Mössbauer effect study of Y(Fe0.022 Co0.978)2 at temperatures between 0.15 and 4.2k

A³He-⁴He dilution refrigerator was constructed to perform Mössbauer measurements well below 4.2K. Results are reported here on the pseudobinary Laves-Phase system Y (Fe_1-x Co_x)₂ for x=0.978. We found that at low temperatures, the Fe ions undergo a disordered magnetic phase transition, with a Curie temperature of approximately 4K and a saturation field of 96K0e. The easy axis of magnetization appears to be the [111] direction. This study is an extension to very low temperatures of previous work on the system with 0X0.978.Supported by the NSF Grant No. DMR 73-07665 AO 3     

Effect of ambient noise on the vocal output and the preferred listening level of conversational speech

The effect of ambient noise on vocal output and the preferred listening level of conversational speech was investigated under conditions typical of everyday speech communication. For a speaker-listener distance of 1 m, vocal output and the preferred listening level in quiet were both about 50 dB(A). Deviations from this value were observed when the noise level exceeded a level of about 40 dB(A). The regression lines for the data points above this level showed a 3 dB rise for a 10 dB rise in noise level. The experiments further suggest that both speaker and listener (when the latter is able to control the playback level of recorded speech) try to compensate for the noise interference by raising the level of speech in order to keep the (subjective) loudness of speech in noise equal to the loudness of speech in quiet.     

On the nonexistence of finite time bubble trees in symmetric harmonic map heat flows from the disk to the 2-sphere

Let and be the unit disk and the unit sphere, and let be a radially symmetric harmonic map heat flow, whose singularities coincide with downward energy jumps. Then its finite time singularities are simple in the sense that precisely one harmonic sphere separates at a time.     

Mössbauer spectroscopic study of core and mantle of rattle stones

Mössbauer spectroscopy has been applied to two rattle stones found in the Netherlands, which have been formed under different pedoenvironment conditions in the past. Ultrafine particles of goethite are dominantly present in both core and mantle of these stones. The latter differs in both composition and mean particle size; this is related to the distinct manner of their formation.     

Equilibrium time correlation functions in the low-density limit

We consider a system of hard spheres in thermal equilibrium. Using Lanford's result about the convergence of the solutions of the BBGKY hierarchy to the solutions of the Boltzmann hierarchy, we show that in the low-density limit (Boltzmann-Grad limit): (i) the total time correlation function is governed by the linearized Boltzmann equation (proved to be valid for short times), (ii) the self time correlation function, equivalently the distribution of a tagged particle in an equilibrium fluid, is governed by the Rayleigh-Boltzmann equation (proved to be valid for all times). In the latter case the fluid (not including the tagged particle) is to zeroth order in thermal equilibrium and to first order its distribution is governed by a combination of the Rayleigh-Boltzmann equation and the linearized Boltzmann equation (proved to be valid for short times).Supported in part by NSF Grant PHY 78-22302.     

Temperature effect on photolytic deposition of platinum ohmic contacts and schottky diodes

An argon laser is used to induce Laser Chemical Vapor Deposition (LCVD) of platinum using platinum bihexafluoroacetyl-acetonate as precursor. The process can be photolytic or pyrolytic depending on the laser power used. These processes are studied by recording the laser light transmitted through of deposit and substrate. Photolytic deposition takes place either in the adsorbed phase or in the gaseous phase depending on the temperature induced by radiation absorption. The induced-temperature calculation using a model developed by us confirms the experimental results obtained. The influence of the substrate base temperature and the precursor product vapour pressure confirms photolytic deposition from the adsorbed phase for low powers and from the vapour phase onwards for high powers. The deposits obtained present a typical 96% Pt composition and its use in Schottky diode manufacture permit obtaining devices with good characteristics in spite of experimental limitations.     

On the Spectra of Striped Sign Patterns

Sign patterns consisting of some positive and some negative columns, with at least one of each kind, are shown to allow any self-conjugate spectrum, and thus to allow any inertia. In the case of the n ×n sign pattern with all columns positive, given any self-conjugate multiset consisting of n -1 complex numbers supplemented by a sufficiently large positive number, it is shown how to construct a positive normal matrix whose spectrum is this multiset. Thus, the positive sign pattern allows any inertia with at least one positive eigenvalue.     

QCD radiative corrections to charged current heavy quark production

The QCD radiative corrections to charged current heavy quark production are given in the limit that the weak partner is massless, i.e. using a bottom structure function for top quark production. The results for charm production in neutrino nucleon scattering agree with those published before, but our method enables us to study all outgoing particles. The corrections to top production at the proposed LEP/LHC electroproton collider are discussed.     

On linear congruence relations for Kubota-Leopoldt 2-adic L-functions

Our purpose in the paper is to find the most general linear congruence relation of the Hardy-Williams type for linear combinations of special values of Kubota-Leopoldt 2-adic L-functions L₂(k,χω^1−k) with k running over any finite subset of not necessarily consisting of consecutive integers (see Acta Arith. 47 (1986) 263; Publ. Math. Fac. Sci. Besançon, Théorie des Nombres, 1995/1996; Publ. Math. Debrecen 56 (2000) 677 and cf. Mathematics and Its Applications, Vol. 511, Kluwer Academic Publishers, Dordrecht, Boston, London, 2000). If k runs over finite subsets of consisting of consecutive integers see Compositio Math. 111 (1998) 289; Publ. Math. Debrecen 56 (2000) 677; Hardy and Williams, 1986; Compositio Math. 75 (1990) 271; Acta Arith. 71 (1995) 273; 52 (1989) 147; J. Number Theory 34 (1990) 362. In order to obtain the most general congruences of this type we make use of divisibility properties of the generalized Vandermonde determinants obtained in Spie? et al. (Divisibility properties of generalized Vandermonde and Cauchy determinants, Preprint 627, Institute of Mathematics, Polish Academy of Sciences, Warsaw, 2002). This allows us to simplify our main Theorem 2 and obtain Theorem 3 where the most general form of the linear congruence relation is given.     

Angular dependent photon-stimulated desorption of ions from a V2O5(010) surface

Using a display-type analyzer, we have measured the angular and energy distribution of O⁺ ions desorbed from a V₂O₅(010) surface by incident photons. The desorbed ions were mass-analyzed using time-of-flight gating techniques. The angular distribution of desorbed ions was found to be strongly peaked in the direction of the surface normal. This strongly directional desorption pattern reflects the local bonding geometry of the topmost oxygen atoms in the surface. The observed photoexcitation spectrum of the ion yiel can be explained with the core level Auger decay model formulated by Knotek and Feibelman.