The difficulty of folding self-folding origami

Why is it difficult to refold a previously folded sheet of paper? We show that even crease patterns with only one designed folding motion inevitably contain an exponential number of `distractor' folding branches accessible from a bifurcation at the flat state. Consequently, refolding a sheet requires finding the ground state in a glassy energy landscape with an exponential number of other attractors of higher energy, much like in models of protein folding (Levinthal's paradox) and other NP-hard satisfiability (SAT) problems. As in these problems, we find that refolding a sheet requires actuation at multiple carefully chosen creases. We show that seeding successful folding in this way can be understood in terms of sub-patterns that fold when cut out (`folding islands'). Besides providing guidelines for the placement of active hinges in origami applications, our results point to fundamental limits on the programmability of energy landscapes in sheets.Comment: 8 pages, 5 figure

Learned multi-stability in mechanical networks

We contrast the distinct frameworks of materials design and physical learning in creating elastic networks with desired stable states. In design, the desired states are specified in advance and material parameters can be optimized on a computer with this knowledge. In learning, the material physically experiences the desired stable states in sequence, changing the material so as to stabilize each additional state. We show that while designed states are stable in networks of linear Hookean springs, sequential learning requires specific non-linear elasticity. We find that such non-linearity stabilizes states in which strain is zero in some springs and large in others, thus playing the role of Bayesian priors used in sparse statistical regression. Our model shows how specific material properties allow continuous learning of new functions through deployment of the material itself

Which is more cost‐effective under the MELD system: primary liver transplantation, or salvage transplantation after hepatic resection or after loco‐regional therapy for hepatocellular carcinoma within Milan criteria?

AbstractObjectiveThe optimal strategy for treating hepatocellular carcinoma (HCC), a disease with increasing incidence, in patients with Child–Pugh class A cirrhosis has long been debated. This study evaluated the cost‐effectiveness of hepatic resection (HR) or locoregional therapy (LRT) followed by salvage orthotopic liver transplantation (SOLT) vs. that of primary orthotopic liver transplantation (POLT) for HCC within the Milan Criteria.MethodsA Markov‐based decision analytic model simulated outcomes, expressed in costs and quality‐adjusted life years (QALYs), for the three treatment strategies. Baseline parameters were determined from a literature review. Sensitivity analyses tested model strength and parameter variability.ResultsBoth HR and LRT followed by SOLT were associated with earlier recurrence, decreased survival, increased costs and decreased quality of life (QoL), whereas POLT resulted in decreased recurrence, increased survival, decreased costs and increased QoL. Specifically, HR/SOLT yielded 3.1QALYs (at US$96000/QALY) and LRT/SOLT yielded 3.9QALYs (at US$74000/QALY), whereas POLT yielded 5.5QALYs (at US$52000/QALY). Sensitivity analyses supported these findings at clinically meaningful probabilities.ConclusionsUnder the Model for End‐stage Liver Disease (MELD) system, in patients with HCC within the Milan Criteria, POLT increases survival and QoL at decreased costs compared with HR or LRT followed by SOLT. Therefore, POLT is the most cost‐effective strategy for the treatment of HCC

Which is more cost‐effective under the MELD system: primary liver transplantation, or salvage transplantation after hepatic resection or after loco‐regional therapy for hepatocellular carcinoma within Milan criteria?

AbstractObjectiveThe optimal strategy for treating hepatocellular carcinoma (HCC), a disease with increasing incidence, in patients with Child–Pugh class A cirrhosis has long been debated. This study evaluated the cost‐effectiveness of hepatic resection (HR) or locoregional therapy (LRT) followed by salvage orthotopic liver transplantation (SOLT) vs. that of primary orthotopic liver transplantation (POLT) for HCC within the Milan Criteria.MethodsA Markov‐based decision analytic model simulated outcomes, expressed in costs and quality‐adjusted life years (QALYs), for the three treatment strategies. Baseline parameters were determined from a literature review. Sensitivity analyses tested model strength and parameter variability.ResultsBoth HR and LRT followed by SOLT were associated with earlier recurrence, decreased survival, increased costs and decreased quality of life (QoL), whereas POLT resulted in decreased recurrence, increased survival, decreased costs and increased QoL. Specifically, HR/SOLT yielded 3.1QALYs (at US$96000/QALY) and LRT/SOLT yielded 3.9QALYs (at US$74000/QALY), whereas POLT yielded 5.5QALYs (at US$52000/QALY). Sensitivity analyses supported these findings at clinically meaningful probabilities.ConclusionsUnder the Model for End‐stage Liver Disease (MELD) system, in patients with HCC within the Milan Criteria, POLT increases survival and QoL at decreased costs compared with HR or LRT followed by SOLT. Therefore, POLT is the most cost‐effective strategy for the treatment of HCC

Hysteresis from Multiscale Porosity: Modeling Water Sorption and Shrinkage in Cement Paste

Cement paste has a complex distribution of pores and molecular-scale spaces. This distribution controls the hysteresis of water sorption isotherms and associated bulk dimensional changes (shrinkage). We focus on two locations of evaporable water within the fine structure of pastes, each having unique properties, and we present applied physics models that capture the hysteresis by dividing drying and rewetting into two related regimes based on relative humidity (RH). We show that a continuum model, incorporating a pore-blocking mechanism for desorption and equilibrium thermodynamics for adsorption, explains well the sorption hysteresis for a paste that remains above approximately 20% RH. In addition, we show with molecular models and experiments that water in spaces of ≲1  nm width evaporates below approximately 20% RH but reenters throughout the entire RH range. This water is responsible for a drying shrinkage hysteresis similar to that of clays but opposite in direction to typical mesoporous glass. Combining the models of these two regimes allows the entire drying and rewetting hysteresis to be reproduced accurately and provides parameters to predict the corresponding dimensional changes. The resulting model can improve the engineering predictions of long-term drying shrinkage accounting also for the history dependence of strain induced by hysteresis. Alternative strategies for quantitative analyses of the microstructure of cement paste based on this mesoscale physical model of water content within porous spaces are discussed.Portland Cement AssociationNational Ready Mixed Concrete Association (Research and Education Foundation)Schlumberger Foundatio

Effects of eight neuropsychiatric copy number variants on human brain structure

Many copy number variants (CNVs) confer risk for the same range of neurodevelopmental symptoms and psychiatric conditions including autism and schizophrenia. Yet, to date neuroimaging studies have typically been carried out one mutation at a time, showing that CNVs have large effects on brain anatomy. Here, we aimed to characterize and quantify the distinct brain morphometry effects and latent dimensions across 8 neuropsychiatric CNVs. We analyzed T1-weighted MRI data from clinically and non-clinically ascertained CNV carriers (deletion/duplication) at the 1q21.1 (n = 39/28), 16p11.2 (n = 87/78), 22q11.2 (n = 75/30), and 15q11.2 (n = 72/76) loci as well as 1296 non-carriers (controls). Case-control contrasts of all examined genomic loci demonstrated effects on brain anatomy, with deletions and duplications showing mirror effects at the global and regional levels. Although CNVs mainly showed distinct brain patterns, principal component analysis (PCA) loaded subsets of CNVs on two latent brain dimensions, which explained 32 and 29% of the variance of the 8 Cohen’s d maps. The cingulate gyrus, insula, supplementary motor cortex, and cerebellum were identified by PCA and multi-view pattern learning as top regions contributing to latent dimension shared across subsets of CNVs. The large proportion of distinct CNV effects on brain morphology may explain the small neuroimaging effect sizes reported in polygenic psychiatric conditions. Nevertheless, latent gene brain morphology dimensions will help subgroup the rapidly expanding landscape of neuropsychiatric variants and dissect the heterogeneity of idiopathic conditions

Battery degradation, and sorption and transport in porous materials

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 111-126).Porous media offer many interesting problems in physics and engineering due to the interaction of phase transitions, surface effects and transport. In this thesis I examine two such problems: the degradation of lithium-ion batteries, and sorption and transport of fluids in porous materials. The dominant capacity fade mechanism in many lithium-ion batteries is the loss of cyclable lithium to a solid-electrolyte interphase layer on the surface of the negative electrode. I develop a single-particle model of this fade mechanism, based on diffusion of the reacting species through the growing layer and reaction at the surface of the active material. This analytical model is justified by comparison with a computational porous electrode model. Temperature is identified as the most important variable influencing the capacity fade rate, and the model is able to make predictions for accelerated aging tests as well as the effect of mismatched internal resistances in battery packs. The quantity of a fluid taken up by a porous material as a function of the partial pressure of the fluid relative to saturation can be used to measure the pore size distribution of the material. However, hysteresis between the wetting and drying paths complicates the interpretation of experimental results. I present a unified model of hysteresis that accounts for both single-pore and network effects, enabling the calculation of not only the pore size distribution but also a parameter measuring the connectivity between large and small pores. I then use the ideas of the model to examine drying shrinkage in hardened cement paste, demonstrating that the hysteresis in this shrinkage is primarily due to water inserted between molecular layers in calcium-silicate-hydrate. Finally, I outline a model of transport of a sorbing fluid with hysteresis, and suggest possible extensions to allow quantitative comparison with experimental results.by Matthew Bede Pinson.Ph. D