A new diacylated labdane diterpenoid from Andrographis wightiana

A new acylated labdane diterpenoid, 14-deoxy-3,19-diacetyl-11,12-didehydroandrographolide (1), together with three known labdane diterpenoids, wightionolide (2), andrographolide (3) and neoandrographolide (4), and three known flavones, echioidinin (5), skullcapflavone I 2'-methyl ether (6) and echioidin (7), were isolated from the whole plant of Andrographis wightiana. The structure of compound 1 was elucidated by 1D and extensive 2D-NMR spectral studies.     

Positive values of non-homogeneous indefinite quadratic forms of type (1, 4)

Let Г_r,n—r denote the infimum of all number Г > 0 such that for any real indefinite quadratic form inn variables of type (r, n—r), determinantD ≠ 0 and real numbers c₁; c₂,…, c_n, there exist integersx ₁,x₂,…,x_n satisfying 0 < Q(x₁+c₁,x₂ + c₂,…,x_n + c_n) ≤(Г|Z > |)^1/n. All the values of Г_r,n—r are known except for г_1,4. Earlier it was shown that 8 ≤Г_1,4 ≤16. Here we improve the upper bound to get Г_1,4 < 12.     

Polarographic study of mixed ligand complexes of Pb(II) with carboxylate ions and imidazole

Mixed complexes of Pb(II) with some carboxylate ions, viz. tartrate (tart^2?), malonate (mal^2?) and citrate (citr^3?); and imidazole (im) have been studied polarographically at 25°C and at constant ionic strength μ = 2.0 (NaNO₃) and at pH 6. The polarographic reduction of the complexes in each case is reversible and diffusion-controlled. Pb(II) forms a single mixed complex with tartrate and imidazole, viz [Pb(tart)(im)] with stability constant log β₁₁ = 4.19; with mal^2? and im, three mixed complexes, [Pb(mal)(im)], [Pb(mal)(im)₂] and [Pb(mal)₂(im)]^2? with stability constants log β₁₁ = 4.3, log β₁₂ = 7.3 and log β₂₁ = 5.5 respectively are formed. With citr^3? and im a single mixed species, [Pb(citr)(im)]^? with stability constant log β₁₁ = 8.0 is formed. Various equilibria involved in the mixed systems have been discussed.     

Synthesis of some new mesoionic heterocycles

The synthesis of various substituted 1-hydroxy-2-chloroacetyl-6-thia-10b-aza-2a-azoniaaceanthrylene hydroxide inner salt, 1-hydroxy-6-thia-10b-aza-2a-azoniaaceanthrylene hydroxide inner salt, 1-hydroxy-2-piperidinoacetyl-6-thia-10b-aza-2a-azoniaaceanthrylene hydroxide inner salt is described. The ir is also included.     

Polarographic study of Eu(III)-succinate-ethylenediamine and Eu(III)-malonate-ethylenediamine mixed systems

The mixed complexes of Eu(III) with succinate (succ^2?) and malonate (mal^2?) and ethylenediamine (en) have been studied polarographically at 25°C and at constant ionic strength, μ = 0.1 (NaNO₃) and pH 6. The reduction of the complexes in each case is quasi-reversible and diffusion-controlled. In each system three mixed complexes are formed, viz. [Eu(succ)(en)]⁺, [Eu(succ)(en)2]⁺ and [Eu(succ)₂(en)]^? with stability constants log β₁₁ = 9.2, log β₁₂ = 17.5 and log β₂₁ = 11.7; and [Eu(mal)(en)]⁺, [Eu(mal)₂(en)₂]^? and [Eu(mal)₃(en)]^3? with stability constants log β₁₁ = 11.4, log β₂₂ = 19.08 and log β₃₁ = 13.5 respectively.     

Thermal decomposition studies on cobalt(II) complexes of 4-N-(4’-antipyrylmethylidene)aminoantipyrine with varying counter ions

The phenomenological, kinetic and mechanistic aspects of the nitrate, chloride, bromide and iodide complexes of cobalt(II) with 4-N-(4-antipyrylmethylidene)aminoantipyrine (AA) have been studied by TG and DTG techniques. The kinetic parameters such as activation energy, pre-exponential factor and entropy of activation were computed. The rate controlling process at all stages of decomposition is random nucleation with one nucleus on each particle (Mampel model)     

DLTS and in situ C–V analysis of trap parameters in swift 50 MeV Li3+ ion-irradiated Ni/SiO2/Si MOS capacitors

Ni/SiO₂/Si MOS structures were fabricated on n-type Si wafers and were irradiated with 50 MeV Li³⁺ ions with fluences ranging from 1×10¹⁰ to 1×10¹² ions/cm². High frequency C–V characteristics are studied in situ to estimate the build-up of fixed and oxide charges. The nature of the charge build-up with ion fluence is analyzed. Defect levels in bulk Si and its properties such as activation energy, capture cross-section, trap concentration and carrier lifetimes are studied using deep-level transient spectroscopy. Electron traps with energies ranging from 0.069 to 0.523 eV are observed in Li ion-irradiated devices. The dependence of series resistance, substrate doping and accumulation capacitance on Li ion fluence are clearly explained. The study of dielectric properties (tan δ and quality factor) confirms the degradation of the oxide layer to a greater extent due to ion irradiation.     

Generic pole assignability,structurally constrained controllers and unimodular completion

In this paper we assume dynamical systems are represented by linear differential-algebraic equations (DAEs) of order possibly higher than one. We consider a structured system of DAEs for both the to-be-controlled plant and the controller. We model the structure of the plant and the controller as an undirected and bipartite graph and formulate necessary and sufficient conditions on this graph for the structured controller to generically achieve arbitrary pole placement. A special case of this problem also gives new equivalent conditions for structural controllability of a plant. Use of results in matching theory, and in particular, ‘admissibility’ of edges and ‘elementary bipartite graphs’, make the problem and the solution very intuitive. Further, our approach requires standard graph algorithms to check the required conditions for generic arbitrary pole placement, thus helping in easily obtaining running time estimates for checking this. When applied to the state space case, for which the literature has running time estimates, our algorithm is faster for sparse state space systems and comparable for general state space systems.     

An analysis of phase-modulated heteronuclear dipolar decoupling sequences in solid-state nuclear magnetic resonance

The design of variants of the swept-frequency two-pulse phase modulation sequence for heteronuclear dipolar decoupling in solid-state NMR is reported, their performance evaluated, and compared with other established sequences like TPPM and SPINAL. Simulations performed to probe the role of the homonuclear (1)H-(1)H bath show that the robustness of the decoupling schemes improves with the size of the bath. In addition, these simulations reveal that the homonuclear (1)H-(1)H bath also leads to broad baselines at high MAS rates. Results from a study of the SPINAL decoupling scheme indicate that optimisation of the starting phase and phase increment improves its performance and efficiency at high MAS rates. Additionally, experiments performed on a liquid crystal display the role of the initial phase in SPINAL-64 and sequences in the SW(f)-TPPM family.     

Experimental study on novel phase change composites for thermal energy storage

Journal of Thermal Analysis and Calorimetry - In this study, beeswax is studied as a phase change material (PCM) to store heat due to its high latent heat. The disadvantages of using beeswax were...