Littérature scientifique sur le sujet « Zipping motion »
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Articles de revues sur le sujet "Zipping motion"
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Imafuku, Yasuhiro, et Neil Thomas. « 1P195 Zipping dynamics of RNA hairpin and kinesin neck liner(Molecular motor,The 48th Annual Meeting of the Biophysical Society of Japan) ». Seibutsu Butsuri 50, supplement2 (2010) : S53. http://dx.doi.org/10.2142/biophys.50.s53_5.
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Houston, Adam L., et Robert B. Wilhelmson. « Observational Analysis of the 27 May 1997 Central Texas Tornadic Event. Part I : Prestorm Environment and Storm Maintenance/Propagation ». Monthly Weather Review 135, no 3 (1 mars 2007) : 701–26. http://dx.doi.org/10.1175/mwr3300.1.
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Abstract A detailed analysis of the 27 May 1997 central Texas tornadic storm complex is undertaken in an attempt to document the prestorm environment and identify the roles played by preexisting boundaries on storm maintenance/propagation and rotation. Analysis is carried out using a broad suite of synoptic and subsynoptic data but focuses on the level-II and -III Weather Surveillance Radar-1988 Doppler (WSR-88D) data from three Texas radars. The 27 May 1997 event was characterized by a back-building (propagation against the mean flow) storm complex that produced at least 12 tornadoes including the F5 Jarrell, Texas, tornado. Furthermore, five of the eight longest-lived cells during the analysis period are shown to contain midlevel mesocyclones. However, one-dimensional metrics calculated using representative vertical profiles of state variables reveal that, despite the extreme values of CAPE in place (>6500 J kg−1), the (1D) environment associated with this event is best classified as only marginally favorable for supercells and unfavorable for significant, supercellular tornadoes. Furthermore, the observed wind shear values are shown to be more in line with the vertical shear values typically associated with nonsevere back-building storms. Examples of propagation controlled by quasi-continuous maintenance of a single cell as well as successive discrete cell redevelopment are found. In all situations, two preexisting boundaries in place during this event (a cold front and a dryline) are found to have been necessary for the maintenance/propagation of the storm complex. Specifically, it is argued that the “zippering” of the cold front and dryline (the collision of the dryline and cold front that allowed the cold front to overtake the dryline and penetrate into the most unstable air to the east) was essential for the back-building of the storm complex in this event since it resulted in new cell development at points farther south. While midlevel mesocyclones were present in five of the eight longest-lived and well-sampled cells, analysis of the relationship between observed cell motion, expected cell motion, expected supercellular deviation, and boundary motion for the longest-lived and well-sampled cells reveals little evidence that deviate motions generated through supercellular dynamics governed cell motions. Instead, it is shown that boundary motions largely controlled the propagation of individual cells.
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Fung, Jennifer C., Wallace F. Marshall, Abby Dernburg, David A. Agard et John W. Sedat. « Homologous Chromosome Pairing in Drosophila melanogaster Proceeds through Multiple Independent Initiations ». Journal of Cell Biology 141, no 1 (6 avril 1998) : 5–20. http://dx.doi.org/10.1083/jcb.141.1.5.
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The dynamics by which homologous chromosomes pair is currently unknown. Here, we use fluorescence in situ hybridization in combination with three-dimensional optical microscopy to show that homologous pairing of the somatic chromosome arm 2L in Drosophila occurs by independent initiation of pairing at discrete loci rather than by a processive zippering of sites along the length of chromosome. By evaluating the pairing frequencies of 11 loci on chromosome arm 2L over several timepoints during Drosophila embryonic development, we show that all 11 loci are paired very early in Drosophila development, within 13 h after egg deposition. To elucidate whether such pairing occurs by directed or undirected motion, we analyzed the pairing kinetics of histone loci during nuclear cycle 14. By measuring changes of nuclear length and correlating these changes with progression of time during cycle 14, we were able to express the pairing frequency and distance between homologous loci as a function of time. Comparing the experimentally determined dynamics of pairing to simulations based on previously proposed models of pairing motion, we show that the observed pairing kinetics are most consistent with a constrained random walk model and not consistent with a directed motion model. Thus, we conclude that simple random contacts through diffusion could suffice to allow pairing of homologous sites.
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Tomishige, Michio, et Ronald D. Vale. « Controlling Kinesin by Reversible Disulfide Cross-Linking ». Journal of Cell Biology 151, no 5 (27 novembre 2000) : 1081–92. http://dx.doi.org/10.1083/jcb.151.5.1081.
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Conventional kinesin, a dimeric molecular motor, uses ATP-dependent conformational changes to move unidirectionally along a row of tubulin subunits on a microtubule. Two models have been advanced for the major structural change underlying kinesin motility: the first involves an unzippering/zippering of a small peptide (neck linker) from the motor catalytic core and the second proposes an unwinding/rewinding of the adjacent coiled-coil (neck coiled-coil). Here, we have tested these models using disulfide cross-linking of cysteines engineered into recombinant kinesin motors. When the neck linker motion was prevented by cross-linking, kinesin ceased unidirectional movement and only showed brief one-dimensional diffusion along microtubules. Motility fully recovered upon adding reducing agents to reverse the cross-link. When the neck linker motion was partially restrained, single kinesin motors showed biased diffusion towards the microtubule plus end but could not move effectively against a load imposed by an optical trap. Thus, partial movement of the neck linker suffices for directionality but not for normal processivity or force generation. In contrast, preventing neck coiled-coil unwinding by disulfide cross-linking had relatively little effect on motor activity, although the average run length of single kinesin molecules decreased by 30–50%. These studies indicate that conformational changes in the neck linker, not in the neck coiled-coil, drive processive movement by the kinesin motor.
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Houston, Adam L., et Robert B. Wilhelmson. « The Impact of Airmass Boundaries on the Propagation of Deep Convection : A Modeling-Based Study in a High-CAPE, Low-Shear Environment ». Monthly Weather Review 140, no 1 (1 janvier 2012) : 167–83. http://dx.doi.org/10.1175/mwr-d-10-05033.1.
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Abstract A suite of experiments conducted using a cloud-resolving model is examined to assess the role that preexisting airmass boundaries can play in regulating storm propagation. The 27 May 1997 central Texas tornadic event is used to guide these experiments. The environment of this event was characterized by multiple preexisting airmass boundaries, large CAPE, and weak vertical shear. Only the experiments with preexisting airmass boundaries produce back-building storm propagation (storm motion in opposition to the mean wind). When both the cold front and dryline are present, storm maintenance occurs through the quasi-continuous maintenance of a set of long-lived updrafts and not through discrete updraft redevelopment. Since the cold front is not required for back building, it is clear that back building in this environment does not require quasi-continuous updraft maintenance. The back-building storm simulated with both the cold front and dryline is found to be anchored to the boundary zipper (the intersection of the cold front and dryline). However, multiple preexisting airmass boundaries are not required for back building since experiments with only a dryline also support back building. A conceptual model of back building and boundary zippering is developed that highlights the important role that preexisting boundaries can play in back-building propagation.
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Krishnan, A., M. E. Bisher et M. M. J. Treacy. « In-Situ TEM Study of Domain Propagation in Ferroelectric Barium Titanate, and Its Role in Fatigue ». MRS Proceedings 541 (1998). http://dx.doi.org/10.1557/proc-541-475.
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AbstractWe have conducted in-situ transmission electron microscopy (TEM) experiments on thinned single crystal barium titanate in order to study the effects of applied electric field, temperature, electron beam irradiation and UV irradiation on domain nucleation and propagation. We observe two basic modes of domain wall motion; (i) a lateral motion which uniformly widens or narrows the total domain width; (ii) a “zipping” motion in which one end of a domain narrows to a point, which then propagates lengthwise, widening (or narrowing) the domain behind it. Both domain creation and destruction can occur by this latter process. When cooling from above Tc, domain growth usually occurs by the “zipping” motion. We believe that both the lateral and “zipping” modes of motion are related. The “zipping” mode tends to occur in the presence of inhomogeneous long-range strain fields, or when trapped charges are present locally. In some instances, the trapped charge is strong enough to show significant image contrast in bright-field. Domain motion, initiated by heat, electric fields or UV irradiation, moves such charges. A model of domain motion is presented which shows how displacement charge can be injected into the ferroelectric, and which may contribute to the fatigue of these materials.
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Walter, J. C., A. Ferrantini, E. Carlon et C. Vanderzande. « Fractional Brownian motion and the critical dynamics of zipping polymers ». Physical Review E 85, no 3 (16 mars 2012). http://dx.doi.org/10.1103/physreve.85.031120.
Texte intégralThèses sur le sujet "Zipping motion"
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Sîrbu, Ion-dan. « Liquid-based electroactive polymers (LEAP) for a new class of soft actuators and generators ». Doctoral thesis, Università degli studi di Trento, 2023. https://hdl.handle.net/11572/364692.
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Future robotic systems will be pervasive technologies operating autonomously in unknown spaces that are shared with humans. Such complex interactions make it compulsory for them to be lightweight, soft, and efficient in a way to guarantee safety, robustness and long-term operation. This set of qualities can be achieved using soft multipurpose systems that combine, integrate and commute between conventional electromechanical and fluidic drives, as well as harvest energy during inactive actuation phases for increased energy efficiency. Recent research work has shown that dielectric fluids with specific properties, can be combined with stretchable or flexible shell structures made of polymeric dielectric/electrode composite films, to implement a novel type of soft electrically-driven fluidic transducers with self-healing and self-sensing capabilities that take the name of Liquid-based Electro-Active Polymer transducers (LEAPs). These devices are similar to dielectric elastomer transducers in regards to their electrostatic working principle, but they can potentially produce larger displacements due to their lower mechanical stiffness. In this thesis a novel electrostatic transducer is presented; the transducer is made of thin polymer films and liquid dielectrics, combined with rigid stiffening elements to form a circular electrostatic bellow muscle (EBM) unit capable of out-of-plane contraction. These units are easy to manufacture and can be arranged in arrays and stacks that can be employed as contractile artificial muscles, pumps for fluid-driven soft robots, or as energy harvesters. As artificial muscles, EBMs of 20 - 40 millimeters in diameter can exert forces of up to 6 newtons, lift loads over a hundred times their own weight, and reach contractions of over 40 per cent with strain rates over 1200 per cents per second, with a bandwidth over 10 Hz. As pump drivers, EBMs produce flow rates of up 0.63 liters per minute and maximum pressure head of 6 kilopascals, whereas as generators, they reach a conversion efficiency close to 20 per cent. The compact shape, low cost, simple assembling procedure, high reliability and large contractions make the EBM a promising technology for high-performance robotic systems.
Livres sur le sujet "Zipping motion"
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Pearson, Debora. Alphabeep : A zipping, zooming ABC. New York : Holiday House, 2003.
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Pearson, Debora. Alphabeep ! : A Zipping, Zooming ABC. Holiday House, 2006.
Trouver le texte intégralActes de conférences sur le sujet "Zipping motion"
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Guo, Dongzhi, Jingsheng Gao, Alan J. H. McGaughey, Matthew Moran, Suresh Santhanam, Gary K. Fedder, Bill Anderson et Shi-Chune Yao. « Design and Evaluation of MEMS-Based Stirling Cycle Micro-Refrigeration System ». Dans ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-63084.
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A Stirling cycle micro-refrigeration system composed of arrays of silicon MEMS cooling elements has been designed and evaluated thermodynamically. The cooling elements are each 5 mm-long, 2.25 mm-wide, have a thickness of 300 μm, and are fabricated in a stacked array on a silicon wafer. A 0.5 mm-long regenerator is placed between the compression (hot side) and expansion (cold side) diaphragms. The diaphragms are 2.25 mm circles driven electrostatically. Helium is the working fluid, pressurized at 2 bar and sealed in the system. Under operating conditions, the hot and cold diaphragms oscillate sinusoidally 90° out of phase such that heat is extracted to the expansion space and released from the compression space. The bulk silicon substrate on which the device is grown is etched with “zipping” shaped chambers under the diaphragms. The silicon enables efficient heat transfer between the gas and heat source/sink as well as reduces the dead volume of the system, thus enhancing the cooling capacity. In addition, the “zipping” shaped substrates reduce the voltage required to actuate the diaphragms. An array of vertical silicon pillars in the regenerator serves as a thermal capacitor transferring heat to and from the working gas during a cycle. In operation, the push-pull motion of the diaphragm makes a 300 μm stroke and actuates at a frequency of 2 kHz. Parametric study of the design shows the effects of phase lag, swept volume ratio between the hot space and cold space, and dead volume ratio on cooling capacity. At TH = 313.15 K and TC = 288.15 K and assuming a perfect regenerator, the thermodynamic optimization analysis gives a heat extraction rate of 0.22 W per element and cooling capacity of 30 W/cm2 for the stacked system. Evaluation of the stacked system shows that the COP will reach 6.3 if the expansion work from the cold side is recovered electrostatically and used to drive the hot side diaphragm.
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Tanaka, Yuki, et Hiroyuki Takahira. « Effects of Phospholipid Layers on the Motion of Microbubbles Under Pressure Variations ». Dans ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-33011.
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The shrinking and growth of microbubbles under pressure variations are observed with a CCD camera. The influence of gas diffusion on the stability of microbubbles covered with phospholipid layers is investigated. The microbubbles are made with acoustic liposomes encapsulating phosphate buffer solution and perfluoropropane gas. It is shown that when the ambient liquid pressure increases, the observed microbubbles shrink accompanied with the cyclic surface buckling and smoothing process. The bubble surface smoothing in the process shows that the excess phospholipid layers are removed from the surface, which results in the instantaneous bubble shrinkage. It is also shown that the smaller the initial radius is, the more the growth of microbubbles is reduced. The bubble model by Takahira and Ito, in which the dynamic surface tension and the gas permeation resistance of molecular layers are considered, is utilized to simulate the experiments. The simulation is in qualitative agreement with the experimental result except for the instantaneous bubble shrinkage. The model is improved so as to consider the instantaneous increase of surface tension. The instantaneous bubble shrinkage is simulated successfully with the improved model. The results suggest that the instantaneous increase of surface tension is caused by the shedding of the excess phospholipid layer material due to the zippering process proposed by Borden and Longo.