Clifford algebras from quotient ring spectra

We give natural descriptions of the homology and cohomology algebras of regular quotient ring spectra of even E-infinity ring spectra. We show that the homology is a Clifford algebra with respect to a certain bilinear form naturally associated to the quotient ring spectrum F. To identify the cohomology algebra, we first determine the derivations of F and then prove that the cohomology is isomorphic to the exterior algebra on the module of derivations. We treat the example of the Morava K-theories in detail.Comment: Final version (to appear). Changes: new paragraph in 1.1, amended Definition 2.14, new Remark 3.6, amended proof of Proposition 5.1 (reference problem eliminated), various minor change

The Long-run Performance of Seasoned Equity Offerings with rights evidence from the Swiss Market

We examine the long-run performance of firms that offer seasoned equity on the Swiss market. Swiss firms use offerings with rights to raise new equity and they can issue three types of securities. Moreover, the tax law has for some firms the effect of increasing the issuing frequency. We find that most SEOs are small as a percentage of the firm’s market capitalisation. The leverage ratios change often (up and down) during a three-period post-SEO horizon. The long-run abnormal returns are insignificant relative to size and book-to-market matching portfolios. These findings are corroborated by the fact that a portfolio of issuing firms do not exhibit a risk adjusted (Fama and French three factor model and Time-varying beta) abnormal performance. These findings are in accordance with the growing literature showing that the US SEOs do no more have abnormal negative performance. Finally, we show that Swiss firms have an incentive to use SEOs as a substitute to stock dividends. This particular feature help to explain the high frequency of SEOs in Switzerland before 1992.

A brief introduction to the model microswimmer {\it Chlamydomonas reinhardtii}

The unicellular biflagellate green alga {\it Chlamydomonas reinhardtii} has been an important model system in biology for decades, and in recent years it has started to attract growing attention also within the biophysics community. Here we provide a concise review of some of the aspects of {\it Chlamydomonas} biology and biophysics most immediately relevant to physicists that might be interested in starting to work with this versatile microorganism.Comment: 16 pages, 7 figures. To be published as part of EPJ S

Universal entrainment mechanism governs contact times with motile cells

Contact between particles and motile cells underpins a wide variety of biological processes, from nutrient capture and ligand binding, to grazing, viral infection and cell-cell communication. The window of opportunity for these interactions is ultimately determined by the physical mechanism that enables proximity and governs the contact time. Jeanneret et al. (Nat. Comm. 7: 12518, 2016) reported recently that for the biflagellate microalga Chlamydomonas reinhardtii contact with microparticles is controlled by events in which the object is entrained by the swimmer over large distances. However, neither the universality of this interaction mechanism nor its physical origins are currently understood. Here we show that particle entrainment is indeed a generic feature for microorganisms either pushed or pulled by flagella. By combining experiments, simulations and analytical modelling we reveal that entrainment length, and therefore contact time, can be understood within the framework of Taylor dispersion as a competition between advection by the no slip surface of the cell body and microparticle diffusion. The existence of an optimal tracer size is predicted theoretically, and observed experimentally for C. reinhardtii. Spatial organisation of flagella, swimming speed, swimmer and tracer size influence entrainment features and provide different trade-offs that may be tuned to optimise microbial interactions like predation and infection.Comment: New analytical entrainment theory; includes Supplementary informations as Appendix; Supplementary movies available upon reques

Hamiltonian traffic dynamics in microfluidic-loop networks

Recent microfluidic experiments revealed that large particles advected in a fluidic loop display long-range hydrodynamic interactions. However, the consequences of such couplings on the traffic dynamics in more complex networks remain poorly understood. In this letter, we focus on the transport of a finite number of particles in one-dimensional loop networks. By combining numerical, theoretical, and experimental efforts, we evidence that this collective process offers a unique example of Hamiltonian dynamics for hydrodynamically interacting particles. In addition, we show that the asymptotic trajectories are necessarily reciprocal despite the microscopic traffic rules explicitly break the time reversal symmetry. We exploit these two remarkable properties to account for the salient features of the effective three-particle interaction induced by the exploration of fluidic loops

What makes a host profitable? Parasites balance host nutritive resources against immunity

Numerous host qualities can modulate parasite fitness, and among these, host nutritive resources and immunity are of prime importance. Indeed, parasite fitness increases with the amount of nutritive resources extracted from the host body and decreases with host immune response. To maximize fitness, parasites have therefore to balance these two host components. Yet, because host nutritive resources and immunity both increase with host body condition, it is unclear whether parasites perform better on hosts in prime, intermediate, or poor condition. We investigated blood meal size and survival of the ectoparasitic louse fly Crataerina melbae in relation to body condition and cutaneous immune response of their Alpine swift (Apus melba) nestling hosts. Louse flies took a smaller blood meal and lived a shorter period of time when feeding on nestlings that were experimentally food deprived or had their cutaneous immune response boosted with methionine. Consistent with these results, louse fly survival was the highest when feeding on nonexperimental nestlings in intermediate body condition. Our findings emphasize that although hosts in poor condition had a reduced immunocompetence, parasites may have avoided them because individuals in poor condition did not provide adequate resources. These findings highlight the fact that giving host immunocompetence primary consideration can result in a biased appraisal of host-parasite interactions

Impact of low-input meadows on arthropod diversity at habitat and landscape level

In Switzerland, in order to preserve and enhance arthopod diversity in grassland ecosystems (among others), farmers had to convert at least 7 % of their land to ecological compensation areas – ECA. Major ECA are low input grassland, traditional orchards, hedges and wild flower strips. In this paper the difference in species assemblages of 3 arthropod groups, namely spiders, carabid beetles and butterflies between intensively managed and low input meadows is stressed by means of multivariate statistics. On one hand, the consequences of these differences are analysed at the habitat level to promote good practices for the arthropod diversity in grassland ecosystems. On the other hand, the contribution of each meadow type to the regional diversity is investigated to widen the analysis at the landscape level

Emergent hyperuniformity in periodically-driven emulsions

We report the emergence of large-scale hyperuniformity in microfluidic emulsions. Upon periodic driving confined emulsions undergo a first-order transition from a reversible to an irreversible dynamics. We evidence that this dynamical transition is accompanied by structural changes at all scales yielding macroscopic yet finite hyperuniform structures. Numerical simulations are performed to single out the very ingredients responsible for the suppression of density fluctuations. We show that as opposed to equilibrium systems the long-range nature of the hydrodynamic interactions are not required for the formation of hyperuniform patterns, thereby suggesting a robust relation between reversibility and hyperuniformity which should hold in a broad class of periodically driven materials.Comment: 5p, 3f, submitte