Cytoskeleton and Cell Motility

The present article is an invited contribution to the Encyclopedia of Complexity and System Science, Robert A. Meyers Ed., Springer New York (2009). It is a review of the biophysical mechanisms that underly cell motility. It mainly focuses on the eukaryotic cytoskeleton and cell-motility mechanisms. Bacterial motility as well as the composition of the prokaryotic cytoskeleton is only briefly mentioned. The article is organized as follows. In Section III, I first present an overview of the diversity of cellular motility mechanisms, which might at first glance be categorized into two different types of behaviors, namely "swimming" and "crawling". Intracellular transport, mitosis - or cell division - as well as other extensions of cell motility that rely on the same essential machinery are briefly sketched. In Section IV, I introduce the molecular machinery that underlies cell motility - the cytoskeleton - as well as its interactions with the external environment of the cell and its main regulatory pathways. Sections IV D to IV F are more detailed in their biochemical presentations; readers primarily interested in the theoretical modeling of cell motility might want to skip these sections in a first reading. I then describe the motility mechanisms that rely essentially on polymerization-depolymerization dynamics of cytoskeleton filaments in Section V, and the ones that rely essentially on the activity of motor proteins in Section VI. Finally, Section VII is devoted to the description of the integrated approaches that have been developed recently to try to understand the cooperative phenomena that underly self-organization of the cell cytoskeleton as a whole.Comment: 31 pages, 16 figures, 295 reference

Strategies of anomalies detection in bridges and tunnels as a tool for structural health management. New approaches and AI support.

L'abstract è presente nell'allegato / the abstract is in the attachmen

Current State of Research on Pressurized Water Reactor Safety

For more than 40 years, IPSN then IRSN has conducted research and development on nuclear safety, specifically concerning pressurized water reactors, which are the reactor type used in France. This publication reports on the progress of this research and development in each area of study – loss-of-coolant accidents, core melt accidents, fires and external hazards, component aging, etc. –, the remaining uncertainties and, in some cases, new measures that should be developed to consolidate the safety of today’s reactors and also those of tomorrow. A chapter of this report is also devoted to research into human and organizational factors, and the human and social sciences more generally. All of the work is reviewed in the light of the safety issues raised by feedback from major accidents such as Chernobyl and Fukushima Daiichi, as well as the issues raised by assessments conducted, for example, as part of the ten-year reviews of safety at French nuclear reactors. Finally, through the subjects it discusses, this report illustrates the many partnerships and exchanges forged by IRSN with public, industrial and academic bodies both within Europe and internationally

The Second Conference on Lunar Bases and Space Activities of the 21st Century, volume 1

These papers comprise a peer-review selection of presentations by authors from NASA, LPI industry, and academia at the Second Conference (April 1988) on Lunar Bases and Space Activities of the 21st Century, sponsored by the NASA Office of Exploration and the Lunar Planetary Institute. These papers go into more technical depth than did those published from the first NASA-sponsored symposium on the topic, held in 1984. Session topics covered by this volume include (1) design and operation of transportation systems to, in orbit around, and on the Moon, (2) lunar base site selection, (3) design, architecture, construction, and operation of lunar bases and human habitats, and (4) lunar-based scientific research and experimentation in astronomy, exobiology, and lunar geology

Retrofit Solutions for New Zealand Hollow-Core Floors and Investigation of Reliable Diaphragm Load-Paths in Earthquakes

Standard floor diaphragm design relies on compression struts and tension ties within the floor to transfer large forces between lateral load resisting structural elements and stiffen the building during earthquakes. Floors in reinforced concrete frame buildings have been observed with wide cracks around the floor perimeter following earthquakes, raising questions about how compression struts can form between the floor and frame elements. An experimental investigation into reliable floor diaphragm force transfer mechanisms, and by extension load-paths, was undertaken using a full-scale two-way super- assembly frame specimen. Two tests were conducted where the specimen was subjected to simultaneous bi-directional inter-storey drift demands to induce realistic earthquake cracking damage between the floor and the frame. At different floor damage states, in-plane shear deformations were applied to the frame specimen to capture the deterioration of diaphragm transfer load-paths. Wide perimeter cracking was anticipated to eliminate diaphragm compression strut load-paths until shear deformation of the support frame-initiated binding with the floor, as it changed to a rhomboidal shape. This behaviour was not observed due to two observed phenomena across the two tests. In the first test, loss of beam torsional stiffness governed as the diaphragm load-path failure mechanism. Beam-to-floor continuity reinforcement acting in tension exceeded the weak-axis shear and torsion capacity of the perimeter frame beam plastic hinges. Beam elongation deformation incompatibility demands were relieved by the tops of the beams rotating into the floor. Deformation concentrated in the beam plastic hinges rather than forming cracks at the beam-to-floor interface. In the second test, wide cracks developed at the support-beam-to-floor interfaces. However, despite this, the diaphragm in-plane shear stiffness deteriorated less than what was observed during the first test. It was found that diaphragm struts could form across wide beam-to-floor cracks due to aggregate rubble falling into the cracks and providing a residual contact stress load-path. Evidence of compression strut formation was recorded up to crack widths of 5.5 mm. An initial suggestion is that compression struts can cross wide cracks that are smaller than ¼ of the aggregate size used in the floor topping concrete mixture. This only applies where there is ductile continuity reinforcement crossing the critical crack interface. The rate of diaphragm shear stiffness degradation with increasing inter-storey drift demands was highly dependent on the ratio of simultaneous bi-directionality, due to the impact simultaneous bending actions had on beam torsional capacity. For low ratios of inter-storey drift simultaneous bi-directionality, beam torsional stiffness was maintained to a greater degree, providing higher diaphragm in-plane shear stiffness. An adjacent research stream was conducted related to hollow-core flooring systems. Hollow-core floors were widely installed in multi-storey buildings throughout New Zealand in the 1980s and 1990s. Hollow-core units were designed to act as simply supported members. Unfortunately, continuity reinforcement used to sustain floor diaphragm load-paths enforces deformation incompatibility demands on the floor during earthquakes, subjecting hollow-core units to substantial positive and negative bending moment demands they were not designed for. These demands can initiate a range of brittle failure mechanisms in the units. Concerns regarding the potential for commonly installed retrofits, used to increase seating widths for hollow-core units, to promote brittle failure of hollow-core units under negative moment demands prompted an experimental investigation. Six hollow-core unit sub-assembly experiments were used to identify unfavourable seating details which could cause negative moment failure of the floor during an earthquake and verify retrofit solutions to prevent this from occurring. Successful retrofits were installed in a full-scale two-way super-assembly frame specimen subjected to simultaneous bi-directional earthquake demands with full three-dimensional effects for further rigorous verification. Four viable retrofit strategies were identified and verified to prevent negative moment failure from occurring while providing adequate seating for the hollow-core units. Hollow-core units seated on beam plastic hinges extending out of interior frame columns, named beta units, were experimentally tested with seismic demands for the first time in the super-assembly experiment. Following inter-storey drift demands of 3%, the residual gravity carrying capacity of a beta unit with substantial web-splitting was tested. Shear failure of the unit near the support occurred at gravity load demands aligning to 91% of the NZS1170.5 (Standards New Zealand, 2016) design live load combination (1.2G + 1.5Q), demonstrating the vulnerability of beta units. Retrofit strategies to prevent brittle failure and collapse of vulnerable hollow-core units seated at the ends of support beams were also tested in the super-assembly specimen, providing verification and design improvements for catch-frame and hanger retrofits

Европейский и национальный контексты в научных исследованиях

Tом 3. Predstavleny trudy molodyh uchenyh po estestvennym i tochnym naukam, tehnicheskim i prikladnym naukam. = Т.3. Представлены труды молодых ученых по естественным и точным наукам, техническим и прикладным наукам