Mechanics of Fibrous Biological Materials With Hierarchical Chirality

2016 ◽  
Vol 83 (10) ◽  
Author(s):  
Huijuan Zhu ◽  
Takahiro Shimada ◽  
Jianshan Wang ◽  
Takayuki Kitamura ◽  
Xiqiao Feng

Chirality simultaneously exists at different length scales in many biological materials, e.g., climbing tendrils and bacterial flagella. It can transfer from lower structural levels to higher structural levels, which is tightly associated with the growth and assembly of biological materials. In this paper, a continuum mechanics model is presented for understanding the bottom–up transfer of chirality in fibrous biological materials. Basic physical mechanisms underlying the chirality transfer in biological world are revealed. It is demonstrated that the chirality of constituent elements at the microscale can induce the twisting of higher-level structures, which may further transfer into the macroscopic morphology in different manners, rendering the formation of hierarchically chiral structures in tissues or organs. The bottom–up transfer mechanism of chirality may provide a limit to the macroscopic size of biological materials through the accumulative contribution of twisting.

2018 ◽  
Vol 14 (6) ◽  
pp. 975-1001 ◽  
Author(s):  
DAVID A. HARPER

AbstractThis introduction canvasses broad themes relating to the nexus of innovation and institutions. It first examines the notion of a “new combination” – a core analytical concept in economic theories of innovation and explanations of emergent novelty through bottom-up processes. Following Schumpeter, different theorists have made different claims about the composition and structure of new combinations. Possible constituent elements include factors of production, capital goods, routines, information, ideas, technologies, and property rights. The article then looks synoptically at the institutional dimensions of innovation from alternative perspectives that focus upon different kinds of institutional rules and policy solutions to innovation problems. Neoclassical and evolutionary approaches tend to emphasize specific policy interventions in markets to channel behavior toward particular desired outcomes, whereas institutional and Austrian approaches tend to focus upon general institutional rules (e.g. property and contract) that frame markets and innovation processes. Finally, this article summarizes the papers in the special issue.


2021 ◽  
Author(s):  
Michio Homma ◽  
Hiroyuki Terashima ◽  
Hiroaki Koiwa ◽  
Seiji Kojima

Bacterial flagella are the best-known rotational organelles in the biological world. The spiral-shaped flagellar filaments that extending from the cell surface rotate like a screw to create a propulsive force. At the base of the flagellar filament lies a protein motor that consists of a stator and a rotor embedded in the membrane. The stator is composed of two types of membrane subunits, PomA(MotA) and PomB(MotB), which are energy converters that assemble around the rotor to couple rotation with the ion flow. Recently, stator structures, where two MotB molecules are inserted into the center of a ring made of five MotA molecules, were reported. This structure inspired a model in which the MotA ring rotates around the MotB dimer in response to ion influx. Here, we focus on the Vibrio PomB plug region, which is involved in flagellar motor activation. We investigated the plug region using site-directed photo-crosslinking and disulfide crosslinking experiments. Our results demonstrated that the plug interacts with the extracellular short loop region of PomA, which is located between transmembrane helices 3 and 4. Although the motor stopped rotating after crosslinking, its function recovered after treatment with a reducing reagent that disrupted the disulfide bond. Our results support the hypothesis, which has been inferred from the stator structure, that the plug region terminates the ion influx by blocking the rotation of the rotor as a spanner. Importance The biological flagellar motor resembles a mechanical motor. It is composed of a stator and a rotor. The force is transmitted to the rotor by the gear-like stator movements. It has been proposed that the pentamer of MotA subunits revolves around the axis of the B subunit dimer in response to ion flow. The plug region of the B subunit regulates the ion flow. Here, we demonstrated that the ion flow was terminated by crosslinking the plug region of PomB with PomA. These findings support the rotation hypothesis and explain the role of the plug region in blocking the rotation of the stator unit.


2010 ◽  
Vol 278 (1705) ◽  
pp. 519-525 ◽  
Author(s):  
Zuoqi Zhang ◽  
Yong-Wei Zhang ◽  
Huajian Gao

Load-bearing biological materials such as shell, mineralized tendon and bone exhibit two to seven levels of structural hierarchy based on constituent materials (biominerals and proteins) of relatively poor mechanical properties. A key question that remains unanswered is what determines the number of hierarchical levels in these materials. Here we develop a quasi-self-similar hierarchical model to show that, depending on the mineral content, there exists an optimal level of structural hierarchy for maximal toughness of biocomposites. The predicted optimal levels of hierarchy and cooperative deformation across multiple structural levels are in excellent agreement with experimental observations.


Predictions have been made of the deformation and failure history of a pipe weldment using a finite element creep continuum damage mechanics model, which incorporates the characteristic material properties of the parent metal, the weld metal and heat-affected zone microstructures of the weldment. It is shown that the computer predictions are in close agreement with the results of large-scale pressure vessel tests, provided that the material characterization is carried out correctly, and that the constitutive equations which control the evolution of creep strain and damage, represent the dominant physical mechanisms present.


2021 ◽  
Author(s):  
Michio Homma ◽  
Hiroyuki Terashima ◽  
Hiroaki Koiwa ◽  
Seiji Kojima

AbstractBacterial flagella are the only real rotational motor organs in the biological world. The spiral-shaped flagellar filaments that extend from the cell surface rotate like a screw to create a propulsive force. The base of the flagellar filament has a protein motor consisting of a stator and a rotor embedded in the membrane. The motor part has stators composed of two types of membrane subunits, PomA(MotA) and PomB(MotB), which are energy converters coupled to the ion flow that assemble around the rotor. Recently, structures of the stator, in which two molecules of MotB stuck in the center of the MotA ring made of five molecules, were reported and a model in which the MotA ring rotates with respect to MotB, which is coupled to the influx of ions, was proposed. We focused on the Vibrio PomB plug region, which has been reported to control the activation of flagellar motors. We searched for the plug region, which is the interacting region, through site-directed photo-cross-linking and disulfide cross-linking experiments. Our results demonstrated that it interacts with the extracellular short loop region of PomA, which is between transmembrane 3 and 4. Although the motor halted following cross-linking, its function was recovered with a reducing reagent that disrupted the disulfide bond. Our results support the hypothesis, which has been inferred from the stator structure, that the plug region terminates the ion inflow by stopping the rotation of the rotor.ImportanceThe flagellar biological motor resembles a mechanical motor, which is composed of stator and rotor and where the rotational force is transmitted by gear-like movements. We hypothesized that the flagellar the rotation of stator that the pentamer of A subunits revolves around the axis of the B subunit dimer with ion flow. The plug region of the B subunit has been shown to regulate the ion flow. Herein, we demonstrated that the ion flow was terminated by the crosslinking between the plug region and the A subunit. These finding support the rotation hypothesis and explain the role of the plug region in terminating the rotation.


2007 ◽  
Vol 31 (1) ◽  
pp. 053-095 ◽  
Author(s):  
Seth Monahan

Critics have long viewed Mahler's Sixth Symphony in A Minor (1904) as the composer's consummate essay in musical tragedy or negativity, one with deeply personal implications. Its enormous finale draws together materials from all the preceding movements and enacts a terrible conflict ending in failure. Yet few studies have looked beneath the work's bombastic rhetorical-expressive surface to explore how its negativity might be reflected in its tonal, formal, and thematic processes. This study sets out to link that negative expressivity to a breakdown of what Adorno called the "novelistic" character of Mahler's symphonies. For Adorno, Mahler pioneered a new, emancipatory symphonic idiom, one that liberated its musical materials from the dictates of preconceived formal totalities. Unlike the Classical symphony, where the parts exist for the sake of a symmetrical, tightly knit whole, the "novel-symphony" follows no predetermined path. Instead, it unfolds according to the dictates of its constituent elements, realizing its unique form from the "bottom up" rather than the "top down."Yet (as Adorno suggests) in the finale of the Sixth this integrating totality returns with a vengeance. We can read the movement as a clash between Adorno's novelistic and Classical paradigms, a showdown between the impulsive freedom of certain recalcitrant thematic elements on the one hand, and the increasingly punitive demands of rigid minor-mode sonata on the other. This drama--one that caricaturizes "classicism" itself as a repressive or stifling force--plays out on both formal and thematic levels. Several writers have noted the claustrophobic effect created by Mahler's incessant recycling of certain key motives, an "inescapable" coherence in which the organicist imperatives of the grand tradition themselves become corrupt and, ultimately, corrosive. As these generic, subthematic particles proliferate, the movement's "novelistic" themes--those seeking to subvert the strict sonata--are systematically denuded of the differentiating features and dissolved beyond recognition. In the end, the movement's infamously brutal minor-mode conclusion reveals itself to be the culmination of a musical plot spanning the entire movement, one that gathers its many details into an inexorably tragic narrative whole.


Author(s):  
Hedayatollah Soltani Nezhad ◽  
Javad Hazeri

The objective of the investigation is to analyze the constituent elements of vertical agreements prohibited by Iran's competition law, in accordance with Chapter IX of the Law on the Implementation of General Policies and in accordance with Article 44 of the Constitution and, as set out in European Union competition law, Article 101 of the Treaty on the Functioning of the European Union. By vertical agreements it can be said that one of the types of agreements is wanted in the competition law. Any reference between natural or legal persons in the longitudinal direction (whether top to bottom or bottom up) that is not close to the consumer's interest is agreed. These agreements may include free clauses that are not compatible with the objectives of competition law. Methodologically, this is a documentary research close to comparative and legal hermeneutics. It is concluded that, to prohibit vertical agreements, they need to have the anti-competitive object or effect and also have a tangible impact on the closure of competition on the market.


2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Qiang Zhu ◽  
Suxi Wang ◽  
Xizu Wang ◽  
Ady Suwardi ◽  
Ming Hui Chua ◽  
...  

AbstractThe recent advancements in thermoelectric materials are largely credited to two factors, namely established physical theories and advanced materials engineering methods. The developments in the physical theories have come a long way from the “phonon glass electron crystal” paradigm to the more recent band convergence and nanostructuring, which consequently results in drastic improvement in the thermoelectric figure of merit value. On the other hand, the progresses in materials fabrication methods and processing technologies have enabled the discovery of new physical mechanisms, hence further facilitating the emergence of high-performance thermoelectric materials. In recent years, many comprehensive review articles are focused on various aspects of thermoelectrics ranging from thermoelectric materials, physical mechanisms and materials process techniques in particular with emphasis on solid state reactions. While bottom-up approaches to obtain thermoelectric materials have widely been employed in thermoelectrics, comprehensive reviews on summarizing such methods are still rare. In this review, we will outline a variety of bottom-up strategies for preparing high-performance thermoelectric materials. In addition, state-of-art, challenges and future opportunities in this domain will be commented.


Author(s):  
R. C. Moretz ◽  
G. G. Hausner ◽  
D. F. Parsons

Electron microscopy and diffraction of biological materials in the hydrated state requires the construction of a chamber in which the water vapor pressure can be maintained at saturation for a given specimen temperature, while minimally affecting the normal vacuum of the remainder of the microscope column. Initial studies with chambers closed by thin membrane windows showed that at the film thicknesses required for electron diffraction at 100 KV the window failure rate was too high to give a reliable system. A single stage, differentially pumped specimen hydration chamber was constructed, consisting of two apertures (70-100μ), which eliminated the necessity of thin membrane windows. This system was used to obtain electron diffraction and electron microscopy of water droplets and thin water films. However, a period of dehydration occurred during initial pumping of the microscope column. Although rehydration occurred within five minutes, biological materials were irreversibly damaged. Another limitation of this system was that the specimen grid was clamped between the apertures, thus limiting the yield of view to the aperture opening.


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