Oxygen Requirement and Inhibition of C4 Photosynthesis . An Analysis of C4 Plants Deficient in the C3 and C4 Cycles

The basis for O2 sensitivity of C4 photosynthesis was evaluated using a C4-cycle-limited mutant of Amaranthus edulis (a phosphoenolpyruvate carboxylase-deficient mutant), and a C3-cycle-limited transformant of Flaveria bidentis (an antisense ribulose-1,5-bisphosphate carboxylase/oxygenase [Rubisco] small subunit transformant). Data obtained with the C4-cycle-limited mutant showed that atmospheric levels of O2 (20 kPa) caused increased inhibition of photosynthesis as a result of higher levels of photorespiration. The optimal O2 partial pressure for photosynthesis was reduced from approximately 5 kPa O2 to 1 to 2 kPa O2, becoming similar to that of C3 plants. Therefore, the higher O2 requirement for optimal C4 photosynthesis is specifically associated with the C4 function. With the Rubisco-limited F. bidentis, there was less inhibition of photosynthesis by supraoptimal levels of O2 than in the wild type. When CO2 fixation by Rubisco is limited, an increase in the CO2 concentration in bundle-sheath cells via the C4 cycle may further reduce the oxygenase activity of Rubisco and decrease the inhibition of photosynthesis by high partial pressures of O2 while increasing CO2 leakage and overcycling of the C4 pathway. These results indicate that in C4 plants the investment in the C3 and C4 cycles must be balanced for maximum efficiency

The Stress Transmission Universality Classes of Periodic Granular Arrays

The transmission of stress is analysed for static periodic arrays of rigid grains, with perfect and zero friction. For minimal coordination number (which is sensitive to friction, sphericity and dimensionality), the stress distribution is soluble without reference to the corresponding displacement fields. In non-degenerate cases, the constitutive equations are found to be simple linear in the stress components. The corresponding coefficients depend crucially upon geometrical disorder of the grain contacts.Comment: 7 pages, 1 figur

Geology of Exeter and its environs

A 225 km² area around Exeter, described in this report, extends from the villages of Brampford Speke and Whimple in the north to Aylesbeare, Exminster and Woodbury in the south. It is underlain by Carboniferous, Permian, and Triassic solid formations and by a variety of Quaternary superficial deposits. The Namurian Crackington Formation comprises mainly tightly folded shales with subordinate sandstone interbeds. The Permian rocks consist of a lower, predominantly: breccia, sequence (Whipton Formation, Teignmouth Breccia, Monkerton Member) that thins and disappears northwards against a possibly fault-controlled ridge of Crackington Formation; the breccias are overlain by sandstones and mudstones (Dawlish Sandstone and Aylesbeare Mudstone). Volcanic rocks occur at the base of the Permian sequence and possibly within the Dawlish Sandstone. The latter splits into five alternating sandstone and mudstone members when traced northwards from Exeter into the Crediton Trough (an area of thick Permian sediments). The Aylesbeare Mudstone is divisible south of Aylesbeare into two members, the lower containing impersistent sandstones. It is overlain by the basal Triassic gravels (Budleigh Salterton Pebble Beds) which are in turn succeeded by the Otter Sandstone

Solving Lattice QCD systems of equations using mixed precision solvers on GPUs

Modern graphics hardware is designed for highly parallel numerical tasks and promises significant cost and performance benefits for many scientific applications. One such application is lattice quantum chromodyamics (lattice QCD), where the main computational challenge is to efficiently solve the discretized Dirac equation in the presence of an SU(3) gauge field. Using NVIDIA's CUDA platform we have implemented a Wilson-Dirac sparse matrix-vector product that performs at up to 40 Gflops, 135 Gflops and 212 Gflops for double, single and half precision respectively on NVIDIA's GeForce GTX 280 GPU. We have developed a new mixed precision approach for Krylov solvers using reliable updates which allows for full double precision accuracy while using only single or half precision arithmetic for the bulk of the computation. The resulting BiCGstab and CG solvers run in excess of 100 Gflops and, in terms of iterations until convergence, perform better than the usual defect-correction approach for mixed precision.Comment: 30 pages, 7 figure

APPLIED GEOLOGICAL MAPPING SOUTHAMPTON AREA: area covered by 1:50,000 Geological sheet No. 315 (Southampton) OS 1:10,000 sheets SU31 and 41, and parts of SU20, 21, 22, 30, 32, 40, 42, 50, 51 and 52

This study was commissioned by the Department of the Environment to develop and apply techniques of applied geological mapping for the purposes of land-use planning and development. It covers the area of the British Geological Survey (BGS) 1:50,000 geological map of Southampton. The study involved the computer manipulation of existing geological, geotechnical, hydrogeological and mineral resource data. The objectives were to develop the methodology, and to provide an archive of information, a set of applied geological maps, and descriptive reports in a form appropriate to all potential users. The computer is a powerful tool for bringing together spatially referenced information from many sources. There was collaboration with the Ordnance Survey and also with the Soil Survey of England and Wales who have been commissioned to undertake a study in the same area

Chiral properties of domain-wall fermions from eigenvalues of 4 dimensional Wilson-Dirac operator

We investigate chiral properties of the domain-wall fermion (DWF) system by using the four-dimensional hermitian Wilson-Dirac operator. We first derive a formula which connects a chiral symmetry breaking term in the five dimensional DWF Ward-Takahashi identity with the four dimensional Wilson-Dirac operator, and simplify the formula in terms of only the eigenvalues of the operator, using an ansatz for the form of the eigenvectors. For a given distribution of the eigenvalues, we then discuss the behavior of the chiral symmetry breaking term as a function of the fifth dimensional length. We finally argue the chiral property of the DWF formulation in the limit of the infinite fifth dimensional length, in connection with spectra of the hermitian Wilson-Dirac operator in the infinite volume limit as well as in the finite volume.Comment: Added a reference and modified the acknowledgmen

Diffusion and Localization of Cold Atoms in 3D Optical Speckle

In this work we re-formulate and solve the self-consistent theory for localization to a Bose-Einstein condensate expanding in a 3D optical speckle. The long-range nature of the fluctuations in the potential energy, treated in the self-consistent Born approximation, make the scattering strongly velocity dependent, and its consequences for mobility edge and fraction of localized atoms have been investigated numerically.Comment: 8 pages, 11 figure

Insight into nucleon structure from generalized parton distributions

The lowest three moments of generalized parton distributions are calculated in full QCD and provide new insight into the behavior of nucleon electromagnetic form factors, the origin of the nucleon spin, and the transverse structure of the nucleon.Comment: 3 pages, Lattice2003(Theoretical developments

Moments of nucleon spin-dependent generalized parton distributions

We present a lattice measurement of the first two moments of the spin-dependent GPD H-tilde(x,xi,t). From these we obtain the axial coupling constant and the second moment of the spin-dependent forward parton distribution. The measurements are done in full QCD using Wilson fermions. In addition, we also present results from a first exploratory study of full QCD using Asqtad sea and domain-wall valence fermions.Comment: Lattice2003(Theory), 3 pages, 3 figures, to appear in the Proceedings of Lattice 200