178 research outputs found
Collective dynamics in crystalline polymorphs of ZnCl: potential modelling and inelastic neutron scattering study
We report a phonon density of states measurement of -ZnCl using
the coherent inelastic neutron scattering technique and a lattice dynamical
calculation in four crystalline phases of ZnCl using a transferable
interatomic potential. The model calculations agree reasonably well with the
available experimental data on the structures, specific heat, Raman frequencies
and their pressure variation in various crystalline phases. The calculated
results have been able to provide a fair description of the vibrational as well
as the thermodynamic properties of ZnCl in all its four phases.Comment: Accepted in J. Phys.: Condens. Matte
Classification of Chest Diseases using Wavelet Transforms and Transfer Learning
Chest X-ray scan is a most often used modality by radiologists to diagnose
many chest related diseases in their initial stages. The proposed system aids
the radiologists in making decision about the diseases found in the scans more
efficiently. Our system combines the techniques of image processing for feature
enhancement and deep learning for classification among diseases. We have used
the ChestX-ray14 database in order to train our deep learning model on the 14
different labeled diseases found in it. The proposed research shows the
significant improvement in the results by using wavelet transforms as
pre-processing technique.Comment: 8 pages, 4 figures, Presented in International Conference On Medical
Imaging And Computer-Aided Diagnosis (MICAD 2020), proceeding will be
published with Springer in their "Lecture Notes in Electrical Engineering
(LNEE)" (ISSN: 1876-1100
Tillage impact on soil erosion by water: Discrepancies due to climate and soil characteristics
No-tillage (NT) is promoted for soil and water conservation, but research findings on overland flow and soil erosion are inconsistent across different ecosystems, with some studies showing no benefits of NT over conventional tillage (CT). A global literature review was conducted to quantify the impact of NT on water runoff, sediment concentration and soil losses. The objective was to identify the underlying causes of the variability in the performance of NT across different environments. Data from 282 paired NT and CT runoff plots from 41 research studies worldwide were analysed using meta-analysis and principal component analysis (PCA). Sediment concentration and soil losses were 56 and 60% lower under NT than CT, respectively. These tended to be greater under CT than NT on long plots (90% for sediment concentration and 94% for soil losses) and steepest slopes (79 and 77%, respectively). Greater differences in sediment concentration and soil losses between NT and CT were observed in low clay soils and under temperate climates. While on average there were no differences on runoff coefficient, NT decreased runoff coefficient by about 40% compared to CT in mulched soils, under cool climate (5 years. Overall, the results indicated that NT has greater potential to reduce runoff and soil losses in temperate regions where soils of peri-glacial influence are relatively young, moderately weathered and fragile compared to the heavily weathered clayey tropical soils that are well aggregated and less erodible. The results of this study are expected to inform scientists, practitioners and policy makers on the links between land management and soil functioning processes. Policy makers and development implementers will be able to make informed choices of land management techniques for effective NT implementation, for instance by having more mulch input under warm climates
The atomic structure of large-angle grain boundaries and in and their transport properties
We present the results of a computer simulation of the atomic structures of
large-angle symmetrical tilt grain boundaries (GBs) (misorientation
angles \q{36.87}{^{\circ}} and \q{53.13}{^{\circ}}),
(misorientation angles \q{22.62}{^{\circ}} and \q{67.38}{^{\circ}}). The
critical strain level criterion (phenomenological criterion)
of Chisholm and Pennycook is applied to the computer simulation data to
estimate the thickness of the nonsuperconducting layer enveloping
the grain boundaries. The is estimated also by a bond-valence-sum
analysis. We propose that the phenomenological criterion is caused by the
change of the bond lengths and valence of atoms in the GB structure on the
atomic level. The macro- and micro- approaches become consistent if the
is greater than in earlier papers. It is predicted that the
symmetrical tilt GB \theta = \q{53.13}{^{\circ}} should demonstrate
a largest critical current across the boundary.Comment: 10 pages, 2 figure
High-Temperature Phonon Spectra of Multiferroic BiFeO3 from Inelastic Neutron Spectroscopy
We report inelastic neutron scattering measurements of the phonon spectra in
a pure powder sample of the multiferroic material BiFeO3. A high-temperature
range was covered to unravel the changes in the phonon dynamics across the Neel
(T_N ~ 650 K) and Curie (T_C ~ 1100 K) temperatures. Experimental results are
accompanied by ab-initio lattice dynamical simulations of phonon density of
states to enable microscopic interpretations of the observed data. The
calculations reproduce well the observed vibrational features and provide the
partial atomic vibrational components. Our results reveal clearly the signature
of three different phase transitions both in the diffraction patterns and
phonon spectra. The phonon modes are found to be most affected by the
transition at the T_C. The spectroscopic evidence for the existence of a
different structural modification just below the decomposition limit (T_D ~
1240 K) is unambiguous indicating strong structural changes that may be related
to oxygen vacancies and concomitant Fe3+ to Fe2+ reduction and spin transition
Ab initio studies of phonon softening and high pressure phase transitions of alpha-quartz SiO2
Density functional perturbation theory calculations of alpha-quartz using
extended norm conserving pseudopotentials have been used to study the elastic
properties and phonon dispersion relations along various high symmetry
directions as a function of bulk, uniaxial and non-hydrostatic pressure. The
computed equation of state, elastic constants and phonon frequencies are found
to be in good agreement with available experimental data. A zone boundary (1/3,
1/3, 0) K-point phonon mode becomes soft for pressures above P=32 GPa. Around
the same pressure, studies of the Born stability criteria reveal that the
structure is mechanically unstable. The phonon and elastic softening are
related to the high pressure phase transitions and amorphization of quartz and
these studies suggest that the mean transition pressure is lowered under
non-hydrostatic conditions. Application of uniaxial pressure, results in a
post-quartz crystalline monoclinic C2 structural transition in the vicinity of
the K-point instability. This structure, intermediate between quartz and
stishovite has two-thirds of the silicon atoms in octahedral coordination while
the remaining silicon atoms remain tetrahedrally coordinated. This novel
monoclinic C2 polymorph of silica, which is found to be metastable under
ambient conditions, is possibly one of the several competing dense forms of
silica containing octahedrally coordinated silicon. The possible role of high
pressure ferroelastic phases in causing pressure induced amorphization in
silica are discussed.Comment: 17 pages, 8 figs., 8 Table
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