1,908 research outputs found
Frictional dissipation of polymeric solids vs interfacial glass transition
We present single contact friction experiments between a glassy polymer and
smooth silica substrates grafted with alkylsilane layers of different coverage
densities and morphologies. This allows us to adjust the polymer/substrate
interaction strength. We find that, when going from weak to strong interaction,
the response of the interfacial junction where shear localizes evolves from
that of a highly viscous threshold fluid to that of a plastically deformed
glassy solid. This we analyse as resulting from an interaction-induced
``interfacial glass transition'' helped by pressure
Baryons Still Trace Dark Matter: Probing CMB Lensing Maps For Hidden Isocurvature
Compensated isocurvature perturbations (CIPs) are primordial fluctuations that balance baryon and dark-matter isocurvature to leave the total matter density unperturbed. The effects of CIPs on the cosmic microwave background (CMB) anisotropies are similar to those produced by weak lensing of the CMB: smoothing of the power spectrum and generation of non-Gaussian features. Here, an entirely new CIP contribution to the standard estimator for the lensing-potential power spectrum is derived. Planck measurements of the temperature and polarization power spectrum, as well as estimates of CMB lensing, are used to place limits on the variance of the CIP fluctuations on CMB scales, Δ2rms(RCMB). The resulting constraint of Δ2rms(RCMB)\u3c4.3×10−3 at 95% confidence level (CL) using this new technique improves on past work by a factor of ∼3. We find that for Planck data our constraints almost reach the sensitivity of the optimal CIP estimator. The method presented here is currently the most sensitive probe of the amplitude of a scale-invariant CIP power spectrum, ACIP, placing an upper limit of ACIP\u3c0.017 at 95% CL. Future measurements of the large-scale CMB lensing-potential power spectrum could probe CIP amplitudes as low as Δ2rms(RCMB)=8×10−5 at 95% CL (corresponding to ACIP=3.2×10−4)
Do we (need to) care about canopy radiation schemes in DGVMs? Caveats and potential impacts
Dynamic global vegetation models (DGVMs) are an essential part of current state-of-the-art Earth system models. In recent years, the complexity of DGVMs has increased by incorporating new important processes like, e.g., nutrient cycling and land cover dynamics, while biogeophysical processes like surface radiation have not been developed much further. Canopy radiation models are however very important for the estimation of absorption and reflected fluxes and are essential for a proper estimation of surface carbon, energy and water fluxes.
The present study provides an overview of current implementations of canopy radiation schemes in a couple of state-of-the-art DGVMs and assesses their accuracy in simulating canopy absorption and reflection for a variety of different surface conditions. Systematic deviations in surface albedo and fractions of absorbed photosynthetic active radiation (faPAR) are identified and potential impacts are assessed.
The results show clear deviations for both, absorbed and reflected, surface solar radiation fluxes. FaPAR is typically underestimated, which results in an underestimation of gross primary productivity (GPP) for the investigated cases. The deviation can be as large as 25% in extreme cases. Deviations in surface albedo range between −0.15 ≤ Δα ≤ 0.36, with a slight positive bias on the order of Δα ≈ 0.04. Potential radiative forcing caused by albedo deviations is estimated at −1.25 ≤ RF ≤ −0.8 (W m−2), caused by neglect of the diurnal cycle of surface albedo.
The present study is the first one that provides an assessment of canopy RT schemes in different currently used DGVMs together with an assessment of the potential impact of the identified deviations. The paper illustrates that there is a general need to improve the canopy radiation schemes in DGVMs and provides different perspectives for their improvement
The evolution, distribution and diversity of endogenous circoviral elements in vertebrate genomes
Circoviruses (family Circoviridae) are small, non-enveloped viruses that have short, single-stranded DNA genomes. Circovirus sequences are frequently recovered in metagenomic investigations, indicating that these viruses are widespread, yet they remain relatively poorly understood. Endogenous circoviral elements (CVe) are DNA sequences derived from circoviruses that occur in vertebrate genomes. CVe are a useful source of information about the biology and evolution of circoviruses. In this study, we screened 362 vertebrate genome assemblies in silico to generate a catalog of CVe loci. We identified a total of 179 CVe sequences, most of which have not been reported previously. We show that these CVe loci reflect at least 19 distinct germline integration events. We determine the structure of CVe loci, identifying some that show evidence of potential functionalization. We also identify orthologous copies of CVe in snakes, fish, birds, and mammals, allowing us to add new calibrations to the timeline of circovirus evolution. Finally, we observed that some ancient CVe group robustly with contemporary circoviruses in phylogenies, with all sequences within these groups being derived from the same host class or order, implying a hitherto underappreciated stability in circovirus-host relationships. The openly available dataset constructed in this investigation provides new insights into circovirus evolution, and can be used to facilitate further studies of circoviruses and CVe
Pressure-induced melting of the orbital polaron lattice in La1-xSrxMnO3
We report on the pressure effects on the orbital polaron lattice in the
lightly doped manganites , with . The
dependence of the orbital polaron lattice on chemical pressure is
studied by substituting Pr for La in
. In addition, we have studied
its hydrostatic pressure dependence in
. Our results strongly
indicate that the hopping significantly contributes to the stabilization of
the orbital polaron lattice and that the orbital polarons are ferromagnetic
objects which get stabilized by local double exchange processes. The analysis
of short range orbital correlations and the verification of the Grueneisen
scaling by hard x-ray, specific heat and thermal expansion data reinforces our
conclusions.Comment: 7 figure
On the Construction and the Structure of Off-Shell Supermultiplet Quotients
Recent efforts to classify representations of supersymmetry with no central
charge have focused on supermultiplets that are aptly depicted by Adinkras,
wherein every supersymmetry generator transforms each component field into
precisely one other component field or its derivative. Herein, we study
gauge-quotients of direct sums of Adinkras by a supersymmetric image of another
Adinkra and thus solve a puzzle from Ref.[2]: The so-defined supermultiplets do
not produce Adinkras but more general types of supermultiplets, each depicted
as a connected network of Adinkras. Iterating this gauge-quotient construction
then yields an indefinite sequence of ever larger supermultiplets, reminiscent
of Weyl's construction that is known to produce all finite-dimensional unitary
representations in Lie algebras.Comment: 20 pages, revised to clarify the problem addressed and solve
Magnetisation of hole-doped CuO2 spin chains in Sr14-xCaxCu24O41
We report on magnetisation measurements of Sr14-xCaxCu24O41, with 0 <= x <=
12, in magnetic fields up to 16 T. The low temperature magnetic response of the
CuO2 spin chains changes strongly upon doping. For x = 0, the ground state with
nearly independent dimers is confirmed. Reduction of the number of holes in the
chains through Ca-doping leads to an additional contribution to the
magnetisation, which depends linearly on the magnetic field. Remarkably, the
slope of this linear contribution increases with the Ca content. We argue that
antiferromagnetic spin chains do not account for this behaviour but that the
hole dynamics might be involved.Comment: In v2, spelling of author names has been change
The Interior of Jupiter
Jupiter, owing to its large mass and rapid formation, played
a crucial role in shaping the solar system as we know it
today. Jupiter mostly contains hydrogen and helium (more
than 87% by mass), and as such bears a close resemblance
to the Sun. However, the Sun has only 2% of its mass in elements
other than hydrogen and helium (the heavy elements),
whereas Jupiter has between 3 and 13%. The exact amount
of these heavy elements in the planet and their distribution
are keys to understanding how the solar system formed
Fundamental properties of the mammalian innate immune system revealed by multispecies comparison of type I interferon responses
The host innate immune response mediated by type I interferon (IFN) and the resulting up-regulation of hundreds of interferon-stimulated genes (ISGs) provide an immediate barrier to virus infection. Studies of the type I ‘interferome’ have mainly been carried out at a single species level, often lacking the power necessary to understand key evolutionary features of this pathway. Here, using a single experimental platform, we determined the properties of the interferomes of multiple vertebrate species and developed a webserver to mine the dataset. This approach revealed a conserved ‘core’ of 62 ISGs, including genes not previously associated with IFN, underscoring the ancestral functions associated with this antiviral host response. We show that gene expansion contributes to the evolution of the IFN system and that interferomes are shaped by lineage-specific pressures. Consequently, each mammal possesses a unique repertoire of ISGs, including genes common to all mammals and others unique to their specific species or phylogenetic lineages. An analysis of genes commonly down-regulated by IFN suggests that epigenetic regulation of transcription is a fundamental aspect of the IFN response. Our study provides a resource for the scientific community highlighting key paradigms of the type I IFN response
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