Predicting the amount of nitrate-nitrogen and water in the soil profile

Non-Peer ReviewedFour simulation models were used to predict the amount and distribution of nitrate-N and water in soil from long-term spring wheat (Triticum aestivum L.) rotations at the end of the 1990 growing season at Melfort, Saskatchewan. There were significant differences between models in accurately simulating the nitrate-N and water status of the soil profile

SN 2007gr: a Normal Type Ic Supernova with a Mildly Relativistic Radio Jet?

A nearby type Ic supernova, SN 2007gr was observed with the EVN in two epochs 60 days apart (second observation also included the Green Bank Telescope). In both cases one of the EVN stations was the Westerbork Synthesis Radio Telescope (WSRT), which recorded the observational data not only in the VLBI mode, but also in its normal interferometric mode. Thus it provided an important reference observation. In the first epoch the fluxes measured by the VLBI network and the WSRT alone match well. However in the second epoch the peak brightness observed in the VLBI experiment is much lower than the total flux recorded by the WSRT. There could be multiple reasons for this discrepancy: a resolution effect, coherence losses in VLBI, or extended emission contaminating the WSRT measurement. With new WSRT observations we costrain the level of background emission and find that there is still a difference between the corrected total flux density and the VLBI peak brightness. If one assumes that this is dominated by resolution, this would correspond to an average apparent expansion speed of ~0.4c

The ASK Network: developing a virtuous cycle of subsurface data and knowledge exchange

Knowledge of the subsurface is essential in delivering successful construction and regeneration projects. Inadequate understanding of subsurface ground conditions can constrain effective development of urban areas and is a key factor in project delay and overspending. Improving this situation demands much better use, and re-use, of subsurface data and knowledge. The establishment of ASK subsurface data and knowledge exchange network has led to substantial improvements in how urban subsurface data is reported and exchanged between the public and private sectors. Implementation of the GSPEC standardised digital data reporting format has improved the integrity and accessibility of data. ASK and GSPEC are enabling the expansion and exchange of high quality systematic subsurface datasets, improving development of robust 3D ground models which can be used to promote more cost effective and better informed ground engineering investigations, and monitoring and regulation of resources in the urban environment. The work underway in Glasgow is acting as a standard for change, both within the UK and Europe

Response of an Excitatory-Inhibitory Neural Network to External Stimulation: An Application to Image Segmentation

Neural network models comprising elements which have exclusively excitatory or inhibitory synapses are capable of a wide range of dynamic behavior, including chaos. In this paper, a simple excitatory-inhibitory neural pair, which forms the building block of larger networks, is subjected to external stimulation. The response shows transition between various types of dynamics, depending upon the magnitude of the stimulus. Coupling such pairs over a local neighborhood in a two-dimensional plane, the resultant network can achieve a satisfactory segmentation of an image into ``object'' and ``background''. Results for synthetic and and ``real-life'' images are given.Comment: 8 pages, latex, 5 figure

Path Integral Description of a Semiclassical Su-Schrieffer-Heeger Model

The electron motion along a chain is described by a continuum version of the Su-Schrieffer-Heeger Hamiltonian in which phonon fields and electronic coordinates are mapped onto the time scale. The path integral formalism allows us to derive the non local source action for the particle interacting with the oscillators bath. The method can be applied for any value of the {\it e-ph} coupling. The path integral dependence on the model parameters has been analysed by computing the partition function and some thermodynamical properties from $T= 1K$ up to room temperature. A peculiar upturn in the low temperature {\it heat capacity over temperature} ratio (pointing to a glassy like behavior) has been ascribed to the time dependent electronic hopping along the chain

Is Vtb=1 ?

The strongest constraint on Vtb presently comes from the 3 x 3 unitarity of the CKM matrix, which fixes Vtb to be very close to one. If the unitarity is relaxed, current information from top production at Tevatron still leaves open the possibility that Vtb is sizably smaller than one. In minimal extensions of the standard model with extra heavy quarks, the unitarity constraints are much weaker and the EW precision parameters entail the strongest bounds on Vtb. We discuss the experimental perspectives of discovering and identifying such new physics models at the Tevatron and the LHC, through a precise measurement of Vtb from the single top cross sections and by the study of processes where the extra heavy quarks are produced.Comment: 19 pages, 8 figure

Constraints on the Variation of the Fine Structure Constant from Big Bang Nucleosynthesis

We put bounds on the variation of the value of the fine structure constant $\alpha$, at the time of Big Bang nucleosynthesis. We study carefully all light elements up to $^7$Li. We correct a previous upper limit on $|\Delta \alpha / \alpha|$ estimated from $^4$He primordial abundance and we find interesting new potential limits (depending on the value of the baryon-to-photon ratio) from $^7$Li, whose production is governed to a large extent by Coulomb barriers. The presently unclear observational situation concerning the primordial abundances preclude a better limit than |\Delta \alpha/\alpha| \lsim 2\cdot 10^{-2}, two orders of magnitude less restrictive than previous bounds. In fact, each of the (mutually exclusive) scenarios of standard Big Bang nucleosynthesis proposed, one based on a high value of the measured deuterium primordial abundance and one based on a low value, may describe some aspects of data better if a change in $\alpha$ of this magnitude is assumed.Comment: 21 pages, eps figures embedded using epsfig macr

Vibrational Properties of Nanoscale Materials: From Nanoparticles to Nanocrystalline Materials

The vibrational density of states (VDOS) of nanoclusters and nanocrystalline materials are derived from molecular-dynamics simulations using empirical tight-binding potentials. The results show that the VDOS inside nanoclusters can be understood as that of the corresponding bulk system compressed by the capillary pressure. At the surface of the nanoparticles the VDOS exhibits a strong enhancement at low energies and shows structures similar to that found near flat crystalline surfaces. For the nanocrystalline materials an increased VDOS is found at high and low phonon energies, in agreement with experimental findings. The individual VDOS contributions from the grain centers, grain boundaries, and internal surfaces show that, in the nanocrystalline materials, the VDOS enhancements are mainly caused by the grain-boundary contributions and that surface atoms play only a minor role. Although capillary pressures are also present inside the grains of nanocrystalline materials, their effect on the VDOS is different than in the cluster case which is probably due to the inter-grain coupling of the modes via the grain-boundaries.Comment: 10 pages, 7 figures, accepted for publication in Phys. Rev.