2,938 research outputs found
Fossils and living taxa agree on patterns of body mass evolution:A case study with Afrotheria
Most of life is extinct, so incorporating some fossil evidence into analyses of macroevolution is typically seen as necessary to understand the diversification of life and patterns of morphological evolution. Here we test the effects of inclusion of fossils in a study of the body size evolution of afrotherian mammals, a clade that includes the elephants, sea cows and elephant shrews. We find that the inclusion of fossil tips has little impact on analyses of body mass evolution; from a small ancestral size (approx. 100 g), there is a shift in rate and an increase in mass leading to the larger-bodied Paenungulata and Tubulidentata, regardless of whether fossils are included or excluded from analyses. For Afrotheria, the inclusion of fossils and morphological character data affect phylogenetic topology, but these differences have little impact upon patterns of body mass evolution and these body mass evolutionary patterns are consistent with the fossil record. The largest differences between our analyses result from the evolutionary model, not the addition of fossils. For some clades, extant-only analyses may be reliable to reconstruct body mass evolution, but the addition of fossils and careful model selection is likely to increase confidence and accuracy of reconstructed macroevolutionary patterns
Quantum oscillations without quantum coherence
We study numerically the damping of quantum oscillations and the dynamics of the density matrix in model many-spin systems decohered by a spin bath. We show that oscillations of some density matrix elements can persist with considerable amplitude long after other elements, along with the entropy, have come close to saturation, i.e., when the system has been decohered almost completely. The oscillations exhibit very slow decay, and may be observable in experiments.
Parity Effects in Spin Decoherence
We demonstrate that decoherence of many-spin systems can drastically differ
from decoherence of single-spin systems. The difference originates at the most
basic level, being determined by parity of the central system, i.e. by whether
the system comprises even or odd number of spin-1/2 entities. Therefore, it is
very likely that similar distinction between the central spin systems of even
and odd parity is important in many other situations. Our consideration
clarifies the physical origin of the unusual two-step decoherence found
previously in the two-spin systems.Comment: RevTeX 4, 5 pages, 2 figures; acknowledgments added; replaced with
the published version; journal reference adde
Decoherence by a chaotic many-spin bath
We numerically investigate decoherence of a two-spin system (central system)
by a bath of many spins 1/2. By carefully adjusting parameters, the dynamical
regime of the bath has been varied from quantum chaos to regular, while all
other dynamical characteristics have been kept practically intact. We
explicitly demonstrate that for a many-body quantum bath, the onset of quantum
chaos leads to significantly faster and stronger decoherence compared to an
equivalent non-chaotic bath. Moreover, the non-diagonal elements of the
system's density matrix decay differently for chaotic and non-chaotic baths.
Therefore, knowledge of the basic parameters of the bath (strength of the
system-bath interaction, bath's spectral density of states) is not always
sufficient, and much finer details of the bath's dynamics can strongly affect
the decoherence process.Comment: 4 pages, RevTeX, 5 eps figure
Overview of Serological Techniques for Influenza Vaccine Evaluation: Past, Present and Future
Serological techniques commonly used to quantify influenza-specific antibodies include the Haemagglutination Inhibition (HI), Single Radial Haemolysis (SRH) and Virus Neutralization (VN) assays. HI and SRH are established and reproducible techniques, whereas VN is more demanding. Every new influenza vaccine needs to fulfil the strict criteria issued by the European Medicines Agency (EMA) in order to be licensed. These criteria currently apply exclusively to SRH and HI assays and refer to two different target groups—healthy adults and the elderly, but other vaccine recipient age groups have not been considered (i.e., children). The purpose of this timely review is to highlight the current scenario on correlates of protection concerning influenza vaccines and underline the need to revise the criteria and assays currently in use. In addition to SRH and HI assays, the technical advantages provided by other techniques such as the VN assay, pseudotype-based neutralization assay, neuraminidase and cell-mediated immunity assays need to be considered and regulated via EMA criteria, considering the many significant advantages that they could offer for the development of effective vaccines
Sorghum bicolor INDETERMINATE1 is a conserved primary regulator of flowering
IntroductionA fundamental developmental switch for plants is transition from vegetative to floral growth, which integrates external and internal signals. INDETERMINATE1 (Id1) family proteins are zinc finger transcription factors that activate flowering in grasses regardless of photoperiod. Mutations in maize Id1 and rice Id1 (RID1) cause very late flowering. RID1 promotes expression of the flowering activator genes Early Heading Date1 (Ehd1) and Heading date 1 (Hd1), a rice homolog of CONSTANS (CO).Methods and resultsMapping of two recessive late flowering mutants from a pedigreed sorghum EMS mutant library identified two distinct mutations in the Sorghum bicolor Id1 (SbId1) homolog, mutant alleles named sbid1-1 and sbid1-2. The weaker sbid1-1 allele caused a 35 day delay in reaching boot stage in the field, but its effect was limited to 6 days under greenhouse conditions. The strong sbid1-2 allele delayed boot stage by more than 60 days in the field and under greenhouse conditions. When sbid1-1 and sbid1-2 were combined, the delayed flowering phenotype remained and resembled that of sbid1-2, confirming late flowering was due to loss of SbId1 function. Evaluation of major flowering time regulatory gene expression in sbid1-2 showed that SbId1 is needed for expression of floral activators, like SbCO and SbCN8, and repressors, like SbPRR37 and SbGhd7.DiscussionThese results demonstrate a conserved role for SbId1 in promotion of flowering in sorghum, where it appears to be critical to allow expression of most major flowering regulatory genes
Non-Reciprocal Interactions Induced by Water in Confinement
Water mediates electrostatic interactions via the orientation of its dipoles
around ions, molecules, and interfaces. This induced water polarization
consequently influences multiple phenomena. In particular, water polarization
modulated by nanoconfinement affects ion adsorption and transport, biomolecular
self-assembly, and surface chemical reactions. Therefore, it is of paramount
importance to understand how water-mediated interactions change at the
nanoscale. Here we show that near the graphene surface anion-cation
interactions do not obey the translational and isotropic symmetries of
Coulomb's law. We identify a new property, referred to as non-reciprocity,
which describes the non-equivalent and directional interaction between two
oppositely charged ions near the confining surface when their positions with
respect to the interface are exchanged. Specifically, upon exchange of the two
ions' positions along the surface normal direction the interaction energy
changes by about 5. In both cases, confinement enhances the attraction
between two oppositely charged ions near the graphene surface, while
intercalation of one ion into the graphene layers shifts the interaction to
repulsive. While the water permittivity in confinement is different from that
in bulk, the effects observed here via molecular dynamics simulations and X-ray
reflectivity experiments cannot be accounted for by current permittivity
models. Our work shows that the water structure is not enough to infer
electrostatic interactions near interfaces.Comment: 18 pages, 13 figures, Accepted in Physical Review Researc
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