Method for detecting moment connection fracture using high-frequency transients in recorded accelerations

The 1994 Northridge earthquake caused brittle fractures in steel moment frame building connections, despite causing little visible building damage in most cases. Future strong earthquakes are likely to cause similar damage to the many un-retrofitted pre-Northridge buildings in the western US and elsewhere. Without obvious permanent building deformation, costly intrusive inspections are currently the only way to determine if major fracture damage that compromises building safety has occurred. Building instrumentation has the potential to provide engineers and owners with timely information on fracture occurrence. Structural dynamics theory predicts and scale model experiments have demonstrated that sudden, large changes in structure properties caused by moment connection fractures will cause transient dynamic response. A method is proposed for detecting the building-wide level of connection fracture damage, based on observing high-frequency, fracture-induced transient dynamic responses in strong motion accelerograms. High-frequency transients are short (<1 s), sudden-onset waveforms with frequency content above 25 Hz that are visually apparent in recorded accelerations. Strong motion data and damage information from intrusive inspections collected from 24 sparsely instrumented buildings following the 1994 Northridge earthquake are used to evaluate the proposed method. The method’s overall success rate for this data set is 67%, but this rate varies significantly with damage level. The method performs reasonably well in detecting significant fracture damage and in identifying cases with no damage, but fails in cases with few fractures. Combining the method with other damage indicators and removing records with excessive noise improves the ability to detect the level of damage.     

Biofilm growth and characteristics in an alternating pumped sequencing batch biofilm reactor (APSBBR)

A novel biofilm reactor-alternating pumped sequencing batch biofilm reactor (APSBBR)-was developed to treat synthetic dairy wastewater at a volumetric chemical oxygen demand (COD) loading rate of 487 g COD m(-3) d(-1) and an areal loading rate of 5.4 g COD m(-2) d(-1). This biofilm reactor comprised two tanks, Tanks 1 and 2, with two identical plastic biofilm modules in each tank. The maximum volume of bulk fluid in the two-tank reactor was the volume of one tank. The APSBBR was operated as a sequencing batch biofilm reactor with five operational phases-fill (25 min), anoxic (9 h), aerobic (9 h), settle (6 h) and draw (5 min). The fill, anoxic, settle and draw phases occurred in Tank 1. In the aerobic phase, the wastewater was circulated between the two tanks with centrifugal pumps and aeration was mainly achieved through oxygen absorption by micro-organisms in the biofilms when they were exposed to the air. In this paper, the biofilm growth and characteristics in the APSBBR were studied in a 98-day laboratory-scale experiment. During the course of the study, it was found that the biofilm thickness (delta) in Tank 1 ranged from 1.2 to 7.2 mm and that in Tank 2 from 0.5 to 2.2 mm; the biofilm growth against time (t) can be simulated as delta=0.07t0.99 (R2 = 0.97, P = 0.002) in Tank 1 and delta = 0.08t0.66 (R2 = 0.81, P = 0.04) in Tank 2. The biomass yield coefficient, Y, was 0.18 g volatile solids (VS) g(-1) COD removal. The biofilm density in both tanks, X, decreased as the biofilm thickness increased and can be correlated to the biofilm thickness, delta .     

Presence of Enterococcus faecalis in broiler litter and wild bird feces for bacterial source tracking

When Enterococcus faecalis is isolated from fresh feces, its host range appears to be limited to humans and birds. Although E. faecalis is found in human sewage, the extent to which the bacterium is found in broiler litter and in the feces of wild birds is unclear. These results have implications for bacterial source tracking. We determined if media designed for the isolation of fecal enterococci affected this host range, and if E. faecalis was routinely found in broiler litter and in the feces of wild birds. Of five different isolation media, none affected the isolation of E. faecalis. Enterococcus faecalis was routinely found in fresh broiler feces (522 of 1092 isolates; 48%), but rarely in broiler litter (12 of 1452 isolates; <2%). Therefore, broiler litter selects against this bacterium, and broiler litter is an unlikely environmental source of this bacterium. The presence of E. faecalis in eight wild bird species was highly variable. Unless the fecal loading rate from migratory or resident wild birds is high, water samples collected during baseflow conditions with high numbers of E. faecalis may indicate human fecal contamination.     

Stereology‐based quantitative characterization of dispersion from TEM micrographs of polymer–clay nanocomposites

Quantitative characterization of the state of dispersion and extent of exfoliation is critical in developing processing structure–property relationships in polymer–clay nanocomposites. Quantification of dispersion, exfoliation, and nanostructure in polymer–clay nanocomposites by 3D stereological parameters using image analysis of 2D transmission electron microscopy (TEM) micrographs were recently proposed. The 3D dispersion quantifying parameters are designed such that they are free of the bias associated with not sampling the true particle diameter in a 2D TEM section. In this article, the ability of the proposed 3D dispersion quantifying parameters to describe the dispersion over the entire possible range of exfoliation, and to capture independent aspects of dispersion are demonstrated by quantifying several sets of samples that were designed using a polypropylene (PP)/maleated PP/clay system. The details of the image analysis procedure, the underlying challenges, and errors involved in the segmentation process are also discussed. The 3D dispersion quantifying parameters, exfoliation number and inter‐particle distance, were critically compared against the standard 2D dispersion quantifying parameters, such as mean length, thickness, and aspect ratio. In all cases examined in this study, the sensitivity and resolution of the 3D parameters in terms of quantifying the dispersion of the nanostructure appeared comparable if not better than the standard 2D parameters. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Computational coupling of moisture diffusion and mechanical deformation in polymer matrix composites

A computationally efficient multiscale–multiphysics model aimed at predicting mechanical response of thermoplastic composites subjected to different levels of moisture was developed. The mathematical model of the coupled moisture‐diffusion–mechanical‐deformation phenomenon was stated at the microscale, based on the observed experimental data, and then upscaled using a mathematical homogenization approach. A two‐way coupling between moisture diffusion and mechanical deformation was introduced by which diffusivity was enhanced by hydrostatic strain, whereas strength and stiffness were assumed to degrade because of moisture ingression, which also gives rise to swelling. The computational complexity of analyzing the two coupled physical processes at multiple scales was reduced via a model reduction scheme for multiple physical processes. The model was validated for 30% by weight filled glass fiber and carbon fiber reinforced thermoplastic composites. The moisture conditioning and uniaxial tension experiments were utilized to identify diffusion and mechanical properties at a fine scale. The identified properties were then used to validate the formulation in the three‐point bending test. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of supercritical CO2 on the interactions between maleated polypropylene and alkyl‐ammonium organoclay

Supercritical carbon dioxide (scCO₂) has been proposed as an effective exfoliating agent for the preparation of polymer‐layered silicate nanocomposites, though there is limited fundamental understanding of this mechanism. This study looks at the interactions of this unique green solvent with three maleated polypropylenes of varying anhydride content and molecular size with an alkyl‐ammonium organoclay. Mixtures of compatibilizers and organoclay were melt‐annealed in a high pressure batch vessel at 200°C and subjected to either a blanket of nitrogen or scCO₂ at a pressure of 9.7 MPa. The structures and properties of these melt‐annealed mixtures were characterized by X‐ray diffraction, transmission electron microscopy, Fourier Transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and contact angle measurement. The results indicate that the plasticizing influence of scCO₂ aided intercalation and exfoliation for intercalants of moderate molecular size and anhydride content which would otherwise have limited diffusion into the clay galleries. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Characterization of the elastin binding domain in the cell-surface 25-kDa elastin-binding protein of staphylococcus aureus (EbpS)

Our previous studies have established that a cell-surface 25-kDa elastin-binding protein of Staphylococcus aureus (EbpS) mediates binding of this pathogen to the extracellular matrix protein elastin. Results from binding assays examining the activity of various EbpS fragments suggested that the elastin recognition domain is contained within the first 59 amino acids. In this report, we have used functional analyses with synthetic peptides and recombinant truncated forms of EbpS to localize the elastin binding domain to a 21-amino acid region contained within residues 14-34 of EbpS. Further evidence for the importance of this domain was obtained by demonstrating that the inhibitory activity of anti-EbpS antibodies on staphylococcal elastin binding was neutralized when these antibodies were pre-absorbed with a truncated recombinant EbpS construct containing residues 1-34. Overlapping synthetic peptides corresponding to EbpS residues 14-36 were then generated and tested for elastin binding activity to define further the elastin binding domain, and results from these studies showed that sequences spanning amino acids Gln14-Asp23, Asp17-Asp23, and Thr18-Glu34 inhibit binding of Staphylococcus aureus to elastin. Our analyses indicate that the hexameric sequence Thr18-Asn-Ser-His-Gln-Asp23 is the minimal sequence common to all active synthetic peptides, proteolytic fragments, and recombinant constructs of EbpS. Furthermore, substitution of Asp23 with Asn abrogated the blocking activity of the synthetic peptides, demonstrating the requirement for a charged amino acid at this location. The composite data indicate that staphylococcal elastin binding is mediated by a discrete domain defined by short peptide sequences in the amino-terminal extracellular region of EbpS.     

The aminoacceptor stem of the yeast tRNA(Lys) contains determinants of mitochondrial import selectivity

The effect of quinine, a cinchona alkaloid, was studied on gastrointestinal transit in mice. Intraperitoneal (i.p.) administration of quinine inhibited the intestinal propulsion of a charcoal suspension at a dose of 100 mg/kg, comparing favorably with 5 mg/kg morphine. In an attempt to probe into the mechanism underlying this inhibition, a possible modulation by minoxidil (1 mg/kg, p.o.) and glibenclamide (1 mg/kg, p.o.), the drugs that, respectively, open and close ATP-sensitive K+ channels was tested on gastrointestinal transit in animals treated or not with quinine or morphine. While minoxidil produced no significant change of normal transit, glibenclamide significantly increased it. However, both drugs blocked the quinine-induced reduction in gastrointestinal transit. In contrast, the inhibitory effect of morphine on gastrointestinal transit was not modified by either drug. The effects of quinine as well as of morphine on gastrointestinal transit were significantly antagonized by naloxone (2 mg/kg, s.c.), a mu-opioid receptor antagonist but not by yohimbine (1 mg/kg, i.p.), an alpha2-adrenoceptor antagonist. Furthermore, quinine at a lower dose (25 mg/kg) that showed no per se effect on gastrointestinal transit, significantly potentiated the response to 2.5 mg/kg morphine. Although the role of ATP-sensitive K+ channels in the action of quinine and morphine was not clarified by the present results, a possible involvement of endogenous opioid(s) in the quinine-induced inhibition of gastrointestinal transit can be suggested.     

Role of maintenance treatment in opioid dependence

Methadone maintenance treatment (MMT) involves the daily administration of the oral opioid agonist methadone as a treatment for opioid dependence-a persistent disorder with a substantial risk of premature death. MMT improves health and reduces illicit heroin use, infectious-disease transmission, and overdose death. However, its effectiveness is compromised if low maintenance doses of methadone (<60 mg) are used and patients are pressured to become prematurely abstinent from methadone. Pregnancy and psychiatric comorbidity are not contraindications for MMT. As an alternative to MMT, other oral opioid agents (eg, naltrexone, buprenorphine) may increase patient choice and avoid some of the more unpleasant aspects of MMT. The public-health challenge for the future is to develop and continue to deliver safe and effective forms of opioid maintenance treatment to as many opioid-dependent individuals as can benefit from them.