146 research outputs found
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
Magnetic Lattice Dynamics of the Oxygen-Free FeAs Pnictides: How Sensitive are Phonons to Magnetic Ordering?
To shed light on the role of magnetism on the superconducting mechanism of
the oxygen-free FeAs pnictides, we investigate the effect of magnetic ordering
on phonon dynamics in the low-temperature orthorhombic parent compounds, which
present a spin-density wave. The study covers both the 122 (AFe2As2; A=Ca, Sr,
Ba) and 1111 (AFeAsF; A=Ca, Sr) phases. We extend our recent work on the Ca
(122 and 1111) and Ba (122) cases by treating computationally and
experimentally the 122 and 1111 Sr compounds. The effect of magnetic ordering
is investigated through detailed non-magnetic and magnetic lattice dynamical
calculations. The comparison of the experimental and calculated phonon spectra
shows that the magnetic interactions/ordering have to be included in order to
reproduce well the measured density of states. This highlights a
spin-correlated phonon behavior which is more pronounced than the apparently
weak electron-phonon coupling estimated in these materials. Furthermore, there
is no noticeable difference between phonon spectra of the 122 Ba and Sr,
whereas there are substantial differences when comparing these to CaFe2As2
originating from different aspects of structure and bonding
Electron-phonon anomaly related to charge stripes: static stripe phase versus optimally-doped superconducting La1.85Sr0.15CuO4
Inelastic neutron scattering was used to study the Cu-O bond-stretching
vibrations in optimally doped La1.85Sr0.15CuO4 (Tc = 35 K) and in two other
cuprates showing static stripe order at low temperatures, i.e.
La1.48Nd0.4Sr0.12CuO4 and La1.875Ba0.125CuO4. All three compounds exhibit a
very similar phonon anomaly, which is not predicted by conventional band
theory. It is argued that the phonon anomaly reflects a coupling to charge
inhomogeneities in the form of stripes, which remain dynamic in superconducting
La1.85Sr0.15CuO4 down to the lowest temperatures. These results show that the
phonon effect indicating stripe formation is not restricted to a narrow region
of the phase diagram around the so-called 1/8 anomaly but occurs in optimally
doped samples as well.Comment: to appear in J. Low Temp. Phy
Growth attributes of malt barley (Hordeum vulgare) as influenced by fertility levels and liquid biofertilizers
The experiments were conducted during winter (rabi) seasons of 2020–21 and 2021–22 at Rajasthan College of Agriculture, Maharana Pratap University of Agriculture and Technology, Udaipur, Rajasthan to study the effect of fertility levels and biofertilizers on malt barley (Hordeum vulgare L.). Factorial randomized block design (F-RBD) was used comprising 15 treatment combinations involved 3 fertility levels, viz. 50 N + 25 P2O5 + 15 K2O kg/ha; 60 N + 30 P2O5 + 20 K2O kg/ha; and 70 N + 40 P2O5 + 25 K2O kg/ha; alongside 5 liquid biofertilizers, viz. control; Azotobacter; Phosphorous solubilizing bacteria; Potassium mobilizing bacteria; and Azotobacter + Phosphorous solubilizing bacteria + Potassium mobilizing bacteria. The findings indicate that applying a fertilizer combination of 70 N + 40 P2O5 + 25 K2O kg/ha to malt barley crop significantly enhanced plant height at harvest (118.74 cm), dry- matter accumulation/m row at harvest (356.88 g), leaf area index (LAI) at 50 DAS (days after sowing) (1.69) and 75 DAS (2.87), number of total tillers (89.97) and growth efficiency values, substantially greater than other fertility levels. The findings demonstrated that inoculating seeds with a combination of liquid biofertilizers containing Azotobacter + Phosphorous solubilizing bacteria + Potassium mobilizing bacteria significantly improved growth parameters, viz. plant height at harvest (117.55 cm), dry-matter accumulation/m row at harvest (371.25 g), LAI at 50 DAS (1.68) and 75 DAS (2.96), number of total tillers (90.08) and growth efficiency values
Soil Erosion under Land Use Change from Three Catchments in Laos, Thailand and Vietnam
Abstract: The systems often identified as "traditional" undergo rapid changes as a response to demographic, economic, political and cultural drivers. These transitional periods are often most critical for soil erosion. The on-site impacts of soil erosion reduce the soil chemical fertility through nutrient and organic depletion, and acid subsoil exposure. Erosion also damages the physical fertility by removing surface soil, reducing the soil depth and water holding capacity, and exposing gravel and rocks. These combined processes result in less productive soils, hence lower farm income. To obtain the initial crop yield prior to erosion, increased amounts of inputs are needed, which is most often beyond the economic capacity of the small holders. To study the impact of land use change upon erosion, concurrent case studies, as seen with a dynamic perspective, can compensate for long-term monitoring studies. This approach provides data, which can be used for prediction soil erosion based on global change scenarios. The main objective of this study was to assess the influence of the rapid change of cropping systems on water erosion from three small catchments in three countries of South-East Asia (Laos, Thailand, Vietnam), using a multidisciplinary approach. These three catchments were selected because of their similar biophysical components (very steep slopes on shales; Janeau et al., submitted) and their land use intensification gradient. This investigation was conducted under the auspices the Management of Soil Erosion Consortium (MSEC) started in 1998 (Amado et al., 2002). Water discharge and soil erosion were monitored during three years at the outlet of each catchment using weirs. These data were used to calibrate and validate the PCARES model (Predicting Catchment Runoff and Soil Erosion for Sustainability) in each cachment. This GISbased model was developed in the Philippines for very steep slope condition
Solar System Processes Underlying Planetary Formation, Geodynamics, and the Georeactor
Only three processes, operant during the formation of the Solar System, are
responsible for the diversity of matter in the Solar System and are directly
responsible for planetary internal-structures, including planetocentric nuclear
fission reactors, and for dynamical processes, including and especially,
geodynamics. These processes are: (i) Low-pressure, low-temperature
condensation from solar matter in the remote reaches of the Solar System or in
the interstellar medium; (ii) High-pressure, high-temperature condensation from
solar matter associated with planetary-formation by raining out from the
interiors of giant-gaseous protoplanets, and; (iii) Stripping of the primordial
volatile components from the inner portion of the Solar System by super-intense
solar wind associated with T-Tauri phase mass-ejections, presumably during the
thermonuclear ignition of the Sun. As described herein, these processes lead
logically, in a causally related manner, to a coherent vision of planetary
formation with profound implications including, but not limited to, (a) Earth
formation as a giant gaseous Jupiter-like planet with vast amounts of stored
energy of protoplanetary compression in its rock-plus-alloy kernel; (b) Removal
of approximately 300 Earth-masses of primordial gases from the Earth, which
began Earth's decompression process, making available the stored energy of
protoplanetary compression for driving geodynamic processes, which I have
described by the new whole-Earth decompression dynamics and which is
responsible for emplacing heat at the mantle-crust-interface at the base of the
crust through the process I have described, called mantle decompression
thermal-tsunami; and, (c)Uranium accumulations at the planetary centers capable
of self-sustained nuclear fission chain reactions.Comment: Invited paper for the Special Issue of Earth, Moon and Planets
entitled Neutrino Geophysics Added final corrections for publicatio
Anomalous Dispersion of Longitudinal Optical Phonons in Determined by Inelastic X-ray Scattering
The phonon dispersions of along
the direction have been determined by inelastic x-ray scattering.
Compared to the undoped parent compound, the two highest longitudinal phonon
branches, associated with the Cu-O bond-stretching and out-of-plane oxygen
vibration, are shifted to lower energies. Moreover, an anomalous softening of
the bond-stretching band is observed around . These
signatures provide evidence for strong electron-phonon coupling in this
electron-doped high-temperature superconductor.Comment: 4 pages, 4 figure
C-axis lattice dynamics in Bi-based cuprate superconductors
We present results of a systematic study of the c axis lattice dynamics in
single layer Bi2Sr2CuO6 (Bi2201), bilayer Bi2Sr2CaCu2O8 (Bi2212) and trilayer
Bi2Sr2Ca2Cu3O10 (Bi2223) cuprate superconductors. Our study is based on both
experimental data obtained by spectral ellipsometry on single crystals and
theoretical calculations. The calculations are carried out within the framework
of a classical shell model, which includes long-range Coulomb interactions and
short-range interactions of the Buckingham form in a system of polarizable
ions. Using the same set of the shell model parameters for Bi2201, Bi2212 and
Bi2223, we calculate the frequencies of the Brillouin-zone center phonon modes
of A2u symmetry and suggest the phonon mode eigenvector patterns. We achieve
good agreement between the calculated A2u eigenfrequencies and the experimental
values of the c axis TO phonon frequencies which allows us to make a reliable
phonon mode assignment for all three Bi-based cuprate superconductors. We also
present the results of our shell model calculations for the Gamma-point A1g
symmetry modes in Bi2201, Bi2212 and Bi2223 and suggest an assignment that is
based on the published experimental Raman spectra. The
superconductivity-induced phonon anomalies recently observed in the c axis
infrared and resonant Raman scattering spectra in trilayer Bi2223 are
consistently explained with the suggested assignment.Comment: 29 pages, 13 figure
Electron-phonon coupling reflecting dynamic charge inhomogeneity in copper-oxide superconductors
The attempt to understand cuprate superconductors is complicated by the
presence of multiple strong interactions. While many believe that
antiferromagnetism is important for the superconductivity, there has been
revived interest in the role of electron-lattice coupling. The recently studied
conventional superconductor MgB2 has a very strong electron-lattice coupling,
involving a particular vibrational mode (phonon), that was predicted by
standard theory and confirmed quantitatively by experiment. Here we present
inelastic scattering measurements that show a similarly strong anomaly in the
Cu-O bond-stretching phonon in the cuprate superconductors La2-xSrxCuO4 (with
x=0.07, 0.15). This is in contrast to conventional theory, which does not
predict such behavior. The anomaly is strongest in La1.875Ba0.125CuO4 and
La1.48Nd0.4Sr0.12CuO4, compounds that exhibit spatially modulated charge and
magnetic order, often called stripe order. It occurs at a wave vector
corresponding to the charge order. These results suggest that this giant
electron-phonon anomaly, which is absent in undoped and over-doped
non-superconductors, is associated with charge inhomogeneity. It follows that
electron-phonon coupling may be important to our understanding of
superconductivity, although its contribution to the mechanism is likely to be
indirect.Comment: to appear in Nature, 16 pages, 4 figures, very minor changes in text
and figures from previous versio
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