Analytic solutions for optimized ellipsometric measurements of interfaces and surface layers in thin film structures

The maximum experimental sensitivity in ellipsometric measurements for samples that include a composite (two-layer) film on a substrate is treated with mathematical generality. A detailed theoretical computation is made for a system consisting of a moderately thick film on a substrate and including either an interface layer between the film and substrate or a thin surface layer on top of the moderately thick film. Analytical conditions for the sensitivity of p or s wave suppression are determined. For the air/SiO₂/Si system a numerical calculation is performed to determine the optimum sensitivity for interfacial layer studies.     

Rupture strength of surface layers subjected to contact interaction

A criterion characterizing the effect of changes in the structure and chemical composition of surface alloys subjected to contact interaction is proposed. The results of investigation of the wear products by methods of x-ray-structural and emission-spectrum analyses are used for the development of this criterion.The enthalpy of wear-product formation during contact interaction is taken as a characteristic of the effect of structural-energy processes on the stabilization of wear products, which define the proposed criterion. An example of the calculation of the proposed criterion is given for the case of interaction between alloy OT4 and steel 45.Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 9, pp. 50–55, September, 1989.     

Mapping bacterial surface population physiology in real-time: infrared spectroscopy of Proteus mirabilis swarm colonies

We mapped the space-time distribution of stationary and swarmer cells within a growing Proteus mirabilis colony by infrared (IR) microspectroscopy. Colony mapping was performed at different positions between the inoculum and the periphery with a discrete microscope-mounted IR sensor, while continuous monitoring at a fixed location over time used an optical fiber based IR-attenuated total reflection (ATR) sensor, or "optrode." Phenotypes within a single P. mirabilis population relied on identification of functional determinants (producing unique spectral signals) that reflect differences in macromolecular composition associated with cell differentiation. Inner swarm colony domains are spectrally homogeneous, having patterns similar to those produced by the inoculum. Outer domains composed of active swarmer cells exhibit spectra distinguishable at multiple wavelengths dominated by polysaccharides. Our real-time observations agree with and extend earlier reports indicating that motile swarmer cells are restricted to a narrow (approximately 3 mm) annulus at the colony edge. This study thus validates the use of an IR optrode for real-time and noninvasive monitoring of biofilms and other bacterial surface populations.     

Mapping the structure of science through usage

Summary Science has traditionally been mapped on the basis of authorship and citation data. Due to publication and citation delays such data represents the structure of science as it existed in the past. We propose to map science by proxy of journal relationships derived from usage data to determine research trends as they presently occur. This mapping is performed by applying a principal components analysis superimposed with a k-means cluster analysis on networks of journal relationships derived from a large set of article usage data collected for the Los Alamos National Laboratory research community. Results indicate that meaningful maps of the interests of a local scientific community can be derived from usage data. Subject groupings in the mappings corresponds to Thomson ISI subject categories. A comparison to maps resulting from the analysis of 2003 Thomson ISI Journal Citation Report data reveals interesting differences between the features of local usage and global citation data.     

Electrical isolation of dislocations in Ge layers on Si(001) substrates through CMOS-compatible suspended structures

Abstract

Suspended crystalline Ge semiconductor structures are created on a Si(001) substrate by a combination of epitaxial growth and simple patterning from the front surface using anisotropic underetching. Geometric definition of the surface Ge layer gives access to a range of crystalline planes that have different etch resistance. The structures are aligned to avoid etch-resistive planes in making the suspended regions and to take advantage of these planes to retain the underlying Si to support the structures. The technique is demonstrated by forming suspended microwires, spiderwebs and van der Pauw cross structures. We finally report on the low-temperature electrical isolation of the undoped Ge layers. This novel isolation method increases the Ge resistivity to 280 Ω cm at 10 K, over two orders of magnitude above that of a bulk Ge on Si(001) layer, by removing material containing the underlying misfit dislocation network that otherwise provides the main source of electrical conduction.     

Electrical isolation of dislocations in Ge layers on Si(001) substrates through CMOS-compatible suspended structures

Suspended crystalline Ge semiconductor structures are created on a Si(001) substrate by a combination of epitaxial growth and simple patterning from the front surface using anisotropic underetching. Geometric definition of the surface Ge layer gives access to a range of crystalline planes that have different etch resistance. The structures are aligned to avoid etch-resistive planes in making the suspended regions and to take advantage of these planes to retain the underlying Si to support the structures. The technique is demonstrated by forming suspended microwires, spiderwebs and van der Pauw cross structures. We finally report on the low-temperature electrical isolation of the undoped Ge layers. This novel isolation method increases the Ge resistivity to 280 Ω cm at 10 K, over two orders of magnitude above that of a bulk Ge on Si(001) layer, by removing material containing the underlying misfit dislocation network that otherwise provides the main source of electrical conduction.     

Effect of modifying surface layers on the creep of molybdenum

High-temperature creep of polycrystalline molybdenum with presence of a strengthened (weakened) surface layer is studied. The possibility is analyzed of calculating the effect of strengthening the surface layer on the creep of solid specimens according to the mixture rule for composites.Translated from Problemy Prochnosti, No. 7, pp. 58–62, July, 1990.     

Transition modelling of surface flaws to through cracks

Cracks starting at surfaces will grow under fatigue loading conditions both along the surface and in the thickness directions of the component geometry. In those cases where the crack grows through the thickness, the fatigue crack may transition to a corresponding through crack geometry. While the fatigue crack growth behaviour of both the surface flaws and complete through cracks are well understood, the method for modelling the process by which they transition from one to the other is not. This paper seeks to bring greater clarity and understanding to the transition process by implementing a transition method and developing the associated codes and equations to do so based on careful consideration of boundary conditions, experimental data, and finite element simulations.     

改进的细菌觅食优化算法及其在框架结构设计中的应用

在细菌觅食算法(bacterial foraging algorithm,BFA)基本原理的基础上,结合“和声搜索”算法,提出了一种改进的细菌觅食算法,并应用于框架结构优化.采用该优化算法分别对一单跨8层框架和双跨5层框架结构进行离散变量的质量优化设计,并与细菌觅食算法的计算结果进行了比较.计算结果表明改进的细菌觅食算法应用在结构优化中具有较好的收敛速度和精度,可应用于工程结构的优化设计.     

A methodological approach to evaluate structural building projects through the Environmental Economic Index

Clean Technologies and Environmental Policy - The construction industry has a relevant social and economic role and has become critical to improving global sustainability. This industry contributes...     

Degradation of the surface layers of superalloys and thermal-fatigue damage to the structural elements of gas-turbine engines

We study the phase composition, the structure of the surface degraded layer, and the concentrations of elements of a directionally crystallized superalloy tested in a high-temperature gas flow. The dependences of the degree of damage to the surface layer on the level of thermal stresses are established. __________ Translated from Problemy Prochnosti, No. 5, pp. 72–80, September–October, 2008.     

Incremental Mountain Clustering Method to find building blocks for constructing structures of proteins

In this paper we propose an algorithm named Incremental Structural Mountain Clustering Method (ISMCM) with a view to finding a library of building blocks for reconstruction of 3-D structures of proteins/peptides. The building blocks are short structural motifs that are identified based on an estimate of local "density" of 3-D fragments computed using a measure of structural similarity. The structural similarity is computed after the best-molecular-fit alignment of pairs of fragments. The algorithm is tested on two well known benchmark data sets. Following the protocols used by other researchers, for the first data set we reconstruct a set of 71 test peptides (up to first 60 residues) whereas for the second data set we reconstruct all 143 test peptides. The ISMCM algorithm is found to successfully reconstruct the test peptides in terms of both global-fit root-mean-square (RMS) error and local-fit RMS error. The low values of local-fit RMS errors suggest that these building blocks extracted by ISMCM are good quantizers, which can represent nearby fragments quite accurately. To further assess the quality of building blocks we use two alternative graphical ways. We also use Shannon's entropy to show the structural similarity of the clusters found by our algorithm. This is important as building blocks that represent clusters with structurally similar fragments will be very effective in reconstruction. The entropic analysis reveals a very interesting fact that the secondary structure of the central residue of the fragments in a cluster is most strongly conserved (minimum entropy) over the cluster, which might be an indicator that central residue of the structural motif plays a dominant role in local folding.