270 research outputs found
Multimodal Surface Instabilities in Curved FilmâSubstrate Structures
Structures of thin films bonded on thick substrates are abundant in biological systems and engineering applications. Mismatch strains due to expansion of the films or shrinkage of the substrates can induce various modes of surface instabilities such as wrinkling, creasing, period doubling, folding, ridging, and delamination. In many cases, the film-substrate structures are not flat but curved. While it is known that the surface instabilities can be controlled by film-substrate mechanical properties, adhesion and mismatch strain, effects of the structures' curvature on multiple modes of instabilities have not been well understood. In this paper, we provide a systematic study on the formation of multimodal surface instabilities on film-substrate tubular structures with different curvatures through combined theoretical analysis and numerical simulation. We first introduce a method to quantitatively categorize various instability patterns by analyzing their wave frequencies using fast Fourier transform (FFT). We show that the curved film-substrate structures delay the critical mismatch strain for wrinkling when the system modulus ratio between the film and substrate is relatively large, compared with flat ones with otherwise the same properties. In addition, concave structures promote creasing and folding, and suppress ridging. On the contrary, convex structures promote ridging and suppress creasing and folding. A set of phase diagrams are calculated to guide future design and analysis of multimodal surface instabilities in curved structures. Keywords: instability, curvature, filmâsubstrate structure, morphogenesisUnited States. Office of Naval Research (N00014-14-1-0528)Massachusetts Institute of Technology. Institute for Soldier NanotechnologiesNational Science Foundation (U.S.) (CMMI1253495
Chinese-Iranian Mutual Strategic Perceptions
This article analyzes Sino-Iranian relations and mutual strategic perceptions, highlighting several types of tension in Sino-Iranian ties alongside areas of deeper cooperation. We examine in particular the policy debates about China between conservatives and reformists within Iran, and we compare their views of China to the views of Iran held by Chinese commentators. To that end, we extensively survey both the official media and scholarly literature in Farsi and in Chinese, since each strand reveals different sentiments and is accorded a different degree of openness
On the Elastic Stability of Folded Rings in Circular and Straight States
Single-loop elastic rings can be folded into multi-loop equilibrium
configurations. In this paper, the stability of several such multi-loop states
which are either circular or straight are investigated analytically and
illustrated by experimental demonstrations. The analysis ascertains stability
by exploring variations of the elastic energy of the rings for admissible
deformations in the vicinity of the equilibrium state. The approach employed is
the conventional stability analysis for elastic conservative systems which
differs from most of the analyses that have been published on this class of
problems, as will be illustrated by reproducing and elaborating on several
problems in the literature. In addition to providing solutions to two basic
problems, the paper analyses and demonstrates the stability of six-sided rings
that fold into straight configurations
Genome-wide analysis of aberrant methylation in human breast cancer cells using methyl-DNA immunoprecipitation combined with high-throughput sequencing
<p>Abstract</p> <p>Background</p> <p>Cancer cells undergo massive alterations to their DNA methylation patterns that result in aberrant gene expression and malignant phenotypes. However, the mechanisms that underlie methylome changes are not well understood nor is the genomic distribution of DNA methylation changes well characterized.</p> <p>Results</p> <p>Here, we performed methylated DNA immunoprecipitation combined with high-throughput sequencing (MeDIP-seq) to obtain whole-genome DNA methylation profiles for eight human breast cancer cell (BCC) lines and for normal human mammary epithelial cells (HMEC). The MeDIP-seq analysis generated non-biased DNA methylation maps by covering almost the entire genome with sufficient depth and resolution. The most prominent feature of the BCC lines compared to HMEC was a massively reduced methylation level particularly in CpG-poor regions. While hypomethylation did not appear to be associated with particular genomic features, hypermethylation preferentially occurred at CpG-rich gene-related regions independently of the distance from transcription start sites. We also investigated methylome alterations during epithelial-to-mesenchymal transition (EMT) in MCF7 cells. EMT induction was associated with specific alterations to the methylation patterns of gene-related CpG-rich regions, although overall methylation levels were not significantly altered. Moreover, approximately 40% of the epithelial cell-specific methylation patterns in gene-related regions were altered to those typical of mesenchymal cells, suggesting a cell-type specific regulation of DNA methylation.</p> <p>Conclusions</p> <p>This study provides the most comprehensive analysis to date of the methylome of human mammary cell lines and has produced novel insights into the mechanisms of methylome alteration during tumorigenesis and the interdependence between DNA methylome alterations and morphological changes.</p
Transcriptional regulation of connective tissue growth factor by sphingosine 1-phosphate in rat cultured mesangial cells
AbstractConnective tissue growth factor (CTGF) is induced by transforming growth factor-β (TGF-β) via Smad activation in mesangial cells. We recently reported that sphingosine 1-phosphate (S1P) induces CTGF expression in rat cultured mesangial cells. However, the mechanism by which S1P induces CTGF expression is unknown. The present study revealed that S1P-induced CTGF expression is mediated via pertussis toxin-insensitive pathways, which are involved in the activation of small GTPases of the Rho family and protein kinase C. We also showed by luciferase reporter assays and chromatin immunoprecipitation that S1P induces CTGF expression via Smad activation as TGF-β does
Multiple equilibrium states of a curved-sided hexagram:Part I-Stability of states
The stability of the multiple equilibrium states of a hexagram ring with six
curved sides is investigated. Each of the six segments is a rod having the same
length and uniform natural curvature. These rods are bent uniformly in the
plane of the hexagram into equal arcs of 120deg or 240deg and joined at a cusp
where their ends meet to form a 1-loop planar ring. The 1-loop rings formed
from 120deg or 240deg arcs are inversions of one another and they, in turn, can
be folded into a 3-loop straight line configuration or a 3-loop ring with each
loop in an "8" shape. Each of these four equilibrium states has a uniform
bending moment. Two additional intriguing planar shapes, 6-circle hexagrams,
with equilibrium states that are also uniform bending, are identified and
analyzed for stability. Stability is lost when the natural curvature falls
outside the upper and lower limits in the form of a bifurcation mode involving
coupled out-of-plane deflection and torsion of the rod segments. Conditions for
stability, or lack thereof, depend on the geometry of the rod cross-section as
well as its natural curvature. Rods with circular and rectangular
cross-sections will be analyzed using a specialized form of Kirchhoff rod
theory, and properties will be detailed such that all four of the states of
interest are mutually stable. Experimental demonstrations of the various states
and their stability are presented. Part II presents numerical simulations of
transitions between states using both rod theory and a three-dimensional finite
element formulation, includes confirmation of the stability limits established
in Part I, and presents additional experimental demonstrations and
verifications
Stiffness Change for Reconfiguration of Inflated Beam Robots
Active control of the shape of soft robots is challenging. Despite having an
infinite number of passive degrees of freedom (DOFs), soft robots typically
only have a few actively controllable DOFs, limited by the number of degrees of
actuation (DOAs). The complexity of actuators restricts the number of DOAs that
can be incorporated into soft robots. Active shape control is further
complicated by the buckling of soft robots under compressive forces; this is
particularly challenging for compliant continuum robots due to their long
aspect ratios. In this work, we show how variable stiffness can enable shape
control of soft robots by addressing these challenges. Dynamically changing the
stiffness of sections along a compliant continuum robot can selectively
"activate" discrete joints. By changing which joints are activated, the output
of a single actuator can be reconfigured to actively control many different
joints, thus decoupling the number of controllable DOFs from the number of
DOAs. We demonstrate embedded positive pressure layer jamming as a simple
method for stiffness change in inflated beam robots, its compatibility with
growing robots, and its use as an "activating" technology. We experimentally
characterize the stiffness change in a growing inflated beam robot and present
finite element models which serve as guides for robot design and fabrication.
We fabricate a multi-segment everting inflated beam robot and demonstrate how
stiffness change is compatible with growth through tip eversion, enables an
increase in workspace, and achieves new actuation patterns not possible without
stiffening
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