3,466 research outputs found
User oriented ERTS-1 images
Photographic reproduction of ERTS-1 images are capable of displaying only a portion of the total information available from the multispectral scanner. Methods are being developed to generate ERTS-1 images oriented towards special users such as agriculturists, foresters, and hydrologists by applying image enhancement techniques and interactive statistical classification schemes. Spatial boundaries and linear features can be emphasized and delineated using simple filters. Linear and nonlinear transformations can be applied to the spectral data to emphasize certain ground information. An automatic classification scheme was developed to identify particular ground cover classes such as fallow, grain, rape seed or various vegetation covers. The scheme applies the maximum likelihood decision rule to the spectral information and classifies the ERTS-1 image on a pixel by pixel basis. Preliminary results indicate that the classifier has limited success in distinguishing crops, but is well adapted for identifying different types of vegetation
Reversible strain effect on the magnetization of LaCoO3 films
The magnetization of ferromagnetic LaCoO3 films grown epitaxially on
piezoelectric substrates has been found to systematically decrease with the
reduction of tensile strain. The magnetization change induced by the reversible
strain variation reveals an increase of the Co magnetic moment with tensile
strain. The biaxial strain dependence of the Curie temperature is estimated to
be below 4K/% in the as-grown tensile strain state of our films. This is in
agreement with results from statically strained films on various substrates
Geological mapping of Sierra Leone : baseline assessment and next steps
Sierra Leone is a resource-rich country, with extensive known and potential mineral and petroleum
resources. However, knowledge about the geology of the country is limited, with very little modern
data in the public domain, and this hinders sustainable development of these resources for the
national good. The lack of data is now being addressed by the Extractive Industries Technical
Assistance Programme Phase 2 (EITAP 2) which is funded by the World Bank, and which aims
to deliver a national airborne geophysical survey and subsequent geological mapping of the
country (World Bank, 2017).
Alongside EITAP 2, the UK government is funding the British Geological Survey (BGS) to work
in partnership with relevant institutions in Sierra Leone, including the National Minerals Agency
(NMA), the Petroleum Directorate (PD) and Fourah Bay College (FBC), to build their capacity to
collect, manage and disseminate geological data. As part of that work, a field reconnaissance was
carried out across Sierra Leone in January 2018 to assess the state of current geological mapping,
visit mines and exploration projects, and to discuss how best to plan and carry out a mapping
programme. The field trip was led by three British Geological Survey (BGS) staff members
(Kathryn Goodenough, Jon Ford, and Darren Jones) together with 11 geologists from the NMA,
two geologists from the PD, and two staff members from the Geology Department at Fourah Bay
College. Pauline Scott and Avril Jamieson from the Department for International Development
(DFID) joined the first two days of the trip.
This report describes the conclusions arising from that field reconnaissance and associated
literature review, including a baseline assessment of the current geological mapping of Sierra
Leone, and suggestions for next steps. Some information is also derived from separate field visits
to the AMR Gold licence area in the Loko Hills (April 2017) and coastal outcrops in the Lungi
area (June 2017)
Electric-field control of magnetic ordering in the tetragonal BiFeO3
We propose a way to use electric-field to control the magnetic ordering of
the tetragonal BiFeO3. Based on systematic first-principles studies of the
epitaxial strain effect on the ferroelectric and magnetic properties of the
tetragonal BiFeO3, we find that there exists a transition from C-type to G-type
antiferromagnetic (AFM) phase at in-plane constant a ~ 3.905 {\AA} when the
ferroelectric polarization is along [001] direction. Such magnetic phase
transition can be explained by the competition between the Heisenberg exchange
constant J1c and J2c under the influence of biaxial strain. Interestingly, when
the in-plane lattice constant enlarges, the preferred ferroelectric
polarization tends to be canted and eventually lies in the plane (along [110]
direction). It is found that the orientation change of ferroelectric
polarization, which can be realized by applying external electric-field, has
significant impact on the Heisenberg exchange parameters and therefore the
magnetic orderings of tetragonal BiFeO3. For example, at a ~ 3.79 {\AA}, an
electric field along [111] direction with magnitude of 2 MV/cm could change the
magnetic ordering from C-AFM to G-AFM. As the magnetic ordering affects many
physical properties of the magnetic material, e.g. magnetoresistance, we expect
such strategy would provide a new avenue to the application of multiferroic
materials.Comment: 4 pages, 4 figure
Phase formation, phonon behavior, and magnetic properties of novel ferromagnetic La3BAlMnO9 (B = Co or Ni) triple perovskites
In the quest for novel magnetoelectric materials, we have grown, stabilized
and explored the properties of La3BAlMnO9 (B = Co or Mn) thin films. In this
paper, we report the influence of the growth parameters that promote B/Al/Mn
ordering in the pseudo-cubic unit cell and their likely influence on the
magnetic and multiferroic properties. The temperature dependence of the
magnetization shows that La3CoAlMnO9 is ferromagnetic up to 190 K while
La3NiAlMnO9 shows a TC of 130 K. The behavior of these films are compared and
contrasted with related La2BMnO6 double perovskites. It is observed that the
insertion of AlO6 octahedra between CoO6 and MnO6 suppresses significantly the
strength of the superexchange interaction, spin-phonon and spin-polar coupling.Comment: 13 pages, 3 fig
Long-range Ni/Mn structural order in epitaxial double perovskite La2NiMnO6 thin films
We report and compare the structural, magnetic, and optical properties of
ordered La2NiMnO6 thin films and its disordered LaNi0.5Mn0.5O3 counterpart. An
x-ray diffraction study reveals that the B-site Ni/Mn ordering induces
additional XRD reflections as the crystal symmetry is transformed from a
pseudocubic perovskite unit cell in the disordered phase to a monoclinic form
with larger lattice parameters for the ordered phase. Polarized Raman
spectroscopy studies reveal that the ordered samples are characterized by
additional phonon excitations that are absent in the disordered phase. The
appearance of these additional phonon excitations is interpreted as the
clearest signature of Brillouin zone folding as a result of the long-range
Ni/Mn ordering in La2NiMnO6. Both ordered and disordered materials display a
single ferromagnetic-to-paramagnetic transition. The ordered films display also
a saturation magnetization close to 4.8 mB/f.u. and a transition temperature
(FM-TC) around 270 K, while the disordered ones have only a 3.7 mB/f.u.
saturation magnetization and a FM-TC around 138 K. The differences in their
magnetic behaviours are understood based on the distinct local electronic
configurations of their Ni/Mn cations.Comment: 15 pages, 5 fig
CCRS proposal for evaluating LANDSAT-D MSS and TM data
Accomplishments in the evaluation of LANDSAT 4 data are reported. The objectives of the Canadian proposal are: (1) to quantify the LANDSAT-4 sensors and system performance for the purpose of updating the radiometric and geometric correction algorithms for MSS and for developing and evaluating new correction algorithms to be used for TM data processing; (2) to compare and access the degree to which LANDSAT-4 MSS data can be integrated with MSS imagery acquired from earlier LANDSAT missions; and (3) to apply image analysis and information extraction techniques for specific user applications such as forestry or agriculture
Electronic structure and magnetic properties of pyroxenes (Li,Na)TM(Si,Ge)2O6: novel low-dimensional magnets with 90 bonds
The results of the LSDA+U calculations for pyroxenes with diverse magnetic
properties (Li,Na)TM(Si,Ge)O, where TM is the transition metal ion
(Ti,V,Cr,Mn,Fe), are presented. We show that the anisotropic orbital ordering
results in the spin-gap formation in NaTiSiO. The detailed analysis of
different contributions to the intrachain exchange interactions for pyroxenes
is performed both analytically using perturbation theory and basing on the
results of the band structure calculations. The antiferromagnetic
exchange is found to decrease gradually in going from Ti to Fe.
It turns out to be nearly compensated by ferromagnetic interaction between
half-filled and empty orbitals in Cr-based pyroxenes. The
fine-tuning of the interaction parameters by the crystal structure results in
the ferromagnetism for NaCrGeO. Further increase of the total number of
electrons and occupation of sub-shell makes the contribution
and total exchange interaction antiferromagnetic for Mn- and Fe-based
pyroxenes. Strong oxygen polarization was found in Fe-based pyroxenes. It is
shown that this effect leads to a considerable reduction of antiferromagnetic
intrachain exchange. The obtained results may serve as a basis for the analysis
of diverse magnetic properties of pyroxenes, including those with recently
discovered multiferroic behavior.Comment: 11 pages, 10 figure
Structural relaxation due to electronic correlations in the paramagnetic insulator KCuF3
A computational scheme for the investigation of complex materials with
strongly interacting electrons is formulated which is able to treat atomic
displacements, and hence structural relaxation, caused by electronic
correlations. It combines ab initio band structure and dynamical mean-field
theory and is implemented in terms of plane-wave pseudopotentials. The
equilibrium Jahn-Teller distortion and antiferro-orbital order found for
paramagnetic KCuF3 agree well with experiment.Comment: 4 pages, 3 figure
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