8,454 research outputs found
Use of thermal infrared and colour infrared imagery to detect crop moisture stress
The author has identified the following significant results. In the presence of variable plant cover (primarily percent cover) and variable available water content, the remotely sensed apparent temperatures correlate closely with plant cover and poorly with soil water. To the extent that plant cover is not systematically related to available soil water, available water in the root zone values may not be reliably predicted from the thermal infrared data. On the other hand, if plant cover is uniform and the soil surface is shown in a minor way, the thermal data indicate plant stress and consequently available water in the soil profile
The role of cosmic rays and Alfven waves in the structure of the galactic halo
The effect that cosmic rays and the Alfven waves they generate have on the structure of the plasma distribution perpendicular to the galactic disk is examined. It is shown that the plasma distribution exhibits two length scales and the predicted values of gas density far from the galactic plane indicate that models involving hydrostatic equilibrium should be replaced by those allowing for a galactic wind
Spin Fluctuations and the Pseudogap in Organic Superconductors
We show that there are strong similarities in the spin lattice relaxation of
non-magnetic organic charge transfer salts, and that these similarities can be
understood in terms of spin fluctuations. Further, we show that, in all of the
kappa-phase organic superconductors for which there is nuclear magnetic
resonance data, the energy scale for the spin fluctuations coincides with the
energy scale for the pseudogap. This suggests that the pseudogap is caused by
short-range spin correlations. In the weakly frustrated metals
k-(BEDT-TTF)_2Cu[N(CN)_2]Br, k-(BEDT-TTF)_2Cu(NCS)_2, and
k-(BEDT-TTF)_2Cu[N(CN)_2]Cl (under pressure) the pseudogap opens at the same
temperature as coherence emerges in the (intralayer) transport. We argue that
this is because the spin correlations are cut off by the loss of intralayer
coherence at high temperatures. We discuss what might happen to these two
energy scales at high pressures, where the electronic correlations are weaker.
In these weakly frustrated materials the data is well described by the chemical
pressure hypothesis (that anion substitution is equivalent to hydrostatic
pressure). However, we find important differences in the metallic state of
k-(BEDT-TTF)_2Cu_2(CN)_3, which is highly frustrated and displays a spin liquid
insulating phase. We also show that the characteristic temperature scale of the
spin fluctuations in (TMTSF)_2ClO_4 is the same as superconducting critical
temperature, which may be evidence that spin fluctuations mediate the
superconductivity in the Bechgaard salts.Comment: 7 pages, 4 figures; to appear in PR
Spin Bose-Metal phase in a spin-1/2 model with ring exchange on a two-leg triangular strip
Recent experiments on triangular lattice organic Mott insulators have found
evidence for a 2D spin liquid in proximity to the metal-insulator transition. A
Gutzwiller wavefunction study of the triangular lattice Heisenberg model with
appropriate four-spin ring exchanges has found that the projected spinon Fermi
sea state has a low variational energy. This wavefunction, together with a
slave particle gauge theory, suggests that such spin liquid possesses spin
correlations that are singular along surfaces in momentum space ("Bose
surfaces"). Signatures of this state, which we refer to as a "Spin Bose-Metal"
(SBM), are expected to be manifest in quasi-1D ladder systems: The discrete
transverse momenta cut through the 2D Bose surface leading to a distinct
pattern of 1D gapless modes. Here we search for a quasi-1D descendant of the
triangular lattice SBM state by exploring the Heisenberg plus ring model on a
two-leg strip (zigzag chain). Using DMRG, variational wavefunctions, and a
Bosonization analysis, we map out the full phase diagram. Without ring exchange
the model is equivalent to the J_1 - J_2 Heisenberg chain, and we find the
expected Bethe-chain and dimerized phases. Remarkably, moderate ring exchange
reveals a new gapless phase over a large swath of the phase diagram. Spin and
dimer correlations possess particular singular wavevectors and allow us to
identify this phase as the hoped for quasi-1D descendant SBM state. We derive a
low energy theory and find three gapless modes and one Luttinger parameter
controlling all power laws. Potential instabilities out of the zigzag SBM give
rise to other interesting phases such as a period-3 VBS or a period-4 Chirality
order, which we discover in the DMRG; we also find an interesting SBM state
with partial ferromagnetism.Comment: 30 pages, 23 figure
Spin Bose-Metal and Valence Bond Solid phases in a spin-1/2 model with ring exchanges on a four-leg triangular ladder
We study a spin-1/2 system with Heisenberg plus ring exchanges on a four-leg
triangular ladder using the density matrix renormalization group and Gutzwiller
variational wave functions. Near an isotropic lattice regime, for moderate to
large ring exchanges we find a spin Bose-metal phase with a spinon Fermi sea
consisting of three partially filled bands. Going away from the triangular
towards the square lattice regime, we find a staggered dimer phase with dimers
in the transverse direction, while for small ring exchanges the system is in a
featureless rung phase. We also discuss parent states and a possible phase
diagram in two dimensions.Comment: 4 pages, 5 figures, v3 is the print versio
H-bond competition experiments in solution and the solid state
The H-bonding outcomes in crystal structures of simple molecules, where two potential H-bonds can be formed, have been used to calculate relative H-bond probabilities for 59 combinations of Hbond donors and H-bond acceptors. H-bond probabilities are shown to correlate well with the difference in solution phase free energy between the two competing H-bonds.We acknowledge the financial support from the EPSRC through a CASE award scheme in collaboration with the Cambridge Crystallographic Data Centre.This is the author accepted manuscript. The final version is available from RSC via http://dx.doi.org/10.1039/C5CE02223
An evolving approach to developing academics understanding of transition for first year students. A Practice Report
The purpose of this paper is to describe the strategies used in the First Year Experience (FYE) Project at the University of Technology, Sydney (UTS) to engage and support academics to address student transition and diversity. The UTS FYE framework has provided a mechanism for third generation transition pedagogy which has been realised through a range of strategies including the establishment of a UTS FYE Coordinator overseeing the design and implementation of FYE Forums, the FYE small grant scheme, and supporting the First Year Transition Experience (FYTE) coordinators in faculties. These strategies have resulted in an evolving learning community in which staff have a sense of belonging and identity and their learning is situated and negotiated. The impact of this project on academics is demonstrated through the increasing participation in forums, increasing sophistication of grant applications and the leadership of the FYTE coordinators
Achieving academic engagement: Supporting academics to embed first year transition pedagogies in the curriculum
This paper describes a small grants scheme aimed at supporting academics to embed first year (FY) transition pedagogies in the curriculum, as part of a university-wide FYE strategy. The scheme enables first year subject coordinators to apply for funding to address one or more of the six transition pedagogy principles in ways appropriate for their disciplines and students. Over three years, fifty grants have been awarded to coordinators from all faculties for projects that range from resource creation to tutor development to changes in assessment and feedback practices. The paper describes the operation of the scheme and provides an initial analysis of the successes and challenges of its first two years from the perspectives of the grant holders and the UTS FYE Coordinator. Two examples of FYE grants are used to illustrate some features of successful projects
Ant litter fauna of forest, forest edges and adjacentgrassland in the Atlantic rain forest region of Bahia, Brazil
The litter ant fauna was sampled by Winkler sacks and pitfall traps along transects running through Atlantic rain forest into an adjacent grassland. Transects ran 65 m into the forest and 45 m into the field. Ninety-seven species of ants were sampled and scored, 85 were found in the forest, 48 were found in the field and 36 were common to both habitats. There was some evidence that species richness was lowest in the field and high at the deepest point within the forest. The composition of the ant community at the different distances into the forest and field was analysed by a number of hierarchical clustering procedures and also by ordinating the data in three-dimensional space. A two-way table of the ant assemblages derived from the clustering procedure versus the groupings of transect distances obtained by the same procedure indicated that certain ant species had preferences for the field or particular distances into the forest. It is concluded that although the ant fauna of Atlantic rain forest is severely affected by clearing, a forest-like ant fauna is able to persist right up to the interior edge of the forest
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