Adhesion transition of flexible sheets Evans, Arthur A; Lauga, Eric
Physical review. E, Statistical, nonlinear, and soft matter physics,
06/2009, Letnik:
79, Številka:
6 Pt 2
Journal Article
Odprti dostop
Intermolecular forces are known to precipitate adhesion events between solid bodies. Inspired by a macroscale experiment showing the hysteretic adhesion of a piece of flexible tape over a plastic ...substrate, we develop here a model of far-field dry adhesion between two flexible sheets interacting via a power-law potential. We show that phase transitions from unadhered to adhered states occur as dictated by a dimensionless bending parameter representing the ratio of interaction strength to bending stiffness. The order of the adhesion transitions, as well as their hysteretic nature, is shown to depend on the form of the interaction potential between the flexible sheets. When three or more sheets interact, additional geometrical considerations determine the hierarchical or sequential nature of the adhesion transitions.
The capillary assembly of stimulus-responsive hydrogel particles with programmed multipolar interactions defined by their prescribed three-dimensional (3D) shapes is demonstrated. Low-energy bending ...deformations of the particles, driven by surface tension, modifies the interactions between particles, while their temperature-dependent swelling enables switchable assembly.
The capillary assembly of stimulus-responsive hydrogel particles with programmed multipolar interactions defined by their prescribed three-dimensional (3D) shapes is demonstrated.
Abstract
Increasing the long-term survival of memory T cells after immunization is key to a successful vaccine. In the past, the generation of large numbers of memory T cells in vivo has been ...difficult because Ag-stimulated T cells are susceptible to activation-induced cell death. Previously, we reported that OX40 engagement resulted in a 60-fold increase in the number of Ag-specific CD4+ memory T cells that persisted 60 days postimmunization. In this report, we used the D011.10 adoptive transfer model to examine the kinetics of Ag-specific T cell entry into the peripheral blood, the optimal route of administration of Ag and αOX40, and the Ag-specific Ab response after immunization with soluble OVA and αOX40. Finally, we compared the adjuvant properties of αOX40 to those of αCTLA-4. Engagement of OX-40 in vivo was most effective when the Ag was administered s.c. Time course studies revealed that it was crucial for αOX40 to be delivered within 24–48 h after Ag exposure. Examination of anti-OVA Ab titers revealed a 10-fold increase in mice that received αOX40 compared with mice that received OVA alone. Both αOX40 and αCTLA-4 increased the percentage of OVA-specific CD4+ T cells early after immunization (day 4), but αOX40-treated mice had much higher percentages of OVA-specific memory CD4+ T cells from days 11 to 29. These studies demonstrate that OX40 engagement early after immunization with soluble Ag enhances long-term T cell and humoral immunity in a manner distinct from that provided by blocking CTLA-4.
The transmission of solar radiation within the crop canopies of oilseed rape is decreased both by the plant's yellow petals during flowering, and by the horizontal posture of the pods once they are ...formed. The significance of each of these morphologies was assessed, in the 1991/92 and 1992/93 growing seasons, by comparing the performances of an apetalous breeding line (N-o-112) and one with erectophile pods (N-5-130) with two conventional commercial genotypes (Falcon and Tapidor). The apetalous floral layer of line N-o-112 reflected and absorbed significantly less radiation than those of the conventional, petalled genotypes. This resulted in a greater transmission of photosynthetically active radiation (PAR) to the leaf and bract canopy situated below. At peak flowering, 70% more PAR was transmitted through the apetalous floral layer. The erectophile pods of line N-5-130 were angled 20–25° further from the horizontal than the conventional genotypes. The extinction coefficient (K) of its pod layer during late pod growth ranged from 0·35 to 0·44 as compared to 0·45 to 0·55 in the commercial varieties. Line N-5-130 carried a greater proportion of its total fertile pod number in the lower regions of the pod canopy compared to the two conventional genotypes. It also had a greater overall mean number of seeds per pod, and the number decreased proportionately less with depth in the canopy. The line was thus better able to maintain a higher photosynthetic area and to sustain pod and seed growth at the lower levels of the crop canopy than the conventional, commercial varieties. The potential physiological effects of apetalous flowers and erectophile pods are considered to be sufficiently beneficial for their introgression into near-isogenic lines to be pursued.
Although broadly admired for its aesthetic qualities, the art of origami is now being recognized also as a framework for mechanical metamaterial design. Working with the Miura-ori tessellation, we ...find that each unit cell of this crease pattern is mechanically bistable, and by switching between states, the compressive modulus of the overall structure can be rationally and reversibly tuned. By virtue of their interactions, these mechanically stable lattice defects also lead to emergent crystallographic structures such as vacancies, dislocations, and grain boundaries. Each of these structures comes from an arrangement of reversible folds, highlighting a connection between mechanical metamaterials and programmable matter. Given origami's scale-free geometric character, this framework for metamaterial design can be directly transferred to milli-, micro-, and nanometer-size systems.
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