equatorial/axial conversion in piperidine and phosphorinane with different substituents wereinvestigated with great details. three possible routes, i.e. heteroatom inversion and two ring inversiontype were considered. ring conversion can occur via two pathways one starts with ring flatteningfrom the heteroatom site (nitrogen in piperidine and phosphorous in phosphorinane) and the otherinitiates...

the effect of alkyl substituents on the c-phenyl and/or the n-phenyl ring of benzophenylhydroxamic acid on their molecular structure and hydrogen bonding has been investigated. the predominant configuration in chcl3 is determined by steric and electronic effects. substituents on the c-phenyl ring favor the cis configuration, while substituents in the n-phenyl ring favor a trans configuration. t...

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 elemen...

Let $R$ be a ring (not necessarily commutative) with nonzero identity. We define $Gamma(R)$ to be the graph with vertex set $R$ in which two distinct vertices $x$ and $y$ are adjacent if and only if there exist unit elements $u,v$ of $R$ such that $x+uyv$ is a unit of $R$. In this paper, basic properties of $Gamma(R)$ are studied. We investigate connectivity and the girth of $Gamma(R)$, where $...

an efficient and simple method for the preparation of si-imidazole-hso4 functionalized magnetic fe3o4 nanoparticles (si-im-hso4 mnps) and used as an efficient and reusable magnetic catalysts for the regioselective ring opening of epoxides under green conditions in water. this catalyst was used for the ring opening of epoxide corresponding to the thiocyanohydrins and azidohydrines. compared to t...

In this paper, a channel drop ring resonator filter based on two dimensional photonic crystal is proposed which is suitable for all optical communication systems. The multilayer of silicon rods in the center of resonant ring enables one to adjust resonant wavelength of the ring and enhance power coupling efficiency between ring and waveguide. Refractive index and radius of multilayer rods insid...

purpose : to assess the results of intracorneal ring (icr) segments for treatment of patients with pellucid marginal degeneration (pmd) methods : in this prospective interventional case series study, eight eyes of 5 patients with pmd who were contact lens intolerant received one or two intacs (intacs, addition technology) segments. preoperative and postoperative evaluations included slit-lamp e...

a positive solution of the problem of the existence of nontrivial pairs of zero-divisors in group rings of free burnside groups of sufficiently large odd periods $n>10^{10}$ obtained previously by s. v. ivanov and r. mikhailov extended to all odd periods $ngeq 665$‎.

We introduce the class of “right almost V-rings” which is properly between the classes of right V-rings and right good rings. A ring R is called a right almost V-ring if every simple R-module is almost injective. It is proved that R is a right almost V-ring if and only if for every R-module M, any complement of every simple submodule of M is a direct summand. Moreover, R is a right almost V-rin...