in this paper, we investigate various kinds of extensions of twin-good rings. moreover, we prove that every element of an abelian neat ring r is twin-good if and only if r has no factor ring isomorphic to z2  or z3. the main result of [24] states some conditions that any right self-injective ring r is twin-good. we extend this result to any regular baer ring r by proving that every element of a...

Four known flavonoids: quercetin 3-O-β-D-rutinoside (Q3Rut), myricetin 3-O-β-D-galactopyranoside (M3Gal), quercetin 3-O-β-D-galactopyranoside (Q3Gal) and quercetin 3-O-β-D-glucopyranoside (Q3Glc), for the first time were isolated from aerial parts of Euphorbia microsciadia. The chemical structure of them was elucidated on the basis of 1 and 2 D-NMR spectra and different spectroscopic techniques...

The conformational analysis of the organic compounds specially the biologically active natural products has attracted the consideration of different research groups. Therefore, in the present study the MP2/6-311+g(d,p)//B3LYP/6-311+g(d,p) level of theory was used to study the conformations of dapdiamide D. The identity of interactions in selected conformers was studied using atom in molecule ap...

The title compound, C24H33NO4·H2O, the reaction product of de-acetyl-cinobufagin with ammonium acetate, consists of three cyclo-hexane rings (A, B and C), one five-membered ring (D), one six-membered lactone ring (E) and an epoxide ring (F). The stereochemistry of the ring junctures are A/B cis, B/C trans, C/D cis and D/F cis. Cyclo-hexane rings A, B and C have normal chair conformations. The f...

The title compound, C(24)H(37)BrO(3), is a tetra-cyclic diterpenoid with a beyerane skeleton, synthesized by esterification of isosteviol. It comprises a fused four-ring system A/B/C/D. Rings A and B have a chair conformation, whereas ring C is an unsymmetrical distorted chair; the remaining five-membered ring D adopts an envelope conformation. The stereochemistry of the A/B and B/C ring juncti...

Ring-Y chromosomes are recovered infrequently from crosses of ring-Y-bearing males to females of certain strains (OSTER 1964). Experiments described here have unveiled a diverse class of genes that exert a maternal effect on the behavior during cleavage of these "filicidal" ring chromosomes. Cytological observations of inviable embryos have revealed that the ring-Y chromosome causes gross disor...

Let $R$ be a commutative Noetherian ring, $fa$ anideal of $R$ and $mathcal{D}(R)$ denote the derived category of$R$-modules. For any homologically bounded complex $X$, we conjecture that$sup {bf L}Lambda^{fa}(X)leq$ mag$_RX$. We prove thisin several cases. This generalize the main result of Hatamkhani and Divaani-Aazar cite{HD} for complexes.

A t-(v, k, λ) covering is an incidence structure with v points, each block incident on exactly k points, such that every set of t distinct points is incident on at least λ blocks. By considering certain geometries over finite principal ideal rings, we construct infinite families of t-(v, k, λ) coverings having many interesting combinatorial properties. c © 1999 John Wiley & Sons, Inc. J Combin ...

The universal enveloping algebra U (G) of a Lie algebra G acts on its representation ring R through D(R), the ring of differential operators on R. A quantised universal enveloping algebra (or quantum group) is a deformation of a universal enveloping algebra and acts not through the differential operators of its representation ring but through the quantised differential operators of its represen...