다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Annual review of condensed matter physics

Analysis of Development Edited by Prof Benjamin H Willier, Prof Paul A Weiss and Prof Viktor Hamburger Pp xii + 735 (Philadelphia and London: W B Saunders Company, 1955) 105s

Mechanisms of Development

Seminars in cell & developmental biology.

We provide the theoretical basis of calorimetry for a class of active particles subject to thermal noise. Simulating AC-calorimetry, we numerically evaluate the heat capacity of run-and-tumble particles in double-well and in periodic potentials, and of systems with a flashing potential. Low-temperature Schottky-like peaks show the role of activity and indicate shape transitions, while regimes of negative heat capacity appear at higher propulsion speeds. From there, a significant increase in heat capacities of active systems may be inferred at low temperatures, as well as the possibility of diagnostic tools for the activity of self-motile artificial or biomimetic systems based on heat capacity measurements. 

/pdf/calorimetry-for-active-systems-2nwqye6i.pdf

Calorimetry for active systems

Liquid crystal elastomers (LCEs) can undergo large reversible contractions along their nematic director upon heating or illumination. A spatially patterned director within a flat LCE sheet thus encodes a pattern of contraction on heating, which can morph the sheet into a curved shell, akin to how a pattern of growth sculpts a developing organism. Here we consider, theoretically, numerically and experimentally, patterns constructed from regions of radial and circular director, which, in isolation, would form cones and anticones. The resultant surfaces contain curved ridges with sharp V-shaped cross-sections, associated with the boundaries between regions in the patterns. Such ridges may be created in positively and negatively curved variants and, since they bear Gauss curvature (quantified here via the Gauss-Bonnet theorem), they cannot be flattened without energetically prohibitive stretch. Our experiments and numerics highlight that, although such ridges cannot be flattened isometrically, they can deform isometrically by trading the (singular) curvature of the V angle against the (finite) curvature of the ridge line. Furthermore, in finite thickness sheets, the sharp ridges are inevitably non-isometrically blunted to relieve bend, resulting in a modest smearing out of the encoded singular Gauss curvature. We close by discussing the use of such features as actuating linear features, such as probes, tongues and limbs, and highlighting the similarities between these patterns of shape change and those found during the morphogenesis of several biological systems.

Shape programming lines of concentrated Gaussian curvature

Liquid crystal elastomers (LCEs) can undergo large reversible contractions along their nematic director upon heating or illumination. A spatially patterned director within a flat LCE sheet, thus, encodes a pattern of contraction on heating, which can morph the sheet into a curved shell, akin to how a pattern of growth sculpts a developing organism. Here, we consider theoretically, numerically, and experimentally patterns constructed from regions of radial and circular director, which, in isolation, would form cones and anticones. The resultant surfaces contain curved ridges with sharp V-shaped cross sections, associated with the boundaries between regions in the patterns. Such ridges may be created in positively and negatively curved variants and, since they bear Gauss curvature (quantified here via the Gauss–Bonnet theorem), they cannot be flattened without energetically prohibitive stretch. Our experiments and numerics highlight that, although such ridges cannot be flattened isometrically, they can deform isometrically by trading the (singular) curvature of the V angle against the (finite) curvature of the ridge line. Furthermore, in finite thickness sheets, the sharp ridges are inevitably non-isometrically blunted to relieve bend, resulting in a modest smearing out of the encoded singular Gauss curvature. We close by discussing the use of such features as actuating linear features, such as probes, tongues, and grippers. We speculate on similarities between these patterns of shape change and those found during the morphogenesis of several biological systems.

Actomyosin networks play essential roles in many cellular processes including intracellular transport, cell division, and cell motility, exhibiting a myriad of spatiotemporal patterns. Despite extensive research, how the interplay between network mechanics, turnover and geometry leads to these different patterns is not well understood. We focus on the size-dependent behavior of contracting actomyosin networks in the presence of turnover, using a reconstituted system based on cell extracts encapsulated in water-in-oil droplets. We find that the system can self-organize into different global contraction patterns, exhibiting persistent contractile flows in smaller droplets and periodic contractions in the form of waves or spirals in larger droplets. The transition between continuous and periodic contraction occurs at a characteristic length scale that is inversely dependent on the network contraction rate. These dynamics are recapitulated by a theoretical model, which considers the coexistence of different local density-dependent mechanical states with distinct rheological properties. The model shows how large-scale contractile behaviors emerge from the interplay between network percolation essential for long-range force transmission and rearrangements due to advection and turnover. Our findings thus demonstrate how varied contraction patterns can arise from the same microscopic constituents, without invoking specific biochemical regulation, merely by changing the system’s geometry.

Size-dependent transition from steady contraction to waves in actomyosin networks with turnover

A self-propelled particle is a basic ingredient of active matter. Any handle on its noise characteristics is thus of both fundamental and applied interest. In this paper, we show that geometric constraints are a route to affect the emergent noise properties of a single active particle, thus demonstrating that seemingly different active particle classes are equivalent to each other. Specifically, we find that the chiral active Brownian motion of a self-propelled particle seen in two-dimensions switches to a run-and-tumble like motion when confined to a quasi-one-dimensional channel. Our analysis of this switching behavior connects the resulting active stochastic dynamics to that of a two-state molecular motor. The emergent tuning of active noise characteristics by unbiased external driving, as we demonstrate here, is illustrative of generic mechanisms of active noise control in other systems. 

/pdf/geometric-constraints-alter-the-emergent-dynamics-of-an-3kce690u.pdf

Geometric constraints alter the emergent dynamics of an active particle

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Shape programming lines of concentrated Gaussian curvature

Shape programming lines of concentrated Gaussian curvature

Size-dependent transition from steady contraction to waves in actomyosin networks with turnover

Geometric constraints alter the emergent dynamics of an active particle