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Due to the spontaneous deformations of ferroelectric crystals in their ferroelectric phases, twins (domains) may be separated only by those composition planes (domain walls) which satisfy the mechanical compatibility conditions; such planes are in an infinite crystal called permissible walls. A mathematical treatment is proposed which makes it possible to find all permissible walls in any ferroelectric species. It is shown that different types of permissible walls exist: Woo walls with arbitrary orientation, crystallographically prominent WI walls, and S walls whose indices depend on P s and the electromechanical coefficients. The orientations of such S walls are necessarily temperature dependent. Two particular domains may be separated by a Woo wall or by one of two mutually perpendicular permissible walls of WI and/or S type. In a number of species, however, there are pairs of domains between which no wall is permissible. It is shown that the occurrence of Woo and W, walls can be predicted from the symmetry properties of the paraelectric phase. The properties of S walls are discussed in detail. Among the known ferroelectrics, Swails are most likely to exist in MASD and in boracites. The available data on nickel-chlorine boracite suggest that S walls have been observed in this material. 1 I. S. Zheludev and L.

Algae with secondary plastids of a red algal origin, such as ochrophytes (photosynthetic stramenopiles), are diverse and ecologically important, yet their evolutionary history remains controversial. We sequenced plastid genomes of two ochrophytes, Ochromonas sp. CCMP1393 (Chrysophyceae) and Trachydiscus minutus (Eustigmatophyceae). A shared split of the clpC gene as well as phylogenomic analyses of concatenated protein sequences demonstrated that chrysophytes and eustigmatophytes form a clade, the Limnista, exhibiting an unexpectedly elevated rate of plastid gene evolution. Our analyses also indicate that the root of the ochrophyte phylogeny falls between the recently redefined Khakista and Phaeista assemblages. Taking advantage of the expanded sampling of plastid genome sequences, we revisited the phylogenetic position of the plastid of Vitrella brassicaformis, a member of Alveolata with the least derived plastid genome known for the whole group. The results varied depending on the dataset and phylogenetic method employed, but suggested that the Vitrella plastids emerged from a deep ochrophyte lineage rather than being derived vertically from a hypothetical plastid-bearing common ancestor of alveolates and stramenopiles. Thus, we hypothesize that the plastid in Vitrella, and potentially in other alveolates, may have been acquired by an endosymbiosis of an early ochrophyte.

Euglenids are a group of protists that comprises species with diverse feeding modes. One distinct and diversified clade of euglenids is photoautotrophic, and its members bear green secondary plastids. In this paper we present the plastid genome of the euglenid Eutreptiella, which we assembled from 454 sequencing of Eutreptiella gDNA. Comparison of this genome and the only other available plastid genomes of photosynthetic euglenid, Euglena gracilis, revealed that they contain a virtually identical set of 57 protein coding genes, 24 genes fewer than the genome of Pyramimonas parkeae, the closest extant algal relative of the euglenid plastid. Searching within the transcriptomes of Euglena and Eutreptiella showed that 6 of the missing genes were transferred to the nucleus of the euglenid host while 18 have been probably lost completely. Euglena and Eutreptiella represent the deepest bifurcation in the photosynthetic clade, and therefore all these gene transfers and losses must have happened before the last common ancestor of all known photosynthetic euglenids. After the split of Euglena and Eutreptiella only one additional gene loss took place. The conservation of gene content in the two lineages of euglenids is in contrast to the variability of gene order and intron counts, which diversified dramatically. Our results show that the early secondary plastid of euglenids was much more susceptible to gene losses and endosymbiotic gene transfers than the established plastid, which is surprisingly resistant to changes in gene content.

We present the observation of ferroelastoelectric switching in a ferroelectric material. It is achieved in barium titanate thin film by simultaneously applying electric field and compressive stress with the tip of a scanning force microscope. For low compressive stresses, the presented measurements reveal classical ferroelectric domain reversal, i.e., the spontaneous polarization is aligned parallel to the applied electric field. However, for high compressive stresses the direction of polarization after switching is antiparallel to the poling field, demonstrating ferroelastoelectric switching.

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ANR-20-NEUC-0005-01 -Brainstim, by the European Union's Horizon 2020 research and innovation programme under grant agreement No. 945539 (SGA3) Human Brain Project and VirtualBrainCloud No. 826421.