1,020 research outputs found
Wigner transform and pseudodifferential operators on symmetric spaces of non-compact type
We obtain a general expression for a Wigner transform (Wigner function) on
symmetric spaces of non-compact type and study the Weyl calculus of
pseudodifferential operators on them
Unmanned aerial vehicle remote sensing of snow: improving snowmelt prediction
Non-Peer Reviewe
Greenhouse gas intensity of an irrigated cropping system in Saskatchewan
Non-Peer ReviewedIn response to increasing global food demands, the proportion of irrigated agricultural land within the Canadian Prairies is likely to increase. However, the implications of this with respect to the agricultural greenhouse gas (GHG) balance are not well understood. This study investigates and compares the greenhouse gas intensity of a typical irrigated and dryland cropping system in Saskatchewan, a semi-arid region of the Canadian Prairies. Compared to their dryland counterpart, irrigated cropping systems have higher GHG emissions which are a result of the energy used for pumping and larger nitrous oxide (N2O) production rates associated with higher N-fertilizer application and moist soil conditions. These emissions may be partially offset by increased carbon sequestration from the greater productivity realized through irrigation. This investigation focuses on the quantification of soil GHG emissions through chamber-based flux measurements. Factors driving these emissions have been determined through in-situ soil temperature, matric potential, and moisture measurements. The emissions associated with pumping and other crop management activities are accounted for using the Intergovernmental Panel on Climate Change (IPCC) literature and methodology. Preliminary results from the first season of study confirm that irrigated cropping systems have greater greenhouse gas intensity. Soil N2O emissions from the irrigated system were four times greater than the dryland and were the greatest source of emissions for the irrigated system. Diesel combustion used to power equipment was comparable between cropping systems. Emissions associated with pumping were notable; however, due to the wet growing season they remained smaller than could be expected most years. The information derived from this study will aid in the development of regional specific soil emission factors, improved management strategies, and will identify new approaches for mitigating emissions
Pre-irrigation of a severely-saline soil with in-situ water to establish dryland forages
Non-Peer ReviewedAlfalfa serves as one of the most important forage plants in North America. It is also the recommended remedial crop for dryland salinity control. But, because of its limited salt tolerance, it does not establish satisfactorily in severely or moderately saline soils. A series of irrigations with the in-situ ground water located beneath a severely-saline site were delivered across seedbeds prepared within the same site prior to seeding ‘Beaver’ alfalfa (Medicago sativa) and ‘ AC Saltlander’ green wheatgrass (Elymus Hoffmannii). In this field study conducted in semiarid Saskatchewan, fall irrigations with 4.6 dS/m-water from a shallow, on-site, backhoe-dug well fitted with a solar-powered pump preceded spring seeding. Irrigation treatments ranged from zero to 2530 mm in total applied water. Plant emergence, spacing, height, cover, and forage yield of the alfalfa were significantly improved following pre-irrigation. Mean plant emergence increased from 20 to 79% for the alfalfa. The wheatgrass height and forage yield also improved significantly, but showed only an upward trend in emergence, spacing, height, and cover. The mean plant height in July increased from 90 to 159 mm for the wheatgrass and from 35 to 140 mm for the alfalfa. Based on linear regression of irrigated volume, every 119.3 mm of irrigated, in-situ water up to 2530 mm increased alfalfa forage yield by 10 g/m2
Aerodynamic and Radiative Controls on the Snow Surface Temperature
Abstract
The snow surface temperature (SST) is essential for estimating longwave radiation fluxes from snow. SST can be diagnosed using finescale multilayer snow physics models that track changes in snow properties and internal energy; however, these models are heavily parameterized, have high predictive uncertainty, and require continuous simulation to estimate prognostic state variables. Here, a relatively simple model to estimate SST that is not reliant on prognostic state variables is proposed. The model assumes that the snow surface is poorly connected thermally to the underlying snowpack and largely transparent for most of the shortwave radiation spectrum, such that a snow surface energy balance among only sensible heat, latent heat, longwave radiation, and near-infrared radiation is possible and is called the radiative psychrometric model (RPM). The RPM SST is sensitive to air temperature, humidity, ventilation, and longwave irradiance and is secondarily affected by absorption of near-infrared radiation at the snow surface that was higher where atmospheric deposition of particulates was more likely to be higher. The model was implemented with neutral stability, an implicit windless exchange coefficient, and constant shortwave absorption factors and aerodynamic roughness lengths. It was evaluated against radiative SST measurements from the Canadian Prairies and Rocky Mountains, French Alps, and Bolivian Andes. With optimized and global shortwave absorption and aerodynamic roughness length parameters, the model is shown to accurately predict SST under a wide range of conditions, providing superior predictions when compared to air temperature, dewpoint, or ice bulb calculation approaches.</jats:p
Volume of the set of unistochastic matrices of order 3 and the mean Jarlskog invariant
A bistochastic matrix B of size N is called unistochastic if there exists a
unitary U such that B_ij=|U_{ij}|^{2} for i,j=1,...,N. The set U_3 of all
unistochastic matrices of order N=3 forms a proper subset of the Birkhoff
polytope, which contains all bistochastic (doubly stochastic) matrices. We
compute the volume of the set U_3 with respect to the flat (Lebesgue) measure
and analytically evaluate the mean entropy of an unistochastic matrix of this
order. We also analyze the Jarlskog invariant J, defined for any unitary matrix
of order three, and derive its probability distribution for the ensemble of
matrices distributed with respect to the Haar measure on U(3) and for the
ensemble which generates the flat measure on the set of unistochastic matrices.
For both measures the probability of finding |J| smaller than the value
observed for the CKM matrix, which describes the violation of the CP parity, is
shown to be small. Similar statistical reasoning may also be applied to the MNS
matrix, which plays role in describing the neutrino oscillations. Some
conjectures are made concerning analogous probability measures in the space of
unitary matrices in higher dimensions.Comment: 33 pages, 6 figures version 2 - misprints corrected, explicit
formulae for phases provide
Symmetric spaces of higher rank do not admit differentiable compactifications
Any nonpositively curved symmetric space admits a topological
compactification, namely the Hadamard compactification. For rank one spaces,
this topological compactification can be endowed with a differentiable
structure such that the action of the isometry group is differentiable.
Moreover, the restriction of the action on the boundary leads to a flat model
for some geometry (conformal, CR or quaternionic CR depending of the space).
One can ask whether such a differentiable compactification exists for higher
rank spaces, hopefully leading to some knew geometry to explore. In this paper
we answer negatively.Comment: 13 pages, to appear in Mathematische Annale
Generalized quantum tomographic maps
Some non-linear generalizations of classical Radon tomography were recently
introduced by M. Asorey et al [Phys. Rev. A 77, 042115 (2008), where the
straight lines of the standard Radon map are replaced by quadratic curves
(ellipses, hyperbolas, circles) or quadratic surfaces (ellipsoids,
hyperboloids, spheres). We consider here the quantum version of this novel
non-linear approach and obtain, by systematic use of the Weyl map, a
tomographic encoding approach to quantum states. Non-linear quantum tomograms
admit a simple formulation within the framework of the star-product
quantization scheme and the reconstruction formulae of the density operators
are explicitly given in a closed form, with an explicit construction of
quantizers and dequantizers. The role of symmetry groups behind the generalized
tomographic maps is analyzed in some detail. We also introduce new
generalizations of the standard singular dequantizers of the symplectic
tomographic schemes, where the Dirac delta-distributions of operator-valued
arguments are replaced by smooth window functions, giving rise to the new
concept of "thick" quantum tomography. Applications for quantum state
measurements of photons and matter waves are discussed.Comment: 8 page
On the scattering theory of the classical hyperbolic C(n) Sutherland model
In this paper we study the scattering theory of the classical hyperbolic
Sutherland model associated with the C(n) root system. We prove that for any
values of the coupling constants the scattering map has a factorized form. As a
byproduct of our analysis, we propose a Lax matrix for the rational C(n)
Ruijsenaars-Schneider-van Diejen model with two independent coupling constants,
thereby setting the stage to establish the duality between the hyperbolic C(n)
Sutherland and the rational C(n) Ruijsenaars-Schneider-van Diejen models.Comment: 15 page
Nonnegatively curved homogeneous metrics obtained by scaling fibers of submersions
We consider invariant Riemannian metrics on compact homogeneous spaces G/H
where an intermediate subgroup K between G and H exists, so that the
homogeneous space G/H is the total space of a Riemannian submersion. We study
the question as to whether enlarging the fibers of the submersion by a constant
scaling factor retains the nonnegative curvature in the case that the
deformation starts at a normal homogeneous metric. We classify triples of
groups (H,K,G) where nonnegative curvature is maintained for small
deformations, using a criterion proved by Schwachh\"ofer and Tapp. We obtain a
complete classification in case the subgroup H has full rank and an almost
complete classification in the case of regular subgroups.Comment: 23 pages; minor revisions, to appear in Geometriae Dedicat
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