthesized at 3.5, 5.5 and 7.5 pH values by Pechini polymeric complex sol–gel method using potassium nitrate, gadolinium nitrate, ammonium paratungstate, citric acid and ethylene glycol as starting materials. Deionized water was used as solvent. Polymeric precursor gel was formed with citric acid as complexing agent and ethylene glycol as binder. Synthesized gel was analyzed by FT-IR spectroscopy. Prepared precursor gels were further annealed using resistive and microwave processes at 550 and 700 °C, respectively. The properties of heat treated samples were characterized by powder XRD, FT-IR, Raman and SEM analysis to understand the crystallinity, organic liberation, tungstate ribbon formation and surface morphology, respectively. The phase formation and different phases of intermediate oxides in pre-fired samples were investigated by powder XRD. Organic liberation in the samples in relation to temperature, and the carbon content in the pre-fired powder was analyzed using FT-IR spectrum. Raman spectrum reveals the formation of tungsten ribbons as well as the quality of the samples. The morphological changes at different synthesis conditions were observed with SEM micrographs.     

Effects of polyacrylic acid on the room-temperature phosphorescence of selected compounds

Polyacrylic acid solutions of 4-phenylphenol, p-aminobenzoic acid, 1,2-benzocarbazole, and 5,6-benzoquinoline were spotted on filter paper and the results obtained by room-temperature phosphorescence were compared with similar samples spotted on filter paper without polyacrylic acid. Improvements in sensitivity ranged from 26 times to 1.1 times and limits of detection from 100 times to 1.1 times for the samples on filter paper with polyacrylic acid. The relative standard deviations for the samples with polyacrylic acid added were also improved.     

Solid-surface derivative room-temperature luminescence spectrometry of mixtures

Derivative solid-surface room-temperature fluorescence and phosphorescence were combined for the identification of components in binary and ternary mixtures of nanogram amounts of nitrogen heterocycles. Direct, and first and second derivative room-temperature phosphorescence excitation, room-temperature fluorescence and room-temperature phosphorescence spectra were used in the identification of the components in the mixtures by matching spectral wavelengths from mixtures with spectral wavelengths from standards. The criteria for matching wavelengths, subtracting background signals and obtaining derivative spectra at the 0.5-ng level are discussed.     

Photon condensation: A new paradigm for Bose–Einstein condensation

Bose–Einstein condensation is a state of matter known to be responsible for peculiar properties exhibited by superfluid Helium-4 and superconductors. Bose–Einstein condensate (BEC) in its pure form is realizable with alkali atoms under ultra-cold temperatures. In this paper, we review the experimental scheme that demonstrates the atomic Bose–Einstein condensate. We also elaborate on the theoretical framework for atomic Bose–Einstein condensation, which includes statistical mechanics and the Gross–Pitaevskii equation. As an extension, we discuss Bose–Einstein condensation of photons realized in a fluorescent dye filled optical microcavity. We analyze this phenomenon based on the generalized Planck’s law in statistical mechanics. Further, a comparison is made between photon condensate and laser. We describe how photon condensate may be a possible alternative for lasers since it does not require an energy consuming population inversion process.     

A new numerical technique for the analysis of parametrically excited nonlinear systems

A new computational scheme using Chebyshev polynomials is proposed for the numerical solution of parametrically excited nonlinear systems. The state vector and the periodic coefficients are expanded in Chebyshev polynomials and an integral equation suitable for a Picard-type iteration is formulated. A Chebyshev collocation is applied to the integral with the nonlinearities reducing the problem to the solution of a set of linear algebraic equations in each iteration. The method is equally applicable for nonlinear systems which are represented in state-space form or by a set of second-order differential equations. The proposed technique is found to duplicate the periodic, multi-periodic and chaotic solutions of a parametrically excited system obtained previously using the conventional numerical integration schemes with comparable CPU times. The technique does not require the inversion of the mass matrix in the case of multi degree-of-freedom systems. The present method is also shown to offer significant computational conveniences over the conventional numerical integration routines when used in a scheme for the direct determination of periodic solutions. Of course, the technique is also applicable to non-parametrically excited nonlinear systems as well.     

A new computational technique for the stability analysis of slender rods

Summary A new computational technique for the stability analysis of slender rods with variable cross-sections under general loading conditions is presented. In this approach, the dependent variable and the variable coefficients appearing in the governing equations are expanded in a finite series of Chebyshev polynomials. The main feature of this technique is that the original boundary value problem associated with the differential equation is reduced to an algebraic eigenvalue problem. The proposed technique is applied to study the static buckling of Euler column and the flutter behavior of a cantilever column subjected to uniformly distributed tangential loading. The numerical results from the suggested technique are found to be extremely accurate when compared to other techniques available in literature. It is shown that this approach can also be employed in a symbolic form. The merits of the present method in comparison to the standard solution procedures like finite difference and Galerkin methods are discussed.

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Ein neues Berechnungsverfahren für die Stabilitätsanalyse schlanker Stäbe

Übersicht Es wird ein neues Berechnungsverfahren für die Stabilitätsanalyse schlanker Stäbe mit veränderlichem Querschnitt unter allgemeinen Belastungen vorgestellt. Dabei werden die abhängigen Variablen und die variablen Koeffizienten der Bestimmungsgleichung in eine endliche Reihe von Tschebyscheff-Polynomen entwickelt. Die wesentliche Eigenschaft dieses Verfahrens ist die Reduzierung des ursprünglichen Randwertproblems einer Differentialgleichung auf ein algebraisches Eigenwertproblem. Angewandt wird die vorgeschlagene Methode auf die Euler-Knickung und das Flatterverhalten eines Kragträgers unter tangentialer Folgelast als konstanter Streckenlast. Die numerischen Ergebnisse nach diesem Verfahren erweisen sich als sehr genau im Vergleich zu Ergebnissen anderer Methoden, die in der Literatur zu finden sind. Es wird gezeigt, daß bei dieser Methode auch symbolische Lösungsverfahren angewandt werden können. Der Vorzug dieser neuen Methode gegenüber den Standard-Lösungsverfahren wie Finite-Differenzen- und Galerkin-Verfahren wird diskutiert.

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Dedicated to the memory of late Professor H. H. E. Leipholz     

Regio and stereoselectivity in ionic cycloadditions

Acridizinium cation (ACR) and 2,3-dimethylisoquinolinium ion (DMIQ) undergo [2 + 4⁺] addition with dienophiles methyl vinyl ether (MVE) and propylene (PY) and the addition takes place across the diene unit containing the cationic centre and the dienophile acts as the electron donor. These reactions have two regiochemical paths and in each of them two possible stereo adducts could be formed. DFT calculations performed at B3LYP/6-31G(d) level have shown that the reactions pass through concerted mechanism and the TSs are highly asynchronous. Methoxy group in the dienophile can take up cis or trans orientation with respect to the double bond and in that trans orientation of the methoxy group is preferred. Calculations further show that syn 2 adduct is kinetically and thermodynamically more favoured in both the reactions in excellent agreement with the experimental observations. ACR is found to be more reactive than DMIQ as a diene and as a dienophile MVE is found to be more reactive than PY. Computed bond orders establish that the syn 2 transition states are the most ‘reactant’ like. Though the reactions have both electrostatic control and frontier orbital control the former dominates in the initial stages of the reaction. Presented in the Theoretical Chemistry Symposium 2006 held during 11–13 December 2006 in Tiruchirappalli, India     

Generation of Bragg solitons through modulation instability in a Bragg grating structure

In this article, we consider the continuous wave (cw) propagation through the nonlinear periodic structure that consists of alternating layers of both positive and negative Kerr coefficients along the propagation direction. We investigate the modulational instability (MI) conditions required for the generation of ultrashort pulses for the nonlinearity management system. We study the occurrence of MI at the top and bottom edges of the photonic band gap (PBG) where the forward and backward propagating waves are strongly coupled because of the presence of the grating structure. We also study the MI when cw is detuned from the edges of the PBG into the anomalous and normal dispersion regimes. In addition, we discuss the existence of gap solitons for the nonlinearity management system in the upper and lower branches of the dispersion curve through the MI gain spectra. We observe the generation of higher order solitons in the nonlinear periodic structure when the input power is increased beyond a certain critical level. Finally, we discuss the generation of higher order Bragg grating solitons through the intensity evolution of the forward and backward propagating fields.