Stress tensor and elastic properties for hard and soft spheres

Properties determined from the microscopic stress tensor are discussed for the related systems of a steeply repulsive pair potential and hard spheres. The microscopic stress tensors determined from the local conservation law for momentum are different in these two cases. Consequences are discussed for both fluid and solid phases.     

Model order determination and noise removal for modal parameter estimation

Given a noisy impulsive response function (IRF) that has been contributed by an unknown number of modes, this article proposes a different approach from the traditional methods for estimating modal parameters from this noisy IRF. The major difference lies in the way of handling noise and choosing the computational model order. Whereas the traditional approach accommodates noise by purposely increasing the computational model order, the proposed approach uses the actual system order as the computational model order and rejects noise prior to performing the modal parameter estimation. The proposed approach includes three steps: (1) model order (or number of modes) determination from the measured IRF—by finding the rank of a Hankel matrix constructed from the measured IRF, (2) noise removal from the measured IRF to obtain a filtered IRF—by implementing Cadzow's algorithm for the structured low rank approximation (SLRA) on the Hankel matrix, and (3) modal parameters estimation from the filtered IRF—by using the complex exponential method (Prony's method). Numerical studies include both synthesized and experimental data. While measured IRFs with mild and strong noise levels are simulated for a 5 degree-of-freedom mass-spring-dashpot system, the modal parameter estimations based on the filtered IRFs are very good for both noise levels. While experimental data are measured from two accelerometers mounted at a cantilever beam, the modal parameters estimated from the filtered IRFs of the two accelerometers are in excellent agreement.     

Assessment of Hillside Coal Waste Embankment Failures Using Qualitative Analysis

Qualitative assessment provides a sound process for defining specific aspects of risk associated with potentially unstable slopes. Field observations, experience, field data, and back analysis from eleven past slope failures have been used to identify common and significant factors associated with the potential failure of coal waste embankments located in southwest Virginia. A database containing information about site location, characteristics, and conditions has been developed using Office of Surface Mining program narratives and engineering reports. It was observed that the pattern of failure was almost identical at each site and driven by the same phenomena. Degradation of the spoil material, accelerated by poor drainage conditions and periods of increased precipitation, lead to a decrease in interparticle strength and failure along a “lubricated,” or highly weathered, surface. The development of a rating system for the identification of potentially unstable coal waste embankments, based on the factors and characteristics reviewed here, will eventually lead to the implementation of a preventive maintenance program. Preventative maintenance will most likely need to include monitoring of the area, installation of a proper drainage system, and revegetation.     

Cobalt Ferrite in YSZ for Use as Reactive Material in Solar Thermochemical Water and Carbon Dioxide Splitting, Part II: Kinetic Modeling

The kinetics of 10 wt.% cobalt ferrite (CoFe₂O₄) in 8 mol.% yttria-stabilized zirconia, synthesized via the co-precipitation method and formed into a porous structure, are investigated in support of simulating the performance of a solar thermochemical reactor. Kinetic parameters for the thermal reduction (T-R) of CoFe₂O₄ at temperatures of 1325–1500°C were investigated by thermogravimetry. A nonlinear best fit of a uniform conversion model was used to determine kinetic parameters from experimental data. In the temperature range of 1375–1450°C, the activation energy and preexponential term were found to be 386 ± 13 kJ mol^?1 and 8.8 × 10⁹ ± 2.0 × 10⁸ min^?1, respectively, while increasing at higher temperatures. Simultaneous thermogravimetric analysis and differential scanning calorimetry studies showed an increase in the reaction rate of T-R upon the onset of melting (1440°C). Oxidation studies of the material using CO₂ yield an activation energy and preexponential term of 52.1 ± 6.8 kJ mol^?1 and 2.86 ± 0.2 min^?1, respectively, which is in good agreement with past work. The reaction order for CO₂ was determined to be 0.750 ± 0.08. The reaction kinetics for oxidation using CO₂ were best described by a 3-D diffusion Jander model.     

On the use of multi-path inductorless TIAs for larger transimpedance limit

This paper discusses the use of mutli-path inductorless transimpedance amplifiers (TIAs), consisting of several different second-order shunt-feedback sub-TIAs (SF-sTIAs) driven by the photodiode, to break the single-stage technology-dependent transimpedance limit. The advantage of the MP-TIA that is explored in this work is in its third-order transfer function, which provides additional degrees of freedom in tailoring the performance. Pole and zero locations of the MP-TIA transfer function are examined and verified with behavioural simulations. The theoretical transimpedance limit for MP-TIAs based on two SF-sTIAs is derived. The possibility of further increasing the transimpedance limit vs bandwidth trade-off by combining three and four sub-TIAs is investigated with simulations. A transistor-level design example of an MP-TIA is presented. The 0.13-μm CMOS MP-TIA achieves the largest figure-of-merit among published TIAs.     

Computability and Complexity in Self-assembly

This paper explores the impact of geometry on computability and complexity in Winfree’s model of nanoscale self-assembly. We work in the two-dimensional tile assembly model, i.e., in the discrete Euclidean plane ℤ×ℤ. Our first main theorem says that there is a roughly quadratic function f such that a set A⊆ℤ⁺ is computably enumerable if and only if the set X _A ={(f(n),0)∣n∈A}—a simple representation of A as a set of points on the x-axis—self-assembles in Winfree’s sense. In contrast, our second main theorem says that there are decidable sets D⊆ℤ×ℤ that do not self-assemble in Winfree’s sense.     

An Investigation into the Effect of Laundering on the Repellency Behaviour of a Fluorochemical-treated Cotton Fabric

The water- and oil-repellency of a cotton fabric treated with a fluorocarbon finish is shown to decrease with extended laundering. The nature of this diminishing performance is investigated by time-of-flight secondary-ion-mass spectrometry (ToF—SIMS) and X-ray photoelectron spectroscopy (XPS), which reveal an increase in the surfactants on the fibre surface and a decrease in the fluorocarbon coating as a result of laundering. The effect of heat-pressing on fabric repellency is also investigated by using XPS.