2,408 research outputs found
A Predictive Algorithm For Wetlands In Deep Time Paleoclimate Models
Methane is a powerful greenhouse gas produced in wetland environments via microbial action in anaerobic conditions. If the location and extent of wetlands are unknown, such as for the Earth many millions of years in the past, a model of wetland fraction is required in order to calculate methane emissions and thus help reduce uncertainty in the understanding of past warm greenhouse climates. Here we present an algorithm for predicting inundated wetland fraction for use in calculating wetland methane emission fluxes in deep time paleoclimate simulations. The algorithm determines, for each grid cell in a given paleoclimate simulation, the wetland fraction predicted by a nearest neighbours search of modern day data in a space described by a set of environmental, climate and vegetation variables. To explore this approach, we first test it for a modern day climate with variables obtained from observations and then for an Eocene climate with variables derived from a fully coupled global climate model (HadCM3BL-M2.2). Two independent dynamic vegetation models were used to provide two sets of equivalent vegetation variables which yielded two different wetland predictions. As a first test the method, using both vegetation models, satisfactorily reproduces modern data wetland fraction at a course grid resolution, similar to those used in paleoclimate simulations. We then applied the method to an early Eocene climate, testing its outputs against the locations of Eocene coal deposits. We predict global mean monthly wetland fraction area for the early Eocene of 8 to 10 × 106km2 with corresponding total annual methane flux of 656 to 909 Tg, depending on which of two different dynamic global vegetation models are used to model wetland fraction and methane emission rates. Both values are significantly higher than estimates for the modern-day of 4 × 106km2 and around 190Tg (Poulter et. al. 2017, Melton et. al., 2013
Spectra of Urea and Thiourea in the 3µ Region
Observations are reported on the polarized infrared spectra of single crystals of urea and thiourea in the 3µ region. Complex structures accompanying the N [Single Bond] H fundamentals appear, at least in considerable part, to be attributable to combinations and overtones of fundamentals in the neighborhood of 1650 cm^—1
ANALYZING PEST CONTROL STRATEGIES FOR COTTON WITH AN ENVIRONMENTAL IMPACT MATRIX
Environmental Economics and Policy,
Recommended from our members
Determining how atmospheric carbon dioxide concentrations have changed during the history of the Earth
The reconstruction of ancient atmospheric carbon dioxide concentrations is essential to understanding the history of the Earth and life. It is also an important guide to identifying the sensitivity of the Earth system to this greenhouse gas and, therefore, constraining its future impact on climate. However, determining the concentration of CO2 in ancient atmospheres is a challenging endeavour requiring the application of state-of-the-art analytical chemistry to geological materials, underpinned by an understanding of photosynthesis and biochemistry. It is truly an interdisciplinary challenge
On-shelļ methods for perturbative QCD
We present new on-shell techniques for the calculation of colour ordered helicity amplitudes in QCD. We review the methods of on-shell recursion and the MHV rules before applying them to tree-level processes within the Standard Model. The MHV rules are applied to QCD corrections to Higgs amplitudes in the heavy top quark limit at tree- level, generating simple n֊point expressions for specific helicity configurations as well as developing more generally applicable recursion relations. We then generalise the on-shell recursion relations for massless QCD to include massive propagating particles and apply them to amplitudes with massive scalar particles, vector bosons and fermions. We then apply on-shell methods to compute the cut-constructible parts of 1-loop Higgs plus multi-gluon amplitudes fixing the remaining rational terms through Feynman diagrams. In all cases we find that the on-shell methods generate simpler analytic expressions than the traditional off-shell methods
ECONOMIC IMPACTS OF LAND USE CHANGES FROM A RESTRICTED NITROGEN FERTILIZER STRATEGY
Land Economics/Use,
On-shell recursion relations for all Born QCD amplitudes
We consider on-shell recursion relations for all Born QCD amplitudes. This
includes amplitudes with several pairs of quarks and massive quarks. We give a
detailed description on how to shift the external particles in spinor space and
clarify the allowed helicities of the shifted legs. We proof that the
corresponding meromorphic functions vanish at z --> infinity. As an application
we obtain compact expressions for helicity amplitudes including a pair of
massive quarks, one negative helicity gluon and an arbitrary number of positive
helicity gluons.Comment: 30 pages, minor change
The safety of electrical stimulation in patients with pacemakers and implantable cardioverter defibrillators: A systematic review
Introduction:
A number of patients are excluded from electrical stimulation treatment because there is concern that electrical stimulation could cause electromagnetic interference with pacemakers and implanted cardioverter defibrillators. The decision to use electrical stimulation in these patients needs to be supported by an assessment of benefit and harm.
Methods:
We conducted a systematic review of the risk of electromagnetic interference between electrical stimulation and pacemakers or implanted cardioverter defibrillators. We included the electronic databases MEDLINE and EMBASE in the time period between 1966 and 26 August 2016.
Results:
18 papers fulfilled the inclusion criteria (eight safety studies and ten case studies). Although we were unable to accurately estimate the risk of electromagnetic interference, the studies revealed that patients having electrical stimulation of the lower limb are less susceptible to electromagnetic interference.
Conclusions:
The results suggest that electrical stimulation could be used safely to help drop foot in patients with pacemakers or implanted cardioverter defibrillators. However, in order to obtain an accurate estimate of the risk of electromagnetic interference, a large, long-term, and intervention-specific safety study is required. Until such a study is undertaken, electrical stimulation should be used with caution in patients with pacemakers and implanted cardioverter defibrillators
Multigluon tree amplitudes with a pair of massive fermions
We consider the calculation of n-point multigluon tree amplitudes with a pair
of massive fermions in QCD. We give the explicit transformation rules of this
kind of massive fermion-pair amplitudes with respect to different reference
momenta and check the correctness of them by SUSY Ward identities. Using these
rules and onshell BCFW recursion relation, we calculate the analytic results of
several n-point multigluon amplitudes.Comment: 15page
- …