1,019 research outputs found
XRD and XPS studies of surface MMC layers developed by laser alloying Ti6Al4V using a combination of a dilute nitrogen environment and SiC powder
Using a continuous-wave CO2 laser, surface engineering of a Ti-6Al-4V alloy through a combined treatment of laser nitriding and SiC preplacement was undertaken. Under spinning laser beam conditions, a surface alloyed / metal matrix composite (MMC) layer over 300ÎŒm in depth and 24mm wide was produced in the alloy by the overlapping of 12 tracks. Microstructural and chemical changes were studied as a function of (a) depth in the laser formed composite layer and (b) of the track position. Using X- ray diffraction (XRD) and X-ray photospectrographic (XPS) techniques, it was shown that the composite layer contained a complex microstructure which changed with depth. At the surface, a non-stoichiometric, cubic TiNx solid solution ( possibly a carbonitride) containing C and Si , where x â 0.65-0.8, was prominent, but was replaced by αâČ-Ti with increasing depth to 300ÎŒm. TiC phase was also identified, and the presence of TiN0.3 and Ti5Si3 phases considered a distinct possibility.
Modelling spatial and inter-annual variations of nitrous oxide emissions from UK cropland and grasslands using DailyDayCent
This work contributes to the Defra funded projects AC0116: âImproving the nitrous oxide inventoryâ, and AC0114: âData Synthesis, Management and Modellingâ. Funding for this work was provided by the UK Department for Environment, Food and Rural Affairs (Defra) AC0116 and AC0114, the Department of Agriculture, Environment and Rural Affairs for Northern Ireland, the Scottish Government and the Welsh Government. Rothamsted Research receives strategic funding from the Biotechnology and Biological Sciences Research Council. This study also contributes to the projects: N-Circle (BB/N013484/1), U-GRASS (NE/M016900/1) and GREENHOUSE (NE/K002589/1).Peer reviewedPublisher PD
Magnetoelectric ordering of BiFeO3 from the perspective of crystal chemistry
In this paper we examine the role of crystal chemistry factors in creating
conditions for formation of magnetoelectric ordering in BiFeO3. It is generally
accepted that the main reason of the ferroelectric distortion in BiFeO3 is
concerned with a stereochemical activity of the Bi lone pair. However, the lone
pair is stereochemically active in the paraelectric orthorhombic beta-phase as
well. We demonstrate that a crucial role in emerging of phase transitions of
the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order
types belongs to the change of the degree of the lone pair stereochemical
activity - its consecutive increase with the temperature decrease. Using the
structural data, we calculated the sign and strength of magnetic couplings in
BiFeO3 in the range from 945 C down to 25 C and found the couplings, which
undergo the antiferromagnetic-ferromagnetic transition with the temperature
decrease and give rise to the antiferromagnetic ordering and its delay in
regard to temperature, as compared to the ferroelectric ordering. We discuss
the reasons of emerging of the spatially modulated spin structure and its
suppression by doping with La3+.Comment: 18 pages, 5 figures, 3 table
Segregation and charge-density-wave order in the spinless Falicov-Kimball model
The spinless Falicov-Kimball model is solved exactly in the limit of
infinite-dimensions on both the hypercubic and Bethe lattices. The competition
between segregation, which is present for large U, and charge-density-wave
order, which is prevalent at moderate U, is examined in detail. We find a rich
phase diagram which displays both of these phases. The model also shows
nonanalytic behavior in the charge-density-wave transition temperature when U
is large enough to generate a correlation-induced gap in the single-particle
density of states.Comment: 10 pages, 10 figure
Strong Final State Interactions in gamma.gamma --> W+W-
We study the effects of a possible strong final state interaction among
longitudinal W's in gamma.gamma --> W+W-. The relevant partial wave amplitudes
are modified by an Omn\`es function approximated by a Breit-Wigner form factor.
We study the fractional cross section f_{00} = \sigma_{LL}/\sigma_{Total} with
both W's longitudinally polarised, in the presence of a J = 2 resonance (M =
2.5 TeV, Width = 500 GeV) or a J = 0 resonance (M = 1 TeV, Width = 1 TeV),
whose parameters are scaled up from the f_2 and \sigma resonances in the \pi\pi
system. We also examine the effects of final state interaction in the case of
polarised photons (J_z = 0 or J_z = 2), and the impact on the
Drell-Hearn-Gerasimov sum rule.Comment: 12 pages including figure
Constraints on the Local Sources of Ultra High-Energy Cosmic Rays
Ultra high-energy cosmic rays (UHECRs) are believed to be protons accelerated
in magnetized plasma outflows of extra-Galactic sources. The acceleration of
protons to ~10^{20} eV requires a source power L>10^{47} erg/s. The absence of
steady sources of sufficient power within the GZK horizon of 100 Mpc, implies
that UHECR sources are transient. We show that UHECR "flares" should be
accompanied by strong X-ray and gamma-ray emission, and that X-ray and
gamma-ray surveys constrain flares which last less than a decade to satisfy at
least one of the following conditions: (i) L>10^{50} erg/s; (ii) the power
carried by accelerated electrons is lower by a factor >10^2 than the power
carried by magnetic fields or by >10^3 than the power in accelerated protons;
or (iii) the sources exist only at low redshifts, z<<1. The implausibility of
requirements (ii) and (iii) argue in favor of transient sources with L>10^{50}
erg/s.Comment: 7 pages, 1 figure, submitted to JCA
The contribution of cattle urine and dung to nitrous oxide emissions: Quantification of country specific emission factors and implications for national inventories
Publication history: Accepted - 10 April 2018; Published online - 24 April 2018.Urine patches and dung pats from grazing livestock create hotspots for production and emission of the greenhouse
gas, nitrous oxide (N2O), and represent a large proportion of total N2O emissions in many national agricultural
greenhouse gas inventories. As such, there is much interest in developing country specific N2O emission
factors (EFs) for excretal nitrogen (EF3, pasture, range and paddock) deposited during gazing. The aims of this
study were to generate separate N2O emissions data for cattle derived urine and dung, to provide an evidence
base for the generation of a country specific EF for the UK from this nitrogen source. The experiments were
also designed to determine the effects of site and timing of application on emissions, and the efficacy of the nitrification
inhibitor, dicyandiamide (DCD) on N2O losses. This co-ordinated set of 15 plot-scale, year-long field experiments
using static chambers was conducted at five grassland sites, typical of the soil and climatic zones of
grazed grassland in the UK. We show that the average urine and dung N2O EFs were 0.69% and 0.19%, respectively,
resulting in a combined excretal N2O EF (EF3), of 0.49%, which is b25% of the IPCC default EF3 for excretal
returns from grazing cattle. Regression analysis suggests that urineN2O EFs were controlledmore by composition
than was the case for dung, whilst dung N2O EFs were more related to soil and environmental factors. The urine
N2O EF was significantly greater from the site in SW England, and significantly greater from the early grazing season urine application than later applications. Dycandiamide reduced the N2O EF fromurine patches by an average
of 46%. The significantly lower excretal EF3 than the IPCC default has implications for the UK's national inventory
and for subsequent carbon footprinting of UK ruminant livestock productsThe authors are grateful to the UK Department for Environment,
Food and Rural Affairs (Defra), the Department of Agriculture and Rural
Development (now the Department of Agriculture, Environment and
Rural Affairs) in Northern Ireland, and the Scottish Government and
the Welsh Government for financial support via the InveN2Ory project
(AC0116). The work by Rothamsted Research was additionally supported
by the Biotechnology and Biological Sciences Research Council
(BBS/E/C/000I0320). We would also like to thank Jon Moorby (IBERS,
Wales, UK), Reading University, SRUC (Scotland, UK) and Conrad Ferris
(AFBI, Northern Ireland, UK), for provision of cattle urine and dung
Magnetic and thermal properties of 4f-3d ladder-type molecular compounds
We report on the low-temperature magnetic susceptibilities and specific heats
of the isostructural spin-ladder molecular complexes L[M(opba)]_{3\cdot
xDMSOHO, hereafter abbreviated with LM (where L =
La, Gd, Tb, Dy, Ho and M = Cu, Zn). The results show that the Cu containing
complexes (with the exception of LaCu) undergo long range magnetic
order at temperatures below 2 K, and that for GdCu this ordering is
ferromagnetic, whereas for TbCu and DyCu it is probably
antiferromagnetic. The susceptibilities and specific heats of TbCu
and DyCu above have been explained by means of a model
taking into account nearest as well as next-nearest neighbor magnetic
interactions. We show that the intraladder L--Cu interaction is the predominant
one and that it is ferromagnetic for L = Gd, Tb and Dy. For the cases of Tb, Dy
and Ho containing complexes, strong crystal field effects on the magnetic and
thermal properties have to be taken into account. The magnetic coupling between
the (ferromagnetic) ladders is found to be very weak and is probably of dipolar
origin.Comment: 13 pages, 15 figures, submitted to Phys. Rev.
Weak-coupling Treatment of Electronic (Anti-)Ferroelectricity in the Extended Falicov-Kimball Model
We study the (spinless) Falicov-Kimball model extended by a finite band width
(hopping ) of the localized (f-) electrons in infinite dimensions in the
weak-coupling limit of a small local interband Coulomb correlation for half
filling. In the case of overlapping conduction- and f-bands different kinds of
ordered solutions are possible, namely charge-density wave (CDW) order,
electronic ferroelectricity (EFE) and electronic antiferroelectricity (EAFE).
The order parameters are calculated as a function of the model parameters and
of the temperature. There is a first-order phase transition from the CDW-phase
to the EFE- or EAFE-phase. The total energy is calculated to determine the
thermodynamically stable solution. The quantum phase diagrams are calculated.Comment: 7 pages, 8 figure
Polarization phenomena in open charm photoproduction processes
We analyze polarization effects in associative photoproduction of
pseudoscalar () charmed mesons in exclusive processes , , . Circularly polarized photons
induce nonzero polarization of the -hyperon with - and -components
(in the reaction plane) and non vanishing asymmetries and for polarized nucleon target. These polarization observables can be
predicted in model-independent way for exclusive -production processes
in collinear kinematics. The T-even -polarization and asymmetries for
non-collinear kinematics can be calculated in framework of an effective
Lagrangian approach. The depolarization coefficients , characterizing
the dependence of the -polarization on the nucleon polarization are also
calculated.Comment: 36 pages 13 figure
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