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Soil-structure interaction (SSI) analysis evaluates the collective response anddynamic interplay of three linked systems: the structure, the foundation, and the soil underlying and surrounding the foundation. Problems associated with practical application of SSI for building structures are rooted in a poor understanding of fundamental SSI principles. Implementation in practice is hindered by a literature that is difficult to understand, and codes and standards that contain limited guidance and, in some cases, are proprietary. A recent report published by the National Institute of Standards and Technology (NIST) provides a mechanism for advancing the state of practice in SSI for practicing engineers. It offers a synthesis of the body of SSI literature, distilled into a concise narrative and harmonized under a consistent set ofvariables and units. Techniques are described by which SSI phenomena such as foundation-soil compliance and damping (inertial interaction), and foundation-to-free-field ground motion change (kinematic interaction) can be evaluated in engineering practice. Specific recommendations for modeling these and other seismic soil-structure interaction effects on building structures are provided. The resulting recommendations are illustrated and tested though simulations of two example buildings with earthquake recordings.

A complete model of a soil-foundation-structure system for use in response history analysis requires modification of input motions relative to those in the free-field to account for kinematic interaction effects, foundation springs and dashpots to represent foundation-soil impedance, and a structural model. The recently completed ATC-83 project developed consistent guidelines for evaluation of kinematic interaction effects and foundation impedance for realistic conditions. We implement those procedures in seismic response history analyses for two instrumented buildings in California, one a 13-story concrete-moment frame building with two levels of basement and the other a 10-story concrete shear wall core building without embedment. We develop three-dimensional baseline models (MB) of the building and foundation systems (including SSI components) that are calibrated to reproduce observed responses from recorded earthquakes. SSI components considered in the MB model include horizontal and vertical springs and dashpots that represent the horizontal translation and rotational impedance, kinematic ground motion variations from embedment and base slab averaging, and ground motion variations over the embedment depth of basements. We then remove selected components of the MB models one at a time to evaluate their impact on engineering demand parameters (EDPs) such as inter-story drifts, story shear distributions, and floor accelerations. We find that a “bathtub” model that retains all features of the MB approach except for depth-variable motions provides for generally good above-ground superstructure responses, but biased demand assessments in subterranean levels. Other common approaches using a fixed-based representation can produce poor results.

Ground motions at the foundation levels of structures differ from those in the free-field as a result of inertial and kinematic interaction effects. Inertial interaction effects tend to produce narrow-banded ground motion modification near the fundamental period of the soil-structure system, whereas kinematic effects are relatively broad-banded and concentrated at high frequencies. Kinematic interaction effects can be predicted using relatively costly finite element analyses with incoherent input or simplified models. The simplified models are semi-empirical in nature and derived from California data. These simplified models are the basis for seismic design guidelines used in the western United States, such as ASCE-41 and a pending report published by NIST. We compile some available data from building and ground instrumentation arrays in Japan for comparison to these two sets of models. We demonstrate that the model predictions for the sites under consideration are very similar to each other for modest foundation sizes (equivalent radii under about 50 m). However, the data show that both approaches overestimate the transfer function ordinates relative to those from Japanese data. This indicates that the semi-empirical models currently in use are conservative relative to these data sets. We speculate as to possible causes for the observed discrepancies.

Thermally activated chemical vapor-phase etching of titanium nitride (TiN) is studied by utilizing either alternate exposures of niobium pentafluoride (NbF5) and carbon tetrachloride (CCl4) or by using CCl4 alone. Nitrogen (N2) gas purge steps are carried out in between every reactant exposure. Titanium nitride is etched in a non-self-limiting way by NbF5-CCl4 based binary chemistry or by CCl4 at temperatures between 370 and 460 °C. Spectroscopic ellipsometry and a weight balance are used to calculate the etch per cycle. For the binary chemistry, an etch per cycle of ≈0.8 Å is obtained for 0.5 and 3 s long exposures of NbF5 and CCl4, respectively at 460 °C. On the contrary, under the same conditions, the etch process with CCl4 alone gives an etch per cycle of about 0.5 Å. In the CCl4-only etch process, the thickness of TiN films removed at 460 °C varies linearly with the number of etch cycles. Furthermore, CCl4 alone is able to etch TiN selectively over other materials such as Al2O3, SiO2, and Si3N4. X-ray photoelectron spectroscopy and bright field transmission electron microscopy are used for studying the post-etch surfaces. To understand possible reaction products and energetics, first-principles calculations are carried out with density functional theory. From thermochemical analysis of possible reaction models, it is found that NbF5 alone cannot etch TiN while CCl4 alone can etch it at high temperatures. The predicted byproducts of the reaction between the CCl4 gas molecules and TiN surface are TiCl3 and ClCN. Similarly, TiF4, NbFCl3, and ClCN are predicted to be the likely products when TiN is exposed to both NbF5 and CCl4. A more favorable etch reaction is predicted when TiN is exposed to both NbF5 and CCl4 (ΔG = -2.7 eV at 640 K) as compared to exposure to CCl4 only (ΔG = -2 eV at 640 K) process. This indicates that an enhanced etch rate is possible when TiN is exposed alternately to both NbF5 and CCl4, which is in close agreement with the experimental results. [ABSTRACT FROM AUTHOR]

An analysis of the transparency carrier density in strained layer In(x)Ga(1 - x)As-GaAs quantum well heterostructure lasers in theory and practice is presented. Results show that laser threshold current density is determined by considering the optical waveguide with the most significant results. Short cavity effects should also be considered even with cavity lengths of more than 1,000 micrometers. A comparison of results from various studies show that threshold current density in the short cavity limit are influenced by even minimal changes in structural variables.

The Resistive RAM (RRAM) technology is currently in a level of maturity that calls for its integration into CMOS compatible memory arrays. This CMOS integration requires a perfect understanding of the cells performance and reliability in relation to the deposition processes used for their manufacturing. In this paper, the impact of the precursor chemistries and process conditions on the performance of HfO2 based memristive cells is studied. An extensive characterization of HfO2 based 1T1R cells, a comparison of the cell-to-cell variability, and reliability study is performed. The cells' behaviors during forming, set, and reset operations are monitored in order to relate their features to conductive filament properties and process-induced variability of the switching parameters. The modeling of the high resistance state (HRS) is performed by applying the Quantum-Point Contact model to assess the link between the deposition condition and the precursor chemistry with the resulting physical cells characteristics. [ABSTRACT FROM AUTHOR]