In situ Investigation of Individual Filament Growth in Conducting Bridge Memristor by Contact Scanning Capacitance Microscopy

We report on the application of Contact Scanning Capacitance Microscopy (CSCM) to trace the growth of an individual Ni filament in a ZrO2(Y) film on a Ni sublayer (together with a conductive Atomic Force Microscope probe composing a nanometer-sized virtual memristor). An increasing of the filament length in the course of electro-forming results in an increasing of the capacitance between the probe and the sample, which can be detected by CSCM technique. This way, the filament growth can be monitored in real time in situ.

On filament fragmentation and the impact of ambient environment on it

Filaments are crucial intermediaries in the star formation process. Recent observations of filaments show that - (i) a number of them are non-singular entities, and rather a bundle of velocity coherent fibres, and (ii) while a majority of filaments spawn cores narrower than their natal filaments, some cores are broader. We explore these issues by developing hydrodynamic simulations of an initially sub-critical individual filament that is allowed to accrete gas from its neighbourhood and evolves under self-gravity. Results obtained here support the idea that fibres form naturally during the filament formation process. We further argue that the ambient environment, i.e., the magnitude of external pressure, and not the filament linemass alone, has bearing upon the morphology of its evolution. We observe that a filament is susceptible to the sausage-type instability irrespective of the external pressure. The fragments, however, are pinched in a filament experiencing pressure comparable to that in the Solar neighbourhood (∼104 K cm−3). By contrast, fragments are broad and spherical - having density profiles similar to that of a stable Bonnor - Ebert sphere - when the filament experiences a higher pressure, typically ≥105 K cm−3, but ≤106 K cm−3). The filament tends to rupture at even higher external pressure (≥107 K cm−3). These observations collectively mean that star formation is less efficient with increasing external pressure.

Relationship between Dynamic Instability of Individual Microtubules and Flux of Subunits into and out of Polymer

ABSTRACTBehaviors of dynamic polymers such as microtubules and actin are frequently assessed at one or both of two scales: (i) net assembly or disassembly of bulk polymer, (ii) growth and shortening of individual filaments. Previous work has derived various forms of an equation to relate the rate of change in bulk polymer mass (i.e., flux of subunits into and out of polymer, often abbreviated as “J”) to individual filament behaviors. However, these versions of this “J equation” differ in the variables used to quantify individual filament behavior, which correspond to different experimental approaches. For example, some variants of the J equation use dynamic instability parameters, obtained by following particular individuals for long periods of time. Another form of the equation uses measurements from many individuals followed over short time steps. We use a combination of derivations and computer simulations that mimic experiments to (i) relate the various forms of the J equation to each other; (ii) determine conditions under which these J equation forms are and are not equivalent; and (iii) identify aspects of the measurements that can affect the accuracy of each form of the J equation. Improved understanding of the J equation and its connections to experimentally measurable quantities will contribute to efforts to build a multi-scale understanding of steady-state polymer behavior.

Observations on the Fibre Distribution and Fibre Strain in a Woven Fabric Reinforcement

The distribution of the fibres within a tow of a plain weave fabric composite appears to be non-uniform with a systematic variation. In a different composite system, the strain along a fibre in a similar fabric has been shown to vary along each individual filament in an ordered manner. It is proposed that the highest fibre strains occur at the centre of the tow crossing points. An optical micrograph of matrix cracking in the transverse tows adjacent to the proposed highest strain point would appear to confirm this hypothesis. This analysis is based on limited evidence, but is presented to permit other researchers to confirm or refute the proposition.

Filament lengths in resting and excited muscles

According to the sliding filament model, changes in muscle length take place by movement of the two sets of filaments past each other without change in the individual filament lengths. Yet, when measurements of filament lengths are made in the electron microscope, it is found that they are not the same in excited muscle as in resting muscle. Both the A- and the /-filaments are shorter in muscles fixed while at rest than in those muscles which were fixed during an isometric contraction. The important point in interpreting these findings is whether or not length changes have occurred during preparation, and if so, whether the extent of these changes is the same in each case. An investigation has therefore been made of the changes produced under different conditions by the preparative procedures, to see whether or not there are genuine differences between the filament lengths in resting and excited muscles. It has also been possible as a result of this study to determine the value of the fine periodicity that is visible along the length of the A -filaments. Previous measurements of this periodicity have given values ranging from 250 to 400 A; and as it has not been clear how much shortening had occurred in these muscles during preparation, there has remained considerable uncertainty concerning both the actual magnitude of the periodicity, and any possible functional changes in it. The experiments have been carried out with frog and chicken muscles, in which the corresponding filaments have the same length.