345 research outputs found
Recommended from our members
Notations and conventions in molecular spectroscopy: part 2. Symmetry notation
The field of Molecular Spectroscopy was surveyed in order to determine a set of
conventions and symbols which are in common use in the spectroscopic literature. This
document, which is Part 2 in a series, establishes the notations and conventions used for the
description of symmetry in rigid molecules, using the Schoenflies notation. It deals firstly
with the symmetry operators of the molecular point groups (also drawing attention to the
difference between symmetry operators and elements). The conventions and notations of the
molecular point groups are then established, followed by those of the representations of these
groups as used in molecular spectroscopy. Further parts will follow, dealing inter alia with
permutation and permutation-inversion symmetry notation, vibration-rotation spectroscopy
and electronic spectroscopy
Tree stem bases are sources of CH<sub>4</sub> and N<sub>2</sub>O in a tropical forest on upland soil during the dry to wet season transition
Tropical forests on upland soils are assumed to be a methane (CH4) sink and a weak source of nitrous oxide (N2O), but studies of wetland forests have demonstrated that tree stems can be a substantial source of CH4,and recent evidence from temperate woodlands suggests that tree stems can also emit N2O. Here, we measured CH4 and N2O fluxes from the soil and from tree stems in a semi-evergreen tropical forest on upland soil. To examine the influence of seasonality, soil abiotic conditions, and substrate availability (litter inputs) on trace greenhouse gas (GHG) fluxes, we conducted our study during the transition from the dry to the wet season in a long-term litter manipulation experiment in Panama, Central America. Trace GHG fluxes were measured from individual stem bases of two common tree species and from soils beneath the same trees. Soil CH4 fluxes varied from uptake in the dry season to minor emissions in the wet season. Soil N2O fluxes were negligible during the dry season but increased markedly after the start of the wet season. By contrast, tree stembases emitted CH4 and N2O throughout the study. Although we observed no clear effect of litter manipulation on trace GHG fluxes, tree species and litter treatments interacted to influence CH4 fluxes from stems and N2O fluxes from stems and soil, indicating complex relationships between tree species traits and decomposition processes that can influence trace GHG dynamics. Collectively, our results show that tropical trees can act as conduits for trace GHGs that most likely originate from deeper soil horizons, even when they are growing on upland soils. Coupled with the finding that the soils may be a weaker sink for CH4 than previously thought, our research highlights the need to reappraise trace gas budgets in tropical forests
Recommended from our members
Notations and conventions in molecular spectroscopy: part 1. General spectroscopic notation
The field of Molecular Spectroscopy was surveyed in order to determine a set of
conventions and symbols which are in common use in the spectroscopic literature. This
document, which is Part I in a series, establishes the notations and conventions used for
general spectroscopic notations and deals with quantum mechanics, quantum numbers
(vibrational states, angular momentum and energy levels), spectroscopic transitions, and
miscellaneous notations (e.g. spectroscopic terms). Further parts will follow, dealing inter
alia with symmetry notation, permutation and permutation-inversion symmetry notation,
vibration-rotation spectroscopy and electronic spectroscopy
Recommended from our members
Modelling Bourdieu: An Extension of The Axelrod Cultural Diffusion model
Infectious disease and health systems modelling for local decision making to control neglected tropical diseases
Most neglected tropical diseases (NTDs) have complex life cycles and are challenging to control. The â2020 goalsâ of control and elimination as a public health programme for a number of NTDs are the subject of significant international efforts and investments. Beyond 2020 there will be a drive to maintain these gains and to push for true local elimination of transmission. However, these diseases are affected by variations in vectors, human demography, access to water and sanitation, access to interventions and local health systems. We therefore argue that there will be a need to develop local quantitative expertise to support elimination efforts. If available now, quantitative analyses would provide updated estimates of the burden of disease, assist in the design of locally appropriate control programmes, estimate the effectiveness of current interventions and support âreal-timeâ updates to local operations. Such quantitative tools are increasingly available at an international scale for NTDs, but are rarely tailored to local scenarios. Localised expertise not only provides an opportunity for more relevant analyses, but also has a greater chance of developing positive feedback between data collection and analysis by demonstrating the value of data. This is essential as rational program design relies on good quality data collection. It is also likely that if such infrastructure is provided for NTDs there will be an additional impact on the health system more broadly. Locally tailored quantitative analyses can help achieve sustainable and effective control of NTDs, but also underpin the development of local health care systems
Dust and the spectral energy distribution of the OH/IR star OH 127.8+0.0: Evidence for circumstellar metallic iron
We present a fit to the spectral energy distribution of OH 127.8+0.0, a
typical asymptotic giant branch star with an optically thick circumstellar dust
shell. The fit to the dust spectrum is achieved using non-spherical grains
consisting of metallic iron, amorphous and crystalline silicates and water ice.
Previous similar attempts have not resulted in a satisfactory fit to the
observed spectral energy distributions, mainly because of an apparent lack of
opacity in the 3--8 micron region of the spectrum. Non-spherical metallic iron
grains provide an identification for the missing source of opacity in the
near-infrared. Using the derived dust composition, we have calculated spectra
for a range of mass-loss rates in order to perform a consistency check by
comparison with other evolved stars. The L-[12 micron] colours of these models
correctly predict the mass-loss rate of a sample of AGB stars, strengthening
our conclusion that the metallic iron grains dominate the near-infrared flux.
We discuss a formation mechanism for non-spherical metallic iron grains.Comment: 10 pages, 6 figures, accepted for publication by A&
Positron-molecule interactions: resonant attachment, annihilation, and bound states
This article presents an overview of current understanding of the interaction
of low-energy positrons with molecules with emphasis on resonances, positron
attachment and annihilation. Annihilation rates measured as a function of
positron energy reveal the presence of vibrational Feshbach resonances (VFR)
for many polyatomic molecules. These resonances lead to strong enhancement of
the annihilation rates. They also provide evidence that positrons bind to many
molecular species. A quantitative theory of VFR-mediated attachment to small
molecules is presented. It is tested successfully for selected molecules (e.g.,
methyl halides and methanol) where all modes couple to the positron continuum.
Combination and overtone resonances are observed and their role is elucidated.
In larger molecules, annihilation rates from VFR far exceed those explicable on
the basis of single-mode resonances. These enhancements increase rapidly with
the number of vibrational degrees of freedom. While the details are as yet
unclear, intramolecular vibrational energy redistribution to states that do not
couple directly to the positron continuum appears to be responsible for these
enhanced annihilation rates. Downshifts of the VFR from the vibrational mode
energies have provided binding energies for thirty species. Their dependence
upon molecular parameters and their relationship to positron-atom and
positron-molecule binding energy calculations are discussed. Feshbach
resonances and positron binding to molecules are compared with the analogous
electron-molecule (negative ion) cases. The relationship of VFR-mediated
annihilation to other phenomena such as Doppler-broadening of the gamma-ray
annihilation spectra, annihilation of thermalized positrons in gases, and
annihilation-induced fragmentation of molecules is discussed.Comment: 50 pages, 40 figure
Identification and assessment of cardiolipin interactions with E. coli inner membrane proteins
Integral membrane proteins are localized and/or regulated by lipids present in the surrounding bilayer. While bacteria have relatively simple membranes, there is ample evidence that many bacterial proteins bind to specific lipids, especially the anionic lipid cardiolipin. Here, we apply molecular dynamics simulations to assess lipid binding to 42 different Escherichia coli inner membrane proteins. Our data reveal an asymmetry between the membrane leaflets, with increased anionic lipid binding to the inner leaflet regions of the proteins, particularly for cardiolipin. From our simulations, we identify >700 independent cardiolipin binding sites, allowing us to identify the molecular basis of a prototypical cardiolipin binding site, which we validate against structures of bacterial proteins bound to cardiolipin. This allows us to construct a set of metrics for defining a high-affinity cardiolipin binding site on bacterial membrane proteins, paving the way for a heuristic approach to defining other protein-lipid interactions
- âŠ