Sputtering mechanisms near the threshold energy

Threshold energies for sputtering cannot be calculated directly but have to be evaluated from the energy dependence of the sputtering yields. This paper investigates trajectories of projectile and recoils near the threshold energy for sputtering, where the collision cascade becomes increasingly simple. Statistics of the different collision events show which processes dominate the sputtering close to the threshold energy for selfbombardment of different light and heavy targets. The differential cross-sections for scattering and recoil production explain qualitatively the probability for the various processes.     

Role of Amines in Adhesion of Polybutadiene to Glass Substrates. II. Reactions of Amines with Trimethoxysilanol and/or Fumed Silica

This paper is part of a larger investigation of the role of amines in the adhesion of polybutadiene to glass substrates. It describes near infrared, infrared and nuclear magnetic resonance spectroscopy studies of the interaction of amines with silanol groups usually under ambient conditions but sometimes when heated in air. Additional supporting evidence was obtained from gas liquid chromatography, mass spectrometry and elemental analyses. In order to assure a sufficiently high concentration of silanol groups, triethylsilanol and fused silica were used as models for the glass surface. The mechanism of interaction of aliphatic amines and of the aminosilane was different from that of aromatic amines. Most notably, reaction of aliphatic amines with carbon dioxide in the air and/or dissolved/adsorbed in/on the silanol occurred almost instantaneously, whereas the corresponding reaction of the aromatic amines with carbon dioxide was not observed under the experimental conditions used. The carbamates formed underwent further reactions much more rapidly than either the simple aromatic amines or the unmodified aliphatic amines.     

Visual signal detection in structured backgrounds. III. Calculation of figures of merit for model observers in statistically nonstationary backgrounds

Models of human visual detection have been successfully used in computer-generated noise. For these backgrounds, which are generally statistically stationary, model performance can be readily calculated by computing the index of detectability d' from the noise power spectrum, the signal profile, and the model template. However, model observers are ultimately needed in more real backgrounds, which may be statistically non-stationary. We investigated different methods to calculate figures of merit for model observers in real backgrounds based on different assumptions about image stationarity. We computed performance of the nonpre-whitening matched-filter observer with an eye filter on mammography and coronary angiography for an additive or a multiplicative signal. Performance was measured either by applying the model template to the images or by computing closed-form expressions with various assumptions about image stationarity. Results show first that the structured backgrounds investigated cannot be considered stationary. Second, traditional closed-form expressions of detectability calculated from the noise power spectra with the assumption of background stationarity lead to erroneous estimates of model performance. Third, the most accurate way of measuring model performances is by directly applying the model template on the images or by computing a closed-form expression that does not assume image stationarity.     

Derivation of a detectability index for correlated responses in multiple-alternative forced-choice experiments

In a recent paper [J. Opt. Soc. Am. A 17, 206 (2000)], a modified detectability index, d'r, was proposed to accommodate correlations between internal responses in multiple-alternative forced-choice (MAFC) experiments. The derivation given in that work pertained only to two-alternative forced choice, although it was shown empirically that the result held for general MAFC tasks when the correlation between responses is constant. Here we present a rigorous derivation that shows that the d'r result generalizes to MAFC tasks in this case.     

Determination of thorium in plutonium by X-ray spectrometry

An X-ray fluorescence method for the determination of thorium (0.1 to 1.2 %) in plutonium-238 was developed. The PuO₂ is mounted in a dimpled slide, and the slide is packaged so that the plutonium and thorium L-alpha lines can be counted in a nonradioactive laboratory. A standard deviation of 0.02 % is estimated. The method is applicable to both solid and solution samples.     

Surgical correction of torsion of the penis

Torsion of the penis is a rare anomaly, believed to be due to abnormal skin attachment and not to any structural abnormality of the corpora. The rotation is usually to the left in a counter-clockwise fashion. The urethral meatus is placed in a oblique position and the median raphe makes a spiral curve from the base of the penis towards the meatus. Three boys with congenital torsion of the penis are reported. A corrective operative for this condition is described. Penile torsion was first described by Verneuil in 1857, but in the past no operative correction was recommended, since attempts to move the skin around were believed not to correct the spiral alignment of the corpora cavernosa.     

Über die Altersbestimmung von Eichenholz in Norddeutschland mit Hilfe der Dendrochronologie

Zusammenfassung Die M?glichkeiten einer Alterbestimmung von Eichenholz in Norddeutschland mit Hilfe der dendrochronologischen Methode wurden an einigen Beispielen aufgezeigt und er?rtert. Daraus kann man folgern, da? eine dem Süden entsprechende Standardkurve für Norddeutschland nicht aufgebaut werden kann. Eine erfolgreiche Absolutdatierung ist meist nur mit Hilfe von gesicherten, streng standort-bezogenen Kurven durchführbar. Aber auch Relativdatierungen geben h?ufig genügend Aufschlu?. Die Altersbestimmungen der Klosteranlage Wienhausen/Celle bzw. der ausgegrabenen Siedlung Haithabu mit Hilfe norddeutscher Standortchronologien zeigen den Wert und die M?glichkeit der dendrochronologischen Datierung in Norddeutschland. Mitunter k?nnen Absolutdatierungen auch mit der süddeutschen Standardkurve erfolgen, wenn n?mlich Holz aus südlicheren Gegenden in Norddeutschland verbaut wurde. Auf diese Weise lie? sich die Bauzeit der mittelalterlichen Bremer Kogge ermitteln.

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On the dating of oakwood in Northern Germany by the dendrochronological method

Summary The possibilities of dating oakwood by the dendrochronological method have been demonstrated and discussed in relation to specimens from various sites in Northern Germany. It has been shown that a standard growth-ring series, such as that corresponding to the whole of Southern Germany, cannot be established for Northern Germany. In most cases a successful dating can be realized only by means of a definite growth-ring series related to a narrow site. However, the correlation between older and younger materials often procides sufficient information. The determination of the age of the monastry in Wienhausen/Celle and of the excavated settlement Haithabu illustrates the value and the possibilities of dendrochronology in Northern Germany. Absolute dating occasionally may be possible with the standard growth-ring series of Southern Germany; namely where wood from southern regions has been used in Northern Germany. In this way the date of construction of the Bremer Kogge was determined.

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Herrn Prof. Dr. Hans Mayer-Wegelin zur Vollendung des 70. Lebensjahres gewidmet.