Synthesis and conformational study of 1,2,3,4,5,6,7,8-octahydro-1,6-naphthiridines

A new class of endocyclic enamines, 1,6-disubstituted 1,2,3,4,5,6,7,8-octahydro-1,6-naphthiridines, was synthesized from 4-piperidone imines by successive subjecting the latter to lithiation with lithium diethylamide, to alkylation with 1-bromo-3-chloropropane, and to intramolecular cyclization. All stages were carried out as a unique process without isolation of the intermediate compounds. A thorough optimization of the process conditions, workup, and product storage was carried out. The conformational study of 1,6-disubstituted 1,2,3,4,5,6,7,8-octahydro-1,6-naphthiridines was performed.     

The isometric immersion of strongly parabolic metrics in the class of strongly parabolic surfaces

It is known that a k-strongly parabolic surface in Euclidean space (index of relative nullity is at least k) inherits a k-strongly parabolic metric (index of nullity is at least k). For the definitions of the index of relative nullity (x) and the index of nullity (x) see Sh. Kobayashi and K. Nomizu, Foundations of Differential Geometry, Interscience Publishers, New York (1969), Vol. II, pp. 347–348. The converse is not true. In particular, there exists an analytic, three-dimensional, 1-strongly parabolic metric that does not admit a local isometric immersion into Euclidean space of any dimension in the class of three-dimensional 1-strongly parabolic surfaces. The proof is carried out with the help of the method of exterior Cartan forms.Translated from Ukrainskii Geometricheskii Sbornik, No. 33, pp. 27–37, 1990.     

Stability of the single-domain state in single crystals of triglycine sulphate

The stability of the single-domain state in single crystals of triglycine sulfate is investigated using the Barkhausen effect. Barkhausen jumps are detected upon invariable macroscopic polarization. The parameters of the observed Barkhausen jumps are estimated and compared.     

EIT Ground State Cooling Scheme of <Superscript>171</Superscript>Yb<Superscript>+</Superscript> Based on the <Superscript>2</Superscript>S<Subscript>1/2</Subscript>→<Superscript>2</Superscript>P<Subscript>1/2</Subscript> Cooling Transition

We propose a method for EIT ground state cooling of ¹⁷¹Yb+ ion, which involves three light fields with detuning on a MHz scale. The steady-state mean vibrational quantum number is calculated to be less than 0.005. Efficient cooling is achievable in a motional-mode frequency range of 2π · (1.5 ± 0.5 MHz).     

Stripe correlations in Na(0.75)CoO2

We present a combined high-energy x-ray diffraction and local-density approximation study of the sodium ordering in Na(0.75)CoO2. The obtained results rule out previously proposed Na-ordering models and provide strong evidence for the formation of sodium-density stripes in this material. The local-density approximation calculations prove that the sodium-density stripes lead to a sizable dip in the density of the Co states at the Fermi level, pointing to band structure effects as a driving force for the stripe formation. This indicates that the sodium ordering is connected to stripelike charge correlations within the CoO2 layers, leading to an astonishing similarity between the doped cuprates and the NaxCoO2 compounds.     

Scattering of Quasi-Two-Dimentional Electrons of the GaAs/Al x Ga1–x As Superlattice by Polar Optical Phonons in the Dielectric Continuum Model

The longitudinal and transverse mobility of electrons in the ground miniband of the GaAs/AlGaAs superlattice (SL) is calculated for the case of scattering on the long-range potential of polar optical (PO) phonons at T = 300 K. The partial contributions of different oscillation modes of the long-range PO-phonon potential to the mobility and effective relaxation time are analyzed. The dependences of the mobility and pulse effective relaxation time on the SL parameters are investigated. The calculation is made using a linearized Boltzmann equation. The scalar PO-phonon potential is calculated within the dielectric continuum model.     

Cylindrical multidimensional surfaces in Lobachevsky space

We study complete, strongly parabolic metrics with constant relative index of nullity _c=k and complete, strongly parabolic surfaces with constant index of relative nullityv=k in a constant curvature space Rⁿ(c) under the assumption that there exists a surface orthogonal to the fibers of total geodesity, and if c<0, under the additional condition that the orthogonal surface be totally umbilical. For c>0 we have _c=l;v=l, for c=0 the Riemannian manifold is a metric product of the metric of R^l–k and the Euclidean space E^k while the surface is a cylinder in Euclidean space. For c<0 the metric has a special form and the surface is a cylindrical surface in Lobachevsky space.Translated from Ukrainskii Geometricheskii Sbornik, No. 33, pp. 18–27, 1990.