The asymptotic manifold of a perturbed linear differential equation as determined by the comparison principle

The asymptotic properties of the solutions of a linear homogeneous system of differential equations determine, under suitable restrictions, the asymptotic properties of a set of solutions of a nonlinear perturbation of this linear equation. The comparison principle is used here to generate an asymptotic manifold of the perturbed equation. The majorant function that is used in connection with the comparison technique is usually assumed to be nondecreasing in the dependent variable. However, properties of the asymptotic manifold are discussed here under the opposite monotonicity assumption, namely, that the majorant function is nonincreasing in the dependent variable. This type of majorant, function arises, for example, in certain gravitation problems. The main result on the structure of asymptotic manifolds which have an asymptotic uniformity is that solutions close to the manifold are either in the manifold or do not exist in the future. This research was supported in part by the National Science Foundation under grant GP-11543. Entrata in Redazione il 6 giugno 1970.     

Cell effects in optoacoustic spectrometry

Summary A single-beam optoacoustic spectrometer has been constructed to study the effect of cell material, sample backing and sample thickness on the magnitude of the optoacoustic signal for a solid sample. Statistical analysis of the results gave an idea of their precision. The intensity of the signal is dependent upon the cell material in the order PTFE > stainless steel > aluminium brass copper > nylon 6 > perspex. The precision of the measurement is also dependent on the material, results obtained from the plastic cells being significantly less precise than those from metal cells. The intensity of the signal is also dependent upon the material of the cell holder and on the thickness of the sample. These findings have considerable implications for the analysis of surfaces by optoacoustic spectroscopy (OAS).

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Einflu\ der Probenkammer bei optoakustischen Messungen

Zusammenfassung Ein einstrahliges optoakustisches Spektrometer wurde konstruiert, um den Einflu\ des Materials der Probenkammer, der Probenhalterung sowie der Probendicke auf die StÄrke des optoakustischen Signals im Falle einer festen Probe zu untersuchen. Die SignalstÄrke hÄngt vom Kammermaterial in folgender Reihenfolge ab: PTFE > rostfreier Stahl > Aluminium Messing Kupfer > Nylon 6 > Perspex. Auch die Me\genauigkeit ist vom Material abhÄngig: sie ist bei Kunststoffkammern bedeutend geringer als bei Metallkammern. Die StÄrke des Signals hÄngt weiterhin ab vom Material der Probenhalterung und von der Dicke der Probe. Die Versuchsergebnisse sind von gro\er Bedeutung für die OberflÄchenanalyse durch optoakustische Spektrometrie.

     

Phosphorus and hydrogen atoms on the (0 0 1) surface of silicon: A comparative scanning tunnelling microscopy study of surface species with a single dangling bond

We present a comparative scanning tunnelling microscopy (STM) study of two features on the Si(0 0 1) surface with a single dangling bond. One feature is the Si-P heterodimer—a single surface phosphorus atom substituted for one Si atom of a Si-Si dimer. The other feature is the Si-Si-H hemihydride—a single hydrogen atom adsorbed to one Si atom of a Si-Si dimer. Previous STM studies of both surface species have reported a nearly identical appearance in STM which has hampered an experimental distinction between them to date. Using voltage-dependent STM we are able to distinguish and identify both heterodimer and hemihydride on the Si(0 0 1) surface. This work is particularly relevant for the fabrication of atomic-scale Si:P devices by STM lithography on the hydrogen terminated Si(0 0 1):H surface, where it is important to monitor the distribution of single P dopants in the surface. Based on the experimental identification, we study the lateral P diffusion out of nanoscale reservoirs prepared by STM lithography.     

Infrared cryogenic studies: Part 14. Chloromethane in various matrices at 10 K

Infrared spectra are reported for chloromethane in argon, krypton, nitrogen, and carbon monoxide matrices at 10 K. No evidence was found for rotation of chloromethane in any of the matrices. In Kr band splitting of the A modes due to intermolecular coupling was observed. In CO, and possibly N₂, minor perturbations of the v₃ mode due to multiple trapping sites were observed. Concentration studies in all matrices show the growth of multimer bands, the predominant species is believed to be an open-chain dimer.     

Reconstruction of the signal produced by a directional sound source from remote multi-microphone recordings

A mathematical method for reconstructing the signal produced by a directional sound source from knowledge of the same signal in the far field, i.e., microphone recordings, is developed. The key idea is to compute inverse filters that compensate for the directional filtering of the signal by the sound source directivity, using a least-square error optimization strategy. Previous work pointed out how the method strongly depends on arrival times of signal in the microphone recordings. Two strategies are used in this paper for calculating the time shifts that are afterward taken as inputs, together with source directivity, for the reconstruction. The method has been tested in a laboratory environment, where ground truth was available, with a Polaroid transducer as source. The reconstructions are similar with both strategies. The performance of the method also depends on source orientation.     

Laser illumination for manipulation of hydrogen charge states in silicon solar cells

This Letter investigates the important parameters of illumination for control of hydrogen charge states in p‐type silicon solar cells. Through variations in the wavelength and intensity of illumination, evidence is provided for the importance of the neutral charge state of interstitial hydrogen, H⁰, for the passivation of defects in upgraded metallurgical grade (UMG) silicon. It is shown that through this approach minority carrier lifetimes may be achieved in excess of those realised through previous techniques, resulting in open‐circuit voltages (iV_OC) over 710 mV. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)