308 research outputs found
Electric field distortions in structures of the twist bend nematic (NTB) phase of a bent-core liquid crystal
Dielectric spectroscopy of a twist bend nematic phase of an achiral bent core
liquid crystalline compound under DC bias is used to investigate its response
to electric field. Two collective relaxation processes are revealed, these are
assigned to distortions of helicoidal structure by the external bias field.
Frequency of the mode depends primarily on the helicoidal angle and has
anomalous, softening- like behaviour at the nematic to the twist bend nematic
transition. A coupling of dielectric anisotropy with electric field gives rise
to a new equilibrium periodic structure in the time scale involved. The modulus
of the wave vector gradually vanishes on increasing the bias field (except for
the initial behaviour, which is just the opposite). Transition from the twist
bend to the splay bend structure is clearly observed by a sudden drop in the
frequency of this mode, which decreases almost linearly with increasing field.
Results agree with predictions from current models for the periodically
distorted a twist bend nematic phase.Comment: 14 PAGES, 7 FIGURES, submitted to Physical Review Letter
gSLM: The Initial Steps for the Specification of a Service Management Standard for Federated e-Infrastructures
New data from Monoplacophora and a carefully-curated dataset resolve molluscan relationships
Relationships among the major lineages of Mollusca have long been debated. Morphological studies have considered the rarely collected Monoplacophora (Tryblidia) to have several plesiomorphic molluscan traits. The phylogenetic position of this group is contentious as morphologists have generally placed this clade as the sister taxon of the rest of Conchifera whereas earlier molecular studies supported a clade of Monoplacophora +Polyplacophora (Serialia) and phylogenomic studies have generally recovered a clade of Monoplacophora +Cephalopoda. Phylogenomic studies have also strongly supported a clade including Gastropoda, Bivalvia, and Scaphopoda, but relationships among these taxa have been inconsistent. In order to resolve conchiferan relationships and improve understanding of early molluscan evolution, we carefully curated a high-quality data matrix and conducted phylogenomic analyses with broad taxon sampling including newly sequenced genomic data from the monoplacophoran Laevipilina antarctica. Whereas a partitioned maximum likelihood (ML) analysis using site-homogeneous models recovered Monoplacophora sister to Cephalopoda with moderate support, both ML and Bayesian inference (BI) analyses using mixture models recovered Monoplacophora sister to all other conchiferans with strong support. A supertree approach also recovered Monoplacophora as the sister taxon of a clade composed of the rest of Conchifera. Gastropoda was recovered as the sister taxon of Scaphopoda in most analyses, which was strongly supported when mixture models were used. A molecular clock based on our BI topology dates diversification of Mollusca to similar to 546 MYA (+/- 6 MYA) and Conchifera to similar to 540 MYA (+/- 9 MYA), generally consistent with previous work employing nuclear housekeeping genes. These results provide important resolution of conchiferan mollusc phylogeny and offer new insights into ancestral character states of major mollusc clades
Probing a non-biaxial behavior of infinitely thin hard platelets
We give a criterion to test a non-biaxial behavior of infinitely thin hard
platelets of symmetry based upon the components of three order
parameter tensors. We investigated the nematic behavior of monodisperse
infinitely thin rectangular hard platelet systems by using the criterion.
Starting with a square platelet system, and we compared it with rectangular
platelet systems of various aspect ratios. For each system, we performed
equilibration runs by using isobaric Monte Carlo simulations. Each system did
not show a biaxial nematic behavior but a uniaxial nematic one, despite of the
shape anisotropy of those platelets. The relationship between effective
diameters by simulations and theoretical effective diameters of the above
systems was also determined.Comment: Submitted to JPS
Monoplacophoran mitochondrial genomes: convergent gene arrangements and little phylogenetic signal
Background: Although recent studies have greatly advanced understanding of deep molluscan phylogeny, placement of some taxa remains uncertain as different datasets support competing class-relationships. Traditionally, morphologists have placed Monoplacophora, a group of morphologically simple, limpet-like molluscs as sister group to all other conchiferans (shelled molluscs other than Polyplacophora), a grouping that is supported by the latest large-scale phylogenomic study that includes Laevipilina. However, molecular datasets dominated by nuclear ribosomal genes support Monoplacophora + Polyplacophora (Serialia). Here, we evaluate the potential of mitochondrial genome data for resolving placement of Monoplacophora. Results: Two complete (Laevipilina antarctica and Vema ewingi) and one partial (Laevipilina hyalina) mitochondrial genomes were sequenced, assembled, and compared. All three genomes show a highly similar architecture including an unusually high number of non-coding regions. Comparison of monoplacophoran gene order shows a gene arrangement pattern not previously reported;there is an inversion of one large gene cluster. Our reanalyses of recently published polyplacophoran mitogenomes show, however, that this feature is also present in some chiton species. Maximum Likelihood and Bayesian Inference analyses of 13 mitochondrial protein-coding genes failed to robustly place Monoplacophora and hypothesis testing could not reject any of the evaluated placements of Monoplacophora. Conclusions: Under both serialian or aculiferan-conchiferan scenarios, the observed gene cluster inversion appears to be a convergent evolution of gene arrangements in molluscs. Our phylogenetic results are inconclusive and sensitive to taxon sampling. Aculifera (Polyplacophora + Aplacophora) and Conchifera were never recovered. However, some analyses recovered Serialia (Monoplacophora + Polyplacophora), Diasoma (Bivalvia + Scaphopoda) or Pleistomollusca (Bivalvia + Gastropoda). Although we could not shed light on deep evolutionary traits of Mollusca we found unique patterns of gene arrangements that are common to monoplacophoran and chitonine polyplacophoran species but not to acanthochitonine Polyplacophora
Topical treatments and their molecular/cellular mechanisms in patients with peripheral neuropathic pain : narrative Review
Anomalous temperature dependence of layer spacing of de Vries liquid crystals: Compensation model
Cherenkov Telescope Array Data Management
Very High Energy gamma-ray astronomy with the Cherenkov Telescope Array (CTA)
is evolving towards the model of a public observatory. Handling, processing and
archiving the large amount of data generated by the CTA instruments and
delivering scientific products are some of the challenges in designing the CTA
Data Management. The participation of scientists from within CTA Consortium and
from the greater worldwide scientific community necessitates a sophisticated
scientific analysis system capable of providing unified and efficient user
access to data, software and computing resources. Data Management is designed
to respond to three main issues: (i) the treatment and flow of data from remote
telescopes; (ii) "big-data" archiving and processing; (iii) and open data
access. In this communication the overall technical design of the CTA Data
Management, current major developments and prototypes are presented.Comment: 8 pages, 2 figures, In Proceedings of the 34th International Cosmic
Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions
at arXiv:1508.0589
Step-wise evolution of complex chemical defenses in millipedes: a phylogenomic approach
With fossil representatives from the Silurian capable of respiring atmospheric oxygen, millipedes
are among the oldest terrestrial animals, and likely the first to acquire diverse and complex chemical defenses against predators. Exploring the origin of complex adaptive traits is critical for understanding the evolution of Earth’s biological complexity, and chemical defense evolution serves as an ideal
study system. The classic explanation for the evolution of complexity is by gradual increase from simple to complex, passing through intermediate “stepping stone� states. Here we present the first phylogenetic-based study of the evolution of complex chemical defenses in millipedes by generating the largest genomic-based phylogenetic dataset ever assembled for the group. Our phylogenomic results demonstrate that chemical complexity shows a clear pattern of escalation through time. New pathways are added in a stepwise pattern, leading to greater chemical complexity, independently in a number of derived lineages. This complexity gradually increased through time, leading to the advent of three distantly related chemically complex evolutionary lineages, each uniquely characteristic of each of the respective millipede groups
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