IR absorption spectrum of hydrogen xanthane

The normal vibration frequencies of hydrogen xanthane are calculated on the basis of a mechanical model. The IR absorption spectrum was measured in the range 400–3600 cm^–1 for tablets of this substance with KBr and in vaseline and fluorinated oil. The spectrum is interpreted. The effects of the change in the structure of the cyclopentane molecule on the vibration spectrum and symmetry of the heterosubstituted molecules are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 50–54, November, 1970.     

Nuclear spin-lattice and nuclear spin-spin relaxation time measurements in EuB6 at low temperatures using the spin-echo technique

Experimental results on the nuclear spin-lattice and nuclear spin-spin relaxation times in the ferromagnetic EuB₆ at temperatures below 4·2 K are presented using the external magnetic field,H _ext, in the range of 0 ⩽H _ext ⩽ 10 kG. Nuclear spin-spin relaxation time computed on the basis of the Suhl-Nakamura process turns out to be 3·2μs, which compares well with the experimental value 11·1μs obtained with the 10 kG magnetic field at 1·7 K. It is found that in the ferromagnetic EuB₆,T ₁ is approximately 5 × 10³ times larger thanT ₂ at 1·7 K with the 10 kG magnetic field. Thus the effect ofT ₁ onT ₂ can be neglected. From the experimental value ofT ₂, the value of the homogeneous line broadening is found to be 14 kHz. The corresponding value obtained from the cw method is 175 kHz. This evidently shows the presence of the inhomogeneous line broadening in the cw NMR.     

Switching during pulsed breakdown of an air-filled gap in the nanosecond range

An experimental study has been made of the effect of various factors on the length and nature of the switching process during the pulsed breakdown of air-filled gaps in the nanosecond range. Practical recommendations are given for choosing optimum conditions for sharpening the pulse front.     

Observation of Species of Intermediate Oxidation Degrees, Formed during Anodic Dissolution of Chromium, by the Rotating Ring–Disk Electrode Method

The possibilities and limitations of the RRDE method in recording and identifying intermediate and target products of chromium dissolution in sulfuric acid solutions of pH 0.3–2 are analyzed on the basis of own and literature data. From the experimental data, partial currents of chromium dissolution to Cr(II) ions in the region of active dissolution of chromium and its transition into a passive state are computed. The Cr(III) ions can be discovered through the reaction of their reduction on an Hg(Au) ring electrode only at pH 1.8. The current efficiency of reactions that lead to the formation of Cr(II) and Cr(III) ions near the anodic-dissolution peak is other than 100%. Assumptions as to the causes of this effect are made. In the solutions studied, Cr(VI) ions are recorded with a 100-% current efficiency on a gold ring electrode in a transpassive region of the chromium disk potentials.     

Antifriction properties of new fluorine-containing derivatives of natural graphite

Interaction of natural graphite with potassium salts of perfl uoro(ω-chloroperfl uoro)carboxylic acids in the presence of potassium persulfate was studied. The derivatives obtained were used as independent lubricants for a chromium-containing-steel friction pair.     

The field of a point source near planar and cylindrical boundaries of a metamaterial

The properties of the two-dimensional electromagnetic fields excited by a filamentary source located near planar and cylindrical boundaries of bodies made of metamaterials with their permittivity and permeability close to minus one are considered. The subwavelength field localization effects, the phenomena associated with the resonances of surface waves, and the nonresonant field enhancement effects are investigated.     

Role of electronic correlations in the Fermi surface formation of Na<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CoO<Subscript>2</Subscript>

Band structure of metallic sodium cobaltate Na _x CoO₂ (x = 0.33, 0.48, 0.61, 0.72) has been investigated by local density approximation + Hubbard U (LDA+U) method and within Gutzwiller approximation for the Co-t _2g manifold. Correlation effects being taken into account results in suppression of the e′ _g hole pockets at the Fermi surface in agreement with recent angle-resolved photoemission spectroscopy (ARPES) experiments. In the Gutzwiller approximation the bilayer splitting is significantly reduced due to the correlation effects. The formation of high spin (HS) state in Co d-shell was shown to be very improbable.     

Number of no nisomorphic subgraphs in an n-point graph

LetG(n) be the set of all nonoriented graphs with n enumerated points without loops or multiple lines, and let v_k(G) be the number of mutually nonisomorphic k-point subgraphs of G G(n). It is proved that at least |G(n)| (1–1/n) graphs G G(n) possess the following properties: a) for any k [6log₂n], where c=–c log₂c–(1–c)×log₂(1–c) and c>1/2, we havev _k(G) > C _n ^k (1–1/n²); b) for any k [cn + 5 log₂n] we havev _k(G) = C _n ^k . Hence almost all graphs G G(n) containv(G) 2ⁿ pairwise nonisomorphic subgraphs.Translated from Matematicheskie Zametki, Vol. 9, No. 3, pp. 263–273, March, 1971.