A new class of separators and planarity of chordal graphs

We introduce a new class of clique separators, called base sets, for chordal graphs. Base sets of a chordal graph closely reflect its structure. We show that the notion of base sets leads to structural characterizations of planar k-trees and planar chordal graphs. Using these characterizations, we develop linear time algorithms for recognizing planar k-trees and planar chordal graphs. These algorithms are extensions of the Lexicographic_Breadth_First_Search algorithm for recognizing chordal graphs and are much simpler than the general planarity checking algorithm. Further, we use the notion of base sets to prove the equivalence of hamiltonian 2-trees and maximal outerplanar graphs.

New family of thallium cuprate superconductors not containing calcium or barium: TlSrn+1−xLnxCunO2n+3+δ (Ln=La, Pr, or Nd)

The first two members of the new TlSrn+1−xLnxCunO2n+3+δ (Ln=La, Pr, or Nd) series of superconducting cuprates possessing 1021 and 1122 type structures are described. The n=1 (1021) members with Tcs around 40 K have electrons or holes as the majority charge carriers depending on x. The n=2 (1122) cuprate (Ln=Pr or Nd) shows a Tc in the 80–90 K range.

New type of high field electrooptic response in nematics

We have made concurrent measurements of ionic current and optical transmission between crossed polarisers on several nematics with positive dielectric anisotropy under the action of applied low frequency (< 1KHz) square wave voltages. When the field E is low, the measured current is linear in E and there is no electrooptic response. Beyond some value of the field (E(0)similar to 100 esu), the current becomes independent of the field (phenomenon of limiting current). Further an electrooptic signal is measured at twice the frequency of the applied voltage, which exhibits a peak as a function of the field. The width of the peak is 3 to 4 times the value of E-0, and the signal level at the peak decreases as the frequency is increased. These measurements have been made on three highly polar compounds with cyano end groups. Careful observations do not show any evidence of electrohydrodynamic instabilities in the sample. It is argued that the observations can be understood if at the onset of the phenomenon of the limiting current, a strong electric field gradient is established near one of the electrodes due to the sweeping of an ionic species with high mobility. The field gradient produces a flexoelectric deformation of the director field, which in turn gives rise to the electrooptic effect. At higher fields, the stabilising dielectric torque takes over to suppress this instability.

Al/SiC carriers for microwave integrated circuits by a new technique of pressureless infiltration

Materials with high thermal conductivity and thermal expansion coefficient matching with that of Si or GaAs are being used for packaging high density microcircuits due to their ability of faster heat dissipation. Al/SiC is gaining wide acceptance as electronic packaging material due to the fact that its thermal expansion coefficient can be tailored to match with that of Si or GaAs by varying the Al:SiC ratio while maintaining the thermal conductivity more or less the same. In the present work, Al/SiC microwave integrated circuit (MIC) carriers have been fabricated by pressureless infiltration of Al-alloy into porous SiC preforms in air. This new technique provides a cheaper alternative to pressure infiltration or pressureless infiltration in nitrogen in producing Al/SiC composites for electronic packaging applications. Al-alloy/65vol% SiC composite exhibited a coefficient of thermal expansion of 7 x 10(-6) K-1 (25 degrees C-100 degrees C) and a thermal conductivity of 147 Wm(-1) K-1 at 30 degrees C. The hysteresis observed in thermal expansion coefficient of the composite in the temperature range 100 degrees C-400 degrees C has been attributed to the presence of thermal residual stresses in the composite. Thermal diffusivity of the composite measured over the temperature range from 30 degrees C to 400 degrees C showed a 55% decrease in thermal diffusivity with temperature. Such a large decrease in thermal diffusivity with temperature could be due to the presence of micropores, microcracks, and decohesion of the Al/SiC interfaces in the microstructure (all formed during cooling from the processing temperature). The carrier showed satisfactory performance after integrating it into a MIC.

Synthetic investigations on illudinine: a new synthesis of methyl 8-methoxy-2,2-dimethyl-7-oxo-1,2,3,5,6,7-hexahydro-s-indacene-4-carboxylate

A new strategy for the total synthesis of methyl 8-methoxy-2,2-dimethyl-7-oxo-1,2,3,5,6,7-hexahydro-s-indacene-4-carboxylate 4, a key intermediate in the synthesis of illudalanes, is reported. The key step in this strategy is a new method of preparation of indanones from tetralones. Thus, the furfurylidene derivative of 6-methoxy-3,4-dihydronaphthalen-1-(2H)-one is oxidised to the dicarboxylic acid 9a which is cyclodehydrated to methyl 7-methoxy-1-oxoindan-4-carboxylate 10. Similar reactions on the tetrahydronaphthalenone 25, obtained from 6-methoxy-1,2,3,4-tetrahydronaphthalene-7-carbaldehyde 11 by sequential transformations including a regiospecific benzylic oxidation resulted in the hexahydro-s-indacenone 4, thus completing a formal synthesis of illudinine 1.

Synthesis and Identification of a new class of antileukemic agents containing 2-(arylcarboxamide)-(S)-6-amino-4,5,6,7-tetrahydrobenzod]thiazole

Recently we have reported the effect of (S)-6-aryl urea/thiourea substituted-2-amino-4,5,6,7-tetrahydrobenzod]thiazole derivatives as potent anti-leukemic agents. To elucidate further the Structure Activity Relationship (SAR) studies on the anti-leukemic activity of (S)-2,6-diamino-4,5,6,7 tetrahydrobenzod]thiazole moiety, a series of 2-arlycarboxamide substituted-(S)-6-amino-4,5,6,7-tetrahydrobenzod]thiazole were designed, synthesized and evaluated for their anti-leukemic activity by trypan blue exclusion, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH) assays and cell cycle analysis. Results suggest that the position, number and bulkiness of the substituent on the phenyl ring of aryl carboxamide moiety at 2nd position of 6-amino-4,5,6,7-tetrhydrobenzod]thiazole play a key role in inhibiting the proliferation of leukemia cells. Compounds with ortho substitution showed poor activity and with meta and para substitution showed good activity. (C) 2010 Elsevier Masson SAS. All rights reserved.

A2MoTiO7−x (Atriple bond; length as m-dashrare earth or Y): a new series of oxide pyrochlores prepared by topochemical reduction of A2MoTiO8 scheelites

A series of anion-deficient pyrochlore oxides of the formula A2MoTiO7−x (xless-than-or-equals, slant0.5), where Atriple bond; length as m-dashSm, Gd, Tb, Dy, Ho, Er, Lu and Y, has been prepared by reduction of A2MoTiO8 scheelites. The scheelite-to-pyrochlore conversion is reversible, indicating that the reaction is likely to be topochemical. The oxidation states of molybdenum and titanium are most probably Mo(III) and Ti(IV) for the limiting composition of the pyrochlores A2MoTiO6.5. The new pyrochlores are non-metallic and paramagnetic as expected.

Structure and superconducting properties of a new family of thallium cuprates, TlSr3−xLnxCu2O7

Cuprates of the formula TlSr3−xLnxCu2O7 (Ln=Pr, NdorY) derived from the hypothetical TlSr3Cu2O7 show superconductivity with Tcs up to 95 K when 0.5less, approximatex≤0.75, the x=1.0 compositions being insulators. Rietveld analysis of X-ray diffraction profiles has been carried out for two superconducting members of this family. The unit cell a-parameter, and hence the in-plane Cu-O distance, increases with increase in x. The Tc value decreases with increase in x or the in-plane Cu-O distance in all the series of cuprates. Superconductivity in the Tl1−yPbySr3−xNdxCu2O7 systems is found with the highest Tc of 95 K when y=0.2 and x=0.5. The in-plane Cu-O distances in all the cuprates studied fall in the range found in the Sr-class of cuprate superconductors.

A new theory of gravitation with parity-violating propagating torsion

A new theory of gravitation has been proposed in a more general space-time than Riemannian. It is a generalization of the ECSK and Brans-Dicke (BD) theory of gravitation. It is found that, in contrast to the standard the ECSK theory, a parity-violating propagating torsion is generated by the BD scalar field. The interesting consequence of the theory is that it can successfully predict solar system experimental results to desired accuracy.

Boson Inverse Operators and a New Family of Two-photon Annihilation Operators

We introduce the inverse of the Hermitian operator (acircacirc†) and express the Boson inverse operators acirc-1 and acirc†-1 in terms of the operators acirc, acirc† and (acircacirc†)-1. We show that these Boson inverse operators may be realized by Susskind-Glogower phase operators. In this way, we find a new two-photon annihilation operator and denote it as acirc2(acircacirc†)-1. We show that the eigenstates of this operator have interesting non-classical properties. We find that the eigenstates of the operators (acircacirc†)-1 acirc2, acirc(acircacirc†)-1 acirc and acirc2(acircacirc†)-1 have many similar properties and thus they constitute a family of two-photon annihilation operators.

A New Class of Exactly Solvable Interacting Fermion Models in One Dimension

We investigate a model containing two species of one-dimensional fermions interacting via a gauge field determined by the positions of all particles of the opposite species. The model can be salved exactly via a simple unitary transformation. Nevertheless, correlation functions exhibit nontrivial interaction-dependent exponents. A similar model defined on a lattice is introduced and solved. Various generalizations, e.g., to the case of internal symmetries of the fermions, are discussed. The present treatment also clarifies certain aspects of Luttinger's original solution of the "Luttinger model."