Black-box modeling of passive systems by rational function approximation

In this paper, a rational interpolation approach is used to approximate the transfer function of passive systems characterized by sampled data. Orthogonal polynomials are used to improve the numerical stability of the ill-conditioned Vandermonde-like interpolation matrix associated with the ordinary power series. First, the poles of the system are obtained by efficiently and accurately transforming the coefficients of the orthogonal polynomials to the ordinary power series using Clenshaw's recurrence algorithm. Then, the residues are solved in real or in complex conjugate pairs to insure a physically realizable system. Finally, the passivity of the system is enforced by applying certain constraints on the poles and residues of the system. The performances of the three most common orthogonal polynomials, Legendre and Chebyshev of the first and second kinds, are also compared to that of the power series.     

A clinical trial of antioxidant vitamins to prevent colorectal adenoma. Polyp Prevention Study Group

BACKGROUND: People who consume a diet high in vegetables and fruits have a lower risk of cancer of the large bowel. Antioxidant vitamins, which are present in vegetables and fruits, have been associated with a diminished risk of cancers at various anatomical sites. We conducted a randomized, controlled clinical trial to test the efficacy of beta carotene and vitamins C and E in preventing colorectal adenoma, a precursor of invasive cancer. METHODS: We randomly assigned 864 patients, using a two-by-two factorial design, to four treatment groups, which received placebo; beta carotene (25 mg daily); vitamin C (1 g daily) and vitamin E (400 mg daily); or the beta carotene plus vitamins C and E. In order to identify new adenomas, we performed complete colonoscopic examinations in the patients one year and four years after they entered the study. The primary end points for analyses were new adenomas identified after the first of these two follow-up examinations. RESULTS: Patients adhered well to the prescribed regimen, and 751 completed the four-year clinical trial. There was no evidence that either beta carotene or vitamins C and E reduced the incidence of adenomas; the relative risk for beta carotene was 1.01 (95 percent confidence interval, 0.85 to 1.20); for vitamins C and E, it was 1.08 (95 percent confidence interval, 0.91 to 1.29). Neither treatment appeared to be effective in any subgroup of patients or in the prevention of any subtype of polyp defined by size or location. CONCLUSIONS: The lack of efficacy of these vitamins argues against the use of supplemental beta carotene and vitamins C and E to prevent colorectal cancer. Although our data do not prove definitively that these antioxidants have no anticancer effect, other dietary factors may make more important contributions to the reduction in the risk of cancer associated with a diet high in vegetables and fruits.     

Integrative cognitive therapy for depression: A randomized pilot comparison.

This pilot study examined the efficacy of an integrative form of cognitive therapy (ICT) for depression that incorporates specific strategies for addressing alliance ruptures. Although a previous study on depression found that ICT was superior to a wait-list condition (L. G. Castonguay et al., 2004), the current study provides the 1st direct comparison between ICT and traditional cognitive therapy (CT). Twenty-two depressed adults were randomly assigned to ICT or CT (11 patients per condition), which were delivered by clinicians in training. Outcome was assessed with a specific depression measure and a global symptomatology measure. The groups were also compared on patient-perceived alliance quality and therapist empathy. Effect size estimates revealed that ICT patients evidenced greater posttreatment improvement on both outcome measures (with small to medium effects) and more clinically significant change than did CT patients. ICT patients also had higher alliance and empathy scores across treatment (with medium to large effects). The findings, albeit very preliminary, support the potential viability of ICT and the potential causal influence of the rupture-repair interventions on treatment process and outcome. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lack of association between the polyadenylation polymorphism in the NAT1 (acetyltransferase 1) gene and colorectal adenomas

Smoking and a high intake of red meat are risk factors for colorectal tumors. These effects could be due to aromatic amine carcinogens. Individual susceptibility to aromatic amines has been related to acetylation phenotype, which plays a role in the bioactivation of arylamines. Polymorphisms in both N-acetyltransferase genes, NAT1 and NAT2, have been associated with an increased risk of colorectal tumors. We studied the NAT1*10 fast acetylator allele (1088 T-->A mutation) and distal adenomas in a sigmoidoscopy-based case-control study (441 cases, 484 controls). We found neither an increased adenoma prevalence in subjects homozygous or heterozygous for the NAT1*10 fast acetylator allele (odds ratio 1.04; 95% confidence interval 0.79-1.36), nor a gene-gene interaction between NA1 and NAT2 (P(interaction) = 0.59). Further NAT1 alleles must be considered for more conclusive results regarding the relevance of NAT1 activity to colorectal tumorigenesis.     

Synthesis and Characterization of Phosphonates from Methyl Linoleate and Vegetable Oils

Phosphonates were synthesized on a medium scale (~200 g) from three lipids—methyl linoleate (MeLin), high‐oleic sunflower oil (HOSO) and soybean oil (SBO), and three dialkyl phosphites—methyl, ethyl and n‐butyl, using a radical initiator. A staged addition of the lipid and the initiator was used to achieve good yields. Good results were observed with MeLin (94–99% conversions of the double bonds, as determined by NMR, and 83–99% isolated yields) and HOSO (99–100% NMR conversions, 87–96% isolated yields) using tert‐butyl perbenzoate as the initiator. With SBO, benzoyl peroxide was used as the initiator, due to its capability to generate radicals at a higher rate at slightly lower temperatures, and thus to shorten the reaction time. Conversions of 91–93% (by NMR) and isolated yields of 80–94% were achieved. The progress of the reaction was monitored with GC–MS. The products were characterized using ¹H, ¹³C and ³¹P NMR, IR and gel permeation chromatography. A prolonged reaction led to some transesterification between the carboxylic and phosphite ester groups. Conditions favoring higher reaction rates led to the formation of more oligomers and benzoate fatty ester byproducts. The benzoate fatty ester byproducts were formed by the attack of a benzoate radical on a double bond. The more double bonds that were present per lipid molecule, the more oligomers were formed: MeLin 2–8%, HOSO 3–9% and SBO 8–29%.     

A piezomicrobalance system for high‐temperature mass relaxation characterization of metal oxides: A case study of Pr‐doped ceria

A system for mass relaxation studies based on a gallium phosphate piezocrystal microbalance has been developed, built, and successfully used to characterize a representative mixed ionic and electronic conducting material. The apparatus is constructed to achieve reactor gas exchange times as short as 2 seconds and temporal resolution in mass measurement of 0.1 seconds. These characteristics enabled evaluation of mass relaxations that occurred on the 6 seconds time scale. Proof of concept for materials characterization capabilities of the system was carried out using 10% praseodymium‐doped cerium oxide (PCO), a material that undergoes, at selected temperatures and oxygen partial pressures, changes in mass but not in conductivity. Thin films were deposited on the piezocrystals via pulsed laser deposition (PLD). Mass relaxation curves were collected at 700°C upon application of a small step change in oxygen partial pressure, . Using two different films, the surface reaction constant, k_S, was obtained over the range from 10^?4 to 0.1 atm. Its value is found to vary between 9.7 × 10^?6 and 1.7 × 10^?4 cm/s, displaying a power law dependence on , with a law exponent of 0.67 ± 0.02, as averaged over the two sets of results. This steep dependence of k_S on is surprisingly independent of a change in dominant defect type within the range of measurement.     

High‐temperature structural stability of ceria‐based inverse opals

The use of ceria‐based inverse opals as a catalyst system for the thermochemical production of fuels from sunlight offers the potential of improved fuel production kinetics over materials with random porosity. Quantitative methods for characterizing ordered porosity are lacking, thus limiting the ability to predict the lifetime of ordered structures at elevated temperatures. In the present work, Fourier transform image analysis was used to determine the effect of composition and temperature on ordered porosity for a series of CeO₂‐ZrO₂ inverse opals having pore sizes ranging from 300 nm to 1 μm. An order parameter, γ, derived from the image analysis, was applied to scanning electron microscopy images and used to determine the degree of order in the inverse opal. The thermal stability studies indicate that loss of ordered porosity is highly dependent on temperature and that gas cycling effects have a minor effect on periodicity. A minimum Zr content of 20 at.% is necessary to retain periodicity for annealing up to 1000°C with pore diameters larger than 1 μm. These results show that CeO₂‐ZrO₂ inverse opals can be used at higher temperatures than previously thought for efficient thermochemical hydrogen production without loss of the benefits associated with ordered porosity.     

Effect of the blooming of chemical curatives on the cyclic fatigue life of natural rubber filled with a silanized silica nanofiller

When partly soluble chemical curatives are mixed with raw rubber, they migrate to the rubber surface, which can be detrimental to the rubber properties. Two rubber compounds with different amounts of curatives were prepared by mixing natural rubber with a high loading of precipitated amorphous white silica nanofiller. The silica surfaces were pretreated with bis(3‐triethoxysilylpropyl)‐tetrasulfide coupling agent to chemically adhere silica to the rubber. The chemical bonding between the filler and rubber was optimized via the tetrasulfane groups of bis(3‐triethoxysilylpropyl)‐tetrasulfide by adding accelerator and activator. The rubber compounds were cured and stored at ambient temperature for up to 65 days. One compound showed extensive blooming as a function of storage time. The cyclic fatigue life of the rubber vulcanizates was subsequently measured at a constant strain amplitude and test frequency at ambient temperature. The blooming of the chemical curatives reduced the cyclic fatigue life of the rubber vulcanizate by more than 100%. The migrated chemical curatives produced a thin layer approximately 15 μm in size beneath the rubber surface. When the rubber was stressed repeatedly in the fatigue test, cracks initiated in this layer and subsequently grew, causing the fatigue life of the vulcanizate to decrease. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of Chlorinated Paraffin and ZDDP Concentrations on Boundary Lubrication Properties of Mineral and Soybean Oils

Concentration effects of chlorinated paraffin and zinc di-ethylhexyl dithio phosphate on boundary lubrication properties were tested in vegetable and mineral base stocks. Solvent refined low sulfur paraffinic mineral oil (150 N oil) and conventional food grade soybean oil (soy oil) with EP additive concentration of 0–20% (w/w) were used in ASTM D2783 four-ball extreme pressure (4-ball EP) and Twist Compression Tribotests (TCT). Weld points in 4-ball EP and times to failure in TCT at 200 MPa showed that 150 N oil needed more than double treat levels of EP additives to achieve similar boundary lubrication performance as their 5% blends in soy oil. Also, incorporation of 20% soy oil into 150 N oil-based EP additive blends improved the performance to nearly the same level as soy oil only blends of corresponding additives. Boundary lubricity of some soy oil samples was similar to that of a commercial straight oil chlorinated metal forming lubricant. Several suggestions are provided to explain such pronounced influence of the base stock type on EP additive response. The findings suggest that soy oil and other farm-based oils may provide strategies for formulating cost effective industrial fluids and other lubricants.     

Elastohydrodynamic Study of Blends of Bio-Based Esters with Polyalphaolefin in the Low Film Thickness Regime

The film thickness in elastohydrodynamic (EHD) conditions for soybean oil (SBO), oleic estolide ester (EST) and their binary blends with polyalphaolefins (PAO2 or PAO40) were studied at 30 and 100 °C. Changes with time, for up to 200 min, were monitored. SBO and its blends with the lower viscosity PAO2 showed initially good agreement with the Hamrock–Dowson (H–D) equation down to 1–3 nm film thickness. 60 min or more after the start of the measurements, boundary layers with thickness up to 4.7 nm were observed. The blend of SBO with the more viscous PAO40 showed initially a good agreement with H–D at 100 °C. Negative deviations in film thickness were observed 15 min after the start of the measurements. At extended periods of time, up to 200 min, they were less pronounced but still detectable. EST–PAO2 blend showed initially formation of boundary layers with thickness around 2 nm. The boundary layer at 30 °C did not change for 200 min, while at 100 °C showed a decrease in thickness and/or viscosity with time. The EST and the EST–PAO40 blends showed good agreement with the H–D equation and did not display a boundary or fractionation layer within 200 min.