Testing the role of intraflagellar transport in flagellar length control using length-altering mutants of Chlamydomonas

Cilia and flagella are ideal model organelles in which to study the general question of organelle size control. Flagellar microtubules are steady-state structures whose size is set by the balance of assembly and disassembly. Assembly requires intraflagellar transport (IFT), and measurements of IFT have shown that the rate of entry of IFT particles into the flagellum is a decreasing function of length. It has been proposed that this length dependence of IFT may be the basis for flagellar length control. Here, we test this idea by showing that three different long-flagella mutations in Chlamydomonas all cause increased IFT injection, thus confirming that IFT can influence length control. However, quantitative comparisons with mathematical models suggest that the increase in injection is not sufficient to explain the full increase in length seen in these mutants; hence, some other mechanism may be at work. One alternative mechanism that has been proposed is length-regulated binding of tubulin to the IFT particles. However, we find that the apparent length dependence of tubulin loading that has previously been reported may actually reflect length-dependent organization of IFT trains. This article is part of the Theo Murphy meeting issue ‘Unity and diversity of cilia in locomotion and transport’.

On the dependence of standard and gradient elastic material constants on a field of defects

In this work, we consider a strain gradient elasticity theory with an extended number of field variables: the displacement vector and an additional scalar field defining the internal micro-deformation. The total internal energy of the model depends on the strain, the micro-deformation function, their gradients, and the coupling. The considered model can be treated as gradient/micromorphic. Moreover, the micro-deformation field can be treated as a field of scalar defects distributed along the medium. Based on analytic (one-dimensional) solutions of uniform/non-uniform deformation of the rod, we introduce (i) an apparent stiffness and (ii) an apparent length scale parameter. Subsequently, we provide a variant of continuum-on-continuum homogenization by equating tip displacements for the gradient/micromorphic medium and an equivalent strain gradient one. Elongation of the gradient/micromorphic rod is therefore equated with the corresponding elongation of the equivalent strain gradient rod, whose behavior is characterized by the apparent material constants. Subsequently, the non-dimensional coupling number is identified with a damage parameter. It is shown that, on the one hand, the apparent stiffness of the rod is reduced when such parameter increases. On the other hand, the apparent length scale parameter (i.e. the apparent second gradient elastic coefficient) increases when the damage parameter increases. Therefore, it is shown that the presence of defects in a second gradient linear elastic material may increase its apparent strain gradient behavior.

Characterization of a Twin-Entry Radial Turbine under Pulsatile Flow Condition

In automotive applications radial gas turbines are commonly fitted with a twin-entry volute connected to a divided exhaust manifold, ensuring a better scavenge process owing to less interference between engines’ cylinders. This paper is concerned with the study of the unsteady performances related to the pulsating flows of a twin-entry radial turbine in engine-like conditions and the hysteresis-like behaviour during the pulses period. The results show that the aerodynamic performances deviate noticeably from the steady state and depend mainly on the time shifting between the actual output power and the isentropic power, which is distantly related to the apparent length. The maximum of efficiency and output shaft power are accompanied by low entropy generation through the shroud entry side, and their instantaneous behaviours tend to follow mainly the inlet total pressure curve. As revealed a billow is created by the interaction between the main flow and the infiltrated flow, affecting the flow incidence at rotor entry and producing high losses.

The rhythm of fountains: the length and time scales of rise height fluctuations at low and high Froude numbers

The magnitude and frequency of vertical fluctuations of the top of an axisymmetric miscible Boussinesq fountain forms the focus of this work. We present measurements of these quantities for saline-aqueous fountains in uniform quiescent surroundings. Our results span source Froude numbers $0. 3\leq {\mathrm{Fr} }_{0} \leq 40$ and, thereby, encompass very weak, weak, intermediate and forced classes of fountain. We identify distinct scalings, based on known quantities at the fountain source, for the frequency of fountain height fluctuations which collapse our data within bands of ${\mathrm{Fr} }_{0} $. Notably, our scalings reveal that the (dimensionless) frequency takes a constant value within each band. These results highlight characteristic time scales for the fluctuations which we decompose into a single, physically apparent, length scale and velocity scale within each band. Moreover, within one particular band, spanning source Froude numbers towards the lower end of the full range considered, we identify unexpectedly long-period fluctuations indicating a near balance of inertia and (opposing) buoyancy at the source. Our analysis identifies four distinct classes of fluctuation behaviour (four bands of ${\mathrm{Fr} }_{0} $) and this classification matches well with existing classifications of fountains based on rise heights. As such, we show that an analysis of the behaviour of the fountain top alone, rather than the entire fountain, provides an alternative approach to classifying fountains. The similarity of classifications based on the two different methods confirms that the boundaries between classes mark tangible changes in the physics of fountains. For high ${\mathrm{Fr} }_{0} $ we show that the dominant fluctuations occur at the scale of the largest eddies which can be contained within the fountain near its top. Extending this, we develop a Strouhal number, ${\mathrm{Str} }_{top} $, based on experimental measures of the fountain top, defined such that ${\mathrm{Str} }_{top} = 1$ would suggest the dominant fluctuations are caused by a continual cycle of eddies forming and collapsing at this largest physical scale. For high-${\mathrm{Fr} }_{0} $ fountains we find ${\mathrm{Str} }_{top} \approx 0. 9$.

LIGAMENT LENGTH DURING CIRCUMDUCTION OF THE TRAPEZIOMETACARPAL JOINT AFTER LIGAMENT SECTIONING

Thumb motion and stability were examined after sequential division of support ligaments of the trapeziometacarpal (TMC) to simulate the pathologic condition of ligament laxity. The motion obtained with passive circumduction was measured with a magnetic tracking system. The lengths of the TMC joint ligaments were approximated by measuring the distance between origin and insertion of each ligament. The change in this apparent interorigin distance of the ligaments was measured before and after ligament sectioning. The anterior oblique ligament (AOL) and the ulnar collateral ligament (UCL) had the greatest effect on TMC joint stability during circumduction of the thumb. Division of the first intermetacarpal ligament (IML) did not produce a change in apparent length of other ligaments. We conclude that small changes in ligament length affect thumb stability and alter the path of circumduction. Neither the IML or posterior oblique ligaments were major stabilizers of the TMC joint during circumduction, prehensile grasp, or tip pinch. Reconstruction of the AOL and UCL ligaments should be considered for treatment of the initial stages of TMC instability.

Effects of Figure Context on the Apparent Length of a Line

This study investigated the effects of figure context on the apparent length of a line. In Exp. 1, ten participants were asked to adjust the length of a comparison line to match a standard line enclosed within a rectangle. The participants consistently overestimated the length of the standard line, demonstrating the stretching effect of figure context on the apparent length of a line. In Exp. 2 (12 participants), the size of the context figure was varied and it had no significant influence on the magnitude of the context effect. In Exp. 3 (nine participants), the context effect was shown not only for squares and rectangles but also for other shapes of figures such as circles and 5-pointed stars. We discuss the possible mechanism of the figure-context effect within Gregory's (1970, 1978) misapplied constancy theory of visual illusions.