Polymerization of chlorophenyl glycidyl ethers. VI

Summary Polymerization of p-chlorophenyl glycidyl ether initiated by potassium glycolates (ethylene, propylene and 2-methyl propylene glycolatea) in DMSO containing some 18-crown-6 ether or glycol was investigated. For the reaction system containing the propylene glycolate asymmetrically substituted with a methyl group, relatively high polymerization rates were obtained as compared with those found for the other systems studied, the resultant polymers also having higher molecular weights and comparatively low polydispersities. Aliphatic double bonds were found to be absent in the polymers synthesized, which would suggest that in the anionic polymerization process studied the growing chain is not transferred to the monomer.Dedicated to Prof. C.I. Simionescu on the occasion of the 60th anniversary of his birthday     

Kinetik und Mechanismus der Oxydation und Reduktion von Wüstit in Wasserdampf-Wasserstoff-Gemischen

Deuterium-Austausch zwischen Wasserdampf und Wasserstoff an der Wüstitoberfläche. Widerstandsmessungen zur Untersuchung der Sauerstoffübertragung. Nachweis der Teilschritte H₂O = OH(ad) + H(ad) und OH(ad) = O(ad) + H(ad) bei der Sauerstoffübertragung. Geschwindigkeitsgleichungen der Teilschritte. Abhängigkeit von Druck, Sauerstoffaktivität und Temperatur. Kontrolle der Reaktionsgeschwindigkeit durch die Teilreaktionen.     

Probleme der Querkraftbiegung des geraden Stabs

Zusammenfassung Aus den Verformungsbedingungen für einen dünnwandigen Stabquerschnitt lassen sich beim zweidimensionalen Spannungszustand die Verw?lbung des Querschnitts durch die Querkraft und daraus dann die von der Querkraft hervorgerufenen Normalspannungen ermitteln. Man kann auch die Verschiebung der Stabachse durch die Querkraft auf diese Weise berechnen und die jetzt übliche, von A. Ritter stammende N?herungsformel durch einen genauen Ausdruck ersetzen. Das Verfahren wird an zwei Beispielen, dem Rechteckquerschnitt und dem Kreisringquerschnitt, n?her erl?utert.     

Visual-aesthetic components in the cybernetics of urban planning

The research work summarized here has been conducted at the Cathedra for Urban Planning at the Faculty for Architecture, Engineering and Geodesy of the University of Ljubljana, Slovenia, from 1972 to 1974. The theoretical and methodological foundations were tested succesfully in the area of Kozarje near Ljubljana, and the research was extended to cover the whole metropolitan region of Ljubljana as part of the Year 2000 Master Plan, worked out for the City Council of Ljubljana.One of the basic goals of this research was to find a scientific method of managing the visual environment, which would enable society to control, simulate and decide on changes in its aesthetic qualities. Therefore, we must encompass the visual message in some operational system, where it is quantifiable.At this stage it must be pointed out that our goal was not to develop mathematical aesthetics — beauty from a black box — but to rationalize visual-aesthetic relations in space; to determine objective conditions and solution spaces, within which architectural creation could be realized. A classical heuristic and intuitive approach in design problem-solving can be qualitatively higher than through the methodology shown here. However, rapid urbanization, personal mobility and behavioural changes and the involvement of numerous designers, all make control of the overall design of cities and regions increasingly difficult. The overall impact and interactive nature of visual phenomena seem to be impossible to govern without an objective, quantifiable model. We have tried to establish some objective limits to possible changes, so that the basic visual-aesthetic qualities should not be lost or even altered.     

Fatty acid composition of plasma lipids in hyperlipidemia associated with ischemic heart disease

The authors compared plasma lipid and lipoprotein values and the fatty acid composition in plasma lipids of a group of 38 men with primary hyperlipoproteinaemia (HLP) type II B and IV with a history of myocardial infarction (IM) and in a control group of 63 men with the same type of HLP without a history of ischaemic heart disease (IHD). Hyperlipidaemic subjects after IM differed from controls by the apolipoprotein (apo) B concentration in LDL lipoproteins and by the composition of fatty acids in plasma phosphatidylcholine (PC) and triglycerides (TG). In the discriminating function which makes it possible in the given group of patients to classify correctly hyperlipidaemic subjects after IM and without detectable IHD the independent variables are apo-B concentration in LDL, apo-A-I in plasma, eicosapentaenoic acid in TG, gamma-linolenic acid in cholesterol esters and stearic and oleic acid in PC. These findings confirm the practical value of assessment of apolipoproteins for detection of hyperlipidaemic subjects with a specially high risk of IHD and indicate also the role of essential FA in the pathogenesis of IM.     

A thermodynamic model for composition and chemical driving force for nucleation of complex carbonitrides in microalloyed steel

The extent and degree of dispersion of carbonitrides in high strength low alloy (HSLA) steels is controlled by nucleation and growth processes. A thermodynamic model is presented enabling calculation of the composition of the carbonitride embryo as well as the chemical driving force for nucleation (CDF) in the austenite region of a multicomponent microalloyed steel. The analysis made for a Nb-Ti HSLA steel indicates that the critical carbonitride nucleus is richer in N and Ti than the bulk precipitate at equilibrium at a given temperature and the difference increases when the holding temperature decreases. The results also show that the Ti addition has an optimum value defined by the maximum in the ratio of bound Ti and Nb to their total content. The maximum CDF correlated with the minimum Ti content sufficient to form a carbonitride at the austenitizing temperature.     

Crystallography and Structure–Property Relationships in 2,2′,2″,2′′′,4,4′,4″,4′′′,6,6′,6″,6′′′‐Dodecanitro‐1,1′ : 3′1″ : 3″,1′′′‐ Quaterphenyl (DODECA)

X‐ray crystallographic study of 2,2′,2″,2′′′,4,4′,4″,4′′′,6,6′,6″,6′′′‐dodecanitro‐1,1′ : 3′1″ : 3″,1′′′‐quaterphenyl (DODECA) has been carried out. Nonbonding interatomic distances of oxygen atoms inside of all the nitro groups are shorter than those corresponding to the intermolecular contact radii for oxygen. By means of the DFT B3LYP/6‐31(d, p) method a difference of 136 kJ mol⁻¹ between the X‐ray and DFT structures of DODECA was found. The bearer of the highest initiation reactivity in its molecule in solid phase should be the nitro group at 4′′′‐position, in contrast to those at 2′‐ or 2″‐positions in its isolated molecule. The most reactive nitro group in the DODECA molecule can be well specified by the relationship between net charges on nitro groups and charges on their nitrogen atoms, both of them for the X‐ray structure. The ¹⁵N chemical shift, corresponding to this nitro group for the initiation by impact and shock, correlates very well with these shifts of the reaction centers of the other six “genuine” polynitro arenes.     

New aspects of initiation reactivities of energetic materials demonstrated on nitramines

A brief survey is presented of the author's results obtained from studies of the chemical micro-mechanisms of nitramines initiation from the point of view of organic chemistry. The relationships have been presented and discussed between the characteristics of impact and electric spark sensitivities, detonation and thermal decomposition, on the one hand, and (15)N NMR chemical shifts of nitrogen atoms of nitramino groups, on the other. In the case of the impact sensitivity, the said relationships involve the (15)N shifts of the amino nitrogen atoms carrying the nitro group primarily split off from the molecule. In the case of the initiation by shock, heat and electric spark, the (15)N shifts of nitrogen atoms in the primarily split off nitro groups themselves are involved. Also, the relationships are presented between the characteristics of thermal reactivity and values of the electronic charges at the nitro groups that are primarily split off. It has been stated that the chemical micro-mechanisms of primary fission processes of molecules of nitramines in the initiation by mechanical stimuli (inclusive the detonation course) and electric spark should be the same as in the case of their low-temperature thermal decomposition. It has been found that the electron structure and close neighbourhood of nitrogen atom of the primarily leaving nitro group is a dominant factor in initiation by shock, electric spark and heat. In the case of initiation by impact a key role plays characteristics of amino nitrogen atoms which are carriers of these most reactive nitro groups. Also mentioned is relevance of the modified Evans-Polanyi-Semenov relationship. On the basis of the findings presented it also has been stated that the detonation transformation itself of the nitramines should be preceded by an induction period.     

Effect of β-cyclodextrin on antioxidant activity of coumaric acids

Inclusion complexes of o-, m- and p-coumaric acid (CA) with β-cyclodextrin (βCD) were prepared in stoichiometric ratios (1:1) and stability constants and antioxidant activity of the complexes were studied. The apparent stability constants in aqueous solution of 0.39 × 10³ M⁻¹, 2.81 × 10³ M⁻¹ and 49 × 10³ M⁻¹ for o-, m- and p-CA complexes, respectively, were determined by phase solubility tests. Different analytical techniques (IR, MS) in combination with different solvent washing procedures, were used for confirmation of the nature of the inclusion complexes. Dioxan was a suitable solvent for removal of only free CA and CA adsorbed on the surface of the βCD, while methanol removed absorbed, included and free CA from the complexes. In the case of o- and m-CA–βCD complexes, antioxidant activity was significantly increased while, in p-CA–βCD, it remained unchanged. The impact of complex structure on antioxidant activity of CA isomers was clarified.     

Study of digital systems for the automatic phase lock of a sequential resonance inverter

The digital phase system for the automatic phase lock of a resonance inverter that feeds into an inductor system is studied. The transient processes that develop if the circuit frequency changes are considered. A method for calculating the dead zone of the relay element of a phase detector, which enables free oscillations of the stabilized difference of the current and voltage phases to be removed, is considered. Dependences of the dead zone on the Q factor of the oscillatory circuit and the step of frequency tuning are derived