6,815 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 Late Time Light Curve of SN 1998bw Associated with GRB980425
We report 139 photometric observations through the B, V, and I filters of the
supernova SN 1998bw, an object which is associated with the Gamma-Ray Burst GRB
980425. Detailed light curves of this unique supernova can be compared to
theoretical models, so we report here our light curve for 123 days between 27
June 1998 and 28 October 1998. The light curve of SN 1988bw is consistent with
those of the Type Ic class. We find that the magnitude-versus-time relation for
this supernova is linear to within 0.05 mags in all colors over the entire
duration of our study. Our measured uniform decline rates are , , and magnitudes per day in the
B, V, and I bands. The linear decline and the rate of that decline suggest that
late time light curve is powered by the radioactive decay of cobalt with some
leakage of the gamma rays.Comment: 15 pages, 1 figure, 1 table, Accepted for publication in PAS
Spin-liquid and magnetic phases in the anisotropic triangular lattice: the case of -(ET)X
The two-dimensional Hubbard model on the anisotropic triangular lattice, with
two different hopping amplitudes and , is relevant to describe
the low-energy physics of -(ET)X, a family of organic salts. The
ground-state properties of this model are studied by using Monte Carlo
techniques, on the basis of a recent definition of backflow correlations for
strongly-correlated lattice systems. The results show that there is no magnetic
order for reasonably large values of the electron-electron interaction and
frustrating ratio , suitable to describe the non-magnetic
compound with X=Cu(CN). On the contrary, N\'eel order takes place for
weaker frustrations, i.e., , suitable for
materials with X=Cu(SCN), Cu[N(CN)]Cl, or Cu[N(CN)]Br.Comment: 7 pages, Physical Review B 80, 064419 (2009
Humans of interiors – diversity by design
Within the disciplines of Interior Architecture and Design, visual depiction of spaces is a powerful tool to communicate use, users and qualities of the designed/proposed spaces. With a mixture of techniques we can produce images capable of plunging viewers directly into these imagined spaces. Visual depictions of people demonstrate social norms and values, teaching viewers how the world works and their place within it via symbolic socialisation. Such visualisations, so provocative and seductive, are carefully designed to communicate the atmosphere that the designer is aiming to create, but if they fail to include a fair representation of the people those spaces are designed for, they misrepresent the aim of the project. This distinct lack of diversity and inclusivity within visuals is indicative of both a lack of consideration of the existence of people who are not the same as the designers themselves (who are overwhelmingly young, white and able- bodied1) and an equally problematic lack of understanding of the needs of these populations. The paper is the account of a collaboration, a research project and a series of workshops conducted over the last few years by the University of Lincoln and Middlesex University London. Humans of Interiors/Diversity by Design aims at promoting a discussion across education and industry on the impact that visualization has on the representation of future spaces and whom these spaces are addressed and designed for: a discourse about social sustainability of spatial design. The research activities underpinning Humans of Interiors/Diversity by Design and the workshops devised internationally, help establish EDI as an integral part of the design process and enable participants to apply their own critically reflective knowledge and understanding of these principles to the development of their design
Superconducting Pairing Symmetries in Anisotropic Triangular Quantum Antiferromagnets
Motivated by the recent discovery of a low temperature spin liquid phase in
layered organic compound -(ET)Cu(CN) which becomes a
superconductor under pressure, we examine the phase transition of Mott
insulating and superconducting (SC) states in a Hubbard-Heisenberg model on an
anisotropic triangular lattice. We use a renormalized mean field theory to
study the Gutzwiller projected BCS wavefucntions. The half filled electron
system is a Mott insulator at large on-site repulsion , and is a
superconductor at a moderate . The symmetry of the SC state depends on the
anisotropy, and is gapful with symmetry near the
isotropic limit and is gapless with symmetry at small anisotropy
ratio.Comment: 6 pages, 5 figure
Quantum entanglement between a nonlinear nanomechanical resonator and a microwave field
We consider a theoretical model for a nonlinear nanomechanical resonator
coupled to a superconducting microwave resonator. The nanomechanical resonator
is driven parametrically at twice its resonance frequency, while the
superconducting microwave resonator is driven with two tones that differ in
frequency by an amount equal to the parametric driving frequency. We show that
the semi-classical approximation of this system has an interesting fixed point
bifurcation structure. In the semi-classical dynamics a transition from stable
fixed points to limit cycles is observed as one moves from positive to negative
detuning. We show that signatures of this bifurcation structure are also
present in the full dissipative quantum system and further show that it leads
to mixed state entanglement between the nanomechanical resonator and the
microwave cavity in the dissipative quantum system that is a maximum close to
the semi-classical bifurcation. Quantum signatures of the semi-classical
limit-cycles are presented.Comment: 36 pages, 18 figure
Effects of Fertilizer Rates and Pasture Type on Soil Mineral Nitrogen Concentration under Dairy Pasture
The effects of three rates of nitrogen (N) fertilizer applied to monocultures of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.), and mixed ryegrass / clover swards, grazed by dairy cows on soil mineral nitrogen levels in the top 10cm of soil were studied on a dryland pasture in south-western, Victoria, Australia. Ammonium and nitrate were monitored for 14 months. Clover monocultures had significantly greater NO3- levels, however a similar trend was not observed for NH4+ . Increasing fertilizer application rate significantly increased both NO3- and NH4+ levels under all pasture types
A Unified Picture of the FIP and Inverse FIP Effects
We discuss models for coronal abundance anomalies observed in the coronae of
the sun and other late-type stars following a scenario first introduced by
Schwadron, Fisk & Zurbuchen of the interaction of waves at loop footpoints with
the partially neutral gas. Instead of considering wave heating of ions in this
location, we explore the effects on the upper chromospheric plasma of the wave
ponderomotive forces. These can arise as upward propagating waves from the
chromosphere transmit or reflect upon reaching the chromosphere-corona
boundary, and are in large part determined by the properties of the coronal
loop above. Our scenario has the advantage that for realistic wave energy
densities, both positive and negative changes in the abundance of ionized
species compared to neutrals can result, allowing both FIP and Inverse FIP
effects to come out of the model. We discuss how variations in model parameters
can account for essentially all of the abundance anomalies observed in solar
spectra. Expected variations with stellar spectral type are also qualitatively
consistent with observations of the FIP effect in stellar coronae.Comment: 25 pages, 4 figures, submitted to Ap
Nonlinear Diffusive Shock Acceleration with Magnetic Field Amplification
We introduce a Monte Carlo model of nonlinear diffusive shock acceleration
allowing for the generation of large-amplitude magnetic turbulence. The model
is the first to include strong wave generation, efficient particle acceleration
to relativistic energies in nonrelativistic shocks, and thermal particle
injection in an internally self-consistent manner. We find that the upstream
magnetic field can be amplified by large factors and show that this
amplification depends strongly on the ambient Alfven Mach number. We also show
that in the nonlinear model large increases in the magnetic field do not
necessarily translate into a large increase in the maximum particle momentum a
particular shock can produce, a consequence of high momentum particles
diffusing in the shock precursor where the large amplified field converges to
the low ambient value. To deal with the field growth rate in the regime of
strong fluctuations, we extend to strong turbulence a parameterization that is
consistent with the resonant quasi-linear growth rate in the weak turbulence
limit. We believe our parameterization spans the maximum and minimum range of
the fluctuation growth and, within these limits, we show that the nonlinear
shock structure, acceleration efficiency, and thermal particle injection rates
depend strongly on the yet to be determined details of wave growth in strongly
turbulent fields. The most direct application of our results will be to
estimate magnetic fields amplified by strong cosmic-ray modified shocks in
supernova remnants.Comment: Accepted in ApJ July 2006, typos corrected in this versio
Theory of magnon-polaritons in quantum Ising materials
We present a theory of magnon-polaritons in quantum Ising materials, and
develop a formalism describing the coupling between light and matter as an
Ising system is tuned through its quantum critical point. The theory is applied
to Ising materials having multilevel single-site Hamiltonians, in which
multiple magnon modes are present, such as the insulating Ising magnet
LiHoF . We find that the magnon-photon coupling strengths may be tuned by
the applied transverse field, with the coupling between the soft mode present
in the quantum Ising material and a photonic resonator mode diverging at the
quantum critical point of the material. A fixed system of spins will not
exhibit the diamagnetic response expected when light is coupled to mobile spins
or atoms. Without the diamagnetic response, one expects a divergent
magnon-photon coupling strength to lead to a superradiant quantum phase
transition. However, this neglects the effects of damping and decoherence
present in any real system. We show that damping and decoherence may block the
superradiant quantum phase transition, and lead to weak coupling between the
soft magnon mode and the resonator mode. The results of the theory are applied
to experimental data on the model system LiHoF in a microwave resonator.Comment: 22 pages, 6 figure
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