Excimer Laser Processing of Grey Cast Iron: Microstructural and Tribological Characterization

Pearlitic grey iron was treated by means of a XeCl laser to remelt only a shallow layer. This process allows to modify the heteregeneous surfaces of cast irons in order to improve their tribological behaviour. The energy density ranged from 0.3 to 3 J/cm² and the number of shots from 4 to 40. It is shown that after laser irradiation austenite is formed in the melted layer; compressive stresses at the surface were exhibited as well as the deposition of graphite and the formation of carbides. It is shown that excimer laser processing highly decreases the coefficient of friction and the wear rate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Estimates for the Rapid Decay of Concentration Functions of n-Fold Convolutions

We estimate the concentration functions of n-fold convolutions of one-dimensional probability measures. The Kolmogorov–Rogozin inequality implies that for nondegenerate distributions these functions decrease at least as O(n ^–1/2). On the other hand, Esseen⁽³⁾ has shown that this rate is o(n ^–1/2) iff the distribution has an infinite second moment. This statement was sharpened by Morozova.⁽⁹⁾ Theorem 1 of this paper provides an improvement of Morozova's result. Moreover, we present more general estimates which imply the rates o(n ^–1/2).     

On the nature of the γ-α transition in cerium

In 1964 Davis and Adams established that the large increase of the thermal expansion and compressibility in the critical region of the γ-to α-Ce phase transition occurs predominantly in the α phase. This provides strong evidence that a tricritical point is realized in Ce. This also means that the aforementioned transition is not isomorphic and that α-Ce should have a distorted fcc structure. A careful examination of Jayaraman’s data (1965) shows that a second-order transition line continues beyond the tricritical point to the vicinity of a triple point on the melting curve. The phase boundary with the tricritical point and the minimum of the melting curve are reconstructed within the framework of Landau theory. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 111–117 (25 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Buchbesprechungen

Ohne Zusammenfassung

---

Book reviews

     

A differential calculus on the quantum groupSU q (2) comparible with the gauge-transformation structure

We consider a three-dimensional bicovariant differential calculus on the quantum group SU_q(2) that is compatible with the structure of gauge transformations. In the approach based on the global covariance with respect to the stability subgroup U(1), we show that the gauge-covariant exterior differential algebra on SU_q(2) is uniquely determined. We construct explicit representations of q-deformed Lie algebras in terms of differential operators. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 116, No. 2, pp. 265–276, August. 1998.     

Kinetics of the reactions of the IO radical with dimethyl sulfide,methanethiol, ethylene,and propylene

The reactions of IO radicals with CH₃SCH₃, CH₃SH, C₂H₄, and C₃H₆ have been studied using the discharge flow method with direct detection of IO radicals by mass spectrometry. The absolute rate constants obtained at 298 K are the following: IO + CH₃SCH₃ → products (1): k₁ = (1.5 ± 0.2) × 10^?14; IO + CH₃SH → products (2): k₂ = (6.6 ± 1.3) × 10^?16; IO + C₂H₄ →products (3): k₃ < 2 × 10^?16; IO + C₃H₆ → products (4): k₄ < 2 × 10^?16 (units are cm³ molecule^?1 s^?1). CH₃S(O)CH₃ and HOI were found as products of reactions (1) and (2), respectively. The present lower value of k₁ compared to our previous determination is discussed.     

Wave attenuation in an elastic medium

This article examines the propagation of viscoelastic (elastic) waves in a medium consisting of two layers of finite thickness. It is found that there is a mechanical effect manifest in the monotonic dependence of the damping factor on the parameters of the system. These dependences have distinct maxima and minima, thus making it possible to optimize the damping properties of systems by varying their geometric parameters.Translated from Dinamicheskie, Sistemy, No. 4, pp. 57–62, 1985.     

Lipid chain mobility in interdigitated DPPC systems

The segmental lipid chain mobility in the gel phase of dipalmitoylphosphatidylcholine (DPPC) multilayers dispersed in buffer and in the interdigitated gel phase induced by glycerol, ethylene glycol, ethanol and chaotropic salt NaClO₄ was compared by using conventional electron spin resonance (ESR) spectroscopy. The stearic acids bearing the nitroxide moiety at different positions down the acyl chain (n-NSA,n-5, 7, 10, 12 and 16) were used to characterized the chain motion, and the outer hyperfine splittings of the spectra, 2A _max, were taken as indices of the rotational mobility of the chain in the gel phase. The ESR measurements revealed a gradient of increased mobility on proceeding towards the terminal methyl end in the fully hydrated gel phase of DPPC bilayers. This gradient was reduced in the interdigitated gel phase induced by ethanol and chaotropic salt NaClO₄, whereas the rotational mobility throughout the length of the chain was comparable to that near the polar/apolar interface in the interdigitated gel phase in glycerol and ethylene glycol. Moreover, the motional anisotropy was much less affected by temperature in the interdigitated gel state of DPPC in glycerol and ethylene glycol as compared both to normal bilayer gel phase and to the other interdigitated DPPC systems. Finally, there was no evidence for chain interdigitation in the fluid phase of DPPC dispersions in any medium.