Cytoskeletal turnover and Myosin contractility drive cell autonomous oscillations in a model of Drosophila Dorsal Closure

Oscillatory behaviour in force-generating systems is a pervasive phenomenon in cell biology. In this work, we investigate how oscillations in the actomyosin cytoskeleton drive cell shape changes during the process of Dorsal Closure, a morphogenetic event in Drosophila embryo development whereby epidermal continuity is generated through the pulsatile apical area reduction of cells constituting the amnioserosa (AS) tissue. We present a theoretical model of AS cell dynamics by which the oscillatory behaviour arises due to a coupling between active Myosin-driven forces, actin turnover and cell deformation. Oscillations in our model are cell-autonomous and are modulated by neighbour coupling, and our model accurately reproduces the oscillatory dynamics of AS cells and their amplitude and frequency evolution. A key prediction arising from our model is that the rate of actin turnover and Myosin contractile force must increase during DC in order to reproduce the decrease in amplitude and period of cell area oscillations observed in vivo. This prediction opens up new ways to think about the molecular underpinnings of AS cell oscillations and their link to net tissue contraction and suggests the form of future experimental measurements.Comment: 17 pages, 6 figures; added references, modified and corrected Figs. 1 and 3, corrected typos, expanded discussio

Asymptotic safety in higher-derivative gravity

We study the non-perturbative renormalization group flow of higher-derivative gravity employing functional renormalization group techniques. The non-perturbative contributions to the $\beta$-functions shift the known perturbative ultraviolet fixed point into a non-trivial fixed point with three UV-attractive and one UV-repulsive eigendirections, consistent with the asymptotic safety conjecture of gravity. The implication of this transition on the unitarity problem, typically haunting higher-derivative gravity theories, is discussed.Comment: 8 pages; 1 figure; revised versio

Joblessness

The U.S. labor market has been experiencing unprecedented high average unemployment duration. The shift in the unemployment duration distribution can be traced back to the early nineties. In this paper, censored quantile regression methods are employed to analyze the changes in the US unemployment duration distribution. We explore the decomposition method proposed by Machado and Mata (2005) to disentangle the contribution of compositional vis-à-vis structural changes. The data used in this inquiry are taken from the nationally representative Displaced Worker Surveys of 1988 and 2008. Apart from the effect of economic improvement we find that the sensitivity of joblessness duration to education and the aging of the population were the two main forces behind the increase of the unemployment duration, in the last twenty years. We tentatively argue that firms use education as a signaling device during recessions, but the signaling power of education during the recent low-unemployment environment faded significantly.

US unemployment duration: has long become longer or short become shorter?

The U.S. labor market has been experiencing unprecedented high average unemployment duration. The shift in the unemployment duration distribution can be traced back to the early nineties. In this study, censored quantile regression methods are employed to analyze the changes in the US unemployment duration distribution. We explore the decomposition method proposed by Machado and Mata (2005) to disentangle the contribution of the changes generated by the covariate distribution and by the conditional distribution. The data used in this inquiry are taken from the nationally representative Displaced Worker Surveys of 1988 and 1998. We provide evidence that the change in the unemployment duration distribution is mainly produced by the opposing effects of a sharp rise in job-to-job transition rates and an increased sensitivity of unemployment duration to unemployment rates. Compositional changes in the labor force played a limited role. We rationalize our findings by arguing that improved screening technology is likely to be the relevant underlying mechanism at work

The reservation wage unemployment duration nexus

A thorny problem in identifying the determinants of reservation wages and particularly the role of continued joblessness in their evolution is the simultaneity issue. We deploy a natural control function approach to the problem that involves conditioning elapsed duration on completed unemployment duration in the reservation wage equation. Our analysis confirms that the use of elapsed duration alone compounds two separate and opposing influences. Only with the inclusion of completed duration is the negative effect of continued joblessness on reservation wages apparent. For its part, the completed duration coefficient suggests that higher reservation wages negatively influence the probability of exiting unemployment