A Stochastic model for dynamics of FtsZ filaments and the formation of Z-ring

Understanding the mechanisms responsible for the formation and growth of FtsZ polymers and their subsequent formation of the $Z$-ring is important for gaining insight into the cell division in prokaryotic cells. In this work, we present a minimal stochastic model that qualitatively reproduces {\it in vitro} observations of polymerization, formation of dynamic contractile ring that is stable for a long time and depolymerization shown by FtsZ polymer filaments. In this stochastic model, we explore different mechanisms for ring breaking and hydrolysis. In addition to hydrolysis, which is known to regulate the dynamics of other tubulin polymers like microtubules, we find that the presence of the ring allows for an additional mechanism for regulating the dynamics of FtsZ polymers. Ring breaking dynamics in the presence of hydrolysis naturally induce rescue and catastrophe events in this model irrespective of the mechanism of hydrolysis.Comment: Replaced with published versio

ROLE OF FLUID ON THE CONTACT DEFORMATION RESPONSE OF BIOLOGICAL TISSUE

This paper will focus on the role of fluids on the indentation deformation response of tooth and eye tissues. All natural biological materials contain fluid and function in a fluidic environment, which plays a critical role in responding to loading events as well as tissue nutrition. The location of this fluid varies and is considered as both bound and mobile with much of it located in cell compartments that are also able to respond directly to loading. The extent of the fluid content varies from less than 10 % in the case of the highly mineralised enamel to more than 80 % in the case of soft eye tissues. The role of the fluid and its response during loading is also complicated by the hierarchical structure of biological tissues, be they mineralised or not. The mechanisms by which the presence of fluid in these materials influences the mechanical response is still poorly understood and has not been systematically investigated. The present paper presents data generated over many years on both the above biological tissues and attempts to present indications as to the mechanism(s) by which the presence of fluid contributes to the deformation. The situation associated with contact loading with the presence of mobile fluid in the tissues results in a more complex situation than the classic elastic-plastic contact situation, but the latter still forms the basis for much of the analysis of instrumented indentation force-displacement load-unloading curves using various shapes of indenters, especially for mineralised structures. In the case of soft tissues the absence of agreed protocols for interpretation of force-displacement-time responses is restricting clinical/biological applications

Transport and magnetic properties in YBaCo2O5.45: Focus on the high-temperature transition

The electronic transport properties and the magnetic susceptibility were measured in detail in $YBaCo_2O_{5.45}$. Close to the so-called metal-insulator transition, strong effects of resistance relaxation, a clear thermal hysteresis and a sudden increase of the resistance noise are observed. This is likely due to the first order character of the transition and to the underlying phases coexistence. Despite these out of equilibrium features, a positive and linear magneto-resistance is also observed, possibly linked to the heterogeneity of the state. From a magnetic point of view, the paramagnetic to ordered magnetic state transition is observed using non linear susceptibilty. This transition shows the characteristics of a continuous transition, and time dependent effects can be linked with the dynamics of magnetic domains in presence of disorder. Thus, when focusing on the order of the transitions, the electronic one and the magnetic one can not be directly associated.Comment: accepted for publication in PR

Giant pop-ins and amorphization in germanium during indentation

Sudden excursions of unusually large magnitude (>1 μm), “giant pop-ins,” have been observed in the force-displacement curve for high load indentation of crystalline germanium(Ge). A range of techniques including Raman microspectroscopy, focused ion-beam cross sectioning, and transmission electron microscopy, are applied to study this phenomenon. Amorphous material is observed in residual indents following the giant pop-in. The giant pop-in is shown to be a material removal event, triggered by the development of shallow lateral cracks adjacent to the indent. Enhanced depth recovery, or “elbowing,” observed in the force-displacement curve following the giant pop-in is explained in terms of a compliant response of plates of material around the indent detached by lateral cracking. The possible causes of amorphization are discussed, and the implications in light of earlier indentation studies of Ge are considered

Nanoindentation-induced deformation of Ge

The deformation mechanisms of crystalline (100) Ge were studied using nanoindentation, cross sectional transmission electron microscopy (XTEM) and Raman microspectroscopy. For a wide range of indentation conditions using both spherical and pointed indenters, multiple discontinuities were found in the force–displacement curves on loading, but no discontinuities were found on unloading. Raman microspectroscopy, measured from samples which had plastically deformed on loading, showed a spectrum shift from that in pristine Ge, suggesting only residual strain. No evidence (such as extra Raman bands) was found to suggest that any pressure-induced phase transformations had occurred, despite the fact that the material had undergone severe plastic deformation.Selected area diffraction pattern studies of the mechanically damaged regions also confirmed the absence of additional phases. Moreover, XTEM showed that, at low loads, plastic deformation occurs by twinning and dislocation motion. This indicates that the hardness of Gemeasured by indentation is not primarily dominated by phase transformation, rather by the nucleation and propagation of twin bands and/or dislocations

General Patton and Lieutenant Winters: a contrast in leadership

The concept of emotional intelligence (EI) has received an increasing amount of focus in recent years from psychological, sociological and organizational scientists (Côté, 2014). However, while researchers from these various disciplines have endeavored to explain the variance between outcomes of interest (e.g. effectiveness as a leader) and a person’s general mental ability or personality, the way these scientists have conceptualized EI has not always been in complete agreement (Livingstone and Day, 2005). The most popular competing models in existence fall into one of two general categories: ability-based or mixed-model (Mayer et al., 2000, 2008). The ability-based conceptualization of EI views EI as a set of several skills or capacities related to perceiving, understanding, facilitating and managing emotions, and views EI as a classically defined intelligence or aptitude (like traditional IQ). This ability-based conceptualization posits that EI can be developed over time or through training (Van Rooy and Viswesvaran, 2004).https://digitalcommons.usmalibrary.org/books/1055/thumbnail.jp

Nulling interferometry: performance comparison between Antarctica and other ground-based sites

Detecting the presence of circumstellar dust around nearby solar-type main sequence stars is an important pre-requisite for the design of future life-finding space missions such as ESA's Darwin or NASA's Terrestrial Planet Finder (TPF). The high Antarctic plateau may provide appropriate conditions to perform such a survey from the ground. We investigate the performance of a nulling interferometer optimised for the detection of exozodiacal discs at Dome C, on the high Antarctic plateau, and compare it to the expected performance of similar instruments at temperate sites. Based on the currently available measurements of the turbulence characteristics at Dome C, we adapt the GENIEsim software (Absil et al. 2006, A&A 448) to simulate the performance of a nulling interferometer on the high Antarctic plateau. To feed a realistic instrumental configuration into the simulator, we propose a conceptual design for ALADDIN, the Antarctic L-band Astrophysics Discovery Demonstrator for Interferometric Nulling. We assume that this instrument can be placed above the 30-m high boundary layer, where most of the atmospheric turbulence originates. We show that an optimised nulling interferometer operating on a pair of 1-m class telescopes located 30 m above the ground could achieve a better sensitivity than a similar instrument working with two 8-m class telescopes at a temperate site such as Cerro Paranal. The detection of circumstellar discs about 20 times as dense as our local zodiacal cloud seems within reach for typical Darwin/TPF targets in a integration time of a few hours. Moreover, the exceptional turbulence conditions significantly relax the requirements on real-time control loops, which has favourable consequences on the feasibility of the nulling instrument.Comment: 10 pages, accepted for publication in A&

The crustacean and molluscan fauna of Tasmanian saltmarshes

The crustaceans and molluscs of 65 saltmarshes and brackish marshes around the coast of Tasmania and the major Bass Strait islands were surveyed. Over 50 species were collected, but only eight (three talitrid amphipods, one crab and four gastropods) were confined to saltmarshes; the typical saltmarsh assemblage consisted of two talitrid amphipods, three oniscoid isopods, two crabs, two prosobranch snails and two pulmonate snails. The greatest species richness was found in marshes from the southeast and the far northwest, where the most extensive saltmarshes have developed. Several undescribed talitrids were collected and the range of two coastal species was extended significantly. The native woodlouse Plymophiloscia ulverstonensis was commonly found on the upper parts of the marshes, as was the introduced slater Porcellio scaber. The burrowing grapsid crab Helograpsus haswellianus was common on the marshes, though it was replaced by the ocypodid Heloecius cordiformis in brackish marshes, and by another grapsid, Paragrapsus gaimardii, in the only marsh examined on King Island. The hymenosomatid crab Amarinus paralacustris was recorded from the state for the first time at Hendersons Lagoon. Amphibolid and ellobiid snails typified the molluscan fauna of the marshes. The introduced ellobiid Phytia myosotis appears to have a major disjunction in its distribution between the southeast and northern sites. Tasmanian saltmarshes have a similar diversity of crustaceans and molluscs to those of New Zealand and South Africa. They are richer in species than saltmarshes of the northeast Atlantic coasts but have fewer crustaceans than the temperate east coast marshes of North America, and fewer molluscs than those of the coasts of the Pacific northwest