Take a drinking straw and bend it from its ends. After sufficient bending, the tube buckles forming a kink, where the curvature is localized in a very small area. This instability, known generally as the Brazier effect, is inherent to thin-walled cylindrical shells, which are particularly ubiquitous in living systems, such as rod-shaped bacteria. However, tubular biological structures are often pressurized, and the knowledge of the mechanical response upon bending in this scenario is limited. In this work, we use a computational model to study the mechanical response and the deformations as a result of bending pressurized tubes. In addition, we develop a model inspired by tension-field theory to analytically describe the mechanical behavior before and after the wrinkling transition. Furthermore, we investigate the development and evolution of wrinkle patterns beyond the instability, showing different wrinkled configurations. We discover the existence of a multiwavelength mode following the purely sinusoidal wrinkles and anticipating the kinked configuration of the tube.
This paper demonstrates the use of microlens projection lithography using gray-scale masks to fabricate arrays of microstructures in photoresist. In microlens projection lithography, an array of microlenses (diameter d = 1−1000 μm) reduces a common, centimeter-scale pattern in an illuminated mask to a corresponding pattern of micrometer-scale images in its image plane. The pattern of intensity projected by the array of microlenses depends on the shape and gray-level distribution of the pattern on the illuminated mask and on the shape and pattern of the lenses. The distribution of intensity in the microimages could be adjusted using gray-scale masks. After the recording of this intensity distribution in layers of photoresist and developing, the developed resist showed arrays of 3D microstructures over areas larger than 10 cm2. We used these arrays of 3D microstructures as masters and cast transparent elastomer onto them to generate complementary replicas. For a specific microlens array and a fixed light source, the profile of the 3D microstructures generated by this method depended on the pattern on the illuminated mask and on the distance of the mask from the lens array. An appropriate mask with noncircular, gray-level patterns generated arrays of 3D microstructures that acted as lenses. This technique generates arrays of noncircular microlenses over areas larger than 10 cm2 in a single exposure.
Nutritional epidemiology today is characterized by “big data.” The last 50 years have seen an accumulation of numerous large-scale prospective studies as well as countless smaller epidemiologic studies of varying quality, providing us with a wealth of information on the dietary underpinnings of a wide range of health outcomes, particularly chronic diseases. Such a profusion of data creates a need to summarize findings into a cohesive body of evidence. Systematic reviews, carried out by following a predefined, systematic, reproducible methodology, constitute the preferred method of summarizing literature in nutritional epidemiology. These are usually divided into two categories on the basis of how data from the individual studies are summarized. If the review provides a qualitative summary of evidence, it is simply called a systematic review. If, on the other hand, a review quantitatively summarizes individual study results into one effect estimate, it is called a meta-analysis. Several such summaries of evidence have shown that diets characterized by high intakes of plant-source foods (e.g., whole grains, fruits, vegetables, nuts, tea, and coffee) or high intakes of fish and low-fat dairy, in addition to low intakes of certain animal-source foods (e.g., red and processed meats), sugar-sweetened beverages, and refined grains, are associated with a reduced risk of several chronic diseases, including cardiovascular disease, diabetes, obesity, and certain cancers.1–4 Although the concept of systematically reviewing and summarizing scientific evidence dates back to the early 20th century, its introduction into the field of epidemiology has been relatively recent.5 Despite this, developments in this methodology within the field of epidemiology have advanced rapidly, with the number of systematic reviews and meta-analyses published increasing at an astronomical rate. A PubMed search with the search strategy [“meta-analysis” or “systematic reviews”] results in 12,403 citations in 2013 alone, compared with just 1 citation in …
This paper describes a simple, microscale method for generating and evaluating libraries of derivatives of poly(acrylic acid) (pAA) that present mixtures of side chains that influence their biological activity. The method is based on the one-step conversion of poly(acrylic anhydride) (pAAn) to linear polymers presenting multiple units of R on side chains, pAA(R): the polymers are obtained by ultrasonication of a suspension of pAAn and aqueous RNH2 contained in a 250-μL well of a microtiter plate. Using this method, derivatives of pAA having N-acetylneuraminic acid (NeuAc-L-NH2) as a side chain, pAA(NeuAc-L), were generated and assayed for ability to inhibit hemagglutination (HAI) of chicken erythrocytes by influenza virus A (X-31); the constant ( ) describing this inhibition is calculated on the basis of the concentration of NeuAc groups in solution, rather than the concentration of polymer molecules. Co-polymeric pAA(NeuAc-Ln; Ln = different linking groups) with a range of mole fractions of NeuAc-L-NH2 (χNeuAc-L = 0.02−0.11) exhibited HAI activities with values between 27 and 0.30 μM. Using combinations of NeuAc-L-NH2 and one of 26 different primary amines RNH2, a variety of ter-polymeric pAA(NeuAc-L; R) (χNeuAc-L ∼ 0.05; χR ∼ 0.06) were also generated and assayed. Certain ter-polymers yielded values of that were lower by a factor of ∼104 than that of the parent co-polymeric pAA(NeuAc-L): the most active inhibitor was pAA(NeuAc-L; l-3-(2'-naphthyl)alanine)) ( ≈ 0.5 nM). Typically, the incorporation of hydrophobicespecially aromaticside chains enhanced activities. These polymers (pAA(NeuAc-L; R)) belong to a new class of polymeric, polyvalent sialosides that are potent inhibitors of the adsorption of influenza virus to erythrocytes. They were active with only low to moderate levels of incorporation of functional groups into the side chains: χNeuAc-L ∼ 0.05; χR ∼ 0.06.
The modeling of stresses generated during the growth of thin silicon sheets at high speeds is an important part of the EFG technique since the experimental measurement of the stresses is difficult and prohibitive. The residual stresses which arise in such a growth process lead to serious problems which make thin Si ribbons unsuitable for fabrication. The constitutive behavior is unrealistic because at high temperature (close to the melting point) Si exhibits considerable creep which significantly relaxes the residual stresses. The effect of creep on the residual stresses generated during the growth of Si sheets at high speeds was addressed and the basic qualitative effect of creep are reported.
