Reconfigurations and diffusion of trivacancy in silicon

Disappearance of the divacancy (V₂) and trivacancy (V₃) complexes upon isochronal and isothermal annealing of electron irradiated Si:O crystals has been studied by means of deep level transient spectroscopy. The annealing studies have shown that the V₂ and V₃ defects are mobile in Si at T>200 °C and in oxygen-rich material are trapped by interstitial oxygen atoms so resulting in the appearance of V₂O and V₃O defects. The activation energies for diffusion of the V₂ and V₃ centers have been determined. Density functional modeling calculations have been carried out to investigate the migration and reorientation mechanisms of V₃ in large silicon supercells. It is proposed that these comprise a sequence of transformations between V₃(D₃) and V₃(C_2v) configurations.     

On moment conditions for normed sums of independent variables and martingale differences

Let X₁, X₂,… be a sequence of i.i.d. random variables and S_n their partial sums. Necessary and sufficient conditions are given for $\text{{n}{}^{\mathrm{<mtext>?1</mtext><mtext>q</mtext>}}\text{S}{}_{\mathrm{n}}\text{}}{}^{\mathrm{\propto }}{}_1$ to have uniformly bounded pth moments, 0<p<q?2.Some of the results are generalized to martingle differences.     

ESR studies of thermally oxidized silicon wafers

We have performed ESR measurements on oxidized (111) silicon wafers and found two ESR centers. One, the previously known P_b center,was found to be a two level interface trap by corona bias studies. The other one, previously known as “damaged silicon” center was found to be a silicon center, probably related to the oxide growth process.     

Application of principal component analysis to 13C NMR shifts of chalcones and their thiophene and furan analogues: A useful tool for the shift assignment and for the study of substituent effects

¹³C NMR shifts of 54 chalcones and their thiophene and furan analogues are analyzed by principal component analysis. Thus, a mathematical model is derived for the variation of the carbon shifts in each of seven classes. Two component models are found to be adequate by cross-validation. The first component corresponds to ordinary σ_para values, while the second one differentiates benzenes, thiophenes and furans. This type of data analysis is a useful tool for checking the consistencies of spectral parameters. The model parameters, which describe systematic variations within each class, are also used for the study of substituent effects and discussed in relation to substituent constants in linear free energy relationships.     

On the limiting distribution of the number of ‘near-matches’

When (R₁,...,R_n) is a random permutation of the numbers (1,...,n), a ‘near-match’ at the ith place is defined to have occured if |R_i ? i| < k, for some fixed integer k. This note studies the asymptotic distribution of the number of ‘near-matches’ when k is fixed and when k is allowed to go to infinity with n.     

The initial growth of Au on GaAs(001)-c(4 × 4)

The metal growth when depositing a monolayer (ML) of Au at 200° C on MBE-grown surfaces of GaAs(001)-c(4 × 4) was studied by AES and RHEED. The surface interaction can be characterized to proceed in two stages depending on the surface coverage of Au. At a coverage of less than 0.3 ML the gold atoms are mainly dispersed on the surface with a small in depth diffusion. Above 0.4 ML there is a rapid intermixing and a tendency of arsenic accumulation to the surface.     

Response spectrum methods in tank-vehicle design

Existing design rules for tank vehicles have proved insufficient, because vibrations often cause fatigue cracks. Measurements have been performed on the tank to provide a picture of the influence of different road types and filling ratios. Shock response spectrum analysis (SRS) was used to obtain a measure of single-dynamic events. To get a basis for dimensioning against fatigue a calculation of fatigue-damage response spectra (FDRS) has been performed. This relates the vibrations in the tank to the risk of fatigue damage. In lieu of cycle counting by rain-flow count techniques, which has certain disadvantages, a new model, the so called HdM model, for fatigue-life assessment based on level crossing has been used. Further development of the results of the analysis can be used to improve design criteria in transport tank regulations, as well as to determine optimum inspection intervals for, in particular, tanks for hazardous materials.     

Dynamic buckling of a beam with transverse constraints

A nonlinear dynamic system with continuously distributed mass is studied using several approaches: experimentally, numerically as well as analytically. The nonlinearity of the system consists of geometrical constraints imposed on the motion. It is harmonically loaded and it is demonstrated that for certain choices of the loading parameters, periodic, quasi-periodic or chaotic behaviour may occur depending on the initial conditions. An important issue is to investigate the number of degrees of freedom needed in order to analytically model the system accurately enough that the important characteristics of the motion are retained in the solution. It is found that the impact conditions at the constraints are of crucial importance and a new approach is proposed for modelling of the impacts. The method is based on the fact that the free motion can be approximated with quite a few degrees of freedom, while at impact all the infinite number of degrees of freedom are considered.