Origami, the art of paper folding, is a technologically transformative art with applications at many length scales from material microstructure design to space deployable structures. The ...transformation of a two-dimensional fold pattern to a three-dimensional structure makes origami a practical basis for deployability, light-weight materials, and self-actuation. In order to predict the complex motions of origami structures including path traversal of instabilities, accurate and efficient modeling techniques are required. While many approaches consider rigid facets and/or linear approximations to rotations, a truss and hinge finite element method is presented here within a global coordinate system framework to accurately capture the geometric nonlinearities while allowing for small to moderate facet deformation. Accurately capturing these modes of deformation is critical toward understanding the elastic energetic states required for design and analysis of multistable origami structures and mechanical metamaterials. Particular formulation developments that we address to solve origami mechanics problems include formulation of a continuous and differentiable fold angle, strategy for selecting fold path off the flat state, and integration of common numerical approaches important for origami (large rotation formulation, enforcement of periodic boundary conditions for tessellations, arc-length continuation method for solving highly nonlinear loading paths, and a perturbation strategy for handling bifurcations). After formulating this truss finite element method, we verify our modified finite element method on well-studied structures. The waterbomb fold pattern is studied, and the interplay of the stretching and folding energies are considered toward design of a bistable structure that exhibits a fold based snap-through instability. This study is followed by analysis of a cylindrical network of waterbombs (axial periodicity) that exhibits a stretch driven instability. Lastly, a tessellated square twist pattern, exhibiting multiple bifurcations off the flat state is presented that employs all aspects of our numerical method.
A new design methodology for producing highly miniaturized patch antennas is introduced. The methodology uses complementary split-ring resonators placed horizontally between the patch and the ground ...plane. By optimizing the geometry of the split rings, sub-wavelength resonance of the patch antenna can be achieved with a good impedance match and radiation characteristics comparable to those of a traditional patch antenna on a finite ground plane. Construction of the optimized antenna is straightforward, requiring only the sandwiching of two etched circuit boards. High levels of miniaturization are demonstrated through simulations and experiments, with reductions of a factor of more than four in transverse dimension achieved for a circular patch resonant at 2.45 GHz. Although miniaturization is accompanied by a decrease in antenna radiation efficiency and a loss of fractional bandwidth, antenna performance remains acceptable even for a 1/16 reduction in patch area.
A foldable frequency selective surface (FSS) is introduced that may be tuned by changing the folding state. The FSS comprises periodic elements arranged in an origami-like fashion on a dielectric ...sheet. By folding and unfolding the FSS, the interaction with the incident field and the mutual interactions between the elements may be altered, resulting in a shift in resonance frequency. A sample design of a tunable FSS folded into a chevron pattern and decorated with cross-shaped copper prints allows a 19% shift of resonant frequency with a change in folding angle of 60°.
To examine movement and morphologic alteration in the menisci during knee flexion.
Twenty healthy knees were imaged at 0 degrees, 45 degrees, and 90 degrees of passive non-weight-bearing flexion in ...the sagittal plane with MR. In each meniscus, posterior movement distance during knee flexion and the ratio of anteroposterior (a.p.) diameter at flexion to that at extension were calculated.
Each meniscus moved posteriorly during knee flexion. Movement was greater in the anterior horn than in the posterior horn, and greater in the medial meniscus than in the lateral meniscus (p<0.05). The a.p. diameter of each meniscus was reduced at flexion (p<0.05).
Knee flexion normally leads to posterior movement and shortening of the a.p. diameter of the menisci, which may be related to the positioning and curvature of femoral condyles at the femorotibial contact point at knee flexion.
A new methodology for designing metamaterial-inspired antennas using an in situ optimization technique is introduced. Through this approach, an optimization tool such as a genetic algorithm is used ...to design a metamaterial pattern adjacent to an antenna to enhance the antenna's performance. As an example, the technique is used for miniaturization purposes where a loop antenna initially resonant at 2.45 GHz is made resonant at 960 MHz, providing a sevenfold reduction in antenna area over a conventional loop designed to operate at 960 MHz.
The purpose of this study was to assess the degree of meniscal movement during knee flexion on MR images and to correlate it with the severity of cartilage damage in the femorotibial joint.
Sagittal ...MR images were obtained at extension and 45 degrees of flexion in 35 knees. A shortening ratio in the distance between the anterior and posterior horns at 0-45 degrees of knee flexion was calculated in each meniscus and was correlated with the degree of cartilage abnormality in the femorotibial joint.
The shortening ratio of the meniscus was reduced in knees with cartilage abnormality in the femorotibial joint. The shortening ratio of the medial meniscus was inversely correlated with the degree of cartilage abnormality in the medial femoral condyle and with that in the medial tibial plateau.
Restricted shortening ratio of the meniscus may be related to cartilage damage in the femorotibial joint.
Session 1A (Panel Session) Fuchi, K.; Hughes, P.; Hünke, H. ...
International Conference on Software Engineering: Proceedings of the 7th international conference on Software engineering : Orlando, Florida, United States; 26-29 Mar. 1984,
03/1984
Conference Proceeding
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