Characterization of residual stresses from cold expansion using spatial statistics

Residual stress fields from cold expansion have been widely used to extend the fatigue life of aircraft structures. However, the spatial statistical character of these residual stress fields has not been established and has not been incorporated in current analysis methods. The objective of this study was to establish a spatial statistical method to quantify the residual stress field around a cold expanded hole. A framework called the Spatial Analysis of Residual Stress (SpARS) was developed utilizing spatial correlation, response surface modelling techniques and statistical resampling methods to characterize the residual stress field. Our results showed that tolerance bounds on residual stress can be quantified using this method. We also demonstrated the SpARS method using recently published round robin case studies. The newly developed model will be useful for aircraft structural fatigue crack growth analyses to incorporate residual stress fields for extending inspection intervals for fatigue and fracture critical structures.     

Evaluation of markov program models in virtual memory systems

A first order Markov model of program behaviour is developed from FORTRAN program instruction data. The program model is evaluated by using it to generate page references for input into a simple virtual memory operating system (VMOS) simulation model. The actual trace data are also used to drive the VMOS model. In both cases the fault probability is obtained for different replacement rules, memory sizes and page sizes. A comparison of fault probabilities is used to determine the effectiveness of the Markov program model.     

Heat degradation studies of solar heat transfer fluids

Destructive distillation of solar heat transfer fluids was conducted to determine the types of pyrolytic products which might be formed in solar collectors under conditions of stagnation or malfunction. The distillates were analyzed by gas chromatography/mass spectrometry (GC/MS) to determine the types of compounds which were present and the minor components which might be formed. Dehydration products were formed from ethylene and propylene glycols with ethylene oxide and propylene oxide being minor products. A high aromatic petroleum heat transfer fluid yielded distillation fractions enriched in quinolines or isoquinolines and methylated derivatives thereof. Fractionation of this aromatic heat transfer fluid showed that the basic fraction of unheated fluid also contained aza-arenes which exhibited mutagenic activity in the Ames' bioassay. GC/MS showed that the basic fraction from unheated heat transfer fluid also contained benzoquinolines which appeared to be lacking in heat degraded samples of the same fluid. Fractionation of heat transfer fluids, in particular petroleum-based fluids, may often be necessary in order to concentrate minor components so that they can be identified by GC/MS and in order to detect mutagenic activities without interference from cytotoxic components.     

Effects of Relative Humidity on the Ultraviolet Induced Inactivation of Airborne Bacteria

Ultraviolet germicidal irradiation (UVGI) as an engineering control against infectious bioaerosols necessitates a clear understanding of environmental effects on inactivation rates. The response of aerosolized Serratia marcescens, Bacillus subtilis, and Mycobacterium parafortuitum to ultraviolet irradiation was assessed at different relative humidity (RH)levels in a 0.8 m³ completely-mixed chamber. Bioaerosol response was characterized by physical factors including median cell aerodynamic diameter and cell water sorption capacity and by natural decay and UV-induced inactivation rate as determined by direct microscopic counts and standard plate counts. All organisms tested sorbed water from the atmosphere at RH levels between 20% and 95% (up to 70% of dry cell mass at 95% RH); however, no concomitant change in median aerodynamic diameter in this same RH range was observed. Variations in ultraviolet spherical irradiance were minor and not statistically significant in the 20-95% RH range. Cell water sorption and inactivation response was similar for each of the pure cultures tested: when RH exceeded approximately 50%, sorption increased markedly and a sharp concurrent drop in UV-induced inactivation rate was observed.     

Quantitative evaluation of perceived whiteness based on a color vision model

This article describes a new perceived whiteness index, C/V index, which focuses on the brightness‐enhancement effect of color components included in the spectral reflectance factor distribution of approximate white objects or in the spectral power distribution of illuminations. The index is developed on the basis of a color vision model. The perceived whiteness of 18 approximate white samples was evaluated, and then a predictability of the index was compared with 17 types of existing whiteness indices. As a result, the C/V index was one of the indices indicating the best predicting performance. The aforementioned findings show that the C/V index is effective in evaluating the perceived whiteness of approximate white objects and the brightness‐enhancement effect of color components is an important factor in determining the perceived whiteness. © 2009 Wiley Periodicals, Inc. Col Res Appl, 2010