479 research outputs found
Why musical hierarchies?
Comentari a l'article:
Savage, P., Loui, P., Tarr, B., Schachner, A., Glowacki, L., Mithen, S., & Fitch, W. (2021). Music as a coevolved system for social bonding. Behavioral and Brain Sciences, 44, E59. Postprint: https://centaur.reading.ac.uk/95527/ . doi:10.1017/S0140525X20000333[eng] Credible signaling may have provided a selection pressure for producing and discriminating increasingly elaborate proto-musical signals. But, why evolve them to have hierarchical structure? We argue that the hierarchality of tonality and meter is a byproduct of domain-general mechanisms evolved for reasons other than credible signaling
Discrimination between O-H…N and O-H…O=C Complexes of 3-Methyl-4-pyrimidone and Methanol. A Matrix-isolation FT-IR and Theoretical DFT/B3LYP Investigation
FT-IR matrix-isolated spectra for 3-methyl-4-pyrimidone and its H-bonded complexes with methanol in Ar were studied with the aim of discriminating between O-H…N and O-H…O=C complexes. Theoretical calculations were carried out using the DFT/B3LYP/6-31+G(d) methodology in an attempt to predict the preferred interaction site of the 3-methyl-4-pyrimidone molecule with proton donors. The observed frequency decrease of the ν(C=O) mode of 3-methyl-4-pyrimidone and the appearance of a broad ν(OH…O) band in the spectrum of the complex with methanol suggest that H-bonding with methanol occurs at the carbonyl group. Computed binding energies of the hydrogen-bonded complexes (ΔEc) and computed intermolecular distances (r(O…H)) confirm that the O-H…O=C complex is preferred with methanol. However, for H-bonding with stronger acids such as HCl, the computational data suggest that the H-bonding occurs at the N1 ring atom of 3-methyl-4-pyrimidone.Keywords: Matrix-isolation, 3-methyl-4-pyrimidone, methanol, FT-IR spectroscopy, DFT/B3LYP calculation
Foldamers of β-peptides : conformational preference of peptides formed by rigid building blocks : The first MI-IR spectra of a triamide nanosystem
To determine local chirality driven conformational preferences of small aminocyclobutane-1-carboxylic acid derivatives, X-(ACBA) n -Y, their matrix-isolation IR spectra were recorded and analyzed. For the very first time model systems of this kind were deposited in a frozen (~10 K) noble gas matrix to reduce line width and thus, the recorded sharp vibrational lines were analyzed in details. For cis-(S,R)-1 monomer two “zigzag” conformers composed of either a six or an eight-membered H-bonded pseudo ring was identified. For trans-(S,S)-2 stereoisomer a zigzag of an eight-membered pseudo ring and a helical building unit were determined. Both findings are fully consistent with our computational results, even though the relative conformational ratios were found to vary with respect to measurements. For the dimers (S,R,S,S)-3 and (S,S,S,R)-4 as many as four different cis,trans and three different trans,cis conformers were localized in their matrix-isolation IR (MI-IR) spectra. These foldamers not only agree with the previous computational and NMR results, but also unambiguously show for the first time the presence of a structure made of a cis,trans conformer which links a “zigzag” and a helical foldamer via a bifurcated H-bond. The present work underlines the importance of MI-IR spectroscopy, applied for the first time for triamides to analyze the conformational pool of small biomolecules. We have shown that the local chirality of a β-amino acid can fully control its backbone folding preferences. Unlike proteogenic α-peptides, β- and especially (ACBA) n type oligopeptides could thus be used to rationally design and influence foldamer’s structural preferences
Nullity conditions in paracontact geometry
The paper is a complete study of paracontact metric manifolds for which the
Reeb vector field of the underlying contact structure satisfies a nullity
condition (the condition \eqref{paranullity} below, for some real numbers and ). This class of pseudo-Riemannian manifolds,
which includes para-Sasakian manifolds, was recently defined in \cite{MOTE}. In
this paper we show in fact that there is a kind of duality between those
manifolds and contact metric -spaces. In particular, we prove
that, under some natural assumption, any such paracontact metric manifold
admits a compatible contact metric -structure (eventually
Sasakian). Moreover, we prove that the nullity condition is invariant under -homothetic deformations and determines the whole curvature tensor
field completely. Finally non-trivial examples in any dimension are presented
and the many differences with the contact metric case, due to the non-positive
definiteness of the metric, are discussed.Comment: Different. Geom. Appl. (to appear
Curvature homogeneous spacelike Jordan Osserman pseudo-Riemannian manifolds
Let s be at least 2. We construct Ricci flat pseudo-Riemannian manifolds of
signature (2s,s) which are not locally homogeneous but whose curvature tensors
never the less exhibit a number of important symmetry properties. They are
curvature homogeneous; their curvature tensor is modeled on that of a local
symmetric space. They are spacelike Jordan Osserman with a Jacobi operator
which is nilpotent of order 3; they are not timelike Jordan Osserman. They are
k-spacelike higher order Jordan Osserman for ; they are k-timelike
higher order Jordan Osserman for , and they are not k timelike
higher order Jordan Osserman for .Comment: Update bibliography, fix minor misprint
Convergence of vector bundles with metrics of Sasaki-type
If a sequence of Riemannian manifolds, , converges in the pointed
Gromov-Hausdorff sense to a limit space, , and if are vector
bundles over endowed with metrics of Sasaki-type with a uniform upper
bound on rank, then a subsequence of the converges in the pointed
Gromov-Hausdorff sense to a metric space, . The projection maps
converge to a limit submetry and the fibers converge to
its fibers; the latter may no longer be vector spaces but are homeomorphic to
, where is a closed subgroup of ---called the {\em wane
group}--- that depends on the basepoint and that is defined using the holonomy
groups on the vector bundles. The norms converges to a map
compatible with the re-scaling in and the -action
on converges to an action on compatible with the
limiting norm.
In the special case when the sequence of vector bundles has a uniform lower
bound on holonomy radius (as in a sequence of collapsing flat tori to a
circle), the limit fibers are vector spaces. Under the opposite extreme, e.g.
when a single compact -dimensional manifold is re-scaled to a point, the
limit fiber is where is the closure of the holonomy group of the
compact manifold considered.
An appropriate notion of parallelism is given to the limiting spaces by
considering curves whose length is unchanged under the projection. The class of
such curves is invariant under the -action and each such curve preserves
norms. The existence of parallel translation along rectifiable curves with
arbitrary initial conditions is also exhibited. Uniqueness is not true in
general, but a necessary condition is given in terms of the aforementioned wane
groups .Comment: 44 pages, 1 figure, in V.2 added Theorem E and Section 4 on
parallelism in the limit space
The curvature tensor of (\ka,\mu,\nu)-contact metric manifolds
We study the Riemann curvature tensor of (\kappa,\mu,\nu)-contact metric
manifolds, which we prove to be completely determined in dimension 3, and we
observe how it is affected by D_a-homothetic deformations. This prompts the
definition and study of generalized (\kappa,\mu,\nu)-space forms and of the
necessary and sufficient conditions for them to be conformally flat
Challenges in measuring nitrogen isotope signatures in inorganic nitrogen forms: An interlaboratory comparison of three common measurement approaches
Rationale
Stable isotope approaches are increasingly applied to better understand the cycling of inorganic nitrogen (Ni) forms, key limiting nutrients in terrestrial and aquatic ecosystems. A systematic comparison of the accuracy and precision of the most commonly used methods to analyze δ15N in NO3− and NH4+ and interlaboratory comparison tests to evaluate the comparability of isotope results between laboratories are, however, still lacking.
Methods
Here, we conducted an interlaboratory comparison involving 10 European laboratories to compare different methods and laboratory performance to measure δ15N in NO3− and NH4+. The approaches tested were (a) microdiffusion (MD), (b) chemical conversion (CM), which transforms Ni to either N2O (CM-N2O) or N2 (CM-N2), and (c) the denitrifier (DN) methods.
Results
The study showed that standards in their single forms were reasonably replicated by the different methods and laboratories, with laboratories applying CM-N2O performing superior for both NO3− and NH4+, followed by DN. Laboratories using MD significantly underestimated the “true” values due to incomplete recovery and also those using CM-N2 showed issues with isotope fractionation. Most methods and laboratories underestimated the at%15N of Ni of labeled standards in their single forms, but relative errors were within maximal 6% deviation from the real value and therefore acceptable. The results showed further that MD is strongly biased by nonspecificity. The results of the environmental samples were generally highly variable, with standard deviations (SD) of up to ± 8.4‰ for NO3− and ± 32.9‰ for NH4+; SDs within laboratories were found to be considerably lower (on average 3.1‰). The variability could not be connected to any single factor but next to errors due to blank contamination, isotope normalization, and fractionation, and also matrix effects and analytical errors have to be considered
Low NO and variable CH fluxes from tropical forest soils of the Congo Basin
Globally, tropical forests are assumed to be an important source of atmospheric nitrous oxide (NO) and sink for methane (CH). Yet, although the Congo Basin comprises the second largest tropical forest and is considered the most pristine large basin left on Earth, in situ NO and CH flux measurements are scarce. Here, we provide multi-year data derived from on-ground soil flux (n = 1558) and riverine dissolved gas concentration (n = 332) measurements spanning montane, swamp, and lowland forests. Each forest type core monitoring site was sampled at least for one hydrological year between 2016 - 2020 at a frequency of 7-14 days. We estimate a terrestrial CH uptake (in kg CH-C ha yr) for montane (−4.28) and lowland forests (−3.52) and a massive CH release from swamp forests (non-inundated 2.68; inundated 341). All investigated forest types were a NO source (except for inundated swamp forest) with 0.93, 1.56, 3.5, and −0.19 kg NO-N ha yr for montane, lowland, non-inundated swamp, and inundated swamp forests, respectively
Reconciling biodiversity and carbon stock conservation in an Afrotropical forest landscape
Protecting aboveground carbon stocks in tropical forests is essential for mitigating global climate change and is assumed to simultaneously conserve biodiversity. Although the relationship between tree diversity and carbon stocks is generally positive, the relationship remains unclear for consumers or decomposers. We assessed this relationship for multiple trophic levels across the tree of life (10 organismal groups, 3 kingdoms) in lowland rainforests of the Congo Basin. Comparisons across regrowth and old-growth forests evinced the expected positive relationship for trees, but not for other organismal groups. Moreover, differences in species composition between forests increased with difference in carbon stock. These variable associations across the tree of life contradict the implicit assumption that maximum co-benefits to biodiversity are associated with conservation of forests with the highest carbon storage. Initiatives targeting climate change mitigation and biodiversity conservation should include both old-growth and regenerating forests to optimally benefit biodiversity and carbon storage
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