9,094 research outputs found
The Doppler Spectra of Medium Grazing Angle Sea Clutter; Part 1: Characterisation
No full textThis paper is concerned with the characterisation of Doppler spectra from high range resolution X-band radar sea clutter observed from an airborne platform over the range of grazing angles, 15° to 45°. It is observed that when looking up or down wind there is a strong correlation between mean Doppler shift and local spectrum intensity. When combined with random fluctuations of spectrum width, these characteristics give the spectra a temporal and spatial variability. This behaviour has previously been observed in low grazing angle data and these results confirm the wider applicability of the models developed using that data. The modelling method is also extended here to capture the bimodal behaviour observed with high intensity returns from breaking waves looking up or down-wind
Halecium interpolatum Ritchie 1907
No full textHalecium interpolatum Ritchie, 1907 (Fig. 3F) Halecium interpolatum —watson, 2008: 171–172, fig. 7A, B; Peña Cantero, 2014c: 261 –263, figs 5G–J, 8A–B (synonymy). Material examined. 48EV194 , a few tiny stems up to 2 mm high, on S. glacialis (IK–2012–10437). Remarks. Incipient stems with up to two hydrothecae. Species easily recognizable by the characteristic long and straight basal part of internodes (Fig. 3F) and the size of the microbasic eurytele nematocysts (10 X 5 µm). Ecology and distribution. Our material was collected at depths from 325 to 409 m, epibiotic on Symplectoscyphus glacialis. Watson’s (2008) material was found at a depth of 4–13 m, in Commonwealth Bay. Circum-Antarctic distribution (Peña Cantero 2014c).Published as part of Peña Cantero, Álvaro L. & Marzal, Marina Fresneda, 2018, Benthic hydroids (Cnidaria: Hydrozoa) from off George V Coast (East Antarctica), pp. 121-136 in Zootaxa 4441 (1) on page 128, DOI: 10.11646/zootaxa.4441.1.7, http://zenodo.org/record/130192
Spatial distribution of roots and water uptake of Maize (Zea mays L.) as affected by soil structure.
No full textA strategic and tactical management approach to select optimal N fertilizer rates for wheat in a spatially variable field
No full textWheat yield and protein content in a field are spatially variable due to inherent variability of soil properties and landscape. In Mediterranean environments yield variability in space and time is caused by irregular weather patterns, particularly rainfall, and by position in the landscape. A tested crop simulation model, SALUS, was used to select optimal nitrogen fertilizer rates using strategic and tactical approaches in a spatially variable field where three distinct management zones had been previously identified. The crop model was tested and then used to simulate seven N rates from 0 to 180 kg N ha−1 with a 30 kg N ha−1 increments for 56 years using historical weather data. The available soil water at the time of N sidedressing each year and each management zone was correlated with yield response to N to evaluate the possibility of using the stored soil water to tactically determine N rates. Assuming recent production costs and grain prices the simulations helped identify an optimal N rate for each of the zones based on agronomic, economic and environmental sustainability of N management. Results showed the high yielding zone had a maximum economic return and minimal environmental impact in terms of nitrate leaching by applying 90 kg N ha−1 annually. On the other hand, the low yielding zone had little economic returns for application higher than 30 kg N ha−1. When simulated soil root-zone water was low at sidedressing, a lower fertilizer rate increased profit and decreased N leaching in the medium and high yielding zones
Impact of compost, manure, and inorganic fertilizer on nitrate leaching and yield in a six-year maize-alfalfa rotation.
No full textAn accurate estimate of nitrate (NO3–N) leaching from agricultural land is critical to environment impact studies. Although
NO3–N are almost always present in groundwater, their continued increase in managed agricultural land can lead to nitrate
concentrations in groundwater above acceptable human health standards. The amount of NO3–N leached during the growing
season may be minimal compared to leaching losses that occur between the harvest of one crop and the planting of the next. In
this study we compared the effect of inorganic N and raw and composted animal manure on crop productivity and N leaching
under field conditions in a maize–alfalfa system using undisturbed drainage lysimeters in Michigan. The cropping system
rotation consisted of 3 years of continuous maize (Zea mays L.) and 3 years of continuous alfalfa (Medicago sativa L.). One
cropping system consisted of a maize crop grown in the 1994–1996 seasons and alfalfa in the 1997–1999 seasons. The other
cropping system was alfalfa (1994–1996) then maize (1997–1999). Four N treatments were imposed on the cropping systems.
Treatment 1 was a check, no N fertilizer; Treatment 2 was manure; Treatment 3 was compost; Treatment 4 was inorganic
fertilizer. No significant differences in yields of maize and alfalfa were found between N treatments in the 6-year rotation,
although the no N treatment in maize had consistently lower yields. The highest amount of NO3–N leaching was measured in the
manure treatment with a mean annual value of 55 kg NO3–N ha1 in maize–alfalfa rotation and 59 kg NO3–N ha1 in alfalfa–
maize, followed by compost (35 kg NO3–N ha1 in alfalfa–maize and 30 kg NO3–N ha1 in maize–alfalfa), inorganic N (33 kg
NO3–N ha1 in alfalfa–maize and 25 kg NO3–N ha1 in maize–alfalfa) and no N (27 kg NO3–N ha1 in alfalfa–maize and
25 kg NO3–N ha1 in maize–alfalfa). The highest rates of NO3–N losses were also observed in the manure treatment with a
mean value for the 6-year rotation of 0.14 kg NO3–N mm1 in alfalfa–maize and 0.35 kg NO3–N mm1 in maize–alfalfa
Long-term wheat response to nitrogen in a rainfed Mediterranean environment: Field data and simulation analysis
No full textAppropriate nitrogen management is one of the main challenges of agricultural production and for the environment. The objectives of this study were to evaluate the efficiency of crop N uptake in a longterm wheat crop in a Mediterranean environment of Southern Italy, and to identify optimal N rate for reasonable economic returns and minimum nitrate leaching using SAWS crop simulation model. The study was part of a long-term monoculture wheat system that started in 1991/1992 season, with two levels of nitrogen (0 and 90 kg N ha(-1)). Simulations of the treatment with no nitrogen (0N) and 90 kg N ha(-1) (90 N) were performed using the SALUS crop model for wheat. The model was tested against measurements of harvested grain yield, final N uptake, soil water content and total soil N. Long-term simulation over 56 years showed that grain yield median value was 3435 kg ha(-1) for 0N and 3876 kg ha(-1) for 90 N. Simulation scenarios with different N rates (0, 30, 60, 90, 120, 180 kg N ha(-1)) showed that yield response was higher for 120 N (3528 kg ha(-1)), with the 60 and 90 N yields giving the same response, 3010 and 3054 kg ha(-1), respectively. The most profitable treatments were 120 N (302 Euro ha(-1)), followed by the 60 N (220 Euro ha(-1)). The simulation results showed that nitrate leaching was higher for the N rate of 120 and 180 with a mean annual value of 49 and 81 kg ha(-1), respectively. Results suggest that in such environment 60 kg N ha(-1) can be the most appropriate as an N fertilization management due to the best trade-off between leaching and economic. Since N fertilization rates are linked to nitrous oxide (N(2)O) emissions and N leaching, a trade-off between N fertilization rates profit and grain yield should be thought as way to reduce environmental pollution while keeping productivity and profit. The adoption of simulation models to approximate the best N rate for durum wheat in rainfed Mediterranean environment proved to be a useful tool for supporting management decisions through quantifying the temporal variability related to weather uncertainty as it influences on the yield and nutrient dynamics. (C) 2010 Elsevier B.V. All rights reserved
Recommended from our members
Solid-state photonic interfaces using semiconductor quantum dots
No full textNew technologies based on the properties of quantum mechanics promise
to revolutionise the way information is processed by outperforming what is
possible using classical devices. Examples include massively parallel processing
using quantum computers, verifiably secure communication using quantum
cryptography, and measurement with sensitivity beyond classical limitation
with quantum metrology. Realising the full potential of these technologies
necessitates the ability to communicate quantum information over large
distances, a key requirement for future quantum networks. However, developing
practical implementations of long-distance quantum communication
is challenging as it necessitates three major ingredients: light-matter interfaces,
elementary quantum operations, and quantum memories. This thesis
describes work that has been undertaken to address these requirements using
semiconductor nanotechnology.
We have first demonstrated that single InAs quantum dots embedded inside
conventional diode structures constitute high-fidelity controllable interfaces
between optical qubits and solid-state qubits. Indeed, the polarisation
state of a photon was transferred into the spin state of an electron-hole pair
and eventually restored through radiative recombination of the electron and
the hole with a fidelity up to 95%. Moreover, spins were manipulated using
subnanosecond modulation of a vertical electric field applied to the quantum
dots. By controlling this electrical modulation, we demonstrated elementary
phase-shift and spin-flip gate operations with near-unity fidelities.
An electron-hole pair confi ned in a single quantum dot has a short radiative
lifetime limiting therefore its use as an excitonic quantum memory.
The solution we proposed was to use a quantum dot molecule to control the
spatial separation of the electron and the hole and therefore prevent their
recombination. Comprehensive studies of electric field eff ects upon the photoluminescence
of quantum dot molecules lead to a clear understanding and
a good control over their physical properties. Single photons were stored in
individual quantum dot molecules up to 1μs and read out on a subnanosecond time scale. Moreover, the circular polarisation of individual photons was
transferred into the spin state of electron-hole pairs with a fidelity above
90%, which does not degrade for storage times up to the 12.5 ns repetition
period of the experiment.
Our work on single quantum dots could be extended in the near future to
allow for two-qubits quantum operations by con fining a second electron-hole
pair to be electrically manipulated. Storage of a superposition of spin states
in a quantum dot molecule should also be possible if the spin states are made
degenerate, which is feasible using the electric fi eld dependence of the energy
splitting between the spin states discussed in this thesis. We believe that
combining both approaches will lead to the development of a controllable
multi-qubit quantum memory for polarised light, a building block for long distance
quantum communication based on semiconductor nanotechnology
Impact of animal manure and inorganic fertilizer on nitrate leaching in a corn-alfalfa rotation
No full text- …
