6,332 publications from this institution
We describe a convenient lithographic technique that can produce simple, repetitive micropatterns over large areas (several square centimeters). The technique uses an illuminated array of micrometer-scale lenses to generate an array of optical patterns in an image plane located within micrometer distances from the lens array. A layer of photoresist, placed in the image plane, records the patterns. Microlenses with different sizes, profiles, composition, and indices of refraction produce corresponding patterns in exposed and developed photoresist. Both spherical and nonspherical microlenses were examined. Several types of optical element containing arrays of microlenses were fabricated and used to demonstrate that this technique can generate uniform micropatterns over large areas (>4 cm2) in a single exposure. The smallest features produced had dimensions of approximately 100 nm.
Retardation of necking under biaxial stretching of bilayer plates comprised of an elastomer layer bonded to a metal layer is studied. Substantial increases in necking limits and consequent energy absorption can be achieved in metal–elastomer bilayers for both quasi-static and dynamic stretching. The phenomena is tied to the fact that under stretching the incremental modulus of the elastomer remains essentially unchanged, or increases, while the incremental modulus of the metal steadily decreases. The effective incremental modulus of the bilayer decreases with stretching but at a lower rate than the metal itself. Since necking instabilities are associated with an erosion of the incremental modulus, necking in the bilayer is delayed to larger strains. Although the strength of a bilayer having the same mass/area as an all-metal plate is reduced, it can nevertheless absorb more energy than the metal plate if the ratio of the elastomer modulus to metal yield stress is sufficiently large. The first part of the paper derives necking limits and energy absorption capacities for bilayers under quasi-static biaxial stretching. The second part of the paper analyses axisymmetric neck development in clamped circular bilayers subject to impulsive pressure loads. The ability of the bilayer to sustain intense impulses is compared to the performance of metal plates of the same material and total mass. Outstanding issues requiring further study are discussed.
An exploratory study is carried out of various aspects of the development of instabilities of traction-free surfaces of statically strained, rate-independent elastic-plastic solids. Existence of surface instabilities as predicted by either a bifurcation analysis or a quasi-static, imperfection-growth analysis, is found to be strongly dependent on the type of constitutive law assumed. In most instances no instabilities are found using the standard plastic flow law based on a smooth yield surface and isotropic hardening. Instabilities are predicted when a finite strain deformation theory is assumed. These are documented for a full range of proportional overall straining histories using a bifurcation analysis. A finite element analysis employing a corner theory of plasticity is used to study the non-linear growth of the instabilities starting from small initial surface undulations for the case of plane strain deformation. Some experimental observations of surface irregularities which may be due to surface instabilities are reported and discussed.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLiquid-phase oxidation of 2-propanol to acetone by dioxygen using supported platinum catalystsJames W. Nicoletti and George M. WhitesidesCite this: J. Phys. Chem. 1989, 93, 2, 759–767Publication Date (Print):January 1, 1989Publication History Published online1 May 2002Published inissue 1 January 1989https://pubs.acs.org/doi/10.1021/j100339a050https://doi.org/10.1021/j100339a050research-articleACS PublicationsRequest reuse permissionsArticle Views640Altmetric-Citations54LEARN 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 InRedditEmail Other access optionsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts
This note examines two aspects of the theory which treats localization of deformation as a bifurcation from homogeneous deformation. The results are obtained for solids modelled as elastic-plastic and having smooth yield and plastic potential surfaces, but it is not required that inelastic strain increments be normal to the yield surface. First, it is demonstrated that discontinuous bifurcations, for which elastic unloading occurs outside the zone of incipient localization, first become possible at the point of continuous bifurcation, for which further plastic deformation is assumed to occur both inside and outside of the zone of localization. Second, we investigate an apparent paradox which arises in the rigid plastic limit of an elastic-plastic localization calculation if normality does not apply. This is resolved by consideration of the relative amounts of the bifurcation mode corresponding to elastic and to plastic deformation and it is demonstrated that even for very small amounts of elasticity, bifurcation modes which are inadmissible in the rigid plastic case become possible.
Spectrally-encoded endoscopy (SEE) is an ultraminiature endoscopy technology that acquires high-definition images of internal organs through a sub-mm endoscopic probe. In SEE, a grating at the tip of the imaging optics diffracts the broadband light into multiple beams, where each beam with a distinctive wavelength is illuminated on a unique transverse location of the tissue. By encoding one transverse coordinate with the wavelength, SEE can image a line of the tissue at a time without using any beam scanning devices. This feature of the SEE technology allows the SEE probe to be miniaturized to sub-mm dimensions. While previous studies have shown that SEE has the potential to be utilized for various clinical imaging applications, the translation of SEE for medicine has been hampered by challenges in fabricating the miniature grating inherent to SEE probes. This paper describes a new fabrication method for SEE probes. The new method uses a soft lithographic approach to pattern a high-aspect-ratio grating at the tip of the miniature imaging optics. Using this technique, we have constructed a 500 μm-diameter SEE probe. The miniature grating at the tip of the probe had a measured diffraction efficiency of 75%. The new SEE probe was used to image a human finger and formalin fixed mouse embryos, demonstrating the capability of this device to visualize key anatomic features of tissues with high image contrast. In addition to providing high quality imaging SEE optics, the soft lithography method allows cost-effective and reliable fabrication of these miniature endoscopes, which will facilitate the clinical translation of SEE technology.
