The influence of a medium on the rate of the reaction between N,N′-dioctylurea and <Emphasis Type="Italic">n</Emphasis>-octanol

The kinetics and mechanism of alcoholysis of symmetrical dioctylurea in inert solvents were studied. The reaction was found to follow two parallel pathways, one involving the destruction of initial urea and the other, bimolecular interaction. For the reaction series under consideration, the influence of the nature of solvents on the rate of the reaction was studied.     

Convergence of Metropolis-type algorithms for a large canonical ensemble

In this paper, we study the convergence of Metropolis-type algorithms used in modeling statistical systems with a fluctuating number of particles located in a finite volume. We justify the use of Metropolis algorithms for a particular class of such statistical systems. We prove a theorem on the geometric ergodicity of the Markov process modeling the behavior of an ensemble with a fluctuating number of particles in a finite volume whose interaction is described by a potential bounded below and decreasing according to the law r ^?3?α, α ≥ 0, as r → 0.     

On a new class of function systems of Faber-Schauder type

In this paper, we introduce a new class of function systems generalizing the classical Faber-Schauder system. Under the condition that the generating sequence is bounded, we show that systems of such a class constitute bases in the space of continuous functions and prove some properties of series expansions of functions in these systems.     

Assessment of the Formant Frequencies in Normal and Laryngectomized Individuals Using Linear Predictive Coding

The objective of this study was to assess the difference in voice quality as defined by acoustical analysis using sustained vowel in laryngectomized patients in comparison with normal volunteers. This was designed as a retrospective single center cohort study. An adult tertiary referral unit formed the setting of this study. Fifty patients (40 males) who underwent total laryngectomy and 31 normal volunteers (18 male) participated. Group comparisons with the first three formant frequencies (F1, F2, and F3) using linear predictive coding (LPC) (Laryngograph Ltd, London, UK) was performed. The existence of any significant difference of F1, F2, and F3 between the two groups using the sustained vowel /i/ and the effects of other factors namely, tumor stage (T), chemoradiotherapy, pharyngectomy, cricothyroid myotomy, closure of pharyngoesophageal segment, and postoperative complication were analyzed. Formant frequencies F1, F2, and F3 were significantly different in male laryngectomees compared to controls: F1 (P<0.001, Mann-Whitney U test), F2 (P<0.001, Student's t test), and F3 (P=0.008, Student's t test). There was no significant difference between females in both groups for all three formant frequencies. Chemoradiotherapy and postoperative complications (pharyngocutaneous fistula) caused a significantly lower formant F1 in men, but showed little effect in F2 and F3. Laryngectomized males produced significantly higher formant frequencies, F1, F2, and F3, compared to normal volunteers, and this is consistent with literature. Chemoradiotherapy and postoperative complications significantly influenced the formant scores in the laryngectomee population. This study shows that robust and reliable data could be obtained using electroglottography and LPC in normal volunteers and laryngectomees using a sustained vowel.     

Diffusion of aromatic hydrocarbons in silicalite/HZSM-5

Diffusion of benzene and the xylene isomers in silicalite/HZSM-5 has been studied by a wide range of different experimental techniques. The available data are reviewed in an attempt to draw general conclusions concerning the intracrystalline diffusion process. The results for benzene are remarkably consistent, and the conformity between transport and tracer diffusion and between single crystal membrane and ZLC and frequency response data suggests that diffusion is essentially isotropic with no significant difference between the self and “corrected” transport diffusivity. The situation is more complex for p-xylene which shows clear evidence of non-isotropic behavior and a significant difference between tracer and transport diffusivities.     

Stereochemical aspects of the formation of toxisterols A

Mechanisms for the formation of toxisterol A are suggested. The connection between the conformation of the initial previtamin and the stereochemistry of the reaction products is discussed.Lensoviet Leningrad Technological Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 225–229, March–April, 1989.