Mode I steady-state crack growth is analysed under plane strain conditions in small scale yielding. The elastic-plastic solid is characterized by a generalization of J2 flow theory which accounts for the influence of the gradients of plastic strains on hardening. The constitutive model involves one new parameter, a material length l, specifying the scale of nonuniform deformation at which hardening elevation owing to strain gradients becomes important. Gradients of plastic strain at a sharp crack tip result in a substantial increase in tractions ahead of the tip. This has important consequences for crack growth in materials that fail by decohesion or cleavage at the atomic scale. The new constitutive law is used in conjunction with a model which represents the fracture process by an embedded traction-separation relation applied on the plane ahead of the crack tip. The ratio of the macroscopic work of fracture to the work of the fracture process is calculated as a function of the parameters characterizing the fracture process and the solid, with particular emphasis on the role of l.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSelf-assembled monolayers of alkanethiols on gold: comparisons of monolayers containing mixtures of short- and long-chain constituents with methyl and hydroxymethyl terminal groupsJohn P. Folkers, Paul E. Laibinis, and George M. WhitesidesCite this: Langmuir 1992, 8, 5, 1330–1341Publication Date (Print):May 1, 1992Publication History Published online1 May 2002Published inissue 1 May 1992https://doi.org/10.1021/la00041a015Request reuse permissionsArticle Views2644Altmetric-Citations359LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-Alertsclose Get e-Alerts
Obesity induced inflammation may promote periodontal tissue destruction and bone resorption inducing tooth loss. We examined the association between measures of adiposity and self‐reported periodontal disease, using data from 36,910 healthy male participants of the Health Professionals Follow‐Up Study (HPFS) who were free of periodontal disease at baseline and followed for ≤20 years (1986–2006). Self‐reported height, weight, and periodontal disease data were collected at baseline, weight and periodontal disease were additionally collected on biennial follow‐up questionnaires and waist and hip circumference were self‐reported in 1987. These self‐reported measures have been previously validated. The multivariable adjusted associations between BMI (kg/m 2 ), waist circumference (WC), waist‐to‐hip ratio (WHR), and first report of periodontal disease diagnosis were evaluated using time‐varying Cox models. We observed 2,979 new periodontal disease diagnoses during 596,561 person‐years of follow‐up. Significant associations and trends were observed between all measures of adiposity and periodontal disease after adjusting for age, smoking, race, dental profession, physical activity, fruit and vegetable intake, alcohol consumption, and diabetes status at baseline. BMI ≥30 kg/m 2 compared to BMI 18.5–24.9 kg/m 2 was significantly associated with greater risk of periodontal disease (hazard ratios (HR) = 1.30; 95% confidence interval (CI): 1.17–1.45). Elevated WC and WHR were significantly associated with a greater risk of periodontal disease (HR for extreme quintiles: WC = 1.27, 95% CI: 1.11–1.46; WHR = 1.34, 95% CI: 1.17–1.54). The associations of BMI and WC were significant even among nondiabetics and never smokers. Given the high prevalence of overweight, obesity, and periodontal disease this association may be of substantial public health importance.
Clinical tests based on primer-initiated amplification of specific nucleic acid sequences achieve high levels of sensitivity and specificity. Despite these desirable characteristics, these tests have not reached their full potential because their complexity and expense limit their usefulness to centralized laboratories. This paper describes a device that integrates sample preparation and loop-mediated isothermal amplification (LAMP) with end point detection using a hand-held UV source and camera phone. The prototype device integrates paper microfluidics (to enable fluid handling) and a multilayer structure, or a "paper machine", that allows a central patterned paper strip to slide in and out of fluidic path and thus allows introduction of sample, wash buffers, amplification master mix, and detection reagents with minimal pipetting, in a hand-held, disposable device intended for point-of-care use in resource-limited environments. This device creates a dynamic seal that prevents evaporation during incubation at 65 °C for 1 h. This interval is sufficient to allow a LAMP reaction for the Escherichia coli malB gene to proceed with an analytical sensitivity of 1 double-stranded DNA target copy. Starting with human plasma spiked with whole, live E. coli cells, this paper demonstrates full integration of sample preparation with LAMP amplification and end point detection with a limit of detection of 5 cells. Further, it shows that the method used to prepare sample enables concentration of DNA from sample volumes commonly available from fingerstick blood draw.
This paper describes the design and operation of a liquid-core liquid-cladding (L(2)) lens formed by the laminar flow of three streams of liquids in a microchannel whose width expands laterally in the region where the lens forms. Two streams of liquid with a lower refractive index (the cladding) sandwich a stream of liquid with a higher refractive index (the core). As the core stream enters the expansion chamber, it widens and becomes biconvex in shape, for some rates of flow. This biconvex fluidic element focuses light. Manipulating the relative rates of flow of the streams reconfigures the shape, and therefore the focal distance, of the L(2) lens. This paper also describes a technique for beam tracing, and for characterization of a lens in an enclosed micro-scale optical system. The use of a cladding liquid with refractive index matched to that of the material used in the fabrication of the microfluidic system (here, poly(dimethylsiloxane)) improves the quality of the focused beam.
The physical basis for delayed aftereffects of large crustal earthquakes is analyzed. These effects apparently range in scale from typical aftershocks near